Hydratable Alumina-Bonded Suspensions: Evolution of Microstructure and Physical Properties During First Heating

Hydratable alumina (HA) is a calcium-free and high-refractoriness binder for alumina-based suspensions. Although recent studies have improved its dispersion, mixing and drying behaviours, a drawback related to its loss of strength between 250 and 900°C remains unexplored. Pores generated after decomposition of HA curing products are usually an explanation for the effect; however, no experimental result has supported this hypothesis so far. This study investigated the effects of thermal treatment (120–1500°C) upon the microstructure and physical properties of calcined alumina suspensions containing different amounts of HA (10–40 vol.-%). Porosity, compression strength and flexural elastic modulus measurements, thermal linear variation and thermogravimetric analysis were compared with scanning electron microscopy and X-ray diffraction results. The average matrix particle size and amount of HA in the formulation play major roles in the types of curing products that are formed. The strength reduction observed during first heating was not directly associated with the increase in porosity.