Effect of MgO on the microstructure and properties of mullite membranes made by phase-inversion tape casting

Flat microfiltration mullite (3Al₂O₃2SiO₂) membranes were prepared via phase-inversion tape casting method. The sintering temperature has been reduced from 1700°C to 1450°C by adding 3 wt.% of magnesium oxide (MgO) as a sintering aid. The effect of this compound on the membrane properties was systematically investigated. The presence of MgO promoted at the same time a change in membrane morphology resulting in a symmetric structure, which is opposite to the asymmetrical structure obtained for mullite membranes prepared without this sintering aid. Porosity of 38.9% and average pore size of 2.33 μm was achieved. Water and n-heptane vapor adsorption analysis showed an increment in hydrophilic behavior due to MgO. The reduction of sintering temperature from 1700°C (MgO free) to 1450°C (MgO added) produced mechanical stable samples with flexural strength about 15.3 MPa. The membrane was resistant enough to withstand the water flux permeation test up to 3 bar. Compared to the pure mullite membranes, the MgO containing sample displayed higher water permeation fluxes, which might be related to both the larger superficial pore size and its hydrophilicity.