Preparation of mullite-alumina composite by reaction sintering between Algerian kaolin and amorphous aluminum hydroxide

Abstract The objective of this work is to obtain a multifunctional ceramic composite material at low cost with improved properties and that can be used in many structural applications like: electrical, refractory support and tribological elements. A mullite-alumina composite were prepared by using Algerian kaolin and amorphous aluminum hydroxide as starting materials. Two mixtures were used by varying the amorphous aluminum hydroxide content 61.5 % and 50 wt %. chosen an abundant kaolin has been chosen with a high alumina content and an amorphous alumina trihydrate to lower the temperature of the reaction with the excess of silica in the kaolin. The advantage of adding an amount of amorphous aluminum hydroxide is that it reacts at high temperature with the amorphous phase of silica issue from kaolin. The objective is to increase the amount of the mullite phase formed. When alumina is added in excess, a part will be dispersed in the mullite matrix to form a mullite-alumina composite. The results revealed that mullite is the major phase and alumina the minor phase in the samples sintered at 1600 °C. At this firing temperature, no silica phases (SiO2) are detected. The microstructure shows a higher aspect ratio of mullite crystals. The addition of alumina reduces the size of mullite grains and their aspect ratio. The density and hardness of the resulting mullite-alumina composites increase with sintering temperature and alumina content.