Microstructural changes and evolutions of elastic properties versus temperature of alumina and alumina–magnesia refractory castables

This paper deals with the evolutions of thermo-mechanical properties of castable refractories versus temperature. The measured properties are mainly Youngʹs modulus evaluated by a high temperature ultrasonic technique and thermal expansion followed by dilatometry. Materials are alumina-based low cement castables with a fraction of alumina eventually substituted by spinel or magnesia. The granularity of the different used raw materials is chosen by using a packing model, in order to reduce the final porosity in the hydrated state. The interpretation of results is carried out by considering the materials as composites, constituted of aggregates (size > 100 μm) into a matrix where most of chemical and phase transformations occur. By using two-phase analytical models, it is shown that the evolutions of thermo-elastic properties of castables can be qualitatively predicted from measurements performed in a matrix-equivalent simplified material. Moreover, considering the elastic properties after heat treatment, the castable with magnesia is comparable to the castable processed with synthetic spinel.