Mechanism of diamond-to-graphite transformation at diamond-stable conditions |
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Authors: | ChuangYi Zang XiaoZhou Chen Qiang Hu HongAn Ma and XiaoPeng Jia |
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Institution: | (1) Institute of Materials Science and Engineering, Henan Polytechnic University, Jiaozuo, 454000, China;(2) State Key Laboratory of Superhard Materials, Jilin University, Changchun, 130012, China |
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Abstract: | The diamond-to-graphite transformation at diamond-stable conditions is studied by temperature gradient method (TGM) under
high pressure and high temperature (HPHT), although it is unreasonable from the view of thermodynamic considerations. It is
found that, at diamond-stable conditions, for example, at 5.5 GPa and 1550 K, with fine diamond grits as carbon source and
NiMnCo alloy as metal solvent assisted, not only large diamond crystals, but metastable regrown graphite crystals would be
grown by layer growth mechanism, and the abundance of carbon source in the higher temperature region is indispensable for
the presence of metastable regrown graphite crystals. From this transformation, it is concluded that, with metal solvent assisted,
although the mechanism of crystal growth could be understood by the macro-mechanism of solubility difference between diamond
and graphite in metal solvents, from the point of micro-mechanism, the minimum growth units for diamond or graphite crystals
should be at atomic level and unrelated to the kinds of carbon source (diamond or graphite), which could be accumulated free-selectively
on the graphite with sp2п or diamond crystals with sp3 bond structure.
Supported by the National Natural Science Foundation of China (Grant No. 50572-032), Foundation of He’nan Educational Committee
(Grant No. 2009A430014), and Open Research Fund Program of State Key Laboratory of Superhard Materials of Jilin University
(Grant No. 200801) |
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Keywords: | transformation diamond graphite HPHT |
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