Measurement of Phase Abundance in Magnesia‐Partially‐Stabilized Zirconia by Rietveld Analysis of X‐ray Diffraction Data

Abstract

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.