Bismuth


Bismuth is a chemical element; it has symbol Bi and atomic number 83. It is a post-transition metal and one of the pnictogens, with chemical properties resembling its lighter group 15 siblings arsenic and antimony. Elemental bismuth occurs naturally, and its sulfide and oxide forms are 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. Surface oxidation generally gives samples of the metal a somewhat rosy cast. Further oxidation under heat can give bismuth a vividly iridescent appearance due to thin-film interference. Bismuth is both the most diamagnetic element and one of the least thermally conductive metals known.
Bismuth was formerly understood to be the element with the highest atomic mass whose nuclei do not spontaneously decay. However, in 2003 it was found to be very slightly radioactive. The metal's only primordial isotope, bismuth-209, undergoes alpha decay with a half-life roughly a billion times longer than the estimated age of the universe.
Bismuth metal has been known since ancient times. Before modern analytical methods bismuth's metallurgical similarities to lead and tin often led it to be confused with those metals. The etymology of "bismuth" is uncertain. The name may come from mid-sixteenth-century Neo-Latin translations of the German words weiße Masse or Wismuth, meaning 'white mass', which were rendered as bisemutum or bisemutium.
Bismuth compounds account for about half the global 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 as it solidifies is responsible for some of its uses, as in the casting of printing type. Bismuth, when in its elemental form, has unusually low toxicity for a heavy metal. As the toxicity of lead and the cost of its environmental remediation became more apparent during the 20th century, suitable bismuth alloys have gained popularity as replacements for lead. Presently, around a third of global bismuth production is dedicated to needs formerly met by lead.

History and etymology

Bismuth metal has been known since ancient times. It was one of the first 10 metals to have been discovered. The name bismuth dates to around 1665 and is of uncertain etymology. The name possibly comes from obsolete German Bismuth, Wismut, Wissmuth, perhaps related to Old High German hwiz. The Neo-Latin bisemutium is from the German Wismuth, itself perhaps from weiße Masse, meaning "white mass".
The element was confused in early times with tin and lead because of its resemblance to those elements. Because bismuth has been known since ancient times, no one person is credited with its discovery. Agricola 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. Bismuth was also known to the Incas and used in a special bronze alloy for knives.
File:Bismuth symbol.svg|thumb|upright=0.5|right|Alchemical symbol used by Torbern Bergman
Beginning with Johann Heinrich Pott in 1738, 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.

Characteristics

Physical characteristics

Bismuth is a brittle metal with a dark, silver-pink hue, often 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 cause 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. Its toxicity is much lower than that of its neighbors in the periodic table, such as lead and antimony.
No other metal is verified to be more naturally diamagnetic than bismuth. Of any metal, it has one of the lowest values of thermal conductivity and the highest Hall coefficient. It has a high electrical resistivity. When deposited in sufficiently thin layers on a substrate, bismuth is a semiconductor, despite being a post-transition metal. Elemental bismuth is denser in the liquid phase than the solid, a characteristic it shares with germanium, silicon, and gallium. 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 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, so crystals may be grown using a household stove, although the resulting crystals will tend to be of lower quality than lab-grown crystals.
At ambient conditions, bismuth shares the same layered structure as the metallic forms of arsenic and antimony, crystallizing in the rhombohedral lattice. 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-V 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.

Chemical characteristics

Bismuth is stable to both dry and moist air at ordinary temperatures. At sufficiently high temperatures, it can react with water vapor to make bismuth oxide.
It reacts with fluorine to form bismuth fluoride at or bismuth fluoride at lower temperatures ; with other halogens it yields only bismuth 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 sulfate and sulfur dioxide.
It reacts with nitric acid to make bismuth nitrate.
It also dissolves in hydrochloric acid, but only with oxygen present.

Isotopes

The only primordial isotope of bismuth, bismuth-209, had long been regarded as the heaviest stable nuclide, but was suspected on theoretical grounds to be unstable to alpha decay. This was finally demonstrated in 2003, when researchers at the Institut d'astrophysique spatiale in Orsay, France, detected this decay; the best value of the half-life is now , over times longer than the estimated age of the universe. Due to its hugely long half-life, for all known medical and industrial applications, bismuth can be treated as stable. The radioactivity is of academic interest because bismuth is one of a few elements whose radioactivity was suspected and theoretically predicted before being detected in the laboratory. Bismuth has the longest known α-decay half-life, though tellurium-128 has the longest known by any mode: double beta decay at about.
Six isotopes of bismuth with short half-lives occur in the natural radioactive decay chains of actinium, radium, thorium, and neptunium; and more have been synthesized.
For medical use, bismuth-213 can be produced, as the parent isotope actinium-225, by bombarding radium with bremsstrahlung photons from a linear particle accelerator. In 1997, an antibody conjugate with bismuth-213 was used to treat leukemia patients, and it has been used in other cancer treatment, for example, in the targeted alpha therapy experimental program.

Chemical compounds

Chemically, bismuth resembles arsenic and antimony, but is much less toxic. In almost all known compounds, bismuth has oxidation state +3; a few have states +5 or −3.
The trioxide and trisulfide can both be made from the elements, although the trioxide is extremely corrosive at high temperatures. The pentoxide is not stable at room temperature, and will evolve oxygen| gas if heated. Both oxides form complex anions, and NaBiO3 is a strong oxidising agent. The trisulfide is common in bismuth ore.
Similarly, bismuth forms all possible trihalides, but the only pentahalide is. All are Lewis acids. Bismuth forms several formally- halides; these are complex salts with unusually structured polyatomic cations and anions.
In strongly acidic aqueous solution, the ion solvates to form. As pH increases, the cations polymerize until the octahedral bismuthyl complex, often abbreviated. Although bismuth oxychloride and bismuth oxynitrate have stoichiometries suggesting the ion, they are double salts instead. Bismuth nitrate hydrolysys in water, forming oxynitrate.
Bismuth forms very few stable bismuthides, intermetallic compounds in which it attains oxidation state −3. The hydride spontaneously decomposes at room temperature and stabilizes only below. Sodium bismuthide has interest as a topological Dirac insulator.

Occurrence and production

Production

The reported abundance of bismuth in the Earth's crust varies significantly by source from 180ppb to 8ppb. The most important ores of bismuth are bismuthinite and bismite. Native bismuth is known from Australia, Bolivia, and China.
CountryProduction
Year
World16,0002024
China

Price

The price for pure bismuth metal was 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.
Before World War II, demand for bismuth was small and mainly 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 during the war and at $2.25 per pound from 1950 until 1964.
In the early 1970s, the price rose 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 1981–1982. 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 United States federal government, but intensified around 2005. This resulted in a rapid and continuing increase in price.