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 grai n and GB regions are crystallized independently at two different temperatur es. The bulk grains are crystallized into tetragonal symmetry above 750 deg rees C with an average crystallite size of 10 nm. The GB regions are crysta llized above 950 degrees C. These crystallization temperatures increase wit h Al2O3 concentrations At 1300 degrees C phase transition occurs for specim ens with low concentration of Al2O3 (less than 10 wt%. With 15 wt% of Al2O3 , the system remains in tetragonal symmetry even above 1300 degrees C. In o rder to control the growth rate of the crystallites at high temperatures, t he stable composition YSTZ-15wt%Al2O3 was dispersed in a SiO2 glassy matrix . The dispersed product also crystallized with tetragonal symmetry. In addi tion to the presence of t-ZrO2, the mullite phase also exists in the disper sed product at 1300 degrees C. (C) 1999 Acta Metallurgica Inc.