Microstructural evolution and thermal shock resistance mechanism of calcium magnesium aluminate (CMA) aggregate in alumina castables

Abstract

The microstructural evolution and thermal shock resistance mechanism of calcium magnesium aluminate (CMA) aggregate after its introduction into alumina castables remain unclear. The hydration behavior of alumina castables containing CMA aggregates with various particle sizes under 25°C curing conditions is investigated. Additionally, the microstructural evolution and the interfacial properties of CMA‐containing castables with temperatures, as well as the recovery of castable strength of CMA‐containing aggregates after resintering, are comprehensively examined. The results indicate that CMA aggregate enhances early strength and promotes CAC hydration of castables, forming a “core–shell” structure with spinel–calcium aluminate (CA)–calcium dialuminate (CA₂) as the “core” and hydration phase as the “shell.” Sintering at 1600°C causes different overflow behavior in CMA aggregates, affecting the castable strength. Following resintering at 1700°C, the recovery ratio of flexural strength of castables containing CMA aggregate exceeds 15%, attributed to the overflow of CA/CA₂ in the CMA aggregate, which repairs microcracks and enhances thermal shock resistance.