Microstructural development during final-stage sintering of nanostructuredzirconia based ceramics

The microstructural evolution of nanostructured zirconia based ceramics dur ing pressureless final-stage sintering in vacuum was followed using X-ray d iffraction, high resolution scanning electron microscopy and small-angle ne utron scattering (SANS). The ultra-fine zirconia and yttria powders were sy nthesized by the inert gas condensation technique, the ultra-fine alumina b y chemical vapor condensation. Powder compacts of ZrO2 and dispersion mixed 5 mol% Y2O3 partially stabilized ZrO2 and ZrO2 + 14 wt.% Al2O3 were sinter ed at temperatures between 1000 and 1200 degrees C for 2 h. Densification a nd concurrent grain growth as a function of temperature revealed a signific ant suppression of grain growth in the zirconia/alumina composite. Due to a homogeneous distribution of the alumina second phase in the zirconia matri x nearly full density and grain sizes <40 nm were achieved. Changes in the microstructure of monoclinic zirconia sintered at T > 1050 degrees C were d etected by SANS and could be attributed to the detrimental effects of the m onoclinic to tetragonal martensitic phase transformation. The log-normal po re size distributions were also evaluated for the ceramics. (C) 2000 Elsevi er Science S.A. All rights reserved.