SYNTHESIS OF DIAMOND FROM GRAPHITE CARBONATE SYSTEMS UNDER VERY HIGH-TEMPERATURE AND PRESSURE

Although transition metals such as Fe, Co, Ni and their alloys have been used as diamond-producing solvent-catalysts under very high temperature and pressure, non-metallic compounds such as carbonates and oxides have also been claimed in the patents as the catalysts. In the present study, to make clear the catalytic effect of carbonates on the formation of diamond, high pressure experiments were carried out in the mixture of graphite and the carbonates of Li, Na, Mg, Ca and Sr. Diamond could reproducibly be synthesized from graphite in the presence of these carbonates at high pressure and temperature of 7.7 GPa and 2150°C. Although starting graphite was completely transformed to diamond in the presence of the carbonates, no transformation to diamond could be detected from graphite only at the same pressure and temperature condition. Therefore, it can be concluded that the carbonates have strong solvent-catalytic effect on the transformation of graphite to diamond. © 1990.