Tin (chemical symbol Sn, atomic number 50) is a silvery, malleable metal that is not easily oxidized in air and resists corrosion. It is obtained chiefly from the mineral cassiterite, in which it occurs as an oxide.
This metal is an important component of many alloys, including bronze, pewter, bell metal, and solder. In addition, it is used to coat items made of steel, lead, and zinc to prevent corrosion. As the most tonally resonant metal, tin is used in manufacturing organ pipes. The flat surface of window glass can be made by floating molten glass on molten tin. Also, glass can be given an electrically conductive coating by spraying it with certain tin salts. Tin(II) chloride is used as a mordant (dye-fixing agent) in the calico printing process, and a niobium-tin compound is used in wires for superconducting magnets.
Tin (Anglo-Saxon tin, Latin stannum) is mined in about 35 countries throughout the world. Nearly every continent has an important tin-mining country. This metal is a relatively scarce element, with an abundance in the Earth's crust of about two parts per million, compared with 94 parts per million for zinc, 63 parts per million for copper, and 12 parts per million for lead. Most of the world's tin is produced from placer deposits; at least one-half comes from Southeast Asia. Tasmania hosts some important deposits of historical importance, most importantly Mount Bischoff and Renison Bell.
The only mineral of commercial importance as a source of tin is cassiterite (SnO2). Tin is produced by reducing the ore with coal in a reverberatory furnace. In addition, small quantities of tin are recovered from complex sulfides such as stannite, cylindrite, franckeite, canfieldite, and teallite. Secondary (scrap) tin is also an important source of the metal.
HistoryThe alchemical symbol for tin
Tin is one of the earliest metals known and was used as a component of bronze from antiquity. Given its hardening effect on copper, tin was used in bronze implements as early as 3500 B.C.E. Tin mining is believed to have started in Cornwall and Devon (especially Dartmoor) in classical times, and a thriving tin trade developed with civilizations of the Mediterranean. The pure metal, however, was not used until about 600 B.C.E. The last Cornish tin mine, at South Crofty near Camborne, closed in 1998, bringing four thousand years of mining in Cornwall to an end. Tradition has it that Joseph of Arimathea was a tin trader and that he brought his nephew Jesus with him to Cornwall on some of his journeys.
The word "tin" has cognates in many Germanic and Celtic languages. The American Heritage dictionary speculates that the word was borrowed from a pre-Indo-European language.
In modern times, the word "tin" is often (improperly) used as a generic phrase for any silvery metal that comes in thin sheets. Most everyday objects that are commonly called tin, such as aluminum foil, beverage cans, and tin cans, are actually made of steel or aluminum, although tin cans do have 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 thin coating of tin to inhibit rust.
Tin is located in group 14 (former group 4A) of the periodic table, between germanium and lead. In addition, it lies in period 5, between indium and antimony. It is sometimes known as a "poor metal," a name given to metals that come after the transition metals in the periodic table.
This silvery-white metal is malleable, ductile, and highly crystalline. When a bar of tin is bent, a strange crackling sound known as the "tin cry" is produced, caused by breakage of the crystals. The metal resists corrosion from distilled water, seawater, and soft, tap water, but it can be attacked by strong acids, alkalis, and acid salts. It acts as a catalyst when oxygen is in solution and helps accelerate chemical attack.
When heated in the presence of air, tin forms the dioxide (SnO2). The dioxide, in turn, is feebly acidic and forms stannate (SnO3-2) salts with basic oxides. Tin can be highly polished and is used as a protective coat for other metals, to prevent corrosion or other chemical action. This metal combines directly with chlorine and oxygen and displaces hydrogen from dilute acids. It is malleable at ordinary temperatures but is brittle when heated.
Tin becomes a superconductor below 3.72 Kelvin (K). In fact, tin was one of the first superconductors to be studied. The Meissner effect, one of the characteristic features of superconductors, was first discovered in superconducting tin crystals. A superconducting magnet weighing only a couple of kilograms is capable of producing magnetic fields comparable to a conventional electromagnet weighing tons.
Tin has ten stable isotopes (listed in the box), making it the element with the highest number of stable isotopes. Many additional, unstable isotopes are known.
Solid tin has two allotropes at normal pressure. At low temperatures, it exists as gray or alpha tin, which has a cubic crystal structure, similar to that of silicon and germanium. When warmed above 13.2 °C, it changes into white or beta tin, which is metallic and has a tetragonal structure. When cooled, it slowly returns to the gray form, a phenomenon called tin pest or tin disease. This transformation, however, is affected by impurities such as aluminum and zinc and can be prevented from occurring by the addition of antimony or bismuth.
- Tin(II) chloride, or stannous chloride (SnCl2): It is a white, crystalline solid that forms a stable dihydrate. It can dissolve in less than its own mass of water without apparent decomposition, but as the solution is diluted, hydrolysis occurs to form an insoluble, basic salt. Therefore, to maintain tin(II) chloride as a clear solution, hydrochloric acid must be added. A solution of this chloride containing a little hydrochloric acid is used for the tin-plating of steel, to make tin cans. It is also widely used as a reducing agent, such as for silvering mirrors, where silver metal is deposited on glass. In addition, it is used as a catalyst in the production of the plastic polylactic acid (PLA).
- Tin(IV) chloride, tin tetrachloride, or stannic chloride (SnCl4): At room temperature, it is a colorless liquid that reacts violently with water and is extremely corrosive to the skin. On contact with air, it releases severely irritating fumes of hydrogen chloride. It forms a white pentahydrate, formerly known as butter of tin because of its consistency. It was used as a chemical weapon in World War I. It is also used in the glass container industry for making an external coating containing tin(IV) oxide, which toughens the glass. It is a starting material for organotin compounds.
- Stannic acid or stannic hydroxide (Sn(OH)4): It refers to hydrated tin dioxide (SnO2). Despite the name stannic acid, this compound is amphoteric-it can behave as an acid and as a base. For example, it dissolves in base to form the stannate ion, Sn(OH)62-, which can then form stannate compounds. In strongly acidic conditions, Sn(OH)4 releases the tin(IV) ion, Sn4+. Stannic acid is a poor oxidizer. Combined with a good reducing agent, it can form stannous hydroxide, Sn(OH)2, but it is as likely to form metallic tin.
- Tributyltin oxide (TBTO) or bis(tri-n-butyltin)oxide (C24H54OSn2): This pale yellow liquid is an organotin compound that was chiefly used as a biocide (fungicide and molluscicide), especially as a wood preservative. It is a potent skin irritant. Tributyltin compounds were once used as marine anti-biofouling agents. Concerns over toxicity of these compounds (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. It is now considered a severe marine pollutant.
- Tin bonds readily to certain metals, particularly iron, and has been used to coat steel, lead, or zinc 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. Americans call these containers "tin cans" or just "cans," and those who speak British English call them "tins."
- Some important tin alloys are: bronze, bell metal, Babbitt metal, die casting alloy, pewter, phosphor bronze, soft solder, and White metal.
- The most important salt of tin is tin(II) chloride (stannous chloride), which is used 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.
- Window glass is most often made by floating molten glass on top of molten tin (creating float glass), to make a flat surface. This is called the "Pilkington process."
- Tin is one of the two fundamental elements (the other being lead) used since the Renaissance in the manufacture of organ pipes. The proportion between the two metals may vary, but the most common mix is 50:50. The amount of tin in the pipe defines the pipe's tone, tin being the most tonally resonant of all metals. When the tin/lead alloy cools, the lead cools slightly faster and makes a mottled or spotted effect, and the alloy is therefore referred to as spotted metal.
- Tin is also used in solders for joining pipes or electric circuits, in bearing alloys, glass-making, and a wide range of tin chemical applications. The use of pure tin or tin alloyed with other metals in these applications is rapidly supplanting the use of lead-containing alloys, to eliminate the problems of toxicity caused by lead.
- Tin foil was once a common wrapping material for foods and drugs. It was replaced in the early twentieth century by the use of aluminum foil, which is still commonly called tin foil. Hence the slang term "tinnie" or "tinny" is used for a small retail package of a drug such as cannabis or a can of beer.
- A niobium-tin compound (Nb3Sn) is commercially used as wires for superconducting magnets, because of the material's high critical temperature (18 K) and critical magnetic field (25 tesla).
Biologic effects of organic tin compounds
The small amount of tin found in canned foods is not harmful to humans. Certain organic tin compounds, such as triorganotins, are toxic and are used as industrial fungicides and bactericides.
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All links retrieved December 9, 2015.
- WebElements.com - Tin
- Tin by Theodore Gray
- Tributyltin oxide use - PAN Pesticides Database - California Pesticide Use