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| Bismuth | |
Chemical Formula |
Bi |
Species |
Native Elements |
Crystal System |
Trigonal |
Mohs Scale |
2-2.5 |
Specific Gravity |
9.753 |
Color |
Reddish-white to creamy-white; tarnishes iridescent pinkish, yellowish or bluish |
Streak |
Silver-white |
Luster |
Metallic |
Diaphaneity |
Opaque |
Cleavage |
PerfectPerfect , Good , poor |
Bismuth metal has been known from ancient times, although until the 18th century it was often confused with lead and tin, as all three metals have similar physical properties. The etymology is uncertain, but possibly comes from Arabic bi ismid, meaning having the properties of antimony or German words weisse masse or wismuth ("white mass"), translated in the mid sixteenth century to New Latin bisemutum.
Bismuth has long been considered as the highest-atomic-mass element that is stable. However, it is slightly radioactive: its only primordial isotope bismuth-209 alpha decays with a half life more than a billion times the estimated age of the universe.
Bismuth compounds account for about half the production of bismuth. They 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, there is an increasing use of bismuth alloys (presently about a third of bismuth production) as a replacement for lead.
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 German Bismuth, Wismut, Wissmuth (early 16th century); perhaps related to Old High German hwiz ("white"). The New Latin bisemutum (due to Georgius Agricola, who Latinized many German mining and technical words) is from the German Wismuth, perhaps from wei?e Masse, "white mass." 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 (ca. 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. 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.
Beginning with Johann Heinrich Pott in 1738, Carl Wilhelm Scheele and Torbern Olof Bergman the distinctness of lead and bismuth became clear and Claude Fran?ois Geoffroy demonstrated in 1753 that this metal is distinct from lead and tin. Bismuth was also known to the Incas and used (along with the usual copper and tin) in a special bronze alloy for knives.
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 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, tin, tellurium, antimony, and polonium.
No other metal is verified to be more naturally diamagnetic than bismuth. (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. It has a high electrical resistance. When deposited in sufficiently thin layers on a substrate, bismuth is a semiconductor, rather than a poor metal.
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 a component of low-melting typesetting alloys, where it compensated for the contraction of the other alloying components, 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.
At ambient conditions bismuth crystallizes in the rhombohedral lattice (Pearson symbol hR6, space group R3m No. 166), which is often classed into trigonal or hexagonal crystal systems. 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.
Bismuth is stable to both dry and moist air at ordinary temperatures. When red-hot, it reacts with water to make bismuth(III) oxide.
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. The trihalides are corrosive and easily react with moisture, forming oxyhalides with the formula BiOX.
Bismuth dissolves in concentrated sulfuric acid to make bismuth(III) sulfate and sulfur dioxide.
It reacts with nitric acid to make bismuth(III) nitrate.
It also dissolves in hydrochloric acid, but only with oxygen present.
It is used as a transmetalating agent in the synthesis of alkaline-earth metal complexes:
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 209Bi to be 1.9×1019 yr, 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 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. Bismuth-213 is also found on the decay chain of uranium-233.
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, e.g. in the targeted alpha therapy (TAT) program.
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.
At elevated temperatures, the vapors of the metal combine rapidly with oxygen, forming the yellow trioxide, Bi2O3. When molten, at temperatures above 710 °C, this oxide corrodes any metal oxide, and even platinum. 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 Li3BiO3 is actually a cubic octameric anion, Bi8O24?
24, whereas the anion in Na3BiO3 is tetrameric.
The dark red bismuth(V) oxide, Bi2O5, is unstable, liberating O2 gas upon heating.
Bismuth sulfide, Bi2S3, occurs naturally in bismuth ores. It is also produced by the combination of molten bismuth and sulfur.
Bismuth oxychloride (BiOCl, see figure at right) and bismuth oxynitate (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).
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. Bismuthides are intermetallic compounds between bismuth and other metals.
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. The Bi5+
9 cation has a distorted tricapped trigonal prismatic 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.:50 Other polyatomic bismuth cations are also known, such as Bi2+
8, found in Bi8(AlCl4)2. 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. In oxidation state +3, bismuth forms trihalides with all of the halogens: BiF3, BiCl3, BiBr3, and BiI3. All of these except BiF3 are hydrolyzed by water to form the bismuthyl cation, BiO+
, the commonly-encountered bismuth (III) oxycation noted above.
Bismuth(III) chloride reacts with hydrogen chloride in ether solution to produce the acid HBiCl4.
The oxidation state +5 is less frequently encountered. One such compound is BiF5, a powerful oxidizing and fluorinating agent. It is also a strong fluoride acceptor, reacting with xenon tetrafluoride to form the XeF+
3 cation:
In aqueous solution, the Bi3+
ion exists in various states of hydration, depending on the pH:
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).
In the Earth's crust, bismuth is about twice as abundant as gold. The most important ores of bismuth are bismuthinite and bismite. Native bismuth is known from Australia, Bolivia, and China.
According to the United States Geological Survey, the world mining production of bismuth in 2010 was 8,900 tonnes, with the major contributions from China (6,500 tonnes), Peru (1,100 tonnes) and Mexico (850 tonnes). The refinery production was 16,000 tonnes, of which China produced 13,000, Mexico 850 and Belgium 800 tonnes.
The difference between world bismuth mine and refinery production reflects bismuth's status as a byproduct of extraction of other metals such as lead, copper, tin, molybdenum and tungsten. 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.
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.
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.
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 diseases 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.
In the early 1970s, the price grew rapidly due to 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. 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.
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). 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.
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. There is very little life-cycle information on other bismuth alloys or compounds.
Bismuth has few commercial applications, none of which are particularly large. Taking the US as an 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, 7% into bismuth alloys, solders and ammunition, and the balance into research and other uses.
In the early 1990s, researchers began to evaluate bismuth as a nontoxic replacement for lead in various applications.
Bismuth is an ingredient in some pharmaceuticals, although the use of some of these substances is declining.
Bismuth oxychloride (BiOCl) is sometimes used in cosmetics, as a pigment in paint for eye shadows, hair sprays and nail polishes. 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.
The density difference between lead (density 11.32 g·cm?3) and bismuth (density 9.78 g·cm?3) 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, the UK and 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.
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.
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. 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.
Bismuth has been evaluated as a replacement for lead in free-machining brasses for plumbing applications, although it does not equal the performance of leaded steels.
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. Low-melting allows, 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.
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. Similarly, alloys containing comparable parts of bismuth and 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. Bismuth is also used as an alloying agent in production of malleable irons and as a thermocouple material.
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 Cs cathodes. 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.
Scientific literature concurs that bismuth and most of its compounds are less toxic compared to other heavy metals (lead, antimony, etc.) and that it is not bioaccumulative. They have low solibilities in the blood, are easily removed with urine, and showed no carcinogenic, mutagenic or teratogenic effects in long-term tests on animals (up to 2 years). 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.
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.
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. Limited information however means that a close eye should be kept on its impact.
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