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.