Influence of the reactive mixture density on the diamond yield from a synthetic process

Abstract

The yield of a diamond synthesis process using high-pressure and high-temperature transformation of graphite in the presence of a catalyst/solvent metal depends basically on three parameters: time, temperature and pressure. However, to attain specific values for the pressure inside the reaction cell it is necessary to have a certain density for the graphite–metal reactive mixture. In the present work evidences for the influence of the reactive mixture density on the diamond yield and the crystal granulometry are presented. These evidences were obtained by changing the density of reactive mixtures composed of equal amounts of graphite and a Ni–Mn catalyst/solvent alloy. The synthesis process was carried out at a pressure of 4.7 GPa and a temperature of 1250 °C. It has been observed that the reactive mixture density must vary within fixed limits. Outside those limits the diamond yield will be relatively lower or crystal formation may be inhibited.