PITTING OF FE IN PH 7.4 ACETATE BUFFER

The passivation and pitting of Fe in pH 7.4 acetate buffer solution has been investigated as a function of the acetate and chloride concentrations. The efficiency of passivation was found to depend on the concentrations of both solutes, with the highest efficiency in the more concentrated solutions. Cl- did not interfere with the establishment of passivity, either in potential sweep or potential sweep or potential step experiments, but was significantly less effective in promoting efficient passivation than acetate. Cl- only has a deleterious effect on passivation after the film has formed. Potentiostatic results obtained above the pitting potential in concentrated acetate solution suggest that the onset of pitting is associated with an interaction of the Cl- with a certain stage of development of the passive film, based on the similarity of results with those obtained previously in borate buffer solution. 1 M acetate acts as a more effective inhibitor for pitting than 0.2 M borate.