Superplastically foaming method to make closed pores inclusive rigid ceramics

Porous ceramics incorporates pores to improve several properties including thermal insulation maintaining inherent ceramic properties such as corrosion resistance and large mechanical strength. Conventional porous ceramics is usually fabricated through an insufficient sintering. Since the sintering accompanies the exclusion of pores, it must be terminated at the early stage to maintain the high porosity, leading to degraded strength and durability. Contrary to this, we have innovated superplastically foaming method to make ceramic foam only in the solid state. In this method, the previously inserted foam agent evaporates after the full densification of matrix at around the sintering temperature. Closed pores expand utilizing the superplastic deformation driven by the evolved gas pressure. The typical features of this superplastically foaming method are listed as follows: 1. The pores are introduced after sintering the solid polycrystal. 2. Only closed pores are introduced, improving the insulation of gas and sound in addition to heat. 3. The pore walls are fully densified expecting a large mechanical strength. 4. Compared with the melt foaming method, the superplastically foaming method is practical because the fabrication temperature (around the sintering temperature) is far below the melting point and it does not need mold. 5. The size and the location of pores can be controlled by the amount and position of the foam agent. In this chapter we introduce the superplastically faburicated ceramics mainly focused on the combination of 3 mol% yttria stabilized zirconia (3YSZ) and a silicon carbide (SiC) as matrix and foam agent, respectively.