University of Illinois Urbana-Champaign

The high temperature structural evolution of hafnia

Haggerty, Ryan P.

Content Files
Haggerty_Ryan.pdf

Permalink

https://hdl.handle.net/2142/26202

Description

Title
The high temperature structural evolution of hafnia
Author(s)
Haggerty, Ryan P.
Issue Date
2011-08-25T22:18:38Z
Director of Research (if dissertation) or Advisor (if thesis)
Kriven, Waltraud M.
Doctoral Committee Chair(s)
Kriven, Waltraud M.
Committee Member(s)
  • Bass, Jay D.
  • Dillon, Shen J.
  • Petrov, Ivan G.
  • Zuo, Jian-Min
Department of Study
Materials Science & Engineerng
Discipline
Materials Science & Engr
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Date of Ingest
2011-08-25T22:18:38Z
Keyword(s)
  • Hafnia
  • Hafnium Dioxide (HfO2)
  • Zirconia
  • Zirconium Dioxide (ZrO2)
  • Phase Transformation
  • Martensite
  • Martensitic transformation
  • Thermal Expansion
  • High Temperature
  • X-ray Diffraction
  • Synchrotron
  • Zero Thermal Expansion
  • Thermal Shock Resistance
  • Transformation Toughener
Abstract
The transformations of HfO2 are often described as analogous with the transformations in ZrO2 because of the similar crystal structures; however the phase transformations in HfO2 occur at higher temperatures. Even though this phase transformation has been extensively studied in ZrO2 , the respective transformation in HfO2 is relatively unstudied and the properties that are reported are inconsistent. Much of the difficulty associated with studying HfO2 is related to the high temperatures needed and the sensitivity of the crystal to the environmental partial pressure of O2 . HfO2 is expected to be capable of producing the same level of transformation toughening as ZrO2 at temperatures beyond 1000◦ C, the thermodynamic limit for toughened ZrO2. Despite significant effort the toughening acquired has not met with expectation. By providing information on the structure of HfO2 as it undergoes transformation, this study makes a significant step towards solving this problem. Significant advancements in experimentation have enabled a systematic study of the structure of HfO2 in its monoclinic and tetragonal phases in air. Using a quadrupole lamp furnace and a novel curved image plate detector the structure of HfO2 and ZrO2 have been characterized by high temperature x-ray diffraction. The structural information provided by these experiments allows the properties of the transformation to be further investigated. Using phenomenological theory of martensite crystallography, the strain associated with the transformation from the tetragonal to the monoclinic phase has been described and provides insight into the lack of transformation toughening found in HfO2 . Further characterization includes determination of the transformation temperature in air, the change in volume associated with the transformation and the temperature hysteresis of the transformation. In addition to transformation properties, the thermal expansion of HfO2 and ZrO2 has been thoroughly described as a function of temperature and crystallographic direction. The monoclinic phases of ZrO2 and HfO2 have largely anisotropic thermal expansion which can only be fully described in tensor form, due to the low symmetry of the crystal. A systematic procedure for analyzing the thermal expansion of such low symmetry materials has been developed. Full characterization of the thermal expansion of the crystals has provided insight into the relationship on of the bonds in the structure to the expansion on heating. Use of advanced x-ray scattering experimentation for high temperature materials is also discussed, in particular the use of fixed incident reflection geometry.
Graduation Semester
2011-08
Permalink
http://hdl.handle.net/2142/26202
Copyright and License Information
Copyright 2011 Ryan P. Haggerty

Owning Collections

Graduate Dissertations and Theses at Illinois PRIMARY
Graduate Theses and Dissertations at Illinois
Dissertations and Theses - Materials Science and Engineering