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.