Thermal shock parameters [R, R‴ and R‴′] of magnesia–spinel composites

Thermal shock parameters (R, R‴ and R‴′) have been calculated using measured strength and modulus values for model magnesia-spinel composite materials. The R‴ and R‴′ parameters vary with both spinel content (0–30%) and spinel particle size (3–22 μm). In general, the larger the spinel content, the higher the values of R‴ and R‴′. It is predicted that the coarsest (22 μm) spinel provides a significant improvement in resistance to thermal shock damage through maximised difficulty of crack propagation, with a maximum at ∼20% addition. These predictions were also matched by thermal shock testing. After quenching from 1000 °C, the 20% 22 μm spinel composite had a retained strength ∼4.5 times higher than that for similarly quenched pure magnesia.