NEW NONMETALLIC CATALYSTS FOR THE SYNTHESIS OF HIGH-PRESSURE, HIGH-TEMPERATURE DIAMOND

The synthesis of diamond using new non-metallic catalysts is briefly reviewed based on our recent work. It is clear from our studies that diamond can be reproducibly synthesized at 7.7 GPa and 2150-degrees-C from graphite in the presence of 11 non-metallic catalysts such as MgCO3, Mg(OH)2, MgSO4 and Na2SO4. The morphology of diamond crystals was strongly dependent on the nature of the catalysts. The diamond-producing region in the graphite-Na2SO4 system was determined under the conditions 6.5-7.7 GPa and 1600-2200-degrees-C. At a higher pressure of 7.7 GPa, diamond could be synthesized even at temperatures of 1700-degrees-C, but diamond was synthesized at 2000-degrees-C at a pressure of only 7 GPa. Also, the morphology of diamond crystals was strongly dependent on the, synthesizing temperature. Diamond crystals grown from the graphite-Na2SO4 system changed from a cubic shape to an octahedral shape with increasing temperature.