- Email: [email protected]
75. Thermal expansivity and thermal diffusivity of silicon-alloyed pyrocarbons
680
ABSTRACTS
using experimental values for the anharmonic coefficients (a&,/de,,) and (aC,,/ae,,) and allowing the coefficient (as/de,) where 6 is the bond bending coefficient to vary. The value of (as/se,,) must lie in the range 0.00 to-O.50 X 10m3cm2/sec in order to fit experiment. 75. Thermal expansivity and thermal diffusivity of silicon-alloyed pyrocarbons R. J. Price and K. Koyama (Gulf General Atomic Company, San Diego, California). Measurements were made of the thermal expansivity and thermal diffusivity of isotropic fluidized-bed pyrocarbons containing up to 34 wt per cent silicon. The thermal expansivities decreased with increasing silicon content and agreed with the expected values for silicon carbide-polycarbon composites. The thermal conductivities of the silicon-alloyed carbons were consistently lower than those of pure polycarbons with similar apparent crystallite heights &). 76. The interstitial mechanism of diffusion R. M. Mayer (Atomic Energy Board, Private Bag256X, Pretoria, South Africa) and P. A. Thrower (Pennsylvania State University, University Park, Pennsylvania). The interstitialcy mechanism of diffusion is examined for the case of self diffusion in graphite and is found to fit the available experimental data. A critical review of the investigations concerning the migration energy of an interstitial within the basal plane leads to the conclusion that this energy is less than 0.10 eV and could be as small as 092 eV. 77. Diffusion of uranium and thorium in pyrocarbon P. Koss (Ins&it fiir Metallurgic, Forschungszentrum Seibersdorf, &tew. Studiengesellschaft fur Atomenergie Ges.m.b.H., 1082 Wien, Lenaugasse 10, Austria); E. Balthesen (Projekt HTRB, Kernforschungsanlage Jiilich, 5170 Jiilich I, W. Germany) and H. Nickel (Znstitiitfur Reaktorwerkstoffe, Kernforschungsanlage Jiilich, 5170 Jiilich 1, W. Germany). A systematic survey of the structure dependence of uranium and thorium diffusion in pyrocarbon was performed. Crystallite size, anisotropy, density and the hydrocarbon used have shown to be controlling parameters for the chemical potential and the diffusion coefficients. A dependence on the source of the diffusing element e.g. oxide or carbide was observed. 78. Pulsed laser induced vaporization of graphite and carbides* R. T. Meyer (San&a Laboratories, High Temperature Sciences Division 5324, Albuquerque, New Mexico). The vapor compositions for graphite and for metal carbides, heated by a normal-mode pulsed laser, have been studied by time resolved mass spectrometry for the purpose of comparison with the equilibrium vapor compositions. C3 is the dominant carbon vapor species for Tic, VC, ZrC, WC, Sic and B&, whereas C1 is the dominant species for HfC and TaC. For Tic, VC and WC, the metal is also a dominant vapor species, indicating that the metal may be preferentially vaporized. Preferential vaporization of the metal produces a carbon-rich condensed phase and yields a carbon vapor composition similar to that for pure carbon. However, the activity of carbon in HfC and TaC appears to be less than unity. The vapor species UC3 and UC, are newly identified from UC2.2 and are present in the vapor along with U, UC*, and UC,. The vapor pressures from NbC and MO& appear to be significantly less (10-100X) than from the other carbides. The vaporization characteristics from the carbides heated with a Q-switched laser have also been examined. *This work supported by the US Atomic Energy Commission. 79. Measurement of carbon vapor pressure and formation of liquid carbon at low pressure by laser heating* A. G. Whittaker (The Aerospace Corporation, El Segundo, California) and L. S. Nelson (Sandia Corporation, Albuquerque, New Mexico). Carbon vapor pressure was measured at - 4000°K; the data were essentially parallel to the December, 1969, JANAF values, but were - 110°C higher at 760 Torr. These results also indicate that the solid-liquid-gas triple point cannot be at - 100 atm and 4200°K. Evidence of liquid carbon was found at 190 Torr. ‘“This work reflects research supported Contact FO4701-72-C-0073.
under U.S. Air Force Space and Missile Systems Organization
(SAMSO)
ABSTRACTS
using experimental values for the anharmonic coefficients (a&,/de,,) and (aC,,/ae,,) and allowing the coefficient (as/de,) where 6 is the bond bending coefficient to vary. The value of (as/se,,) must lie in the range 0.00 to-O.50 X 10m3cm2/sec in order to fit experiment. 75. Thermal expansivity and thermal diffusivity of silicon-alloyed pyrocarbons R. J. Price and K. Koyama (Gulf General Atomic Company, San Diego, California). Measurements were made of the thermal expansivity and thermal diffusivity of isotropic fluidized-bed pyrocarbons containing up to 34 wt per cent silicon. The thermal expansivities decreased with increasing silicon content and agreed with the expected values for silicon carbide-polycarbon composites. The thermal conductivities of the silicon-alloyed carbons were consistently lower than those of pure polycarbons with similar apparent crystallite heights &). 76. The interstitial mechanism of diffusion R. M. Mayer (Atomic Energy Board, Private Bag256X, Pretoria, South Africa) and P. A. Thrower (Pennsylvania State University, University Park, Pennsylvania). The interstitialcy mechanism of diffusion is examined for the case of self diffusion in graphite and is found to fit the available experimental data. A critical review of the investigations concerning the migration energy of an interstitial within the basal plane leads to the conclusion that this energy is less than 0.10 eV and could be as small as 092 eV. 77. Diffusion of uranium and thorium in pyrocarbon P. Koss (Ins&it fiir Metallurgic, Forschungszentrum Seibersdorf, &tew. Studiengesellschaft fur Atomenergie Ges.m.b.H., 1082 Wien, Lenaugasse 10, Austria); E. Balthesen (Projekt HTRB, Kernforschungsanlage Jiilich, 5170 Jiilich I, W. Germany) and H. Nickel (Znstitiitfur Reaktorwerkstoffe, Kernforschungsanlage Jiilich, 5170 Jiilich 1, W. Germany). A systematic survey of the structure dependence of uranium and thorium diffusion in pyrocarbon was performed. Crystallite size, anisotropy, density and the hydrocarbon used have shown to be controlling parameters for the chemical potential and the diffusion coefficients. A dependence on the source of the diffusing element e.g. oxide or carbide was observed. 78. Pulsed laser induced vaporization of graphite and carbides* R. T. Meyer (San&a Laboratories, High Temperature Sciences Division 5324, Albuquerque, New Mexico). The vapor compositions for graphite and for metal carbides, heated by a normal-mode pulsed laser, have been studied by time resolved mass spectrometry for the purpose of comparison with the equilibrium vapor compositions. C3 is the dominant carbon vapor species for Tic, VC, ZrC, WC, Sic and B&, whereas C1 is the dominant species for HfC and TaC. For Tic, VC and WC, the metal is also a dominant vapor species, indicating that the metal may be preferentially vaporized. Preferential vaporization of the metal produces a carbon-rich condensed phase and yields a carbon vapor composition similar to that for pure carbon. However, the activity of carbon in HfC and TaC appears to be less than unity. The vapor species UC3 and UC, are newly identified from UC2.2 and are present in the vapor along with U, UC*, and UC,. The vapor pressures from NbC and MO& appear to be significantly less (10-100X) than from the other carbides. The vaporization characteristics from the carbides heated with a Q-switched laser have also been examined. *This work supported by the US Atomic Energy Commission. 79. Measurement of carbon vapor pressure and formation of liquid carbon at low pressure by laser heating* A. G. Whittaker (The Aerospace Corporation, El Segundo, California) and L. S. Nelson (Sandia Corporation, Albuquerque, New Mexico). Carbon vapor pressure was measured at - 4000°K; the data were essentially parallel to the December, 1969, JANAF values, but were - 110°C higher at 760 Torr. These results also indicate that the solid-liquid-gas triple point cannot be at - 100 atm and 4200°K. Evidence of liquid carbon was found at 190 Torr. ‘“This work reflects research supported Contact FO4701-72-C-0073.
under U.S. Air Force Space and Missile Systems Organization
(SAMSO)