Crevice corrosion is one of the forms of occluded cell corrosion (OCC) discussed by B. F. Brown.1 Such cells have been reported widely in the literature. Particular attention is invited to review articles by France2 and by Rosenfeld & Marshakov.3 It is widely believed that crevice corrosion cells may be categorized as concentration cells of various kinds including metal-ion cells, differential aeration cells, active-passive cells, and other concentration cells. The final category (other concentration cells) includes hydrogen ion, neutral salt and inhibitor cells. That there can be dramatic differences between the chemical composition of the bulk electrolyte and the electrolyte within active crevices is beyond dispute. Numerous authors have reported such differences in explaining the mechanisms involved. It is not the purpose of this paper to review the past literature, but rather to report briefly on two sets of experiments (one with copper base alloys and one with binary Fe-Cr alloys) which relate crevice corrosion behavior of these alloys with their experimental potential-pH diagrams in saline environments. In the first set of experiments several chromium modified, cupronickel alloys were investigated4 with the result that a so-called "crevice protection potential" was determined below which crevice corrosion did not continue. In the second set of experiments binary iron-chromium alloys5 were employed to test thermodynamic predictions of the limiting pH, and the pH-determining species which occurred in crevices.
