Stability, Instability, Metastability and Grain Size in Nanocrystalline Ceramic Oxide Systems

Giora Kimmel, Jacob Zabicky

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

9 Scopus citations

Abstract

The following nanocrystalline binary oxide systems were studied: Mg-Ti, Ni-Ti, Zr-Al, as well as some pure and doped unary oxides. The xerogels were heated at a constant T (200 to 1600°C) for 3 to 6 hours. There was a threshold tempearture for oxide formation and in many cases the products were metastable nanocrystalline phases, depending on the grain size and composition, including doping. The oxide phases of Ni-Ti, Mg-Ti, and Zr-Al, formed at 900°C are different from those formed at higher temperature. New ranges of solid solutions and the formations of higher temperature structures were found. A transition phase can be defined as a structure formed at relative low tempearture, irreversibly transforming at higher temperature into an equilibrium phase of the same elemental composition. Some low temperature transition phases have a structure similar to that of a high temperature equilibrium phase, e.g., (the equilibrium phase is given in parentheses) tetragonal ZrO2 (monoclinic) and low-T qandilite-like solid solutions (qandilite + geikielite). Others are unique with no representation in the equilibrium phase diagram, e.g., gamma-like alumina (corundum) and anatase (rutile), which are formed as nanocrystalline oxides due to a low growth rate caused either by a low temperature of calcination or due to additives. To asses the importance of crystal size in the stabilization of transition phases, the following studies were undertaken: (a) XRPD analysis of all unary, doped and binary compositions; (b) the evolution of transition phases in HT XRPD of the Mg titanates; (c) the phase evolution was studied with time at temperatures were mixtures of transition and equilibrium phases were found; (d) the retention of pure tetragonal ZrO2 on quenching Al-Zr oxides after calcinations at high tempetature; (e) additional evidence from HRTEM, SEM and DTA experiments was also collected. A model, correlating the size effect with the unusual phases and structures is proposed.

Original languageEnglish
Title of host publicationPerspectives of Nanoscience and Nanotechnology, Acta Materialia Gold Medal Workshop, European Materials Research Society, Fall Meeting
EditorsWitold Lojkowski, John R. Blizzard
PublisherTrans Tech Publications Ltd
Pages29-36
Number of pages8
ISBN (Print)9783908451570
DOIs
StatePublished - 2008
EventEuropean Materials Research Society, Fall Meeting, E-MRS 2007 - Warsaw, Poland
Duration: 17 Sep 200721 Sep 2007

Publication series

NameSolid State Phenomena
Volume140
ISSN (Print)1012-0394
ISSN (Electronic)1662-9779

Conference

ConferenceEuropean Materials Research Society, Fall Meeting, E-MRS 2007
Country/TerritoryPoland
CityWarsaw
Period17/09/0721/09/07

Keywords

  • Amorphous oxides
  • HTXRD
  • Magnesium titanates
  • Metastable ceramic oxides
  • Nanocrystalline oxides
  • Stability of ceramic oxides
  • Synthesis of ceramic oxides by sol-gel technique
  • Thermodynamics of nano structural materials
  • Titania
  • X-ray powder diffraction
  • Zirconia-alumina

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics
  • Materials Science (all)
  • Condensed Matter Physics

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