Solubility of sulfur in the solid oxide of the calcium-aluminate system

Abstract

The formation of CaS around CaO–Al2O3 causes pitting corrosion in ferritic stainless steel. To prevent the precipitation of CaS, the solubility of CaS in both the liquid and solid CaO–Al2O3 system has to be clarified. In this study, the sulfur content in the CaS-saturated solid CaO–Al2O3 system was measured. The results showed that, sulfur was soluble only in 12CaO·7Al2O3 at approximately 1.2 mass% while the sulfur content in the other solid compounds was very low. In addition, the sulfur content of 12CaO·7Al2O3 was independent of the heating temperature and was higher than that in the liquid oxide of the same composition. Therefore, 12CaO·7Al2O3 can dissolve sulfur in the solid state, preventing CaS formation.