Corrosion
introduction
electrochemistry
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galvanic
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Electrochemistry 1

In this section we will examine

  • chemical processes of corrosion,
  • necessary components for corrosion
  • electrochemical series (explained later)

Corrosion of metals occurs through electron transfer, involving two processes, oxidation and reduction. In oxidation, the metal atoms lose electrons. The surrounding environment then gains the electrons in reduction.

The metal (or part of the metal object) where electrons are lost, is called the anode. The metal, liquid or gas which gains the electrons is called the cathode.

Typically in corrosion metal atoms give up electrons to become positively charged ions, in the oxidation reaction:

M right arrow Mn+ + ne-

(for metal M with n valence electrons)

oxidation reaction diagram
  The site at which oxidation takes place is called the anode.

Examples:

Iron: Fe right arrow Fe2+ + 2e-
Aluminium: Al right arrow Al3+ + 3e-


The electrons generated from the metal are transferred to another material. This is a reduction reaction:

2H+ + 2e- right arrow H2

(in this reduction reaction)

reduction reaction diagram
The site at which reduction takes place is called the cathode.

Examples:

Acid solution: O2 + 4H+ + 4e- right arrow 2H2O
Neutral/Basic solution: O2 +2H2O + 4e- right arrow 4(OH-)

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