Carbon pyrolytic graphite

Carbon electrodes are also employed in electroanalytical applications due to the very low residual current over a wide range of potentials that makes it possible to study electrochemical reactions even at the level of trace concentration. Among the different types of such electrodes, wax-impregnated graphite rods, carbon powder bound with an inert viscous liquid (carbon paste), glassy carbon, pyrolytic graphite and carbon fibers, and, more recently, nanotubes and fullerenes can be mentioned. Carbon fibers have radial, random, or anion distributions that lead to a different distribution of step and step—step interactions. 

New methods for improving the sustainability of the methane thermocatalytic decomposition process have been developed. Studies indicate that the presence of small amounts of moisture and H2S (<3 v.%) in the hydrocarbon feedstock is not detrimental for the catalyst activity and process efficiency. This implies that commercial hydrocarbon fuels could potentially be employed as feedstocks for the process. A bench-scale thermocatalytic reactor was designed, fabricated and operated using methane and propane as feedstocks. The TCR produced hydrogen-rich gas free of CO/CO2 impurities the gas was directly fed to PEM fuel cell. Material characterization studies indicated that depending on operational conditions, carbon could be produced in several valuable forms including turbostratic carbon, pyrolytic graphite, spherical carbon particles, or filamentous carbon. 

Electrochemistry of P450s has been investigated on graphite, glassy carbon, pyrolytic graphite, gold, platinum, or on metal oxide electrodes or nanostructured electrodes [223-225]. 

See Acheson graphite, artificial graphite, electrographite, graphitized carbon, pyrolytic graphite... 

Perhaps the single most versatile class of material is carbon. Pyrolytic graphite, glassy (vitreous) carbon, various polymers or oil-impregnated or paste electrodes have been used. There is a growing awareness of the complex surface chemistry of carbons, coupled to an appreciation of the great electrochemical differences between apparently similar forms of the material In practice, mechanical chemical and electrochemical pretreatment methods are usually essential if reproducible results are to be achieved. 

Carbon, Carbides, and Nitrides. Carbon (graphite) is a good thermal and electrical conductor. It is not easily wetted by chemical action, which is an important consideration for corrosion resistance. As an important stmctural material at high temperature, pyrolytic graphite has shown a strength of 280 MPa (40,600 psi). It tends to oxidize at high temperatures, but can be used up to 2760°C for short periods in neutral or reducing conditions. The use of new composite materials made of carbon fibers is expected, especially in the field of aerospace stmcture. When heated under... 

Of the many forms of carbon and graphite produced commercially, only pyrolytic graphite (8,9) is produced from the gas phase via the pyrolysis of hydrocarbons. The process for making pyrolytic graphite is referred to as the chemical vapor deposition (CVD) process. Deposition occurs on some suitable substrate, usually graphite, that is heated at high temperatures, usually in excess of 1000°C, in the presence of a hydrocarbon, eg, methane, propane, acetjiene, or benzene. 

The largest quantity of commercial pyrolytic graphite is produced in large, inductively heated furnaces in which natural gas at low pressure is used as the source of carbon. Deposition temperatures usually range from 1800 to 2000°C on a deposition substrate of fine-grain graphite. 

Wei and Robbins [10] have reviewed much of the work performed on the thermal physical properties of CBCF. Fhe emissivity parallel to the fibers was 0.8 over the temperature range from 1000 to 1800 °C. This value is higher than the emissivity of c-direction pyrolytic graphite (0.5-0.6), but is close to values for graphite and dense carbon-carbon composite (0.8-0.95). 

Kelly, B.T. and Brocklehurst J.E., Dimensional changes of pyrolytic graphite at very high fast neutron doses. In Proc. Fifth SCI Conf. on Industrial Carbons and Graphites, SCI London, (1979, pp. 892 897. 

Fig. 2. Raman spectra (T = 300 K) from various sp carbons using Ar-ion laser excitation (a) highly ordered pyrolytic graphite (HOPG), (b) boron-doped pyrolytic graphite (BHOPG), (c) carbon nanoparticles (dia. 20 nm) derived from the pyrolysis of benzene and graphitized at 2820°C, (d) as-synthesized carbon nanoparticles ( 850°C), (e) glassy carbon (after ref. [24]).

Property Conventional electro-graphite Glassy or harp carbon Pyrolytic carbon ... 

Impervious graphites, that is electro-graphites with appropriate resin impregnation are used in cascade-, shell- apd tube-type coolers, condensers, pre-heaters etc. in a wide variety of chemical plants. Similar resistance to corrosion applies to glassy carbon vessels and pyrolytic carbons and graphites. The corrosion resistance to principal chemical agents is given in Table 18.2. 

The deposition of pyrolytic graphite in a fluidized bed is used in the production of biomedical components such as heart valves, ] and in the coating of uranium- and thorium-carbides nuclear-fuel particles for high temperature gas-cooled reactors, for the purpose of containing the products of nuclear fission.fl" The carbon is obtained from the decomposition of propane (CgHg) or propylene (CgHg) at 1350°C, or of methane (CH4) at 1800°C. Its structure is usually isotropic (see Ch. 4). 

---