Effect of solid solutions and second phases on the thermal conductivity of zirconium diboride ceramics

<p>"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.</p> <p>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.</p> <p>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.</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

• Harrington, Gregory John Kenneth

• Electrical conductivity
• Lorenz number
• Thermal conductivity
• Ultra-high temperature ceramics
• ZrB2
• Ceramic Materials

Repository record dc:identifier

https://scholarsmine.mst.edu/doctoral_dissertations/2343

OAI identifier oai:identifier

oai:scholarsmine.mst.edu:doctoral_dissertations-3345