Stretch graphitization

The overwhelming success of PAN-based carbon fibers over rayon and pitch can be attributed to several key aspects.f Structurally, PAN has a faster rate of pyrolysis without much disturbance to its basic structure and to the preferred orientation of the molecular chains along the fiber axis present in the original fiber. By contrast, carbon fibers from rayon suffer from extremely low carbon yield (20-25%) due to chain fragmentation, which eliminates the orientation of the precursor fiber. While improved properties can be achieved by stretch graphitization, this process is expensive and does not compensate for the low yields. 

There are some interesting allusions in earlier literature to the potential for liquid crystalline character in inorganic materials. Bragg demonstrated in 1960 that he could stretch graphite rod at temperatures... 

According to one process, cellulose fibers are carbonized at temperatures above 2400° C and simultaneously stretched to 150% their original length. Graphite crystals oriented in the fiber direction are produced by this stretch graphitization. The desired high modulus of elasticity can only be produced in this way. 

The properties of stretched-graphitized rayon-based carbon fibers are shown in Table 8.9. The data is to be considered for its historical value, since the material is no longer produced commercially (data from Union Carbide Corp.)... 

YOUNG S modulus of stretch graphitized carbon fibres (20)... 

Carbon and Graphite Fibers. Carbon and graphite fibers (qv) are valued for their unique combination of extremely high modulus and very low specific gravity. Acrylic precursors are made by standard spinning conditions, except that increased stretch orientation is required to produce precursors with higher tenacity and modulus. The first commercially feasible process was developed at the Royal Aircraft Fstablishment (RAF) in collaboration with the acrylic fiber producer, Courtaulds (88). In the RAF process the acrylic precursor is converted to carbon fiber in a two-step process. The use of PAN as a carbon fiber precursor has been reviewed (89,90). 

Graphite is widely distributed throughout the world though much of it is of little economic importance. Large crystals or flake occur in metamorphosed sedimentary silicate rocks such as quartz, mica schists and gneisses crystal size varies from <1 mm up to about 6 mm (average 4mm) and the deposits form lenses up to 30 m thick stretching several... 

Fig.2 shows the infrared absorption spectrum of the tin oxide film. In order to analyze the molecular structure of the deposited film, we deposited the tin oxide film on a KBr disc with thickness of 1 mm and diameter of 13 mm. Various peaks formed by surface reaction are observed including O-H stretching mode at 3400 cm, C=C stretching mode at 1648 cm, and Sn02 vibration mode at 530 cm. The formation of sp structure with graphite-like is due to ion bombardment with hydrogen ions at the surface and plasma polymerization of methyl group with sp -CHa. 

Practically every battery system uses carbon in one form or another. The purity, morphology and physical form are very important factors in its effective use in all these applications. Its use in lithium-ion batteries (Li-Ion), fuel cells and other battery systems has been reviewed previously [1 -8]. Two recent applications in alkaline cells and Li-Ion cells will be discussed in more detail. Table 1 contains a partial listing of the use of carbon materials in batteries that stretch across a wide spectrum of battery technologies and materials. Materials stretch from bituminous materials used to seal carbon-zinc and lead acid batteries to synthetic graphites used as active materials in lithium ion cells. 

Raman spectroscopy is one of the most powerful techniques for the characterization of nanocarbons. It is also a convenient technique because it involves almost no sample preparation and leaves the material unharmed. There are four characteristic bands for CNTs The band at 200 cm-1 is called radial breathing mode (RBM). It depends on the curvature and can be used to calculate the diameter of SWCNTs [61]. The relatively broad D-band at 1340 cm-1 is assigned to sp2-related defects and disorder in the graphitic structure of the material. The tangential C-C stretching mode is located at -1560 cm 1 (G-band). The second order mode of the D-band can be observed (G -band,... 

This means that it is necessary to have a high degree of preferred orientation of hexagonal planes along the fiber axis if a high modulus is desired. To improve the orientation of graphite crystals, various kinds of thermal and stretching treatments. 

The IR spectrum of 133 was obtained by laser vaporization of graphite and subsequent condensation of the reaction products in solid argon at 10 K. However, only the most intense mode at 1695 cm could be detected. " The antisymmetric stretching vibration of the linear isomer 132 is observed at 1952 cm . " " The assignment could be corroborated by measuring the spectra of isotopically labeled compounds. In a more recent theoretical work, the UV spectra of 133 and 134 were calculated, " " but experimental data are lacking so far. 

Carbonaceous material (Fig. 12.8b) is intimately mixed with silicates and is very abundant (carbon abundance averages 13% and varies up to 50%) in CP IDPs. Some carbon is elemental (graphite), but C-H stretching resonances in infrared spectra show that aliphatic hydrocarbons are also present. Polycyclic aromatic hydrocarbons (PAHs) also occur. Nanodiamonds have been identified in cluster IDPs, but not in smaller CP IDPs. Enormous D/H and 15N/14N anomalies have been measured in bulk IDPs, and the hydrogen isotopic anomalies are correlated with organic-rich domains. Ratios of D/H as high as 25 times the solar ratio suggest the presence of molecular cloud materials. 

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