High purity mullite ceramics by reaction sintering

Abstract

A review of studies of the synthesis and densification of mullite ceramics suggests that reaction sintering could be the best way to obtain high purity, dense mullite from common materials (amorphous silicon dioxide and α-aluminum oxide). The use of fine grain powder mixtures allows us to obtain dense ceramics after firing at 1600° C, because such fine powders favour densification more than mullite formation, which slows down the sintering rate. The aluminium oxide to silicon dioxide ratio appears to be a critical parameter: densification reaches its maximum (97%) for the stoichiometric 3Al2O3·2SiO2 (mullite), whereas it reaches its minimum for compositions close to 75·0 wt% Al2O3, in which excessive grain growth occurs. Moreover, these compositions seem to correspond to the solubility limit of Al2O3 in mullite.