Effects of pre-calcining temperature of andalusite on the properties of mullite-corundum refractories

In order to verify the thermal expansion behaviour of andalusite aggregates with different mullitization degrees and its influence on the properties (thermal shock resistance and especially volume stability) of mullite-corundum refractories, the properties of mullite-corundum refractories with uncalcined and different pre-calcined andalusite aggregates (1–3 mm) are investigated in terms of permanent liner change, thermal shock resistance, cold modulus of rupture, modulus of elasticity and apparent porosity. The experimental results show the volume stability of samples increases when the pre-calcining temperature of andalusite is improved (1300–1500 °C), as less residual andalusite in the pre-calcined aggregates leads to smaller volume expansion in the refractory samples during firing at high temperatures. Meanwhile, mullite-corundum refractories with andalusite aggregates (1–3 mm) pre-calcined at higher temperature have better cold modulus of rupture, because the increase of pre-calcining temperature could promote mullization degree and thereby bring down the length of microcracks and also enhance the densification of these as-prepared refractories. Moreover, mullite-corundum refractories with uncalcined and pre-calcined andalusite aggregates present good thermal shock resistance; the corresponding residual strength ratio of mullite-corundum refractories containing 1500 °C or 1600 °C pre-calcined andalusite aggregates is still higher than 90%. Overall, the volume stability and cold modulus of rupture of the mullite-corundum refractories could be significantly enhanced through the incorporation of 1500 °C pre-calcined andalusite aggregates (1–3 mm), and all mullite-corundum refractories with uncalcined and pre-calcined andalusite aggregates (1–3 mm) exhibit good thermal shock resistance.