Influence of Rhombohedral Graphite Phase on the Diamond Nucleation

Abstract

The high pressure and temperature, synthesis of diamond from carbonaceous materials, is a complex process highly dependent on variables such as the catalyst/solvent, the crystalline structure of the precursor material, the processing conditions and the type of compressive chamber. The optimum susceptible precursors to be transformed into diamond are those possessing the perfect hexagonal graphite structure, which is the thermodynamically most stable form of carbon at atmospheric pressure and ambient temperature. However, the majority of both industrial and natural graphites, presents a mixture of different atomic structural arrangements that greatly influence the process of diamond synthesis. In this works the influence of rhombohedral and hexagonal phases existing in the graphite was performed by means of a software refinement of the crystal structures using the Rietveld method. The thermobaric treatment, which determine the structural parameters, was conducted in a high pressure anvil type device with a central concavity. All experiments were carried out at 1200°C and pressures varying from 4.3 to 5.0 GPa. It was determined that the degree of graphite to diamond transformation is directly associated with the content of rhombohedral phase.