Page 8 - Curriculum Visions Dynamic Book

Corrosion of iron: rust
The environment is a hazardous place for materials. Even in “clean” country air, materials will slowly show signs of surface change because of the effects of water and gases in the air. The change in the surface of materials is a reaction with oxygen in the air. It is called corrosion and produces a coating called an oxide.
Iron is particularly susceptible to corrosion, known as rusting, in damp air or oxygen-rich water because it is a reactive material.
 This jar is called a desiccator. The blue crystals in
the bottom are silica gel coloured with cobalt chloride. They absorb any moisture in the air. The nails are therefore in completely dry air. Although they have been sealed in this desiccator for many years, they show no signs of rust. This indicates that both moisture and oxygen are required to form rust.
 Steel nails need water and oxygen from the air to rust quickly. Water alone is a poor corroding agent. However, when oxygen is present, such as when water is left uncovered, nails left in water will rust (oxidise) very rapidly.
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