beryllium bərĭlˈēəm [key] [from beryl ], metallic chemical element; symbol Be; at. no. 4; at. wt. 9.01218; m.p. about 1,278℃; b.p. 2,970℃ (estimated); sp. gr. 1.85 at 20℃; valence +2. Beryllium is a strong, extremely light, high-melting, silver-gray metal with a close-packed hexagonal crystalline structure. It is an alkaline-earth metal in Group 2 of the periodic table. Beryllium is resistant to corrosion; weight for weight, it is stronger than steel, and because of its low density (about 1/3 that of aluminum) it has found extensive use in the aerospace industry.

Beryllium is soluble in hot nitric acid, dilute hydrochloric and sulfuric acids, and sodium hydroxide. Like aluminum and magnesium, which it resembles chemically, it readily forms compounds with other elements; it is not found free in nature. However, like aluminum, it is resistant to oxidation in air, even at a red heat; it is thought to form a protective oxide film that prevents further oxidation. The compounds of beryllium are sweet-tasting and highly toxic; this toxicity has limited the use of beryllium as a rocket fuel, even though it yields more heat on combustion for its weight than any other element.

Beryllium transmits X rays much better than glass or other metals; this property, together with its high melting point, makes it desirable as a window material for high-intensity X-ray tubes. Because beryllium resists attack by liquid sodium metal, it is employed in cooling systems of nuclear reactors that use liquid sodium as the heat-transfer material; because it is a good reflector and absorber of neutrons, it is also used as a shield and as a moderator in nuclear reactors.

The addition of 2% to 3% of beryllium to copper makes a nonmagnetic alloy six times stronger than pure copper. This alloy is used to make nonsparking tools for use in oil refineries and other places where sparks constitute a fire hazard; it is also used for small mechanical parts, such as camera shutters. When beryllium is alloyed with other metals such as aluminum or gold it yields substances with a higher melting point, greater hardness and strength, and lower density than the metal with which it is alloyed.

Beryllium aluminum silicates, especially beryl (of which emerald and aquamarine are varieties), constitute the chief sources of the metal. Although its ores occur widely in North America, Europe, and Africa, the cost of extracting the metal limits its commercial use. Beryllium may be prepared by electrolysis of its fused salts; it is prepared commercially by reduction of the fluoride with magnesium metal.

Beryllium was discovered in 1798 as the oxide beryllia by L. N. Vauquelin, a French chemist. Vauquelin analyzed beryl and emerald at the urging of R. J. Haüy, a French mineralogist, who had noted that their optical properties were identical. Beryllium was first isolated in 1828 independently by F. Wöhler in Germany and W. Bussy in France by fusing beryllium chloride with metallic potassium.

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