Beryllium Be

Beryllium (Be)


a chemical element of Group II of Mendeleev’s periodic system. Its atomic number is 4; its atomic mass is 9.01218. It is a light metal of lightgray color, and it has one stable isotope, 9Be. Beryllium was discovered in 1798 in the form of the oxide BeO and isolated from the mineral beryl by L. Vauquelin. Metallic beryllium was first obtained in 1828 by F. Wöhler and independently by A. Bussy. Since certain salts of beryllium have a sweet taste, it was first called glucinum or glycinium. The name “glicinium” (symbolGI) is used (together with “beryllium”) only in France. The use of beryllium began in the 1940’s, although its valuable properties as a component of alloys were discovered even earlier and its unusual nuclear properties were discovered in the early 1930’s.

Beryllium is a rare element: its average content in the earth’s crust is 6 × 10-4 percent by mass. Beryllium is a typical lithophilic element, characteristic of acidic, subal-kaline, and alkaline magma. Approximately 40 beryllium minerals are known. Of these, beryl is of the greatest practical value; phenakite, helvite, chrysoberyl, and bertrandite are promising and are in use to some extent.

Physical and chemical properties. The crystalline lattice of beryllium is hexagonal and closely packed, with constants a = 2.855 angstroms (Å) and c = 3.5840 Å. Beryllium is lighter than aluminum; its density is 1,847.7 kg/m3. (The density of aluminum is approximately 2,700 kg/m’.) The melting point of beryllium is 1284° C, and its boiling point is 2450° C.

Beryllium has the highest heat capacity of any metal (1.80 kilojoules per kg · °K or 0.43 calories per kg · °C), high thermal conductivity (178 watts per m · °K or 0.45 calories per cm · sec · ° C at 50° C), and low electrical resistance (3.6–4.5 microhm · cm at 20°C); its coefficient of linear expansion is 10.3–131 (25°-100°C). These properties depend on the quality and structure of the metal and change appreciably with temperature. The modulus of elongation (Young’s modulus) is 300 giganewtons per sq m (GN/m2) or 3 × 104 kilograms-force per sq mm (kgf/mm2). The mechanical properties of beryllium depend on the purity of the metal, the grain size, and the texture, which is determined by the nature of processing. The tensile strength of beryllium is 200–550 MN/m2 (20–55 kgf/mm2); the elongation is 0.2–2 percent. Pressure working leads to a specific orientation of the beryllium crystals, anisotropy develops, and considerable improvement of the properties becomes possible. The ultimate strength in the direction of stretching reaches 400–800 MN/m2 (40–80 kgf/mm2), the yield limit is 250–600 MN/m2 (25–60 kgf/mm2), and the relative elongation is as much as 4–12 percent. The mechanical properties in the direction perpendicular to the stretching are almost unchanged. Beryllium is a brittle metal; its impact strength is 10–50 kJ/m2 (0.1–0.5 kgf m/cm2). The temperature of transition of beryllium from the brittle state to the plastic state is 200°-400° C.

In chemical compounds beryllium is bivalent (its outer electron configuration is 2s2). Beryllium has high chemical activity, but the compact metal is stable in air owing to the formation of a thin, tough film of the oxide BeO. Upon heating above 800° C it oxidizes rapidly. Up to 100° C, beryllium practically does not react with water. It dissolves easily in hydrofluoric, hydrochloric, and dilute sulfuric acids, reacts slightly with concentrated sulfuric and dilute nitric acids, and does not react with concentrated nitric acid. It dissolves in aqueous alkaline solutions, forming beryllate salts—for example, Na2BeO2. At room temperature it reacts with fluorine, and at increased temperatures, with other halogens and with hydrogen sulfide. It reacts with nitrogen at temperatures above 650° C, with the formation of the nitride Be3N2; at temperatures above 1200° C it reacts with carbon, forming the carbide Be2C. It does not react with hydrogen over practically the entire range of temperatures. The hydride of beryllium is obtained by the decomposition of beryllo-organic compounds, and it is stable up to 240° C. At high temperatures beryllium reacts with the majority of metals to form beryllides; with aluminum and silicon it yields eutectic alloys. The solubility of impurities in beryllium is unusually low. Finely divided beryllium powder burns in the vapors of sulfur, selenium, and tellurium. Molten beryllium reacts with the majority of oxides, nitrides, sulfides, and carbides. Beryllium oxide is the only suitable material for a crucible for melting beryllium.

The hydroxide Be(OH)2 is a weak base with amphoteric properties. Beryllium salts are strongly hygroscopic and, with a few exceptions (phosphate, carbonate), are readily soluble in water; their aqueous solutions, owing to hydrolysis, have an acidic reaction. The fluoride BeF2, with the fluorides of the alkali metals and ammonia, forms fluoroberyllates such as Na2BeF4, that have great industrial value. A number of complex beryllo-organic compounds are known; the hydrolysis and oxidation of some of them proceed explosively.

Production and use. In industry, metallic beryllium and its compounds are obtained by the conversion of beryl into the hydroxide Be(OH)2 or the sulfate BeS04. In one of these processes, ground beryl is calcined with Na2SiF6, and the sodium fluoroberyllates Na2BeF4 and NaBeF3 that are formed are extracted from the mixture with water; by adding NaOH to this solution, Be(OH)2 precipitates. In the other process, beryl is calcined with lime or chalk, and the slurry is treated with sulfuric acid; the BeS04 that is formed is leached with water, and Be(OH)2 is precipitated with ammonia. A more complete purification is achieved by repeated crystallization of BeS04, from which BeO is obtained by roasting. The decomposition of beryl by chlorination or by the action of phosgene is also known. Further processing is carried out in order to obtain BeF2 or BeCl2.

Metallic beryllium is produced by the reduction of BeF2 by magnesium at 900°-1300° C or by the electrolysis of BeCl2 mixed with NaCl at 350° C.

The metal obtained is melted in a vacuum. Metal of high purity is obtained by vacuum distillation and small quantities by zone melting; electrolytic refining is also used.

Because of the difficulties of obtaining high-grade castings, the billets for beryllium products are prepared by methods of powder metallurgy. Beryllium is ground into a powder and subjected to hot molding in a vacuum at 1140o-1180°C. Bars, tubes, and other shapes are obtained by extrusion at 800°-1050°C (hot extrusion) or at 400–500° C (thermal extrusion). Sheets of beryllium are obtained by the rolling of hot-pressed billets or extruded flat bars at 760°-840° C. Other types of processing—such as forging, stamping, and drawing—are also used. In the mechanical machining of beryllium, a hard-alloy instrument is used.

The combination of low atomic mass, small capture cross section of thermal neutrons (0.009 barn per atom), and satisfactory durability under conditions of radiation makes beryllium one of the best materials for the production of neutron moderators and reflectors in atomic reactors. Beryllium profitably combines low density and high elastic modulus, strength, and heat conduction. Beryllium surpasses all metals in specific strength. Owing to this, at the end of the 1950’s and beginning of the 1960’s beryllium began to be used in aviation, rocket, and space technology and in gyroinstrument production. However, beryllium’s extreme brittleness at room temperature is the chief obstacle to its widespread use as a construction material.

Beryllium is a component of alloys based on Al, Mg, Cu, and other nonferrous metals.

Some beryllides of the refractory metals are considered to be promising construction materials for airplanes and rockets. Beryllium is also used for the surface beryllization of steel. The windows of X-ray tubes are made of beryllium because of its high permeability to X rays (17 times as large as that of aluminum). Beryllium is used in radium-, polonium-, actinium-, and plutonium-based neutron sources because it has the property of producing intense neutron radiation when bombarded by alpha particles. Beryllium and certain of its compounds are considered to be promising solid rocket fuels with the highest specific impulses.

The large-scale production of pure beryllium began after World War II. The treatment of beryllium is complicated by the toxicity of volatile compounds and powders containing beryllium; thus, special measures are necessary when working with beryllium and its compounds.

Beryllium in the organism. Beryllium is present in the tissues of many plants and animals. The beryllium content in the soil varies from 2 × 10-4 to 1 x 10–3 percent; in the ash of plants there is approximately 2 × 10–4 percent. In animals, beryllium is found in all the organs and tissues; the ash of bones contains from 5 x 10–4 to 7 x 10–3 percent beryllium. Approximately 50 percent of the beryllium assimilated by the animal is excreted in the urine, approximately 30 percent is absorbed by the bones, and 8 percent is found in the liver and kidneys. The biological importance of beryllium has been only slightly elucidated; it is determined by the participation of beryllium in the exchange of Mg and P in bony tissue. In cases of an excess of beryllium, it appears that there is a binding in the intestines of the ions of phosphoric acid to the unassimilable beryllium phosphate. The activity of certain enzymes (alkaline phosphatase, adenosine triphosphatase) is inhibited by small beryllium concentrations. Under the influence of beryllium in cases of phosphorus deficiency, beryllium rickets—which is not curable by Vitamin D—is found in animals in those biogeochemical provinces that are rich in beryllium.


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References in periodicals archive ?
Studies in the early 1970s showed that beryllium causes lung cancer in lab animals, which was enough evidence for OSHA to propose in 1975--although not require--that workplace limits for beryllium be reduced to the lowest feasible levels, considered at the time to be 1 [micro]g/[m.