Insights on self-assembly of carbon in the processes of thermal transformations under high pressures

Abstract

Peculiarities of the processes of self-assembly of carbon under pressure up to 8 GPa and temperatures up to 1600°C in pure carbon, hydrocarbon, fluorocarbon, organometallic systems and binary mixtures of all-carbon, hydrocarbon, and fluorocarbon compounds have been revealed in the course of studies of pressure and temperature-induced transformations of different carbon-containing systems. It was shown that the character of the processes of self-assembly of carbon in different systems is controlled in the first place by the mobility of carbon atoms. The low diffusion mobility of carbon atoms in a condensed state at temperatures below 2000° C leads to the fact that in pure carbon systems studied on the examples of fullerite C60 and closed polyhedral carbon nanoparticles, carbon self-organization can occur only due to processes associated with small movements of carbon atoms that ensure the formation of intermolecular bonds in cases of polymerization of C60 or the restructuring of the internal structure of a polyhedral particle, strictly limited to the confines of a single nanoparticle. In the hydrocarbon and fluorocarbon systems, the character of transformation changes drastically due to formation of volatile low-molecular hydrocarbon and fluorocarbon fractions, which ensure a high gas-phase or fluid mobility to carbon atoms. Studies of pressure and temperature-induced transformations of different hydrocarbon, fluorocarbon compounds and their homogeneous binary mixtures revealed a clear synergistic effect of fluorine and hydrogen on processes of carbonization, graphitization, and formation of diamond in these systems in relation to industrially significant reduction of p,T parameters for formation of graphite, diamond and increase in the content of nanosize diamond fractions in the products of transformations of binary mixtures in comparison with pure hydrocarbon and fluorocarbon compounds. Discovery of this synergistic effect opens new opportunities for synthesis of high-purity and doped ultranano-, nano-, submicro-, and micronsized diamonds with the specific properties for different applications in quantum physics and biomedicine. Studies of particularities of self-assembly of carbon in processes of thermal transformations of ferrocene at high pressures demonstrated the possibility of preparation of iron carbide nanoparticles encapsulated into carbon shells, Fe7C3@C and Fe3C@C, considered as perspective magneto-controlled platforms for different biomedical nanocomplexes.

Keywords

• carbon-containing systems
• pressure-temperature induced transformation