Diffusion-limited sulfidation of wustite

Abstract

The sulfidation of wustite in H2S−H2O−H2−Ar atmospheres has been studied at temperatures of 700, 800, and 900°C with thermogravimetric techniques. Polycrystalline wustite wafers were equilibrated in a flowing H2O−H2−Ar gas stream and then sulfidizedin situ. During an initial transient stage a protective layer of FeS formed on the sample, and an intermediate layer of Fe3O4 formed between the FeO and FeS layers. Subsequently, the reaction followed a parabolic rate law. The parabolic rate constant varied from 0.22×10−2 mg2 cm−4 min−1 at 700°C to 6.5×10−2 mg2 cm−4 min−1 at 900°C. The reaction rate was limited by the diffusion of iron through the intermediate Fe3O4 layer which grew concurrently with the FeS layer and at the expense of the FeO core. After the FeO core was completely converted to Fe3O4, the process entered a passive stage during which no further mass changes could be detected.