Beryllium

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Beryllium

Beryllium is the chemical element in the periodic table that has the symbol Be and atomic number 4. A toxic bivalent element, beryllium is a steel grey, strong, light-weight yet brittle, alkaline earth metal, that is primarily used as a hardening agent in alloys (most notably beryllium copper).

Notable characteristics

Beryllium has one of the highest melting points of the light metals. The modulus of elasticity of beryllium is approximately 1/3 greater than that of steel. It has excellent thermal conductivity, is nonmagnetic and resists attack by concentrated nitric acid. It is highly permeable to X-rays, and neutrons are liberated when it is hit by alpha particles, as from radium or polonium (about 30 neutrons/million alpha particles). At standard temperature and pressures beryllium resists oxidation when exposed to air (although its ability to scratch glass is probably due to the formation of a thin layer of the oxide). The speed of sound in beryllium (12,500m/s) is greater than in any other element.

Applications

Beryllium is used as an alloying agent in the production of beryllium-copper because of its ability to absorb large amounts of heat. Beryllium-copper alloys are used in a wide variety of applications because of their electrical and thermal conductivity, high strength and hardness, nonmagnetic properties, along with good corrosion and fatigue resistance. These applications include the making of spot-welding electrodes, springs, non-sparking tools and electrical contacts.
Due to their stiffness, light weight, and dimensional stability over a wide temperature range, beryllium-copper alloys are also used in the defense and aerospace industries as light-weight structural materials in high-speed aircraft, missiles, space vehicles and communication satellites.
Thin sheets of beryllium foil are used with X-ray detection diagnostics to filter out visible light and allow only X-rays to be detected.
In the field of X-ray lithography beryllium is used for the reproduction of microscopic integrated circuits.
In the telecommunications industry, Beryllium is made into tools that are used to tune the highly magentic klystrons used for high power microwave transmissions for safety.
Because it has a low thermal neutron absorption cross section, the nuclear power industry uses this metal in nuclear reactors as a neutron reflector and moderator.
Beryllium is used in nuclear weapons for similar reasons. For example, the critical mass of a plutonium sphere is significantly reduced if the plutonium is surrounded by a beryllium shell.
Beryllium is sometimes used in neutron sources, in which the beryllium is mixed with an alpha emitter such as ²¹⁰Po, ²²⁶Ra, ²³⁹Pu or ²⁴¹Am.
Beryllium is also used in the making of gyroscopes, various computer equipment, watch springs and instruments where light-weight, rigidity and dimensional stability are needed.
Beryllium oxide is useful for many applications that require an excellent heat conductor, with high strength and hardness, with a very high melting point, and that acts as an electrical insulator.
Beryllium compounds were once used in fluorescent lighting tubes, but this use was discontinued because of berylliosis in the workers manufacturing the tubes (see below).
The James Webb Space Telescope (Beryllium related details from NASA here) will have 18 hexagonal beryllium sections for its mirrors. Because JWST will face a temperature of −240 degrees Celsius (30 kelvins), the mirror is made of beryllium, a material capable of handling extreme cold better than glass. Beryllium contracts and deforms less than glass — and thus remains more uniform — in such temperatures.
Beryllium is also used in the Joint European Torus fusion research facility, to condition the plasma facing components.

See also Beryllium compounds.

History

The name beryllium comes from the Greek beryllos, beryl, from Prakrit veruliya, from Pāli veuriya; possibly from or simply akin to a Dravidian source represented by Tamil veiruor, viar, "to whiten, become pale." ^* At one time beryllium was referred to as glucinium (from Greek glykys, sweet), due to the sweet taste of its salts. This element was discovered by Louis Vauquelin in 1798 as the oxide in beryl and in emeralds. Friedrich Wöhler and A. A. Bussy independently isolated the metal in 1828 by reacting potassium and beryllium chloride.

Occurrence

Beryllium is an essential constituent of about 100 out of about 4000 known minerals, the most important of which are bertrandite (Be₄Si₂O₇(OH)₂), beryl (Al₂Be₃Si₆O₁₈), chrysoberyl (Al₂BeO₄), and phenakite (Be₂SiO₄). Precious forms of beryl are aquamarine and emerald. Along with hydrogen, helium, and lithium, some beryllium was created in the big bang.

The most important commercial sources of beryllium and its compounds are beryl and bertrandite. Beryllium metal did not become readily available until 1957. Currently, most production of this metal is accomplished by reducing beryllium fluoride with magnesium metal. The price on the US market for vacuum-cast beryllium ingots was 338 States dollar|US$" target="_blank" >^* per pound ($745/kg) in 2001. ^*

BeF₂ + Mg → MgF₂ + Be

See also Beryllium minerals.

Isotopes

Of beryllium's 10 isotopes, only ⁹Be is stable. Cosmogenic ¹⁰Be is produced in the atmosphere by cosmic ray spallation of oxygen and nitrogen. Because beryllium tends to exist in solution at pH levels less than about 5.5 (and most rainwater has a pH less than 5), it will enter into solution and be transported to the Earth's surface via rainwater. As the precipitation quickly becomes more alkaline, beryllium drops out of solution. Cosmogenic ¹⁰Be thereby accumulates at the soil surface, where its relatively long half-life (1.51 million years) permits a long residence time before decaying to ¹⁰B. ¹⁰Be and its daughter products have been used to examine soil erosion, soil formation from regolith, the development of lateritic soils, as well as variations in solar activity and the age of ice cores.

The fact that ⁷Be and ⁸Be are unstable has profound cosmological consequences as it means that elements heavier than beryllium could not be produced by nuclear fusion in the Big Bang. Moreover, the nuclear energy levels of ⁸Be are such that carbon can be produced within stars, thus making life possible. (See triple-alpha process and Big Bang nucleosynthesis).

The shortest-lived known isotope of beryllium is ¹³Be which decays through neutron emission. It has a half-life of 2.7 × 10^-21 seconds. ⁶Be also is also very short-lived with a half-life of 5.0 × 10^-21 seconds.

Precautions

Beryllium and its salts are toxic substances and potentially carcinogenic. Chronic berylliosis is a pulmonary and systemic granulomatous disease caused by exposure to beryllium. Acute beryllium disease in the form of chemical pneumonitis was first reported in Europe in 1933 and in the United States in 1943. Cases of chronic berylliosis were first described in 1946 among workers in plants manufacturing fluorescent lamps in Massachusetts. Chronic berylliosis resembles sarcoidosis in many respects, and the differential diagnosis is often difficult.

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.

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 substance. 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).

This substance can be handled safely if certain procedures are followed. No attempt should be made to work with beryllium before familiarization with correct handling procedures.

A successful test for beryllium on different surface areas has been recently developed. The procedure uses fluorescence when beryllium is bound to sulfonated hydroxybenzoquinoline to detect up to 10 times lower than the recommended limit for beryllium concentration in the work place. Fluorescence increases with increasing beryllium concentration. The new procedure has been successfully tested on a variety of surfaces.

Health effects

Inhalation

Beryllium can be harmful if inhaled and the effects depend on period of exposure. If beryllium air levels are high enough (greater than 100 µg/m³), an acute condition can result, called acute beryllium disease, which resembles pneumonia. Occupational and community air standards are effective in preventing most acute lung damage. Long term exposure to beryllium can increase the risk of developing lung cancer. The more common and serious health hazard from beryllium today is chronic beryllium disease (CBD), discussed below. It continues to occur in industries as diverse as metal recycling, dental laboratories, alloy manufacturing, nuclear weapons production, defense industries, and metal machine shops that work with alloys containing small amounts of beryllium.

Chronic beryllium disease (CBD)

Some people (1-15%) become sensitive to beryllium. These individuals may develop an inflammatory reaction that principally targets the respiratory system and skin. This condition is called chronic beryllium disease (CBD), and can occur within a few months or many years after exposure to higher than normal levels of beryllium (greater than 0.02 µg/m³). This disease causes fatigue, weakness, night sweats and can cause difficulty in breathing and a persistent dry cough. It can result in anorexia, weight loss, and may also lead to right-side heart enlargement and heart disease in advanced cases. Some people who are sensitized to beryllium may not have any symptoms. The disease is treatable but not curable. CBD occurs when the body's immune system recognizes beryllium particles as foreign material and mounts an immune system attack against the particles. Because these particles are typically inhaled into the lungs, the lungs becomes the major site where the immune system responds. The lungs become inflamed, filled with large numbers of white blood cells that accumulate wherever beryllium particles are found. The cells form balls around the beryllium particles called "granulomas." When enough of these granulomas develop, they interfere with the normal function of the organ. Over time, the lungs become stiff and lose their ability to help transfer oxygen from the air into the bloodstream. Patients with CBD develop difficulty inhaling and exhaling sufficient amounts of air and the amount of oxygen in their bloodstreams falls. Treatment of such patients includes use of oxygen and medicines that try to suppress the immune system's over-reaction to beryllium. A class of immunosuppressive medicines called glucocorticoids (example: prednisone), is most commonly used as treatment. The general population is unlikely to develop acute or chronic beryllium disease because ambient air levels of beryllium are normally very low (0.00003-0.0002 µg/m³).

Ingestion

Swallowing beryllium has not been reported to cause effects in humans because very little beryllium is absorbed from the stomach and intestines. Ulcers have been seen in dogs ingesting beryllium in the diet. Beryllium contact with skin that has been scraped or cut may cause rashes or ulcers, or bumps under the skin called "granulomas."

The United States Department of Health and Human Services (DHHS) and the International Agency for Research on Cancer (IARC) have determined that beryllium is a human carcinogen. The U.S. Environmental Protection Agency (EPA) has determined that beryllium is a probable human carcinogen. The EPA has estimated that lifetime exposure to 0.04 µg/m³ beryllium can result in a one in a thousand chance of developing cancer.

Effects on children

There are no studies on the health effects of children exposed to beryllium, although individual cases of CBD have been reported in children of beryllium workers from the 1940s. It is likely that the health effects seen in children exposed to beryllium will be similar to the effects seen in adults. It is unknown whether children differ from adults in their susceptibility to beryllium. It is unclear whether beryllium is teratogenic.

Detection in the body

Beryllium can be measured in the urine and blood. The amount of beryllium in blood or urine may not indicate time or quantity of exposure. Beryllium levels can also be measured in lung and skin samples. While such measurements may help establish that exposure has occurred, other tests are used to determine if that exposure has resulted in health effects. A blood test, the blood beryllium lymphocyte proliferation test (BeLPT), identifies beryllium sensitization and has predictive value for CBD. The BeLPT has become the standard test for detecting beryllium sensitization and CBD in individuals who are suspected of having CBD and to help distinguish it from similar conditions such as sarcoidosis. It is also the main test used in industry health programs to monitor whether disease is occurring among current and former workers who have been exposed to beryllium on the job. The test can detect disease that is at an early stage, or can detect disease at more advanced stages of illness as well. The BeLPT can also be performed using cells obtained from a person's lung by a procedure called "bronchoscopy."

Industrial release limits

Typical levels of beryllium that industries may release into the air are of the order of 0.01 µg/m³, averaged over a 30-day period, or 2 µg/m³ of workroom air for an 8-hour work shift. Compliance with the current U.S. Occupational Safety and Health Administration (OSHA) permissible exposure limit for beryllium of 2 µg/m³ has been determined to be inadequate to protect workers from developing beryllium sensitization and CBD. The American Conference of Governmental Industrial Hygienists (ACGIH), which is an independent organization of experts in the field of occupational health, has established a threshold limit value (TLV) of 0.02 µg/m³. This TLV is 100 times lower than the current OHSA permissible exposure limit, reflecting the ACGIH analysis of best available peer-reviewed research data concerning how little airborne beryllium is required to cause sensitization and CBD. Because it can be difficult to control industrial exposures to beryllium, it is advisable to use any methods possible to reduce airborne and surface contamination by beryllium, to minimize the use of beryllium and beryllium-containing alloys whenever possible, and to educate people about the potential hazards if they are likely to encounter beryllium dust or fumes.

References

Los Alamos National Laboratory – Beryllium

Burrell, AK. Ehler, DS. McClesky, TM. Minogue, EM. Taylor, TP. Development of a New Fluorescence Method for the Detection of Beryllium on Surfaces. Journal of ASTM International (JAI). 2005. Vol 2: Issue 9. http://www.astm.org/cgi-bin/SoftCart.exe/JOURNALS/JAI/PAGES/JAI13168.htm?E+mystore

Infante PF, Newman LS. Commentary: Beryllium exposure and Chronic Beryllium Disease. Lancet 2004; 415-16.

Newman LS. Beryllium. Chemical & Engineering News, 2003; 36:38.

Kelleher PC, Martyny JW, Mroz MM, Maier LA, Ruttenber JA, Young DA, Newman LS. Beryllium particulate exposure and disease relations in a beryllium machining plant. J Occup Environ Med 2001; 43:238-249.

Mroz MM, Balkissoon R, Newman LS. Beryllium. In: Bingham E, Cohrssen B, Powell C (eds.) Patty’s Toxicology, Fifth Edition. New York: John Wiley & Sons 2001, 177-220.

Beryllium and Compounds: TLV® Chemical Substances Draft Documentation, Notice of Intended Change ACGIH® Publication #7NIC-042

External links

Chemical elements | Alkaline earth metals | Toxicology

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