セラミック材料 多孔質アルミナの力学特性に及ぼす気孔率および気孔形態の影響

Abstract

Porous alumina samples were prepared with a fine alumina powder containing glass balloon or polyvinyl alcohol (PVA) as pore-former. After calcination, alumina samples with different porosities and pore morphologies were synthesized at 1623K by pressureless sintering. Referential porous alumina samples without the pore-former was obtained by reducing the sintering temperatures. Density, porosity and microstructure of porous alumina samples thus obtained were characterized. Young's modulus and Poisson's ratio were estimated by the linear strain under compressive stress and fracture strength was measured by three-point bending test. With adding the pore-former, the spherical pores with 10-20μm in diameter were observed uniformly in alumina matrix. Closed pores were pre-dominant for porous alumina samples prepared with glass balloon, and open or continuous pores were for porous alumina samples with PVA. Continuous but small pores were mainly observed in alumina samples sintered at lower temperatures. Young's modulus of porous alumina decreased with increasing porosity, independent of pore shape and size. A slight decrease in Poisson's ratio was observed for porous alumina samples prepared with glass balloon and PVA, and a clear decrease for referential porous alumina samples sintered incompletely. The fracture strength also decreased with an increase in porosity. Especially, the continuous and large pores accompanied with sharp and large flaws were found to cause strength reduction. These mechanical properties of porous alumina were discussed in terms of power law based on the minimum solid segment or area model.