Electrochemical behaviors of Mg2+ and B3+ deposition in fluoride molten salts

By using cyclic and linear sweep voltammetry, the electrochemical deposition behaviors of Mg2+ and B3+ in fluorides molten salts of KF-MgF2 and KF-KBF4 at 880 °C were investigated, respectively. The results show that the electrochemical reduction of Mg2+ is a one-step reaction as Mg2++2e−→Mg in KF-1%MgF2 molten salt, and the electrochemical reduction of B3+ is also a one-step reaction as B3++3e−→B in KF-KBF4 (1%, 2% KBF4) molten salts. Both the cathodic reduction reactions of Mg2+ and B3+ are controlled by diffusion process. The diffusion coefficients of Mg2+ in KF-MgF2 molten salts and B3+ in KF-KBF4 molten salts are 6.8×10−7 cm2/s and 7.85×10−7 cm2/s, respectively. Moreover, the electrochemical synthesis of MgB2 by co-deposition of Mg and B was carried out in the KF-MgF2-KBF4 (molar ratio of 6:1:2) molten salt at 750 °C. The X-ray diffraction analysis indicates that MgB2 can be deposited on graphite cathode in the KF-MgF2-KBF4 molten salt at 750 °C.