Uranium Metal Surface Nitriding Layer Antioxidant Mechanism Of Xps/aes

As a surface modification technique developed for a long time, Nitriding treatment on Uranium can form a nitride layer with good resistence against air corrosion, of which the mechanism was unknown. In order to reveal it, in-situ Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) were used to study the oxidation behavior of sesquinitride layer (U2N3+X) at room temprature, X-ray diffraction (XRD) was also used to study the heating oxidation behavior.Two kinds of nitride layer named1#and2#were formed by DC glow plasma nitriding technique, with the main component of U2N3+X. whose N:U were calculated to be1.70and1.66by AES.In-situ XPS and AES peak analysis showed that the main component of oxide layer formed was not UO2, but might be UNxOy. During the depth profile the AES peak of oxide layer shifted to lower kinetic energy and then to higher kinetic energy, like what happened in uranium oxide layer, due to the deviation fo fermi level between oxide layer and spectroscopy caused by conductivity change. It also showed that enrichment of nitrogen atoms happened in the oxide layer, indicating the substitution of nitrogen atoms by oxygen atoms. XPS observed that within5nm depths of the outermost film N1s shift to395.8eV, suggesting that the nitrogen atoms been replaced by oxygen atoms might stay in the oxide film in the form of chemical adsorption, which could also diffuse into nitride layer.XPS differential peak analysis and fitting analysis of U4f7/2peak showed that two kinds of UNxOy with different oxidation state might exist during the oxidation of the nitride:the one with lower oxitaion state could be formed by the diffusion of O to the nitride layer,with the higher one formed by the replacement of N by O atoms.Compare the oxidation behavior of1#and2#at room temprature., it showed that2#had faster reaction rate than1#corresponding to different nitrogen vacancies of themselves. Exposure to oxygen they showed nearly the same U4f peak and AES peak. Depth profile results indicated that both of the oxide layer structure of the different nitride layer are like the same.XRD experiments showed that peaks remain nerely the same when heating below300℃in the glove box(mainly He);(440) peaks of U2N3+X shifted to lower angle when heating5min at300℃; apparent oxidation of the nitride layer happen at350℃; After heating65minutes at350℃there were no peaks of other uranium oxides Nvith hiher oxidation state. It implied that UNxOx can block the formation of uranium oxides with hiolier oxidation state...