Applications diamond/boron nitrides

Cubic boron nitride (c-BN) is a different material altogether from h-BN, with a structure similar to that of diamond, which is characterized by extremely high hardness (second to diamond) and high thermal conductivity.As such, it is a material of great interest and a potential competitor to diamond, particularly for cutting and grinding applications. Its characteristics and properties are shown in Table 10.3... 

Cubic Phase of Boron Nitride c-BN. The cubic phase of boron nitride (c-BN) is one of the hardest materials, second only to diamond and with similar crystal structure. It is the first example of a new material theoretically predicted and then synthesized in laboratory. From automated synthesis a microcrystalline phase of cubic boron nitride is recovered at ambient conditions in a metastable state, providing the basic material for a wide range of cutting and grinding applications. Synthetic polycrystalline diamonds and nitrides are principally used as abrasives but in spite of the greater hardness of diamond, its employment as a superabrasive is limited by a relatively low chemical and thermal stability. Cubic boron nitride, on the contrary, has only half the hardness of diamond but an extremely high thermal stability and inertness. 

Cubic BC2N. Hetero-diamond B C—N compounds have recently received a great interest because of their possible applications as mechanical and optical devices. The similar properties and structures of carbon and boron nitrides (graphite and hexagonal BN, diamond, and cubic BN) suggested the possible synthesis of dense compounds with all the three elements. Such new materials are expected to combine the best properties of diamond (hardness) and of c-BN (thermal stability and chemical inertness). Several low-density hexagonal phases of B,C, and N have been synthesized [534] while with respect to the high-density phases, different authors report contradictory data [535-538], but the final products are probably solid mixtures of c-BN and dispersed diamonds [539]. 

Bogatyreva G.P., Marinich M.A., Gvyazdovskya V.L., Bazalij G.A. (2003) Prospects for Using Diamonds as Adsorbents Proc. An International Technical Conference on Diamond, Cubic Boron Nitride and their Applications (INTERTECH 2003), 48. 

Ronning C., Felderman H., Hofsass H., Growth, doping and applications of cubic boron nitride thin films, Diamond Relat. Mater., 9 (2000) pp. 1767-1773. 

Grinding and polishing is one of the oldest applications for wide band-gap materials primarily owing to the property of hardness that some of these materials possess (e.g., diamond). SiC and cubic boron nitride, in addition to diamond, have found a commercial market in grinding and polishing, primarily for ferromagnetic materials with high carbon solubility. 

Because of the hardness of band-gap materials such as diamond, SiC, and boron nitride, wide band-gap materials have found applications in the tool and die industry.f ° lWide band-gap materials have been successfully used for coating field emission tips in SEM with results showing reduction in turn-on voltage by lOOV and more uniform emission during low-voltage operation.f ... 

The synthesis of diamond and cubic boron nitride has strongly motivated improvements in the development of high-pressure equipment and increased the interest in these materials, which have exceptional properties. Single crystals are required for optical and electronic applications. Consequently, specific crystal-growth processes have been set up under very high-pressure conditions. The principle is similar to that described, at lower pressures, for the preparation of single crystals of a-Si02. 

Sodium borohydride is marketed in powdered or pellet form, and in solution, for use in fuel cells. Boron nitride can withstand temperatures of up to 650°C (1,202°E) when subjected to high pressures and temperatures, it forms cubic crystals whose hardness rivals that of diamond. Boron carbide, produced by reacting coke and boric acid at 2,600°C (4,712°E), is a highly refractory material and one of the hardest substances known. It has both abrasive and abrasion-resistant applications, and is used in nuclear shielding, see ALSO Davy, Humphry Gay-Lussac, Joseph-Louis Nuclear Chemistry. 

S. Miyake, S. Watanabe, M. Murakawa, R. Kaneko, and T. Miyamoto. A Tribological Study of Cubic Boron Nitride Film. In Y. Tzeng, M. Yoshikawa, M. Murakawa, and A. Feldman, editors. Applications of Diamond Films and Related Materials. Materials Science Monographs, Volume 73. Elsevier, New York, 1991, p. 669. 

Silicon carbide (SiC) is the most widely used nonoxide ceramic. Its major application is in abrasives because of its hardness (surpassed only by diamond, cubic boron nitride, and boron carbide). Silicon carbide does not occur in nature and therefore must be synthesized. It occurs in two crystalline forms the cubic P phase, which is formed in the range 1400-1800°C, and the hexagonal a phase, formed at >2000°C. 

Boron nitride is an entirely synthetic material (with no natural occurrence) and the cubic crystal structure is synthesized from the softer hexagonal (HBN) aUotrope using ultrahigh pressures as in the case of diamond. CBN crystals exhibit less than half the hardness of diamond, but there are no industrial applications for such materials. Instead, aU industrially relevant materials are polycrystal-Une in nature, produced by sintering micron cBN... 

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