Transformation probability of graphite-diamond assisted by nonmetallic catalysts at high pressure and high temperature
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Transformation probability of graphite-diamond assisted by nonmetallic catalysts at high pressure and high temperature Liling Sun and Qi Wu Institute of Physics, Chinese Academy of Sciences, Beijing 100080, People’s Republic of China
Yafei Zhang Department of Physics, Lanzhou University, Lanzhou, 730000, People’s Republic of China
Wenkui Wang Institute of Physics, Chinese Academy of Sciences, Beijing 100080, People’s Republic of China (Received 24 September 1997; accepted 19 November 1998)
The tendency of graphite-diamond transformation assisted by nonmetallic catalysts of carbonates, sulfates, or phosphorus under high pressure and high temperature has been investigated by calculating the activation energy and transformation probability of the carbon atoms over a potential barrier. It was found that the activation energy is highly sensitive to the catalyst chosen. The value of activation energy in the systems of graphitecarbonates, graphite-phosphorus, and graphite-sulfate are 130.71 3 103 , 206.03 3 103 , and 221 3 103 Jymol, respectively. If fd stands for the probability of the transformation from graphite to diamond, the probability sequence of graphite-diamond transformation in different systems was put forward: fd (gr.-carbonate) . fd (gr.-phosphorus) . fd (gr.-sulfate) .
Since artificial diamond was reproducibly synthesized by researchers at the General Electric Company in 1955,1 many experimental investigations and applications have been carried out and these led to a commercial business.2 – 8 The successful process utilized not only high pressure and high temperature (HP and HT) methods, but also the molten metals of group VIII elements of the periodic table, such as iron, nickel, cobalt, platinum, palladium, manganese, chromium, and tantalum,9 which are good carbon solvents. There was no evidence, however, to demonstrate any ability of these new carbon solvents for diamond formation before 1990. Akaishi et al. first reported the details of successful synthesis of diamond from graphite as the carbon source at HP-HT with the nonmetallic catalysts of carbonates, hydroxides, sulfates, water, and phosphorus,10 –14 which gives rise to the revolutionary idea that diamond could be synthesized and grown by the aid of a nonmetallic catalyst. It is currently a topic at the frontier of high-pressure physics and materials research, because a large number of inorganic compounds and nonmetallic elements exist in the earth,15,16 especially since some diamond crystals grown with these compounds show the same surface characteristics as natural diamond.17 So far, none of the quantitative thermodynamic information of this type that the activation energy and transformation probability of graphite-diamond assisted by nonmetallic catalysts of J. Mater. Res., Vol. 14, No. 3, Mar 1999
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carbonates, sulfate, and phosphorus has been reported. This paper is intended to fill this gap by thermodynamic calculations. It is expected tha
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