What are the factors that affect corrosion?
Corrosion is a term for the oxidation of metals. The factors that affect corrosion are:
1. Nature of the metal: Some metals corrode more easily than others. The metals in Group 1 of the periodic table are the most reactive. The least reactive are called the Noble Metals: Ruthenium, rhodium, palladium, silver, osmium, iridium, platinum, and gold. Corrosion is an oxidation-reduction reaction, and those metals with the lowest standard reduction potential are most likely to be oxidized (corroded). Contact between two dissimilar metals will speed up the corrosion of the more reactive of the two.
2. Nature of the oxide film that forms: Some metals, such as aluminum, form an insoluble oxide film that adheres and prevents further corrosion. Others, such as iron, form oxides that crumble away or dissolve and expose the metal below to further oxidation.
3. Moisture: The rate of corrosion increases in the presence of water, particularly oxygenated water. Water and its dissolved solutes comprise an electrolyte solution which facilitates the transfer of electrons between cathodic (-) and anoxic (+) regions of the metal.
4. Salt: Corrosion occurs faster in a marine environment because salt increases the electrolytes in the moisture.
5. Acid: Acid anhydrides enter the atmosphere from the burning of fossil fuels. They combine with water in the atmosphere to form acids that are corrosive to metals.
6. Temperature: the rate of corrosion, like that of most chemical reactions, increases as the temperature increases.