Relationship between the strength and microstructure of CAC-bonded castables under intermediate temperatures

Abstract There have been reports on the strength decrease of CAC-bonded corundum-based castables without silica fume due to dehydration and decomposition of CAC hydrates when temperature is raised from 110 °C to 900 °C. It is found in this work that there are two steps of strength decrease of the CAC-bonded castables at temperatures of 300 °C and 700 °C respectively. In this paper, corundum-based refractory castables were prepared using tabular alumina and α-Al2O3 micro-powder as starting materials and calcium aluminate cement (CAC) as binder. The phase composition and microstructure of the castable matrix after heating at temperature between 110 °C and 1200 °C were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The strength decreases of the castables at temperatures of 300 °C and, in particular, 700 °C is illustrated using the phase and microstructure evolution of CAC-bonded castable matrixes after heating treatment at different temperatures. For the first time, investigated are the strength increase of the CAC-bonded castables and its causes at temperatures between 900 °C and 1000 °C with emphasis on the structure evolution of the hydrates examined by SEM using high magnification.