Porous alumina-based ceramics with very low thermal conductivity prepared by the starch consolidation route

Alumina-based porous ceramics were fabricated via the starch consolidation casting route, using titanium oxide as a sintering additive. Alumina-titania-starch slurries with starch contents of 2.5, 5, 7.5, and 10 wt% relative to the alumina-titania system were prepared. Titania was added to the slurries in proportions of 0, 1, 3, and 5 wt%, relative to alumina. The effects of starch and titania contents in the green bodies on the linear and volumetric shrinkage, as well as the total and open porosities of the sintered alumina product, were investigated. The effect of titania addition on mechanical, electrical, and thermal properties of the obtained porous alumina ceramics was studied. Microstructure and pores morphology were characterized by SEM. The alumina-based ceramics obtained had external porosities that varied between 54 and 76 vol%. Thermal conductivities as low as 0.06-0.1 W/m.K were achieved and the volume electrical resistivity ranged from 3.6 to 600 G Omega<middle dot>m, while compressive strengths up to 2.8 MPa for a titania ratio of 1 wt% were attained.