Formation of pure polycrystalline diamond by direct conversion of graphite at high pressure and high temperature

Details Formation of pure polycrystalline diamond by direct conversion of graphite at high pressure and high temperature Formation of pure polycrystalline diamond by direct conversion of graphite at high pressure and high temperature

Jun 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004pepi..143..593i&link_type=abstract

Physics of the Earth and Planetary Interiors, Volume 143, p. 593-600.

Physics

14

Scientific paper

Polycrystalline diamond aggregates have been synthesized by direct conversion of graphite at pressures of 12-25GPa and temperatures 1800-2500°C using a multianvil apparatus. The synthesized diamond was optically transparent and colorless, and was of cubic symmetry as determined by micro-focus X-ray diffraction. TEM analyses revealed that the sample consists of minute crystals of typically 10-20nm, and only a very weak and broad band at ~1332cm-1 was observed by Raman spectroscopy. An indentation test demonstrated that the present polycrystalline diamond possesses a Knoop hardness of up to 140GPa, which is equivalent to or even higher than those of natural and synthetic single-crystal diamonds (~60-130GPa) and nearly twice as high as those of synthetic polycrystalline diamonds containing binders (~50-70GPa). The present results imply that natural polycrystalline diamonds may have been formed by a rapid transformation from metastable graphite present in cold subducted crust, when encountering in warmer regions, such as rising plumes in the mantle transition region.

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