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Corrosionist The Website of Corrosion and Corrosion Control |
| You are here >>> Corrosion Prevention Home - Corrosion Fundamentals - How does rust form, Corrosion Metal Definition, What causes Corrosion |
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HOW DOES RUST FORMRust is a generic term to describe a series of different oxides, Fe(OH)2, Fe(OH)3, FeO(OH), Fe2O3.H2O that forms when iron corrodes. The common form of Rust is a Red products:Fe2O3. Rust forms due to a reaction between the iron and water; either water condensing from air or rain. The oxygen in the air dissolves in the water and causes rust to form. There are always two distinct chemical reactions in a corrosion process, the basic chemistry of corrosion is: 1) Anodic Dissolution of Metal (Iron) that goes into solution (water) Fe -----> Fe2+ + 2e- 2) Cathodic Reduction of Oxygen dissolved into water
O2 + 2H2O + 4e- ---->
4OH- The final reaction is: Fe2+ + 2OH- -----> Fe(OH)2 This oxide will then further reacts with oxygen to give the final red product:Fe2O3.H2O
Corrosion of Metals The corrosion of metals is an electrochemical process. That is, it is an electrical circuit where the exchange of electrons (electricity) is conducted by chemical reactions in part of the circuit. These chemical reactions occur at the surface of the metal exposed to the electrolyte. Oxidation reactions (corrosion) occur at the surface of the anode and reduction reactions occur at the surface of the cathode. |
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Corrosion metal definitionThere are different corrosion metal definition, but the basic principle is the same: an interaction of the metal with its environments. These are some example of corrosion metal definition: |
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| Corrosion of metals can be defined as the destructive attack of a metal through interaction with its environment | ||
| Corrosion is a process that occurs when a material deteriorates due to its interaction with the surrounding environment in which an electrochemical reaction consumes the material through oxidation. | ||
What causes corrosion |
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As seen above a Corrosion process is the results of the
interaction of a metals with its environments. Usually
what causes corrosion, at
least what we can see in our daily life, is
what is called "wet" corrosion. "Wet" corrosion means that there is a water
phase, humidity, rain, seawater..., in contact with the metal surface. So
what causes corrosion is the
interaction of the water, or better the oxygen dissolved in the water, through the reactions seen above, with the metal. |
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