Kinetics and Mechanisms of Re-oxiation of Freshly Reduced Iron Compacts.

Hematite compactswere isothermally reduced with hydrogen at 973-1 273 K.The reduction was carried out up to 90-95 •/o reduction degree using thermogravimetric technique.Thereduced products were subjected to re-oxidation in dry air.The rates of re-oxidation at 473-1 073 Kas a function of time was studied.Micro- scopic examination, and porosimetric measurementswere used to elucidate the kinetics and mechanisms of reduction and re-oxidation.During reduction of iron oxide, the rate was increased with temperature and the structure of sponge iron produced was temperature dependent.Three transition temperatures were identified during re-oxidation.Reoxidation at the initial stages was controlled by interfacial chemical reaction whereas at both the intermediate and later stages, solid-state diffusion was the rate controlling step.