Characteristics

Physical properties

 

Droplet of solidified molten tin

Tin is a malleable, ductile and highly crystalline silvery-white metal. When a bar of tin is bent, a crackling sound known as the tin cry can be heard due to the twinning of the crystals. Tin melts at a low temperature of about 232 °C (450 °F), which is further reduced to 177.3 °C (351.1 °F) for 11-nm particles.

β-tin (the metallic form, or white tin), 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 where 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 upon addition of Sb or Bi the transformation may 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 there are few elements that 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. 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.

Chemical properties

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. In this case the formation of a protective oxide layer is used to prevent further oxidation. This oxide layer forms on pewter and other tin alloys. Tin acts as a catalyst when oxygen is in solution and helps accelerate chemical attack.

Applications

 

World consumption of refined tin by end use, 2006

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

Solder

 

A coil of lead-free solderwire

Tin has long been used as a solder in the form of an alloy with lead, tin accounting for 5 to 70% w/w. Tin forms a eutectic mixture with lead containing 63% tin and 37% lead. Such solders are primarily used for solders for joining pipes or electric circuits. Since the European Union Waste Electrical and Electronic Equipment Directive (WEEE Directive) and Restriction of Hazardous Substances Directivecame 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. 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 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", while speakers of American English 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.

Specialized alloys[edit]

 

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 also sometimes been used in coinage; for example, it once formed a single-digit figure percentage (usually five percent or less) of the American and Canadian pennies. Because copper is often the major metal in such coins, and zinc is sometimes present as well, these could technically be called bronze and/or brass alloys.

 

Tin plated metal from can

 

Artisan Alfonso Santiago Leyva and his son working tin sheets

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 as little as two kilograms is capable of producing magnetic fields comparable to a conventional electromagnet weighing tons.

The addition of a few percent of tin is commonly used in zirconium alloys for the cladding of nuclear fuel.

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.^{[dubious – discuss]} 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.

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 geography or 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. Punched tin lanterns and other punched tin articles were created in the New World from the earliest European settlement. A well-known example is the Revere type 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 came into 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. Modern reproductions of these articles remain popular in North America.

Window glass is most often made by floating molten glass on top of molten tin (creating float glass) in order to produce a flat surface. This is 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^[which?] 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 combined with 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, to give 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

Organotin compounds can have a relatively high toxicity, which is both advantageous and problematic. They have been used for their biocidal effects in/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, for example the dog whelk.The EU banned the use of organotin compounds in 2003,while concerns over the toxicity of these compounds to marine life and their effects on the reproduction and growth of some marine species,(some reports describe biological effects to marine life at a concentration of 1 nanogram per liter) have led to a worldwide ban by the International Maritime Organization. Many nations now restrict the use of organotin compounds to vessels over 25 meters long.

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 and it makes it a potentially attractive material. 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 in employing it in commercial cells. The problem was partially solved by Sony. Tin inter-metallic compound with cobalt, mixed with carbon, has been implemented by Sony in its Nexelion cells released in late 2000's. The composition of the active materials is close to 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[edit]