Anisotropic behaviour of andalusite particles used as aggregates on refractory castables

Andalusite is a well known alumino-silicate mineral largely employed in the refractory industry in order to provide high mechanical properties and thermal shock resistance. This work is devoted to the study of the thermal expansion behaviour of andalusite aggregates used in refractory castables. Anisotropic thermal expansion behaviour has been underlined by dilatometric measurements on andalusite single crystals according to their crystallographic axes. This behaviour can be magnified by the presence of quartz, even in small quantity, as impurities in the andalusite particle. The anisotropy of dilation is preserved after mullitisation of andalusite. These important results make it possible to explain the origin of the diffuse damage observed in andalusite-based castables which is most probably responsible for the enhancement of the strain to rupture required for the good thermal shock performance of such material.