Physical and chemical properties of the heat resistant diamond compacts from diamond-magnesium carbonate system

The sintering behaviour of natural diamond powder with a grain size from 20 to 30 μm was investigated at high pressure and high temperatures of 7.7 GPa and 1800–2450 °C with magnesium carbonate. A well sintered diamond, with a homogeneous microstructure, was synthesized under conditions of 7.7 GPa at above 2200 °C using magnesium carbonate as a sintering agent, which had a knoop hardness of 67 GPa. By the hot hydrochloric acid treatment of the well sintered diamond for 15.5 h, a marked extrusion or dissolution of the magnesium carbonate was not confirmed. Neither graphitization nor crackings were observed in and on the compact after the heat treatment between 900–1400 °C for 30 min in the vacuum. Knoop hardness of the compact treated above 1300 °C decreased to 55 GPa while those treated below 1100 °C were unchanged.