Preparation and properties of barium-ferrite-containing glass ceramic fibers via an electrospinning/sol–gel process

Barium-ferrite-containing glass ceramic fibers were successfully prepared by the combination of a sol–gel process and electrospinning technique using basic iron formate, barium acetate and boric acid as the starting materials. After leaching of barium borate matrix, pure phase BaFe₁₂O₁₉ fibers were obtained. The relationship of aged time and viscosity of the precursor solution was studied and the results showed that the viscosity corresponding to the spinnable state was 1–4 Pa s. The morphology, structure and magnetic properties of the obtained fibers were characterized with scanning electron microscopy, transmission electron microscopy, fourier transform infrared spectroscopy, thermo gravimetric analysis–differential scanning calorimetry, vibrating sample magnetometer. The X-ray diffraction results indicate that only the M-type Ba-ferrite and Ba-borate exist. The fibers had rough surface and hollow structure with the diameter no more than 1 μm. The fibers were composed of 40 nm BaFe₁₂O₁₉ nanoparticles embedded in the borate matrix. The coercivity and saturation magnetization of the synthesized fibers were 4,106.9 Oe and 17.8 emu/g, respectively.     

Preparation of silica capsules via an acid-catalyzed sol–gel process in inverse miniemulsions

Silica capsules were prepared via a sol–gel process using tetraethyl orthosilicate (TEOS) in inverse miniemulsions under highly acidic conditions (pH?<?2). Formation of silica capsules under acidic conditions proceeded via internal phase separation of silica species in the droplets. This mechanism is different from the well-known interfacial reaction mechanism for most syntheses of silica capsules. The driving force for the formation of capsules was the interaction between silica species and cetyltrimethylammonium bromide (CTAB) as well as between silica species and the hydrophilic block of the block copolymer surfactant, poly(ethylene-co-butylene)-b-poly(ethylene oxide) (P(E/B)-PEO). The effects of synthetic parameters on the particle morphology and size were systematically investigated in terms of the reaction time, amount of TEOS, CTAB, P(E/B)-PEO, and hydrochloric acid concentration, as well as addition of ethanol.     

Preparation and properties of VO2 thin films by a novel sol–gel process

Vanadium dioxide (VO₂) thin films were fabricated using a simple and novel sol–gel process in which V₂O₅ was used as the vanadium source; oxalic acid was used as the reducing agent; and polyvinyl alcohol was used as the film former to control the viscosity of the VO₂ precursor solution and bond vanadium ions. The microstructure and surface morphology of VO₂ films were studied by X-ray diffraction and scanning electron microscopy, respectively. The results showed that using polyvinyl alcohol forms porous nanostructure of VO₂ films with a uniform grain size of ~25 nm. The measured optical reflectance shows well-defined phase transition as observed by an increase of reflectance upon heating above the transition temperature from ~11 to ~30 % at 1,100 nm. Upon cooling, the expected hysteresis is observed.     

Preparation and properties of sol–gel waterborne polyurethane adhesive

Waterborne polyurethane (WBPU) sol–gel adhesives were prepared through a prepolymer process followed by a sol–gel reaction of (3-aminopropyl)triethoxysilane (APTES). The terminal amine group of APTES reacted with the NCO group of the prepolymer, and the ethoxy group created Si–O–Si branching by hydrolysis and condensation reactions in water at the dispersion step. Water swelling (%), tensile strength and Young’s modulus of the synthesized WBPU sol–gel adhesives were improved by increasing APTES content. Synthesized WBPU sol–gel adhesives were used for bonding nylon fabrics. A significant improvement in adhesive strength was recorded, and the potential for good adhesive strength under water at moderately high temperature (up to 75 °C) was observed with 6.84 mol% APTES in WBPU sol–gel adhesives.     

Preparation of photocurable silica–titania hybrid coatings by an anhydrous sol–gel process

Photocurable silica-titania hybrid coatings were prepared through an anhydrous sol–gel process. Moreover, test samples were prepared by the addition of definite ratios of fluoro acrylate oligomers into the formulations to manage the optical properties of transmitted light. Formulations were applied to corona-treated polycarbonate substrates. Upon adding the inorganic component to the coating material, thermal, mechanical, and other properties, such as hardness, gloss, contact angle, and flame resistance were improved. The photocured hybrid films showed an increase in the refractive index with increasing the titanium tetraisopropoxide content. As expected, a decrease was observed in the refractive index of the coatings with the incorporation of fluoro acrylate resin. The surface morphology of the hybrid films was characterized by ESEM analysis. In addition the chemical composition of the surface of the coatings was identified by ESEM–EDS technique. ESEM studies indicated that inorganic particles were dispersed homogenously throughout the organic matrix.     

Synthesis and characterization of silica xerogels obtained via fast sol–gel process

The synthesis and physical properties of high surface area silica xerogels obtained by a two-step sol–gel process in the absence of supercritical conditions are reported. The hydrolysis and condensation reactions were followed by infrared spectroscopy. The increment in the bands corresponding to silanol and hydroxyl groups suggests that the hydrolysis reaction was complete during the first 30 min. The effect on surface area and global reaction time under various reaction conditions, such as type of alkaline catalyst and solvents, water–monomer and solvent–monomer molar ratios, was also studied. The obtained results suggest that surface area was increased using 3-aminopropyltriethoxysilane as catalyst. The use of isopropyl alcohol as solvent promotes the reduction of the capillary stress, giving a well-structured xerogel. As a conclusion, with H₂O/i-PrOH/TEOS in a molar ratio of 10:4:1, it was possible to obtain silica xerogels with surface areas about 1,240 m²/g. Such surface areas are comparable with those obtained under supercritical conditions (aerogels), and higher than those xerogels conventionally obtained under normal condition (500–800 m²/g).     

Structural stability and electrochemical properties of Gd-doped ZrO2 nanoparticles prepared by sol–gel

Cubic, tetragonal and monoclinic Gd-doped zirconia nanoparticles with nominal composition Gd_xZr_1?xO₂ in the range 0 ≤ x ≤ 0.2, were prepared by annealing dried gels of Gd-containing zirconia at temperatures over the range between 450 and 1,300 °C. The synthesized zirconia-based nanoparticles with increased gadolinium load were characterized by X-ray powder diffraction, infrared and Raman spectroscopies, and transmission electron microscopy. The stabilization of the crystalline forms of Gd-doped ZrO₂ solid solutions depends on the amount of Gd dopant and the annealing temperature. For low Gd loads in Gd_xZr_1?xO₂ being x < 0.05, the tetragonal form is the single phase up to 1,100 °C, whereas the monoclinic is the crystalline form detected up to 1,300 °C. Within the range of compositions 0.05 ≤ x < 0.1, is the tetragonal the only stabilized zirconia crystalline structure over the whole range of temperature up to 1,300 °C. For higher Gd-contents, in the range 0.1 ≤ x ≤ 0.2, is the cubic zirconia form the only stable phase for the whole range of annealing temperatures. Solid-state electrochemistry of the gadolinium-doped zirconia performed by the voltammetry of microparticles approach allowed distinguishing different electrochemical answers of Gd cation associated with slightly different local coordination surrounding of cations. Enantioselective electrocatalytic effect of monoclinic Gd-doped ZrO₂ on the oxidation of l-(+)-tartaric acid and d-(?)-tartaric was also studied.     

Preparation and optical properties of sol–gel materials doped with coumarin molecules

New optical materials containing coumarin (3-(3-(4-(dimethylamino)phenyl)propenoyl)-2H-chromen-2-one) in silica are reproducibly prepared by a sol–gel technique and characterized with UV/Vis and luminescence spectroscopy. The incorporation of the coumarin molecules in the silica gels is monitored with UV/Vis spectroscopy. The coumarin doped gels change their color with time which is attributed to a protonation of the dimethylamino group of the coumarin molecules during aging of the gels and is proved by UV/Vis spectroscopy. The process of protonation of the dimethylamino group is described as a second order reaction. The luminescence spectra of the coumarin doped gels at room temperature also are given.     

Fabrication of sol–gel derived ZrO2 thin film for HR coatings via rapid thermal annealing process

The properties of sol–gel derived ZrO₂ thin films heated via a novel method of rapid thermal annealing process were studied. We investigated the effects of heat-treatment schedules with different ramp rates on the refractive index and thickness of ZrO₂ thin films as well. By controlling the heating treatment parameter, the refractive index of the ZrO₂ coatings can be adjusted from 1.69 up to 1.9 continuously, which can meet different requirement for high reflectance well. The thickness of crack-free ZrO₂ coatings can be easily controlled by employing different experimental parameters. The result of X-ray diffraction shows that as-deposited film is amorphous, and it remains stable up to the heating temperature of 400 °C. However, it begins to crystallize as the temperature increases further attaining 500 °C. Meanwhile, the surface morphology was evaluated by atomic force microscopy and the result shows that the surface of the ZrO₂ coating is smooth and uniform with root means square of 0.63 nm for the measured area of 5 × 5 μm. As a typical example, ZrO₂ thin films with refractive index of 1.9 are chosen for highly reflective coatings. Nearly full reflective mirror at 1,064 nm was fabricated on fused silica substrate. The laser induced damage thresholds of 22 J/cm² (1,064 nm, 10 ns) and 14.6 J/cm² (1,064 nm, 10 ns) are obtained for ZrO₂ coating and ZrO₂/SiO₂ multilayer coatings respectively.     

Synthesis of MCM-48 from silatrane via sol–gel process

High-quality cubic MCM-48 is successfully synthesized using a new silica source known as silatrane and cetyltrimethylammonium bromide (CTAB) as the structure-directing agent via sol–gel process. The effects of synthesis parameters, viz. crystallization temperature, crystallization time, surfactant concentration, quantity of NaOH, and silica source, on the product structure are investigated. The synthesized samples are characterized using X-ray diffractometer (XRD), N₂ adsorption–desorption isotherms, and electron microscopy. Optimally, this product is synthesized from samples crystallized at 140°C for 16 h with a CTAB/SiO₂ ratio of 0.3 and NaOH/SiO₂ ratio of 0.5. The XRD result exhibits a well-resolved pattern, corresponding to the Ia3d space group of MCM-48. The BET surface area of this product is as high as 1,300 m²/g with a narrow pore-size distribution of 2.86 nm. The scanning electron microscopic (SEM) images also show the truncated octahedral shape and well-ordered pore system of MCM-48 particles.     

Preparation and characterization of boron-based bioglass by sol−gel process

45S5 bioglass has been widely studied in the last few decades because of its bioactivity and promising applications in the biomedical field. Boron, even few studied, represents a potential element to improve the properties of the 45S5 bioglass derivatives. The bioglasses are conventionally prepared by heat treatment of oxides and silicon. Here, the sol?gel method is proposed for the preparation of the boron-based 45S5 bioglass (45S5B) and the classical 45S5 bioglass (45S5), using water-soluble salts as raw materials. The bioglasses were characterized by FTIR, XRD, and SEM, indicating the success of the sol?gel method for preparation of the samples. The bioglasses were also tested in vitro for bioactivity in biological conditions and cytotoxicity against eukaryotic cells. The bioactivity of 45S5B was similar to the bioactivity of 45S5 bioglass, indicated by the deposition of hydroxyapatite crystals at the surface of the pristine bioglasses. The results of cytotoxicity tests revealed that the IC₅₀ of 45S5B (IC₅₀?=?7.56?mg?mL^?1) was similar to the IC₅₀ of 45S5 (IC₅₀?=?8.15?mg?mL^?1), indicating its safety for application in the biomedical field.

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Preparation of SiO2–wood composites by an ultrasonic-assisted sol–gel technique

The vacuum impregnation assisted sol–gel technique is a promising and environmentally-friendly method for the inorganic modification of wood by the formation of wood-inorganic composites. However, vacuum impregnation is relatively cumbersome and time-consuming. In this study, SiO₂–wood composites were prepared by an ultrasonic-assisted sol–gel method, which is an innovative and simple method. Using this method, we found an increase in the degree of silicon incorporation into the cell walls of the wood. The impregnation of silica inside the cell walls were verified by Fourier-transform infrared spectra, X-ray diffraction, scanning electron microscopy and energy dispersive spectrometry. Leaching test proved that the internal cross-linking silica is stably bonded to the wood cell walls. This modified method significantly reduced the hygroscopicity of the wood and consequently improved the mechanical performance of the modified wood. Thermogravimetric and differential thermal analyses showed that the incorporation of silicon retards thermal decomposition and the complete combustion of the wood matrix and it enhances the thermal stability of wood.     

Preparation and characterization of film-forming raspberry-like polymer/silica nanocomposites via soap-free emulsion polymerization and the sol–gel process

Herein, we report on the synthesis of film-forming poly(styrene-co-butyl acrylate-co-acrylic acid)/SiO₂ [P(St-BA-AA)/SiO₂] nanocomposites by in situ formation of SiO₂ nanoparticles from TEOS via sol–gel process in the presence of poly(acrylic acid) (PAA)-functionalized poly(styrene-co-butyl acrylate) [P(St-BA)] particles fabricated by soap-free emulsion polymerization. The formed silica particles could be absorbed by polyacrylate chains on the surface of PAA-functionalized P(St-BA) particles; thus, raspberry-like polymer/silica nanocomposites would be obtained. Transmission electron microscopy, Fourier transform infrared spectroscopy, attenuated total reflectance infrared spectrum, ultraviolet–visible transmittance spectra, and thermogravimetric analysis were used to characterize the resulting composites. The results showed that the hybrid polymer/silica had a raspberry-like structure with silica nanoparticles anchored on the surface of polymer microspheres. The thermal, fire retardant, and mechanical properties and water resistance of the film were improved by incorporating silica nanoparticles, while the optical transmittance was seldom affected due to nanosized silica particles uniformly dispersed in the film.

Preparation of superhydrophobic silica nanoparticles by microwave assisted sol–gel process

Hydrophobic silica nanoparticles were obtained by microwave assisted sol–gel method using a two-step procedure. In the first step different size silica particles were generated from tetraethyl orthosilicate and in the second one the silica particles were hydrophobized using hexadecyl trimethoxysilane (HDTMOS). Under microwave irradiation, high conversion degrees were obtained at relatively short reaction times. The HDTMOS added in the second step instead of coating the silica nanoparticles generated new ones and therefore the final product showed a bimodal size distribution. All the synthesized nanoparticles gave rise to high water contact angles (≈150°) and low hysteresis values.     

One-pot synthesis of organo-silica hybrids with high thermal properties via a simple sol–gel process

Journal of Thermal Analysis and Calorimetry - Organic–inorganic hybrid composites have received much attention of scientists in the recent years due to the notable improvement of thermal...     

Preparation of three-component TEOS-based composites for stone conservation by sol–gel process

Tetraethoxysilane (TEOS) is the most commonly used silicon-based stone consolidant in art conservation. However, it is known that the resulting silica gel phase tends to develop cracks inside the stone as the gel shrinks during aging and drying. Such phenomenon may lead to severe damage to the protected objects. By introducing silica nanoparticles into TEOS, a so-called particle modified consolidant (PMC), may minimize such shrinkage by reducing the volume loss and forming mesoporous structure to weaken the capillary forces. But many previous results show significant color changes on the surface of PMC-treated stones which can not be tolerated in the conservation treatments of cultural heritage. In this work, we designed a three-component composite consolidant which consists of 15 nm silica particles, α,ω-hydroxyl-terminated polydimethylsilane (PDMS-OH) and TEOS. Among the three components, TEOS provides the consolidation function, silica nanoparticles prevent the cracking and increase the salt resistance and PDMS-OH further reduces cracking, decreases the color alteration and increases the resistance to wetting of the stone. Experimental results show that the three components have significant synergistic effect, which makes the material exhibiting best overall performance in terms of cultural heritage protection.     

High water solubility and sol–gel transition behavior of titania nanoparticles obtained by an in situ functionalization sol–gel process

Herein, addition reaction occurred between glycidol and partially hydrolyzed Ti⁴⁺ complexes provides a opportunity to obtain dry anatase nanopowder with high redispersity in water. This property is considered to be originated from the two OH groups located in the two ends of glycidol resulted chlorinated propandiol molecules. In aqueous solution, the two OH groups are respectively connected with particle surface and external free water by the formation of hydrogen bonds, resulting in high water redispersity of nanoparticles. Due to the much less amount of chlorinated propandiol molecules than adsorbed molecule water on particle, the wide space between organic molecules facilitates the mutual physical surface touch of individual particles to form hydrogen bond between them. A novel property is then obtained for surface modified titania nanoparticles, which is the gelation of redispered nanoparticles in aqueous solution.