References of "Pirard, René"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailThe role of the main silica precursor and the additive in the preparation, of low-density xerogels
Alié, Christelle ULg; Pirard, René ULg; Pirard, Jean-Paul ULg

in Journal of Non-Crystalline Solids (2002), 311(3), 304-313

The incorporation of an additive during sol-gel synthesis reduces shinkage during ambient drying. The following additives have been studied: 3-,(2-aminoethylamino)propyltrimethoxysilane (EDAS), 3 ... [more ▼]

The incorporation of an additive during sol-gel synthesis reduces shinkage during ambient drying. The following additives have been studied: 3-,(2-aminoethylamino)propyltrimethoxysilane (EDAS), 3-aminopropyltriethoxysilane (AES) and 3-(2-aminoethylamino)propyltriethoxysilane (EDAES) and the main silica precursors were tetraethylorthosilicate (TEOS) and tetrapropylorthosilicate (TPOS). When the additive contains methoxy groups (EDAS), it acts as a nucleation agent of the silica particles and exactly the same properties (pore volume, specific surface area, particle and aggregate size) are obtained whether the main reagent is TEOS or TPOS. The nucleation mechanism is based on the difference in reactivity between additive and main reagent. In case of nucleation by the additive, the nucleation agent fixes the properties whatever the main silica precursor is. When both the additive and the main reagent contain ethoxy groups (series AES-TEOS and EDAES-TEOS), there is no nucleation mechanism by the additive, and the silica particle size remains nearly constant. With less reactive main reagent (series AES-TPOS and EDAES-TPOS), pore volumes up to 17 cm(3)/g have been obtained with pore sizes up to nearly 10 pm and very big particles (similar to100 nm). The absence of nucleation by the additive for the couples AES-TPOS and EDAES-TPOS could be due to the fact that the difference in reactivity between ethoxy groups and propoxy groups is not sufficient to initiate the nucleation mechanism by the additive. In the absence of nucleation by the additive, the main reagent plays a role: highly porous materials with very large p. ores are prepared with TPOS. (C) 2002 Elsevier Science B.V. All rights reserved. [less ▲]

Detailed reference viewed: 30 (11 ULg)
Full Text
Peer Reviewed
See detailMercury porosimetry applied to porous silica materials: successive buckling and intrusion mechanisms
Alié, Christelle ULg; Pirard, René ULg; Pirard, Jean-Paul ULg

in Colloids and Surfaces A : Physicochemical and Engineering Aspects (2001), 187

Some silica low-density xerogels exhibit two successive volume variation mechanisms, compaction and intrusion when submitted to mercury porosimetry. The position of the pressure of transition P-t between ... [more ▼]

Some silica low-density xerogels exhibit two successive volume variation mechanisms, compaction and intrusion when submitted to mercury porosimetry. The position of the pressure of transition P-t between the two mechanisms is characteristic of the tested material and allows to compute the buckling constant used to determine the pore size distribution in the compaction part of the experiment. The analysis of the mercury porosimetry data of a low-density xerogel wrapped in a tight membrane by the buckling law (intrusion is prevented and the sample is crushed during the whole porosimetry experiment) leads to a continuous unimodal distribution similar to the distribution of the unwrapped sample obtained by applying the buckling law below P-t and the intrusion law above P-t. This experiment confirms the validity of the use of the buckling law. The behaviour of the low-density xerogels can be related to one of their morphological characteristics. As the size of the aggregates of silica particles increases, the strength towards crushing increases and the change of mechanism from crushing to intrusion takes place at a lower pressure. (C) 2001 Elsevier Science B.V. All rights reserved. [less ▲]

Detailed reference viewed: 17 (0 ULg)
Full Text
Peer Reviewed
See detailImage analysis, impedance spectroscopy and mercury porosimetry characterisation of freeze-drying porous materials
Blacher, Silvia ULg; Maquet, Véronique; Pirard, René ULg et al

in Colloids and Surfaces A : Physicochemical and Engineering Aspects (2001), 187-188

Image analysis and impedance spectroscopy have been used as potential tools for the characterization of the texture of ultramacroporous PLA foams prepared by freeze-drying. It has been shown that these ... [more ▼]

Image analysis and impedance spectroscopy have been used as potential tools for the characterization of the texture of ultramacroporous PLA foams prepared by freeze-drying. It has been shown that these two techniques actually provide valuable information on the structure of this material. They are complementary to mercury porosimetry, which does not allow morphological details to be distinguished. Image analysis of SEM micrographs of transverse cross-sections at two different magnifications gave information on both the macroporosity (1 μm < width < 10 μm) and ultramacroporosity (width > 10 μm). Impedance spectroscopy was used to investigate the transport properties of the three-dimensional porous matrices by measurement of ionic conduction [less ▲]

Detailed reference viewed: 49 (8 ULg)
Full Text
Peer Reviewed
See detailThe use of additives to prepare low-density xerogels
Alié, Christelle ULg; Pirard, René ULg; Lecloux, A. J. et al

in Journal of Non-Crystalline Solids (2001), 285

Detailed reference viewed: 11 (5 ULg)
Full Text
Peer Reviewed
See detailPreparation of low-density xerogels by incorporation of additives during synthesis
Alié, Christelle ULg; Ferauche, Fabrice; Pirard, René ULg et al

in Journal of Non-Crystalline Solids (2001), 289(1-3), 88-96

Low-density xerogels were prepared by incorporation of an additive to alcogels prior to gelation. The additives studied are 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS), 3 ... [more ▼]

Low-density xerogels were prepared by incorporation of an additive to alcogels prior to gelation. The additives studied are 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS), 3-aminopropyltrimethoxysilane (AMS), propyltrimethoxysilane (PMS), tetramethylorthosilicate (TMOS) and 3-aminopropyltriethoxysilane (AES) using tetraethylorthosilicate (TEOS) as main silica precursor. Samples were also prepared with EDAS as additive and TMOS as main silica reagent. When the additive contains methoxy groups, it reacts first, forms nuclei on which the main reagent TEOS reacts to form the silica particles. The nucleation mechanism by the additive occurs only in case of a difference of reactivity between additive and main silica precursor. The other group of the additive (amine, alkyl group, ...) influences only the gelation time. In case of ethoxy groups (series AES/TEOS) or methoxy groups (series EDAS/TMOS) for both additive and main reagent, there is no nucleation by the additive. (C) 2001 Elsevier Science B.V. All rights reserved. [less ▲]

Detailed reference viewed: 10 (2 ULg)
Full Text
Peer Reviewed
See detailMercury porosimetry: applicability of the buckling-intrusion mechanism to low-density xerogels
Alié, Christelle ULg; Pirard, René ULg; Pirard, Jean-Paul ULg

in Journal of Non-Crystalline Solids (2001), 292(1-3), 138-149

Mineral materials can be either crushed or invaded by mercury during mercury porosimetry experiments. It has been shown here that many low-density xerogels exhibit the two volume variation mechanisms ... [more ▼]

Mineral materials can be either crushed or invaded by mercury during mercury porosimetry experiments. It has been shown here that many low-density xerogels exhibit the two volume variation mechanisms successively, compaction followed by intrusion. when submitted to mercury porosimetry and that a unimodal pore size distribution can be obtained by applying Pirard's collapse model below the pressure of transition P-1 and Washburn's intrusion theory above P-t. To confirm the validity of the use of the buckling law, one low-density xerogel was wrapped in a tight membrane (intrusion is prevented and the sample is crushed during the whole porosimetry experiment). The analysis of the mercury porosimetry data of the wrapped sample by the buckling law leads to a continuous unimodal distribution similar to the distribution of the unwrapped sample obtained by applying the buckling law below P-t and the intrusion law above P-t. The position of P-t is characteristic of the tested material: when submitted to mercury pressure. aerogels and low-density xerogels only collapse in case of very small aggregates whereas they are crushed and then intruded in case of larger silica aggregates. The fact that compacted slabs of monodisperse non-aggregated silica spheres (of the same size range as the xerogels and aerogels) show only intrusion during mercury porosimetry experiments implies that the particles need to be aggregated so that the compaction mechanism takes place. The position of the change of mechanism from crushing to intrusion is not directly related to the size of the elementary particles but is linked to the size of the aggregates of silica particles. (C) 2001 Elsevier Science B.V. All rights reserved. [less ▲]

Detailed reference viewed: 22 (4 ULg)
Full Text
Peer Reviewed
See detailCharacterization of porous polylactide foams by image analysis and impedance spectroscopy
Maquet, Véronique; Blacher, Silvia ULg; Pirard, René ULg et al

in Langmuir (2000), 16(26), 10463-10470

The texture of highly porous polylactide foams prepared by freeze-drying of poly-L-lactide (L-PLA) and poly-DL-lactide (DL-PLA) solutions of various concentrations was investigated by two novel ... [more ▼]

The texture of highly porous polylactide foams prepared by freeze-drying of poly-L-lactide (L-PLA) and poly-DL-lactide (DL-PLA) solutions of various concentrations was investigated by two novel methodologies, image analysis and impedance spectroscopy. Image analysis of scanning electron micrographs of transverse cross-sections at two different magnifications gave information on both the macroporosity (1 mum < width 10 <mu>m) and ultramacroporosity (width > 10 mum). Impedance spectroscopy was used to investigate the transport properties of the three-dimensional porous matrices by measurement of ionic conduction. Image analysis showed that: (a) the macroporosity, which mainly contributes to porosity, is independent of the sample composition; (b) when the concentration of the polymer solution is increased, the density of the ultramacropores decreases and their average diameter increases; (c) the distribution of the ultramacropores is more homogeneous in the semicrystalline L-PLA. foams than in the amorphous DL-PLA counterparts, in which the ultramacropores tend to make clusters. The dielectric properties changed at low frequency, in relation to modifications in the ultramacroporosity. Ultramacropores of the L-PLA foams were found to be more open and more sensitive to the concentration of the polymer solutions compared with DL-PLA. Expectedly, the mechanical properties of the PLA foams changed with the structure of the ultramacroporous network. These results encourage further investigations on the texture of porous supports, to collect pertinent information on the physical macro- and ultramacroenvironment in which cells will reside. [less ▲]

Detailed reference viewed: 37 (11 ULg)
Full Text
Peer Reviewed
See detailFractal characterization of wide pore range catalysts: Application to Pd-Ag/SiO2 xerogels
Blacher, Silvia ULg; Heinrichs, Benoît ULg; Sahouli, Bendida et al

in Journal of Colloid & Interface Science (2000), 226(1), 123-130

Fractal analysis has been applied to characterize the structure of Pd-Ag/SiO2 catalysts dried under vacuum (150 degrees C and 12 hPa) with different concentrations of Pd-Ag, Nitrogen adsorption-desorption ... [more ▼]

Fractal analysis has been applied to characterize the structure of Pd-Ag/SiO2 catalysts dried under vacuum (150 degrees C and 12 hPa) with different concentrations of Pd-Ag, Nitrogen adsorption-desorption, mercury porosimetry, and small-angle X-ray scattering measurements have been used. The different approaches to fractal analysis and their conditions of applicability are briefly described. Results are discussed in relation to those derived previously from classical interpretations. This analysis shows that Pd-Ag/SiO2 xerogels exhibit a very open self-similar pore structure analogous to the structure of supercritically dried aerogels and that the micropore texture can be tailored by varying the silver content. (C) 2000 Academic Press. [less ▲]

Detailed reference viewed: 34 (5 ULg)
Full Text
Peer Reviewed
See detailMicropore size distributions of activated carbons
Blacher, Silvia ULg; Sahouli, Bendida; Heinrichs, Benoît ULg et al

in Langmuir (2000), 16(16), 6754-6756

Detailed reference viewed: 29 (7 ULg)
Full Text
Peer Reviewed
See detailTextural properties of low-density xerogels
Alié, Christelle ULg; Benhaddou, Arnaud; Pirard, René ULg et al

in Journal of Non-Crystalline Solids (2000), 270(1-3), 77-90

The extent of shrinkage during drying is controlled by the balance between the capillary pressure developed in the pore liquid and the modulus of the solid network. One first method to obtain low-density ... [more ▼]

The extent of shrinkage during drying is controlled by the balance between the capillary pressure developed in the pore liquid and the modulus of the solid network. One first method to obtain low-density xerogels consists in strengthening TEOS-based alcogels by providing new monomers to the alcogel after gelation. In the second method, low-density xerogels are produced by surface modification (silylation) of the wet gel with trimethylchlorosilane. The capillary pressure is reduced and the presence of non-reactive species on the surface makes the shrinkage reversible. A reduction of the capillary pressure can be achieved by introduction of a substituted alkoxide 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS) to a TEOS-based alcogel, synthesised in a single base-catalysed step. This additive acts as a nucleation agent leading to big silica particles (similar to 20 nm) with a low EDAS/TEOS ratio (similar to 0.03). The pores between those particles are also large and the drying stress is reduced. The textural properties of those three materials are compared: bulk densities of the samples modelled on the first and third method are varying in the same range (0.25-0.35 g/cm(3)) while xerogels obtained by the surface modification process are less dense (0.1-0.15 g/cm(3)). The biggest pores are observed in the third method. (C) 2000 Elsevier Science B.V. All rights reserved. [less ▲]

Detailed reference viewed: 12 (2 ULg)
Full Text
Peer Reviewed
See detailFractal Analysis of Mercury Porosimetry Data in the Framework of the Thermodynamic Method
Sahouli, B; Blacher, Silvia ULg; Pirard, René ULg et al

in Journal of Colloid & Interface Science (1999), 214(2), 450-454

The thermodynamic method for fractal analysis is applied to mercury intrusion data. The results for representative commercial carbon black samples and a series of resorcinol-formaldehyde (RF) freeze-dried ... [more ▼]

The thermodynamic method for fractal analysis is applied to mercury intrusion data. The results for representative commercial carbon black samples and a series of resorcinol-formaldehyde (RF) freeze-dried gels for different values of the molar ratio of resorcinol (R) to catalyst (C) are discussed in relation with the type of behavior exhibited by the samples during mercury porosimetry measurements. The obtained surface fractal dimensions are compared with those derived previously from the small-angle X ray scattering (SAXS) and the nitrogen adsorption. Copyright 1999 Academic Press. [less ▲]

Detailed reference viewed: 1 (0 ULg)
Full Text
Peer Reviewed
See detailSequentially compressive and intrusive mechanisms in mercury porosimetry of carbon blacks
Pirard, René ULg; Sahouli, Bendida; Blacher, Silvia ULg et al

in Journal of Colloid & Interface Science (1999), 217(1), 216-217

The mechanism of mercury penetration in two different commercial carbon blacks is studied. We show that the volume variation measured by mercury porosimetry in these systems is due to three successive ... [more ▼]

The mechanism of mercury penetration in two different commercial carbon blacks is studied. We show that the volume variation measured by mercury porosimetry in these systems is due to three successive mechanisms, which occur as the pressure increases: (1) mercury invasion of voids between macroscopic grains, (2) compaction and elastic compression of macroscopic grains, (3) intrusion in the voids of aggregates formed by primary particles. The cumulative surface calculated by the Rootare-Prenzlow equation (S-RP) in the intrusion part and the BET surface area measured by nitrogen adsorption (S-BET) are compared. (C) 1999 Academic Press. [less ▲]

Detailed reference viewed: 18 (2 ULg)
Full Text
Peer Reviewed
See detailPreparation of low-density xerogels through additives to TEOS-based alcogels
Alié, Christelle ULg; Pirard, René ULg; Lecloux, A. J. et al

in Journal of Non-Crystalline Solids (1999), 246(3), 216-228

A new process for preparing silica xerogels with similar textural properties to silica aerogels by drying under vacuum has been studied. The xerogels are produced by adding, before gelation, 3-(2 ... [more ▼]

A new process for preparing silica xerogels with similar textural properties to silica aerogels by drying under vacuum has been studied. The xerogels are produced by adding, before gelation, 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS) to tetraethylorthosilicate (TEOS)-based alcogels, synthesised in a single base-catalysed (NH3) step. It is hypothesized that EDAS acts as a nucleation agent leading to silica particles with a hydrolysed EDAS core and a shell principally made of hydrolysed TEOS. The EDAS concentration and the basicity of the aqueous NH3 solution are important parameters influencing the resistance of the gel to drying stress. A decreasing EDAS/TEOS ratio or an increasing concentration of NH3 at constant EDAS content leads to less shrinkage during drying and so the final pore volume is larger. Gels prepared with a low EDAS/TEOS ratio (about 0.03) contain large particles (similar to 20 nm) due to the nucleation process by EDAS, thus the pores between those particles are also large and the drying stress is reduced. (C) 1999 Published by Elsevier Science B.V. All rights reserved. [less ▲]

Detailed reference viewed: 24 (3 ULg)
Full Text
Peer Reviewed
See detailMercury porosimetry applied to low density xerogels; relation between structure and mechanical properties
Pirard, René ULg; Heinrichs, Benoît ULg; Van Cantfort, Olivier et al

in Journal of Sol-Gel Science and Technology (1998), 13(1-3), 335-339

Samples of low density xerogels were submitted to mercury porosimetry at pressures up to 200 MPa. These samples show an unusual behavior: they are first crushed by the isostatic mercury pressure without ... [more ▼]

Samples of low density xerogels were submitted to mercury porosimetry at pressures up to 200 MPa. These samples show an unusual behavior: they are first crushed by the isostatic mercury pressure without mercury intrusion and are then intruded by the mercury above a certain pressure. This transition allows the easy determination of the one constant found in the buckling model that is used to interpret the crushing part of the mercury porosimetry experiment. The relation between this constant and the structure of the xerogels determined by TEM and nitrogen adsorption is discussed. [less ▲]

Detailed reference viewed: 17 (2 ULg)
Full Text
Peer Reviewed
See detailTexture control of freeze-dried resorcinol-formaldehyde gels
Kocklenberg, Régine; Mathieu, Bernard; Blacher, Silvia ULg et al

in Journal of Non-Crystalline Solids (1998), 225

Detailed reference viewed: 47 (3 ULg)
Full Text
Peer Reviewed
See detailRheological characterization of BaTiO3 sol-gel transition
Brasseur, Alain; Michaux, Bernard; Pirard, René ULg et al

in Journal of Sol-Gel Science and Technology (1997), 9(1), 5-15

BaTiO3 gels were prepared by hydrolysis and polycondensation reactions between titanium isopropoxide and barium hydroxide in presence of methoxyethanol, methanol and water. The rheology of the sol-gel ... [more ▼]

BaTiO3 gels were prepared by hydrolysis and polycondensation reactions between titanium isopropoxide and barium hydroxide in presence of methoxyethanol, methanol and water. The rheology of the sol-gel transition was studied with a rheometer allowing low amplitude sinusoidal oscillations. Experimental data show a continuous increase in the complex viscosity along with time, showing the progressive character of the transition. The influence of synthesis operating variables was studied. The gelation time, which definition is based on viscoelastic measurements, increases exponentially when the water content is increased, when the dilution due to the methoxyethanol is reduced or when the temperature is lowered. Different growth models were used for the characterization of the particles in the solution. These models suggest that the polymerisation first produces spherical particles (mass fractals) and that these spherical particles then agglomerate to form a linear network. [less ▲]

Detailed reference viewed: 48 (5 ULg)
Peer Reviewed
See detailMercury porosimetry applied to low density xerogels
Pirard, René ULg; Heinrichs, Benoît ULg; Pirard, Jean-Paul ULg

in Characterization of Porous Solids IV (1997)

Detailed reference viewed: 13 (6 ULg)
Full Text
Peer Reviewed
See detailRheological characterization on the BaTiO3 sol-gel transition
Van Cantfort, Olivier; Brasseur, Alain; Michaux, Bernard et al

in Faraday Discussions (1997), 101

Detailed reference viewed: 20 (3 ULg)