PROCESSING OF NANOSTRUCTURED ZIRCONIA CERAMICS

The inert gas condensation (IGC) technique was employed to synthesize nonagglomerated nanoparticles of ZrO2 and Y2O3 with different average particle sizes ranging from 4 to 14 nm. High pressure phases were found in the as-prepared powders of both n-Y2O3 and n-ZrO2. This has been explained on the basis of Gibbs-Thomson effect. The sintering behaviors (in air and vacuum) of single phase n-ZrO2 (monoclinic crystal structure) and Y2O3-ZrO2 mixture (Y-TZP) were studied in terms of densification rate and final sintering temperature. There was a strong correlation between densification characteristics and properties of the starting powder compacts, such as average particle size, particle and pore size distributions. n-ZrO2 was sintered to full density in air at temperatures as low as 1125 degrees C (0.47 T-m) and in vacuum at 975 degrees C (0.42 T-m). Although the grain sizes in the fully sintered samples were well below 100 nm, the grains had grown by a factor of at least 10, as compared to the initial particle size. Therefore, pressure-assisted sintering techniques, such as sinter-forging and hot pressing, were employed to further reduce the densification temperature and final grain size. Threshold effects in these processes are also discussed.