1. Introduction What is Corrosion?
Corrosion is the destructive attack of a metal by its reaction with the environment
Note that the word “corrosion” refers to the degradation of a metal by its environment.

2. What is rusting ? What is white rust ?
According to ‘ASTM' corrosion glossary, corrosion is defined as "the chemical or electrochemical
reaction between a material, usually a metal, and
its environment that produces a deterioration of the material and its properties”.
Other definitions include Fontana's description that corrosion is the extractive metallurgy in reverse,2 which is expected since metals thermodynamically are less stable in their elemental forms than in their compound forms as ores.
What is rusting ?
What is white rust ?

3. Physical Processes of Degradation
Physical degradation processes include the following:
Fracture
Fatigue
Wear
Erosion or cavitation erosion
Radiation damage

4. Red rust
Waterline

5. Environmentally Assisted Degradation Processes
Table 1.1 Physical degradation processes and their environmentally assisted counterparts
Environmentally assisted
process
Example
Fracture
Stress-corrosion cracking
Stress-corrosion cracking of bridge
cables, of landing gear on aircraft
Fatigue
Corrosion fatigue
Vibrating structures, such as aircraft
wings, bridges, offshore platforms
Wear
Fretting corrosion
Ball bearings in chloride-contaminated oil

6. Cavitation erosion
Cavitation corrosion
Ship propellers, pumps, turbine blades,
fast fluid flow in pipes
Radiation damage
Radiation corrosion
Increased susceptibility of stainless steels
to dissolution or to stress-corrosion
cracking [1, 2]

7. Half-Cell Reactions Electrochemical Reactions
Corrosion is an electrochemical process. That is, corrosion usually occurs not by direct chemical reaction of a metal with its environment but rather through the operation of coupled electrochemical half-cell reactions.
Half-Cell Reactions

8. Anodic Reactions
The loss of metal occurs as an anodic reaction. Examples are
Fe(s) → Fe2+(aq) + 2e− (1)
Al(s) → Al3+(aq) + 3e− (2)
2Cu(s) + H2O(1) → Cu2O(s) + 2H+(aq) + 2e− (3)

9. The following reaction is also an anodic reaction:

10. Cathodic Reactions
In a cathodic reaction?
2H+(aq) + 2e− → H2(g)

11. Another common cathodic reaction is the reduction of dissolved oxygen to hydroxyl ions, a reduction reaction which occurs in neutral or basic solutions.
O2(g) + 2H2O + 4e− → 4OH−(aq)

12. Coupled Electrochemical Reactions
At anodic sites:
Fe Fe+2 + 2e–
At cathodic sites:
2 H+ + 2e– H2
Overall reaction:
Fe + 2 H Fe+2 + H2

13. The reason that two different electrochemical half-cell reactions can occur on the same metal surface lies in the heterogeneous nature of a metal surface.
The heterogeneous nature of a metal surface showing various types of imperfections

14. Kesimpulan :
Rx oksidasi
Rx reduksi
Media elektrolit
Jalan untuk perpindahan

15. A Note About Atmospheric Corrosion
The need for the presence of an electrolyte as a condition for corrosion to occur is illustrated by the phenomenon of atmospheric corrosion, i.e., the corrosion of metals in the natural outdoor atmosphere.

16. Fig. 2. 7 The continuation of reactions initiated in Fig. 2. 6
Fig. 2.7 The continuation of reactions initiated in Fig (a) The precipitation of ferrous hydroxide on the iron surface. (b) The conversion of ferrous hydroxide to a hydrated ferric oxide

17. The Faraday and Faraday’s Law
Faraday’s law states that the mass (w) of metal corroded is given by