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Tin is a chemical element with the symbol Sn ( ) and atomic number 50. It is a main group metal in group 14 of the periodic table. Tin shows chemical similarity to both neighboring group 14 elements, germanium and lead, like the two possible oxidation states +2 and +4. Tin is the 49th most abundant element and has, with 10 stable isotopes, the largest number of stable isotopes in the periodic table. Tin is obtained chiefly from the mineral cassiterite, where it occurs as tin dioxide, SnO2.

This silvery, malleable poor metal is not easily oxidized in air, and is used to coat other metals to prevent corrosion. The first alloy used in large scale since 3000 BC was bronze, an alloy of tin and copper. After 600 BC pure metallic tin was produced. Pewter, which is an alloy of 85% to 90% tin with the remainder commonly consisting of copper, antimony and lead, was used for flatware from the Bronze Age until the 20th century. In modern times tin is used in many alloys, most notably tin/lead soft solders, typically containing 60% or more of tin. Another large application for tin is corrosion-resistant tin plating of steel. Because of its low toxicity, tin-plated metal is also used for food packaging, giving the name to tin cans, which are made mostly out of aluminium or tin-plated steel.

Characteristics

Physical and allotropes

Tin is a malleable, ductile, and highly crystalline silvery-white metal. It is malleable at ordinary temperatures but is brittle when it is cooled, due to the properties of its two major allotropes, α- and β-tin. When a bar of tin is bent, a crackling sound known as the tin cry can be heard due to the twinning of the crystals. The two allotropes that are encountered at normal pressure and temperature, α-tin and β-tin, are more commonly known as gray tin, and respectively white tin. Two more allotropes, γ and σ, exist at temperatures above 161 °C and pressures above several GPa. White tin, or the β-form, is metallic, and is the stable one at room conditions or at higher temperatures. Below 13.2 °C, tin exists in the gray α-form, which has a diamond cubic crystal structure, similar to diamond, silicon or 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 α-β transformation temperature is nominally 13.2 °C, impurities (e.g. Al, Zn, etc.) lower the transition temperature well below 0 °C, and upon addition of Sb or Bi the transformation may not occur at all. This conversion 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.

Chemistry and compounds

Tin resists corrosion from distilled, sea and soft tap water, but can be attacked by strong acids, alkalis, and acid salts. Tin can be highly polished and is used as a protective coat for other metals in order to prevent corrosion or other chemical action. Tin acts as a catalyst when oxygen is in solution and helps accelerate chemical attack.

Tin forms the dioxide SnO2 (cassiterite) when it is heated in the presence of air. SnO2, in turn, is feebly acidic and forms stannate (SnO32−) salts with basic oxides. There are also stannates with the structure [Sn(OH)6]2−, like K2[Sn(OH)6], although the free stannic acid H2[Sn(OH)6] is unknown.

Tin combines directly with chlorine forming tin chloride, while reacting tin with hydrochloric acid in water gives tin chloride and hydrogen. Several other compounds of tin exist in the +2 and +4 oxidation states, such as tin sulfide and tin sulfide (Mosaic gold). There is only one stable hydride, however: stannane (SnH4), where tin is in the +4 oxidation state.

The most important salt 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.

Organotin compounds or stannanes are chemical compounds based on tin with hydrocarbon substituents. Organotin compounds usually have high toxicity and have been used as biocides, but their use is slowly being phased out.The first organotin compound was diethyltin diiodide ( ), discovered by Edward Frankland in 1849. Organotin compounds differ from their lighter analogues of germanium and silicon in that there is a greater occurrence of the +2 oxidation state due to the "inert pair effect"; it also has a greater range of coordination numbers, and the common presence of halide bridges between polynuclear compounds. Most organotin compounds are colorless liquids or solids that are usually stable to air and water. The tetraalkyl stannates ( ) always have a tetrahedral geometry at the tin atom. The halide derivatives often form chained structures with Sn-X-Sn bridges. Alkyltin compounds are usually prepared via Grignard reagent reactions such as in:

+ 4 RMgBr → + 4 MgBrCl


Isotopes

Tin is the element with the greatest number of stable isotopes, ten; these include all those with atomic masses between 112 and 124, with the exception of 113, 121 and 123. Of these, the most abundant ones are 120Sn (at almost a third of all tin), 118Sn, and 116Sn, while the least abundant one is 115Sn. The isotopes possessing even atomic numbers have no nuclear spin while the odd ones have a spin of +1/2. Tin, with its three common isotopes 115Sn, 117Sn and 119Sn, is among the easiest elements to detect and analyze by NMR spectroscopy, and its chemical shifts are referenced against .

This large number of stable isotopes is thought to be a direct result of tin possessing an atomic number of 50, which is a "magic number" in nuclear physics. There are 28 additional unstable isotopes that are known, encompassing all the remaining ones with atomic masses between 99 and 137. Aside from 126Sn, which has a half-life of 230,000 years, all the radioactive isotopes have a half-life of less than a year. The radioactive 100Sn is one of the few nuclides possessing a "doubly magic" nucleus and was discovered relatively recently, in 1994. Another 30 metastable isomers have been characterized for isotopes between 111 and 131, the most stable of which being 121mSn, with a half-life of 43.9 years.

Etymology

The English word 'tin' is Germanic; related words are found in the other Germanic languages—German zinn, Swedish tenn, etc.—but not in other branches of Indo-European except by borrowing (e.g. Irish tinne). Its origin is unknown.

The Latin name stannum originally meant an alloy of silver and lead, and came to mean 'tin' in the 4th century BCE—the earlier Latin word for it was plumbum candidum 'white lead'. Stannum apparently came from an earlier stāgnum (meaning the same thing), the origin of the Romance and Celtic terms for 'tin'. The origin of stannum/stāgnum is unknown; it may be pre-Indo-European. The Meyers Konversationslexikon speculates on the contrary that stannum is derived from Cornish stean, and is proof that Cornwall in the first centuries AD was the main source of tin.

History

Antiquity



Tin is one of the earliest metals known. Late Stone Age metal-workers discovered that putting a small amount of tin, about 5%, in molten copper produced an alloy called bronze that was easier to work and much harder than copper. This discovery so revolutionized civilization that any culture that made widespread use of bronze to make tools and weapons became part of what archaeologists call the Bronze Age. The Bronze Age arrived in Egypt, Mesopotamia and the Indus Valley culture by around 3000 BC.

As of 2001, the oldest tin mine found is in the Taurus Mountainsmarker in Turkey. Younger but still ancient tin mines are located in Spain, Brittany, and Great Britain. European tin mining is believed to have started in Cornwall and perhaps on Dartmoor in Devonmarker in Classical times, and a thriving tin trade developed with the civilizations of the Mediterraneanmarker. Securing these strategically important sites is one reason why the Romans invaded and occupied Great Britain.



A Bronze Age shipwreck of about 1750 BC was found at the mouth of the river Erme in Devon, with ingots of tin. A shipwreck at Uluburun, Turkey dating to 1336 BC contains a shipment of tin, perhaps originating in Afghanistan.

Although pure tin metal was not widely used until about 600 BC, one of the oldest tin artifacts is a ring and bottle made mostly of tin that was found in an 18th Dynasty (1580–1350 BC) tomb in Egypt, even though no tin ore reserves are known to exist in that country.

Modern times

During the Middle Ages, and again in the early 19th century Cornwall was the major tin producer. This changed after large amounts of tin were found in the Bolivianmarker tin belt and the east Asian tin belt, stretching from China through Thailandmarker and Laosmarker to Malayamarker and Indonesiamarker. Tasmaniamarker also hosts deposits of historical importance, most notably Mount Bischoffmarker and Renison Bell.

In 1931 the tin producers founded the International Tin Committee, followed in 1956 by the International Tin Council, an institution to control the tin market. After the collapse of the market in October 1985 the price for tin nearly halved.

Today, the word "tin" is often improperly used as a generic term 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".

Occurrence

Crystals of cassiterite tin ore
Tin output in 2005
Tin ore


Tin is the 49th most abundant element in the Earth's crust, representing 2 ppm compared with 75 ppm for zinc, 50 ppm for copper, and 14 ppm for lead.

Tin does not occur naturally by itself, and must be extracted from a base compound, usually cassiterite (SnO2), the only commercially important source of tin, although small quantities of tin are recovered from complex sulfides such as stannite, cylindrite, franckeite, canfieldite, and teallite. Minerals with tin are almost always in association with granite rock, which when contain the mineral, have a 1% tin oxide content.

Because of the higher specific gravity of tin and its resistance to corrosion, about 80% of mined tin is from secondary deposits found downstream from the primary lodes. Tin is often recovered from granules washed downstream in the past and deposited in valleys or under sea. The most economical ways of mining tin are through dredging, hydraulic methods or open cast mining. Most of the world's tin is produced from placer deposits, which may contain as little as 0.015% tin.

It was estimated in January 2008 that there were 6.1 million tons of economically recoverable primary reserves, from a known base reserve of 11 million tons. Below are the nations with the 10 largest known reserves.

Estimates of tin production have historically varied with the dynamics of economic feasibility and the development of mining technologies, but it is estimated that, at current consumption rates and technologies, the Earth will run out of tin that can be mined 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.

World tin mine reserves and reserve base in tons
Country Reserves Reserve base
1,700,000 3,500,000
1,000,000 1,200,000
710,000 1,000,000
800,000 900,000
540,000 2,500,000
450,000 900,000
300,000 350,000
170,000 250,000
150,000 300,000
  Other 180,000 200,000


Estimated economically recoverable
world tin reserves in million tons
1965 4,265
1970 3,930
1975 9,060
1980 9,100
1985 3,060
1990 7,100
2008 6,100


Secondary, or scrap, tin is also an important source of the metal and the recovery of tin through secondary production, or recycling of scrap tin, is increasing rapidly. While the United States has neither mined since 1993 nor smelted tin since 1989, it was the largest secondary producer, recycling nearly 14,000 tons in 2006.

New deposits are reported to be in southern Mongoliamarker, and in 2009, new deposits of tin were discovered in Colombia, South America, by the Seminole Enterprises Group.

Production

Tin is produced by reducing the ore with coal in a reverberatory furnace.

Mining and smelting

In 2006, total worldwide tin mine production was 321,000 tons, and smelter production was 340,000 tons. From its production level of 186,300 tons in 1991, around where it had hovered for the previous decades, production of tin shot up 89%, to 351,800 tons in 2005. Most of the increase came from China and Indonesia, with the largest spike in 2004–2005, when it increased 23%. While in the 1970s Malaysia was the largest producer, with around a third of world production, it has steadily fallen, and now remains a major smelter and market center.In 2007, the People's Republic of Chinamarker was the largest producer of tin, where the tin deposits are concentrated in the southeast Yunnan tin belt, with 43% of the world's share, followed by Indonesiamarker, with an almost equal share, and Perumarker at a distant third, reports the USGS.

The table below shows the countries with the largest mine production and the largest smelter output.

Mine and smelter production (tons), 2006
Country Mine production Smelter production
Chinamarker 114,300 129,400
Indonesiamarker 117,500 80,933
Perumarker 38,470 40,495
Boliviamarker 17,669 13,500
Thailandmarker 225 27,540
Malaysiamarker 2,398 23,000
Belgiummarker 0 8,000
Russiamarker 5,000 5,500
Congo-Kinshasa marker 15,000 0


After the discovery of tin in what is now Bisie, North Kivu in the Democratic Republic of Congo in 2002, illegal production has increased there to around 15,000 tons. This is largely fueling the ongoing and recent conflicts there, as well as affecting international markets.

Industry

The ten largest companies produced most of world's tin in 2007. It is not clear which of these companies include tin smelted from the mine at Bisie, Congo-Kinshasa, which is controlled by a renegade militia and produces 15,000 tons.Most of the world's tin is traded on the London Metal Exchangemarker (LME), from 8 countries, under 17 brands.

Largest tin mining companies by production in tons
Company Polity 2006 2007 %Change
Yunnan Tin China 52,339 61,129 16.7
PT Timah Indonesia 44,689 58,325 30.5
Minsur Peru 40,977 35,940 −12.3
Malay China 52,339 61,129 16.7
Malaysia Smelting Corp Malaysia 22,850 25,471 11.5
Thaisarco Thailand 27,828 19,826 −28.8
Yunnan Chengfeng China 21,765 18,000 −17.8
Liuzhou China Tin China 13,499 13,193 −2.3
EM Vinto Bolivia 11,804 9,448 −20.0
Gold Bell Group China 4,696 8,000 70.9


Prices of tin were at $11,900 per ton as of Nov 24, 2008. Prices reached an all-time high of nearly $25,000 per ton in May 2008, largely because of the effect of the decrease of tin production from Indonesia, and have been volatile because of reliance from mining in Congo-Kinshasa.

Applications

In 2006, the categories of tin use were solder (52%), tinplate (16%), chemicals (13%), brass and bronze (5.5%), glass (2%), and variety of other applications (11%)

Metal or alloy

Pewter plate
Tin is used by itself, or in combination with other elements for a wide variety of useful alloys. Tin is most commonly alloyed with copper. Pewter is 85–99% tin; Babbitt metal has a high percentage of tin as well. Bronze is mostly copper (12% tin), while addition of phosphorus gives phosphor bronze. Bell metal is also a copper-tin alloy, containing 22% tin.
Tin plated metal from can
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. A tinplate canister for preserving food was first manufactured in London in 1812. 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.

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").

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.

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 pipe for use of a drug such as cannabis or for a can of beer.

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.

Solder

A coil of lead-free solder wire
Tin has long been used as a solder in the form of an alloy with lead, tin comprising 5 to 70% w/w. Tin forms a eutectic mixture with lead containing 63% tin and 37% lead. Such solders are primarily used for solders for joining pipe or electric circuits. Since the European Union Waste Electrical and Electronic Equipment Directive (WEEED) and Restriction of Hazardous Substances Directive (RoHS) came into effect on 1 July 2006, the use of lead in such alloys has decreased. Replacing lead has many problems, including a higher melting point, and the formation of tin whiskers causing electrical problems. Replacement alloys are rapidly being found, however.

Organotin compounds

Organotin compounds have the widest range of uses of all main-group organometallic compounds, with an annual worldwide industrial production of probably exceeding 50,000 tonnes. Their major application is in the stabilization of halogenated PVC plastics, which would otherwise rapidly degrade under heat, light, and atmospheric oxygen, to give discolored, brittle products. It is believed that the tin scavenges labile chlorine ions (Cl-), which would otherwise initiate loss of HCl from the plastic material.

Organotin compounds have a relatively high toxicity, and for this they have been used for their biocidal effects in/as fungicides, pesticides, algacides, wood preservatives, and antifouling agents. Tributyltin oxide is used as a wood preservative. Tributyltin was used as additive for ship paint to prevent growth of marine organisms on ships. The use declined after organotin compounds were recognized as persistent organic pollutants with a extremely high toxicity for some marine organisms, for example the dog whelk. The EU banned the use of organotin compounds in 2003. Concerns over toxicity of these compounds to marine life and their effects over the reproduction and growth of some marine species, (some reports describe biological effects to marine life at a concentration of 1 nanogram per liter) have led to a worldwide ban by the International Maritime Organization. Many nations now restrict the use of organotin compounds to vessels over 25 meters long.

The Stille reaction couples organotin compounds with organic halides or pseudohalides.

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 salts are. The corrosion of tin plated food cans by acidic food and beverages has caused several intoxications with soluble tin compounds. Nausea, vomiting and diarrhea have been reported after ingesting canned food containing 200 mg/kg of tin. This observation led, for example, the Food Standards Agency in the UK to propose upper limits of 200 mg/kg. A study showed that 99.5% of the controlled food cans contain tin in an amount below that level.

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

See also



Notes



References

  1. Only H, F, P, Tl and Xe have a higher receptivity for NMR analysis for samples containing isotopes at their natural abundance.
  2. Oxford English Dictionary, 2nd edition, 1989.
  3. Encyclopedia Britannica, 11th Edition, 1911, s.v. 'tin', citing H. Kopp
  4. American Heritage Dictionary
  5. Martin Ewans. Afghanistan. Harper Collins, 2001. ISBN 0-06-050508-7
  6. Estimates vary between USGS and The British Geological Survey. The latter was chosen because it indicates that the most recent statistics are not estimates, and estimates match more closely with other estimates found for Congo-Kinshasa.


Bibliography

  • {{cite book
title = The Encyclopedia of the Chemical Elements
publisher = Reinhold Book Corporation
location = New York
year = 1968
editor = Clifford A. Hampel (editor)
id = LCCN 68-29938
last = MacIntosh
first = Robert M.
coauthors =
chapter = Tin
pages= 722–732
ref = CITEREF{Author}1968}}

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