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split tin

Tin

Tin is a chemical element with the symbol Sn (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. It can be alloyed with copper to make bronze. Pewter alloys contain from 85% up to 99% tin.

Characteristics

Tin is a malleable, ductile, highly crystalline, silvery-white metal; when a bar of tin is bent, a strange crackling sound, known as the tin cry, can be heard due to the twinning of the crystals. Tin is malleable at ordinary temperatures but is brittle when it is cooled.

Chemical

Tin 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 the dioxide SnO2 when it is heated in the presence of air. SnO2, in turn, is feebly acidic and forms stannate (SnO32-) 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.

Allotropes

Tin's chemical properties fall between those of metals and non-metals, just as the semiconductors silicon and germanium do. Tin has two allotropes at normal pressure and temperature: gray tin and white tin. A third allotrope, called brittle tin, exists at temperatures above 161 °C.

Below 13.2 °C, it exists as gray or alpha tin, which has a cubic crystal structure similar to silicon and germanium. Gray tin has no metallic properties at all, is a dull-gray powdery material, and has few uses, other than a few specialized semiconductor applications.

Although the transformation temperature is 13.2 °C, the change does not take place unless the metal is of high purity, and only when the exposure temperature is well below 0 °C. This process is known as tin disease or tin pest. Tin pest was a particular problem in northern Europe in the 18th century as organ pipes made of tin alloy would sometimes be affected during long cold winters. Some sources also say that during Napoleon's Russian campaign of 1812, the temperatures became so cold that the tin buttons on the soldiers' uniforms disintegrated, contributing to the defeat of the Grande Armée. The veracity of this story is debatable, because the transformation to gray tin often takes a reasonably long time. Commercial grades of tin (99.8%) resist transformation because of the inhibiting effect of the small amounts of bismuth, antimony, lead, and silver present as impurities. Alloying elements such as copper, antimony, bismuth, cadmium, and silver increase its hardness. Tin tends rather easily to form hard, brittle intermetallic phases, which are often undesirable. It does not form wide solid solution ranges in other metals in general, and there are few elements that have appreciable solid solubility in tin. Simple eutectic systems,however, occur with bismuth, gallium, lead, thallium, and zinc.

History

Tin (Old English: tin, Old Latin: plumbum candidum ("white lead"), Old German: tsin, Late 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. A shipwreck at Uluburun, Turkey dating to 1336 BC contains a shipment of tin, perhaps originating in Afghanistan. European 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 lone metal was not used until about 600 BC. The last Cornish tin mine, at South Crofty near Camborne, closed in 1998 bringing 4,000 years of mining in Cornwall to an end, but as of 2007 increased demand from China may lead to its re-opening.

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. The later name "stannum" and its Romance derivatives come from the lead-silver alloy of the same name for the finding of the latter in ores; the former "stagnum" was the word for a stale pool or puddle.

In modern times, the word "tin" is often improperly used as a generic phrase for any silvery metal that comes in sheets. Most everyday materials that are commonly called "tin", such as aluminium foil, beverage cans, corrugated building sheathing and tin cans, are actually made of steel or aluminium, although tin cans (tinned cans) do contain a thin coating of tin to inhibit rust. Likewise, so-called "tin toys" are usually made of steel, and may or may not have a coating of tin to inhibit rust. The original Ford Model T was known colloquially as the Tin Lizzy.

Historical Cornwall was the major tin producer, this changed after large amounts of tin have been found in the Bolivian tin belt and the east asian tin belt stretching from China through Thailand and Laos to Malaya and Indonesia. The tin produceres founded in 1931 the International Tin Comittee followed in 1956 by the International Tin Council a institution to control the tin market. After the collapse of the market in October 1985 the price for tin nearly halved.

Occurrence

In 2007, the People's Republic of China was the largest producer of tin, where the tin deposites are concentrated in the southeast Yunnan tin belt, with 43% of the world's share, followed by Indonesia and Peru, reports the USGS.

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. 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 stannite, cylindrite, franckeite, canfieldite, and teallite. Secondary, or scrap, tin is also an important source of the metal.

Tasmania hosts some deposits of historical importance, most notably Mount Bischoff and Renison Bell. New deposits are also reported to be in southern Mongolia.

It is estimated that, at current consumption rates, the Earth will run out of tin in 40 years. However Lester Brown has suggested tin could run out within 20 years based on an extremely conservative extrapolation of 2% growth per year. However this is offset by the increased use of secondary, or scrap tin, as a readily available source of the metal.

See also Tin minerals

Applications

Metall and Alloy

Tin bonds readily to iron, and is 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. Speakers of British English call them "tins"; Americans call them "cans" or "tin cans". One thus-derived use of the slang term "tinnie" or "tinny" means "can of beer". The tin whistle is so called because it was first mass-produced in tin-plated steel.

  • Tin foil was once a common wrapping material for foods and drugs; replaced in the early 20th century by the use of aluminium foil, which is now 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 or for a can of beer.
  • Tin is used extensively for alloys, some important tin alloys are bronze, bell metal, Babbitt metal, die casting alloy, pewter, phosphor bronze, soft solder, and White metal.
  • Most metal pipes in a pipe organ are made of varying amounts of a tin/lead alloy, with 50%/50% being the most common. The amount of tin in the pipe defines the pipe's tone, since tin is the most tonally resonant of all metals. When a tin/lead alloy cools, the lead cools slightly faster and makes a mottled or spotted effect. This metal alloy is referred to as spotted metal.
  • 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 electric circuits, in bearing alloys, in glass-making, and in a wide range of tin chemical applications. Although of higher melting point than 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 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 (18 K) 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.

Compounds

  • For a long time the antifouling property of organotin compounds was used for the preservation of wood and to prevent growth of marine organisms on ships. Tributyltin was used as additive for ship paint. The use declined after organotin compounds where recognised as persistent organic pollutants with a extremly high toxicity for some marine organism, for example dog whelk. The EU banned the use of organotin compounds in 2003.
  • The most important salt formed is stannous 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.
  • Tin is added to some dental care products as stannous fluoride (SnF2). Stannous fluoride can be mixed with calcium abrasives while the more common sodium fluoride gradually becomes biologically inactive combined with calcium. It has also been shown to be more effective than sodium fluoride in controlling gingivitis.

Compounds

For discussion of Stannate compounds (SnO32−) see Stannate. For Stannite (SnO2) see Stannite. See also Stannous hydroxide (Sn(OH)2), Stannic acid (Stannic Hydroxide - Sn(OH)4), Tin dioxide (Stannic Oxide - SnO2), Tin(II) oxide (Stannous Oxide - SnO), Tin(II) chloride (SnCl2), Tin(IV) chloride (SnCl4)

See also Tin compounds

Isotopes

Tin is the element with the greatest number of stable isotopes (ten), which is probably related to the fact that 50 is a "magic number" of protons. 28 additional unstable isotopes are known, including the "doubly magic" tin-100 (100Sn) (discovered in 1994).

Precautions

Tin plays no known natural biological role in humans, and possible health effects of tin are a subject of dispute. Tin itself is not toxic but most tin compounds are.

Triorganotins are very toxic. Tri-n-alkyltins are phytotoxic and depending on the organic groups, they can be powerful bactericides and fungicides. Other triorganotins are used as miticides and acaricides.

See also

References

External links

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