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Inhibitors having relatively strong oxidizing anions, such as sodium chromate and nitrite, passivate iron both in the presence of air and in deaerated solutions. Much weaker oxidizing agents such as sodium tungstate and molybdate behave similarly to chromate and nitrite in the presence of air but do not prevent corrosion in deaerated solutions despite the fact that potential/time and polarization curves indicate that slow film formation is occurring. Tungstate ions, however, are effective oxidizing agents toward iron when discharged anodically at high current density.Solutions of sodium acetate, benzoate, carbonate, hydroxide, orthophosphate, and silicate, which do not contain oxidizing anions, passivate iron only when they contain dissolved air. When these solutions are deaerated they attack iron very slowly, potential/time and polarization curves indicating that this attack is mainly under cathodic control.It is postulated that oxygen dissolved in solution is mainly responsible for passivity by virtue of its heterogeneous reaction with surface iron atoms to form a thin film of γ‐Fe2O3 , approximately 200 Å thick, in a manner similar to that by which oxide films are formed in air. This film, if kept in constant repair, prevents iron ions from the metal passing into solution. It is considered that, in inhibitors containing oxidizing anions, the passivity film is formed mainly by dissolved oxygen, whereas in other inhibitors, which do not contain oxidizing anions, the oxide is formed entirely by dissolved oxygen.

The distribution of a-c resistance throughout the thickness of oxide film on aluminum specimens, conditioned by pre-exposure to 1.0N solutions of sodium chloride and sulfate, has been determined by an electrical method. This method involves measurement of series capacitance and dielectric loss of the oxide covered aluminum as the surface films thin slowly in a slightly alkaline, passivating, sodium chromate solution. Results show that chloride ions become included at certain selected locations in the oxide film, create additional current carriers, and lower the ionic resistance of the film. Sulfate ions do not appear to become included in aluminum oxide films under these conditions and do not lower the film resistance. Aluminum oxide films containing chloride ions dissolve more rapidly in the chromate solution than similar untreated films or films that have been treated in sodium sulfate solution. These observations are held to throw new light on the well defined tendency of oxide covered aluminum to pit severely in nearly neutral sodium chloriae solutions. ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 131.215.225.9 Downloaded on 2015-05-25 to IP Vol. 112, No. 1 EFFECTS OF CHLORIDE IONS ON ALUMINUM ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 131.215.225.9 Downloaded on 2015-05-25 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 131.215.225.9 Downloaded on 2015-05-25 to IP

Potentiostatic experiments in 0.5N NaCl at -0.25 VsHE show that the kinetics of dealloying of copper base binary alloys fall in the order Cu-A1 > Cu-Mn > Cu-Zn > Cu-Ni For the solutes A1 and Zn, the kinetics of dealloying may be expressed by the relationship Log Se = KC~ where Se is the excess solute dissolved and Cs is the atom percent solute. K is related qualitatively to the reversible potential of the solute element. It is shown that dealloying cannot propagate into the alloys by diffusion of solute from the bulk to the surface. Instead, dealloying is maintained by solution intrusion under conditions where continuous solute paths exist in the alloy and where solute removal results in atomic rearrangement of the depleted alloy.Extensive studies have been conducted on the dealloying of copper base alloys and particularly Cu-Zn alloys. An earlier significant issue was whether dealloying involved selective removal of Zn atoms from the lattice (1-5) or whether zinc and copper dissolved proportionately from the alloy with the copper subquently being redeposited on the alloy surface (6-1~.). Except for a few special oases, this does not now appear to be a major issue. Stillwell and Turnipseed (1) succeeded in dealloying e brass in dilute HCI first to -y, then to ~, and finally to ~ brass. Pickering (5) also succeeded in dealloying ~ and 7 brass to more copperrich intermetallic componds in deaerated sodium sulfate solution. In these eases, there was no significant doubt that the mechanism of dealloying involved selective removal of Zn atoms from the lattices of the intermetallic phases. More recently, one of the authors (11) has shown that Cu-lVin alloys can be dealloyed in sodium chloride solution without a change in grain size or shape, thereby extending proof of selective removal of solute atoms to the solid solution region.A second and more fundamental mechanistic issue involves the means by which deal!oying is maintained over more than a few atom layers. Pickering and Wagner (12), in a study of the selective dissolution of copper from Au-Cu alloys and zinc from Cu-Zn alloys, proposed that dealloying was supported by solid-state diffusion. Because the diffusion rate of solute at room temperature is much too low to maintain the dealloying kinetics, they suggested that the selective electrochemical dissolution of more electronegative solute atoms from the alloy surface resulted in vacancy injection into the alloy. Diffusion of solute atoms to the surface was believed to be greatly accelerated by rapid divacancy diffusion, thereby permitting propagation of the dealloying process. This concept has been embraced by other investigators (13). In contrast, one of the authors (11) pointed out that the kinetics of dealloying of three copper solid solutions followed the order of Cu-NIn > Cu-Zn > Cu-Ni but that the diffusion coefficients did not fall in the same qualitative order. A mechanism involving electrochemical removal of more electronegative solute atoms from the surface, followed by rapid collapse of residual Cu ato...