Chromium boride

Chromium Borides. At least three cmpds are known CrB (ciysts, mp 1550°, d 6.21 ... 

Recent research has explored a wide variety of filler-matrix combinations for ceramic composites. For example, scientists at the Japan Atomic Energy Research Institute have been studying a composite made of silicon carbide fibers embedded in a silicon carbide matrix for use in high-temperature applications, such as spacecraft components and nuclear fusion facilities. Other composites that have been tested include silicon nitride reinforcements embedded in silicon carbide matrix, carbon fibers in boron nitride matrix, silicon nitride in boron nitride, and silicon nitride in titanium nitride. Researchers are also testing other, less common filler and matrix materials in the development of new composites. These include titanium carbide (TiC), titanium boride (TiB2), chromium boride (CrB), zirconium oxide (Zr02), and lanthanum phosphate (LaP04). 

In 1997, the major manufacturers of chromium compounds were (1) chromic(VI) acid, including chromic(VI) anhydride and chromic(VI) trioxide (total capacity 76,000 metric tons) American Chrome Chemicals Inc., Corpus Christi, Texas Occidental Chemical Corporation Specialty Business Group, Castle Hayne, North Carolina (2) chromium(III) sulfate Blue Grass Chemical Specialties, L.P., New Albany, Indiana Johnson Matthey, Inc., Ward Hill, Massachusetts Wayne Chemical Corp., Amarillo, Texas, Dakota City, Nebraska, and Milwaukee, Wisconsin (3) chromium(III) acetate Blue Grass Chemical Specialties, L.P., McGean-Rohco, Inc., Cleveland, Ohio The Shepard Chemical Company, Cincinnati, Ohio (4) chromium acetylacetonate MacKenzie Corporation, Bush, Louisiana The Shepard Chemical Company, Cincinnati, Ohio (5) chromium boride Cerac Incorporated, Milwaukee,... 

Chromium nitrides have been prepared by several routes heating of chromium metal in N2, reaction of chromium borides with NH3, and heating of CrCly in gaseous NH3. The two stable nitrides have the composition Cr2N and CrN see Nitrides Transition Metal Solid-state Chemistry). At very high temperatures, both decompose into the constituent elements (CrN, > 1425 °C CryN, >700 °C). CrN is very stable chemically, while CryN dissolves in dilute acid with liberation OfH2. 

Chromium Borides, At least three cmpds are known CrB (ctysts, mp 1550, d 6.21 8c Mob s hardness 8.5) CBr (ctysts, mp 1850° d 5 15j hardness 2010 Knoopj resists oxidation lip to 1100°) and CBr, (ctysts, d 6.1 Moh s hardness 9+). Because of their high mp s, high hardness and corrosion resistance they were proposed for use in Jet and rocket engines (See also Borides in Vol 2,pB249-R) Re/.-CondChem Diet (1961), 274... 

Titanium diboride and the chromium borides are virtually the only borides utilized industrially ... 

In addition to the titanium borides, the chromium borides, CrB and CrB2, are utilized in abrasion resistant layers on the basis of Ni-Cr-B-Si and in scaling-resistant composite materials. 

Chromium boride Hafnium boride Molybdenum boride... 

E. Kunheim also heated a mixture of chromic sulphate and carbon in an electric arc-fumace, and obtained chromium. A. Binet du Jassonneix found that a mixture of horon and chromic oxide in a magnesia crucible heated in the electric arc-fumace furnishes chromium if a carbon crucible is employed, the chromium always contains carbon. If the chromium boride be heated with copper in an electric furnace, and the product digested with nitric acid, chromium remains. H. Goldschmidt, L. Franck, T. Fujibayashi, and T. Goldschmidt found that chromic oxide can be reduced by the thermite process in which a mixture of chromic oxide and aluminium in a crucible is ignited by a fuse. E. Vigouroux, and J. W. Richards said that chromium produced by the thermite process is free from carbon. 

With allowances for the actual metal content of zirconium (a small correction is also necessary for the hafnium content of about 2 /2%) and postulation of barium zirconate formation (see Table 27), reasonable accord between calculated and measured caloric output is established. However, the situation is more complex with boron mixtures where one encounters increase of heat output with increase of the percentage of boron in the mixtures much beyond the amounts of Equation (la). Thus, even with the reasonable assumption of secondary barium borate formation, the stoichiometry and heat output of the mixtures with more than about 10% of technical boron theoretical 8%) is obscure. Chromium boride formation may be a fector. 

Chromium Borides. At least seven chromium borides have been reported. The compound that has received most attention is the diboride, CrB2 m.p. approx. 1900°C sp. gr. approx. 5.5 thermal expansion 5.0 x 10- . When heated in air, a coating of B2O3 is formed and prevents further oxidation up to the limiting temperature at which B2O3 itself ceases to be stable. It has been used for the flame-spraying of combustion-chamber linings. 

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