Solubility and microstructural development of TiO2-containing 3Al2O3·2SiO2 and 2Al2O3·SiO2 mullites obtained from single-phase gels

Tailoring the microstructure of mechanoactivated Al2O3 and SiO2 mixtures with TiO2 addition

“…Interestingly, as will be presented in this study, TiO 2 can play multiple roles in affecting mullitization, densification and anisotropic growth. Also, some observations regarding TiO 2 doping found in the present work are significantly different from those observed when using gel-derived mullite precursors [16,17,19]. …”

“…Effect of TiO 2 on mullite phase formation has been reported in the literature [15][16][17][18][19]. The results indicate that the amount of TiO 2 incorporated into SiO 2 matrix by the substitution of tetrahedrally coordinated Ti 4+ for Si 4+ can be as high as 11.5 wt% TiO 2 in a sol-gel processed TiO 2 -SiO 2 system [16].…”

“…Consequently, almost full densification can be achieved at 1500 • C for the milled samples with TiO 2 contents of ≥5 wt%. As stated previously, the addition of TiO 2 could reduce the glass viscosity and increase mobility of the diffusing species, thus promoting densification [16,19]. Baudin and Moya [26] reported that the addition of TiO 2 below its solubility limit enhances the initial sintering and grain size, while excessive amounts of TiO 2 inhibit sintering and drastically increase the total porosity and mean grain size.…”

“…TiO 2 is a common impurity present in mullite. As a result, studies on TiO 2 doping effects have been carried out by many researchers [15][16][17][18][19]. It is reported that solubility limits of TiO 2 are in the range of 3.8-4.2 and 4.1-4.4 wt% TiO 2 for 3:2 and 2:1 mullites [19], respectively.…”

“…As a result, studies on TiO 2 doping effects have been carried out by many researchers [15][16][17][18][19]. It is reported that solubility limits of TiO 2 are in the range of 3.8-4.2 and 4.1-4.4 wt% TiO 2 for 3:2 and 2:1 mullites [19], respectively. Anisotropic growth takes place at >1500 • C in gel-derived millite ceramics with the addition of TiO 2 exceeding the solubility limit [17,18] [20], CoO [20], NiO [20], B 2 O 3 [21], and W 2 O 3 [9], have been explored.…”