Direct and Indirect Dissolution of Sapphire in Calcia–Magnesia–Alumina–Silica Melts: Dissolution Kinetics

The dissolution rate of sapphire into CaO-MgO-Al₂O₃-SiO₂ (CMAS) melts was investigated at 1450° and 1550°C. The effects of immersion time, specimen rotation rate, and magnesia concentration in the bulk melt on the sapphire dissolution rate and on the growth rate of magnesium aluminate spinel at the sapphire/melt interface were determined. The processes of direct and indirect sapphire dissolution into CMAS melts are discussed, with the support of kinetic and microprobe data.¹ A model of indirect sapphire dissolution^1,2 is used along with the equations of Tedmon³ to describe the kinetics of indirect dissolution and spinel layer growth during forced-convective and static sapphire dissolution.