关键词: LiF, 铝电解, 阴极电化学, 循环伏安, 铝钨金属间化合物

Abstract: Electrochemical reactions of Al³⁺ and formation mechanism of Al-W intermetallic compound on tungsten electrode were investigated by means of cyclic voltammetry and theoretical calculation analysis. Al³⁺ was reduced to Al metal in a single step and the deposition potential of sodium was more negative than aluminum in molten cryolite system. In both Na₃AlF₆-Al₂O₃ system and Na₃AlF₆-Al₂O₃-LiF system, the deposition reaction of Al³⁺ as Al-W intermetallic compounds on tungsten electrode was quasi-reversible, involving diffusion process from the sweep rate range of 50 mV·s^-1 to 150 mV·s^-1. During the forming process of Al-W intermetallic compound, Al³⁺ diffusion coefficient increased from 4.54×10^-9 cm²·s^-1 to 5.71×10^-9 cm²·s^-1, and reaction activation energy decreased from 11.14 kJ·mol^-1 to 10.47 kJ·mol^-1. Al-W intermetallic compound was insoluble in both Na₃AlF₆-Al₂O₃ system and Na₃AlF₆-Al₂O₃-LiF system. In Na₃AlF₆-Al₂O₃-LiF system, Li did not deposit out on tungsten electrode during the reduction process and oxidation current was larger than that in Na₃AlF₆-Al₂O₃ system during the formation process of Al-W intermetallic compound. In the constant current electrolysis experiment, XRD, SEM, EDS showed that Al-W intermetallic compound was insoluble in molten salt, but adhered to the surface of the working electrode. Adding LiF decreased Al-W intermetallic compound (WAl₄) quantity but increased Al₂O₃ quantity. With the formation of Al-W intermetallic compound, Li-Al intermetallic compound also formed at the same time and it was soluble in Na₃AlF₆-Al₂O₃-LiF system. It confirmed that the working electrode was more stable during the electrolysis process after adding LiF. LiF inhibited the growth of WAl₄ and increased the activity of Al^{3 +} in Na₃AlF₆-Al₂O₃-LiF system. As the cathode of aluminum electrolysis, alloying effect was obvious on tungsten electrode during the electrolysis process. In order to guarantee normal electrolysis, tungsten wire electrode should be pretreated to form a stable alloy.

Key words: LiF, aluminum electrolysis, cathodic electrochemistry, cyclic voltammetry, Al-W intermetallic compound