Influence of the preparation history of α-Fe 2O 3 on its reactivity for hydrogen reduction

Abstract

TG experiments on the hydrogen reduction of α-Fe 2O 3 were carried out to elucidate the influence of the preparation history of the oxide on its reactivity. α-Fe 2O 3 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 Cu 2+, Ni 2+, etc. were used as doping agents. The reactivity of the oxide was indicated by the initial reduction temperature ( T i. α-Fe 2O 3 prepared at lower temperatures showed lower T i values and the reduction proceeded stepwise (Fe 2O 3 → Fe 3O 4 → Fe). T i values increased with the rise in the preparation temperature of the oxide. The oxides prepared at higher temperatures showed that two reduction steps (Fe 2O 3 → Fe 3O 4 → Fe) proceed simultaneously. the preparation in oxygen gave higher T i than that in air or nitrogen. The doping by metal ions, except Ti 4+, lowered the T i of α-Fe 2O 3. The Cu 2+ ion showed the lowest T i, while Ti 4+ showed the highest T i and the inhibition effect. The reduction process was expressed by two equations; Avrami—Erofeev's equation for α-Fe 2O 3 → Fe 3O 4 and Mampel's equation for Fe 3O 4 → Fe.