Crystal structures boron nitride

By subjecting boron nitride (a white powder) to high pressure and temperature small crystals of a substance harder than diamond, known as borazon, are obtained. This pressure-temperature treatment changes the structure from the original graphite-like layer structure (p. 163) to a diamond-like structure this hard form can withstand temperatures up to 2000 K. 

It is stable up to 2000 K and melts under pressure at 2500 K. The crystal structure of aluminium nitride resembles that of boron nitride and diamond, but unlike both of these it is rapidly and exothermically hydrolysed by cold water ... 

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. 

Saitoh, H., Yoshida, K., and Yarborough, W., Crystal Structure of New Composition Boron Rich Boron Nitride Using Raman Spectroscopy, J. Mater. Res., 8(1) 8-11 (Jan. 1993)... 

Elements dissolved in boron influence its crystal structure. Dissolved impurities also influenee the physical and chemical properties of boron, especially the electrical properties, because boron is a semiconductor. Preparation of solid solutions in jS-rh boron requires a careful choice of crucible material. To avoid contamination, boron nitride or a cold, coinage-metal crucible should be used or the levitation or floating-zone melting techniques applied. 

The prototype hard metals are the compounds of six of the transition metals Ti, Zr, and Hf, as well as V, Nb, and Ta. Their carbides all have the NaCl crystal structure, as do their nitrides except for Ta. The NaCi structure consists of close-packed planes of metal atoms stacked in the fee pattern with the metalloids (C, N) located in the octahedral holes. The borides have the A1B2 structure in which close-packed planes of metal atoms are stacked in the simple hexagonal pattern with all of the trigonal prismatic holes occupied by boron atoms. Thus the structures are based on the highest possible atomic packing densities consistent with the atomic sizes. 

Cubed compound, in PVC siding manufacture, 25 685 Cube lattice, 8 114t Cubic boron nitride, 1 8 4 654 grinding wheels, 1 21 hardness in various scales, l 3t physical properties of, 4 653t Cubic close-packed (CCP) structure, of spinel ferrites, 11 60 Cubic ferrites, 11 55-57 Cubic geometry, for metal coordination numbers, 7 574, 575t. See also Cubic structure Cubic symmetry Cubic silsesquioxanes (CSS), 13 539 Cubic structure, of ferroelectric crystals, 11 94-95, 96 Cubic symmetry, 8 114t Cubitron sol-gel abrasives, 1 7 Cucurbituril inclusion compounds,... 

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. 

PI5.9 Boron nitride (BN) is isoelectronic with carbon and the B, C, and N atoms are about the same size. The result is that BN forms crystal structures similar to those of carbon, in that it crystallizes in a hexagonal (graphite-like hBN) and a cubic (diamond like cBN) structure. The data summarized at the end of the problem are available for the two forms of BN.17... 

Boron phosphide occurs in two forms, one of which, cubic BP, has a diamondlike structure analogous to cubic boron nitride (see above). The other variety, Bi2PL8, has a partially disordered crystal structure that contains icosahedral Bi2 units, as found in many metal borides (Section 5-3). Cubic BP is extremely inert, resisting attack by boiling concentrated acids or bases, is not oxidized in air below... 

The crystal structure of boron nitride resembles that of graphite. The boron and nitrogen atoms form plane regular hexagonal nets which are arranged parallel to one another at a distance of 3.33 A. An essential difference between graphite and boron nitride is that in the latter there are no free electrons. Pure boron nitride is white and does not conduct electricity. 

Cubic boron nitride (cBN) has a zinc blende-type crystal structure with a lattice constant of 3.615 A, which is very close to that of diamond (3.567 A). The difference is only about 1.3%. According to RHEED measurements with the electron beam parallel to the 111 layer of cBN, a growth of diamond by DC plasma CVD on cBN(lll) [150] using c = 0.5%CH4/H2, T = 900°C, and F=180Torr led to a result that a smooth (111) layer of diamond was epitaxially deposited in such a way that the [110] direction of diamond was parallel to that of cBN. Namely, D 111 //cBN(lll and D[110]//cBN[110]. In the RHEED pattern, however, extra spots were observed, which were presumably due to the twinnings of (111 diamond layers. In the Raman spectra, there were two lines due to cBN at 1054.5 and... 

Boron nitride (BN) exists in a hexagonal modification with a graphite-like crystal structure and a cubic high temperature/high pressure modification with a diamondlike structure. 

In view of its similarity to graphite in crystal structure and in the lamellar properties of the crystallites, it was expected that boron nitride would function effectively as a solid lubricant. However, it has been found that the friction of boron nitride is characteristically higher than that of graphite under the same circumstances. D. H. Buckley [82] observed a value of v = 1.0 for the friction of pyrolytic boron nitride in high vacuum (10 torr) at 296 K G. W. Rowe [54] obtained v... 

Two boron phosphides have been isolated, BP and Bi2P2-Heating elemental boron and red phosphorus at 900-1100 °C yields BP as refractory brown crystals having a cubic zinc blende structure similar to cubic boron nitride. This material can also be prepared by a number of other methods including the pyrolysis of CHP-BCH, reaction of boron or boron trichloride with zinc phosphide or phosphine, and hydrogen reduction of CRP-BCls. 

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