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Last updated on April 19, 2014 at 18:42 EDT

Tin

Tin is a chemical element in the periodic table that has the symbol Sn (L. Stannum) and atomic number 50. This silvery, malleable poor metal that is not easily oxidized in air and resists corrosion is found in many alloys and is used to coat other metals to prevent corrosion. Tin is obtained chiefly from the mineral cassiterite where it occurs as an oxide.

Notable characteristics

Tin is a malleable, ductile, highly crystalline, silvery-white metal whose crystal structure causes a “tin cry” when a bar of tin is bent (caused by crystals breaking). This metal resists corrosion from distilled sea and soft tap water, but can be attacked by strong acids, alkalis, and by acid salts. Tin acts as a catalyst when oxygen is in solution and helps accelerate chemical attack.

Tin forms Sn2 when it is heated in the presence of air. Sn2, in turn, is feebly acidic and forms stannate (tin) salts with basic oxides. Tin can be highly polished and is used as a protective coat for other metals in order to prevent corrosion or other chemical action. This metal combines directly with chlorine and oxygen and displaces hydrogen from dilute acids. Tin is malleable at ordinary temperatures but is brittle when it is heated.

Allotropes

Solid tin has two allotropes at normal pressure. At low temperatures it exists as gray or alpha tin, which has a cubic crystal structure similar to silicon and germanium. When warmed above that 13.2 °C it changes into white or beta tin, which is metallic and has a tetragonal structure. It slowly changes back to the gray form when cooled, which is called the tin pest or tin disease. However, this transformation is affected by impurities such as aluminium and zinc and can be prevented from occurring through the addition of antimony or bismuth.

Applications

Tin bonds readily to iron, and has been used for coating lead or zinc and steel to prevent corrosion. Tin-plated steel containers are widely used for food preservation, and this forms a large part of the market for metallic tin. British English calls them “tins”; Americans call them “cans”. One thus-derived use of the slang term “tinnie” or “tinny” means “can of beer”.

Other uses:

- Some important tin alloys are: bronze, bell metal, Babbitt metal, die casting alloy, pewter, phosphor bronze, soft solder, and White metal.
- The most important salt formed is tin chloride, which has found use as a reducing agent and as a mordant in the calico printing process. Electrically conductive coatings are produced when tin salts are sprayed onto glass. These coatings have been used in panel lighting and in the production of frost-free windshields.
- Window glass is most often made via floating molten glass on top of molten tin (creating float glass) in order to make a flat surface (this is called the “Pilkington process”).
- Tin is also used in solders for joining pipes or electrical/electronic circuits, in bearing alloys, in glass-making, and in a wide range of tin chemical applications. Although of higher melting point that a lead-tin alloy the use of pure tin or tin alloyed with other metals in these applications is rapidly supplanting the use of the previously common lead”“containing alloys in order to eliminate the problems of toxicity caused by lead.
- Tin foil was once a common wrapping material for foods and drugs; now replaced by the use of aluminum foil, which is commonly referred to as tin foil. Hence one use of the slang term “tinnie” or “tinny” for a small retail package of a drug such as cannabis.

Tin becomes a superconductor below 3.72 K. In fact, tin was one of the first superconductors to be studied; the Meissner effect, one of the characteristic features of superconductors, was first discovered in superconducting tin crystals. The niobium-tin compound Nb3Sn is commercially used as wires for superconducting magnets, due to the material’s high critical temperature (18K) and critical magnetic field (25 T). A superconducting magnet weighing only a couple of kilograms is capable of producing magnetic fields comparable to a conventional electromagnet weighing tons.

History

Tin (anglo-Saxon, tin, Latin stannum) is one of the earliest metals known and was used as a component of bronze from antiquity. Because of its hardening effect on copper, tin was used in bronze implements as early as 3,500 BC. Tin mining is believed to have started in Cornwall and Devon ( esp Dartmoor) in Classical times, and a thriving tin trade developed with the civilizations of the Mediterranean. However the pure metal was not used until about 600 BC.

The word “tin” has cognates in many Germanic and Celtic languages. The American Heritage Dictionary speculates that the word was borrowed from a pre-Indo-European language.

In modern times, the word “tin” is often (improperly) used as a generic phrase for any silvery metal that comes in thin sheets. Most everyday objects that are commonly called tin, such as aluminium foil, beverage cans, and tin cans, are actually made of steel or aluminium, although tin cans do contain a small coating of tin to inhibit rust. Likewise, so-called “tin toys” are usually made of steel, and may or may not have a small coating of tin to inhibit rust.

Occurrence

About 35 countries mine tin throughout the world. Nearly every continent has an important tin-mining country. Tin is produced by reducing the ore with coal in a reverberatory furnace. This metal is a relatively scarce element with an abundance in the earth’s crust of about 2 ppm, compared with 94 ppm for zinc, 63 ppm for copper, and 12 ppm for lead. Most of the world’s tin is produced from placer deposits; at least one-half comes from Southeast Asia. The only mineral of commercial importance as a source of tin is cassiterite (SnO2), although small quantities of tin are recovered from complex sulfides such as stanite, cylindrite, frankeite, canfieldite, and teallite. Secondary, or scrap, tin is also an important source of the tin.

Isotopes

Tin is the element with the greatest number of stable isotopes (ten). 18 additional unstable isotopes are known.

Precautions

The small amount of tin that is found in canned foods is not harmful to humans. Organotin compounds such as tributyltin oxide are biocides and need to be handled with care.

Tin