Corrosion & Environmental Degradation
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Crevice Corrosion
· Composition differences between regions of an electrolyte gives rise to different electrode potentials with the same material, and hence local corrosion. 
· A dilute electrolyte region gives rise to a more anodic electrode than a concentrated electrolyte. The reaction: M < - > M2+ + 2e goes from left to right in a dilute system and from right to left in a concentrated system, measured in comparison to the equilibrium concentration.
· In the structure illustrated, the transport of electrolyte to the interior of the crevice is restricted and its local concentration is below that at the exterior surfaces. Anodic corrosion, therefore, occurs in the crevice region and is hard to detect by exterior inspection. 
From: Van Vlack, 
"Elements of Materials Science and Engineering," Addison Wesley (1985)