POROUS ALUMINA AND ZIRCONIA BODIES OBTAINED BY A NOVEL GEL CASTING PROCESS

An improved gel-casting procedure was successfully exploited to produce porous ceramic bodies having controlled porosity features in terms of mean pore size, total pore volume as well as pore geometry. The gel-casting process in which a natural gelatine for food industry is used as gelling agent was firstly set-up to prepare dense alumina and zirconia components, by using two commercial powders, precisely TM-DAR Taimicron alumina and TOSOH TZ-3YS zirconia. To prepare porous components, commercial polyethylene (PE) spheres, sieved to select proper dimensional ranges, were added to the ceramic slurries as pore-forming agent. In the case of zirconia, components having 50 vol.% porosity were prepared by using PE spheres in the size range 125-300 mu m. For alumina porous materials, three different porosity percentages were investigated, precisely 40, 50 and 60 vol.%, using PE spheres in the range 224-300 mu m . A suitable thermal treatment was set-up for burning-out the organic phases (PE and gelatine) and subsequent densification of the ceramic network. The fired components presented spherical pores surrounded by highly dense ceramic walls and struts, having a homogeneous and fine microstructure. The mean pore size was directly dependent on the adopted sieved fraction of PE spheres. Hg porosimetry was coupled to image analyses performed on SEM micrographs for a full characterization of the porosity features.