共查询到20条相似文献,搜索用时 15 毫秒
1.
Giancarlo R. Salazar-Banda Sandra R. Moraes Artur J. Motheo Sergio A. S. Machado 《Journal of Sol-Gel Science and Technology》2009,52(3):415-423
The development of efficient anti-corrosion and environmentally friendly coating systems are needed for the replacement of
the highly toxic Cr-based conversion coatings for corrosion protection of aluminum alloys. In this study, we demonstrate that
the direct application of ceramic cerium-based sol–gel coatings to AA7075-T6 substrates produces high-performance anti-corrosion
layers. Electrochemical experiments and analyses of the microstructure demonstrate that the protective layers are very efficient
for the passivation of the alloy surfaces operating as both passive and active barrier for corrosion protection. 相似文献
2.
Ying Zhang Faming Gao Lihua Gao Li Hou Yufeng Jia 《Journal of Sol-Gel Science and Technology》2012,62(2):134-139
Antireflective coatings (ARCs) on tri-layer thin film stacks were studied in this paper. Silica sols have been prepared by
acid-catalyzed or base-catalyzed hydrolysis and condensation reactions of tetraethyl orthosilicate. Antireflective nanometric
SiO2/TiO2 films are formed on both sides of the glass substrates by combining the sol–gel method and the dip-coating technique. Seen
from the transmittance spectra of different films, a maximum light transmittance of 99.9% was obtained at the band of 300–800 nm.
Scanning electron microscope (SEM) and atomic force microscopy (AFM) confirm the well-covered surface morphology. By the SEM
observations we can see that the films are full of coverage on glass surface and containing no voids or cracks. The image
root mean square roughness of the two types of ARCs provided by the AFM is 1.21 and 3.04 nm, respectively. Furthermore, a
surface profiler was used to determine the thickness of each layer in the obtained multi-layer coating system. 相似文献
3.
Anderson G. M. da Silva Patrícia A. Robles-Dutenhefner Anderson Dias Humberto V. Fajardo Adriana S. P. Lovón Juan J. Lovón-Quintana Gustavo P. Valença 《Journal of Sol-Gel Science and Technology》2013,67(2):273-281
Noble-metal-based catalysts supported on silica (Au/SiO2, Pd/SiO2 and Au–Pd/SiO2) were prepared by the sol–gel method and were evaluated in the steam reforming of ethanol for hydrogen production. The catalysts were characterized by N2 physisorption (BET/BJH methods), X-ray diffraction, temperature programmed reduction analysis, H2 chemisorption, atomic absorption spectrophotometry and Raman spectroscopy. The structural characterization of the Au- and Pd-containing catalysts after calcination showed that the solids are predominantly formed by Au0, Pd0 and PdO species and was observed that the metallic Pd dispersion diminished in the presence of Au0. The results revealed that the catalytic behavior could be influenced by the experimental conditions and the nature of the catalyst employed. The Pd/SiO2 catalyst showed the best performance among the catalysts tested at the highest reaction temperature (600 °C) due to the more effective action of the metallic active phase, which covers a greater area in this sample. At this same reaction temperature, the Au–Pd/SiO2 catalyst showed a significant deactivation, probably due to the lower Pd dispersion presented by this catalyst. 相似文献
4.
Ana C. Marques Himanshu Jain Carol Kiely Kai Song Christopher J. Kiely Rui M. Almeida 《Journal of Sol-Gel Science and Technology》2009,51(1):42-47
Development of optimal scaffolds for bone tissue engineering and regeneration is still a challenge, since many materials and
structures have been proposed but few have reached clinical expectations. This work reports on the preparation and characterization
of SiO2-CaO and SiO2-CaO-P2O5 sol–gel derived monoliths, with potential application as glass scaffolds for bone regeneration, exhibiting a nano/macro trimodal
pore size distribution, including pores of ~100’s of micrometers (μm), several microns and just a few nanometers (nm) in size.
Interconnected macropores (~20–200 μm) have been obtained in the present work by polymerization-induced spinodal phase separation
along with the sol–gel transition, when a water soluble polymer [poly(ethylene oxide)] was added to the sol–gel solution;
the several-micron pores are spherical and isolated and might be the result of secondary phase separation by nucleation-growth
mechanism; the interconnected nanopore (~5–25 nm) structure of the macroporous gel skeleton, on the other hand, was tailored
by solvent exchange procedures. The morphological and textural characterization of these materials was performed by scanning
electron microscopy (SEM), transmission electron microscopy (TEM), X-ray ultra microscopy (XuM), nitrogen adsorption and mercury
intrusion porosimetry. The factors affecting the porosity exhibited by the scaffolds, such as glass composition and solvent
exchange conditions, have been assessed.
相似文献
Ana C. MarquesEmail: |
5.
Nadir Kiraz Ömer Kesmez Esin Burunkaya Leyla Budama Burçin Acar Meltem Asiltürk H. Erdem Çamurlu Ertuğrul Arpaç 《Journal of Sol-Gel Science and Technology》2010,56(3):227-235
This paper describes the preparation and characterization of glass films consisting of SiO2, Li2O, Na2O, K2O or MgO in varying compositions on stainless steel and aluminum substrates by sol–gel method. Silver phosphate or silver
incorporated zeolite was also introduced into the sols for obtaining antibacterial effect. The SiO2/Li2O/Na2O system having the composition of 85:5:10 wt% was found as the optimum for obtaining a stable sol and film formation. The
films were investigated by scanning electron microscopy (SEM) and electron dispersive analysis by X-ray (EDX), Fourier transformed
infrared (FTIR) spectroscopy, thermo-gravimetric analysis (TGA) and differential thermal analysis (DTA). Homogenous films
having 300 ± 20 nm thicknesses were formed by spin coating and then by curing at 500 °C for 1 h. Obtained films had high adherence
to the metal substrates and they were also durable in acidic, basic or NaCl environments. They also presented a powerful antibacterial
effect against E. coli. 相似文献
6.
F. Ayari M. Mhamdi G. Delahay A. Ghorbel 《Journal of Sol-Gel Science and Technology》2009,49(2):170-179
A series of Cr/Al2O3 and Co/Al2O3 catalysts were tested in the selective ammoxidation of ethylene to acetonitrile. Catalysts were prepared either by sol–gel
method or by impregnation with chromium or cobalt acetylacetonate salts. Physicochemical properties of catalysts were accomplished
by several techniques such as chemical analysis, physisorption of N2, X-ray diffraction (XRD), 27Al MAS NMR, UV–Visible diffuse reflectance (DRS) and Raman spectroscopy and temperature programmed reduction of H2 (H2–TPR). Textural analysis reveals that mesoporous materials with pronounced surface areas were obtained using sol–gel procedure
while impregnation of the support produces a moderate decrease of its surface area and pore volume. XRD analysis confirms
the presence of highly dispersed metal species which reside essentially on the surface and measure less than 4 nm. Furthermore,
27Al MAS NMR shows that for xerogels, part of metal species occupies sites on/in A12O3 in close vicinity of octahedral 27Al. This, apparently, is not the case for aerogels. For Cr/Al2O3 catalysts, isolated Cr6+, mono and polychromate species were identified using DRS, Raman Spectroscopy and H2–TPR which seem to play a key role in the ammoxidation of ethylene. Furthermore, for cobalt doped catalysts, CoAl2O4 was identified as active phase on the basis of DRS and H2–TPR results. From the supercritical drying, it results generally better catalysts than catalysts calcined by ordinary procedure
which leads to inactive agglomerated Co3O4 and CoO–Al2O3 phase. 相似文献
7.
《Journal of molecular catalysis. A, Chemical》2004,207(1):27-33
The reaction of dichlorodifluoromethane and hydrogen has been studied in the gas phase at temperatures 438–538 K and atmospheric pressure over Pd and Ru supported AlF3 catalysts prepared by sol–gel method. For the hydrogenation of CF2Cl2, CH2F2 and CH4 represented more than 97% of the products. The catalytic properties of the catalysts are unchanged with time and they showed no significant difference in their activities. At the steady state, the kinetics of the reaction described by a mechanism of a halogenation/dehalogenation of the Pd and Ru surfaces by CF2Cl2 and H2, respectively. The values of the respective rate constants were then determined. It was concluded that at 448 K, the interaction between the Pd and Ru surfaces with CF2Cl2 or H2 is of the same order of magnitude. The conversion ratio on Ru/Pd supported catalysts within the temperature range used was increased from 1.5 to 4.1, while the selectivity of CH2F2/CH4 ratio was decreased from about 17.4 to 1.8 on the surfaces of both catalysts. This leads to the proposition that the high dispersion of Pd and Ru over the support are responsible for the high activity and high selectivity in CH2F2. 相似文献
8.
9.
Hydrogen production through diesel steam reforming over rare-earth promoted Ni/γ-Al_2O_3 catalysts
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Rare-earth (La, Ce, Yb) promoted Ni/γ-Al2O3 catalysts were prepared by impregnation method. Activity and carbon formation resistance of the prepared catalysts were evaluated under various reaction conditions. Catalyst characterizations with TG, TPR and H2 chemisorption were carried out to investigate the promoting mechanism. Experimental results show that rare-earth promoters, especially Yb promoter, obviously improve the activity and carbon formation resistance of Ni/γ-Al2O3 catalyst, and Yb-Ni catalyst shows even higher performance than several commercial catalysts. According to the characterization results, Yb promoter enhances the interaction between the active metal and support, thus increasing the active metal’s dispersion and improving its performance. Furthermore, the obvious difference in diesel conversion between Yb-Ni catalyst and others was shown in the temperature range of 450-550 °C, which would be the reason for its excellent carbon resistance. 相似文献
10.
Iron and cobalt doped zinc oxide were prepared by the sol–gel method. The doping concentration was varied between 5 and 10?wt.%. Structural and morphological features of the samples were investigated comparatively by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and Fourier transform infrared spectroscopy (FTIR). They were also placed in an electric circuit and their sensing characteristics toward ethanol vapors were studied. It was found that, the gas response was impressed by doping. The optimal operating temperature, dynamic response, sensitivity and response and recovery times of the samples have been measured. The operating temperature and the time of response and recovery of the sensor were generally reduced after doping. According to our results, by considering the time of rising/ falling, the doped samples have a relatively better status than pure zinc oxide sample and in particular, the sample with 10% cobalt doped (ZC10) had a competitive attitude compared to pure zinc oxide due to significant reduction in response/recovery times. 相似文献
11.
V. Caratto L. Setti S. Campodonico M. M. Carnasciali R. Botter M. Ferretti 《Journal of Sol-Gel Science and Technology》2012,63(1):16-22
The N-doped TiO2 has been synthesized by sol?Cgel method, using titanium isopropoxide, isopropanol and an aqueous solution of ammonia with ratio 2:1:10. The concentrations used for the NH3 aqueous solution were 3, 7, 10 and 15?%. The samples have been analysed by X-ray diffraction, electron microscopy (SEM and TEM) thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), micro-Raman spectroscopy and diffuse reflectivity. TEM, SEM, DSC and TGA showed that the morphology is influenced by the presence of N3? ions but not by the concentration of the solution. Instead reflectance gave us a relation between values of the energy gap and the concentration of N3? ions: the gap between valence and conduction band lowers as the concentration of NH3 in the starting solution increases. From these results we can say that the properties of the material have been tuned by doping with nitrogen ions because the particles absorb more light in the visible range, and this is important for photovoltaic and photocatalytic applications. 相似文献
12.
Polycarbonate/epoxy/silica hybrid films were prepared by curing an epoxy reaction via in situ sol–gel process. The influence
of the synthetic conditions, such as the ratio of different epoxy reagents and the contents of [2-(3,4-epoxycyclohexyl)ethyl]trimethoxysilane
on the physical and optical properties of these hybrid films were investigated in details. The coefficient of thermal expansion,
surface roughness, and light transmittance at a wavelength range from 250 to 800 nm were measured. These excellent overall
performances make it a promising photonic packaging material. 相似文献
13.
Stable highly concentrated TiO2 sol has been synthesized using binary titanyl ammonium sulfate monohydrate, (NH4)2TiO(SO4)2 · H2O. Treatment of the sol with an ammonia solution has yielded a stable hydrogel, which, after being dried, is transformed into a TiO2 xerogel. Study of the structure-related sorption and crystalline-chemical properties of the synthesized xerogel has shown that it represents a semicrystalline micro/mesoporous material with a rather developed specific surface area (Ssp = 120 m2/g). According to potentiometric titration data, the point of zero charge (PZC) of this material is located at pH 3.9. Measurements of the electrophoretic mobility (by microelectrophoresis) of TiO2 xerogel particles in solutions of HCl, NaOH, and salts of mono-, bi-, and trivalent cations have shown that (1) the isoelectric point (IEP) of the particles lies in the vicinity of pH 6.2, i.e., at a much higher pH than that for PZC; (2) the presence of increasing amounts of 1: 1 and 2: 1 electrolytes causes a gradual and a dramatic reduction in the ζ potential of the particles, respectively; and (3), in the presence of an electrolyte with a trivalent counterion, the surface charge is reversed. The behavior of TiO2 xerogel in an electric field is similar to that of lyophobic particles, with the difference that there is no maximum in the ζ potential versus 1: 1 electrolyte concentration dependence and the measured IEP of the xerogel is much higher than its PZC. Possible reasons for this discrepancy have been discussed. 相似文献
14.
N-doped TiO2 has been prepared by use of sol–gel systems containing titanium alkoxide, with nitric acid as the nitrogen source. The time
needed for gelation of the systems was drastically reduced by ultrasonic irradiation. The peaks assigned to the nitrate and
nitrous ions were observed by FT-IR measurement during the sol–gel reaction. The N-doping was confirmed by the observation
of N–O peaks in the XPS spectrum of the sample heated at 400 °C. The nitrate ion acted as an oxidizer of the ethanol solvent
and titanium species. The TiO2 became doped with nitrogen oxide species as a result of reduction of nitrate ion incorporated into the dried gel samples.
These results indicated that the added nitric acid was reduced during the sol–gel transition and heating process, and the
resulting NO species were situated in the titania networks. The UV and visible photocatalytic activity of the samples was
confirmed by the degradation of trichloroethylene. 相似文献
15.
Mayra G. Álvarez Adriana Urdă Vicente Rives Silvia R.G. Carrazán Cristina Martín Didier Tichit Ioan-Cezar Marcu 《Comptes Rendus Chimie》2018,21(3-4):210-220
The catalytic properties of ZnAlVO mixed oxides derived from decavanadate-exchanged ZnAl–layered double hydroxide (LDH) precursors prepared by a sol–gel method (ZnAlVO–LDHx,y) were investigated in the oxidative dehydrogenation of propane and compared with those of supported catalysts obtained by conventional impregnation of NH4VO3 on ZnO (ZnVO-I,y) and ZnAlO mixed oxide (ZnAlVO-I,y) supports. The effects of composition and calcination time on the catalytic behavior were particularly examined. Higher propane conversions were achieved at higher vanadium content and calcination time of the precursors. The LDH-derived catalysts were the most active ones in all the temperature range studied (300–425 °C). The order of activity for propane conversion for the different catalyst families varies as ZnAlVO–LDHx,y > ZnAlVO-I > ZnVO-I and follows the strength of the Lewis and Brønsted acid sites determined by monitoring of pyridine adsorption by Fourier transform infrared spectroscopy, whereas the propene selectivities are close together in agreement with the similar densities of basic sites determined by CO2–temperature-programmed desorption measurements. It was indeed established that the acidity, rather than the nature of the crystalline phases, the reducibility, or the specific surface area of the samples, governs the catalytic activity. 相似文献
16.
Go Gwang Sub Lee Hong Joo Moon Dong Ju Kim Young Chul 《Research on Chemical Intermediates》2016,42(1):289-304
Research on Chemical Intermediates - In this study, we focused on the catalytic activity, stability, and kinetics of glycerol steam reforming (GSR) for the hydrogen production over... 相似文献
17.
Ruby Chauhan Ashavani Kumar Ram Pal Chaudhary 《Research on Chemical Intermediates》2012,38(7):1443-1453
Undoped and silver-doped TiO2 nanoparticles (Ti1?x Ag x O2, where x?=?0.00?C0.10) were synthesized by a sol?Cgel method. The synthesized products were characterized by X-ray diffraction (XRD), particle size analyzer (PSA), scanning electron microscope (SEM), and UV?CVisible spectrophotometer. XRD pattern confirmed the tetragonal structure of synthesized samples. Average crystallite size of synthesized nanoparticles was determined from X-ray line broadening using the Debye?CScherrer formula. The crystallite size was varied from 8 to 33?nm as the calcination temperature was increased from 300 to 800?°C. The incorporation of 3 to 5% Ag+ in place of Ti4+ provoked a decrease in the size of nanocrystals as compared to undoped TiO2. The SEM micrographs revealed the agglomerated spherical-like morphology of particles. SEM, PSA, and XRD measurements show that the particles size of the powder is in nanoscale. Optical absorption measurements indicated a red shift in the absorption band edge upon silver doping. Direct allowed band gap of undoped and Ag-doped TiO2 nanoparticles measured by UV?CVis spectrometer were 3.00 and 2.80?eV, respectively, at 500?°C. 相似文献
18.
Hugo B. Suffredini Giancarlo R. Salazar-Banda Luis A. Avaca 《Journal of Sol-Gel Science and Technology》2009,49(2):131-136
One of the key objectives in fuel-cell technology is to improve the performance of the anode catalyst for the alcohol oxidation
and reduce Pt loading. Here, we show the use of six different electrocatalysts synthesized by the sol–gel method on carbon
powder to promote the oxidation of methanol in acid media. The catalysts Pt–PbO
x
and Pt–(RuO2–PbO
x
) with 10% of catalyst load exhibited significantly enhanced catalytic activity toward the methanol oxidation reaction as
compared to Pt–(RuO2)/C and Pt/C electrodes. Cyclic voltammetry studies showed that the electrocatalysts Pt–PbO
x
/C and Pt–(RuO2–PbO
x
)/C started the oxidation process at extremely low potentials and that they represent a good novelty to oxidize methanol.
Furthermore, quasi-stationary polarization experiments and cronoamperometry studies showed the good performance of the Pt–PbO
x
, Pt–(RuO2–PbO
x
)/C and Pt–(RuO2–IrO2)/C catalysts during the oxidation process. Thus, the addition of metallic Pt and PbO
x
onto high-area carbon powder, by the sol–gel route, constitutes an interesting way to prepare anodes with high catalytic
activity for further applications in direct methanol fuel cell systems. 相似文献
19.
Qing Ren Yuanyuan Zhang Ying Chen Genshui Wang Xianlin Dong Xiaodong Tang 《Journal of Sol-Gel Science and Technology》2013,67(1):170-174
La1?xSrxMnO3 (x = 0.33) (LSMO) thin films have been fabricated successfully by sol–gel method on two different types of substrates, Si (111) and SrTiO3 (STO) (001). Microstructure and magnetic properties of LSMO thin films have been investigated. The X-ray diffraction studies of the films confirm the pure phase of the LSMO thin films. In contrast with LSMO thin films on Si substrate, the performances of LSMO on STO substrate are superior both from structural and magnetic properties. For the samples deposited on STO substrate, highly preferred orientation as well as less strain and grain defects was found; in other aspect, the magnetization, the residual and saturation moment value, tended greater while a decreased coercive field required merely (saturation moment value was about five times and coercive field was only about 13 % of those on Si substrate). The Curie temperature of LSMO thin films on Si and STO substrates is estimated to be about 349.7 and 359 K, respectively. 相似文献
20.
Rajesh V. Pai Shovit Bhattacharya S. K. Mukerjee V. Venugopal 《Journal of Sol-Gel Science and Technology》2014,72(3):455-463
Varying amounts of Na and K doped lanthanum–titanium oxides were synthesized by gel entrapment technique. These ceramics were characterized by X-ray diffraction. Microstructural investigations revealed grain growth in the doped material compared to undoped sample. Dielectric relaxations of these compounds were investigated in the temperature range 250–900 °C. A high degree of dispersion of the permittivity of un-doped lanthanum–titanium oxide and K and Na doped lanthanum–titanium oxide was observed in the frequency range <100 kHz which was attributed to oxygen vacancies. An increase in the permittivity values were observed with 1 % Na and K doped samples. The permittivity values further deteriorated with the dopant concentration. Using the Cole–Cole model, an analysis of the dielectric loss with frequency was performed, assuming a distribution of relaxation time. The dielectric loss was found to decrease by doping K in lanthanum–titanium oxide matrix. The dc conductivity studies showed that a temperature dependent hopping type mechanism is responsible for electrical conduction in the system. 相似文献