Kinetics and Mechanisms of Re-oxidation of Freshly Reduced Iron Compacts

Abstract

Hematite compacts were isothermally reduced with hydrogen at 973-1273 K. The reduction was carried out up to 90-95% reduction degree using thermogravimetric technique. The reduced products were subjected to re-oxidation in dry air. The rates of re-oxidation at 473-1073 K as a function of time was studied. Microscopic examination, and porosimetric measurements were 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.