| Abstract: | To investigate the mechanism and influence of oxide and niobium metal on the electrodeposition of niobium, the electrochemical reaction mechanisms of niobium ions in LiF-NaF-KF eutectic (FLINAK) melt at 973 K was studied by chronopotentiometry, chronoamperometry and cyclic voltammetry. The electrochemical reduction process of Nb(V) (K2NbF7) in FLINAK melt relates to the complex anions. A two-step electrochemical reduction with disproportionate and catalytic reactions is proposed. The metallic niobium in K2NbF7-FLINAK melt can reduce the catalytic reaction. The influence of oxide (Na2O) on the electrochemical processes of Nb(V) in K2NbF7-FLINAK-O2- melts without and with niobium metal present was also studied. When oxide present in K2NbF7-FLINAK melt, a much stable oxyfluorocomplex ion is formed. Cyclic voltammetry showed that the reduction potential of oxyfluoro-complex ion is more negative than that of fluorocomplex ion (NbF2-6). The electrochemical stability of is higher than those of and . An optimum composition for a coherent niobium metal coating on low-carbon steel is found to be 2.7%K2NbF7-0.5～2.0%Na2O-FLINAK in molar fraction. The cathodic current density is about 90 mA/cm2. |
