Influence of Preparation Conditions on Mullite Formation in Clay-Alumina Mixtures

TLDR: In this article, the influence of repeated calcination and grinding of mixtures calcined between 1200° and 1500°C and sintered at 1400° and1500°C for duration of ½ hr to 4 hrs was investigated, with a view to accelerating the formation of mullite phase.

Abstract: Attempts were made to study the relation between calcination treatments and formation of mullite in clay-alumina mixtures, with a view to developing mullite body compositions. The influence of repeated calcination and grinding of mixtures calcined between 1200° and 1500°C and sintered at 1400° and 1500°C for duration of ½ hr to 4 hrs was investigated, with a view to accelerating the formation of mullite phase. Minor addition of MgCO3 was made in some trials. Mixtures repeatedly calcined at 1500°C and ground, and sintered at the same temperature attained bulk densities over 95% T.D. With MgCO3 addition, densiflcation of the same order was obtained at a lower temperature of sintering (1400°C). Microstructural studies on thin sections of the sintered samples as well as X-ray diffraction studies revealed that batches with stoichiometric ratio of clay and alumina would need repeated calcination and sintering at 1500°C for the substantial formation of mullite phase; while with MgCO3 addition, larger proportion ...