REFRACTORY BORON COMPOUNDS

Borides have metallic characteristics such as high electrical conductivity and positive coefficients of electrical resistivity. Many of them, particularly the borides of metals of Groups 4 (IVB), 5 (VB), and 6 (VIB), the MB compounds of Groups 2(11) and 13(111), and the borides of aluminum and siUcon, have high melting points, great hardness, low coefficients of thermal expansion, and good chemical stabiUty. 

Borides are inert toward nonoxidizing acids however, a few, such as Be2B and MgB2, react with aqueous acids to form boron hydrides. Most borides dissolve in oxidizing acids such as nitric or hot sulfuric acid and they ate also readily attacked by hot alkaline salt melts or fused alkaU peroxides, forming the mote stable borates. In dry air, where a protective oxide film can be preserved, borides ate relatively resistant to oxidation. For example, the borides of vanadium, niobium, tantalum, molybdenum, and tungsten do not oxidize appreciably in air up to temperatures of 1000—1200°C. Zirconium and titanium borides ate fairly resistant up to 1400°C. Engineering and other properties of refractory metal borides have been summarized (1). 

Molecular Boride CAS Registry Mp °C Molecular Boride CAS Registry Mp °C 

Be2B diberyUium boride [12536-51-5] 1520 Pd3B tripalladium boride [12429-53-7] 820, d 

C14B tetrachromium boride [12006-81-4] 1680 TaB2 tantalum diboride [12007-35-1] 3100 

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Next to Cr C2, TiC is the principal component for heat and oxidation-resistant cemented carbides. TiC-based boats, containing aluminum nitride, AIN, boron nitride, BN, and titanium boride, TiB2, have been found satisfactory for the evaporation of metals (see Boron compounds, refractory boron compounds Nitrides). 

The main chemical products produced from these minerals are (a) boron oxides, boric acid and borates, (b) esters of boric acid, (c) refractory boron compounds (borides, eu .), (d) boron halides, (e) boranes and carbaboranes and (f) organoboranes. The main industrial and domestic uses of boron compounds in Europe (USA in parentheses) are ... 

Boron forms B—N compounds that are isoelectronic with graphite (see Boron compounds, refractory boron compounds). The small size also has a significant role in the interstitial alloy-type metal borides boron forms. Boron forms borides with metals that are less electronegative than itself including titanium, zirconium, and hafnium. 

BORONCOMPOUNDS - REFRACTORY BORON COMPOUNDS] (Vol 4) Magnesium bromide [7789-48-2]... 

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. 

T. Lundstrom, and H. Bokngren, On Refractory Boron Compounds Crystallizing in B4C-type Structures, in Proceeding of the 11th International Symposium on Boron, Borides and Related Compounds Jap. J. Appl. Physics, Series No. 10, eds. R. Uno and I. Higashi, Tokyo, 1994, 1. 

Elemental boron is a refractory material that is usually isolated either as a shiny black crystalline solid or a softer, browner, more impure amorphous solid. Reduction of readily available boron compounds containing boron oxygen bonds to elemental boron is energy intensive and costly. This has limited the extent of conunercial use of this material. Many related refractory boron compounds have been prepared and characterized including metal borides, boron carbides, boron nitrides, and various boron metal alloys. These refractory materials and elemental boron are also discussed in some detail in the article Borides Solid-state Chemistry. Other general references are available on elemental boron and other refractory boron compounds. " ... 

Wentorf, R. H., Jr., Refractory Boron Compounds, in Kirk Othmer, Encyclopedia of Chemical Technology, John Wiley Sons, New York... 

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