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Chitosan (CS) is a natural biopolymer that shows promise as a biomaterial for bone-tissue regeneration. However, because of their limited ability to induce cell differentiation and high degradation rate, among other drawbacks associated... more
Chitosan (CS) is a natural biopolymer that shows promise as a biomaterial for bone-tissue regeneration. However, because of their limited ability to induce cell differentiation and high degradation rate, among other drawbacks associated with its use, the creation of CS-based biomaterials remains a problem in bone tissue engineering research. Here we aimed to reduce these disadvantages while retaining the benefits of potential CS biomaterial by combining it with silica to provide sufficient additional structural support for bone regeneration. In this work, CS-silica xerogel and aerogel hybrids with 8 wt.% CS content, designated SCS8X and SCS8A, respectively, were prepared by sol-gel method, either by direct solvent evaporation at the atmospheric pressure or by supercritical drying in CO2, respectively. As reported in previous studies, it was confirmed that both types of mesoporous materials exhibited large surface areas (821 m2g−1–858 m2g−1) and outstanding bioactivity, as well as os...
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Nowadays the sol–gel process is used by an increasing number of researchers for the pre-paration of various products, including bulk materials, films, membranes or fibers. The application of ultrasound (sonocatalysis) to the precursors... more
Nowadays the sol–gel process is used by an increasing number of researchers for the pre-paration of various products, including bulk materials, films, membranes or fibers. The application of ultrasound (sonocatalysis) to the precursors gives rise to materials with new properties, known as sonogels. The absence of additional solvent and, mainly, the effects of ultrasonic cavitation create a unique environ-ment for sol–gel reactions leading to particular features in the resulting gels: high density, fine texture, homogeneous structure etc. These prop-erties determine the evolution of sonogels on further processing and the final material struc-ture. In this sense, the full exploitation of sonocatalysis requires a thorough understanding of the processes involved and their sensitivity to reaction parameters. For this purpose, we have used diverse techniques to investigate the micro-structural evolution during different steps in the sonogel process. The results of these studies are report...
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Abstract This paper presents the rheological properties of three types of lime putty, specifying the influence of their origin. The study aims to compare a special lime putty prepared from phosphogypsum with a commercial lime powder and... more
Abstract This paper presents the rheological properties of three types of lime putty, specifying the influence of their origin. The study aims to compare a special lime putty prepared from phosphogypsum with a commercial lime powder and an aged lime putty. The results obtained in terms of chemical composition, crystalline structure, grain size and rheological characterization, (linear viscoelasticity, shear rate and time-dependent flow behaviour) are presented in the study. Putties studied present a similar rheological response, which mainly depends on the particle size and water content. Lower values of the linear viscoelastic functions and viscosity were found for the phosphogypsum lime putty, in agreement with the higher particle size. Transient flow tests reveal a predominant elastic response with no significant shear-induced structural perturbations. However, either a thickening phenomenon over time, i.e. rheopexy, favoured at low shear rates, or a viscosity decrease, i.e. thixotropy, favoured at high shear rates, was observed.
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SiO2 organically modified silicate (ormosil) gels doped with different concentration of PbS quantum dots ranging from 0.5 to 4 wt%, were synthesised via sol-gel. The synthesis implied a process including the hydrolysis assisted with high... more
SiO2 organically modified silicate (ormosil) gels doped with different concentration of PbS quantum dots ranging from 0.5 to 4 wt%, were synthesised via sol-gel. The synthesis implied a process including the hydrolysis assisted with high power ultrasounds of tetramethylorthosilicate (TMOS) mixed with polydimethylsiloxane (PDMS). Colloidal dispersions of PbS embedded in sono-ormosil matrices were obtained by using two different control size
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Research Interests: Chemical Engineering, Condensed Matter Physics, Materials Science, Inorganic Chemistry, Microstructure, and 12 moreElectron Microscopy, Small Angle X Ray Scattering, Nanoparticles, Transmission Electron Microscopy, Porosity, High Resolution Transmission Electron Microscopy, Functionalization, Silica, Surface Area, Microstructures, Functional Group, and Surface Analysis
An analysis of the atomic radial distribution function of Al 0.20 As 0.30 Te 0.30 , Al 0.10 As 0.40 Te 0.50 and Al 0.10 As 0.20 Te 0.70 amorphous alloys obtained from quenching of the molten mixture of the elements was performed. A... more
An analysis of the atomic radial distribution function of Al 0.20 As 0.30 Te 0.30 , Al 0.10 As 0.40 Te 0.50 and Al 0.10 As 0.20 Te 0.70 amorphous alloys obtained from quenching of the molten mixture of the elements was performed. A structure in which all the Al atoms are ...
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Research Interests: Materials Engineering, Materials Science, Microstructure, Monte Carlo Simulation, Monte Carlo Simulations, and 11 moreMonte Carlo Methods, Porous Materials, Porosity, Computer Simulation, Non crystalline solids, Specific surface area, Microstructures, Porous Material, Structural model, Cluster model, and Monte Carlo Integration
Organic-inorganic hybrid materials were synthesized by controlled hydrolysis of tetraethoxysilane (TEOS), methyltrimethoxysilane (MTES), synthetic wollastonite powders and polydimethylsiloxane (PDMS) in an ethanol solution. Aerogels were... more
Organic-inorganic hybrid materials were synthesized by controlled hydrolysis of tetraethoxysilane (TEOS), methyltrimethoxysilane (MTES), synthetic wollastonite powders and polydimethylsiloxane (PDMS) in an ethanol solution. Aerogels were prepared from acid hydrolysis of TEOS and MTES with different volume ratio in ethanol, followed by addition of wollastonite powder and PDMS in order to obtain aerogels with 20 wt% of PDMS and 5 wt% of CaO of the total silica. Finally, when the wet gels were obtained, they were supercritically dried at 260 degrees C and 90 bar, in ethanol. In order to obtain its bioactivity, one method for surface activation is based on a wet chemical alkaline treatment. The particular interest of this study is that we introduce hybrid aerogels, in a 1 M solution of NaOH, for 30 s at room temperature. We evaluate the bioactivity of TEOS-MTES aerogel when immersed in a static volume of simulated body fluid (SBF). An apatite layer of spherical-shaped particles of uniform size smaller than 5 microns is observed to form on the surface of the aerogels after 25 days soaking in SBF.
Research Interests: Materials Engineering, Materials Science, Biomedical Engineering, Materials, Polymers, and 15 moreMedicine, Humans, Silica, Pressure, Room Temperature, Polydimethylsiloxane, Materials Testing, Calcium Compounds, Silicates, Biocompatible Materials, Simulated Body Fluid, Silicones, Body Fluids, Acid hydrolysis, and silanes
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En el presente trabajo se pretende evidenciar la utilidad de los ultrasonidos en el procesado de polvos cerámicos como elemento acelerador del proceso de cristalización y herramienta eficaz de redispersión. Palabras clave: YSZ,... more
En el presente trabajo se pretende evidenciar la utilidad de los ultrasonidos en el procesado de polvos cerámicos como elemento acelerador del proceso de cristalización y herramienta eficaz de redispersión. Palabras clave: YSZ, ultrasonidos, dispersión. Using ultrasounds to optimize YSZ ceramic powders processing This work tries to show out the utility of ultrasounds in ceramic powders processing as a speeding element for crystallization process and as useful tool for redispersion.
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En el presente trabajo se pretende evidenciar la utilidad de los ultrasonidos en el proeceesado de povlos ceramicos como elemento acelerador del proceso de cristalizacion y herramienta eficaz de redispersion.
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SiO2 gels obtained by sonocatalytic method combined with DCCA were used as host-matrices for extremely fine dispersions of CdS semiconductor particles. Small crystallites were produced "in situ" by H2S gas diffusion method. The... more
SiO2 gels obtained by sonocatalytic method combined with DCCA were used as host-matrices for extremely fine dispersions of CdS semiconductor particles. Small crystallites were produced "in situ" by H2S gas diffusion method. The particles were characterized by TEM and HRTEM, EXAFS, UV-Vis and Raman spectroscopies. The size of crystallites ranged from 5 to 10 nm. The optical transmission spectra showed the characteristic blue shift as a function of the particles size, as predicted by the theory. The optical and mechanical qualities of the samples were substantially improved by an infiltration method using a sono-sol which sealed the superficial pores thus ensuring greater longevity and the possibility of obtaining transparent gels by polishing.
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This work addresses the reuse of waste products as a raw material for lime putties, which are one of the components of mortar. 1:3 Lime/sand mortars very similar to conventional construction mortars were prepared using a lime putty... more
This work addresses the reuse of waste products as a raw material for lime putties, which are one of the components of mortar. 1:3 Lime/sand mortars very similar to conventional construction mortars were prepared using a lime putty obtained from the treatment of phosphogypsum with sodium hydroxide. The physical, rheological and mechanical properties of this phosphogypsum-derived mortar have been studied, as well as the mineralogical composition, microstructure by scanning electron microscope (SEM) and curing process by monitoring carbonation and ultrasonic propagation velocity. Considering the negative influence of sulphates on the hardened material, the behaviour of the material after sulphates precipitation by adding barium sulphate was additionally tested. Carbonation progressed from the outside to the inside of the specimen through the porous system by Liesegang rings patterns for mortars with soluble sulphates, while the carbonation with precipitated sulphates was controlled by...
An analysis of the atomic radial distribution function of A10.2oAs0.5oTeo.3o, Alo.loASo.aoTeo.5o and Al0.aoAso.2oTeo.vo amorphous alloys obtained from quenching of the molten mixture of the elements was performed. A structure in which all... more
An analysis of the atomic radial distribution function of A10.2oAs0.5oTeo.3o, Alo.loASo.aoTeo.5o and Al0.aoAso.2oTeo.vo amorphous alloys obtained from quenching of the molten mixture of the elements was performed. A structure in which all the AI atoms are tetrahedrally bonded to the other types of atoms in the material, would satisfy the requirements of the experimental curve. Tetrahedral groups might be linked to each other by As and Te atoms, or directly through a Te or As atom belonging to more than one tetrahedra.
Industrial wet phosphoric acid production in Huelva (SW Spain) has led to the controversial stockpiling of waste phosphogypsum (PG) byproducts, resulting in the release of significant quantities of toxic impurities in salt marshes in... more
Industrial wet phosphoric acid production in Huelva (SW Spain) has led to the controversial stockpiling of waste phosphogypsum (PG) byproducts, resulting in the release of significant quantities of toxic impurities in salt marshes in the Tinto river estuary. A twofold objective is proposed: removing hazardous and unpleasant wastes and mitigating the emission of greenhouse gases into the atmosphere. Thus, the first aim of this research is to synthesize materials with the ability for CO2 sequestration from wastes as preliminary work for designing industrial processes, which involve a reduction of CO2 emissions. In this regard, PG from the fertilizer industry, soda solutions, and liquid alkaline wastes from aluminum industries have been considered as precursors. Our results demonstrate the high efficiency of portlandite precipitation by PG dissolution using alkaline solutions. Carbonation experiments performed at ambient pressure and temperature resulted in total conversion of the port...
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ABSTRACT Thin and very uniform silica–alumina films were deposited by dip-coating onto AISI-304 stainless steel and submitted to different heat treatments. They were prepared by simultaneous ultrasound-assisted hydrolysis and... more
ABSTRACT Thin and very uniform silica–alumina films were deposited by dip-coating onto AISI-304 stainless steel and submitted to different heat treatments. They were prepared by simultaneous ultrasound-assisted hydrolysis and polycondensation of tetraethylorthosilicate and aluminium-sec-butylate or aluminium nitrate in an atmosphere rich in water vapour. The resulting materials were characterised by ellipsometry in order to optimise the process of avoiding porosity which was submitted to molecular probing. This method informs us of the micropore size distribution, using adsorptive different-sized molecules.The thickness ranges from 60 to 350 nm, depending on the sol processing and heat treatment. In some samples most of the micropores are only sensitive to molecular probe below 0.7 nm diameter. These and other characteristics will be discussed.
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La presente invención se refiere a la síntesis de materiales secuestradores de CO2, tipo silicatos de calcio, a partir de residuos, subproductos o co-productos con contenido en calcio y silicio tales como el hidróxido cálcico de la... more
La presente invención se refiere a la síntesis de materiales secuestradores de CO2, tipo silicatos de calcio, a partir de residuos, subproductos o co-productos con contenido en calcio y silicio tales como el hidróxido cálcico de la industria de producción del acetileno (vía carburo), cáscara de arroz, co-producto de la industria arrocera, sílice en polvo y cloruro de calcio. Así mismo, la presente invención se refiere a la aplicación del material en la captura selectiva de CO2 en corrientes gaseosas, mediante proceso de carbonatación en condiciones húmedas y presión y temperatura ambiental.
Research Interests: Monte Carlo Simulation, Information Extraction, Computer Simulation, Physical sciences, Wide Angle X-Ray Scattering, and 9 moreCHEMICAL SCIENCES, Fourier transform, Information Gain, Coordination number, Spatial structure, Short Range Order, extended x-ray absorption fine structure (EXAFS), Spatial Model, and Distribution Function
ABSTRACTThe copolymerization between TEOS (tetraethoxysilane) and silane derivatives was promoted by the application of high power ultrasound to the precursor liquid mixtures in the same way as in the classical sol-gel method. The... more
ABSTRACTThe copolymerization between TEOS (tetraethoxysilane) and silane derivatives was promoted by the application of high power ultrasound to the precursor liquid mixtures in the same way as in the classical sol-gel method. The specific organic precursor was selected from the silanol-terminated polymer family with different molecular functionality and the inorganic precursor was from the silicon alkoxide family. Ultrasound, through the acoustic cavitation process, influences the formation of a very fine distribution of silica particles and avoids cyclidation of the polymer, thus favoring copolymerization with the inorganic particles and leading to the formation of a highly porous and rubber-like solid aerogel. Creep compliance curves, corresponding to the time-dependent depth response to a step load, are imprint site dependent, with pore, soft and stiff sites discerned. In all cases, an instantaneous elastic deformation is apparent. For longer test times, depending on the imprint...
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The invention relates to a CO2 y SO2 capture method comprising the following steps consisting in: a) introducing an aqueous stream of a hydroxide of an alkali or alkaline-earth metal and another gas stream of CO2 into a bubble column... more
The invention relates to a CO2 y SO2 capture method comprising the following steps consisting in: a) introducing an aqueous stream of a hydroxide of an alkali or alkaline-earth metal and another gas stream of CO2 into a bubble column purifier/reactor, in order to form a carbonate of the alkali or alkaline-earth metal; b) introducing the carbonate of the alkali or alkaline-earth metal into a bubble column purifier/reactor, into which a stream of a gas mixture of CO2 and SO2 is introduced in order to form sulphite of an alkali or alkaline-earth metal and carbon dioxide; c) transforming the sulphite from step (b) into sulphate of said metal by means of oxidation with air; and d) re-circulating the unreacted CO2 produced during step (b) by reacting the slurry with the SO2, in the reactor from step (a).
ABSTRACT Ultrasonic treatment of mixtures of TEOS + water enables gels to be obtained without the necessity of using alcohol as a common solvent. The effects of composition, length of sonication and temperature of treatment on the... more
ABSTRACT Ultrasonic treatment of mixtures of TEOS + water enables gels to be obtained without the necessity of using alcohol as a common solvent. The effects of composition, length of sonication and temperature of treatment on the properties of the sonogels and their conversion into glasses were studied
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The properties (texture, mechanical behaviour, etc.) of hybrid organic–inorganic silica aerogels change dramatically when the concentration of the organic additive is varied from a given value. It has been known for several years that... more
The properties (texture, mechanical behaviour, etc.) of hybrid organic–inorganic silica aerogels change dramatically when the concentration of the organic additive is varied from a given value. It has been known for several years that this critical concentration is around 40% of the total weight of silica present in the sample. We have made use of a new structural model to
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Abstract Synthetic wollastonite has been used as the active phase embedded into two different silica aerogel composites. These composites are different in respect of the route used for the synthesis of the wollastonite powder. Texture and... more
Abstract Synthetic wollastonite has been used as the active phase embedded into two different silica aerogel composites. These composites are different in respect of the route used for the synthesis of the wollastonite powder. Texture and composition of both types of ...
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ABSTRACT The object of this paper is to evaluate behaviour during drying of two stone consolidants: Wacker OH and Tegovakon V, containing tetraethoxysilane. During drying, the gel network contracts due to capillary pressure generated by... more
ABSTRACT The object of this paper is to evaluate behaviour during drying of two stone consolidants: Wacker OH and Tegovakon V, containing tetraethoxysilane. During drying, the gel network contracts due to capillary pressure generated by solvent evaporation. When the consolidant dries inside the stone porous structure, the shrinkage is constrained in all three dimensions. In these conditions, the dried gel suffers a high stress that could cause it to crack. When there is a free surface, as for a consolidant layer on the surface of a pore, the stress can relax in the direction normal to the surface. In this case, the stress is controlled by network rigidity.
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A thermal programmed decompn. study combined with Raman spectrometry of SiO2-P2O5 sonogels and their classic counterparts shows that the chem. reactivity of Et3PO4 is less than that of Si(OEt)4. The P losses during the heat treatment for... more
A thermal programmed decompn. study combined with Raman spectrometry of SiO2-P2O5 sonogels and their classic counterparts shows that the chem. reactivity of Et3PO4 is less than that of Si(OEt)4. The P losses during the heat treatment for densification are due to evapn. of unreacted alkoxide P radicals. A way to decrease these losses is the use of more reactive P compd. precursors. The chem. reactions that occur are the same in both methods, although the structure of the final glasses is quite different. It indicates that ultrasound treatment is not only an external agent used to accelerate catalysis, but is also a way to modify the structure of glasses. [on SciFinder(R)]
Se han preparado polvos de circonia dopada con itria al 6 molar % a partir de diferentes precursores, tanto de naturaleza orgánica como inorgánica, con objeto de estudiar la influencia ejercida por ellos sobre la morfología de los polvos... more
Se han preparado polvos de circonia dopada con itria al 6 molar % a partir de diferentes precursores, tanto de naturaleza orgánica como inorgánica, con objeto de estudiar la influencia ejercida por ellos sobre la morfología de los polvos obtenidos; pues la com-pactación y posterior sinterización se ven influenciadas por ella. Palabras claves: YSZ, polvos cerámicos, morfología, procesado. Influence of the precursor on YSZ powders morphology 6 mol % yttria doped zirconia powders have been prepared starting from different precursors, both organic and inorganic, in order to study their influence on the morphology of the resulting powders, since it has influence on compaction and sintering.
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ABSTRACT The object of this paper is to evaluate behaviour during drying of two stone consolidants: Wacker OH and Tegovakon V, containing tetraethoxysilane. During drying, the gel network contracts due to capillary pressure generated by... more
ABSTRACT The object of this paper is to evaluate behaviour during drying of two stone consolidants: Wacker OH and Tegovakon V, containing tetraethoxysilane. During drying, the gel network contracts due to capillary pressure generated by solvent evaporation. When the consolidant dries inside the stone porous structure, the shrinkage is constrained in all three dimensions. In these conditions, the dried gel suffers a high stress that could cause it to crack. When there is a free surface, as for a consolidant layer on the surface of a pore, the stress can relax in the direction normal to the surface. In this case, the stress is controlled by network rigidity.
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Page 1. Journal of Sol-Gel Science and Technology 26, 947951, 2003 cс 2003 Kluwer Academic Publishers. Manufactured in The Netherlands. Photoluminescence from CdS Quantum Dots in Silica Gel NICOL ´AS DE LA ROSA-FOX ∗ ...
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ABSTRACTHost-matrix gels were prepared by hydrolysis of TEOS with the addition of cadmium nitrate, formamide as DCCA (drying control chemical additive) and submitted to a preselected dose of high power ultrasound. The impregnation of the... more
ABSTRACTHost-matrix gels were prepared by hydrolysis of TEOS with the addition of cadmium nitrate, formamide as DCCA (drying control chemical additive) and submitted to a preselected dose of high power ultrasound. The impregnation of the dry “sonogel” with KSeCN solution under vacuum conditions promoted the formation of the CdSe nanocrystals and enhanced the mechanical properties of the matrix. A transparent red xerogel was obtained and characterized by optical spectroscopy, TEM and SAXS measurements. The results support a structural model of a porous matrix containing CdSe nanocrystals exhibiting a bimodal size distribution that depends on the Se content of the impregnating solutions. The blue shift of the optical absorption bands reveal the quantum-size confinement effects of CdSe nanocrystals.
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Organic/inorganic hybrids silica aerogels were synthesized by the classical sol-gel method with application of high power ultrasounds to the liquid mixture. Precursors were tetraethoxysilane (TEOS), as inorganic phase, and polydimethyl... more
Organic/inorganic hybrids silica aerogels were synthesized by the classical sol-gel method with application of high power ultrasounds to the liquid mixture. Precursors were tetraethoxysilane (TEOS), as inorganic phase, and polydimethyl siloxane (PDMS), as organic one. These hybrid organic-inorganic materials are known as ORMOSIL (ORganically MOdified SILicates). Monolithic aerogels were obtained by supercritical drying in ethanol. Failure tests by uniaxial compression shows an increase of the rupture modulus as well as a decrease of the Young’s modulus with the polymer content, tuning from a brittle solid to a rubbery-like one. These hybrid aerogels behave as elastomers showing a decrease in the relaxation viscoelastic modulus. Nanoindentation tests have been performed in these hybrid aerogels: load/unload cycles about 1.5 mN of maximum load have shown a decreasing value of the reduced modulus, as well as both plastic and elastic work with the organic content, while hardness remains...
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ABSTRACT Sol-gel technology was used to design a new, energetically efficient and economically viable CO2 sequestration technology. Calcium silicate grains were embedded into an inorganic silica matrix. These composites were used for the... more
ABSTRACT Sol-gel technology was used to design a new, energetically efficient and economically viable CO2 sequestration technology. Calcium silicate grains were embedded into an inorganic silica matrix. These composites were used for the mineral sequestration of CO2; that is, for permanent carbon fixation. It was found that the mineral grains presented better carbonation efficiency when embedded into an inorganic porous silica matrix. The reaction by-products were calcite particles of a few microns and silica particles of a few tenths of nanometres in size. They could be recycled as raw materials for commercial processes, such as coatings and mortar, for example, depending on their morphology, purity, and particle size and on calculations of the total cost scenarios. Finally, sol-gel composites can also be tailored to capture other atmospheric gases, not just CO2, favouring the viability of this technology.
ABSTRACTWe have prepared organic-inorganic hybrid materials (OIHM), incorporating an organic phase in the inorganic precursor sol, using high power ultrasound for assistance with agitation. A sono-ormosil results after gelation. Colloidal... more
ABSTRACTWe have prepared organic-inorganic hybrid materials (OIHM), incorporating an organic phase in the inorganic precursor sol, using high power ultrasound for assistance with agitation. A sono-ormosil results after gelation. Colloidal silica particles have been added to these hybrids to enable network porous volume and pore radius to be tailored to specific requirements. Finally, in vitro bioactivity of this material has been promoted by adding calcium to the initial sol. The structure and bioactivity of these materials have been subjected to preliminary study, including their mechanical behaviour. These materials have a very fine structure especially after colloidal silica particles have been included. When immersed in a solution simulating blood plasma, they are bioactive, and the sample with colloid particles presents a better behaviour in vitro
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This work explored several synthesis routes to obtain calcium silicates from different calcium-rich and silica-rich industrial residues. Larnite, wollastonite and calcium silicate chloride were successfully synthesised with moderate heat... more
This work explored several synthesis routes to obtain calcium silicates from different calcium-rich and silica-rich industrial residues. Larnite, wollastonite and calcium silicate chloride were successfully synthesised with moderate heat treatments below standard temperatures. These procedures help to not only conserve natural resources, but also to reduce the energy requirements and CO2 emissions. In addition, these silicates have been successfully tested as carbon dioxide sequesters, to enhance the viability of CO2 mineral sequestration technologies using calcium-rich industrial by-products as sequestration agents. Two different carbon sequestration experiments were performed under ambient conditions. Static experiments revealed carbonation efficiencies close to 100% and real-time resolved experiments characterised the dynamic behaviour and ability of these samples to reduce the CO2 concentration within a mixture of gases. The CO2 concentration was reduced up to 70%, with a carbon...
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Acoustic cavitation effects in sol-gel liquid processing permits to obtain nanostructured materials, with size-dependent properties. The so-called “hot spots” produce very high temperatures and pressures which act as nanoreactors.... more
Acoustic cavitation effects in sol-gel liquid processing permits to obtain nanostructured materials, with size-dependent properties. The so-called “hot spots” produce very high temperatures and pressures which act as nanoreactors. Ultrasounds force the dissolution and the reaction stars. The products (alcohol, water and silanol) help to continue the dissolution, being catalyst content, temperature bath and alkyl group length dependent. Popular choices used in the preparation of silica-based gels are tetramethoxysilane (TMOS), Si(OCH3)4, and tetraethoxysilane (TEOS), Si(OC2H5)4. The resultant “sonogels” are denser gels with finer and homogeneous porosity than those of classic ones. They have a high surface/volume ratio and are built by small particles (1 nm radius) and a high cross-linked network with low –OH surface coverage radicals. In this way a cluster model is presented based on randomly-packed spheres in several hierarchical levels that represent the real sonoaerogel. Organic ...
Size and size distribution of the semiconductor nanocrystals embedded in a dielectric matrix play a dominant role in line broadening and the exciton quantum confinement level. The results show new aspects of the CdS and CdSe crystal... more
Size and size distribution of the semiconductor nanocrystals embedded in a dielectric matrix play a dominant role in line broadening and the exciton quantum confinement level. The results show new aspects of the CdS and CdSe crystal growth as quantum dots using small angle neutron scattering techniques (SANS). Thus, the crystal growth influences the aggregation process of the silica network.
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PbS semiconductor nanocrystals were grown inside an organically modified silicate (ORMOSIL) matrix prepared by the sol–gel method assisted by high power ultrasounds. Surface capping agent was used to control the growth and aggregation of... more
PbS semiconductor nanocrystals were grown inside an organically modified silicate (ORMOSIL) matrix prepared by the sol–gel method assisted by high power ultrasounds. Surface capping agent was used to control the growth and aggregation of PbS nanocrystals. The SANS intensity exhibits a crossover at 0.1 nm−1. Data analysis using a two-correlation function indicates a medium-range structure built by PbS nanocrystals (6.5
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Crack-free monolithic gels were prepared from different mixtures of colloidal silica with a sol solution containing tetraethoxysilane, under powerful ultrasonic agitation (sonosol). Recently, information on the structure of these gels,... more
Crack-free monolithic gels were prepared from different mixtures of colloidal silica with a sol solution containing tetraethoxysilane, under powerful ultrasonic agitation (sonosol). Recently, information on the structure of these gels, inferred from N2 adsorption and mercury intrusion porosimetry, was presented. In the present paper, these data were used to construct structural models of the gels using Monte Carlo calculations on the basis of random close packing (RPC) premises. In addition, the structure of gels under study was investigated by transmission and scanning electron microscopy. The material can be described as a composite in which the sonogel is the matrix and the colloid particles the reinforcing phase. For low colloid content, the colloid forms discrete clusters, and the main structural characteristic of sonogels, i.e., a network of uniformly sized particles of approximately 3-4-nm radius, remains unmodified. However, for high colloid silica content, a multimode distribution appears, the structure is discontinuous, and only colloid aggregates larger than 100 nm are observed. For medium colloid content, aggregates of approximately 50-100 nm can be seen, but the sonogel structure extends throughout the whole material. By the processing method and election of a suitable precursor concentration, it is possible to design the composite for specific purposes.
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... Author Contact Information , E-mail The Corresponding Author , V. Morales-Flórez a , JA Toledo-Fernández a , M. Piñero b , R. Mendoza-Serna a ... 10 and 11 Typically used are the Maxwell model, the KelvinVoigt model and the so-called... more
... Author Contact Information , E-mail The Corresponding Author , V. Morales-Flórez a , JA Toledo-Fernández a , M. Piñero b , R. Mendoza-Serna a ... 10 and 11 Typically used are the Maxwell model, the KelvinVoigt model and the so-called Burger model, 12 a Kelvin chain with ...
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Five mol% yttria doped zirconia powders were prepared by controlled hydrolysis of alkoxides. Their sintering behavior was monitored by dilatometry to optimize the sintering schedule. The compact bodies were characterized by SEM and... more
Five mol% yttria doped zirconia powders were prepared by controlled hydrolysis of alkoxides. Their sintering behavior was monitored by dilatometry to optimize the sintering schedule. The compact bodies were characterized by SEM and quantitative analysis of ...
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ABSTRACT In situdevelopment of La-ß-Al2O3(LBA) platelets in alpha-Al2O3was studied as a function of the preparation method: a conventional solid-state reaction of commercial Al2O3powder and La(NO3)3as well as a sol-gel method starting... more
ABSTRACT In situdevelopment of La-ß-Al2O3(LBA) platelets in alpha-Al2O3was studied as a function of the preparation method: a conventional solid-state reaction of commercial Al2O3powder and La(NO3)3as well as a sol-gel method starting with boehmite and the same La2O3precursor. In both cases, homogeneous distribution of the reinforcing phase was achieved, and a noteworthy inhibition of Al2O3grain growth resulted. However, samples prepared by solid-state reaction densified more easily than those prepared via sol-gel, but the formation of the LBA phase occurred at a lower temperature in samples prepared by the sol-gel approach. Results on the correlation of the onset of LBA grain growth and densification to microstructure are discussed.
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Abstract The increasingly evident impact of anthropogenic CO 2 emissions on climate change and associated environmental effects is stimulating the search for viable methods to remove this gas. One of the most promising strategies is the... more
Abstract The increasingly evident impact of anthropogenic CO 2 emissions on climate change and associated environmental effects is stimulating the search for viable methods to remove this gas. One of the most promising strategies is the long-term storage of CO 2 in ...
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The properties (texture, mechanical behaviour, etc.) of hybrid organic–inorganic silica aerogels change dramatically when the concentration of the organic additive is varied from a given value. It has been known for several years that... more
The properties (texture, mechanical behaviour, etc.) of hybrid organic–inorganic silica aerogels change dramatically when the concentration of the organic additive is varied from a given value. It has been known for several years that this critical concentration is around 40% of the total weight of silica present in the sample. We have made use of a new structural model to
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Abstract Synthetic wollastonite has been used as the active phase embedded into two different silica aerogel composites. These composites are different in respect of the route used for the synthesis of the wollastonite powder. Texture and... more
Abstract Synthetic wollastonite has been used as the active phase embedded into two different silica aerogel composites. These composites are different in respect of the route used for the synthesis of the wollastonite powder. Texture and composition of both types of ...
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We have modified the inorganic silica network of aerogels with polydimethylsiloxane (PDMS), a hydroxyl-terminated polymer, to obtain an organic modified silicate (ORMOSIL). Reactions were assisted by high-power ultrasounds. The resulting... more
We have modified the inorganic silica network of aerogels with polydimethylsiloxane (PDMS), a hydroxyl-terminated polymer, to obtain an organic modified silicate (ORMOSIL). Reactions were assisted by high-power ultrasounds. The resulting gels were dried under supercritical conditions of the solvent to obtain a monolithic sono-aerogel. The mechanical behaviour of these aerogels can be tuned from brittle to rubbery as a function
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Abstract Monolithic gels, prepared from different mixtures of colloidal silica in a sol solution containing tetraethoxysilane under powerful ultrasonic agitation (sonosols), were compacted at an isostatic pressure of 390 MPa. Then N 2... more
Abstract Monolithic gels, prepared from different mixtures of colloidal silica in a sol solution containing tetraethoxysilane under powerful ultrasonic agitation (sonosols), were compacted at an isostatic pressure of 390 MPa. Then N 2 adsorption-desorption data were used to ...
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... (2) The second type, hereafter called sono-aero-gel, was prepared by mixing the components under ultrasonic irradiation without using any common sol-vent. ... Solids 104 (1988) 129. [11] S. Prabakar, KJ Rao and CNR Rao, J. Mater. Res.... more
... (2) The second type, hereafter called sono-aero-gel, was prepared by mixing the components under ultrasonic irradiation without using any common sol-vent. ... Solids 104 (1988) 129. [11] S. Prabakar, KJ Rao and CNR Rao, J. Mater. Res. 6 (1991) 592. ...
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ABSTRACT
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... 0022-3093/90/$03.50 1990 - Elsevier Science Publishers BV (North-Holland) M.Ramirez-del-Solar et aL / Effect of preparation ... was obtained by mercury volumetry, and their specific surfaces were estimated, using nitrogen adsorption,... more
... 0022-3093/90/$03.50 1990 - Elsevier Science Publishers BV (North-Holland) M.Ramirez-del-Solar et aL / Effect of preparation ... was obtained by mercury volumetry, and their specific surfaces were estimated, using nitrogen adsorption, by the Brunauer-Emmett-Teller ...
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ABSTRACT A very high-speed rotatory blender was used to enhance the homogenization of TEOS + H2O mixtures. The effects of several reaction parameters on the gelation rate of these solutions and those submitted to ultrasonic treatment were... more
ABSTRACT A very high-speed rotatory blender was used to enhance the homogenization of TEOS + H2O mixtures. The effects of several reaction parameters on the gelation rate of these solutions and those submitted to ultrasonic treatment were studied. Comparison of the results points to differing accelerating mechanisms in each case.
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The ultrastructural evolution of aerogels on sintering into glass must be understood on the basis of a detailed description of a solid backbone and porosity. Silica aerogels from ‘sonogels’ have been studied over a wide length-scale... more
The ultrastructural evolution of aerogels on sintering into glass must be understood on the basis of a detailed description of a solid backbone and porosity. Silica aerogels from ‘sonogels’ have been studied over a wide length-scale range, using small-angle X-ray scattering and gas adsorption measurements. An aggregation model of a hierarchical nature can be formulated with a variable clustering index
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ABSTRACT This work presents the application of a geometrical model to dry gels prepared by ultrasonic energy applied to alkoxide-water mixtures (sonogel). The xerogel structure is described as a hierarchical arrangement of spherical units... more
ABSTRACT This work presents the application of a geometrical model to dry gels prepared by ultrasonic energy applied to alkoxide-water mixtures (sonogel). The xerogel structure is described as a hierarchical arrangement of spherical units clustered in successive steps. The model takes into consideration the clustering index (number of elementary units in a cluster) and the hierarchical ratio (quotient of cluster to elementary unit size), and accounts for the degree of branching and connectivity along sintering. The structural parameters have been evaluated from small-angle X-ray scattering and gas adsorption data (Brunauer-Emmett-Teller method). The results reveal ultrasonic dose-dependent structural changes on sintering in the 200–900 °C temperature range.
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The atomic arrangements around Ti atoms in titania doped silica gels were studied by X-ray absorption spectroscopy. The gels were prepared by ultrasonic treatment of an alkoxide and acidic water mixture (sonogel) and conventionally in... more
The atomic arrangements around Ti atoms in titania doped silica gels were studied by X-ray absorption spectroscopy. The gels were prepared by ultrasonic treatment of an alkoxide and acidic water mixture (sonogel) and conventionally in alcoholic solution. From the comparison of gels, XANES spectra with those of SrTiO3, anatase and rutile TiO2, an octahedral environment of Ti in the SiO2
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CdS-silica xerogel composites were prepared from tetramethoxysilane, acidic water, and formamide mixtures homogenized by high power ultrasounds. Different concentrations of Cd(NO3)2 were added. CdS semiconductor nanoparticles were... more
CdS-silica xerogel composites were prepared from tetramethoxysilane, acidic water, and formamide mixtures homogenized by high power ultrasounds. Different concentrations of Cd(NO3)2 were added. CdS semiconductor nanoparticles were precipitated by H2S gas diffusion through the sonogel porous structure. Composite mechanical properties were enhanced by an impregnation process by the gel soaking in the same sol as-prepared. Textural parameters evolution is compared to the salt content in order to find the best performance to CdS nanocrystal growth. The impregnation process allows a better composite protection.
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ABSTRACT Semiconductor PbS quantum dots doped-SiO2 organically modified silicate (ormosil) gels were synthesised via sol-gel by using high-power ultrasounds (sonogel). The effect of PbS crystal concentration and the addition of... more
ABSTRACT Semiconductor PbS quantum dots doped-SiO2 organically modified silicate (ormosil) gels were synthesised via sol-gel by using high-power ultrasounds (sonogel). The effect of PbS crystal concentration and the addition of (3-mercaptopropyl)trimethoxysilane acting as surface capping agent (SCA) were investigated. By adjustment of the SCA to lead ratio, PbS nanoparticles of different sizes and morphologies were obtained. Textural parameters were calculated from N2 physisorption isotherms. The PbS galena phase was identified by x-ray diffraction, the crystal size by high-resolution transmission electron microscopy, and the exciton confinement by ultraviolet–visible–near-infrared spectrophotometry. Crystallite mean sizes of spheres and cubes ranging from 6.5 to 10.5 nm and needles 7-nm wide and 15–20 nm long, for different PbS and SCA concentrations, were obtained. These results differ from those predicted by the effective mass approximation corroborating the band gap modifications in the smallest nanocrystals. The method allows the control of the crystal size and improves the stabilization of the PbS nanocrystals.
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Research Interests: Engineering, Carbon Dioxide, Porosity, Silica, Reaction Time, and 15 moreAtmospheric Pressure, Hazardous Materials, Composite Material, Grain size, Specific surface area, Gels, Powder, Room Temperature, Chemical Composition, Carbonation, Autoclave, Silicon Dioxide, High Efficiency, Ethylene Glycol, and Carbon mineralization
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... Isabel Izquierdo-Barba 1 ,; Agustina Asenjo 2 ,; Luis Esquivias 3 ,; María Vallet-Regí 1. ... The films are characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray dispersiveenergy spectroscopy (EDS),... more
... Isabel Izquierdo-Barba 1 ,; Agustina Asenjo 2 ,; Luis Esquivias 3 ,; María Vallet-Regí 1. ... The films are characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray dispersiveenergy spectroscopy (EDS), reflection ellipsometry and scanning force microscopy ...
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Several CaO− SiO2− PDMS hybrid sono-aerogels were investigated. Only that one containing 20 wt% PDMS and 20 wt% CaO exhibited in vitro bioactive response. HRTEM showed crystallized CaSiO3 nanodomains in this material that could facilitate... more
Several CaO− SiO2− PDMS hybrid sono-aerogels were investigated. Only that one containing 20 wt% PDMS and 20 wt% CaO exhibited in vitro bioactive response. HRTEM showed crystallized CaSiO3 nanodomains in this material that could facilitate the apatite-...
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Abstract. The influence of using TMOS or TEOS in the formation of CdS quantum dots in a silica matrix have been studied by X-ray absorption spectroscopy (XAS). The amount of Cd S bonds have been monitored as a function of the nominal Cd... more
Abstract. The influence of using TMOS or TEOS in the formation of CdS quantum dots in a silica matrix have been studied by X-ray absorption spectroscopy (XAS). The amount of Cd S bonds have been monitored as a function of the nominal Cd concentration. The relative amount ...
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Nicolás de la Rosa-Fox*, Manuel Piñeroa and Luis Esquivias. Dpto. Física Materia Condensada. Facultad de Ciencias a Dpto. Física Aplicada. CASEM. Universidad de Cádiz. 11510 Puerto Real (Cádiz). SPAIN. ... 2.- Sol-Gel Process steps... more
Nicolás de la Rosa-Fox*, Manuel Piñeroa and Luis Esquivias. Dpto. Física Materia Condensada. Facultad de Ciencias a Dpto. Física Aplicada. CASEM. Universidad de Cádiz. 11510 Puerto Real (Cádiz). SPAIN. ... 2.- Sol-Gel Process steps (mixing, gelation, aging, ...