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 and has two possible oxidation states, +2 and +4, with the +4 state being slightly more stable than the 2+ state. 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, SnO
2.
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 of steel.
Characteristics
Physical properties, allotropes, and tin pest
Tin is a
malleable,
ductile, and highly
crystalline silvery-white
metal. 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.
β-tin(the metallic form), which exists at room temperature and hotter, is malleable; while the α-tin(nonmetallic form), formed when tin is cooled below 13.2 °C, is brittle. It has a diamond cubic crystal structure, similar to diamond, silicon or germanium. α-tin has no metallic properties at all. It is a dull-gray powdery material with no common 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, increasing the durability of the tin.
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.
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 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.
Creation
Tin is created via the long
S-process in low-medium mass stars (.6 -> 10 solar masses). This takes thousands of years to do. It requires an
Indium atom to capture a
neutron and then undergo
Beta decay.
History
Antiquity
Tin extraction and use can be dated to the beginnings of the Bronze Age around 3000 BC, when it was observed that copper objects formed of polymetallic ores with different metal contents had different physical properties. The earliest bronze objects had tin or arsenic content of less than 2% and are therefore believed to be the result of unintentional alloying due to trace metal content in the copper ore It was soon discovered that the addition of tin or arsenic to copper increased its hardness and made casting much easier, which revolutionized metal working techniques and brought humanity from the Copper Age or Chalcolithic to the Bronze Age around 3000 BC.
The first evidence of tin use for making bronze appears in the Near East and the Balkans around 3000 BC. Demand for tin created a large and thriving network amongst Mediterranean cultures of Classical times. By the Medieval period, Iberia's and Germany's deposits lost importance and were largely forgotten while Devon and Cornwall began dominating the European tin market.
Other regions of the world developed tin mining industries at a much later date. In Africa, the Bantu culture extracted, smelted and exported tin between the 11th and 15th centuries AD,
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 have a coating of tin to inhibit rust. The original Ford Model T was known colloquially as the "Tin Lizzy".
Compounds and Chemistry
Tin forms the dioxide SnO
2 (cassiterite) when it is heated in the presence of
air. SnO
2 is
amphoteric and forms
stannate (SnO
32−) salts with bases and tin(IV) salts with acids. There are also stannates with the structure
[Sn(OH)
6]2−, like K
2[Sn(OH)
6], although the free stannic acid H
2[Sn(OH)
6] is unknown.
Tin combines directly with chlorine forming tin(IV) chloride, while reacting tin with hydrochloric acid in water gives tin(II) chloride and hydrogen gas. Several other compounds of tin exist in the +2 and +4 oxidation states, such as tin(II) sulfide and tin(IV) sulfide (Mosaic gold). There is only one hydride, however: stannane (SnH4), where tin is in the +4 oxidation state. as stannous fluoride (SnF2). Tin(II) fluoride can be mixed with calcium abrasives while the more common sodium fluoride gradually becomes biologically inactive combined with calcium compounds. 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:
Tin does not occur naturally by itself, and must be extracted from a base compound, usually cassiterite (SnO2). Cassiterite is 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 they contain the mineral, have a 1% tin oxide content.
Because of the higher specific gravity of tin dioxide, 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.
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 Mongolia,
-->
{| class="wikitable sortable" style="text-align:left;float:left"
|+World tin mine reserves and reserve base in tons with 43% of the world's share, followed by Indonesia, with an almost equal share, and Peru at a distant third, reports the USGS.
The table below shows the countries with the largest mine production and the largest smelter output.
{| class="wikitable sortable" style="text-align:left;float:left"
|+Mine and smelter production (tons), 2006
|-
!Country||Mine production||Smelter production
|-
|China
|114,300||129,400
|-
|Indonesia
|117,500||80,933
|-
|Peru
|38,470||40,495
|-
|Bolivia
|17,669||13,500
|-
|Thailand
|225||27,540
|-
|Malaysia
|2,398||23,000
|-
|Belgium
|0||8,000
|-
|Russia
|5,000||5,500
|-
|Congo-Kinshasa ('08)
|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 Exchange (LME), from 8 countries, under 17 brands.
{| class="wikitable sortable" style="text-align:left;float:left"
|+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, about half of tin produced was used in solder. The rest was divided between tin plating, tin chemicals, brass and bronze, and other uses. See graph at right.
Metal or alloy
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 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
Tin has long been used as a
solder in the form of an alloy with lead, tin accounting for 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
pipes 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 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, Many nations now restrict the use of organotin compounds to vessels over 25 meters long.
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.
See also
Stannary
Tinning
Cassiterides (the mythical Tin Islands)
Tin pest
Whisker (metallurgy) (tin whiskers)
Terne
Tin mining in Britain
Notes
References
Bibliography
External links
WebElements.com – Tin
Theodore Gray's Wooden Periodic Table Table: Tin samples and castings
Base Metals: Tin
Category:Chemical elements
Category:Poor metals
Category:Tin
