Characterization of porous alumina bodies fabricated by high-temperature evaporation of boric acid with sodium impurity

For steel-making refractories, porous alumina bodies fabricated by the evaporation of chemical impurities at high temperatures was studied. Boron hydroxide and sodium carbonate were added in different proportions as impurities into the starting aluminum hydroxide powder compacts, which were heated at various temperatures for 1 h to form porous alumina bodies. During heating, the borate compounds that reacted with sodium seems to be formed in the liquid phase, so that all alumina particles were able to grow into platelets. Although the sodium inside the compacts was completely evaporated by 1400 °C, the boron melt was maintained above 1400 °C. Hence, alumina platelets grew with a card-house structure, which preserved the high porosity of the alumina body. After heating at 1600 °C for 1 h, the remaining boron oxide was completely evaporated and sintering between the alumina particles began to decrease the porosity. The compressive strength and porosity of the alumina bodies obtained by heating at 1700 °C for 1 h were 0.8 MPa and 64%, respectively. It is expected that the resulting porous alumina bodies can be used as castable porous clinkers.