Causes of Corrosion Currents

Abstract

Localized attack of metal specimens is often the result of electrochemical corrosion, not of simple chemical solution. The appearance of specimens suffering this type of attack has led laymen to attribute it to the presence of impurities in the corroding metal.However, impurities are only one possible cause for this type of attack.Other known or possible causes are: (1) grain boundaries, (2) orientation of grains,(3) differential grain size, (4) differential thermal treatment, (5) surface roughness, (6) local scratches or abrasions, (7) difference in shape, (8) differential strain, (9) differential pre-exposure to air or oxygen, IN MANY neutral solutions the corrosion of the common structural metals appears to be associated with the flow of electric currents between various parts of the metal surface at finite distances from one another. This statement is supported by much qualitative evidence, and in the case of steel ( 14) and of aluminum (7) the quantities of current flowing during corrosion account for the amount of corrosion which occurs.

Stress corrosion cracking and corrosion fatigue

“…At the time, several studies [137][138][139] estimated the electrode potentials of freshlytom metal surfaces. In particular, Mears and Brown [137] reported a potential less than -3000 mV for commercially pure AI from which the surface oxide film was removed by scratching the surface with a glass stylus in the electrolyte.…”

The Use of Hydrometallurgy in Treatment of Secondary Raw Materials and Low – Grade Ores

“…Hydrogen ion can dissolve many active metals even under reducing conditions. [17]. The E-pH diagrams developed by Pourbaix became widely known in 1949 [18].…”

Aluminum and Aluminum Alloys

“…Metallurgical structure has little effect on the pitting potential of aluminum, nor do second phases in the amounts present in its alloy have significant effect. Severe cold work makes the potential more anodic by a few millivolts, and this change, although small, is sufficient to affect the extent to which pitting develops, for example, more pitting on machined or sheared edges [16].…”