Kinetics of the graphitization of dispersed diamonds at “low” temperatures

Abstract

The bulk density of graphitized ultradisperse diamond (UDD) was measured by a gamma-ray attenuation method at 1370–1870 K. These data combined with small angle x-ray scattering and true density measurements of the samples heated at various fixed temperatures were used to study the graphitization kinetics of the UDD. The reaction rate was modeled as a migration rate of the interface between the developing graphite-like carbon and the remaining diamond phase. A “reducing sphere” model was used to obtain the rates from the changes in densities. The estimated kinetic parameters in an Arrhenius expression, namely the activation energy, E=45±4 kcal/mol, and the pre-exponential factor, A=74±5 nm/s, allow quantitative calculations of the diamond graphitization rates in and around the indicated temperature range. The calculated graphitization rates agree well with the graphitization rates of diamonds with different dispersity estimated from high-resolution transmission electron microscopy data. The large difference between the rates and the kinetic parameters obtained in this study and those estimated by G. Davies and T. Evans [Proc. R. Soc. London 328, 413 (1972)] for the temperature range 2150–2300 K indicates that there are different graphitization mechanisms operating in the “low” and “high” temperatures regions.

Photoemission study of onionlike carbons produced by annealing nanodiamonds

“…39 According to small-angle x-ray scattering ͑SAXS͒ and HRTEM studies the size of ND particles varies from 2 to 20 nm with an average particle size of 4.7 nm. 26 The various samples studied in this work were prepared by high temperature annealing of the ND under a vacuum of 10 −5 Torr for 1-1.5 h at the temperatures mentioned above, as described elsewhere. 26 X-ray photoelectron spectroscopy ͑XPS͒ was performed using the ESCA 300 photoelectron spectrometer at the National Centre for Electron Spectroscopy and Surface Analysis ͑NCESS͒, Daresbury Laboratory, UK.…”

“…26 The various samples studied in this work were prepared by high temperature annealing of the ND under a vacuum of 10 −5 Torr for 1-1.5 h at the temperatures mentioned above, as described elsewhere. 26 X-ray photoelectron spectroscopy ͑XPS͒ was performed using the ESCA 300 photoelectron spectrometer at the National Centre for Electron Spectroscopy and Surface Analysis ͑NCESS͒, Daresbury Laboratory, UK. The samples were deposited by dropping an isopropanol suspension of the ND onto a sample cut from a silicon wafer with a native oxide layer.…”

“…The appearance of these new features was explained by the cur-vature of the graphitic walls of the carbon onions. 23 Kuznetsov et al 25,26 developed a process for generating several grams of OLC based on annealing nanodiamonds ͑ND͒, with sizes in the range 2-20 nm, in vacuum. It has been shown that, depending upon temperature and duration of ND annealing, different forms of OLC can be produced.…”

Bulk and surface thermal stability of ultra nanocrystalline diamond films with 10–30 nm grain size prepared by chemical vapor deposition

“…2 Graphitization mechanism of diamond and the preferential energetic stability of nanodiamond crystallites over graphitic particles of the same size has been the subject of rigorous research in the past decades. [2][3][4][5][6][7][8][9][10][11] The size, surface termination, and intergranular phase and chemical composition of the diamond crystallites affect the physical and electronic film properties, including the dielectric constant, 12,13 electron and field emission 14,15 and tribological properties, 16 etc. Elevated temperatures were also found to improve the field emission, 17 thermionic emission, 18 and secondary electron emission properties.…”

Quinone‐Decorated Onion‐Like Carbon/Carbon Fiber Hybrid Electrodes for High‐Rate Supercapacitor Applications

“…[18] Although there are many different synthesis methods for OLCs, currently the only scalables ynthesis route employs thermala nnealing of detonation nanodiamond above 1000 8C, yieldingahigh level of control over the resulting OLC structures. [19] The excellent power-handling ability of OLC is related to the absence of intraparticle porosity and the dominance of externals urface area, giving rise to beneficially high ion mobility, [20] even at operational temperatures below 0 8C. [21] However,t he absence of internal particlep orosity [22] and the nanoscopic particle diameter of around5 -10 nm limits the total specific surfacea rea (SSA) to around2 00-600m 2 g À1 .…”