Solubility of TiO 2, Fe 2O 3 and MgO in mullite

Abstract

The temperature dependent solubility of titanium, iron and magnesium in mullites coexisting with SiO 2-rich partial melts in a used chamotte brick was studied with a high-resolving microprobe. The mullites of the starting material have relatively high mean Fe 2O 3 (≈2.4 wt%), but lower TiO 2 (≈1.4 wt%), and very low MgO contents (≈0.5 wt%). Cation removal from mullite to coexisting glass phase is observed at high temperature: the onset of exsolution is about 1300°C for magnesium, 1350°C for iron, and 1400°C for titanium. Sample specimens annealed at 1650°C have mullites with about 0·5wt% Fe 2O 3, 0·9 wt% TiO 2, and traces of MgO. Cation exsolution curves follow exponential laws, the exsolution rate being considerably higher for Fe 2O 3 than for TiO 2 and MgO. The study documents a much higher mobility of the iron ion as compared to that of titanium.