Cubic crystalline boron nitride

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. 

Two modifications of crystalline boron nitride are known. In the cubic modification, each B atom is surrounded by four N atoms at the comers of a tetrahedron and vice versa. The mean bond energy calculated from the energy of atomization is 321 kJ mol and about 2.5 times larger than the N-B bond dissociation energy of the amine borane complex. 

Boron nitride has two crystalline forms, hexagonal (h-BN) and cubic (c-BN), with much different properties. Hexagonal BN is the more important and has many industrial applications. Its structure is similar to that of graphite which it resembles in many ways. It has a very large anisotropy in the crystal with resulting anisotropic properties. 

Boron nitride has two crystalline forms, hexagonal and cubic. These forms are similar to the two common forms of carbon, graphite and diamond. 

Zhang, X.W. Yin, H. Boyen, H.-G. Ziemann, R Ozawa, M. 2005. Effects of crystalline quality on the phase stability of cubic boron nitride thin films under medium-energy ion irradiation. Diamond and Related Materials, 14(9) 1482-1488. 

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. 

Poly crystalline Diamond and Cubic Boron Nitride... 

Cubic boron nitride (CBN) has superior thermochemical stability compared to diamond. Ultrafine-crystalline CBN (CBN-U) is a special type of CBN, which has a grinding ratio that is eight times higher, and a higher wear resistance than conventional CBN (Chen et al. 2002). For grinding of ferrous components and other materials that react with diamond, cubic boron nitride is the best choice. 

Structurally, the cubic form of BN resembles diamond (Figure 6.19) and the two materials are almost equally hard. Crystalline cubic BN is called borazon and is used as an abrasive. A third polymorph of boron nitride with a wurtzite-type structure is formed by compression of the layered form at 12 kbar. 

Like carbon, boron nitride (BN) exists in two main crystalline structures, a hexagonal structure (h-BN) and a cubic zinc blend structure (c-BN). The c-BN is... 

Boron nitride exists in many different structures due to the special bonding behaviors of boron and nitrogen. Although the most well-defined crystallographic structures are hexagonal BN (h-BN), cubic BN (c-BN), and wurtzitic BN (w-BN), other crystalline structures, such as explosion boron nitride (e-BN) and ion beam-deposited boron nitride (i-BN) [124—135] and amorphous BN (a-BN) [136,137] also exist. 

Crystalline BP resists oxidation up to 800°C and is not dissolved by boiling mineral acids or cold concentrated alkali. Boiling with the latter produces phosphine and with steam above 400°C, some phosphine and boric acid are formed. Boron phosphide reacts on heating with halogens to form addition compounds. When heated to high temperatures in an atmosphere of ammonia, cubic boron nitride and phosphine are formed. 

As stated in Ch. 12, boron nitride exists in two crystalline forms hexagonal and cubic with much different properties. Nis] ]( was first synthesized as a powder in 1842 but for many years remained a laboratory curiosity since the powder was thought too difiGcult to mold into useful shapes. In the 1950 s, the Carborundum Co. found a way to hot-press the material and the Raytheon Co. developed a chemical vapor dqiosition process.1 1 Boron nitride is now used extensively as a solid lubricant, as a chemically resistant container, and as a dielectric in electronic applications. It should be stressed that the reported property values often vary considerably and the values given here are a general average. 

Cubic boron nitride, c-BN, is considered in this section because of its diamond-like properties. Dark c-BN crystalline powders prepared with B excess contain two types of defect centres. The centres are called D1 and D2 (dark) with g values of 2.0063 and 2.0084. At X-band the two lines overlap and D2 (dark) was only observed at temperatures above 100 K. A single crystal study of small plate-like samples of c-BN at 95 GHz was carried out from room temperature to 5 K. The D1 spectrum at 10 K was found to come mainly from anisotropic paramagnetic centres with electron spin S = 1/2, local symmetry axis along one of the crystal [111] axes and principal g values g y = 2.0032 and = 2.0094. No hyperhne splitting was observed in the spectra down to 5 K, so the origin of the D1 defect cannot be determined at present. Several theoretical models of defect sites in B-rich c-BN were discussed in the paper. 

The B-N system is accepted ITom [2003Rec]. Only one intermediate phase BN exists in this system. Boron nitride has four crystalline stractural modifications cubic (cBN), wurtzite (wBN), hexagonal (ABN) and rhombohedral (rBN). Except for that, there are two other ordered BN phases EBN, obtained by explosion (E) of a mixture of ABN and aBN, compressed ABN attributable to a monoclinic lattice distortion of ABN and two disordered BN phases turbostratic BN (tBN) and amorphous BN (uBN). 

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