Metals and Non-Metals -II
Corrosion is the process of deterioration of a metal as a result of its reaction with air and water surrounding it. Corrosion of iron is called rusting.
Rusting is the slow oxidation of iron by the atmospheric oxygen in the presence of water or moisture. Iron, when exposed to moist air, reacts with oxygen and water to form hydrated iron (III) oxide (rust). Rust is of reddish brown colour. It is a soft, porous and powdery substance easily falls off from the surface of iron. It is basic in nature. The necessary conditions for rusting of iron are presence of air and water or moisture.
A green colour deposit is formed on the surface of copper when exposed to air. This is due to the formation of basic copper carbonate. Corrosion can be prevented by various methods such as by surface coating, by galvanisation, by electroplating or chrome plating and by tinning.
In surface coating process, surface of an object is coated with oil, grease, paint, etc. so that air and moisture cannot come in contact of iron.
Galvanisation is the process of depositing a thin layer of zinc metal on iron objects.
In electroplating process, iron objects are electroplated with a more resistant metal such as chromium or nickel.
In tinning process, iron is prevented by the coating of tin on iron objects.
Metalloids are the chemical elements which show some properties of metals and some properties of non-metals. They are all solids. Examples of some metalloids are silicon, germanium, arsenic and antimony.