Asymmetric mullite membranes manufactured by phase-inversion tape casting from polymethylsiloxane and aluminum diacetate

Polymethylsiloxane (MK) and aluminum diacetate have been stoichiometrically combined to synthesize a mullite-based powder (3Al(2)O(3)center dot 2SiO(2)) at 850 degrees C (5 h) or 1200 degrees C (3 h). High-purity crystalline mullite ( > 99%) was obtained by heating the mixture in the air (thermal oxidation) at 1200 degrees C for 3 h, mainly due to the formation of highly reactive silica and alumina precursors. Afterward, the mullite-based powders were used to prepare planar asymmetric microfiltration membranes by phase-inversion tape casting. The green membranes were sintered at 1600, 1650 or 1700 degrees C during 2 h. The asymmetric morphology identified in the membranes by scanning electron microscopy analysis reveals a thin skin-layer (microfiltration layer, < 10 mu m) followed by a porous support, in which two different structures were observed: finger- and/or sponge-like layer. Water permeation performance in a dead-end configuration was investigated at different pressures (3, 4, and 5 bar). The obtained results clearly indicated an improved water permeation flux compared to a symmetric commercial membrane (133.6 m(3)/m(2).h compared to 14.7 m(3)/m(2).h, respectively, at 5 bar). This observation could be ascribed to the asymmetric morphology resultant from the phase-inversion process.