Solids and liquids in the (Fe, Mg, Ca)S-system: experimentally determined and thermodynamically modelled phase relations
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2025-06
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Journal Article
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Abstract
Thermodynamic descriptions and experimentally verified phase relations in the FeS-MgS-CaS system are important both for steelmaking and for natural reduced systems. Experimental and thermodynamic data for such oxygen-poor systems are sparse due to the difficulty of conducting experiments under conditions at which these sulfides are stable. In this study, phase relationships were determined for FeS-MgS at 1170-1550 ⁰C, for FeS-CaS at 1025-1600 ⁰C, for MgS-CaS at 900-1500 ⁰C and for FeS-MgS-CaS at 1050 and 1360 ⁰C. Experiments were performed in evacuated silica glass tubes with excess Fe⁰ to favour troilite (FeS) rather than pyrrhotite (Fe₁₋ₓS) for the FeS-rich phase. Textural interpretations and measured compositions indicate that the FeS-CaS system melts eutectically at 1063 ± 3 ⁰C at 7 ± 1 mol% CaS. The FeS-MgS system is also modelled to be eutectic (at 1180 and 2.5 mol% MgS), yet, experimentally, its eutectic or peritectic character could not be unequivocally determined. This system's liquidus has a higher dT/dX than previously reported. The MgS-CaS system was found to have a symmetric miscibility gap that closes at 1210 ⁰C. Differences to the outcome of previous experimental studies can be explained by the presence of troilite rather than pyrrhotite in our experiments when Fe-rich solid solution coexists with liquid or solid solution. The experimental data are fit by a thermodynamic model that reproduces the experimentally determined phase relations, and is capable of predicting melting phase relations for the FeS-MgS-CaS ternary.
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52 (2)
Pages / Article No.
12
Publisher
Springer
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Subject
Niningerite; Troilite; Oldhamite; Sulfides; Phase equilibria; Mercury
Organisational unit
09784 - Sossi, Paolo Angelo / Sossi, Paolo Angelo
03592 - Schmidt, Max / Schmidt, Max