ELECTROCHEMICAL-BEHAVIOR 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 pit ting corrosion of Uranus 65 stainless steel was studied in phosphate a lkaline buffer (pH = 11.5) with and without chloride ions by using pot ential step, potentiodynamic techniques and scanning electron microsco py. Results are explained through changes in the structure and composi tion of the passive layer during anodization. Two different Cr(III) sp ecies can be voltammetrically detected at long anodization times, name ly an outer weakly bound Cr(III) species which is electrooxidized to s oluble cremate and an inner Cr(III) species which is electrooxidized t o Cr(IV) but retained in the film at potentials near the transpassive region. The transpassive dissolution has been investigated using cycli c voltammetry; a transpassive anodic peak preceding oxygen evolution h as been, detected together with the corresponding reduction peak, both being attributed to Fe(VI) species.