What Are Some of the Important Factors
in Oxidation of Fe Alloys?
- Rust is non adherent, and therefore, is not a
- Rust (Fe2O3/Fe3,O4) forms electro-chemically
at ambient temperatures in moist air.
temperatures accelerate the process in some
instances, e.g., process equipment and power
generation systems, etc.
- Differences in electrical potential among small areas
on the steel surface forming anodes and cathodes
connected by an electrolyte (moist air, etc.)
- Impurities in the electrolyte increase conductivity, which
increases the rate of corrosion. Transfer of electrons
from the anodic grains to the cathodic adjacent grains at
the start, then to the rust as it forms.
- On a steel surface, there are millions of exposed anodes
and cathodes (grains) with minute current flows among
them in the presence of an electrolyte (moist air).
- As the rusting process proceeds, anodes and cathodes
(grains) are consumed and new ones are created. As
the metal is consumed in the anodic area, a small electric
current begins to flow. The iron ions produced in the anode
combine with the environment and form the loose, flaky iron
oxide known as rust.
- As anode areas corrode, new material of different
composition and structure is exposed. A gradual change
takes place in the electrical potentials and the anodic
and cathodic site locations.
- As the rusting process proceeds, previously uncorroded
areas are attacked, and a uniform surface corrosion is
produced. The process continues until the steel is entirely