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Bismuth is a chemical element with symbol Bi and atomic number 83. Bismuth, a pentavalent post-transition metal and one of the pnictogens, chemically resembles its lighter homologs arsenic and antimony. Elemental bismuth may occur naturally, 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 surface oxidation can give it a pink tinge. Bismuth is the most naturally diamagnetic element, and has one of the lowest values of thermal conductivity among metals. Bismuth metal has been known since ancient times, although it was often confused with lead and tin, which share some physical properties. The etymology is uncertain, but possibly comes from Arabic bi ismid, meaning having the properties of antimony or the German words weiße Masse or Wismuth ("white mass"), translated in the mid-sixteenth century to New Latin bisemutum. Bismuth was long considered the element with the highest atomic mass that is stable. However, in 2003 it was discovered to be extremely weakly radioactive: its only primordial isotope, bismuth-209, decays via alpha decay with a half-life more than a billion times the estimated age of the universe. Because of its tremendously long half-life, bismuth may still be considered stable for almost all purposes. Bismuth compounds account for about half the production of bismuth. They are used in cosmetics, pigments, and a few pharmaceuticals, notably bismuth subsalicylate, used to treat diarrhea. Bismuth's unusual propensity to expand upon freezing is responsible for some of its uses, such as in casting of printing type. Bismuth has unusually low toxicity for a heavy metal. As the toxicity of lead has become more apparent in recent years, there is an increasing use of bismuth alloys (presently about a third of bismuth production) as a replacement for lead.
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Bismuth

Bismuth

Bismuth,  83Bi
General properties
Pronunciation /ˈbɪzməθ/
BIZ-məth
Appearance lustrous brownish silver
Standard atomic weight (Ar) 208.98040(1)[1]
Bismuth in the periodic table
Sb

Bi

Mc
leadbismuthpolonium
Atomic number (Z) 83
Group, period group 15 (pnictogens), period 6
Block p-block
Element category   post-transition metal
Electron configuration [Xe] 4f14 5d10 6s2 6p3
Electrons per shell
2, 8, 18, 32, 18, 5
Physical properties
Phase (at STP) solid
Melting point 544.7 K ​(271.5 °C, ​520.7 °F)
Boiling point 1837 K ​(1564 °C, ​2847 °F)
Density (near r.t.) 9.78 g/cm3
when liquid (at m.p.) 10.05 g/cm3
Heat of fusion 11.30 kJ/mol
Heat of vaporization 179 kJ/mol
Molar heat capacity 25.52 J/(mol·K)
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 5, 4, 3, 2, 1, −1, −2, −3 ​(a mildly acidic oxide)
Electronegativity Pauling scale: 2.02
Ionization energies
  • 1st: 703 kJ/mol
  • 2nd: 1610 kJ/mol
  • 3rd: 2466 kJ/mol
  • (more)
Atomic radius empirical: 156 pm
Covalent radius 148±4 pm
Van der Waals radius 207 pm
Miscellanea
Crystal structurerhombohedral[2]
Speed of sound thin rod 1790 m/s (at 20 °C)
Thermal expansion 13.4 µm/(m·K) (at 25 °C)
Thermal conductivity 7.97 W/(m·K)
Electrical resistivity 1.29 µΩ·m (at 20 °C)
Magnetic ordering diamagnetic
Magnetic susceptibility −280.1·10−6 cm3/mol[3]
Young's modulus 32 GPa
Shear modulus 12 GPa
Bulk modulus 31 GPa
Poisson ratio 0.33
Mohs hardness 2.25
Brinell hardness 70–95 MPa
CAS Number 7440-69-9
History
Discovery Claude François Geoffroy (1753)
Main isotopes of bismuth
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct
207Bi syn 31.55 y β+ 207Pb
208Bi syn 3.68×105 y β+ 208Pb
209Bi 100% 1.9×1019 y α 205Tl
210Bi trace 5.012 d β 210Po
α 206Tl
210mBi syn 3.04×106 y IT 210Bi
α 206Tl
| references | in Wikidata

Bismuth is a chemical element with symbol Bi and atomic number 83. Bismuth, a pentavalent post-transition metal and one of the pnictogens, chemically resembles its lighter homologs arsenic and antimony. Elemental bismuth may occur naturally, 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 surface oxidation can give it a pink tinge. Bismuth is the most naturally diamagnetic element, and has one of the lowest values of thermal conductivity among metals.

Bismuth metal has been known since ancient times, although it was often confused with lead and tin, which share some physical properties. The etymology is uncertain, but possibly comes from Arabic bi ismid, meaning having the properties of antimony[4] or the German words weiße Masse or Wismuth ("white mass"), translated in the mid-sixteenth century to New Latin bisemutum.[5]

Bismuth was long considered the element with the highest atomic mass that is stable. However, in 2003 it was discovered to be extremely weakly radioactive: its only primordial isotope, bismuth-209, decays via alpha decay with a half-life more than a billion times the estimated age of the universe.[6][7] Because of its tremendously long half-life, bismuth may still be considered stable for almost all purposes.[7]

Bismuth compounds account for about half the production of bismuth. They are used in cosmetics, pigments, and a few pharmaceuticals, notably bismuth subsalicylate, used to treat diarrhea.[7] Bismuth's unusual propensity to expand upon freezing is responsible for some of its uses, such as in casting of printing type.[7] Bismuth has unusually low toxicity for a heavy metal.[7] As the toxicity of lead has become more apparent in recent years, there is an increasing use of bismuth alloys (presently about a third of bismuth production) as a replacement for lead.

History

The name bismuth dates from around the 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 German Bismuth, Wismut, Wissmuth (early 16th century); perhaps related to Old High German hwiz ("white").[5] The New Latin bisemutum (due to Georgius Agricola, who Latinized many German mining and technical words) is from the German Wismuth, perhaps from weiße Masse, "white mass".[8] 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 (c. 1546) states that bismuth is a distinct metal in a family of metals including tin and lead. This was based on observation of the metals and their physical properties.[9] Miners in the age of alchemy also gave bismuth the name tectum argenti, or "silver being made," in the sense of silver still in the process of being formed within the Earth.[10][11][12]

Beginning with Johann Heinrich Pott in 1738,[13] 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.[11][14][15] Bismuth was also known to the Incas and used (along with the usual copper and tin) in a special bronze alloy for knives.[16]

Characteristics

Bismuth crystal illustrating the many iridescent refraction hues of its oxide surface
Artificially grown bismuth crystal illustrating the stairstep crystal structure, with a 1 cm3 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 bismuth crystals 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 burned in oxygen, bismuth burns with a blue flame and its oxide forms yellow fumes.[14] Its toxicity is much lower than that of its neighbors in the periodic table, such as lead, antimony, and polonium.

No other metal is verified to be more naturally diamagnetic than bismuth.[14][17] (Superdiamagnetism is a different physical phenomenon.) Of any metal, it has one of the lowest values of thermal conductivity (after manganese, and maybe neptunium and plutonium) and the highest Hall coefficient.[18] It has a high electrical resistivity.[14] When deposited in sufficiently thin layers on a substrate, bismuth is a semiconductor, despite being a post-transition metal.[19]

Elemental bismuth is denser in the liquid phase than the solid, a characteristic it shares with antimony, germanium, silicon, gallium and water.[20] Bismuth expands 3.32% on solidification; therefore, it was long a component of low-melting typesetting alloys, where it compensated for the contraction of the other alloying components,[14][21][22][23] to form almost isostatic bismuth-lead eutectic 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.[24]

At ambient conditions bismuth shares the same layered structure as the metallic forms of arsenic and antimony,[25] crystallizing in the rhombohedral lattice[26] (Pearson symbol hR6, space group R3m No. 166), which is often classed into trigonal or hexagonal crystal systems.[2] When compressed at room temperature, this Bi-I structure changes first to the monoclinic Bi-II at 2.55 GPa, then to the tetragonal Bi-III at 2.7 GPa, and finally to the body-centered cubic Bi-IV at 7.7 GPa. The corresponding transitions can be monitored via changes in electrical conductivity; they are rather reproducible and abrupt, and are therefore used for calibration of high-pressure equipment.[27][28]

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.[29]

2 Bi + 3 H2O → Bi2O3 + 3 H2

It reacts with fluorine to make bismuth(V) fluoride at 500 °C or bismuth(III) fluoride at lower temperatures (typically from Bi melts); with other halogens it yields only bismuth(III) halides.[30][31][32] The trihalides are corrosive and easily react with moisture, forming oxyhalides with the formula BiOX.[33]

2 Bi + 3 X2 → 2 BiX3 (X = F, Cl, Br, I)

Bismuth dissolves in concentrated sulfuric acid to make bismuth(III) sulfate and sulfur dioxide.[29]

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.[29]

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:

3 Ba + 2 BiPh3 → 3 BaPh2 + 2 Bi

Isotopes

The only primordial isotope of bismuth, bismuth-209, was traditionally regarded as the heaviest stable isotope, but it had long been suspected[34] 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 years,[35] over a billion times longer than the current estimated age of the universe.[7] 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 theoretically predicted before being detected in the laboratory.[7] Bismuth has the longest known alpha decay half-life, although tellurium-128 has a double beta decay half-life of over 2.2×1024 years.[36]

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. Bismuth-213 is also found on the decay chain of uranium-233.[37]

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 bismuth-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, for example, in the targeted alpha therapy (TAT) program.[38][39]

Chemical compounds

Bismuth forms trivalent and pentavalent compounds, the trivalent ones being 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 vapors of the metal combine rapidly with oxygen, forming the yellow trioxide, Bi
2
O
3
.[20][40] When molten, at temperatures above 710 °C, this oxide corrodes any metal oxide, and even platinum.[32] On reaction with base, it forms two series of oxyanions: BiO
2
, which is polymeric and forms linear chains, and BiO3−
3
. The anion in Li
3
BiO
3
is actually a cubic octameric anion, Bi
8
O24−
24
, whereas the anion in Na
3
BiO
3
is tetrameric.[41]

The dark red bismuth(V) oxide, Bi
2
O
5
, is unstable, liberating O
2
gas upon heating.[42] The compound NaBiO3 is a strong oxidising agent.[43]

Bismuth sulfide, Bi
2
S
3
, occurs naturally in bismuth ores.[44] It is also produced by the combination of molten bismuth and sulfur.[31]

Bismuth oxychloride (BiOCl, see figure at right) and bismuth oxynitrate (BiONO3) stoichiometrically appear as simple anionic salts of the bismuthyl(III) cation (BiO+) which commonly occurs in aqueous bismuth compounds. However, in the case of BiOCl, the salt crystal forms in a structure of alternating plates of Bi, O, and Cl atoms, with each oxygen coordinating with four bismuth atoms in the adjacent plane. This mineral compound is used as a pigment and cosmetic (see below).[45]

Bismuthine and bismuthides

Unlike the lighter pnictogens nitrogen, phosphorus, and arsenic, but similar to antimony, bismuth does not form a stable hydride. Bismuth hydride, bismuthine (BiH
3
), is an endothermic compound that spontaneously decomposes at room temperature. It is stable only below −60 °C.[41] Bismuthides are intermetallic compounds between bismuth and other metals.

In 2014 researchers discovered that sodium bismuthide can exist as a form of matter called a “three-dimensional topological Dirac semi-metal” (3DTDS) that possess 3D Dirac fermions in bulk. It is a natural, three-dimensional counterpart to graphene with similar electron mobility and velocity. Graphene and topological insulators (such as those in 3DTDS) are both crystalline materials that are electrically insulating inside but conducting on the surface, allowing them to function as transistors and other electronic devices. While sodium bismuthide (Na
3
Bi
) is too unstable to be used in devices without packaging, it can demonstrate potential applications of 3DTDS systems, which offer distinct efficiency and fabrication advantages over planar graphene in semiconductor and spintronics applications. [46][47]

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
2
Cl2−
8
anions.[41][48] The Bi5+
9
cation has a distorted tricapped trigonal prismatic molecular geometry, and is also found in Bi
10
Hf
3
Cl
18
, 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
.[41]:50 Other polyatomic bismuth cations are also known, such as Bi2+
8
, found in Bi
8
(AlCl
4
)
2
.[48] Bismuth also forms a low-valence bromide with the same structure as "BiCl". There is a true monoiodide, BiI, which contains chains of Bi
4
I
4
units. BiI decomposes upon heating to the triiodide, BiI
3
, and elemental bismuth. A monobromide of the same structure also exists.[41] In oxidation state +3, bismuth forms trihalides with all of the halogens: BiF
3
, BiCl
3
, BiBr
3
, and BiI
3
. All of these except BiF
3
are hydrolyzed by water.[41]

Bismuth(III) chloride reacts with hydrogen chloride in ether solution to produce the acid HBiCl
4
.[29]

The oxidation state +5 is less frequently encountered. One such compound is BiF
5
, a powerful oxidizing and fluorinating agent. It is also a strong fluoride acceptor, reacting with xenon tetrafluoride to form the XeF+
3
cation:[29]

BiF
5
+ XeF
4
XeF+
3
BiF
6

Aqueous species

In aqueous solution, the Bi3+
ion solvated to form the aqua ion Bi(H
2
O)3+
8
in strongly acidic conditions.[49] At pH > 0 polynuclear species exist, the most important of which is believed to be the octahedral complex [Bi
6
O
4
(OH)
4
]6+
.[50]

Occurrence and production

Bismite mineral

In the Earth's crust, bismuth is about twice as abundant as gold. The most important ores of bismuth are bismuthinite and bismite.[14] Native bismuth is known from Australia, Bolivia, and China.[51][52]

According to the United States Geological Survey, the world mining production of bismuth in 2014 was 13,600 tonnes, with the major contributions from China (7,600 tonnes), Vietnam (4,950 tonnes) and Mexico (948 tonnes).[53] The refinery production in 2010 was 16,000 tonnes, of which China produced 13,000, Mexico 850 and Belgium 800 tonnes.[54] The difference reflects bismuth's status as a byproduct of extraction of other metals such as lead, copper, tin, molybdenum and tungsten.[55]

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 which separates the impurities as slag, or the electrolytic Betts process. Bismuth will behave similarly with another of its major metals, copper.[56] The raw bismuth metal from both processes 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.[56][57][58]

Price

The price for pure bismuth metal has been relatively stable through most of the 20th century, except for a spike in the 1970s. Bismuth has always been produced mainly as a byproduct of lead refining, and thus the price usually reflected the cost of recovery and the balance between production and demand.[59]

Demand for bismuth was small prior to World War II and was pharmaceutical – bismuth compounds were used to treat such conditions as digestive disorders, sexually transmitted infections and burns. Minor amounts of bismuth metal were consumed in fusible alloys for fire sprinkler systems and fuse wire. During World War II bismuth was considered a strategic material, used for solders, fusible alloys, medications and atomic research. To stabilize the market, the producers set the price at $1.25 per pound (2.75 $/kg) during the war and at $2.25 per pound (4.96 $/kg) from 1950 until 1964.[59]

In the early 1970s, the price rose rapidly as a result of increasing demand for bismuth as a metallurgical additive to aluminium, iron and steel. This was followed by a decline owing to increased world production, stabilized consumption, and the recessions of 1980 and 1981–82. In 1984, the price began to climb as consumption increased worldwide, especially in the United States and Japan. In the early 1990s, research began on the evaluation of bismuth as a nontoxic replacement for lead in ceramic glazes, fishing sinkers, food-processing equipment, free-machining brasses for plumbing applications, lubricating greases, and shot for waterfowl hunting.[60] Growth in these areas remained slow during the middle 1990s, in spite of the backing of lead replacement by the US Government, but intensified around 2005. This resulted in a rapid and continuing increase in price.[59]

Recycling

Whereas bismuth is most available today as a byproduct, its sustainability is more dependent on recycling. Bismuth is mostly a byproduct of the smelting of lead, and also of tungsten and 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).[61] 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. Bismuth spread in the environment in these products is unrecoverable with present technology.

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 to which the constraint on bismuth can be relieved is going to be tested by the future of the lead storage battery, since 90% of the world market for lead is currently 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.[62]

Applications

Bismuth has few commercial applications, and those applications that use it generally require small quantities relative to other raw materials. In the United States, for example, 884 tonnes of bismuth were consumed in 2010, of which 63% went into chemicals (including pharmaceuticals, pigments, and cosmetics); 26% into metallurgical additives for casting and galvanizing;[63] 7% into bismuth alloys, solders and ammunition; and 4% into research and other uses.[54]

Some manufacturers use bismuth as a substitute in equipment for potable water systems such as valves to meet "lead-free" mandates in the U.S. (began in 2014). This is a fairly large application since it covers all residential and commercial building construction.

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

Medicines

Bismuth is an ingredient in some pharmaceuticals,[7] although the use of some of these substances is declining.[45]

Cosmetics and pigments

Bismuth oxychloride (BiOCl) is sometimes used in cosmetics, as a pigment in paint for eye shadows, hair sprays and nail polishes.[7][45][67][68] This compound is found as the mineral bismoclite and in crystal form contains layers of atoms (see figure above) that refract light chromatically, resulting in an iridescent appearance similar to nacre of pearl. It was used as a cosmetic in ancient Egypt and in many places since. Bismuth white (also "Spanish white") can refer to either bismuth oxychloride or bismuth oxynitrate (BiONO3), when used as a white pigment.

Metal and alloys

Bismuth is used in metal alloys with other metals such as iron, to create alloys to go into automatic sprinkler systems for fires. It was also used to make bismuth bronze which was used in the Bronze Age.

Lead replacement

The density difference between lead (11.32 g/cm3) and bismuth (9.78 g/cm3) is small enough that for many ballistics and weighting applications, bismuth can 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, Denmark, England, Wales, the US, 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.) Bismuth's lack of malleability does, however, make it unsuitable for use in expanding hunting bullets.[citation needed]

Bismuth, as a dense element of high atomic weight, is used in bismuth-impregnated latex shields to shield from X-ray in medical examinations, such as CTs, mostly as it is considered non-toxic.[69]

The European Union's Restriction of Hazardous Substances Directive (RoHS) 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.[54] 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.[70]

Bismuth has been evaluated as a replacement for lead in free-machining brasses for plumbing applications,[71] although it does not equal the performance of leaded steels.[70]

Other metal uses and specialty alloys

Many bismuth alloys have low melting points and are found in specialty applications such as solders. Many automatic sprinklers, electric fuses, and safety devices in fire detection and suppression systems contain the eutectic In19.1-Cd5.3-Pb22.6-Sn8.3-Bi44.7 alloy that melts at 47 °C (117 °F)[14] This is a convenient temperature since it is unlikely to be exceeded in normal living conditions. Low-melting alloys, such as Bi-Cd-Pb-Sn alloy which melts at 70 °C, are also used in automotive and aviation industries. Before deforming a thin-walled metal part, it is filled with a melt or covered with a thin layer of the alloy to reduce the chance of breaking. Then the alloy is removed by submerging the part in boiling water.[72]

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 compensate each other and therefore lead and bismuth are often used in similar quantities.[73][74] Similarly, alloys containing comparable parts of bismuth and lead exhibit a very small change (on the order 0.01%) upon melting, solidification or aging. Such alloys are used in high-precision casting, e.g. in dentistry, to create models and molds.[72] Bismuth is also used as an alloying agent in production of malleable irons and as a thermocouple material.[14][54]

Bismuth is also used in aluminium-silicon cast alloys in order to refine silicon morphology. However, it indicated a poisoning effect on modification of strontium (Sr).[75][76] Some bismuth alloys, such as Bi35-Pb37-Sn25, are combined with non-sticking materials such as mica, glass and enamels because they easily wet them allowing to make joints to other parts. Addition of bismuth to caesium enhances the quantum yield of caesium cathodes.[45] Sintering of bismuth and manganese powders at 300 °C produces a permanent magnet and magnetostrictive material, which is used in ultrasonic generators and receivers working in the 10–100 kHz range and in magnetic memory devices.[77]

Other uses as compounds

  • Bismuth is included in BSCCO (bismuth strontium calcium copper oxide) which is a group of similar superconducting compounds discovered in 1988 that exhibit the highest superconducting transition temperatures.[78]
  • Bismuth subnitrate is a component of glazes that produces an iridescence and is used as a pigment in paint.
  • Bismuth telluride is a semiconductor and an excellent thermoelectric material.[45][79] Bi2Te3 diodes are used in mobile refrigerators, CPU coolers, and as detectors in infrared spectrophotometers.[45]
  • Bismuth oxide, in its delta form, is a solid electrolyte for oxygen. This form normally 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 compound is 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.[80][81]
  • A catalyst for making acrylic fibers.[14]
  • As an electrocatalyst in the conversion of CO2 to CO.[82]
  • Ingredient in lubricating greases.[83]
  • In crackling microstars (dragon's eggs) in pyrotechnics, as the oxide, subcarbonate or subnitrate.[84][85]

Toxicology and ecotoxicology

See also bismuthia, a rare dermatological condition that results from the prolonged use of bismuth.

Scientific literature indicates that some of the compounds of bismuth are less toxic to humans via ingestion compared to other heavy metals (lead, arsenic, antimony, etc.)[7] presumably due to the comparatively low solubility of bismuth salts.[86] Its biological half-life for whole-body retention is reported to be 5 days but it can remain in the kidney for years in people treated with bismuth compounds.[87]

Bismuth poisoning can occur and has according to some reports been common in relatively recent times.[86][88] As with lead, bismuth poisoning can result in the formation of a black deposit on the gingiva, known as a bismuth line.[89][90][91] Poisoning may be treated with dimercaprol; however, evidence for benefit is unclear.[92][93]

Bismuth's environmental impacts are not well known; it may be less likely to bioaccumulate than some other heavy metals, and this is an area of active research.[94][95]

Bioremediation

The fungus Marasmius oreades can be used for the biological remediation of bismuth in polluted soils.[96]

See also


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