• zirconia: partially stabilized;
  • phases;
  • X-ray diffraction;
  • crystals;
  • polymorphs

The relative abundance of the cubic (c), tetragonal (t), monoclinic (m), and orthorhombic (o) polymorphs of ZrO2, and the δ phase, Mg2Zr5O12, present in samples of 3.4-wt%-magnesia-partially-stabilized zirconia have been determined by Rietveld analysis of X-ray powder diffraction data. The samples studied correspond to the as-fired (AF), and subetectoid-aged maximum-strength (MS) and thermalshock (TS) states, with their surfaces in the ground or polished condition. The polymorph abundances of the bulk and near-surface regions are discussed in relation to the type of surface treatment. Grinding produces significant quantities of both m- and o-ZrO2 in the near-surface regions of all samples. The m content increases from about 5 wt% in the bulk, to 10, 24, and 33 wt% in AF, MS, and TS material, respectively, while the o content increases from trace amounts to about 11 wt% in all samples. The m and o phases both increase at the expense of t-ZrO2, and the transformation is accompanied by significant lattice distortion and/or crystal size reduction. Thus, measurement of only the ‘ground-surface-monoclinic’ content does not give an accurate indication of the total amount of transformable t-ZrO2 in ceramics of this kind. Polishing removes some of the ground-surface m-ZrO2 in MS and TS, and all of the m-ZrO2 in AF material. The o-ZrO2 produced by grinding also declines substantially in AF and MS, but is not removed by polishing of TS. As a result, the bulk composition cannot be guaranteed, in the general case, to be accessible by X-ray analysis of polished surfaces.