Carbon diamonds

CARBON - DIAMOND,NATURAL] (Vol 4) pXPLOSIVES AND PROPELLANTS - EXPLOSIVES] (Vol 10)... 

Diamond. Diamond [7782 0-3] is the hardest substance known (see Carbon, diamond, natural). It has a Knoop hardness of 78—80 kN/m (8000—8200 kgf/m ). The next hardest substance is cubic boron nitride with a Knoop value of 46 kN/m, and its inventor, Wentorf, beheves that no manufactured material will ever exceed diamond s hardness (17). In 1987 the world production of natural industrial diamonds (4) was about 110 t (1 g = 5 carats). It should be noted that whereas the United States was the leading consumer of industrial diamonds in 1987 (140 t) only 260 kg of natural industrial diamonds were consumed this is the lowest figure in 48 years (4), illustrating the impact that synthetic diamonds have made on the natural diamond abrasive market. 

Synthetic Diamond. In 1955 the General Electric Company announced the successful production of diamonds (see Carbon, diamond, synthetic) from graphite under very high pressure and temperature ia the presence of a metal catalyst. It was later reported that a Swedish company, Allmana Svenska Electriska AB (ASEA), had succeeded ia ptoduciag diamond ia 1953 (35). 

Many trade names have been used for each of these imitations (see Carbon-diamond, synthetic). 

Other Industrial Applications. High pressures are used industrially for many other specialized appHcations. Apart from mechanical uses in which hydrauhc pressure is used to supply power or to generate Hquid jets for mining minerals or cutting metal sheets and fabrics, most of these other operations are batch processes. Eor example, metallurgical appHcations include isostatic compaction, hot isostatic compaction (HIP), and the hydrostatic extmsion of metals. Other appHcations such as the hydrothermal synthesis of quartz (see Silica, synthetic quartz crystals), or the synthesis of industrial diamonds involve changing the phase of a substance under pressure. In the case of the synthesis of diamonds, conditions of 6 GPa (870,000 psi) and 1500°C are used (see Carbon, diamond, synthetic). 

Lead sesquioxide is used as an oxidation catalyst for carbon monoxide ia exhaust gases (44,45) (see Exhaust control), as a catalyst for the preparation of lactams (46) (see Antibiotics, P-lactams), ia the manufacture of high purity diamonds (47) (see Carbon, diamond-natural), ia fireproofing compositions for poly(ethylene terephthalate) plastics (48), ia radiation detectors for x-rays and nuclear particles (49), and ia vulcanization accelerators for neoprene mbber (50). 

Nickel and other transition metals function as solvent-catalysts for the transformation of carbon species into the diamond aHotrope. At temperatures high enough to melt the metal or metal—carbon mixture and at pressures high enough for diamond to be stable, diamond forms by what is probably an electronic mechanism (see Carbon, diamond-synthetic). 

Boron and carbon form one compound, boron carbide [12069-32-8] B C, although excess boron may dissolve ia boron carbide, and a small amount of boron may dissolve ia graphite (5). Usually excess carbon appears as graphite, except for the special case of boron diffused iato diamonds at high pressures and temperatures, eg, 5 GPa (50 kbar) and 1500°C, where boron may occupy both iaterstitial and substitutional positions ia the diamond lattice, a property utilized ia synthetic diamonds (see Carbon, diamond, synthetic). 

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