Effect of MgO Addition on the Mechanical and Thermal Properties of Mullite Synthesised through Reaction Sintering of Al2O3 and Algerian Kaolin

Abstract

The influence of MgO addition on the structure and properties of mullite prepared through reaction sintering of Algerian kaolin and Al2O3 was investigated. The raw powders were wet ball milled, dried and cold compacted using a uniaxial press. The green compacts were sintered 8 hours at 1600 and 1650°C. The microstructure of samples was characterized using a scanning electron microscope. Mechanical and thermal properties were characterized using Vicker’s hardness tester, a universal testing machine and a dilatometer. It was found that the increase of MgO content from 0 to 3 wt-% increased the hardness of samples sintered 8 hours at 1600°C from 1039 to 1316.57 HV. Also, the increase of MgO content in samples sintered 8 hours at 1600 and 1650°C increased the compressive strength up to a maximum then decreased it. For a sintering temperature of 1600°C, the increase of MgO content up to 2 wt-% increased the flexural strength, but a further increase of MgO to 3 wt-% decreased it again, while for a sintering temperature of 1650°C, the increase of MgO content from 0 to 3 wt-% increased the flexural strength from 103.45 to 472.25 MPa. Amongst MgO containing samples, the increase of MgO content increased the coefficient of thermal expansion; however, it remained lower than the coefficient of thermal expansion of the sample without MgO addition.