Graphitized Materials

The scanning tunnel microscopy revealed a somewhat different structure of carbon black particles (Bonnet and Custodero 1992, Donnet 1994, Donnet et al. 1995). The crystallites forming carbon black particles have differently extended structures and exhibit several clearly visible turbostratic bends. 

The particle surface has the shape of a curved staircase formed by overlapped crystallites. In the case of both of the types of carbon black particles on the boundaries of crystallites, there can be a great number of hydrogen atoms, oxidized carbon atoms, and broken carbon bonds. Atom force microscopy (AFM) images of carbon black (Tanahashi et al. 1990, Donnet 1994) showed that crystallites are presented on the surface and they have the form of rectangles, but their arrangement can be random. It is evident that the differences in the carbon black particle structure observed by various techniques for diverse materials reflect the diversity of synthesized carbonaceous materials 

FIGURE 3.1 Schematic representation of the constitution of a carbon crystallite where Li and Lj is the thickness and sizes a crystallite, y is the angle characterizes concentration of intrinsic defects of graphite planes. (Taken from Carbon, 31, Bourrat, X., Electrically conductive grades of carbon black Structure and properties, 287-302, 1993. Copyright 1993, with permission from Elsevier.) 

The textural features of the constitution of nanoporous ACs, synthesized as a result of pyrolysis of cellulose, were studied by the TEM method (Kaneko et al. 1992), with the method being applied to carbons differing in the temperature of their heat treatment in the argon atmosphere over 

FIGURE 3.2 (a) HRTEM image of AC (5 bet= 1664 m /g) showing the turbostratic structure and (b) an AC model with the geometry optimized by MM (CharMM force field) and then by semiempirical method PM6. (A Taken from Carbon, 50, Gun ko, V.M., Kozynchenko, O.P., Tennison, S.R., Leboda, R., Skubiszewska-Zi ba, J., and Mikhalovsky, S.V., Comparative study of nanopores in activated carbons by HRTEM and adsorption methods, 3146-3153, 2012a. Copyright 2012, with permission from Elsevier.) 

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The bifunctionality of the bis-diene and bis-dienophile monomers is apparent from the condensation product, structure [XXI], which still contains a diene and a dienophile in the same molecule. This polymer is crystalline, indicating a high degree of stereoregularity in the condensed rings. It decomposes to a graphitic material before melting. 

A siHcon carbide-bonded graphite material in which graphite particles are distributed through the siHcon carbide matrix has high thermal shock resistance and is suitable for appHcations including rocket nose cones and nozzles and other severe thermal shock environments (155) (see Ablative materials). 

Carbon—graphite materials employed for mechanical appHcations are prepared by mixing selected sizes and types of carbon and graphite with biader materials such as pitches and resias. The mixtures are formed iato compacts and baked to temperatures of ca 1000—3000°C. Specific raw materials and processiag techniques are employed to obtain desired properties for the finished carbon—graphite materials (24). 

Carbon—graphite materials do not gall or weld even when mbbed under excessive load and speed. Early carbon materials contained metal fillers to provide strength and high thermal conductivity, but these desirable properties can now be obtained ia tme carboa—graphite materials that completely eliminate the galling teadeacy and other disadvantages of metals. 

Various forms of carbon, semigraphite, and graphite materials have found wide apphcation ia the metals iadustry, particularly ia connection with the productioa of iroa, alumiaum, and ferroalloys. Carbon has been used as a refractory material siace 1850, though full commercial acceptance and subsequent rapid iacrease ia use has occurred only siace 1945. 

This wear is caused primarily from high thermal and mechanical stress, chemical attack, attack by iron and slag, oxidation, and severe thermal shock. Thus the design of the hearth wall and the concepts employed ate just as important as the carbon or graphite materials chosen for the refractory material. Despite their benefits and properties, no carbon or graphite material can overcome the problems of an improper hearth wall design concept. 

N. J. Fechter and P. S. Petmnich, Development of Seal Ring Carbon-Graphite Materials., NASA Contract Reports CR-72799, Jan. 1971 CR-72986, Aug. 1971 CR-120955, Aug. 1972 and CR-121092, Union Carbide Corp., Parma, Ohio, Jan. 1973. 

Test Method for Moduli of Elasticity and Eundamental Erequencies of Carbon and Graphite Materials by... 

Test Method for Rockwell Hardness of Eine-Grained Graphite Materials... 

Method for Soleroscope Hardness Testing of Eine-Grained Carbon and Graphite Materials... 

ITie major component of atmospheric haze is sulfate particulate matter (particularly ammonium sulfate), along with varying amounts of nitrate particulate matter, which in some areas can equal the sulfate. Other components include graphitic material, fine fly ash, and organic aerosols. 

It has been established that, when mesophase pitch is carbonized, the morphology of the pitch is the primary factor [20] in determining the microstructure of the resulting graphitic material. This may be attributed to the stacking behavior of mesophase molecules (quite similar to the planar stacking in turbostratic graphite), which may be visualized as shown in Fig. 5. 

As discussed earlier, the first wall materials in next generation machines will receive from 0.005 to 30 displacements per atom. At the lower end of this range (<0.01 dpa) there are essentially no mechanical property changes expected in graphite materials. However, even at these low doses thermal conductivity and stored energy are of concern. For displacement levels >0.01 dpa other property... 

Fig. 7. Irradiation induced thermal conductivity degradation of selected graphite materials.

T. D. Burchell, M. O. Tucker and B. McEnaney. Qualitative and Quantitative Studies of Fracture in Nuclear Graphites, Materials for nuclear reactor core applications. BNES, London, 1987, pp. 95-103. 

Conductive Polymers Anodes currently available consist of a conductive-polymer graphite material coated on to a multistrand copper conductor. The polymer provides an active surface but shields the conductor from chemical attack. A non-conductive outer braid may be used to give abrasion resistance and avoid direct contact with the cathode. The finished anode has the appearance of an electric cable and is claimed to have applications for buried/immersed structures and for internal protection of tanks, etc. Anode current densities are typically given as 14-30mAm ... 

Soft carbon is also classified by its crystallinity. For example, acetylene black and carbon black are regarded as typical carbon materials with low crystallinity. Coke materials are carbon materials with intermediate crystallinity. It is easy to obtain these materials because they are made from petroleum and coal and they were actively studied in the 1980s. In contrast, there are some graphite materials which have high crystallinity their capacity is greater than that of coke materials, and these materials have been studied more recently, in the 1990s [76-80]. 

Graphite materials with high crystallinity are further classified by their production method. Graphite materials made by... 

Figure 59. Charge-discharge characteristics of some graphite material electrodes (1st cycle current density 0.2 raA cm 2).

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