Sintering of commercial mulite powder: Effect of MgO dopant

Abstract

MgO is one of the sintering aids most commonly used in the processing of mullite bodies. However, few studies have investigated the influence of MgO on the densification and microstructural development of mullite bodies, and the amount of MgO to be used as dopant is still a matter of controversy. Thus, this work investigated the efficiency of small amounts of MgO in the sintering of industrial mullite. MgO was added to obtain dopant concentrations of 0.1 and 0.5 wt.% in the mullite samples. Doped and nondoped samples were produced by cold isostatic pressing (CIP) at 200 MPa and pressureless sintering at 1500, 1550, 1600 and 1650 °C for 2 h. The use of 0.1 and 0.5 wt.% of MgO increased the final density of the sintered samples, with the doped samples reaching densities of 99% and the nondoped samples reaching densities of 95%. Elongated mullite grains were observed in the nondoped samples when their density fell below 95%, while the microstructures of bodies containing 0.1 wt.% of MgO were controlled up to densities of 98%. The 0.5% doped samples required lower sintering temperatures, however elongated mullite grains were observed when densities of 99% were reached.