Influence of mullite additions on thermal shock resistance of dense alumina materials. Part 2: Thermal properties and thermal shock behaviour

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Abstract
The thermal properties and thermal shock behaviour of homogeneous, fine grained (≈ 0·5–2 µm), dense (≥ 98% of theoretical density) alumina–mullite (5–15 vol.-%) composites have been studied and compared with those of a reference alumina ceramic with similar microstructure. Thermal expansion (25–600°C) thermal diffusivity, and thermal conductivity (25–400°C) were determined and a correlation between these results and microstructural characteristics was established. On the basis of the predicted theoretical relative performance under thermal shock, one of the composites (10 vol.-% mullite) was chosen and the thermal shock behaviour on quenching was compared with that of the reference alumina. A test that accounts for the detrimental effect of mullite on the heat transfer properties of alumina has been proposed. The results obtained agree with the theoretical predictions. In particular, the composite material had a critical temperature increment for failure larger (∼ 12%) than that of alumina.

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