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59. Reactivity of carbon: some current problems and future trends (Charles Pettinos Award Lecture).
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CARBON
58. Adsorption of polar gases by carbon- interpretationby the Dubinin equation E. M. Freeman, T. Siemieniewska and M. Marsh (Northern Coke Research Laboratories, School of Chemistry, The University of Newcastle upon Tyne, Newcastle upon Tyne, NEI 7RU, U.K.). It is considered that one requirement (among others) for the Dubinin equation to linearise adsorption isotherms of carbons is the forces of adsorption should be essentially non-polar, Van der Waals forces. To test this assumption molecules with permanent dipoles, e.g. NH3 and H2S have been adsorbed on selected carbons. Although linear Dubinin plots can be obtained, the temperature dependence is without meaning and the Dubinin equation cannot be used to predict micropore volume. IV. REACTIVITY STUDIES 59. Reactivity of carbon: some current problems and future trends (Cbarles Pettinos Award Lecture). J. M. Thomas (Department of Chemistry, University College ofNorth Wales, Bangor, Caemturvonshire, U.K.) 60. Low pressure reaction of sulfur dioxide with grapbon* W. C. Rovesti, F. J. Vastola and P. L. Walker, Jr. (The Pennsylvania State University, Materials Science Department, University Park, Pennsylvania). Various aspects of the mechanism of the carbon-sulfur dioxide reaction have been studied at pressures below 50 millitorr and temperatures between 500” and 600°C. The differing reactivities of the surface complexes and the participation of these complexes in the over-all reaction shall be discussed. The use of isotopic tracers in the understanding of the surface reactions shall be emphasized. *Supported by U.S. Public Health Service Grant AP-00406 and U.S. Public Health Service Fellowship 1 F3 AP 33,951-01 from the Division of Air Pollution. 61. Effect of temperature, pressure, gas-composition, particle size and the nature of carbon on the rate of oxidation of carbons in C02-CO gas mixtures E. T. Turkdogan (Research Center, U.S. Steel Corporation, Monroeville, Pennsylvania). The rates of oxidation of coconut charcoal, electrode graphite and metallurgical coke granules in C02-CO gas mixtures at various pressures were measured within the range of 700”-1400°C. The experimental results (for the case of almost complete pore diffusion) can be interpreted reasonably well in terms of a reaction mechanism involving the formation of an activated complex (&O,)+ from carbon, adsorbed oxygen and carbon monoxide. Retardation of the rate of oxidation by carbon monoxide is attributable to the strong chemisorption of carbon monoxide on the pore surface of carbon. The characteristics of the pore structure of various types of carbon are investigated by measuring nitrogen adsorption at 195% the pore size distribution using a mercury porosimeter and interdiffusivity of C02-CO and H20-H at temperatures from 25” to 900°C. Indications are that much of the internal surfaces in charcoal and coke are due to micropores. Using the kinetic data for the oxidation of fine granules and the diffusivity data, a mathematical formulation is given for the oxidation of large coke particles where the rate is controlled both by pore-diffusion and pore-surface reaction. The rates thus computed for large coke particles are found to be in reasonable accord with those measured. 62. Microstructural changes in nuclear graphites produced by gas-gaphite reactions S. S. Jones (Battelle Northwest, Battelle Memorial Institute, Pacific Northwest Laboratory, Richland, Washington). An exploratory investigation has been made of the changes in structure of typical nuclear graphites produced by gas-graphite reactions. Graphite gasification has been accomplished by reaction with several gases including oxygen, carbon dioxide, and water vapor. The reactions have been initiated both thermally, at temperatures up to 6OOO”C,and by electronic excitation of the gas phase. A variety of microstructural changes have been observed and interpreted. 63. Factors which influence the product ratio of the graphon-oxygen reaction* R. Phillips, F. J. Vastola and P. L. Walker, Jr. (The Pennsylvania State University, Materials Science Department, University Park, Pennsylvania). A static, low pressure reactor, connected to a mass spectrometer, has been used to study the effects of degree of burn-off (O-25%), reaction temperature (525”675°C) and initial oxygen pressure (lo-200 millitorr) on the product ratio of the Graphon-oxygen reaction. *Supported
by the Atomic Energy Commission on Contract No. AT(30-l)-1710.
CARBON
58. Adsorption of polar gases by carbon- interpretationby the Dubinin equation E. M. Freeman, T. Siemieniewska and M. Marsh (Northern Coke Research Laboratories, School of Chemistry, The University of Newcastle upon Tyne, Newcastle upon Tyne, NEI 7RU, U.K.). It is considered that one requirement (among others) for the Dubinin equation to linearise adsorption isotherms of carbons is the forces of adsorption should be essentially non-polar, Van der Waals forces. To test this assumption molecules with permanent dipoles, e.g. NH3 and H2S have been adsorbed on selected carbons. Although linear Dubinin plots can be obtained, the temperature dependence is without meaning and the Dubinin equation cannot be used to predict micropore volume. IV. REACTIVITY STUDIES 59. Reactivity of carbon: some current problems and future trends (Cbarles Pettinos Award Lecture). J. M. Thomas (Department of Chemistry, University College ofNorth Wales, Bangor, Caemturvonshire, U.K.) 60. Low pressure reaction of sulfur dioxide with grapbon* W. C. Rovesti, F. J. Vastola and P. L. Walker, Jr. (The Pennsylvania State University, Materials Science Department, University Park, Pennsylvania). Various aspects of the mechanism of the carbon-sulfur dioxide reaction have been studied at pressures below 50 millitorr and temperatures between 500” and 600°C. The differing reactivities of the surface complexes and the participation of these complexes in the over-all reaction shall be discussed. The use of isotopic tracers in the understanding of the surface reactions shall be emphasized. *Supported by U.S. Public Health Service Grant AP-00406 and U.S. Public Health Service Fellowship 1 F3 AP 33,951-01 from the Division of Air Pollution. 61. Effect of temperature, pressure, gas-composition, particle size and the nature of carbon on the rate of oxidation of carbons in C02-CO gas mixtures E. T. Turkdogan (Research Center, U.S. Steel Corporation, Monroeville, Pennsylvania). The rates of oxidation of coconut charcoal, electrode graphite and metallurgical coke granules in C02-CO gas mixtures at various pressures were measured within the range of 700”-1400°C. The experimental results (for the case of almost complete pore diffusion) can be interpreted reasonably well in terms of a reaction mechanism involving the formation of an activated complex (&O,)+ from carbon, adsorbed oxygen and carbon monoxide. Retardation of the rate of oxidation by carbon monoxide is attributable to the strong chemisorption of carbon monoxide on the pore surface of carbon. The characteristics of the pore structure of various types of carbon are investigated by measuring nitrogen adsorption at 195% the pore size distribution using a mercury porosimeter and interdiffusivity of C02-CO and H20-H at temperatures from 25” to 900°C. Indications are that much of the internal surfaces in charcoal and coke are due to micropores. Using the kinetic data for the oxidation of fine granules and the diffusivity data, a mathematical formulation is given for the oxidation of large coke particles where the rate is controlled both by pore-diffusion and pore-surface reaction. The rates thus computed for large coke particles are found to be in reasonable accord with those measured. 62. Microstructural changes in nuclear graphites produced by gas-gaphite reactions S. S. Jones (Battelle Northwest, Battelle Memorial Institute, Pacific Northwest Laboratory, Richland, Washington). An exploratory investigation has been made of the changes in structure of typical nuclear graphites produced by gas-graphite reactions. Graphite gasification has been accomplished by reaction with several gases including oxygen, carbon dioxide, and water vapor. The reactions have been initiated both thermally, at temperatures up to 6OOO”C,and by electronic excitation of the gas phase. A variety of microstructural changes have been observed and interpreted. 63. Factors which influence the product ratio of the graphon-oxygen reaction* R. Phillips, F. J. Vastola and P. L. Walker, Jr. (The Pennsylvania State University, Materials Science Department, University Park, Pennsylvania). A static, low pressure reactor, connected to a mass spectrometer, has been used to study the effects of degree of burn-off (O-25%), reaction temperature (525”675°C) and initial oxygen pressure (lo-200 millitorr) on the product ratio of the Graphon-oxygen reaction. *Supported
by the Atomic Energy Commission on Contract No. AT(30-l)-1710.