Buffering of the Sintering Stress for Fabrication of Microporous Al2O3/Stainless-steel Membranes

Based on porous stainless-steel disks, three methods were used to fabricate microporous Al2O3/stainless-steel membranes by coating Al2O3 powder with a mean particle diameter size of 0.5 mu m. The surface and cross-sectional morphologies were characterized by scanning electron microscople (SEM) and metallographic microscople, respectively. Pore size distribution of the Al2O3/stainless-steel membranes was measured by capillary flow method. The membrane adhesion was tested by means of ultrasonic shocking treatment. It is found that the problem of membrane peeling can be solved by introducing all intermediate layer of stainless-steel fine powder between the substrate and the alumina layer and then performing a co-sintering treatment. The microporous Al2O3/stainless-steel membranes with a thickness of 40-50 mu m were successfully achieved. Such an intermediate layer not only helps to modify the substrate surface but also buffers the thermal expansion and sintering shrinkage stresses in the Al2O3 layer during the heat-treatment. Moreover, it can also bond the Al2O3 layer onto the substrate and therefore enhances the membrane adhesion. The co-sintering approach introduced in this study simplifies fabrication process and saves energy. During co-sintering period the sintering, temperature plays a key role in membrane adhesion and pore size distribution. After being co-sintered at 1100, 1150, 1200 and 1250 degrees C, the mean pore sizes of the Al2O3/stainless-steel membranes are 0.2, 0.3, 0.5 and 3.9 mu m, respectively, and the pure water fluxes of the membranes are 3.8, 4.1, 6.9 and 20.5 m(3)/(m(2).h.bar), respectively.