Document Type

Dissertation

Degree

Doctor of Philosophy (PhD)

Department

Materials Science and Engineering

Advisor's Name

Surendra K. Saxena

Advisor's Title

Committee Chair

Advisor's Name

Jiuhua G. Chen

Advisor's Name

Kinzy Jones

Advisor's Name

Gautam Sen

Advisor's Name

Guoyin Shen

Keywords

transition metals, titanium, zirconium, hafnium, high pressure, high temperature, equation of state, phase diagram, thermal conductivity, diamond anvil cell, laser

Date of Defense

6-19-2012

Abstract

Transition metals (Ti, Zr, Hf, Mo, W, V, Nb, Ta, Pd, Pt, Cu, Ag, and Au) are essential building units of many materials and have important industrial applications. Therefore, it is important to understand their thermal and physical behavior when they are subjected to extreme conditions of pressure and temperature. This dissertation presents:

  • An improved experimental technique to use lasers for the measurement of thermal conductivity of materials under conditions of very high pressure (P, up to 50 GPa) and temperature (T up to 2500 K).
  • An experimental study of the phase relationship and physical properties of selected transition metals, which revealed new and unexpected physical effects of thermal conductivity in Zr, and Hf under high P-T.
  • New phase diagrams created for Hf, Ti and Zr from experimental data.
  • P-T dependence of the lattice parameters in α-hafnium. Contrary to prior reports, the α-ω phase transition in hafnium has a negative dT/dP slope.
  • New data on thermodynamic and physical properties of several transition metals and their respective high P-T phase diagrams.
  • First complete thermodynamic database for solid phases of 13 common transition metals was created. This database has:
  • All the thermochemical data on these elements in their standard state (mostly available and compiled).
  • All the equations of state (EoS) formulated from pressure-volume-temperature data (measured as a part of this study and from literature).
  • Complete thermodynamic data for selected elements from standard to extreme conditions.

The thermodynamic database provided by this study can be used with available thermodynamic software to calculate all thermophysical properties and phase diagrams at high P-T conditions. For readers who do not have access to this software, tabulated values of all thermodynamic and volume data for the 13 metals at high P-T are included in the APPENDIX. In the APPENDIX, a description of several other high-pressure studies of selected oxide systems is also included.

Thermophysical properties (Cp, H, S, G) of the high P-T ω-phase of Ti, Zr and Hf were determined during the optimization of the EoS parameters and are presented in this study for the first time. These results should have important implications in understanding hexagonal-close-packed to simple-hexagonal phase transitions in transition metals and other materials.

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