Novel microwave method for the synthesis and sintering of mullite from kaolinite

Abstract

A novel and potentially economical microwave route has been developed for the synthesis and sintering of mullite from the naturally available minerals kaolinite and alumina. Mullite obtained by this route could be sintered to as high as 98% of theoretical density in under 60 min. A detailed structural investigation has been carried out using XRD, IR, and MAS NMR. It is clearly evident from the structural studies that there is a partial conversion of octahedral Al to tetrahedral Al with time during the formation of mullite. Also, it is evident that the exsolved SiO₂ reacts with the added Al₂O₃ to form secondary mullite over primary mullite which is nucleated from the decomposition of kaolinite. A detailed microstructural evolution of this conversion has been followed. A possible microwave-material interaction has been discussed for the rapid formation of mullite.