HYDROTHERMAL BEHAVIOR OF DIAMOND

The interaction of two diamond powders and synthetic diamond single cr ystals with H2O has been studied in the temperature range of 650-850 d egrees C under pressures up to 500 MPa. The reaction products were cha racterized using electron paramagnetic resonance (EPR), Raman and Four ier transform infra-red spectroscopy, X-ray diffraction, scanning elec tron microscopy, transmission electron microscopy (TEM) and selected a rea diffraction. A noticeable interaction of fine grain diamond powder s with H2O starts at approx. 700 degrees C while single crystals are s table up to 800 degrees C. At 800-850 degrees C, etching pits appear o n the single crystal diamond surface. Thermodynamic calculations predi ct the formation of hydrogen, carbon oxides and hydrocarbons. Formatio n of graphitic carbon via the fluid is observed. Redeposition of nanoc rystalline diamond and healing of crystal defects are suggested by TEM and EPR investigations. (C) 1998 Elsevier Science S.A. All rights res erved.