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B

BORON

(Ar. büraq, Pers. bürah)

B  at. wt. 10.811
   at. no. 5
   m.p. 2300° C
   sublimes 2550° C 
   sp. gr. of crystals 2.34
   sp. gr. of amorphous variety 2.37
   valence 3.

**Electronic configuration**
SHELL	K	L	M	N	O	P	Q
SUB SHELL	He	Neon	Argon	Krypton	Xenon	Radon	Eka-radon
SUB SHELL	1s	2s 2p	3s 3p	3d 4s 4p	4d 5s 5p	4f 5d 6s 6p	5f 6d 7s 7p
Boron	1s²2s²2p¹
Symbol	²P_½

Boron compounds have been known for thousands of years, but the element was not discovered until 1808 by Sir Humphry Davy and by Gay-Lussac and Thenar4. The element is not found free in nature, but occurs as orthoboric acid usually in certain volcanic spring waters and as borates in borax and coleman- ite. Ulexite, another boron mineral, is interesting as it is nature's own version of "fiber optics." By far the most important source of boron is the mineral rasorite, also known as kernite, foand in the Mojave desert of California. .Bxten- sive borax deposits are also found in Turkey. Boron exists naturally as 19.78% 5B'0 isotope and 80.22% 5B11 isotope. High-purity crystalline boron may be prepared by the vapor phase reduction of boron trichloride or tribromide with hydrogen on electrically heated filaments. The impure, or amorphous boron, a brownish-black powder, can be ob- tained by heating the trioxide with magnesium powder. Boron of 99.9999% purity has been produced and is avail- able commercially. Elemental boron has an energy band gap of 1.50 to 1.56 electrost volts, which is higher than that of either silicon or germanium. It has interesting optical characteristics, transmitting portions of the infrared, and is a poor conductor of electricity at room temperature, but a good conductor at high temperature. Amorphous boron is used in pyrotechnic flares to provide a distinctive green color, and in rockets as an igniter. The most important compounds of boron are boric, or boracic acid widely used as a mild antiseptic, and borax (Na2B4O7 10H20), which serves as a cleansing flux in welding and as a water softener 'in washing powders. Boron compounds are used in produc- tion of enamels for covering steel of refrigerators, washing machines, and like products. Boron compounds are also extensively used in the manufacture of borosilicate glasses. The isotope boron 10 is used as a control for nuclear reactors, as a shield for nuclear radiation, and in instruments used for detectirig neutrons. Boron nitride has remarkable properties and can be used to make a material as hard as diamond. The nitride also behaves like an electrical insulator but conducts heat like a metal. It also has lubricating properties similar to graphite. The hydrides are easily oxidized with considerable energy liberation, and are being studied for use as rocket fuels. Demand is increasing for boron filaments, a high- strength, light-weight materialchieflyemployed for advanced aero-space structures. Amorphous boron (90 %-92 % grade) costs about $12 to $30/lb. depending on quantity ordered. Elemental boron is not considered to be a poison, but assimilation of its compounds has a cumulative poisonous effect.

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B

BORON

(Ar. büraq, Pers. bürah)

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