In situ X-ray observations of the decomposition of brucite and the graphite-diamond conversion in aqueous fluid at high pressure and temperature

Okada, Taku; Utsumi, Wataru; Kaneko, Hiroshi*; Yamakata, Masaaki*; Shimomura, Osamu

An experimental technique to make real-time observations at high pressure and temperature of the diamond forming process in candidate material of mantle fluids as a catalyst has been established for the first time. In situ X-ray diffraction experiments using synchrotron radiation have been performed upon a mixture of brucite (Mg(OH)) and graphite as starting material. Brucite decomposes into periclase (MgO) and HO at 3.6 GPa and 1050C while no periclase is formed after the decomposition of brucite at 6.2 GPa and 1150C, indicating that the solubility of the MgO component in HO greatly increases with increasing pressure. The conversion of graphite to diamond in aqueous fluid has been observed at 7.7 GPa and 1835C. Time-dependent X-ray diffraction profiles for this transformation have been successfully obtained.