bismuth

lead ← bismuth → polonium Sb ↑ Bi ↓ Uup 83Bi Periodic table
Appearance
lustrous silver
General properties
Name, symbol, number	bismuth, Bi, 83
Pronunciation	/ˈbɪzməθ/ BIZ-məth
Element category	post-transition metal
Group, period, block	15, 6, p
Standard atomic weight	208.98040(1)
Electron configuration	[Xe] 4f14 5d10 6s2 6p3
Electrons per shell	2, 8, 18, 32, 18, 5 (Image)
Physical properties
Phase	solid
Density (near r.t.)	9.78 g·cm−3
Liquid density at m.p.	10.05 g·cm−3
Melting point	544.7 K, 271.5 °C, 520.7 °F
Boiling point	1837 K, 1564 °C, 2847 °F
Heat of fusion	11.30 kJ·mol−1
Heat of vaporization	151 kJ·mol−1
Molar heat capacity	25.52 J·mol−1·K−1
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 941 1041 1165 1325 1538 1835
Atomic properties
Oxidation states	3, 5 (mildly acidic oxide)
Electronegativity	2.02 (Pauling scale)
Ionization energies (more)	1st: 703 kJ·mol−1
	2nd: 1610 kJ·mol−1
	3rd: 2466 kJ·mol−1
Atomic radius	156 pm
Covalent radius	148±4 pm
Van der Waals radius	207 pm
Miscellanea
Crystal structure	trigonal[1]
Magnetic ordering	diamagnetic
Electrical resistivity	(20 °C) 1.29 µΩ·m
Thermal conductivity	7.97 W·m−1·K−1
Thermal expansion	(25 °C) 13.4 µm·m−1·K−1
Speed of sound (thin rod)	(20 °C) 1790 m·s−1
Young's modulus	32 GPa
Shear modulus	12 GPa
Bulk modulus	31 GPa
Poisson ratio	0.33
Mohs hardness	2.25
Brinell hardness	94.2 MPa
CAS registry number	7440-69-9
Most stable isotopes
Main article: Isotopes of bismuth
iso NA half-life DM DE (MeV) DP 207Bi syn 31.55 y ε, β+ 2.399 207Pb 208Bi syn 368,000 y ε, β+ 2.880 208Pb 209Bi 100% (1.9 ± 0.2) ×1019y α 3.14 205Tl 210mBi syn 3.04×106y IT 0.271 210Bi
v t e · r

Bismuth ( /ˈbɪzməθ/ BIZ-məth) is a chemical element with symbol Bi and atomic number 83. Bismuth, a trivalent poor metal, chemically resembles arsenic and antimony. Elemental bismuth may occur naturally uncombined, although its sulfide and oxide form important commercial ores. The free element is 86% as dense as lead. It is a brittle metal with a silvery white color when freshly produced, but is often seen in air with a pink tinge owing to surface oxidation. Bismuth metal has been known from ancient times, although until the 18th century, it was often confused with lead and tin, which each have some of the metal's bulk physical properties. The etymology is uncertain, but possibly comes from Arabic bi ismid, meaning having the properties of antimony^[2] or German words weisse masse or wismuth meaning "white mass".^[3]

Bismuth is the most naturally diamagnetic of all metals, and only mercury has a lower thermal conductivity.

Bismuth has classically been considered to be the heaviest naturally occurring stable element, in terms of atomic mass. Recently, however, it has been found to be very slightly radioactive: its only primordial isotope bismuth-209 decays via alpha decay into thallium-205 with a half-life of more than a billion times the estimated age of the universe.^[4]

Bismuth compounds (accounting for about half the production of bismuth) are used in cosmetics, pigments, and a few pharmaceuticals, notably Pepto-Bismol. Bismuth has unusually low toxicity for a heavy metal. As the toxicity of lead has become more apparent in recent years, alloy uses for bismuth metal (presently about a third of bismuth production), as a replacement for lead, have become an increasing part of bismuth's commercial importance.

Characteristics

Bismuth crystal illustrating the many iridescent refraction hues of its oxide surface

Artificially grown bismuth crystal illustrating the stair-step crystal structure, with a 1-cm cube of bismuth metal

Physical 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.^[5] Its toxicity is much lower than that of its neighbors in the periodic table, such as lead, tin, tellurium, antimony, and polonium.

No other metal is verified to be more naturally diamagnetic than bismuth.^[6] It is the most diamagnetic of naturally occurring elements.^[7] (Superdiamagnetism is a different physical phenomenon.) Of any metal, it has the second lowest thermal conductivity^[8][9] (after mercury) and the highest Hall coefficient.^[10] It has a high electrical resistance.^[5] When deposited in sufficiently thin layers on a substrate, bismuth is a semiconductor, rather than a poor metal.^[11]

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 component of low-melting typesetting alloys, where it compensated for the contraction of the other alloying components, ^{[5][12][13][14]} to form almost isostatic bismuth-lead eutectics alloys.

Though virtually unseen in nature, high-purity bismuth can form distinctive, colorful hopper crystals. It 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.^[15]

Chemical characteristics

Bismuth is stable to both dry and moist air at ordinary temperatures. When red-hot, it reacts with water to make bismuth(III) oxide.^[16]

2 Bi + 3 H₂O → Bi₂O₃ + 3 H₂

It reacts with large amounts of fluorine to make bismuth(V) fluoride.^[16]

2 Bi + 5 F₂ → 2 BiF₅

It reacts with small amounts of fluorine to make bismuth(III) fluoride.^[16]

2 Bi + 3 F₂ → 2 BiF₃

It also reacts with the other halogens to make bismuth(III) halides.^[16]

2 Bi + 3 Cl₂ → 2 BiCl₃

2 Bi + 3 Br₂ → 2 BiBr₃

2 Bi + 3 I₂ → 2 BiI₃

It dissolves in concentrated sulfuric acid to make bismuth(III) sulfate and sulfur dioxide.^[16]

6 H₂SO₄ + 2 Bi → 6 H₂O + Bi₂(SO₄)₃ + 3 SO₂

It reacts with nitric acid to make bismuth(III) nitrate.

Bi + 6 HNO₃ → 3 H₂O + 3 NO₂ + Bi(NO₃)₃

It also dissolves in hydrochloric acid, but only with oxygen present.^[16]

4 Bi + 3 O₂ + 12 HCl → 4 BiCl₃ + 6 H₂O

It is used as a transmetalating agent in the synthesis of alkaline-earth metal complexes:

Ba + BiPh₃ → BaPh₃ + Bi

Isotopes

The only primordial isotope of bismuth, bismuth-209, was traditionally regarded as the heaviest stable isotope, but 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 209
Bi to be 1.9×10¹⁹ yr,^[17] 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 nonradioactive. 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 laboratory. Bismuth has the longest known alpha decay half-life, although tellurium-128 has a double beta decay half-life of over 2.2×10²⁴ yr.

Several isotopes of bismuth with short half-lives occur within the radioactive disintegration chains of actinium, radium, and thorium, and more have been synthesized experimentally.

Commercially, the radioactive isotope bismuth-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.^[18] Bismuth-213 is also found on the decay chain of uranium-233.

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, tungsten (China), tin, copper, and silver (indirectly) or other metallic elements.^[19]

Production

Bismite mineral

Bismuth output in 2005

The most important ores of bismuth are bismuthinite and bismite.^[5] 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.^[3][21]

According to the United States Geological Survey, world 2009 mine production of bismuth was 7,300 tonnes, with the major contributions from China (4,500 tonnes), Mexico (1,200 tonnes) and Peru (960 tonnes).^[22] World 2008 bismuth refinery production was 15,000 tonnes, of which China produced 78%, Mexico 8% and Belgium 5%.^[19]

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). 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.^[23]

The raw bismuth metal from both process contains still considerable amounts of other metals foremost lead. By reacting the molten mixture with chlorine gas the metals are converted to their chlorides while bismuth remains unchanged. Impurities can also be removed by various other methods for example with fluxes and treatments yielding high-purity bismuth metal (over 99% Bi). World bismuth production from refineries is a more complete and reliable statistic.^[23][24][25]

According to the Bismuth Advocate News,^[20] the price for bismuth metal from year-end 2000 to September 2005 ranged from $2.60 to $4.15 per pound, 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.^[26]

Recycling

Whereas 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's solder consumption is in electronics (i.e., circuit boards).^[27] 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 higher silver content will be more worthwhile 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.

Bismuth in uses where it is dispersed most widely include stomach medicines (bismuth subsalicylate), paints (bismuth vanadate) on a dry surface, pearlescent cosmetics (bismuth oxychloride), and bismuth-containing bullets that have been fired. The bismuth scattered in these uses is unrecoverable with present technology.

Bismuth can also be available sustainably from greater efficiency of use or substitution, most likely stimulated by a rising price.^{[citation needed]} It would be more difficult to find an alternative to bismuth oxychloride in cosmetics to give the pearlescent effect.^{[citation needed]} However, the many alloying formulas for solders allow for 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.^[28] There is very little life-cycle information on other bismuth alloys or compounds.

Chemical compounds

Bismuth forms trivalent and pentavalent compounds; the trivalent ones are more common. Many of its chemical properties are similar to those of arsenic and antimony, although they are less toxic than derivatives of those lighter elements.

Oxides and sulfides

At elevated temperatures, the vapours of the metal combine rapidly with oxygen, forming the yellow trioxide, Bi₂O₃.^[29] 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.^[30]

The dark red bismuth(V) oxide, Bi₂O₅, is unstable, liberating O₂ gas upon heating.^[31]

Bismuth sulfide, Bi₂S₃, occurs naturally in bismuth ores.^[32] It is also produced by the combination of molten bismuth and sulfur.^[29]

Bismuthine and bismuthides

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. Bismuth hydride, bismuthine (BiH₃), is an endothermic compound that spontaneously decomposes at room temperature. It is stable only below −60 °C.^[30] Bismuthides are intermetallic compounds between bismuth and other metals.

Halides

The halides of bismuth in low oxidation states have been shown to adopt 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 Bi
2Cl2−
8 anions.^[30][33] The Bi5+
9 cation has a distorted tricapped trigonal prismic molecular geometry, and is also found in Bi₁₀Hf₃Cl₁₈, which is prepared by reducing a mixture of hafnium(IV) chloride and bismuth chloride with elemental bismuth, having the structure [Bi⁺][Bi5+
9][HfCl2−
6]₃.^[30]:50 Other polyatomic bismuth cations are also known, such as Bi2+
8, found in Bi₈(AlCl₄)₂.^[33] 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.^[30]

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.^[30] Bismuth(III) chloride reacts with hydrogen chloride in ether solution to produce the acid HBiCl₄.^[34]

The oxidation state +5 is less frequently encountered. One such compound is BiF₅, a powerful oxidising and fluorinating agent. It is also a strong fluoride acceptor, reacting with xenon tetrafluoride to form the XeF+
3 cation:^[34]

BiF₅ + XeF₄ → XeF+
3BiF−
6

Aqueous species

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).^[35]

History

The name Bismuth is from ca. 1660s and is of uncertain etymology. It is one of the first 10 metals to have been discovered. Bismuth appears in the 1660s, from obsolete Ger. Bismuth, Wismut, Wissmuth (early 16c.); perhaps related to O.H.G. hwiz ("white").^[36] The New Latin bisemutum is from German Wismuth, perhaps from weiße Masse, "white mass."^[37] The element was confused in early times with tin and lead because of its resemblance to those elements. Bismuth has been known since ancient times, 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.^[38] The name miners gave the metal also the name tectum argenti.^[39][40]

Beginning with Johann Heinrich Pott in 1738,^[41] Carl Wilhelm Scheele and Torbern Olof Bergman the distinctness of lead and bismuth became clear and Claude François Geoffroy demonstrated in 1753 that this metal is distinct from lead and tin.^[5][40][42]

Bismuth was also known to the Incas and used (along with the usual copper and tin) in a special bronze alloy for knives.^[43]

Applications

Bismuth has few commercial applications, none of which are large. Taking the U.S. as an example, 1,090 tonnes of bismuth were consumed in 2008, of which 55% were chemicals (including pharmaceuticals, pigments, and cosmetics), 34% were metallurgical additives for casting and galvanizing,^[44] 7% were bismuth alloys, solders and ammunition, and the balance went for research and other uses.^[19]

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

Health and cosmetics

Bismuth is an ingredient in some pharmaceuticals, although the use of some of these substances is declining.^[7] Bismuth subsalicylate is used as an antidiarrheal; it is the active ingredient in such "Pink Bismuth" preparations as Pepto-Bismol, as well as the 2004 reformulation of Kaopectate. It is also used to treat some other gastro-intestinal diseases. The mechanism of action of this substance is still not well documented, although an oligodynamic effect may be involved in at least some cases. Bibrocathol is an organic bismuth-containing compound used to treat eye infections. Bismuth subgallate, the active ingredient in Devrom, is used as an internal deodorant to treat malodor from flatulence ("gas") and feces. Bismuth compounds were formerly used to treat syphilis, and today bismuth subsalicylate and bismuth subcitrate are used to treat peptic ulcers. Bismuth subnitrate and bismuth subcarbonate are also used in medicines.^[5]

Bismuth oxychloride is sometimes used in cosmetics.

Metal and alloys

• Many bismuth alloys have low melting points and are found in specialty applications such as solders. Fire detection and suppression system safety devices widely use In-Cd–Pb-Sn-Bi which melts at 47 °C.^[5]
• The "RoHS" initiative for reduction of lead has broadened bismuth's use in electronics as a component of low-melting point solders, as a replacement for traditional tin-lead solders.^[19] 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.^[45]
• Bismuth has been evaluated as a replacement for lead in free-machining brasses for plumbing applications,^[46] although it doesn't equal the performance of leaded steels^[45].
• Because bismuth is the most diamagnetic naturally occurring element, it is used for diamagnetic levitation.^[47]
• Bismuth is used to make free-machining steels and free-machining aluminium alloys for precision machining properties. It has similar effect to lead and improves the chip breaking during machining. The shrinking on solidification in lead and the expansion of bismuth compensates each other and therefore lead and bismuth are often used in similar quantities.^[48][49]
• The density difference between lead (density 11.32 g·cm⁻³) and bismuth (density 9.78 g·cm⁻³) is small enough that for most application bismuth can be a substitute for lead. For example it can replace lead as a dense material in fishing sinkers. It has been used as a replacement for lead in shot, bullets and less-lethal riot gun ammunition. The Netherlands, the UK and 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, or even prohibit the use of lead for all hunting, such as in the Netherlands. 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.
• Bismuth is also used as an alloying agent in production of malleable irons and as a thermocouple material.^[5][19]

Other uses as compounds

Bismuth vanadate, a yellow pigment

• Superconductors. 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.^[50]
• Bismuth subnitrate is a component of glazes that produces an iridescence.
• Bismuth telluride (a semiconductor) is an excellent thermoelectric material.^[51] Bi₂Te₃ diodes are used in mobile refrigerators and CPU coolers. Also used as detectors in infrared spectrophotometers.
• Bismuth oxide when it exists in delta form 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.
• Bismuth vanadate is an opaque yellow pigment in artists' oil and acrylic paint. This pigment is generally considered to be a non-toxic lightfast substitute for lemon yellow pigments such as the cadmium sulfides and the lead/strontium/barium chromates. Unlike lead chromate+lead sulfate lemon, bismuth vanadate does not readily blacken with UV exposure.^[52][53]
• A catalyst for making acrylic fibers.^[5]
• Ingredient in lubricating greases.^[54]
• In crackling microstars (dragon's eggs) in pyrotechnics, as the oxide, subcarbonate or subnitrate.^[55][56]
• Bismuth oxychloride is used as a special effect pigment in cosmetics (Pearlescent coating).^[57][58]

Toxicology and ecotoxicology

This section requires expansion.

Scientific literature concurs with the idea that bismuth and its compounds are less toxic than lead or its other periodic table neighbours (antimony, polonium)^[59] and that it is not 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.^[60] In the industry, it is considered as one of the least toxic heavy metals.

Bismuth poisoning exists and mostly affects the kidney, liver, and bladder. 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.^[61][62]

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.^[63] Limited information however means that a close eye should be kept on its impact.^[64][65][66]

See also

	Book: Bismuth
Wikipedia books are collections of articles that can be downloaded or ordered in print.

• Lead-bismuth eutectic
• Bismuth minerals

References

External links

Wikimedia Commons has media related to: Bismuth

Look up bismuth in Wiktionary, the free dictionary.

• Bismuth Advocate News (BAN)
• 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