Tin

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Tin,  ₅₀Sn

Tin
Allotropes	alpha, α (gray); beta, β (white)
Appearance	silvery-white (beta, β) or gray (alpha, α)
Standard atomic weight Ar, std(Sn)	118.710(7)
Tin in the periodic table
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson Ge ↑ Sn ↓ Pb indium ← tin → antimony
Atomic number (Z)	50
Group	group 14 (carbon group)
Period	period 5
Block	p-block
Element category	post-transition metal
Electron configuration	[Kr] 4d10 5s2 5p2
Electrons per shell	2, 8, 18, 18, 4
Physical properties
Phase at STP	solid
Melting point	505.08 K ​(231.93 °C, ​449.47 °F)
Boiling point	2875 K ​(2602 °C, ​4716 °F)
Density (near r.t.)	white, β: 7.265 g/cm3 gray, α: 5.769 g/cm3
when liquid (at m.p.)	6.99 g/cm3
Heat of fusion	white, β: 7.03 kJ/mol
Heat of vaporization	white, β: 296.1 kJ/mol
Molar heat capacity	white, β: 27.112 J/(mol·K)
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, −3, −2, −1, +1, +2, +3, +4 (an amphoteric oxide)
Electronegativity	Pauling scale: 1.96
Ionization energies	1st: 708.6 kJ/mol 2nd: 1411.8 kJ/mol 3rd: 2943.0 kJ/mol
Atomic radius	empirical: 140 pm
Covalent radius	139±4 pm
Van der Waals radius	217 pm
Spectral lines of tin
Other properties
Natural occurrence	primordial
Crystal structure	​body-centered tetragonal white (β)
Crystal structure	​face-centered diamond-cubic gray (α)
Speed of sound thin rod	2730 m/s (at r.t.) (rolled)
Thermal expansion	22.0 µm/(m·K) (at 25 °C)
Thermal conductivity	66.8 W/(m·K)
Electrical resistivity	115 nΩ·m (at 0 °C)
Magnetic ordering	gray: diamagnetic white (β): paramagnetic
Magnetic susceptibility	(white) +3.1·10−6 cm3/mol (298 K)
Young's modulus	50 GPa
Shear modulus	18 GPa
Bulk modulus	58 GPa
Poisson ratio	0.36
Brinell hardness	50–440 MPa
CAS Number	7440-31-5
History
Discovery	around 3500 BC
Main isotopes of tin
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct 112Sn 0.97% stable 114Sn 0.66% stable 115Sn 0.34% stable 116Sn 14.54% stable 117Sn 7.68% stable 118Sn 24.22% stable 119Sn 8.59% stable 120Sn 32.58% stable 122Sn 4.63% stable 124Sn 5.79% stable 126Sn trace 2.3×105 y β− 126Sb

Tin is a chemical element with the symbol Sn (from Latin: stannum) and atomic number 50. It is a post-transition metal in group 14 of the periodic table of elements. It is obtained chiefly from the mineral cassiterite, which contains stannic oxide, SnO₂. Tin shows a chemical similarity to both of its neighbors in group 14, germanium and lead, and has two main oxidation states, +2 and the slightly more stable +4. Tin is the 49th most abundant element and has, with 10 stable isotopes, the largest number of stable isotopes in the periodic table, thanks to its magic number of protons. It has two main allotropes: at room temperature, the stable allotrope is β-tin, a silvery-white, malleable metal, but at low temperatures it transforms into the less dense grey α-tin, which has the diamond cubic structure. Metallic tin does not easily oxidize in air.

The first tin alloy used on a large scale was bronze, made of 1/8 tin and 7/8 copper, from as early as 3000 BC. After 600 BC, pure metallic tin was produced. Pewter, which is an alloy of 85–90% 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, which are typically 60% or more tin, and in the manufacture of transparent, electrically conducting films of indium tin oxide in optoelectronic applications. Another large application for tin is corrosion-resistant tin plating of steel. Because of the low toxicity of inorganic tin, tin-plated steel is widely used for food packaging as tin cans. However, some organotin compounds can be almost as toxic as cyanide.

Characteristics

Physical

Droplet of solidified molten tin

 

Tin is a soft, 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 from the twinning of the crystals. Tin melts at low temperatures of about 232 °C (450 °F), the lowest in group 14. The melting point is further lowered to 177.3 °C (351.1 °F) for 11 nm particles.

β-tin (the metallic form, or white tin, BCT structure), which is stable at and above room temperature, is malleable. In contrast, α-tin (nonmetallic form, or gray tin), which is stable below 13.2 °C (55.8 °F), is brittle. α-tin has a diamond cubic crystal structure, similar to diamond, silicon or germanium. α-tin has no metallic properties at all because its atoms form a covalent structure in which electrons cannot move freely. It is a dull-gray powdery material with no common uses other than a few specialized semiconductor applications. These two allotropes, α-tin and β-tin, are more commonly known as gray tin and white tin, respectively. Two more allotropes, γ and σ, exist at temperatures above 161 °C (322 °F)  and pressures above several GPa. In cold conditions, β-tin tends to transform spontaneously into α-tin, a phenomenon known as "tin pest". Although the α-β transformation temperature is nominally 13.2 °C (55.8 °F), impurities (e.g. Al, Zn, etc.) lower the transition temperature well below 0 °C (32 °F) and, on the addition of antimony or bismuth, the transformation might not occur at all, increasing the durability of the tin.

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 few elements have appreciable solid solubility in tin. Simple eutectic systems, however, occur with bismuth, gallium, lead, thallium and zinc.

Tin becomes a superconductor below 3.72 K and 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.

Chemical

Tin resists corrosion from water, but can be attacked by acids and alkalis. Tin can be highly polished and is used as a protective coat for other metals. A protective oxide (passivation) layer prevents further oxidation, the same that forms on pewter and other tin alloys. Tin acts as a catalyst when oxygen is in solution and helps to accelerate the chemical reaction.

Isotopes

Tin has ten stable isotopes, with atomic masses of 112, 114 through 120, 122 and 124, the greatest number of any element. Of these, the most abundant are ¹²⁰Sn (almost a third of all tin), ¹¹⁸Sn, and ¹¹⁶Sn, while the least abundant is ¹¹⁵Sn. The isotopes with even mass numbers have no nuclear spin, while those with odd have a spin of +1/2. Tin, with its three common isotopes ¹¹⁶Sn, ¹¹⁸Sn and ¹²⁰Sn, is among the easiest elements to detect and analyze by NMR spectroscopy, and its chemical shifts are referenced against SnMe
₄.

This large number of stable isotopes is thought to be a direct result of the atomic number 50, a "magic number" in nuclear physics. Tin also occurs in 29 unstable isotopes, encompassing all the remaining atomic masses from 99 to 137. Apart from ¹²⁶Sn, with a half-life of 230,000 years, all the radioisotopes have a half-life of less than a year. The radioactive ¹⁰⁰Sn, discovered in 1994, and ¹³²Sn are one of the few nuclides with a "doubly magic" nucleus: despite being unstable, having very lopsided proton–neutron ratios, they represent endpoints beyond which stability drops off rapidly. Another 30 metastable isomers have been characterized for isotopes between 111 and 131, the most stable being ^121mSn with a half-life of 43.9 years.

The relative differences in the abundances of tin's stable isotopes can be explained by their different modes of formation in stellar nucleosynthesis. ¹¹⁶Sn through ¹²⁰Sn inclusive are formed in the s-process (slow neutron capture) in most stars and hence they are the most common isotopes, while ¹²²Sn and ¹²⁴Sn are only formed in the r-process (rapid neutron capture) in supernovae and are less common. (The isotopes ¹¹⁷Sn through ¹²⁰Sn also receive contributions from the r-process.) Finally, the rarest proton-rich isotopes, ¹¹²Sn, ¹¹⁴Sn, and ¹¹⁵Sn, cannot be made in significant amounts in the s- or r-processes and are considered among the p-nuclei, whose origins are not well understood yet. Some speculated mechanisms for their formation include proton capture as well as photodisintegration, although ¹¹⁵Sn might also be partially produced in the s-process, both directly, and as the daughter of long-lived ¹¹⁵In.

Etymology

The word tin is shared among Germanic languages and can be traced back to reconstructed Proto-Germanic *tin-om; cognates include German Zinn, Swedish tenn and Dutch tin. It is not found in other branches of Indo-European, except by borrowing from Germanic (e.g., Irish tinne from English).

The Latin name stannum originally meant an alloy of silver and lead, and came to mean 'tin' in the 4th century—the earlier Latin word for it was plumbum candidum, or "white lead". Stannum apparently came from an earlier stāgnum (meaning the same substance), 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 Konversations-Lexikon speculates on the contrary that stannum is derived from (the ancestor of) Cornish stean, and is proof that Cornwall in the first centuries AD was the main source of tin.

History

Ceremonial giant bronze dirk of the Plougrescant-Ommerschans type, Plougrescant, France, 1500–1300 BC.

 

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 a 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. The addition of a second metal to copper increases its hardness, lowers the melting temperature, and improves the casting process by producing a more fluid melt that cools to a denser, less spongy metal. This was an important innovation that allowed for the much more complex shapes cast in closed molds of the Bronze Age. Arsenical bronze objects appear first in the Near East where arsenic is commonly found in association with copper ore, but the health risks were quickly realized and the quest for sources of the much less hazardous tin ores began early in the Bronze Age. This created the demand for rare tin metal and formed a trade network that linked the distant sources of tin to the markets of Bronze Age cultures.

Cassiterite (SnO₂), the tin oxide form of tin, was most likely the original source of tin in ancient times. Other forms of tin ores are less abundant sulfides such as stannite that require a more involved smelting process. Cassiterite often accumulates in alluvial channels as placer deposits because it is harder, heavier, and more chemically resistant than the accompanying granite. Cassiterite is usually black or generally dark in color, and these deposits can be easily seen in river banks. Alluvial (placer) deposits could be easily collected and separated by methods similar to gold panning.

Compounds and chemistry

In the great majority of its compounds, tin has the oxidation state II or IV.

Inorganic compounds

Halide compounds are known for both oxidation states. For Sn(IV), all four halides are well known: SnF₄, SnCl₄, SnBr₄, and SnI₄. The three heavier members are volatile molecular compounds, whereas the tetrafluoride is polymeric. All four halides are known for Sn(II) also: SnF₂, SnCl₂, SnBr₂, and SnI₂. All are polymeric solids. Of these eight compounds, only the iodides are colored.

Tin(II) chloride (also known as stannous chloride) is the most important tin halide in a commercial sense. Illustrating the routes to such compounds, chlorine reacts with tin metal to give SnCl₄ whereas the reaction of hydrochloric acid and tin produces SnCl₂ and hydrogen gas. Alternatively SnCl₄ and Sn combine to stannous chloride by a process called comproportionation:

SnCl₄ + Sn → 2 SnCl₂

Tin can form many oxides, sulfides, and other chalcogenide derivatives. The dioxide SnO₂ (cassiterite) forms when tin is heated in the presence of air. SnO₂ is amphoteric, which means that it dissolves in both acidic and basic solutions. Stannates with the structure [Sn(OH)₆]²⁻, like K₂[Sn(OH)₆], are also known, though the free stannic acid H₂[Sn(OH)₆] is unknown. 

Sulfides of tin exist in both the +2 and +4 oxidation states: tin(II) sulfide and tin(IV) sulfide (mosaic gold).

Ball-and-stick models of the structure of solid stannous chloride (SnCl₂).

Hydrides

Stannane (SnH₄), with tin in the +4 oxidation state, is unstable. Organotin hydrides are however well known, e.g. tributyltin hydride (Sn(C₄H₉)₃H). These compound release transient tributyl tin radicals, which are rare examples of compounds of tin(III).

Organotin compounds

Organotin compounds, sometimes called stannanes, are chemical compounds with tin–carbon bonds. Of the compounds of tin, the organic derivatives are the most useful commercially. Some organotin compounds are highly toxic and have been used as biocides. The first organotin compound to be reported was diethyltin diiodide ((C₂H₅)₂SnI₂), reported by Edward Frankland in 1849.

Most organotin compounds are colorless liquids or solids that are stable to air and water. They adopt tetrahedral geometry. Tetraalkyl- and tetraaryltin compounds can be prepared using Grignard reagents:

SnCl
₄ + 4 RMgBr → R
₄Sn + 4 MgBrCl

The mixed halide-alkyls, which are more common and more important commercially than the tetraorgano derivatives, are prepared by redistribution reactions:

SnCl
₄ + R
₄Sn → 2 SnCl₂R₂

Divalent organotin compounds are uncommon, although more common than related divalent organogermanium and organosilicon compounds. The greater stabilization enjoyed by Sn(II) is attributed to the "inert pair effect". Organotin(II) compounds include both stannylenes (formula: R₂Sn, as seen for singlet carbenes) and distannylenes (R₄Sn₂), which are roughly equivalent to alkenes. Both classes exhibit unusual reactions.

Occurrence

Sample of cassiterite, the main ore of tin.

 

Granular pieces of cassiterite, collected by placer mining

 

Tin is generated via the long s-process in low-to-medium mass stars (with masses of 0.6 to 10 times that of Sun), and finally by beta decay of the heavy isotopes of indium.

Tin is the 49th most abundant element in 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 as the native element but must be extracted from various ores. Cassiterite (SnO₂) 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 associated with granite rock, usually at a level of 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 the sea. The most economical ways of mining tin are by dredging, hydraulicking, or open pits. Most of the world's tin is produced from placer deposits, which can contain as little as 0.015% tin.

About 253,000 tonnes of tin have been mined in 2011, mostly in China (110,000 t), Indonesia (51,000 t), Peru (34,600 t), Bolivia (20,700 t) and Brazil (12,000 t). 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 mine-able tin in 40 years. 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. Recovery of tin through secondary production, or recycling of scrap tin, is increasing rapidly. Whereas the United States has neither mined since 1993 nor smelted tin since 1989, it was the largest secondary producer, recycling nearly 14,000 tonnes in 2006.

New deposits are reported in southern Mongolia, and in 2009, new deposits of tin were discovered in Colombia by the Seminole Group Colombia CI, SAS.

Production

Tin is produced by carbothermic reduction of the oxide ore with carbon or coke. Both reverberatory furnace and electric furnace can be used.

Mining and smelting

Industry

Candlestick made of tin

 

The ten largest companies produced most of the world's tin in 2007. Most of the world's tin is traded on the London Metal Exchange (LME), from 8 countries, under 17 brands.

An International Tin Council was established in 1947 to control the price of tin, until it collapsed in 1985. In 1984, an Association of Tin Producing Countries was created, with Australia, Bolivia, Indonesia, Malaysia, Nigeria, Thailand, and Zaire as members.

Price and exchanges

World production and price (US exchange) of tin.

 

Tin is unique among other mineral commodities because of the complex agreements between producer countries and consumer countries dating back to 1921. The earlier agreements tended to be somewhat informal and sporadic and led to the "First International Tin Agreement" in 1956, the first of a continuously numbered series that effectively collapsed in 1985. Through this series of agreements, the International Tin Council (ITC) had a considerable effect on tin prices. The ITC supported the price of tin during periods of low prices by buying tin for its buffer stockpile and was able to restrain the price during periods of high prices by selling tin from the stockpile. This was an anti-free-market approach, designed to assure a sufficient flow of tin to consumer countries and a profit for producer countries. However, the buffer stockpile was not sufficiently large, and during most of those 29 years tin prices rose, sometimes sharply, especially from 1973 through 1980 when rampant inflation plagued many world economies.

During the late 1970s and early 1980s, the U.S. Government tin stockpile was in an aggressive selling mode, partly to take advantage of the historically high tin prices. The sharp recession of 1981–82 proved to be quite harsh on the tin industry. Tin consumption declined dramatically. The ITC was able to avoid truly steep declines through accelerated buying for its buffer stockpile; this activity required the ITC to borrow extensively from banks and metal trading firms to augment its resources. The ITC continued to borrow until late 1985 when it reached its credit limit. Immediately, a major "tin crisis" followed — tin was delisted from trading on the London Metal Exchange for about three years, the ITC dissolved soon afterward, and the price of tin, now in a free-market environment, plummeted sharply to $4 per pound and remained at that level through the 1990s. The price increased again by 2010 with a rebound in consumption following the 2008–09 world economic crisis, accompanying restocking and continued growth in consumption by the world's developing economies.

London Metal Exchange (LME) is the principal trading site for tin. Other tin contract markets are Kuala Lumpur Tin Market (KLTM) and Indonesia Tin Exchange (INATIN).

The price per kg over years: 

Tin (US$ per kg)

	2008	2009	2010	2011	2012
Price	18.51	13.57	20.41	26.05	21.13

Applications

World consumption of refined tin by end use, 2006

 

In 2006, about half of all tin produced was used in solder. The rest was divided between tin plating, tin chemicals, brass and bronze alloys, and niche uses.

Solder

A coil of lead-free solder wire

 

Tin has long been used in alloys with lead as solder, in amounts 5 to 70% w/w. Tin with lead forms a eutectic mixture at the weight proportion of 61.9% tin and 38.1% lead (the atomic proportion: 73.9% tin and 26.1% lead), with melting temperature of 183 °C (361.4 °F) . Such solders are primarily used for joining pipes or electric circuits. Since the European Union Waste Electrical and Electronic Equipment Directive (WEEE Directive) and Restriction of Hazardous Substances Directive came into effect on 1 July 2006, the lead content in such alloys has decreased. Replacing lead has many problems, including a higher melting point, and the formation of tin whiskers causing electrical problems. Tin pest can occur in lead-free solders, leading to loss of the soldered joint. Replacement alloys are rapidly being found, although problems of joint integrity remain.

Tin plating

Tin bonds readily to iron and is used for coating lead, 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", while speakers of American English call them "cans" or "tin cans". One derivation of such use is the slang term "tinnie" or "tinny", meaning "can of beer" in Australia. The tin whistle is so called because it was first mass-produced in tin-plated steel. Copper cooking vessels such as saucepans and frying pans are frequently lined with a thin plating of tin, since the combination of acid foods with copper can be toxic.

Specialized alloys

Pewter plate

 

Tin in combination with other elements forms a wide variety of useful alloys. Tin is most commonly alloyed with copper. Pewter is 85–99% tin; bearing 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 has sometimes been used in coinage; for example, it once formed a single-digit percentage (usually five percent or less) of American and Canadian pennies. Because copper is often the major metal in such coins, sometimes including zinc, these could be called bronze and/or brass alloys. 

Tin plated metal from a can.

 

Artisan Alfonso Santiago Leyva and his son working with tin sheets.

 

The niobium–tin compound Nb₃Sn is commercially used in coils of superconducting magnets for its high critical temperature (18 K) and critical magnetic field (25 T). A superconducting magnet weighing as little as two kilograms is capable of the magnetic field of a conventional electromagnet weighing tons.

A small percentage of tin is added to zirconium alloys for the cladding of nuclear fuel.

Most metal pipes in a pipe organ are of a tin/lead alloy, with 50/50 being the most common composition. The proportion of tin in the pipe defines the pipe's tone, since tin has a desirable tonal resonance. When a tin/lead alloy cools, the lead cools slightly faster and produces a mottled or spotted effect. This metal alloy is referred to as spotted metal. Major advantages of using tin for pipes include its appearance, its workability, and resistance to corrosion.

Optoelectronics

The oxides of indium and tin are electrically conductive and transparent, and are used to make transparent electrically conducting films with applications in Optoelectronics devices such as liquid crystal displays.

Other applications

A 21st-century reproduction barn lantern made of punched tin.

 

Punched tin-plated steel, also called pierced tin, is an artisan technique originating in central Europe for creating housewares that are both functional and decorative. Decorative piercing designs exist in a wide variety, based on local tradition and the artisan's personal creations. Punched tin lanterns are the most common application of this artisan technique. The light of a candle shining through the pierced design creates a decorative light pattern in the room where it sits. Lanterns and other punched tin articles were created in the New World from the earliest European settlement. A well-known example is the Revere lantern, named after Paul Revere.

Before the modern era, in some areas of the Alps, a goat or sheep's horn would be sharpened and a tin panel would be punched out using the alphabet and numbers from one to nine. This learning tool was known appropriately as "the horn". Modern reproductions are decorated with such motifs as hearts and tulips. 

In America, pie safes and food safes were in use in the days before refrigeration. These were wooden cupboards of various styles and sizes – either floor standing or hanging cupboards meant to discourage vermin and insects and to keep dust from perishable foodstuffs. These cabinets had tinplate inserts in the doors and sometimes in the sides, punched out by the homeowner, cabinetmaker or a tinsmith in varying designs to allow for air circulation while excluding flies. Modern reproductions of these articles remain popular in North America.

Window glass is most often made by floating molten glass on molten tin (float glass), resulting in a flat and flawless surface. This is also called the "Pilkington process".

Tin is also used as a negative electrode in advanced Li-ion batteries. Its application is somewhat limited by the fact that some tin surfaces catalyze decomposition of carbonate-based electrolytes used in Li-ion batteries.

Tin(II) fluoride is added to some dental care products as stannous fluoride (SnF₂). Tin(II) fluoride can be mixed with calcium abrasives while the more common sodium fluoride gradually becomes biologically inactive in the presence of calcium compounds. It has also been shown to be more effective than sodium fluoride in controlling gingivitis.

Organotin compounds

Of all the chemical compounds of tin, the organotin compounds are most heavily used. Worldwide industrial production probably exceeds 50,000 tonnes.

PVC stabilizers

The major commercial application of organotin compounds is in the stabilization of PVC plastics. In the absence of such stabilizers, PVC would otherwise rapidly degrade under heat, light, and atmospheric oxygen, resulting in discolored, brittle products. Tin scavenges labile chloride ions (Cl⁻), which would otherwise initiate loss of HCl from the plastic material. Typical tin compounds are carboxylic acid derivatives of dibutyltin dichloride, such as the dilaurate.

Biocides

Some organotin compounds are relatively toxic, with both advantages and problems. They are used for biocidal properties as fungicides, pesticides, algaecides, 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, with use declining after organotin compounds were recognized as persistent organic pollutants with an extremely high toxicity for some marine organisms (the dog whelk, for example). The EU banned the use of organotin compounds in 2003, while concerns over the toxicity of these compounds to marine life and damage to 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 greater than 25 m (82 ft) long.

Organic chemistry

Some tin reagents are useful in organic chemistry. In the largest application, stannous chloride is a common reducing agent for the conversion of nitro and oxime groups to amines. The Stille reaction couples organotin compounds with organic halides or pseudohalides.

Li-ion batteries

Tin forms several inter-metallic phases with lithium metal, making it a potentially attractive material for battery applications. Large volumetric expansion of tin upon alloying with lithium and instability of the tin-organic electrolyte interface at low electrochemical potentials are the greatest challenges to employment in commercial cells. The problem was partially solved by Sony. Tin inter-metallic compound with cobalt and carbon has been implemented by Sony in its Nexelion cells released in the late 2000s. The composition of the active material is approximately Sn_0.3Co_0.4C_0.3. Recent research showed that only some crystalline facets of tetragonal (beta) Sn are responsible for undesirable electrochemical activity.

Precautions

Cases of poisoning from tin metal, its oxides, and its salts are almost unknown. On the other hand, certain organotin compounds are almost as toxic as cyanide.

Exposure to tin in the workplace can occur by inhalation, skin contact, and eye contact. The Occupational Safety and Health Administration (OSHA) has set the legal limit (permissible exposure limit) for tin exposure in the workplace as 2 mg/m³ over an 8-hour workday. The National Institute for Occupational Safety and Health (NIOSH) has determined a recommended exposure limit (REL) of 2 mg/m³ over an 8-hour workday. At levels of 100 mg/m³, tin is immediately dangerous to life and health.

Centers for Disease Control and Prevention

From Wikipedia, the free encyclopedia

Agency overview
Formed	July 1, 1946; 72 years ago
Preceding agencies	Office of National Defense Malaria Control Activities (1942) Office of Malaria Control in War Areas (1942–1946) Communicable Disease Center (1946–1967) National Communicable Disease Center (1967–1970) Center for Disease Control (1970–1980) Centers for Disease Control (1980–1992)
Jurisdiction	Federal government of the United States
Headquarters	Atlanta, Georgia, U.S.
Employees	15,000
Annual budget	US$11.1 billion (FY18)
Agency executive	Robert R. Redfield, Director
Parent agency	United States Department of Health and Human Services
Website	www.cdc.gov

The Centers for Disease Control and Prevention (CDC) is the leading national public health institute of the United States. The CDC is a United States federal agency under the Department of Health and Human Services and is headquartered in Atlanta, Georgia.

Its main goal is to protect public health and safety through the control and prevention of disease, injury, and disability in the US and internationally. The CDC focuses national attention on developing and applying disease control and prevention. It especially focuses its attention on infectious disease, food borne pathogens, environmental health, occupational safety and health, health promotion, injury prevention and educational activities designed to improve the health of United States citizens. In addition, the CDC researches and provides information on non-infectious diseases such as obesity and diabetes and is a founding member of the International Association of National Public Health Institutes.

History

CDC headquarters in Atlanta, Georgia, as seen from Emory University

 

CDC's Roybal campus in Atlanta, Georgia

 

Arlen Specter Headquarters and Emergency Operations Center

 

Tom Harkin Global Communications Center

 

CDC and MSF staff preparing to enter an Ebola treatment unit in Liberia, August 2014

The Communicable Disease Center was founded July 1, 1946, as the successor to the World War II Malaria Control in War Areas program of the Office of National Defense Malaria Control Activities.

Preceding its founding, organizations with global influence in malaria control were the Malaria Commission of the League of Nations and the Rockefeller Foundation. The Rockefeller Foundation greatly supported malaria control, sought to have the governments take over some of its efforts, and collaborated with the agency.

The new agency was a branch of the U.S. Public Health Service and Atlanta was chosen as the location because malaria was endemic in the Southern United States. The agency changed names (see infobox on top) before adopting the name Communicable Disease Center in 1946. Offices were located on the sixth floor of the Volunteer Building on Peachtree Street. 

With a budget at the time of about $1 million, 59 percent of its personnel were engaged in mosquito abatement and habitat control with the objective of control and eradication of malaria in the United States.

Among its 369 employees, the main jobs at CDC were originally entomology and engineering. In CDC's initial years, more than six and a half million homes were sprayed, mostly with DDT. In 1946, there were only seven medical officers on duty and an early organization chart was drawn, somewhat fancifully, in the shape of a mosquito. Under Joseph Walter Mountin, the CDC continued to advocate for public health issues and pushed to extend its responsibilities to many other communicable diseases.

In 1947, the CDC made a token payment of $10 to Emory University for 15 acres (61,000 m²) of land on Clifton Road in DeKalb County, still the home of CDC headquarters today. CDC employees collected the money to make the purchase. The benefactor behind the “gift” was Robert W. Woodruff, chairman of the board of The Coca-Cola Company. Woodruff had a long-time interest in malaria control, which had been a problem in areas where he went hunting. The same year, the PHS transferred its San Francisco based plague laboratory into the CDC as the Epidemiology Division, and a new Veterinary Diseases Division was established. An Epidemic Intelligence Service (EIS) was established in 1951, originally due to biological warfare concerns arising from the Korean War; it evolved into two-year postgraduate training program in epidemiology, and a prototype for Field Epidemiology Training Programs (FETP), now found in numerous countries, reflecting CDC's influence in promoting this model internationally.

The mission of CDC expanded beyond its original focus on malaria to include sexually transmitted diseases when the Venereal Disease Division of the U.S. Public Health Service (PHS) was transferred to the CDC in 1957. Shortly thereafter, Tuberculosis Control was transferred (in 1960) to the CDC from PHS, and then in 1963 the Immunization program was established.

It became the National Communicable Disease Center (NCDC) effective July 1, 1967. The organization was renamed the Center for Disease Control (CDC) on June 24, 1970, and Centers for Disease Control effective October 14, 1980. An act of the United States Congress appended the words "and Prevention" to the name effective October 27, 1992. However, Congress directed that the initialism CDC be retained because of its name recognition.

Currently the CDC focus has broadened to include chronic diseases, disabilities, injury control, workplace hazards, environmental health threats, and terrorism preparedness. CDC combats emerging diseases and other health risks, including birth defects, West Nile virus, obesity, avian, swine, and pandemic flu, E. coli, and bioterrorism, to name a few. The organization would also prove to be an important factor in preventing the abuse of penicillin. In May 1994 the CDC admitted having sent several biological warfare agents to the Iraqi government from 1984 through 1989, including Botulinum toxin, West Nile virus, Yersinia pestis and Dengue fever virus.

On April 21, 2005, then–CDC Director Julie Gerberding formally announced the reorganization of CDC to "confront the challenges of 21st-century health threats". The four Coordinating Centers—established under the G. W. Bush Administration and Gerberding—"diminished the influence of national centers under [their] umbrella", and were ordered cut under the Obama Administration in 2009.

Today, the CDC's Biosafety Level 4 laboratories are among the few that exist in the world, and serve as one of only two official repositories of smallpox in the world. The second smallpox store resides at the State Research Center of Virology and Biotechnology VECTOR in the Russian Federation. The CDC revealed in 2014 that it had discovered several misplaced smallpox samples and also that lab workers had potentially been infected with anthrax.

Organization

The CDC is organized into "Centers, Institutes, and Offices" (CIOs), with each organizational unit implementing the agency's activities in a particular area of expertise while also providing intra-agency support and resource-sharing for cross-cutting issues and specific health threats. Generally, CDC "Offices" are subdivided into Centers, which in turn are composed of Divisions and Branches. However, the Center for Global Health and the National Institute for Occupational Safety and Health are freestanding organizational units and do not belong to a parent Office. 

The current CIOs are:

• CDC Washington Office
• Center for Global Health
• National Institute for Occupational Safety and Health
• Office for State, Tribal, Local and Territorial Support
• Office of Equal Employment Opportunity
• Office of Infectious Diseases
  • National Center for Emerging and Zoonotic Infectious Diseases
  • National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention
  • National Center for Immunization and Respiratory Diseases
• Office of Minority Health and Health Equity
• Office of Noncommunicable Diseases, Injury and Environmental Health
  • National Center for Chronic Disease Prevention and Health Promotion
  • National Center for Environmental Health/Agency for Toxic Substances and Disease Registry
  • National Center for Injury Prevention and Control
  • National Center on Birth Defects and Developmental Disabilities
• Office of Public Health Preparedness and Response
• Office of Public Health Scientific Services
  • Center for Surveillance, Epidemiology and Laboratory Services
  • National Center for Health Statistics
• Office of the Associate Director for Communication
• Office of the Associate Director for Laboratory Science and Safety
• Office of the Associate Director for Policy
• Office of the Associate Director for Science
• Office of the Chief of Staff
• Office of the Chief Operating Officer

The Office of Public Health Preparedness was created during the 2001 anthrax attacks shortly after the terrorist attacks of September 11, 2001. Its purpose was to coordinate among the government the response to a range of biological terrorism threats.

Budget and operations

In addition to its Atlanta headquarters, the CDC has other locations in the United States and Puerto Rico. Those locations include Anchorage; Cleveland; Cincinnati; Detroit; Fort Collins; Hyattsville; Morgantown; Pittsburgh; Research Triangle Park; San Juan, Puerto Rico; Spokane, Washington; and Washington, D.C.

The CDC offers grants that help many organizations each year advance health, safety and awareness at the community level throughout the United States. The CDC awards over 85 percent of its annual budget through these grants.

Workforce

As of 2008, CDC staff numbered approximately 15,000 (including 6,000 contractors and 840 Commissioned Corps officers) in 170 occupations. Eighty percent held bachelor's degrees or higher; almost half had advanced degrees (a master's degree or a doctorate such as a PhD, D.O., or M.D.).

Common CDC job titles include engineer, entomologist, epidemiologist, biologist, physician, veterinarian, behavioral scientist, nurse, medical technologist, economist, public health advisor, health communicator, toxicologist, chemist, computer scientist, and statistician.

The CDC also operates a number of notable training and fellowship programs, including those indicated below.

Epidemic Intelligence Service (EIS)

The Epidemic Intelligence Service (EIS) is composed of "boots-on-the-ground disease detectives" who investigate public health problems domestically and globally. When called upon by a governmental body, EIS officers may embark on short-term epidemiological assistance assignments, or "Epi-Aids", to provide technical expertise in containing and investigating disease outbreaks. The EIS program is a model for the international Field Epidemiology Training Program.

Public Health Associates Program

The CDC also operates the Public Health Associate Program (PHAP), a two-year paid fellowship for recent college graduates to work in public health agencies all over the United States. PHAP was founded in 2007 and currently has 159 associates in 34 states.

Leadership

David Sencer points to a depiction of Triatomine sp., which transmits Chagas disease.

 

The Director of CDC is a Senior Executive Service position that may be filled either by a career employee, or as a political appointment that does not require Senate confirmation, with the latter method typically being used. The director serves at the pleasure of the President and may be fired at any time. The CDC director concurrently serves as the Administrator of the Agency for Toxic Substances and Disease Registry.

Sixteen directors have served the CDC or its predecessor agencies.

• Louis L. Williams Jr., MD (1942–1943)
• Mark D. Hollis, ScD (1944–1946)
• Raymond A. Vonderlehr, MD (1947–1951)
• Justin M. Andrews, ScD (1952–1953)
• Theodore J. Bauer, MD (1953–1956)
• Robert J. Anderson, MD, MPH (1956–1960)
• Clarence A. Smith, MD, MPH (1960–1962)
• James L. Goddard, MD, MPH (1962–1966)
• David J. Sencer, MD, MPH (1966–1977)
• William H. Foege, MD, MPH (1977–1983)
• James O. Mason, MD, MPH, Ph.D (1983–1989)
• William L. Roper, MD, MPH (1990–1993)
• David Satcher, MD, PhD (1993–1998)
• Jeffrey P. Koplan, MD, MPH (1998–2002)
• Julie Gerberding, MD, MPH (2002–2008)
• Thomas R. Frieden, MD, MPH (2009–Jan 2017)
• Anne Schuchat, MD, RADM USPHS (Jan–July 2017, acting)
• Brenda Fitzgerald, MD (July 2017–Jan 2018)
• Anne Schuchat, MD (Jan–Mar 2018, acting)
• Robert R. Redfield, MD (March 2018–)

Datasets and survey systems

• CDC Scientific Data, Surveillance, Health Statistics, and Laboratory Information.
• Behavioral Risk Factor Surveillance System (BRFSS), the world’s largest, ongoing telephone health-survey system.
• Mortality Medical Data System.
• Abortion statistics in the United States

Areas of focus

Donald Henderson as part of the CDC's smallpox eradication team in 1966.

Communicable diseases

The CDC's programs address more than 400 diseases, health threats, and conditions that are major causes of death, disease, and disability. The CDC's website has information on various infectious (and noninfectious) diseases, including smallpox, measles, and others.

Influenza

The CDC has launched campaigns targeting the transmission of influenza, including the H1N1 swine flu, and launched websites to educate people in proper hygiene.

Division of Select Agents and Toxins

Within the division are two programs: the Federal Select Agent Program (FSAP) and the Import Permit Program. The FSAP is run jointly with an office within the U.S. Department of Agriculture, regulating agents that can cause disease in humans, animals, and plants. The Import Permit Program regulates the importation of "infectious biological materials."

The CDC runs a program that protects the public from rare and dangerous substances such as anthrax and the Ebola virus. The program, called the Federal Select Agent Program, calls for inspections of labs in the U.S. that work with dangerous pathogens.

During the 2014 Ebola outbreak in West Africa, the CDC helped coordinate the return of two infected American aid workers for treatment at Emory University Hospital, the home of a special unit to handle highly infectious diseases.

As a response to the 2014 Ebola outbreak, Congress passed a Continuing Appropriations Resolution allocating $30,000,000 towards CDC's efforts to fight the virus.

Non-communicable diseases

The CDC also works on non-communicable diseases, including chronic diseases caused by obesity, physical inactivity and tobacco-use.

Antibiotic resistance

The CDC implemented their National Action Plan for Combating Antibiotic Resistant Bacteria as a measure against the spread of antibiotic resistance in the United States. This initiative has a budget of $161 million and includes the development of the Antibiotic Resistance Lab Network.

Global health

The CDC works with other organizations around the world to address global health challenges and contain disease threats at their source. It works closely with many international organizations such as the World Health Organization (WHO) as well as ministries of health and other groups on the front lines of outbreaks. The agency maintains staff in more than 60 countries, including some from the U.S. but even more from the countries in which it operates. The agency's global divisions include the Division of Global HIV and TB (DGHT), the Division of Parasitic Diseases and Malaria (DPDM), the Division of Global Health Protection (DGHP), and the Global Immunization Division (GID).

The CDC is integral in working with the WHO to implement the International Health Regulations (IHR), a legally binding agreement between 196 countries to prevent, control, and report on the international spread of disease, through initiatives including the Global Disease Detection Program (GDD).

The CDC is also a lead implementer of key U.S. global health initiatives such as the President's Emergency Plan for AIDS Relief (PEPFAR) and the President's Malaria Initiative.

Travelers' health

The CDC collects and publishes health information for travelers in a comprehensive book, CDC Health Information for International Travel, which is commonly known as the "yellow book." The book is available online and in print as a new edition every other year and includes current travel health guidelines, vaccine recommendations, and information on specific travel destinations. The CDC also issues travel health notices on its website, consisting of three levels: 

"Watch": Level 1 (practice usual precautions) 

"Alert": Level 2 (practice enhanced precautions) 

"Warning": Level 3 (avoid nonessential travel)

Foundation

The CDC Foundation operates independently from CDC as a private, nonprofit 501(c)(3) organization incorporated in the State of Georgia. The creation of the Foundation was authorized by section 399F of the Public Health Service Act to support the mission of CDC in partnership with the private sector, including organizations, foundations, businesses, educational groups, and individuals.

Popular culture and controversies

Historically, the CDC has been relatively free of political manipulation.

Tuskegee Study of Untreated Syphilis in the Negro Male

For 15 years, the CDC had direct oversight over the Tuskegee syphilis experiment. In the study, which lasted from 1932 to 1972, a group of African American men (nearly 400 of whom had syphilis) were studied to learn more about the disease. Notably, the disease was left untreated in the research subjects and they never gave their informed consent to serve as research subjects. The Tuskegee Study was initiated in 1932 by the Public Health Service. The CDC took over the study in 1957.

The CDC's response to the AIDS crisis in the 1980s has been criticized for promoting some public health policies that harmed HIV+ people and for providing ineffective public education. The agency's response to the 2001 anthrax attacks was also criticized for ineffective communication with other public health agencies and with the public.

CDC zombie apocalypse outreach campaign

On May 16, 2011, the Centers for Disease Control and Prevention's blog published an article instructing the public on what to do to prepare for a zombie invasion. While the article did not claim that such a scenario was possible, it did use the popular culture appeal as a means of urging citizens to prepare for all potential hazards, such as earthquakes, tornadoes, and floods.

According to David Daigle, the Associate Director for Communications, Public Health Preparedness and Response, the idea arose when his team was discussing their upcoming hurricane-information campaign and Daigle mused that "we say pretty much the same things every year, in the same way, and I just wonder how many people are paying attention." A social-media employee mentioned that the subject of zombies had come up a lot on Twitter when she had been tweeting about the Fukushima Daiichi nuclear disaster and radiation. The team realized that a campaign like this would most likely reach a different audience from the one that normally pays attention to hurricane-preparedness warnings and went to work on the zombie campaign, launching it right before hurricane season began. "The whole idea was, if you're prepared for a zombie apocalypse, you're prepared for pretty much anything," said Daigle.

Once the blog article became popular, the CDC announced an open contest for YouTube submissions of the most creative and effective videos covering preparedness for a zombie apocalypse (or apocalypse of any kind), to be judged by the "CDC Zombie Task Force". Submissions were open until October 11, 2011. They also released a zombie-themed graphic novella available on their website. Zombie-themed educational materials for teachers are available on the site.

Gun violence

One area of current partisan dispute related to CDC funding is studying gun violence. The 1996 Dickey Amendment states "none of the funds made available for injury prevention and control at the Centers for Disease Control and Prevention may be used to advocate or promote gun control". Advocates for gun control oppose the amendment and have tried to overturn it.

In 1992, Mark L. Rosenberg and five CDC colleagues founded the CDC’s National Center for Injury Prevention and Control, with an annual budget of c. $260,000 that focused on "identifying the root causes of firearm deaths and the best methods to prevent them". Their first report which was published in the New England Journal of Medicine in 1993, entitled "Gun Ownership as a Risk Factor for Homicide in the Home" reported that the "mere presence of a gun in a home increased the risk of a firearm-related death by 2.7 percent, and suicide fivefold—a "huge" increase." In response, the NRA launched a "campaign to shut down the Injury Center." Doctors for Responsible Gun Ownership and Doctors for Integrity and Policy Research joined the pro-gun effort and by 1995, politicians also supported the pro-gun initiative. In 1996, Jay Dickey (R) Arkansas introduced the Dickey Amendment statement "which stated "none of the funds made available for injury prevention and control at the Centers for Disease Control and Prevention may be used to advocate or promote gun control" as a rider in the 1996 appropriations bill." In 1997, "Congress redirected all of the money previously earmarked for gun violence research to the study of traumatic brain injury." David Satcher, who was the CDC head from 1993 to 1998 advocated for gun violence research until he left in 1998. In 1999 Rosenberg was fired. Over a dozen "public health insiders, including current and former CDC senior leaders" told The Trace interviewers that CDC senior leaders took an overly cautious stance in their interpretation of the Dickey amendment. They could have done much more. Rosenberg told The Trace in 2016, "Right now, there is nothing stopping them from addressing this life-and-death national problem.”

The American Medical Association, the American Psychological Association and the American Academy of Pediatrics sent a letter to the leaders of the Senate Appropriations Committee in 2013 asking them "to support at least $10 million within the Centers for Disease Control and Prevention (CDC) in FY 2014 along with sufficient new funding at the National Institutes of Health to support research into the causes and prevention of gun violence. Furthermore, we urge Members to oppose any efforts to reduce, eliminate, or condition CDC funding related to gun violence prevention research." Congress maintained the ban in subsequent budgets.

Language guidelines

In December 2017, The Washington Post reported that the Trump administration had issued a list of seven words that were forbidden in official CDC documentation. Yuval Levin, after contacting HHS officials, wrote in National Review that the Post story was not accurate.

Publications

• CDC publications
• State of CDC report
• CDC Programs in Brief
• Morbidity and Mortality Weekly Report
• Emerging Infectious Diseases (monthly journal)
• Preventing Chronic Disease
• Vital statistics