Hydrothermal study and geological implication of fullerene (C60)
Date Issued
2005
Date
2005
Author(s)
Lai, Shih-Ho
DOI
zh-TW
Abstract
Fullerenes (typically C60) are carbon cage molecules initially synthesized during laser ablation of carbon by Kroto et al. in 1985. The occurrence of nature fullerene has been reported from meteorites, sediments from the K-T boundary and P-T boundary, carbon-rich rocks (organic origin), pillow lavas cutting black shales, and others such as fulgurite, ink sticks, dinosaur eggs and tree char. Some of these, like graphite and diamond, may probably be the metamorphic products of local organic matter. The objective of this study is to examine the kinetics that C60 transforms into amorphous carbon and estimate the temperature and time that fullerenes can survive in the earth, especially under hydrothermal condition in the crust.
C60 powder and distiller water were sealed into gold capsules and reacted at the temperature, 525, 550, 575, 600, 625°C, and the pressure at 3~4 kbar for periods between 30 min and 168 h. The run products were characterized using the Raman spectrum and TEM while the transformation ratio of C60 to amorphous carbon is determined by x-ray diffraction. The preliminary results show that the decomposition rate of C60 can be described by a first-order kinetic model with an activation energy of 278 kJmol-1. The extrapolation to geological hydrothermal condition reveals that C60 will survive about 0.1 million years at 290°C and 1 billion years at 220°C, which represents the time-temperature limit that C60 can survive under hydrothermal condition. Compared with the non-hydrothermal fullerene decomposition kinetics, it reveals that water strongly accelerates transformation of fullerenes. This implies that fullerene may survive at longer time or higher temperature if the water activity of geological environment is lower than hydrothermal environment. In addition, the Raman spectrum and TEM results confirm that the fcc crystal structure of C60 revealed by XRD has been thermally decomposed along with the disintegration of the C60 molecule revealed by Raman spectroscopy.
Subjects
碳六十
地源富勒烯
無定型碳
熱水狀態
反應動力學
C60
terrestrial fullerenes
amorphous carbon
hydrothermal
Raman spectrum
kinetic
Type
thesis
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