- Email: [email protected]
98. The chemical vapor deposition of carbon on graphite surfaces
214
Abstracts
ivity is oriented towards respectively light olefins’ or methane with iron-cobalt or iron-cobalt or iron-nickel products. 92. A TPR-tracer study of the Boudouard reaction catalyzed by potassium carbonate? J. M. Saber, J. L. Falconer and L. F. Brownt (Department of Chemical Engineering, Box 424, University of Colorado, Boulder, CO 80309, U.S.A.).
Temperature-programmed reaction (TPR) of physical mixtures of carbon with ‘%- and ‘sO-labelled carbonates shows that most of the carbon and oxygen in the carbonate exchanged with the gas-phase CO* (0.1 atm) below 1000 K. Carbon catalyzed the exchange. Above lOOOK, potassium carbonate catalyzed the CO, gasification of carbon. tSupported
by the Department
DE-FG22-82PC50798. IPresent address, Los Alamos Alamos, New Mexico.
National
of Energy Grant Laboratory,
Los
93. Gasification kinetics and surface areas of cata-
lyzed carbonaceous chars P. G. Kosky, E. J. Lamby, D. W. McKee and C. L. Spiro (General Electric R&D Center, P.O. Box 8, Schenectady, NY 12301, U.S.A.). Various catalysts were added to coals which were then pyrolyzed to chars. BET surface areas were measured for these chars; then they were reacted with H,O(g) or CO,. While, in general, the reactivity increased with catalyst loading, the micropore area (N,-probe) and the ultramicropore area (CO,-probe) showed steady decreases. 94. Transient behaviour in the potassium catalyzed
CO, gasification of carbon M. B. Cerfontain and J. A. Moulijn (Institute for Chemical Technology, University of Amsterdam, Plantage Muidergracht 30, 1018 TV Amsterdam, The Netherlands). It is known that K&0,/C decomposes
during heat treatment in He with evolution of CO, and CO. After switching from He to CO* at 1073 K a fast oxidation of the carbon surface; co2-tco + osurf, was measured. The amount of oxygen captured is proportional to the amount of potassium present. These results indicate that the potassium catalyzed gasification proceeds via a fast oxidation/rate determining reduction cycle. 95. The effect of heat treatment on alkali carbonate/
carbon systems F. Kapteijn, J. Jurriaans and J. A. Moulijn (Znstitute for Chemical Technology, University of Amsterdam, Plantage Muidergracht 30, 1018 TV Amsterdam, The Netherlands). The effect of mixing alkali
metals with an activated carbon and a semianthracite coal char and the effect of heat treatment of these carbon samples with alkali carbonates at 1100 K in Nz is studied by X-ray diffraction. The
diffraction patterns reveal that metallic K, Rb and Cs can destroy the coal structure in the order K < Rb < Cs via intercalation. This effect is enhanced with increasing metal content. Li and Na do not exhibit this behaviour. Combination of the intercalation properties of the alkali metals with the extent to which the metal oxides can be reduced by the carbon can account for the catalytic reactivity order of the alkali metals in the gasification of char and activated carbon. 96. Reactivity measurements of catalytic carbon gasification by temperature programmed reaction F. Kapteijn and J. A. Moulijn (Institute for Chemical Technology, University of Amsterdam, Plantage Muidergracht 30, 1018 TV Amsterdam, The Netherlands). Temperature programmed reactivity mea-
surement is applied to the potassium catalysed gasification of an activated carbon as an alternative method to determine the reactivity of the carbon and the activation energy of the process. The results are similar to those of isothermal experiments. Moreover, the measurement can be carried out over a small burn-off range, leaving the carbon essentially unchanged. By a combined weight and product gas analysis it is shown that potassium reduced at high temperatures in He is oxidised by CO* above 673 K with an activation energy of 65 kJ/mol. The gasification process above 873 K has an activation energy changing from 205 to 190 kJ/mol with increasing K&O3 content (5-10 wt.%). 97. Potassium catalysed gasification of carbon; CO, vs Hz0 F. Kapteijn and J. A. Moulijn (Institute for Chemical Technology, University of Amsterdam, Plantage Muidergracht 30, 1018 TV Amsterdam, The Netherlands). Results are presented of the potassium cata-
lysed gasification of an activated carbon at 1050 K at low H,O pressure and atmospheric and low CO* pressure. The behaviour of the absolute reaction rate as a function of the burn-off, pressure, reactant and catalyst loading (5 and 10 wt.% K,COJ) suggests that different reaction mechanisms or different active sites are operative in the Hz0 and CO? gasification. 98. The chemical vapor deposition of carbon on graphite surfaces D. F. Cummings? and R. J. Diefendorf (Materials Engineering Department, Rensselaer Polytechnic Znstitute, Troy, NY 12181, U.S.A.). The understanding
of the chemical vapor deposition of carbon is complicated by usually not knowing the relative importance of gas phase and surface reactions, and the rates of the various sites on the deposition surface. Highly annealed pyrolytic graphite surfaces were used to evaluate the deposition rate on basal planes, edges and emerging c-axis emerging screw dislocations. Depositions were performed under typical commercial deposition conditions for short times, and at
215
Abstracts much lower supersaturations, and conditions where gas phase reactions are minimized. Methane, acetylene and higher hydrocarbons were investigated.
TPresently with Pfizer Corporation,
Easton,
Pennsyl-
vania.
99. Kinetics of the reaction of iron/chromium binary alloys with carbon monoxide A. M. Emsley and M. P. Hill (Central Electricity Generating Board, CERL, Leatherhead, Surrey, England). A range of iron/chromium binary alloys (I-347; Cr) have been reacted in CO at 550°C to form surface carbon deposits. The dependence of the reaction rate on chromium content has been established. Analytical data on the reaction product at the metal interface, and in the bulk deposit is used to deduce aspects of the deposition mechanism.
100. The performance of chromium coatings in carbon deposition A. M. Emsley and M. P. Hill (Central Electricity Generating Board, CERL, Leatherhead, Surrey, Eng/and). Chromium coatings of two types, vacuum evaporation and diffusion bonded, have been applied to iron and steel surfaces, and their effectiveness at reducing carbon deposition in carbon monoxide and methane atmospheres has been assessed. Reasons for the behaviour of the coatings in relation to known carbon deposition mechanisms have been discussed. 101. Surface mobility in iron-carbon layers A. M. Brown and M. P. Hill (Central Electricity Generating Board, CERL, Leatherhead, Surrey, Englund). In -situ scanning electron microscopy studies of carbon deposition from methane on iron foils have shown that at certain stages of the reaction, the Fe-C surface phase has significant mobility. Some deposit morphologies arising from the mobility are identified and it is suggested that the mobile phase may have an important intermediate role in the carbon deposition process.
102. Nickel and molybdenum compounds as catalysts for CO methanation and carbon gasification Teus Wigmans, Hans van Werkhoven and Jacob A. Moulijn (Institute for Chemical Technology, Plantage Muidergracht 30, 1018 TV Amsterdam, The Netherkunds). In this study, results will be presented of activated carbon supported nickel and molybdenum as a catalyst for CO methanation and support gasification. It will be shown that the carbon support has an essential influence on the chemical state of the catalyst. Reduction to the metallic state, oxycarbide formation and dissolution of carbon in the metal appear to be phenomena that have a predominant influence on the behaviour of the activated carbon supported catalyst during reaction.
IV. PHYSICS
OF INTERCALATION
COMPOUNDS
103. Anomalies in the thermal conductivity and thermopower in CoCI, intercalated graphite Ko Sugihara (Center for Materials Science and En gineering, MIT, Room, 13-3021, Cambridge, MA 02139, U.S.A.). The thermal conductivity and thermopower (TEP) of a stage-3 CoCl,-GIC exhibit anomalies near T = 9.5 K, which corresponds to the magnetic phase transition. The extra contribution to the thermal conductivity is ascribed to the heat current carried by the magnous and the TEP anomaly is explained in consideration of the spin-disorder scattering. 104. Anomalous pressure dependences of the superconducting transition temperature of graphite intercalation compounds L. E. Delong,? V. Yeh,? V. Tondigliat and P. C. Eklundt (Department of Physics and Astronomy, University of Kentucky, Lexington, KY 40506, U.S.A.). S. E. Lambertt and M. B. Maple: (Department of Physics, University of Caltfornia, San Diego, La Jolla, CA 92093, U.S.A.). Measurements of the pressure (P) dependences of the superconducting transition temperature T? of KHgC,, KHgC,, KTl&, KC,, and RbC, are reported over the range 0 5 P 6 20 kbar with T,.& l.3K, and for O
by
USDOE
Contract
by
USDOE
Contract
105. Magnetoresistance of acceptor compounds of graphite K. J. Volin and I. L. Spain (Department of Physics, Colorado State University, Ft. Collins, CO 80523, U.S.A.). Calculations of the magnetoresistance of graphite acceptor compounds are made using a tightbinding mode1 for the carrier dispersion proposed by Blinowski et al. and measured values of the zero-field resistivity. Suggestions for the origin of the magnetoresistance are made. 106. Electronic properties of barium graphite intercalation compounds U. M. Gubler, V. Geiser, P. Oelhafen and H.-J. Giintherodt (Institut fur Physik, Universitat Basel, CH-4056 Basel, Switzerland) E. Cartier and F. Heinrich (Laboratorium fur Festkiirperphysik. ETH Zurich, CH-8093 Zurich, Switzerland). J. Evers and A. Weiss (Institut fur Anorganische Chemie, Universitat Munchen, D-8000 Munchen, Germany). Barium stage- 1 graphite intercalation compounds have been prepared by vapour phase reaction and a new liquid phase method. UPS and XPS measurements as well as positron annihilation experiments are presented and compared with a recent band structure calculation and with other experiments.
Abstracts
ivity is oriented towards respectively light olefins’ or methane with iron-cobalt or iron-cobalt or iron-nickel products. 92. A TPR-tracer study of the Boudouard reaction catalyzed by potassium carbonate? J. M. Saber, J. L. Falconer and L. F. Brownt (Department of Chemical Engineering, Box 424, University of Colorado, Boulder, CO 80309, U.S.A.).
Temperature-programmed reaction (TPR) of physical mixtures of carbon with ‘%- and ‘sO-labelled carbonates shows that most of the carbon and oxygen in the carbonate exchanged with the gas-phase CO* (0.1 atm) below 1000 K. Carbon catalyzed the exchange. Above lOOOK, potassium carbonate catalyzed the CO, gasification of carbon. tSupported
by the Department
DE-FG22-82PC50798. IPresent address, Los Alamos Alamos, New Mexico.
National
of Energy Grant Laboratory,
Los
93. Gasification kinetics and surface areas of cata-
lyzed carbonaceous chars P. G. Kosky, E. J. Lamby, D. W. McKee and C. L. Spiro (General Electric R&D Center, P.O. Box 8, Schenectady, NY 12301, U.S.A.). Various catalysts were added to coals which were then pyrolyzed to chars. BET surface areas were measured for these chars; then they were reacted with H,O(g) or CO,. While, in general, the reactivity increased with catalyst loading, the micropore area (N,-probe) and the ultramicropore area (CO,-probe) showed steady decreases. 94. Transient behaviour in the potassium catalyzed
CO, gasification of carbon M. B. Cerfontain and J. A. Moulijn (Institute for Chemical Technology, University of Amsterdam, Plantage Muidergracht 30, 1018 TV Amsterdam, The Netherlands). It is known that K&0,/C decomposes
during heat treatment in He with evolution of CO, and CO. After switching from He to CO* at 1073 K a fast oxidation of the carbon surface; co2-tco + osurf, was measured. The amount of oxygen captured is proportional to the amount of potassium present. These results indicate that the potassium catalyzed gasification proceeds via a fast oxidation/rate determining reduction cycle. 95. The effect of heat treatment on alkali carbonate/
carbon systems F. Kapteijn, J. Jurriaans and J. A. Moulijn (Znstitute for Chemical Technology, University of Amsterdam, Plantage Muidergracht 30, 1018 TV Amsterdam, The Netherlands). The effect of mixing alkali
metals with an activated carbon and a semianthracite coal char and the effect of heat treatment of these carbon samples with alkali carbonates at 1100 K in Nz is studied by X-ray diffraction. The
diffraction patterns reveal that metallic K, Rb and Cs can destroy the coal structure in the order K < Rb < Cs via intercalation. This effect is enhanced with increasing metal content. Li and Na do not exhibit this behaviour. Combination of the intercalation properties of the alkali metals with the extent to which the metal oxides can be reduced by the carbon can account for the catalytic reactivity order of the alkali metals in the gasification of char and activated carbon. 96. Reactivity measurements of catalytic carbon gasification by temperature programmed reaction F. Kapteijn and J. A. Moulijn (Institute for Chemical Technology, University of Amsterdam, Plantage Muidergracht 30, 1018 TV Amsterdam, The Netherlands). Temperature programmed reactivity mea-
surement is applied to the potassium catalysed gasification of an activated carbon as an alternative method to determine the reactivity of the carbon and the activation energy of the process. The results are similar to those of isothermal experiments. Moreover, the measurement can be carried out over a small burn-off range, leaving the carbon essentially unchanged. By a combined weight and product gas analysis it is shown that potassium reduced at high temperatures in He is oxidised by CO* above 673 K with an activation energy of 65 kJ/mol. The gasification process above 873 K has an activation energy changing from 205 to 190 kJ/mol with increasing K&O3 content (5-10 wt.%). 97. Potassium catalysed gasification of carbon; CO, vs Hz0 F. Kapteijn and J. A. Moulijn (Institute for Chemical Technology, University of Amsterdam, Plantage Muidergracht 30, 1018 TV Amsterdam, The Netherlands). Results are presented of the potassium cata-
lysed gasification of an activated carbon at 1050 K at low H,O pressure and atmospheric and low CO* pressure. The behaviour of the absolute reaction rate as a function of the burn-off, pressure, reactant and catalyst loading (5 and 10 wt.% K,COJ) suggests that different reaction mechanisms or different active sites are operative in the Hz0 and CO? gasification. 98. The chemical vapor deposition of carbon on graphite surfaces D. F. Cummings? and R. J. Diefendorf (Materials Engineering Department, Rensselaer Polytechnic Znstitute, Troy, NY 12181, U.S.A.). The understanding
of the chemical vapor deposition of carbon is complicated by usually not knowing the relative importance of gas phase and surface reactions, and the rates of the various sites on the deposition surface. Highly annealed pyrolytic graphite surfaces were used to evaluate the deposition rate on basal planes, edges and emerging c-axis emerging screw dislocations. Depositions were performed under typical commercial deposition conditions for short times, and at
215
Abstracts much lower supersaturations, and conditions where gas phase reactions are minimized. Methane, acetylene and higher hydrocarbons were investigated.
TPresently with Pfizer Corporation,
Easton,
Pennsyl-
vania.
99. Kinetics of the reaction of iron/chromium binary alloys with carbon monoxide A. M. Emsley and M. P. Hill (Central Electricity Generating Board, CERL, Leatherhead, Surrey, England). A range of iron/chromium binary alloys (I-347; Cr) have been reacted in CO at 550°C to form surface carbon deposits. The dependence of the reaction rate on chromium content has been established. Analytical data on the reaction product at the metal interface, and in the bulk deposit is used to deduce aspects of the deposition mechanism.
100. The performance of chromium coatings in carbon deposition A. M. Emsley and M. P. Hill (Central Electricity Generating Board, CERL, Leatherhead, Surrey, Eng/and). Chromium coatings of two types, vacuum evaporation and diffusion bonded, have been applied to iron and steel surfaces, and their effectiveness at reducing carbon deposition in carbon monoxide and methane atmospheres has been assessed. Reasons for the behaviour of the coatings in relation to known carbon deposition mechanisms have been discussed. 101. Surface mobility in iron-carbon layers A. M. Brown and M. P. Hill (Central Electricity Generating Board, CERL, Leatherhead, Surrey, Englund). In -situ scanning electron microscopy studies of carbon deposition from methane on iron foils have shown that at certain stages of the reaction, the Fe-C surface phase has significant mobility. Some deposit morphologies arising from the mobility are identified and it is suggested that the mobile phase may have an important intermediate role in the carbon deposition process.
102. Nickel and molybdenum compounds as catalysts for CO methanation and carbon gasification Teus Wigmans, Hans van Werkhoven and Jacob A. Moulijn (Institute for Chemical Technology, Plantage Muidergracht 30, 1018 TV Amsterdam, The Netherkunds). In this study, results will be presented of activated carbon supported nickel and molybdenum as a catalyst for CO methanation and support gasification. It will be shown that the carbon support has an essential influence on the chemical state of the catalyst. Reduction to the metallic state, oxycarbide formation and dissolution of carbon in the metal appear to be phenomena that have a predominant influence on the behaviour of the activated carbon supported catalyst during reaction.
IV. PHYSICS
OF INTERCALATION
COMPOUNDS
103. Anomalies in the thermal conductivity and thermopower in CoCI, intercalated graphite Ko Sugihara (Center for Materials Science and En gineering, MIT, Room, 13-3021, Cambridge, MA 02139, U.S.A.). The thermal conductivity and thermopower (TEP) of a stage-3 CoCl,-GIC exhibit anomalies near T = 9.5 K, which corresponds to the magnetic phase transition. The extra contribution to the thermal conductivity is ascribed to the heat current carried by the magnous and the TEP anomaly is explained in consideration of the spin-disorder scattering. 104. Anomalous pressure dependences of the superconducting transition temperature of graphite intercalation compounds L. E. Delong,? V. Yeh,? V. Tondigliat and P. C. Eklundt (Department of Physics and Astronomy, University of Kentucky, Lexington, KY 40506, U.S.A.). S. E. Lambertt and M. B. Maple: (Department of Physics, University of Caltfornia, San Diego, La Jolla, CA 92093, U.S.A.). Measurements of the pressure (P) dependences of the superconducting transition temperature T? of KHgC,, KHgC,, KTl&, KC,, and RbC, are reported over the range 0 5 P 6 20 kbar with T,.& l.3K, and for O
by
USDOE
Contract
by
USDOE
Contract
105. Magnetoresistance of acceptor compounds of graphite K. J. Volin and I. L. Spain (Department of Physics, Colorado State University, Ft. Collins, CO 80523, U.S.A.). Calculations of the magnetoresistance of graphite acceptor compounds are made using a tightbinding mode1 for the carrier dispersion proposed by Blinowski et al. and measured values of the zero-field resistivity. Suggestions for the origin of the magnetoresistance are made. 106. Electronic properties of barium graphite intercalation compounds U. M. Gubler, V. Geiser, P. Oelhafen and H.-J. Giintherodt (Institut fur Physik, Universitat Basel, CH-4056 Basel, Switzerland) E. Cartier and F. Heinrich (Laboratorium fur Festkiirperphysik. ETH Zurich, CH-8093 Zurich, Switzerland). J. Evers and A. Weiss (Institut fur Anorganische Chemie, Universitat Munchen, D-8000 Munchen, Germany). Barium stage- 1 graphite intercalation compounds have been prepared by vapour phase reaction and a new liquid phase method. UPS and XPS measurements as well as positron annihilation experiments are presented and compared with a recent band structure calculation and with other experiments.