ABSTRACT
The kaolinite-mullite reaction series of eight kaolin samples have been studied with XRD, IR, DTA and MAS NMR spectra. The acquired results clearly show that the evolution of 29Si and 27 Al spectra of the various samples may differ from each other significantly. In the metakaolinite studied, the Al is universally present and it appears as a sign of the variation of the structure and some properties of the metakaolinites. It can be suggested from many experimental results that the high-temperatural phase occurring after the exothermal peak should be y -AI2O3 rather than Al-Si spinel, and the mullite-formation path in the studied samples involve two steps: first, the primary mullite formed directly from the metakaolinite around 850 °C; Second step, the secondary mullite developped extensively by reaction between segregated SiC2 and γ -Al2O3 at about 1200–1300 °C and the composition or/and structure of secondary mullite may be visibly different depending on the content of the impurity mica minerals.
