Preparation of Porous Al2O3 via Oxidation of Al3BC3

This paper describes a new, simple, and convenient method to prepare porous Al₂O₃ through oxidation of Al₃BC₃ via a direct pore-forming approach using only Al₃BC₃ powder as a starting material. Oxidation of Al₃BC₃ to Al₁₈B₄O₃₃ started at 1150 °C, and a porous microstructure was formed because of the volatilization (sublimation) of B₂O₃ and CO₂. When heated at high temperature for a long period, Al₁₈B₄O₃₃ decomposed, accompanied by further volatilization of B₂O₃, resulting in monophasic Al₂O₃ with high porosity. The highest porosity was 71.6%, and small pores of 1–4 µm and large pores of 20 µm were observed in the present study. The pore size could be controlled by varying the heat-treatment temperature. The bending strength was 34.7–36.3 MPa, which is superior to those of other porous ceramics despite the high porosity of the Al₂O₃. This high bending strength is likely due to the high homogeneity of the Al₂O₃ and the formation of a porous Al₂O₃ network structure in which the particles are firmly bonded together at high temperatures. The proposed method easily provides a homogeneous porous Al₂O₃ sample without awkward processes such as mixing or dispersing a pore-forming agent into the matrix material.