Significations et usages de Bismuth

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Bismuth (pronounced /ˈbɪzməθ/, BIZ-məth) is a chemical element that has the symbol Bi and atomic number 83. This trivalent poor metal chemically resembles arsenic and antimony. Bismuth is heavy and brittle; it has a silvery white color with a pink tinge owing to the surface oxide. Bismuth is the most naturally diamagnetic of all metals, and only mercury has a lower thermal conductivity. It is generally considered to be the last naturally occurring stable, non-radioactive element on the periodic table, although it is actually slightly radioactive, with an extremely long half-life.

Bismuth compounds are used in cosmetics, medicines, 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.

Characteristics

Bismuth is a brittle metal with a white, silver-pink hue, often occurring in its native form with an iridescent oxide tarnish showing many colors from yellow to blue. The spiral stair stepped structure of a bismuth crystal is the result of a higher growth rate around the outside edges than on the inside edges. The variations in the thickness of the oxide layer that forms on the surface of the crystal causes different wavelengths of light to interfere upon reflection, thus displaying a rainbow of colors. When combusted with oxygen, bismuth burns with a blue flame and its oxide forms yellow fumes.^[1] Its toxicity is much lower than that of its neighbors in the periodic table such as lead, tin, tellurium, antimony, and polonium.

Although ununpentium is theoretically more diamagnetic, no other metal is verified to be more naturally diamagnetic than bismuth.^[1] (Superdiamagnetism is a different physical phenomenon.) Of any metal, it has the second lowest thermal conductivity (after mercury) and the highest Hall coefficient. It has a high electrical resistance.^[1] When deposited in sufficiently thin layers on a substrate, bismuth is a semiconductor, rather than a poor metal.^[2]

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). Bismuth expands 3.32% on solidification; therefore, it was long an important component of low-melting typesetting alloys, where it compensated for the contraction of the other alloying components.^[1]

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 271 °C, so crystals may be grown using a household stove, although the resulting crystals will tend to be lower quality than lab-grown crystals.^{[citation needed]}

Isotopes

While bismuth was traditionally regarded as the element with the heaviest stable isotope, bismuth-209, 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 × 10¹⁹ years,^[3] over a billion times longer than the current estimated age of the universe. Owing to its extraordinarily long half-life, for all presently-known medical and industrial 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.

History

Bismuth (New Latin bisemutum from German Wismuth, perhaps from weiße Masse, "white mass") was confused in early times with tin and lead because of its resemblance to those elements. Bismuth has been known since ancient times, and so no one person is credited with its discovery. Agricola, in De Natura Fossilium states that bismuth is a distinct metal in a family of metals including tin and lead in 1546 based on observation of the metals and their physical properties.^[4] Claude François Geoffroy demonstrated in 1753 that this metal is distinct from lead and tin.^[1]

"Artificial bismuth" was commonly used in place of the actual metal. 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.^{[citation needed]}

Bismuth was also known to the Incas and used (along with the usual copper and tin) in a special bronze alloy for knives.^[5]

Occurrence and production

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, tungsten (China), tin, copper, and also silver (indirectly) or other metallic elements.

The most important ores of bismuth are bismuthinite and bismite.^[1] In 2005, China was the top producer of bismuth with at least 40% of the world share followed by Mexico and Peru, reports the British Geological Survey. Native bismuth is known from Australia, Bolivia, and China.

According to the USGS, world 2006 bismuth mine production was 5,700 tonnes, of which China produced 3,000 tonnes, Mexico 1,180 tonnes, Peru 950 tonnes, and the balance Canada, Kazakhstan and other nations. World 2006 bismuth refinery production was 12,000 tonnes, of which China produced 8,500 tonnes, Mexico 1,180 tonnes, Belgium 800 tonnes, Peru 600 tonnes, Japan 510 tonnes, and the balance Canada and other nations.^[7]

For the year 2007, the USGS Minerals Yearbook stated that world bismuth refinery production was of 15,000 tonnes, of which China was responsible for 77%, Mexico 8% and Belgium 5%.^[8]

The difference between world bismuth mine production and refinery production reflects bismuth's status as a byproduct metal. Bismuth travels in crude lead bullion (which can contain up to 10% bismuth) through several stages of refining, until it is removed by the Kroll-Betterton process or the Betts process. The Kroll-Betterton process uses a pyrometallurgical separation from molten lead of calcium-magnesium-bismuth drosses containing associated metals (silver, gold, zinc, some lead, copper, tellurium, and arsenic), which are removed by various fluxes and treatments to give high-purity bismuth metal (over 99% Bi). The Betts process takes cast anodes of lead bullion and electrolyzes them in a lead fluorosilicate-hydrofluorosilicic acid electrolyte to yield a pure lead cathode and an anode slime containing bismuth. Bismuth will behave similarly with another of its major metals, copper. Thus world bismuth production from refineries is a more complete and reliable statistic.

According to the Bismuth Advocate News,^[6] the price for bismuth metal from year-end 2000 to September 2005 was stuck in a range from $2.60 to $4.15 per lb., but after this period the price started rising rapidly as global bismuth demand as a lead replacement and other uses grew rapidly. New mines in Canada and Vietnam may relieve the shortages, but prices are likely to remain above their previous level for the foreseeable future. The Customer-Input price for bismuth is more oriented to the ultimate consumer; it started at US$39.40 per kilogram ($17.90 per pound) in January 2008 and reached US$35.55 per kg (US$16.15 per lb.) in September 2008.^[9]

Recycling

While bismuth is most available today as a byproduct, its sustainability is more dependent on recycling. Bismuth is mostly a byproduct of lead smelting, along with silver, zinc, antimony, and other metals, and also of tungsten production, along with molybdenum and tin, and also of copper production. Recycling bismuth is difficult in many of its end uses, primarily because of scattering. Probably the easiest to recycle would be bismuth-containing fusible alloys in the form of larger objects, then larger soldered objects. Half of the world solder consumption is in electronics (i.e., circuit boards).^[10] As the soldered objects get smaller or contain little solder or little bismuth, the recovery gets progressively more difficult and less economic, although solder with a sizable silver content will be more worth recovering. Next in recycling feasibility would be sizeable catalysts with a fair bismuth content, perhaps as bismuth phosphomolybdate, and then bismuth used in galvanizing and as a free-machining metallurgical additive. Finally, the bismuth in the uses where it gets scattered the most, in stomach medicines (bismuth subsalicylate), paints (bismuth vanadate) on a dry surface, pearlescent cosmetics (bismuth oxychloride), and bismuth-containing bullets. The bismuth is so scattered in these uses as to be unrecoverable with present technology. Bismuth can also be available sustainably from greater efficiency of use or substitution, most likely stimulated by a rising price. For the stomach medicine, another active ingredient could be substituted for some or all of the bismuth compound^{[citation needed]}. It would be more difficult to find an alternative to bismuth oxychloride in cosmetics to give the pearlescent effect. However, there are many alloying formulas for solders and therefore many alternatives.

The most important sustainability fact about bismuth is its byproduct status, which can either improve sustainability (i.e., vanadium or manganese nodules) or, for bismuth from lead ore, constrain it; bismuth is constrained. The extent that the constraint on bismuth can be ameliorated or not is going to be tested by the future of the lead storage battery, since 90% of the world market for lead is in storage batteries for gasoline or diesel-powered motor vehicles.

The life-cycle assessment of bismuth will focus on solders, one of the major uses of bismuth, and the one with the most complete information. The average primary energy use for solders is around 200 MJ per kg, with the high-bismuth solder (58% Bi) only 20% of that value, and three low-bismuth solders (2% to 5% Bi) running very close to the average. The global warming potential averaged 10 to 14 kg carbon dioxide, with the high-bismuth solder about two-thirds of that and the low-bismuth solders about average. The acidification potential for the solders is around 0.9 to 1.1 kg sulfur dioxide equivalent, with the high-bismuth solder and one low-bismuth solder only one-tenth of the average and the other low-bismuth solders about average.^[11] There is very little life-cycle information on other bismuth alloys or compounds.

Chemistry

Bismuth forms trivalent and pentavalent compounds. The trivalent compounds are more common. Many of its chemical properties are similar to other elements in its group; namely, arsenic and antimony.

Bismuth is stable to both dry and moist air at ordinary temperatures. At elevated temperatures, the vapours of the metal combine rapidly with oxygen, forming the yellow trioxide, Bi₂O₃.^[12] On reaction with base, this oxide forms two series of oxyanions: BiO−2, which is polymeric and forms linear chains, and BiO3−3. The anion in Li₃BiO₃ is actually a cubic octameric anion, Bi₈O24−24, whereas the anion in Na₃BiO₃ is tetrameric.^[13]

Bismuth sulfide, Bi₂S₃, occurs naturally in bismuth ores.^[14] It is also produced by the combination of molten bismuth and sulfur.^[12]

Unlike earlier members of group 15 elements such as nitrogen, phosphorus, and arsenic, and similar to the previous group 15 element antimony, bismuth does not form a stable hydride analogous to ammonia and phosphine. Bismuth hydride, bismuthine (BiH₃), is an endothermic compound that spontaneously decomposes at room temperature. It is stable only below −60°C.^[13]

The halides of bismuth in low oxidation states have been shown to have unusual structures. What was originally thought to be bismuth(I) chloride, BiCl, turns out to be a complex compound consisting of Bi5+9 cations and BiCl2−5 and Bi₂Cl2−8 anions.^[13][15] The Bi5+9 cation is also found in Bi₁₀HfCl₁₈, prepared by reducing a mixture of hafnium(IV) chloride and bismuth chloride with elemental bismuth. Other polyatomic bismuth cations are also known, such as Bi2+8, found in Bi₈(AlCl₄)₂.^[15] Bismuth also forms a low-valence bromide with the same structure as "BiCl". There is a true monoiodide, BiI, which contains chains of Bi₄I₄ units. BiI decomposes upon heating to the triiodide, BiI₃, and elemental bismuth. A monobromide of the same structure also exists.^[13]

In oxidation state +3, bismuth forms trihalides with all of the halogens: BiF₃, BiCl₃, BiBr₃, and BiI₃. All of these, except BiF₃, are hydrolysed by water to form the bismuthyl cation, BiO⁺, a commonly encountered bismuth oxycation.^[13] Bismuth(III) chloride reacts with hydrogen chloride in ether solution to produce the acid HBiCl₄.^[16]

Bismuth dissolves in nitric acid to form bismuth(III) nitrate, Bi(NO₃)₃. In the presence of excess water or the addition of a base, the Bi³⁺ ion reacts with the water to form BiO⁺, which precipitates as (BiO)NO₃.^[17]

The oxidation state +5 is less frequently encountered. One such compound is BiF₅, a powerful oxidising and fluorinating agent. It reacts with xenon tetrafluoride to form the XeF+3 cation:^[16]

BiF₅ + XeF₄ → XeF+3BiF−6

The dark red bismuth(V) oxide, Bi₂O₅, is unstable, liberating O₂ gas upon heating.^[18]

In aqueous solution, the Bi³⁺ ion exists in various states of hydration, depending on the pH:

pH range	Species
<3	Bi(H2O)3+6
0-4	Bi(H2O)5OH2+
1-5	Bi(H2O)4(OH)2+
5-14	Bi(H2O)3(OH)3
>11	Bi(H2O)2(OH)4−

These mononuclear species are in equilibrium. Polynuclear species also exist, the most important of which is BiO⁺, which exists in hexameric form as the octahedral complex [Bi₆O₄(OH)₄]⁶⁺ (or 6 [BiO⁺]·2 H₂O).^[19]

Applications

Bismuth oxychloride is sometimes used in cosmetics. Bismuth subnitrate and bismuth subcarbonate are used in medicine.^[1] Bismuth subsalicylate (the active ingredient in Pepto-Bismol and (modern) Kaopectate) is used as an antidiarrheal and to treat some other gastro-intestinal diseases (oligodynamic effect). Also, the product Bibrocathol is an organic molecule containing Bismuth and is used to treat eye infections. Bismuth subgallate (the active ingredient in Devrom) is used as an internal deodorant to treat malodor from flatulence (or gas) and faeces. Historically Bisthmuth compounds were used to treat Syphilis and today Bismuth subsalicylate and Bismuth subcitrate are used to treat the Peptic ulcer.

Some other current uses

• Strong permanent magnets can be made from the alloy Bismanol (BiMn).^[20]

• Bismuth has a potential role in electronic circuits and in manufacturing next-generation solar cells which would have a greater efficiency. Bismuth allows for the creation of new diodes that can reverse their direction of current flow.^[21]
• Many bismuth alloys have low melting points and are widely used for fire detection and suppression system safety devices.^[1]
• Bismuth is used as an alloying agent in production of malleable irons.^[1]
• It is also used as a thermocouple material.^[1]
• A carrier for U-235 or U-233 fuel in nuclear reactors.^[1]
• Bismuth is also 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 (a semiconductor) is an excellent thermoelectric material. BiTe diodes are used in mobile refrigerators and CPU coolers. Also used as detectors in Infra red spectrophotometers.
• A replacement propellant for xenon in Hall effect thrusters
• Bismuth is included in BSCCO (Bismuth Strontium Calcium Copper Oxide) which is a group of similar superconducting compounds discovered in 1988 among which is the highest temperature superconductor yet known with a transition temperature of 110K.^[22]
• Bi-213 can be produced by bombarding radium with bremsstrahlung photons from a linear particle accelerator. 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. This isotope has also been tried in cancer treatment, e.g. in the Targeted Alpha Therapy (TAT) program.^[23]
• The delta form of bismuth oxide when it exists at room temperature is a solid electrolyte for oxygen. This form normally only exists above and breaks down below a high temperature threshold, but can be electrodeposited well below this temperature in a highly alkaline solution.
• In low-melting alloys used in fire detection and extinguishing systems
• RoHS initiative for reduction of Lead have broadened Bisthmus' use in electronics et al. as a component of low melting solders as a replacement for traditional Tin-Lead solders.

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 lead-free solders^[8]; its low toxicity will be especially important for solders to be used in food processing equipment and copper water pipes, although it can also be used in other applications including those in the automobile industry, in the EU for example.^[24]
• A pigment in artists' oil and acrylic paint (Bismuth Vanadate)
• Ingredient in free-machining brasses for plumbing applications, although it doesn't equal leaded steels' performance^[24]
• Ingredient in free-machining steels for precision machining properties
• A catalyst for making acrylic fibers^[1]
• Ingredient in lubricating greases
• Dense material for fishing sinkers
• In crackling microstars (dragon's eggs) in pyrotechnics, as the oxide, subcarbonate, or subnitrate
• 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 owing 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 more poorly performing alternative is "steel" shot, which is actually soft iron.) The lack of malleability does, however, make bismuth unsuitable for use in expanding hunting bullets.
• Fabrique Nationale de Herstal uses bismuth in the projectiles for its FN 303 less-lethal riot gun.

According to the USGS, U.S. bismuth consumption in 2006 totaled 2,050 tonnes, of which chemicals (including pharmaceuticals, pigments, and cosmetics) were 510 tonnes, bismuth alloys 591 tonnes, metallurgical additives 923 tonnes, and the balance other uses.

Toxicology and ecotoxicology

Scientific literature concurs with the idea that bismuth and its compounds are less toxic than lead or its other periodic table neighbours (antimony, polonium)^[25] and that it isn't bioaccumulative. Its biological half-life for whole-body retention is 5 days but it can remain in the kidney for years in patients treated with bismuth compounds.^[26] In the industry, it is considered as one of the least toxic heavy metals.

Bismuth poisoning exists and mostly affects the kidney and liver. Skin and respiratory irritation can also follow exposure to respective organs. As with lead, overexposure to bismuth can result in the formation of a black deposit on the gingiva, known as a bismuth line.^[27]

Bismuth's environmental impacts are not very well known. It is considered that its environmental impact is small, due in part to the low solubility of its compounds.^[28] Limited information however means that a close eye should be kept on its impact.

Other characteristics

Fine bismuth powder can be pyrophoric.^[12]

See also

• Lead-bismuth eutectic
• Bismuth minerals

References

External links

• WebElements.com - Bismuth
• USGS 2006 Minerals Yearbook: Bismuth
• Bismuth Advocate News (BAN)
• Bismuth Statistics and Information - United States Geological Survey minerals information for bismuth
• Laboratory growth of large crystals of Bismuth by Jan Kihle Crystal Pulling Laboratories, Norway
• Bismuth breaks half-life record for alpha decay
• Bismuth Crystals – Instructions & Pictures