References of "Gommes, Cédric"
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See detailQuantization of pore corrugation in SBA-15 by image analysis of electron tomograms
Friedrich, Heiner; Gommes, Cédric ULg; de Jongh, Petra et al

Conference (2009, March)

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See detailWater desorption from resorcinol-formaldehyde hydrogels and adsorption in the resulting xerogels
Escalona, Ivonne; Gommes, Cédric ULg; Job, Nathalie ULg et al

in Microporous and Mesoporous Materials (2009), 117

Water desorption isotherms of resorcinol-formaldehyde (RF) hydrogels and subsequent water adsorption isotherms of the resulting xerogels are determined using the static gravimetric method, at various ... [more ▼]

Water desorption isotherms of resorcinol-formaldehyde (RF) hydrogels and subsequent water adsorption isotherms of the resulting xerogels are determined using the static gravimetric method, at various temperatures. Isotherms obtained from samples synthesized at various pH are compared. Two different mechanisms are involved in RF hydrogels water desorption. At large relative humidity the capillary tension resulting from water removal induces a macroscopic shrinkage of the gel, whereas at low humidity water is evaporated with no network deformation. These two mechanisms are analyzed using a plastic deformation model and the Guggenheim-Anderson-de Boer (GAB) model, respectively. Adsorption isotherms of RF xerogels are analyzed using the GAB model. [less ▲]

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See detailQuantitative Structural Analysis of Binary Nanocrystal Superlattices by Electron Tomography
Friedrich, Heiner; Gommes, Cédric ULg; Overgaag, Karin et al

in Nano Letters (2009), 9

Binary nanocrystal superlattices, that is, ordered structures of two sorts of nanocolloids, hold promise for a series of functional materials with novel collective properties. Here we show that based on ... [more ▼]

Binary nanocrystal superlattices, that is, ordered structures of two sorts of nanocolloids, hold promise for a series of functional materials with novel collective properties. Here we show that based on electron tomography a comprehensive, quantitative, three-dimensional characterization of these systems down to the single nanocrystal level can be achieved, which is key in understanding the emerging materials properties. On four binary lattices composed of PbSe, CdSe, and Au nanocrystals, we illustrate that ambiguous interpretations based on two-dimensional transmission electron microscopy can be prevented, nanocrystal sizes and superlattice parameters accurately determined, individual crystallographic point and plane defects studied, and the order/disorder at the top and bottom surfaces imaged. Furthermore, our results suggest that superlattice nucleation and growth occurred at the suspension/air interface and that the unit cells of some lattices are anisotropically deformed upon drying. [less ▲]

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See detailTwo methods of random seed generation to avoid over-segmentation with stochastic watershed: application to nuclear fuel micrographs
Cativa Tolosa, Sebastian; Blacher, Silvia ULg; Denis, Alicia et al

in Journal of Microscopy (2009), 236

A stochastic version of the watershed algorithm is obtained by choosing randomly in the image the seeds from which the watershed regions are grown. The output of the procedure is a probability density ... [more ▼]

A stochastic version of the watershed algorithm is obtained by choosing randomly in the image the seeds from which the watershed regions are grown. The output of the procedure is a probability density function (PDF) corresponding to the probability that each pixel belongs to a boundary. In the present paper, two stochastic seed-generation processes are explored to avoid over-segmentation. The first is a non-uniform Poisson process, the density of which is optimized on the basis of opening granulometry. The second process positions the seeds randomly within disks centered on the maxima of a distance map. The two methods are applied to characterize the grain structure of nuclear fuel pellets. Estimators are proposed for the total edge length and grain number per unit area, LA and NA, which take advantage of the probabilistic nature of the PDF and do not require segmentation. [less ▲]

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See detailQuantitative Characterization of Pore Corrugation in Ordered Mesoporous Materials Using Image Analysis of Electron Tomograms
Gommes, Cédric ULg; Friedrich, Heiner; Wolters, Mariska et al

in Chemistry of Materials (2009), 21

Electron tomography and image analysis are combined to characterize ordered mesoporous silica SBA-15. The morphology of the mesopores with average diameter 6 nm is analyzed in terms of cylinders having ... [more ▼]

Electron tomography and image analysis are combined to characterize ordered mesoporous silica SBA-15. The morphology of the mesopores with average diameter 6 nm is analyzed in terms of cylinders having variable radii and centers that are statistically centered on the points of a distorted hexagonal lattice. The variations in the mesopore centers and radii add up and result in pore wall corrugation with amplitude of 1.6 nm. The correlation length of the corrugation along the pore axis was found to be 4-5 nm. The amplitude of the corrugation compared well with the 1.9 nm thick microporous corona obtained from X-ray diffraction (XRD). In general, the present approach provides a detailed microscopic 3D model of nanostructured materials that complements macroscopic measurements such as physisorption and XRD. [less ▲]

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See detailIn situ SAXS of resorcinol-formaldehyde gel formation: either microphase separation or colloid aggregation
Gommes, Cédric ULg; Roberts, Anthony; Goderis, Barts

Scientific conference (2008, December)

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See detailDetermination of the tortuosity of porous materials from binary or grey-tone tomographic reconstructions
Gommes, Cédric ULg; Almazan, Maria del Carmen; Léonard, Angélique ULg et al

Conference (2008, November)

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See detailIn-situ SAXS of resorcinol-formaldehyde gel formation: either colloid aggregation or microphase separation
Gommes, Cédric ULg; Roberts, Anthony; Goderis, Bart

Poster (2008, October)

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See detailQuantitative characterization of pore corrugation in SBA-15 mesoporous silica using image analysis of electron tomograms
Gommes, Cédric ULg; Friedrich, Heiner; Wolters, Mariska et al

Poster (2008, September)

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See detailNi/SiO2 Catalyst Preparation Studies using SBA-15 as a Model Support and quantitative Electron Tomography Characterisation
de Jongh, Petra; Friedrich, Heiner; Gommes, Cédric ULg et al

Poster (2008, September)

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See detailAnalysis of 3DTEM and SAXS of ordered mesoporous silica with the same stochastic morphological model
Gommes, Cédric ULg; Friedrich, Heiner; Wolters, Mariska et al

Scientific conference (2008, May)

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See detailDetermination of the coordination number of particulate nano-materials using nitrogen adsorption
Gommes, Cédric ULg; Ravikovitch, Peter; Neimak, Alex

Scientific conference (2008, April)

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See detail3D covariance of ordered mesoporous materials and its modelling with random cylinders
Gommes, Cédric ULg; Friedrich, H; Wolters, M et al

Scientific conference (2008, February)

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See detailFormation mechanism of Y-junctions in arrays of multi-walled carbon nanotubes
Zilli, Dario; Blacher, Silvia ULg; Cukierman, Ana Lea et al

in Colloids and Surfaces A : Physicochemical and Engineering Aspects (2008), 327(1-3), 140-143

Transmission electron microscopy of arrays of multi-walled carbon nanotubes reveals the presence of numerous Y-junctions. The diameter distributions of the samples are found to be bimodal, with one mode ... [more ▼]

Transmission electron microscopy of arrays of multi-walled carbon nanotubes reveals the presence of numerous Y-junctions. The diameter distributions of the samples are found to be bimodal, with one mode corresponding to the branches and the other mode to the trunk of the Y-junctions. The analysis of the micrographs shows that the junctions form via the merger of metal particles during the tip-growth of the tubes. (C) 2008 Elsevier B.V. All rights reserved. [less ▲]

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See detailEffect of the counter-ion of the basification agent on the pore texture of organic and carbon xerogels
Job, Nathalie ULg; Gommes, Cédric ULg; Pirard, René ULg et al

in Journal of Non-Crystalline Solids (2008), 354(40-41), 4698-4701

Organic and carbon xerogels were prepared by polycondensation of resorcinol with formaldehyde in water, followed by evaporative drying and, eventually, pyrolysis. The pH of the precursor's solution was ... [more ▼]

Organic and carbon xerogels were prepared by polycondensation of resorcinol with formaldehyde in water, followed by evaporative drying and, eventually, pyrolysis. The pH of the precursor's solution was fixed at 6.0 in all cases by adding various hydroxides as basification agent. Three alkali metal hydroxides (LiOH, NaOH and KOH) and three alkaline earth metals hydroxides (Ca(OH)(2), Ba(OH)(2), Sr(OH)(2)) were used. It was found that the pore texture of the organic and carbon xerogels is totally independent on the cation size, but depends on the charge and concentration of the counter-cation. Indeed, the pore size of the alkaline earth metal loaded samples is larger than that of the alkali metal-doped xerogels. As a matter of fact, to reach the same initial pH, the concentration in alkali metal hydroxide must be twice that of the alkaline earth metal base. The effect of ions on the pore texture was thus attributed to electrostatic effects on the microphase separation process that occurs prior to gelation. (C) 2008 Elsevier B.V. All rights reserved. [less ▲]

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See detailStructure development of resorcinol-formaldehyde gels: either microphase separation or colloid aggregation
Gommes, Cédric ULg; Roberts, Anthony

in Physical Review. E : Statistical, Nonlinear, and Soft Matter Physics (2008), 77

Time-resolved small-angle x-ray scattering (SAXS) is used to follow the formation of resorcinol-formaldehyde (RF) gels. An existing morphological model based on Gaussian random fields, and validated on RF ... [more ▼]

Time-resolved small-angle x-ray scattering (SAXS) is used to follow the formation of resorcinol-formaldehyde (RF) gels. An existing morphological model based on Gaussian random fields, and validated on RF aerogels, is generalized to analyze the data. The generalization is done in two different ways, one being relevant to colloid aggregation and the other to microphase separation. The SAXS data do not enable discrimination between the two mechanisms of gel formation, which shows that aggregation and microphase separation can generate very similar morphologies at the length scales explored by SAXS. Furthermore, physical arguments suggest that, in the case of RF gels, aggregation and microphase separation can be regarded as two idealizations of the same complex physical process. [less ▲]

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