Electrical boron compounds

For a large number of applications involving ceramic materials, electrical conduction behavior is dorninant. In certain oxides, borides (see Boron compounds), nitrides (qv), and carbides (qv), metallic or fast ionic conduction may occur, making these materials useful in thick-film pastes, in fuel cell apphcations (see Fuel cells), or as electrodes for use over a wide temperature range. Superconductivity is also found in special ceramic oxides, and these materials are undergoing intensive research. Other classes of ceramic materials may behave as semiconductors (qv). These materials are used in many specialized apphcations including resistance heating elements and in devices such as rectifiers, photocells, varistors, and thermistors. 

Various boron compounds have been used as rocket fuels, diamond substitutes, and additives to aluminum alloys to improve electrical and thermal conductivity, as well as for grain refining. Boron hydrides are sensitive to shock and can detonate easily. Boron halides ate corrosive and toxic. 

Boron Carbide. Boron carbide [12069-32-87, B4C, is produced by the reaction of boron oxide and coke in an electric arc furnace (70% B4C) or by that of carbon and boric anhydride in a carbon resistance furnace (80% B4C) (see Boron compounds, refractory BORON compounds). It is primarily used as a loose abrasive for grinding and lapping hard metals, gems, and optics (18).. Although B4C is oxidation-prone, the slow speed of lapping does not generate enough heat to oxidize the abrasive. 

The rapid development of carborane chemistry is mainly due to their practical applications. For instance, the potential utility of carborane polymers as gaskets, O-rings, and electrical connector inserts has been reported. Their functionality for solvent extraction of radionuchdes as well as the potential medicinal value of the isoelectronic and isostructural boron analogues of biologically important molecules has been the subject of many review articles. For example, a number of boron compounds have been found to possess anti-inflammatory and antiarthritic activity in animal model studies. Boron compounds have also been implicated in studies designed to probe the importance of the so-called anionic subsite of acetylcholine esterase and Ach receptors. But, by far the most interesting practical apphcations of carboranes are in areas of boron neutron capture therapy (BNCT) and supramolecular assembly. 

Gajhede, M. (1985). Ab initio electric field gradient calculations for a series of oxygen-containing boron compounds. Chem. Phys. Lett. 120, 266-71. 

There are few useful reactions in which new B—H bonds are formed. Although the formation of boranes from the protolysis of borides or the reduction of boron compounds with Hj, either in electrical discharges or in the presence of active metals, have historical importance, these methods have no importance or utility today. Indeed, the preparation of boranes is so dominated by the single common starting material, the tetrahydroborate ion, that the only important reactions in which B—H bonds are formed are those in which hydride ion either reduces species with B—O or B-halogen bonds to form boranes or adds to trifunctional boron compounds to form hydroborates. 

Boron, an element, occurs in many compounds, including borax, borates, boric acid, and carboxyboranes used in glass, ceramics, detergents, bleaches, fire retardants, disinfectants, alloys, specialty metals, preservatives, pesticides, and fertilizers (Mastromatteo and Sullivan 1994). Boron compounds also constitute an important group of dopants in the semiconductor industry. Dopants alter crystalline substrates electrical conductivities in the manufacturing of diodes, transistors, and capacitors (Lewis 1986). 

Uses Catalyst in organic synthesis source of boron compounds refining of alloys soldering flux electrical resistors extinguishing magnesium fires in heat-treating furnaces mfg. of diborane semiconductor dopant boron vapor deposition raw material (boron fibers)... 

Boron carbide is either prepared from boron ores or from pure boron. The process involves the reduction of a boron compound. Usually, boron carbide is obtained by reacting boric acid or boron oxide and carbon at ca. 2500°C in an electric-arc furnace. 

Boron, atomic number 5, has three electrons in its valence shell. To bond with three other atoms, boron uses sp hybrid orbitals. The unoccupied 2p orbital of boron is perpendicular to the plane created by boron and the three other atoms to which it is bonded. An example of a stable, trivalent boron compound is boron ttifluotide, BF3, a planar molecule with F—B—F bond angles of 120° (Section 1.2E). Because of the vacant 2p orbital in the valence shell of boron, BH3, BF3, and aU other trivalent compounds of boron are electrophiles. These compounds of boron resemble carbocations, except that, unlike carbocations, they are electrically neutral. BH3 is a planar molecule with H— B—H bond angles of 120° (see margin). 

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