Aromatic layers

Asphaltenes are obtained in the laboratory by precipitation in normal heptane. Refer to the separation flow diagram in Figure 1.2. They comprise an accumulation of condensed polynuclear aromatic layers linked by saturated chains. A folding of the construction shows the aromatic layers to be in piles, whose cohesion is attributed to -it electrons from double bonds of the benzene ring. These are shiny black solids whose molecular weight can vary from 1000 to 100,000. 

Fig. 6. Aromatic layer plane with functional side groups.

The HRTEM observation of the cross section of a coated fiber showed that the core is constituted of aromatic layers highly misoriented, whereas they are preferentially oriented in parallel for the thin coating pairs of stacked layers form mainly Basic Structural Units (BSUs) in which the average interlayer distance is smaller than between the aromatic layers in the bulk of the fiber. Since the nanotexture is more dense for the pyrolytic carbon than for the fiber itself, it acts as a barrier which prevents the diffusion of the large solvated lithium ions to the core of the fiber, allowing the passivation layer to be less developed after this treatment. Hence, the major amount of lithium inserted is involved in the reversible contribution therefore this composite material is extremely interesting for the in-situ 7Li NMR study of the reversible insertion. 

In general, differences in chemical bonding and electron configuration between carbon atoms and dopants mandate the deviation from the geometric and electronic equilibrium structure of the aromatic layers in CNTs. As a consequence, topological defects such as Stone-Wales defects are formed with increased probability [37]. 

The hydrogen in carbon black is bound as CH groups at the edge of the carbon layers. Nitrogen seems to be primarily integrated into the aromatic layer system as heteroatoms. 

X-ray scattering from coal was the subject of several early studies which led to the postulation that coal contains aromatic layers about 20 to 30 A in diameter, aligned parallel to near-neighbors at distances of about 3.5 A (Hirsch, 1954). Small-angle x-ray scattering, which permits characterization of the open and closed porosity of coal, has shown a wide size distribution and the radius of gyration appears to be insufficient to describe the pore size. Application of the Fourier transform technique indicated that some coals have a mesoporosity with a mean radius of 80 to 100 A (Guet, 1990). 

Mechanical properties, electrical properties, thermodynamic stability, surface chemical activity, and other important parameters can all be discussed relative to the structure of the carbon network, composed of both aromatic layers and 3D-arranged (diamond-like) phases. 

Figure 6 shows transmitted x-ray diffraction patterns for the POD films with progressive HTT. The characteristic (101) and (112) reflections are absent for HTT s below 2200 C and suddenly appear at 2500 C. This result implies that the three-dimensional order of the graphite lattice is not established at lower HTT s, namely the condensed aromatic layers exist as individuals and have a highly two-dimensional character. This may have come from the absence of cross-linked network structures at lower HTT s and may have facilitated the the recrystallization of graphite at such low temperatures and without pressure. 

Victorian brown coals are thought to be largely amorphous, containing aromatic layers of single substituted benzene rings crosslinked by aliphatic chains to form a three dimensional structure. Their carbon content is quite low, varying from 60 to 70. One would therefore expect its porous system to be somewhat like that of an open structure having micropores which are randomly-oriented. In this preliminary study two samples of Yallourn ream coal were taken from the Yallourn open cut mine in the Latrobe Valley, Victoria, Australia. The samples, a pale and a medium dark lithotype, are representative of the extremes in coal types found in the Yallourn ream. 

Figure 2.16 Schematic model of the aUgnment of aromatic layers in carbon spherules with radial point orientation of basic structural units (BSUs). Several types of sections and the corresponding cross-sections of the spherules are also indicated. (Reprinted from Ref. [82] with permission from Elsevier.)...

Nucleation is a crucial step in the whole process of carbonaceous particle formation. According to Frenklach and Wang (1990, 1994), nucleation is controlled mainly by the sticking of PAH sheets during their collisions. Physically bound clusters of PAH are then formed and successively evolve toward aerosol, solid particles and crystallites. As shown in Fig. 25, different polycyclic aromatic layers can form more or less regularly ordered graphite structures, all of which have interlayer distances of about 0.35 nm. These two to four-layer structures are assumed as the threshold of the formation of the solid phase particle inception typically takes place at molecular masses of 1,000-2,000 amu. 

Suspend 4-f-butylcalix[4]arene (1.5 g, 2.0 mmol) and phenol (0.28 g, 3.0 mmol) in toluene (30 mL) in a two-necked round-bottomed flask (125 mL) with an inlet providing a flux of inert gas and an outlet fitted with a calcium chloride guard tube. Add anhydrous aluminium trichloride (1.5 g, 11 mmol), which clarifies the suspension slightly, and stir for 4h. During this time the mixture turns from colourless to yellow then orange. A red oil may be observed to separate. After 4 h, add hydrochloric acid (65 mL of a 1m aqueous solution) and continue to stir vigorously for a further 1 h. Ensure that all the sticky red oil is removed from the sides of the vessel and is stirred into the biphasic solution. It may be necessary to use a spatula to free this material. The upper aromatic layer will turn yellow and solids will precipitate out within it. Once all the oil has been stirred to yield a powdery product, leave the mixture to settle for 20 min. Separate the upper organic... 

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