SYNTHESIS OF POLYCRYSTALLINE DIAMOND COMPACT WITH MAGNESIUM CARBONATEAND ITS PHYSICAL-PROPERTIES

The sintering behavior of natural diamond powder with grain size in th e range 6-12 mu m was investigated under 7.7 GPa at 1500-2450 degrees C for 5 or 30 min in the presence of magnesium carbonate. Although dia mond powder was not sintered at 1800 degrees C, a sintered diamond wit h a high grinding resistance could be synthesized at 7.7 GPa and above 2000 degrees C for 30 min. A well sintered diamond with a homogeneous microstructure and high hardness was synthesized at 7.7 GPa and above 2150 degrees C. The thermal resistance of the polycrystalline diamond obtained at 2300 degrees C and 7.7 GPa for 30 min was investigated at high temperatures of 1000-1500 degrees C in a vacuum of (1-1.5) x 10( -3) Pa. At 1400 degrees C, neither graphitization nor cracking were ob served inside or on the surface of the polycrystalline diamond after t he treatment. A large amount of graphitization was observed in the sin tered diamond after the heat treatment at 1500 degrees C for 30 min in vacuum, but no cracking was detected on the surface of the polycrysta lline diamond.