DU Study The Corrosion Behavior And Mechanism And Even U-2Nb Alloy Electricity

Depleted uranium(DU) and uranium alloys have many civil applications in fields of nuclear reactor, nuclear power station or shielding for radioactive waste, due to its excellent nuclear properties, high-density and low neutron section. In most actual applications, physical touch or electrically contact with dissimilar metals is required to meet the mechanical joint demands, which is very prone to occurring galvanic corrosion. Therefore, it is vitally important and valuable to study the galvanic corrosion behaviors of DU or uranium alloys in corrosive mediums.In this paper, the galvanic corrosion behaviors of DU/2A12, DU/40Cr, DU/45, U-2Nb/45couples in3.5%NaCl solution and atmosphere with relative humidity of90%were studied combined with experimental and numerical simulation methods. Electrchemical parameters were obtained via electrochemical tests of open circuit potential (OCP), linear polarization resistance (Rp), potentiodynamics polarization (PD), and the galvanic potentials and current densities were monitored in3.5%NaCl solution. Scanning Kelvin Probe (SKP) technology was ultilized to study the process of galvanic corrosion in atmosphere with humidity of RH90%. Scanning electron microscope (SEM) and energy-dispersive spectroscopy (EDS) were applied to analyze morphologies and components of the corrosion products, respectively. A numerical simulation method with multi-physical fields coupling was used to simulate the galvanic corrosin behaviors of DU/40Cr steel in3.5%NaCl solution. The galvanic potential, potential in solution, electrode reaction current density, shape and mass change of DU sample, diffusion and migration of U4+and change of the temperature were calculated.The main conclusions are presented as follows:The potential order for the metals mentioned in this research is DU,2A12,45,40Cr, U-2Nb with the potential values increase and the electrochemical activities decrease from left to right.The DU/45and DU/40Cr couples show a simlar galvanic corrosion behavior in3.5%NaCl solution as some facts of following. DU acts as anode and the galvanic corrosion rate is2-3times than that of its self-corrosion, while both steel40Cr and45steel act as cathodes with an depressed corrosion process; both couples almost have the same galvanic potential value of-780mV, while a little difference of their galvanic corrosion rate of17.5μA·cm-2and12.5μA·cm-2for DU/40Cr and DU/45couple, respectively; both couples have the same galvanic corrosion dynamic process of which the rate-determing step (RDP) changes from oxygen to hydrogen evolution with the reaction progress.There shows a two-stage electrochemical process for DU/2A12couple with the galvanic potential in the range from-780mV to-805mV in3.5%NaCl solution. When the corrosion time less than24hours, there exists a big gap of potential between DU (acting as anode) and2A12(as cathode) which leads to a larger galvanic current density of approximately6μA·cm-2and the DU corrodes accelerately. The galvanic corrosion current density decreases to approximately5.5μA·cm-2, which is almost the same magnitude of its self-corrosion rate, due to a small potential gap existing between the two metals with the process proceeds.The45steel acts as anode when electro-coupled with U-2Nb and occurring galvanic corrosion in3.5%NaCl solution with the galvanic potential in the range from-650mV to-690mV and the galvanic corrosion current density of approximately13.6μA·cm-2. The galvanic corrosion process for the U-2Nb/45couple is relatively complex, which proceeds with three rate-dterming steps of electrochemical activity of oxygen evolution at first, then concentration of oxygen, and the hydrogen evolution at last.Chloride ion has obvious effects on the individual and the galvanic corrosion of specimens in NaCl solution. With the concentration of chloride ion increases, the galvanic potential of DU/40Cr decreases, and the galvanic corrosion current density increases first, then decreases.There exists the following sort order according to the value of galvanic corrosion current densities for the couples in atmosphere with humidity of RH90%:U-2Nb/45> DU/2A12> U-2Nb/40Cr> U-2Nb/2A12(the galvanic corrosion current densities decrease from left to right). The galvanic corrosion current density decreases with a magnitude of four to five times smaller for each couple in this condition compared to in3.5%NaCl solution.The galvanic potential and the current density calculated with multi-physical fields coupling method are according well with the experimental results for DU/40Cr steel couple in3.5%NaCl solution when the ratio of cathode/anode equals to one, which implies that the numerical simulation method and the mathematical models are suitabe for simulating the galvanic corrosion process in3.5%NaCl solution.