Monday, October 25, 2010

Corrosion

What is Corrosion ?

  1. Corrosion is deterioration of essential properties in a material due to reactions with its surroundings.
  2. In the most common use of the word, this means a loss of an electron of metals reacting with water and oxygen.
  3. Weakening of iron due to oxidation of the iron atoms is a well-known example of electrochemical corrosion. This is commonly known as rust.
  4. This type of damage usually affects metallic materials, and typically produces oxides and/or salts of the original metal.
  5. Corrosion also includes the dissolution of ceramic materials and can refer to discoloration and weakening of polymersby the sun's ultraviolet light.

Rusting
Rust,the most familiar example of corrosion. This electrochemical process requires the presence of water, oxygen and an electrolyte and leads to the formation of hydrated iron oxides.
Reaction:
Fe(s) -> Fe2+(aq) + 2 e-
2 H2O(l) + O2 (g) + 4 e-(aq) -> 4 OH-(aq)
Fe2+(aq) + 2 OH-(aq) -> Fe(OH)2(s)
4Fe2+(aq) + 4H+(aq) + O2(aq) -> 4Fe3+(aq) + 2H2O(l)
Fe3+(aq) + 3OH-(aq) -> Fe(OH)3(s)
2Fe(OH)3(s) -> Fe2O3•H2O(s) + 2H2O(l)

Rust factor

  1. Acidity/ alkalinity of surrounding
  2. Electrolyte contact
  3. Condition of metal
  4. Potential electrode
  5. Contact with another metal

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