Sol-gel derived YSTZ-Al2O3 and YSTZ-Al2O3-SiO2 nanocomposites

Yttria stabilized tetragonal zirconia (YSTZ) - alumina nanocomposite system has been synthesized by the sol-gel route. Investigations reveal that grain and GB regions are crystallized independently at two different temperatures. The bulk grains are crystallized into tetragonal symmetry above 750°C with an average crystallite size of 10 nm. The GB regions are crystallized above 950°C. These crystallization temperatures increase with Al2O3 concentrations. At 1300°C phase transition occurs for specimens with low concentration of Al2O3 (less than 10 wt%). With 15 wt% of Al2O3, the system remains in tetragonal symmetry even above 1300°C. In order to control the growth rate of the crystallites at high temperatures, the stable composition YSTZ-15wt% Al2O3 was dispersed in a SiO2 glassy matrix. The dispersed product also crystallized with tetragonal symmetry. In addition to the presence of t-ZrO2, the mullite phase also exists in the dispersed product at 1300°C.