INFLUENCE OF THE PREPARATION HISTORY OF ALPHA-FE2O3 ON ITS REACTIVITY FOR HYDROGEN REDUCTION

TG experiments on the hydrogen reduction of α-Fe2O3 were carried out to elucidate the influence of the preparation history of the oxide on its reactivity. α-Fe2O3 samples were prepared by the thermal decomposition of seven iron salts in a stream of oxygen, air or nitrogen at temperatures of 500-1200°C for 1 h. Thirteen metal ions such as Cu2+, Ni2+, etc. were used as doping agents. The reactivity of the oxide was indicated by the initial reduction temperature (Ti. α-Fe2O3 prepared at lower temperatures showed lower Ti values and the reduction proceeded stepwise (Fe2O3 → Fe3O4 → Fe). Ti values increased with the rise in the preparation temperature of the oxide. The oxides prepared at higher temperatures showed that two reduction steps (Fe2O3 → Fe3O4 → Fe) proceed simultaneously. the preparation in oxygen gave higher Ti than that in air or nitrogen. The doping by metal ions, except Ti4+, lowered the Ti of α-Fe2O3. The Cu2+ ion showed the lowest Ti, while Ti4+ showed the highest Ti and the inhibition effect. The reduction process was expressed by two equations; Avrami-Erofeev's equation for α-Fe2O3 → Fe3O4 and Mampel's equation for Fe3O4 → Fe. © 1979.