MATHEMATICAL MODELING FOR COMPUTATIONAL SIMULATION OF THE TEMPERATURE DISTRIBUTION DURING THE SYNTHESIS OF POLYCRYSTALLINE DIAMOND

Abstract

For more than half century, synthetic diamonds have been successfully produced for a large range of technological applications. This synthesis is, today, a well known process associated with a system capable of simultaneously generating the high pressure and high temperature, HPHT, necessary to produce diamond from graphite in the presence of a catalyst metallic alloy. The graphite to diamond transformation, G→D, is usually performed at pressures and temperatures that may reach, respectively, 6 GPA and 2000 K. These severe conditions require a special high pressure device, HPD that takes the load from press equipment and converts it to the high pressure inside a reaction chamber where the G→D transformation takes place. The high temperature, which is also necessary for this transformation, is attained via the heat generated by an electrical current established from an applied voltage. In the past, studies have investigated the association of the voltage with the temperature established inside high pressure equipment. The desired level of temperature is obtained by controlling the applied voltage to the electrical resistance circuit, which includes metallic conductors as well as the graphite parts, heater sleeve and bulk material, inside the chamber. Since the bulk graphite partially transforms into diamond, the value of the applied voltage will change during transformation. As a consequence, heating gradients will be formed within the reaction chamber resulting in a specific local distribution of temperatures. This distribution depends on factors such as the geometrical shape and the materials of both, the HPD and the chamber, as well as the physical arrangement of graphite plus catalytic alloy. A relevant point is that this distribution of temperature inside the Abstract