Thermal resistance of porous alumina ceramics prepared from the spray pyrolyzed powders

Porous alumina ceramics were prepared using spray pyrolyzed powders and thermal resistance of the porous properties was investigated. The powders were prepared by use of precursor solutions of AlCl₃6H₂O(AC), Al(NO₃)₃ 9H₂O(AN), Al₂(SO₄)₃ 16H₂O(AS), NH₄Al(SO₄)₂ 12H₂O(AM) and Al₂(C₂O₄)₃ 5H₂O(AO). The solutions with Al concentrations in 0.2-2.0 M were sprayed at 900°C through a pressure type atomizer under various combinations of solution flow rates and gas flow rates. The sprayed powders were hollow and spherical shape in several to several tens μ m in diameter. The specific surface area of the as-sprayed powders ranged from 5.5 m²/g in the AO sample to 128 m²/g in the AC sample. With elevating the firing temperature above 1000°C, the surface area of the fired bodies decreased monotonously and the pore size increased correspondingly. A clear relation as smaller the pore size in the green body higher the surface area of the fired body up to high temperatures was observed. The highest surface area after firing at 1500°C for 2 h was 9.3 m²/g in the AC sample and was higher than those of porous alumina ceramics prepared by the different methods reported so far.