Intrinsic Properties of Zirconium Carbide Ceramics

非技术描述：本项目主要研究碳化锆陶瓷的固有机械、热学和电学性能。碳化锆是在极端环境中使用的候选材料，例如与高超声速飞行、核裂变、聚光太阳能和高速加工相关的环境。这些应用涉及极端温度、热流、辐射水平或其他超出当今可用材料能力的条件。其他研究小组之前的研究报告称，由于碳化学计量比(例如最终陶瓷的C：ZR比)和杂质的存在等外部影响，名义上相同的碳化锆陶瓷的行为似乎相互矛盾。因此，机械、热和电性能正在以系统和受控的方式进行研究。该项目使用了密苏里科技大学独特的实验设施，其中包括生产高纯度致密陶瓷的能力，以及从室温到至少2000°C的表征性能。这些研究需要提供数据，然后可以用来设计用于极端环境的碳化锆陶瓷，并实现性能和效率的革命性改进。该项目正在对两名研究生进行极端环境下材料的加工、致密化、表征和分析方面的培训，同时也为他们在航空航天和发电行业的职业生涯做准备。研究生正在指导本科生，这些本科生被分配了研究任务，并协助开展外展活动。该项目团队还向农村高中的教师和学生伸出援手，这些教师和学生无法获得课堂项目所需的研究设施。高中生小组被邀请使用校园实验室，其目的是在每个夏天从这些小组中雇佣至少一名高中生来参与该项目。技术细节：该项目正在促进对碳化锆陶瓷的基本性质的基础知识，这些碳化锆陶瓷的含钼量低(0.01至0.4at%)，已知的氧和氮杂质水平尽可能低。主要的四个重点领域是：1)高纯碳化锆的反应合成；2)碳化锆的本征性质；3)超高温微结构-性能关系；以及4)碳化学计量比、Hf含量和其他杂质对热传输的影响。一个有重点的实验研究得到了基于物理的模型的补充，以将性质测量与基本的电子结构、成键和输运性质联系起来。通过揭示内在致密化机制、超高温下的结构-性能关系以及碳化学计量比、氧含量和其他杂质水平对性能的影响，人们对碳化锆陶瓷的认识正在转变。从事该项目的研究生和本科生正在学习为极端环境设计表征方法和性能测试，这些方法和性能测试迄今尚未通过实验方法进行探索，为他们未来在航空航天、核能或替代能源等领域的职业生涯提供独特的技能。

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.