title: Reconciling in vivo and in vitro kinetics of the polymorphic transformation in zirconia-toughened alumina for hip joints: III. Molecular scale mechanisms.
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 Al2O3and ZrO2of 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 ZrO2near the metal stain, while the overall Al2O3lattice tends to dehydroxylate by forming oxygen vacancies. A mechanism for chemically driven "reactive metastability" is suggested, which results in accelerating the polymorphic transformation. The Al2O3matrix is found to play a key-role in the ZrO2transformation 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.
authors.affiliation: Ceramic Physics Laboratory, Kyoto Institute of Technology, Sakyo-ku, Matsugasaki, 606-8126 Kyoto, Japan. Electronic address: pezzotti@kit.ac.jp.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Pezzotti
authors.affiliation: Department of Orthopaedic Surgery, University of Missouri, Columbia, MO 65212, United States; Amedica Corporation, 1885 West 2100 South, Salt Lake City, UT 84119, United States.
authors.forename: B Sonny
authors.initials: BS
authors.lastname: Bal
authors.affiliation: Ceramic Physics Laboratory, Kyoto Institute of Technology, Sakyo-ku, Matsugasaki, 606-8126 Kyoto, Japan.
authors.forename: Matteo
authors.initials: M
authors.lastname: Zanocco
authors.affiliation: Ceramic Physics Laboratory, Kyoto Institute of Technology, Sakyo-ku, Matsugasaki, 606-8126 Kyoto, Japan.
authors.forename: Elia
authors.initials: E
authors.lastname: Marin
authors.affiliation: Department of Medical Engineering for Treatment of Bone and Joint Disorders, Osaka University, 2-2 Yamadaoka, Suita, Osaka 565-0854, Japan.
authors.forename: Nobuhiko
authors.initials: N
authors.lastname: Sugano
authors.affiliation: Amedica Corporation, 1885 West 2100 South, Salt Lake City, UT 84119, United States.
authors.forename: Bryan J
authors.initials: BJ
authors.lastname: McEntire
authors.affiliation: Department of Medical Engineering for Treatment of Bone and Joint Disorders, Osaka University, 2-2 Yamadaoka, Suita, Osaka 565-0854, Japan. Electronic address: wlzhu2002@hotmail.com.
authors.forename: Wenliang
authors.initials: W
authors.lastname: Zhu
mesh_terms: D000537:Aluminum Oxide / Q000737:chemistry / Q000493:pharmacokinetics / Q000494:pharmacology; D006622:Hip Prosthesis; D006801:Humans; D007700:Kinetics; D008954:Models, Biological; D008956:Models, Chemical; D015040:Zirconium / Q000737:chemistry / Q000493:pharmacokinetics / Q000494:pharmacology
chemical_list: D015040:Zirconium; D000537:Aluminum Oxide; C028541:zirconium oxide
keywords: Femoral heads; Oxygen vacancy; Polymorphic transformation; Transition metals; Zirconia-toughened alumina