Corrosion of pure iron in slightly acidified sodium sulfate solutions (mainly pH 4.5) at room temperature (10-15°C) was studied with a rotating disk electrode method. Visual observations of the corroded iron surfaces showed that belts of solid films of yellowish brown color (rust) formed along vortex streamlines. Microscopic observations of the surfaces revealed that the iron disk initially corroded locally with the formation of pits of 10-30 microns in diameter followed by the ring formation of the precipitates around the pits. The amount of iron left in the precipitated film and the total amount of iron corroded, both measured colorimetrically, increased parabolically with time of immersion. The amount of iron in the film increased in proportion to the total amount of corrosion “independently of the speed of rotation.” The fraction of area of iron surface still uncovered with the precipitated film decreased with time during the first one hour of immersion and reached a steady value after three hours or later. The steady value was small at high speed of rotation. At both initial and final stage of corrosion the total corrosion rate of iron evaluated for unit surface area still uncovered with the rust film was about 0.70-0.83 times the corrosion rate of iron in pH 3.0 solutions. The experimental results suggest that the corrosion of iron in the sodium sulfate solution of pH 4.5 is controlled by the diffusion of oxygen from the bulk of the solution to the surface of iron and the precipitated film on iron impedes oxygen diffusion.

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From the authors' studies on organic corrosion inhibitors, they concluded that best inhibitors had two types of adsorption mechanism. They could be adsorbed on metal surface by protonation as well as by electron-donation, as follows:
From this point of view, water is a typical compound which can be adsorbed on metal surface by the two ways. Metal, exposed to the air, should be surely anchored with water, as described below:
More detailed study should be needed about the water, but a few facts were made clear. The water can protect metal at lower temperature than its critical temperature of adsorption. And the water is displaced by electron-donating inhibitors when metal surface (M) contacts with inhibitors in corrosive media. This displacement can be shown as the following equations.
Inhibitors pull off the water from the metal and electron-accepting sites will come out on the metal. When amounts of inhibitors added are too small to cover metal surface, electron-accepting sites are left intact (II stage of the equations). The active sites will be produced chemically on metal as done physically, for example, by thermal vibration. In this report electron-accepting sites on metal, made by desorption of the water, were taken up. Limited amounts of RN(CH₃)₂ could promote Ni-catalysed hydrogenation reaction, as they could pull off the adsorbed water from the Ni surface to create electron-accepting sites on it where π electrons of olefinic linkage were attracted. With the help of limited amounts of RN(CH₃)₂ aluminum reacted with several alkyl halides whose electron-donating abilities were stronger than inhibitors. Iron also could react in the same manner. In every case corrosion on metal surface was concentrated at pointed parts and the surface otherwise was left as it was. These reactions in non-aqueous media started after some induction periods which were mainly decided by metal itself and the adsorbed water on it.

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Nielsen's technique of platinum decoration for anodic sites was applied to detect the active sites and micro-pits produced by chloride attack in the passive film of Type 304 stainless steel. The number of active sites and micro-pits was found to depend on the potential of the film formation. Active sites on the anodically activated surface are evenly distributed, their number being 1.5×10¹⁰cm^-2. On the surface covered with the passive film, the heterogeneous distribution is observed of active sites and also micro-pits. In the passivation potential region below 0.50 volt (vs. SCE), ca. 2.5×10⁹cm^-2 of sites including active sites and micro-pits is counted, while at 0.60 volt the number of sites decreases to 4.7×10⁸cm^-2 and again increases with potential, reaching to 1.2×10⁹cm^-2 at 0.90 volt. A correlation between the site density and the induction time for the growth to macro-pits is discussed.

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Cu-Ni alloys were firstly anodized, and then the alloy surfaces were examined by means of Auger electron spectroscopy and the metallic ions dissolved into the bulk solution were analyzed through atomic absorption analysis. Some corrosion behaviors of Cu-Ni alloys were clarified in the potential ranges of anodic corrosion and passivation.

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