Direct Synthesis of Ceramic Membranes by Sol-Gel Process

Ceramic ultrafiltration and nanofiltration membranes (TiO₂) are prepared by sol-gel route using a special arrangement which allows the reaction of the reactants directly in the pores of a tubular Al₂O₃ support or on its surface, respectively. By this direct synthesis the number of technological steps can be reduced which is the main advantage of the method. The produced layers are well joined with the Al₂O₃ support and the reaction can be adjusted by various technological parameters. The dried and sintered coatings are characterized by X-Ray diffraction, FESEM and AFM. In addition, pore size distribution and filtration properties are investigated and discussed.     

Fabrication of Sol-Gel Optical Waveguide by Hot-Dip Coating Process

The TiO₂: Sb nanoscale thin films were deposited on glass substrates by the sol–gel dip-coating method. The influence of the dopant density on the structure and the phase transformation of the thin films were investigated by X-ray diffraction (XRD) and Raman spectra. From the results of XRD, the thin films were in a majority of anatase state. The results of Raman spectra indicated that the non-doped TiO₂ thin film composed of not only anatase but also brookite phase. Dopant Sb enhances the transformation of the TiO₂ from brookite to anatase phase. After doping proper amount of Sb, the thin films show more superhydrophilicity than the non-doped TiO₂ thin film as well. The crystal size of the TiO₂ : Sb is about 13.3–20 nm calculated from the XRD patterns.     

Design of Sol-Gel Coating Media for Ink-Jet Printing

Image transfer and storage is rapidly becoming one of the most important technologies in the communication age. Ink-jet printing by which multicolor images are transferred onto paper and transparencies is a major branch of this technology. In this technology electronic image transfer capabilities are often limited by the shortcomings in the materials used. The coating designed to receive the ink determines the ink-dry time, edge acuity or patterns, color fidelity, as well as light and water fastness of the print. These in turn govern the speed, resolution and quality of the image transferred. Chemical, structural and process parameters involved in the design of a transparent, single layer sol-gel coating media for ink-jet printing are discussed. Design goals include quick drying of the print, water resistance, edge acuity without bleeding, UV protection of color dyes, and being printer nonspecific.     

Effect of Aging on the Stability of Ceramic Foams Prepared by Thermostimulated Sol-Gel Process

This work presents a new route of preparation of zirconium ceramic foams based on the thermostimulated sol-gel process. This method produces gelled bodies with up to 90% of porosity in the wet gel and can be used to make complex-shaped components. Unfortunately, the shrinkage during the drying step allows to a catastrophic reduction (>50%) of the foam porosity. To improve the foam stability we carried out a systematic study of the effect of gel foam aging on the drying process. Samples were aged in closed vessel at 25°C during different time period (from 6 to 240 h). The shrinkage and the mass loss during drying at 50°C were measured in situ, using a non-contact technique performed with a special apparatus. The results show that the total linear shrinkage decreases from 46% to 8% as the aging period increase from 6 to 240 h. This behavior is followed by a small change of total mass loss, from 42 to 54%. It indicates that by aging the structural stiffness of the foams increases due to secondary condensation reactions. Thus, by controlling the aging period, the porosity can be increased from 67 to 75% and the average size of mesopores of dried foams can be screened from 0.3 to 0.9 m. Finally, these results demonstrate that the thermostimulated sol-gel transition provides a potential route to ceramic foams manufacture.     

A Generic Technique for Coating Doped Sol-Gel Films onto the Inside of Tubes for Use as Colorimetric Sensors

Sol-gel thin films have been doped with bromophenol blue and eriochrome cyanine RC for measuring pH and Cu⁺⁺ in solution respectively. The films were coated inside glass tubes by a novel method. Films doped with bromophenol blue responded to pH changes from pH 3 to 8. They were stable to variations in temperature from 20°C to 40°C. The sensing films have been subjected to leaching studies in different pH buffer solutions. Copper ions in solution have been measured to a minimum concentration of 0.6 ppm by eriochrome immobilised in sol-gel films. The interferences of other metal ions were also studied. Doped sol-gel films coated onto the inside of test tubes offer a simple, none-invasive, reusable and fast optical chemical sensing technique for the measurement of colour by spectroscopy or colorimetry.     

The Use of a Thin Glass-Ceramic Rod as a Surface for Sol-Gel Coating in the Preparation of SPME Fibers

The efficiency of a glass-ceramic rod as a base for the preparation of SPME fibers using sol-gel technology was investigated. Glass-ceramic rod was coated with PDMS using sol-gel reaction, and its surface characteristic was determined for SEM. Optimum conditions for the preparation of the fiber are presented. The same procedure was used for coating the fused silica rod. The fibers thickness and absorption capacity were compared. The proposed fiber was used for the extraction of a mixture of BTEX, from aqueous samples. The results obtained proved the superiority of glass-ceramic as a new base for SPME fiber, resulting in a thickness of ~44 m against 6 m for fused silica base. The calibration graphs for BTEX were linear (r > 0.998) and the detection limits were below 0.8 g L^–1.     

Pore Modification in Porous Ceramic Membranes With Sol-Gel Process and Determination of Gas Permeability and Selectivity

Summary: The aim of the study was to investigate the variation in total surface area, porosity, pore size, Knudsen and surface diffusion coefficients, gas permeability and selectivity before and after the application of sol-gel process to porous ceramic membrane in order to determine the effect of pore modification. In this study, three different sol-gel process were applied to the ceramic support separately; one was the silica sol-gel process which was applied to increase porosity, others were silica-sol dip coating and silica-sol processing methods which were applied to decrease pore size. As a result of this, total surface area, pore size and porosity of ceramic support and membranes were determined by using BET instrument. In addition to this, Knudsen and surface diffusion coefficients were also calculated. After then, ceramic support and membranes were exposed to gas permeation experiments by using the CO₂ gas with different flow rates. Gas permeability and selectivity of those membranes were measured according to the data obtained. Thus, pore surface area, porosity, pore size and Knudsen diffusion coefficient of membrane treated with silica sol-gel process increased while total surface area was decreasing. Therefore, permeability of ceramic support and membrane treated with silica sol-gel process increased, and selectivity decreased with increasing the gas flow rate. Also, surface area, porosity, pore size, permeability, selectivity, Knudsen and surface diffusion coefficients of membranes treated with silica-sol dip coating and silica-sol processing methods were determined. As a result of this, porosity, pore size, Knudsen and surface diffusion coefficients decreased, total surface area increased in both methods. However, viscous flow and Knudsen flow permeability were detected as a consequence of gas permeability test and Knudsen flow was found to be a dominant transport mechanism in addition to surface diffusive flow owing to the small pore diameter in both methods. It was observed that silica-sol processing method had lower pore diameter and higher surface diffusion coefficient than silica-sol dip coating method.     

Anti-Reflective Coatings for CRTs by Sol-Gel Process

Anti-reflective and electromagnetic shielding double-layered coatings were developed for cathode ray tubes (CRTs) by wet chemical process. An outer SiO₂ layer is formed over a porous inner tin-doped indium oxide (ITO) particle layer. ITO particles used in the inner layer lower the sheet resistance below 10³ohm/sq. and an electromagnetic shielding property is attained. To improve the abrasion wear resistance of the film, the structure of the film and hydrolysis-polymerization condition of tetraethoxy-silane (TEOS) are estimated. An outer SiO₂ layer component penetrates into the inner layer and adheres to the glass surface. As the extent of hydrolysis of TEOS proceeds and the molecular weight of hydrolyzed TEOS becomes small, the abrasion wear resistance of the film enhances. The relation between the curing condition of the film and surface resistance of the film is investigated. The surface resistance of the film lowers by curing the film in reductive atmosphere. The transmittance of the film in the near-infrared region shows that the lowering of surface resistance of the film is caused by the increase of carrier concentration of ITO particles. The double layered coatings are successfully applied to the panel glass for CRTs on an industrial-scale.     

Anti-Reflective Coatings for CRTs by Sol-Gel Process

Two types of anti-reflective coatings composed of nano-particles were developed for cathode ray tubes (CRTs). The anti-reflective and anti-static coating is composed of two layers. An outer SiO₂ layer is formed over a porous inner layer composed of titanium oxynitride (TiO _x N_y), antimony-doped tin oxide (ATO) and SiO₂. To control the reflection of the film, a porous structure is formed using a mixed sol composed of TiO _x N _y -ATO particles and hydrolyzed-polymerized tetraethoxy-silane (TEOS). The resulting double layered coating is shown to consist in a nanocomposite pseudo three-layer structure. The antireflective electromagnetic-wave-shielding coating is also composed of two layers. An outer SiO₂ layer is formed over an electric-conductive inner layer composed of silver colloids, TiO _x N _y nano particles. Silver colloids are used to obtain a film having low surface resistivity and TiO _x N _y nano-particles contained in the inner layer enhance the durability of the film. To reduce the plasma-resonance absorption caused by silver colloids, silver ions are added to the outer layer solution. The silver ions diffuse into the inner layer from the outer layer when the film is cured, touch to the surface of silver colloids, suppress the silver colloid growth and reduce the specific absorption of the film. These coatings are successfully applied to the panel glass for CRTs on an industrial scale.     

Water Repellent Coating for Welding Electrodes Based on Sol-Gel Technology

Silicone resin coatings prepared by the sol-gel method were applied on welding electrodes to protect them against water absorption during storage or transportation. The performance of the electrodes was tested by measuring the free and total water content of the weld. The total water content of the coated electrode was just slightly above the permitted level (<0.2%) due to the organic part of the silicone resins that decomposes during welding liberating a very small quantity of water.     

碱/酸两步催化法制备耐候性SiO2增透膜的研究

以正硅酸乙酯(TEOS)为先驱体,采用碱/酸两步催化溶胶-凝胶法制备出一种兼具碱催化增透膜的高透过率和酸催化增透膜的良好耐摩擦性能的优点的SiO2增透膜。对酸碱催化SiO2相对比例及酸催化时水含量的系统研究表明,当酸催化SiO2的含量为50%时,增透膜综合性能最好,即具有高透过率和高耐摩擦性;当nH2O/nHCl=1∶0.0010时,增透膜的透过率最高。碱/酸两步催化法制备的增透膜与水的接触角仅为11.3°,本文进一步用六甲基二硅氧烷(HMDS)对增透膜表面进行了修饰,修饰后增透膜的接触角提高至52.5°,增透膜的疏水性及环境稳定性得到较大的提高。     

Prospects of Sol-Gel Process for Spectral Hole-Burning Glasses

Persistent spectral hole burning was studied in Eu³⁺ ions-doped Al₂O₃-SiO₂ glass prepared by a sol-gel method. The gel synthesized by the hydrolysis of Si- and Al-alkoxides and EuCl₃·6H₂O was heated in air and hydrogen gas atmospheres. For the glass heated in air to contain OH bonds, the hole was formed by the photoinduced rearrangement of the OH bonds surrounding the Eu³⁺ ions, and was thermally refilled and erased above 200 K. On the other hand, the glass heated in hydrogen gas showed the hole spectrum above 200 K. It was found that the hole depth was independent of the temperature and was 7% of the total intensity at room temperature. The proposed mechanism was the electron transfer between the Eu³⁺ ions and the defect centers formed in glass matrix.     

溶胶-凝胶血红蛋白电化学传感器的研制

运用溶胶-凝胶技术将血红蛋白(Hb)固载于玻碳电极(GC)表面,制得Hb/Sol-Gel/GC修饰电极,找出了制备Hb/Sol-Gel/GC修饰电极的最佳实验条件,建立了一种测定过氧化氢的新的、灵敏的方法.同时对该电极与过氧化氢的作用机理进行了探讨.     

A Sol-Gel Precursor as a Powder Binder for PZT Ceramic Fabrication

A lead zirconate titanate (PZT) precursor sol was prepared by a diol sol-gel route and used as a binder for assisting the uniaxial die pressing of PZT powders. The powders, of composition Pb(Zr_0.52Ti_0.48) O₃, were prepared by a two step mixed oxide route using lead carbonate, zirconia and titania starting powders. The densification characteristics of the powders, which were not milled after the final calcination step, were compared to samples prepared using PVA as a conventional binder. Improved sintering behaviour was observed for the novel sol-gel binder system. For example, using a sol concentration, equivalent to 7 wt% of PZT derived from the binder, pellets of 95% theoretical density were obtained after firing at 1150°C for 4 h, whereas for the same firing conditions, samples blended with PVA resulted in a density of only 78% theoretical.     

溶胶-凝胶法制备(Ca1-xMgx)SiO3陶瓷及其微波介电性能

以硝酸钙、硝酸镁、正硅酸乙酯为先驱体, 利用溶胶-凝胶法合成(Ca1-xMgx)SiO3(x=0.1、0.2、0.3、0.4、0.5)陶瓷粉体, 研究了Mg2+取代Ca2+对陶瓷物相组成、烧结特性以及微波介电性能的影响规律. 结果表明, Mg2+在CaSiO3中的最大固溶度不超过0.2；随着Mg2+对Ca2+取代量的增加, 陶瓷在烧结后的主晶相出现从CaSiO3相向CaMgSi2O6相的转变,陶瓷的烧结特性及介电性能出现先增加后下降的趋势；当x=0.3 时, 陶瓷体中CaSiO3相与CaMgSi2O6相共存, 克服了单相CaSiO3或CaMgSi2O6易成片长大的缺点,有效减少了陶瓷中残留的气孔, 提高烧结体致密性. (Ca0.7Mg0.3)SiO3在1320 益烧结后介电常数为6.62, 品质因数为36962 GHz.     

Sol-Gel Processing of Functional and Structural Ceramic Oxide Fibers

Structural ceramic oxide fibers like α-Al₂O₃, MgAl₂O₄ (spinel), Y₃Al₅O₁₂ (YAG) and eutectic Al₂O₃−Y₃Al₅O₁₂ as well as the functional Pb(Zr_1−xTi_x)O₃ (PZT) fibers were successfully prepared by sol-gel processing. All precursors are based on metal oxohydroxopropionates. A comparative study of sol-gel routes leading to spinnable sols demonstrates the key role of propionic acid as an excellent agent for controlling hydrolysis and condensation reactions.     

苄基锡烯或炔基膦酸酯的合成

合成了具有通式为（ＰｈＣＨ２Ｓｎ）ｎ－１Ｏ２Ｐ（Ｏ）Ｒ（ｎ＝２，３；Ｒ＝－Ｃ＝ＣＰｈ，－Ｃ＝ＣＣ５ｈ１１－ｎ，－Ｃ＝ＣＣＨ２ＯＣＨ３，－ＣＨ＝ＣＣＩＰＨ）的８个苄基锡烯或炔基膦酸酯，并通过元素分析、ＩＲ和１ＨＮＭＲ对其进行了表征。     

Fabrication of PbTiO3 Ceramic Fibers by Sol-Gel Processing

The sol-gel processing was applied to the fabrication of PbTiO₃ fibers. Pb(CH₃COO)₂·3H₂O and Ti(OC₃H ₇ ⁱ )₄ were refluxed with stirring in 2-methoxyethanol to form Pb-methoxyethoxide and Ti-methoxyethoxide, respectively, followed by mixing with stirring in 2-methoxyethanol to form Pb−Ti double alkoxide. The hydrolysis and polycondensation reaction of this double alkoxide gave polymerized products, and as a result the viscosity of the solution increased, suggesting that linear polymers were produced through the hydrolysis and polycondensation reaction. Homogeneous PbTiO₃ gel fibers were drawn from the spinnable viscous solutions, which were wellcrystallized into perovskite type PbTiO₃ at 650°C. The heat-treated fibers were a few centimeters long and from 10 to 100 μm in diameter. The fiber was made up of extremely uniform grains. Electron diffraction revealed a preferred growth of (101) planes along the fiber axis, which might be due to the linear molecular characteristics of the alkoxide.     

Fabrication and Characterisation of Leak-Tight Glassy Carbon Electrodes,Sealed in Glass Employing Silicon Coating,for Use in Electrochemical Detection

Abstract

Glassy carbon discs have been coated with silicon in a chemical vapour deposition process to obtain leak-tight electrodes, sealed in glass. Electrodes with coatings thicker than 5μm prove to be leak-tight in contrast with uncoated ones. Silicon-coated electrodes show faster decay of charging current, less noise and decreased background current. Leak-tightness and electron microscope information correlate well with the electrochemical data. All results can be ascribed to the absence of a void between glassy carbon and glass at Si-coated electrodes. By silicon coating, signal-to-noise ratios are improved with a factor of about 5, as is demonstrated for catecholamines and metabolites in liquid chromatography with electrochemical detection.