Bulk porous mullite supports for ceramic membranes were prepared directly using a mixture of industrial waste fly ash and bauxite by dry-pressing, followed by sintering between 1200 and 1550 °C. The effects of sintering temperature on the phase composition and shrinkage percent of porous mullite were studied. The XRD results indicate that secondary mullitization reaction took place above 1200 °C, and completed at 1450 °C. During sintering, the mixture samples first shrunk, then expanded abnormally between 1326 and 1477 °C, and finally shrunk again above 1477 °C. This unique volume self-expansion is ascribed to the secondary mullitization reaction between bauxite and fly ash. More especially, the micro-structural variations induced by this self-expansion sintering were verified by SEM, porosity, pore size distribution and nitrogen gas permeation flux. During self-expansion sintering, with increasing temperature, an abnormal increase in both open porosity and pore size is observed, which also results in the increase of nitrogen gas flux. The mineral-based mullite supports with increased open porosity were obtained. Furthermore, the sintered porous mullite membrane supports were characterized in terms of thermal expansion co-efficient and mechanical strength.
Bibliographical noteFunding Information:
This work was financially supported by the Ministry of Science and Technology of China for the financial supports (the international cooperation project: contract no. 2009DFB50490; the 973 project: contract no. 2003CB615700). The authors would also like to thank the Public Education Department of Jiangxi Province for financial support (GJJ08509, GJJ08510, and GJJ08511).
- Fly ash
- Membrane supports
- Self-expansion sintering
- Waste recycling
ASJC Scopus subject areas
- Environmental Engineering
- Environmental Chemistry
- Waste Management and Disposal
- Health, Toxicology and Mutagenesis