1. Reconciling in vivo and in vitro kinetics of the polymorphic transformation in zirconia-toughened alumina for hip joints: III. Molecular scale mechanisms.
- Author
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Pezzotti, Giuseppe, Bal, B. Sonny, Zanocco, Matteo, Marin, Elia, Sugano, Nobuhiko, McEntire, Bryan J., and Zhu, Wenliang
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ZIRCONIUM oxide , *ALUMINUM oxide , *CHEMICAL kinetics , *POLYMORPHIC transformations , *PHASE transitions , *STOICHIOMETRY , *SURFACE chemistry - Abstract
Understanding the intrinsic reason(s) for the enhanced tetragonal to monoclinic ( t → m ) polymorphic phase transformation observed on metal-stained surfaces of zirconia-toughened alumina (ZTA) requires detailed knowledge of off-stoichiometry reactions at the molecular scale. In this context, knowledge of the mechanism(s) for oxygen vacancy creation or annihilation at the material surface is a necessary prerequisite. The crucial aspect of the surface destabilization phenomenon, namely the availability of electrons and holes that allow for vacancy creation/annihilation, is elucidated in this paper. Metal-enhanced alterations of the oxygen sublattice in both Al 2 O 3 and ZrO 2 of the ZTA composite play a decisive role in accelerating the polymorphic transformation. According to spectroscopic evidences obtained through nanometer-scale analyses, enhanced annihilation of oxygen vacancies triggers polymorphic transformation in ZrO 2 near the metal stain, while the overall Al 2 O 3 lattice tends to dehydroxylate by forming oxygen vacancies. A mechanism for chemically driven “reactive metastability” is suggested, which results in accelerating the polymorphic transformation. The Al 2 O 3 matrix is found to play a key-role in the ZrO 2 transformation process, with unambiguous confirmation of oxygen and hydrogen transport at the material surface. It is postulated that this transport is mediated by migration of dissociated O and H elements at the surface of the stained transition metal as they become readily available by the thermally activated surrounding. [ABSTRACT FROM AUTHOR]
- Published
- 2017
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