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Exercise 12: Some Investigations on Corrosion of Iron

I. Introduction Corrosion can be defined as the degradation of a material due to a reaction with its environment. Although this definition is applicable to any type of material, it is usually reserved for metallic alloys, in which the oxidation process M → M+ + e– is facilitated by the presence of suitable electron acceptor. The chemical reactions that take place in corrosion processes are reduction-oxidation (redox) reactions. Such reactions require a species of material that is oxidized (the metal), and another that is reduced (the oxidizing agent). In oxidation, the metal loses electrons. The zone in which this happens is known as the anode. In the reduction reaction, the oxidizing agent gains the electrons that have been shed by the metal, and the zone in which this happens is known as the cathode. (Brown, 2000)

The presence of water is necessary in order to transport ions to and from the metal, but a thin film of adsorbed moisture can be sufficient. A corrosion system can be regarded as a short-circuited electrochemical cell in which the anodic process is something like
Fe(s) → Fe2+(aq) + 2 e–

and the cathodic steps can be any of
O2 + 2 H2O + 4e– → 4 OH–
H+ + e– → ½ H2(g)
M2+ + 2e– → M(s) where M is a metal.
(Brown, 2000) Which parts of the metal serve as anodes and cathodes can depend on many factors. In this report, the effects of the following factors on the corrosion of iron will be observed: 1. acidity and basicity of the solution in contact with the metal; 2. mechanical stress applied on the metal; and 3. contact with other metals.

II. Materials

A. Reagents

* NaOH * NaCl * HCl * KOH * KNO3 * HNO3 * H2SO4 * NaSCN * Na3PO4 * Phenolphthalein * K3Fe(CN)6

B. Apparatus

* Test…...

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