In situ SAXS analysis of silica gel formation with an additive

in Journal of Physical Chemistry B (2004), 108(26), 8983-8991

Time-resolved small-angle X-ray scattering (SAXS) measurements performed during the formation of tetraethyl orthosilicate (TEOS) based silica gels in alcohol with 3-(2-aminoethylamino ... [more ▼]

Time-resolved small-angle X-ray scattering (SAXS) measurements performed during the formation of tetraethyl orthosilicate (TEOS) based silica gels in alcohol with 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS) as an additive are reported. The measurements reveal no discontinuity of the nanostructure at the gel point. A chemically induced spinodal phase separation is found to give a coherent picture of the collected data. Increasing the amount of EDAS induces the phase separation on a smaller length scale, which finally leads to a modified gel morphology. The SAXS measurements and the electron micrographs associated with the dry gels could be interpreted in terms of the suggested wet gel formation mechanism. [less ▲]

Xérogels de carbone chargés en métaux par solubilisation de sels dans la solution de précurseurs : influence sur la texture des matériaux carbonés

Conference (2004, March 15)

Synthesis of transition metal-doped carbon xerogels by solubilization of metal salts in resorcinol-formaldehyde aqueous solution

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 ▲]

Preparation of macroporous biodegradable poly(L-lactide-co-epsilon-caprolactone) foams and characterization by mercury intrusion porosimetry, image analysis, and impedancy spectroscopy

in Journal of Biomedical Materials Research (2003), 66A(2), 199-213

Two poly(L-lactide-co-epsilon-caprolactone) random copolymers containing 5 and 40 mol% of epsilon-CL, namely P(LA-co-CL5) and P(LA-co-CL40), respectively, have been made macroporous by freeze-drying ... [more ▼]

Two poly(L-lactide-co-epsilon-caprolactone) random copolymers containing 5 and 40 mol% of epsilon-CL, namely P(LA-co-CL5) and P(LA-co-CL40), respectively, have been made macroporous by freeze-drying solutions in dimethylcarbonate. Most of the freeze-dried foams, prepared by varying polymer concentration and cooling rate, exhibited two main pore populations: (1) longitudinally oriented tube-like macropores with diameters greater than or equal to100 mum, and (2) interconnected micropores (10-100 mum). Pore characteristics, including macropore density, mean diameter, and interdistance, as well as micropore density, area, and shape, were determined by image analysis of scanning electron micrographs in order to study the influence of processing and formulation parameters on foam structure and properties. The pore orientation and the 3-D texture also were studied by image analysis and impedance spectroscopy. In the case of the P(LA-co-CL5), the macropore diameter increased with the cooling rate while the micropore diameter decreased. The micropores also became more circular when the cooling rate was increased. The pore size and morphology of the P(LA-co-CL40) were quite unchanged by varying the cooling rate. All the other conditions being the same, the P(LA-co-CL5) foams were better organized than the P(LA-co-CL40) foams, and pore orientation was improved at the higher cooling rate. Pore size and morphology also can be controlled by changing the polymer concentration (Cp), as we showed by studying P(LA-co-CL5) foams prepared by freeze-drying solutions in the 1-10 w/v% Cp range. Macropore density, average diameter, and interdistance of P(LA-co-CL5) foams increased with Cp, but the micropore characteristics remained almost unchanged no matter the Cp. The reliability of the characterization methods has been discussed, with special attention to mercury intrusion porosimetry, which is used primarily for measurement of pore volume and pore size distribution. However, this technique is reported here as a destructive and unreliable method for the characterization of fragile P(LA-co-CL40) foams. This study shows that image analysis and impedance spectroscopy can give reliable information relative to the pore morphology and anisotropy of freeze-dried foams. [less ▲]

Porous carbon material

Patent (2003)

Multiscale texture characterization of wastewater sludges dried in a convective rig

in Drying Technology (2003), 21(8), 1507-1526

Secondary sludges from two different wastewater treatment plants are conditioned and dewatered in the same way before drying in a lab-scale convective rig at the same operating conditions. Several ... [more ▼]

Secondary sludges from two different wastewater treatment plants are conditioned and dewatered in the same way before drying in a lab-scale convective rig at the same operating conditions. Several techniques are used to characterize the texture of the dried materials over a wide range of scales from nm up to mm. Texture and porosity of the dried products are studied by SEM imaging, nitrogen absorption isotherms (0.5 < d(p) < 50 nm), mercury porosimetry (7.5 nm < d(p) < 150 mum) and X-ray microtomography (spatial resolution= 41 mum). The image analysis of cross-sections reconstructed by microtomography also allows following shrinkage and textural evolution during drying. [less ▲]

Single step synthesis of metal catalysts supported on porous carbon with controlled texture

Poster (2002, September 09)

Characterization of porous texture of hyperporous materials by mercury porosimetry using densification equation

in Powder Technology (2002), 128(2-3), 242-247

The purpose of this paper is to propose a method of analyzing the mercury porosimetry data in the case of materials called hyperporous. This class of material does not undergo intrusion by mercury ... [more ▼]

The purpose of this paper is to propose a method of analyzing the mercury porosimetry data in the case of materials called hyperporous. This class of material does not undergo intrusion by mercury; instead, it shrinks under the mercury isostatic pressure and its density increases. The phenomenon is partially or completely irreversible. The proposed method enables computing the pore volume distribution as a function of the pore size in the same way as Washburn's method does in the case of mercury intrusion. (C) 2002 Elsevier Science B.V. All rights reserved. [less ▲]

Characterisation of silica low-density xerogels in presence of additives by image analysis and nitrogen adsorption-desorption

in Characterization of Porous Solids VI (2002)

Micro- and mesopore structure modifications in silica low-density xerogels induced by additives in TEOS-based alcogels precursors are discussed on the basis of image analysis of transmission electron ... [more ▼]

Micro- and mesopore structure modifications in silica low-density xerogels induced by additives in TEOS-based alcogels precursors are discussed on the basis of image analysis of transmission electron microscopy (TEM) micrographs and nitrogen adsorption-desorption experiments. To perform image analysis, novel image processing has been developed on the basis of classical signal treatment and mathematical morphology theory. The obtained results have been correlated with classical and fractal interpretation of nitrogen adsorption-desorption measurements. [less ▲]

The role of the main silica precursor and the additive in the preparation, of low-density xerogels

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 ▲]