STRUCTURE OF ZIRCONIA PREPARED BY HOMOGENEOUS PRECIPITATION

The structure of pure zirconia powders prepared by homogeneous precipitation was examined by electron microscopy. Some of these powders consisted of metastable tetragonal zirconia in the form of spherical aggregates up to 1 mu m in diameter. The size of single crystals within these particles exceeded 100 nm, which is much larger than usually reported for metastable zirconia. We conclude that the existence of these large tetragonal monocrystals is due principally to the very fine internal porosity within the domains, which gave rise to a surface area/volume ratio sufficient to stabilize tetragonal zirconia by the same mechanism as in nanocrystalline powders.