Alumina membranes - Colloidal processing and evolution of functional properties

In this thesis the whole preparation cycle of the ceramic alumina membrane is studied. Study is focused on colloidal processing with different additives, modeling of absorption on multiplayer substrate and on layer growth during dip coating and the effect of colloidal processing on growth kinetics. Other focus is laid on sintering and its effect on functional properties such as pore size, pore morphology and permeability. The prepared membrane performance is studied in different industrial processes. Studies were done with submicron alumina powders having different purity grades. The deflocculation behaviour was studied with electrostatic and electrosteric mechanisms by using pH control and a polyelectrolyte as dispersant. The verification of absorption model led to finding that the wetting behavior of solution deviates from the prediction of Young equation. The effect of reduced capillary pressure with polyvinyl alcohol (PVA) addition can be clearly seen from layer growth rates. The used polyelectrolyte, sodium polymetacrylic acid (Na-PMAA) did not fully deflocculated the dip coating slip and resulted in fast and hard-to-control layer growth and highly porous membrane layer. Sintering studies showed that at high sintering temperatures, where shrinkage should occur, the pore size coarsens and the size distribution broadens for supported particulate film, while the macroscopic densification is almost insignificant. Small deviations from ideal packing are suggested to lead to local densification, which causes pore size growth and broadening of distribution. Local densification also leads to pore channel straightening, which was found in analysis of permeability values. The alumina membranes were tested at several applications. The filtration tests were conducted for different industrial wastewaters. Feeds varied from paper mill wastewaters, stone cutting wastewaters, oily waters to dwell waters.