- Email: [email protected]
65. Catalysis of the oxidation of graphite in the temperature range 1000°-2000°C
ABSTRACTS
719
64. The anisotropic reaction of oxygen with pyrolytic graphite W. S. Horton (Institutefor Materials Research, National Bureau of Standards, Washington, DC.). Although several authors have found anisotropy of the chemical reactivity of pyrolytic graphite they disagree regarding the existence of a temperature coefficient. New data are presented which together with earlier data show the rate ratio for the two major directions is temperature dependent with an activation energy difference of about 19 kilojoules (4500 thermochemical calories) per gram atom of carbon reacted. This probably arises because the relative number of sites is sufficiently different to cause a shift in which reaction step is rate-controlling. On the ‘faces’ chemisorption is slow followed by rapid decomposition of surface oxides. On the ‘edges’ chemisorption is rapid followed by decomposition. 65. Catalysis of the oxidation of graphite in the temperature range 1000”-fOOO°C J. R. Egerton and R. F. Strickland-Constable (Department of Chemical Engineering and Chemical Technology, Imperial College, London, U.K.). A study has been made of the catalytic effect of substances applied to the surface of graphite filaments in the temperature range 900”-2000°C on the rate of oxidation with oxygen and also with nitrous oxide. Strong catalysis was observed with some metals, but boron and silicon appear to have little effect. Further studies have been made of the so-called hysteresis effect: the effect is found to change sign above a certain rather low pressure. 66. The effect of substitutional boron on the kinetics of the graphite-oxygen reaction D. Alladrice and P. L. Walker, Jr. (The Pennsylvania State University, Materials Science Department, University Park, Pennsylvania). The oxidation kinetics of seven spectroscopically pure natural graphite samples, substitutionally doped with up to 1% boron, have been investigated. Boron inhibits the reaction in dry 0, (550”-650°C and 2.5-200 Torr. pressure). However, the activation energy decreases with increasing boron content, paralleling the decrease in Fermi level (due to the boron). Inhibition is attributed to the accumulation of Bz03 which masks the surface as the oxidation proceeds. Both the BET surface and the oxidation rate decrease with burn-off for the boronated samples. 67. Study of the oxidation products of ultrapure graphite at 0°C. Retention of ethylene glycol, surface area, and kinetics of the oxidation process J. L. Gonzales, A. M. Rodrigez and F. D. Vega (Facultad de Ciencias, Departmento de QuimicaZnorganica, Universidad de Granada, Spain). The retention capacity of ethylene glycol on the products resulting from the cold (0°C) oxidation of ultrapure graphite increases with the oxidation degree of the mentioned products. The surface areas of these products were determined from the amounts of ethylene glycol retained at the pressure of 0.02 Torr. The surface area covered by the ethylene glycol molecule was determined by two different methods, being 22 A”. A kinetic study of the oxidation process of graphite (mineralogical and artificial) has been initiated. 68. Oxidation studies of a furnace carbon black by ozone in aqueous medium J. B. Donnet and P. Ehrburger (Laboratoire de Chimie Physique, ESCM, M&house, France). Ozone oxidation studies of an aqueous suspension of a furnace black lead to the following conclusions: (1) Carbon dioxide evolution, degradation products formation and oxygen fixation are simultaneous reactions which are not related during the initial oxidation process. (2) Oxygen formation per unit area increases rapidly at the beginning of the reaction and then reaches a limit. The proportion of oxygen identified as acidic surface groups increases constantly during the oxidation. (3) The contribution of the surface chemical groups to the formation of carbon dioxide becomes only sensible as the oxygen content per unit area becomes constant. 69. Thermal degradation of coal-tar pitch I. Shapiro and G. Asawa (Western Division, McDonnell-Douglas Astronautics Company, Santa Monica, Calzjxnia). Derivative thermogravimetric analysis has been used to correlate components of pitch obtained by thermal fractionation and solvent extraction. Benzene-soluble portion can be vacuum distilled without decomposition at 500°C. Nitrobenzene-soluble portion decomposes at higher temperatures to yield high coke values and low molecular weight products. Effect of oxidation and pressure with chemical and infrared analyses of temperature fractions will be presented.
719
64. The anisotropic reaction of oxygen with pyrolytic graphite W. S. Horton (Institutefor Materials Research, National Bureau of Standards, Washington, DC.). Although several authors have found anisotropy of the chemical reactivity of pyrolytic graphite they disagree regarding the existence of a temperature coefficient. New data are presented which together with earlier data show the rate ratio for the two major directions is temperature dependent with an activation energy difference of about 19 kilojoules (4500 thermochemical calories) per gram atom of carbon reacted. This probably arises because the relative number of sites is sufficiently different to cause a shift in which reaction step is rate-controlling. On the ‘faces’ chemisorption is slow followed by rapid decomposition of surface oxides. On the ‘edges’ chemisorption is rapid followed by decomposition. 65. Catalysis of the oxidation of graphite in the temperature range 1000”-fOOO°C J. R. Egerton and R. F. Strickland-Constable (Department of Chemical Engineering and Chemical Technology, Imperial College, London, U.K.). A study has been made of the catalytic effect of substances applied to the surface of graphite filaments in the temperature range 900”-2000°C on the rate of oxidation with oxygen and also with nitrous oxide. Strong catalysis was observed with some metals, but boron and silicon appear to have little effect. Further studies have been made of the so-called hysteresis effect: the effect is found to change sign above a certain rather low pressure. 66. The effect of substitutional boron on the kinetics of the graphite-oxygen reaction D. Alladrice and P. L. Walker, Jr. (The Pennsylvania State University, Materials Science Department, University Park, Pennsylvania). The oxidation kinetics of seven spectroscopically pure natural graphite samples, substitutionally doped with up to 1% boron, have been investigated. Boron inhibits the reaction in dry 0, (550”-650°C and 2.5-200 Torr. pressure). However, the activation energy decreases with increasing boron content, paralleling the decrease in Fermi level (due to the boron). Inhibition is attributed to the accumulation of Bz03 which masks the surface as the oxidation proceeds. Both the BET surface and the oxidation rate decrease with burn-off for the boronated samples. 67. Study of the oxidation products of ultrapure graphite at 0°C. Retention of ethylene glycol, surface area, and kinetics of the oxidation process J. L. Gonzales, A. M. Rodrigez and F. D. Vega (Facultad de Ciencias, Departmento de QuimicaZnorganica, Universidad de Granada, Spain). The retention capacity of ethylene glycol on the products resulting from the cold (0°C) oxidation of ultrapure graphite increases with the oxidation degree of the mentioned products. The surface areas of these products were determined from the amounts of ethylene glycol retained at the pressure of 0.02 Torr. The surface area covered by the ethylene glycol molecule was determined by two different methods, being 22 A”. A kinetic study of the oxidation process of graphite (mineralogical and artificial) has been initiated. 68. Oxidation studies of a furnace carbon black by ozone in aqueous medium J. B. Donnet and P. Ehrburger (Laboratoire de Chimie Physique, ESCM, M&house, France). Ozone oxidation studies of an aqueous suspension of a furnace black lead to the following conclusions: (1) Carbon dioxide evolution, degradation products formation and oxygen fixation are simultaneous reactions which are not related during the initial oxidation process. (2) Oxygen formation per unit area increases rapidly at the beginning of the reaction and then reaches a limit. The proportion of oxygen identified as acidic surface groups increases constantly during the oxidation. (3) The contribution of the surface chemical groups to the formation of carbon dioxide becomes only sensible as the oxygen content per unit area becomes constant. 69. Thermal degradation of coal-tar pitch I. Shapiro and G. Asawa (Western Division, McDonnell-Douglas Astronautics Company, Santa Monica, Calzjxnia). Derivative thermogravimetric analysis has been used to correlate components of pitch obtained by thermal fractionation and solvent extraction. Benzene-soluble portion can be vacuum distilled without decomposition at 500°C. Nitrobenzene-soluble portion decomposes at higher temperatures to yield high coke values and low molecular weight products. Effect of oxidation and pressure with chemical and infrared analyses of temperature fractions will be presented.