Fabrication And Characterization Of Porous Alumina Ceramics With High Porosity And High Strength

Because porous ceramics possess functional pores with special pore size and structure, they are widely used in filtration, catalyst support, sound absorption, heat insulation field, etc. But the contradiction between high porosity and high strength restricts further development of porous ceramics.Tert-butyl alcohol(TBA) was used as solvent for its high freeze point and high saturated vapor pressure, and porous alumina ceramics with high porosity and high strength were fabricated, with two types of different micro structures. One was porous alumina ceramics with three-dimensional connection fabricated by gel-casting method; the other was porous alumina ceramics with aligned channels structures fabricated by freezing-casting method.Fabrication processes of slurry and green body were researched. The influences of dispersant kinds and contents, pH values on slurry's rheology, and the influences of catalyst, initiator and polymerization environment on in-situ polymerization reaction were researched. Porous alumina green bodies with high porosity, no obvious shrinkage, and smooth surface were fabricated. Adding long chain polymer-polyvinylpyrrolidone(PVP) had strengthened green body successfully.Heating procedure of polymer removal and sintering was also investigated, and powder embedded sintering method could avoid cracks. Physical properties of porous alumina ceramics with different solid loadings and sintering temperatures were measured, such as porosity, compressive strength, specific surface area, pore size distribution. TBA-based porous alumina ceramics fabricated by gel-casting process were macro-pore porous ceramics, with pore size of micron magnitude. The mean pore size was determined by solid loading, and pore size distribution and specific surface area were determined by sintering temperature. Adding magnesia as sintering aid could raise compressive strength sharply while porosity declines slightly. SEM observation indicated that pores were constructed by particle accumulative interspace and three-dimensional connection. The variation of physical parameters was explained through micro-topography as grain size and compact degree observed by SEM.Porous alumina ceramics with aligned channels structure were fabricated by freezing-casting method. Influences of solid loading and cool side temperature to mechanical properties, microstructures, and pore size distribution in different freezing positions were researched. Ceramics present"plastic"properties, and axial strength far exceeds radial strength. Inner micro structure was long aligned pores approximate to hexagonal prisms, and pore walls were straight and flat. Pore size showed a double peaks distribution, which changed with positions in temperature field.