Upon heating, the monoclinic phase in zirconia starts transforming to the tetragonal phase at 1,461 K, peaks at 1,471 K, and finishes at 1,480 K. On cooling, the transfor­mation from the tetragonal to the monoclinic phase starts at 1,326 K, peaks at 1,322 K, and finishes at 1,294 K, exhibiting a hysteresis behavior that is […]

Diffusion in zirconia is closely linked to ionic conductivity. Consequently, some diffusion data has already been presented in Sect. 5. This section will include additional results par­ticularly for monoclinic zirconia. Oxygen self-diffusion at a pressure of 300 Torr, as determined by testing zirconia spheres of diameters between 75 and 105 (dm, behaves as shown in […]

Cubic zirconia doped with oxides such as Y2O3 or CaO is the material of choice for many high temperature applications because of its extremely high ionic conductivity at intermediate and high temperatures. A review on the properties of these specialized rare-earth stabilized zirconia materials has been prepared by Comins et al. [50]. The oxygen pressure […]

Using the strain rate data shown in Fig. 12, the activation energy for creep in mono­clinic zirconia has been found to be Qc ~ 330-360 kJ mol-1 [48, 49]. The measured stress exponent, n, from equation: (3) was found to be 1.7 by Roddy et al. [48] and 2.3-2.5 by Yoshida et al. [49]. In […]

The toughness of pure monoclinic zirconia is difficult to obtain because of problems encountered during sintering of these types of specimens. Generally, if a full density is desired for mechanical properties evaluation, the material needs to be heated to a temperature that is above the tetragonal-to-monoclinic transformation temperature (i. e., 1,471 K). This results in […]

The hardness for monoclinic zirconia is approximately 9.2 GPa [31] for samples with a density > 98% and 4.1-5.2 GPa [32] for samples with a density > 95% of theoretical, whereas hardness values for amorphous zirconia vary between 5 and 25 GPa [33]. The hardness increases slightly to values approaching 11 GPa for yttria-stabilized zirconia […]

The measured elastic stiffness and compliance moduli for monoclinic zirconia have been summarized by Chan et al. [30]. The Young’s and shear moduli of this same Table 4 Polycrystalline Young’s and shear moduli for monoclinic zirconia in GPa (adapted from Chan et al. [30] 20°C 300°C 600°C 800°C 1,000°C 266 256 250 245 239 EReuss […]

Measurements of the mechanical properties of pure tetragonal and cubic zirconia are exceedingly difficult because of the higher temperatures required for such measure­ments. Hence, only monoclinic zirconia has been thoroughly studied in pure form. The mechanical properties of tetragonal and cubic zirconia have been determined for many stabilized zirconias and, because of the importance of […]

Oxygen vacancies in cubic zirconia result in a calculated displacement pattern as shown in Fig. 9 [2]. In this figure, the vacancy is depicted as a small cube, the oxygen Fig. 8 Charge density in the plane through ZrA, OA, and O., and a schematic diagram of a neutral oxygen interstitial (О,) near a triple-bonded […]

Interstitial defects in monoclinic zirconia have been modeled in detail by Foster et al. [24]. Using plane wave density functional theory, the tetragonal bonding and triple­planar bonding geometries of lattice oxygen ions were determined. In addition, it was determined that interstitial defects can form stable defect pairs with either type of lattice oxygen ions (i. […]