Recycling of fly ash for preparing porous mullite membrane supports with titania addition

In order to effectively utilize industrial waste fly ash, porous mullite ceramic membrane supports were prepared from fly ash and calcined bauxite with chemically pure titania as sintering additive. The effects of TiO₂ on the sintering behaviors and main properties of porous mullite were studied in detail. Due to the addition of titania, the sintering of the flyash-based mullite was inhibited at low temperatures, but effectively improved at high temperatures, the latter is suitable for preparing porous mullite membrane supports by incomplete sintering. Titania entered into liquid glassy phase with low high-temperature viscosity during sintering, resulting in the improvement of sintering activity, as well as the lowering of secondary mullitization temperature (where 2.0% titania). Between 1300 and 1500°C, with increasing titania content, the samples exhibit increased trends in both linear shrinkage percent and bulk density, but a slightly decreased trend in open porosity, at all sintering temperatures. At 1300-1500°C, the samples sintered at 1450°C for 2h exhibit the lowest shrinkage and bulk density, as well as the highest open porosities in the investigated titania content range of 0-6.0wt.%. Also, with increasing titania content, the pore size decreases slightly but the three-point flexural strength increases gradually at 1450°C.