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Low temperature anomalies in specific heat of soft carbons
544
Abstracts
magnetothermal oscillations have been observed in pyrolytic graphite. Four de-Haas van Alphen frequencies were detected. The results point towards a correlation between one of the minority frequencies and the difference of the two majority frequencies.
chamber with a focused continuous CO, laser beam. Temperature was measured by pyrometers with < O.Olset reaction time. A pressure range of 0~0016-6~0atm was covered, and the carbon solid-liquid-gas triple point was located at 3780 + 30°K at 0.19 + 0.02 atm.
12. Change of electronic properties of neutron irradiated pyrocarbon under thermal annealing A. S. Kotosonov (V/O “Soyuzuglerod,” Mowcow, 111123, U.S.S.R.). No short abstract submitted.
tThis work reflects research supported under U.S. Air Force Space and Missile Systems Organization (SAMSO) Contract No. FO4701-74-C-0075 and the Atomic Energy Commission.
13. Model of structure for interstitial carbon in graphite J. Conard and H. Estrade (C.R.S.O.C.I.-CNRS, 4.5045 Orleans, France). This paper discusses interstitial carbon grafted 1.2 A above the center of aromatic ring. For this point defect an electronic structure is proposed which uses overlap of sp,, px, py, orbitals of carbon and II electrons of aromatic ring. It is shown that graphitic situation increases stabilization. The carbon is negatively charged giving induced ionic bond with opposite aromatic plane. This model would explain creation of a varying gap, Hall anomaly and other properties of graphitizable carbons. 14. Association of nuclei during carbon black formationin thermal systems G. Prado and J. Lahaye (Center De Recherches SW La Physic0 -Chimie Des Surfaces Solides, Mulhouse, France). The liquid droplets, precursors of carbon black particles formed during thermal decomposition of benzene can collide and stick together. A computer simulation of these particle associations points out that they account well for the distortion of the size distribution curves during the particle growth step, as experimentally observed previously. 15. Behavior of diamond under positive ion bombardment and CO, laser irradiation at very high power densityt A. G. Whittaker (The Aerospace Corporation, El Segundo, CA). A brief experimental study was made of the transformation of diamond to graphite or chaoite by a 20-kV 02+ ion beam. Small slabs of diamond with (100) and (111) polished faces were used. Transformation to graphite appeared to depend mainly on crystal imperfections, but transformation to chaoite occurred only on the (111) face and depended upon the current density of the ion beam. Small craters in the (111) face produced by a CO, laser at very high power density were examined. It was found that graphite and chaoite were formed simultaneously.
17. Macroscopic model for the interlayer thermal expans-
ion of a series of pyrocarbons G. Fug, P. Delhaes and H. Gasparoux (Centre de Recherches Paul Pascal, 33405Talence , France). Thermal expansion of a series of pyrocarbon samples, heat treated at dierent H.T.T., has been measured between 20 and 2400 K. The theoretical analysis of these data, by the means of a macroscopic model adapted to non cristalline anisotropic solids behaviour, leads to the interpretation of some peculiar phenomena and to the prediction of specific heat of these pyrocarbon. 18. Triple point pressureof carbon as determinedby laser heatingt D. M. Haaland (Sandia Laboratories, Albuquerque, NM 87115). The triple point pressure of carbon has been accurately determined using a high pressure gas autoclave with Nd:YAG cw laser heating. The minimum melt pressure for samples of pyrolytic graphite in both helium and argon has been found to be 107 + 2 atmospheres. This minimum melt pressure has been identified as the triple point pressure of carbon. tThis work supported by the U.S. Energy Research and Development Administration. 19. Magnetic field dependenceof the specific heat peak at
0.6-OPK in soft carbonst A. S. Vagh and S. Mrozowski (State University New York at Bufalo and Ball State University, Muncie, IN). The dependence of the relatively broader specific heat peak in neutron irradiated graphite (5Ohr dose) and of the sharper one in the soft carbon (HTT 1250°C) on the magnetic field were investigated. In both cases the specific heat increases with the field in the whole range of temperature 0.4-4.5”K and the position of the peak shifts slightly to higher temperature. The reasons for this behavior is discussed. tSupported by the National Science Foundation.
20. Low temperature anomalies in specific heat of soft tThis work was supported by the U.S. Air Force Under Space carbons? and Missile Systems Organization Contract No. FO4701-74-C-0075. 16. Carbon solid-liquid-vapor triple point and the behav-
ior of superheatedliquid carbon? A. G. Whittaker and P. L. Kintner (The Aerospace Corporation, El Segundo, CA) and L. S. Nelson and N. Richardson (Sandia Laboratory, Albuquerque, NM). The total vapor pressure of carbon was determined by heating pyrolytic graphite in a controlled pressure
S. Mrozowski and A. S. Vagh (State University New York at Buffalo and Ball State University, Muncie, IN). With an improved apparatus the shape of the specific heat peak at around 060~7°K was investigated for two series of variously heattreated soft carbons (coal tar pitch base and petroleum base) and for polycrystalline graphite tSupported by the National Science Foundation.
Abstracts irradiated to various doses. The peak is a lambda-type phase transition of the antiferromagnetically interacting fraction of randomly distributed localized spins. The linear temperature term and its relation to this effect are also discussed.
neutron
21. Relation between thermal and electrical conductivities of fast neutron irradiated reactor graphite W. Van Witzenburg and H. J. Veringa (Reactor Centrum Nederland, Petten, The Netherlands). No short abstract submitted. 22. A second low temperaturepeak in the specificbeat of a soft carbon? A. S. Vagh and S. Mrozowski (NASA Lewis Research Center, Cleveland, OH and Ball State University, Muncie, IN). Using a dilution refrigerator, the specific heat measurements were extended down to O.OS’K.For a sample of soft carbon heattreated to 1250°Cin addition to the known first peak at 064”K, an even stronger but very similar in appearance second peak at 0*32”Kwas found. Work on other carbon samples is in preparation. (No long abstract submitted.) tSupported by the National Science Foundation. IU. CARBONIZATIONAND GRAPHITIZATION 23. Hot-stage microscopy of mesopbase pitches R. T. Lewis (Union Carbide Corporation, Parma, OH 44130). Hot-stage microscopy has been used to directly
observe the mesophase development in pitch at temperatures up to 450°C. Observations of melting behavior have been used to estimate the viscosities of the isotropic and the anisotropic phases in mesophase pitches. In some pitches, a portion of the mesophase present at a given temperature has been observed to dissolve in the isotropic phase at higher temperatures. 24. Binder materials modified by sulfur E. Fitzer and H. Tillmanns (Universitat Karlsruhe, W. Germany). The paper describes the effect of sulfur additions to coaltar binder pitch up to 33 wt% on the baking behaviour and the bulk properties of molded laboratory samples with pitch coke as filler. The results, which confirm the known effect on the increase of strength but show also a decrease of electrical resistivity are discussed in view of systematic and basic research on the pyrolysis chemistry with binder modified by added elemental sulfur. 25. Linear free energy relationships in carbon film deposition D. B. Murphy and R. W. Carroll (Herbert H. Lehman College (CLJNY), Bronx, NY 10468). The kinetics of carbon film deposition has been studied between 1063and 1373K. Two linear free energy relationships have been found, one for cyclic, and the second for straight-chain hydrocarbons (excluding methane). Within each series the reaction mechanism is similar and involves a slow step on the carbon surface.
545
26. Mechanismsof formation of needle coke J. L. White, G. Johnson and J. E. Zimmer (The Aerospace Corporation, P.O. Box 92957, Los Angeles, CA 90009). The mesophase microstructures formed in the
pyrolysis of a petroleum pitch and a decant oil were studied by polarized-light microscopy. Mesophase fibers were also drawn from partially transformed pitch. The observations show that the fine fibrous bands of needle coke result from plastic deformation as the mesophase hardens. 27. The structure of needle coke J. E. Zimmer and J. L. White (The Aerospace Corporation,
P.O. Box 92957,. Los Angeles, CA 9ooo9).
The microconstituent uniquely characteristic of needle coke acicular particles has been identified as the fine fibrous structure consisting of folded, corrugated arrays of graphitic layers which are straight and parallel along the particle axis. These fine fibrous bands comprise only a moderate fraction of typical delayed needle coke. 28. Hydrogendesorption:a possible rate determining step in pyrocarbonformation J. Hill and K. R. Norman (AWRE, MOD(PE), Aldermaston, Berks, UK). Pyrocarbon has been deposited from methane onto a resistively heated carbon string with a large surface area. The effect of methane pressure on the initial deposition rate is consistent with hydrogen desorption being rate controlling. The whole deposition process could be described by linear weight gain vs log (time) plots. 29. Factors controlling the mesophase microstructure produced during pyrolysis of aromatic hydrocarbons D. 0. Rester (Naval Surface Weapons Center, Silver Spring, MD 20910). Mesophase formation in hydrocarbons has been studied using test tube pyrolysis methods and hot stage microscopy. Direct observation of mesophase formation and growth during pyrolysis revealed that gas bubble percolation produces coalescence and deformation of mesophase droplets. These results will be discussed in relation to needle coke production. 30. Formationand structureof coke from non-cokingcoals by carbonization in hydrogen B. N. Nandi, M. Ternan, B. I. Parsons and D. S. Montgomery (Canada Centre for Mineral & Energy Technology, Ottawa, Canada). The coking properties can be restored to non-coking coals of all ranks by partial hydrogenation at appropriate temperatures and pressures. Sufficient fluidity was developed by this process to form an agglomerated coke. Microscopic examination reveals the formation of coarse and grain mosaic structure in the cokes. Infrared analyses suggests that the opening of the oxygen ether linkages produced the development of the coking properties. 31. Inhomogeneousmodel for carbonization F. Carmona and P. Delhaes (Centre de Recherches Paul Pascal, 33405talence, France). An inhomogeneous model for the “semi-conductor-to-metal” transition in
Abstracts
magnetothermal oscillations have been observed in pyrolytic graphite. Four de-Haas van Alphen frequencies were detected. The results point towards a correlation between one of the minority frequencies and the difference of the two majority frequencies.
chamber with a focused continuous CO, laser beam. Temperature was measured by pyrometers with < O.Olset reaction time. A pressure range of 0~0016-6~0atm was covered, and the carbon solid-liquid-gas triple point was located at 3780 + 30°K at 0.19 + 0.02 atm.
12. Change of electronic properties of neutron irradiated pyrocarbon under thermal annealing A. S. Kotosonov (V/O “Soyuzuglerod,” Mowcow, 111123, U.S.S.R.). No short abstract submitted.
tThis work reflects research supported under U.S. Air Force Space and Missile Systems Organization (SAMSO) Contract No. FO4701-74-C-0075 and the Atomic Energy Commission.
13. Model of structure for interstitial carbon in graphite J. Conard and H. Estrade (C.R.S.O.C.I.-CNRS, 4.5045 Orleans, France). This paper discusses interstitial carbon grafted 1.2 A above the center of aromatic ring. For this point defect an electronic structure is proposed which uses overlap of sp,, px, py, orbitals of carbon and II electrons of aromatic ring. It is shown that graphitic situation increases stabilization. The carbon is negatively charged giving induced ionic bond with opposite aromatic plane. This model would explain creation of a varying gap, Hall anomaly and other properties of graphitizable carbons. 14. Association of nuclei during carbon black formationin thermal systems G. Prado and J. Lahaye (Center De Recherches SW La Physic0 -Chimie Des Surfaces Solides, Mulhouse, France). The liquid droplets, precursors of carbon black particles formed during thermal decomposition of benzene can collide and stick together. A computer simulation of these particle associations points out that they account well for the distortion of the size distribution curves during the particle growth step, as experimentally observed previously. 15. Behavior of diamond under positive ion bombardment and CO, laser irradiation at very high power densityt A. G. Whittaker (The Aerospace Corporation, El Segundo, CA). A brief experimental study was made of the transformation of diamond to graphite or chaoite by a 20-kV 02+ ion beam. Small slabs of diamond with (100) and (111) polished faces were used. Transformation to graphite appeared to depend mainly on crystal imperfections, but transformation to chaoite occurred only on the (111) face and depended upon the current density of the ion beam. Small craters in the (111) face produced by a CO, laser at very high power density were examined. It was found that graphite and chaoite were formed simultaneously.
17. Macroscopic model for the interlayer thermal expans-
ion of a series of pyrocarbons G. Fug, P. Delhaes and H. Gasparoux (Centre de Recherches Paul Pascal, 33405Talence , France). Thermal expansion of a series of pyrocarbon samples, heat treated at dierent H.T.T., has been measured between 20 and 2400 K. The theoretical analysis of these data, by the means of a macroscopic model adapted to non cristalline anisotropic solids behaviour, leads to the interpretation of some peculiar phenomena and to the prediction of specific heat of these pyrocarbon. 18. Triple point pressureof carbon as determinedby laser heatingt D. M. Haaland (Sandia Laboratories, Albuquerque, NM 87115). The triple point pressure of carbon has been accurately determined using a high pressure gas autoclave with Nd:YAG cw laser heating. The minimum melt pressure for samples of pyrolytic graphite in both helium and argon has been found to be 107 + 2 atmospheres. This minimum melt pressure has been identified as the triple point pressure of carbon. tThis work supported by the U.S. Energy Research and Development Administration. 19. Magnetic field dependenceof the specific heat peak at
0.6-OPK in soft carbonst A. S. Vagh and S. Mrozowski (State University New York at Bufalo and Ball State University, Muncie, IN). The dependence of the relatively broader specific heat peak in neutron irradiated graphite (5Ohr dose) and of the sharper one in the soft carbon (HTT 1250°C) on the magnetic field were investigated. In both cases the specific heat increases with the field in the whole range of temperature 0.4-4.5”K and the position of the peak shifts slightly to higher temperature. The reasons for this behavior is discussed. tSupported by the National Science Foundation.
20. Low temperature anomalies in specific heat of soft tThis work was supported by the U.S. Air Force Under Space carbons? and Missile Systems Organization Contract No. FO4701-74-C-0075. 16. Carbon solid-liquid-vapor triple point and the behav-
ior of superheatedliquid carbon? A. G. Whittaker and P. L. Kintner (The Aerospace Corporation, El Segundo, CA) and L. S. Nelson and N. Richardson (Sandia Laboratory, Albuquerque, NM). The total vapor pressure of carbon was determined by heating pyrolytic graphite in a controlled pressure
S. Mrozowski and A. S. Vagh (State University New York at Buffalo and Ball State University, Muncie, IN). With an improved apparatus the shape of the specific heat peak at around 060~7°K was investigated for two series of variously heattreated soft carbons (coal tar pitch base and petroleum base) and for polycrystalline graphite tSupported by the National Science Foundation.
Abstracts irradiated to various doses. The peak is a lambda-type phase transition of the antiferromagnetically interacting fraction of randomly distributed localized spins. The linear temperature term and its relation to this effect are also discussed.
neutron
21. Relation between thermal and electrical conductivities of fast neutron irradiated reactor graphite W. Van Witzenburg and H. J. Veringa (Reactor Centrum Nederland, Petten, The Netherlands). No short abstract submitted. 22. A second low temperaturepeak in the specificbeat of a soft carbon? A. S. Vagh and S. Mrozowski (NASA Lewis Research Center, Cleveland, OH and Ball State University, Muncie, IN). Using a dilution refrigerator, the specific heat measurements were extended down to O.OS’K.For a sample of soft carbon heattreated to 1250°Cin addition to the known first peak at 064”K, an even stronger but very similar in appearance second peak at 0*32”Kwas found. Work on other carbon samples is in preparation. (No long abstract submitted.) tSupported by the National Science Foundation. IU. CARBONIZATIONAND GRAPHITIZATION 23. Hot-stage microscopy of mesopbase pitches R. T. Lewis (Union Carbide Corporation, Parma, OH 44130). Hot-stage microscopy has been used to directly
observe the mesophase development in pitch at temperatures up to 450°C. Observations of melting behavior have been used to estimate the viscosities of the isotropic and the anisotropic phases in mesophase pitches. In some pitches, a portion of the mesophase present at a given temperature has been observed to dissolve in the isotropic phase at higher temperatures. 24. Binder materials modified by sulfur E. Fitzer and H. Tillmanns (Universitat Karlsruhe, W. Germany). The paper describes the effect of sulfur additions to coaltar binder pitch up to 33 wt% on the baking behaviour and the bulk properties of molded laboratory samples with pitch coke as filler. The results, which confirm the known effect on the increase of strength but show also a decrease of electrical resistivity are discussed in view of systematic and basic research on the pyrolysis chemistry with binder modified by added elemental sulfur. 25. Linear free energy relationships in carbon film deposition D. B. Murphy and R. W. Carroll (Herbert H. Lehman College (CLJNY), Bronx, NY 10468). The kinetics of carbon film deposition has been studied between 1063and 1373K. Two linear free energy relationships have been found, one for cyclic, and the second for straight-chain hydrocarbons (excluding methane). Within each series the reaction mechanism is similar and involves a slow step on the carbon surface.
545
26. Mechanismsof formation of needle coke J. L. White, G. Johnson and J. E. Zimmer (The Aerospace Corporation, P.O. Box 92957, Los Angeles, CA 90009). The mesophase microstructures formed in the
pyrolysis of a petroleum pitch and a decant oil were studied by polarized-light microscopy. Mesophase fibers were also drawn from partially transformed pitch. The observations show that the fine fibrous bands of needle coke result from plastic deformation as the mesophase hardens. 27. The structure of needle coke J. E. Zimmer and J. L. White (The Aerospace Corporation,
P.O. Box 92957,. Los Angeles, CA 9ooo9).
The microconstituent uniquely characteristic of needle coke acicular particles has been identified as the fine fibrous structure consisting of folded, corrugated arrays of graphitic layers which are straight and parallel along the particle axis. These fine fibrous bands comprise only a moderate fraction of typical delayed needle coke. 28. Hydrogendesorption:a possible rate determining step in pyrocarbonformation J. Hill and K. R. Norman (AWRE, MOD(PE), Aldermaston, Berks, UK). Pyrocarbon has been deposited from methane onto a resistively heated carbon string with a large surface area. The effect of methane pressure on the initial deposition rate is consistent with hydrogen desorption being rate controlling. The whole deposition process could be described by linear weight gain vs log (time) plots. 29. Factors controlling the mesophase microstructure produced during pyrolysis of aromatic hydrocarbons D. 0. Rester (Naval Surface Weapons Center, Silver Spring, MD 20910). Mesophase formation in hydrocarbons has been studied using test tube pyrolysis methods and hot stage microscopy. Direct observation of mesophase formation and growth during pyrolysis revealed that gas bubble percolation produces coalescence and deformation of mesophase droplets. These results will be discussed in relation to needle coke production. 30. Formationand structureof coke from non-cokingcoals by carbonization in hydrogen B. N. Nandi, M. Ternan, B. I. Parsons and D. S. Montgomery (Canada Centre for Mineral & Energy Technology, Ottawa, Canada). The coking properties can be restored to non-coking coals of all ranks by partial hydrogenation at appropriate temperatures and pressures. Sufficient fluidity was developed by this process to form an agglomerated coke. Microscopic examination reveals the formation of coarse and grain mosaic structure in the cokes. Infrared analyses suggests that the opening of the oxygen ether linkages produced the development of the coking properties. 31. Inhomogeneousmodel for carbonization F. Carmona and P. Delhaes (Centre de Recherches Paul Pascal, 33405talence, France). An inhomogeneous model for the “semi-conductor-to-metal” transition in