Effects of Addition of Titania and Alumina Powder into Permeable Magnesia Ceramics

Abstract

Properties of permeable magnesia refractory containing titania and alumina powder in the matrix were investigated in order to produce permeable refractory with high thermal shock resistance, corrosion resistance and low penetration of molten steel, By adding titania and alumina powder in the matrix, bright glossy portion and dark glossy portion were observed in the matrix and in the grain boundary of magnesia, Bright glossy portion was CaTiO3 (Perovskite) from X-ray diffraction and EPMA analyses, Dark glossy portion was suspected to be Al2TiO5 (Aluminum Titanate) from EPMA analyses although Al2TiO5 was not detected by X-ray diffraction. The collapse of magnesia grains was caused by the generation of CaTiO3 and Al2TiO5 in the magnesia grain boundary. Apparent porosity, mean pore diameter and permeability became high and large as TiO2/Al2O3 molar ratio decreased, and reached the maximum value at the equivalent molar ratio. However, above the equivalent molar ratio the values became low and small. Permeability was proportional to the product of apparent porosity and the square of average pore diameter, Thermal shock resistance increased twice compared with no addition of TiO2/Al2O3. Although corrosion resistance deteriorated by adding TiO2/Al2O3. it was superior to the conventional porous alumina refractory, Penetration thickness of molten steel was not dependent on TiO2/Al2O3 addition, and was very small compared with conventional one. This permeable magnesia refractory will have a good possibility of being used on actual operation.