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CORROSION AND SURFACE CHEMISTRY OF METALS Dieter Landolt
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In the simplest sense, corrosion induced by microorganisms are a range of chemical reactions driven by microorganism metabolism (consumption of nutrients) that changes the environment on and around a concrete material resulting in a subsequent chemical reaction with the concrete that causes its deterioration. Shaped corrosion pits on the metal surface protection films because of the destruction caused by metal corrosion rate of speed which is different from one place to another place on the metal surface. Corrosion process is the transformation of metal into their compounds, especially so in an Pitting corrosion. The chemical used in the passivation process may affect the material in other part of the sealed product when we do a full post-passivation. The chemical formula of iron rust is Fe2O3.xH2O. This naturally occurring oxide layer prevents chemical attack of the underlying metal surface. Localized corrosion has an electrochemical nature and is caused by a difference in corrosion potential in a local cell formed by differences in or on the metal surface. This behavior also means, however, that high corrosion resistance can be expected only under neutral or oxidizing conditions. 3- The fact that the surface is “unfinished” will have little or no effect on the corrosion resistance, but if the jacket area was not passivated after welding, it would be very susceptable to corrosion. The important condition for this and other high nickel chromium alloys, is that iron metal is not allowed to contaminate the surface. Acidothiobacillus bacteria release acid, lower the environmental pH (yellow zone) leading to microbial induced corrosion of concrete and metals.