References of "Journal of Non-Crystalline Solids"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailCharacterization of surface and porous properties of synthetic hybrid lamellar silica
Toussaint, Gilles ULg; Rodriguez, Miguel Angel; Cloots, Rudi ULg et al

in Journal of Non-Crystalline Solids (2011), 357

Synthetic lamellar silica and hybrid lamellar silicas have been prepared by liquid crystal templating, template extraction and silanization. The samples have been characterized by thermogravimetric ... [more ▼]

Synthetic lamellar silica and hybrid lamellar silicas have been prepared by liquid crystal templating, template extraction and silanization. The samples have been characterized by thermogravimetric analysis (TGA), carbon analysis, spectroscopy, X-ray diffraction (XRD) and nitrogen adsorption. The XRD analyses have shown that the lamellar periodic stacking is preserved for all samples. The quantity and type of organic molecules at the silica surface have been evaluated by carbon analysis, TGA and spectroscopy. The covalent grafting of the solvent used for extraction of the initial surfactant has been highlighted by these analyses. The nitrogen adsorption analyses have revealed three categories of pores and two types of samples. The initial lamellar silica exhibits a very low specific surface area and plate-like type of pores. The second type of samples is made up of the hybrid samples and the initial substrate from whom the surfactant has been extracted. These samples show a significantly higher specific surface area with interlamellar spaces corresponding to narrow-slit like mesopores around 4 nm. The nitrogen adsorption data analysis has highlighted the presence of micropores within the silica sheets. The difference of the specific surface is due to pore blocking by the surfactant impeding the access to nitrogen into interlamellar spaces and by the silanes covering the pores once the surface modified. The presence of micro and mesopores combined to a high BET specific surface of 612 m²/g makes these lamellar silicas interesting materials for catalysis applications. [less ▲]

Detailed reference viewed: 35 (9 ULg)
Full Text
Peer Reviewed
See detailPreparation and characterization of ZnO-TiO(2) films obtained by sol-gel method
Ivanova, T.; Harizanova, A.; Koutzarova, T. et al

in Journal Of Non-Crystalline Solids (2011), 357(15), 2840-2845

The sol-gel route has been applied to obtain ZnO-TiO(2) thin films. For comparison, pure TiO(2) and ZnO films are also prepared from the corresponding solutions. The films are deposited by a spin-coated ... [more ▼]

The sol-gel route has been applied to obtain ZnO-TiO(2) thin films. For comparison, pure TiO(2) and ZnO films are also prepared from the corresponding solutions. The films are deposited by a spin-coated method on silicon and glass substrates. Their structural and vibrational properties have been studied as a function of the annealing temperatures (400-750 degrees C). Pure ZnO films crystallize in a wurtzite modification at a relatively low temperature of 400 degrees C, whereas the mixed oxide films show predominantly amorphous structure at this temperature. XRD analysis shows that by increasing the annealing temperatures, the sol-gel Zn/Ti oxide films reveal a certain degree of crystallization and their structures are found to be mixtures of wurtzite ZnO, Zn(2)TiO(4), anatase TiO(2) and amorphous fraction. The XRD analysis presumes that Zn(2)TiO(4) becomes a favored phase at the highest annealing temperature of 750 degrees C. The obtained thin films are uniform with no visual defects. The optical properties of ZnO-TiO(2) films have been compared with those of single component films (ZnO and TiO(2)). The mixed oxide films present a high transparency with a slight decrease by increasing the annealing temperature. (C) 2011 Elsevier B.V. All rights reserved. [less ▲]

Detailed reference viewed: 44 (3 ULg)
Full Text
Peer Reviewed
See detailEvolution of mechanical properties and final textural properties of resorcinol-formaldehyde xerogels during ambient air drying
Léonard, Angélique ULg; Blacher, Silvia ULg; Crine, Michel ULg et al

in Journal of Non-Crystalline Solids (2008), 354(10-11), 831-838

Porous carbon xerogels can be obtained by convective drying of resorcinol (R)-formaldehyde (F) hydrogels, followed by pyrolysis. Drying conditions have to be carefully controlled when crack-free monoliths ... [more ▼]

Porous carbon xerogels can be obtained by convective drying of resorcinol (R)-formaldehyde (F) hydrogels, followed by pyrolysis. Drying conditions have to be carefully controlled when crack-free monoliths with well-defined shape and size are required. The knowledge of the mechanical properties of the RF xerogels and their evolution with water content is essential to model their thermo-hygro-mechanical behavior during convective drying and avoid mechanical stresses leading to deformation and cracking of the sample. The shrinkage behavior and the mechanical properties of RF xerogels obtained with R/C ratio ranging from 300 to 1500 were investigated. R/C greatly influences the shrinkage and mechanical properties of the wet gel, on the one hand, and the mechanical and textural properties of the dried gel, on the other hand. The smaller the R/C, the higher the shrinkage, the stiffening, and the viscoelastic character of the xerogels. Water content has an influence on both the stiffness of the gels and the viscoelastic response. Generally, samples lose their mechanical viscous character and become more rigid when they are dried. Finally., mercury porosimetry measurements showed that the gels exhibit a marked lowering of their stiffness upon compression, interpreted as a result of the heterogeneity of the microstructure. (C) 2007 Elsevier B.V. All rights reserved. [less ▲]

Detailed reference viewed: 52 (5 ULg)
Full Text
Peer Reviewed
See detailMicrowave drying as an effective method to obtain porous carbon xerogels
Zubizarreta, Leire; Arenillas, Ana; Menendez, J. A. et al

in Journal of Non-Crystalline Solids (2008), 354(33), 4024-4026

Microwave drying was used to prepare resorcinol-formaldehyde aqueous gels, without performing any pretreatment, and to see whether it was possible to use this drying option to obtain porous carbon ... [more ▼]

Microwave drying was used to prepare resorcinol-formaldehyde aqueous gels, without performing any pretreatment, and to see whether it was possible to use this drying option to obtain porous carbon xerogels with controlled textural properties. By using microwave drying, the process for obtaining carbon gels is greatly simplified, textural properties are controlled likewise with other drying methods, but the time involved in the process is significantly reduced and no pretreatment is necessary. Therefore, microwave drying could help to simplify the carbon xerogels synthesis and reduce the associated costs. (C) 2008 Elsevier B.V. All rights reserved. [less ▲]

Detailed reference viewed: 29 (2 ULg)
Full Text
Peer Reviewed
See detailIron(III) species dispersed in porous silica through sol-gel chemistry
Heinrichs, Benoît ULg; Rebbouh, Leila; Geus, John W et al

in Journal of Non-Crystalline Solids (2008), 354(2-9), 665-672

Fe/SiO2 catalysts have been prepared by two different sol-gel methods, cogelation and dissolution. The cogelation and dissolution preparative methods lead to xerogels with fundamentally different pore ... [more ▼]

Fe/SiO2 catalysts have been prepared by two different sol-gel methods, cogelation and dissolution. The cogelation and dissolution preparative methods lead to xerogels with fundamentally different pore width distributions. The nature of the iron species obtained has been examined in detail by UN-visible and Mossbauer spectroscopy, and magnetic, transmission electron microscopy, and X-ray diffraction studies. There is no evidence for the presence of any ordered iron(III) oxides in the samples but all three contain two types of iron species, specifically paramagnetic high-spin iron(III) ions isolated in silica and iron(III) containing nanoparticles with a broad width distribution centered on 1.5 nm, nanoparticles that contain antiferromagnetically coupled clusters of a few ligated bridged iron(III) ions. (C) 2007 Elsevier B.V. All rights reserved. [less ▲]

Detailed reference viewed: 57 (29 ULg)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 81 (13 ULg)
Full Text
Peer Reviewed
See detailBranching, aggregation, and phase separation during the gelation of tetraethoxysilane
Gommes, Cédric; Goderis, Bart; Pirard, Jean-Paul ULg et al

in Journal of Non-Crystalline Solids (2007), 353(24-25), 2495-2499

Time-resolved small-angle X-ray scattering is used to follow in situ the structuring of silica sols and gels in various chemical conditions. The acid-catalyzed and base-catalyzed polymerizations of TEOS ... [more ▼]

Time-resolved small-angle X-ray scattering is used to follow in situ the structuring of silica sols and gels in various chemical conditions. The acid-catalyzed and base-catalyzed polymerizations of TEOS, as well as the copolymerization of TEOS with organically modified trialkoxysilanes, are followed. The analysis points to the diversity of the mechanisms that govern the structuring of the reacting solutions, and most notably to the important role of physical forces. (C) 2007 Elsevier B.V.All rights reserved. [less ▲]

Detailed reference viewed: 25 (7 ULg)
Full Text
Peer Reviewed
See detailSynthesis of transition metal-doped carbon xerogels by cogelation
Job, Nathalie ULg; Pirard, René ULg; Vertruyen, Bénédicte ULg et al

in Journal of Non-Crystalline Solids (2007), 353(24-25), 2333-2345

The cogelation process, i.e. the co-polymerization of a metal complex with the gel precursors, was used for the synthesis of transition metal-doped resorcinol-formaldehyde gels. The aim of this process is ... [more ▼]

The cogelation process, i.e. the co-polymerization of a metal complex with the gel precursors, was used for the synthesis of transition metal-doped resorcinol-formaldehyde gels. The aim of this process is to anchor the metal to the polymer so that the former does not sinter during the pyrolysis step leading to porous carbon. Cu-, Ni-, Pd- or Pt-loaded gels were prepared by this technique. After drying and pyrolysis, Pd and Pt were obtained as metal nanoparticles (2-5 nm in diameter) inserted in the carbon nodules, when the complexing agent and the synthesis conditions were well chosen. These small metal particles were inaccessible to reactive gases, probably due to carbon deposit at the metal surface during pyrolysis: CO almost did not chemisorb. Oxidation of the support or pyrolysis under reductive atmosphere was applied to the metal-doped gels and carbons in order to make the surface of the metal particles accessible, but these treatments develop the macropores only. The cogelation process is then suitable to prepare metal nanoparticles protected from the outside by encapsulation in the carbon matrix. (C) 2007 Elsevier B.V. All rights reserved. [less ▲]

Detailed reference viewed: 83 (22 ULg)
Full Text
Peer Reviewed
See detailMultigram scale synthesis and characterization of low-density silica xerogels
Alié, Christelle ULg; Tcherkassova, Natalia ULg; Ferauche, Fabrice et al

in Journal of Non-Crystalline Solids (2006), 352(26-27), 2763-2771

The synthesis of silica with preserved porosity and tailored morphology by sol-gel process can be achieved by hybrid organic-inorganic synthesis: a modified alkoxide, viz. 3-(2-aminoethylamino ... [more ▼]

The synthesis of silica with preserved porosity and tailored morphology by sol-gel process can be achieved by hybrid organic-inorganic synthesis: a modified alkoxide, viz. 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS), is introduced during the base catalysed synthesis with TEOS as main silica precursor. Additives with methoxy groups induce a nucleation mechanism because of their higher reactivity compared to main reagents with ethoxy groups. The nucleation model presented in previous papers was refined by taking into account the porosity of the particles and calculating the number of additive molecules by nucleus for each value of the ratio of additive/main reagent. The extrapolation of the synthesis process to semi-industrial scale goes through the replacement of laboratory grade reagents by industrial grade reagents and the scaling up to the production of higher quantities. At each of these two steps, the morphology and porosity of the samples has been compared to those of laboratory grade samples. It was shown that the texture and particle size has quasi totally been preserved. (c) 2006 Elsevier B.V. All rights reserved. [less ▲]

Detailed reference viewed: 45 (12 ULg)
Full Text
Peer Reviewed
See detailMethods for the preparation of bimetallic xerogel catalysts designed for chlorinated wastes processing
Lambert, Stéphanie ULg; Ferauche, Fabrice; Heinrichs, Benoît ULg et al

in Journal of Non-Crystalline Solids (2006), 352(26-27), 2751-2762

The aim of this work is to simplify and generalize the synthesis procedure of bimetallic supported catalysts by sol-gel process. For Pd-Ag/SiO2, co-gelled xerogels catalysts a number of synthesis ... [more ▼]

The aim of this work is to simplify and generalize the synthesis procedure of bimetallic supported catalysts by sol-gel process. For Pd-Ag/SiO2, co-gelled xerogels catalysts a number of synthesis procedures were compared: use of one or two specific alkoxides able to form a chelate with palladium and/or silver cations, reagent mixing in one or two steps, use of industrial grade chemicals instead of laboratory grade chemicals. The catalysts obtained are quite similar: same metal dispersion, same tailored morphology, same localization and accessibility of Pd-Ag alloy nanoparticles inside microporous silica, same activity and selectivity for hydrodechlorination of 1,2-dichloroethane into ethylene. For catalyst production at large scale the synthesis can be achieved in one step with 3-(2-aminoethyl)aminopropyltrimethoxysilane of industrial grade as chelating alkoxide, tetraethylorthosilicate (TEOS) of industrial grade and ethanol denatured with diethyl phthalate. (c) 2006 Elsevier B.V. All rights reserved. [less ▲]

Detailed reference viewed: 43 (10 ULg)
Full Text
Peer Reviewed
See detailSynthesis optimization of organic xerogels produced from convective air-drying of resorcinol-formaldehyde gels
Job, Nathalie ULg; Panariello, Fabian; Marien, José ULg et al

in Journal of Non-Crystalline Solids (2006), 352(1), 24-34

Resorcinol-formaldehyde gels were produced at 50, 70 and 90 degrees C and with three different R/C ratios (500, 1000 and 2000). The effect of these variables combined with that of aging time was studied ... [more ▼]

Resorcinol-formaldehyde gels were produced at 50, 70 and 90 degrees C and with three different R/C ratios (500, 1000 and 2000). The effect of these variables combined with that of aging time was studied in order to optimize the synthesis conditions. The convective air-drying process was used, and the drying duration was studied with regard to the synthesis conditions. The aging time has no effect on the pore texture after 24 h at 90 degrees C or 48 h at 70 C, whatever the R/C value. The synthesis-aging step can be shortened by increasing the temperature. Nevertheless, the pore size tends then to decrease, especially when R/C is high, but this can be counterbalanced by increasing R/C. Moreover, bubbles often appear in the gel at high synthesis temperature, which limits the temperature to about 70 degrees C in the case of monolithic parts. At 70 degrees C and with an air velocity of 2 m/s, the elimination of 90% of the solvent requires 1 h drying when the pore size reaches 400-600 nm, 2.5 h for 50 nm wide pores and 3 h when the pore size decreases to 15-20 nm. The drying duration does not exceed 8 h in all cases and could be shortened by increasing the temperature at the end of the process. (c) 2005 Elsevier B.V. All rights reserved. [less ▲]

Detailed reference viewed: 40 (1 ULg)
Full Text
Peer Reviewed
See detailFormation and structural characteristics of Pd-Ag/SiO2 and Pd-Cu/SiO2 catalysts synthesized by cogelation
Lambert, Stéphanie ULg; Gommes, Cédric ULg; Alié, Christelle ULg et al

in Journal of Non-Crystalline Solids (2005), 351(52-54), 3839-3853

Pd-Ag/SiO2 and Pd-Cu/SiO2 xerogel catalysts have been synthesized by cogelation of tetraethoxysilane (TEOS) and chelates of either Pd and Ag or Pd and Cu with 3-(2-aminoethylamino)propyltrimethoxysilane ... [more ▼]

Pd-Ag/SiO2 and Pd-Cu/SiO2 xerogel catalysts have been synthesized by cogelation of tetraethoxysilane (TEOS) and chelates of either Pd and Ag or Pd and Cu with 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS). After an extensive study of the influences of synthesis operating variables over structural characteristics of gels, highly dispersed bimetallic Pd-Ag/SiO2 and Pd-Cu/SiO2 xerogel catalysts were obtained. These samples are then composed of completely accessible Pd-Ag and Pd-Cu alloy crystallites with sizes of 2-3.5 nm located inside silica particles exhibiting a monodisperse microporous distribution. It appears also that the metal complex acts as a nucleation agent in the formation of silica particles. (c) 2005 Elsevier B.V. All rights reserved. [less ▲]

Detailed reference viewed: 35 (6 ULg)
Full Text
Peer Reviewed
See detailPreparation and characterization of xerogel catalyst microspheres
Alié, Christelle ULg; Ferauche, Fabrice; Heinrichs, Benoît ULg et al

in Journal of Non-Crystalline Solids (2004), 350

For easier handling and use in fixed bed reactors, Pd-Ag/SiO2 aerogel-like xerogel catalysts were shaped into microspheres using the microencapsulation process developed by BRACE GmbH. Before the bead ... [more ▼]

For easier handling and use in fixed bed reactors, Pd-Ag/SiO2 aerogel-like xerogel catalysts were shaped into microspheres using the microencapsulation process developed by BRACE GmbH. Before the bead production process, the xerogel catalyst was ground in water and mixed with ethylene glycol and sodium alginate, the latter of which is the gelation agent. The beads were formed at a vibrating nozzle and solidified during their fall in a water tank containing calcium ions, which induce cross-linking of the alginate and consequent bead hardening. Preliminary work was done using a syringe instead of the material-consuming BRACE unit. The beads were made from a suspension of dried only, dried and calcined, or dried, calcined, and reduced catalyst. The textural properties of the beads were analyzed by nitrogen adsorption-desorption isotherms and mercury porosimetry; and bead catalytic activity was tested for selective hydrodechlorination of 1,2-dichloroethane. The beads made from a suspension of dried catalyst appear to have properties the closest to that of the xerogel reference catalyst. Porosity and surface area are maintained at their level before bead formation. However conversion of 1,2-dichloroethane decreases after the production process, possibly due to poisoning by calcium ions. (C) 2004 Elsevier B.V. All rights reserved. [less ▲]

Detailed reference viewed: 45 (2 ULg)
Full Text
Peer Reviewed
See detailSynthesis of SiO2 xerogels and Pd/SiO2 cogelled xerogel catalysts from silylated acetylacetonate ligand
Lambert, Stéphanie ULg; Sacco, Luigi; Ferauche, Fabrice et al

in Journal of Non-Crystalline Solids (2004), 343(1-3), 109-120

SiO2 xerogels and Pd/SiO2 cogelled xerogel catalysts have been prepared in a mixture of tetrahydrofurane (THF) and ethanol containing tetraethoxysilane (TEOS), and an aqueous ammonia solution of 0.18 mol ... [more ▼]

SiO2 xerogels and Pd/SiO2 cogelled xerogel catalysts have been prepared in a mixture of tetrahydrofurane (THF) and ethanol containing tetraethoxysilane (TEOS), and an aqueous ammonia solution of 0.18 mol/l, from synthesized new silylated acetylacetonate ligands, respectively, 3-[3-(trimethoxysilyl)propyl]-2,4-pentanedione (MS-acac-H), 2,2,6,6-tetramethyl-4-[3-(trimethoxysilyl)propyl]-3,5-heptanedione (MS-dPvM), and 1,3-diphenyl-2-[3-(trimethoxysilyl)propyl]-1,3-propanedione (MS-dBzM), able to form a chelate with a metal ion such as Pd2+. All samples form homogeneous colored gels. The resulting catalysts are composed of palladium crystallites with a diameter of about 3.5 nm, located inside primary silica particles exhibiting a monodisperse microporous distribution as well as large palladium particles from 20 to 50 nm, situated outside the silica aggregates. The silylated organic ligand has a strong influence on the textural properties of xerogels and catalysts, both before and after calcination and reduction steps. Changing the nature of the silylated ligand permits tailoring textural properties such as pore volume, pore size and surface area. Although small palladium crystallites are located inside the silica particles, their complete accessibility, via the micropore network, has been shown. 1,2-Dichloroethane hydrodechlorination over Pd/SiO2 catalysts mainly produces ethane and the reaction rate increases linearly with palladium dispersion. Hydrodechlorination over Pd/SiO2 cogelled xerogel catalysts is a structure insensitive reaction compared to the ensemble size concept. (C) 2004 Elsevier B.V. All rights reserved. [less ▲]

Detailed reference viewed: 42 (10 ULg)
Full Text
Peer Reviewed
See detailOptical non-linearity in disperse red 1 dye-doped sol-gel
Rosso, Vanessa ULg; Loicq, Jerôme ULg; Renotte, Yvon ULg et al

in Journal of Non-Crystalline Solids (2004), 342(1-3), 140-145

A third-order non-linear optical effect, the optical Kerr effect, was studied in DR1-doped sol-gel using the Z-scan method which allows studying both processes of non-linear absorption and refraction. The ... [more ▼]

A third-order non-linear optical effect, the optical Kerr effect, was studied in DR1-doped sol-gel using the Z-scan method which allows studying both processes of non-linear absorption and refraction. The materials under study are sol-gel substrates, amorphous silica glasses doped by the azo-dye Disperse Red 1. Modifying the conditions of the sol-gel synthesis, in particular the pH of the catalytic medium, enabled us to vary the morphology of the sol-gel substrate. Non-linear effects of various amplitudes were observed in so-gel substrates of various porosities, involving different non-linear mechanisms. (C) 2004 Elsevier B.V. All rights reserved. [less ▲]

Detailed reference viewed: 50 (4 ULg)
Full Text
Peer Reviewed
See detailStudy of textural properties and nucleation phenomenon in Pd/SiO2, Ag/SiO2 and Cu/SiO2 cogelled xerogel catalysts
Lambert, Stéphanie ULg; Alié, Christelle ULg; Pirard, Jean-Paul ULg et al

in Journal of Non-Crystalline Solids (2004), 342(1-3), 70-81

Pd/SiO2, Ag/SiO2 and CU/SiO2 xerogel catalysts have been synthesized by cogelation of tetraethoxysilane (TEOS) and chelates of Pd, Ag and Cu with 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS). The ... [more ▼]

Pd/SiO2, Ag/SiO2 and CU/SiO2 xerogel catalysts have been synthesized by cogelation of tetraethoxysilane (TEOS) and chelates of Pd, Ag and Cu with 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS). The resulting materials are composed of completely accessible metallic crystallites with a diameter of about 3 nm, located inside silica particles exhibiting a monodisperse microporous distribution centered on a pore width of about 0.8 nm. Voids between silica particles and between aggregates of silica particles constitute the material meso- and macroporous texture. The EDAS/TEOS ratio is the main operating variable to tailor the material morphology. When the EDAS/TEOS ratio decreases, metallic particle size decreases, whereas silica particle size increases. Thus the meso- and macropores between silica particles are larger. So the total pore volume can reach 5 cm(3)/g when the EDAS/TEOS ratio decreases. The remarkable morphology of these materials can be explained by the rule in which the EDAS metal complex acts as a nucleation agent in the formation of silica particles. A nucleation mechanism by EDAS-metal complex based on mass equations and the nuclei formation kinetics allows fitting the entire results. (C) 2004 Elsevier B.V. All rights reserved. [less ▲]

Detailed reference viewed: 26 (14 ULg)
Full Text
Peer Reviewed
See detailPreparation of low-density xerogels from mixtures of TEOS with substituted alkoxysilanes. I. O-17 NMR study of the hydrolysis-condensation process
Alié, Christelle ULg; Pirard, Jean-Paul ULg

in Journal of Non-Crystalline Solids (2003), 320(1-3), 21-30

Low-density xerogels were synthesised by incorporation of an additive to base catalysed tetraethylorthosilicate (TEOS) alcogels directly during the preparation of the sol. The nucleation mechanism by the ... [more ▼]

Low-density xerogels were synthesised by incorporation of an additive to base catalysed tetraethylorthosilicate (TEOS) alcogels directly during the preparation of the sol. The nucleation mechanism by the additive was established by experiments during sol-gel transition. O-17 NMR spectroscopy on TEOS-ethanol-water, 3-(2-aminoethylamino)propyltrimethoxysilane (EDAS)-ethanol-water and EDAS-TEOS-ethanol-water solutions shows that the hydrolysis-condensation of EDAS is much faster than that of TEOS. Consequently it can be assumed that EDAS forms nuclei, onto which TEOS condenses later to form the silica particles. (C) 2003 Elsevier Science B.V. All rights reserved. [less ▲]

Detailed reference viewed: 22 (3 ULg)
Full Text
Peer Reviewed
See detailPreparation of low-density xerogels from mixtures of TEOS with substituted alkoxysilanes. II. Viscosity study of the sol-gel transition
Alié, Christelle ULg; Pirard, René ULg; Pirard, Jean-Paul ULg

in Journal of Non-Crystalline Solids (2003), 320(1-3), 31-39

Mixtures of TEOS with substituted methoxysilanes generate low-density xerogels due to a nucleation mechanism involving the substituted alkoxysilane. The sol-gel transition of these mixtures was followed ... [more ▼]

Mixtures of TEOS with substituted methoxysilanes generate low-density xerogels due to a nucleation mechanism involving the substituted alkoxysilane. The sol-gel transition of these mixtures was followed by theological characterisation. The transition from sol to gel takes place in a few minutes at ambient temperature. For the series exhibiting nucleation by the additive. the gel time goes through a slight minimum when the ratio of additive/main reagent increases. The elastic modulus increases with increasing ratio of additive/main reagent as the particle size decreases because of the nucleation mechanism by the additive. Samples with smaller particles exhibit the highest modulus for equal silica concentrations. (C) 2003 Elsevier Science B.V. All rights reserved. [less ▲]

Detailed reference viewed: 16 (4 ULg)
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 detailComputer simulation of liquid semiconductors
Bichara, C.; Gaspard, Jean-Pierre ULg; Raty, Jean-Yves ULg

in Journal of Non-Crystalline Solids (2002), 312

We discuss two examples of computer simulation of liquid semiconductors by two different techniques. Both examples are concerned with the relationship between thermodynamic properties and the atomic ... [more ▼]

We discuss two examples of computer simulation of liquid semiconductors by two different techniques. Both examples are concerned with the relationship between thermodynamic properties and the atomic structure in the liquid state. By means of ab initio molecular dynamics we analyze the atomic structure of liquid Ge15Te85 eutectic alloys. We show that the changes observed in the experimental total structure factor S(q) are located in the GeTe partial structure factor, the TeTe partial structure factor remaining essentially unaltered. Using a semi-empirical tight binding approach, coupled with Gibbs ensemble and constant pressure Monte Carlo calculations, we can calculate the liquid vapor equilibrium of selenium. We obtain a liquid-vapor equilibrium curve and a critical point in the correct range of magnitude and an atomic structure of the liquid phase in good agreement with the experimental data. (C) 2002 Elsevier Science B.V. All rights reserved. [less ▲]

Detailed reference viewed: 18 (0 ULg)