Tin

Tin has been a known and well-utilized metal since the Bronze Age (around 3500 BC). Bronze, a copper–tin alloy, first appeared in the Middle East although there were no tin mines in that region, a fact that constitutes a historical enigma. Pure tin was produced in China and Japan around 1800 BC. Tin cutlery was frequently used in France around the 17th century, but such usage occasionally led to accidents due to traces of arsenic found in the metal.

At the beginning of the 19th century Appert discovered that food products could be preserved in airtight vessels after being heated; this observation eventually led to the so-called tin cans.

The word tin comes from the Latin stannum. The Greeks called the metal κασσιτερο (kassiteros), hence the name of cassiterite given to its ore. The word bronze comes from the town of Brindisi in Italy.

Properties

• A silvery white metal that is malleable and ductile.
• When a tin bar is bent the noise made by the crystals on deforming is clearly heard; this is known as the tin-cry.
• The β-Sn or white tin variety is stable at room temperature and crystallizes in the tetragonal system. It can be rolled into very thin sheet (tin foil).
• Below 13.2°C, the thermodynamically stable variety is the non-metallic phase α-Sn or grey tin, which crystallizes in the cubic system.
• Upon expanding, the metal disaggregates, a feature that was formerly considered a disease known as tin plague.

Applications

• Tin–lead alloys are used for soldering; particularly in the manufacture of printed circuits.
• Tin has long been employed as an anti-corrosion coating for soft iron in the manufacture of food and beverage cans. This application currently accounts for about 33% of tin consumption. The protection provided by the coating is thus effective only if the layer is free from defects; the slightest crack or pit leading to corrosion.
• Their colour ranges from red through yellow to white, depending on their copper content. Bronzes are used in springs, gears and bearings.
• Alother uses include organ pipes, the manufacture of superconductors, in glass making to obtain a perfectly smooth surface, in lead electrodes and lead-acid batteries, and as a replacement for lead in wine-bottle caps.
• Tin tetrachloride SnCl4 hydrolyses easily and is used as a mordant and as a starting material for the preparation of organo-stannic compounds used, for instance, in agriculture and as stabilisers in PVC-type plastics.
• Mixed indium–tin oxides are used as conducting coatings on certain glasses, such as those for windscreens, to facilitate de-icing and for LCD screens and touch screens.

Recycling

In the recycling of tin cans, tin from the thin metal coating is recovered by electrolysis in a NaOH solution. Tin is also recovered from solder alloys and from processes such as the production of tin-containing targets for conductive coatings.