Non-Supported and Supported Alumina membranes were made by drying aluminum hydroxide sols prepared according to Yoldas method. The boehmite contents and viscosity at the time of casting sols play an important role on the non-supported membrane formation. When the sol reach a certain viscosity between 10cP and 100cP, membrane could be made. The sol with excess acid has lower content of boehmite than those sols with low acidity when they same viscosity. In order to investigate the role of DCCA (drying control chemical agent), glycerol was put into the sols.
The glycerol in sols not only decrease the rate of water loss in sols but strengthen the boehmite gel structure, which makes the best surface state of membranes. Non-Supported Membrane had ultra-fine pores with a narrow pore size distribution. The microstructure could be influenced by the calcination temperature and the acid concentration of the precuror sol.
Supported Alumina Membranes were prepared by dip-coating method. According to this method, the sol particles were concentrated at the entrance of support pores and a gel layer was formed. Low boehmite contents in sols and low viscosity are necessary to coat uniformly on the support with a constant thickness. Repeatiton of dip-coating led to thicker thickness. The permeability of supported membranes could be explained by Knudsen flow mechanism.
