F. Sibieude

Use of solar energy for direct and two-step water decomposition cycles

Abstract In this study, the feasibility of using concentrated solar energy at high temperatures to decompose water is experimentally demonstrated. The preliminary studies show that direct decomposition of water at 2000–2500°C is possible and the main development should be directed to reactor design and the separation of product gases. On the other hand, it is shown that two step thermochemical cycles for hydrogen production are feasible when the reactions are carried out at appropriate high temperatures in a solar furnace. The thermal decomposition of zinc oxide, suitable for such a two step cycle, is studied in detail.

High temperature experiments with a solar furnace: The decomposition of Fe3O4, Mn3O4, CdO

The decomposition of some oxides, proposed for hybrid or thermochemical short cycles, was tested at the focus of a heliostat parabolic furnace or an arc image furnace, either on a water cooled support or in a black body cavity with a heat exchanger. The influence of temperature, partial pressure of oxygen and quenching speed on the decomposition rate of magnetite (Fe3O4) is presented. When Fe3O4 is heated 300°C above its melting point in an air atmosphere there is 40% decomposition; in an argon atmosphere complete decomposition is reached. Mn3O4 is more than 70% decomposed when heated in air. With the described conditions it was not possible to obtain Cd when pure CdO was used as a starting material. By dilution in an oxide it is shown that, at atmospheric pressure, high yields are obtained from the condensed vapours in the temperature range 900–1500°C. The influence of total pressure is also shown at high temperature. As a conclusion, the feasibility of these reactions is discussed.

Identification of binary compounds in the system Ce2O3WO3

Abstract The systems CeO2Ce2O3WO3 and Ce2O3WO3W are studied at high temperature. Six compounds were found as stable phases in the system Ce2O3WO3. The compound 3Ce2O3 · WO3 has a fluoritelike cubic structure of a0 = 11.040 A and forms solid solutions with constituent oxides or CeO2. The compound 3Ce2O3 · 2WO3, which seems to be isostructural with 3La2O3 · 2WO3, is stable only in the temperature range, 1545 ∼ 1730°C. The compound Ce2O3 · WO3, which has a monoclinic structure, transforms reversibly at 1360°C to a tetragonal structure with the cell parameters a0 = 5.469 A, c0 = 8.790 A. The compound Ce2O3 · 2WO3 identified to be monoclinic, also has a reversible transformation at 1105°C. Its high-temperature phase has a cubic cell with the cell parameter a = 7.046 A. As is well known, Ce2O3 · 3WO3 appeared to have similar high-temperature behavior to La2O3 · 3WO3. The compound 2Ce2O3 · 9WO3, whose structure could not be analyzed, melts congruently at 1026°C.

Dissociation of magnetite in a solar furnace for hydrogen production. Tentative production evaluation of a 1000 kW concentrator from small scale (2 kW) experimental results

Abstract For experiment results obtained in a 2 kW solar concentrator, the FeO production by thermal dissociation of magnetite (Fe 3 O 4 ) was extrapolated to the 1000 kW solar furnace of Odeillo, France. If this reaction is used in a two step thermochemical water splitting cycle, one can expect an extrapolated value of 137 m 3 day −1 hydrogen production when Fe 3 O 4 is dissocated at 2090 K, under an inert atmosphere, during 0.5 min and cooled down by a splat cooling quench technique.

Etude a haute température des systèmes formés par les sesquioxydes de lanthane avec les sesquioxydes de lanthanides II. Influence de la trempe sur la nature des phases obtenues à la température ambiante

Splat cooling from the solar-furnace melt of mixed-oxide solutions of lanthanide oxides in La 2 O 3 changes the range of solid solution or produces phases of crystal structure not observed for the individual oxides in the pure state. Significant inertness to hydration has been obtained for type A hexagonal solutions enriched in Yb 2 O 3 by the effect of quenching.

Note on the condensation of the vapor phase above a melt of iron oxide in a solar parabolic concentrator

γFe2O3 was obtained after vaporization and condensation of αFe2O3 in a 2kW solar furnace. The condensates were characterised by X-ray powder diffractometry and by gravimetry after hydrogen reduction of the samples.

Preparation of cadmium by thermal dissociation of cadmium oxide using solar energy

Abstract Cadmium oxide vapors were decomposed at the focus of a 2 kW solar furnace by direct heating under argon circulation. Pure CdO was difficult to decompose by this method. Condensates containing 80 wt% Cd were obtained when CdO was dispersed in a ZrO 2 matrix (20 wt% CdO in ZrO 2 ) after melting of the mixed oxide. Other matrixes were also tested: Y 2 O 3 , Al 2 O 2 , SiO 2 . The CdO decomposition was also investigated by indirect heating in a reaction tube contained within a blackbody cavity receiving the concentrated radiation of a xenon arc image furnace: 70 wt% Cd-containing condensates were obtained, using pure CdO as starting material. An electrostatic separator was used for the collection of the Cd rich condensed vapors.

Étude au microscope électronique de structures modulées dans les régions du système La2O3CeO2 riches en La2O3

Abstract Samples in the binary system La 2 O 3 CeO 2 on the La 2 O 3 -rich side were melted in a solar furnace. The structure of the compounds obtained corresponds to a more or less regular insertion of lamellae of another structure, presumably ceria, within the lamellar structure of La 2 O 3 . The phenomenon was first detected by X rays and can be illustrated through high-resolution electron microscopy, which shows that the period of the insertion depends on the amount of cerium in the sample.

On the kinetics of the thermal decomposition of sulfates related with hydrogen water splitting cycles

Abstract The purpose of this paper is to present a set of kinetic results on the decomposition of MgSO4, NiSO4, ZnSO4 and to discuss these in relation to the theoretical models. Isothermal and non-isothermal thermogravimetric studies as functions of temperature, gas flowrate, shape and solid additives have been performed. The gas effluent analysis in the three cases show that the products are SO2 and O2. For NiSO4 and ZnSO4 the contracting sphere model, chemically controlled, gives a good representation of the results. In the case of MgSO4 a diffusion shrinking-core model had been derived. The reaction is controlled by the mass transfer in the product layer.