【作者】 梁威；

【导师】 张政军； 刘柯钊；

【作者基本信息】 清华大学 ， 核科学与技术， 2018， 博士

【摘要】 铀（U）作为一种重要的战略核能源材料,广泛应用于核能和国防领域。铀化学性质十分活泼,极易发生腐蚀而影响其物理化学性质及核性能,因此铀的腐蚀机理和防腐蚀研究一直受到人们的关注。由于铀具有放射性,易对人体和环境造成危害,而铈（Ce）具有与铀相近似的电子层结构,化学性质也十分相似且无放射性,适合替代U等核材料开展其防腐蚀方法及相关性能研究,从而为铀等核材料的防腐蚀研究提供借鉴和参考。本文的主要研究内容和成果如下:首先,开展了Ce氧化腐蚀相关实验研究。Ce在大气环境中极易氧化腐蚀,其氧化产物十分复杂。Ce在初始反应阶段反应速率很快,整个反应动力学曲线成抛物线型。湿度对Ce氧化腐蚀的影响很大,潮湿环境会导致Ce的加速腐蚀。其次,基于对Ce表面进行氮化改性的思路,利用双离子束溅射沉积系统通过反应溅射和氮化处理在Ce表面制备形成了CeN薄膜。研究发现CeN薄膜本身不稳定,在大气环境中容易氧化生成CeO₂,故单纯进行表面氮化并不能有效提升Ce的耐腐蚀性能。因此在氮化处理后的样品表面再进一步沉积惰性氮化钛（TiN）陶瓷层,即在Ce表面制备形成了CeN/TiN双层复合膜,研究表明这种复合膜可以有效提高Ce的抗腐蚀性能,但是长期贮存镀层容易起泡脱落而失效。第三,利用金属钛（Ti）质地较软、韧性较好、与Ce和TiN热匹配性较好等优点,在Ce表面先沉积制备Ti作为过渡层,再沉积TiN惰性层,形成Ti/TiN双层复合膜,并调控获得了不同厚度比例的Ti/TiN双层复合膜。实验研究和分析表明,在Ce和TiN之间引入Ti作为过渡层,可以增加Ce和TiN之间的相容性及结合致密性,从而提高膜层质量,同时也大幅提升了样品的抗腐蚀等性能;在膜层总厚度为400nm时,调控获得的200nmTi/200nmTiN双层复合膜抗腐蚀等性能最优。最后,为进一步探索用金属Ce模拟钚（Pu）材料,尝试采用氦离子定量注入的方法,在Ti/TiN双层复合膜及基体Ce中引入定量的氦杂质并形成辐照损伤。研究表明,经过氦离子辐照,Ti/TiN双层复合膜晶体结构没有发生明显变化,杨氏模量下降约11%,膜基结合力有所提高,抗腐蚀性能未见明显下降。更多还原

【Abstract】 Uranium（U）is an important strategic nuclear energy material widely used in national defense and nuclear energy fields.Uranium has a unique electronic structure,thus it is highly active and prone to corrode easily in atmosphere,which reduces its lifetime,working efficiency and performance.Therefore,the research of uranium corrosion mechanism and anticorrosion method is attracting people’s attention.Due to its radioactive and harmful to the human body and environment,it’s difficult to conduct experiments directly on uranium.It is more convenient and suitable to study corrosion and protection properties of cerium（Ce）,since it has similar electronic configuration with uranium but no radioactivity,which can be used logically as reference for uranium.Firstly,the experimental study of cerium oxidation corrosion has been carried out.Cerium is very easy to oxidize and corrode in atmospheric environment and generates complex oxidation products.The oxidation reaction rate at the initial stage of cerium is very fast and the whole reaction kinetics curve is parabolic.The oxidation corrosion of cerium is greatly influenced by the humidity,and could be accelerated in wet environment.Secondly,based on the idea of nitriding modification on the surface of Ce,the CeN film was prepared by reactive sputtering and nitriding on the surface of Ce using double ion beam sputtering deposition system（DIBS）.It is found that the CeN film is unstable and can be easily oxidized to CeO₂ in the atmosphere environment,indicating that surface nitriding cannot improving the corrosion resistance of the cerium.Therefore,the inert TiN ceramic layer is further deposited on the surface of the sample after nitriding and the CeN/TiN bilayer composite film has been deposited on the cerium surface.It is found that the CeN/TiN bilayer composite film can effectively improve the corrosion resistance of cerium,while this coating is easy to blister for long term storage,resulting in the failure of the coating.Thirdly,based on the advantages of titanium for good toughness and good thermal matching with cerium and titanium nitride,Ti film was deposited on the Ce surface as a transition layer,then the inert TiN film was deposited,and Ti/TiN bilayer composite film is prepared.Ti/TiN bilayer composite film with different thickness ratios can be obtained by deposition regulation.The results show that the introduction of Ti between Ce and TiN as transition layer improves the compatibility and the binding density between Ce and TiN,leading to a large improvement of the quality and corrosion resistance of the films.The 200 nmTi/200 nmTiN bilayer composite film has the best corrosion resistance when the total thickness of film is limited to 400nm.Finally,helium ion implantation is used to further explore the study of plutonium material simulated with metal cerium.The quantitative helium impurity is introduced into the Ti/TiN bilayer composite film and Ce,and the radiation damage is formed.It is shown that the crystal structure of Ti/TiN bilayer composite film is not changed by helium ion irradiation,while the young’s modulus decreases about 11%.Besides,the bonding force of the film and base is improved,however,the corrosion resistance is not significantly decreased.更多还原