Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

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Publishing type：Research paper (scientific journal)   Publisher：Wiley  

Abstract

In order to produce electricity beyond insolation hours and supply to the electrical grid, thermal energy storage (TES) system plays a major role in CSP (concentrated solar power) plants. Current CSP plants use molten salts as both sensible heat storage media and heat transfer fluid, to operate up to 560°C. To meet the future high operating temperature and efficiency, thermochemical storage (TCS) emerged as an attractive alternatives for next generation CSP plants. In these systems, the solar thermal energy is stored by endothermic reaction and subsequently released when the energy is needed by exothermic reversible reaction. This review compares and summarizes different thermochemical storage systems that are currently being investigated, especially TCS based on metal oxides. Various experimental, numerical, and technological studies on the development of particle reactors and materials for high‐temperature TCS applications are presented. Advantages and disadvantages of different types heat storage systems (sensible, latent, and thermochemical), and particle receivers (stacked, fluidized, and entrained), have been discussed and reported.

This article is categorized under:Sustainable Energy > Solar Energy

Emerging Technologies > Energy Storage

Emerging Technologies > Materials

DOI： 10.1002/wene.440

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Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/wene.440

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

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Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Mechanical Engineers  

DOI： 10.1299/jtst.22-00061

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Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

The effects of doping manganese ions into a cerium oxide lattice for a thermochemical two-step water-splitting cycle to produce oxygen and hydrogen and new synthesis methods were experimentally investigated. In order to comparison of oxygen/hydrogen producing performance, pristine CeO2, a coprecipitation method for Mn-CeO2, and a direct depositing method for Mn-CeO2 with different particle sizes (50~75, 100–212, over 212 μm) and doping extents (0, 5, 15 mol%) were tested in the context of synthesis and fabrication processes of reactive metal oxide coated ceramic foam devices. Sample powders were coated onto zirconia (magnesium partially stabilized zirconia oxide, MPSZ) porous foam at 30 weight percent using spin coating or a direct depositing method, tested using a solar reactor at 1400 °C as a thermal reduction step and at 1200 °C as a water decomposition step for five repeated cycles. The sample foam devices were irradiated using a 3-kWth sun-simulator, and all reactive foam devices recorded successful oxygen/hydrogen production using the two-step water-splitting cycles. Among the seven sample devices, the 5 mol% Mn-CeO2 foam device, that synthesized using the coprecipitation method, showed the greatest hydrogen production. The newly suggested direct depositing method, with its contemporaneous synthesis and coating of the Mn-CeO2 foam device, showed successful oxygen/hydrogen production with a reduction in the manufacturing time and reactants, which was lossless compared to conventional spin coating processes. However, proposed direct depositing method still needs further investigation to improve its stability and long-term device durability.

DOI： 10.3390/en14216919

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Frontiers Media SA  

A copper–germanium alloy (Cu–Ge alloy) was examined as a phase change material, at temperatures exceeding 600°C, for latent heat storage in solar thermal applications. First, the thermo-physical properties of the Cu–Ge alloy were examined using differential scanning calorimetry, thermomechanical analysis, and laser flash analysis. Second, to evaluate the thermal response and reliability of the Cu–Ge alloy, the cyclic properties of thermal charge/discharge were examined under various thermal conditions. The alloys obtained after the tests were examined for their chemical compatibility with the stainless steel container using an electron probe micro analyzer. The elemental distribution of each Cu–Ge alloy was evaluated using cyclic performance tests. Finally, the chemical compatibility of the Cu–Ge alloy was evaluated using a high-temperature test with candidate materials of a phase change material container vessel [stainless steel (SUS310S), Inconel625, silicon carbide (SiC), and alumina (Al2O3)]. The Cu–Ge alloy exhibited significant potential as a latent heat storage material in next-generation solar thermal power plants because it demonstrates various advantages, including a superior storage capacity at a temperature of 644°C, temperature coherence to the phase diagram, a quick thermal response, satisfactory cyclic behavior of charge/discharge modes, a thermodynamically stable metallographic structure, and non-reactivity with container ceramic materials (SiC and Al2O3).

DOI： 10.3389/fenrg.2021.696213

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Authorship：Lead author,　Corresponding author   Publishing type：Research paper (international conference proceedings)  

Latent heat storage technology in CSP plant has been studied to enhance the dispatchability of solar energy in order to meet fluctuating electricity needs. A novel concept using metal alloys as latent heat storage material gives way to achieve this technology. In this paper, we analyzed the structural and thermal properties of Cu-Ge alloy to evaluate the potential of metallic PCM for high temperature TES application. Containment options for metallic PCM were explored and the materials are selected for long term operation. Compatibility tests of stainless steel, alumina and SiC ceramics under inert atmosphere were performed at high temperatures (800°C) for a duration of 1 month (720 h) in order to develop a suitable container material for thermal energy storage system.

DOI： 10.1063/5.0028722

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Publishing type：Research paper (international conference proceedings)  

Considerable attention is being paid in recent years to develop and improve alternative technologies to replace fossil fuels due to pollution problems and limited conventional energy sources. Solar thermal energy has been considering as one of the most attractive renewable sources to provide solution to the aforementioned problems. In recent years, latent thermal energy storage systems using phase change materials (PCMs) have been developed to aid energy supply and demand of solar thermal power plants. As one of the obstacles of these systems is the low thermal conductivity of PCMs, ceramic fin has been used in this study to enhance heat transfer rate between the PCM and heat transfer fluid. To assess the heat transfer characteristics of the triplex-tube thermal energy storage system with ceramic fin, a numerical model has been developed and the effect of fin for various Stefan numbers has been studied numerically. The heat transfer and solidification rates are significantly enhanced when connecting the fins between the inner and outer tubes.

DOI： 10.1063/5.0028873

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Authorship：Corresponding author   Publishing type：Research paper (international conference proceedings)  

A thermochemical two-step water-splitting cycle using perovskite oxide of La0.7Sr0.3Mn0.9Cr0.1O3 was examined for carbon monoxide production from CO2 using concentrated solar radiation. Previously, the authors proved the perovskite oxide can thermochmically split H2O via two-step process into oxygen and hydrogen in an individual step. In this study, a thermochemical two-step CO2 splitting cycle using the perovskite oxide was examined for the reactivity and repeatability of redox reaction at CO2 spitting temperatures of 1000-1200 °C. The reactivity and repeatability for two-step CO2 splitting was compared to those for H2O splitting operating at the same temperature level.

DOI： 10.1063/5.0028681

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Publishing type：Research paper (international conference proceedings)  

In this paper, the effect of doping of Manganese on to Cerium oxide for thermochemical two-step water splitting cycle for produce the hydrogen was experimentally studied. In order to compare the oxygen/hydrogen productivity, pure CeO2, coprecipitation method applied Mn-CeO2, and direct doping calcination method adopted Mn-CeO2 were used to thermo-chemical two-step water splitting cycle tests. The synthesized sample powders were coated on the reticulated porous foam device and tested in the fixed bed type reactor for the temperature of 1400 C for thermal reduction step, and 1200 C for water decomposition step through 5 cyclic tests. The redox reactive foam devices were irradiated by 3kW sun-simulator, and all samples recorded successful oxygen/hydrogen production. Among the 3 sample devices, the 15 mol% Mn-CeO2 foam device which synthesized by direct doping calcination method shows highest hydrogen production amount and H2/O2 conversion ratio. o o

DOI： 10.1063/5.0029890

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Authorship：Lead author,　Corresponding author   Publishing type：Research paper (international conference proceedings)  

A thermochemical two-step water-splitting cycle using perovskite oxide of La0.7Sr0.3Mn0.9Cr0.1O3 was examined for hydrogen production from water using concentrated solar radiation. The impact of the thermal reduction temperatures of 1000–1350 °C on oxygen/hydrogen productivity and repeatability was examined for hydrogen production at a water decomposition temperature of 1200 °C. The sample displayed relatively high evolution rates of oxygen at TR temperatures of 1350-1300°C, and showed similar rate at TR temperatures of 1000-1200 °C. After the sample was subjected to the TR step at temperatures of 1350-1300 °C, the obtained samples were superior hydrogen production rate to the others. On the other hand, the sample provided relatively good reactivities and repeatabilities for oxygen release and hydrogen production with a small production level without coagulation or sintering during the TR temperatures of 1000-1200 °C.

DOI： 10.1063/5.0028720

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

A thermochemical two-step water-splitting cycle using perovskite oxides based on LaSrMnAlO was examined for hydrogen production from water using concentrated solar radiation. Concurrent Sr and Mn substitutions in La Sr Mn Al O , Sr and Al substitutions in La Sr Mn Al O , and substitution of Al by Cr in La Sr Mn Cr O were examined, and their kinetics, oxygen/hydrogen productivity, and repeatability were compared against LaSrMnAlO . The impact of the chemical compositions of the perovskite oxides was systematically examined at a thermal reduction temperature of 1350 °C and water decomposition temperatures of 1000–1200 °C. From the viewpoints of average amounts of oxygen and hydrogen produced and the H /O ratios, La Sr Mn Cr O and La Sr Mn Cr O provided the most reproducible productions of oxygen and hydrogen in the thermochemical two-step water-splitting cycle. 3 1-x x x 1-x 3 1-y y 1-y y 3 0.7 0.3 1-z z 3 3 2 2 0.7 0.3 0.9 0.1 3 0.7 0.3 0.8 0.2 3

DOI： 10.1016/j.tca.2019.178374

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Language：English   Publishing type：Research paper (scientific journal)  

To perform thermochemical cycles using non-volatile metal oxides to split water and produce hydrogen, a directly irradiated fluidized bed reactor is designed and fabricated for beam-down configuration. As the main aim of this investigation is to analyze the heat transfer and particulate flow of the reactor, chemically inert particles are used. A transient 3D heat and mass transfer model is formulated by the combined approach of discrete element method and computational fluid dynamics. The radiative transfer is solved using the discrete ordinate radiation model. Experimental validation is accomplished by the measured temperatures, obtained with the fluidized bed reactor prototype tested under 30 kW high-flux solar simulator. The model is applied to analyze the granular flow characteristics and efficiency of the reactor for various superficial gas velocities and bed masses. The results indicate that higher gas flow rate increases the velocity and convection loss of the bed and decreases the bed temperature and efficiency of the reactor. th

DOI： 10.1016/j.ces.2018.09.012

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Fe-doped manganese oxides for solar thermochemical storage are studied using thermogravimetric reactor in a laboratory scale. The operation process of Fe-doped Mn O /Mn O redox pair for two-step thermochemical cycle are optimized from the viewpoint of redox temperatures and thermochemical storage capacity, and the impact of operation temperatures on redox performances were experimentally evaluated. In addition, the thermochemical storage potentials of some Fe-X-doped manganese oxides are examined with regards to reaction rate, short-term cycling stability, storage capacity and redox temperatures. 2 3 3 4

DOI： 10.1063/1.5117752

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Gasification of carbonaceous materials using concentrated solar thermal radiation has been considered as one of the promising renewable pathways to produce syngas. In this study, thermal performance of a recently developed solar thermochemical reactor is presented. To analyze the gas–solid flow and heat transfer characteristics of the reactor, a transient three dimensional numerical model has been developed using discrete element method and computational fluid dynamics. Particle collision dynamics has been solved by the spring-dashpot model based on the soft-sphere method. To perform model verification, experiments have been performed using 30kW fluidized bed reactor prototype under high flux solar simulator. The particulate and thermal characteristics of spout, annulus and fountain of the fluidized bed are analyzed for different irradiation power, loaded powder and gas flow rates. The results indicate that large and small size particles govern the bottom and fountain part of the bed respectively due to gravitational force, and the peak temperature is moved from fountain core to the fountain periphery of the bed when increasing the gas flow rate. th

DOI： 10.1016/j.cej.2018.10.111

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

La Sr (Mn, Fe, Co)O , and Ba Sr CoO perovskite oxide powders were investigated as potential thermochemical energy storage (TES) materials operated at high temperatures above 600 °C. The purpose of the research is to provide complete characterization of the impact of partial A- and B-site substitution on the reactivity, kinetics, redox reaction repeatability and charging/discharging storage capacity. The perovskite oxides were investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) at temperatures of 500–1100 °C. Thermal energy storage was evaluated in terms of the enthalpy of the reversible reactions of oxygen release (reduction) and uptake (oxidation) upon heating the oxide materials in air stream. Among the perovskites tested, Ba Sr CoO and Ba Sr CoO powders were suitable thermochemical storage materials operating at above 600 °C in terms of chemical reactivity, charging/discharging temperatures and storage capacities, kinetics of oxygen uptake/release, and repeatability of thermochemical cycling. Further, charging/discharging capacity for both perovskites was comparable to that for Fe-doped manganese oxide. x 1-x 3-δ y 1-y 3-δ 0.3 0.7 3-δ 0.7 0.3 3-δ

DOI： 10.1016/j.energy.2019.01.081

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The operational mode of a batch-type fluidized bed reactor containing quartz sand and coal-coke particles was tested under xenon arc lamp (Xe-light) illumination to develop processes for the continuous feeding and gasification of coke particles in the quartz sand fluidized bed. This paper focuses on the fluidizing, heating, and steam gasification performances of a windowed internally circulating fluidized bed reactor. The operational modes explored in this study were: (1) elevated temperature processes associated with the use of Xe-light radiation to reach gasification temperatures, and, (2) the gasification process driving steam gasification at high-temperatures, working with stream gasification of continuously-fed coal-coke. The gasification performances were used to evaluate the performance of quartz sand as a thermal-transfer/sensible heat-storage medium. The peak rate of gas production was greatly enhanced for the high volume fraction of coal-coke. In addition, the light-to-energy conversion rate of 11.0–13.2% and carbon conversion rate up to 80% were reached in the simplified distributor structure of gasification reactor.

DOI： 10.1016/j.energy.2018.10.036

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Publishing type：Research paper (international conference proceedings)  

The first performance test of a novel windowed solar fluidized bed reactor was carried out for a two-step water splitting cycle with ceria particles by using a 30-kW sun-simulator. O and H were successfully produced by the reactor system. During the thermal reduction step of the two-step water splitting, a fluidized bed of ceria particles was created by passing N gas through the perforated bottom plate of the reactor, and about 30 kW of high flux visible light from 19 xenon-arc lamps of the sun-simulator was directed inside the reactor through a quartz window to directly irradiate the top of the fluidized bed. The central bed temperature reached the temperature of 1400 to 1500°C in the thermal reduction step. The subsequent water decomposition or hydrolysis step was performed at the central bed temperature of 800 - 900°C. About 6 - 12 Ndm of hydrogen was produced by one cycle. th 2 2 2 th 3

DOI： 10.1063/1.5067143

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Solar gasification is one of the promising techniques to convert the carbonaceous materials to clean chemical fuels, which offers the advantages of being transportable as well as storable for extended period of time. In this study, thermal performance of a recently developed 5 kW fluidized bed reactor for solar gasification has been investigated and reported. Discrete element method (DEM) has been used for modeling the granular flow, and computational fluid dynamics (CFD) method has been used for modeling the multiphase flow. To validate the developed model, experiments were preformed and compared with modeling results. Discrete ordinate radiation model has been used to solve the radiative transfer equation. The thermal performance of the reactor and particulate flow behavior have been predicted and the effect of particle size, particle size distribution and gas flow rate are analyzed. The results indicate that the performance of the bed increases when fluidizing the annulus region particles as the high porosity increases the diffusion rate of radiation throughout the bed. th

DOI： 10.1016/j.ijhydene.2018.06.033

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The particles flow and heat transfer characteristics of a high temperature solar thermochemical fluidized bed reactor have been studied for solar beam-down concentrating systems. A numerical model has been developed by the combined approach of computational fluid dynamics (CFD) and discrete element method (DEM) collisional model since it is an effective approach for studying the gas-solid flow. The discrete ordinate model has been used to solve the radiation heat transfer. An experimental visualization of particles circulation pattern and mixing of two-tower fluidized bed system has been presented. A good agreement has been found between the experimental measurements and numerical predictions. The effect of gas superficial velocity, bed mass and inlet gas temperature on the flow pattern and temperature characteristics of the bed have been investigated. The results showed that the maximum and average temperature of the bed, depends on the top layer position and focal point of the concentrated radiation, decreased when increasing the total mass of the bed. (C) 2017 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijheatmasstransfer.2017.09.015

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A combined numerical and experimental investigation of hydrodynamics and heat transfer of internally circulating fluidized bed reactor for solar gasification of coal coke to produce syngas is reported. As the main objective of this study is to study the thermal performance of the reactor, chemically inert quartz particles have been used. A numerical model has been developed by the combined approach of computational fluid dynamics and discrete element method (CFD-DEM). The radiation transfer equation has been solved by the discrete ordinate (DO) model. The experimental data have been used for model validation. The thermal performance of the reactor and the spout-annulus flow have been predicted by the model and other hydrodynamic parameters such as internal solid volume fraction, velocity and temperature of the particles are analyzed as a function of superficial gas velocity (gas flow rate) at different initial conditions.

DOI： 10.1016/j.energy.2018.06.212

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

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Language：English   Publishing type：Research paper (international conference proceedings)  

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Language：English   Publishing type：Research paper (international conference proceedings)  

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)  

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Language：English   Publishing type：Research paper (international conference proceedings)  

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Begell House Inc.  

This study focuses on the conjugate radiation-convection-conduction heat-transfer problem for a square channel of volumetric solar receiver with concentrated irradiation for Concentrated Solar Power (CSP). A single channel of a honeycomb receiver is directly irradiated from the outside, via a transparent wall. Atmospheric air flows through the channel and absorbs the sensible heat. Governing equations are continuity, Navier-Stokes and energy equations for solid/fluid region, and radiative transfer equation. Radiation was solved by the Discrete Ordinates (DO) model. The effects of the number of mesh grids and direction vectors on the DO model were confirmed to be negligible. This study analyzed the heat-transfer performance of stainless-steel receivers with different channel geometry. Three different types and sizes of channels were treated
L-shaped cuts were made at the channel top. The heat transfer performance of these channels, i.e. bulk air temperature and pressure drop at the outlet were improved by the L-shape cutting. The wall heat flux difference between simple and cut channel was clarified by the contour plots of inner walls. Across the entire inner wall, the conduction heat flux contributed to the heating of the flowing air, while the radiation heat-flux dominated near the inlet due to high incident radiation. As a result, the wall heat-flux had characteristic profile along the channel depth (-z) direction. This study elucidates conjugate heat transfer mechanism in the honeycomb-like channel receivers with highly concentrated radiation.

DOI： 10.1615/ihtc16.nee.023436

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Begell House Inc.  

In concentrated solar thermal industry, fluidized-bed technology has been used to produce hydrogen and synthetic gas by two-step water splitting cycles and gasification of coal cokes respectively. A two tower fluidized bed reactor has been developed in this study for solar thermochemical conversions. To study the granular flow and heat transfer characteristics of the two tower fluidized bed reactor, a numerical model has been developed by combined approach of discrete element method and computational fluid dynamics. Particle collision dynamics has been solved by the spring-dashpot model based on the soft-sphere method. Discrete ordinate radiation model has been used to solve the radiative transfer equation. To validate the model, the predicted heat transfer characteristics of the bed have been compared with the reported experimental data. A reasonable agreement has been found between the predicted and experimental results. Particulate flow dynamics of the bed filled with ceria powder is presented with temperature distributions. Using this model, the key operating parameters can be optimized.

DOI： 10.1615/ihtc16.mpf.023665

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier Ltd  

This paper describes a volumetric solar receiver that is vertically integrated with beam-down optics for condensed light irradiation. The heat-transfer performance of a silicon carbide honeycomb receiver was investigated using a 30-kWth solar simulator and numerical simulation. The experiments achieved an air temperature of 840 K at the receiver outlet by varying the operational parameters. Numerical simulations were performed for a vertical honeycomb block with beam-down irradiation and a horizontal honeycomb block with tower-type irradiation to elucidate the effects of buoyancy. Three blocks with different sizes were simulated for a variety of operational parameters. When the block was oriented vertically, the flow and temperature fields remained nearly symmetric in and near the receiver. In contrast, when it was oriented horizontally, the flow and temperature became asymmetric, with the hot spot moving toward the receiver's side wall and the stream in the receiver being reversed. The vertical orientation's robustness to buoyancy effects prevented any reduction in the receiver efficiency or outlet temperature and suppressed the thermal leakage.

DOI： 10.1016/j.energy.2017.11.147

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Utilization of solar thermal power for high temperature fuel production has the potential to significantly reduce the fossil fuel dependence of our current economy. Over the past two decades, remarkable progress has been made in the development of solar driven thermochemical reactors for the production of hydrogen and syngas as they are promising energy carriers for transportation, domestic and industrial applications. However, there are solar peculiarities in comparison to conventional thermochemical processes high thermal flux density and frequent thermal transients because of the fluctuating insolation-, and conventional industrial thermochemical reactors are generally not suitable for solar driven reactors. Therefore, solar-specific modifications of reactor design are necessary to realize efficient solar driven thermochemical processes. In solar thermochemical reactors, the methods for solar-heating particulate solid feedstock to high temperatures can be broadly classified as solar "directly" and "indirectly" absorbing reactors. On solar thermochemical processes involving reacting solid particles at high temperatures, such as "solar two-step water splitting with metal oxides" and "solar gasification", various types of solar directly and indirectly absorbing particle reactors have been developed. In this review, recent development of solar particle reactors for the above solar thermochemical processes is described. (C) 2017 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.solener.2017.05.084

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

In this study, a numerical model has been developed by the combined approach of computational fluid dynamics (CFD) and discrete element method (DEM) collisional model to study the particle-fluid flow of the fluidized bed reactor for solar beam-down concentrating system. The contact forces between the particles have been calculated by the spring-dashpot model, based on the soft-sphere method. An experimental visualization of particles circulation pattern and mixing of two-tower fluidized bed system has been presented. A good agreement has been found between the experimental measurements and numerical predictions. To investigate the influence of fluid flow rate and particle size on the flow pattern of the reactor, simulations have been performed for various conditions. The results indicate that the large size particles induce three-dimensional effects as they are accumulated at the central axis region. The average bed height of the left tower increased by 23.4% when increasing the flow rate about 70%. (C) 2017 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.powtec.2017.06.060

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

The present authors (Niigata University, Japan) have developed a tubular reactor system using novel "double-walled" reactor/receiver tubes with carbonate molten-salt thermal storage as a phase change material (PCM) for solar reforming of natural gas and with Al-Si alloy thermal storage as a PCM for solar air receiver to produce high-temperature air. For both of the cases, the high heat capacity and large latent heat (heat of solidification) of the PCM phase circumvents the rapid temperature change of the reactor/receiver tubes at high temperatures under variable and uncontinuous characteristics of solar radiation. In this study, we examined cyclic properties of thermal storage/discharge for Cu-Si alloy in air stream in order to evaluate a potentiality of Cu-Si alloy as a PCM thermal storage material. Temperature-increasing performances of Cu-Si alloy are measured during thermal storage (or heat-charge) mode and during cooling (or heat-discharge) mode. A oxidation state of the Cu-Si alloy after the cyclic reaction was evaluated by using electron probe micro analyzer (EPMA).

DOI： 10.1063/1.4984465

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

This paper presents a numerical analysis of unconstrained melting of high temperature(>1000K) phase change material (PCM) inside a cylindrical container. Sodium chloride and Silicon carbide have been used as phase change material and shell of the capsule respectively. The control volume discretization approach has been used to solve the conservation equations of mass, momentum and energy. The enthalpy-porosity method has been used to track the solidliquid interface of the PCM during melting process. Transient numerical simulations have been performed in order to study the influence of radius of the capsule and the Stefan number on the heat transfer rate. The simulation results show that the counter-clockwise Buoyancy driven convection over the top part of the solid PCM enhances the melting rate quite faster than the bottom part.

DOI： 10.1063/1.4984427

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

A window-type, solar fluidized bed receiver with quartz sand particles was tested by a 100-kWth novel beam-down solar concentrating system at Miyazaki, Japan. A compound parabolic concentrator (CPC) was placed above the quartz window of the receiver to increase the concentration of the solar fluxes from the beam-down solar concentrating system. The solar tests were performed in the middle of December, 2015. The central bed temperature of the receiver was reached around 960-1100 degrees C. It was found that only 20 Ndm(3)/min of air flow rate was enough to create the uniform fluidization of the particles at the given temperature range. It was predicted that if the central bed temperature could have been higher than 1100 degrees C if solar receiver test had conducted in other seasons than winter. The next solar campaign of the receiver test will be carried out in October, 2016.

DOI： 10.1063/1.4984469

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

A solar reactor containing a CeO2-coated reactive foam device for producing hydrogen via a thermochemical two-step water splitting cycle was proposed and experimentally tested. Modeling of the optical properties of the 40 kW(th) KIER (Korea Institute of Energy Research) solar furnace was performed to design and prepare the optimized foam matrix shape and the new solar reactor. Solar demonstration of the solar reactor was accomplished in the KIER 40 kW(th) solar furnace and hydrogen was produced successfully during the water decomposition step. The conical shape foam device was suggested and tested the temperature gradients and hydrogen productivity. Finally, five cyclic test was conducted with the conical shape CeO2-coated foam device, the total hydrogen production was 1394.32 Ncm(3) during the five cycles and the average hydrogen production per cycle was 278.86 Ncm(3).

DOI： 10.1063/1.4984460

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Language：Japanese   Publisher：The Japan Institute of Energy  

<p>Perovskite-type metal oxides were synthesized by Pechini method. Then, they were examined its reduction/oxidation reactivity by thermogravimetric analysis. After TGA testing, high redox-capacity materials were selected, and its reaction enthalpy was measured by DSC analysis. These results showed that the redox reactivity was improved by decreasing Lanthanum ion activity and increasing Barium ion concentration of samples. It was revealed that Ba-containing samples are potential thermochemical energy storage application.</p>

DOI： 10.20550/jietaikaiyoushi.26.0_176

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Language：Japanese   Publisher：The Japan Institute of Energy  

<p>Mitaka Koki Co., LTd., Miyazaki prefecture, Miyazaki University and Niigata University build a beam-down (BD) solar concentrating system in August 2012 at Miyazaki University for solar demonstration of the receiver/reactor. Both universities started an R&D joint project since 2011 to demonstrate the up-scaled receiver/reactor under a concentrated solar radiation. Niigata University has a 30 kW sun-simulator for testing of solar reactor. In this study, the first results of the receiver/reactor using 30 kW sun-simulator are reported. Quartz sand is used as a fluidization particle to examine performances of the receiver/reactor, while air is used as a passing gas. The temperatures of air and quartz sand are shown in the paper. In addition, cerium oxide powder is used as a fluidization/reaction particle to perform thermochemical two-step water-splitting cycle. The oxygen and hydrogen production are reported in this paper.</p>

DOI： 10.20550/jietaikaiyoushi.26.0_172

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

A copper-silicon alloy (Cu-Si alloy) was examined and evaluated as a phase-change material (PCM) for thermal energy storage applications such as load shaving and peak load shifting when coupled to a solar thermochemical reactor, reformer, or gasifier for the production of solar fuel. The Cu-Si alloy was selected as a high-temperature PCM thermal storage medium alternative to molten carbonate salts, and the compatibility of this alloy with a graphite-carbon encapsulation material was experimentally examined. The cyclic thermal storage/discharge properties of the Cu-Si alloy as a latent-heat energy storage material were studied with respect to thermal cycles. A thermal stability test was performed on Cu-20 wt% Si, Cu-25 wt% Si, and Cu-30 wt% Si alloys placed in a graphite container under vacuum. The performances of the Cu-Si alloys with increasing and decreasing temperature were measured during the thermal storage (heat-charge) and cooling (heat-discharge) modes, respectively. The elemental distribution of each Cu-Si alloy after the cyclic reaction was evaluated using an electron probe microanalyzer (EPMA). The heat storage capacities before and after the cyclic reaction were evaluated using differential scanning calorimetry (DSC) and were compared to the thermal storage properties of the molten carbonate salt. (C) 2016 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.energy.2016.07.005

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Language：English   Publishing type：Research paper (international conference proceedings)  

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

A novel concept of particles fluidized bed receiver/reactor with a beam-down solar concentrating optics was performed using a 30-kW(th) window type receiver by a big sun-simulator. A fluidized bed of quartz sand particles was created by passing air from the bottom distributor of the receiver, and about 30 kW(th) of high flux visible light from 19 xenon-arc lamps of the sun-simulator was directly irradiated on the top of the fluidized bed in the receiver through a quartz window. The particle bed temperature at the center position of the fluidized bed went up to a temperature range from 1050 to 1200 degrees C by the visible light irradiation with the average heat flux of about 950 kW/m(2), depending on the air flow rate. The output air temperature from the receiver reached 1000 - 1060 degrees C.

DOI： 10.1063/1.4949206

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

In 2014, Niigata University and the Institute of Applied Energy developed a point-concentration receiver-evaluation system using a silicon carbide (SiC) honeycomb and a three-dimensional simulation method. The system includes several improvements over its forerunner, including the ability to increase/decrease the power-on aperture (POA), air-mass flow-rate (AMF) and the height of the focal surface. This paper will focus on the results of tests using an improved receiver evaluation system, at a focal height of 1600 mm. Maximum outlet air temperature reached as high as 800 K, but exerted no untoward effects on the system. Also, receiver efficiency rated between 45 % and 70 %, according to POA. A numerical, 3D method of analysis was created at the same time, in order to analyze temperature and flow-distribution, in detail. This simulation, based on the dual-cell approach, reproduced the thermal non-equilibrium between the solid and fluid domain of the receiver material. The most interesting feature of this simulation, is that, because it includes upper and lower computational domains, it can be used to analyze the influence of both inward-and outward-flowing receiver materials.

DOI： 10.1063/1.4949078

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

The impacts of internal circulation of a mixture of coal-coke particles and quartz sand on the fluidization state in a fluidized bed reactor are investigated by a cold test with a benchtop set-up in order to design 10-30 kWth scale prototype windowed fluidized-bed reactor. Firstly, a basic relationship between pressure loss of inlet gas and gas velocity was experimentally examined using quartz sand with different particle sizes by a small-scale quartz tube with a distributor at ambient pressure and temperature. Based on the results, an appropriate particle range of quartz sand and layer height/layer diameter ratio (L/D ratio) was determined for a design of the fluidized bed reactor. Secondly, a windowed reactor mock-up was designed and fabricated for solar coke gasification using quartz sand as a bed material. The pressure loss between the inlet and outlet gases was examined, and descending cokes and sand particles on the sidewall of the reactor was observed in the reactor mock-up. The moving velocity and distance of descending particles/sands from the top to bottom of fluidized bed were measured by the visual observation of the colored tracer particles on outside wall of the reactor.

DOI： 10.1063/1.4949204

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Language：Japanese   Publisher：The Japan Institute of Energy  

<p>Perovskite oxide powder was examined as a redox material on reactivity of thermochemical two-step water-splitting for converting high-temperature heat into chemical fuels. In this study, in order to examine reactivity of the redox material at lower temperature in the thermochemical two-step water-splitting cycle, the amount of oxygen and hydrogen, its stoichiometry were investigared using LaSrAlMnO_3-δ powder at thermal reduction temperature of 1350 °C and water-decomposition temperture of 1000 °C.</p>

DOI： 10.20550/jietaikaiyoushi.25.0_134

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Language：Japanese   Publisher：The Japan Institute of Energy  

<p>Mitaka Koki Co., LTd., Miyazaki prefecture, Miyazaki University and Niigata University build a beam-down (BD) solar concentrating system in August 2012 at Miyazaki University for solar demonstration of the receiver/reactor. Both universities started an R&D joint project since 2011 to demonstrate the up-scaled receiver/reactor under a concentrated solar radiation. In this study, the first demonstration results of the receiver/reactor using BD solar concentrating system are reported. Quartz sand is used as a fluidization particle to examine performances of the receiver/reactor, while air is used as a passing gas. The temperatures of air and quartz sand are shown in the paper.</p>

DOI： 10.20550/jietaikaiyoushi.25.0_136

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Language：Japanese   Publisher：The Japan Institute of Energy  

<p>Solar hydrogen production via thermochemical water-splitting cycle by concentrated high-temperature heat has extensively investigated in a world. In this study, a thermochemical two-step water-splitting using redox material of Mn doped-ceria powder was examined in consecutive thermal reduction-decomposition steps by switching a passing gas from high purity Nitrogen in the TR step into the gas mixture of N2 and steam in the WD step. The reactivity of Mn doped-ceria powder with 5-30 mol% Mn doping was evaluated in this study.</p>

DOI： 10.20550/jietaikaiyoushi.25.0_132

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The characteristics of oxygen/hydrogen productivity using 30-mol%-M (M = Fe, Co, Ni, Mn)-doped CeO2-delta (30-mol%-M-CeO2-delta) were studied for the thermochemical two-step water splitting cycle comprising TR (thermal reduction) at 1500 degrees C and WD (water decomposition) at 1150 degrees C. The reproducibility of oxygen evolution was evaluated using 30-mol%-M-CeO2-delta and the effects of different M dopants were compared in the TR temperature range of 1200-1500 degrees C. Two solid phases detected in the 30-mol%-M- CeO2-delta powders were involved in the redox reaction of the thermochemical two-step water splitting cycle. Among the M-CeO2-delta samples evaluated, Mn-doped CeO2-delta provided the most stable and reproducible results and the highest reactivity for oxygen evolution at all temperatures employed for the TR step of the thermochemical two-step water-splitting cycle. (C) 2015 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.energy.2015.06.085

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The thermochemical two-step water-splitting cycle using transition element-doped cerium oxide (M CeO2-delta; M=Fe, Co, Ni, Mn) powders was studied for hydrogen production from water. The oxygen/hydrogen productivity and repeatability of M CeO2-delta materials with M doping contents in the 5-15 mol% range were examined using a thermal reduction (TR) temperature of 1500 degrees C and water decomposition (WD) temperatures in the 800-1150 degrees C range. The temperature, steam partial pressure, and steam flow rate in the WD step had an impact on the hydrogen productivity and production rate. 5 mol% Fe- and Co-doped CeO2-delta enhances hydrogen productivity by up to 25% on average compared to undoped CeO2, and shows stable repeatability of stoichiometric oxygen and hydrogen production for the cyclic thermochemical two-step water-splitting reaction. In addition, 5 mol% Mn-doped CeO2-delta, 10 and 15 mol% Fe- and Mn-doped CeO2-delta show near stoichiometric reactivities. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tca.2015.08.036

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The joint international project between Niigata University (Japan) and the Korea Institute of Energy Research, KIER (Korea) on "Solar Demonstration of Water-Splitting Reactor using Ceramic Foam Device" has two goals. (1) Develop a solar reactor using reactive cerium oxide foam devices for high-temperature two-step thermochemical water-splitting cycle. (2) Test its performance under various operational methods using a 40 kW(th) solar furnace driven by natural solar energy. The reactive CeO2/MPSZ (MgO partially stabilized zirconia) foam device for two-step water-splitting was developed and prepared by Niigata University/Japan; it involves coating an inert zirconia foam matrix with reactive CeO2. In this paper, highly reactive CeO2 particles were used the redox material in CeO2/MPSZ foam devices to investigate the use of solar energy for hydrogen production. The solar-driven thermochemical two-step water-splitting cycle was demonstrated using the 40 kWth KIER solar furnace in Korea combined with the CeO2/MPSZ foam device. At the center of the foam device, temperatures were 1500 degrees C-1600 degrees C during the thermal reduction step and 600 degrees C-1100 degrees C during the subsequent water decomposition step. Hydrogen was successfully produced from the CeO2/MPSZ foam device, and profiles for hydrogen production and CeO2 conversion indicated definitely improved operations compared to earlier studies. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijhydene.2014.10.084

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

A laboratory-scale prototype windowed reactor using a fluidized bed of coal coke particles was tested for thermochemical gasification using concentrated Xe light radiation as an energy source. The fluidized-bed reactor, designed to be combined with a solar reflective tower or beam-down optics, is evaluated for steam gasification of coal coke according to gasification performance: CO, H-2, and CO2 production rates; carbon conversion; light-to-chemical efficiency. Internal circulation of coal coke particles inside the reactor increases gasification performance, which is further enhanced by higher steam partial pressure of the inlet gas. (C) 2014 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.energy.2014.11.012

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

The point-concentration receiver evaluation system was developed using the world class 30 kWth light source of 19 arc xenon lamps. The system comprises of a receiver unit, heat exchanger, blower, chiller and light source. Precise measurement of the thermal power absorbed by air was performed by the enthalpy rise of the coolant water and that of the exhausted air. The experimental test was performed using silicon carbide honeycomb in order to achieve a high air temperature of 560 degrees C. The efficiency of the receiver, based on the power of the aperture, was 40% to 80%. A three-dimensional simulation based on the dual cell approach was made to reveal detailed information of the flow and temperature fields. This successfully reproduced the thermal nonequilibrium between the solid and fluid parts of the receiver. The air exit temperature and efficiency of the numerical simulation were consistent with that determined experimentally. Air was suctioned from the broad space above the receiver top surface. The adopted simulation model with the free stream was confirmed to be essential for evaluating an open loop receiver. (C) 2015 Published by Elsevier Ltd.

DOI： 10.1016/j.egypro.2015.03.058

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This study describes the flow and thermal field of a two-tower fluidized receiver, aimed to be incorporated into a beam-down reflector system. An experimental visualization and numerical simulation were made to accumulate phenomenological knowledge, in order to complete the design of a demonstration model. Visualization of the cold particle bed with no irradiation revealed that global circulation occurs between the two towers by the aeration with different line velocities. The numerical simulation revealed that this global circulation enhances the transport of sensible heat from the irradiated layer in the high pressure tower to the low pressure tower. The global circulation in the two-tower fluidized receiver has the potential to be extended for use in a thermal receiver and direct storage system. Unexpectedly, local circulations occur on the high and low pressure sides, and are stronger than the global circulation. These local circulations contribute to the thermal mixing in each tower. The bottom distributor on the low pressure side can cause an uprising flow which leads to the local circulation. The design of the distributor is suggested to be elaborated based on these findings. (C) 2015 The Authors. Published by Elsevier Ltd.

DOI： 10.1016/j.egypro.2015.03.057

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：International Solar Energy Society  

A windowed fluidized bed reactor prototype was studied and developed for solar thermochemical gasification of coal cokes with steam and CO2. The windowed fluidized bed reactor is assumed to be combined with a newly developed beam-down optics. Recently, quartz sand was employed as a chemically-inert bed material for the fluidized bed and worked as a thermal transfer/storage medium inside the reactor for coke gasification under direct light irradiation. In order to design a laboratory-scale prototype windowed fluidized-bed containing of quartz sand and coke particles, the reactor model of fluidized bed was made from a transparent acrylic resin to allow us to observe a fluidizing particle through the sidewall of the reactor body
a branching tube is equipped with the sidewall of the reactor to continuously supply coal-coke particles from a screw feeder. In the present study, in order to evaluate fluidization performance of coal-cokes, the pressure loss between the inlet and outlet gases was examined, and descending coal-coke particles on the sidewall of the reactor was observed in the reactor model. The moving velocity and distance of descending particles from the top to bottom of fluidized bed were measured by the visual observation of the tracer particles on outside wall of reactor model.

DOI： 10.18086/swc.2015.04.24

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：International Solar Energy Society  

Thermochemical energy storage using redox pair of Co3O4/CoO powders was studied for thermal energy storage (TES) using concentrated solar radiation as the energy source. Reversible chemical reactions (reduction - oxidation redox cycles) of oxides under air atmosphere are used to storage significant thermal energy via the enthalpies of the chemical reactions at high-temperature. A promising concept for solar TES is proposed using fluidized bed with Co3O4/CoO redox pair. In the present study, the effects of particles size of Co3O4/CoO powders on thermochemical storage performances are investigated in order to explore the potential of the material for fluidized-particle bed reactor. The Co3O4 powders with particle sizes of 100-200, 200-300, 300-500 and 500-700 μm were used to test redox performances by thermo-gravimetric analysis. A flowability (fluidization state) of Co3O4 powders in a fluidized bed reactor for thermochemical energy storage is also examined in this study. A basic relationship between pressure drop of inlet gas and gas flow rate was experimentally examined using bed materials with different particle sizes by a small-scale quartz reactor at ambient pressure and temperature.

DOI： 10.18086/swc.2015.04.25

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Institute of Energy  

This study proposes a t wo-tower t ype fluidized receiver for receiving concentrated s olar light at high temperatures is proposed. This fluidized receiver is coupled with the Miyazaki beam-down reflector system. The visualization and the numerical simulation was made for the laboratory model to show the fluid-dynamics and the heat transport as well as to elaborate the existing demonstration model. The experimental visualization of the cold model demonstrated that in each tower, the particles are moved by the aerated organized flow. The numerical simulation was made using the thermal input cited from the 5.0kWth sun simulator. The numerical simulation demonstrated that the inner particles are heated above 950 °C after 3.0 minutes of the aeration start time. The increase in temperature is caused by the intrusion of the heated particles from the high-pressure side tower to the low-pressure side tower. It is thus suggested that collective circulation occurs between high- and low-pressure side towers and this can be utilized for a direct thermal storage system.

DOI： 10.3775/jie.94.1323

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

The flux distributions on the device in the solar reactor with the solar furnace were studied. This study aims to understand of characters of concentrated sun rays through KIER solar furnace and design of device shape for uniform heat distribution on the device surface. For the calculation of heat flux on the device with the KIER solar furnace, the optical modeling program Soltrace was used. At first, the KIER 45 kW(th) solar furnace and flat disk type device shape was simulated for understand of past experimental results. And then 3 cylinder shape device model and 1 conical shape device model was suggested and the heat flux intensity on the device was calculated. Finally, 5 models which is including flat disk type device shape, 3 cylinder shape, and 1 conical shape device models was calculated and compared. The results show that the concentrated sun rays from dish and heat flux intensity are has a directional characteristic concentrated to normal direction than perpendicular direction. The results will be applied to next solar demonstrations which are design of new solar reactor and new device shape. (C) 2015 The Authors. Published by Elsevier Ltd.

DOI： 10.1016/j.egypro.2015.03.088

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

Thermal energy storage using phase-change materials (PCM) can be utilized for load shaving or peak load shifting when coupled to a solar thermochemical reactor, reformer, or gasifier for the production of solar fuel. The PCM is embedded in packages or used in bulk in these storage systems, and therefore the compatibility of the encapsulation materials and the selection of the PCM are key factors for ensuring the long operational life of the system. Various kinds of molten fluoride, chloride and carbonate salts, and mixed molten salt, which function at high temperatures of over 500 degrees C, are known to cause corrosion or thermal degradation. It is therefore worth studying new high-temperature PCM thermal storage alternatives to these molten salts for use in solar thermochemical processes. In this study, the focus was on aluminum-silicon alloy (Al-Si alloy) as a high-temperature PCM thermal storage medium, and the compatibility of this alloy with graphite-carbon encapsulation material was experimentally examined. The cyclic properties of thermal storage/discharge for Al-Si alloy as a latent-heat energy storage material was studied with respect to various thermal cycles. A thermal stability test was performed for the Al-20wt% Si, Al-25wt% Si, Al-30wt% Si, and Al-35wt% Si alloys placed in the graphite container in vacuum. The temperature increasing and cooling performances of the Al-Si alloy were measured during the thermal storage (heat-charge) mode and during the cooling (heat-discharge) mode. The oxidation level of the Al-Si alloy after the cyclic reaction (20 cycles) was evaluated using an electron probe microanalyzer (EPMA). (C) 2015 The Authors. Published by Elsevier Ltd.

DOI： 10.1016/j.egypro.2015.03.145

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

Hydrogen production by solar thermochemical process uses concentrated solar radiation as its energy source. Various thermochemical processes operating at technically manageable temperatures which are a solar thermochemical two-step water splitting and solar gasification of carbonaceous material have been extensively studied and demonstrated by researchers around the world. These processes are capable of converting high-temperature heat from concentrated solar radiation into clean hydrogen from water. In this study, in order to control a flowability (fluidization state) of bed materials in a fluidized bed reactor for thermochemical processes (two-step water splitting cycle and gasification of coal coke), firstly, a basic relationship between pressure drop of inlet gas and gas flow rate was experimentally examined using bed materials with different particle sizes by a small-scale quartz reactor at ambient pressure and temperature. Secondly, the CeO2 particles having the size determined by above-described flowability test were tested using a windowed fluidized bed reactor prototype. The fluidized bed of CeO2 particles was exposed to a concentrated Xe light by sun-simulator with an input power of about 5 kWth for the T-R step in order to release oxygen. The production rate and productivity of oxygen and the reactivity of CeO2 particles were examined in this paper. (C) 2015 The Authors. Published by Elsevier Ltd.

DOI： 10.1016/j.egypro.2015.03.143

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

A windowed reactor prototype of internally-circulating fluidized bed is tested and demonstrated at laboratory scale for steam gasification of coal coke irradiated directly by concentrated Xe light from a 3-kWth sun simulator. The bed material is composed of particle mixture of coal coke and quartz sand. A coal coke of the bed material works as a carbonous feedstock, while quartz sand functions as a thermal storage/transfer medium inside the reactor. The fluidized bed reactor, having a transparent window due to incoming radiation of concentrated solar beam on the ceiling of the reactor, is designed to be combined with a solar reflective tower or beam-down optics. A potential of quartz sand in the internally-circulating fluidized bed reactor is evaluated for steam gasification of coal coke by gasification performance (CO, H-2 and CO2 production rates, carbon conversion, and lightto- chemical efficiency). The gasification performances for use of the particle mixture in the reactor are compared with that for use of coal coke particle. The fluidized bed of a particle mixture including coal coke and quartz sand was gasified at lower temperature with a higher rate in comparison to that of a coal coke. Furthermore, a use of smaller and lighter coal coke particles were easily converted to gaseous species due to larger surface area as well as the gasification rates. (C) 2015 The Authors. Published by Elsevier Ltd.

DOI： 10.1016/j.egypro.2015.03.140

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Language：Japanese   Publisher：The Japan Institute of Energy  

We have developed reactive foam devices in Niigata University for solar thermochemical two-step water-splitting to produce hydrogen from water. The hydrogen productivity of the reactive foam devices was cyclically examined as an international collaboration research by using 45kW_<th> dish type solar concentrator in Korea Institute of Energy Research at Korea. Different shape of foam devices and radiation method of solar furnace were tested for solar demonstration.

DOI： 10.20550/jietaikaiyoushi.24.0_176

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Language：Japanese   Publisher：The Japan Institute of Energy  

Cerium oxide was examined as a redox material on cyclic reactivity for converting high-temperature heat into chemical fuels via solar two-step thermochemical water-splitting. In this study, in order to increase hydrogen and oxygen production in comparison to pure CeO_2, we synthesized a doping of 30mol% metal ion to the CeO_2 (30mol%M-CeO_<2-δ>), and tested the 30mol%M-CeO_<2-δ> powder for thermochemical two-step water-splitting to produce hydrogen and oxygen during cyclic reaction. The reactivity of the M-CeO_<2-δ> powder was evaluated for several cycles.

DOI： 10.20550/jietaikaiyoushi.24.0_174

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

A laboratory-scale prototype windowed internally circulating fluidized-bed reactor made of quartz sand and coal coke particles was investigated for steam gasification using concentrated Xe-light radiation as the energy source. The quartz sand was used as a chemically inert bed material for the fluidized bed, while the coal coke particles functioned as the reacting particles for the endothermic gasification reaction. The advantages of using quartz sand as the bed material for the directly irradiated gasification reactor are as follows: (1) The bed height is maintained at a constant level during the gasification. (2) The quartz sand functions as a thermal transfer/storage medium inside the reactor. The gasification performances such as the production rates of CO, H-2, and CO2; carbon conversion; and light-to-chemical energy conversion were evaluated for the fluidized-bed reactor with a thermal transfer/storage medium (quartz sand). The effects of using the bed material (quartz sand) on the gasification performance are described in this paper. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijhydene.2014.05.124

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Double-walled reactor tubes containing thermal storage materials based on the molten carbonate salts-100 wt% Na2CO3 molten salt, 90 wt% Na2CO3/10 wt% MgO and 80 wt% Na2CO3/20 wt% MgO composite materials were studied for the performances of the reactor during the heat charging mode, while those of methane reforming with steam during heat discharging mode for solar steam reforming. The variations in the temperatures of the catalyst and storage material, methane conversion, duration of reforming for obtaining high levels of methane conversion (&gt; 90%), higher heating value (HHV) power of reformed gas and efficiency of the reactor tubes were evaluated for the double-walled reactor tubes and a single-wall reactor tube without the thermal storage. The results for the heat charging mode indicated that the composite thermal storage could successfully store the heat transferred from the exterior wall of the reactor in comparison to the pure molten-salt. The double-walled reactor tubes with the 90 wt% Na2CO3/10 wt% MgO composite material was the most desirable for steam reforming of methane to realize large HHV amounts of reformed gas and higher efficiencies during heat-discharging mode. (C) 2014 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.energy.2014.01.107

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

Thermochemical two-step water splitting cycle by concentrated solar heat has been studied as an energy conversion of solar energy into hydrogen energy. The thermochemical two-step water splitting cycle using metal oxide redox pair was composed of thermal reduction (T-R) step of metal oxide at higher temperature to release oxygen and, subsequent water decomposition (W-D) step of the reduced metal oxide with steam at lower temperature to produce hydrogen. Recently, cerium oxide (CeO2) is concerned as a redox pair of the thermochemical cycle for highly reactivity and cyclicity at high temperature. In this study, we focused a kinetic analysis of thermochemical two-step water splitting using cerium oxide. Various theoretical reaction models for thermal reduction (T-R) step of CeO2 particles are examined, and the appropriate reaction model for experimental results of thermogravimetric analysis was found by Master plot method. Finally, the reaction rate equation of thermal reduction is estimated. (C) 2013 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).

DOI： 10.1016/j.egypro.2014.03.209

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

Nickel ferrite (NiFe2O4) and pure cerium oxide (CeO2) supported on monoclinic zirconia (NiFe2O4/m-ZrO2) are proposed as promising redox materials for the production of hydrogen from water via a thermochemical two-step water splitting cycle. Ceramic foam devices coated with NiFe2O4/m-ZrO2 or pure CeO2 particles are prepared as a receiver/reactor operating a thermochemical water splitting cycle to produce hydrogen. The foam devices are examined in a directly irradiated receiver/reactor by a sun simulator on a laboratory scale. The purpose of this study is to examine the evolution of oxygen and hydrogen during the cyclization reaction different thermal-reduction (T-R) temperatures of 1450 and 1550 degrees C, and to compare the reproducible and stoichiometric oxygen/hydrogen production for both foam devices through a repeatable two-step reaction. In this study, a zirconia ceramic foam was used as a matrix for the reacting materials of NiFe2O4/m-ZrO2 or CeO2 particles. The zirconia ceramic foam has a diameter of 60 mm, a thickness of 15 mm, and a porosity of 10 cpi (cell number per linear inch). The loading amounts of reacting materials are 5 wt% for NiFe2O4/m-ZrO2 and 40 wt% for CeO2 particles. A concentrated Xe-beam is radiated to the foam device in a N-2 stream for the T-R step and in a N-2/steam gas mixture for the subsequent water-decomposition (W-D) step. (C) 2013 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).

DOI： 10.1016/j.egypro.2014.03.210

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A two-step thermochemical water splitting cycle using nonstoichiometric cerium oxide is a promising solar thermochemical hydrogen production process. One of the present authors has developed new solar reactors using "internally circulating fluidized beds" with cerium oxide particles for the high-temperature cycle. These solar reactors need to be combined with a beam-down solar concentrating system. Niigata University, University of Miyazaki, and Mitaka Kohki Co. Ltd. recently started an R&D joint project to demonstrate the up-scaled fluidized bed reactors with solar. A new type of 100 kW(th) beam-down solar concentrating system was built in August, 2012 at the campus of University of Miyazaki. This paper describes the first results of solar flux measurements on the new Miyazaki beam-down system for demonstration of thermochemical water splitting reactors. The fluxes of concentrated solar radiation at the focus point were measured by moving an array of thirteen Gardon gauges. The solar power in an area of 130 x 130 cm in the focal spot was larger than 90 kWth during three hours of daytime radiation, exceeding 110 kW(th) around noon on October 12, 2012. A new CPC specific to this new beam-down system was designed and fabricated to concentrate the solar fluxes into a 44 cm diameter circle of the solar reactor aperture. The solar demonstration of the reactors will start at the Miyazaki beam-down system from October 2013. (C) 2013 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).

DOI： 10.1016/j.egypro.2014.03.211

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The joint international project of Niigata University (Japan) - Korea Institute of Energy Research, KIER (Korea) on the "Solar demonstration of Water-Splitting Reactor using Ceramic Foam Device" aims to develop a novel-type of solar reactor with reactive cerium oxide foam devices for high-temperature two-step thermochemical water splitting cycle, and to demonstrate its performances on sun with a 45-kW(th) solar furnace. The reactive CeO2 foam device for the two-step water splitting is proposed and prepared by Niigata University, Japan, and involves coating inert zirconia foam with reactive CeO2. The project includes the development of reactive foam devices, the new design and the fabrication of solar reactor with the reactive foam devices, and finally the solar demonstration on the KIER's 45-kW(th) solar furnace in Korea. In this paper, highly-active CeO2 particles were used as a redox material for preparing CeO2 foam devices. A ceramic foam disk made of MgO partially-stabilized Zirconia (MPSZ) was used as a ceramic matrix that was coated with the CeO2 particles. Solar thermochemical two-step water splitting was demonstrated with solar furnace in Korea system using the prepared CeO2-coated MPSZ (CeO2/MPSZ) foam devices. The prepared CeO2/MPSZ foam device has a diameter of 15 and 20cm and thickness of 2.5 cm, the loading of CeO2 was set to approximately 20 wt%.
Then, the temperatures of the foam device at a center position were 1400-1600 degrees C for the T-R step, and 900-1100 degrees C for the subsequent W-D step. Hydrogen was successfully produced from the CeO2-MPSZ foam by a solar thermochemical two-step water-splitting, and the rate of hydrogen production and CeO2 conversion using 15 cm CeO2/MPSZ foam device were 215.6 mL/min and 3.67%, at 1st cycle. We also performed continuous testing for 20 cm diameter of the CeO2-MPSZ device, the rate of hydrogen production and CeO2 conversion were 443 ml/min and 3.27%, 1st cycle. (C) 2013 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).

DOI： 10.1016/j.egypro.2014.03.204

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This study proposes a novel fluidized receiver for absorbing concentrated solar light at high temperatures. Previously, a tubular receiver and a volumetric receiver were developed to make high-temperature air for a solar gas turbine system. The aim was to combine these elements with a tower reflector; however, it was challenging to install these heavy receivers on the top of the tower. Currently, a fluidized receiver prototype is tested by a 3 kWh solar simulator in preparation for a field test at the Miyazaki beam-down reflector system. The fluid dynamics of the prototype receiver is numerically investigated. The currently treated receiver is an inner-circulating fluidized bed spouted by concentric gas streams with high and low velocities in the center and outer annulus, respectively. The draft tube is submerged in the particles to organize particle circulation. Concentrated light irradiates the particles through a quartz window at the top of the receiver container. Such a fluidized bed was first adopted by Kodama et al. for thermochemical reactions; however, it is currently pursued for its potential as a high-temperature receiver aimed at concentrated solar power generation. Experiments of the prototype receiver (inner diameter = 45 mm) demonstrated that the inner particles are heated to a temperature greater than 900 degrees C and that an increase of the central gas velocity removes the excess temperature near the particle bed surface. A numerical computation suggests that the large-scale circulation of particles leads to the activation of thermal mixing. The currently proposed receiver is thus expected to attenuate re-radiation losses likely to occur in a conventional volumetric porous receiver. The scale-up of the receiver is being considered by the numerical computation for a field test in the Miyazaki 100 kWh beam-down reflector system. (C) 2013 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license

DOI： 10.1016/j.egypro.2014.03.048

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Steam reforming of methane is a candidate process for converting concentrated high-temperature solar heat to chemical fuels because it is a high-temperature, highly endothermic process. We developed a tubular reformer system using novel double-walled reactor tubes with molten-salt thermal storage for solar reforming to produce hydrogen or synthetic gas (CO + H-2) from a gas mixture of methane and steam using concentrated solar radiation as an energy source. The high heat capacity and large latent heat (heat of solidification) of the molten salt circumvents rapid temperature changes in the reactor tubes at high temperatures under fluctuating insolation. In this paper, we focused on under intermittent heating-cooling mode, the steam reforming performance of double-walled reactor tubes with Na2CO3/MgO composite thermal storage in comparison to pure Na2CO3 thermal storage. A heating mode using an electric furnace simulates reactor startup in the morning and reheating of the reactor by concentrated solar radiation after brief periods of cloud passage. The intermittent heating-cooling mode simulates fluctuating incident solar radiation during cyclic short-term cloud passage. The temperature variations of the catalyst and storage material, methane conversion, and higher heating value power of the reformed gas were examined for the double-walled reactor tubes and a single-wall (C) 2013 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).

DOI： 10.1016/j.egypro.2014.03.206

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Thermochemical two-step water-splitting using CeO2 (cerium oxide) particles was studied to examine oxygen and hydrogen productivity and repeatability at thermal reduction (T-R) temperatures of 1300-1550 degrees C and water decomposition (W-D) temperatures of 400-1000 degrees C for the production of hydrogen from water using concentrated solar radiation as the energy source. The temperature dependency of oxygen and hydrogen productivity and the cyclic repeatability of CeO2 are reported in this paper. The characteristic features of CeO2 particles in the thermochemical two-step water-splitting cycle are compared with the well-known highly active reactive mediums of zirconia-supported Ni-ferrites (NiFe2O4/m-ZrO2 and NiFe2O4/c-YSZ) and unsupported NiFe2O4. Copyright (C) 2013, Hydrogen En ergy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijhydene.2013.08.108

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We investigated the thermal reduction (T-R) of NiFe2O4, either supported by m-ZrO2 or unsupported, as the oxygen-releasing step of a solar thermochemical water splitting cycle based on a ferrite/wustite redox system, by performing the Rietveld analysis using powder X-ray diffraction. The solid materials obtained after the T-R step at 1300-1400 degrees C were subjected to Rietveld analysis. The amounts and chemical compositions of the wustite phase produced by the T-R step and the remaining ferrite phase were identified quantitatively. Chemical reaction formulas for the different T-R temperatures were determined from the results. Consistency for the chemical reactions of the thermal reduction was discussed and evaluated comparing the O2 amounts predicted by the chemical reaction formulas and measured experimentally by mass spectrometry. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijhydene.2013.02.014

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Language：Japanese   Publisher：The Japan Institute of Energy  

Cerium oxide was examined as a redox material on cyclic reactivity for converting high-temperature heat into chemical fuels via solar two-step thermochemical water-splitting. In this study, the thermal reduction of metal-doped cerium particles was examined at 1500℃, and the subsequent water-decomposition step was performed at 800-1150℃. The oxygen and hydrogen productivity were measured at each step, and the stoichiometry was evaluated.

DOI： 10.20550/jietaikaiyoushi.22.0_178

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Language：Japanese   Publisher：The Japan Institute of Energy  

Cerium oxide was examined as a redox material on cyclic reactivity for converting high-temperature heat into chemical fuels via solar two-step thermochemical water-splitting. The thermal reduction of the cerium particles was conducted at 1000-1500℃, and oxygen production rate were measured. The kinetics of oxygen production for thermal reduction step was analyzed, then Arrhenius parameter and reaction model equation were evaluated.

DOI： 10.20550/jietaikaiyoushi.22.0_180

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Language：Japanese   Publisher：The Japan Institute of Energy  

Joint international project of Niigata University (Japan) -Korean Institute of Energy Research, KIER (Kora) on the "Solar demonstration of Water-Splitting Reactor using Ceramic Foam Device" aims to develop a novel-type of solar reactor with reactive cerium- or iron oxides-coated foam devices for high-temperature two-step thermochemical water splitting cycle, and to demonstrate its performances on sun with a 40-kW_<th> solar furnace. The reactive CeO_2 foam device for the two-step water splitting is proposed and prepared by Niigata University, Japan, and involves coating an inert zirconia foam with reactive CeO_2 or ferrite-zirconia redox materials. The project includes the development of reactive foam devices, the new design and the fabrication of solar reactor with the reactive foam devices, and finally the solar demonstration on the KIER's 45-kW_<th> solar furnace in Korea. In this paper, highly-active CeO_2 particles were used as a redox material for preparing CeO_2 foam devices. A ceramic foam disk made of MgO partially-stabilized Zirconia (MPSZ) was used as a ceramic matrix that was coated with the CeO_2 particles. Solar thermochemical two-step water splitting was demonstrated using the prepared CeO_2-coated MPSZ (CeO_2/MPSZ) foam devices in Korea.

DOI： 10.20550/jietaikaiyoushi.22.0_184

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Language：Japanese   Publisher：The Japan Institute of Energy  

Thermochemical two-step water-splitting cycle, which utilizes concentrated solar radiation as a energy source and uses steam as a chemical source, is a one of the most promising hydrogen productions from water, We are developing 2 types of windowed solar chemical reactors with internally-circulating fluidized bed of cerium oxide particles for hydrogen production via thermochemical two-step water-splitting. In the present work, the performance of each solar reactor with the internally circulating fluidized beds was examined for two-step water splitting of thermal reduction and water-decomposition using their particles under 5kW_<th> sun-simulator.

DOI： 10.20550/jietaikaiyoushi.22.0_182

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

For the solar thermochemical gasification of coal coke to produce CO + H-2 synthetic gas using concentrated solar radiation, a windowed reactor prototype is tested and demonstrated at laboratory scale for CO2 gasification of coal coke using concentrated Xe light from a 3-kW(th) sun simulator. The reactor was designed to be combined with a solar reflective tower or beam-down optics. The results for gasification performance (CO production rate, carbon conversion, and light-to-chemical efficiency) are shown for various CO2 flow rates and ratios. A kinetics analysis based on homogeneous and shrinking core models and the temperature distributions of the prototype particle bed are compared with those for a conventional fluidized bed reactor tested under the same Xe light irradiation and CO2 flow-rate conditions. The effectiveness and potential impacts of internally circulating fluidized bed reactors for enhancing gasification performance levels and inducing consistently higher bed temperatures are discussed in this paper. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijhydene.2012.05.133

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A two-step thermochemical water splitting cycle using a redox system of non-volatile metal oxide is one of the promising processes for converting concentrated solar high-temperature heat into clean hydrogen in sun-belt regions. In the 1st step of the cycle or the thermal reduction step, metal oxide is thermally reduced to release oxygen molecules in an inert gas atmosphere at a higher temperature above 1400 degrees C. In the second step or the water-decomposition step at a lower temperature, the thermally-reduced metal oxide reacts with steam to produce hydrogen. As the reactive redox metal oxide materials to be capable of working below 1400 degrees C, nickel-doped iron oxides or Ni-ferrites supported on zirconia, and non-stoichiometric cerium oxides are the promising working materials. In the present work, a series of the nickel-ferrite redox materials of monoclinic-zirconia-supported, cubicYSZ(yttrium-stabilized zirconia)-supported, and non-supported Ni-ferries and non-stoichiometric cerium oxide were compared on reactivity for two-step thermochemical water splitting cycle. The monoclinic-zirconia-supported Ni-ferrite produced the most quantity of hydrogen in the repeated cycles when the thermal reduction step was performed for 30 mm at 1400 degrees C and the water decomposition step for 60 min at 1000 degrees C.

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We have developed reactive foam devices for solar thermochemical two-step water-splitting to produce hydrogen from water. We have researched the hydrogen production activity of the reactive foam devices by 3kW sun-simulator in Niigata University and by 5kW dish type solar concentrator in Inha University in Korea. Solar hydrogen productions were cyclically demonstrated for nine cycles at solar irradiation test at Korea.

DOI： 10.20550/jietaikaiyoushi.21.0_226

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Language：Japanese   Publisher：The Japan Institute of Energy  

Catalytically-activated ceramic foam device has been developed as a solar receiver/absorber for use in methane reforming under concentrated solar radiation as an energy source. Ni/MgO-Al_2O_3 catalysts were loaded on the SiC ceramic foam. Catalytic activity and kinetics for methane reforming were studied using Ni/MgO-Al_2O_3/SiC foam device under Xe-light irradiation and electric furnace, respectively.

DOI： 10.20550/jietaikaiyoushi.21.0_230

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Language：Japanese   Publisher：The Japan Institute of Energy  

Double-walled reactor tubes with molten-salt thermal storage were developed for solar air receiver to generate electricity and for solar reforming to produce solar fuel. A mixture of Na_2CO_3 and MgO was loaded as a thermal storage medium into the outer annulus of that. Performances of the reactor tubes were studied as an air receiver and as a reformer tube in the present study.

DOI： 10.20550/jietaikaiyoushi.21.0_232

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Thermochemical two-step water splitting using a redox system of iron-based oxides or ferrites is a promising process for producing hydrogen without CO2 emission by the use of high-temperature solar heat as an energy source and water as a chemical source. In this study, thermochemical hydrogen production by two-step water splitting was demonstrated on a laboratory scale by using a single reactor of an internally circulating fluidized bed. This involved the successive reactions of thermal-reduction (T-R) and water-decomposition (W-D). The internally circulating fluidized bed was exposed to simulated solar light from Xe lamps with an input power of 2.4-2.6 kW(th) for the T-R step and 1.6-1.7 kW(th) for the subsequent W-D step. The feed gas was switched from an inert gas (N-2) in the T-R step to a gas mixture of N-2 and steam in the W-D step. NiFe2O4/m-ZrO2 and unsupported NiFe2O4 particles were tested as a fluidized bed of reacting particles, and the production rate and productivity of hydrogen and the reactivity of reacting particles were examined. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijhydene.2011.01.076

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

A Ferrite/zirconia foam device in which reticulated ceramic foam was coated with zirconia-supported Fe(3)O(4) or NiFe(2)O(4) as a reactive material was prepared by a spin-coating method. The spin-coating method can shorten the preparation period and reduce the coating process as compared to the previous wash-coating method. The foam devices were examined for hydrogen productivity and cyclic reactivity in thermochemical two-step water-splitting. The reactivity of these foam devices were studied for the thermal reduction of ferrite on a laboratory scale using a sun simulator to simulate concentrated solar radiation, while the thermally reduced foam devices were reacted with steam in another quartz reactor under homogeneous heating in an infrared furnace. The most reactive foam device, NiFe(2)O(4)/m-ZrO(2)/MPSZ, was tested for successive two-step water-splitting in a windowed single reactor using solar-simulated Xe-beam irradiation with a power input of 0.4-0.7 kW(th). The production of hydrogen continued successfully in the 20 cycles that were demonstrated using the NiFe(2)O(4)/m-ZrO(2)/MPSZ foam device. The NiFe(2)O(4)/m-ZrO(2)/MPSZ foam device produced hydrogen at a rate of 1.1-4.6 cm(3) per gram of device through 20 cycles and reached a maximum ferrite conversion of 60%. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijhydene.2010.11.034

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The kinetics of methane reforming over Ru/gamma-Al2O3-catalyzed high porosity Ni-Cr-Al foam were examined at temperatures of 650-900 degrees C in a quartz tubular reactor using an electric furnace. The kinetic data were analyzed by four different types of kinetic models based on the basic, Eley-Rideal, Langmuir-Hinshelwood, and stepwise mechanisms. Validation of the kinetic models was carried out by calculating the determination coefficient r(2) between the predicted and the experimental results for each model. The absolute average deviation percentage (AAD%) between the predicted and the experimental results was also estimated for each model. The kinetic model based on the reversible stepwise mechanism provided the best prediction of the experimental reforming rates with an AAD value of 6% in the range 650-850 degrees C. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijhydene.2010.09.042

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Cerium oxide was examined as a redox material on cyclic reactivity for converting high-temperature heat into chemical fuels via solar two-step thermochemical water-splitting. The thermal reduction of the cerium particles was conducted at 1300-1550℃, and the subsequent water-decomposition step was performed at 1000℃. The oxygen and hydrogen productivity were measured at each step, and the stoichiometry was evaluated.

DOI： 10.20550/jietaikaiyoushi.20.0_216

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Language：Japanese   Publisher：The Japan Institute of Energy  

A windowed solar chemical reactor with an internally-circulating fluidized bed of metal oxides particles has been developed for realizing hydrogen production from water via the thermochemical two-step water-splitting cycle. In this research, the authors tried to systemize the two-step water-splitting processes into single-step in an internally-circulating fluidized bed reactor. The single-step systemized reactor using the internally-circulating fluidized bed of reacting particles was tested by solar-simulated Xe light irradiation and evaluated on hydrogen productivity.

DOI： 10.20550/jietaikaiyoushi.20.0_218

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Language：Japanese   Publisher：The Japan Institute of Energy  

Reactive ceramics of m-ZrO_2-supported NiFe_2O_4 and unsupported NiFe_2O_4 were analyzed by Rietveld method for enhancing hydrogen productivity for solar thermochemical two-step water-splitting. In this paper, the reduced phase (wustite phase) and the remaining ferrite phase obtained after that their reactive ceramics were thermally reduced at 1300-1400℃ was examined, and the composition and the existence ratio of them were determined. The relation between the reduction temperature and the reaction activity was discussed.

DOI： 10.20550/jietaikaiyoushi.20.0_214

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Language：Japanese   Publisher：The Heat Transfer Society of Japan  

DOI： 10.11368/nhts.2011.0.343.0

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ASME-AMER SOC MECHANICAL ENG  

Solar thermochemical processes, such as solar gasification of coal, require the development of a high temperature solar reactor operating at temperatures above 1000 degrees C. Direct solar energy absorption by reacting coal particles provides efficient heat transfer directly to the reaction site. In this work, a windowed reactor prototype designed for the beam-down optics was constructed at a laboratory scale and demonstrated for CO(2) gasification of coal coke using concentrated visible light from a sun-simulator as the source of energy. Peak conversion of light energy to chemical fuel ( CO) of 14% was obtained by irradiating a fluidized bed of 500-710 mu m coal coke size fraction with a power input of about 1 kW and a CO(2) flow-rate of 6.5 dm(3) min(-1) at normal conditions. [DOI: 10.1115/1.4002081]

DOI： 10.1115/1.4002081

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In this work, we compare the activity of unsupported and monoclinic zirconia supported nickel ferrites, calcined at two different temperatures, for solar hydrogen production by two-step water-splitting thermochemical cycles at low thermal reduction temperature. Commercial nickel ferrite, both as-received and calcined in the laboratory, as well as laboratory made supported NiFe(2)O(4), are employed for this purpose. The samples leading to higher hydrogen yields, averaged over three cycles, are those calcined at 700 degrees C in each group (supported and unsupported) of materials. The comparison of the two groups shows that higher chemical yields are obtained with the supported ferrites due to better utilisation of the active material. Therefore, the highest activity is obtained with ZrO(2)-supported NiFe(2)O(4) calcined at 700 degrees C. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijhydene.2010.05.032

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Ni catalyst supported on MgO-Al2O3 (Ni/MgO-Al2O3) prepared from hydrotalcite, and Ni-Mg-O catalyst are studied in regard to their activity in the CO2 reforming of methane at high temperatures in order to develop a catalytically activated foam receiver absorber for use in solar reforming. First, the activity of their powder catalysts is examined. Ni/MgO-Al2O3 powder catalyst exhibits a remarkable degree of high activity and thermal stability as compared with Ni-Mg-O powder catalyst. Secondly, a new type of catalytically activated ceramic foam absorber - Ni/MgO-Al2O3/SiC - and Ni-Mg-O catalyzed SiC foam absorber are prepared and their activity is evaluated using a laboratory-scale receiver reactor with a transparent quartz window and a sun-simulator. The present Ni-based catalytic absorbers are more cost effective than conventional Rh/gamma-Al2O3 catalyzed alumina and SiC foam absorbers and the alternative Ru/gamma-Al2O3 catalyzed SiC foam absorbers. Ni/MgO-Al2O3 catalyzed SiC foam absorber, in particular, exhibits superior reforming performance that provides results comparable to that of Rh/gamma-Al2O3 catalyzed alumina foam absorber under a high flux condition or at high temperatures above 1000 degrees C. Ni/MgO-Al2O3 catalyzed SiC foam absorber will be desirable for use in solar receiver reactor systems to convert concentrated high solar fluxes to chemical fuels via endothermic natural-gas reforming at high temperatures. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijhydene.2010.04.040

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ASME  

A windowed internally circulating fluidized bed reactor was tested using m-ZrO2-supported NiFe2O4 (NiFe2O4/m-ZrO2) particles as redox material for thermochemical two-step water splitting to produce hydrogen from water. The internally circulating fluidized bed of NiFe2O4/m-ZrO2 particles is directly heated by solar-simulated Xe light irradiation through a transparent quartz window mounted on top of the reactor. A sun simulator with three Xe lamps at laboratory scale has been newly installed in our laboratory for testing the fluidized bed reactor. The input power of incident Xe light can be scaled up to 2.6 kW(th). Temperature distributions within the fluidized bed are measured under concentrated Xe light irradiation with an input power of 2.6 kW(th). Hydrogen productivity and reactivity for the fluidized bed of NiFe2O4/m-ZrO2 particles are examined using two different reactors under the N-2 flow rate and flow ratio, which yield a higher bed temperature. The feasibility of successive two-step water splitting using the fluidized bed reactor is examined by switching from N-2 gas flow in the thermal reduction step to a steam/N-2 gas mixture in the water decomposition step. It is confirmed that hydrogen production takes place in the single fluidized bed reactor by successive two-step water splitting. [DOI: 10.1115/1.4001154]

DOI： 10.1115/1.4001154

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Reforming performances for the double-walled reactor tubes with Na2CO3/MgO composite thermal storage was examined by an intermittent heating The intermittent heating of the reactor tubes is composed of the heat-discharge (or cooling) mode and the subsequent heating mode. The heat-discharging mode simulates a fluctuating Insolation for cloud passages The heating mode simulates a heating of reactor due to concentrated solar radiation by using an electric furnace. The internal tube of the reactor was packed with the 2wt%Ru/Al2O3 catalyst balls while the thermal storage materials were filled in the annular region of the reactor tubes The reactor was heated up to 920 degrees C in the cylindrical electric furnace and the CH4/CO2 mixture was fed into the internal catalyst tube at gas hourly space velocity (GHSV) of 12500 h(-1).
Through the cooling mode and the subsequent heating mode, temperature variations of reactor tubes, catalyst and composite material, H-2/CO ratio variations of effluent gas from the reactor, higher heating value (HHV) power of reformed gas were respectively examined for the double-walled reactor tubes and a single-wall reactor tube without the thermal storage.

DOI： 10.1115/ES2010-90114

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We have developed ferrite-coated foam devices for solar thermochemical two-step water-splitting to produce hydrogen from water. The reactivity of the foam device was firstly tested by 1 kW solar simulator at a laboratory scale experiment. Hydrogen was continuously produced for 20 cycles. Then, the foam device was tested by 5 kW dish type solar concentrator in Inha University in Korea. As a result, solar hydrogen production was demonstrated for several cycles.

DOI： 10.20550/jietaikaiyoushi.19.0_232

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Language：Japanese   Publisher：The Japan Institute of Energy  

Reactive ceramic was studied as a redox material for converting high-temperature heat into chemical fuels via solar two-step thermochemical water-splitting. In the present study, cyclic reactivity of reactive ceramic such as, Fe-containing YSZ particles was examined using thermal reduction temperatures of 1400-1500°C.

DOI： 10.20550/jietaikaiyoushi.19.0_230

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Language：Japanese   Publisher：The Japan Institute of Energy  

Catalytically-activated ceramic foam device has been developed as a solar receiver/absorber for use in methane reforming under concentrated solar radiation as an energy source. Ni-Mg-O and Ni/MgO-Al_2O_3 catalysts were loaded on the SiC ceramic foam. They were examined on activity in CO_2 reforming of methane under solar -simulated Xe light radiation by a windowed reformer.

DOI： 10.20550/jietaikaiyoushi.19.0_234

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The molten-salt tubular absorber/reformer (MoSTAR) project aims to develop a novel type of "double-walled" tubular absorber/reformer with molten-salt thermal storage at high temperature for use in solar natural-gas reforming and solar air receiver, and to demonstrate its performances on the sun with a 5 kW(t) dish-type solar concentrator. The new concept of double-walled reactor tubes is proposed for use in a solar reformer by Niigata University, Japan, and involves packing a molten/ceramic composite material in the annular region between the internal catalyst tube and the exterior solar absorber wall. This solar tubular absorber concept may be also applied to solar air receiver for solar thermal power generation. The MoSTAR project includes the development of molten-salt thermal storage media, the new design and the fabrication of absorber/reformer with the double-walled absorber tubes, and finally the solar demonstration on the 5 kW(t) dish concentrator of Inha University in Korea. In this paper, thermal storage media of the series of Na2CO3-MgO composite materials were tested in a double-walled reformer tube with a thermal storage capacity of about 0.3 kWh. The chemical reaction performances for dry reforming of methane during cooling or heat-discharge mode of the reactor tube were investigated using an electric furnace. The experimental results obtained under feed gas mixture of CH4/CO2=1:3 at a residence time of 0.3 s and at 1 atm showed that the single reactor tube with 90 wt % Na2CO3/10 wt % MgO composite material successfully maintained a high methane conversion above 90% with about 0.9 kW reforming scale based on high heating value during 45 min of the heat-discharge mode. The chemical reaction performances of the reactor tube were investigated also for the solar-simulating operation mode. The application of the new reactor tubes to solar tubular reformers is expected to help realize stable operation of the solar reforming process under fluctuating insolation during a cloud passage.

DOI： 10.1115/1.3197840

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Composite materials with alkali carbonate and magnesia have been examined for high-temperature thermal storage in solar tubular reformers. The concept of a double-walled reactor tube involves packing a molten-salt/ceramic composite material into the annular region between internal catalyst tube and exterior solar-absorber wall. In this paper, the shape and interior structure of the reactor tube are newly designed for use in solar cavity-type reformers using straight reactor tubes. Na2CO3, K2CO3, and Li2CO3 composite materials with magnesia were tested as thermal storage media for CO2 reforming of methane during cooling mode of the reactor tube at a laboratory scale. The efficiency of Na2CO3/MgO composite with various MgO contents was also estimated. Composite materials of Na2CO3 80-90 wt% and MgO 20-10 wt% were successfully delayed the cooling of the catalyst bed and sustained methane conversion at &gt;90%. A solar cavity-type reformer consisting of multiple straight reactor tubes is expected to enable stable operation of the solar reforming process under fluctuating solar insolation during cloud passage. (C) 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijhydene.2009.06.047

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A thermochemical two-step water splitting cycle is examined for NiFe2O4 and Fe3O4 supported on monoclinic ZrO2 (NiFe2O4/m-ZrO2 and Fe3O4/m-ZrO2) in order to produce hydrogen from water at a high-temperature. The evolution of oxygen and hydrogen by m-ZrO2-supported ferrite powders was studied, and reproducible and stoichiometric oxygen/hydrogen productions were demonstrated through a repeatable two-step reaction. Subsequently, a ceramic foam device coated with NiFe2O4/m-ZrO2 powder was made and examined as a water splitting device by the direct irradiation of concentrated Xe-light in order to simulate solar radiation. The reaction mechanism of the two-step water splitting cycle is associated with the redox transition of ferrite/wustite on the surface of m-ZrO2. A hydrogen/oxygen ratio for these redox powder systems exhibited good reproducibility of approximately two throughout the repeated cycles. The foam device loaded NiFe2O4/m-ZrO2 powder was also successful with respect to hydrogen production through 10 repeated cycles. A ferrite conversion of 24-76% was obtained over an irradiation period of 30 min. (C) 2008 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.solener.2008.10.003

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ASME-AMER SOC MECHANICAL ENG  

The thermal reduction of metal oxides as part of a thermochemical two-step water-splitting cycle requires the development of a high-temperature solar reactor operating at 1000-1500 degrees C. Direct solar energy absorption by metal-oxide particles provides direct efficient heat transfer to the reaction site. This paper describes the experimental results of a windowed small reactor using an internally circulating fluidized bed of reacting metal-oxide particles under direct solar-simulated Xe-beam irradiation. Concentrated Xe-beam irradiation directly heats the internally circulating fluidized bed of metal-oxide particles. NiFe(2)O(4)/m-ZrO(2) (Ni-ferrite on zirconia support) particles are loaded as the working redox material and are thermally reduced by concentrated Xe-beam irradiation. In a separate step, the thermally reduced sample is oxidized back to Ni-ferrite with steam at 1000 degrees C. The conversion efficiency of ferrite reached 44% (+/- 1.0%), which was achieved using the reactor at 1 kW of incident Xe lamp power. The effects of preheating temperature and NiFe(2)O(4)/m-ZrO(2) particle size on the performance of the reactor for thermal reduction using an internally circulating fluidized bed were evaluated.

DOI： 10.1115/1.3027511

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Two-step thermochemical water-splitting using monoclinic ZrO2-supported Fe3O4 (Fe3O4/m-ZrO2) for hydrogen production was examined at high thermal reduction temperatures of 1400-1600 degrees C. After thermal reduction of Fe3O4/m-ZrO2, the reduced sample was quenched in liquid nitrogen, and was subsequently subjected to the water-decomposition step at 1000 degrees C. Quenching of the solid sample was conducted for analysis of the chemical reactions, such as phase transitions, occurring at high-temperature. The hydrogen productivity of Fe3O4 on a m-ZrO2 support and the conversion of Fe3O4 to FeO were significantly enhanced with higher thermal reduction temperatures. The Fe3O4-to-FeO conversion reached 60% when the Fe3O4/m-ZrO2 was thermally reduced at 1600 degrees C. The phase transition of m-ZrO2 support to tetragonal ZrO2 (t-ZrO2) did not occur during the thermal reduction at 1400-1500 degrees C, but it did proceed slightly at 1600 degrees C. Fe ions from Fe3O4 did not enter the ZrO2 lattice during high-temperature thermal reduction. Thus, the Fe3O4 loaded on a m-ZrO2 support can continuously contribute as a Fe3O4-FeO redox reactant for thermochemical water-splitting at high-temperatures of 1400-1600 degrees C. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijhydene.2008.12.007

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Ni-Cr-Al metallic foam absorber with high porosity was catalytically activated using a Ru/gamma-Al2O3 catalyst, and was subsequently tested with respect to CO2 reforming of methane in a small-scale volumetric receiver-reactor by using a sun-simulator. A chemical storage efficiency of 37% was obtained for a mean light flux of 325 kW m(-2). Furthermore, the activity and the stability of the metallic foam absorber were compared with those of a SiC foam absorber activated with the same Ru/gamma-Al2O3 catalyst for 50 h of light irradiation, and it was found that the metallic foam absorber has superior catalytic stability in comparison to the SiC form absorber. In addition, unlike ceramic foams such as SiC, metallic foams feature superior plasticity, which prevents the emergence of cracks caused by mechanical or thermal shock.
The kinetics of CO2 reforming of methane over Ru/gamma-Al2O3/metallic foams was also examined for temperatures of 600-750 degrees C using a quartz tube reactor and an electric furnace. The experiments were performed by varying the methane/CO2 ratios of 0.3-3.0. Moreover, the kinetic data were fitted to four different types of kinetic models, namely the Langmuir-Hinshelwood, Basic, Eley-Rideal, and Stepwise mechanisms. The kinetic model which provided the best prediction of the experimental reforming rates was the Langmuir-Hinshelwood mechanism for temperatures of 600-700 degrees C. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijhydene.2008.12.018

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Ni-Cr-Al alloy foam absorber with high porosity was catalytically activated using a Ru/gamma-Al(2)O(3) catalyst, and was subsequently tested with respect to CO(2) reforming of methane in a small-scale volumetric receiver-reactor by using a sun simulator. A chemical storage efficiency of about 40% was obtained for a mean light flux of 325 kW m(-2). Furthermore, the activity and the stability of the metallic foam absorber were compared with those of a SiC foam absorber activated with the same Ru/gamma-Al(2)O(3) catalyst for 50 h of light irradiation, and it was found that the metallic foam absorber has superior catalytic stability in comparison to the SiC form absorber. In addition, unlike ceramic foams such as SiC, metallic foams feature superior plasticity, which prevents the emergence of cracks caused by mechanical or thermal shock.
The kinetics of CO(2) reforming of methane over metallic foam absorbers were also examined for temperatures of 600-750 degrees C using a quartz tube reactor and an electric furnace. The experiments were performed by varying the methane/CO(2) ratios of 0.5-2.3. Moreover, the kinetic data were fitted to four different types of kinetic models, namely the Langmuir-Hinshelwood, Basic, Eley-Rideal, and Stepwise mechanisms. The kinetic model which provided the best prediction of the experimental reforming rates was the Langmuir-Hinshelwood mechanism.

DOI： 10.1016/j.ijhydene.2008.12.018

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A two-step water-splitting thermochemical cycle using redox working material of iron-based oxide (ferrite) particles has been developed for converting solar energy into hydrogen. The two-step thermochemical cycle for producing a solar hydrogen from water requires a development of a high temperature solar-specific receiver-reactor operating at 1000-1500 degrees C.
In the present work, ferrite-loaded ceramic foams with a high porosity (7 cells per linear inch) were prepared as a water splitting device by applying ferrite/zirconia particles on a MgO-partially stabilized Zirconia (MPSZ) ceramic foam. The water splitting foam device was prepared using a new method of spin coating. A spin coating method we newly employed that has advantages of shortening preparation period and reducing of the coating process in comparison to previous preparation method reported. The water-splitting foam devices, thus prepared, were examined on hydrogen productivity and reactivity through a two-step thermochemical cycle.
NiFe(2)O(4)/m-ZrO(2)/MPSZ and Fe(3)O(4)/c-YSZ/MPSZ foam devices were firstly tested for thermal reduction of ferrite using the laboratory scale receiver-reactor by a sun-simulator to simulate concentrated solar radiation. Subsequently, with another quartz reactor the light-irradiated device was reacted with steam by infrared furnace. As a result, it was possible to perform cyclic reactions over several times and to produce hydrogen through thermal-reduction at 1500 degrees C and water-decomposition at 1100-1200 degrees C.
In further experiments, the NiFe(2)O(4)/m-ZrO(2)/MPSZ foam device was successfully demonstrated in a windowed single reactor for cyclic hydrogen production by solar-simulated Xe-beam irradiation with input power of 1 kW. The NiFe(2)O(4)/m-ZrO(2)/MPSZ foam device produced hydrogen of 70-190 mu mol per gram of device through 6 cycles and reached ferrite conversion of 60% at a maximum.

DOI： 10.1115/ES2009-90172

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER SOC MECHANICAL ENGINEERS  

The Molten-Salt Tubular Absorber/Reformer (MoSTAR) Project, which is jointly conducted by Niigata University, Japan, and Inha University, Korea, aims to develop a novel-type of "double-walled" tubular absorbers/reformers with molten-salt thermal storage at high temperature for use in solar natural-gas reforming and solar air receiver, and to demonstrate their performances on sun with a 5-kW, dish-type solar concentrator. The new concept of "double-walled" reactor tubes was proposed for use in a solar reformer by Niigata University, Japan, and involves packing a molten salt in the annular region between the internal catalyst tube and the exterior solar absorber tube of the double reactor tube. In this work, "metal-plate-bridged" double reactor tubes are newly proposed for use in a solar reformer. Two different sized reactor tubes are constructed, and tested on chemical reaction performance for dry reforming of methane during cooling or heat-discharge mode of the reactor tube using an electric furnace. The experimental results obtained under feed gas mixture of CH(4)/CO(2) = 1:3 at a residence time of 0.36 s and at 1 atm showed that the double reactor tube with the heat storage medium Na(2)CO(3) in the annular region successfully sustained a high methane conversion above 90% with about 0.7-kW output power of the reformed gas based on HHV for 40 min of the heat-discharge mode. The application of the new reactor tubes to solar tubular reformers is expected to help realize stable operation of the solar reforming process under fluctuating insolation during a cloud passage.

DOI： 10.1115/ES2009-90230

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER SOC MECHANICAL ENGINEERS  

Ni-Cr-Al alloy foam absorber with high porosity was catalytically activated using a Ru/gamma-Al(2)O(3) catalyst, and was subsequently tested with respect to CO(2) reforming of methane in a small-scale volumetric receiver-reactor by using a sun simulator. A chemical storage efficiency of about 40% was obtained for a mean light flux of 325 kW m(-2). Furthermore, the activity and the stability of the metallic foam absorber were compared with those of a SiC foam absorber activated with the same Ru/gamma-Al(2)O(3) catalyst for 50 h of light irradiation, and it was found that the metallic foam absorber has superior catalytic stability in comparison to the SiC form absorber. In addition, unlike ceramic foams such as SiC, metallic foams feature superior plasticity, which prevents the emergence of cracks caused by mechanical or thermal shock.
The kinetics of CO(2) reforming of methane over metallic foam absorbers were also examined for temperatures of 600-750 degrees C using a quartz tube reactor and an electric furnace. The experiments were performed by varying the methane/CO(2) ratios of 0.5-2.3. Moreover, the kinetic data were fitted to four different types of kinetic models, namely the Langmuir-Hinshelwood, Basic, Eley-Rideal, and Stepwise mechanisms. The kinetic model which provided the best prediction of the experimental reforming rates was the Langmuir-Hinshelwood mechanism.

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A thermochemical two-step water splitting cycle using a redox system of iron-based oxides or ferrites is one of the promising processes for converting solar energy into clean hydrogen in sunbelt regions. Fe3O4 supported on YSZ (Yttrium-Stabilized Zirconia) or Fe3O4/YSZ is a promising working material for the two-step water splitting cycle. In the water splitting cycle, an iron-containing YSZ or Fe2+-YSZ is formed by a high-temperature reaction between Fe3O4 and YSZ support at 1400 degrees C in an inert atmosphere. The Fe2+-YSZ reacts with steam and generate hydrogen at 1000 degrees C, to form Fe3+-YSZ that is re-activated by a thermal reduction ill a;separate step at 1400 degrees C under an inert atmosphere. In the present work, the thermal reduction was performed in a higher temperature range of 1400-1500 degrees C while the hydrolysis reaction was carried Out at 1000 degrees C. It was confirmed by XRD analysis that the cyclic redox reactions Occurred based on the same reaction mechanism when using a thermal reduction temperature between 1400 and 1500 degrees C. The conversions of Fe3O4 to Fe2+-YSZ were 20, 26 and 47% when the thermal reduction temperature were 1400, 1450, and 1500 degrees C respectively, indicating that the x values in the formed Fe2+-YSZ or Fex2+YyZr1-yO2-y/2+x, were 0.08, 0.11, and 0.19 respectively, where y = 0.15. The conversions of Fe2+-YSZ to Fe3+-YSZ ill the hydrolysis reaction (at 1000 degrees C), however, decreased from 90% to 60% when the thermal reduction temperature increased from 1400 to 1500 degrees C. As the results, the hydrogen production reactivity of Fe3O4 supported on YSZ increased from 5.6 x 10(-4) to 7.5 x 10(-4) g per gram of Fe3O4/YSZ for one cycle on the cycle average by elevated thermal reduction temperature from 1400 to 1500 degrees C.

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Language：Japanese   Publisher：The Japan Institute of Energy  

A windowed solar chemical reactor with internally-circulating fluidized bed of ferrite particles has been developed for realizing hydrogen production from water via the thermochemical cycle. In this research, unsupported NiFe_2O_4 and m-ZrO_2 supported NiFe_2O_4 were tested for successive two-step water-splitting using the internally-circulating fluidized bed reactor by solar-simulated Xe light irradiation.

DOI： 10.20550/jietaikaiyoushi.18.0_312

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Language：Japanese   Publisher：The Japan Institute of Energy  

Catalytically-activated metallic foam device has been developed for methane reforming under direct solar radiation. Ru/γ-Al_2O_3 catalyst was loaded on the metallic foam, and was tested on activity in CO_2 reforming of methane under solar-simulated Xe light irradiation by volumetric reactor. Kinetics of methane reforming with CO_2 was also examined using the foam devices in the temperature range of 750-850℃ by uniform heating using electric furnace.

DOI： 10.20550/jietaikaiyoushi.18.0_306

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Language：Japanese   Publisher：The Japan Institute of Energy  

Two-step thermochemical water-splitting cycle were examined on activity and reactivity for NiFe_2O_4/m-ZrO_2 and NiFe_2O_4/c-YSZ using thermal reduction temperatures of 1400-1500℃ for the purpose of converting solar-high temperature heat into hydrogen. In addition, reaction mechanism of two-step water splitting was evaluated for NiFe_2O_4/m-ZrO_2 and NiFe_2O_4/c-YSZ using XRD analysis and chemical analysis.

DOI： 10.20550/jietaikaiyoushi.18.0_304

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Language：Japanese   Publisher：The Japan Institute of Energy  

A solar reformer of the "double-walled" reactor tubes with molten-salt has been developed for carbon dioxide reforming of methane using high-temperature solar heat. Ru/Al_2O_3 catalyst particles were loaded in the inner tube of the double-walled tubular reactor while a mixture of Na_2CO_3 and MgO was loaded as a thermal storage medium into the outer annulus of that. In the present work, variation of insolation due to cloud passage was simulated by intermittent heating, and reforming performances of the reformer tubes were examined.

DOI： 10.20550/jietaikaiyoushi.18.0_308

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN INST METALS  

The faceting of the grain boundary in the binary Cu-Bi system was experimentally observed by transmission electron microscopy (TEM). For the observation, Cu bicrystals with Sigma 33, Sigma 9 and Sigma 11[110] symmetric tilt boundaries were doped with Bi at 1173 K for 120 h, and then homogenized at 1173 K for 48 h. followed by furnace cooling or water quenching. The misorientation angle between the [001] directions of the two single-crystals is 20.1 degrees, 39.9 degrees and 50.5 degrees for the Sigma 33, Sigma 9 and Sigma 11 boundaries, respectively. According to the TEM observation, the grain boundary is faceted markedly in the bicrystal with furnace cooling but barely in that with water quenching. Thus, the faceting takes place during furnace cooling but not during homogenization. The faceting was analyzed quantitatively on the basis of the inclination angle dependence of the boundary energy in Cu. The analysis yields that the contribution of the torque term to the faceting is important. Comparing the boundary diffusivities of Bi and Cu in Cu, we may expect that the mobility is much greater for the grain boundary with Bi than for that without Bi. As a result, the faceting during furnace cooling takes place considerably for the grain boundary with Bi but scarcely for that without Bi. [doi: 10.2320/matertrans.MRA2008062]

DOI： 10.2320/matertrans.MRA2008062

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Fe3O4 supported on cubic yttria-stabilized zirconia (Fe3O4/C-YSZ) is proposed as a promising redox material for the production of hydrogen from water via a thermochemical two-step water-splitting cycle. In this study, the evolution of oxygen and hydrogen during the cyclic reaction was examined using Fe3O4/C-YSZ particles in order to demonstrate reproducible and stoichometric oxygen/hydrogen production through a repeatable two-step reaction. Subsequently, a ceramic foam device coated with Fe3O4 and c-YSZ particles was prepared and examined as a thermochemical water-splitting device in a directly irradiated receiver/reactor hydrogen production system. The Fe3O4/C-YSZ system formed a Fe-containing YSZ (Fe-YSZ) by high-temperature reaction between Fe3O4 and the c-YSZ support at 1400 degrees C in an inert atmosphere. The reaction mechanism of the two-step water-splitting cycle is associated with the redox transition of Fe2+-Fe3+ ions in the c-YSZ lattice. The Fe-YSZ particles exhibit good reproducibility for reaction with a hydrogen/oxygen ratio of approximately 2.0 throughout repeated cycles. The foam device coated with Fe-YSZ particles was also successful for continual hydrogen production through 32 repeated cycles. A 20-27% ferrite conversion was obtained using 10.5 wt% Fe3O4 loading over an irradiation period of 60 min. (C) 2008 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.energy.2008.04.011

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Considerable intergranular embrittlement of Cu takes place due to segregation of Bi on grain boundaries. However, the concentration of Bi for the grain boundary segregation varies depending on the character of the grain boundary. In order to examine the relationship between the embrittlement and the character of the grain boundary, the dependence of the behavior of fracture on the inclination angle was experimentally observed at temperatures of T = 298 and 77 K for the Sigma 9 [110] asymmetric tilt boundary in Cu doped with Bi. For the high-energy boundary, the brittle fracture occurs in an intergranular manner at both temperatures. On the other hand, for the low-energy boundary, the ductile fracture takes place in a transgranular manner at T = 298 K but in a transgranular or intergranular manner at T = 77 K. The concentration of Bi for the grain boundary segregation may be large in the high-energy boundary but small in the low-energy boundary. According to estimation, the thermodynamic interaction between Cu and Bi in the grain boundary is repulsive, Furthermore, the repulsive interaction is more notable for the high-energy boundary than for the low-energy boundary. Consequently. the fracture occurs brittlely for the high-energy boundary with a large Bi concentration but ductilely for the low-energy boundary with a small Bi concentration. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.msea.2007.11.015

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We developed novel magnetic nano-carriers around 180 mn in diameter for affinity purification. Prepared magnetic nano-carriers possessed uniform core/shell/shell nano-structure composed of 40 nm magnetite particles/poly(styrene-co-glycidyl methacrylate (GMA))/polyGMA, which was constructed by admicellar polymerization. By utilizing relatively large 40 nm magnetite particles with large magnetization, the magnetic nanocarriers could show good response to permanent magnet. Thanks to uniform polymer shell with high physical/chemical stability, the magnetic nano-carriers could disperse in a wide range of organic solvent without disruption of core/shell structure and could immobilize various kinds of drugs. We examined affinity purification using our prepared magnetic nano-carriers with anti-cancer agent methotrexate (MTX) as ligand. Our magnetic nano-carriers showed higher performance compared to commercially available magnetic beads in terms of purification efficiency of target including extent of non-specific binding protein. (c) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.colsurfb.2008.01.013

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A thermochemical two-step water-splitting cycle using a redox system of iron-based oxides or ferrites was examined on hydrogen productivity and reactivity of ferrite in order to convert solar energy into hydrogen in sunbelt regions. In the present paper, a new concept is proposed for a windowed thermochemical water-splitting reactor, using an internally circulating fluidized bed of NiFe2O4/m-ZrO2 particles, and thermal reduction of the bed is demonstrated on a laboratory scale by using a solar-simulating Xe-beam irradiation. The concept is that concentrated solar radiation passes through the transparent window and directly heats the internally circulating fluidized bed. The fluidized bed reactor enabled the NiFe2O4/M-ZrO2 sample to remain in powder form without sintering and agglomerating during direct Xe-beam irradiation over 30 min. Approximately 45% of the NiFe2O4 was converted to the reduced phase by the solar-simulated high-flux beam, and was then completely reoxidized with steam at 1000 degrees C to generate hydrogen. (c) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijhydene.2008.02.044

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A silica particle observation (SPO) method was used in order to determine experimentally the boundary energies of Sigma 9 [110] asymmetric tilt boundaries with a misorientation angle of theta = 38.9 degrees in Cu for various inclination angles between phi = 0 degrees and 90 degrees. The SPO method has no drawbacks which are inevitable in boundary grooving and tri-junction methods. The boundary energy takes the maximum value at phi = 0 degrees but the minimum value at phi = 65 degrees. The minimum value is 65% of the maximum value. The inclination angle dependence of the boundary energy was utilized to evaluate quantitatively the possibility of faceting and dissociation for the boundary. According to the evaluation, the faceting into the {112} {552} and {552} {112} boundaries is possible for the {778} {110}, {554} {17, 17, 4} and {221} {221} boundaries. Furthermore, the dissociation into the Sigma 3 {111} {111} and {112} {112} twin boundaries is feasible for the {111} {115}, {447} {001} and {778} {110} boundaries. (c) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.msea.2007.05.029

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Solar thermochemical processes require the development of a high-temperature solar reactor operating at 1000-1500 degrees C, such as solar gasification of coal and the thermal reduction of metal oxides as part of a two-step water splitting cycle. Here, we propose to apply "an internally circulating fluidized bed" for a windowed solar chemical reactor in which reacting particles are directly illuminated. The prototype reactor was constructed in a laboratory scale and demonstrated on CO2 gasification of coal coke using solar-simulated, concentrated visible light from a sun simulator as the energy source. About 12% of the maximum chemical storage efficiency was obtained by the solar-simulated gasification of the coke.

DOI： 10.1115/1.2807213

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An iron-containing yttria-stabilized zirconia (YSZ) or Fe-YSZ was found to be a promising working redox material for the thermochemical two-step water-splitting cycle. The Fe-YSZ was formed by a high-temperature reaction between YSZ doped with more than 8 mol % Y2O3 and Fe3O4 supported on the YSZ at 1400 degrees C in an inert atmosphere. The formed Fe-YSZ reacted with steam to generate hydrogen at 1000 degrees C. The oxidized Fe-YSZ was reactivated by a thermal reduction at 1400 degrees C in an inert atmosphere. The alternative O-2 and H-2 generations in the repeated two-step reactions and the X-ray diffraction and chemical analysis studies on the solid materials indicated that the two-step water splitting was associated with a redox transition between Fe2+-Fe3+ ions in the cubic YSZ lattice.

DOI： 10.1115/1.2807197

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A thermochemical two-step water-splitting cycle using a redox metal oxide was examined for Ni(II) ferrites or NixFe3-xO4 (0 &lt;= x &lt;= 1) for the purpose of converting solar high-temperature heat to hydrogen. The Ni(II) ferrite was decomposed to Ni-doped wustite (NiyFe1-yO) at 1400 degrees C under an inert atmosphere in the first thermal-reduction step of the cycle; it was then reoxidized with steam to generate hydrogen at 1000 degrees C in the second water-decomposition step. Although nondoped Fe3O4 powders formed a nonporous, dense mass of iron oxide by the fusion of FeO and its subsequent solidification after the thermal-reduction step, Ni(II)-ferrite powders were converted into a porous, soft mass after the step. This was probably because Ni doping in the FeO phase raised the melting point of wustite above 1400 degrees C. Supporting the Ni(II) ferrites on m-ZrO2 (monoclinic zirconia) alleviated the high-temperature sintering of iron oxide; as a result, the supported ferrites exhibited greater reactivity and assisted the repeatability of the cyclic water splitting process as compared to the unsupported ferrites. The reactivity increased with the doping value x, and was maximum at x = 1.0 in the NixFe3-xO4/m-ZrO2 system. (C) 2007 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.solener.2007.03.005

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The composite materials of molten alkali-carbonate/MgO-ceramics are examined as thermal storage media in a tubular reformer using a double-walled reactor tube of a laboratory scale. The concept of a double-walled reformer tube is proposed as a solar tubular reformer and involves packing a molten salt/ceramic composite material in the annular region between the internal catalyst tube and the exterior solar absorber wall. The composite materials of Na(2)CO(3), K(2)CO(3), and Li(2)CO(3) with magnesia are tested as thermal storage media. The reforming performances of the composite materials are tested in the cooling mode of the double-walled reactor tube. The experimental result obtained under feed gas mixture of CH(4)/CO(2) = 1:3 at 1 atm shows that the use of 80 wt%Na(2)CO(3)/20 wt%MgO composite material successfully delayed the cooling time of the catalyst bed by 5-19 min in comparison to the case without a composite material. In addition, the Li(2)CO(3)/MgO and Na(2)CO(3)/MgO composite materials relatively revealed good performances: they prolonged the cooling time by over 10 min in the gas hourly space velocity (GHSV) range of 5000-12,500 h(-1). The application of the reactor tubes to solar tubular reformers is expected to realize stable operation of the solar reforming process under fluctuating insolation during cloud passage. (C) 2008 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.solener.2008.05.011

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DOI： 10.20550/jietaikaiyoushi.17.0_208

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DOI： 10.20550/jietaikaiyoushi.17.0_204

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DOI： 10.1021/cr050188a

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Size-controlled magnetite nanoparticles (MNPs) with several dozen nanometers ( nm) were synthesized for biomedical applications. Nanoparticles of single-phase magnetite, as revealed by X-ray analyses and magnetic measurements, were prepared by oxidizing ferrous hydroxide (Fe(OH)(2)) with a weak oxidant NaNO3 in an N-2-deaerated aqueous NaOH solution ( pH = 12-13) at various temperatures below 37 degrees C. As the synthesis temperature increases from 4 to 37 degrees C, the MNPs are decreased in size (d) from 102 +/- 5.6 to 31.7 +/- 4.9 nm and widened in size distribution, Delta d/d increases from 5.5% to 15%. Prepared without using any surfactant, the MNPs are advantageous for immobilizing functional molecules stably on the surfaces for biomedical applications. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.10.795

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Despite the wide utility of ferrite nanoparticles (FP), a methodology to conjugate heterologous molecules to FP is still limited and characterization of small molecule-conjugated FP is not well known. Here, we describe what kinds of proteins and amino acids are selectively immobilized onto FP when FP is synthesized in the presence of these molecules. Two-dimentional gel electrophoresis (2D SDS-PAGE) showed that proteins with low pl value were selectively bound to FP. Quantitative analyses using HPLC suggested that L-aspartic acid (Asp) and L-cysteine (Cys) were bound to FP selectively among natural amino acids examined. Additional analysis of compounds-conjugated FP revealed that selective binding of Asp to FP was attributed with its molecular structure. It was found that the substructure of amino acid-bound to FP specifically was composed of a defined chelation of two carboxyl groups separated by two carbon atoms as deduced from FT-IR measurement. Thus, we concluded that molecules possessing two carboxyl groups separated by two carbons were bound to FP spontaneously and selectively, which might enable the attachment of free functional groups onto the FP surface if their molecules have functional groups other than carboxyl groups. The resulting complex might be applicable as a chemical tag to immobilize various molecules onto FP. (C) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.colsurfb.2006.10.039

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A thermochemical two-step water splitting cycle using a redox system of iron-based oxides or ferrites is one of the promising processes for converting and storing solar energy into a fuel in sunbelt regions. The ZrO2-supported ferrite (or the ferrite/ZrO2) powders exhibit superior performances on activity and repeatability of the cyclic reactions when compared to conventional unsupported ferrites. In the first step at 1400 degrees C under an inert atmosphere, ferrite on ZrO2 support is thermally decomposed to the reduced phase of wustite that is oxidized back to ferrite on ZrO2 with steam in a separate second step at 1000 degrees C. In this paper, a number of ZrO2-supporetd ferrites, Mn-, Mg-, Co-, Ni- and Co-Mn-ferrites, are examined on activity. The NiFe2O4/ZrO2 powder was found to have a greatest activity between them. This paper also describes a new concept of a windowed solar chemical reactor using an internally circulating fluidized bed of ferrite/ZrO2 particles. In this concept, concentrated solar radiation passes downwards through the transparent window and directly heats the internally circulating fluidized bed. The exploratory experimental studies on this reactor concept are carried out in a laboratory scale for the thermal decomposition of NiFe2O4/ZrO2 particle bed as part of two-step water splitting cycle.

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For thermal storage in solar tubular reformers, high-temperature composite materials with alkali carbonate and magnesia have been examined. The new concept of "double-walled reactor tube" was previously proposed to use in solar tubular reformers, which involves storing the molten-salt/ceramic composite material in the annular regions between an internal catalyst tube and the exterior solar absorber wall. The shape and structure of the reactor tube can be modified to match with design of a solar tubular reformer. In this paper, the interior structure of the reactor tube has been modified for use in cavity-type reformers using straight reactor tubes. The Na2CO3, K2CO3 and Li2CO3 composite materials with magnesia were prepared, and tested on heat-discharge mode performances for CO2 reforming of methane in the modified reactor tube of a laboratory scale.

DOI： 10.1115/ISEC2006-99062

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The thermal reduction of metal oxides as part of a thermochemical two-step water splitting cycle requires the development of a high temperature solar reactor operating at 1000-15000 degrees C. Direct solar energy absorption by metal-oxide particles provides efficient heat transfer directly to the reaction site. This paper describes experimental results of a windowed thermochemical water-splitting reactor using an internally circulating fluidized bed of the reacting metal-oxide particles under direct solar irradiation. The reactor has a transparent quartz window on the top as aperture. The concentrated solar radiation passes downward through the window and directly heats the internally circulating fluidized bed of metal-oxide particles. Therefore, this reactor needs to be combined with a solar tower or beam down optics.
NiFe2O4/M-ZrO2 (Ni-ferrite supported on zirconia) particles is loaded as the working redox material in the laboratory scale reactors, and thermally reduced by concentrated Xe-beam irradiation. In a separate step, the thermally-reduced sample is oxidized back to Ni-ferrite with steam at 1000 degrees C. As the results, the conversion of ferrite reached about 44% of maximum value in the reactor by 1 kW of incident solar power. The effects of preheating temperature and particle size of NiFe2O4/m-ZrO2 were tested for thermal reduction of internally circulating fluidized bed in this paper.

DOI： 10.1115/1.3027511

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A thermochemical two-step water splitting cycle using a redox system of iron-based oxides or ferrites is one of the promising processes for converting solar energy into clean hydrogen in sunbelt regions. An iron-containing YSZ (Yttrium-Stabilized Zirconia) or Fe-YSZ is a promising working redox material for the two-step water splitting cycle. The Fe2+-YSZ is formed by a high-temperature reaction between YSZ, and Fe3O4 supported on the YSZ at 1400 degrees C in an inert atmosphere. The Fe2+-YSZ reacts with steam and generate hydrogen at 1000-1100 degrees C, to form Fe3+-YSZ that is re-activated by a thermal reduction in a separate step at temperatures above 1400 degrees C under an inert atmosphere. In the present work, a ceramic foam coated with the Fe-YSZ particles is examined as the thermochemical water splitting device for use in a solar-directly-irradiated receiver/reactor system. The Fe-YSZ particles were coated on an Mg-partially-stabilized zirconia foam disk and the foam device was tested on the two-step water splitting cycle being performed alternately at temperatures between 1100 and 1400 degrees C. The foam device was irradiated by concentrated visible light from a sun-simulator at the peak flux density of 1000 kW/m(2) and the average flux density of 470 kW/m(2) in a N-2 gas stream, and then, was reacted with steam at 1100 degrees C while heating by an infrared furnace. Hydrogen successfully continued to be produced in the repeated cycles.

DOI： 10.1115/1.3090819

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A thermochemical two-step water splitting cycle using a redox system of iron-based oxides or ferrites is one of the promising processes for converting solar energy into clean hydrogen in sunbelt regions. An iron-containing YSZ (Yttrium-Stabilized Zirconia) or Fe-YSZ is a promising working redox material for the two-step water splitting cycle. The Fe2+-YSZ is formed by a high-temperature reaction between YSZ, and Fe3O4 supported on the YSZ at 1400 degrees C in an inert atmosphere. The Fe2+-YSZ reacts with steam and generate hydrogen at 1000-1100 degrees C, to form Fe3+-YSZ that is re-activated by a thermal reduction in a separate step at temperatures above 1400 degrees C under an inert atmosphere. In the present work, a ceramic foam coated with the Fe-YSZ particles is examined as the thermochemical water splitting device for use in a solar-directly-irradiated receiver/reactor system. The Fe-YSZ particles were coated on an Mg-partially-stabilized zirconia foam disk and the foam device was tested on the two-step water splitting cycle being performed alternately at temperatures between 1100 and 1400 degrees C. The foam device was irradiated by concentrated visible light from a sun-simulator at the peak flux density of 1000 kW/m(2) and the average flux density of 470 kW/m(2) in a N-2 gas stream, and then, was reacted with steam at 1100 degrees C while heating by an infrared furnace. Hydrogen successfully continued to be produced in the repeated cycles.

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The thermal reduction of metal oxides as part of a thermochemical two-step water splitting cycle requires the development of a high temperature solar reactor operating at 1000-15000 degrees C. Direct solar energy absorption by metal-oxide particles provides efficient heat transfer directly to the reaction site. This paper describes experimental results of a windowed thermochemical water-splitting reactor using an internally circulating fluidized bed of the reacting metal-oxide particles under direct solar irradiation. The reactor has a transparent quartz window on the top as aperture. The concentrated solar radiation passes downward through the window and directly heats the internally circulating fluidized bed of metal-oxide particles. Therefore, this reactor needs to be combined with a solar tower or beam down optics.
NiFe2O4/M-ZrO2 (Ni-ferrite supported on zirconia) particles is loaded as the working redox material in the laboratory scale reactors, and thermally reduced by concentrated Xe-beam irradiation. In a separate step, the thermally-reduced sample is oxidized back to Ni-ferrite with steam at 1000 degrees C. As the results, the conversion of ferrite reached about 44% of maximum value in the reactor by 1 kW of incident solar power. The effects of preheating temperature and particle size of NiFe2O4/m-ZrO2 were tested for thermal reduction of internally circulating fluidized bed in this paper.

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DOI： 10.20550/jietaikaiyoushi.16.0_256

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High-temperature solar reforming of methane with CO2 is investigated using a directly solar-irradiated absorber subjected to a solar mean flux level above 400 kW m(-2) (the peak flux of about 700 kW m(-2)). The new type of catalytically activated ceramic foam absorber-a Ru/Ni-Mg-O catalyzed SiC-foam absorber-was prepared, and its activity was tested in a laboratory-scale volumetric receiver-reactor with a transparent (quartz) window by using a sun-simulator Compared to conventional Rh/Al2O3 catalyzed SiC-foam absorber, this new catalytic absorber is more cost effective and is found to exhibit a superior reaction performance at the high solar flux or at high temperatures, especially above 950 degrees C. This new absorber will be applied in solar receiver-reactor systems for converting concentrated high solar fluxes to chemical fuels via endothermic natural-gas reforming at high temperatures.

DOI： 10.1115/1.2210497

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

Direct observation of sulfur sites for sulfur-containing compounds (cysteine and its oxidative derivatives) on ferrite nanoparticles (FP) was performed by X-ray adsorption near edge structure (XANES) measurements. XANES spectra of cysteine derivatives conjugated with FP indicated that redox reactions occurred on the FP surface. Cysteine was completely oxidized to cystine and cysteinesulfinic acid and cysteic acid were partially reduced. These studies revealed that the FP surface should possess both an oxidation and reduction reactive center for sulfur-containing functional groups.

DOI： 10.1246/cl.2006.974

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This paper proposes a novel-type of "double-walled" reactor tube with molten-salt thermal storage at high temperatures for use in solar tubular reformers. The prototype reactor tube is demonstrated on the heat-discharge and chemical reaction performances during cooling mode of the reactor tube at laboratory scale. The Na2CO3 composite material with MgO ceramics was filled into the outer annulus of the double-walled reactor tube while the Ru-based catalyst particles were filled into the inner tube. The heat discharge form the molten Na2CO3 circumvented the rapid temperature change of the catalyst bed, which resulted in the alleviation of decrease in chemical conversion during cooling mode of the reactor tube. The application of the new reactor tribes to solar tubular reformers is expected to help realize stable operation of the solar reforming process under fluctuating insolation during a cloud passage.

DOI： 10.1115/1.2183803

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High-temperature solar reforming of methane with CO2 is investigated using a directly solar-irradiated 2 absorber subjected to a solar mean flux level above 400 kWm(-2) (the peak flux of about 700 kWm(-2)). The new type of catalytically-activated ceramic foam absorber - an Ru/Ni-Mg-O catalyzed SiC foam absorber - was prepared and its activity was tested in a laboratory-scale volumetric receiver-reactor with a transparent (quartz) window by using a sun-simulator. Compared to conventional Rh/Al2O3 catalyzed SiC foam absorber, this new catalytic absorber is more cost-effective and is found to exhibit a superior reaction performance at the high solar flux or at high temperatures, especially above 950 degrees C. This new absorber will be applied in solar receiver-reactor systems for converting concentrated high solar fluxes to chemical fuels via endothermic natural-gas reforming at the high temperatures.

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This paper proposes a novel type of "double-walled" reactor tube with molten-salt thermal storage at high temperatures for use in solar tubular reformers. The prototype reactor tube is demonstrated on the heat-discharge and chemical reaction performances during cooling mode of the reactor tube at laboratory scale. The Na2CO3 composite material with MgO ceramics was filled into the outer annulus of the double-walled reactor tube while the Ru-based catalyst particles were filled into the inner tube. The heat discharge form the molten Na2CO3 circumvented the rapid temperature change of the catalyst bed, which resulted in the alleviation of decrease in chemical conversion during cooling mode of the reactor tube. The application of the new reactor tubes to solar tubular reformers is expected to help realize stable operation of the solar reforming process under fluctuating insolation during a cloud passage.

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Language：Japanese   Publisher：The Japan Institute of Energy  

DOI： 10.20550/jietaikaiyoushi.15.0_279

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A two-step water splitting process using the ZnFe2O4/Zn/Fe3O4 reaction system was proposed for H-2 generation utilizing concentrated solar heat. The mixture of Zn and Fe3O4 was heated to 873 K in flowing steam with an Ar carrier gas, and the H2 gas was generated at 93.4% of the theoretical yield for the reaction of 3Zn+2Fe(3)O(4)+ 4H(2)O=3ZnFe(2)O(4)+4H(2) (H-2 generation step). The XRD and Mossbauer spectroscopy showed that the Zn-submitted ferrite (ZnxFe3-xO4; 0.2 &lt;= x &lt;= 1) (main solid product) and ZnO (minor) were formed in the solid products after the H-2 generation reaction. The ZnFe2O4 product, which was formed after the H-2 generation step during the two-step water splitting process with the ZnFe2O4/Zn/Fe3O4 system, could be decomposed into Zn (and ZnO) and Fe3O4 by the Xe beam irradiation at 1900 K after 3 min with a 67.8% yield for the reaction of 3ZnFe(2)O(4) = 3Zn + 2Fe(3)O(4) + 2O(2) (O-2 releasing step = solar thermal step). (c) 2004 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.energy.2004.08.020

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We found out that chemical compounds with carboxyl, mercapto and sulfonic groups have high affinity to ferrite surface, previously. The fact implies that polymer-coated ferrite nanoparticles as a substrate of affinity chromatography are easily and strategically yielded by using chemical compounds with these functional groups and such hydrophobic region as to mediate hydrophobic monomer. In order to promote copolymerization with monomer, chemical compounds (connecter) carrying their functional groups and vinyl group were selected. In this study, maleic acid, allyl mercaptan, p-styrenesulfonic acid sodium salt, and 2-acrylamido-2-methylpropane-sulfonic acid as connecter, and styrene and glycidyl methacrylate as monomer additives were used. To investigate physical properties of the connecter-modified ferrite samples, x-ray diffraction, thermogravimetry and differential thermal analysis, and magnetic field dependences of magnetization were carried out. The results revealed that the connecters have affinity to ferrite surface. Polymer coating was performed by soap-free emulsion polymerization method. The polymer-coated ferrite particles were observed by transition electron microscopy. It was confirmed that ferrite particles were not coated by polymer without connecters. We proposed that connecters would give a new light for development of a substrate not only in affinity chromatography, but also in various applicational field.

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Language：Japanese   Publisher：The Japan Institute of Energy  

DOI： 10.20550/jietaikaiyoushi.14.0_234

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The hydrogen generation reaction in the H2O/ZnO/MnFe2O4 system was studied to clarify the possibility of whether this reaction system can be used for the two-step water splitting to convert concentrated solar heat to chemical energy of H-2. At 1273 K, the mixture of ZnO and MnFe2O4 reacted with water to generate H-2 gas in 60% yield. X-ray diffractometry and chemical analysis showed that 48 mol% of Mn-II (divalent manganese ion) in the A-site of MnFe2O4 was substituted with Zn-II (divalent zinc ion) and that chemical formula of the solid product was estimated to be (Zn0.58Mn0.42Mn0.39Fe1.61O4)-Mn-II-Fe-III (Mn-III : trivalent manganese ion). Its lattice constant was smaller than that of the MnFe2O4 (one of the two starting materials). From the chemical composition, the reaction mechanism of the H-2 generation with this system was discussed. Since the Mn ions in the product solid after the H-2 generation reaction are oxidized to Mn3+, which can readily release the O2- ions as O-2 gas around 1300 K, the two-step of H-2 generation and O-2 releasing seem to be cyclic. (C) 2003 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.solener.2003.08.033

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The O-2 generation step in two-step water splitting with Zn-ferrite/Zn, Fe3O4 system was studied with a stainless steel reactor having a window of quartz glass plate (Sandwich Reactor) using the 15 kW solar dish concentrator in Australian National University. The reactant flat layer with a small thickness in the Sandwich Reactor was assumed to simulate the flow section of the particle cloud reactor. The temperature of the sample attained 1750 K in a few minutes by concentrated solar radiation, and 40% molar of the Zn-ferrite was decomposed into Fe3O4 to produce Zn0.4Fe2.6O4, which is the solid solution between ZnFe2O4 and Fe3O4. The laboratory experiment with the Xe beam irradiation showed that the Zn-ferrite decomposition reaction proceeds according to (3)/2ZnFe2O4 = (3)/Zn-2 + Fe3O4 + O-2. In the solar furnace experiment, the metal Zn vapor produced according to this equation seems to be deposited on the surface of the inner wall of the reactor, or it seems to recombine with the released O-2, converting to ZnO under the condition without quenching system in the present experimental setup. (C) 2003 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.solener.2003.08.034

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A photocatalytic effect of ZnO on carbon gasification with CO2 was studied using a concentrated Xe beam to enhance the gasification rate in solar/chemical energy conversion process. The sample, activated carbon impregnated with ZnO (5 wt%), was heated at 873 K by a Xe beam irradiation with UV (&lt; 400 nm). The gasification rate at 873 K increased 2 folds in comparison with the Xe irradiation without UV, but, the difference of the rate of CO evolution decreased with the increasing temperature from 873 to 1073 K. The carbothermal reduction of ZnO (ZnO + C --&gt; Zn + CO) proceeded at above 950 K, which was demonstrated by XRD analysis and thermodynamic calculation. These results indicate that the photocatalytic effect of ZnO with the UV irradiation enhance the gasification rate of carbon at low temperature (873 K). (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.solmat.2003.08.016

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The M(II)-substituted magnetite (M = Ni, Co and Mn) formation in the wet process in a high magnetic field from 0 to 8 T generated by a superconducting magnet has been studied at the iron ion concentration of 1500 mg/l and the Fe(II)/ Fe(III) mole ratios (R-f) of 1/2 and 2/1. The particle size of the M(II)-substituted magnetite was about 12 nm at R-f and T about 7 nm at R-f The Ni(II) content of the Ni(II)-substituted magnetite at R-f = 2 was lower than that at R-f=1/2 . In 2 T 2 the Ni(II)-substituted magnetite, the lattice parameter increases with an increase in the magnetic field from 0 to 8 T, indicating that high magnetic fields enhance the formation of the Ni(II)-substituted magnetite (solubility enhancement of Ni(II) to magnetite). Also, the lattice parameter of the Co (II)- substituted magnetite decreased with the increasing magnetic field, however, an increase in the lattice parameter was not found in the Mn(II)-substituted magnetite. The presence of large amounts of vacancies was found in the Ni(II)-substituted magnetite formed in high magnetic fields by XRD and atomic absorption analysis. This result is supported by the experimental result in which the magnetite formed in a high magnetic field tends to adsorb Ni(II) in a high magnetic field, and results in the higher incorporation of Ni(II) into the spinel structure. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0304-8853(02)00582-6

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Several ideas on the reaction mechanism of H2O/Zn/Fe3O4 water splitting system were considered from the aspect of Zn mobility. The vapor deposition of Zn onto the Fe3O4 surface was confirmed by H-2 generation reaction with Zn and Fe3O4 set separately. XPS measurements suggested that the surface of Fe3O4 is covered by Zn before the reaction with steam. The rapid reaction process has been supported by this Zn deposition, which greatly enlarges the number of sites of Zn/Fe3O4 pair that is ready to react with steam. In order to keep the Zn from vaporizing off the system, the Zn/Fe3O4 mixture was covered with additional Fe3O4 to capture the Zn vapor. This resulted in improved H2 yield of 99.5%. (C) 2002 Published by Elsevier Science Ltd on behalf of the International Association for Hydrogen Energy.

DOI： 10.1016/S0360-3199(02)00012-5

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The relationship between the particle size of iron ion coprecipitates and magnetic coagulation reaction has been studied for application to water purification using magnetic separation system. The Fe(III) phosphate complex (IP) precipitate was used as a paramagnetic substance. At a high magnetic field of 8 T, the IP amount recovered by magnetic separation gradually increased with increasing Fe(III) ion concentration in the solution (by increasing the Fe/P mole ratio). However, at a low magnetic field of 0.8 T, it remained constant at about 30%. The magnetic coagulation reaction of the paramagnetic particles of the IP (Fe/P = 1.68) was enhanced by the addition of ferrimagnetic Fe3O4 particles, and that the recovery efficiency became higher with a smaller particle size of Fe3O4. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0304-8853(02)00074-4

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The aqueous ferrite formation reaction with addition of Fe(II) and Fe(111) ions in an alkaline solution in a high magnetic field has been investigated at iron ion concentrations of 150, 750 and 1500 ppm and at Fe(II)/Fe(III) mole ratio of 1 (chemical composition of the stoichiometric Fe3O4) and 2/1 (chemical composition of GR-I In the case of 2 Fe(II)/Fe(III) = 1/2, the magnetic coagulation reaction occurring in the magnetic field range of 0-1 T is different from that in the range of 2-10 T. The higher magnetic field enhanced the reaction rate of the aqueous ferrite formation due to the increase in the intermediate concentration at Fe(II)/Fe(III) = 2/1. The increase in the initial reaction rate can be explained in terms of the increase in the nucleus numbers in the nuclei formation period. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0304-8853(01)00703-X

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Language：English   Publisher：The Society of Eco-Engineering  

Two-step water splitting with Zn/Fe<SUB>3</SUB>O<SUB>4</SUB> - ZnFe<SUB>2</SUB>O<SUB>4</SUB> reaction system is suggested for H<SUB>2</SUB> generation to utilize concentrated solar heat. When mixture of Zn and Fe<SUB>3</SUB>O<SUB>4</SUB> was heated to 873 K and steam was passed through, the H<SUB>2</SUB> was obtained in 93.4% of the theoretical yield. Formation of ZnFe<SUB>2</SUB>O<SUB>4</SUB> with several zinc content (Zn<SUB>x</SUB>Fe<SUB>3-x</SUB>O<SUB>4</SUB>; 0.2&le;x&le;l) and ZnO was determined by XRD and M&ouml;ssbauer spectroscopy. The yield of ZnO was 26-29%, which shows the ratio of the competition-reaction (H<SUB>2</SUB>O Zn system) effects less in the total H<SUB>2</SUB> yield. O<SUB>2</SUB> generation (also energy storage) step can be proceeded at the temperature of ca. 1800 K. The reaction took place very fast, and it can be seen that a large amount of O<SUB>2</SUB> was released from irradiated ZnFe<SUB>2</SUB>O<SUB>4</SUB>. The stoichiometry and the reaction mechanism of the system are discussed upon the analyses for the solid product.

DOI： 10.11450/seitaikogaku.14.4_3

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society on Water Environment  

To develop a practical environmental protection technology for purification of lakes, ponds and arm of the sea, an efficient magnetic separation system for phosphate and heavy metal ions removal was studied using ferrimagnetic fine particles (FMFP), which can be prepared from Fe²⁺ and Fe³⁺ ions in the alkali aqueous solution. With the Fe³⁺ ions of 15 mg·<i>l</i>^-1 (without addition of FMFP), the phosphate ion recovery decreased from 80% to 20% with decreasing the magnetic field from H=8T to 0.8T. By addition of the FMFP of 5 mg·<i>l</i>^-1 along with the Fe³⁺ ions of 15 mg·<i>l</i>^-1, above 95% recovery was achieved in a wide range of the magnitude of magnetic field (H=0.8-8T). In case of using cadmium ion instead of the phosphate ion, addition of the FMFP of 5 mg·<i>l</i>^-1 together with the Fe³⁺ ions of 20 mg·<i>l</i>^-1 enhanced recovery of the Cd²⁺ ion. We demonstrated that in the presence of the FMFP all of the heavy metal ions were recovered 80% yields or more. These would come from a high magnetic gradient characteristically generated on the surface of FMFP, which results in the enhancement of the magnetic coagulation of the complex with the phosphate or the heavy metal ions and the Fe³⁺ ions.

DOI： 10.2965/jswe.25.33

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Methane dry reforming with CO2 using FeO powder in molten salt has been investigated at various flow rates of CH4/CO3 mixed gases (CH4/CO2 = 1) between 50 and 400 ml/min at 1223 K in an infrared furnace. This work is carried out to determine the usefulness of this method for the chemical storage of solar energy. The CH4/CO2 mixed gases passing through the molten salt (Na2CO3/K2CO3 = 1) containing the FeO powder were catalytically decomposed into CO, H-2 and H2O. The product gas mole ratios, CO/H-2/H2O, were shown to be 3:1:1 for a high flow rate of 200 ml/min and to be CO/H-2 = 2:1 for a low flow rate of 50 ml/min. The results were explained in terms of the kinetics of the CH4-reforming reaction and the thermodynamics of the redox process of FeO powder mixed in the molten salt;
CH4 + 2FeO double right arrow 2Fe + H-2 + CO + H2O
Fe + CO2 double right arrow FeO + CO
for a high How rate, and
FeO + CH4 double right arrow Fe + 2H(2) + CO
Fe + CO4 double right arrow FeO + CO
for a low flow rate. (C) 2002 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0038-092X(01)00097-4

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The phase diagram of the Na2O-MnO-Fe2O3 system forms the basis for thermodynamic consideration of H-2 production in water splitting with the Na2CO3/MnFe2O4/Fe2O3 system. Sodium iron manganese oxides Na0.7-1 (Mn1-x, Fe-x)O2+delta. were observed in the phase diagram at T = 1273 K under P-O2 = 1.23 X 10(-5) atm. Confirmation of this phase, especially for x &gt; 0.5, suggests the possibility of H-2 generation under this oxygen partial pressure and results in a value of 1:37 for the ratio of P-H2:P-H2O in the H-2 generation step of water splitting. This oxygen partial pressure is realized by the decomposition of carbon dioxide (CO2 = CO + 0.5O(2)) and it is concluded that the H-2 generation step can proceed under CO2 atmosphere. (C) 2002 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0038-092X(02)00012-9

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Funtai Funamtsu Yakin Kyokai/Japan Soc. of Powder Metallurgy  

The Ni2+-substituting magnetite formation in the wet process in a high magnetic field from 0 to 8 T generated with a 10 T cryocooler-cooled superconducting magnet has been studied at iron ions concentration of 1500 mg/l at Fe2+/Fe3+(Rf) mole ratio of 1/2 and 2/1. The particle size (nanoparticles) of Ni2+-substituting magnetite was decreased with increasing magnetic field. Also, the magnetic field enhanced the reaction rate of ferrite formation. The Ni2+ content of Ni2+ -substituting magnetite at Rf= 2/1 was lower than that at Rf= 1/2. In the Ni2+-substituting magnetite, the lattice parameter decreases with an increase of magnetic field from 0 to 8 T, indicating that high magnetic fields enhance a formation of Ni2+-substituting magnetite (enhancement of solubility of Ni2+ into magnetite). This result is supported by the experimental result which the magnetite formed in a high magnetic field tends to adsorb Ni2+ in the reaction solution in a high magnetic field, indicating that a high magnetic field enhances the higher incorporation of Ni2+ into spinel structure.

DOI： 10.2497/jjspm.49.710

Scopus

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MARCEL DEKKER INC  

An efficient magnetic separation system for phosphate ion removal has been studied for developing a practical environmental protection technology for water purification in rivers, lakes, etc. using ferrimagnetic fine particles (FMFPs), which can be prepared from FeCl2 and FeCl3,aqueous solutions. With 15 mg/L of FeCl3 solution, without the addition of FMFP, phosphate ion recovery increased from 20 to 80% with increasing magnetic field from 0.8 to 8 T. By the addition of 5 mg/L of FMFP with 15 mg/L of FeCl3 solution, above 95% recovery was achieved in a wide range of magnetic field (H = 0.8-8 T). A high magnetic field gradient generated in the vicinity of steel wool caused the enhancement of the magnetic coagulation of the complex with phosphate ion and Fe(III) ion, and the paramagnetic iron-phosphate complexes were attracted to FMFP in the reactor, which resulted in high (95%) recovery in a wide range of magnetic fields.

DOI： 10.1081/SS-120014831

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Reactivities of three metal oxides (Fe2O3, TiO2 and MnO2) with Na2CO3, and of their reaction products with CO2, have been studied to enhance the O-2-releasing step in the two-step water splitting by the MnFe2O4-Na2CO3 system. X-ray diffraction analysis and thermogravimetric measurements showed that the reaction of alpha -Fe2O3 with Na2CO3 (mole ratio=1:1) completed within 10 min at 1073 K to produce NaFeO2 (Fe2O3+Na2CO3--&gt; NaFeO2+CO2). Also, the regeneration of Fe2O3 and Na2CO3 proceeded readily by passing CO2 gas through NaFeO2 (71% yield). TiO2 reacted with Na2CO3 (mole ratio=1:1) at 1073 K for 1 h to form Na8Ti5O14 and Na2TiO3 (93% yield). However, in the reaction of the products with CO2, the starting material (TiO2) was not reproduced at the temperature range from 673 K to 1073 K, but Na4Ti5O12 (having a lower Na content than the form Na8Ti5O14) was formed. In the case of MnO2 with Na2CO3 (mole ratio=2:1), Na0.7MnO2-2.05 and NaMnO2 were produced at 1073 K for 1 h (80% yield), but the reaction between these products and CO2 hardly proceeded. (C) 2001 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0360-5442(01)00041-X

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Water splitting with H2O/Zn/Fe3O4 reaction system is suggested for H-2 generation in order to utilize concentrated solar heat. This system has the possibility of generating more H-2 per 1 mol of Zn than Zn/H2O reaction system at the same temperature, which is noted recently. When a mixture of Zn and FC3O4 was heated to 873 K and steam was passed through, H-2 was obtained in 93.4% of the theoretical yield. The formation of Zn-ferrites with high content of zinc (ZnxFe3-xO4; 0.2 less than or equal to x less than or equal to 1) and ZnO was determined by XRD and Mossbauer spectroscopy. The yield of ZnO was 26-29%, which shows that the ratio of the competition-reaction (Zn/H2O system) has less effects on the total H-2 yield. The stoichiometry and the reaction mechanism of the system are discussed upon the analyses for the solid product. (C) 2001 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0360-3199(01)00039-8

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

In the O-2-releasing step of water splitting system, MnFe2O4 was completely regenerated from Na(Mn1/3Fe2/3)O2+delta by enhancement of O-2-releasing step with Fe2O3 at 1273 K. Thermodynamic data for the enhancement of the O-2-releasing step with alpha -Fe2O3 in the water splitting with the MnFe2O3-Na2CO3 system are experimentally confirmed. The amount of released oxygen attained to the theoretical value at around 1273 K (Po-2 = 10(-6)) and about 1240 K (Po-2 = 10(-7)). At higher temperature above 1273 K (Po-2 = 10(-6)) and 1240 K (Po-2 = 10(-7)), the released oxygen amount increased. In the three-step water splitting system with MnFe2O3-Na2CO3-Fe2O3, we proposed that there are some advantages required for application to the solar thermochemical process. (C) 2001 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0022-3697(01)00034-8

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Language：English   Publishing type：Research paper (international conference proceedings)  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CERAMIC SOC  

Oxygen uptake and release of (Li,Mn) ferrite [LMF; (Li0.60Mn1.20Fe1.20)(1-delta)O-4; delta = 0.007 to 0.033] was investigated concerning the relations between redox reactions of ferrite and cation migration. Mossbauer spectroscopy and X-ray diffractometry showed that some of the Li+ and Fe3+ ions migrated from the A sites to the B sites of the spinel-type structure and Mn4+ ions migrated from the B sites to the A sites during oxygen uptake at 573 K. The cation-deficient LMF formed by the oxygen uptake released oxygen molecules in He gas only at 660 K. The cation migration during the oxygen release was in the opposite direction of the movement during oxygen uptake at 573 K.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The growth behavior of fine grains produced due to diffusion induced recrystallization (DIR) was experimentally studied for the Cu(Zn) system using single crystal Cu specimens. The Cu specimens were annealed at 693 K for various times together with st Zn source alloy by a capsule zincification technique and then DIR was observed to take place on the surfaces of the specimens. The DIR region consists of an almost single layer of fine grains. Although the average height I and the average diameter s of the fine grains increase with increasing annealing time, the aspect ratio s/l is kept to be nearly unity during annealing. The Zn concentration on the specimen surface is smaller than that in the Zn source alloy at early stages of the reaction. Such lower Zn concentrations could be explained using the maximum driving force model proposed by Kajihara and Gust (Acta metall. mater., 1991, 39, 2565). The composition on the specimen surface gradually approaches the equilibrium value with increasing annealing time. This means that the amount of the Zn source alloy is large enough to maintain the supply of Zn atoms to the specimen in each zincification capsule. The kinetic model by Li and Hillert (Acta metall., 1981, 29, 1949) and the extended model by Kawanami ct al. (ISIJ int., 1997, 37, 921) could rather well reproduce the annealing time dependence of the growth rate of the DIR region. The contribution of volume diffusion to the transfer of Zn atoms from the surface to the moving boundaries in the DIR region was estimated to be negligible. Thus, the chemical driving force is considered to be the most important driving force for the grain boundary migration and the boundary diffusion along the grain boundaries in the DIR region is recognized to be the rate controlling process of DIR. (C) 2000 Acta Metallurgica Inc. Published by Elsevier Science Lid. AII rights reserved.

DOI： 10.1016/S1359-6454(00)00096-3

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The boundary energies of Sigma 11 [110] asymmetric tilt boundaries with a misorientation angle of theta = 50.5 degrees in Cu have been experimentally determined by a silica particle observation method for various inclination angles between phi = 0 and 90 degrees. This method has no drawbacks that are inevitable in boundary grooving and tri-junction methods. In the boundary energy vs inclination angle diagram, three deep cusps exist at phi = 10, 64.8 and 90 degrees whereas a shallow cusp appears at phi = 35.3 degrees. Such inclination angle dependence of the boundary energy has been utilized to analyze the faceting of the boundary. The observations on the faceting reported for Sigma 11 [110] tilt boundaries in face-centered cubic (f.c.c.) metals have been quantitatively accounted for by the present analysis. (C) 2000 Acta Metallurgica inc. Published by Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S1359-6454(00)00103-8

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The characteristic features of diffusion induced grain boundary migration (DIGM) in the Cu(Zn) system were experimentally studied for [110] asymmetric tilt boundaries using Cu bicrystals annealed at 693 K for various times by a capsule zincification technique. The experiment was carried out for the boundaries with inclination angles of phi = 0, 20, 35, 55, 65 and 90 degrees and with a constant misorientation angle of theta = 39 degrees (Sigma 9). During annealing, the grain boundary migrates towards a crystal grain of larger coherency strain energy with higher probability due to DIGM. Taking elastic anisotropy of each crystal grain into consideration, the difference between the probabilities of grain boundary migration towards both side grains can be accounted for by the coherency strain model proposed by Hillert. The migration rate v of the moving boundary is almost constant regardless of the annealing time t between t = 72 and 384 h (2.59 x 10(5) and 1.38 x 10(6) s). The value of v monotonically decreases with increasing inclination angle. This implies that the boundary diffusion coefficient of Zn in Cu is a monotone decreasing function of the inclination angle. The experimental results on the kinetics at the steady state stage were theoretically analyzed using the energy balance model proposed by Kajihara and Gust (Scripta mater., 1998, 38, 1621. The analysis indicates that the effective driving force Delta(ef)G for the grain boundary migration is merely one-thirtieth of the chemical driving force, whereas it still remains three times greater than the minimum value corresponding to the coherency strain energy during DIGM under the present, experimental conditions. The mobility of the moving boundary was evaluated to be M = 3.77 x 10(-17) m(4)/Js from the values of v and Delta(ef)G according to the relationship M = v/Delta(ef)G. This value of M is close to the results estimated by Yamamoto et al, (Acta mater., 1999, 47, 1757) for the [100] twist and random boundaries in the Cu(Zn) system. (C) 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S1359-6454(99)00424-3

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Language：Japanese   Publishing type：Doctoral thesis  

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Total pages：vi, 239p  

CiNii Books

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Total pages：vii, 218p   Language：Japanese

CiNii Books

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Total pages：354  

ASIN

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Total pages：174  

ASIN

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Authorship：Lead author,　Last author,　Corresponding author   Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

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Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

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Authorship：Lead author,　Last author,　Corresponding author   Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

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J-GLOBAL

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Language：Japanese   Publisher：The Japan Institute of Energy  

The current technologies for solar chemical fuel productions using concentrated solar radiation as an energy source and carbonaceous resources as a chemical source such as coal cokes and natural gas were mainly reviewed in this paper. These energy conversion technologies enable productions of long term storable clean energy carrier from solar energy and solar energy transportation from sunbelt to remote countries, such as Japan. Concentrated solar radiation has some specific properties such as high density, heterogeneous distribution of thermal flux, and frequent thermal transients due to the fluctuating insolation. Thus, some solarspecific reactors/reformers have been developed to convert the high temperature solar heat into hydrogen and synthetic gas of carbon monoxide and hydrogen via solar thermochemical processes of water-splitting, natural gas reforming and coal gasification. In this paper, research activities in Niigata University are mainly introduced in this paper.

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Language：Japanese   Publisher：The Japan Institute of Energy  

Solar thermochemical water-splitting cycles have been developed to convert concentrating solar radiation or heat to hydrogen in world sun-belt regions with abundant insolation. Hybrid sulfur cycle and metal-oxide cycles have been mostly investigated for solar thermochemical water splitting because these cycles can be operated only by two steps. In order to perform these cycles, solar concentrating system, active catalysts, metal oxides, and solar reactors have been developed since these cycles require temperatures around 1000 - 1500℃. Several concepts of solar reactor systems has been demonstrated by solar furnace, solar tower, etc., and in the demonstrations, solar power input is about 10 - 100 kW_<th>. Niigata University is developing two types of solar reactors, the foam device reactor type and the fluidized beds reactor type, and the two reactor concepts have been up-scaled and tested on solar.

CiNii Article

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Language：Japanese   Publisher：The Japan Institute of Energy  

This paper reviews the recent technology for solar fuel production using concentrated solar high temperature heat as an energy source and water and fossil fuels as a chemical source. This technology enables production of long term storable clean energy carrier from solar energy and solar energy transportation from sunbelt to remote countries, such as Japan. Concentrated solar radiation has some specific properties such as high density, heterogeneous distribution of thermal flux, and frequent thermal transients due to the fluctuating insolation. Thus, some solar-specific reactors/reformers have been developed to convert the high temperature solar heat into hydrogen and synthetic gas of carbon monoxide and hydrogen via solar thermochemical processes of thermochemical water-splitting, natural gas reforming and coal gasification. The technical development and feasibility of these solar fuel production processes is discussed, and recent international collaboration researches for demonstration of solar fuel production are introduced here.

CiNii Article

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Language：Japanese   Publisher：エネルギー総合工学研究所  

CiNii Article

CiNii Books

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Language：Japanese  

CiNii Article

CiNii Books

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Language：Japanese  

CiNii Article

CiNii Books

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Language：English   Publishing type：Rapid communication, short report, research note, etc. (bulletin of university, research institution)  

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