boron (redirected from Boron (element))

boron (bōr`ŏn) [New Gr. from borax], chemical element; symbol B; at. no. 5; at. wt. 10.81; m.p. about 2,300°C;; sublimation point about 2,550°C;; sp. gr. 2.3 at 25°C;; valence +3. Boron is a nonmetallic element existing as a dark brown to black amorphous powder or as an extremely hard, usually jet-black to silver-gray, brittle, lustrous, metallike crystalline solid (see allotropy). One tetragonal and two rhombohedral forms of crystalline boron are known. The chemistry of boron more closely resembles the chemistry of silicon than that of the other elements in Group 13 of the periodic table, of which it is a member. The chemical reactivity of boron depends on its form; generally, the crystalline form is far less reactive than the amorphous form. For example, the amorphous powder is oxidized slowly in air at room temperature and ignites spontaneously at high temperatures to form an oxide; the crystalline form is oxidized only very slowly, even at higher temperatures. Boron forms compounds with oxgen, hydrogen, the halogens, nitrogen, phosphorus, and carbon (only diamond is harder than boron carbide). It also forms organic compounds. It is most commonly used in its compounds, especially borax and boric acid. Boron is used as a deoxidizer and degasifier in metallurgy. Because it absorbs neutrons, it is used in the shielding material and in some control rods of nuclear reactors. Boron fibers, which have a very high tensile strength, can be added to plastics to make a material that is stronger than steel yet lighter than aluminum. Boron does not occur free in nature. Large deposits of borax, kermite, colemanite, and other boron minerals are found in the arid regions of the W United States. It occurs also in the mineral tourmaline. The simplest method of preparing boron is the reduction of boron trioxide by heating with magnesium; this yields the amorphous powder. Boron was first isolated in England in 1807 by Sir Humphry Davy and then in France in 1808 by Joseph Louis Gay-Lussac and Louis Jacques Thénard.

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boron

Semimetallic chemical element, chemical symbol B, atomic number 5. Pure crystalline boron is a black, lustrous, very hard but brittle semiconductor that does not occur naturally. Boron compounds are found widely dispersed as various minerals, including borax and the gemstone tourmaline. The element is used to harden certain steels, among other metallurgical uses, and is also used in semiconductor devices. Its borate compounds, in which it has valence 3, are essential to plant growth and have many uses in soaps, mild antiseptics, and eye ointments. Industrially, they are used as herbicides, fire retardants in fabrics, and catalysts in numerous organic chemical reactions. They are also used in electroplating and glass and ceramic formulations. The exceptional hardness and inertness of certain boron compounds, including boron carbide, aluminum boride, and boron nitride (which has an electronic structure resembling that of diamond), make them useful as abrasives and reinforcing agents, particularly for high-temperature applications.

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boron

a very hard almost colourless crystalline metalloid element that in impure form exists as a brown amorphous powder. It occurs principally in borax and is used in hardening steel. The naturally occurring isotope boron-10 is used in nuclear control rods and neutron detection instruments. Symbol: B; atomic no.: 5; atomic wt.: 10.81; valency: 3; relative density: 2.34 (crystalline), 2.37 (amorphous); melting pt.: 2092°C; boiling pt.: 4002°C

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boron [′bȯ‚rän]

(chemistry)

A chemical element, symbol B, atomic number 5, atomic weight 10.811; it has three valence electrons and is nonmetallic.