Microstructure evolution during the heating process and its effect on the elastic properties of CAC-bonded alumina castables

In this paper, the alumina-based refractory castables were prepared using calcium aluminate cement (CAC) as binder. The phase composition and microstructural evolution of the castable samples during the heating process were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), differential thermal analysis (DTA), and thermal expansion analysis. The relationship between the microstructural characteristics of castables and the properties of elastic modulus was investigated. The results showed that, after the castables were cured at room temperature for 24 h and dried at 110 °C for 24 h, the main phases present after hydration were Al 2 O 3 , C 3 AH 6 , and AH 3 . C 3 AH 6 and AH 3 would be transformed into C 12 A 7 and AlO(OH) or Al 2 O 3 , as temperature increased from 110 °C to 800 °C, the microcrack caused by decomposition of the hydrates will led to the lower values of both the elastic modulus and strength of the castable samples. From 900 °C to 1000 °C, CA was recrystallized through the reaction between C 12 A 7 and A, resulting in an increase in elastic modulus and strength. Between 1100 °C and 1200 °C, CA 2 would be formed, which resulted in a volume expansion of the material and a slight increase in elastic modulus. Finally, the CA 6 phase was formed as the temperature increased to 1400 °C. The enhancement of the strength and elastic modulus of the castable samples could be attributed to their strong interlocking bonds between platelet CA 6 and matrix particles at high temperature.