Effect of TiO2 on the interaction of dehydroxylated kaolinite with Al(OH)3 gel in relation to mullitisation

Microstructural evolution, phase transformation, and variations in physical properties of coal series kaolin powder compact during firing

“…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.…”

Sintering and microstructural study of mullite prepared from kaolinite and reactive alumina: Effect of MgO and TiO2

“…2 wt% titania at 1600°C in the clay-alumina system causes densification up to 80% as per reported earlier. 24 Present work proves only 1% titania is sufficient to improve densification up to 94% at 1600°C. The use of reactive alumina here helps to reduce the dose of additive resulting in removing the possibilities of formation of secondary phases like aluminum titanate and magnesium aluminate spinel.…”

“…22 The role of MgO and TiO 2 as sintering additives in mullite system is reported by different researchers. 5,18,[23][24][25] The addition of TiO 2 (up to 4 wt%) in mullite formation using beach sand sillimanite and calcined alumina enhanced densification by solid solution formation. 23 Mullite prepared from clay, Al(OH) 3 gel, and different percentages of TiO 2 (0%-2%) reported that titania containing liquid phase formed at 1600°C due to which sintering occurred.…”

“…23 Mullite prepared from clay, Al(OH) 3 gel, and different percentages of TiO 2 (0%-2%) reported that titania containing liquid phase formed at 1600°C due to which sintering occurred. 24 Mullite formed from two different commercially available sources of alumina and silica reported the impact of the addition of 1-6 wt% MgO on sintering of mullite ceramics. It showed that density values till 4 wt% were improved and with higher addition deterioration occurred due to a greater extent of liquid phase formation.…”

“…The maximum theoretical density of mullite formed from clay alumina system was 91% and 80% in the presence of 3% MgO and 2% titania additive. 25,24 In the present work, combustion synthesized α-Al 2 O 3 and calcined clay are used to form the clay-alumina system. TiO 2 and MgO were already established as a sintering aid for mullite densification.…”