Environment-oriented low-cost porous mullite ceramic membrane supports fabricated from coal gangue and bauxite

Porous mullite ceramic supports for filtration membrane were successfully fabricated via recycling of coal gangue and bauxite at sintering temperatures from 1100 to 1500 degrees C with corn starch as poreforming agent. The dynamic sintering behaviors, phase evolution, shrinkage, porosity and pore size, gas permeation flux, microstructure and mechanical property were systematically studied. A unique volume-expansion stage was observed at increased temperatures from 1276 to 1481 degrees C caused by a mullitization-crystal-growth process. During this stage, open porosity increases and pore size distributions broaden, which result in a maximum of nitrogen gas flux at 1400 degrees C. The X-ray diffraction results reveal that secondary mullitization took place from 1100 degrees C and the major phase is mullite with a content of similar to 84.7 wt.% at 1400 degrees C. SEM images show that the as-fabricated mullite supports have a porous microstructure composed of sintered glassy particles embedded with inter-locked mullite crystals, which grew gradually with increasing temperature from rod-like into blocky-like morphologies. To obtain mullite membrane supports with sufficient porosity and acceptable mechanical strength, the relationship between porosity and mechanical strength was investigated, which was fitted using a parabolic equation. (C) 2014 Elsevier B.V. All rights reserved.