PHOSPHORIC-ACID PASSIVATED NIOBIUM AND TANTALUM EIS-COMPARATIVE STUDY

Many investigations concerning oxide him growth on niobium and tantalu m in aqueous solutions have been conducted. Recent work has shown that the corrosion and passivation behavior of valve metals has no standar d 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 an d tantalum under the same conditions. Comparison of the behavior of th e two systems Nb-oxide-electrolyte and Ta-oxide-electrolyte showed tha t the passive films formed on niobium in phosphoric acid solutions do not behave as perfect dielectric like those formed on Ta under the sam e conditions. The Nb-oxide-electrolyte system cannot be represented by a simple equivalent circuit whereas the Ta-oxide-electrolyte system c an be.