.

Beryllium is the chemical element with the symbol Be and atomic number 4.

A bivalent element, beryllium is found naturally only combined with other elements in minerals. Notable gemstones which contain beryllium include beryl (aquamarine, emerald) and chrysoberyl. The free element is a steel-gray, strong, lightweight brittle alkaline earth metal. It is primarily used as a hardening agent in alloys, notably beryllium copper. Structurally, beryllium's very low density (1.85 times that of water), high melting point (1278 °C), high temperature stability, and low coefficient of thermal expansion, make it in many ways an ideal aerospace material, and it has been used in rocket nozzles and is a significant component of planned space telescopes. Because of its relatively high transparency to X-rays and other ionizing radiation types, beryllium also has a number of uses as filters and windows for radiation and particle physics experiments.

Commercial use of beryllium metal presents technical challenges due to the toxicity (especially by inhalation) of beryllium-containing dusts. Beryllium produces a direct corrosive effect to tissue, and can cause a chronic life-threatening allergic disease called berylliosis in susceptible persons.

Beryllium is a relatively rare element in both the Earth and the universe. The element is not known to be necessary or useful for either plant or animal life.

History
Beryllium was discovered by Louis-Nicolas Vauquelin in 1798 as a component of beryl and in emeralds. Friedrich Wöhler[5] and Antoine Bussy independently isolated the metal in 1828 by reacting potassium and beryllium chloride. Beryllium's chemical similarity to aluminum was probably why beryllium was missed in previous searches.[6]

Etymology

The name beryllium comes (via Latin: Beryllus and French: Béryl) from the Greek βήρυλλος, bērullos, beryl, from Prakrit veruliya (वॆरुलिय‌), from Pāli veḷuriya (वेलुरिय); veḷiru (भेलिरु) or, viḷar (भिलर्), "to become pale," in reference to the pale semiprecious gemstone beryl.[7] The original source of the word "Beryllium" is the Sanskrit word: वैडूर्य vaidurya-, which is of Dravidian origin and could be derived from the name of the modern city of Belur.[8] For about 160 years, beryllium was also known as glucinum or glucinium (with the accompanying chemical symbol "Gl"[9]), the name coming from the Greek word for sweet: γλυκυς, due to the sweet taste of its salts.

Characteristics

Physical

Beryllium has one of the highest melting points of the light metals. It has exceptional flexural rigidity (Young's modulus 287 GPa). The modulus of elasticity of beryllium is approximately 50% greater than that of steel. The combination of this modulus plus beryllium's relatively low density gives it an unusually fast sound conduction speed at standard conditions (about 12.9 km/s). Other significant properties are the high values for 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 ensure that beryllium demonstrates a unique degree of dimensional stability under conditions of thermal loading.[10]

At standard temperature and pressures beryllium resists oxidation when exposed to air (its ability to scratch glass is due to the formation of a thin layer of the hard oxide BeO). It resists corrosion by concentrated nitric acid.[11]

Nuclear

Beryllium has a large scattering cross section for high-energy neutrons, thus effectively slowing the neutrons to the thermal energy range where the cross section is low (0.008 barn). The predominant beryllium isotope 9Be also undergoes a (n,2n) neutron reaction to 8Be, that is beryllium is a neutron multiplier, releasing more neutrons than it absorbs. Beryllium is highly permeable to X-rays, and neutrons are liberated when it is hit by alpha particles.[10]

Isotopes
Main articles: Isotopes of beryllium and beryllium-10
Plot showing variations in solar activity, including variation in 10Be concentration. Note that the beryllium scale is inverted, so increases on this scale indicate lower beryllium-10 levels

Of beryllium's isotopes, only 9Be is stable and the others are relatively unstable or rare. It is thus a mononuclidic element.

Cosmogenic 10Be is produced in the atmosphere by cosmic ray spallation of oxygen and nitrogen. Cosmogenic 10Be accumulates at the soil surface, where its relatively long half-life (1.36 million years) permits a long residence time before decaying to 10B. Thus, 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. Solar activity is inversely correlated with 10Be production, because solar wind decreases flux of galactic cosmic rays which reach Earth.

Nuclear explosions also form 10Be by a reaction of fast neutrons with 13C in the carbon dioxide in air. This is one of the historical indicators of past activity at nuclear test sites.[12]

The fact that 7Be and 8Be have very short half-lives has profound cosmological consequences. Elements heavier than beryllium could not be produced by nuclear fusion in the Big Bang. This is due to the lack of sufficient time during the Big Bang nucleosynthesis phase to produce carbon by fusion of 4He nuclei and the very low concentrations of available 8Be. Astronomer Fred Hoyle first showed that the energy levels of 8Be and 12C allow carbon production by the triple-alpha process in helium-fueled stars where more synthetic time is available, thus making life possible from the supernova "ash" from these stars. (See also Big Bang nucleosynthesis).[13]

7Be decays by electron capture, therefore its decay rate is dependent upon its electron configuration – a rare occurrence in nuclear decay.[14]

The shortest-lived known isotope of beryllium is 13Be which decays through neutron emission. It has a half-life of 2.7 × 10⁻²¹ second. 6Be is also very short-lived with a half-life of 5.0 × 10−21 second.[11]

The exotic isotopes 11Be and 14Be are known to exhibit a nuclear halo.[15]

Chemical

Beryllium has the electronic configuration [He] 2s2. In its chemistry beryllium exhibits the +2 oxidation state and the only evidence of lower valence of beryllium is in the solubility of the metal in BeCl2.[16] The small atomic radius ensures that the Be2+ ion would be highly polarizing leading to significant covalent character in beryllium's bonding.[17] Beryllium is 4 coordinate in complexes e.g. [Be(H2O)4]2+ and tetrahaloberyllates, BeX42−. This characteristic is used in analytical techniques using EDTA as a ligand which preferentially forms octahedral complexes – thus absorbing other cations such as Al3+ which might interfere, for example in the solvent extraction of a complex formed between Be2+ and acetylacetone.[18]

Beryllium metal sits above aluminium in the electrochemical series and would be expected to be a reactive metal, however it is passivated by an oxide layer and does not react with air or water even at red heat.[17] Once ignited however beryllium burns brilliantly forming a mixture of beryllium oxide and beryllium nitride.[17] Beryllium dissolves readily in non-oxidizing acids, such as HCl and H2SO4, but not in nitric as this forms the oxide and this behavior is similar to that of aluminium metal. Beryllium, again similarly to aluminium, dissolves in warm alkali to form the beryllate anion, Be(OH)42−, and hydrogen gas. The solutions of salts, e.g. beryllium sulfate and beryllium nitrate are acidic because of hydrolysis of the [Be(H2O)4]2+ ion; for example

[Be(H2O)4]2+ + H2O is in equilibrium with [Be(H2O)3(OH)]+ + H3O+

Compounds
See also: Category:Beryllium compounds

Beryllium forms binary compounds with many non-metals. Beryllium hydride is an amorphous white solid believed to be built from corner-sharing {BeH4} tetrahedra.[19]

All four anhydrous halides are known. BeF2 has a silica-like structure with corner-shared BeF4 tetrahedra. BeCl2 and BeBr2 have chain structures with edge-shared tetrahedra. They all have linear monomeric gas phase forms.[17]

Beryllium oxide, BeO, is a white, high-melting-point solid, which has the wurtzite structure with a thermal conductivity as high as some metals. BeO is amphoteric. Beryllium hydroxide, Be(OH)2 has low solubility in water and is amphoteric. Salts of beryllium can be produced by reacting Be(OH)2 with acid.[17]

Beryllium sulfide, selenide and telluride all have the zincblende structure.[16]

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.[16]

A number of beryllium borides are known, Be5B, Be4B, Be2B, BeB2, BeB6, BeB12.[16]

Beryllium carbide, Be2C, is a high melting, brick red compound that reacts with water to give methane.[16] No beryllium silicide has been identified.[17]

Basic beryllium nitrate and basic beryllium acetate have similar tetrahedral structures with four beryllium atoms coordinated to a central oxide ion.[16]

Occurrence
See also: Category:Beryllium minerals

The beryllium concentration of the Earth's surface rocks is ca. 4–6 ppm. Beryllium is a 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, bixbite and emerald.[10]

Production

Because of its high affinity for oxygen at elevated temperatures and its ability to reduce water when its oxide film is removed, the extraction of beryllium from its compounds is very difficult. Although electrolysis of a fused mixture of beryllium and sodium fluorides was used to isolate the element in the nineteenth century, the metal's high melting point makes this process more energy intensive than the corresponding production of alkali metals. Early in the twentieth 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 proved to be uneconomic for volume production.[20]

Beryllium metal did not become readily available until 1957. Currently, most is produced by reducing beryllium fluoride with magnesium metal. The price on the US market for vacuum-cast beryllium ingots was 338 US$ per pound ($745/kg) in 2001.[21]

BeF2 + Mg → MgF2 + Be

Applications

Radiation windows

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. Extreme demands are placed on purity and cleanliness of Be 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.[10]

Because of its low atomic number beryllium is almost transparent to energetic particles. Therefore it is used to build the beam pipe around the collision region in collider particle physics experiments. Notably all four main detector experiments at the Large Hadron Collider accelerator (ALICE, ATLAS, CMS, LHCb) use a beryllium beam-pipe.

Also many high-energy particle physics collision experiments such as the Large Hadron Collider, the Tevatron, the SLAC and others contain beam pipes made of beryllium. Beryllium's low density 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.[22]

Mechanical

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, missiles, space vehicles and communication satellites. Several liquid-fuel rockets use nozzles of pure beryllium.[23][24]

Beryllium is used as an alloying agent in the production of beryllium copper, which contains up to 2.5% beryllium. Beryllium-copper alloys are used in many applications because of their combination of high 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.

Beryllium was also used in Jason pistols which were used to strip paint from the hulls of ships. In this case, beryllium was alloyed to copper and used as a hardening agent.[25]

The excellent elastic rigidity of beryllium has led to its extensive use in precision instrumentation, e.g. in gyroscope inertial guidance systems, and in support structures for optical systems.[10]

Beryllium mirrors are a field 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 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.[10]

The James Webb Space Telescope[26] will have 18 hexagonal beryllium sections for its mirrors. Because JWST will face a temperature of 33 degrees K, the mirror is made of beryllium, capable of handling extreme cold better than glass. Beryllium contracts and deforms less than glass—and remains more uniform—in such temperatures.[27] For the same reason, the optics of the Spitzer Space Telescope are entirely built of beryllium metal.[28]

An earlier major application of beryllium was in brakes for military aircraft because of its hardness, high melting point and exceptional heat dissipation. Environmental considerations have led to substitution by other materials.[10]

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.[10]

Magnetic

Beryllium is non-magnetic. Therefore, beryllium-based tools are used by military naval EOD-personnel when working on or around naval mines, as these often have fuzes that detonate on direct magnetic contact or when influenced by a magnetic field.[29] They are also found in maintenance and construction materials near MRI scanners. Magnetic tools would be pulled by the scanner's strong magnetic field. Apart from being difficult to remove once magnetic items are stuck in the scanner, the missile-effect can have dangerous consequences.[30] In the telecommunications industry, tools made of beryllium are used to tune the highly magnetic klystrons used for high power microwave applications.

Nuclear

Beryllium is used in nuclear weapon designs as the outer layer of the pit of the primary stage, surrounding the fissile material. It is a good pusher for implosion, and a very good neutron reflector, as in beryllium moderated reactors.[31]

Beryllium is sometimes used in neutron sources, in which the beryllium is mixed with an alpha emitter such as 210Po, 226Ra, 239Pu or 241Am. The "Urchin" neutron initiator in early nuclear weapons used beryllium-polonium combination.[31]

Beryllium is used in the Joint European Torus fusion research facility and will be used in ITER, to condition the plasma facing components.[32] Beryllium has also been proposed as a cladding material for nuclear fuel, due to its combination of mechanical, chemical, and nuclear properties.[10]

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 molten salt reactor designs.

Acoustics

Beryllium's characteristics (low weight and high rigidity) make it useful as a material for high-frequency speaker drivers. Until recently, most beryllium tweeters used an alloy of beryllium and other metals due to beryllium's high cost and difficulty to form. These challenges, coupled with the high performance of beryllium, caused some manufacturers to falsely claim using pure beryllium.[33] Some high-end audio companies manufacture pure beryllium tweeters or speakers using these tweeters. Because beryllium is many times more expensive than titanium, hard to shape due to its brittleness, and toxic if mishandled, these tweeters are limited to high-end and public address applications.[34][35][36]

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).[37]

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 RF transmitters for telecommunications. Beryllium oxide is also being studied for use in increasing the thermal conductivity of uranium dioxide nuclear fuel pellets.[38]

Beryllium compounds were used in fluorescent lighting tubes, but this use was discontinued because of berylliosis in the workers manufacturing the tubes.[39]

Toxicity
Main article: Beryllium poisoning
The toxicity of beryllium depends upon the duration, intensity and frequency of exposure (features of dose), as well as the form of beryllium and the route of exposure (i.e. inhalation, dermal, ingestion).

Beryllium chemistry and processing, Kenneth A. Walsh

Beryllium: environmental analysis and monitoring, Michael J. Brisson, Amy A. Ekechukwu

Beryllium: sampling and analysis, Issue 1473, Kevin Ashley, ASTM International. Committee D22 on Air Quality, ASTM International Committee D22 on Air Quality. Subcommittee D22.04 on Sampling and Analysis of Workplace Atmospheres, ASTM International. Beryllium Health and Safety Committee. Sampling and Analysis Subcommittee

See also

* Category:Beryllium compounds
* Sucker Bait, a story by Isaac Asimov in which the health hazard of beryllium dust is an important plot point

References

1. ^ "Beryllium: Beryllium(I) Hydride compound data". bernath.uwaterloo.ca. http://bernath.uwaterloo.ca/media/252.pdf. Retrieved 2007-12-10.
2. ^ "Published by J. C. Slater in 1964". http://en.wikipedia.org/wiki/Atomic_radii_of_the_elements_%28data_page%29.
3. ^ "Calculated data". http://en.wikipedia.org/wiki/Atomic_radii_of_the_elements_%28data_page%29.
4. ^ sound
5. ^ Wöhler, Friedrich (1828). "Ueber das Beryllium und Yttrium". Annalen der Physik 89 (8): 577–582. doi:10.1002/andp.18280890805.
6. ^ Weeks, Mary Elvira (1933). "XII. Other Elements Isolated with the Aid of Potassium and Sodium: Beryllium, Boron, Silicon and Aluminium". The Discovery of the Elements. Easton, PA: Journal of Chemical Education. ISBN 0-7661-3872-0.
7. ^ "The American Heritage Dictionary of the English Language: beryl". Houghton Mifflin Company. 2000. http://www.bartleby.com/61/74/B0207400.html. Retrieved 2008-09-18.
8. ^ Harper, Douglas. "beryl". Online Etymology Dictionary. http://www.etymonline.com/index.php?term=beryl.
9. ^ Black, The MacMillian Company, New York, 1937
10. ^ a b c d e f g h i Behrens, V. (2003). "11 Beryllium". in Beiss, P.. Landolt-Börnstein – Group VIII Advanced Materials and Technologies: Powder Metallurgy Data. Refractory, Hard and Intermetallic Materials. 2A1. Berlin: Springer. pp. 1–11. doi:10.1007/10689123_36. ISBN 978-3-540-42942-5.
11. ^ a b Lide, D. R., ed. (2005), CRC Handbook of Chemistry and Physics (86th ed.), Boca Raton (FL): CRC Press, ISBN 0-8493-0486-5
12. ^ Whitehead, N; Endo, S; Tanaka, K; Takatsuji, T; Hoshi, M; Fukutani, S; Ditchburn, Rg; Zondervan, A (Feb 2008). "A preliminary study on the use of (10)Be in forensic radioecology of nuclear explosion sites.". Journal of environmental radioactivity 99 (2): 260–70. doi:10.1016/j.jenvrad.2007.07.016. ISSN 0265-931X. PMID 17904707.
13. ^ Arnett, David (1996). Supernovae and nucleosynthesis. Princeton University Press. p. 223. ISBN 0691011478. http://books.google.com/books?id=PXGWGnPPo0gC&pg=PA223.
14. ^ Johnson, Bill (1993). "How to Change Nuclear Decay Rates". University of California, Riverside. http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/decay_rates.html. Retrieved 2008-03-30.
15. ^ Hansen, P. G.; Jensen, A. S.; Jonson, B. (1995). "Nuclear Halos". Annual Review of Nuclear and Particle Science 45: 591. doi:10.1146/annurev.ns.45.120195.003111.
16. ^ a b c d e f Wiberg, Egon; Holleman, Arnold Frederick (2001). Inorganic Chemistry. Elsevier. ISBN 0123526515.
17. ^ a b c d e f Greenwood, Norman N.; Earnshaw, A. (1997), Chemistry of the Elements (2nd ed.), Oxford: Butterworth-Heinemann, ISBN 0080379419
18. ^ Okutani, T.; Tsuruta, Y.; Sakuragawa, A. (1993). "Determination of a trace amount of beryllium in water samples by graphite furnace atomic absorption spectrometry after preconcentration and separation as a beryllium-acetylacetonate complex on activated carbon". Anal. Chem. 65: 1273–1276. doi:10.1021/ac00057a026.
19. ^ Sampath, Sujatha; Lantzky, Kristina M.; Benmore, Chris J.; Neuefeind, Jörg; Siewenie, Joan E. (2003). "Structural quantum isotope effects in amorphous beryllium hydride". J. Chem. Phys. 119: 12499. doi:10.1063/1.1626638.
20. ^ Babu, R. S.; Gupta, C. K. (1988). "Beryllium Extraction – A Review". Mineral Processing and Extractive Metallurgy Review 4: 39. doi:10.1080/08827508808952633.
21. ^ "Beryllium Statistics and Information". United States Geological Survey. http://minerals.usgs.gov/minerals/pubs/commodity/beryllium/. Retrieved 2008-09-18.
22. ^ Wieman, H (2001). "A new inner vertex detector for STAR". Nuclear Instruments and Methods in Physics Research Section a Accelerators Spectrometers Detectors and Associated Equipment 473: 205. doi:10.1016/S0168-9002(01)01149-4.
23. ^ Davis, Joseph R. (1998). "Beryllium". Metals handbook. ASM International. pp. 690–691. ISBN 9780871706546. http://books.google.com/books?id=IpEnvBtSfPQC&pg=PA690.
24. ^ Mel M. Schwartz (2002). Encyclopedia of materials, parts, and finishes. CRC Press. p. 62. ISBN 1566766613. http://books.google.com/books?id=6fdmMuj0rNEC&pg=PA62.
25. ^ "Defence forces face rare toxic metal exposure risk". 1 February 2005. http://www.smh.com.au/news/National/Defence-forces-face-rare-toxic-metal-exposure-risk/2005/02/01/1107228681666.html. Retrieved 2009-08-08.
26. ^ "Beryllium related details from NASA". NASA. http://www.jwst.nasa.gov/mirror.html. Retrieved 2008-09-18.
27. ^ Gardner, Jonathan P. (2007). "The James Webb Space Telescope". Poceedings of Science. http://pos.sissa.it/archive/conferences/052/005/MRU_005.pdf.
28. ^ Werner, M. W.; Roellig, T. L.; Low, F. J.; Rieke, G. H.; Rieke, M.; Hoffmann, W. F.; Young, E.; Houck, J. R. et al. (2004). "The Spitzer Space Telescope Mission". Astrophysical Journal Supplement 154: 1. doi:10.1086/422992. http://arxiv.org/abs/astro-ph/0406223v1.
29. ^ Kojola, Kenneth ; Lurie, William (9 August 1961). "The selection of low-magnetic alloys for EOD tools". Naval Weapons Plant Washington DC. http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=AD0263919.
30. ^ Dorsch, Jerry A. and Dorsch, Susan E. (2007). Understanding anesthesia equipment. Lippincott Williams & Wilkins. p. 891. ISBN 0781776031. http://books.google.com/books?id=EqtlqFNkWwQC&pg=PT891.
31. ^ a b Barnaby, Frank (1993). How nuclear weapons spread. Routledge. p. 35. ISBN 0415076749. http://books.google.com/books?id=yTIOAAAAQAAJ&pg=PA35.
32. ^ Clark, R. E. H.; Reiter, D. (2005). Nuclear fusion research. Springer. p. 15. ISBN 3540230386. http://books.google.com/books?id=9ngHTkC8hG8C&pg=PA15.
33. ^ Svilar, Mark (2004-01-08). "Analysis of "Beryllium" Speaker Dome and Cone Obtained from China". http://www.electrofusionproducts.com/userfiles/China_Be_Domes_Report.pdf. Retrieved 2009-02-13.
34. ^ Johnson, Jr., John E. (2007-11-12). "Usher Be-718 Bookshelf Speakers with Beryllium Tweeters". http://www.hometheaterhifi.com/speaker-product-reviews/speakers/usher-be-718-bookshelf-speakers-with-beryllium-tweeters.html. Retrieved 2008-09-18.
35. ^ "When only the best will do". Utopia Be. http://www.utopia-be.com/Technology/Beryllium.htm. Retrieved 2008-09-18.
36. ^ "Exposé E8B studio monitor". KRK Systems. http://www.krksys.com/product_expose.php. Retrieved 2009-02-12.
37. ^ Diehl, Roland (2000). High-power diode lasers. Springer. p. 104. ISBN 3540666931. http://books.google.com/books?id=oJs6nK3TZrwC&pg=PA104.
38. ^ "Purdue engineers create safer, more efficient nuclear fuel, model its performance". Purdue University. 2005-09-27. http://news.uns.purdue.edu/UNS/html4ever/2005/050927.Solomon.nuclear.html. Retrieved 2008-09-18.
39. ^ Breslin AJ (1966). "Chap. 3. Exposures and Patterns of Disease in the Beryllium Industry". in Stokinger, HE. in Beryllium: Its Industrial Hygiene Aspects. Academic Press, New York. pp. 30–33.