Investigation of electrochemical behaviour of chromium and tantalum in chloride melt containing their ions

Electrochemical behaviour of Cr and Ta in melted equimolar mixture NaCl-KCl containing Cr(2) and Ta(5) chlorides is studied. Preliminary thermodynamic calculation of the change value of isobaric-isothermal potential has shown that in the result of homogeneous and heterogeneous interaction in the melt the change of oxidation degree of chromium and tantalum ions takes place. The corrosion rate for chromium and tantalum in melted mixtures is measured. Analysis of potentiodynamic anode polarization curves gives a possibility to calculate the oxidation degree of ions transforming into the melt depending on polarizing current density. The corrosion rate value has been taken into account while calculation. It is shown that electrode polarization results in its passivation the limit current of passivation depending on Cr(2) ion concentration in the melt and corresonds to the values at which tantalum dissolution goes mainly in the form of Ta(5) ions