Sintering of Mullite by Different Methods

Abstract

In this study, we have investigated the sintering of mullite by three different methods: (i) reaction sintering by thermal decomposition of kaolinite, followed by reaction with alumina; (ii) reaction sintering of mullite by solid state reaction of pure silica and alumina; (iii) sintering of commercial electrofused mullite powder. In all the cases, the mixtures of powders were compacted by dry pressing and sintered at temperatures between 1000°C and 1600°C using a resistive furnace. The phase identification was performed by X-ray difractometry, and the microstructure was studied by scanning electron microscopy. Density and porosity were obtained using the Archimedes method. The flexural strength and the Vickers hardness were measured to evaluate the mechanical properties. Sintered ceramic bodies with a high content of mullite were produced following the three investigated routes. In both the second and third methods a residual phase of α-alumina was observed on the sintered bodies. The higher values of density and bending strength were achieved by specimens produced by the first method and sintered at 1600°C.