Characterization and production of slip casts mullite–zirconia composites

Abstract

In this study, mullite–zirconia composites were prepared by reaction sintering of alumina, kaolinite zircon and colemanite powder. Slip casting method was also employed for production of these composites. Two different compositions were prepared with and without colemanite additive. The main purpose of this work was to determine the optimum conditions for mullite–zirconia synthesis in addition to the effects of starting composition, solid concentration of aqueous suspensions and sintering temperature. The resulting sintered materials were characterized in terms of bulk and relative density, firing shrinkage, XRD and SEM. XRD peaks suggested fully developed mullite and zirconia phases by reaction sintering of zircon, kaolinite, alumina and colemanite phases. Zircon usually dissociates at a temperature higher than 1650 °C. However, it has been shown in this study that zircon dissociates at about 1450 °C due to the presence of colemanite. The results of the study indicate that 90% of relative density was achieved as the solid concentration is increased up to 55% in case for slip-casted specimens with colemanite additive (MZC55 with 55% solid concentration). The microstructure of all composites is composed of irregularly shaped mullite grains and round-shaped zirconia grains which are distributed intragranularly and intergranularly.