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162. The effect of applied current on electrical conduction in hot-pressed pyrolytic graphite before and after neutron irradiation
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CARBON
scattering at the boundaries is one of the causes and possibly the dominant one for the observed negative magnetoresistance. 161. Non-linear conduction in graphite at high electric field S. Mizushima (School of En~~e~~g, K&o ~n~ve~~, Tokyo, &pan). Saturation of current in graphite at high electric field was found, which is considered to be caused by the electron-phonon interaction, along with concomittant phenomena such as current oscillation and light emission, which are supposedly results of current pinch. 16% The effect of applied current on electrical conduction in hot-pressed pyrolytic graphite before and after neutron irradiation J. D. Cooper, M. L. Yeoman and D. A. Young (Department of ChemzCalEngineering and Chemical Technoes, Im~al CoUege, Loon, S.W. 7, U.K.). The application of hydrostatic pressure to graphite produces a large pressure coefficient of conduction normal to the basal planes. In this direction the pressure coefficient is almost independent of temperature. Parallel to the basal planes, however, the pressure coefficient depends markedly on temperature. 163. Electronic properties of carbon Gbres T. Tsuzuku and S. Arai (N&on University at Namshino, Funabashi, Japan). The magnetoresistance and thermoelectric power of some carbon fibres have been investigated as functions of temperature between 402” and 300°K. A brief discussion will be given on the electronic structure. 164. Electrical properties of carbon fibers C. Herinckx (Union Carbide European Research Associates, S. A, 95, rue Gatti de Gamond, Brusseb 18, Belgium). The electrical conductivity of carbon fibers is of the semiconductor type with very low activation energy of the free carriers. The curvature of the logu vs. 1/T plots is attributed to a distribution of electronic states localized on structural defects. These defects reduce the mobility to low values ( p < 20 cm2/V set) independent of temperature. The Seebeck coefficient indicates complete degeneracy of the carrier gas. The absence of a magnetoresistance effect is related to the scattering mechanism. 165. The Muence of chemisorbed oxygen on the electron spin resonance of a graphitised carbon black* D. E. Brown, G. C. Michael, I?. J, Vastola and P. L. Walker, Jr. (The Pennsylvania State University, Materials S&rue Departmnt, University Park, Pennsylvania). The electron spin resonance of Graphon (H.T.T. 276O”G), having different levels of burn-off, was studied after thermal desorption of the chemisorbed oxygen at a number of different temperatures. It has been found that the removal of chemisorbed oxygen, as CO and COZ, caused a marked decrease in the spin intensity. *Supported by the Atomic Energy Commission on Contract No. AT(30-l)-1710. 166. Anisompy of the electron spin resonance in acenaphthylene coke L. S. Singer and A. R. Cherry (Union Curb& Corporation, Carbon Products Divwion, Parma Technical Center, Clevekznd, Ohio). Anisotropy has been observed in the ESR of single flakes of acenaphthylene coke. Measurements of the anistropy of the g-factor, line width, and spin-lattice relaxation time have been made as a function of heat treatment temperature. The apparent quasi-single crystal behavior indicates an extremely high degree of preferred orientation of the aromatic layers in the coke. 167. ESR of carbons in the transition region and the Hennig-Smaller Effect* S. Mrozowski and E. Klutht (Carbon Research Laboratory, State University of New York at Bu$alo, Bufalo, New York). The broadening of the ESR line observed in the heattreatment range 1066°-1566”C, as well as when a highly heattreated carbon is reheated to these temperatures was investigated. An absolute maximum in width is found for HTT 1366°C. Both broadening effects show in many ways great similarity. Some temperature dependence studies were performed on such broad lines. *Supported by the U.S. Office of Naval Research. tSpeer Carbon Postdoctoral Fellow.
CARBON
scattering at the boundaries is one of the causes and possibly the dominant one for the observed negative magnetoresistance. 161. Non-linear conduction in graphite at high electric field S. Mizushima (School of En~~e~~g, K&o ~n~ve~~, Tokyo, &pan). Saturation of current in graphite at high electric field was found, which is considered to be caused by the electron-phonon interaction, along with concomittant phenomena such as current oscillation and light emission, which are supposedly results of current pinch. 16% The effect of applied current on electrical conduction in hot-pressed pyrolytic graphite before and after neutron irradiation J. D. Cooper, M. L. Yeoman and D. A. Young (Department of ChemzCalEngineering and Chemical Technoes, Im~al CoUege, Loon, S.W. 7, U.K.). The application of hydrostatic pressure to graphite produces a large pressure coefficient of conduction normal to the basal planes. In this direction the pressure coefficient is almost independent of temperature. Parallel to the basal planes, however, the pressure coefficient depends markedly on temperature. 163. Electronic properties of carbon Gbres T. Tsuzuku and S. Arai (N&on University at Namshino, Funabashi, Japan). The magnetoresistance and thermoelectric power of some carbon fibres have been investigated as functions of temperature between 402” and 300°K. A brief discussion will be given on the electronic structure. 164. Electrical properties of carbon fibers C. Herinckx (Union Carbide European Research Associates, S. A, 95, rue Gatti de Gamond, Brusseb 18, Belgium). The electrical conductivity of carbon fibers is of the semiconductor type with very low activation energy of the free carriers. The curvature of the logu vs. 1/T plots is attributed to a distribution of electronic states localized on structural defects. These defects reduce the mobility to low values ( p < 20 cm2/V set) independent of temperature. The Seebeck coefficient indicates complete degeneracy of the carrier gas. The absence of a magnetoresistance effect is related to the scattering mechanism. 165. The Muence of chemisorbed oxygen on the electron spin resonance of a graphitised carbon black* D. E. Brown, G. C. Michael, I?. J, Vastola and P. L. Walker, Jr. (The Pennsylvania State University, Materials S&rue Departmnt, University Park, Pennsylvania). The electron spin resonance of Graphon (H.T.T. 276O”G), having different levels of burn-off, was studied after thermal desorption of the chemisorbed oxygen at a number of different temperatures. It has been found that the removal of chemisorbed oxygen, as CO and COZ, caused a marked decrease in the spin intensity. *Supported by the Atomic Energy Commission on Contract No. AT(30-l)-1710. 166. Anisompy of the electron spin resonance in acenaphthylene coke L. S. Singer and A. R. Cherry (Union Curb& Corporation, Carbon Products Divwion, Parma Technical Center, Clevekznd, Ohio). Anisotropy has been observed in the ESR of single flakes of acenaphthylene coke. Measurements of the anistropy of the g-factor, line width, and spin-lattice relaxation time have been made as a function of heat treatment temperature. The apparent quasi-single crystal behavior indicates an extremely high degree of preferred orientation of the aromatic layers in the coke. 167. ESR of carbons in the transition region and the Hennig-Smaller Effect* S. Mrozowski and E. Klutht (Carbon Research Laboratory, State University of New York at Bu$alo, Bufalo, New York). The broadening of the ESR line observed in the heattreatment range 1066°-1566”C, as well as when a highly heattreated carbon is reheated to these temperatures was investigated. An absolute maximum in width is found for HTT 1366°C. Both broadening effects show in many ways great similarity. Some temperature dependence studies were performed on such broad lines. *Supported by the U.S. Office of Naval Research. tSpeer Carbon Postdoctoral Fellow.