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61.
62.
Rutile Ni
x
Ti1-3x
Sb2x
O2 solid solution nanoparticles were synthesized by a sol-gel route using propylene oxide as a gelation agent. Titanium oxide
nanopowder and 12% TiCl3 solution were used as the source for titanium to investigate the influence of the titanium precursors on the formation of
the target materials. It was found that the nanoparticles prepared using 12% TiCl3 solution showed a much lower phase formation temperature (700°C) as compared to those prepared from TiO2 nanoparticles (1000°C). This lower phase formation temperature allowed a substantial reduction of the aggregation of the
particles during calcination leading to the formation of nearly mono-dispersed nanoparticles of about 20 nm. The results of
this work show that the epoxide assisted sol-gel method is capable to produce titanium-based ternary oxide solid solution
nanoparticles, owing to the formation of a highly homogeneous precursor gel intermediate. 相似文献
63.
A. Al-Kahlout S. Heusing M. A. Aegerter 《Journal of Sol-Gel Science and Technology》2006,39(2):195-206
Films of NiO-TiO2 with Ni concentration of 100, 90, 87, 83, 75, 66, 50 and 33 mol% have been obtained via the sol-gel route by dip coating
technique and sintered in air between 250 and 500°C using ethanolic sols of nickel acetate tetrahydrate (Ni(CH3COO)2·4H2O) and titanium n-propoxide (Ti(O-CH(CH3)2)4) precursors. Xerogels obtai- ned by drying the sols have been studied up to 900°C by thermal analysis (DTA/TG) coupled to
mass and IR spectroscopy. The crystalline structure and morphology of the layers in the as deposited, bleached and colored
states were determined by X-ray diffractometry, scanning electron microscopy and transmission electron microscopy Their electrochromic
properties have been studied in 1 M KOH aqueous electrolyte as a function of the layer composition, thickness and sintering
temperature. Deep brown colour with reversible transmittance changes have been obtained using cycling voltammetry and chronoamperometry
processes. The best composition to get stable sols, a high reversible transmittance change and fast switching times (<10 s)
was obtained with double NiO-TiO2 layers 160 nm thick having 75% Ni molar concentration, and sintered between 300 and 350°C. The mechanism of coloration and
morphology transformation of the layer during cycling are discussed in terms of an activation and degradation period. The
results are in agreement with the accepted Bode model. 相似文献
64.
A novel microwave dielectric powder with composition of Ca2Zn4Ti16O38 was synthesized through a citrate sol-gel process. The development of crystalline phases with heat-treating temperature for the gel derived powders was evaluated by using thermo-gravimetric analysis and X-ray powder diffraction analysis techniques. The pure phase of Ca2Zn4Ti16O38 with crichtonite crystal structure was obtained at relatively low temperature of 1000 °C. The synthesized powder has high reactivity and the dense ceramics with single crystalline phase were obtained at low sintering temperature of 1100 °C. Impedance spectroscopy and microwave dielectric measurements on sintered samples showed the present compound to be a modest dielectric insulator with excellent dielectric properties of εr∼47-49, Qf value ∼27,800-31,600 GHz and τf∼+45 to +50 ppm/°C. It shows comparable microwave dielectric properties to other moderate-permittivity microwave dielectrics, but much lower sintering temperature of 1100 °C. 相似文献
65.
Shuhui Yu Kui Yao Francis Eng Hock Tay 《Journal of Sol-Gel Science and Technology》2007,42(3):357-364
The preferential formation of a pyrochlore structure is a knotty problem in the preparation of Pb(Zn1/3Nb2/3)O3 (PZN)-based thin film materials and its presence is significantly detrimental to the dielectric and piezoelectric properties.
In this study, 40 mol% of PZN was replaced with Pb(Mg1/3Nb2/3)O3 (PMN) for obtaining a perovskite composition around a morphotropic phase boundary (MPB), (1−x)(0.6PZN-0.4PMN)-xPT ((1−x)PZMN-xPT, PT: PbTiO3) where x = 0.23. The thin films with this composition were prepared with a polyethylene glycol (PEG) modi-fied sol-gel method on LaAlO3 substrates. The microstructural evolution of the films on heat treatment was examined with X-ray diffraction. With the aid
of PEG, the formation of the pyrochlore phase was suppressed and the perovskite phase formed directly from the amorphous gel
film. The multilayer films with a thickness around 0.25 μm showed a single perovskite phase without any detectable pyrochlore
structure. Microscopic images showed uniform grain size of a few tens of nanometers. The role of the polymer dramatically
promoting the perovskite phase was investigated with the aid of X-ray photoelectron spectroscopy and thermal analysis. The
dielectric constant of the obtained film was 4160 at 1 kHz. The film demonstrated typical ferroelectric hysteresis loops and
exhibited excellent piezoelectric performance. 相似文献
66.
Marian Čerňanský Přemysl Vaněk Karel Král Radmila Krupková 《Monatshefte für Chemie / Chemical Monthly》2002,133(6):799-806
Summary. In this investigation the crystallization of PbTiO3 upon annealing of pure nanopowders and PbTiO3–SiO2 (1:1 v/v) nanocomposite powders prepared by the sol-gel technique was studied. Using X-ray diffraction phase analysis, the
start of PbTiO3 crystallization in pure PbTiO3 powders was detected at 400°C. Distinct crystallization of PbTiO3 in PbTiO3–SiO2 nanocomposites starts at 700°C, whereas SiO2 remains amorphous. There are indications that an interface interaction between the PbTiO3 and the SiO2 phase plays an important role in hindering the crystallization of PbTiO3. The particle size (size of coherently scattering regions) was estimated from the broadening of the X-ray diffraction line
profiles. The average size of PbTiO3 nanocrystallites increases with temperature and time of annealing, the influence of temperature being more significant than
that of the annealing time. Differential scanning calorimetry confirmed the results of the X-ray diffraction with respect
to the start of the crystallization. Laser beam scattering and scanning electron microscopy provided the statistical distribution
of the grain size and the morphology of the powder grains, showing that each grain of the powders contains several nanocrystallites
(coherently scattering regions).
Received October 4, 2001. Accepted (revised) December 14, 2001 相似文献
67.
Yunyu Yi Ronald Neufeld Selim Kermasha 《Journal of Sol-Gel Science and Technology》2006,38(3):251-259
Entrapment of membrane proteins is a challenging task compared to that involving soluble proteins. Chlorophyllase, a membrane
protein, was successfully entrapped in tetramethoxysilane-derived sol-gel. Pre-gel sol typically consists of an aqueous suspension
of chlorophyllase, precursors including tetramethoxysilane and/or methytrimethoxysilane, and sodium fluoride as catalyst.
To obtain a highly active entrapped enzyme preparation, the effects of various immobilization parameters, including the chemical
compositions of pre-gel sol (water/silane ratio, precursor type and proportions, enzyme loading, sodium fluoride concentration),
and sol-gel process parameters (aging and drying time and approach) have been investigated. Chlorophyllase demonstrated the
highest activity in gel derived from a pre-gel sol with water/silane ratio of 30 and enzyme loading of 0.257 mgprotein/ggel, and showed moderately lower activity in organically modified sol-gel than that in hydrophilic sol-gel. The effects of water/silane
ratio and precursor combinations on the activity of entrapped chlorophyllase were also studied by examining the pore morphology
of gel via nitrogen adsorption-desorption. Longer aging time leads to an entrapped chlorophyllase preparation with higher
activity. Chlorophyllase preparation demonstrated negligible activity after air-drying for 12 h while lyophilized chlorophyllase
preparation demonstrated 8, 4 and 4 times higher activity than air-dried, vacuum-dried and solvent-dried preparations. Chlorophyllase
demonstrated 30% higher activity in the improved sol-gel protocol than that from a non-optimized sol-gel protocol developed
in a previous study. 相似文献
68.
研究了利用铝酸钠溶液碳酸化产生的沉淀, 经胶溶作用制备出纳米氢氧化铝溶胶的过程. 分析了铝酸钠溶液滴加到大量碳酸氢钠溶液中时发生的反应. X射线衍射研究结果表明, 在纳米氢氧化铝溶胶制备过程中, 从无定形氢氧化铝沉淀到拟薄水铝石的晶型转变过程是氢氧化铝沉淀胶溶时溶解再析出的过程. 将碳酸氢钠加入到苛性比为1.7的铝酸钠溶液中, 中和至苛性比为1.3后, 溶液诱导期中的紫外光谱显示270 nm处的Al(OH)3-6吸收增强. 经与含铝原子六配位的晶体紫外光谱对比后表明, 在铝酸钠分解生成氢氧化铝的过程中, 其铝的配位结构从四配位转化为六配位. 拟薄水铝石溶胶粒子的形貌与胶溶所用的酸和分散剂有关. 相似文献
69.
以乙醇为溶剂, 钛酸四丁酯为前驱体, 用溶剂热法制备了Ag表面修饰的负载型纳米二氧化钛光催化剂. 利用X射线衍射(XRD)、N2吸附-脱附(BET)、透射电子显微镜(TEM)、X射线光电子能谱(XPS)、紫外-可见(UV-Vis)光谱等技术对其进行了系统的表征, 以亚甲基蓝(MB)溶液的脱色降解为模型反应, 考察了不同Ag含量样品的光催化性能. 结果表明: 用溶剂热法制备的样品中TiO2皆为锐钛矿相, 金属Ag颗粒沉积在TiO2表面, 粒径为2 nm左右, 比表面积较溶胶凝胶法制备的样品大大增加, 最高可达151.44 m2·g-1; UV-Vis光谱和光催化实验表明: Ag修饰使TiO2对光的吸收能力大大增强, 吸收带边红移至可见光区, 亚甲基蓝在该复合材料上的光催化降解反应遵循一级反应动力学模型; 溶剂热法制备样品的光催化性能明显好于溶胶凝胶法制备的样品, 在紫外光和可见光下, Ag摩尔分数为5%的样品表现出最佳的光催化活性. 相似文献
70.
Li4Ti5O12 thin films for rechargeable lithium batteries were prepared by a sol-gel method with poly(vinylpyrrolidone). Interfacial properties of lithium insertion into Li4Ti5O12 thin film were examined by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and potentiostatic intermittent titration technique (PITT). Redox peaks in CV were very sharp even at a fast scan rate of 50 mV s−1, indicating that Li4Ti5O12 thin film had a fast electrochemical response, and that an apparent chemical diffusion coefficient of Li+ ion was estimated to be 6.8×10−11 cm2 s−1 from a dependence of peak current on sweep rates. From EIS, it can be seen that Li+ ions become more mobile at 1.55 V vs. Li/Li+, corresponding to a two-phase region, and the chemical diffusion coefficients of Li+ ion ranged from 10−10 to 10−12 cm2 s−1 at various potentials. The chemical diffusion coefficients of Li+ ion in Li4Ti5O12 were also estimated from PITT. They were in a range of 10−11-10−12 cm2 s−1. 相似文献