Comparative study of different routes of particulate processing on the characteristics of alumina functionally graded microfilter/membrane supports

This work investigates the preparation and characterization of flat functionally graded alumina microfilters/membrane supports employing different preparation routes of particulate processing, i.e., slip-casting (different rates), sedimentation and centrifugal casting using a similar slip of highly dispersed α-alumina particles. A powder with a cut off diameter of 1.2 μm but comprehending a sub-micron particle size range has been used in order to increase the permeability of the whole body. Permeability, average permeable pore diameter and tortuosity, curvature and top layer characteristics (defects, surface porosity, pore diameter) as a function of sintering temperature and processing routes have been investigated. Reasonable membrane characteristics are obtained at an optimum temperature of 1525 °C for the centrifuge and slow rate slip-casting routes while the sedimentation route results in severe surface macro cracks. At this temperature, the slip-casting route suffers from relatively low surface porosity (2.5%) when compared with the centrifuge samples (10.7%). This is while the surface pore diameter is about 0.1 μm smaller for the latter (0.28 μm).