Preparation of Cubic BN

Cubic boron nitride is an important materia that is widely used in cutting tools and as grinding, abrasive materials. Both Hu et al. [8] and Cui et al. [9] have synthesized cubic BN via this method. By using the solvothermal metathesis reaction of BBrs and LisN, Cui and co-workers obtained better yield of cubic BN, and the TEM image and the XRD pattern are shown in Fig. 3. Some other metastable non-oxides have also been prepared and reported using solvothermal method, e.g. AIN [10-11] and Si3N4 [12]. 

An advantage of metal-bonded grindstone (e.g. brass-bond cubic BN) is the possibility of electrolytic dressing (surface preparation). By applying voltage between the grindstone and an opposite electrode the metal bond can be... 

Boron nitride (BN) can normally be prepared from the reaction of boric acid and urea or melamine. For example, the pyrolysis of MB can yield hexagonal BN. It is commonly referred to as white graphite because of its platy hexagonal structure similar to graphite. Under high pressure and at 1600°C, the hexagonal BN is converted to cubic BN, which has a diamond-like structure. 

Recently, many methods in the synthesis of c-BN films were studied, which include physical vapor deposition [1,5-7] (PVD) and chemical vapor deposition [1,8,9] (CVD, such as PECVD, HFCVD, MW-ECR-CVD). Most experiments have indicated that the commercial application of c-BN films depends on enhancement and improvement in the stability and repeatability of preparation process. Generally, ion energy flow density or ion bombardment was attributed to the essential factor with the influence in the c-BN formation [1,10-13]. However, it is noted that the discrepancy between PVD and CVD maybe result from the difference in the substrate temperature (Ts , ). Unfortunately, the role which Tjub plays on the growth of cubic phase in PVD was seldom investigated systemically. 

T = 2523 K a slight solubility of B4C in h-BN but no solubility of h-BN in B4C . On the other hand Sirota et al. (1977) [265] found 7 mol-% boron carbide solubility in cubic boron nitride. The samples were prepared by hot pressing BN-B4C powder mixtures at 50 kbar and 2173-3073 K. 

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 cubic 2inc blende form of boron nitride is usually prepared from the hexagonal or rhombohedral form at high (4—6 GPa (40—60 kbar)) pressures and temperatures (1400—1700°C). The reaction is accelerated by lithium or alkaline-earth nitrides or amides, which are the best catalysts, and form intermediate Hquid compounds with BN, which are molten under synthesis conditions (11,16). Many other substances can aid the transformation. At higher pressures (6—13 GPa) the cubic or wurt2itic forms are obtained without catalysts (17). 

Cubic boron nitride films have also been prepared by activated reactive evaporation of boric acid in an NH3 plasma formed between a hot filament and an anode [119 to 121]. Other reports on ionized deposition of BN layers [122,123] and on p-BN deposited by sputtering in an NH3 or N2/Ar atmosphere [124, 125] show that the formation of the different BN phases in the resultant coatings depends critically on the conditions of the process. About the effects of the total gas pressure and the type of sputtering gas on the stresses of thin p-BN films, see [138]. 

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