Uranium Metal Surface Of A Full Range Of Ions Injected Into The Nitride Modification

In this paper, Plasma Immersion Ion Implantation (PIII) is used to increase the corrosion resistance of uranium. The structure of modified layer is analysed by AES, XPS, XRD, SEM. The mechanism of nitride layer formation is explained in theory. The corrosion resistance of modified layer is tested by corrosion experiment.AES depth profile shows modified layer consists of uranium, nitride and oxide. The concentration of oxide is high. Distribution of nitrogen concentration has two peaks. The dose of nitrogen is increased while increases the parameters of voltage, frequency, width of pulse, implantation time. Only width of pulse can affect the depth of nitriding. In XPS data, oxygen and nitrogen exist in compound. Chemical state of uranium is complex. In the position where oxygen concentration is high, uranium exists as UO₂, while nitrogen concentration is high, uranium exists as U₂N₃ and metal. The interface between modified layer and metal is gradient. XRD data shows modified layer is mixture of UO₂ and U₂N₃. There is no hint of uranium metal in XRD data.The dose of nitrogen and temperature of sample are calculated in theory. The dose is 10¹⁷～10¹⁸ cm^-2, the temperature is about 400℃. The factors of oxide are analysed. Uranium surface is easy to adsorb oxygen. Between the pulse of implantation, much oxygen adsorbs on uranium. Temperature and ion bombardment make oxygen diffuse to bulk. Therefore the longer implantation, the more oxygen. Formation of two nitrogen peaks is explained by diffusion theory. The first peak is formed by implantation, and the second is by diffusion. Ion bombardment makes nitrogen near surface leave crystal lattice. After some distance of diffusion, nitrogen is trapped by crystal lattice again. Without ion bombardment, diffusion is difficult. So diffusion only occurs during implantation pulse.The corrosion resistance of modified layer is tested by corrosion experiment. In atmosphere, there is no change through SEM observation. After humid-hot corrosion, a little dot corrosion occurs. AES data shows oxygen concentration increases slightly. Oxygen and nitrogen have trend of diffusion to bulk. XPS is used to detect adsorption on sample surface. The oxygen of adsorption is much less on nitriding surface. Electrochemistry is used to test corrosion resistance of modified layer in Cl^- solution, result shows nitride layer is much better than uranium metal. Samples with different nitrogen concentration have no much difference during electrochemistry experiment.Nitriding increases the corrosion resistance of uranium, the modified layer and metal combine tightness, which would have long time corrosion resistance. Though the modified layer contains oxide, with improvement, it would be used in practice.