HR: 0830h
AN: GP31C-0762    [PDF]
TI: Microstructural Study of Synthetic Sintered Diamond and Comparison with Carbonado, a Natural Polycrystalline Diamond
AU: * De, S
EM: sde@alumni.princeton.edu
AF: NASA Ames Research Center (Ames Associate), Exobiology Branch, Moffett Field, CA 94035-1000 United States
AU: Heaney, P J
EM: heaney@geosc.psu.edu
AF: Dept. of Geosciences, Penn State University, University Park, PA 16802 United States
AU: Fei, Y
EM: fei@gl.ciw.edu
AF: Yingwei Fei, Geophysical Laboratory Carnegie Institution 5251 Broad Branch Road., NW Washington, DC 20015 United States
AU: Vicenzi, E P
EM: vicenzi@volcano.si.edu
AF: Dept. of Mineral Sciences, Smithsonian Institution, Washington, DC 20560 United States
AB: The contributions that Rob Hargraves made to paleomagnetism spanned not only great distances (from the Earth to Mars) but a vast expanse in time. His interests in the magnetic character of the Archean Earth led him to compare magnetic polycrystalline diamonds (stewartites) with non-magnetic diamond composites (carbonados). Rob's ideas inspired our attempt to replicate carbonados by sintering diamond powders without metallic catalysts. These experiments employed a multi-anvil press operating at pressures of 6 to 9 GPa, temperatures of $1200\deg$C to $1800\deg$C, and times up to 6 hours. Transmission electron microscopy (TEM) showed that even in the absence of metals serving as solvent-catalysts, sintered compacts were successfully produced for all runs. In all of these compacts, aperiodic slip planes rigorously parallel to {111} consistently emerged in high densities, with lamellar spacings of 3 to 30 nm. In addition, polysynthetic spinel twinning in close association with the partial slip defects were observed in most of the compacts. Compacts compressed at 8 GPa produced some euhedral crystals with very low dislocation densities surrounded by grains in which dislocation densities were quite high. In addition, curviplanar defects loosely constrained to {111} were visible within some specimens sintered at the highest pressures. These textures resembled defect microstructures observed in natural carbonado (De et al. 1998), and the appearance of these features suggests that our experiments at their most extreme pressure and temperature parameters reproduced carbonado-like defect assemblages. The formation of such textures in quasi-hydrostatic experiments indicates that shock metamorphism is not required to produce the periodic defect lamellae observed in carbonado.
DE: 1599 General or miscellaneous
DE: 3630 Experimental mineralogy and petrology
DE: 3699 General or miscellaneous
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting