Friday, March 11, 2011

Tin, Symbol Sn (Stannum)

Tin, Symbol Sn (Strannum), molecular weight = 118.69
An historical epoch, the Bronze Age, was named after the copper tin Alloy.

Occurrence and extraction

Ores: The most important mineral is first produced containing 60 to 70% of tin.

Beatification of Tin:

The ore is freed of oxygen (reduced in shaft furnaces or open hearth furnaces. The crude metal is then refined electrolytically or by sweating. Sweating is the separation of several metals from a mixture by taking advantage of their different melting points.

Properties of Tin:

Physical properties of tin, density 7.3 kg/dm3, with melting point 232 oC.
Chemical properties of tin, have corrosion resistance against air, water, many alkalis and acids.
Mechanical properties, tensile strength about 30 N/mm2, extensibility about 40%.
Technological: it is non poisonous, easily formed and very ductile at 200 oC, tin becomes brittle and friable, below -20 oC it changes into a powder (tin pest). This phenomenon is caused by a change in volume resulting from the collapse of the spatial lattice.

When cast tin strips are bent, the crystals rub against each other producing characteristic “tin cry.”
Tin is ductile and can therefore be easily rolled, beaten and hammered. Foils as thin as 0.01 mm can be produced (tin foil).

In the molten state, tin is a very fluid and can be easily cast. It is used as a coating metal, e.g. termoplate, used as a coating on lead surfaces to prevent lead poisoning.

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