Evaporation Mechanism of Sn and SnS from Liquid Fe: Part II: Residual Site and Evaporation Kinetics via Sn(g) and SnS(g)

Abstract

Evaporation of Sn from molten steel was experimentally investigated for Fe-Sn-S alloy with low initial S (0.0007 < [pct S]₀ < 0.05) or with high initial S (0.55 < [pct S]₀ < 0.894) at 1873 K (1600 °C) using an electromagnetic levitation melting technique, in order to clarify the role of S on the evaporation mechanism of Sn. It was found that increasing initial S concentration, [pct S]₀, decreased the second-order evaporation rate constant of Sn (k _SnS), but there was a residual rate for the evaporation even at high [pct S]₀. The obtained residual rate constant, $k_{\text{SnS}}^{\text{r}}$, was 1.4 × 10⁻⁹ m⁴ mol⁻¹ s⁻¹ at 1873 K (1600 °C). Evaporation of Sn under virtually no S condition ([pct S]₀ = 0.0007) was also measured and corresponding first-order rate constant was determined to be 3.49 × 10⁻⁷ m s⁻¹ at 1873 K (1600 °C). A comprehensive model for the Sn evaporation from molten Fe-Sn-S alloy was developed in the present study, under the condition where mass transfer in gas and liquid phases were fast and interfacial chemical reaction controlled the evaporation of Sn. The model equation is able to represent the evaporation of Sn in the forms of Sn(g) and SnS(g) simultaneously, from very low S melt (when there is no S) to very high S melt investigated in the present study up to ~0.9 mass pct. Gradual transition of major evaporation species from SnS(g) to Sn(g) was well accounted for by the developed model.