Preparation And Corrosion Properties Of Cathodic Micro-arc Electrodeposition Of Depleted Uranium Surface Ceramic Membrane By Constant Pressure Method

Uranium has been widely applied in military, nuclear energy and other fields for its unique nuclear performance. However, uranium shows strong chemical activities so that it is unstable in atmosphere. It can easily react with water, oxygen and so on, which not only results in the deterioration of its performance, but also pollutes the environment and causes radiological hazard to operators. Thus, anticorrosion treatment to uranium is very necessary. Many methods have been reported for preparing anticorrosion coatings on the surface of uranium metal. Cathodic micro-arc deposition is a newly developed surface technology, which can easily produce anticorrosion oxide ceramic coatings on metals. There are two ways to produce ceramic coatings by cathodic micro-arc deposition technology:the constant current method and the constant voltage method. Compared to constant current method, constant voltage method has advantage of more stable in process, which will obtain oxide ceramic coatings with similarities in microstructures and properties. In this paper, the influence of some key parameters of electrolyte and power supply was studied and optimized process parameters were obtained for preparation oxide ceramic coatings of alumina, alumina-zirconia and alumina-yttria composites on the surface of depleted uranium metal. The microstructures, phase constitutions and anti-corrosion properties of the coatings were analyzed. Some results have been obtained as followed.Electrolyte concentration and voltage of power have obvious influence on the deposition process and the microstructures and properties of the coatings. Alumina coating with proper microstructures and good property of anticorrosion could be obtained under the parameters of electrolyte concentration of about 1.0 mol/L and power voltage of 320 V.For the constant voltage process of cathodic micro-arc deposition, the parameter of power voltage has a prominent influence on the thickness, the surface roughness, and the electrochemical corrosion properties of oxide ceramic coatings on the surface of uranium metal. While other parameters, such as power frequency and duty cycle, have somewhat less influence on the microstructures and properties of the coatings. But duty cycle has dominate influence on the amount of a phase in alumina coating.Based on the above researches, optimized parameters were acquired for preparing oxide ceramic coatings with proper microstructures and good anticorrosion property on the surface of uranium metal, including the electrolyte concentration of approximately 1.0 mol/L and the power voltage of 320 V, frequency of 1200 Hz, duty cycle of 10%. Under such conditions, alumina, alumina-zirconia and alumina-yttria coatings with the main phase of y-Al₂O₃,?-Al₂O₃ and c-ZrO2,?-Al₂O₃ and cubic Y2O3, respectively, were prepared on the surface of uranium metal. All these coatings showed good stability in both ambient atmosphere and the hydrothermal air condition of 100 ?,90% RH, and a good corrosion resistant in 50 ?g/g KCl solution, for their corrosion current density was of approximately one order lower than that of uncoated depleted uranium sample. And the composite oxide coatings showed better anticorrosion property than the sole alumina coating.