Abstract
Deviation from stoichiometric composition of ferrous-sulfide Fe1−δS and solid solution sulfides (Fe, Cr)1−δS containing Cr up to 0.3 cation fraction was measured as functions of sulfide composition ξ, sulfur pressures (1∼10−5 Pa) and temperatures (973∼1173 K) using a thermogravimetric technique.
Nonstoichiometry δ increased with increasing Cr content in the (Fe, Cr)1−δS and sulfur pressures, while it decreased with increasing temperature at a constant composition and sulfur pressure. Cation vacancy is a predominant lattice defect in the (Fe, Cr)1−δS sulfide, and from the Libowitz model nonstichiometry δ and sulfur activity aS could be expressed by the following relation:
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oindentwhere μMeS is a free energy change for formation of a sulfide with stoichiometric composition as well as qVMe and σVMe are the formation and interaction energies of cation vacancies. It was observed that the values of σVMe were positive, ranging from 50 to 70 kJ/mol, independent of sulfide compositions, and the values of qVMe decreased from 56 to 17 kJ/mol with increasing sulfide composition.
