Effect of mullite formation on properties of refractory castables

In order to study the effect of the mullite bond phase on the physico-mechanical and refractory properties of the refractory castables, four castable samples were prepared; castable 1 contained 15 wt.% calcium aluminate cement (80% alumina) and 85 wt.% well graded tabular alumina . The other three samples (2, 3, 4) contained 10, 5 and 2% cement and 5, 10 and 13% of an alimina/ silica mixture (in the ratio 2.33:1, the molecular ratio of mullite). Their composition was investigated after firing at different firing temperatures using X-ray diffractin analysis. The physico-mechanical and refractory properties of such castables were determined according to standard specifications. Castable 4 that contained only 2 wt.% cement with 13 wt.% alumina/silica mixture and 85 wt.% well graded tabular alumina aggregate exhibited outstanding physico-mechanical and refractory properties after firing at 1500°C due to the presence of mullite in the bond phase with very little CaO. This enables their use in various refractory applications such as in steel, aluminium, copper, glass, cement, chemical and ceramic production.