Beryllium

Beryllium is a chemical element; it has symbol Be and atomic number 4. It is a steel-gray, hard, strong, lightweight and brittle alkaline earth metal. It is a divalent element that occurs naturally only in combination with other elements to form minerals. Gemstones high in beryllium include beryl and chrysoberyl. 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 into heavier elements. Beryllium constitutes about 0.0004 percent by mass of Earth's crust. The world's annual beryllium production of 220 tons is usually manufactured by extraction from the mineral beryl, a difficult process because beryllium bonds strongly to oxygen.
In structural applications, the combination of high flexural rigidity, thermal stability, thermal conductivity and low density make beryllium a desirable aerospace material for aircraft components, missiles, spacecraft, and satellites. 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. When added as an alloying element to aluminium, copper, iron, or nickel, beryllium improves many physical properties. For example, tools and components made of beryllium copper alloys are strong and hard and do not create sparks when they strike a steel surface. In air, the surface of beryllium oxidizes readily at room temperature to form a passivation layer 1–10 nm thick that protects it from further oxidation and corrosion. The metal oxidizes in bulk when heated above, and burns brilliantly when heated to about.
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, berylliosis, in some people. Berylliosis is typically manifested by chronic pulmonary fibrosis and, in severe cases, right sided heart failure and death.

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. It has exceptional stiffness and a melting point of 1287 °C. The modulus of elasticity of beryllium is approximately 35% 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.
Among all metals, beryllium dissipates the most heat per unit weight, with both high specific heat and thermal conductivity.
Beryllium's conductivity and relatively low coefficient of linear thermal expansion make it uniquely stable under extreme temperature differences.

Nuclear properties

Naturally occurring beryllium, save for slight contamination by the radioisotopes created by cosmic rays, is isotopically pure beryllium-9, which has a nuclear spin of ⁻. The inelastic scattering cross section of beryllium increases with relation to neutron energy, allowing for significant slowing of higher-energy neutrons. Therefore, it works as a neutron reflector and neutron moderator; the exact strength of neutron slowing depends on the purity and size of the crystallites in the material.
The isotope ⁹Be can undergo a neutron reaction with fast neutrons, 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:
The isotope can liberate the neutron when struck by an alpha particle. The nuclear reaction
is strongly exothermic, liberating a fast neutron.
The isotope can also release the neutron when absorbing a gamma ray of sufficient energy at a useful cross-section:
Thus, natural beryllium bombarded by alpha or gamma radiation from a suitable radioisotope is the most common radioisotope-powered neutron source for laboratory use.
Finally, small amounts of tritium are also liberated by the high-energy neutrons in the three-step nuclear reaction
has a half-life of only 0.8 seconds, β⁻ is an electron, and has a high neutron absorption cross section. This is equivalent to the neutron-multiplication reaction with three output neutrons replaced by a triton, and a beta decay allowing that conversion. Tritium is a radioisotope of concern in nuclear reactor waste streams.

Optical properties

As a metal, beryllium is transparent or translucent 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

Natural beryllium is made up of solely the stable isotope beryllium-9. Beryllium is the only monoisotopic element with an even atomic number.
Beryllium-7 and beryllium-8 are key intermediates in stellar nucleosynthesis, but do not last long. It is believed that the beryllium in the universe was created in the interstellar medium when cosmic rays induced fission in heavier elements found in interstellar gas and dust, a process called cosmic ray spallation.
About one billionth of the primordial atoms created in the Big Bang nucleosynthesis were ⁷Be. This is a consequence of the low density of matter when the temperature of the universe cooled enough for small nuclei to be stable. Creating such nuclei requires nuclear collisions that are rare at low density. Although ⁷Be is unstable and decays by electron capture into ⁷Li, with a half-life of 53.22 days under standard conditions, in the early universe the atoms were fully ionized and electron capture not significant. The conversion of ⁷Be to Li was only complete near the time of recombination.
The isotope ⁷Be is also a cosmogenic nuclide and shows an atmospheric abundance inversely proportional to solar activity. It decays exclusively by electron capture, and the 2s electrons of beryllium are the valence electrons responsible for 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.
Be-7 is also produced in cooling water of high-energy accelerators; it can be extracted from the water at high purity and sold for scientific experiments.
The isotope ¹⁰Be is similarly cosmogenic, and is produced in the same way - by cosmic ray spallation of nitrogen and oxygen. Its behavior differ only because of its much longer half-life of 1.387 million years. It entirely accumulates at the soil surface and has a long residence time before decaying to boron-10. Thus, ¹⁰Be and its daughter product 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. As with ⁷Be, production of ¹⁰Be is inversely related to solar activity, because increased solar wind during periods of high solar activity decreases the flux of galactic cosmic rays that reach the Earth. 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.
⁸Be is unstable but has a ground state resonance with an important role in the triple-alpha process in stellar helium burning. As first proposed by British astronomer Sir Fred Hoyle based solely on astrophysical analysis, the energy levels of ⁸Be and ¹²C allow carbon nucleosynthesis by increasing the effective cross-section between the three alpha particles in the carbon production process. The main carbon-producing reaction in the universe is
where ⁴He is an alpha particle.
The exotic isotopes ¹¹Be and ¹⁴Be are known to exhibit a nuclear halo. That is, their nuclei have, respectively, 1 and 4 neutrons orbiting substantially outside the expected nuclear radius and in each case the core the neutrons float around is one of ¹⁰Be.

Occurrence

Beryllium is found in over 100 minerals, but most are uncommon to rare. The more common beryllium-containing minerals include: bertrandite, beryl, chrysoberyl and phenakite. Precious forms of beryl are aquamarine, red beryl and emerald.
The green color in gem-quality forms of beryl comes from varying amounts of chromium.
The two main ores of beryllium, beryl and bertrandite, are found in Argentina, Brazil, India, Madagascar, Russia and the United States. Total world reserves of beryllium ore are greater than 400,000 tonnes.
The Sun has a concentration of 0.1 parts per billion of beryllium. Beryllium has a concentration of 2 to 6 parts per million in the Earth's crust and is the 47th-most abundant element. It is most concentrated in the soils. Trace amounts of ⁹Be are found in the Earth's atmosphere. The concentration of beryllium in sea water is 0.2–0.6 parts per trillion. In stream water, however, beryllium is more abundant, with a concentration of 0.1 ppb.

Extraction

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. Currently the United States, China and Kazakhstan are the only three countries involved in the industrial-scale extraction of beryllium. Kazakhstan produces beryllium from a concentrate stockpiled before the breakup of the Soviet Union around 1991. This resource had become nearly depleted by the mid-2010s.
Production of beryllium in Russia was halted in 1997, and is planned to be resumed in the 2020s.
Image:Beryllium.jpg|thumb|A bead of beryllium from a melt
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 to form sodium fluoroberyllate, aluminium oxide and silicon dioxide. Beryllium hydroxide is precipitated from a solution of sodium fluoroberyllate and sodium hydroxide in water. The extraction of beryllium using the melt method involves grinding beryl into a powder and heating it to. The melt is quickly cooled with water and then reheated in concentrated sulfuric acid, mostly yielding beryllium sulfate and aluminium sulfate. 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 to form beryllium fluoride. Heating the fluoride to with magnesium forms finely divided beryllium, and additional heating to creates the compact metal. Heating beryllium hydroxide forms beryllium oxide, which becomes beryllium chloride when combined with carbon and chlorine. Electrolysis of molten beryllium chloride is then used to obtain the metal.