Cubic boron nitride production

Commercially available organic bonds include ones based on phenolic and modified phenolic resins, alkyds and polyesters, shellac, polyurethanes, epoxies, and rubbers such as natural, synthetic natural, GRS, Neoprene, and acrylics. Further, polyimide bonds find use in diamond and cubic boron nitride products. 

Metal bonded wheels are made nearly exclusively with diamond for very severe applications where high mechanical strength is required. Electroplated cubic boron nitride products are also finding applications, especially of very difficult to grind and very hard steels. 

Diamond. Diamond [7782 0-3] is the hardest substance known (see Carbon, diamond, natural). It has a Knoop hardness of 78—80 kN/m (8000—8200 kgf/m ). The next hardest substance is cubic boron nitride with a Knoop value of 46 kN/m, and its inventor, Wentorf, beheves that no manufactured material will ever exceed diamond s hardness (17). In 1987 the world production of natural industrial diamonds (4) was about 110 t (1 g = 5 carats). It should be noted that whereas the United States was the leading consumer of industrial diamonds in 1987 (140 t) only 260 kg of natural industrial diamonds were consumed this is the lowest figure in 48 years (4), illustrating the impact that synthetic diamonds have made on the natural diamond abrasive market. 

Annual production of powdered BN is ca 180—200 metric tons per year and its cost is 50—250/kg, depending on purity and density. The price of cubic boron nitride is similar to that of synthetic diamond bort. Hot-pressed, dense BN parts are 3—10 times more expensive than reaction-sintered parts. 

Cubic boron nitride is commonly called c-BN in literature, but also z-BN (zinc blende) or /1-BN [13] can be found. Wentorf [18] named c-BN Borazon , which has become the trade name for the products of the General Electric Corporation. Russian companies call abrasive powders of c-BN Elbor or... 

Not included in the production figures in Table 5.7-1, is the production of in-situ produced diamond coatings by gas phase pyrolysis (chemical vapor deposition, CVD), which are acquiring increasing industrial importance. The worldwide market for diamond-like- and CBN-coatings (CBN =cubic boron nitride) had a volume in 1993 of 40 million US, with an annual growth rate to 1998 of 30 to 40%. 

Although some of these saltlike nitrides have high melting points (for instance, thorium nitride 2820"C uranium nitride 2800°C plutonium nitride 2550 beryllium nitride 2200 C barium nitride 2200"C), they are sensitive to hydrolysis and react readily with water or moisture to give ammonia and the corresponding metal oxide or hydroxide. Consequently, they do not meet the refractory requirements as interpreted here. Some of these nitrides are useful industrial materials particularly as sintering additives for the production of silicon nitride, aluminum nitride, and cubic boron nitride (see Ch. 14). 

Human fascination with diamond as a hard gemstone dates back several millennia, while the use of diamond for industrial manufacturing and processing is much more recent and has grown considerably since the development of high-pressure/high-temperature (HPHT) methods for synthesis of diamond and cubic boron nitride (cBN). After a brief historical overview, this chapter will describe the industrial diamond and cBN products in widespread use today and the applications for which they are so well suited ... 

Micron powders of diamond and cBN also occur as by-products of HPHT manufacturing of mesh materials, and have become increasingly important in their own right as their availability increased. Of course, cubic boron nitride micron powder (BMP) did not exist before 1957. Particles smaller than about 50 to 80 /tm are normally considered micron, although there is some overlap with finer sizes of mesh grinding products. It becomes difficult... 

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]. 

The traditional method for the preparation of boron nitride is by the fusion of urea with boric acid in an atmosphere of ammonia at 750 °C.54 The product from these reactions is hexagonal boron nitride with a layer structure like that of graphite. Unlike graphite, it is colorless and is not an electronic conductor. Conversion of the hexagonal form to a cubic modification requires heating at 1,800 °C at 85,000 atmospheres pressure. 

Internal circular grinding is a production technique that is often used to manufacture roller bearings, see Fig. 8.33. The production costs for such components are mainly determined by the required grinding operations, whereby internal circular grinding is the greatest cost factor. This is one of the reasons why in recent years, users have applied grinding wheels with cubic crystalline boron nitride (CBN) embedded in ceramic material, especially for internal circular grinding. 

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