Effect of Carbon Source with Different Graphitization Degrees on the Synthesis of Diamond

Using three kinds of graphites with different graphitization degrees as carbon source and Fe--Ni alloy powder as catalyst, the synthesis of diamond crystals is performed in a cubic anvil high-pressure and high-temperature apparatus (SPD-6×1200). Diamond crystals with perfect hexoctahedron shape are successfully synthesized at pressure from 5.0 to 5.5GPa and at temperature from 1570 to 1770K. The synthetic conditions, nucleation, morphology, inclusion and granularity of diamond crystals are studied. The temperature and pressure increase with the increase of the graphitization degree of graphite. The quantity of nucleation and granularity of diamonds decreases with the increase of graphitization degree of graphite under the same synthesis conditions. Moreover, according to the results of the Mossbauer
spectrum, the composition of inclusions is mainly Fe₃C and Fe-Ni alloy phases in diamond crystals synthesized with three kinds of graphites.