Indirect Dissolution of (Al, Cr)2O3 in CaO—MgO—Al2O3—SiO2 (CMAS) Melts

Abstract

The dissolution of (Al, Cr)2O3 into CaO—MgO—Al2O3—SiO2 melts, under static and forced‐convective conditions was investigated at 1550°C in air. With sufficient MgO in the melt, or sufficient Cr2O3 in (Al, Cr)2O3, a layer consisting of a spinel solid solution, Mg(Al, Cr)2O4, formed at the (Al, Cr)2O3/melt interface. The dissolution kinetics of 1.5 and 10 wt% Cr2O3 specimens were determined as a function of immersion time, specimen rotation rate, and magnesia content of the melt. Electron microprobe analysis was used to characterize concentration gradients in the (Al, Cr)2O3 sample, the Mg(Al, Cr)2O4 spinel, or in the melt after immersion of specimens containing 1.5 to 78 mol% Cr2O3. The dissolution kinetics and microprobe analyses indicated that a steady‐state condition was reached during forced‐convective, indirect (Al, Cr)2O3 dissolution such that spinel layer formation was rate limited by solid‐state diffusion through the spinel layer and/or through the specimen, and spinel layer dissolution was rate limited by liquid‐phase diffusion through a boundary layer in the melt. This is consistent with a model previously developed for the indirect dissolution of sapphire in CMAS melts.