| As an important nuclear material, uranium(U) is easily corroded in many environment medium for its strong chemical activity. This not only leads to worsening material capability, but also to environment pollution and more radio protection work. One of the effective means to protect uranium from corrosion is to coat it with noncorrosive materials. The coating compaction and connection with substrate which ties up with coating technics have important effects on the corrosion resistance. So far as it goes, every technics has its only strongpoint as well as its shortcoming. Here we developed a new way to deposit coatings on uranium. In our work, we dissolved metal in mercury to form amalgam (i.e. mercury alloy). And the amalgam was rolled out on the uranium as film, then the amalgam is resolved in a higher temperature, and mercury can be evaporated for its high saturated vapor pressure, metal is left to form coating. In this thesis, the mechanics and technics of amalgam coating on uranium were studied in detail, coating structure and corrosion resistance were also tested as well.The mechanism of amalgam zinc(Zn) coating on uranium was studied using the first principle calculation which based on density functional theory (DFT). The result suggests that zinc connects with uranium in metal bond; the Zn-U bond length is comparable to the Zn-U distance in U2Zn17, this probably gives an effective criterion to evaluate the capability of zinc coatings. The metallic compound U2Zn17can be found in the XRD spectra of amalgam zinc coating on uranium, which means that zinc reacts with uranium to form compound at a much lower temperature and pressure with the effect of mercury.Comparing with aurum(Au) and tin(Sn), zinc, aurum and tin were selected to prepare amalgam separately. The technics of amalgam coatings on uranium was studied in this thesis. In our experiments, compact tin coating tightly connected with substrate can be obtained at about230℃because of its lower melting point. Compact zinc coating is not easily obtained at higher temperature, because zinc will sublime for its high saturated vapor pressure, and this could be improved at higher pressure.Although aurum has high melting point and low saturated vapor pressure, Compact thicker aurum coating is also not easily obtained in one time. Because mercury can not easily through the compact aurum film forming preferred at surface. This could be improved by attenuating the amalgam rolling out on the uranium and thickening the aurum coating by more times. Experiments suggest that temperature is the key factor to the amalgam coatings’ capability. The technics of preparing metal coatings on uranium using amalgam was developed primly.Zinc coating was amalgam coated on uranium coated with uranium dioxide in air, it was proved that the uranium dioxide was dispersed in the zinc coating in this technics, and this exactly improved the coating connection with substrate.The corrosion resistance of zinc coating on uranium was tested at150℃in argon(Ar) involving40v%oxygen(O2) through thermo gravimetric analysis(TGA). It suggested that the zinc coating can effectively resist uranium from corrosion through forming compact zinc oxide film on the surface. If the zinc coating was exposed to air for a long tine, ZnCO3can be discovered on the coating surface, and this must be the reaction between zinc and water and carbon dioxide in the air. But the ZnCO3would not worsen the corrosion resistance of zinc coating.The corrosion resistance mechanism of zinc coating was studied by Raman spectra analysis. Zinc coatings which uranium had diffused to the surface of coating were exposed to different intensity laser in70RH%air, and the different Raman spectra were obtained. It was improved that zinc is more easily corroded than uranium, and this can also be seen in XRD spectra of zinc coating exposed to air for different time. All of these phenomenons suggest that zinc is corroded preferred as anode in the primary cell formed by zinc and uranium in humid air. |
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