Electrochemical aspects of some alloys behaviour in alkaline media with and without sodium chloride

Abstract

The oxidation mechanism of five different alloys (Orion 26-1, Uranus 65, Uranus 50,472BC, Uranus S1) was studied in phosphate alkaline buffer (pH= 11.5) by using potentiodynamic technique. The results are explained by the changes of the structure and composition of the passive layer during anodization. Two different Cr (III) species can be voltammetrically detected, at long anodization times: an outer weakly bound Cr (III) specie which is electro-oxidized to soluble chromate and an inner Cr (III) specie which is electro-oxidized to Cr NO but is retained in the film at potentials near the transpassive region. The transpassive anodic peak preceding oxygen evolution has been detected together with the corresponding reduction peak, both being attributed to Fe (VI) species.