An Insight into Slag Structure from Sulphide Capacities

The molar sulphide capacities \( C_{\text{S}}^{'} \) = (mol pct S) (\( P_{{{\text{O}}_{2} }} /P_{{{\text{S}}_{2} }} \))^1/2 on four binary systems, MgO-SiO₂, CaO-SiO₂, MnO-SiO₂ and FeO-SiO₂ are elucidated so as to compare the magnitudes of the basicities of four metallic oxides and to estimate the temperature dependencies of the basicities of metallic oxides. The enthalpy changes of the reaction 2O⁻ = O + O²⁻, viz. the silicate polymerization reaction (denoted as \( \Updelta H_{(8)}^{^\circ } \)) have been calculated from the slopes of the log \( C_{\text{S}}^{'} \) vs 1/T curves for four binary silicates. The \( \Updelta H_{(8)}^{^\circ } \) value is considered in the present work to be an index of the basicity of silicate melts. The basicities obtained on the basis of the \( \Updelta H_{(8)}^{^\circ } \) values are in the order MgO < CaO < MnO < FeO, which are determined by two effects; (i) ionicity of chemical bonds between metallic and oxygen ions and (ii) clustering of metallic oxides in silicates. It is also found that the basicity of the FeO-SiO₂ system is larger at higher temperatures.