Tin

Chemical Formula

Background

Tin known since ancient times is chiefly found in cassiterite (SnO₂). It is obtained from the reduction of the ore with coal in a reverberatory furnace.

Tin is a silvery-white lustres metal, with a bluish tinge. It is malleable to a certain extent and is ductile and possesses a highly crystalline structure. Its hardness is only slightly greater than that of lead, and its electrical conductivity is approximately one seventh that of silver. Tin takes on a high polish and is resistant to atmospheric corrosion. It is resistant to distilled, sea and soft tap water however, tin is attacked by strong acids, alkalis and strong salts. The presence of oxygen within solution accelerates the attack.

Tin is considered to have two allotropic forms. Grey tin, or a tin (having a cubic crystal structure) changes at 13.2°C into white, or b tin (having a tetragonal crystal structure), which is considered the ordinary form of the metal. The change from a to b is termed the ‘tin pest’.

Ordinary tin is composed of nine stable isotopes, while eighteen unstable isotopes are known.

Applications

Tin as the metal is used in:

· Soft solders.

· Pewter.

· Bronze.

· Bell metal, and Babbitt metal.

· Electroplating.

· Corrosion resistant coatings

· For the production of molten flat glass, where a bath of molten tin (float glass) is implemented to produce a flat surface (known as the Pilkington process).

· Super conductive magnets (tin-niobium alloy), which are superconducting at very low temperatures.

· Tins for the containing of foodstuffs and the like.

Tin compounds are used for:

· The chloride salt (SnCl₂.H₂O) is very important as a reducing agent and as a mordant in calico printing.

· Stannic oxide (SnO₂) a white powder is used in ceramic glazes as an opacifier and for colour.

· Potassium stannate (K₂SnO₃.3H₂O), or also sodium stannate (Na₂SnO₃.3H₂O) is used for immersion tinning of aluminium.

· Organotin (refer to butyl compounds of the metal) and are used as catalysts, and heat and light stabilisers in vinyl polymers e.g. Stan-Guard 100 (a liquid butyl-tin) containing sulphur, is used as a stabiliser in rigid PVC sheet and butyl-tin maleate is an effective light stabiliser.

· HollicideLT-125, a water soluble organo-trialkyl-tin, is used as a bactericides in paper and textile processing.