| Al-Li alloy has been widely used in aerospace and national defense as a kind of low density and high strength material. The production of aluminum lithium alloy method is mixture method. This process is long, lithium recovery rate is low and burning rate is high, which is very difficult to prepare stable component of aluminum lithium alloy. In this paper, we use liquid aluminum as cathode and Li2CO3 as raw material. In the molten salt system, the lithium ion can be reduced to metallic lithium in the liquid aluminum.A pure lithium salts system Li Cl-Li F is selected and the proportion and electrolysis temperature is determined. The molten salt density and liquidus temperature are measured.The influence of Li2CO3 under different temperature on the electrical conductivity of molten salt system is studied. The results show that temperature has a significant effect on the electrical conductivity of molten salt, with the increase of temperature, the conductivity of the system increased; The influence after adding a small amount of Li2CO3 is not very big, but a slightly smaller, with the amount of lithium carbonate increased the reduction is more obvious. The molten salt density of 39.5%LiF-1%Li2CO3-59.5%LiCl is 1.788 g·cm-3 and liquidus temperature is 470℃.The process method for preparing Al-Li alloy by molten salt electrolysis is introduced in this paper, The current efficiency,the back electromotive force and the period of lithium carbonate are studied, and then explained the reasons of the phenomenon why back electric potential changed before and after charging. In the process of electrolysis, the mechanism of the damage of the graphite anode is explained. The study shows that with the increase of current intensity, the current efficiency increases, at 3.5A,the current efficiency is 72%, and the content of lithium increases with the increase of current intensity. However, it is not very large. The back electromotive force increases with the increase of current before and after feeding Li2CO3, the average back electromotive force reduced about 0.8V. When the current density is in the range of0.05-0.21A/cm2, the polarization voltage enters at the Tafel zone; In 0.21-0.42A/cm2 range,the electrolysis process is controlled by the concentration polarization. The period of feeding 1wt%Li2CO3 is 20 minutes.The electrode process and other related electrochemical mechanism are studied by electrochemical measurement technology. Cyclic voltammetry studies show that the reduction of the metal lithium on the tungsten electrode is a reversible reaction process.The oxidation peak before the peak of chlorine gas is the result of the addition of lithium carbonate. Chronoamperometry studies show that lithium ion on tungsten electrodes in the electrochemical reduction process is controlled by the diffusion process. Before the step potential, the diffusion coefficient is 1.35 x 10-8cm2/s, while in the step of the deposition potential, the diffusion coefficient of 0.75 x 10-8 cm2/s, diffusion coefficient reduced44.4%, nucleation process is a hemisphere shaped three-dimensional instantaneous nucleation. Chronopotentiometric results show that lithium ion in tungsten electrodes in the electrochemical reduction process is controlled by the diffusion process. LiCl-Li F system and after addiing 1wt% Li2CO3 to the system, lithium ion diffusion coefficient reduced by 1.98 * 10-8 cm2/s to 0.82 * 10-8 cm2/s, the minimum reduction current density of lithium metal increased from 0.28A/cm2 to 0.59 A/cm2.Using Li2CO3 as the material not only minimize the environmental pollution but also reduce the cost. The anode product is changed to oxygen or carbon dioxide, which will reduce the corrosion degree of equipment and save the cost of chlorine recovery. |
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