Study On The Process And Mechanism Of Preparing Cu-Li Master Alloy By Molten Salt Electrolysis

Cu-Li based alloys have been widely used in the fields of superconducting materials,non-ferrous alloy degasser and nuclear fusion reactor materials etc.The preparation process of Cu-Li alloy was mainly based on mixing method,however,it had a mount of shortcomings such as discontinuous production,large vacuum and uneven alloy composition and so on.In recent years,foreign scholars had prepared the Cu-Li alloy by cathode alloying method in chloride system at low temperature conditions.However,the product only exists in the surface of cathode copper which was difficult to collect.So the LiCl-LiF-BaF₂ electrolyte and copper bar as the cathode were used to prepare Cu-Li intermediate alloy at 900-1000°C by molten salt electrolysis method,the product was liquid alloy which can be collected effectively.The best electrolyte composition was determined through the study of the effect of LiCl on the physical and chemical properties of LiF-BaF₂ molten salt system.The results showed that the viscosity and the surface tension of the melts decreased 52%and 41% respectively,the density dropped about 6%,the electrical conductivity increased significantly 26% after the addition of 3wt%LiCl at 920?.Secondly,the effect of temperature change on the physical and chemical properties of LiC-LiF-BaF₂ molten salt system was studied.The research indicated that with the increase of temperature,the electrical conductivity increased greatly,and the viscosity,density and surface tension decreased.The electrochemical reduction process of Li⁺ on the W electrode was researched in LiCl-LiF-BaF₂ molten salt system by cyclic voltammetry,chronoamperometry and chronopotentiometry methods at 930°C.It was concluded that the reduction process of Li⁺ on W electrode was occurred in a single step with the exchange of one electron and was controlled by diffusion step.The diffusion coefficient under different temperature was measured through chronopotentiograms and chronoamperograms.The diffusion activation energy of Li⁺ was 26.9±0.7KJ/mol calculated by Arrhenius equation.In addition,the electrochemical reduction process of Li⁺ on Cu electrodewas studied.Through the contrast analysis,it can be found that the deposition potential of Li⁺ on Cu electrode shifted negatively compared with that on W electrode,and peak current values increased.The reduction process of Li⁺ on Cu electrode was also controlled by diffusion step and the diffusion coefficient was 2.945×10-5cm2/s through the analysis of chronopotentiogram.The Cu-Li master alloy was prepared in LiCl-LiF-BaF₂ melts by molten salt electrolysis method using pure Cu cathode and graphite anode.The effects of different temperature and cathode current density on the cell voltage and current efficiency were analyzed.the optimum technological parameters were as follows: current density was 1.2A/cm2,electrolysis temperature was 920°C and the duration time was100 min.The theoretical decomposition voltage of lithium chloride was-2.48 V calculated by polarization curve estimation method.The alloy product was analyzed by X-ray diffraction patterns and scanning electron microscopy,it can be found that the Cu-Li intermediate alloy existed in the form of columnar crystal and equiaxed grains,the metal Li was dispersed in the alloy in the form of solid solution.