STRUCTURE OF NANOSIZED REFRACTORY OXIDE POWDERS

Oxide powders, about 10-20 nm in particle size, were obtained by ball- milling using a planetary apparatus with high speed rotation, Chemical ly homogeneous stabilized zirconias were prepared by mechanical alloyi ng from yttria and monoclinic zirconia mixed powders. The EXAFS (K abs orption edge of Zr) spectra of the nanomaterials indicate that the dis tribution of oxygen neighbours around Zr atoms is similar to that foun d in crystals with the same composition, but that the peak of the seco nd neighbours (Zr-Zr and Zr-Y distances) significantly decreases for n anocrystalline powders. Transformation of monoclinic into tetragonal z irconia and of cubic into monoclinic yttria were induced by ball-milli ng. As well as for stabilized zirconias, XRD and EXAFS studies show th at a significant fraction of the nanocrystalline samples displays a di sordered structure.