Other Forms of Carbon

but also on the different approaches used to introduce carbon materials into Ti02-carbon composites. These approaches may be described in detail in terms of the following subcategories, based on the origin of Ti02 and carbon, as well as the way they are combined in the composites. 

As an alternative way, carbon has been loaded on Ti02 particles. This can be put in practice through the introduction of carbonaceous precursors on the Ti02 particles formed, and subsequent carbonization to produce Ti02-carbon composites. The carbon materials, derived from various carbonaceous precursors, have been practically introduced by means of thermal treatment in n-hexane, ethanol, or cyclohexane vapor [145-147,182-185] and carbonization of a mixture of Ti02 with poly(vinyl alcohol), poly(ethylene terephthalate), cellulose, sucrose, or citric acid [87,132-144,148,149,151]. A chemical vapor deposition method was also used to prepare MWCNTs deposited on Ti02 [198]. 

4 Other Approaches and Concurrent Synthesis of Ti02-Carhon Composites 

UV-vis spectra of carbon-Ti02 composites produces strong changes in photoavailability beyond the spectral region of the neat Ti02 absorbance [23,30,94,125,138,152,176,189], also observed in the case of carbon-doped 

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Other forms of carbon-carbon composites have been or are being developed for space shutde leading edges, nuclear fuel containers for sateUites, aircraft engine adjustable exhaust nozzles, and the main stmcture for the proposed National Aerospace plane (34). For reusable appHcations, a siHcon carbide [409-21 -2] based coating is added to retard oxidation (35,36), with a boron [7440-42-8] h Lsed sublayer to seal any cracks that may form in the coating. 

Processing of baked and graphitized carbon. Properties of manufactured graphite, Appbcations of baked and graphitized carbon. Other forms of carbon and graphite. 

Baked and Graphitized Products, Uses" under "Carbon" in ECT2nd ed., VoL 4, pp. 202—243, by W. M. Gaylord, Union Carbide Corp. "Other Forms of Carbon and Graphite Carbon" under "Carbon (Carbon and Artificial Graphite)" in ECT 3rd ed., Vol. 4, pp. 628—631, by R. M. Bushong, Union Carbide Corp. 

Fullerenes are described in detail in Chapter 2 and therefore only a brief outline of their structure is presented here to provide a comparison with the other forms of carbon. The C o molecule, Buckminsterfullerene, was discovered in the mass spectrum of laser-ablated graphite in 1985 [37] and crystals of C o were fust isolated from soot formed from graphite arc electrodes in 1990 [38]. Although these events are relatively recent, the C o molecule has become one of the most widely-recognised molecular structures in science and in 1996 the codiscoverers Curl, Kroto and Smalley were awarded the Nobel prize for chemistry. Part of the appeal of this molecule lies in its beautiful icosahedral symmetry - a truncated icosahedron, or a molecular soccer ball, Fig. 4A. 

Three other forms of carbon are manufactured on a vast scale and used extensively in industry coke, carbon black, and activated carbon. The production and uses of these impure forms of carbon are briefly discussed in the Panel on p. 274. 

At high pressures, diamond is the stable form of carbon, since it has a higher density than graphite (3.51 vs 2.26 g/cm3). The industrial synthesis of diamond from graphite or other forms of carbon is carried out at about 100,000 atm and 2000°C. 

Dissolution procedures are described for gram samples of graphite or pyrolytic carbon, milligram samples of irradiated fuel particles, and for more readily oxidised forms of carbon, such as charcoal. The first two methods involve heating the samples with mixtures of 70% perchloric and 90% nitric acids (10 1), and must only be used for graphite or pyrolytic carbon. Other forms of carbon must not be oxidised in this way (to avoid explosions), but by a preliminary treatment with nitric acid alone and in portions. 

Graphite produces the large beam currents desirable in electrostatic accelerator dating of radiocarbon. However, samples to be dated can be converted to other forms of carbon with less effort, and still provide satisfactory results. 

Carbon reinforced products that require less energy to produce and that are ten times stronger than steel, lighter than aluminum, and that conduct more heat than copper can be increasingly used to reduce the weight of vehicles, improve the performance of appliances and tools and increase the efficiency of heat-transfer systems. Other forms of carbon will provide super semiconductors and advanced optics. 

Fullerenes are the third natural form of carbon. These have been found to exist in interstellar dust and in geological formations on Earth, but only in 1985 did Smalley, Kroto and co-workers discovered this class of carbon solids and their unusual properties [447, 448]. It has been shown that Ceo, the most common fullerene, could be transformed under high pressure into the other forms of carbon, diamond, and graphite [449] or, at moderately high pressures and temperatures, into new various metastable forms [450 53]. Ceo crystals, fullerites, have/cc structure with weak van der Waals interactions. This structure is stable at ambient temperature up to 20 GPa and at ambient pressure up to 1800 K [454, 455]. 

To complete the list of forms in which elemental carbon was found, we must also list two other forms of carbon ... 

The technique for estimating the total aliphatic carbon (especially methyl carbon) in coal may require further refinements. However, in view of the foregoing discussions on the self-consistency of the estimated methyl content with other forms of carbon in coal, it seems unlikely that there are side chains longer than methyl group in normal coals. 

CARBON - CARBON AND ARTIFICIALGRAPHITE - OTHER FORMS OF CARBON AND GRAPHITE] (Vol 4)... 

Well-characterized vanadium carbide thin films can be prepared by exposing a clean V(110) surface to ethylene or 1,3-butadiene at 600 K. The formation of vanadium carbide, rather than other forms of carbon-containing species such as graphite or carbonaceous overlayers, was confirmed by the characteristic AES and NEXAFS spectra.4 The stoichiometry and average thickness of the thin carbide films can be estimated by... 

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