Beryllium

Beryllium is a chemical element with symbol Be and atomic number 4. It is a relatively rare element in the universe, usually occurring as a product of the spallation of larger atomic nuclei that have collided with cosmic rays. Within the cores of stars beryllium is depleted as it is fused and creates larger elements. It is a divalent element which occurs naturally only in combination with other elements in minerals. Notable gemstones which contain beryllium include beryl (aquamarine, emerald) and chrysoberyl. As a free element it is a steel-gray, strong, lightweight and brittle alkaline earth metal.

Beryllium improves many physical properties when added as an alloying element to aluminium, copper (notably the alloy beryllium copper), iron and nickel.[6] Beryllium does not form oxides until it reaches very high temperatures. Tools made of beryllium copper alloys are strong and hard and do not create sparks when they strike a steel surface. In structural applications, the combination of high flexural rigidity, thermal stability, thermal conductivity and low density (1.85 times that of water) make beryllium metal a desirable aerospace material for aircraft components, missiles, spacecraft, and satellites.[6] Because of its low density and atomic mass, beryllium is relatively transparent to X-rays and other forms of ionizing radiation; therefore, it is the most common window material for X-ray equipment and components of particle detectors.[6] The high thermal conductivities of beryllium and beryllium oxide have led to their use in thermal management applications.

The commercial use of beryllium requires the use of appropriate dust control equipment and industrial controls at all times because of the toxicity of inhaled beryllium-containing dusts that can cause a chronic life-threatening allergic disease in some people called berylliosis.[7]

Beryllium,  4Be
Be-140g
Beryllium
Pronunciation/bəˈrɪliəm/ ​(bə-RIL-ee-əm)
Appearancewhite-gray metallic
Standard atomic weight Ar, std(Be)9.0121831(5)[1]
Beryllium in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
–
↑
Be
↓
Mg
lithium ← beryllium → boron
Atomic number (Z)4
Groupgroup 2 (alkaline earth metals)
Periodperiod 2
Blocks-block
Element category  alkaline earth metal
Electron configuration[He] 2s2
Electrons per shell
2, 2
Physical properties
Phase at STPsolid
Melting point1560 K ​(1287 °C, ​2349 °F)
Boiling point2742 K ​(2469 °C, ​4476 °F)
Density (near r.t.)1.85 g/cm3
when liquid (at m.p.)1.690 g/cm3
Critical point5205 K,  MPa (extrapolated)
Heat of fusion12.2 kJ/mol
Heat of vaporization292 kJ/mol
Molar heat capacity16.443 J/(mol·K)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 1462 1608 1791 2023 2327 2742
Atomic properties
Oxidation states+1,[2] +2 (an amphoteric oxide)
ElectronegativityPauling scale: 1.57
Ionization energies
  • 1st: 899.5 kJ/mol
  • 2nd: 1757.1 kJ/mol
  • 3rd: 14,848.7 kJ/mol
  • (more)
Atomic radiusempirical: 112 pm
Covalent radius96±3 pm
Van der Waals radius153 pm
Color lines in a spectral range
Spectral lines of beryllium
Other properties
Natural occurrenceprimordial
Crystal structure ​hexagonal close-packed (hcp)
Hexagonal close packed crystal structure for beryllium
Speed of sound thin rod12,890 m/s (at r.t.)[3]
Thermal expansion11.3 µm/(m·K) (at 25 °C)
Thermal conductivity200 W/(m·K)
Electrical resistivity36 nΩ·m (at 20 °C)
Magnetic orderingdiamagnetic
Magnetic susceptibility−9.0·10−6 cm3/mol[4]
Young's modulus287 GPa
Shear modulus132 GPa
Bulk modulus130 GPa
Poisson ratio0.032
Mohs hardness5.5
Vickers hardness1670 MPa
Brinell hardness590–1320 MPa
CAS Number7440-41-7
History
DiscoveryLouis Nicolas Vauquelin (1798)
First isolationFriedrich Wöhler & Antoine Bussy (1828)
Main isotopes of beryllium
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct
7Be trace 53.12 d ε 7Li
γ –
9Be 100% stable
10Be trace 1.39×106 y β− 10B

Characteristics

Physical properties

Beryllium is a steel gray and hard metal that is brittle at room temperature and has a close-packed hexagonal crystal structure.[6] It has exceptional stiffness (Young's modulus 287 GPa) and a reasonably high melting point. The modulus of elasticity of beryllium is approximately 50% greater than that of steel. The combination of this modulus and a relatively low density results in an unusually fast sound conduction speed in beryllium – about 12.9 km/s at ambient conditions. Other significant properties are high specific heat (1925 J·kg−1·K−1) and thermal conductivity (216 W·m−1·K−1), which make beryllium the metal with the best heat dissipation characteristics per unit weight. In combination with the relatively low coefficient of linear thermal expansion (11.4×10−6 K−1), these characteristics result in a unique stability under conditions of thermal loading.[8]

Nuclear properties

Naturally occurring beryllium, save for slight contamination by the cosmogenic radioisotopes, is isotopically pure beryllium-9, which has a nuclear spin of 3/2. Beryllium has a large scattering cross section for high-energy neutrons, about 6 barns for energies above approximately 10 keV. Therefore, it works as a neutron reflector and neutron moderator, effectively slowing the neutrons to the thermal energy range of below 0.03 eV, where the total cross section is at least an order of magnitude lower – exact value strongly depends on the purity and size of the crystallites in the material.

The single primordial beryllium isotope 9Be also undergoes a (n,2n) neutron reaction with neutron energies over about 1.9 MeV, to produce 8Be, which almost immediately breaks into two alpha particles. Thus, for high-energy neutrons, beryllium is a neutron multiplier, releasing more neutrons than it absorbs. This nuclear reaction is:[9]

9
4Be
 + n → 2 4
2He
 + 2 n

Neutrons are liberated when beryllium nuclei are struck by energetic alpha particles[8] producing the nuclear reaction

9
4Be
 + 4
2He
 → 12
6C
 + n, where 4
2He
 is an alpha particle and 12
6C
 is a carbon-12 nucleus.[9]

Beryllium also releases neutrons under bombardment by gamma rays. Thus, natural beryllium bombarded either by alphas or gammas from a suitable radioisotope is a key component of most radioisotope-powered nuclear reaction neutron sources for the laboratory production of free neutrons.

Small amounts of tritium are liberated when 9
4Be
 nuclei absorb low energy neutrons in the three-step nuclear reaction

9
4Be
 + n → 4
2He
 + 6
2He
,    6
2He
 → 6
3Li
 + β−,    6
3Li
 + n → 4
2He
 + 3
1H

Note that 6
2He
 has a half-life of only 0.8 seconds, β− is an electron, and 6
3Li
 has a high neutron absorption cross-section. Tritium is a radioisotope of concern in nuclear reactor waste streams.[10]

As a metal, beryllium is transparent to most wavelengths of X-rays and gamma rays, making it useful for the output windows of X-ray tubes and other such apparatus.

Isotopes and nucleosynthesis

Both stable and unstable isotopes of beryllium are created in stars, but the radioisotopes do not last long. It is believed that most of the stable beryllium in the universe was originally created in the interstellar medium when cosmic rays induced fission in heavier elements found in interstellar gas and dust.[11] Primordial beryllium contains only one stable isotope, 9Be, and therefore beryllium is a monoisotopic element.

Solar Activity Proxies
Plot showing variations in solar activity, including variation in sunspot number (red) and 10Be concentration (blue). Note that the beryllium scale is inverted, so increases on this scale indicate lower 10Be levels

Radioactive cosmogenic 10Be is produced in the atmosphere of the Earth by the cosmic ray spallation of oxygen.[12] 10Be accumulates at the soil surface, where its relatively long half-life (1.36 million years) permits a long residence time before decaying to boron-10. Thus, 10Be and its daughter products are used to examine natural soil erosion, soil formation and the development of lateritic soils, and as a proxy for measurement of the variations in solar activity and the age of ice cores.[13] The production of 10Be is inversely proportional to solar activity, because increased solar wind during periods of high solar activity decreases the flux of galactic cosmic rays that reach the Earth.[12] Nuclear explosions also form 10Be by the reaction of fast neutrons with 13C in the carbon dioxide in air. This is one of the indicators of past activity at nuclear weapon test sites.[14] The isotope 7Be (half-life 53 days) is also cosmogenic, and shows an atmospheric abundance linked to sunspots, much like 10Be.

8Be has a very short half-life of about 7×10−17 s that contributes to its significant cosmological role, as elements heavier than beryllium could not have been produced by nuclear fusion in the Big Bang.[15] This is due to the lack of sufficient time during the Big Bang's nucleosynthesis phase to produce carbon by the fusion of 4He nuclei and the very low concentrations of available beryllium-8. The British astronomer Sir Fred Hoyle first showed that the energy levels of 8Be and 12C allow carbon production by the so-called triple-alpha process in helium-fueled stars where more nucleosynthesis time is available. This process allows carbon to be produced in stars, but not in the Big Bang. Star-created carbon (the basis of carbon-based life) is thus a component in the elements in the gas and dust ejected by AGB stars and supernovae (see also Big Bang nucleosynthesis), as well as the creation of all other elements with atomic numbers larger than that of carbon.[16]

The 2s electrons of beryllium may contribute to chemical bonding. Therefore, when 7Be decays by L-electron capture, it does so by taking electrons from its atomic orbitals that may be participating in bonding. This makes its decay rate dependent to a measurable degree upon its chemical surroundings – a rare occurrence in nuclear decay.[17]

The shortest-lived known isotope of beryllium is 13Be which decays through neutron emission. It has a half-life of 2.7 × 10−21 s. 6Be is also very short-lived with a half-life of 5.0 × 10−21 s.[18] The exotic isotopes 11Be and 14Be are known to exhibit a nuclear halo.[19] This phenomenon can be understood as the nuclei of 11Be and 14Be have, respectively, 1 and 4 neutrons orbiting substantially outside the classical Fermi 'waterdrop' model of the nucleus.

Occurrence

Beryllium OreUSGOV
Beryllium ore with 1US¢ coin for scale
Beryl-130023
Emerald is a naturally occurring compound of beryllium.

The Sun has a concentration of 0.1 parts per billion (ppb) of beryllium.[20] Beryllium has a concentration of 2 to 6 parts per million (ppm) in the Earth's crust.[21] It is most concentrated in the soils, 6 ppm.[22] Trace amounts of 9Be are found in the Earth's atmosphere.[22] The concentration of beryllium in sea water is 0.2–0.6 parts per trillion.[22][23] In stream water, however, beryllium is more abundant with a concentration of 0.1 ppb.[24]

Beryllium is found in over 100 minerals,[25] but most are uncommon to rare. The more common beryllium containing minerals include: bertrandite (Be4Si2O7(OH)2), beryl (Al2Be3Si6O18), chrysoberyl (Al2BeO4) and phenakite (Be2SiO4). Precious forms of beryl are aquamarine, red beryl and emerald.[8][26][27] The green color in gem-quality forms of beryl comes from varying amounts of chromium (about 2% for emerald).[28]

The two main ores of beryllium, beryl and bertrandite, are found in Argentina, Brazil, India, Madagascar, Russia and the United States.[28] Total world reserves of beryllium ore are greater than 400,000 tonnes.[28]

Production

The extraction of beryllium from its compounds is a difficult process due to its high affinity for oxygen at elevated temperatures, and its ability to reduce water when its oxide film is removed. The United States, China and Kazakhstan are the only three countries involved in the industrial-scale extraction of beryllium.[29] Beryllium production technology is in early stages of development in Russia after a 20-year hiatus.[30]

Beryllium is most commonly extracted from the mineral beryl, which is either sintered using an extraction agent or melted into a soluble mixture. The sintering process involves mixing beryl with sodium fluorosilicate and soda at 770 °C (1,420 °F) to form sodium fluoroberyllate, aluminium oxide and silicon dioxide.[6] Beryllium hydroxide is precipitated from a solution of sodium fluoroberyllate and sodium hydroxide in water. Extraction of beryllium using the melt method involves grinding beryl into a powder and heating it to 1,650 °C (3,000 °F).[6] The melt is quickly cooled with water and then reheated 250 to 300 °C (482 to 572 °F) in concentrated sulfuric acid, mostly yielding beryllium sulfate and aluminium sulfate.[6] Aqueous ammonia is then used to remove the aluminium and sulfur, leaving beryllium hydroxide.

Beryllium hydroxide created using either the sinter or melt method is then converted into beryllium fluoride or beryllium chloride. To form the fluoride, aqueous ammonium hydrogen fluoride is added to beryllium hydroxide to yield a precipitate of ammonium tetrafluoroberyllate, which is heated to 1,000 °C (1,830 °F) to form beryllium fluoride.[6] Heating the fluoride to 900 °C (1,650 °F) with magnesium forms finely divided beryllium, and additional heating to 1,300 °C (2,370 °F) creates the compact metal.[6] Heating beryllium hydroxide forms the oxide, which becomes beryllium chloride when combined with carbon and chlorine. Electrolysis of molten beryllium chloride is then used to obtain the metal.[6]

Chemical properties

Be3OHW6
Structure of the trimeric hydrolysis product of beryllium
BeHydrolysis
Beryllium hydrolysis as a function of pH. Water molecules attached to Be are omitted in this diagram

A beryllium atom has the electronic configuration [He] 2s2. The predominant oxidation state of beryllium is +2; the beryllium atom has lost both of its valence electrons. Lower oxidation states have been found in, for example, bis(carbene) compounds.[31] Beryllium's chemical behavior is largely a result of its small atomic and ionic radii. It thus has very high ionization potentials and strong polarization while bonded to other atoms, which is why all of its compounds are covalent. Its chemistry has similarities with the chemistry of aluminium, an example of a diagonal relationship. An oxide layer forms on the surface of beryllium metal that prevents further reactions with air unless heated above 1000 °C. Once ignited, beryllium burns brilliantly forming a mixture of beryllium oxide and beryllium nitride. Beryllium dissolves readily in non-oxidizing acids, such as HCl and diluted H2SO4, but not in nitric acid or water as this forms the oxide.This behavior is similar to that of aluminium metal. Beryllium also dissolves in alkali solutions.[6][32]

Binary compounds of beryllium(II) are polymeric in the solid state. BeF2 has a silica-like structure with corner-shared BeF4 tetrahedra. BeCl2 and BeBr2 have chain structures with edge-shared tetrahedra. Beryllium oxide, BeO, is a white refractory solid, which has the wurtzite crystal structure and a thermal conductivity as high as in some metals. BeO is amphoteric. Beryllium sulfide, selenide and telluride are known, all having the zincblende structure.[33] Beryllium nitride, Be3N2 is a high-melting-point compound which is readily hydrolyzed. Beryllium azide, BeN6 is known and beryllium phosphide, Be3P2 has a similar structure to Be3N2. A number of beryllium borides are known, such as Be5B, Be4B, Be2B, BeB2, BeB6 and BeB12. Beryllium carbide, Be2C, is a refractory brick-red compound that reacts with water to give methane.[33] No beryllium silicide has been identified.[32]

The halides BeX2 (X=F, Cl, Br, I) have a linear monomeric molecular structure in the gas phase.[32] Complexes of the halides are formed with one or more ligands donating at total of two pairs of electrons. Such compounds obey the octet rule. Other 4-coordinate complexes such as the aqua-ion [Be(H2O)4]2+ also obey the octet rule.

Solutions of beryllium salts, such as beryllium sulfate and beryllium nitrate, are acidic because of hydrolysis of the [Be(H2O)4]2+ ion. The concentration of the first hydrolysis product, [Be(H2O)3(OH)]+, is less than 1% of the beryllium concentration. The most stable hydrolysis product is the trimeric ion [Be3(OH)3(H2O)6]3+. Beryllium hydroxide, Be(OH)2, is insoluble in water at pH 5 or more. Consequently beryllium compounds are generally insoluble at biological pH. Because of this, inhalation of beryllium metal dust by people leads to the development of the fatal condition of berylliosis. Be(OH)2 dissolves in strongly alkaline solutions. In basic beryllium acetate the central oxygen atom is surrounded by a tetrahedron of beryllium atoms.[33] Beryllium difluoride, unlike the other alkaline earth difluorides, is very soluble in water,[34]. Aqueous solutions of this salt contain ions such as [Be(H2O)3F]+. [35][36][37][38]

Organic chemistry

Organoberyllium chemistry is limited to academic research due to the cost and toxicity of beryllium, beryllium derivatives and reagents required for the introduction of beryllium, such as beryllium chloride. Organometallic beryllium compounds are known to be highly reactive [39] Examples of known organoberyllium compounds are dineopentylberyllium,[40] beryllocene (Cp2Be),[41][42][43][44] diallylberyllium (by exchange reaction of diethyl beryllium with triallyl boron),[45] bis(1,3-trimethylsilylallyl)beryllium [46] and Be(mes)2.[39][47] Ligands can also be aryls[48] and alkynyls.[49]

History

The mineral beryl, which contains beryllium, has been used at least since the Ptolemaic dynasty of Egypt.[50] In the first century CE, Roman naturalist Pliny the Elder mentioned in his encyclopedia Natural History that beryl and emerald ("smaragdus") were similar.[51] The Papyrus Graecus Holmiensis, written in the third or fourth century CE, contains notes on how to prepare artificial emerald and beryl.[51]

Louis Nicolas Vauquelin
Louis-Nicolas Vauquelin discovered beryllium

Early analyses of emeralds and beryls by Martin Heinrich Klaproth, Torbern Olof Bergman, Franz Karl Achard, and Johann Jakob Bindheim always yielded similar elements, leading to the fallacious conclusion that both substances are aluminium silicates.[52] Mineralogist René Just Haüy discovered that both crystals are geometrically identical, and he asked chemist Louis-Nicolas Vauquelin for a chemical analysis.[50]

In a 1798 paper read before the Institut de France, Vauquelin reported that he found a new "earth" by dissolving aluminium hydroxide from emerald and beryl in an additional alkali.[53] The editors of the journal Annales de Chimie et de Physique named the new earth "glucine" for the sweet taste of some of its compounds.[54] Klaproth preferred the name "beryllina" due to the fact that yttria also formed sweet salts.[55][56] The name "beryllium" was first used by Wöhler in 1828.[57]

Friedrich Wöhler Stich
Friedrich Wöhler was one of the men who independently isolated beryllium

Friedrich Wöhler[58] and Antoine Bussy[59] independently isolated beryllium in 1828 by the chemical reaction of metallic potassium with beryllium chloride, as follows:

BeCl2 + 2 K → 2 KCl + Be

Using an alcohol lamp, Wöhler heated alternating layers of beryllium chloride and potassium in a wired-shut platinum crucible. The above reaction immediately took place and caused the crucible to become white hot. Upon cooling and washing the resulting gray-black powder he saw that it was made of fine particles with a dark metallic luster.[60] The highly reactive potassium had been produced by the electrolysis of its compounds, a process discovered 21 years before. The chemical method using potassium yielded only small grains of beryllium from which no ingot of metal could be cast or hammered.

The direct electrolysis of a molten mixture of beryllium fluoride and sodium fluoride by Paul Lebeau in 1898 resulted in the first pure (99.5 to 99.8%) samples of beryllium.[60] However, industrial production started only after the First World War. The original industrial involvement included subsidiaries and scientists related to the Union Carbide and Carbon Corporation in Cleveland OH and Siemens & Halske AG in Berlin. In the US, the process was ruled by Hugh S. Cooper, director of The Kemet Laboratories Company. In Germany, the first commercially successful process for producing beryllium was developed in 1921 by Alfred Stock and Hans Goldschmidt.[61]

A sample of beryllium was bombarded with alpha rays from the decay of radium in a 1932 experiment by James Chadwick that uncovered the existence of the neutron.[28] This same method is used in one class of radioisotope-based laboratory neutron sources that produce 30 neutrons for every million α particles.[21]

Beryllium production saw a rapid increase during World War II, due to the rising demand for hard beryllium-copper alloys and phosphors for fluorescent lights. Most early fluorescent lamps used zinc orthosilicate with varying content of beryllium to emit greenish light. Small additions of magnesium tungstate improved the blue part of the spectrum to yield an acceptable white light. Halophosphate-based phosphors replaced beryllium-based phosphors after beryllium was found to be toxic.[62]

Electrolysis of a mixture of beryllium fluoride and sodium fluoride was used to isolate beryllium during the 19th century. The metal's high melting point makes this process more energy-consuming than corresponding processes used for the alkali metals. Early in the 20th century, the production of beryllium by the thermal decomposition of beryllium iodide was investigated following the success of a similar process for the production of zirconium, but this process proved to be uneconomical for volume production.[63]

Pure beryllium metal did not become readily available until 1957, even though it had been used as an alloying metal to harden and toughen copper much earlier.[28] Beryllium could be produced by reducing beryllium compounds such as beryllium chloride with metallic potassium or sodium. Currently most beryllium is produced by reducing beryllium fluoride with purified magnesium. The price on the American market for vacuum-cast beryllium ingots was about $338 per pound ($745 per kilogram) in 2001.[64]

Between 1998 and 2008, the world's production of beryllium had decreased from 343 to about 200 tonnes, of which 176 tonnes (88%) came from the United States.[65][66]

Etymology

Early precursors of the word beryllium can be traced to many languages, including Latin beryllus; French béry; Ancient Greek βήρυλλος, bērullos, 'beryl'; Prakrit वॆरुलिय‌ (veruliya); Pāli वेलुरिय (veḷuriya), भेलिरु (veḷiru) or भिलर् (viḷar) – "to become pale", in reference to the pale semiprecious gemstone beryl. The original source is probably the Sanskrit word वैडूर्य (vaidurya), which is of South Indian origin and could be related to the name of the modern city of Belur.[67] For about 160 years, beryllium was also known as glucinum or glucinium (with the accompanying chemical symbol "Gl",[68] or "G" [69]), the name coming from the Ancient Greek word for sweet: γλυκύς, due to the sweet taste of beryllium salts.[70]

Applications

Radiation windows

Beryllium target
Beryllium target which "converts" a proton beam into a neutron beam
Be foil square
A square beryllium foil mounted in a steel case to be used as a window between a vacuum chamber and an X-ray microscope. Beryllium is highly transparent to X-rays owing to its low atomic number.

Because of its low atomic number and very low absorption for X-rays, the oldest and still one of the most important applications of beryllium is in radiation windows for X-ray tubes.[28] Extreme demands are placed on purity and cleanliness of beryllium to avoid artifacts in the X-ray images. Thin beryllium foils are used as radiation windows for X-ray detectors, and the extremely low absorption minimizes the heating effects caused by high intensity, low energy X-rays typical of synchrotron radiation. Vacuum-tight windows and beam-tubes for radiation experiments on synchrotrons are manufactured exclusively from beryllium. In scientific setups for various X-ray emission studies (e.g., energy-dispersive X-ray spectroscopy) the sample holder is usually made of beryllium because its emitted X-rays have much lower energies (~100 eV) than X-rays from most studied materials.[8]

Low atomic number also makes beryllium relatively transparent to energetic particles. Therefore, it is used to build the beam pipe around the collision region in particle physics setups, such as all four main detector experiments at the Large Hadron Collider (ALICE, ATLAS, CMS, LHCb),[71] the Tevatron and the SLAC. The low density of beryllium allows collision products to reach the surrounding detectors without significant interaction, its stiffness allows a powerful vacuum to be produced within the pipe to minimize interaction with gases, its thermal stability allows it to function correctly at temperatures of only a few degrees above absolute zero, and its diamagnetic nature keeps it from interfering with the complex multipole magnet systems used to steer and focus the particle beams.[72]

Mechanical applications

Because of its stiffness, light weight and dimensional stability over a wide temperature range, beryllium metal is used for lightweight structural components in the defense and aerospace industries in high-speed aircraft, guided missiles, spacecraft, and satellites. Several liquid-fuel rockets have used rocket nozzles made of pure beryllium.[73][74] Beryllium powder was itself studied as a rocket fuel, but this use has never materialized.[28] A small number of extreme high-end bicycle frames have been built with beryllium.[75] From 1998 to 2000, the McLaren Formula One team used Mercedes-Benz engines with beryllium-aluminium-alloy pistons.[76] The use of beryllium engine components was banned following a protest by Scuderia Ferrari.[77]

Mixing about 2.0% beryllium into copper forms an alloy called beryllium copper that is six times stronger than copper alone.[78] Beryllium alloys are used in many applications because of their combination of elasticity, high electrical conductivity and thermal conductivity, high strength and hardness, nonmagnetic properties, as well as good corrosion and fatigue resistance.[28][6] These applications include non-sparking tools that are used near flammable gases (beryllium nickel), in springs and membranes (beryllium nickel and beryllium iron) used in surgical instruments and high temperature devices.[28][6] As little as 50 parts per million of beryllium alloyed with liquid magnesium leads to a significant increase in oxidation resistance and decrease in flammability.[6]

Beryllium Copper Adjustable Wrench
Beryllium Copper Adjustable Wrench

The high elastic stiffness of beryllium has led to its extensive use in precision instrumentation, e.g. in inertial guidance systems and in the support mechanisms for optical systems.[8] Beryllium-copper alloys were also applied as a hardening agent in "Jason pistols", which were used to strip the paint from the hulls of ships.[79]

Beryllium was also used for cantilevers in high performance phonograph cartridge styli, where its extreme stiffness and low density allowed for tracking weights to be reduced to 1 gram, yet still track high frequency passages with minimal distortion.[80]

An earlier major application of beryllium was in brakes for military airplanes because of its hardness, high melting point, and exceptional ability to dissipate heat. Environmental considerations have led to substitution by other materials.[8]

To reduce costs, beryllium can be alloyed with significant amounts of aluminium, resulting in the AlBeMet alloy (a trade name). This blend is cheaper than pure beryllium, while still retaining many desirable properties.

Mirrors

Beryllium mirrors are of particular interest. Large-area mirrors, frequently with a honeycomb support structure, are used, for example, in meteorological satellites where low weight and long-term dimensional stability are critical. Smaller beryllium mirrors are used in optical guidance systems and in fire-control systems, e.g. in the German-made Leopard 1 and Leopard 2 main battle tanks. In these systems, very rapid movement of the mirror is required which again dictates low mass and high rigidity. Usually the beryllium mirror is coated with hard electroless nickel plating which can be more easily polished to a finer optical finish than beryllium. In some applications, though, the beryllium blank is polished without any coating. This is particularly applicable to cryogenic operation where thermal expansion mismatch can cause the coating to buckle.[8]

The James Webb Space Telescope[81] will have 18 hexagonal beryllium sections for its mirrors. Because JWST will face a temperature of 33 K, the mirror is made of gold-plated beryllium, capable of handling extreme cold better than glass. Beryllium contracts and deforms less than glass – and remains more uniform – in such temperatures.[82] For the same reason, the optics of the Spitzer Space Telescope are entirely built of beryllium metal.[83]

Magnetic applications

BERYLLIUM - KUGEL 1
Sphere Beryllium B52 - Gyrocompass

Beryllium is non-magnetic. Therefore, tools fabricated out of beryllium-based materials are used by naval or military explosive ordnance disposal teams for work on or near naval mines, since these mines commonly have magnetic fuzes.[84] They are also found in maintenance and construction materials near magnetic resonance imaging (MRI) machines because of the high magnetic fields generated.[85] In the fields of radio communications and powerful (usually military) radars, hand tools made of beryllium are used to tune the highly magnetic klystrons, magnetrons, traveling wave tubes, etc., that are used for generating high levels of microwave power in the transmitters.[86]

Nuclear applications

Thin plates or foils of beryllium are sometimes used in nuclear weapon designs as the very outer layer of the plutonium pits in the primary stages of thermonuclear bombs, placed to surround the fissile material. These layers of beryllium are good "pushers" for the implosion of the plutonium-239, and they are good neutron reflectors, just as in beryllium-moderated nuclear reactors.[87]

Beryllium is also commonly used in some neutron sources in laboratory devices in which relatively few neutrons are needed (rather than having to use a nuclear reactor, or a particle accelerator-powered neutron generator). For this purpose, a target of beryllium-9 is bombarded with energetic alpha particles from a radioisotope such as polonium-210, radium-226, plutonium-238, or americium-241. In the nuclear reaction that occurs, a beryllium nucleus is transmuted into carbon-12, and one free neutron is emitted, traveling in about the same direction as the alpha particle was heading. Such alpha decay driven beryllium neutron sources, named "urchin" neutron initiators, were used in some early atomic bombs.[87] Neutron sources in which beryllium is bombarded with gamma rays from a gamma decay radioisotope, are also used to produce laboratory neutrons.[88]

CANDU fuel bundles
Two CANDU fuel bundles: Each about 50 cm in length and 10 cm in diameter. Notice the small appendages on the fuel clad surfaces

Beryllium is also used in fuel fabrication for CANDU reactors. The fuel elements have small appendages that are resistance brazed to the fuel cladding using an induction brazing process with Be as the braze filler material. Bearing pads are brazed in place to prevent fuel bundle to pressure tube contact, and inter-element spacer pads are brazed on to prevent element to element contact.

Beryllium is also used at the Joint European Torus nuclear-fusion research laboratory, and it will be used in the more advanced ITER to condition the components which face the plasma.[89] Beryllium has also been proposed as a cladding material for nuclear fuel rods, because of its good combination of mechanical, chemical, and nuclear properties.[8] Beryllium fluoride is one of the constituent salts of the eutectic salt mixture FLiBe, which is used as a solvent, moderator and coolant in many hypothetical molten salt reactor designs, including the liquid fluoride thorium reactor (LFTR).[90]

Acoustics

The low weight and high rigidity of beryllium make it useful as a material for high-frequency speaker drivers. Because beryllium is expensive (many times more than titanium), hard to shape due to its brittleness, and toxic if mishandled, beryllium tweeters are limited to high-end home,[91][92][93] pro audio, and public address applications.[94][95] Some high-fidelity products have been fraudulently claimed to be made of the material.[96]

Some high-end phonograph cartridges used beryllium cantilevers to improve tracking by reducing mass.[97]

Electronic

Beryllium is a p-type dopant in III-V compound semiconductors. It is widely used in materials such as GaAs, AlGaAs, InGaAs and InAlAs grown by molecular beam epitaxy (MBE).[98] Cross-rolled beryllium sheet is an excellent structural support for printed circuit boards in surface-mount technology. In critical electronic applications, beryllium is both a structural support and heat sink. The application also requires a coefficient of thermal expansion that is well matched to the alumina and polyimide-glass substrates. The beryllium-beryllium oxide composite "E-Materials" have been specially designed for these electronic applications and have the additional advantage that the thermal expansion coefficient can be tailored to match diverse substrate materials.[8]

Beryllium oxide is useful for many applications that require the combined properties of an electrical insulator and an excellent heat conductor, with high strength and hardness, and a very high melting point. Beryllium oxide is frequently used as an insulator base plate in high-power transistors in radio frequency transmitters for telecommunications. Beryllium oxide is also being studied for use in increasing the thermal conductivity of uranium dioxide nuclear fuel pellets.[99] Beryllium compounds were used in fluorescent lighting tubes, but this use was discontinued because of the disease berylliosis which developed in the workers who were making the tubes.[100]

Healthcare

Beryllium is a component of several dental alloys.[101][102]

Occupational safety and health

Beryllium is a health and safety issue for workers. Exposure to beryllium in the workplace can lead to a sensitization immune response and can over time develop chronic beryllium disease (CBD).[103] The National Institute for Occupational Safety and Health (NIOSH) in the United States researches these effects in collaboration with a major manufacturer of beryllium products. The goal of this research is to prevent sensitization and CBD by developing a better understanding of the work processes and exposures that may present a potential risk for workers, and to develop effective interventions that will reduce the risk for adverse health effects. NIOSH also conducts genetic research on sensitization and CBD, independently of this collaboration.[103] The NIOSH Manual of Analytical Methods contains methods for measuring occupational exposures to beryllium.[104]

Precautions

Beryllium
Hazards
GHS pictograms The skull-and-crossbones pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)The health hazard pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)
GHS signal word Danger
H301, H315, H317, H319, H330, H335, H350i, H372
P201, P260, P280, P284, P301, P310, P330, P304, P340, P310[105]
NFPA 704
Flammability code 3: Liquids and solids that can be ignited under almost all ambient temperature conditions. Flash point between 23 and 38 °C (73 and 100 °F). E.g., gasolineHealth code 4: Very short exposure could cause death or major residual injury. E.g., VX gasReactivity code 3: Capable of detonation or explosive decomposition but requires a strong initiating source, must be heated under confinement before initiation, reacts explosively with water, or will detonate if severely shocked. E.g., fluorineSpecial hazards (white): no codeNFPA 704 four-colored diamond
3
4
3

Approximately 35 micrograms of beryllium is found in the average human body, an amount not considered harmful.[106] Beryllium is chemically similar to magnesium and therefore can displace it from enzymes, which causes them to malfunction.[106] Because Be2+ is a highly charged and small ion, it can easily get into many tissues and cells, where it specifically targets cell nuclei, inhibiting many enzymes, including those used for synthesizing DNA. Its toxicity is exacerbated by the fact that the body has no means to control beryllium levels, and once inside the body the beryllium cannot be removed.[107] Chronic berylliosis is a pulmonary and systemic granulomatous disease caused by inhalation of dust or fumes contaminated with beryllium; either large amounts over a short time or small amounts over a long time can lead to this ailment. Symptoms of the disease can take up to five years to develop; about a third of patients with it die and the survivors are left disabled.[106] The International Agency for Research on Cancer (IARC) lists beryllium and beryllium compounds as Category 1 carcinogens.[108] In the US, the Occupational Safety and Health Administration (OSHA) has designated a permissible exposure limit (PEL) in the workplace with a time-weighted average (TWA) 0.002 mg/m3 and a constant exposure limit of 0.005 mg/m3 over 30 minutes, with a maximum peak limit of 0.025 mg/m3. The National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit (REL) of constant 0.0005 mg/m3. The IDLH (immediately dangerous to life and health) value is 4 mg/m3.[109]

The toxicity of finely divided beryllium (dust or powder, mainly encountered in industrial settings where beryllium is produced or machined) is very well-documented. Solid beryllium metal does not carry the same hazards as airborne inhaled dust, but any hazard associated with physical contact is poorly documented. Workers handling finished beryllium pieces are routinely advised to handle them with gloves, both as a precaution and because many if not most applications of beryllium cannot tolerate residue of skin contact such as fingerprints.

Acute beryllium disease in the form of chemical pneumonitis was first reported in Europe in 1933 and in the United States in 1943. A survey found that about 5% of workers in plants manufacturing fluorescent lamps in 1949 in the United States had beryllium-related lung diseases.[110] Chronic berylliosis resembles sarcoidosis in many respects, and the differential diagnosis is often difficult. It killed some early workers in nuclear weapons design, such as Herbert L. Anderson.[111]

Beryllium may be found in coal slag. When the slag is formulated into an abrasive agent for blasting paint and rust from hard surfaces, the beryllium can become airborne and become a source of exposure.[112]

Early researchers tasted beryllium and its various compounds for sweetness in order to verify its presence. Modern diagnostic equipment no longer necessitates this highly risky procedure and no attempt should be made to ingest this highly toxic substance.[6] Beryllium and its compounds should be handled with great care and special precautions must be taken when carrying out any activity which could result in the release of beryllium dust (lung cancer is a possible result of prolonged exposure to beryllium-laden dust). Although the use of beryllium compounds in fluorescent lighting tubes was discontinued in 1949, potential for exposure to beryllium exists in the nuclear and aerospace industries and in the refining of beryllium metal and melting of beryllium-containing alloys, the manufacturing of electronic devices, and the handling of other beryllium-containing material.[113]

A successful test for beryllium in air and on surfaces has been recently developed and published as an international voluntary consensus standard ASTM D7202. The procedure uses dilute ammonium bifluoride for dissolution and fluorescence detection with beryllium bound to sulfonated hydroxybenzoquinoline, allowing up to 100 times more sensitive detection than the recommended limit for beryllium concentration in the workplace. Fluorescence increases with increasing beryllium concentration. The new procedure has been successfully tested on a variety of surfaces and is effective for the dissolution and ultratrace detection of refractory beryllium oxide and siliceous beryllium (ASTM D7458).[114][115]

Notes

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  3. ^ Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). Boca Raton, FL: CRC Press. p. 14.48. ISBN 1439855110.
  4. ^ Weast, Robert (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. pp. E110. ISBN 0-8493-0464-4.
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References

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Further reading

External links

Alkaline earth metal

The alkaline earth metals are six chemical elements in group 2 of the periodic table. They are beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). The elements have very similar properties: they are all shiny, silvery-white, somewhat reactive metals at standard temperature and pressure.Structurally, they have in common an outer s- electron shell which is full;

that is, this orbital contains its full complement of two electrons, which these elements readily lose to form cations with charge +2, and an oxidation state of +2.All the discovered alkaline earth metals occur in nature, although radium occurs only through the decay chain of uranium and thorium and not as a primordial element. Experiments have been conducted to attempt the synthesis of element 120, the next potential member of the group, but they have all met with failure.

Beryl

Beryl ( BERR-əl) is a mineral composed of beryllium aluminium cyclosilicate with the chemical formula Be3Al2Si6O18. Well-known varieties of beryl include emerald and aquamarine. Naturally occurring, hexagonal crystals of beryl can be up to several meters in size, but terminated crystals are relatively rare. Pure beryl is colorless, but it is frequently tinted by impurities; possible colors are green, blue, yellow, red (the rarest), and white. Beryl is also an ore source of beryllium.

Berylliosis

Berylliosis, or chronic beryllium disease (CBD), is a chronic allergic-type lung response and chronic lung disease caused by exposure to beryllium and its compounds, a form of beryllium poisoning. It is distinct from acute beryllium poisoning, which became rare following occupational exposure limits established around 1950. Berylliosis is an occupational lung disease.

While there is no cure, symptoms can be treated.

Beryllium bromide

Beryllium bromide is the chemical compound with the formula BeBr2. It is very hygroscopic and dissolves well in water. The compound is a polymer with tetrahedral Be centres.

Beryllium chloride

Beryllium chloride is an inorganic compound with the formula BeCl2. It is a colourless, hygroscopic solid that dissolves well in many polar solvents. Its properties are similar to those of aluminium chloride, due to beryllium's diagonal relationship with aluminium.

Beryllium copper

Beryllium copper (BeCu), also known as copper beryllium (CuBe), beryllium bronze and spring copper, is a copper alloy with 0.5—3% beryllium and sometimes other elements. Beryllium copper combines high strength with non-magnetic and non-sparking qualities. It has excellent metalworking, forming and machining properties. It has many specialized applications in tools for hazardous environments, musical instruments, precision measurement devices, bullets, and aerospace. Beryllium alloys present a toxic inhalation hazard during manufacture.

Beryllium fluoride

Beryllium fluoride is the inorganic compound with the formula BeF2. This white solid is the principal precursor for the manufacture of beryllium metal. Its structure resembles that of quartz, but BeF2 is highly soluble in water.

Beryllium hydride

Beryllium hydride (systematically named poly[beryllane(2)] and beryllium dihydride) is an inorganic compound with the chemical formula (BeH2)n (also written ([BeH2])n or BeH2). This alkaline earth hydride is a colourless solid that is insoluble in solvents that do not decompose it. Unlike the ionically bonded hydrides of the heavier Group 2 elements, beryllium hydride is covalently bonded (three-center two-electron bond).

Beryllium monohydride

Beryllium monohydride (BeH) is an example of a molecule with a half-bond order according to molecular orbital theory. It is a metastable monoradical species which has only been observed in the gas phase. In beryllium monohydride, beryllium has a valency of one, and hydrogen has a valency of one.

BeH has only 5 electrons and is the simplest open shell neutral molecule, and is therefore extremely important for the benchmarking of ab initio methods. With such a light mass, it is also an important benchmark system for studying the breakdown of the Born-Oppenheimer approximation. Due to its simplicity, BeH is expected to be present in astronomical contexts such as exoplanetary atmospheres, cool stars, and the interstellar medium, but so far has only been found on our Sun. Because of the long lifetime of 11Be, 11BeH is the leading candidate for the formation of the first halo nucleonic molecule.BeH has been studied spectroscopically since 1928 and in over 80 theoretical studies (see for a review).

The bond length is 134.2396(3) pm and the dissociation energy is 17702(200) cm−1.The dimeric molecule Be2H2 has also been observed in an argon matrix at 10 K

Beryllium nitrate

Beryllium nitrate, also known as beryllium dinitrate, is an ionic beryllium salt of nitric acid with the chemical formula Be(NO3)2. Each formula unit is composed of one Be2+ cation and two NO3− anions.

Beryllium oxide

Beryllium oxide (BeO), also known as beryllia, is an inorganic compound with the formula BeO. This colourless solid is a notable electrical insulator with a higher thermal conductivity than any other non-metal except diamond, and exceeds that of most metals. As an amorphous solid, beryllium oxide is white. Its high melting point leads to its use as a refractory material. It occurs in nature as the mineral bromellite. Historically and in materials science, beryllium oxide was called glucina or glucinium oxide. Formation of BeO from beryllium and oxygen releases the highest energy per mass of reactants for any chemical reaction, close to 24 MJ/kg.

Beryllium poisoning

Beryllium poisoning is poisoning by the toxic effects of beryllium, or more usually its compounds. It takes two forms:

Acute beryllium poisoning, usually as a result of exposure to soluble beryllium salts

Chronic beryllium disease (CBD) or berylliosis, usually as a result of long-term exposure to beryllium oxide usually caused by inhalation.

Beryllium sulfide

Beryllium sulfide (BeS) is an ionic compound from the sulfide group with the formula BeS.

Chrysoberyl

The mineral or gemstone chrysoberyl is an aluminate of beryllium with the formula BeAl2O4. The name chrysoberyl is derived from the Greek words χρυσός chrysos and βήρυλλος beryllos, meaning "a gold-white spar". Despite the similarity of their names, chrysoberyl and beryl are two completely different gemstones, although they both contain beryllium. Chrysoberyl is the third-hardest frequently encountered natural gemstone and lies at 8.5 on the Mohs scale of mineral hardness, between corundum (9) and topaz (8).An interesting feature of its crystals are the cyclic twins called trillings. These twinned crystals have a hexagonal appearance, but are the result of a triplet of twins with each "twin" oriented at 120° to its neighbors and taking up 120° of the cyclic trilling. If only two of the three possible twin orientations are present, a "V"-shaped twin results.

Ordinary chrysoberyl is yellowish-green and transparent to translucent. When the mineral exhibits good pale green to yellow color and is transparent, then it is used as a gemstone. The three main varieties of chrysoberyl are: ordinary yellow-to-green chrysoberyl, cat's eye or cymophane, and alexandrite. Yellow-green chrysoberyl was referred to as "chrysolite" during the Victorian and Edwardian eras, which caused confusion since that name has also been used for the mineral olivine ("peridot" as a gemstone); that name is no longer used in the gemological nomenclature.

Alexandrite, a strongly pleochroic (trichroic) gem, will exhibit emerald green, red and orange-yellow colors depending on viewing direction in partially polarised light. However, its most distinctive property is that it also changes color in artificial (tungsten/halogen) light compared to daylight. The color change from red to green is due to strong absorption of light in a narrow yellow portion of the spectrum, while allowing large bands of more blue-green and red wavelengths to be transmitted. Which of these prevails to give the perceived hue depends on the spectral balance of the illumination. Fine-quality alexandrite has a green to bluish-green color in daylight (relatively blue illumination of high color temperature), changing to a red to purplish-red color in incandescent light (relatively yellow illumination). However, fine-color material is extremely rare. Less-desirable stones may have daylight colors of yellowish-green and incandescent colors of brownish red.Cymophane is popularly known as "cat's eye". This variety exhibits pleasing chatoyancy or opalescence that reminds one of the eye of a cat. When cut to produce a cabochon, the mineral forms a light-green specimen with a silky band of light extending across the surface of the stone.

Cosmogenic nuclide

Cosmogenic nuclides (or cosmogenic isotopes) are rare nuclides (isotopes) created when a high-energy cosmic ray interacts with the nucleus of an in situ Solar System atom, causing nucleons (protons and neutrons) to be expelled from the atom (see cosmic ray spallation). These isotopes are produced within Earth materials such as rocks or soil, in Earth's atmosphere, and in extraterrestrial items such as meteorites. By measuring cosmogenic isotopes, scientists are able to gain insight into a range of geological and astronomical processes. There are both radioactive and stable cosmogenic isotopes. Some of these radioisotopes are tritium, carbon-14 and phosphorus-32.

Certain light (low atomic number) primordial nuclides (some isotopes of lithium, beryllium and boron) are thought to have arisen not only during the Big Bang, and also (and perhaps primarily) to have been made after the Big Bang, but before the condensation of the Solar System, by the process of cosmic ray spallation on interstellar gas and dust. This explains their higher abundance in cosmic rays as compared with their ratios and abundances of certain other nuclides on Earth. This also explains the overabundance of the early transition metals just before iron in the periodic table; the cosmic-ray spallation of iron thus produces scandium through chromium on one hand and helium through boron on the other. However, the arbitrary defining qualification for cosmogenic nuclides of being formed "in situ in the Solar System" (meaning inside an already-aggregated piece of the Solar System) prevents primordial nuclides formed by cosmic ray spallation before the formation of the Solar System, from being termed "cosmogenic nuclides"— even though the mechanism for their formation is exactly the same. These same nuclides still arrive on Earth in small amounts in cosmic rays, and are formed in meteoroids, in the atmosphere, on Earth, "cosmogenically." However, beryllium (all of it stable beryllium-9) is present primordially in the Solar System in much larger amounts, having existed prior to the condensation of the Solar System, and thus present in the materials from which the Solar System formed.

To make the distinction in another fashion, the timing of their formation determines which subset of cosmic ray spallation-produced nuclides are termed primordial or cosmogenic (a nuclide cannot belong to both classes). By convention, certain stable nuclides of lithium, beryllium, and boron are thought to have been produced by cosmic ray spallation in the period of time between the Big Bang and the Solar System's formation (thus making these primordial nuclides, by definition) are not termed "cosmogenic," even though they were formed by the same process as the cosmogenic nuclides (although at an earlier time). The primordial nuclide beryllium-9, the only stable beryllium isotope, is an example of this type of nuclide.

In contrast, even though the radioactive isotopes beryllium-7 and beryllium-10 fall into this series of three light elements (lithium, beryllium, boron) formed mostly by cosmic ray spallation nucleosynthesis, both of these nuclides have half lives too short for them to have been formed before the formation of the Solar System, and thus they cannot be primordial nuclides. Since the cosmic ray spallation route is the only possible source of beryllium-7 and beryllium-10 occurrence naturally in the environment, they are therefore cosmogenic.

FLiBe

FLiBe is a molten salt made from a mixture of lithium fluoride (LiF) and beryllium fluoride (BeF2). It is both a nuclear reactor coolant and solvent for fertile or fissile material. It served both purposes in the Molten-Salt Reactor Experiment (MSRE).

The 2:1 mixture forms a stoichiometric compound, Li2BeF4, which has a melting point of 459 °C, a boiling point of 1430 °C, and a density of 1.94 g/cm3. Its volumetric heat capacity is 4540 kJ/m3K, which is similar to that of water, more than four times that of sodium, and more than 200 times that of helium at typical reactor conditions. Its appearance is white to transparent, with crystalline grains in a solid state, morphing into a completely clear liquid upon melting. However, soluble fluorides such as UF4 and NiF2, can dramatically change the color salt in both solid and liquid state. This made spectrophotometry a viable analysis tool, and it was employed extensively during the MSRE operations.The eutectic mixture is slightly greater than 50% BeF2 and has a melting point of 360 °C. This mixture was never used in practice due to the overwhelming increase in viscosity caused by the BeF2 addition in the eutectic mixture. BeF2, which behaves as a glass, is only fluid in salt mixtures containing enough molar percent of Lewis base. Lewis bases, such as the alkali fluorides, will donate fluoride ions to the beryllium, breaking the glassy bonds which increase viscosity. In FLiBe, beryllium fluoride is able to sequester two fluoride ions from two lithium fluorides in a liquid state, converting it into the tetrafluorberyllate ion BeF4−2.

Isotopes of beryllium

Beryllium (4Be) has 12 known isotopes, but only one of these isotopes (9Be) is stable and a primordial nuclide. As such, beryllium is considered a monoisotopic element. It is also a mononuclidic element, because its other isotopes have such short half-lives that none are primordial and their abundance is very low (standard atomic weight is 9.0122). Beryllium is unique as being the only monoisotopic element with both an even number of protons and an odd number of neutrons. There are 25 other monoisotopic elements but all have odd atomic numbers, and even numbers of neutrons.

Of the 11 radioisotopes of beryllium, the most stable are 10Be with a half-life of 1.39 million years and 7Be with a half-life of 53.22 days. All other radioisotopes have half-lives under 13.85 seconds, most under 0.03 seconds. The least stable isotope is 6Be, with a half-life measured as 5.03 × 10−21 seconds.

The natural light-element ratio of equal proton and neutron numbers is prevented in beryllium by the extreme instability of 8Be toward alpha decay, which is favored due to the extremely tight binding of 4He nuclei. The half-life for the decay of 8Be is only 6.7(17)×10−17 seconds.

Beryllium is prevented from having a stable isotope with 4 protons and 6 neutrons by the very large mismatch in proton/neutron ratio for such a light element. Nevertheless, this isotope, 10Be, has a half-life of 1.39 million years, which indicates unusual stability for a light isotope with such a large neutron/proton imbalance. Still other possible beryllium isotopes have even more severe mismatches in neutron and proton number, and thus are even less stable.

Most 9Be in the universe is thought to be formed by cosmic ray nucleosynthesis from cosmic ray spallation in the period between the Big Bang and the formation of the solar system. The isotopes 7Be, with a half-life of 53.22 days, and 10Be are both cosmogenic nuclides because they are made on a recent timescale in the solar system by spallation, like 14C. These two radioisotopes of beryllium in the atmosphere track the sun spot cycle and solar activity, since this affects the magnetic field that shields the Earth from cosmic rays. The rate at which the short-lived 7Be is transferred from the air to the ground is controlled in part by the weather. 7Be decay in the sun is one of the sources of solar neutrinos, and the first type ever detected using the Homestake experiment. Presence of 7Be in sediments is often used to establish that they are fresh, i.e. less than about 3–4 months in age, or about two half-lives of 7Be.

Molten salt reactor

A molten salt reactor (MSR) is a class of nuclear fission reactor in which the primary nuclear reactor coolant and/or the fuel is a molten salt mixture. MSRs offer multiple advantages over conventional nuclear power plants, although for historical reasons, they have not been deployed.

The concept was first established in the 1950s. The early Aircraft Reactor Experiment was primarily motivated by the small size that the technique offered, while the Molten-Salt Reactor Experiment was a prototype for a thorium fuel cycle breeder nuclear power plant. The increased research into Generation IV reactor designs renewed interest in the technology.

Period 2 element

A period 2 element is one of the chemical elements in the second row (or period) of the periodic table of the chemical elements. The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behavior of the elements as their atomic number increases; a new row is started when chemical behavior begins to repeat, creating columns of elements with similar properties.

The second period contains the elements lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine, and neon. This situation can be explained by modern theories of atomic structure. In a quantum mechanical description of atomic structure, this period corresponds to the filling of the 2s and 2p orbitals. Period 2 elements obey the octet rule in that they need eight electrons to complete their valence shell. The maximum number of electrons that these elements can accommodate is ten, two in the 1s orbital, two in the 2s orbital and six in the 2p orbital.

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