Carbonization Mechanism of Aromatic Hydrocarbons
As shown in Table 4.1, the graphite precursors can be divided into two major classes a aromatic hydrocarbons and b polymers, each with different carbonization characteristics. Structure of Aromatic Hydrocarbons. The term hydrocarbon refers to an organic compound that contains only carbon and hydrogen. Aromatics are hydrocarbons characterized by the presence of at least one benzene ring. Aromatics have a graphite-like structure and graphite is often considered as the parent of all these...
The Carbon Covalent sp Bond 1
Like the sp3 bond, the sp2 bond is covalent. It is a strong bond, because of the three sp2 valence electrons and the small size of the atom. The lopsided configuration of the sp2 orbital allows a substantial overlap with other sp2 orbitals. This overlap is similar to the sp3 overlap illustrated in Fig. 2.11, except that it is more pronounced, with a shorter bond length and higher bond energy, as shown in Table 2.7. Like the sp3 orbital, the sp2 is directional and is called a sigma a orbital,...
Structure and Properties of Diamond and Diamond Polytypes
The first part of this book deals with graphite and carbon materials, their structure and properties, and their various processes and applications. In this and the next three chapters, the focus is on the other major allotrope of carbon diamond. Diamond has outstanding properties, summarized as follows It has the highest thermal conductivity of any solid at room temperature, five times that of copper. It is the ideal optical material capable of transmitting light from the far infra-red to the...
C. L. Mantell Carbon And Graphite Handbook Interscience Publishers New York
1. Cram, D. J. and Hammond, G. S., Organic Chemistry, McGraw-Hill Book Co., New York 1964 2. Jenkins, G. M. and Kawamura, K., Polymeric Carbons, Cambridge University Press, Cambridge, UK 1976 3. Wehr, M. R Richards, J. A., Jr. and Adair, T. W ill, Physics of the Atom, Addison-Wesley Publishing Co., Reading, MA 1978 4. Van Vlack, L. H., Elements of Materials Science and Engineering, 4th ed., Addison-Wesley Publishing Co., Reading, MA 1980 5. Eggers, D. F., Gregory, N. W., Halsey, G. D., Jr. and...
Structure of the Graphite Crystal
Graphite is composed of series of stacked parallel layer planes shown schematically in Fig. 3.1, with the trigonal sp2 bonding described in Ch. 2, Sec. 4.0. In Fig. 3.1 and subsequent figures of the carbon structure , the circles showing the position of the carbon atoms do not represent the actual size of the atom. Each atom, in fact, contacts its neighbors. a atoms in full circles have neighbors directly above and below In adjacent planes p atoms in o have no direc In adjacent p a atoms in...
Graphitization Mechanism of Cokes
Graphitization occurs in a series of steps which begins as the increasing temperature passes the carbonization temperature, i.e., 1200 C. 13' Hydrogen, sulfur, and other elements, which might still be present after carbonization, are gradually removed and, as the temperature reaches 2000 C, essentially none remains. 3' Above 1800 C, the conversion from a turbostratic structure to a graphitic structure shown in Figs. 3.4 and 3.2 of Ch. 3 begins slowly at first then more rapidly as the...
The Carbon Phase Diagram
The carbon phase diagram is shown in Fig. 2.20 J61 Another expression of the T-P phase diagram, showing the calculated total vapor pressure of carbon, is shown in Fig. 3.7 of Ch. 3. Carbon vaporizes at 4800 K at a pressure of 1000 atmospheres, which is the area where diamond is stable. The high-pressure conversion of diamondfromgraphiteoccursattemperatures of approximately 3000 Kand pressures above 125 kbars in the absence of catalyst and will be reviewed in Ch. 12.
The Trigonal sp Orbital
In addition to the sp3-tetragonal hybrid orbital reviewed in Sec. 3 above, two other orbitals complete the series of electronic building blocks of all carbon allotropes and compounds the sp2 and the sp orbitals. Whereas the sp3 orbital is the key to diamond and aliphatic compounds, the sp2 or trigonal orbital is the basis of all graphitic structures and aromatic compounds. The mechanism of the sp2 hybridization is somewhat different from that of the sp3 hybridization. The arrangement of the...
Covalent Graphite Compounds
As the name implies, the covalent graphite compounds have covalent two-electron bonds between the foreign and the carbon atoms. These bonds disrupt the n bonds between layers see Ch. 3, Sec. 1.2 and the delocalized ji electrons are no longer free to move, thereby causing a drastic reduction in the electrical conductivity of the material. This is accompanied by a loss of planarization of the layers which are converted to a puckered structure, somewhat similar to that of diamond seeCh. 11, Fig....
The Fullerene Molecules
The recent discovery of a family of large, solid carbon molecules with great stability, the so-called fullerenes, has considerably extended the scope and variety of carbon molecules known to exist and is opening an entirely new chapter on the physics and chemistry of carbon, with many potential applications. The fullerenes can be considered as another major allotrope of carbon and its first stable, finite, discrete molecular form. They are different, in that respect, from the other two...
Precursor Materials and Their Carbon Yield
The carbon yield is defined as the ratio of the weight of the carbon residue after carbonization to the weight of the material prior to carbonization. Typical carbon yields of common and potential precursor materials are shown in Table 4.1 .Pld These yields are not fixed but depend to a great degree on the heating rate, the composition of the atmosphere, the pressure, and other factors see below . The nature of the carbon yield, given in the last column, i.e., coke or char, is reviewed in the...
Gemstones and Industrial Diamond
The diamond business is divided into two major categories gemstones and industrial diamond.'14 '15 Production and market values are shown in Table 12.3. The gemstone business comprises 93 of the diamond business in monetary terms but only approximately 1 on a weight basis, reflecting the very large cost difference between the two categories. The average cost of industrial diamond is 1.10 carat and that of gemstone is gt 1000 carat and, in some extreme cases, may reach 60,000 carat for blue...
Carbon Fibers 1
Thomas Edison made the first carbon fibers on record in 1879 when he carbonized cotton thread to produce afilament for a light bulb. His effort was not entirely successful and Edison eventually replaced the fiber by a tungsten wire. Large-scale production of carbon fibers had to wait until the late 1950's, when cloth and felt from carbonized rayon were commercialized. These materials are still produced now see Sec. 4.0 . High-strength fibers from polyacrylonitrile PAN were developed in the...
PAN as Precursor
Polyacryionitrile PAN is the most favored precursor at this time for the production of high-performance fibers. PAN-based fibers are in the medium price range - 40 kg in 1992 . They have the highest tensile strength of all carbon fibers and a wide range of moduli and are readily available in a variety of tows. Precursor Requirements. To produce the optimum carbon fiber, a precursor fiber should perform the following functions 15 Maximize the preferred orientation of the polycarbon layers in the...
Carbon 1990 28 261-279
1. International Committee for Characterization and Terminology of Carbon, Carbon, 28 5 445-449 1990 2. Bokros, J. C., in Chemistry and Physics of Carbon, P. L. Walker, Jr., ed. , Vol. 5, Marcel Dekker Inc., New York 1969 3. Kohl, W. H., Handbook of Materials and Techniques for Vacuum Devices, Reinhold Publishing, New York 1967 4. Palmer, H. B. and Shelef, M., in Chemistry and Physics of Carbon, P. L. Walker, Jr., ed. , Vol. 4, Marcel Dekker Inc., New York 1968 5. Gustafson, P., Carbon, 24 2...
The Polytypes of Diamond
Hexagonal Diamond. Hexagonal diamond is an allotropic form of carbon which is close to cubic diamond in structure and properties. It is a polytype of diamond, that is a special form of polymorph where the close-packed layers 111 for cubic and 100 for hexagonal are identical but have a different stacking sequence. Hexagonal diamond has an ABAB stacking sequence, so that every second layer is identical as shown in Fig. 11.6.171 This two-layer hexagonal sequence known as 2H diamond is different in...