Development of an environmentally friendly protective coating for the depleted uranium-0.75 wt.% titanium alloy: Part I. Surface morphology and electrochemistry

The surface of the depleted uranium (DU)-0.75 wt.% titanium alloy has been studied using scanning electron microscopy, energy dispersive spectroscopy and optical microscopy. The samples were examined after mechanical polishing and again after nitric acid cleaning. The acicular martensitic microstructure is revealed after chemical etching. Several of the impurities have been identified and their prevalence has been found to change depending on the surface treatments. The impurities have also been found to vary from sample to sample and within the same sample. The electrochemistry and corrosion characteristics of the alloy were studied using open circuit potential measurements and potentiodynamic polarization techniques. This study has been directed towards developing environmentally friendly protective coatings for this alloy. In this paper, we discuss our efforts in finding suitable chemical species to act as inhibitors and activators during coating formation. The effect of various oxyanions, MoO₄^2-, PO₄^3-, VO ₄^3-, MnO4^-, SiO₄^4- and WO₄^2-, on the electrochemical behavior of the depleted uranium alloy in quiescent nitric acid has been explored including their ability to inhibit corrosion. Results indicate that chemical or electrochemical activation of the DU alloy in 0.1 M HNO₃ + 0.025 M MoO ₄^2- can lead to the formation of a rudimentary coating. The effect of several fluorine compounds was also examined and their electrochemical response indicates that several of them may have a potential use as a surface activator.