Mullite fabrication from natural kaolin and aluminium slag

Abstract The structural transformations of kaolin–aluminium slag mixtures during heating were studied using differential thermal analysis (DTA), thermal gravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). The amount of formed mullite increases with the firing temperature. At 1500 °C, the mullitization of the mixture is almost complete. The morphology of the formed mullite is bimodal (primary and secondary phases). The primary mullite, formed from processing of kaolin by the gradual collapse of metakaolin from 990 °C, has a shape of elongated crystals. The other hand, the secondary mullite formed by solution-precipitation from the glass phase in the presence of alumina particles has a shape of acicular grains.