Boron diamond synthesis

The invention of cubic boron nitride (CBN) is closely linked to the synthesis of artificial diamond. Cubic boron nitride synthesis was conducted first in 1957. CBN crystals are produced from boron and nitrogen at high pressures of 50-90 kbar, high temperatures between 1,800 °C and 2,700 °C, and in the presence of a catalyst (Klocke 2009). During the first years on the market, CBN was seen as a competitor to diamond. However, CBN proved to be a better material for machining of hard-to-machine ferrous materials than diamond due to the missing chemical affinity and the higher thermal stability. 

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. 

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]. 

Abstract Boron-doped diamond (BDD) electrodes provide an unusually wide electrochemical window in protic media, since there exist large offset potentials for the evolution of molecular hydrogen and oxygen, respectively. At the anode, alcohols are specifically converted to alkoxyl radicals. These can be used for chemical synthesis. When the enormous reactivity of such intermediate spin centers is not controlled, mineralization or electrochemical incineration dominates. Efficient strategies include either high substrate concentrations or fluorinated alcohols which seem to stabilize the spin centers in the course of reaction. 

Iniesta J, Michaud PA, Panizza M, Comninellis C (2001) Electrochemical oxidation of 3-methylpyridine at a boron-doped diamond electrode application to electroorganic synthesis and wastewater treatment. Electrochem Commun 3 346-351... 

Sudan Saha M., Furuta T. and Nishiki Y. Electrochemical synthesis of sodium peroxycarbonate at boron-doped diamond electrodes, Electrochem. Solid-State Lett. 6 (2003) D5. 

Cubic boron(lll) nitride is manufactured from hexagonal BN in a high pressure synthesis at 50 to 90 kbar and 1500 to 2200°C in the presence of alkali or alkaline earth metals as catalysts. Cubic boron(III) nitride is, after diamond, the hardest known material. It is utilized in the grinding agent sector instead of diamond, due to its better chemical resistance at high temperatures. 

This experimental protocol is also valid for most syntheses under high pressure, for example, the synthesis of diamond or cubic boron nitride in the laboratory or in industry. In the latter case, the high-pressure cell must be much larger (50 mm inner diameter) and it requires large belt-type equipment and a more powerful hydraulic press. 

The synthesis of diamond and cubic boron nitride has strongly motivated improvements in the development of high-pressure equipment and increased the interest in these materials, which have exceptional properties. Single crystals are required for optical and electronic applications. Consequently, specific crystal-growth processes have been set up under very high-pressure conditions. The principle is similar to that described, at lower pressures, for the preparation of single crystals of a-Si02. 

Carbon in the structural form of diamond is the only element used industrially as a hard material. Each year about ten tons of natural diamond and about twenty tons of synthetic diamond (produced via high temperature high pressure synthesis) are marketed as hard materials. While pure diamond is transparent, a yellow tint results from the replacement of some carbon atoms by nitrogen, and a blue, yellow, or even green tint through substitution of carbon by boron atoms. Polycrystalline diamond with impurities, used as an abrasive, is often black. 

We also performed C02-laser heating experiments on borane-dimethylamine BH3 NH(CH3)2 to check if organic materials containing boron and nitrogen can be used for synthesis of ternary BNC compounds with diamond-like structure. Borane-dimethylamine was heated at 23 GPa to about 3000 K. Raman spectra from the heated sample area revealed the presence of cubic BN, and of liquid H2 at pressures below the solidification point of hydrogen (5.5 GPa at room temperature [71]) (Fig. 17). A Raman spectrum of the recovered white agglomerate showed a weak line of diamond in addition to the Raman bands of cubic BN. Thus, borane-dimethylamine transformed to cubic BN, diamond and hydrogen... 

Following the successful commercial synthesis of diamond in the 1950s, the second hardest material known, cubic boron nitride, cBN, was introduced to the market in the 1960s and is complementary to diamond. The iron, and its alloying elements, in ferrous materials has a tendency to react chemically with diamond under machining conditions and this can reduce the efficiency of the tool. cBN, however, although not as hard as diamond, does not react chemically with iron and is therefore particularly well suited to machining hard ferrous materials. 

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