ELECTROCHEMICAL BEHAVIOUR OF URANUS 65 AUSTENITIC STAINLESS STEEL IN ALKALINE BUFFER SOLUTIONS WITH AND WITHOUT SODIUM CHLORIDE

The influence of the composition on the oxidation mechanism in the pitting corrosion of Uranus 65 stainless steel was studied in phosphate alkaline buffer (pH = 11.5) with and without chloride ions by using potential step, potentiodynamic techniques and scanning electron microscopy. Results are explained through changes in the structure and composition of the passive layer during anodization. Two different Cr(III) species can be voltammetrically detected at long anodization times, namely an outer weakly bound Cr(III) species which is electrooxidized to soluble cremate and an inner Cr(III) species which is electrooxidized to Cr(IV) but retained in the film at potentials near the transpassive region. The transpassive dissolution has been investigated using cyclic voltammetry; a transpassive anodic peak preceding oxygen evolution has been, detected together with the corresponding reduction peak, both being attributed to Fe(VI) species.