Abstract

Andalusite and Mullite are widely used as raw materials for many different applications in the refractory industry. These minerals are well known to provide  high thermo-mechanical stability, therefore enhancing key properties such as thermal shock resistance and refractoriness under load. However, the performance of the refractory products based on mullite and andalusite can be strongly affected by the amount and the type of impurities associated with the main mineral.

This paper presents the results of several studies comparing the performance of different types of andalusite and mullite grades. A broad range of commercial products was deeply characterised regarding chemical and mineralogical composition, as well as dilatometry and heating microscopy.

Refractory bricks and castables were produced from each type of andalusite and mullite in a laboratory scale, in order to establish a correlation between the raw material purity and the refractory performance.

For instance, low ferric oxide and alkali/alkali-earth oxide content in certain materials yield outstanding hot properties and CO resistance for the refractories in which they are used. The processing that goes into their production participates in the superior performance, playing an important role in the densification of the material, thus impacting key properties, such as water demand and flowability.

Thermo-mechanical properties such as refractoriness under load, creep resistance  and Hot MOR were investigated, with a particular focus on the impact of impurity level, its enrichment in the matrix, and its influence on the microstructure.