Inhomogeneous graphitization

Parameters estimated for a real regularly inhomogeneous graphite surface... 

Once one layer has formed (the primary nanotube core), further secondary layers appear to deposit with various degrees of epitaxial coherence. When inhomogeneous deposition occurs in PCNTs, the thickening has a characteristic spindle shape, which may be a consequence of non-carbon impurities which impede graphitization (see below) —this is not the case for ACNTs were growth takes place in an essentially allcarbon atmosphere, except, of course, for the rare gas. These spindles probably include the appropriate num-... 

Stricktly speaking, kerogens are always inhomogeneous and always contain impurities" such as graphite particles, carbon-black carbonaceous particles at various degrees of metamorphic alteration and mineral impurities. An electron microscope is a particularily suitable tool for studying these phases present in kerogens, since particles less than 1 pm can be examined (Oberlin et al., 1980) 19). 

The more sophisticated potentials used in the nanowire study point to an important consideration in modeling such systems. Simple potentials are parameterized under bulk homogeneous conditions and may give poor descriptions of the inhomogeneous environment near a crack tip. In an effort to employ a classical potential that is responsive to a rapidly changing environment, Omeltchenko and coworkers ° simulated a graphite sheet modeled by more than a million particles. The authors used a reactive bond order potential developed by Brenner. In this approach, the total potential energy can be written as follows ... 

For powders, electrothermal evaporation may be used as most substances volatilize far below the volatilization temperature of graphite (>3600 °C). This approach is often hampered by the sample inhomogeneity, as it is generally a micromethod, as well as by anion effects causing chemical interferences [187]. Furthermore, transport losses can occur. 

The regularly inhomogeneous surface of the graphite was modelled by the layered adsorbent (interlayer distance 0.335 nm, the mean number atomic density of the carbon atoms in the layer ps — 38.2 nm ), with the surface micropores simulated by infinitely long parallel defects of the external atomic layer. In the calculations the width of the micropores and the interpore distance were varied. Clearly no polarization potential needs to be included in the calculations due to the nature of the interactions involved. 

More interesting is, however, the question concerning the effect of the total surface inhomogeneity on the integral thermodynamic characteristics values. Here it should be noted that the calculations made in [11] for a homogeneous graphite surface were performed with the atom- atom potential well depth reduced by 13% with respect to the values estimated from the quantum mechanical expressions (compare last two entries in both Tables 1 and 2) this enabled a correspondence to be achieved between the calculated and experimental thermodynamic quantities. We believe however (see [14]) that this... 

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