Effect of Small Amount of Insoluble Dopant on Tetragonal to Monoclinic Phase Transformation in Tetragonal Zirconia Polycrystal

摘要

The effect of small amount of insoluble dopant on tetragonal to monoclinic (t-m) phase transformation of 3 mol percent Y_2O_3 stabilized tetragonal zirconia polycrystal (3Y-TZP) is examined by ageing in hot water. The materials used are 3Y-TZP and 0.1 mol percen SiO_2-doped 3Y-TZP with grain size of 0.55 tun. The t-m phase transformation of 3Y-TZP is retarded by 0,1 mol percent SiO_2 doping. Since the doped silicon ion segregates along the grain boundaries, the change in phase transformation behavior must be originated from the change in grain boundary diffusivity of hydroxyl ion. Analysis of the transformation kinetics by the Mehl-Avrami-Johnson equation reveals that the activation energy does not change in the two materials but the pre-exponential term significantly changes. Grain boundary diffusion of hydroxyl ion must be blocked by the presence of silicon ion which reduces the effective area of grain boundary diffusion.