Doctoral Dissertations

Keywords and Phrases

Band gap

Abstract

"Hafnium diboride based ceramics are promising candidate materials for advanced aerospace and nuclear reactor components. The effectiveness of boron carbide and carbon as HfB₂ sintering additives was systematically evaluated. In the first stage of the research, boron carbide and carbon additives were found to improve the densification behavior of milled HfB₂ powder in part by removing oxides at the HfB₂ surface during processing. Boron carbide additives reduced the hot pressing temperature of HfB₂ by 150⁰C compared to carbon, which reduced the hot pressing temperature by ~50⁰C. Reduction of oxide impurities alone could not explain the difference in sintering enhancement, however, and other mechanisms of enhancement were evaluated.

Boron carbides throughout the homogeneity range were characterized to understand other mechanisms of sintering enhancement in HfB₂. Heavily faulted carbon rich and boron rich boron carbides were synthesized for addition to HfB₂. The greatest enhancement to densification was observed in samples containing boron- and carbon-rich compositions whereas B₆.₅C provided the least enhancement to densification. It is proposed that carbon rich and boron rich boron carbides create boron and hafnium point defects in HfB₂, respectively, which facilitate densification. Evaluation of the thermal conductivity (kth) between room temperature and 200⁰C suggested that the stoichiometry of the boron carbide additives did not significantly affect (kth) of HfB₂-BₓC composites. The improved sinterability and the high (kth) (~100 W/m-K at 300K and ~90 W/m-K at 1000⁰C) of HfB₂-BₓC ceramics make them excellent candidates for isotopically enriched reactor control materials"--Abstract, page iv.

Advisor(s)

Fahrenholtz, William

Committee Member(s)

Van Aken, David C.
Hilmas, Greg
Xiao, Hai, Dr.
Smith, Jeffrey D.

Department(s)

Materials Science and Engineering

Degree Name

Ph. D. in Ceramic Engineering

Sponsor(s)

United States. Air Force. Office of Scientific Research
National Science Foundation (U.S.)

Publisher

Missouri University of Science and Technology

Publication Date

Summer 2011

Journal article titles appearing in thesis/dissertation

  • Densification behavior and microstructure evolution of hot pressed HfB₂
  • Optical characterization of heavily faulted boron carbide powders
  • Densification behavior and thermal properties of hafnium diboride with additions of boron carbides
  • Origins of resonant Raman scattering in boron carbide

Pagination

xv, 228 pages

Note about bibliography

Includes bibliographical references.

Rights

© 2011 Harlan James Brown-Shaklee, All rights reserved.

Document Type

Dissertation - Open Access

File Type

text

Language

English

Subject Headings

Hafnium
Optical spectroscopy
Raman spectroscopy

Thesis Number

T 9772

Print OCLC #

775668686

Electronic OCLC #

908572502

Link to Catalog Record

Electronic access to the full-text of this document is restricted to Missouri S&T users. Otherwise, request this publication directly from Missouri S&T Library or contact your local library.

http://merlin.lib.umsystem.edu:80/record=b8481573~S5

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