- Email: [email protected]
62. Effects of deposition conditions and heat treatment on the properties of pyrolytic carbon
342
CARBON
ki
k3
CSO~+MG$C~O+CO+M and CzO+C(S)+CO, kz and permit determination of the activation energy (22 kcal) for step 2. Together with the activation energy (52 kcal) for step 1, one obtains 32 kcal as the heat of dissociation of the C-C bond in CsOz at 1000°K. This figure, which at first seems surprisingly low, leads to a reasonable value (f51 kcal) for the heat of formation of CzO, if one accepts -8 kcal as the heat of formation of CsOz. The resonance energy of CzO (23 kcal) is consistent with the resonance energies of COa (25 kcal) and Cs (31 kcal), all calculated relative to simple double-bonded structures. ‘Work supported by the U.S. Atomic Energy Commission under Contract AT(30-l)-1710. 1. T. J. HIRT and H. B. PALMER, Carbon 1, 65 (1963).
62. Effects of deposition conditions and heat treatment on the properties of pyrolytic carbon* Ji Young Chang,? E. E. Stansburyf and W. 0. Harms (Oak Ridge National Labo~uto~y, Oak Ridge, Tennessee). The purpose of this study was to determine the effects of deposition conditions and heat treatment on the properties of pyrolytic carbon deposited from methane. Deposits up to 1 mm thick were formed on resistance heated graphite substrates over the temperature range 1400 to 2400°C and at deposition rates ranging from 3.2 to 2810 p/hr. Material deposited at 2200°C was heat treated at 2620°C for periods up to 6 hr. The deposits were characterized by microstructure studies, X-ray diffraction analysis (including preferred orientation), and measurements of density and diamagnetic susceptibility. The average density of the columnar deposits increased with deposition temperature from 1.23 g/cm3 at 1400°C to 2.09 g/cm3 at 2400°C. The interlayer spacing decreased from 3.423 to 3.370 A over this temperature range while the crystallite size increased from 100 to 245 A. Values for the specimen heat treated for 6 hr were 3.369 and 220 A, respectively. Anisotropy factors determined by X-ray diffraction increased from 2.0 to 14.6 over the deposition-temperature range 1600 to 2400°C and the specimen heat treated for 160 min gave a value of 24.3. Anisotropy factors determined directly from diamagnetic susceptibility measurements showed a similar trend but were lower by 4 to 10%. These results were analyzed in terms of the degree of perfection of the crystallites in the specimens examined. -*Research sponsored by the U.S. Atomic Energy Commission under contract with the Union Carbide Corporation. tTemporarily assigned at ORNL under an IAEA Fellowship. IConsultant to ORNL from the University of Tennessee.
63. Formation of pyrolytic graphite
R. J. Diefendorf (General Electric Company, Research Laboratory, Schenectady, New York). The rate at which p.g. is deposited is determined partly by the kinetics of the chemical reactions on the substrate, partly by the rate of transport of reactant gas to the substrate surface, and partly by the reactions on the gas phase at points remote from the gas substrate interface. The realm of importance of these reactions can be deduced from the important process variables and their effect on the structure and deposition rate of the deposit. The purpose of this investigation has been to determine the effect of temperature, pressure and flow rate on the structure and deposition rate of carbon at essentially constant geometry, and to suggest a mechanism for the process which will explain the observed effects of time, temperature, flow rates, gas pressure and gas composition on the structure and deposition rate. 64. On the kinetics of graphitization* D. B. Fischbach (Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CuZiforniu). An investigation has been made of the kinetics of layer ordering in both pyrolytic and conventional carbons. In all cases graphitization was found to be a thermally activated process. The behavior of most pyrolytics studied could be represented by a sequence of single first order rate processes in the heat treatment range 2400-3000°C. Layer ordering appeared to be closely related to the apparent crystallite
CARBON
ki
k3
CSO~+MG$C~O+CO+M and CzO+C(S)+CO, kz and permit determination of the activation energy (22 kcal) for step 2. Together with the activation energy (52 kcal) for step 1, one obtains 32 kcal as the heat of dissociation of the C-C bond in CsOz at 1000°K. This figure, which at first seems surprisingly low, leads to a reasonable value (f51 kcal) for the heat of formation of CzO, if one accepts -8 kcal as the heat of formation of CsOz. The resonance energy of CzO (23 kcal) is consistent with the resonance energies of COa (25 kcal) and Cs (31 kcal), all calculated relative to simple double-bonded structures. ‘Work supported by the U.S. Atomic Energy Commission under Contract AT(30-l)-1710. 1. T. J. HIRT and H. B. PALMER, Carbon 1, 65 (1963).
62. Effects of deposition conditions and heat treatment on the properties of pyrolytic carbon* Ji Young Chang,? E. E. Stansburyf and W. 0. Harms (Oak Ridge National Labo~uto~y, Oak Ridge, Tennessee). The purpose of this study was to determine the effects of deposition conditions and heat treatment on the properties of pyrolytic carbon deposited from methane. Deposits up to 1 mm thick were formed on resistance heated graphite substrates over the temperature range 1400 to 2400°C and at deposition rates ranging from 3.2 to 2810 p/hr. Material deposited at 2200°C was heat treated at 2620°C for periods up to 6 hr. The deposits were characterized by microstructure studies, X-ray diffraction analysis (including preferred orientation), and measurements of density and diamagnetic susceptibility. The average density of the columnar deposits increased with deposition temperature from 1.23 g/cm3 at 1400°C to 2.09 g/cm3 at 2400°C. The interlayer spacing decreased from 3.423 to 3.370 A over this temperature range while the crystallite size increased from 100 to 245 A. Values for the specimen heat treated for 6 hr were 3.369 and 220 A, respectively. Anisotropy factors determined by X-ray diffraction increased from 2.0 to 14.6 over the deposition-temperature range 1600 to 2400°C and the specimen heat treated for 160 min gave a value of 24.3. Anisotropy factors determined directly from diamagnetic susceptibility measurements showed a similar trend but were lower by 4 to 10%. These results were analyzed in terms of the degree of perfection of the crystallites in the specimens examined. -*Research sponsored by the U.S. Atomic Energy Commission under contract with the Union Carbide Corporation. tTemporarily assigned at ORNL under an IAEA Fellowship. IConsultant to ORNL from the University of Tennessee.
63. Formation of pyrolytic graphite
R. J. Diefendorf (General Electric Company, Research Laboratory, Schenectady, New York). The rate at which p.g. is deposited is determined partly by the kinetics of the chemical reactions on the substrate, partly by the rate of transport of reactant gas to the substrate surface, and partly by the reactions on the gas phase at points remote from the gas substrate interface. The realm of importance of these reactions can be deduced from the important process variables and their effect on the structure and deposition rate of the deposit. The purpose of this investigation has been to determine the effect of temperature, pressure and flow rate on the structure and deposition rate of carbon at essentially constant geometry, and to suggest a mechanism for the process which will explain the observed effects of time, temperature, flow rates, gas pressure and gas composition on the structure and deposition rate. 64. On the kinetics of graphitization* D. B. Fischbach (Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CuZiforniu). An investigation has been made of the kinetics of layer ordering in both pyrolytic and conventional carbons. In all cases graphitization was found to be a thermally activated process. The behavior of most pyrolytics studied could be represented by a sequence of single first order rate processes in the heat treatment range 2400-3000°C. Layer ordering appeared to be closely related to the apparent crystallite