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A simple model of the effect of interstitial atoms on the inter-layer properties of graphite
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ABSTRACTS
VI. RADIATION DAMAGE 144. The effect of dose rate on irradiation damage in graphite J. W. Harrison, R. W. Henson, A. J. Perks, and J. H. W. Simmons (Atomic Energy Research Establishment, Harwell, Didcot, Berkshire, U.K.). The changes in dimensions and lattice parameters produced by irradiation in two reactors with very different dose rate have been studied over the temperature range 400-700°C. In this range it is found that the activation energy associated with the equivalent temperature concept is not constant. It increases with the amount of damage but is otherwise independent of temperature. The implications of this result of radiation damage and dimensional change theory are discussed. 125. Defects in graphite crystals irradiated at high temperatures P. A. Thrower (The Pennsylvania State University, University Park, Pennsylvania). Single crystals of graphite irradiated at 1250-1300°C to a dose of 13.5-15.0 X 10%’n/cm” (E > 0.18 MeV) have been studied by electron microscopy. Defect structures have been found after annealing above 2000°C which are different from anything previously reported. It is hoped to elucidate these phenomena and relate them to the known dimensional changes of the crystals. 126. A simple model of the effect of interstitial atoms on the inter-layer properties of graphite B. T. Kelly (U.K.A.E.A. Reactor Fuel ~b~ato~es, S~n~e~d Works, Salwick, Nr. Preston, La~c~hire, U.K.). It has frequently been suggested that irradiation induced interstitial carbon atoms in graphite form co-valent bonds with adjacent basal planes. A simple model of the interlayer properties of a graphite crystal in the presence and absence of a uniform interstitial concentration is derived and compared with experimental data on surface energy, C,, and C&s-’ (&,,/ae,,). The results indicate that the interstitial atoms do not form such co-valent bonds. 127. Interpretation of high-temperature irradiation behavior in carbons and graphites G. B. Engle and J. C. Bokros (GudfGeneral Atomic Co., San Diego, Calijwnia). Model carbons and artificial graphites have been irradiated to fluences of up to 2 x 10z2n/cm* at 1200°C. For isotropic carbons there exists a temperature approximately 900 to lOOO”C,where the effects of mechanical interactions among crystallites are maximum. High density enhances the degree of interactions. The behavior of the carbons depends upon an internal stress factor which depends upon the interaction among crystallites, crystallite distortion rates, which continue to increase with temperature, and an irradiation-induced creep factor. The solid portions of artificial graphites behave in a manner similar to that of the carbons except their complex pore networks interact with the crystallite changes to alter their behavior in comparison with the carbons. 128. Electron irradiation damage in graphite S. M. Ohr and T. S. Noggle (Solid State Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee). Radiation damage in graphite at 300-600°C due to the electrons in the illuminating beam in a 200 kV electron microscope has been studied. Black and white spot structures are observed whose contrast behavior indicates they are due to the clustering of the displaced atoms into interstitial type dislocation loops. 129. Effect of high-temperature irradiation on thermal conductivity of artificial graphites K. Koyama and G. B. Engle (GulfGeneral Atomic Company, SanDiego, California). Thermal conductivity was measured on isotropic and anisotropic artificial graphite after irradiation to 7 x 102’ n/cm2 at 1000 and 1200°C. Irradiation induced annealing of lattice defects was dependent on fluence andn irradiation temperature. An activation energy of about 5.8 eV was estimated from the annealing of fractional changes of thermal conductivity on specimens irradiated at 1000°C to 7 X 102’ n/cm*. 130. High resolution microscopy of carbon and graphite M. D. Allen, W. H. Cook, B. C. Leslie and R. J. Gray (Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee). The ceramographic preparation of carbonaceous and graphitic materials is described. The advantages of using a diamond polishing compound are presented on the bases of economy and improved ceramographic preparation. The techniques for obtaining improved resolution of microstructural details without supporting the porous structures with impregnations of epoxy resins or other materials are given. The advantages of utilizing a rotatable, full-wave retardation plate for
ABSTRACTS
VI. RADIATION DAMAGE 144. The effect of dose rate on irradiation damage in graphite J. W. Harrison, R. W. Henson, A. J. Perks, and J. H. W. Simmons (Atomic Energy Research Establishment, Harwell, Didcot, Berkshire, U.K.). The changes in dimensions and lattice parameters produced by irradiation in two reactors with very different dose rate have been studied over the temperature range 400-700°C. In this range it is found that the activation energy associated with the equivalent temperature concept is not constant. It increases with the amount of damage but is otherwise independent of temperature. The implications of this result of radiation damage and dimensional change theory are discussed. 125. Defects in graphite crystals irradiated at high temperatures P. A. Thrower (The Pennsylvania State University, University Park, Pennsylvania). Single crystals of graphite irradiated at 1250-1300°C to a dose of 13.5-15.0 X 10%’n/cm” (E > 0.18 MeV) have been studied by electron microscopy. Defect structures have been found after annealing above 2000°C which are different from anything previously reported. It is hoped to elucidate these phenomena and relate them to the known dimensional changes of the crystals. 126. A simple model of the effect of interstitial atoms on the inter-layer properties of graphite B. T. Kelly (U.K.A.E.A. Reactor Fuel ~b~ato~es, S~n~e~d Works, Salwick, Nr. Preston, La~c~hire, U.K.). It has frequently been suggested that irradiation induced interstitial carbon atoms in graphite form co-valent bonds with adjacent basal planes. A simple model of the interlayer properties of a graphite crystal in the presence and absence of a uniform interstitial concentration is derived and compared with experimental data on surface energy, C,, and C&s-’ (&,,/ae,,). The results indicate that the interstitial atoms do not form such co-valent bonds. 127. Interpretation of high-temperature irradiation behavior in carbons and graphites G. B. Engle and J. C. Bokros (GudfGeneral Atomic Co., San Diego, Calijwnia). Model carbons and artificial graphites have been irradiated to fluences of up to 2 x 10z2n/cm* at 1200°C. For isotropic carbons there exists a temperature approximately 900 to lOOO”C,where the effects of mechanical interactions among crystallites are maximum. High density enhances the degree of interactions. The behavior of the carbons depends upon an internal stress factor which depends upon the interaction among crystallites, crystallite distortion rates, which continue to increase with temperature, and an irradiation-induced creep factor. The solid portions of artificial graphites behave in a manner similar to that of the carbons except their complex pore networks interact with the crystallite changes to alter their behavior in comparison with the carbons. 128. Electron irradiation damage in graphite S. M. Ohr and T. S. Noggle (Solid State Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee). Radiation damage in graphite at 300-600°C due to the electrons in the illuminating beam in a 200 kV electron microscope has been studied. Black and white spot structures are observed whose contrast behavior indicates they are due to the clustering of the displaced atoms into interstitial type dislocation loops. 129. Effect of high-temperature irradiation on thermal conductivity of artificial graphites K. Koyama and G. B. Engle (GulfGeneral Atomic Company, SanDiego, California). Thermal conductivity was measured on isotropic and anisotropic artificial graphite after irradiation to 7 x 102’ n/cm2 at 1000 and 1200°C. Irradiation induced annealing of lattice defects was dependent on fluence andn irradiation temperature. An activation energy of about 5.8 eV was estimated from the annealing of fractional changes of thermal conductivity on specimens irradiated at 1000°C to 7 X 102’ n/cm*. 130. High resolution microscopy of carbon and graphite M. D. Allen, W. H. Cook, B. C. Leslie and R. J. Gray (Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee). The ceramographic preparation of carbonaceous and graphitic materials is described. The advantages of using a diamond polishing compound are presented on the bases of economy and improved ceramographic preparation. The techniques for obtaining improved resolution of microstructural details without supporting the porous structures with impregnations of epoxy resins or other materials are given. The advantages of utilizing a rotatable, full-wave retardation plate for