Thermal conductivity and mechanical properties related to microstructure of a high alumina refractory castable

Thermo-mechanical properties and thermal conductivity of a high alumina refractory containing 10 wt% of synthetic spinel have been studied, from room temperature up to 1600°C. Results have been correlated with the microstructural and mineralogical evolutions by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM) as a function of the firing temperature. The refractory is considered as a composite material, formed by coarse aggregates embedded in a fine matrix. For this purpose, dry castable raw materials mixtures were sieved under 125 microns in order to separate the fraction considered as the matrix of this castable. Matrix samples were obtained for thermomechanical characterization and the results were compared to those corresponding to the whole refractory. The different properties are strongly dependent on the temperature since many transformations occur in the binder from the hydration at room temperature to the sintering process up to 1 600°C. Particularly, the dehydration process from 200°C to 900°C is responsible for the great variation of the thermal and thermomechanical properties. At higher temperatures, crystallisation of calcium aluminates plays a role of major importance on these properties.