Keywords and Phrases
Electrical conductivity; Lorenz number; Thermal conductivity; Ultra-high temperature ceramics; ZrB2
"The research presented in this dissertation is focused on the thermal conductivity (k) of ZrB2 ceramics. The goal was to develop a better understanding of how various solid solutions and second phases affect the thermal and electrical transport in ZrB2, with a focus on the effect of C, W, and ZrC. The first study showed C additions improved densification and it was proposed that the reduction of boria was the impetus for this result. Boron carbide was formed by the reaction of excess C with reduced B and its formation was mitigated by the addition of ZrH2. This allowed the ZrB2-C binary system to be evaluated for study two. Study two showed the k of ZrB2 is reduced by C in solid solution and as a second phase due to the decrease in the electron contribution to thermal conductivity. Conductivities of 99 (25⁰C) and 76 W/m·K (2000⁰C) were obtained for the most pure ZrB2 (0.026 wt% C in solution and 0.2 vol% zirconia) produced in this study, which are the highest reported values for ZrB2 processed using commercial powders since 1980.
The third study evaluated the electrical resistivity of ZrB2 up to 1860⁰C using the van der Pauw technique. Separate linear regimes were observed below and above 950⁰C, whereas, previous studies assumed a linear relation. Finally the effect of ZrC on the (Zr,W)B2 solid solution was evaluated in study four. The formation of (Zr,W)C initially increased k, but further ZrC additions resulted in decreased thermal conductivities.
In the end, this research provides both: (1) usable information for the design of future ultra-high temperature ceramic systems; and (2) fundamental research that lays the groundwork for future studies aimed at understanding thermal transport in diboride based materials"--Abstract, page iv.
Smith, Jeffrey D.
Waddill, George Daniel
Materials Science and Engineering
Ph. D. in Ceramic Engineering
National Science Foundation (U.S.)
Missouri University of Science and Technology
Journal article titles appearing in thesis/dissertation
- Effect of carbon and oxygen on the densification and microstructure of hot pressed zirconium diboride
- Effect of carbon on the thermal and electrical transport properties of zirconium diboride
- High temperature electrical testing of zirconium diboride
- Thermal conductivity modifications to (Zr,W)B2 by ZrC additions
xv, 238 pages
© 2014 Gregory John Kenneth Harrington, All rights reserved.
Dissertation - Open Access
Library of Congress Subject Headings
Ceramic materials -- Thermal conductivity
Materials at high temperatures
Electronic OCLC #
Harrington, Gregory John Kenneth, "Effect of solid solutions and second phases on the thermal conductivity of zirconium diboride ceramics" (2014). Doctoral Dissertations. 2343.