共查询到20条相似文献,搜索用时 31 毫秒
1.
Andrei Jitianu Kristin Lammers Georgia A. Arbuckle-Kiel Lisa C. Klein 《Journal of Thermal Analysis and Calorimetry》2012,107(3):1039-1045
Hybrid melting gels were prepared by a sol–gel process, starting with a mono-substituted siloxane and a di-substituted siloxane,
methyltrimethoxysilane (MTES) together with dimethyldimethoxysilane (DMDES). Five gel compositions were prepared with concentrations
between 50% MTES–50% DMDES and 75% MTES–25% DMDES (in mol.%). The consolidation temperature, the treatment temperature after
which the melting gel no longer softens, increased from 135 to 160 °C with a decrease in the amount of the mono-substituted
siloxane. The glass transition temperature, recorded with differential scanning calorimetry, decreased from −0.3 to −56.7 °C
with a decrease in the amount of the mono-substituted siloxane. When a sample was heat treated isothermally for 2 h at the
consolidation temperature, the glass transition temperature increased by about 15°, indicating further crosslinking of the
siloxane network. 相似文献
2.
Raquel Peña-Alonso Gian Domenico Sorarù 《Journal of Sol-Gel Science and Technology》2007,43(3):313-319
The sol–gel method has been used for the synthesis of borosilicate gels from mixtures of methyltriethoxysilane (MTES) and
dimethyldiethoxysilane (DMDES) and boric acid. The use of boric acid, B(OH)3 allows the hydrolysis and condensation of hybrid silicon alkoxides without further addition of water or catalyst. The use
of difunctional silicon units, –(CH3)2SiO– promote the formation, during the sol–gel process, of linear oligomers which facilitate fiber drawing before gelation.
Gel characterization performed by FT-IR, XRD, TG-DTA and DCS analysis indicates the formation of a mixed network with incorporation
of the boron units via =B-O-Si≡ bridges. The formation of borosiloxane bonds seems favored by the presence of DMDES. SiBOC
glasses were obtained after pyrolysis of the borosilicate gels in argon atmosphere at 1000 °C. TG-DTA study indicates that
the ceramic yield decreases by increasing the amount of DMDES. Gel fibers were successfully prepared from convenient partially-aged
solutions by hand drawing. Pyrolysis of the obtained gel fibers under argon atmosphere at 1000 °C open the possibility to
produce SiBOC homogeneous glass fibers with diameter as low as 10 μm. 相似文献
3.
Dong Qiu Paul Guerry Jonathan C. Knowles Mark E. Smith Robert J. Newport 《Journal of Sol-Gel Science and Technology》2008,48(3):378-383
Phosphosilicate gels with high phosphorus content (P mol% > Si mol%) have been prepared using phytic acid as the phosphorus
precursor, with tetraethyl orthosilicate (TEOS). It is shown that the structure of phytic acid is maintained in both the sols
and those gels dried at a low temperature (i.e. ≤120 °C). Solid state 29Si and 31P NMR suggest that the gel network is primarily based on tetrahedral silicon and that phosphorus is not chemically incorporated
into the silicate network at this point. X-ray diffraction shows the gel to be amorphous at low temperatures. After heat treatment
at higher temperatures (i.e. up to 450 °C), P–O–Si linkages are formed and the silicon coordination changes from tetrahedral
to octahedral. At the same time, the gel crystallizes. Even after this partial calcination, 31P NMR shows that a large fraction of phytic acid remains in the network. The function of phytic acid as chelating agent is
also maintained in the gels dried at 120 °C such that its ability to absorb Ca2+ from aqueous solution is preserved. 相似文献
4.
Leon L. Shaw Chunhui Shen Edwin L. Thomas 《Journal of Sol-Gel Science and Technology》2010,53(1):1-11
We report here the synthesis of gadolinia-doped ceria (GDC) gels and powders via the sol–gel method using cerium acetylacetonate
and gadolinium acetylacetonate as precursors. The dependence of the morphology and nature of the sol–gel product on synthesis
parameters has been investigated in detail. The sol is synthesized and gelled under various conditions to study the effects
of (1) the hydrolysis ratio, (2) the reaction temperature, (3) the reaction time, (4) the addition of acetic acid, and (5)
the as-synthesized condition versus the condition with subsequent calcination at 600 °C. It is found that all of these parameters
exert strong influence on the morphology and nature of the sol–gel product. Crystalline GDC gels are produced when hydrolysis
and gelation are carried out at 55–125 °C. Monolithic gels with low porosity and only micro cracks (shorter than 800 μm and
less than 7 μm wide) can be formed with the proper drying procedure at ambient pressure. Although thermal exposure to 600 °C
leads to grain growth, the size of GDC crystallites is still less than 9 nm after the thermal exposure. 相似文献
5.
Ryoichi Kishi Aritoshi Matsuda Toshiaki Miura Kazunari Matsumura Kokoro Iio 《Colloid and polymer science》2009,287(5):505-512
We prepared thermo-responsive polymer hydrogels by γ-ray irradiation of aqueous solutions of N, N-diethylacrylamide at different temperatures below and above its lower critical solution temperature (LCST). Poly(N, N-diethylacrylamide) gel had a transparent and homogeneous structure when the radiation-induced polymerization and crosslinking
were carried out below the LCST (25 °C) of the polymer. On the other hand, cloudy and heterogeneous gels were formed at temperatures
above the LCST of the polymer (>35 °C). From environmental scanning electron microscopy observations, the gels prepared at
35 and 40 °C were seen to show sponge-like bi-continuous porous structures, while those prepared at 50 °C showed a porous
structure consisting of interconnected microspheres. For temperature changes between 10 and 40 °C, gels with porous structures
showed rapid volume transitions on a time scale of about a minute, not only for shrinking but also for swelling processes,
which is in remarkable contrast to the porous poly(N-isopropylacrylamide) hydrogels. 相似文献
6.
The transparent TiO2 thin films coated on fused-SiO2 substrates were prepared by the sol–gel method and spin-coating technique. Effects of calcination temperature on crystal
structure, grain size, surface texture, and light transmittance of the films were investigated. After calcining at 600–1,200 °C,
the thicknesses of the TiO2 films were all around 80 nm and the molecular structures of the films were anatase, even at 1,200 °C. The calcined TiO2 films had the ultraviolet light (wavelength 200–400 nm) transmittances of ≤29% and the visible light (wavelength 400–800 nm)
transmittance of ≥72%. By photocatalytically decomposing the methylene blue (MB) in water, the photocatalytic activities of
the TiO2 thin films were measured and represented using the characteristic time constant (τ) for the MB degradation. While the films
prepared at 1,000 and 1,200 °C photodecomposed about 54 mol% of the MB in water (the corresponding τ ≈ 14.8 h) after exposing to 365-nm UV light for 12 h, the films prepared at 600 and 800 °C had smaller τ (≈9.0 h) and photodecomposed
about 74 mol% of the MB in water at the same testing conditions. 相似文献
7.
Tsuneo Okubo Daisuke Suzuki Tomoyo Yamagata Koji Horigome Kiyoshi Shibata Akira Tsuchida 《Colloid and polymer science》2011,289(11):1273-1281
Morphology, phase diagram, and reflection spectroscopy of the colloidal crystals of thermosensitive gel spheres, poly(N-isopropylacrylamide) ((200–0.5), 318 and 116 nm in the hydrodynamic diameter at 25°C and 45°C, and 0.5% in the degree of
cross-linking) were studied. Giant colloidal single crystals formed at very low gel concentrations. Densities of the gel spheres
were 0.030 and 0.61 at 25°C and 45°C, respectively. Critical concentration of melting of gel spheres (0.8 wt.% without ion-exchange
resins) decreased sharply to 0.015 wt.% at 25°C as the gel suspension was deionized exhaustively with coexistence of the mixtures
of cation and anion exchange resins. These results demonstrate that the colloidal crystallization takes place by the extended
electrical double layers formed around the gel spheres in addition of the excluded volume effect of the gels. Extent of the contribution of the electrical double layers on the crystallization increased sharply when the
degree of cross-linking increased, the gel spheres shrank, and/or the density of the gel spheres increased. 相似文献
8.
Calcium plumbate Ca2PbO4 was prepared by sol–gel methods (Pechini complex route with two varieties and water soluble polymer method) and by solid
state reaction. The sol–gel prepared samples contained calcium plumbate as the only one phase as early as after 2 h annealing
at 800 °C. Phase composition was detected by XRD measurement and by Raman spectroscopy. The next annealing at 800 °C for 24 h
induced weak Pb losses displayed by present CaO (according to phase equilibrium) and confirmed by XRF measurement. The Pb
losses were smaller for the sol–gel prepared samples probably due to earlier formation of Ca2PbO4. Microstructure and grain size were also established. Sol–gel prepared samples had regularly distributed grains with a small
distribution interval with median value in order of 1 μm. Differences in microstructure of solid state and sol–gel samples
are presented on SEM micrographs. 相似文献
9.
Mika Furukawa Raymond S. Farinato Etsuo Kokufuta 《Colloid and polymer science》2008,286(12):1425-1434
This study aimed to investigate the effect of COOH group distribution within a polymer network having amide groups, with which
the COOH could form hydrogen bonds. We employed here two polyelectrolyte gels composed of N-isopropylacrylamide (NIPA) networks, either copolymerized with acrylic acid (AA) or within which poly(acrylic acid) (PAA)
was entrapped. Both gels (AA–NIPA ∼ 1:4 mol/mol) were prepared by aqueous red-ox polymerization with N,N’-methylenebisacrylamide as the cross-linker. Finely divided gels in NaCl solutions (0.025 and 0.1 M) were titrated with NaOH
and back-titrated with HCl at 25 °C. The results of the copolymer gel (CG) agreed well with those of a linear copolymer and
a nanoscale gel which had a similar AA content to CG. However, marked differences were observed in the titration behaviors
of the AA-copolymerized and PAA-entrapped gels, mainly due to the hydrogen bonding between the entrapped PAA chain and its
surrounding NIPA network. 相似文献
10.
Ruby Chauhan Ashavani Kumar Ram Pal Chaudhary 《Journal of Sol-Gel Science and Technology》2012,61(3):585-591
Undoped and zinc-doped TiO2 nanoparticles (Ti1−xZnxO2 where x = 0.00–0.10) were synthesized by a sol–gel method. The synthesized products were characterized by X-ray diffraction
(XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and UV–VIS spectrometer. XRD pattern confirmed
the tetragonal structure of synthesized samples. Average grain size was determined from X-ray line broadening using the Debye–Scherrer
relation. The crystallite size was varied from 10 to 40 nm as the calcination temperature was increased from 350 to 800 °C.
The incorporation of 3–5 mol% Zn2+ in place of the Ti4+ provoked a slight decrease in the size of nanocrystals as compared to undoped TiO2. The SEM and TEM micrographs revealed the agglomerated spherical-like morphology with a diameter of about 10–30 nm and length
of several nanometers, which is in agreement with XRD results. Optical absorption measurements indicated a blue shift in the
absorption band edge upon 3–5 mol% zinc doping. Direct allowed band gap of undoped and Zn-doped TiO2 nanoparticles measured by UV–VIS spectrometer were 2.95 and 3.00 eV at 550 °C, respectively. 相似文献
11.
Melting gels are a class of organically modified silica gels that are rigid at room temperature, flow at temperature T1 and
consolidate at temperature T2 (T2 > T1), when crosslinking is complete. The process of (a) softening, (b) becoming rigid and
(c) re-softening can be repeated many times. Mixtures of mono-substituted alkoxysilanes and di-substituted alkoxysilanes have
been studied in a systematic way to identify suitable melting gel compositions. The mixtures and the resulting melting gels
have been characterized for their softening temperatures and consolidation temperatures. With an interest in using these materials
for sealing microelectronics, their physical properties have been measured. 相似文献
12.
The physical–chemical properties and fatty acid composition of sheep subcutaneous, tallow, intestinal, and tail fats were
determined. Sheep fat types contained C16:0, C18:0, and C18:1 as the major components of fatty acid composition (19.56–23.40, 20.77–29.50, 32.07–38.30%, respectively). Differential scanning
calorimetry (DSC) study revealed that two characteristic peaks were detected in both crystallization and melting curves. Major
peaks (T
peak) of tallow and intestinal fats were similar and determined as 31.25–24.69 and 7.44–3.90 °C, respectively, for crystallization
peaks and 15.36–13.44 and 45.98–44.60 °C, respectively, for melting peaks in DSC curves; but those of tail fat (18.29 and
−2.13 °C for crystallization peaks and 6.56 and 33.46 °C for melting peaks) differed remarkably from those of other fat types. 相似文献
13.
George Hasegawa Kazuyoshi Kanamori Kazuki Nakanishi Teiichi Hanada 《Journal of Sol-Gel Science and Technology》2010,53(1):59-66
Highly homogeneous transparent titania gels have been successfully prepared from titanium alkoxide by a sol–gel method utilizing
chelating agent, ethyl acetylacetate (EtAcAc), in the presence of strong acid anions. Only catalytic amount of a strong acid
anion suppress the rapid hydrolysis of titanium alkoxide by blocking the nucleophilic attack of HO− and H2O, and the resultant moderate sol–gel reactions thus afford homogeneous gelation, leading to transparent monolithic titania
gels. Gelation time can be widely controlled by changing amounts of water, chelating agent and salt. The ability of salts
to suppress the too abrupt sol–gel reactions is strongly dependent on the electronegativity of anions and valence of cations.
With employing NH4NO3 as a suppressing electrolyte, the obtained titania gels can be converted to pure TiO2 by simple washing and heat-treatment, and transformations to anatase and rutile structures were found to start at 400 and
600 °C, respectively. 相似文献
14.
Carina Gargori García Roberto Galindo Llorach Mario Llusar Vicent Maria Angeles Tena Gómez Guillermo Monrós Tomás Jose A. Badenes March 《Journal of Sol-Gel Science and Technology》2009,50(3):314-320
Glasses on SiO2–CaO–ZnO–B2O3–K2O–Al2O3 oxide system modified by addition of titania (0, 3, 5, 12, and 20% w) have been prepared by sol–gel method. The obtained
gels were aged, dried and fired at 600 °C/1 h in order to stabilise the glass. The resulting fired powders were characterised
by UV–Vis–NIR spectroscopy, scanning electron microscopy, transmission electron microscopy (TEM) and X-ray diffraction (XRD).
Their photocatalytic capacity on the degradation of Orange II dye has been studied. The XRD and TEM studies indicate that
system becomes amorphous with a nanostructured microstructure. From UV–Vis–NIR results the band gap calculated is around 3.5 eV
for all modified glasses. Photoactivity of powders depends on amount of titania in glass composition and the specific surface
area of prepared samples. The sample with highest surface area and lowest addition of titania (3% w sample) shows similar
activity than commercial anatase used as reference. 相似文献
15.
Cellulose films were successfully prepared from NaOH/urea/zincate aqueous solution pre-cooled to −13 °C by coagulating with
5% H2SO4. The cellulose solution and regenerated cellulose films were characterized with dynamic rheology, ultraviolet–visible spectroscope,
scanning electron microscopy, wide angle X-ray diffraction, Fourier transform infrared (FT-IR) spectrometer, thermogravimetry
and tensile testing. The results indicated that at higher temperature (above 65 °C) or lower temperature (below −10 °C) or
for longer storage time, gels could form in the cellulose dope. However, the cellulose solution remained a liquid state for
a long time at 0–10 °C. Moreover, there was an irreversible gelation in the cellulose solution system. The films with cellulose
II exhibited better optical transmittance, high thermal stability and tensile strength than that prepared by NaOH/urea aqueous
solution without zincate. Therefore, the addition of zincate in the NaOH/urea aqueous system could enhance the cellulose solubility
and improve the structure and properties of the regenerated cellulose films. 相似文献
16.
Lifeng Cao Lingxia Li Ping Zhang Haitao Wu 《Journal of Sol-Gel Science and Technology》2009,51(2):251-254
Perovskite-type Ag(Nb0.6Ta0.4)O3 nanopowder was prepared by the sol–gel process from the AgNO3, Ta2O5 and Nb2O5, with help of K2CO3, avoiding use of strong corrosive acid or expensive niobium ethoxide and tantalum ethoxide. The results suggested that thermal
decomposition of the xerogel took place when the xerogel was heated at 450 °C. Well-crystallized single-phased powder was
obtained at low temperature about 680 °C. With the heat-treatment temperature increasing (680–1,100 °C), the intensity of
the diffraction peaks increased. The crystallite size determined by Scherer formula and the result suggested that higher temperature
lead to larger crystallite size. Moreover, the average grain size 30–50 nm was estimated by a field emission scanning electron
microscope. The influence of holding time on microstructures indicated that the homogeneous and small grains were obtained
at 800 °C for 2–4 h while larger ones for 8–16 h. 相似文献
17.
Masoud Salavati-Niasari Masoud Farhadi-Khouzani Fatemeh Davar 《Journal of Sol-Gel Science and Technology》2009,50(3):321-327
Nanocrystalline films of magnetite have been prepared by a novel sol–gel route in which, a solution of iron (III) nitrate
dissolved in ethylene glycol was applied on glass substrates by spin coating. Coating solution showed Newtonian behaviour
and viscosity was found as 0.0215 Pa.s. Annealing temperature was selected between 291 and 350 °C by DTA analysis in order
to obtain magnetite films. In-plane grazing angle XRD and TEM studies showed that magnetite phase was present upon annealing
the films at 300 °C. The films had crack free surfaces and their thicknesses varied between ~10 and 200 nm. UV–Vis spectrum
results showed that transmittance of the films increases with decreasing annealing temperature and increasing spinning rate.
Up to 96% transmittance was observed between the wavelengths of 900–1,100 nm. Vibrating sample magnetometer measurements indicated
that magnetite thin films showed ferromagnetic behavior and the saturation magnetization value was found as ~35 emu/cm3. 相似文献
18.
Bansi Lal Sasmita K. Patro Shivani Singh 《Journal of Sol-Gel Science and Technology》2010,56(3):340-344
Bismuth silicon oxide (Bi12SiO20, BSO) nano crystalline powder was prepared by sol–gel technique using bismuth nitrate and tetraethyl orthosilicate as starting
materials. The prepared samples were sintered at various temperatures (750 °C maximum) and characteristic sillenite single
cubic phase with crystallite size ~38 nm (calculated from room temperature powder XRD measurements) was realized at 750 °C
sintering temperature. SEM analysis showed that the powder contains the nano-sized particles with almost spherical morphology.
The observed frequencies in room temperature FTIR spectrum could be assigned to Bi–O, Si–O and Bi–O–Si bonds. The FWHM (full
width at half maximum) of the diffraction peaks decreased while the intensity of FTIR absorption lines increased with the
increase in the sintering temperature indicating better bond formation and crystallization. The thermograph of the samples
recorded in the temperature range 50–1,000 °C showed almost no weight loss after ~575 °C further confirmed the conclusion
arrived at from XRD and FTIR analysis. The samples sintered at 750 °C showed about 50% absorbance in 400–600 nm region which
was consistent with the pale yellow color of the sample. Broad blue emission centered ~478 nm was observed when excited by
350 nm radiation from a Xe-lamp. The intensity of this broad emission band increased while its FWHM decreased with the increase
in sintering temperature. Self-trapped excitons could be responsible for this emission. 相似文献
19.
A. Zalga Z. Moravec J. Pinkas A. Kareiva 《Journal of Thermal Analysis and Calorimetry》2011,105(1):3-11
The preparation and characterization of the M′–M′′–O nitrate–tartrate (M′ = Ca, Ba, Gd and M′ = W, Mo) precursor gels synthesized
by simple, inexpensive, and environmentally benign aqueous sol–gel method is reported. The obtained gels were studied by thermal
(TG/DSC) analysis. TG/DSC measurements revealed the possible decomposition pathway of synthesized M′–M′′–O nitrate–tartrate
gels. For the synthesis of different metal tungstates and molybdates, the precursor gels were calcined at different temperatures
(650, 800, and 900 °C). According to the X-ray diffraction (XRD) analysis data, the crystalline compounds CaMo1-x
W
x
O4 doped with Ce3+ ions, BaMo1-x
W
x
O4 doped with Eu3+ ions and Gd2Mo3O12 were obtained from nitrate–tartrate gels annealed at 650–900 °C temperatures. The XRD data confirmed that the fully crystalline
single-phase powellite, scheelite, or Gd2(MoO4)3 structures were formed already at 650 °C. Therefore, the suggested sol–gel method based on the complexation of metal ions
with tartaric acid is suitable for the preparation of mixed tungstates–molybdates at relatively low temperature in comparison
with solid-state synthesis. 相似文献
20.
S. Kurajica E. Tkalcec J. Sipusic G. Matijasic I. Brnardic I. Simcic 《Journal of Sol-Gel Science and Technology》2008,46(2):152-160
Nanosized zinc aluminate spinel (gahnite, ZnAl2O4) powders were prepared by sol−gel technique at low sintering temperatures. Aluminium-sec-butoxide [Al(OsBu)3] and zinc nitrate hexahydrate Zn(NO3)2 . 6H2O were used as starting materials. Gels with and without chelating agent were prepared. Ethyl-acetoacetate (C6H10O3) was used as a chelating agent in order to control the rate of hydrolysis of Al(OsBu)3. The dried gels and thermally treated samples were characterized by means of Differential Thermal Analysis and Thermo-Gravimetric
Analysis (DTA, TGA), X-ray Diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR) and Transmission Electron Microscopy
(TEM). The surface area was measured by Brunauer-Emmet-Teller (BET) adsorption–desorption isotherms. It has been established
that chelation enables to obtain a transparent gel. The thermal evolution of gels was characterized by two crystallization
processes in the range 200–400 °C and 600–700 °C. Both processes yielded pure ZnAl2O4 as evidenced by XRD, i.e. zinc aluminate spinel powders were produced by gel heat-treatment at temperatures as low as 300 °C.
The average gahnite crystallite size for the samples sintered in the temperature range of 400–1000 °C has been calculated
from the broadening of XRD lines revealing that nanocrystalline powders were prepared. The surface areas measured for the
samples fired at 700 °C for 2 h were 43.1 and 62.6 m2 g−1, for sample without and with the chelating agent, respectively. TEM micrographs confirmed the nano-scale size of particles. 相似文献