Intrinsic Properties of Zirconium Carbide Ceramics

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NON-TECHNICAL DESCRIPTION: This project focuses on the intrinsic mechanical, thermal, and electrical properties of zirconium carbide ceramics. Zirconium carbide is a candidate material for use in extreme environments such as those associated with hypersonic flight, nuclear fission, concentrated solar power, and high-speed machining. These applications involve extreme temperatures, heat fluxes, radiation levels, or other conditions that are beyond the capabilities of available materials today. Previous studies by other research groups have reported seemingly contradictory behavior for nominally identical zirconium carbide ceramics due to extrinsic effects such as carbon stoichiometry (e.g., the C:Zr ratio of the final ceramic) and the presence of impurities. Accordingly, the mechanical, thermal, and electrical properties are being investigated in a systematic and controlled manner. The project is using the unique experimental facilities at the Missouri University of Science and Technology, which include capabilities for producing dense ceramics with extremely high purity and characterizing properties from room temperature up to at least 2000°C. These studies are needed to provide data that can then be used to design zirconium carbide ceramics for use in extreme environments and enable revolutionary gains in performance and efficiency. This project is training two graduate students in the processing, densification, characterization, and analysis of materials for extreme environments, while also preparing them for careers in the aerospace and power-generation industries. Graduate students are mentoring undergraduates who are assigned research tasks and assist with outreach activities. The project team is also reaching out to teachers and students from rural high schools that lack access to research facilities needed for class projects. Groups of high school students are invited to use campus laboratories and the intent is to hire at least one high school student from those groups to work on the project during each summer.TECHNICAL DETAILS: The project is advancing the fundamental knowledge of the intrinsic properties of zirconium carbide ceramics with low (0.01 to 0.4 at%) hafnium contents and known oxygen and nitrogen impurity levels that are as low as possible. The four primary areas of emphasis are: 1) reactive synthesis of high purity zirconium carbide; 2) intrinsic properties of zirconium carbide; 3) ultra-high temperature microstructure- property relationships; and 4) effects of carbon stoichiometry, hafnium content, and other impurities on thermal transport. A focused experimental study is complemented by physics-based models to connect property measurements with fundamental electronic structure, bonding, and transport properties. The knowledge of zirconium carbide ceramics is being transformed by revealing intrinsic densification mechanisms, structure-property relationships at ultra-high temperatures, and the effects of carbon stoichiometry, oxygen content, and other impurity levels on properties. Graduate and undergraduate students working on this project are learning to design characterization methods and property tests for extreme environments that have heretofore not been explored through experimental methods, providing them with unique skills for future careers in fields such as aerospace, nuclear power, or alternative energy.