Mechanical properties and thermal shock behaviour of model MgO-MgAl 2O4 spinel composite refractories

Abstract

The effects of varying the amounts (5 to 30 wt%) and particle sizes of magnesium aluminate spinel (i.e. preformed and in-situ formed) incorporated in a fully dense MgO, were investigated. Mechanical properties were measured at room temperature. The strength and modulus of the composites decrease with increasing spinel content. However, there is a general increase in work-of-fracture with the addition of spinel that is associated with a marked change from transgranular to intergranular fracture. The critical defect size and extent of interlinking of the microcracking were determined to be functions of spinel particle size and volume fraction, and the reasons for this are examined. Thermal shock tests confirmed that thermal shock parameter, R?, and ?WOF/?i ratios are useful indicators for the prediction of retained strength. The 20% 22 µm spinel composites showed the best improvement in resistance to shock damage, assessed in terms of difficulty of crack propagation. No advantages were obtained with higher levels of addition of spinel.