Abstract:

 Surface modification with rare earths was investigated for improving the hydrothermal stability of γ-Al2O3. The rare earths were added by impregnation or kneading method. Among the rare earths, studied lanthanum is the most effective promoter for inhibiting the reduction of surface area of Al2O3 sintered in wet air(14kPa water vapor) at 1273K for 24h, because its cations with valence 3+ and proper ionic radii can insert into the crystal lattice of Al2O3 and prevent the transition of Al2O3 from sintering and transforming to α-Al2O3. The presence of vapor-phase water in sinter tests was found to have a pronounced effect on surface area of Al2O3. The XRD measurements show that the α-phase increases and the crystal sizes become larger as area decreases. The kinetics for sintering of Al2O3 was studied and the constants, n and k, were used to calculate the rate of area loss at given area level.

Key words: Rare earths, Alumina, Surface area, Thermal stability