Pitch characterization

Cebolla, V. L., Vela, J., Membrado L. et al. (1996) Coal-tar pitch characterization by thin-layer chromatography with flame ionization detection. Chromatographia, 42, 295-9. 

Precursor Pitch. The precursor material is a mesophase pitch, characterized by a high percentage of asphaltene. Table 8.5 shows the approximate composition of three common mesophase compounds. 

The cholesteric phase maybe considered a modification of the nematic phase since its molecular stmcture is similar. The cholesteric phase is characterized by a continuous change in the direction of the long axes of the molecules in adjacent layers within the sample. This leads to a twist about an axis perpendicular to the long axes of the molecules. If the pitch of the heHcal stmcture is the same as a wavelength of visible light, selective reflection of monochromatic light can be observed in the form of iridescent colors. 

Viscosity of Coal- Tar Pitch and Change with Temperature. Because pitch is mainly used as a hot-appHed binder or adhesive, the viscosity and its change with temperature are important in industrial practice. Some useful correlations, by which the viscosity of pitch at any temperature can be predicted, have been developed. The data on which such correlations are based may be from one of the fixed equiviscous points that characterize a pitch (Table 5). 

Mesophase formation in coal-tar pitch is encouraged by a reduction of the natural quinoline-insoluble matter content, which resembles carbon black but is not optically anisotropic and is characterized by an atomic carbon hydrogen ratio of 4 1. In contrast, the atomic carbon hydrogen ratio of mesophase is about 2 1. 

Only a limited number of coal-denved pitches were examined by H NMR because of their low solubility in solvents commonly used m conventional proton magnetic resonance. Table 12 reports the distribution of hydrogen for three of the pitches. Unlike coal-tar pitches, which typically have over 85% of the hydrogen bonded to aromatic carbon, the matenals listed in Table 12 are characterized by a high content of aliphatic hydrogen. 

ESR characterization was performed in situ in order to avoid any contact of the pretreated solids with air. Spectra, recorded as the first derivative of the absorption, were obtained at room temperature or 77K using a Varian E9 spectrometer working in the X band. The g values were measured relative to a DPPH reference (g = 2.0036). The sample tubes were filled with the solid to a height greater than the depth of the resonant cavity and the number of paramagnetic species was calculated by double integration of the recorded spectra normalized to that of Varian Strong Pitch sample (g = 2.0028, 3. lO spins, cm" ). 

Weng T.C., Teng H., Characterization of high porosity carbon electrodes derived from mesophase pitch for electric double-layer capacitors, J. Electrochem. Soc. 2001 148 368-373. 

The majority of work done on VGCF reinforced composites has been carbon/carbon (CC) composites [20-26], These composites were made by densifying VGCF preforms using chemical vapor infiltration techniques and/or pitch infiltration techniques. Preforms were typically prepared using furfuryl alcohol as the binder. Composites thus made have either uni-directional (ID) fiber reinforcement or two-directional, orthogonal (0/90) fiber reinforcement (2D). Composite specimens were heated at a temperature near 3000 °C before characterization. Effects of fiber volume fraction, composite density, and densification method on composite thermal conductivity were addressed. The results of these investigations are summarized below. 

This knowledge and understanding may be helpful to characterize local conformations of other optically active polysilanes in solution. For example, poly(methyl-(-)-(3-pinanylsilane) [(+)-7 Mw = 10,200] prepared by Shinohara and co-workers.281 showed a bisignate CD band at 280 and 303 nm, associated with a broad UV absorption at 300 nm in chloroform at 15°C. Since the spectroscopic features are quite similar to those of i,28d-28e it is possible that the main chain in 7 may contain diastereomeric helical motifs with opposite screw senses and different screw pitches. 

To quantitatively characterize the PM populations using chiroptical characteristics, it may be useful to use the gabs values of 16 at each temperature with reference to the regression curve of these gabs values in 17, which is assumed to adopt a purely P 73-helical structure, instead of the Ae value. The analysis is based on the assumption that the weak temperature dependence of the ymax for 17 is due to a minute modification in the screw pitch of the P helix, rather than any formation of the M-helical motif. 

Some of these cholesteric systems are well-characterized The structure and handedness of the macromolecule is unequivocally known and so is the pitch and handedness of the cholesteric phase. A few attempts were made to correlate the polymer structure to the cholesteric handedness. 

In particular most of the early studies on CPL were based on the incorporation of a luminescent achiral chromophore in a chiral nematic or cholesteric liquid crystal. Chiral nematic liquid crystals (CNLC) are intrinsically birefringent and exhibit a helical supramo-lecular architecture, which is characterized by the pitch length p (Figure 5.11). 

The fuel oils coming out of olefin plants are also characterized by an abundance of polynuclear aromatic molecules, (Same definition as for Figure 2—1). They are sometimes inaccurately referred to as having a high aromatics content. Nomenclature aside, because of this, the burning characteristics of pyrolysis gas oil and pyrolysis pitch are poor. They are smoky, sooty, and gum formers they rend to be more viscous, and because of their polynuclear aromatic concent, they are suspected carcinogens. They are basically a witchs brew of unsavory hydrocarbons.. ... 

Under the optical microscope the texture of products derived from the three coals studied show an anisotropy of the type which already has been described for similar materials (I, 4, 9). The texture of the l.t. pitch coke is entirely isotropic, whereas the h.t. pitch coke is characterized by a pronounced anisotropy in bands. The anisotropy of the carbonization products of mixtures of l.t. and h.t. pitches varies linearly as a function of the composition of the mixture (8). 

The difference in processing behavior between rotors provided with straight blades and those with pitched blades is shown in Figure 6 by an application referring to solvent recovery from a polymer solution of low initial viscosity. The evaporation capacity of a thin-film evaporator equipped with straight blades decreases considerably as soon as the concentrated polymer reaches a viscosity between 1000 and 2000 P. The greatly increased mean film thickness that characterizes this vis-... 

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