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Coordinated isotopic and TEM studies of presolar
graphites from Murchison
Croat T. K., Stadermann F. J., Zinner E., and Bernatowicz
T. J. (2004)
Lunar and Planetary Science XXXV, Abstract #1353, LPI
Houston.
ABSTRACT
Previous microstructural (SEM) and isotopic studies of
the Murchison KFC1 separate (2.15-2.20 g/ml) found many
presolar graphites with an average size of 1.5 microns.
Carbon isotopic ratios ranged over 3 orders of magnitude
(from 0.02 to 80 times the solar value of 89). Two
morphological types of presolar graphites were found, with
dense "onion" graphites and less dense "cauliflower"
graphites, although these types are not isotopically
distinct in carbon. Further transmission electron microscope
(TEM) studies of the "onion" graphites revealed numerous
internal refractory carbides ((Ti,Zr,Mo,Ru)C) and also some
graphites with a nanocrystalline core surrounded by a
well-graphitized rim. Due to their small size, TEM analyses
of graphites that had been isotopically characterized were
not possible. In the present work, more graphites were
examined in TEM, including the larger "cauliflower"
graphites omitted from the earlier study, and isotopic
analysis was performed on the same samples examined in the
TEM.
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