Study On The Preparation And Anticorrosion Properties Of Nitride Films On Cerium Surface

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.