Thursday, 26 February 2015

The many uses of tin

Elizabeth Henderson
Product Development Manager

Tin is one of the elements which have been in use longer than we know.  At Itac it plays a key behind-the-scenes role, as dibutyl tin dilaurate is a catalyst in the manufacture of polyurethanes. We use these polyurethanes as components of our formulated coatings and adhesives. We also use dibutyl tin dilaurate in some of our formulations as a curing agent, but environmental concerns about the use of tin salts mean that we are phasing it out wherever possible. A demonstration of the powerful life-system effects of tin compounds is the sex-change effect of tri butyl tin (TBT) on marine fauna in coastal waters. TBT is an extremely effective biocide and was applied to boats to prevent the accumulation of plants and animals on the bottom. Leaching of TBT from the film, and overspray and waste from the coating processes meant that there was sufficient in the sea to transform female dog whelks into males. Its use has now been superseded in this application by copper compounds.
Tin was a vital component of early antibiotics for human use – ‘Stannoxyl’ was formulated using metallic tin and tin oxide, and was used in experiments on lung infections by being given as pills. It was later used in an ointment for acne and boils.
The primary ore of tin is cassiterite, whose name is derived from the Greek word for tin. It forms tetragonal crystals, space group P42/mnm.  The material is a member of the rutile group, which is named after the titanium dioxide discussed in April 2014. It is very hard (hardness 7, cf agate 7, diamond 10) and thus survives in alluvial placer deposits, sometimes in large enough quantities to be commercially exploitable. Generally the appearance of the crystals is too poor to allow it to be cut into jewellery, but some material is mined for this purpose in Bolivia.
The process developed at Pilkingtons for making large sheets of glass for buildings and other applications in the twentieth century is completely dependent on tin’s physical characteristics. Tin melts at the relatively low temperature of 232°C, and a bath of molten tin forms a perfectly level surface onto which fluid glass can be poured. The glass (introduced at 1100°C) flows over the surface of the tin to form a uniform sheet leaves the float bath at 600°C.
 ‘Tin’ cans have always been made out of steel with a layer of tin on the outside, to prevent corrosion, and it was widely used in cookware and cutlery because of its low density and easy workability.

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