Doctoral Dissertations

Keywords and Phrases

DFT; Reaction processing; UHTCs; ZrB2

Abstract

"This dissertation focuses on the thermophysical properties of high purity zirconium diboride ceramics. These ceramics have shown promise for potential applications such as leading edge materials for next generation hypersonic vehicles. The overall goal of this work was to improve the understanding of the thermal properties and maximize the thermal conductivity of ZrB2. Four main areas were investigated in this work. First, the sintering kinetics and the intrinsic thermal properties of reaction processed ZrB2 were studied and compared to ZrB2 produced by hot pressing commercial powders. The reaction process produced ceramics with higher thermal conductivity and enhanced densification. Next, Hf impurity concentrations were varied showing that decreasing Hf content increased thermal conductivity. Finally, isotope enrichments were performed showing that lighter isotopes increased lattice frequency and subsequently thermal conductivity. Fully enriched Zr10B2 had a thermal conductivity of 145 W/m·K which is the highest value for ZrB2 reported to date. Scattering models based on quantum mechanics were used with density functional theory to analyze the effects of impurities and isotopes on the electron and phonon density of states. Overall, this work adds insight into the fundamental mechanisms behind the thermophysical properties of ZrB2. Tailoring compositions to reduce Hf content and adjusting boron isotope concentration has led to improved thermal properties at all temperatures. The processing conditions, reported properties, and insights gained from models will help the realization of ZrB2 as a leading edge material for the next generation of hypersonic vehicles"--Abstract, page iv.

Advisor(s)

Fahrenholtz, William

Committee Member(s)

Hilmas, Greg
Smith, Jeffrey D.
Rahaman, M. N., 1950-
Waddill, George Daniel

Department(s)

Materials Science and Engineering

Degree Name

Ph. D. in Materials Science and Engineering

Publisher

Missouri University of Science and Technology

Publication Date

Fall 2014

Journal article titles appearing in thesis/dissertation

  • Sintering mechanisms and kinetics for reaction hot pressed ZrB2
  • Zirconium diboride with high thermal conductivity
  • Thermal properties of ZrB2 ceramics with Hf contents up to 0.33 at%
  • Thermal properties of ZrB2 with varying boron isotope ratios
  • The effects of porosity and grain size on thermal properties of ZrB2

Pagination

xiv, 216 pages

Note about bibliography

Includes bibliographical references (pages 207-215).

Rights

© 2014 Jason Michael Lonergan, All rights reserved.

Document Type

Dissertation - Open Access

File Type

text

Language

English

Subject Headings

Ceramics -- Thermal propertiesZirconium -- Thermal propertiesBorides -- Thermal propertiesTransition metals

Thesis Number

T 10614

Electronic OCLC #

902734813

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