Boron suboxides

Boron suboxides with hardness comparable to that of diamond were first reported by A. R. Badzian in 1988 [223]. These suboxides were produced by reacting B2O3 with boron at 1600-2000°C and 7 kbar. Subsequent melting under argon gave a sintered compound with an oxygen content of 4-5% and a microhardness of 60 GPa. 

The introduction of oxygen reduces the electron deficiency of the P-rhombohedral structure of elemental boron. Filling these voids with atoms results in a cross linking of the boron icosahedra and can contribute to a significant increase of the rigidity of the structure. 

Recently McMillan et al. [224] reported the synthesis of BgO icosahedra at pressures of 5-6 GPa. Itoh et al. [225] reported the synthesis of BgO powder by reacting B203with boron at 1350-1400°C and the subsequent sintering of that powder with B4C or cBN at 3-7 GPa and 1500-1800°C for 10-30 min. 

Although the hardness of the resulting compacts exceeded 40 GPa, the fracture toughness did not exceed 1.5 MPam /.  

The synthesis of BgO was patented initially in 1992 [226, 227], but no boron suboxide products have appeared in the market as yet. 

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Lower Oxides. A number of hard, refractory suboxides have been prepared either as by-products of elemental boron production (1) or by the reaction of boron and boric acid at high temperatures and pressures (39). It appears that the various oxides represented as B O, B O, B22O2, and B23O2 may all be the same material ia varying degrees of purity. A representative crystalline substance was determined to be rhombohedral boron suboxide, B12O2, usually mixed with traces of boron or B2O3 (39). A study has been made of the mechanical properties of this material, which exhibits a hardness... 

Jan 11,1972) CA 76,74449 (1972) 47) W.H. Rhodes A.J. Delai, Research on Development and Fabrication of Boron Suboxide Specimens , Avco Corp, Mass, Report No... 

D. He, Y. Zhao, L. Daemen, J. Qian, and T. D. Shen, Boron Suboxide As Hard as Cubic Boron Nitride, Appl. Phys. Lett., 81, 643 (2002). 

See also Borates Boric acid Sodium borates boron oxides, 4 246-249 boron oxides table,4 242t environmental concerns, 4 284—285 health and safety factors, 4 285-288 occurrence, 4 245—246 Boron perchlorates, 18 278 Boron phosphate, 4 242t, 283 Boron removal, from water, 14 418 Boron-stabilized carbanions, 13 660-661 Boron subhalides, 4 141 Boron suboxide, 4 242t Boron tribromide, 4 138 manufacture, 4 145—146 physical properties of, 4 139-140t, 325 reactions, 4 141 specifications, 4 147t uses of, 4 149 Boron trichloride, 4 138 manufacture, 4 145—146 physical properties of, 4 139-140t reactions, 4 141... 

The reader should note the similarity between the icosahedral fragment in BioHh and the icosahedron that is present not only in crystalline elemental boron, but also in a number of boron compounds such as boron carbide (which may be represented as B12C3), boron suboxide (B12BO2), and the salt K2B12H12. Moreover, similar icosahedra of aluminum atoms... 

A special case of molecular boron suboxides is found in the hydroxylated polyhedral boranes (see Boron Hydrides). For example, the icosahedral anion closo- Q 2H 2 and related compounds can be completely hydroxylated to form discrete molecular boron suboxides, including closo-[Bi2(OH)i2] These can be regarded as members of a class of formally hydrated suboxides related to compounds snch as tetrahydroxydiborane, B2(HO)4 (BO H2O). The terminal hydroxyl groups of these compounds can be fimctionahzed as esters or ethers to produce a variety of large molecule derivatives. 

X-ray emission spectra and atomic site determination Boron suboxide The second successful example of the... 

Boron suboxide (BO) and subboric acid B2(0H)4 were mentioned on p. 201. 

Boron suboxides have boron oxygen mole ratios equal to or greater than one. These compounds range from molecular species to refractory solid-state materials. Monomeric vapor-phase BO and B2O2 have been studied by spectroscopic techniques. In addition to these rather unstable high-temperature species, several forms of solid noncrystalline boron suboxides have been reported. A water-soluble low-temperature form is obtained by the vacuum dehydration of tetrahydroxydiborane at 220°C (equation 5). At 500 °C, this form converts to a light brown modification that has also been obtained by reactions of boric oxide with elemental boron, boron carbide, or carbon at high temperatures (>1250 °C). 

Besides diamond and cBN, the well known boron carbide B4C is among the hardest materials and has been comprehensively reviewed by F. Thevenot [103], In the present chapter, the latest developments concerning the binary and ternary systems B-N, boron carbide nitrides (B-C-N), and boron suboxides are discussed. Other hard materials based on boron are described by R. Telle et al. in Part III. 

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