Keywords and Phrases
"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.
Van Aken, David C.
Xiao, Hai, Dr.
Smith, Jeffrey D.
Materials Science and Engineering
Ph. D. in Ceramic Engineering
United States. Air Force. Office of Scientific Research
National Science Foundation (U.S.)
Missouri University of Science and Technology
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
xv, 228 pages
© 2011 Harlan James Brown-Shaklee, All rights reserved.
Dissertation - Restricted Access
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Link to Catalog RecordElectronic 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://laurel.lso.missouri.edu:80/record=b8481573~S5
Brown-Shaklee, Harlan J., "Processing and characterization of boron carbide-hafnium diboride ceramics" (2011). Doctoral Dissertations. 65.