Transformations of polyhedral carbon nanoparticles under high pressures and temperatures

Abstract

Pressure–temperature-induced transformations of polyhedral carbon nanoparticles (PCN) and their binary mixture with naphthalene have been studied at 8 GPa and temperatures up to 1600 °C by X-ray diffraction, small-angle X-ray scattering, Raman spectroscopy, scanning and transmission electron microscopies. Qualitative distinction of the mechanism of PCN transformations in the single-component carbon system from binary hydrocarbon system has been established. The distinguishing feature of the solid-phase PCN transformation in single component system at temperatures above 1000 °C is their structural reorganization associated with the formation of carbonaceous cores with different morphologies, filling the internal cavities of starting PCNs. The structural transformations of PCN may also give rise to alteration of their external polyhedral shape. However, in the entire studied pressure–temperature region, the solid-phase transformations are limited to individual PCNs with the initial sizes in the 30–80 nm range. The combined solid–gas (fluid) phase transformations of PCN at 8 GPa in the hydrogen-containing system are associated with the destruction of PCN already at ∼900 °C and subsequent cumulative recrystallization of decomposition products. The latter process results in formation of micron-sized crystallites of graphite at 1000 °C and diamond at temperatures above 1100 °C.