Sintering of diphasic mullite gel

A monolithic colloidal gel of mullite composition, prepared from SiO2 and boehmite sols, was sintered under isothermal conditions. The sintering process was studied by dilatometry, thermogravimetric analysis, bulk density measurements and discontinuous shrinkage measurements. The silica component of stoichiometric colloidal mullite gel prevented crystallization of alpha-Al2O3 in the system. The initial rapid part of the sintering is controlled by the alumina phase and it is not a viscous sintering process in the sense of Scherer's viscous sintering model. The final part of sintering, above approximately, 80% of the theoretical density, is controlled by the silica component of the gel and agrees very well with the Scherer model.