Processing and characterization of boron carbide-hafnium diboride ceramics

<p>"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.</p> <p>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 (k_th) between room temperature and 200⁰C suggested that the stoichiometry of the boron carbide additives did not significantly affect (k_th) of HfB₂-BₓC composites. The improved sinterability and the high (k_th) (~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.</p>

Name thesis:degree_name

Ph. D. in Ceramic Engineering

Grantor

Missouri University of Science and Technology

Year dc:date.available

2016

Author dc:creator

• Brown-Shaklee, Harlan J.

• Band gap
• Ceramic Materials

Repository record dc:identifier

https://scholarsmine.mst.edu/doctoral_dissertations/65

OAI identifier oai:identifier

oai:scholarsmine.mst.edu:doctoral_dissertations-1067