Coal fly ash industrial waste recycling for fabrication of mullite-whisker-structured porous ceramic membrane supports

Abstract

With recyclable industrial waste coal fly ash and bauxite as starting materials, porous mullite-whisker-structured ceramic membrane supports were fabricated at sintering temperatures ranging from 1100 to 1400 °C with addition of AlF₃ and MoO₃ as crystallization catalyst and mineralizer, respectively. Dynamic sintering of mullite membrane supports was first studied. Then the characterizations were focused on open porosity, pore size distribution, gas flux and mechanical properties, microstructure and phase evolution. It shows that the introduction of MoO₃ effectively promoted the growth of elongated mullite crystals in the membrane support by reducing the high temperature viscosity of the liquid melt. Addition of 5 wt% MoO₃ lowered the secondary mullitization temperature, resulting in more mullite formation at temperatures as low as 1200 °C, while a porosity of 45.4 ± 0.9% was obtained. After sintering at 1200 °C, the open porosity was 47.3 ± 0.6% for the sample containing 4 wt% AlF₃. The co-introduction of MoO₃ and AlF₃ promoted formation of a whisker-interlocked porous structure, which effectively improved open porosity and permeation flux without significant mechanical strength degradation.