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indiumtinantimony
Ge

Sn

Pb
Appearance
silvery lustrous gray
General properties
Name, symbol, number tin, Sn, 50
Element category post-transition metal
Group, period, block 145, p
Standard atomic weight 118.710g·mol−1
Electron configuration [Kr] 4d10 5s2 5p2
Electrons per shell 2, 8, 18, 18, 4 (Image)
Physical properties
Phase solid
Density (near r.t.) (white) 7.365 g·cm−3
Density (near r.t.) (gray) 5.769 g·cm−3
Liquid density at m.p. 6.99 g·cm−3
Melting point 505.08 K, 231.93 °C, 449.47 °F
Boiling point 2875 K, 2602 °C, 4716 °F
Heat of fusion (white) 7.03 kJ·mol−1
Heat of vaporization (white) 296.1 kJ·mol−1
Specific heat capacity (25 °C) (white) 27.112 J·mol−1·K−1
Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k
at T/K 1497 1657 1855 2107 2438 2893
Atomic properties
Oxidation states 4, 2, -4 (amphoteric oxide)
Electronegativity 1.96 (Pauling scale)
Ionization energies 1st: 708.6 kJ·mol−1
2nd: 1411.8 kJ·mol−1
3rd: 2943.0 kJ·mol−1
Atomic radius 140 pm
Covalent radius 139±4 pm
Van der Waals radius 217 pm
Miscellanea
Crystal structure note Tetragonal (white), diamond cubic (gray)
Magnetic ordering (gray)diamagnetic[1], (white) paramagnetic
Electrical resistivity (0 °C) 115 nΩ·m
Thermal conductivity (300 K) 66.8 W·m−1·K−1
Thermal expansion (25 °C) 22.0 µm·m−1·K−1
Young's modulus 50 GPa
Shear modulus 18 GPa
Bulk modulus 58 GPa
Poisson ratio 0.36
Mohs hardness 1.5
Brinell hardness 51 MPa
CAS registry number 7440-31-5
Most stable isotopes
Main article: Isotopes of tin
iso NA half-life DM DE (MeV) DP
112Sn 0.97% 112Sn is stable with 62 neutrons
114Sn 0.66% 114Sn is stable with 64 neutrons
115Sn 0.34% 115Sn is stable with 65 neutrons
116Sn 14.54% 116Sn is stable with 66 neutrons
117Sn 7.68% 117Sn is stable with 67 neutrons
118Sn 24.22% 118Sn is stable with 68 neutrons
119Sn 8.59% 119Sn is stable with 69 neutrons
120Sn 32.58% 120Sn is stable with 70 neutrons
122Sn 4.63% 122Sn is stable with 72 neutrons
124Sn 5.79% 124Sn is stable with 74 neutrons
126Sn trace 2.3×105 y β 0.380 126Sb

Tin is a chemical element with the symbol Sn (Latin: Stannum) 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.

Contents

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.[2] 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.[3] 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.[2]

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.[4] 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.[5]

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.[4]

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.[2]

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(IV) chloride, while reacting tin with hydrochloric acid in water gives tin(II) chloride and hydrogen. 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 stable hydride, however: stannane (SnH4), where tin is in the +4 oxidation state.[2]

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[6][7] 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.[8] It has also been shown to be more effective than sodium fluoride in controlling gingivitis.[9]

Organotin compounds or stannanes are chemical compounds based on tin with hydrocarbon substituents.[10] 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 (Sn(C2H5)2I 2), 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 (R4Sn) always have a tetrahedral geometry at the tin atom. The halide derivatives R3SnX often form chained structures with Sn-X-Sn bridges. Alkyltin compounds are usually prepared via Grignard reagent reactions such as in:[11]

SnCl4 + 4 RMgBr → R4Sn + 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 SnMe4.[note 1][12]

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.[13] 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.[14]

The Latin name stannum originally meant an alloy of silver and lead, and came to mean 'tin' in the 4th century BCE[15]—the earlier Latin word for it was plumbum candidum 'white lead'. Stannum apparently came from an earlier stāgnum (meaning the same thing)[14], the origin of the Romance and Celtic terms for 'tin'.[14][16] The origin of stannum/stāgnum is unknown; it may be pre-Indo-European.[17] 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

Ceremonial giant dirk, 1500–1300 BC.
The alchemical symbol for tin. Also used as the glyph for Jupiter.

Tin is one of the earliest metals known.[18] 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.[19] 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.[20] [21]

As of 2001, the oldest tin mine found is in the Taurus Mountains in Turkey. Younger but still ancient tin mines are located in Spain, Brittany, and Great Britain.[20] European tin mining is believed to have started in Cornwall and perhaps on Dartmoor in Devon in Classical times, and a thriving tin trade developed with the civilizations of the Mediterranean.[22][23] Securing these strategically important sites is one reason why the Romans invaded and occupied Great Britain.[20]

View from Dolcoath Mine towards Redruth, c. 1890

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.[24]

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.[19]

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 Bolivian tin belt and the east Asian tin belt, stretching from China through Thailand and Laos to Malaya and Indonesia. Tasmania also hosts deposits of historical importance, most notably Mount Bischoff 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.[25]

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.[26]

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.[27]

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.[28] However Lester Brown has suggested tin could run out within 20 years based on an extremely conservative extrapolation of 2% growth per year.[29]

World tin mine reserves and reserve base in tons[30]
Country Reserves Reserve base
 China 1,700,000 3,500,000
 Malaysia 1,000,000 1,200,000
 Peru 710,000 1,000,000
 Indonesia 800,000 900,000
 Brazil 540,000 2,500,000
 Bolivia 450,000 900,000
 Russia 300,000 350,000
 Thailand 170,000 250,000
 Australia 150,000 300,000
  Other 180,000 200,000
Estimated economically recoverable
world tin reserves in million tons[27]
1965 4,265
1970 3,930
1975 9,060
1980 9,100
1985 3,060
1990 7,100
2008 6,100[31]

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.[30]

New deposits are reported to be in southern Mongolia,[32] and in 2009, new deposits of tin were discovered in Colombia, South America, by the Seminole Enterprises Group.[33][34]

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 China was the largest producer of tin, where the tin deposits are concentrated in the southeast Yunnan tin belt,[35] with 43% of the world's share, followed by Indonesia, with an almost equal share, and Peru at a distant third, reports the USGS.[31]

The table below shows the countries with the largest mine production and the largest smelter output.[note 2]

Mine and smelter production (tons), 2006[36]
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.[37] 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.[38]

Largest tin mining companies by production in tons[39]
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

TinConsChart.jpg

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%)[40]

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;[41] Babbitt metal has a high percentage of tin as well.[42][43] 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").[44]

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.[45][46]

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.[47] 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.[48] 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 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.[49]

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.[11]

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.[11] Tributyltin oxide is used as a wood preservative.[50]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.[51] The EU banned the use of organotin compounds in 2003.[52] Concerns over toxicity of these compounds to marine life and their effects over the reproduction and growth of some marine species,[11] (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.[53] Many nations now restrict the use of organotin compounds to vessels over 25 meters long.[11]

The Stille reaction couples organotin compounds with organic halides or pseudohalides.[54]

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.[55] This observation led, for example, the Food Standards Agency in the UK to propose upper limits of 200 mg/kg.[56] A study showed that 99.5% of the controlled food cans contain tin in an amount below that level.[57]

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

  1. ^ Only H, F, P, Tl and Xe have a higher receptivity for NMR analysis for samples containing isotopes at their natural abundance.
  2. ^ 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.

References

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  17. ^ American Heritage Dictionary
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  20. ^ a b c Emsley 2001, p. 447
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Bibliography

  • CRC contributors (2006). David R. Lide (editor). ed. Handbook of Chemistry and Physics (87th ed.). Boca Raton, Florida: CRC Press, Taylor & Francis Group. ISBN 0-8493-0487-3.  
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External links


1911 encyclopedia

Up to date as of January 14, 2010

From LoveToKnow 1911

TIN (Lat. stannum, whence the chemical symbol "Sn"; atomic weight =117.6, 0= 16), a metallic chemical element. Being a component of bronze, it was used as a metal thousands of years prior to the dawn of history; but it does not follow that prehistoric bronzes were made from metallic tin. When the unalloyed metal was first introduced cannot be ascertained with certainty. The "tin" of the Bible (KauoLTEpos in the Septuagint) corresponds to the Hebrew bedhil, which is really a copper alloy known as early as 1600 B.C. in Egypt. All we know is that about the 1st century the Greek word Kacroircpos designated tin, and that tin was imported from Cornwall into Italy after, if not before, the invasion of Britain by Julius Caesar. From Pliny's writings it appears that the Romans in his time did not realize the distinction between tin and lead: the former was called plumbum album or candidum to distinguish it from plumbum nigrum (lead proper). The word stannum definitely assumed its present meaning in the 4th century (H. Kopp). By the early Greek alchemists the metal was named Hermes, but at about the beginning of the 6th century, it was termed Zeusor Jupiter, and the symbol 2(assigned to it; it was also referred to as diabolus metallorum, on account of the brittle alloys which it formed.

Table of contents

Occurrence

Grains of metallic tin occur intermingled with the gold ores of Siberia, Guiana and Bolivia, and in a few other localities. Of minerals containing this element mention may be made of cassiterite or tinstone, Sn02, tin pyrites, Cu 4 SnS 4 + (Fe,Zn) 2 SnS 4; the metal also occurs in some epidotes, and in company with columbium, tantalum and other metals. Of these "tinstone" is of the greatest commercial importance. It occurs in its matrix, either in or closely associated with fissure veins or disseminated through rock masses. It is also found in the form of rolled lumps and grains, "stream tin," in alluvial gravels; the latter are secondary deposits, the products of the disintegration of the first-named primary deposits. Throughout the world, primary deposits of tinstone are in or closely connected with granite or acid eruptive rocks of the same type, its mineral associates being tourmaline, fluorspar, topaz, wolfram and arsenical pyrites, and the invariable gangue being quartz: the only exception to this mode of occurrence is to be found in Bolivia, where the tin ore occurs intimately associated with silver ores, bismuth ores and various sulphides, whilst the gangue includes barytes and certain carbonates. Over five-sixths of the world's total production is derived from secondary alluvial deposits, but all the tin obtained in Cornwall (the alluvial deposits having been worked out) and Bolivia is from vein mining, while a small portion of that yielded by Australasia comes from veins and from granitic rocks carrying disseminated tinstone.

Production

During the 18th century the world's supply of tin was mainly drawn from the deposits of England, Saxony and Bohemia; in 1801 England produced about 2500 tons, while the supplies of Saxony and Bohemia had been greatly diminished. The English supply increased, with some oscillations, to between six and seven thousand tons annually in the period 1840-1860, when it suddenly rose to about io,000 tons, and this figure was fairly well sustained until about 1890, when a period of depression set in; the yield for 1900 was 4336 tons, and for 1905 about 4200 tons. In the opening decades of the 19th century supplies began to be drawn from Banka; in 1820 this island contributed 1200 tons; the production was increased to 12,000 tons in 1900, when a diminution set in, 9960 tons being the output during 1905. Billiton became of note in 1853 with a production of 40 tons, which increased to 6000 in 1900 and has since declined to about 3000 tons in 1905. The Straits Settlements ranked as an important producer in 1870 with 2337 tons; it now supplies the greater part of the world's supply, contributing 46,795 tons in 1900, and over 60,000 tons in 1905. Australian deposits were worked in 1872, and in the following year the production was 3000 tons; the maximum outputs were in 1881-1883, averaging 10,000 tons annually; but the supply declined to 2420 tons in 1898 and has since increased to about 5028 tons in 1905. Bolivia produced 501 tons in 1883, 10,245 in 1900 and 12,500 in 1905.

The world's supply in 1900 was 72,911 long tons; this increased in 1904 to 97,790 tons, but in 1905, principally owing to a shortage in the supplies from the Straits and Banka, the yield fell to 94,089 tons.

Metallurgy

The operations in the metallurgy of tin may be enumerated as: (1) mining and dressing, (2) smelting, (3) refining. The first stage has for its purpose the production of a fairly pure tinstone; the second the conversion of the oxide into metallic tin; and the third preparing a tin pure enough for commercial purposes.

Mining and Dressing

The alluvial deposits are almost invariably worked opencast, those of the Malay Peninsula and Archipelago chiefly by Chinese labour: in a few instances hydraulic mining has been resorted to, and in other cases true underground mining is carried on; but the latter is both exceptional and difficult. The alluvial extracted, which in the Malay Peninsula and Archipelago carries from 5 to 60 lb of tinstone (or "black tin," as it is termed by Cornish miners) to the cubic yard of gravel, is washed in various simple sluicing appliances, by which the lighter clay, sand and stones are removed and tinstone is left behind comparatively pure, containing usually 65 to 75% of metallic tin (chemically pure tinstone contains 78.7%).

Lode tin, as tinstone derived from primary deposits is often termed, is mined in the ordinary method, the very hard gangue in which it occurs necessitating a liberal use of explosives. The veinstuff is broken small either by hand or in rock-breakers, and stamped to fine powder in stamp mills, which are practically large mechanically-worked pestles and mortars, the stamp proper weighing from 500 to moo lb. The mineral, crushed small enough to pass a sieve with perforations iu in. in diameter, leaves the stamps in suspension in water, and passes through a series of troughs in which the heavier mineral is collected; this then passes through a series of washing operations, which leaves a mixture consisting chiefly of tinstone and arsenical pyrites, which is calcined and washed again, until finally black tin containing about 60 to 65% of metal is left. The calcination is preferably effected in mechanical roasters, it being especially necessary to agitate the ore continually, otherwise it cakes. The crude tinstuff raised in Cornwall carries on an average a little over 2% of black tin. The Bolivian tin ore is treated by first extracting the silver by amalgamation, &c., and afterwards concentrating the residues; there are, however, considerable difficulties in the way of treating the poorer of these very complex ores, and several chemical processes for extracting their metallic contents have been worked out. Of the impurities of the ore the wolframite (tungstate of iron and manganese) is the most troublesome, because on account of its high specific gravity it cannot be washed away as gangue. To remove it, Oxland fuses the ore with a certain proportion of carbonate of soda, which suffices to convert the tungsten into soluble alkaline tungstate, without producing noteworthy quantities of soluble stannate from the oxide of tin; the tungstate is easily removed by treatment with water.

2. Smelting

The dressed ore is smelted with carbon by one of two main methods, viz. either in the shaft furnace or the reverberatory; the former is the better suited to stream tin, the latter to lode tin, but either ore can be smelted in either way, although reverberatory practice yields a purer metal. Shaft furnace smelting is confined to those parts of the world where charcoal can still be obtained in large quantities at moderate prices. The furnace consists of a shaft, circular (or more rarely rectangular) in plan, into which alternate layers of fuel and ore are charged, an air blast being generally injected near to the bottom of the furnace through one or more tuyeres. This was the primitive process all over the world; in the East, South America and similar regions it still holds its own. In Europe, Australasia and one large works at Singapore it has been practically replaced by the reverberatory furnace process, first introduced into Cornwall about the year 1700. In this process the purified ore is mixed with about one-fifth of its weight of a noncaking coal or anthracite smalls, the mixture being moistened to prevent it from being blown off by the draught, and is then fused on the sole of a reverberatory furnace for five or six hours. The slag and metal produced are then run off and the latter is cast into bars; these are in general contaminated with iron, arsenic, copper and other impurities.

3. Refining

All tin, except a small quantity produced by the shaft furnace process from exceptionally pure stream tin ore, requires refining by liquation and "boiling" before it is ready for the market. In the English process the bars are heated cautiously on an inclined hearth, when relatively pure tin runs off, while a skeleton of impure metal remains. The metal run off is further purified by poling, i.e. by stirring it with the branch of a tree - the apple tree being preferred traditionally. This operation is no doubt intended to remove the oxygen diffused throughout the metal as oxide, part of it perhaps chemically by reduction of the oxide to metal, the rest by conveying the finely diffused oxide to the surface and causing it to unite there with the oxide scum. After this the metal is allowed to rest for a time in the pot at a temperature above its freezing point and is then ladled out into ingot forms, care being taken at each stage to ladle off the top stratum. The original top stratum is the purest, and each succeeding lower stratum has a greater proportion of impurities; the lowest consists largely of a solid or semi-solid alloy of tin and iron.

To test the purity of the metal the tin-smelter heats the bars to a certain temperature just below the fusing point, and then strikes them with a hammer or lets them fall on a stone floor from a given height. If the tin is pure it splits into a mass of granular strings. Tin which has been thus manipulated and proved incidentally to be very pure is sold as grain tin. A lower quality goes by the name of block tin. Of the several commercial varieties Banka tin is the purest; it is indeed almost chemically pure. Next comes English grain tin.

For the preparation of chemically pure tin two methods are employed. (I) Commercially pure tin is treated with nitric acid, which converts the tin proper into the insoluble metastannic acid, while the copper, iron, &c., become nitrates; the metastannic acid is washed first with dilute nitric acid, then with water, and is lastly dried and reduced by fusion with black flux or potassium cyanide. (2) A solution of pure stannous chloride in very dilute hydrochloric acid is reduced with an electric current. According to Stolba, beautiful crystals of pure tin can be obtained as follows: A platinum basin, coated over with wax or paraffin outside, except a small circle at the very lowest point, is placed on a plate of amalgamated zinc, lying on the bottom of a beaker, and is filled with a solution of pure stannous chloride. The beaker also is cautiously filled with acidulated water up to a point beyond the edge of the platinum basin.

The whole is then left to itself, when crystals of tin gradually separate out on the bottom of the basin.

Properties

An ingot of tin is pure white (except for a slight tinge of blue); the colour depends, however, upon the temperature at which it is poured - if too low, the surface is dull, if too high, iridescent. It exhibits considerable lustre and is not subject to tarnishing on exposure to normal air. The metal is pretty soft and easily flattened out under the hammer, but almost devoid of tenacity. That it is elastic, with narrow limits, is proved by its clear ring when struck with a hard body in circumstances permitting of free vibration. The specific gravity of cast tin is 7.29, of rolled tin 7.299, and of electrically deposited tin 7.143 to 7.178. A tin ingot is distinctly crystalline; hence the characteristic crackling noise, or "cry" of tin, which a bar of tin gives out when being bent. This structure can be rendered visible by superficial etching with dilute acid; and as the minuter crystals dissolve more quickly than the larger ones, the surface assumes a frosted appearance (moiree metallique). The metal is dimorphous: by cooling molten tin at ordinary air temperature tetragonal crystals are obtained, while by cooling at a temperature just below the melting point rhombic forms are produced, When exposed for a sufficient time to very low temperatures (to - 39° C. for 14 hours), tin becomes so brittle that it falls into a grey powder, termed the grey modification, under a pestle; it indeed sometimes crumbles into powder spontaneously. At ordinary temperatures tin proves fairly ductile under the hammer, and its ductility seems to increase as the temperature rises up to about 100° C. At some temperature near its fusing point it becomes brittle, and still more brittle from - 14° C. downwards. Iron renders the metal hard and brittle; arsenic, antimony and bismuth (up to 0.5%) reduce its tenacity; copper and lead (1 to 2%) make it harder and stronger but impair its malleability; and stannous oxide reduces its tenacity. Tin fuses at about 230° C.; at a red heat it begins to volatilize slowly; at 1600° to 1800° C. it boils. The hot vapour produced combines with the oxygen of the air into white oxide, Sn02. Its coefficient of linear expansion between 0° and 100° is 0.002717; its specific heat 0.0562; its thermal and electrical conductivities are 145 to 152 and '14.5 to 140. i respectively compared to silver as two.

Industrial Applications

Commercially pure tin is used for making such apparatus as evaporating basins, infusion pots, stills, &c. It is also employed for making two varieties of tin-foil - one for the silvering of mirrors (see Mirror), the other for wrapping up chocolate, toilet soap, tobacco, &c. The mirror foil must contain some copper to prevent it from being too readily amalgamated by the mercury. For making tin-foil the metal is rolled into thin sheets, pieces of which are beaten out with a wooden mallet. As pure tin does not tarnish in the air and is proof against acid liquids, such as vinegar, lime juice, &c., it is utilized for culinary and domestic vessels. But it is expensive, and tin vessels have to be made very heavy to give them sufficient stability of form; hence it is generally employed merely as a protecting coating for utensils made essentially of copper or iron. The tinning of a copper basin is an easy operation. The basin, made scrupulously clean, is heated to beyond the fusing point of tin. Molten tin is then poured in, a little powdered salammoniac added, and the tin spread over the inside with a bunch of tow. The sal-ammoniac removes the last unavoidable film of oxide, leaving a purely metallic surface, to .which the tin adheres firmly. For tinning small objects of copper or brass (i.e. pins, hooks, &c.) a wet-way process is followed. One part of cream of tartar, two of alum and two of common salt are dissolved in boiling water, and the solution is boiled with granulated metallic tin (or, better, mixed with a little stannous chloride) to produce a tin solution; and into this the articles are put at a boiling heat. In the absence of metallic tin there is no visible change; but, as soon as the metal is introduced, an electrolytic action sets in and the articles get coated over with a firmly adhering film of tin. Tinning wrought iron is effected by immersion. The most important form of the operation is making tinned from ordinary sheet iron (making what is called "sheet tin"). This process was mentioned by Agricola; it was practised in Bohemia in 1620, and in England a century, later. The iron plates, having been carefully cleaned with sand and hydrochloric or sulphuric acid, and lastly with water, are plunged into heated tallow to drive away the water without oxidation of the metal. They are next steeped in a bath, first of molten ferruginous, then of pure tin. They are then taken out and kept suspended in hot tallow to enable the surplus tin to run off. The tin of the second bath dissolves iron gradually and becomes fit for the first bath. To tin cast-iron articles they must be decarburetted superficially by ignition within a bath of ferric oxide (powdered haematite or similar material), then cleaned with acid, and tinned by immersion, as explained above. (See TIN-Plate.) By far the greater part of the tin produced metallurgically is used for making tin alloys (see Pewter, Bronze).

Compounds of Tin. Tin forms two well-marked series of salts, in one of which it is divalent, these salts being derived from stannous oxide, SnO, in the other it is tetravalent, this series being derived from stannic oxide, Sn02.

Stannous Oxide, SnO, is obtained in the hydrated form Sn20(OH)2 from a solution of stannous chloride by addition of sodium carbonate; it forms a white precipitate, which can be washed with air-free water and dried at 80° C. without much change by oxidation; if it be heated in carbon dioxide the black SnO remains. Precipitated stannous hydrate dissolves readily in caustic potash; if the solution is evaporated quickly it suffers decomposition, with formation of metal and stannate, 2SnO+2KOH = K2Sn03+Sn+H20. If it is evaporated slowly, anhydrous stannous oxide crystallizes out in forms which are combinations of the cube and dodecahedron. Dry stannous oxide, if touched with a glowing body, catches fire and burns to stannic oxide, Sn02. Stannous oxalate when heated by itself in a tube leaves stannous oxide.

Stannic Oxide, Sn0 2. - This, if the term is taken to include the hydrates, exists in a variety of forms. (I) Tinstone (see above and also Cassiterite) is proof against all acids. Its disintegration for analytical purposes can be effected by fusion with caustic alkali in silver basins, with the formation of soluble stannate, or by fusion with sulphur and sodium carbonate, with the formation of a soluble thiostannate. (2) A similar oxide (flores jovis) is produced by burning tin in air at high temperatures or exposing any of the hydrates to a strong red heat. Such tin-ash, as it is called, is used for the polishing of optical glasses. Flores stanni is a finely divided mixture of the metal and oxide obtained by fusing the metal in the presence of air for some time. (3) Metastannic acid (generally written H10Sn5015, to account for the complicated composition of metastannates, e.g. the sodium salt H8Na2Sn501E) is the white compound produced from the metal by means of nitric acid. It is insoluble in water and in nitric acid and apparently so in hydrochloric acid; but if heated with this last for some time it passes into a compound, which, after the acid mother liquor has been decanted off, dissolves in water. The solution when subjected to distillation behaves very much like a physical solution of the oxide in hydrochloric acid, while a solution of orthostannic acid in hydrochloric acid behaves like a solution of SnC1 4 in water, i.e. gives off no hydrochloric acid, and no precipitate of hydrated Sn02. Metastannic acid is distinguished from orthostannic acid by its insolubility in nitric and sulphuric acids. The salts are obtained by the action of alkalies on the acid. (4) Orthostannic acid is obtained as a white precipitate on the addition of sodium carbonate or the exact quantity of precipitated calcium carbonate to a solution of the chloride. This acid, H 2 Sn0 3, is readily soluble in acids forming stannic salts, and in caustic potash and soda, with the formation of orthostannates. Of these sodium stannate, Na2Sn03, is produced industrially by heating tin with Chile saltpetre and caustic soda, or by fusing very finely powdered tinstone with caustic soda in iron vessels. A solution of the pure salt yields fine prisms of the composition Na2Sn03+10H20, which effloresce in the air. The salt is used as a mordant in dyeing and calico-printing. Alkaline and other stannates when treated with aqueous hydrofluoric acid are converted into fluostannates (e.g. K 2 SnO 3 into K2SnF6), which are closely analogous to, and isomorphous with, fluosilicates.

A colloidal or soluble stannic acid is obtained by dialysing a mixture of tin tetrachloride and alkali, or of sodium stannate and hydrochloric acid. On heating it is converted into colloidal metastannic acid.

A hydrated tin trioxide, Sn03, was obtained by Spring by adding barium dioxide to a solution of stannous chloride and hydrochloric acid; the solution is dialysed, and the colloidal solution is evaporated to form a white mass of 2Sn03 H20.

Stannous Chloride, SnC1 2, can only be obtained pure by heating pure tin in a current of pure dry hydrochloric acid gas. It is a white solid, fusing at 250° C. to an oily liquid which boils at 606°, and volatilizing at a red heat in nitrogen, a vacuum or hydrochloric acid, without decomposition. The vapour density below 700° C. corresponds to Sn2C14, above Soo° C. to nearly SnCl 2. The chloride readily combines with water to form a crystallizable hydrate SnCl 2.2H 2 O, known as "tin salt" or "tin crystals." This salt is also formed by dissolving tin in strong hydrochloric acid and allowing it to crystallize, and is industrially prepared by passing sufficiently hydrated hydrochloric acid gas over granulated tin contained in stoneware bottles and evaporating the concentrated solution produced in tin basins over granulated tin. The basin itself is not attacked. The crystals are very soluble in cold water, and if the salt is really pure a small proportion of water forms a clear solution; but on adding much water most of the salt is decomposed, with the formation of a precipitate of oxychloride, 2Sn(OH)Cl H20. According to Michel and Kraft, one litre of cold saturated solution of tin crystals weighs 1827 grammes and contains 1333 grammes of SnCl 2. The same oxychloride is produced when the moist crystals, or their solution, are exposed to the air. Hence all tin crystals as kept in the laboratory give with water a turbid solution, which contains stannic in addition to stannous chloride. The complete conversion of stannous into stannic chloride may be effected by a great many reagents - for instance, by chlorine (bromine, iodine) readily; by mercuric chloride in the heat, with precipitation of calomel or metallic mercury; by ferric chloride in the heat, with formation of ferrous chloride; by arsenious chloride in strongly hydrochloric solutions, with precipitation of chocolate-brown metallic arsenic. All these reactions are available as tests for "stannosum" or the respective agents. In opposition to stannous chloride, even sulphurous acid (solution) behaves as an oxidizing agent. If the two reagents are mixed a precipitate of yellow stannic sulphide is produced. A strip of metallic zinc when placed in a solution of stannous chloride precipitates the tin in crystals and takes its place in the solution. Stannous chloride is largely used in the laboratory as a reducing agent, in dyeing as a mordant.

Stannic Chloride, SnC1 4, named by Andreas Libavius in 1605 Spiritus argenti vivi sublimate from its preparation by distilling tin or its amalgam with corrosive sublimate, and afterwards termed Spiritus fumans Libavii, is obtained by passing dry chlorine over granulated tin contained in a retort; the tetrachloride distils over as a heavy liquid, from which the excess of chlorine is easily removed by shaking with a small quantity of tin filings and re-distilling. It is a colourless fuming liquid of specific gravity 2.269 at o°; it freezes at - 33° C., and boils at I13.9°. The chloride unites energetically with water to form crystalline hydrates (e.g. SnC1 4.3H 2 O), easily soluble in water. With one-third its weight of water it forms the so-called "butter of tin." It combines readily with alkaline and other chlorides to form double salts, e.g. M 2 SnC1 61 analogous to the chloroplatinates; the salt (NH 4) 2 SnC1 6 is known industrially as - "pink salt" on account of its use as a mordant to produce a pink colour. The oxymuriate of tin used by dyers is SnCl4.5H20. The plain chloride solution is similarly used. It is usually prepared by dissolving the metal in aqua regia.

Stannous Fluoride, SnF 2, is obtained as small, white monoclinic tables by evaporating a solution of stannous oxide in hydrofluoric acid in a vacuum. Stannic Fluoride, SnF 4, is obtained in solution by dissolving hydrated stannic oxide in hydrofluoric acid; it forms a characteristic series of salts, the stannofluorides, M 2 SnF 6, isomorphous with the silico-, titano-, germanoand zirconofluorides. Stannous bromide, SnBr 2, is a light yellow substance formed from tin and hydrobromic acid. Stannic bromide, SnBr 4, is a white crystalline mass, melting at 33° and boiling at 201°, obtained by the combination of tin and bromine, preferably in carbon bisulphide solution. Stannous iodide, Sn12, forms yellow red needles, and is obtained from potassium iodide and stannous chloride. Stannic iodide, Sn14, forms red octahedra and is prepared similarly to stannic bromide. Both iodides combine with ammonia.

Stannous sulphide, SnS, is obtained as a lead-grey mass by heating tin with sulphur, and as a brown precipitate by adding sulphuretted hydrogen to a stannous solution; this is soluble in ammonium polysulphide, and dries to a black powder. Stannic sulphide, SnS 2, is obtained by heating a mixture of tin (or, better, tin amalgam), sulphur and sal-ammoniac in proper proportions in the beautiful form of aurum musivum (mosaic gold) - a solid consisting of golden yellow, metallic lustrous scales, and used chiefly as a yellow "bronze" for plaster-of-Paris statuettes, &c. The yellow precipitate of stannic sulphide obtained by adding sulphuretted hydrogen to a stannic solution readily dissolves in solutions of the alkaline sulphides to form thiostannates of the formula M 2 SnS 31 the free acid, H2SnS3, may be obtained as an almost black powder by drying the yellow precipitate formed when hydrochloric acid is added to a solution of a thiostannate.

Analysis

Tin compounds when heated on charcoal with sodium carbonate or potassium cyanide in the reducing blowpipe flame yield the metal and a scanty ring of white Sn02. Stannous salt solutions yield a brown precipitate of SnS with sulphuretted hydrogen, which is insoluble in cold dilute acids and in real sulphide of ammonium, (NH 4) 2 S; but the yellow, or the colourless reagent on addition of sulphur, dissolves the precipitate as SnS 2 salt. The solution on acidification yields a yellow precipitate of this sulphide. Stannic salt solutions give a yellow precipitate of SnS 2 with sulphuretted hydrogen, which is insoluble in cold dilute acids but readily soluble in sulphide of ammonium, and is re-precipitated therefrom as SnS2 on acidification. Only stannous salts (not stannic) give a precipitate of calomel in mercuric chloride solution. A mixture of stannous and stannic chloride, when added to a sufficient quantity of solution of chloride of gold, gives an intensely purple precipitate of gold purple (purple of Cassius). The test is very delicate, although the colour is not in all cases a pure purple. Tin is generally quantitatively estimated as the dioxide. The solutions are oxidized, precipitated with ammonia, the precipitate dissolved in hydrochloric acid, and re-thrown down by boiling with sodium sulphate. The precipitate is filtered, washed, dried and ignited.

BIBLIOGRAPHY. - FOr the history of tin and statistics of its production, &c., see Bernard Neumann, Die Metalle (1904); A. Rossing, Geschichte der Metalle (1901). For its chemistry see Roscoe and Schorlemmer, Treatise on Inorganic Chemistry, vol. ii.; H. Moissan, Traite de chimie minerale; 0. Dammer, Handbuch der anorganischen Chemie. For its production and metallurgy see Sydney Fawns, Tin Deposits of the World; A. G. Charleton, Tin Mining; Henry Louis, The Production of Tin, and C. Schnabel, Handbook of Metallurgy (English trans. by Louis, 1907). General statistical information, and improvements in the metallurgy, &c., are recorded annually in The Mineral Industry.


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Heb. bedil (Num. 31:22; Ezek. 22:18, 20), a metal well known in ancient times. It is the general opinion that the Phoenicians of Tyre and Sidon obtained their supplies of tin from the British Isles. In Ezek. 27:12 it is said to have been brought from Tarshish, which was probably a commercial emporium supplied with commodities from other places. In Isa. 1:25 the word so rendered is generally understood of lead, the alloy with which the silver had become mixed (ver. 22). The fire of the Babylonish Captivity would be the means of purging out the idolatrous alloy that had corrupted the people.

This entry includes text from Easton's Bible Dictionary, 1897.

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Simple English

Tin is a chemical element. It is chemical element 50 on the periodic table (the number tells us where the element is found on the table). The chemical symbol for tin is Sn. It is in Group 14 on the periodic table. It is not radioactive.

Contents

Properties

Physical properties

File:Zinn
Alpha(α) and beta(β) forms of tin

Tin is a silver, somewhat soft metal. It is a post-transition metal. Its melting point is 231.93°C and its boiling point is 2602°C. It can melt easily in a flame. It is malleable. It makes a crackling sound called tin cry when a piece of it is bent. Tin has more non-radioactive isotopes than any other element.

Tin is found in two allotropes: alpha-tin and beta-tin. Alpha-tin is a brittle, dull, powdery, nonmetallic form of tin. It is made when very pure tin is cooled. Beta-tin is the normal shiny, soft, conductive, metallic form. It is made at higher temperatures. The decay of tin by turning from beta-tin to alpha-tin is called tin pest. Alpha-tin is not wanted in many places. When small amounts of other elements like antimony are added, the tin cannot change into alpha-tin. When alpha-tin is heated, it changes into beta-tin.

Tin can be hardened by adding antimony or copper, as well as some other elements. These also make it resistant to tin pest. Tin can also be made very shiny. Tin can make an alloy with copper called bronze.

Chemical properties

Tin is corrosion resistant to many things. Salt water and fresh water do not affect it. It does dissolve in strong acids to make tin(II) salts. It reacts with some strong bases. Tin can act as a catalyst to make other things corrode when both of them are in a water solution that has dissolved oxygen.

Chemical compounds

Tin forms chemical compounds in two oxidation states: +2 and +4. +2 compounds are reducing agents. Some of them are colorless while others are colored. +4 compounds are more unreactive and act more covalent.

Tin burns in air to make tin(IV) oxide, which is white. Tin(IV) oxide dissolves in acids to make other tin(IV) compounds. Tin(IV) chloride is a colorless fuming liquid when anhydrous and a white solid when hydrated. It easily reacts with water to make tin(IV) oxide and an acid again.

Tin reacts with hydrohalic acids to make tin(II) halides. For example, tin(II) chloride is made when tin dissolves in hydrochloric acid. Tin(IV) halides are made when tin reacts with the halogens. Tin(IV) chloride is made when tin reacts with chlorine. Tin(II) sulfate is different as it does not oxidize to tin(IV) sulfate. Tin(II) oxide is a blue-black solid that burns in air to make tin(IV) oxide.

Occurrence

[[File:|thumb|Cassiterite]] Tin is not found as a metal in the ground. It is normally in the form of cassiterite. Cassiterite is a mineral containg tin(IV) oxide. The cassiterite is normally found downstream of the cassiterite deposit when it is by a stream or river. Tin is also found in some complicated sulfide minerals.

Tin does not have any major job in the human body.

Preparation

Tin is made by heating cassiterite with carbon in a furnace. China is the biggest maker of tin.

History

People discovered tin long ago and used it with other metals. When copper and tin are mixed together, bronze is made. Bronze was important in the past, because it was one of the strongest metals available, which meant it was useful in weapons and tools. Bronze changed the world when it was first invented, starting the Bronze Age. People organized themselves more, because making tools from bronze was harder than making them from rock and wood like they did before.

Uses

File:Pewterplate
Pewter plate
File:Ex Lead
Tin solder without lead

Tin is used in solder. Solder used to contain a mixture of lead and tin. Now the lead is removed because of its toxicity.

Tin is also used to make pewter, which is mainly tin mixed with a small amount of copper and other metals. Babbitt metal also has tin in it. Tin is used to coat several metals, like lead and steel. Tin plated steel containers are used to store foods. The pipes on a pipe organ are made of tin. Tin foil was used before aluminium foil. Tin was one of the first superconductors to be found. Organotin compounds are more common than almost any other organometal compound. They are used in some PVC pipes to stop them from decaying. Organotin compounds are toxic, though.

Safety

Tin is not toxic, but tin compounds are very toxic to marine life. They are a little toxic to humans.

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