Since 1960, several other methods of growing diamond have been developed. In 1970, DuPont launched a polycrystalline material produced by the sudden heat and pressure of an explosive shock. The material was wurtzitic in nature and produced mainly at micron particle sizes suitable more for lapping and polishing than grinding or as a precursor for PCD monolithic material.
In 1970, PCD (Poly Crystalline Diamond) blanks were introduced that consisted of a fine grain sintered diamond structure bonded to a tungsten carbide substrate. The material was produced by the action of high temperatures and pressures on a diamond powder mixed with a metal solvent to promote intergrain growth. Since it contained a high level of metal binder it could be readily fabricated in various shapes using electrodischarge machining (EDM) technology. Although not used in grinding wheels, it is popular as reinforcement in form dress rolls and for wear surfaces on grinding machines. Its primary use, though, is in cutting tools.
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Diamond Produced by Chemical Vapor Deposition (CVD)
In 1976, reports began to come out of Russia of diamond crystals being produced at low pressures through Chemical Vapor Deposition. This was treated with some skepticism in the West even though Russia had a long history of solid research on diamond. However, within 5 years, Japan was also reporting rapid growth of diamond by CVD at low pressures and the product finally became available in commercial quantities by about 1992. The process involves reacting a carbonaceous gas in the presence of hydrogen atoms in near vacuum to form the diamond phase on an appropriate substrate. Energy is provided in the form of hot filaments or plasmas at >800°C to dissociate the carbon and hydrogen into atoms. The hydrogen interacts with the carbon and prevents any possibility of graphite forming while promoting diamond growth on the substrate. The resulting layer can form to a thickness of >1 mm.