Mullitisation behaviour of calcined clay–alumina mixtures

The mullitisation behavior of three south Indian calcined clays with three different alumina sources has been studied. The calcined clays were ground and then mixed with different alumina sources such as reactive alumina, gibbsite and boehmite. Rectangular bars were prepared and sintered at 1600 °C/3 h. The X-ray diffraction and microstructural analysis were carried out to understand the mullitisation behavior. Thermogravimetric and differential thermal analyses of the powders were also carried out. The physical and mechanical properties were measured and discussed. The calcined clay (meta kaolin) derived samples show better strength and density than the uncalcined clay derived sample. The microstructure also shows a higher aspect ratio of mullite crystals. Among the three clay combinations, the calcined Neyveli clay and fine reactive alumina mixture was found to exhibit a better mullitisation behavior compared to other combinations.