Corrosion Behavior Of Surface Nitrided Depleted Uranium In Salt Spray Environment

Uranium is widely used in the key areas such as efficient energy and national security because of its unique properties of nuclear, physics and chemistry. At the same time, uranium is a kind of chemically active metal with terrible radioactivity, so the corrosion problems of which must be taken into consideration in order reduce the waste of resources as well as the environmental pollution during its application in engineering. Research on corrosion preventing of uranium has been carried out for many years, the glow plasma nitriding technology for the surface modification is a rapidly development and broad application prospects of uranium's corrosion preventing in recent years. Uranium shows good corrosion resistance in oxygen, water etc. There is insufficient research on the corrosion behavior of pre-nitrided uranium in salt spray atmosphere, this has seriously restricted the application of uranium.Based on the background above, scanning electron microscopy (SEM), Auger electron spectrometer (AES) and micro area scanning electrochemical probe system were used to make analysis, after some reasonable and in-depth discussion of the various experimental result, we carried out the following aspects of the research work:The artificial accelerated salt spray test were used to simulated marine atmosphere according to method in GB/T 10125-1997, under this condition, corrosion behavior of pre-nitriding uranium metal was studied, The morphology of the sample surface and the corrosion pits were observed, Results show that uranium metal will sag, forming defects, leading to the loss of integrity of the nitride films after surface nitriding treatment, this will easily become the weak region of the passivation protective membrane, may become first to be broken in salt spray accelerated corrosion conditions.The surface morphology and product state of uranium corrosion in salt fog environment were studied by using Auger electron spectroscopy and laser Raman spectroscopy, We found that the ultrafine surface of uranium nitride was slightly oxidized in the range of tens of nanometers under high salt spray corrosion condition, and this oxide film shows chemical inertness on the underlying material, which means no further corrosion, It shows that the complete uranium nitride passivation film has a significant effect on improving the corrosion resistance of uranium metal surface in the high concentration salt spray environment. The corrosion products of pre-nitrided uranium under the condition of salt spray atmosphere are mainly UO2, and with a small amount of U3O8.The formation conditions and failure mechanism of surface passivation films were investigated by using electrochemical workstation with the method of dynamic potential polarization and EIS, We found that 0.05 mol·L-1 is the dividing point to change mechanism of corrosion behavior of surface nitride uranium in solution containing Cl-.The electrochemical characteristic parameters of the local corrosion active region were scanned and analyzed by using the micro area scanning electrochemical workstation, by this way the electrochemical and chemical states of pitting corrosion area have been deepened from the microscopic point of view. After which, reaction mechanism of chlorine ion in the solution of nitride uranium are presented and discussed. The results show that the mechanism can explain most of the experimental phenomena, which has some certain theoretical basis and scientific references.