Showing papers on "Sol-gel published in 1993"
TL;DR: In this article, the authors used tetrabutylorthotitanate as a precursor to titanate coatings and showed that the gel-formation region was obtained as well as stable-layer formation and phase-separation regions in the Ti(OBun)4-C2H5OH-H2O system.
Abstract: Using tetrabutylorthotitanate as a precursor, titanate coatings with and without modifiers such as SnO2 and Fe2O3 have been successfully obtained. The hydrolysis and polycondensation mechanism is discussed in relation to the sol-gel transition. The gel-formation region was obtained as well as stable-layer formation and phase-separation regions in the Ti(OBun)4-C2H5OH-H2O system. Coatings deposited on glass substrates exhibited a strong tendency to aggregate and with increasing temperature to crystallize in anatase or rutile phases (500 and 1000 °C, respectively). Structural characteristics of the gel products were investigated by SEM, X-ray and electron diffraction measurements, as well as by small-angle X-ray scattering. It was established that after thermal treatment at 500 °C for 10 min, spherical aggregates were formed in the coatings, having an average radius of approximately 5.1 nm.
115 citations
TL;DR: In this paper, the sintering process of sol-gel-prepared monodisperse submicrometer CeO2 spheres was studied using transmission electron microscopy.
Abstract: We studied the sintering process of sol-gel-prepared monodisperse submicrometer CeO2 spheres by examining the microstructural changes of single spherical particles after successive heat treatment in oxygen up to 850°C using transmission electron microscopy. Steps of organic phase removal, CeO2 crystallization, grain growth, and particle condensation were clearly illustrated. Grain-size and sphere-diameter changes were measured quantitatively using this technique. CeO2 particles were found to be highly porous until collapse, which occurred at~850°C.
111 citations
TL;DR: In this article, transparent smooth and crack-free BaTiO3 thin films were deposited on stainless steel, fused silica, platinum plates, and platinized silicon wafers using the sol-gel process.
Abstract: Transparent smooth and crack‐free BaTiO3 thin films were deposited on stainless steel, fused silica, platinum plates, and platinized silicon wafers (100) using the sol‐gel process. Barium 2‐ethyl hexanoate and titanium isopropoxide were used as precursors. Annealing of the films at 750 °C for 2 h was necessary to get polycrystalline films. The electrical properties of the films prepared on stainless‐steel substrates showed an electrode barrier effect whereas those prepared on platinum substrates were susceptible to ambient atmospheric humidity. However, films grown on platinum substrates and measured under dry conditions showed very good electrical properties. Ferroelectric hysteresis and C‐V characteristics were also studied on these films.
104 citations
TL;DR: In this article, the lineshape of the Si 2p and Ti 2p peaks indicate that silicon and titanium are present as SiO2 and TiO2 oxide both for the starting and thermal-treated powders.
96 citations
TL;DR: In this paper, a new family of organic-inorganic hybrid materials has been prepared by incorporating polystyrene structure units covalently into the SiO2 glass network via the sol-gel approach.
Abstract: A new family of organic-inorganic hybrid materials has been prepared by incorporating polystyrene structure units covalently into the SiO2 glass network via the sol-gel approach. The polymer precursors were synthesized by free-radical copolymerization of styrene with 3-(trimethoxysilyl)propyl methacrylate (MSMA) at various feeds. These copolymers were then hydrolyzed and co-condensed with tetraethyl orthosilicate in tetrahydrofuran at room temperature to afford monolithic polystyrene-SiO2 hybrid sol-gel materials having SiO2 contents of 15 to 84% by weight. The hybrid materials derived from the copolymers with MSMA contents greater than 22 mol% have excellent optical transparency. In these transparent hybrid materials, the polymer chains should be uniformly distributed in and covalently bonded to the amorphous SiO2 matrices. The bulk properties of these materials including density, refractive index, and hardness were found to be related to their molecular compositions and can be tailored by varying the polymer contents.
92 citations
Patent•
13 Dec 1993TL;DR: Filamentary abrasive particles formed from a sol-gel alumina modified by rare earth metal oxides have excellent abrasive qualities as mentioned in this paper, and they have been shown to have good abrasive properties.
Abstract: Filamentary abrasive particles formed from a sol-gel alumina modified by rare earth metal oxides have excellent abrasive qualities.
86 citations
84 citations
TL;DR: The electrochromic properties of these coatings could be varied to give films with fast kinetics and large optical modulation as discussed by the authors, and the electrochemical properties of sol-gel derived tungsten oxide thin films are described.
84 citations
TL;DR: In this paper, the authors examined thin films of WO3TiO2 produced by the sol-gel method and DC magnetron sputtering, and characterized optically and electrochemically in organic LiClO4 solutions.
83 citations
TL;DR: In this article, the synthesis of polymerizable solutions containing Bi and Ti, and characterization of the resulting Bi4Ti3O12 thin films were discussed, and they were later characterized by X-ray diffraction and SEM.
Abstract: Stoichiometric Bi4Ti3O12 thin films were prepared by sol-gel processing. This paper discusses the synthesis of polymerizable solutions containing Bi and Ti, and characterization of the resulting Bi4Ti3O12 thin films. The formation of metallic alkoxide and acetate alkoxide are indispensable, soluble precursors for these multicomponent systems. The double alkoxide was prepared by allowing Bi acetate to react with Ti alkoxides. The development of the polymerizable solution system containing Bi and Ti required choosing appropriate solvents and metallo-organic sources for the two components. Bismuth acetate, titanium methoxyethoxide and the solvents 2-methoxyethanol and glacial acetic acid were selected based on their successful use in a number of related systems. Thin films of Bi4Ti3O12 were obtained onto platinized Si substrates by spin casting, followed by heat-treated at 700°C. These films were later characterized by X-ray diffraction and SEM. The measured dielectric and ferroelectric properties of Bi4Ti3O12 were as follows: dielectric constant 120, dielectric loss 0.5%, remanent polarization Pr=4 µC/cm2, coercive field Ec=1.8 kV/cm.
83 citations
TL;DR: In this paper, chemical composition and the valency state of elements modified by SnO 2, Fe 2 O 3 and SiO 2 titanium-based coatings has been studied through X-ray photoelectron spectroscopy.
Abstract: Through X-ray photoelectron spectroscopy, chemical composition and the valency state of elements modified by SnO 2 , Fe 2 O 3 and SiO 2 titanium-based coatings has been studied. It has been established that metal alkoxides and salts used as precursors after a certain thermal treatment of the layer are transformed into the respective oxide stable state. At depth in the coatings, oxides of Ti(IV) and Sn(IV) are unstable and exhibit stoichiometrical disturbances. The phenomenon is discussed in relation to argon-ion sputtering conditions, the inhibition of the diffusion of sodium ions from the glass substrate, and the residual carbon from organic radicals
TL;DR: In this paper, a sol-gel process consisting of hydrolysis and condensation of metal alkoxides in the liquid phase was used to obtain desired rutile-type solid solution oxides of ruthenium and titanium with well-defined stoichiometry.
Abstract: Ultrafine binary oxide particles of RuO 2 -TiO 2 have been prepared by a sol-gel process consisting of hydrolysis and condensation of metal alkoxides in the liquid phase. This process enabled us to obtain desired rutile-type solid solution oxides of ruthenium and titanium with well-defined stoichiometry, except for the Ti-rich oxide composition, which appear not to form a homogeneous solid solution
TL;DR: In this article, a glass film with an Au/Si atomic ratio of 0.01 was successfully prepared by the sol-gel method with dip-coating using NaAuCl4⋅2H2O and tetraethyl orthosilicate (TEOS) as starting materials.
Abstract: Au microcrystal-doped glass films with high optical nonlinearity were prepared by the sol-gel method with dip-coating using NaAuCl4⋅2H2O and tetraethyl orthosilicate (TEOS) as starting materials. The glass film with an Au/Si atomic ratio of 0.01 was successfully prepared. The nonlinear susceptibility χ(3) of the film was 7.7×10-9esu. Microcrystals with a radius of about 7A and of about 30A coexisted in the glass film. The nonlinear susceptibility of Au microcrystals itself in the film, χm(3), was 1.0×10-7esu and was two times larger than that observed in Au-doped glasses prepared by the melting method. Subsequent heat treatment of the films at 1000°C changed the absorption spectra and decreased χ(3) by a factor of two. The atomic ratio of Au/Si was able to be increased to 0.04.
TL;DR: In this paper, the effect of Si on phase development and mechanisms of transformation is discussed, while the crystal structure of the final perovskite phase was not affected by the Si addition.
Abstract: Sol-gel methods were used to prepare chemically modified lead titanate (PT) powders. A PT alkoxide solution was synthesized and doped with Si (2–12 mole%) or with equimolar amounts (2–12 mole%) of Si and Pb through the addition of Si and Pb–Si alkoxide solutions, respectively. PT alkoxide solutions were also prepared with excess Pb and Ti (7 and 10 mole%). Gels were prepared through controlled additions of water. Crystalline phase development of gel-derived powders with heat treatment (400–700 °C) was studied using x-ray diffraction (XRD) and differential thermal analysis (DTA). While PT powders without added Si crystallized directly into a perovskite phase, Si modified materials crystallized first into a pyrochlore phase and at a higher temperature transformed into perovskite. The pyrochlore lattice parameter and the temperature for the transformation to perovskite increased with Si content. In all cases, the crystal structure of the final perovskite phase was not affected by the Si addition. The effect of Si on phase development and mechanisms of transformation is discussed.
TL;DR: In this article, a new kind of organic-inorganic hybrid composite was prepared by means of the sol-gel process, and the polymer employed was a mixed-isomer aromatic polyamide having good solubility and thermal stability.
Abstract: A new kind of organic-inorganic hybrid composite was prepared by means of the sol-gel process. The polymer employed was a mixed-isomer aromatic polyamide having good solubility and thermal stability. The silica constituting the inorganic phase was produced by the hydrolysis and condensation of tetramethoxysilane. The bonding between the phases involved aminophenyl-trimethoxysilane, in which the amino group can react with the phthaloyl chloride end-capped polymer, and the methoxysilane groups undergo hydrolysis. The composition of these composites was varied by changing the linear polymer chain length and relative amount of tetramethoxysilane. The gelation time was found to range from a few minutes to several days. Thermogravimetric analyses showed that decomposition starts at approximately 450 °C. Thin films cast from materials having a relatively high silica content were opaque and rigid, but those with low silica content were flexible and transparent.
TL;DR: Pt/SiO 2 catalysts were synthesized by the sol-gel method using a squareplanar metal precursor and tetraathoxysilane as mentioned in this paper, and the results were compared with those obtained in conventionally impregnated catalysts.
Abstract: Pt/SiO 2 catalysts were synthasized by the sol-gel method using a squareplanar metal precursor and tetraathoxysilane. The solids were characterized by FTIR, UV-vis (diffuse reflectance), X-ray diffraction, scanning and transmission electron microscopy, and gas adsorption. The results were compared with those obtained in conventionally impregnated catalysts. If is shown that in the sol-gel catalysts an unusual interaction between the metal and the support exists, which is not present in impregnated catalysts
TL;DR: In this paper, a near-infrared dye laser (HITC) was incorporated in a wide variety of different transparent sol-gel matrices such as silica or aluminum, titanium, and zirconium oxo polymers and inside hybrid organic-inorganic coatings.
TL;DR: Ferroelectric BaTiO3 thin films have been successfully prepared by sol-gel process using barium and titanium isopropoxides as precursor solutions for dip-coating as discussed by the authors.
Abstract: Ferroelectric BaTiO3 thin films have been successfully prepared by sol-gel process using barium and titanium isopropoxides as precursor solutions for dip-coating. Homogeneous BaTiO3 thin films have been obtained on various substrates by preheating gel films at 120°C in a flow of oxygen/water vapor mixed gas, and successive heating at 650°C in oxygen atmosphere. The introduction of water vapor during preheating is very effective for the crystallization of BaTiO3 at relatively low temperatures. These films exhibit good crystallinity and smooth surfaces with grains as small as about 50 nm. BaTiO3 thin films prepared on Pt/SiO2/Si substrates with a thickness of about 0.5 µm show dielectric constants of 800~1000 and loss tangents of 0.07~0.09 at 1 kHz. Ferroelectric hysteresis loops were observed for these thin films which possessed the remanent polarization of 8 µC/cm2 and the coercive field of 25 kV/cm.
TL;DR: In this paper, different methods of synthesis of tetragonal zirconia in SiO2 matrix were compared in order to obtain thermal stability, and a high amount of stabilized TRSZIRconia.
Abstract: ZrO2-transformation-toughened glass-ceramics have been prepared by the sol-gel process from either colloidal gels (CG) or polymeric gels from alkoxides (PG), using, in the latest method, a different catalyst (acid, basic and without catalyst), and different compositions in the ZrO2·SiO2 system (free ZrO2 included). The different methods of synthesis of tetragonal zirconia in SiO2 matrix were compared in order to obtain thermal stability, and a high amount of stabilized tetragonal zirconia. The effect of catalyst, hydrolysis time, chemical composition, critical particle size in ZrO2(t)→ZrO2(m) transformation, the doping with vanadium on the ZrO2(t) stability in SiO2 matrix and Vickers microhardness of samples have also been studied.
TL;DR: In this paper, a novel solgel process for the preparation of grain-oriented thin films of PbTiO3 is reported. But the a-axis orientation increased with further heat treatment at temperatures between 600 and 700°C.
Abstract: A novel sol‐gel process for the preparation of grain‐oriented thin films of PbTiO3 is reported. Using a moisture tolerant molecularly modified titanium isopropoxide and hydrated lead acetate PbTiO3 films with both c‐ and a‐axis orientations could be prepared on platinized silicon substrates at 550 °C. The average grain size of films prepared at 600 °C was ≊0.1 μm. The a‐axis orientation increased with further heat treatment at temperatures between 600 and 700 °C. The relative changes in the thin film orientation may be due to thin films stresses caused by thermal expansion mismatch existing during cooling through the Curie transition temperature.
TL;DR: The effect of water of hydrolysis on nucleation, crystallization, and microstructural development of sol-gel derived single phase LiNbO 3 thin films has been studied using transmission electron microscopy (TEM), AFM, x-ray diffraction (XRD), and differential scanning calorimetry (DSC) as mentioned in this paper.
Abstract: The effect of water of hydrolysis on nucleation, crystallization, and microstructural development of sol-gel derived single phase LiNbO 3 thin films has been studied using transmission electron microscopy (TEM), atomic force microscopy (AFM), x-ray diffraction (XRD), and differential scanning calorimetry (DSC). A precursor solution of double ethoxides of lithium and niobium in ethanol was used for the preparation of sol. DSC results indicated that adding water to the solution for hydrolysis of the double ethoxides lowered the crystallization temperature from 500 °C (no water) to 390 °C (2 moles water per mole ethoxide). The amount of water had no effect on the short-range order in amorphous LiNbO 3 gels but rendered significant microstructural variations for the crystallized films. AFM studies indicated that surface roughness of dip-coated films increased with increasing water of hydrolysis. Films on glass, heat-treated for 1 h at 400 °C, were polycrystalline and randomly oriented. Those made with a low water-to-ethoxide ratio had smaller grains and smaller pores than films prepared from sols with higher water-to-ethoxide ratios. Annealing films with a low water concentration for longer times or at higher temperatures resulted in grain growth. Higher temperatures (600 °C) resulted in grain faceting along close-packed planes. Films deposited on c-cut sapphire made with a 1:1 ethoxide-to-water ratio and heat-treated at 400 °C were epitactic with the c-axis perpendicular to the film-substrate interface. Films with higher concentrations of water of hydrolysis on sapphire had a preferred orientation but were polycrystalline. It is postulated that a high amount of water increases the concentration of amorphous LiNbO 3 building blocks in the sol through hydrolysis, which subsequently promotes crystallization during heat treatment.
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30 Apr 1993-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the glass content of tetraalkoxysilanes possessing polymerizable alkoxides for the production of non-shrinking sol-gel composites was investigated.
Abstract: We, as well as others, have been interested in the sol-gel process for the synthesis inorganic-organic composite materials. Since our first report on the application of tetraalkoxysilanes possessing polymerizable alkoxides for the production of non-shrinking sol-gel composites, we have extended our efforts towards increasing the glass content in these composite materials. The stoichiometry in the tetraalkoxysilanes limits the maximum glass content in the original non-shrinking composites to 10%–18%. In order to increase the glass content to greater than 50%, we focused our efforts on the use of silicic acid oligomers. Molecular weights of the poly(silicic acid) materials were varied from M n = 5000 to M n = 2 000 000 by controlling reaction conditions. In addition, branching ratios ( i.e. linear vs. spherical particles) can be controlled by changing the catalysts used. The properties of the resulting composite can range from a transparent flexible material to a transparent hard material simply by changing the organic polymer in the composite.
TL;DR: In this paper, a crack-free 8.8-mol-yttria-doped zirconia was fabricated using a transparent and spinnable sol prepared by hydrolysis of Zirconium alkoxide with hydrogen peroxide and nitric acid.
Abstract: Coatings of 8.8-mol%-yttria-doped zirconia were fabricated using a transparent and spinnable sol prepared by hydrolysis of zirconium alkoxide with hydrogen peroxide and nitric acid. The sol gave a crack-free coating film consisting of fine grains. The crystalline phase was cubic after heating at 1000° and 1200°C and cubic and tetragonal at 1350°C, with the coating being highly oriented in the (111) plane, especially at 1000°C. Activation energy of the coating films was higher than that of the bulk. Transmittance through a film thickness of about 0.3 μm on each side was 75%.