ANODIC BEHAVIOR OF ZIRCONIUM AND ITS ALLOYS IN FLUORINATED NITRIC MEDIA DISSOLUTION-PASSIVATION MODEL

Current-potential curves for zirconium in fluorinated nitric medium we re obtained using a rotating disc electrode. The curves exhibited four different domains according to the potential, and suggested a seven-s tep reaction model composed of three competing paths. Quantitatively v erified by comparing computed and experimental curves, this model acco unts for the behaviour of either zirconium or its main industrial allo y, Zircaloy 4, over potentials ranging from the corrosion potential up to the zirconia passivation potential. Moreover, the model allows the rate of elementary steps to be determined, as well as the coverage ra tio of the intermediate species considered. These results correlated w ith scanning electron microscopy observations and proved to be particu larly sensitive to slight modifications of the electrochemical system. The model can also be considered as a promising tool in the study of zirconium alloy pickling in acidic media and for optimising the result ing surface quality.