Physico-Mechanical and Microstructure Characteristics of Porous Mullite Ceramics

Abstract

Porous mullite ceramics were prepared from mixtures of Egyptian kaolinite-clay and calcined α-alumina powder. The effects of two methods of compaction as well as two types of binder were investigated. The influence of sintering temperature on the physical properties, crystalline phase, compressive strength and microstructure was studied. Mullite bodies processed by uniaxial pressing utilizing 15wt. % water at 1500°C for 2h exhibited the highest compressive strength of 150 MPa and bulk density of 2.1 g/cm3, as well as, an open porosity of 35%. In the present study, the only stoichiometric mullite was achieved by the crystallization of metakaolin. The mullite crystallizing out from the liquid phase was rich in silica, as determined by EDS, while that resulting from alumina grains was rich in alumina. The microstructure showed that primary mullite appeared at 1200°C, beside the unreacted alumina particles. On the other hand, at 1400°C alumina particles started to react with the glassy phase to form parallel laminates of mullite.