TEOS Solution Research Articles

Impact of SiO2 Modification on the Performance of Nafion Composite Membrane

Using Nafion212 membrane and TEOS solution as raw materials, Nafion212/SiO2 composite membranes were prepared. In the in situ sol-gel reaction process, a series of Nafion/SiO2 composite membranes were prepared by varying the reaction temperature and reaction time. The effects of different modification schemes on Nafion/SiO2 composite membranes were studied using SEM, EDS, TEM, TGA, XRD, and mechanical tensile experiments, among other methods. The results show that Nafion/SiO2 composite membranes prepared at 3°C exhibit a well-separated phase structure and excellent water retention properties, with a water uptake of 29.23% and a swelling ratio of 24.25%. These membranes also demonstrate outstanding physical and chemical performance, with a maximum tensile stress of 13.6 MPa and an elongation at a break of 270%. At 110°C, the proton conductivity of the Nafion/SiO2 composite membrane reaches 0.172 S/cm, meeting the requirements for high-temperature proton exchange membrane fuel cells.

Preparation of a thick sponge-like structured amorphous silica ceramic coating on 6061 aluminum alloy by plasma electrolytic oxidation in TEOS solution

Plasma electrolytic oxidation (PEO) was performed on 6061 aluminum alloy in organosilicon electrolyte using a stepwise constant potential control method for 23 min. The resulting coating was a sponge-like structured amorphous silica ceramic with a thickness of about 130 μm. Its exceptional wear resistance was attributed to the high hardness of the silica ceramic and the low elastic modulus of the sponge-like structure. The corrosion resistance was enhanced by a dense layer of approximately 2 μm between the coating and the substrate. Impressively, the indentation depth of the PEO coating during nano-indentation tests was only 50–60% of that of 6061 aluminium alloy under varying loads, while the recovery depth of the PEO coating after unloading was 2.5–3.1 times greater than that of 6061 aluminium alloy. Due to its special composition and structure, the PEO coating caused serious wear to the high hardness Si3N4 friction balls during the friction and wear test. In the electrochemical tests, the coating reduced the corrosion current density from 1.056 × 10−5A·cm−2 to 1.239 × 10−7A·cm−2, while extending the passivation region from 0.322 V to 1.032 V.

Effects of Carbon Templates in Tetraethyl Orthosilicate-Derived Superhydrophobic Coatings

Superhydrophobic coatings have garnered significant research interest due to their potential applications in areas such as ant-icing and windows. This study focuses on the development of superhydrophobic coatings using air-assisted electrospray and the effect of different carbon additives as templates in the coating. Carbon templates, with their unique topological varieties, offer a cost-effective alternative to other patterning technologies such as photolithography. By introducing dispersed carbon black, carbon nanotubes, and graphene additives in TEOS solution, silica is given the ability of localized secondary growth on or around the carbon surfaces as well as the building structure to provide adequate roughness on the substrate surface. The templated silica formations provide a thin coating with nano-scale roughness for heightened water resistance. As compared with the template-free coating that has small silica particles, a surface roughness of 135 nm, and a water contact angle (WCA) of 101.6° (non-superhydrophobic), the carbon templating effect allowed for increased silica particle size, a surface roughness as high as 845 nm, a WCA above 160°, and the ability to maintain superhydrophobicity over 30 abrasion cycles. The morphological characteristics that resulted from the templating effect correlate directly with heightened performance of the coatings. Herein, the carbon additives have been found to serve as cheap and effective templates for silica formation in thin TEOS-derived superhydrophobic coatings.

Wear behavior of a new composite formulation, with TEOS addition, for abrasive vitrified grinding wheels

Vitrified grinding wheels are used in many manufacturing industries to shape and finish metals and other materials in an efficient way. This work addresses a new approach with the use of tetraethyl orthosilicate solution (TEOS solution or silica sol), as an additive, in vitrified abrasive composites for grinding wheels. Different types of composite were produced using always the same materials and processing methods, but with different TEOS contents. Compared with a reference abrasive grinding wheel, the addition of TEOS promoted an improvement in the abrasive tool performance. The new formulation for vitrified abrasive composites showed better dimensional stability during processing (drying and sintering), and could be applied to the production of grinding tools with high dimensional accuracy. With the addition of 3.75 wt% of TEOS there was an increase in the strength of the matrix bonds. The porosity of the composite increased by 7% (from 43.6 to 46.9%), also improving its wear properties, with the quadrupling of the grinding ratio of the abrasive composite. In addition, the surface roughness of the composite decreased (from Ra = 22.9 to 8.4 μm) allowing to improve the surface finish of the workpieces.

PDMS–PMMA bonding improvement using SiO2 intermediate layer and its application in fabricating gas micro valves

In this study a modified technique is presented for bonding PDMS membrane to PMMA substrate using thin SiO2 intermediate layer to enhance PMMA surface’s hydrophilicity, and increase PMMA stickiness to PDMS via O2 plasma activation. TEOS solution is used to create silica layer on PMMA, and Chloroform is added to sol–gel in order to infuse silica layer to PMMA substrate; this leads to a stronger stickiness of SiO2 layer to PMMA. It is shown that strong and irreversible bond of PMMA which is covered with SiO2 nano particles, to PDMS can be reliably achieved. Furthermore, using this technique, two types of polymeric gas micro valves were fabricated that could cease the gas flow hermetically. Additionally, small solenoid actuators were utilized to control valves which lead to switching from a rather high differential pressure. In order to evaluate bonding and banning capability of the valves, several tests such as strength test and Damming test of the valves were performed. Results of the conducted tests indicate an improvement in PDMS/PMMA bonding strength using TEOS/chloroform solution; moreover, damming pressure of the micro valves, at the best condition, was about 2.5 bars.

Improved porosity and ionic sorption capacity of carbon particles prepared by spray pyrolysis from an aqueous sucrose/NaHCO3/TEOS solution

Spherical carbon spheres with improved mesoporosity and ion sorption properties are synthesized by an ultrasonic spray pyrolysis process from an aqueous sucrose/NaHCO3/TEOS solution.

Stabilization and encapsulation of magnetite nanoparticles

The goal is to stabilize magnetite nanoparticles (NPs) in order to prepare them for encapsulation and to obtain a core–shell structure. Magnetite NPs were obtained by a co-precipitation method and then treated with different stabilizing agents in order to get a full dispersion in an aqueous medium. The dispersed particles were then coated with silica using a TEOS solution. The samples were characterized by Raman spectroscopy, TEM, EDX analysis, and FTIR measurements. The particles are the basis of a core–shell structure where a potential polymer or drug could be anchored on the surface.

Nickel-Impregnated Mesoporous Silica Prepared in an Aerosol Reactor

Nickel-impregnated mesoporous silica was prepared from a solution of TEOS, metal nitrate and Pluronic P123 in a short flight (<30s) through an aerosol reactor by changing the reactor temperature and metal concentration (at% Ni to Si). The dispersion of the metal and morphology of the composite mesospheres were observed with TEM, SAXS, and XRD. The maximum in the d spacing was observed at 400°C with the nickel concentration in mesospheres fixed at 10 at%. On the contrary, the minimum appeared at 10 at% Ni at the reactor temperature fixed at 600°C. Nickel mostly remained either inside mesopores or silica wall (1) in the range of reactor temperatures between 150 and 1000°C with 10 at% and (2) in the range of metal concentrations up to 100 at% at 600°C. Post calcination provided nickel more freedom to penetrate silica wall as the mesophase was spray pyrolyzed at lower temperature. Most findings could be explained by a new model proposed based on metal-promoting formation of silica wall.

ChemInform Abstract: Structures, Properties, and Potential Applications of Ormosils

Ormosils are organic-inorganic hybrid solids in which the organic component may be chemically bonded to a silica matrix. Somewhat similar to inorganic silicate glasses, the structure of the silica network can be modified by the presence of organic groups. The resulting properties of the Ormosils are then governed by the type and concentration of organics used. Examples are presented in which the mechanical, electrical and optical properties of selected Ormosils can be influenced by organic groups. For instance, small amounts of polydimethylsiloxane (PDMS) added to a solution of TEOS will give an Ormosil about ten times harder than the hardest organic polymer. Larger amounts of PDMS (20%) will now yield an Ormosil which is as rubbery as organic rubber. Ormosils in which the organic and inorganic constituents are covalently bound to each other are the focus of this critical review. The potential applications of such Ormosils are discussed.

One-pot synthesis of organo-functionalized monodisperse silica particles in W/O microemulsion and the effect of functional groups on addition into polystyrene

The direct synthesis from TEOS and organosilanes is carried out in W/O microemulsion in order to prepare monodisperse functionalized silica nanoparticles. The well monodisperse particles are obtained successfully from a wide range of concentration of 3-aminopropyltriethoxysilane (APTES), 3-mercaptopropyltrimethoxysilane (MPTMS), phenyltrimethoxysilane (PTMS), vinyltriethoxysilane (VTES) and 3-cyanoethyltriethoxysilane (CETES) in the solution of TEOS and polyoxyethylene nonylphenol ether (NP-5). The particle size can be controlled without widening the distributions. On the other hand, the direct synthesis with these organosilanes and TEOS by conventional Stöber method using no surfactant provides colloidal solutions with DLS plots with wide or bimodal dispersions. NP-5 is removed by washing the colloids with DEGDEE and the decline of IR absorptions due to the benzene ring stretching is observed. The resultant colloidal powder is occluded into polystyrene by the polymerization of styrene monomer in the presence of these functionalized silica nanoparticles. The heat resistance of modified polystyrene is investigated by TG–DTA in dry air. The position of DTA peak due to combustion of the polymer is shifted to a higher temperature with the addition of silica nanoparticles. The considerably large shift is found in silica nanoparticles prepared with VTES and PTMS, whose difference is higher than that by the addition of simple silica nanoparticle with no functional groups.

Synthesis of nanoporous silica aerogel by ambient pressure drying

A crack-free silica aerogel monolith was fabricated from a cheap water glass derived silicic acid solution by adding glycerol, which served as a drying control chemical additive (DCCA). The OH surfaces of the wet gel with glycerol were modified using a TMCS/n-hexane mixture followed by solvent exchange from water to n-hexane. The obtained surface modified wet gel was dried at 75 °C under ambient pressure. The addition of glycerol appears to give the wet gel a more homogeneous microstructure (larger pore size and uniform size distribution) as well as enhanced stiffness. However, glycerol also retards surface modification and solvent exchange. The aerogel synthesized with glycerol added to the silica sol maintained a relatively low bulk density compared with the aerogels aged in a mixed ethanol (EtOH)/TEOS solution. The reproducibility of aerogel production was further improved in the aerogel synthesized with glycerol added to the silica sol and aged in a 70%EtOH/30%TEOS solution.

Chromaticity, brightness and aging of silica spray coated zinc sulfide silver phosphor particles

A spray drying approach was used to coat 15 nm SiO2 continuous films onto ZnS:Ag phosphor particles. The coating was deposited on the particles by simultaneously spraying a slurry consisting of a solution of TEOS and ethanol with the solid phosphor particles into a heated drying column. The cathodoluminescent spectra of silica coated phosphor has CIE 1931 chromaticity coordinates of X ∼ 0.055, Y ∼ 0.085, brightness that is 90% of the uncoated phosphor brightness, and improved aging behavior under laboratory testing conditions.

Ni/SiO 2 prepared by sol–gel process using citric acid

A Ni/SiO 2 with high Ni content over 50 wt% in NiO form was prepared from a solution of TEOS, nickel nitrate and citric acid. The additive citric acid contributes both the formation of mesopores and increase in the Ni dispersion. The Ni/SiO 2 has large mesopores with size of 5–10 nm. The mesopores are formed by eliminating citric acid from the silica–Ni–citric acid composite with small shrinkage, i.e. the spaces occupied with citric acid in the composite directly turn to pores after elimination. Although large shrinkage in pores occurs when the composite is calcined in air, the calcination in an inert atmosphere is effective to suppress the shrinkage during calcination. In addition to the controlled large mesopores, high Ni dispersion is achieved in the Ni/SiO 2. Nickel citrate formed in the as-prepared silica–Ni–citric acid composite effectively suppresses the aggregation of Ni species during drying because of low crystallization ability of nickel citrate. Furthermore, the following calcination in an inert atmosphere has an additional effect to increase Ni dispersion. Thus prepared samples keep small Ni particle size even at high Ni content of ≈50 wt% after reduction at 500 °C, and show high Ni surface area over 30 m 2 g −1.

Characterization and tribological investigation of SiO 2 and La 2O 3 sol–gel films

Thin films of SiO 2 and La 2O 3 were prepared on a glass substrate by a dip-coating process from specially formulated sols. The tribological properties of the resulting thin films sliding against a Si 3N 4 ball were evaluated on a one-way reciprocating friction and wear tester. The morphologies of the unworn and worn surfaces of the films were examined by an atomic force microscope (AFM) and a scanning electron microscope (SEM). La 2O 3 shows the best tribological performance. The coefficient of friction is about 0.1 and the wear life is over 5000 sliding passes both under higher (3 N) and lower load (1 N). The SiO 2 film derived from a specially formulated aqueous solution shows much better performance in resisting wear and reducing friction than the one derived from an ethanol solution. The wear mechanisms of the films are discussed based on SEM observation of the worn surface morphologies. SEM observation of the morphologies of worn surfaces indicates that the worn surface of La 2O 3 is too slight to be observed by SEM. The wear of SiO 2 derived from TEOS solution is the characteristic of delaminating, which is responsible for the abrupt failure of the film. The wear of SiO 2 derived from aqueous solution is the characteristic of fracture. Brittle fracture and severe abrasion dominate the wear of glass substrate.

Laser-Induced Electron-Transfer Processes in a Pyrene–β-Cyclodextrin Complex in Titanosilicate Systems

We have used fluorescent spectroscopy and laser flash photolysis to investigate the photonics of pyrene molecules in a pyrene–β-cyclodextrin inclusion complex in various media. We have observed a protective effect of β-cyclodextrin relative to solubilized pyrene molecules during quenching of fluorescence by Ti ions (or titanium dioxide particles) in mixed colloids. In the presence of a precursor of silica (a TEOS solution), the pyrene molecules react with the colloidal silica particles formed, and the reaction is accompanied by decomposition of the pyrene–β-cyclodextrin inclusion complex and efficient photoionization of pyrene.

Magnetic Iron Oxide/Mullite Nanocomposite Stable up to 1400°C

Magnetic nanocomposites consisting of spherical iron oxide particles of around 13 nm dispersed in a mullite matrix have been obtained by pyrolysis at 600°C of an aerosol generated from a solution of TEOS and iron and aluminum nitrate in methanol and a posterior heat treatment at 1200°–1400°C. Iron contents higher than the solubility limit of Fe in mullite (12 wt% Fe2O3) have been used to prepare the precursor samples. It should be emphasized that the new magnetic nanocomposite presents a saturation magnetization of 3.3 emu/g and a coercivity of 546 Oe at room temperature, and preserves its magnetic character up to 1400°C. This behavior reveals that mullite is an excellent matrix to keep the magnetic particles apart, avoiding sintering during the heat treatment and therefore making phase transformations difficult.

Strengthening of water glass and colloidal sol based silica gels by aging in TEOS

Previous work demonstrated that gels can be strengthened and stiffened by providing new monomers to the alcogel thus giving xerogels ambient pressure dried with properties similar to aerogels with porosity up to 90%. That work is extended to increase the strength and stiffness of wet gels obtained from cheaper water soluble sodium silicate (water glass) and colloidal silica sols (3 and 6 nm). During aging the water glass based gels in a TEOS solution, a more than 10-fold increase in shear G modulus was obtained within 27 h, showing a very high reactivity of this system compared to alkoxide based gels. Water glass based gels generally show a lower xerogel density compared to the gels prepared from colloidal sols and a xerogel density of 0.22 g/cm 3 was obtained. Starting from colloidal sols, a smaller increase in G was observed for the same increase in initial density, however, the larger particle size and hence pore size of these gels reduces the capillary pressure during drying, giving low density xerogels. A lower density was obtained for the xerogels prepared from 6 nm sol compared to 3 nm sol for the gels aged in TEOS. A large decrease in xerogel density was observed when the colloidal sol based gels were aged in TEOS.

Thermal and Temporal Aging of Silica Gels in Monomer Solutions

In previous work we have introduced the idea of preparing ambient pressure dried silica aerogels by increasing the wet gels' stiffness by aging in a TEOS solution until shrinkage during drying is almost eliminated. The present work elucidates the possibilities for obtaining ambient pressure dried aerogels employing this idea, however, cheap water soluble sodium silicate (water glass) precursors have been used to increase the economic feasibility of the process.

INHIBITION OF PB-LEACHING FROM LEAD CRYSTAL GLASS BY COATING WITH FILMS PREPARED BY THE SOL-GEL METHOD

The chemical durability of lead glass tumblers (24% PbO) in a 4% (v/v) acetic acid solution before and after coating with sol-gel derived SiO2 films was assessed to determine the extent of reduction in Pb-leaching that can be achieved. It was found that by coating the internal surface of the glass tumblers with 1 ml of 10% TEOS solutions at 100°C and densifying the coating formed at 500°C for 1 h, it was possible to reduce Pb-leaching to about one quarter of that of the uncoated glass.

Elaboration at 80°C of SiO2 Layers Deposited by Aerosol-Gel Process

The aerosol-gel process is a thin film deposition technique based on the sol-gel polymerization of a liquid film deposited from an ultrasonically sprayed aerosol. SiO2 layers have been deposited by aerosol-gel process from TEOS solutions prepared using a two-step procedure. After a post-treatment at 80°C, the layers have a remarkable abrasion resistance and a high refractive index. In this paper, the chemical mechanisms involved in the formation of SiO2 layers at low temperature are studied by FTIR spectroscopy and related to the processing conditions.