| The corrosion protection of metallic uranium is of great significance for the storage and maintenance of the physical and chemical properties of metallic uranium.The corrosion protection methods of metal uranium mainly include surface alloying and surface modification.Among them,metal uranium surface nitridation modification technology has proven to be an effective means of corrosion protection.Uranium nitrides formed by surface nitriding can effectively prevent further oxidation of metal uranium.From the existing reports,we find that the corrosion protection mechanism of uranium nitride modified layer against metallic uranium is not clear.What are the intermediate products formed during the UN oxidation process?Studies have shown that the UN block itself is not resistant to corrosion.Is this assertion accurate?And why can the UN modified layer on the surface of metal uranium effectively prevent the further oxidation of metal uranium?What are the oxidation intermediates for nitrogen-rich uranium nitrides?These issues require more accurate research,both experimental and theoretical.In addition,how resistant are uranium nitrides with different nitrogen contents to oxidation?How is it related to its structure?We also find that the research on the oxidation kinetics of uranium nitride is still lacking,and the study on the kinetic behavior of uranium nitride oxidation can also help us understand the mechanism of oxidation resistance of uranium nitride.However,it is difficult to observe the oxidation behavior of uranium nitride in situ in real time due to the oxidative properties of materials.Therefore,this paper uses the application of XPS in qualitative and quantitative analysis,combined with XRD,AES and other research methods,to study the oxidation behavior of uranium nitride in a low oxygen partial pressure atmosphere,analyze the oxidation process of uranium nitride,and obtain the uranium nitride.The initial oxidation kinetics further revealed the oxidation resistance mechanism of uranium nitride.In the first experiment,we used XPS qualitative analysis to study the oxidation products and oxidation processes of metal uranium,and used XPS quantitative analysis to study the oxidation kinetics of metal uranium.The purpose of this experiment is to verify the applicability of the XPS quantitative analysis method,the thickness measurement technique,in the uranium-based compound system in combination with the results of previous studies on the oxidation behavior of metallic uranium.The thickness change behavior of the oxide layer on the surface of metal uranium was studied.The oxidation kinetics of metal uranium under different oxygen partial pressures was obtained and the effect of oxygen partial pressure on the oxidation of metal uranium was analyzed.Using the Arrhenius formula,we obtain the activation energy of the thermodynamic parameters of the oxidation of metallic uranium.The activation energy of the oxidation reaction of metallic uranium is 5.7 kcal/mol under the condition that the oxygen pressure is 5 × 10-6 Pa and the temperature is lower than 413 K.By comparing with the existing experimental results,we verified the applicability of the XPS thickness measurement technology in uranium-based compound systems.In the second experiment,we applied the above research methods to the study of the oxidation behavior of uranium nitride.The analysis results show that for UN0.68 whose phase composition is mainly UN,two products of UO2-x and U2N3 are formed in the reaction in the initial oxidation process,and the intermediate product U2N3 is oxidized to form the structure of U2N3-xOy..UO2-x continues to oxidize,its chemical composition tends to UO2,and the chemical composition of U2N3-xOy also tends to a saturation value.When the thickness of the U2N3-xOy layer is increased to a certain value,the diffusion of O in the U2N3-xOy is suppressed,and the U2N3-xOy structure prevents further oxidation.For UN1.66 whose phase composition is mainly U2N3,the initial oxidation produces the U2N3-xOy structure.After a short period of linear growth in the thickness of the oxide layer,the chemical composition of U2N3-xOy reaches saturation,and U2N3-xOy also prevents it.The oxidation of UN1.66 resulted in a maximum thickness of the oxide layer.Comparing the experimental results of the two experiments,we further found that the three materials are arranged according to the magnitude of the oxidation rate:U>UN0.68>UN1.66,that is,the oxidation product UO2-x formed by the oxidation of metal uranium cannot completely prevent the inner metal The oxidation reaction of uranium further occurs,and the oxidation product U2N3-xOy formed by the oxidation of UN1.66 can prevent the diffusion of O in the oxide layer and block the further oxidation reaction of the oxidation medium and the inner layer material. |
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