Effect of TiO 2 on Initial Sintering of Al 2 O 3

Alpha alumina with additions of TiO 2 sintered more rapidly than “pure” alumina. The rate of initial sintering increased approximately exponentially with titania concentration up to a percentage beyond which the rate of sintering remained approximately constant or decreased slightly with additional titania. The concentration which produces the maximum rate of sintering is thought to be the solubility limit of TiO 2 in Al 2 O 3 . For alumina particles larger than about 2 μm, the kinetic process was mainly grain‐boundary diffusion. With smaller particles, volume diffusion increased. The “solubility limit” increased with decreasing particle size, indicating an excess surface concentration of TiO 2 . The data may be interpreted in terms of a region of enhanced diffusion at the grain boundary that increases with TiO 2 concentration. With small alumina particles, this region is large enough to become a significant portion of the volume of the particle, and the small particles appear to sinter by volume diffusion kinetics, but the diffusion coefficient corresponds to an enhanced diffusion coefficient.