Microstructural evolution and phase transformation of different sintered Kaolins powder compacts

Four kinds of Kaolins (K1, K2, K3 and K4) from various origins were studied using X-ray diffraction, 29Si and 27Al MAS-NMR spectroscopy and scanning electron microscopy (SEM). Mineralogical and morphological characteristics of these samples are given. Kaolinte is the principal mineral but other minerals are present in small quantities: Illite, Muscovite and Quartz. The thermal behaviour of K1, K2, K3 and K4 was studied. The transformation heats during heating were quantified from DTA measurements and phase changes were followed by X-ray diffraction analyses and 29Si and 27Al MAS-NMR spectroscopy. Results indicated that a series of phase transformations take place as the Kaolin is fired at elevated temperature. Mullite is first formed at a temperature as low as 1100 °C. Microstructural evolution of this specimen and their mechanical properties are investigated.