Gastight, closed pore inclusive porous ceramics through a superplastically foaming method

Our innovative superplastically foaming method was used to create closed-pore inclusive zirconia-based ceramics. Yttrium oxide was added to monoclinic zirconia to stabilize the matrix. Sintering and superplastic deformation were used to form a solid solution and transform it to a cubic phase. Porous ceramics formed via this post-stabilization method exhibited anomalous thermal expansion due to the silica derived from the foaming agent SiC. This anomalous thermal expansion disappeared following substitution of the SiC foaming agent for AlN. The resulting superplastically foamed porous ceramics exhibited large thermal conductivities, comparable to that of the fully densified ceramics, but with a porosity as great as 35%. This high thermal conductivity was attributed to the alumina derived from the foaming agent AlN. To suppress the formation of alumina, the samples were pre-sintered in an argon atmosphere. The modified superplastically foamed ceramics exhibited smaller pores, with a porosity of 33%, as well as favorable thermal insulation, with a thermal conductivity that was approximately half that of the fully dense material.