1991 Volume 55 Issue 7 Pages 779-785
Oxidation of dense plates of mixed Fe-Co sulfides whose compositions were CoS-10 mass%FeS and CoS-50 mass%FeS was conducted at 973, 1023 and 1073 K in a 20 vol%O2-N2 gas mixture. Mass change of the samples and SO2 concentration of the off gas were continuously measured during the oxidation. Examination of the oxidized samples was carried out by using SEM, EPMA and XRD.
Two types of reactions proceeded during the oxidation; the one is the reaction of forming a dense oxide layer without the evolution of SO2 gas resulting in a mass gain of the sample, and the other is the reaction of forming a porous oxide with the evolution of SO2 gas resulting in a mass loss. The dense oxide formed on the sample surface was CoxFe3−xO4 and the porous oxide formed in the interior of the sample was composed of Fe3O4 and CoO. The concentration profiles of Fe and Co in CoxFe3−xO4 layer were proved to be uniform. The layer thickness grew in accordance with the parabolic rate law, with an activation energy of 145 kJ·mol−1.
