Decomposition of silicon carbide in the presence of organic compounds under hydrothermal conditions

摘要

The synthesis of different carbon polymorphs such as graphite, diamond, amorphous carbon or diamond-like carbon, fullerenes, carbon nanotubes, etc., has attracted considerable interest for a long time because of their importance in science and technology. There are great uncertainties about the phase stabilities of these polyorphs as some of them do not find a place in the carbon pressure-temperature (P-T) diagram and are also known for their contrasting physical properties. The exact physico-chemical phenomena responsible for their forma- tion are yet to be understood. Attempts to synthesize these forms with varied conditions and techniques, sometimes even violating the thermodynamic principles, have met with a fair amount of success. The stabilities of graphite and diamond in nature were mainly controlled by P- T - fO_2 in the C-O-H system 1-6. The role of C-O-H fluids 7,8, as well as the hydrothermal and organic origin 9,10 of these polymorphs, especially with reference to diamond genesis, prompted the material scientists to explore the possibility of synthesizing them at fairly low pressure and temperature conditions. The hydrothermal technique is highly promising for reactions involving volatiles as they attain the supercritical fluid state and supercritical fluids are known for their greater ability to dissolve non-volatile solids II. Silicon carbide powder has been used for the synthesis of carbon polymorphs 12-14, and Gogotsi et al. 15 have reported decomposi- tion of silicon carbide in supercritical water and discussed the formation of various carbon polymorphs. Here we explore the possibility of producing carbon polymorphs under hydrothermal conditions through decomposition of silicon carbide in the presence of organic compounds instead of pure water. The organic compounds decompose into various C-O-H fluids; the main components are CO, OH, CO_2, and C_1H_x radicals. It is very well known that these fluids playa significant role in creating a highly reducing environment in the system and also assist in the dissociation of silicon carbide and precipitation of the carbon phase.