R-AECHE-47

Graph

The degradation of metals due to an electrochemical process.
- Actually refers to iron.
Influences on corrosion:
- Impurities
  - Can either protect iron or enhance rate of corrosion.
- Air and moisture
- Prescence of electrolytes
  - Sea water
  - Strains in metal
  - Dents
  - Scratches
Types of corrosion:
- Dry/Chemical corrosion
  - Reaction of metals with gasses in atmosphere
  - Typically reaction with oxygen.
  - e.g. $2Mg_{(s)} + O_{2(g)} \to 2MgO_{(s)}$
  - Not nitrogen!!!!! Ea is too high to break through triple bond.
  - Molecules with low activation energy tend to be viable for chemical corrosion
    - $O_2, SO_2, CO_2, H_2S$
- Wet/Electrochemical corrosion
  - Requires presence of water, producing microscopic galvanic cell.
  - It occurs due to setting up of a large number of tiny galvanic cells in metal in prescence of impurity as well as in prescence of moisture
  - e.g rusting of iron in moist atomsphere