Bismuth

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Bismuth

Bismuth is a chemical element in the periodic table 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 less thermal conductivity. Lead-free bismuth compounds are used in cosmetics and in medical procedures.

Notable characteristics

It is a brittle metal with a pinkish hue and an iridescent tarnish. Among the heavy metals, bismuth is unusual in that its toxicity is much lower than that of its neighbors in the periodic table such as lead, thallium and antimony. Traditionally, it has also been regarded as the element with the heaviest stable isotope, but this is now known to be untrue (see below). No other metal is more naturally diamagnetic (as opposed to superdiamagnetic) than bismuth. It occurs in its native form, and 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 Semimetal-to-semiconductor transition in bismuth thin films, C. A. Hoffman, J. R. Meyer, and F. J. Bartoli, A. Di Venere, X. J. Yi, C. L. Hou, H. C. Wang, J. B. Ketterson, and G. K. Wong, Phys. Rev. B 48, 11431 (1993) . When combusted with oxygen, bismuth burns with a blue flame and its oxide forms yellow fumes.

Bismuth has long been thought to be unstable on theoretical grounds, but not until 2003 was this demonstrated when researchers at the Institut d'Astrophysique Spatiale in Orsay, France measured the alpha emission half-life of Bi-209 to be 1.9 × 10¹⁹ years, meaning that bismuth is very slightly radioactive, with a half-life over a billion times longer than the current estimated age of the universe. Due to this phenomenal half-life, bismuth can be treated as if it is stable and non-radioactive. Ordinary food containing typical amounts of Carbon-14 is many thousands of times more radioactive than bismuth, as are our own bodies. However, the radioactivity is of academic interest because bismuth is one of few elements whose radioactivity was suspected, and indeed theoretically predicted, before being detected in the lab.

Applications

Bismuth oxychloride is extensively used in cosmetics and bismuth subnitrate and subcarbonate are used in medicine. Bismuth subsalicylate (Pepto-Bismol®) is used as an antidiarrheal. Some other current uses are:

Strong permanent magnets can be made from the alloy bismanol (MnBi).
Many bismuth alloys have low melting points and are widely used for fire detection and suppression system safety devices.
Bismuth is used in producing malleable irons.
Bismuth is finding use as a catalyst for making acrylic fibers.
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.
Bismuth is sometimes used in the production of shot and shotgun slugs. Its advantage over lead in this respect is that it is comparatively non-toxic and therefore legal in the UK and several other countries for the shooting of wetland birds.
FN Herstal uses bismuth in the projectiles for their FN 303 less-lethal launcher.
As a replacement propellant for Xenon in Hall effect thrusters.

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.
As an ingredient of ceramic glazes
As an ingredient in free-machining brasses for plumbing applications
As an ingredient in free-cutting steels for precision machining properties
As a catalyst for making acrylic fibres
As a carrier for uranium fuel in nuclear reactors
In low-melting alloys used in fire detection and extinguishing systems
As an ingredient in lubricating greases
As a dense material for fishing sinkers.
As the oxide, subcarbonate, or subnitrate in crackling microstars (dragon's eggs) in pyrotechnics.
In 1997 an antibody conjugate of 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.

Crystals

Though virtually unseen in nature, high-purity bismuth can form into distinctive hopper crystals. These colorful laboratory creations are typically sold to hobbyists.

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 reducing tin into thin plates, and cementing them by a mixture of white tartar, saltpeter, and arsenic, stratified in a crucible over an open fire. ^*

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. China is the world's largest producer of bismuth, followed by Mexico and Peru. Canada, Bolivia, and Kazakhstan are smaller producers of bismuth.

The average price for bismuth in 2000 was States dollar|US$" target="_blank" >^*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).

References

External links

WebElements.com - Bismuth
"Bismuth Statistics and Information" - United States Geological Survey minerals information for bismuth
Bismuth breaks half-life record for alpha decay
Los Alamos National Laboratory - Bismuth