PHOSPHORIC-ACID PASSIVATED NIOBIUM AND TANTALUM EIS-COMPARATIVE STUDY

Many investigations concerning oxide him growth on niobium and tantalum in aqueous solutions have been conducted. Recent work has shown that the corrosion and passivation behavior of valve metals has no standard case, it depends greatly on the ambient electrolyte. Electrochemical impedance spectroscopy (EIS) was used to obtain detailed information about the difference in behavior of passive films formed on niobium and tantalum under the same conditions. Comparison of the behavior of the two systems Nb-oxide-electrolyte and Ta-oxide-electrolyte showed that the passive films formed on niobium in phosphoric acid solutions do not behave as perfect dielectric like those formed on Ta under the same conditions. The Nb-oxide-electrolyte system cannot be represented by a simple equivalent circuit whereas the Ta-oxide-electrolyte system can be.