“…10 and Table 6 reveals that, besides Al 3+ , Si 4+ , and O 2− , the mullite phase contains Ti 4+ in addition, which demonstrates that the mullite crystals yield from the liquid phase at firing temperature. Impurities as TiO 2 and Fe 2 O 3 have been proven to facilitate mullite formation from kaolin (Kong et al, 2003;Mitra et al, 2002;Sen and Aggarwal, 1994;Soro et al, 2003). Because the growth mechanism of mullite in kaolin, which is known as a dissolution-precipitation process (Ji et al, 2013), is generated by the appearance of a Si-rich liquid phase and promoted by the presence of TiO 2 and Fe 2 O 3 due to their assistance for lowering the formation temperature and viscosity of liquid phase during firing, the dissolution rate of Al 2 O 3 into liquid phase increases with the decrease of the viscosity of liquid phase.…”