Cubic BN

Many attempts have been made to synthesi2e cubic BN at low pressures by some sort of chemical vapor deposition process in analogy with the low pressure deposition of diamond from methane in the presence of H atoms (see Diamond, synthetic). However, the amounts of cubic BN produced in this fashion in 1991 were miniscule, and were at best thin layers only a few do2en atoms thick (12). 

The cubic BN crystals may also be bonded into strong bodies that make excellent cutting tools for hard iron and nickel-based alloys. Such tools produce red-hot chips and permit the wider use of tough, high temperature alloys which would otherwise be prohibitively difficult to shape (12,20,21) (see... 

Mechanical Properties. Measuremeat of the mechanical properties of diamoad is compHcated, and references should be consulted for the vahous qualifications (7,34). Table 1 compares the theoretical and experimental bulk modulus of diamond to that for cubic BN and for SiC (29) and compares the compressive strength of diamond to that for cemented WC, and the values for the modulus of elasticity E to those for cemented WC and cubic BN. 

Diamond and Refractory Ceramic Semiconductors. Ceramic thin films of diamond, sihcon carbide, and other refractory semiconductors (qv), eg, cubic BN and BP and GaN and GaAlN, are of interest because of the special combination of thermal, mechanical, and electronic properties (see Refractories). The majority of the research effort has focused on SiC and diamond, because these materials have much greater figures of merit for transistor power and frequency performance than Si, GaAs, and InP (13). Compared to typical semiconductors such as Si and GaAs, these materials also offer the possibiUty of device operation at considerably higher temperatures. For example, operation of a siUcon carbide MOSFET at temperatures above 900 K has been demonstrated. These devices have not yet been commercialized, however. 

In this younger field of chemistry, some examples of anions may be still missing. One possible candidate is the [BN4] ion with a tetrahedral coordination of boron as in cubic BN, others may be adopted from oxoborates. Another interesting feature is the existence of structures with condensed nitridoborate anions derived from portions of BN structures. Until now the only example with a condensed anion structure is U(BN), containing kinked B-B bonded chains of (BN)x with B-B distances near 188 pm, slightly longer than in [B2N4] . ... 

Good quality OB6 crystals can be grown at high pressures and temperatures from a flux. For an indenter loading force of IN, their VHN is 4500 kg/ mm2 which is only six percent less than the 4800kg/mm2 measured by the same authors for cubic BN. It is about 30 percent greater than values measured for sintered compacts of polycrystalline oxygen hexaboride. 

A benchmark for hardness is diamond, the hardest known substance. Its nominal hardness is 100 GPa (VHN = 10,000kg/mm2),but methods are known that may make it still harder. Based on this benchmark, materials with hardnesses between 20 and 40 GPa are said to be very hard , while a material with hardness greater than 40 GPa is said to be super-hard . The latter are very rare, and there is no true competitor for diamond. However, some property combinations make particular materials more useful than diamond in some applications. For example, cubic-BN is better for cutting iron-based alloys because it reacts chemically with Fe much less strongly than does the carbon of diamond. Therefore, its wear-rate is substantially less. 

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]. 

Utilization of cubic-BN are wear applications like machining tools and polishing powders. 

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... 

Cubic BN is usually manufactured at about 5 GPa and 1500°C from a mixture of graphitic hexagonal BN and a catalyst solvent such as lithium or magnesium nitride. Many other catalyst solvent systems have been found and most of them involve a nitride-forming element. As pressure and temperature increase, the catalyst requirements relax as with carbon. 

Mishima, O. etal. (1987). Cubic BN light-emitting diode, Science 238, 181-183. 

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. 

The BNC nanotubes can have a metallic behavior if they do not have a band gap or a semi conductor behavior if there are band gaps. The importance of this phenomenon is that the electric properties of BCN compoimds can be controlled by varying the atomic composition and atomic arrangement of the compounds. In addition, their mechanical properties could be similar to these of diamond and cubic BN, providing new super-hard materials [14]. 

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]. 

Figure 3. TEM image (left) and XRD patterns (right) of cubic BN [9].

Mirkarimi P. B., Medlin D. L., McCarty K.F., Growth of cubic BN films on P-SiC by ion-assisted pulsed laser deposition, Appl. Phys. Lett., 66 (1995) pp. 2813-2815. 

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