Solution Sol-gel Method Research Articles

In Situ Zirconia: A Superior Reinforcing Filler for High-Performance Nitrile Rubber Composites.

Zirconia particles are generated into a nitrile rubber (NBR) matrix via a solution sol–gel method in a controlled manner. Formation of zirconia particles from their precursor (zirconium(IV) propoxide) occurs under optimized reaction conditions. As a result, the nanoparticles are embedded and well dispersed in the NBR matrix that results in a remarkable improvement in mechanical and thermal properties of the composite. Such reinforcement is not realized when the composites are prepared following the conventional technique of filler loading by physical mixing, although the filler content remains the same. Use of a surface active coupling agent TESPT (bis-(3-triethoxysilylpropyl) tetrasulfide) in the reactive sol–gel system is found to further boost the mechanical performance of the composites. In order to ensure the practical application of the developed composites, a series of studies have been performed that consist of dynamic performance, swelling, thermal degradation, and resistance to oil, ozone, and abrasion. Analysis of the results reveals that in situ zirconia could be an excellent filler for the NBR composites to withstand in a harsh and adverse environment.

Incorporation of titania nanoparticles in elastomer matrix to develop highly reinforced multifunctional solution styrene butadiene rubber composites

Titania nanoparticles are introduced in situ into SSBR matrix (solution of styrene butadiene rubber) by solution sol-gel method under controlled reaction condition that shows outstanding reinforcing efficiency because of its favourable morphological features and enhanced polymer-filler interaction. Surface treatment of titania particles in reactive sol-gel system using an organosilane, TESPT (bis-(3-triethoxysilylpropyl)-tetrasulfide) further strengthens the reinforcement effect. Notably, more than 85% conversion of titania from it's precursor (titanium n-butoxide, TNB) is achieved within 1 h reaction time without employing any catalyst. Additionally, controlled growth of titania particles inside rubber matrix imparts particular characteristics of the titania particles that enables them to deliver rich dielectric and antifungal properties to the composites. In-depth investigation of the composites including rheological, thermal, morphological, mechanical, dynamic mechanical, dielectric and antifungal studies have been carried out and structure-property relationship is established in respect to SSBR gum and externally titania filled composites prepared at similar condition.

Studies on mechanical, rheological, thermal and morphological properties of in situ silica-filled butadiene rubber composites

ABSTRACTSilica is introduced in butadiene rubber (BR) in situ by solution sol–gel method at low and high content. This results in uniformly dispersed spherically shaped silica in rubber matrix as revealed from Scanning electron microscopy study. Incorporation of in situ silica imparts moderate reinforcement to BR composite. Mechanical property and silica distribution are eventually improved by using a silane coupling agent as a surface modifier. Thermal, rheological, morphological, mechanical and melting behaviours of the composites are evaluated and analysed in a comparative manner.

Compatibilization of natural rubber/nitrile rubber blends by sol–gel nano-silica generated by in situ method

Controlled growth of in situ silica, into natural rubber (NR)/nitrile rubber (NBR) blend (40/60 composition by weight) following solution sol–gel method, results in a coherent blend morphology with enhanced composite properties. Similar composites, i.e., in situ silica-filled NR/NBR blend (40/60 by weight), showed better mechanical properties than any other composition that were prepared by soaking sol–gel method in earlier study. However, silica content in the rubber blend was limited to 20 phr (parts per hundred parts of rubber) and could not be increased under experimental condition following soaking sol–gel method. In the present work, silica content is increased (up to 30 phr) beyond that limit for the same blend composition. Accordingly, mechanical properties of the NR/NBR composites are improved. Use of a silane coupling agent, viz., bis-(3-triethoxysilylpropyl)-tetra sulfide, in the reactive sol–gel system during in situ silica generation brings in remarkable effect in silica distribution, rubber–filler interaction and mechanical properties of the composites. TEM micrographs of the selected composites reveal that silica is mostly grown at the interfacial region, when silane is used in particular. This results in further enhancement in mechanical properties and compatibility of the blend at the same silica content as evident from stress–strain and dynamic mechanical analysis studies. The reinforcement of effect in situ silica is assessed by Guth–Gold equation and modified form of Guth equation (with shape factor f = 2.53). The results are supported by the detailed studies on rheological, morphological, mechanical and viscoelastic properties of the composites.

Controlled growth of in situ silica in a NR/CR blend by a solution sol–gel method and the studies of its composite properties

Controlled loading of in situ silica in NR/CR blend by solution sol–gel method for enhancing the reinforcement.

Size-dependent ionic conductivity observed for ordered mesoporous alumina-LiI composite

Ordered mesoporous Al 2O 3 was synthesized by a solution sol-gel method using neutral copolymer surfactants as templates. The pore size was controlled over the range of 2.8–12.5 nm by using different surfactant copolymers under different synthetic conditions. By utilizing cyclohexane as a cosolvent, mesoporous Al 2O 3 having relatively monodispersed particle size was obtained. Composites composed of the synthesized mesoporous Al 2O 3 and the lithium ion conductor (LiI) was prepared by heating the composite in a sealed Pyrex tube at 773 K. Composition dependence of the dc conductivity was determined from a single arc in the observed impedance spectra. The maximum dc electrical conductivity, 2.6×10 −4 S cm −1 at 298 K, was observed for 50 LiI·50 Al 2O 3 composite with 4.2 nm averaged mesoporosity, which was considerably higher than the previously reported LiI-alumina composites. A systematic dependence of conductivity upon pore size was observed, in which the conductivity increased with decreasing the pore size.

Synthesis, structural and chemical properties of iron oxide–silica aerogelsElectronic supplementary information (ESI) available: cumulative pore volumes and t-plots of the calcined aerogels prepared by different sol–gel methods, and of aerogels with different iron loadings. See http://www.rsc.org/suppdata/jm/b1/b108120a/

Iron oxide aerogels were synthesized from tetramethoxysilicon(IV) (TMOS) or tetraethoxysilicon(IV) (TEOS) and iron nitrate using an acid-catalyzed solution–sol–gel method combined with subsequent extraction of the alcoholic solvent with supercritical CO2. The main parameters varied in the sol–gel synthesis were: the type of N-base used as the gelation agent (N,N-diethylaniline, trihexylamine, ammonium carbonate, ammonia), the concentration of the iron precursor, and the water content. The silicon precursor was prehydrolyzed to improve its reactivity. After calcination at 600 °C, the structural and chemical properties of the aerogels containing 0–20wt% nominal Fe2O3 were characterized by means of nitrogen adsorption, X-ray diffraction (XRD), transmission and scanning electron microscopy, temperature programmed reduction, X-ray photoelectron spectroscopy (XPS), UV-Vis, DRIFT and EPR spectroscopy. XRD and electron microscopy indicated that all aerogels were amorphous, irrespective of the sol–gel conditions used. The aerogels were predominantly mesoporous, with pore size maxima ranging between 20–50 nm, but also exhibited some microporosity. For the 10 wt% iron oxide samples, the specific pore volumes ranged from 0.7 to 2 cm3 g−1 and BET-surface areas from 150 to 636 m2 g−1, depending on conditions. With increasing iron content, the BET surface area decreased from 740 to 340 m2 g−1, accompanied by increasing microporosity. XPS revealed significant silicon enrichment on the surface. Spectroscopic investigations (UV-Vis, EPR) uncovered different iron-containing species, ranging from tetrahedrally coordinated iron atoms incorporated in the silica matrix to iron oxide nanoclusters. Formation of isolated iron atoms was favored with low iron content samples. The N-base used to force gelation had a significant effect on the morphology and population density of Fe(OH)Si in the aerogels.

Article

The solution sol-gel method is used to produce thin films of photosensitive hybrid organic-inorganic glass on silicon. Glasses consisted of photoinitiator, methacryloxypropyltrimethoxysilane, methacrylic acid, and zirconium oxide. Clear, low optical loss films are obtained, indicating nanophase homogeneity in the samples. The nanocomposite films are shown to be suitable for fabricating optical components such as ridge wave guides and Bragg diffraction gratings. The increase in the refractive index of the glass relative to the surrounding material during photolithographic processing is identified as a key material parameter in device fabrication. Accordingly, electronic and vibrational spectroscopy are used to provide insight into the structural changes that occur when glasses are irradiated with continuous narrow band 4.9 eV and pulsed 6.4 eV light. Arguments are advanced, linking the changes in refractive index to collateral densification leading to volume compaction of the silicate network during organic free-radical polymerization. This was shown by following the time evolution of relevant IR absorption bands. Free silanol and unreacted methoxysilane are consumed in the process. Matrix densification is indicated by shifts to low wave number in the transverse optical phonon mode associated with decreasing Si-O-Si bond angles of the antisymmetric stretching vibration (compression). Growth in the Si-O-Si framework is observed through increased intensity in this IR absorption. Similar behaviour is observed for films irradiated with 6.4 eV light from an excimer laser. A phase mask in combination with pulsed 6.4 eV light is used to inscribe a 1.5 mm, high-reflectivity polarization-independent Bragg grating into a ridge wave guide. The high reflectivity is thought to arise from a periodic modulation of the volume compaction of the matrix. Overall, the organic component of the glass confers unique properties on the material that allow it to be densified even with 4.9 eV light. By comparison, sol-gel silica with no organic component must be densified at nearly twice the photon energy.Key words: sol-gel, wave guide, Bragg grating, photochemistry, densification, refractive index, photolithography.

Copper- and Silver–Zirconia Aerogels: Preparation, Structural Properties and Catalytic Behavior in Methanol Synthesis from Carbon Dioxide

Copper- and silver-zirconia aerogels containing 10 at% IB metal were prepared from tetra-n-butoxy zirconium(IV) and IB metal acetates using the solution sol-gel method and ensuing high-temperature (HT) and low-temperature (LT) supercritical drying, respectively. The influence of preparation parameters and calcination on the structural and catalytic properties of the aerogels for the synthesis of methanol from carbon dioxide and hydrogen was investigated. After calcination in air at 573 K, the catalysts had BET surface areas in the range of 100–143 m2·g−1(Cu/ZrO2) and 77–125 m2·g−1(Ag/ZrO2), respectively. Due to the reductive alcoholic atmosphere during high-temperature supercritical drying, metallic copper and silver existed in all raw HT-aerogels. The mean size of the copper crystallites was 30 nm. The silver crystallite size for the HT-aerogel prepared with nitric acid was 10 nm, whereas for samples prepared with acetic acid it was 5–7 nm. Calcination in air at 573 K led to the formation of highly dispersed amorphous copper oxide and silver. Comparing the catalytic behavior of the calcined copper–zirconia aerogels with corresponding xerogels prepared by coprecipitation revealed highest activity for the LT-aerogel, whereas the HT-aerogels were least active. In contrast, similar catalytic behavior was observed for the differently dried silver-zirconia samples. Generally, CO2-conversion of the copper–zirconia aerogels was markedly higher than that of the corresponding silver–zirconia aerogels, whereas methanol selectivity was similar.

Synthesis of La(Mg2/3Ta1/3)O3 (LMT) by solution sol–gel method

Mixed oxides containing La, Mg and Ta were prepared by the sol–gel method. A pure phase, La(Mg2/3Ta1/3)O3 was formed by calcining the gel at a low temperature (<1100°C). The gel powders calcined at 1100°C were made into pellets and sintered at 1500°C for 6 h. The room temperature dielectric constant and tangent loss for the ceramics were found to be 22.0 and 24.8×10−4, respectively, at 10 kHz. LMT was characterized by X-ray diffraction and shown to be hexagonal with lattice parameters a=9.1844 A and c=16.8742 A. The melting point of the phase was found to be ∼2000°C by the laser heated pedestal growth technique.

Solution sol–gel processing of Ba(Mg1/3Ta2/3)1−xSnxO3 [x=0.0, 0.2] as substrates for high Tc superconductors

Abstract A solution sol–gel method for preparing Ba(Mg 1/3 Ta 2/3 ) 1− x Sn x O 3 [ x =0.0, 0.2] powders was developed. Single phase Ba(Mg 1/3 Ta 2/3 ) 1− x Sn x O 3 [ x =0.0, 0.2] oxide powders formed at temperature as low as 600°C. The calcined powders sintered at 1500°C for 24 h resulted in ≥95% of the theoretical density. The dielectric constant and tangent loss were determined to be 24 and 10 −4 at 10 kHz respectively.

Photoinduced structural rela×ation and densification in sol-gel-derived nanocomposite thin films: implications for integrated optics device fabrication

The solution sol-gel method is used to produce thin films of photosensitive hybrid organic-inorganic glass on silicon. Glasses consisted of photoinitiator, methacryloxypropyltrimethoxysilane, methacrylic acid, and zirconium oxide. Clear, low optical loss films are obtained, indicating nanophase homogeneity in the samples. The nanocomposite films are shown to be suitable for fabricating optical components such as ridge wave guides and Bragg diffraction gratings. The increase in the refractive index of the glass relative to the surrounding material during photolithographic processing is identified as a key material parameter in device fabrication. Accordingly, electronic and vibrational spectroscopy are used to provide insight into the structural changes that occur when glasses are irradiated with continuous narrow band 4.9 eV and pulsed 6.4 eV light. Arguments are advanced, linking the changes in refractive index to collateral densification leading to volume compaction of the silicate network during organic free-radical polymerization. This was shown by following the time evolution of relevant IR absorption bands. Free silanol and unreacted methoxysilane are consumed in the process. Matrix densification is indicated by shifts to low wave number in the transverse optical phonon mode associated with decreasing Si-O-Si bond angles of the antisymmetric stretching vibration (compression). Growth in the Si-O-Si framework is observed through increased intensity in this IR absorption. Similar behaviour is observed for films irradiated with 6.4 eV light from an excimer laser. A phase mask in combination with pulsed 6.4 eV light is used to inscribe a 1.5 mm, high-reflectivity polarization-independent Bragg grating into a ridge wave guide. The high reflectivity is thought to arise from a periodic modulation of the volume compaction of the matrix. Overall, the organic component of the glass confers unique properties on the material that allow it to be densified even with 4.9 eV light. By comparison, sol-gel silica with no organic component must be densified at nearly twice the photon energy.

Preparation of Monophasic [NZP] Radiophases: Potential Host Matrices for the Immobilization of Reprocessed Commercial High-Level Wastes

ABSTRACTThe compositional flexibility of the sodium zirconium phosphate (NaZr2(PO4)3) structure has been exploited in the design of monophasic radiophases capable of immobilizing the most common cations associated with reprocessed high-level commercial waste streams. Highly crystalline, monophasic members of the NaZr2(PO4)3 structural family ([NZP]) have been prepared with conventional processing methods and equipment. These radiophases were tailored to accommodate 10–20 wt % modified PW-4b simulated calcine as single phases isostructural with NaZr2(PO4)3. To meet the challenge of designing monophasic materials capable of accommodating the chemical complexity of PW-4b, an ionic substitution scheme based on crystal chemical principles was developed. The radiophases were prepared with inexpensive, inorganic precursors and a solution sol-gel method; these materials were heat treated and/or sintered under a variety of conditions to determine the optimum conditions for single phase [NZP] formation. X-ray powder diffraction provided valuable information that was used to assess the suitability of the ionic substitution model developed in this investigation. The results of this investigation suggest that monophasic [NZP] radiophases capable of accommodating 10–20 wt % modified PW-4b simulated calcine may be continuously processed with conventional ceramic processing methods and equipment. Moreover, the relatively low temperatures involved and the reproducibility of the process make [NZP] radiophases economically attractive hosts for radioactive and heavy metal industrial wastes.

Accelerating the Kinetics of Low-Temperature Inorganic Syntheses

This paper reviews several different methods used by the author over the past 40 years and those very recently developed in his laboratory for accelerating reactions in oxide materials at temperatures in the range 0-500°C. The latter include: (1) acoustic wave stimulation (sonochemical), (2) using ionizing and nonionizing radiation, and (3) the hydrothermal process with microwave fields. The results show that several of these methods can accelerate reactions of the most common oxides, especially in aqueous environments, by one to two orders of magnitude, and are therefore technologically significant. The basic science behind the processes is still primitive. The classical methods include: (4) utilizing precursors made via the solution sol-gel method and, recently, epitaxy via nanocomposite gel routes, (5) using low melting "fluxes," (6) hydrothermal processes, hydrothermal process with superimposed electric fields, and hydrothermal process with mechanical forces, and (7) mechanochemical effects including very high uniaxial pressure and shear.

Microstructure and microcracking behaviour of barium zirconium phosphate (BaZr4P6O24) ceramics

Barium zirconium phosphate (BaZr4P6O24), a member of a new family of low-thermal-expansion materials known as NZP, was synthesized by the solution sol-gel method, and sintered ceramics were prepared at 1100–1600 °C. The effect of sintering parameters such as time and temperature on the microstructure and phase composition was studied. BaZr4P6O24 is known to possess anisotropy in its axial thermal expansions, which usually causes microcracking in the sintered bodies when cooled. The microcracking activity of the sintered samples was examined by acoustic emission measurements.

Synthesis and Dielectric Properties of Solution Sol‐Gel‐Derived 0.9Pb(Mg1/3Nb2/3)O3–0.1PbTiO3 Ceramics

A solution sol‐gel method has been developed to prepare 0.9Pb(Mg1/3Nb2/3)O3‐0.1PbTiO3 (0.9PMN‐0.1PT) ceramics. During the processing the gel first converted to cubic pyrochlore phase at a calcination temperature of 600°C followed by the formation of pure perovskite phase at 775°C. The ceramics sintered at 1250°C for 4 h showed ≈98% of the theoretical density. The room‐temperature dielectric constant of the pellets sintered at 1250°C showed a maximum value of 25035 at 1 kHz. Sintering studies at different temperatures revealed that the dielectric constant increased with increasing grain size in these ceramics.

ChemInform Abstract: Low‐Temperature Sol‐Gel Synthesis of NaZr2P3O12.

The NZP family of new low-expansion materials has attracted wide interest for its potential in advanced technological applications. NaZr{sub 2}P{sub 3}O{sub 12}, which is the parent composition of this family, has been synthesized by the solution sol-gel method using special precursor solutions, which led to its formation (although poorly crystalline) at temperatures as low as 120{degrees}C. The lowest temperature of formation of a single phase of NaZr{sub 2}P{sub 3}O{sub 12} with a high degree of crystallinity was found to be 600{degrees}C.

Preparation and densification of forsterite (Mg 2SiO 4) by nanocomposite sol-gel processing

A diphasic nanocomposite sol-gel processing has become an excellent way of producing stoichiometric homogeneous powders with many advantages over the solid state reaction method as well as the solution sol-gel method. This procedure is described for forsterite, Mg 2SiO 4, and resulting densities of 97% for the diphasic and 91% for the monophasic gel powder are reported. In addition, a small amount of enstatite, MgSiO 3, was detected which is consistent with the findings of earlier researchers.