Article

Stabilization of Tetragonal Phase in Polycrystalline Zirconia

Westinghouse Research Laboratories
Journal of Materials Science (Impact Factor: 2.37). 11/1977; 12(12):2421-2426. DOI: 10.1007/BF00553928

ABSTRACT

It is shown that the tetragonal phase can be stabilized in the sintered body of a partially stabilized zirconia (PSZ) containing low concentrations of yttria. Such sintered body containing the metastable phase undergoes stress-induced phase transformation by the absorption of thermal or mechanical stress and exhibits strengths in excess of 690 MPa (100ksi).

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    • "Developing high-strength ceramics [1] [2] [3] led to the increased use of yttrium-stabilized zirconia (3Y-TZP) in dental clinical applications. Typically 3Y-TZP is used in single-or multiunit fixed dental prostheses as a structural material, which is subsequently covered with veneering ceramics. "
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    ABSTRACT: Objectives: The purpose of the study was to assess the hydrothermal resistance of a translucent zirconia with two clinical relevant surface textures by means of accelerated tests (LTD) and to compare predicted monoclinic fractions with experimental values measured after two years aging at 37°C. Methods: Polished (P) and ground (G) specimens were subjected to hydrothermal degradation by exposure to water steam at different temperatures and pressures. The t-m phase transformation was quantified by grazing incidence X-ray diffraction (GIXDR). The elastic modulus and hardness before- and after LTD were determined by nanoindentation. Results: G specimens presented a better resistance to hydrothermal degradation than P samples. Activation energies of 89 and 98kJ/mol and b coefficients of 2.0×10(-5) and 1.8×10(-6) were calculated for P and G samples respectively. The coefficients were subsequently used to predict transformed monoclinic fractions at 37°C. A good correlation was found between the predicted values and the experimental data obtained after aging at 37°C during 2 years. Hydrothermal degradation led to a significant decrease of the elastic moduli and hardness in both groups. Significance: The dependency of the t-m phase transformation rate on temperature must be determined to accurately predict the hydrothermal behavior of the zirconia ceramics at oral temperatures. The current prevailing assumption, that 5h aging at 134°C corresponds to 15-20 years at 37°C, will underestimate the transformed fraction of the translucent ceramic at 37°C. In this case, the mechanical surface treatment influences the ceramic's transformability. While mild grinding could potentially retard the hydrothermal transformation, polishing after occlusal adjustment is recommended to prevent wear of the antagonist teeth and maintain structural strength.
    Full-text · Article · Jan 2016 · Dental materials: official publication of the Academy of Dental Materials
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    • "Phase transformations in ceramics such as martensitic metamorphoses can involve spontaneous strain, and ferroelastic response occurs when such spontaneous strains are modified by, for example, exchange of twin variants (see, e.g., [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]). Such permanent strain, if heterogeneous, gives rise to self-equilibrating residual stresses within the object. "
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    ABSTRACT: In this paper the problem of transformation toughening in anisotropic solids is addressed in the framework of Stroh formalism. The fundamental solutions for a transformed strain nucleus located in an infinite anisotropic elastic plane are derived first. Furthermore, the solution for the interaction of a crack tip with a residual strain nucleus is obtained. On the basis of these expressions, fundamental formulations are presented for the toughening arising from transformations using the Green's function method. Finally, a representative example is studied to demonstrate the relevance of the fundamental formulation.
    Full-text · Article · Sep 2013 · Journal of Applied Mechanics
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    • "There are two ways to stabilize t-and c-ZrO 2 at ambient temperature: (i) doping (e.g. with yttrium or other oversized dopant cations to obtain t-ZrO 2 (YSZ) or c-ZrO 2 ) [28] and (ii) reducing the grain size down to the nanometer scale [29] [30]. While t-ZrO 2 grains have been observed to be size-stabilized below 200 nm [31], c-ZrO 2 was reported to become size-stabilized only for grains of a few nanometers diameter [32]. "
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    ABSTRACT: Zr-L2,3 XANESs of tetravalent zirconium oxides with different coordination numbers and local symmetries are systematically investigated by ab initio multiplet calculations using fully relativistic molecular spinors for model clusters. Experimental Zr-L2,3 XANESs are obtained for SrZrO3, m-ZrO2 (monoclinic) and t-ZrO2 (tetragonal). The theoretical spectra are in good agreement with the experimental data. The multiplet effects are found to play essential roles in determining the peak shape. The shapes of L3- and L2-edges are systematically different. The intensity ratios of the doublet peaks at both L3- and L2-edges are found to be sensitive to the coordination number of Zr. The ratio can therefore be used to estimate the coordination number of Zr in such oxides.
    Full-text · Article · Apr 2013 · Journal of Physics Condensed Matter
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