Corrosion & Environmental Degradation
Table of Contents
Passive Surface Films
· Materials such as Aluminum are protected from corrosion by the presence of adhering insulating oxide surface films which prevent electron transfer to their surroundings.
· The positions of atoms in an Al2O3 film on an aluminum substrate is shown. The {111} plane of the aluminum crystal has a surface atom spacing that is essentially the same as that of aluminum atoms in the (0001) plane of the oxide.
· This coherent layer is stable in thermal and mechanical environments, and it will reform by rapid oxidation if the film is locally damaged. Thick films may be produced by "anodization," the electrochemical formation of Al2O3.
· Alkaline films can dissolve Al2O3 and the corrosion protection is destroyed in these environments.
From: L. van Vlack, 
"Elements of Materials Science and Engineering," 
Addison Wesley (1985)