Preparation of Cr-Ni alloy by electrochemical codeposition in a NaCl-KCl-NaF-Cr2O3-NiO molten salt

Abstract

The feasibility of electrochemical reduction in a NaCl-KCl-NaF-Cr2O3-NiO molten salt is analysed by thermodynamic calculation. The electrochemical reaction mechanism and the electrocrystallization process of chromium and nickel in the same molten salt are investigated at 1073 K by electrochemical workstation. Cyclic voltammetry, chronopotentiometry and chronoamperometry have been used. The results show that it is thermodynamically feasible to reduce NiO and Cr2O3 to pure metal by electrochemical reduction and indicate that the electrochemical reduction from Cr(III) to Cr takes two steps: Cr3+ + e → Cr2+ and Cr2+ + 2e → Cr. Meanwhile, the electrochemical reduction from Ni(II) to Ni takes only one step: Ni2+ + 2e → Ni. All the electrochemical processes of Cr(III), Cr(II) and Ni(II) are reversible reactions, and the electrocrystallization processes of Cr and Ni are an instantaneous hemispheroid three-dimensional nucleation process. The atomic growth process, composition and morphology of the coating are investigated by SEM and EDS, and close and uniform alloy particles are deposited on the substrate. The polarization curves are determined by the potentiodynamic scanning method, and the results show that the corrosion reaction of the alloy coating is higher, and the corrosion rate is lower. It is also found that the corrosion resistance of the Cr-Ni alloy coating is stronger than that of low carbon steel.