Formation of diamond and graphite at high pressure using glassy carbon source

Experimental study on diamond and graphite formation with presence of metal catalysts under 6 GPa and 1300-1600 °C was carried out using pyrolyzed furfuryl alcohol resin (glassy carbon) or graphite and Mg(OH)2 mixture. Diamond was formed from glassy carbon pyrolyzed higher than 1500 °C in vacuum. Graphite crystals were dominantly formed when glassy carbons pyrolyzed below 900 °C or graphite containing Mg(OH)2 higher than 3 wt.% were used as starting carbons even by long reaction time (28 h) or diamond seeding experiments. Degree of graphitization of glassy carbon with catalyst metal was increased markedly under diamond-forming pressure and temperature condition. It was apparent that the lower degree of graphitization of starting carbon is not an essential factor to prevent diamond formation. The results revealed that graphite crystals were grown when starting carbons contained approximately higher than 1000 ppm of hydrogen. It was suggested that if the metal carbon system contains a higher amount of C-O-H fluid than that of threshold, diamond nucleation was prevented and graphite was dominantly precipitated.