Preparation and characterization of alumina membranes on capillary supports: Effect of film-coating on crack-free membrane preparation

Ceramic capillary membrane has received much attention due to its relatively high pack density and favorable mechanical strength. However, it is difficult to prepare capillary membrane on its thin support by a dip-coating method. In this study, alumina microfiltration membranes were prepared on the inner surface of alumina capillary support (outer diameter 4 mm, inner diameter 2.5 mm) by a dip-coating method. Scanning electron microscopy (SEM) observation, gas bubble pressure (GBP) method and membrane permeation test were carried out to evaluate membrane performance. Two major effects in preparation of crack-free membrane, capillary filtration and film-coating, upon the thin support were studied. The as-prepared crack-free membrane presents a narrow pore size distribution, a mean pore size of about 0.6 μm and a high pure water flux of 86000 L·m^-2·h^-1·MPa. It is proved that the membrane thickness should be sufficiently large to overcome the defects of support surface, but it is only one of the prerequisites for the formation of crack-free membrane. Furthermore, it is demonstrated that the capillary filtration effect is greatly restricted for thin capillary support with the dip-coating method and the film-coating effect plays a crucial role in the formation of crack-free membrane.