Elaboration of cobalt spinel CoAl2O4 and manganese spinel MnAl2O4 membranes for ultrafiltration.

Elaboration of cobalt spinel CoAl2O4 and manganese spinel MnAl2O4 membranes for ultrafiltration. New ceramics membranes based on CoAl2O4 and MnAl2O4 spinels were prepared. The sol of spinels were synthesized using the colloidal sol-gel process. After peptization of boehmite (0.5 M) by nitric acid, an aqueous solution of cobalt chloride (0.5 M) for spinel CoAl2O4 or manganese acetate (0.5 M) for spinel MnAl2O4 was poured into the boehmite sol drop by drop under stirring. The sol composed of 70 % spinel sol and 30 % polyvinyl-alcohol (PVA) (12 g PVA + 88 g water) was deposited by slip-casting on the internal surface of an alumina tubular support whose pore diameter is equal to 0.2 mum. After drying at room temperature for 48 h, the membranes were fired at 450 degreesC or 600 degreesC. The microstructure was observed by scanning electron microscopy. No cracks appear on the surface and the membranes thickness is about 3 mum. The pore diameter was measured by nitrogen adsorption-desorption by the BJH method. Other properties of membranes (cut-off and water permeability) were determined.