IMPEDANCE DIAGRAMS OF 18-8 STAINLESS STEEL IN PASSIVE AND TRANSPASSIVE STATES IN Na₂SO₄ SOLUTIONS.

Electrical properties of the interface of 18-8 stainless steel electrode in the passive and transpassive states were studied by using complex impedance diagrams measured in 1 M-Na//2SO//4 with pH 2. 0 and 6. 4. The diagrams obtained in the passive region always showed distorted hemicircles which wre equivalent to the impedance loci of the electrical circuits having several parallel RC circuits connected in series. Therefore, passive films are thought to be composed of several layers whose electrical properties are different from one another. In the transpassive region, the diagrams measured exhibited an inductive loop at extremely low frequencies in addition to a capacitative hemicircle which appeared at high frequencies. The appearance of an inductive loop means that the transpassive dissolution process contains a relaxation process with a large time constant.