References of "Carbon"
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See detailUse of X-ray microtomography to study the homogeneity of carbon nanotube aqueous suspensions and carbon nanotube/polymer composites
Haghgoo, M.; Plougonven, Erwan ULg; Yousefi, Ali Akbar et al

in Carbon (2012), 50(4), 1703-1706

X-ray microtomography was used to study the stability and homogeneity of concentrated carbon nanotube (CNT) aqueous suspensions and CNT/resorcinol–formaldehyde gel composites. Various CNT distribution ... [more ▼]

X-ray microtomography was used to study the stability and homogeneity of concentrated carbon nanotube (CNT) aqueous suspensions and CNT/resorcinol–formaldehyde gel composites. Various CNT distribution states were achieved by modifying the CNT concentration, sonication time and resting time. X-ray microtomography is able to discriminate between zones with different CNT concentration levels and can be used as a non-destructive and fast tool to characterize the homogeneity of suspensions and composite systems at the micron scale. [less ▲]

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See detailKrypton adsorption as a suitable tool for surface characterization of multi-walled CNTs
Zilli, Dario; Bonelli, P.; Gommes, Cédric ULg et al

in Carbon (2011), 49

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See detailA comparison of physical activation of carbon xerogels with carbon dioxide with chemical activation using hydroxides
Contreras, María S; Páez, Carlos A; Zubizarreta, Leire et al

in Carbon (2010), 48(11), 3157-3168

Carbon xerogels synthesized with a fixed resorcinol/sodium carbonate molar ratio (R/C) were physically activated using CO2. The effect of activation temperature and activation time on the final properties ... [more ▼]

Carbon xerogels synthesized with a fixed resorcinol/sodium carbonate molar ratio (R/C) were physically activated using CO2. The effect of activation temperature and activation time on the final properties of the activated carbon xerogels was evaluated. The specific surface area increases from ~600 m2 g-1 to 2000 m2 g-1 and more by increasing the temperature and duration of the activation step. A comparison between physical activation with CO2 and chemical activation with hydroxides was also performed: it was found that both processes produce an increase of the micropore volume and specific surface area without altering the meso-macroporosity developed during the synthesis. However, chemical activation can lead to the development of the narrow microporosity mainly whereas, in physical activation, the widening of the narrow micropores takes place whatever the process conditions. [less ▲]

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See detailNi-doped carbon xerogels for H2 storage
Zubizarreta, Leire; Menendez, J. A.; Job, Nathalie ULg et al

in Carbon (2010), 48

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See detailFunctionalisation and chemical characterisation of cellulose derived carbon aerogels
Grzyb, Bartosz; Hildenbrand, Claudia; Berthon-Fabry, Sandrine et al

in Carbon (2010), 48

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See detailCarbon nanotubes synthesis by CCVD process : kinetic study on a Fe-Co/Al2O3 catalyst
Pirard, Sophie; Douven, Sigrid ULg; Bossuot, Christophe et al

in Carbon (2007), 45(6), 1167-1175

A kinetic study was performed to describe the initial specific rate of multi-walled carbon nanotube synthesis by catalytic chemical vapor deposition (CCVD) on a bimetallic cobalt-iron catalyst at high ... [more ▼]

A kinetic study was performed to describe the initial specific rate of multi-walled carbon nanotube synthesis by catalytic chemical vapor deposition (CCVD) on a bimetallic cobalt-iron catalyst at high temperature using ethylene decomposition to solid carbon and gaseous hydrogen. The study uses a mass spectrometer that allows reaction rate to be inferred from the exhaust gas composition measurements. The aim is to obtain a better understanding of the elementary steps involved in the production of carbon nanotubes so as to derive phenomenological kinetic models in agreement with experimental data. The best models assume the elimination of the first hydrogen atom from adsorbed ethylene as rate determining step and involve a hydrogen adsorption weak enough to be neglected. It was proved that hydrogen partial pressure has no influence on initial reaction rate of carbon nanotube synthesis with the catalyst used for this study. Activation energy and ethylene adsorption enthalpy were found to be equal to around 130 and - 130 kJ mol(-1), respectively. (C) 2007 Elsevier Ltd. All rights reserved. [less ▲]

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See detailA kinetic study of multi-walled carbon nanotube synthesis by catalytic chemical vapor deposition using a Fe-Co/Al2O3 catalyst
Pirard, Sophie ULg; Douven, Sigrid ULg; Bossuot, Christophe et al

in Carbon (2007), 45(6), 1167-1175

A kinetic study was performed to describe the initial specific rate of multi-walled carbon nanotube synthesis by catalytic chemical vapor deposition (CCVD) on a bimetallic cobalt-iron catalyst at high ... [more ▼]

A kinetic study was performed to describe the initial specific rate of multi-walled carbon nanotube synthesis by catalytic chemical vapor deposition (CCVD) on a bimetallic cobalt-iron catalyst at high temperature using ethylene decomposition to solid carbon and gaseous hydrogen. The study uses a mass spectrometer that allows reaction rate to be inferred from the exhaust gas composition measurements. The aim is to obtain a better understanding of the elementary steps involved in the production of carbon nanotubes so as to derive phenomenological kinetic models in agreement with experimental data. The best models assume the elimination of the first hydrogen atom from adsorbed ethylene as rate determining step and involve a hydrogen adsorption weak enough to be neglected. It was proved that hydrogen partial pressure has no influence on initial reaction rate of carbon nanotube synthesis with the catalyst used for this study. Activation energy and ethylene adsorption enthalpy were found to be equal to around 130 and - 130 kJ mol(-1), respectively. (C) 2007 Elsevier Ltd. All rights reserved. [less ▲]

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See detailAnalysis of kinetic models of multi-walled CNT synthesis
Pirard, Sophie ULg; Douven, Sigrid ULg; Pirard, Jean-Paul ULg

in Carbon (2007), 45(15), 3050-3052

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See detailTowards the production of carbon xerogel monoliths by optimizing convective drying conditions
Job, Nathalie ULg; Sabatier, Françoise; Pirard, Jean-Paul ULg et al

in Carbon (2006), 44(12), 2534-2542

Resorcinol-formaldehyde hydrogels prepared at various resorcinol/sodium carbonate ratios, R/C, were convectively air dried. The influence of the drying operating conditions, i.e. air temperature and ... [more ▼]

Resorcinol-formaldehyde hydrogels prepared at various resorcinol/sodium carbonate ratios, R/C, were convectively air dried. The influence of the drying operating conditions, i.e. air temperature and velocity, on the pore texture, shrinkage and cracking of the dried gels were investigated. Shrinkage was found to be isotropic. The shrinkage behaviour and the textural properties of the gels are independent of the drying operating conditions, but are completely determined by the value of the synthesis variables. The analysis of the drying kinetics shows two main drying periods. During the first phase, shrinkage occurs and the external surface of the material remains completely wet: heat and mass transfers are limited by external resistances located in a boundary layer. When shrinkage stops, the second period begins: the evaporation front recedes inside the solid and internal transfer limitations prevail. The drying time can be reduced by increasing the air temperature and/or velocity, but the temperature increase is limited when monolithicity is required, especially when the pores are small. For example, at a temperature of 160 degrees C and a velocity of 2 m/s, about 1 h is needed to dry a 2.8 cm in diameter and 1 cm in height cylinder containing macropores (pore width > 50 nm after drying). The same cylinder presenting small mesopores (pore width = 10-15 nm after drying) requires 20 h at 30 degrees C and 2 m/s to reach complete dryness without the development of cracks. (c) 2006 Elsevier Ltd. All rights reserved. [less ▲]

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See detailCarbon aerogels, cryogels and xerogels: Influence of the drying method on the textural properties of porous carbon materials
Job, Nathalie ULg; Thery, Alexandre; Pirard, René ULg et al

in Carbon (2005), 43(12), 2481-2494

Carbon materials with tailored texture can be obtained from drying and pyrolysis of resorcinol-formaldehyde gels. The pore texture of both dried and pyrolyzed material depends on the drying process ... [more ▼]

Carbon materials with tailored texture can be obtained from drying and pyrolysis of resorcinol-formaldehyde gels. The pore texture of both dried and pyrolyzed material depends on the drying process. Several more or less expensive methods (supercritical drying, freeze-drying, evaporative drying) were tested in order to determine which process is the most suitable for the synthesis of a porous carbon with a definite texture. Supercritical drying leads to the highest pore volume and the widest texture range, but residual surface tensions and shrinkage are not avoided when the pore size is small or when the material density is low; this hampers to fix both the pore volume and the pore size easily. Monoliths are very difficult to obtain by freeze-drying, and the appearance of huge channels due to ice crystal growth at high dilution ratio hinders the fabrication of low density materials. Moreover, gels with small pores do not remain frozen throughout drying, which leads to surface tensions and shrinkage. Although generally replaced by more complicated techniques, evaporative drying is suitable when dense carbons are needed or when the only selection criterion is the pore size: all pore sizes are reachable, but this parameter is in this case strongly correlated to the pore volume. (C) 2005 Elsevier Ltd. All rights reserved. [less ▲]

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See detailAnomalous ESR behavior of carbon nanofilaments grown from palladium seeds
Breton, Y.; Verstraete, Matthieu ULg; Fleurier, R. et al

in Carbon (2004), 42

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See detailInfluence of the operating conditions on the production rate of multi-walled carbon nanotubes in a CVD reactor
Gommes, Cédric ULg; Blacher, Silvia ULg; Bossuot, C. et al

in Carbon (2004), 42(8-9), 1473-1482

A kinetic study is presented for the synthesis of multi-walled carbon nanotubes in a semi-continuous chemical vapor deposition reactor. The study is based on the use of a mass spectrometer that allows the ... [more ▼]

A kinetic study is presented for the synthesis of multi-walled carbon nanotubes in a semi-continuous chemical vapor deposition reactor. The study is based on the use of a mass spectrometer that allows the reaction rate to be inferred from the exhaust gas composition measurements. The tested reactor operating variables are the length and thickness of the catalytic bed, the total feed flow and the molar fraction of hydrocarbon in the feed. The results of the study are analyzed using well known reactor engineering models, which allows the origin of the observed physical limitations to be ascertained. (C) 2004 Elsevier Ltd. All rights reserved. [less ▲]

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See detailBall milling effect on the structure of single-wall carbon nanotubes
Pierard, N.; Fonseca, Antonio; Colomer, Jean-François et al

in Carbon (2004), 42(8-9), 1691-1697

The vibratory mill is used to decrease the single-wall carbon nanotubes (SWNTs) length and to increase their specific surface area. Electron microscopy, Raman spectroscopy, X-ray diffraction and BET ... [more ▼]

The vibratory mill is used to decrease the single-wall carbon nanotubes (SWNTs) length and to increase their specific surface area. Electron microscopy, Raman spectroscopy, X-ray diffraction and BET measurements indicated that the optimum time of treatment seems to be 2 h. After that, the SWNTs quality decreases, with a complete disruption of the tubular structure leading to multi-layered polyaromatic carbon materials observed after 50 h. (C) 2004 Elsevier Ltd. All rights reserved. [less ▲]

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See detailSynthesis of transition metal-doped carbon xerogels by solubilization of metal salts in resorcinol-formaldehyde aqueous solution
Job, Nathalie ULg; Pirard, René ULg; Marien, José ULg et al

in Carbon (2004), 42(15), 3217-3227

The pore texture of carbon materials obtained from evaporative drying and pyrolysis of resorcinol-formaldehyde aqueous gels is controlled by the initial pH of the precursors solution. In order to produce ... [more ▼]

The pore texture of carbon materials obtained from evaporative drying and pyrolysis of resorcinol-formaldehyde aqueous gels is controlled by the initial pH of the precursors solution. In order to produce transition metal-containing carbons with tailored texture, various metallic salts were dissolved in the precursors solution. When necessary, a complexing agent (HEDTA or DTPA) was added to render the metal ions soluble. Ni, Fe and I'd loaded carbon xerogels were synthesized and their pore texture was studied after evaporative drying and after pyrolysis. The carbon texture was also studied with regard to the nature of the metal and the amount of complexing agent. The solubilization of transition metal salts in the resorcinol-formaldehyde aqueous solution does not prevent the texture regulation, even though this texture control is influenced: the limits of the pH interval leading to micro mesoporous carbon materials can slightly differ when a metal salt and/or a complexing agent are added. The pH range shift depends mainly on the amount and nature of the complexing agent, but also slightly on the nature of the metal ion. Nevertheless, the metal particles obtained are rather big (diameter > 15 nm). For catalytic applications, the metal dispersion must be enhanced, especially in the case of expensive metals. (C) 2004 Elsevier Ltd. All rights reserved. [less ▲]

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See detailPorous carbon xerogels with texture tailored by pH control during sol-gel process
Job, Nathalie ULg; Pirard, René ULg; Marien, José ULg et al

in Carbon (2004), 42(3), 619-628

Despite commonly accepted ideas, evaporative drying does not always completely destroy the pore texture of phenolic gel. This work shows that very porous carbon materials can be synthesized by evaporative ... [more ▼]

Despite commonly accepted ideas, evaporative drying does not always completely destroy the pore texture of phenolic gel. This work shows that very porous carbon materials can be synthesized by evaporative drying and pyrolysis of aqueous resorcinol-formaldehyde gels provided that the operating variables are correctly chosen. Moreover, in this manner monoliths can be easily produced. The pore texture of the materials was studied before and after pyrolysis in order to determine which synthesis and/or pyrolysis variables have an influence on the final texture of the carbon. Results show that it is possible to tailor the morphology of these materials by varying the initial pH of the precursors solution in a narrow range. Micro-macroporous, micro-mesoporous, microporous or totally non-porous carbon materials were obtained. The specific surface area is independent from the initial pH whereas the total void volume varies from 0.4 to 1.4 cm(3)/g when the initial pH decreases from 6.25 to 5.45. These materials can be used as catalysts supports or for electrochemical applications, the texture control being an interesting advantage. (C) 2004 Elsevier Ltd. All rights reserved. [less ▲]

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See detailImage analysis characterization of multi-walled carbon nanotubes
Gommes, Cédric ULg; Blacher, Silvia ULg; Masenelli-Varlot, Karine et al

in Carbon (2003), 41(13), 2561-2572

An original image analysis method is presented to characterize multi-walled carbon nanotubes from transmission electron microscopy images. The analysis is performed in three steps: (i) image preprocessing ... [more ▼]

An original image analysis method is presented to characterize multi-walled carbon nanotubes from transmission electron microscopy images. The analysis is performed in three steps: (i) image preprocessing in order to isolate the nanotubes from the background, (ii) image segmentation, aiming at keeping only the measurable sections of nanotubes, and finally (iii) tube characteristics measurement. The measurement is based on a Lambert-like electron absorption law and is performed on the original gray level image itself. Two geometrical and one physical characteristics are determined for each tube, namely, its outer and inner radius and a linear electron absorption coefficient. The method is illustrated by comparing a pristine and an annealed carbon nanotube samples. The compaction of the tube walls during annealing is shown to result from a lowering of the external radius while the inner radius is left unchanged. (C) 2003 Elsevier Ltd. All rights reserved. [less ▲]

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