Benefits of Enhanced Mullitization upon Addition of Micronised Andalusite to Low Cement Castables

Abstract

In the formulation of low cement castables, microfine additives are so selected that predominating phase will be mullite in the matrix of the alumina based castable refractories. Andalusite behaves like a reactive mullite as during mullitization the expelled glass from the grains can be easily combined with required amount of micronised alumina, giving rise to a secondary mullite acting as a binder and converting the total castable matrix into a well distributed mullite. Mullitization process in andalusite depends on its grain size; attrition milled micronised andalusite grains undergo Mullitization even at 1200°C with release of glassy phase through a topochemical and topotactic process resulting in volume stability and high thermal shock resistance. The effect of micronised andalusite and coarse grained andalusite on the properties like bulk density, apparent porosity, volume change, strength before and after spalling cycles of the low cement castables have been compared. XRD studies have been made to identify the phases and SEM studies have been performed to get an idea about the microstructure.