Influence Of Uranium And Uranium-titanium Alloy Corrosion Behavior Of Corrosion Inhibitors

Corrosion of uranium and uranium alloys have drawn much attention due to their important nuclear properties. To enhance the corrosion resistance effectively is a good way to keep long-term stability of uranium and its alloys. Coating on uranium and its alloys surfaces to protect the subsrate is widely used. However, many problems, such as abrasion, adhesion, are not resolved yet. Although the anti-corrosion property of uranium alloys is better than metallic uranium, serious corrosion could happen in high humidity environment, especially where containing chloride ion (C1). Corrosion inhibitors are widely used for metallic materials protection because of low cost, availability and good efficiency. The effection of anode passive inhibitors on corrosion behavior of delpleted uranium (DU) and uranium and titanium alloy (U-Ti) were evaluated by electrochemical methods and weight-loss measurement with surface analysis technologies in this paper. Such research could bring benefits to the development of inhibitors and their application in anti-corrosion engineering of nuclear materials.Inhibition effect of sodium nitrite (NaNO2), sodium molydate (Na2MoO4), sodium chromate (Na2CrO4) and multi-function with other inhibitors for DU and U-Ti alloy were investigated in200mg/L NaCl solution with linear polarization, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The results showed that corrosion rate of DU was accelerated by high concentration NaNO2solution as the passive film on DU surface broke although NaNO2has good performance in resisting pitting corrosion on uranium surface. The inhibition efficiency was improved obviously when NaNO2was combined with triethanolamine (TEA) and the suitable prescription was1g/L NaNO2+10ml/L TEA according to the experimental data. The induction time of pitting corrosion on DU surface grew up with the increment of Na2MoO4concentration, while the corrosion developed faster when Na2MoO4concentration was too low. Na2MoO4combined with NasSiO3and TEA resulted in passivation potential increasing and passive current density decreasing, from which the suitable prescription was induced to be1g/L Na2MoO4+0.2g/LNa2SiO3+10ml/L TEA. The multi-function could be found when Na2Cr04was combined with Na2MoO4which could reduce the consumption of Na2CrO4. The efficiency for U-Ti in the test solution was about99.8%by using the prescription100mg/L Na2CrO4+200mg/L Na2MoO4.The weight-loss testing results showed that temperature affected the inhibition efficiency of NaNO2, Na2MoO4and combinations for DU in the test tap water. NaNO2showed the best inhibition efficiency for DU at85℃. The inhibition efficiency of Na2MoO4was higher than that of NaNO2when the test solution temperature was lower than85℃whereas Na2MoO4promoted U-Ti electrochemical corrosion instead of inhibiting at85℃. The combination inhibitor (100mg/L Na2CrO4+200mg/L Na2MoO4) presented great inhibition effect on U-Ti in200mg/L NaCl solution with the inhibition efficiency to be more than94%even at85℃and hardly influenced by test solution temperature.The results of scanning electron microscope (SEM) showed that NaNO2and Na2MoO4could enhance compactness of the passive film developed on DU and MoO42-tended to be adsorbed in the active field of uranium surface. Laman spectroscopy showed that the main oxidation for uranium and its alloys was UO2in the test solution with and without inhibitors. Two styles of oxidations were found to form on uranium and its alloys surfaces with the help of X-ray photoelectron spectroscopy (XPS). The most outer layer was super stoichiometric UO2+X whose thickness was less than3nm while the inner layer was stoichiometric UO2. According to the surface analysis results, the composition and structure of the passive films changed obviously when adding the inhibitors into the test blank solutions. Cr2O3、CrO3、 CrOOH. could be found in the most outer layer of U-Ti alloy from the simulation of Cr2p with Lorentzian-Gaussian function. The passive film compactness was enhanced by the chrome compounds which could effectively prevent pitting corrosion of Cl-. The combination inhibitors, Na2CrO4+Na2MoO4, presented brilliant inhibition efficiency and could be used to deal with surface passivation and as additive in machining cooling water for U-Ti alloy.