Preparation and study of YSTZ-Al2O3 nanocomposites

Yttria stabilized zirconia-alumina (YSTZ-Al2O3) nanocomposite system with various Al2O3 concentrations has been synthesized by sol-gel route. The experimental techniques XRD, DTA, TGA, FT-Raman, FT-IR, SEM, Vicker′s hardness measurements, density measurements and Impedance spectroscopy were used to characterize the synthesized specimens. DTA result shows two exothermic reactions: one around 760°C and another around 960°C. XRD results confirm that the specimen starts to crystallize on heating above 750°C. Well resolved XRD reflections corresponding to tetragonal (t) ZrO2 were obtained after the specimens were heated at 1000°C. FT-Raman results confirmed that the crystallites developed above 750°C was t-ZrO2. It was observed from the XRD and DTA results that the bulk and grain boundary region crystallize independently in two different temperatures with a difference in temperature of about 200°C. The crystallization temperatures increase with Al2O3 contents. At 1300°C, the pure YSTZ and 5 and 10 wt % Al2O3 added YSTZ specimens underwent structural transformation from tetragonal to monoclinic ZrO2. But, the tetragonal symmetry remains stable at 1300°C with an addition of 15 wt % Al2O3. The system which retain its tetragonal symmetry at its processing temperature (≈1300°C) gives high hardness and maximum density values. Almost 100% theoretical density value was obtained at 1300°C with an addition of 15 wt % of Al2O3.