Cyclic reduction-oxidation of haematite powders

Abstract

The cyclic reduction-oxidation of haematite (Fe₂O₃) powders was investigated over the temperature range 723 to 873 K. The hydrogeon reduction of haematite had an approximate activation energy of 53 KJ mol⁻¹. The air oxidation of the resulting iron gave a product whose composition depended on the thermal history of the sample (number of cycles and temperature). At the lowest cycling temperature (723 K) the primary oxide was Fe₃O₄ and the only influence of cycling was on the relative amount of unreacted iron. At the higher temperatures (798 and 873 K) the primary oxide was Fe₂O₃ at the end of one cycle but changed to Fe₃O₄ for a higher number of cycles. The effect of cycling is explained in terms of sintering during both the reduction and oxidation reactions.