Bismuth

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Bismuth (IPA: [ˈbɪzməθ]) is a chemical element that has the symbol Bi and atomic number 83. This heavy, brittle, white crystalline trivalent poor metal has a pink tinge and chemically resembles arsenic and antimony. Of all the metals, it is the most naturally diamagnetic, and only mercury has a lower thermal conductivity.

Bismuth compounds are used in cosmetics and in medical procedures. As the toxicity of lead has become more apparent in recent years, alloy uses for bismuth metal as a replacement for lead have become an increasing part of bismuth's commercial importance.

[edit] Notable characteristics

Bismuth is a brittle metal with a pinkish hue, often occurring in its native form with an iridescent oxide tarnish showing many refractive colors from yellow to blue. When combusted with oxygen, bismuth burns with a blue flame and its oxide forms yellow fumes. Its toxicity is much lower than that of its neighbors in the periodic table such as lead, thallium, and antimony.

No other metal is more naturally diamagnetic (as opposed to superdiamagnetic) than bismuth, and it has a high electrical resistance. Of any metal, it has the second lowest thermal conductivity and the highest Hall effect. When deposited in sufficiently thin layers on a substrate, bismuth is a semiconductor, rather than a poor metal.^[1]

Elemental bismuth is one of very few substances of which the liquid phase is denser than its solid phase (water being the best-known example). Because bismuth expands on freezing, it was long an important component of low-melting typesetting alloys, which needed to expand to fill printing molds.

While bismuth was traditionally regarded as the element with the heaviest stable isotope, it had long been suspected to be unstable on theoretical grounds. This was finally demonstrated in 2003 when researchers at the Institut d'Astrophysique Spatiale in Orsay, France, measured the alpha emission half-life of ²⁰⁹Bi to be 1.9 x 10¹⁹ years,^[2] over a billion times longer than the current estimated age of the universe. Due to its extraordinarily long half-life, for nearly all applications bismuth can be treated as if it is stable and non-radioactive. The radioactivity is of academic interest, however, because bismuth is one of few elements whose radioactivity was suspected, and indeed theoretically predicted, before being detected in the laboratory.

[edit] History

Bismuth (New Latin bisemutum from German Wismuth, perhaps from weiße Masse, "white mass") was confused in early times with tin and lead due to its resemblance to those elements. Basilius Valentinus described some of its uses in 1450 . Claude François Geoffroy showed in 1753 that this metal is distinct from lead.

Artificial bismuth was commonly used in place of the actual mineral. It was made by hammering tin into thin plates, and cementing them by a mixture of white tartar, saltpeter, and arsenic, stratified in a crucible over an open fire.^[3]

Bismuth was also known to the Incas and used (along with the usual copper and tin) in a special bronze alloy for knives, [2]

[edit] Occurrence

In the Earth's crust, bismuth is about twice as abundant as gold. It is not usually economical to mine it as a primary product. Rather, it is usually produced as a byproduct of the processing of other metal ores, especially lead, but also tungsten or other metal alloys.

The most important ores of bismuth are bismuthinite and bismite. In 2005, China was the top producer of bismuth with at least 40% world share followed by Mexico and Peru reports the British Geological Survey.

The average price for bismuth in 2000 was US$ 7.70 per kilogram. It is relatively cheap, since like lead (but to a much lesser extent), it is radiogenic, being formed from the natural decay of uranium and thorium (specifically, by way of neptunium-237 or uranium-233).

[edit] Crystals

Though virtually unseen in nature, high-purity bismuth can form distinctive hopper crystals. These colorful laboratory creations are typically sold to collectors. Bismuth is relatively nontoxic and has a low melting point just above 273°C, so crystals may be grown using a household stove, although the resulting crystals will tend to be lower quality than lab-grown crystals.

[edit] Applications

Bismuth oxychloride is sometimes used in cosmetics. Also bismuth subnitrate and bismuth subcarbonate are used in medicine. Bismuth subsalicylate (the active ingredient in Pepto-Bismol) is used as an antidiarrheal and to treat some other gastro-intestinal diseases. Also, bismuth subgallate (the active ingredient in Devrom) is used as an internal deodorant to treat malodor from flatulence (or gas) and stool.

Some other current uses:

• Many bismuth alloys have low melting points and are widely used for fire detection and suppression system safety devices.
• Bismuth is used as an alloying agent in production of malleable irons.
• A carrier for U-235 or U-233 fuel in nuclear reactors
• Bismuth has also been used in solders. The fact that bismuth and many of its alloys expand slightly when they solidify make them ideal for this purpose.
• Bismuth subnitrate is a component of glazes that produces an iridescent luster finish.
• Bismuth telluride is an excellent thermoelectric material; it is widely used.
• A replacement propellant for xenon in Hall effect thrusters
• In 1997 an antibody conjugate with Bi-213, which has a 45 minute half-life, and decays with the emission of an alpha-particle, was used to treat patients with leukemia.
• In 2001, Professor Barry Allen and Dr. Graeme Melville at St. George Hospital in Sydney successfully produced Bi-213 in linac experiments which involved bombarding radium with bremsstrahlung photons. This cancer research team used Bi-213 in its Targeted Alpha Therapy (TAT) program.

In the early 1990s, research began to evaluate bismuth as a nontoxic replacement for lead in various applications:

• As noted above, bismuth has been used in solders; its low toxicity will be especially important for solders to be used in food processing equipment and copper water pipes.
• A pigment in artist's oil paint
• Ingredient in free-machining brasses for plumbing applications
• Ingredient in free-cutting steels for precision machining properties
• A catalyst for making acrylic fibres
• In low-melting alloys used in fire detection and extinguishing systems
• Ingredient in lubricating greases
• Dense material for fishing sinkers
• Bismuth(III) oxide, carbonate, or subnitrate in crackling microstars (dragon's eggs) in pyrotechnics
• Replacement for lead in shot and bullets. The UK, U.S., and many other countries now prohibit the use of lead shot for the hunting of wetland birds, as many birds are prone to lead poisoning due to mistaken ingestion of lead (instead of small stones and grit) to aid digestion. Bismuth-tin alloy shot is one alternative that provides similar ballistic performance to lead. (Another less expensive but also poorer-performing alternative is "steel" shot, which is actually soft iron.)

  Bismuth core bullets are also starting to appear for use in indoor shooting ranges, where fine particles of lead from bullets impacting the backstop can be a chronic toxic inhalant problem. Due to bismuth's crystalline nature, the bismuth bullets shatter into a non-toxic powder on impact, making recovery and recycling easy.^{[citation needed]} The lack of malleability does, however, make bismuth unsuitable for use in expanding hunting bullets.

• FN Herstal uses bismuth in the projectiles for their FN 303 less-lethal riot gun.