共查询到20条相似文献,搜索用时 15 毫秒
1.
E.M. Rabinovich D.W. Johnson Jr. A. Mishkevich E.A. Chandross J. Thomson Jr. 《Journal of Sol-Gel Science and Technology》2003,28(1):19-29
Particulate sol-gel technology uses larger particles than that of alkoxide-derived gels and provides larger pore sizes in the gelled object. This allows relatively rapid drying and fabrication of large rods or tubular shapes. However, the formation of more complex or flat shapes, which require extensive surface contact with a mold, is more difficult. The shrinkage during drying, with the significantly greater stress of surface friction due to adhesion, frequently leads to cracking.We have demonstrated a solution to this problem by floating the gel on the surface of a dense liquid. Dry silica panels up to 28 × 40 × 0.7 cm3 were prepared in this way. The use of patterning molds allowed the fabrication of more sophisticated shapes. These bodies were sintered to transparent vitreous silica articles of near net dimensions. 相似文献
2.
For precursor mixtures containing tetraethoxysilane (TEOS) and phenyltriethoxysilane (PhTREOS), time of gelation can be reduced
by up to two orders of magnitude depending on reaction conditions employed when reacting the silicon alkoxide mixture with
formic acid instead of water. Results indicate that time of gelation depends on the amount of PhTREOS in the precursor mixture.
Within the range of concentrations investigated, an exponential law describes best the dependence of reduced time of gelation
on the molar fraction of PhTREOS. Therefore, we conclude that the phenyl ring acts as a steric hindrance to network formation.
Raman spectroscopy is used to characterize the reaction between the alkoxide mixture and formic acid. During the acidolysis
reaction, ethanol is formed as an intermediate. A preliminary reaction scheme is proposed to account for the time dependence
of species involved. Furthermore, Raman spectroscopy is successfully employed to monitor the effects of post-gelation thermal
treatment of the gel samples. The effects observed are interpreted with a model of a phenyl ring trapped in a siloxane cage. 相似文献
3.
Hybrid organic-inorganic particles containing labile organic templates have been prepared by either controlled Sol-Gel processing or co-condensation of colloidal silica particles with organosilicon precursors. Chemical removal of the templating organic spacer led to monomodal, microstructured porous silica particles exhibiting up to 50% porosity. Particle size and distribution, and porosity varied depending upon the process and the chemistry used to remove the porogen organic groups. 相似文献
4.
Masahiro Ita Yoshikuni Uchida Kazunori Matsui 《Journal of Sol-Gel Science and Technology》2003,26(1-3):479-482
The preparation of polyaniline/silica hybrid gel was studied by chemical polymerization of aniline with sodium dodecyl sulfate (SDS) during the sol-gel processing. As a typical procedure, aqueous solutions of SDS, aniline, HCl, and tetramethoxysilane (TMOS) were mixed. Then ammonium peroxodisulfate (APS) in an acidic aqueous solution was added as initiator oxidant into the sol-gel systems at different sol-gel stages: (A) just after mixing (sol), (B) after gelation (wet gel), and (C) after 7 d (dried gel). As for the condition (A), several green areas and several tens of dark green spots with absorption peaks at 343, 422, and 802 nm were seen in the xerogel, indicating that emeraldine salt type polyaniline is aggregated in the silica xerogel. Polymerization of aniline little occurred in the dried gel (C), possibly because APS could not soak the silica pores and/or aniline could not polymerize in the gel. The xerogel from (B) showed a homogeneously green color with peaks at 339, 425, and 769 nm, showing that emeraldine salt type polyaniline can be uniformly dispersed in sol-gel silica. 相似文献
5.
Junjie Yuan Shuxue Zhou Guangxin Gu Limin Wu 《Journal of Sol-Gel Science and Technology》2005,36(3):265-274
This paper presented a novel preparation method of silica coated organic pigment. In this approach, the surfaces of the organic
pigment were first orderly modified by poly(sodium 4-styrenesulfonate) (PSS) and poly(diallyldimethylammonium chloride) (PDADMAC),
then coated by silica via sol-gel process of tetraethylorthosilicate (TEOS). The results showed that PVP, pH value, water
and TEOS contents had significant influence on the morphology of the silica encapsulated organic pigment. Organic pigments
coated silica by this approach could scatter UV ray with wavelength less than 270 nm, and this scattering property increased
with more silica coated. 相似文献
6.
Vlastimil Matějec Miloš Hayer Marie Pospíšilová Ivan KaŠík 《Journal of Sol-Gel Science and Technology》1997,8(1-3):889-893
Preforms for drawing silica optical fibers have been fabricated by using the MCVD method for the preparation of the optical
claddings and the sol-gel method for the preparation of the optical cores consisting of TiO2−SiO2 or RE3+−Al2O3−P2O5−SiO2 (RE=Er, Yb) glasses. A novel method has been developed for depositing thin gel layers on the inner silica tube wall, under
rotation of the tube inclined at a small angle to the horizontal. The gel layers have been deposited from sols prepared by
mixing Si(OC2H5)4, POCl3, Ti(n-OC4H9)4, AlCl3, ErCl3, YbCl3 H2O, C2H5OH and HCl. The gel layers deposited using these sols on the inner tube wall were heat-treated in a flow of CCl4 or POCl3 with O2 at temperatures of from 800° to 1400°C. After collapsing the composite tube into a preform, an optical fiber has been drawn.
The refractive-index profiles of the preforms and the attenuation spectra of the drawn fibers are shown, as well as some results
on the lasing characteristics of Yb3+ sensitized, Er3+ doped fibers. 相似文献
7.
Jue Wang Guangming Wu Jun Shen Tianhe Yang Qinyuan Zhang Bin Zhou Zhongsheng Deng Bin Fan Dongping Zhou Fengshan Zhang 《Journal of Sol-Gel Science and Technology》2000,18(3):219-224
Scratch-resistance of sol-gel derived nano porous silica films were studied. The thin films were prepared with a dip-coating method from both one-step and two-step catalyzed silica sols, and treated in a mixture gas of ammonia and water vapour afterwards. The thin films were characterized by using Atomic Force Microscope (AFM), ellipsometer, Fourier-transform Infrared Spectroscope (FTIR), respectively. Experimental results have shown that the two-step catalysis remarkably improves strength of the films, and abrasion-resistance and adhesion of the silica films were further increased after the mixture gas treatment. It is attributed to the cross-linking of silica particles in the sols by randomly branched or/and entangled linear chains and more Si–O–Si bonds formed by the mixture gas treatment. 相似文献
8.
9.
The sol-gel reaction of tetraethoxysilane was conducted in natural rubber (NR) matrix to obtain NR/in situ silica mixtures. In other words, in situ filling of silica onto NR was conducted. The mixtures were compounded with curing regents, and their viscosities were evaluated. The in situ silica with a coupling agent afforded the lowest viscosity compared not only with a conventional silica (VN-3) but also with a carbon black (HAF). The curing behaviors were most favorable for in situ silica compound. Physical properties of the vulcanizates were also evaluated, and again in situ silica stock gave the best result. 相似文献
10.
Yong-Chun Chen Shu-Xue Zhou Hai-Hua Yang Li-Min Wu 《Journal of Sol-Gel Science and Technology》2006,37(1):39-47
The polyester/silica hybrid resins and their hybrid polyurethanes were prepared via in situ (IS) or blending (BL) method using different silica sols. The effects of preparation methods, silica type and content on
the interaction and microstructure of polymer/silica hybrid materials were investigated by FTIR, viscosity measurement, TGA,
DMA and SAXS, respectively. It was found that both IS and BL methods formed agglomerates of silica-rich phases and primary
silica-rich phases in the hybrid films, but the former caused stronger interaction between silica and polymer than the latter,
resulting in much bigger agglomerates and compacter structure. The ethoxy group at silica was favorable for enhancing the
interaction between silica phase and polymer, even between silica phases as well. The interaction between silica phase and
polymer caused increasing viscosity, modulus and Tg, while the interaction between silica phases themselves increased the
extent of micro-phase separation, especially for the hybrid films prepared by IS method. 相似文献
11.
酚醛树脂是一种广泛使用的合成树脂,包括热固性和热塑性两类,具有良好的阻燃性、耐热性和耐腐蚀性。酚醛纤维是由酚醛树脂所制成的交联纤维,传统的酚醛纤维制备方法有熔融纺丝法和湿法纺丝法,后来出现了静电纺丝法。本文根据酚醛树脂的种类分别介绍了热固性、热塑性和热塑/热固混合酚醛树脂三类材料静电纺丝的研究进展。在改善酚醛纤维特性方面,综述了四种优化措施,包括加入无机盐、微波辐射辅助固化、非匀速阶梯式加热固化、氧化石墨烯修饰的静电纺丝法等。此外,对本实验室制备酚醛纤维的研究也进行了概述,阐述了酚醛纤维当前存在的问题及未来发展方向。 相似文献
12.
13.
Xinshi Luo Congji Zha Barry Luther-Davies 《Journal of Sol-Gel Science and Technology》2004,32(1-3):297-301
Sol-gel synthesis of organic-inorganic hybrid materials for planar waveguides and devices has received growing interest due to its low-cost processing and good suitability for doping. Titania is an important optical dopant, but homogeneous incorporation of titania in silica is difficult to be achieved by the conventional sol-gel process (aqueous system) because of the significant difference between the hydrolysis rates of the precursors. In this paper, we report an anhydrous sol-gel process for synthesising titania-doped siloxane polymers. The process consists of a hydrolysis of 3-methacryloxypropyltrimethoxysilane (MPS) with boric acid under anhydrous conditions, and a condensation with dimethyldimethoxysilane (DMDMS), diphenyldimethoxysilane (DPhDMS) and titanium ethoxide (TET). Optical characterisations for the produced titania-doped polymer were performed, and results showed that TET doping is useful for reducing the OH concentration of the synthesised polymer and is also effective for improving the optical quality of spin coatings. DMDMS and DPhDMS are favourable in reducing the birefringence and in increasing the thermostability of the material, and the methacryl groups of MPS are UV-polymerizable, which is useful for low cost fabrication of waveguides by photolithographic process. The results of ellipsometry scanning measurements show that titania is homogeneously incorporated in the hybrid matrix, suggesting that the anhydrous sol-gel process is useful for preparation of UV-sensitive titania-doped siloxane polymers for optical applications. 相似文献
14.
R. Rodríguez G. Rojas M. Estevez S. Vargas 《Journal of Sol-Gel Science and Technology》2002,23(2):99-105
The fractal characterization of silica particles prepared by the sol-gel method was obtained; from the beginning of the sol-gel synthesis to the aggregation process of these particles by adding metal ions in solution, the fractal dimension was determined. At the beginning of the sol-gel process, unstable structures were formed due, essentially, to the auto-catalytic nature of the sol-gel condensation reactions; these particles are fractal structures with a fractal exponent corresponding to a reaction limited aggregation regime. As the time proceeds, the reactants are consumed approaching the system to equilibrium, stabilizing the size of the silica particles. The silica sol can be flocculated by adding metal ions in solution. The fractal exponent for the aggregation process was determined, obtaining a value corresponding to a diffusion limited aggregation regime. 相似文献
15.
Composites of cobalt ferrite particles dispersed in a silica matrix (CoFe2O4/SiO2) were prepared by the sol-gel process using tetraethylorthosilicate (TEOS) as a precursor of silica and metallic nitrates as precursors of ferrite. Samples of SiO2 and CoFe2O4/SiO2 were prepared in monolithic shape, dried at 110∘C, treated at various temperatures and their characteristics were compared. After the thermal treatment, the surface area of the silica matrix decreased, above 700∘C it densified, and above 1100∘C it crystallized. The same heat treatment in the composite led to the crystallization of CoFe2O4 particles in the SiO2 matrix and the increase in particle size, with the consequent increase in magnetization. The presence of particles in the matrix reinforced its structure, avoiding large changes in surface area and porosity and in the structure of the matrix after high temperature thermal treatment. 相似文献
16.
Chemically doped sol-gel silica has been developed by entrapping organic dye cibacron blue as a complexing reagent in porous silica prepared by the sol-gel method for removal of metal ions from water samples. In the doped sol-gel silica, the large reagent molecules are entrapped inside the pores while small metal ions can diffuse into the pores where they are complexed by the reagent and retained inside the pores. This new solid sorbent was tested for removal of Zn(II) from aqueous solutions. The kinetics, isotherm, and pH effect of the removal were investigated. With a loading of 0.10 mmol cibacron blue/g, the sol-gel silica sorbent had a capacity of 0.09 mmol Zn/g. It was demonstrated that the sol-gel silica sorbent could be regenerated and reused repeatedly. 相似文献
17.
BaTiO3 ceramic fibers were prepared by the sol-gel method in which catechol-complexed titanium isopropoxide and barium acetate hydrate were used as starting materials. The green fibers of ca. 30 cm in length were obtained from the precursor sols. The BaTiO3 ceramic fibers with the average length of ca. 20 cm were of the order of 3 to 10 m in diameter and elliptical shapes in cross section. The green fibers and those sintered at different temperatures were characterized by TGA/DSC, XRD, IR, SEM and TEM techniques. 相似文献
18.
溶胶凝胶法制备超疏水二氧化硅涂膜及其表面润湿行为 总被引:2,自引:0,他引:2
采用溶胶-凝胶法以正硅酸乙酯(TEOS)和甲基三乙氧基硅烷(MTES)为前驱体制备超疏水SiO2涂层。红外光谱(FTIR)和热重分析(TGA)表征合成SiO2的化学组成,通过透射电镜(TEM)和扫描电镜(TEM)观察制备SiO2的结构形貌,扫描电镜(SEM)和原子力显微镜(AFM)观察SiO2涂膜的表面形貌,通过测试水接触角(WCA)讨论SiO2涂层的表面微观结构与其表面疏水性能的关系。结果表明以TEOS和MTES为共前驱体可以制备得到表面带-CH3基团的SiO2溶胶,SiO2溶胶在老化过程中纳米SiO2粒子由于自组装作用形成草莓状微米-纳米双微观结构,这种结构赋予SiO2涂膜表面不同等级的粗糙度,使得水滴与涂膜表面接触时能够形成高的空气捕捉率和较小的粗糙度因子,与SiO2表面疏水性的-CH3基团共同作用形成类荷叶超疏水结构。 相似文献
19.
Yasushi Murakami Kazuhiko Tanaka Yusuke Takechi Saki Takahashi Yuuki Nakano Taki Matsumoto Wataru Sugimoto Yoshio Takasu 《Journal of Sol-Gel Science and Technology》2004,29(1):19-24
Microporous silica was synthesized by the salt catalytic sol-gel process with extremely low content of water to tetramethoxysilane. Silica particles were precipitated even when the extent of hydrolysis was very low, since ammonium carbonate as a salt catalyst made the polycondensation faster than an acid catalyst. Microporous silica with a high surface area (680 m2 g–1) was obtained by combustion of methoxy groups at 450°C. The methoxy groups can be removed by the post-hydrolysis before heating. A high specific surface area (>750 m2g–1) of microporous silica was obtained with pore diameter between 1.2 and 2.0 nm. 相似文献
20.
Kursawe Monika Glaubitt Walther Thierauf Axel 《Journal of Sol-Gel Science and Technology》1998,13(1-3):267-271
Biodegradable silica fibers for reinforcement of medical implants were successfully prepared by sol-gel processing. The spinnable precursor is based on TEOS and shows a characteristic, non-Newtonian rheological behavior in the presence of sol-particles of size 4 to 5 nm. This property suggests a non-covalent, supramolecular structure of the spinnable silica sol.The fibers obtained were characterized using IR, NMR and thermal analysis as well as biological and mechanical testing. The degradation rate of fibers was tested in continuous flow experiments. The results demonstrate a good potential of the fibers for medical applications. 相似文献