The mechanism of oxidation of ferrous sulfide (FeS) powders in the range of 648 to 923 K

The oxidation of FeS powders in flowing dry air was investigated over the temperature range of 648 to 923 K. Thermodynamic calculations and experimental observations showed that the initial stages of oxidation are characterized by the formation of FeS₂ and Fe₃O₄ or Fe₂O₃. Sub-sequently, the oxidation process goes through a formation and eventual oxidation of Fe₂(SO₄)₃ to Fe₂O₃. The kinetics of oxidation of FeS are believed to be controlled by this last step, whose activation energy, 192 kJ-mol^-1, agrees reasonably well with a corresponding value measured for the oxidation of Fe₂(SO₄)3, 219 kJ.mol^-1. Thermodynamic calculations of phase stability diagrams in the Fe-O-S system are presented in support of the proposed oxidation mechanism.