Journal of Thermal Analysis and Calorimetry - Organic–inorganic hybrid composites have received much attention of scientists in the recent years due to the notable improvement of thermal... 相似文献
The sol–gel method for the mullite synthesis is reviewed, with particular emphasis on the characterization of monophasic and
diphasic gels at low, intermediate and high temperatures and the factors that influence the hydrolysis and condensation rate
of the sol–gel process, which in turn determine the properties of the final material. A wide range of studies about mullite
precursors synthesized via sol–gel is discussed here. 相似文献
Nano sized β-SiC particles were synthesized from sol–gel process. Mono dispersed β-SiC nano particles with semi spherical
morphology were obtained by employing APC as a dispersant agent and adjusting pH in the range of 2.5–4. Phenolic resin and
TEOS were employed as precursors and heat treatment was conducted up to 1500 °C. Different techniques such as XRD, DTA, FTIR,
PSA, SEM and TEM were used to characterize the formation of β-SiC. The (Si–O-C) bonds were formed by hydrolysis and condensation
reactions in the gel while the nucleation of crystalline β-SiC was found to be initiated at 1400 °C. The primary particles
in the sol were found to be (< 10 nm) while the size distribution in the final product was recorded in the range of 30–50 nm. 相似文献
Inorganic and hybrid sols obtained from Si, Ti, Zr and Ce organometallic precursors were used to prepare single and multilayer coatings with different thicknesses. Planar step-index waveguides with different refractive indices were thus prepared by dip-coating the above sols onto commercial soda-lime glass substrates, followed by appropriate thermal annealing. The resultant coatings were characterized by transmission electron microscopy and energy dispersive X-ray spectrometry to elucidate the interface and bonding between the sol–gel derived coatings and the glass substrates. Diffusion of alkali and alkaline earth elements from the glass into the coating layer was confirmed and proposed to play a role in the coating-substrate bonding, inducing excellent optical quality planar interfaces. Optical waveguide characterization performed on a 4.15 μm thick hybrid SiO2:CeO2 (95:5) step-index waveguide yielded losses of 1.50 dB/cm. 相似文献
A nanosilica powder was obtained by thermal treatment of rice husk ash using the sol–gel method without adding any extra surfactant, and was characterized by several techniques. Fourier transform infrared measurements revealed the similarity of the absorption curves of both standard nanosilica and synthesized nanosilica. From the nitrogen adsorption–desorption analysis followed that the nanosilica showed very high surface area of 653 m2/g, total pore volume of 0.64647 mL/g, and narrow pore radius of about 1.98 nm. Scanning electron microscopy of the nanosilica sample dried at 120 °C showed separated particles, while the particles of the sample sintered at 700 °C were aggregated. The analysis of transmission electron microscopy (TEM) micrographs and showed that about 69 % of particles had their sizes in the range of 20–25 nm. X-ray diffraction measurements showed the amorphous nature of the synthesized silica. Applying the Debye–Scherrer formula provided the value of the mean crystallite size around 26 nm which agreed with the one determined from TEM. The purity of the prepared nanosilica was higher than 95 % silica which was confirmed by means of energy dispersive X-ray analysis. 相似文献
Molecularly imprinted polymers have been the subject of intense research for several decades in both academic and industrial
settings. In this paper, we introduce a novel microwave-assisted sol–gel method for molecular imprinting of silica microspheres.
The microspheres were characterized, and their adsorption of imprint and non-imprint molecules was investigated. The dye molecules
methyl orange and ethyl orange were used as templates. Good molecular imprinting was observed as evaluated by the re-adsorption
of dye into the silica matrix followed by the removal of dye from the supernatant solution. 相似文献
A novel sol–gel synthetic route using water-soluble precursor salts is presented as a synthetic path for a high-purity negative
thermal expansion material, ZrW2O8. This synthetic route involves a sol–gel method with the use of EDTA as complexing agent. The aqueous solution is transformed
into a ceramic material after a two-step heat treatment: gelation at 60 °C and reactive sintering at 1,180 °C. The decomposition
of the gel is monitored with infrared spectroscopy and TGA. The high-temperature heat treatment results in ZrW2O8 with its characteristic negative thermal expansion behaviour α[75–130 °C]: −9.8 ± 1.6 μm/m °C and α[175–300 °C]: −1.2 ± 0.2 μm/m °C. 相似文献
Sol–gel derived silica antireflective (AR) coatings have been widely used as the optical components for high peak power laser
systems because of their excellent optical properties and high laser-induced damage thresholds. However, the sol–gel derived
coatings have a high surface area that is more susceptible to be contaminated by absorption of trace amounts of water vapor
and other volatile organic compounds from the environment. In this paper, the major approaches to fabricate contamination
resistant sol–gel derived silica AR coatings have been extensively reviewed. Different approaches, including solution-phase
and vapor-phase silanization, ammonia–water vapor treatment and fluorine modification have been discussed. The optical properties
and laser-induced damage thresholds of modified coatings have also been evaluated. The improved sol–gel AR coatings have been
shown to possess superior contamination resistance to work in vacuum systems compare to the traditional sol–gel AR coatings. 相似文献
The effect of ball milling process, co-doped seed and two step sintering technique on the properties of sol–gel derived alumina
abrasive sintered at low temperature was investigated. The results showed that ball milling time with 10 h can be effective
in enhancing the activity of the precursor and the microstructural uniformity of sintered alumina abrasive. A small amount
of Al2O3–(NH4)3AlF6 co-doped seed addition had potential synergistic effects for reducing α-Al2O3 phase transformation temperature and improving the mechanical property of alumina abrasive. A remarkable suppression of grain
growth was achieved by controlling sintering temperature with two-step sintering method. Therefore, by using ball milling
process, co-doping α-Al2O3–(NH4)3AlF6 seed and two-step sintering technique, the sol–gel derived uniform nanocrystalline alumina abrasive is easily achieved at
low temperature. Nanocrystalline alumina abrasive prepared at these conditions exhibited excellent mechanical properties and
wear resistance compared to fused corundum abrasive and those sol–gel derived corundum abrasive with conventional sintering
methods. 相似文献
Aqueous sol–gel technique is reported for synthesizing nanosize, rod shaped lanthanum phosphate particles starting from lanthanum
chloride, which is suitable for variety of applications such as machinable ceramics, thermal barrier coatings and luminescent
materials. The phosphate particles are having rod like morphology having an overall size in the range 25–100 nm and with an
average aspect ratio 4. The morphology is retained even after calcination at 800 °C. The average crystallite size for the
as prepared particles was calculated to be 8 nm using Scherrer equation applied on X-ray diffraction (XRD) data. The particles
obtained were characterized using photon correlation spectroscopy (PCS), FT-IR spectroscopy, XRD and Electron Microscopy techniques
(TEM and SEM). The phase stability was found using thermo gravimetric analysis. The surface wettability monitored using tensiometer
through dynamic contact angle method indicated that lanthanum phosphate surface possesses considerable hydrophobic character. 相似文献
Silica films were grown on polyimide substrate using surface sol–gel reaction, and the film growth process was characterized
by ellipsometry, atomic force microscopy, and X-ray photoelectron spectroscopy. On the activated polyimide surface, silica
film was grown by sequential immersion in SiCl4 solution and H2O. The thickness of silica films is linear with the depositing cycle, about 5.0 nm per cycle. The silica films present an
island-like growth type and are not a strict equilibrium SiO2 structure. Moreover, the result of the tensile test suggests that the silica films have a good adhesion to the polyimide
substrate. 相似文献
Composite using polythiophene as the conducting polymer and different silica sol–gel as the host matrix were prepared by the template method. The electrochemical performance of the composites has been confirmed using cyclic voltammetry and was compared with the results obtained on polythiophene films synthetised under the same condition directly on ITO substrates. UV–Vis–NIR spectroscopy, scanning electron and atomic force microscopic measurements were done on all the different composites. 相似文献
Aim of the present work is to prepare zirconia nanofibers using microwave assisted sol–gel method. Both honey and microwave powers are employed as structure directing agents to improve the stability and reduce the crystallite size. Honey, acting as capping agent, prevents the particles from hard agglomeration. Soft agglomeration or less agglomeration results in smaller crystallite size that prevents the transformation of tetragonal to monoclinic phase resulting in stabilized tetragonal zirconia (t-ZrO2). Zirconium oxychloride is used as precursor of zirconium and deionized water as solvent. Effect of microwave powers, in the range of 100–900?W with interval of 200?W, on zirconia stabilization is observed. X-ray diffraction analysis shows the presence of phase pure t-ZrO2 at low microwave power ~?100?W with crystallite size ~?26?nm. Formation of phase pure t-ZrO2 at low microwave power is due to the presence of sufficient amount of honey to coat the zirconia crystals. Relatively higher x-ray density has been observed in case of phase pure t-ZrO2 at 100?W of microwave power. This high density and phase purity reveals the high value of hardness (~?1503?HV). Scanning electron microscopy analysis reveals the formation of well-separated nanofibers without agglomeration at 100?W. These nanofibers are purposed for bone implants and bone grafting. Structural transformation along with hard agglomeration is observed with increase in microwave powers from 500?W to 900?W. FTIR and Raman fundamental tetragonal bands, appearing at 490?cm?1 and 148?cm?1, respectively, confirm the formation of t-ZrO2 at low microwave power. Sample with phase purity exhibits high grain boundary resistance (1.95?MΩ) along with high dielectric constant (~?74) and low tangent loss (at log f?=?4.0). It is worth mentioning here that phase pure t-ZrO2 at very low microwave power (~100?W) with high density and well-separated nanofibers has been obtained without any post heat treatment.
High-quality cubic MCM-48 is successfully synthesized using a new silica source known as silatrane and cetyltrimethylammonium
bromide (CTAB) as the structure-directing agent via sol–gel process. The effects of synthesis parameters, viz. crystallization
temperature, crystallization time, surfactant concentration, quantity of NaOH, and silica source, on the product structure
are investigated. The synthesized samples are characterized using X-ray diffractometer (XRD), N2 adsorption–desorption isotherms, and electron microscopy. Optimally, this product is synthesized from samples crystallized
at 140°C for 16 h with a CTAB/SiO2 ratio of 0.3 and NaOH/SiO2 ratio of 0.5. The XRD result exhibits a well-resolved pattern, corresponding to the Ia3d space group of MCM-48. The BET surface area of this product is as high as 1,300 m2/g with a narrow pore-size distribution of 2.86 nm. The scanning electron microscopic (SEM) images also show the truncated
octahedral shape and well-ordered pore system of MCM-48 particles. 相似文献
Powders containing mixtures of titania and molybdite in different ratios were prepared by sol–gel processing. The sols were dried and subsequently calcined at 300, 500 and 700 °C. Depending on the ratio of Ti and Mo in the initial sol and the calcination temperature, Ti-doped MoO3, TiO2/MoO3 or Mo-doped TiO2 have been formed. The as prepared samples were characterised by scanning electron microscopy with attached X-ray dispersive energy analysis, X-ray diffractometry, Raman spectroscopy, gas adsorption and optical characterisation by ultraviolet/visible spectroscopy. The latter was used for the analysis of the photocatalytic properties on the decolourisation of methylene blue solutions under visible light irradiation. The phase composition, the specific surface and the photocatalytic activity were influenced by the molybdenum content and the calcination temperature. The final molybdenum content in the samples additionally depends on the calcination temperature. The optimum photocatalytic properties were observed or Ti-doped MoO3. 相似文献
Poly(chloropropyl-methyl)silsesquioxanes (PCMSQ) were prepared using the base catalyzed sol–gel processing on methyltrimethoxysilane (MTMS) and 3-chloropropyltriethoxysilane (CPTES) with 5:5, 6:4, and 7:3 molar ratios in methanol and water. The PCMSQ with 6:4 molar ratio of MTMS:CPTES, which has the maximum yield, according to the elemental analysis, was chosen and some chlorine atoms of the chloropropyl groups were changed to different amines by refluxing it with ethylenediamine (en), diethylenetriamine (dien), ortho-phenylenediamine (opda), and 2-imidazolidinethion (imt). The amine grafted PCMSQ were then used to support MoO2(acac)2 complex and dien grafted PCMSQ with higher metal content was applied to the epoxidation of cis-cyclooctene with TBHP. The product yields were studied by gas liquid chromatography and the catalytic procedure was optimized for the parameters involved such as the solvent and oxidant. The catalytic activity of this catalyst also was investigated toward epoxidation of some other alkenes. It was also applied to check its reuse ability.
In this research, micro-spherical poly-organo-silsesquioxane was prepared using the base catalyzed sol–gel processing of methyltrimethoxysilane and 3-chloropropyltriethoxysilane with different molar ratios. The sample which has the maximum yield, was used to graft MoO2(acac)2 and for the successful anchoring, some chlorine atoms of the chloropropyl side groups were changed to amines. Then the prepared catalyst with higher molybdenum content was used for the epoxidation of cis-cyclooctene and some other alkenes with TBHP.
The present paper gives new insight into the problem of controlling the morphology of reduced graphene oxide/alumina (RGO/Al2O3) nanocomposites. The dry and simplified sol–gel methods of RGO/Al2O3 nanocomposite synthesis were compared and the influence of six key synthesis parameters on the morphology of the resulting nanocomposite powders was investigated to optimize the morphology of RGO/Al2O3 nanocomposites in terms of reducing the undesired agglomeration of RGO/Al2O3 nanocomposite flakes to a significant minority and obtaining the uniform coverage of RGO surface with Al2O3 nanoparticles. Our investigations indicate that, despite the high excess of Al2O3 used (95 wt%), the lowest RGO/Al2O3 flake agglomeration and the formation of a uniform layer composed of Al2O3 nanoparticles with the average size of 58 nm occurred only when 5 wt% of graphene oxide was used as a substrate for the deposition of Al2O3 nanoparticles together with triethyl aluminium as an Al2O3 precursor and dry hexane as the reaction environment. The resulting organic precursor was thermally decomposed at 280 °C for 3 h in air atmosphere (R4 reaction pathway). This was confirmed by the high BET-specific surface area (242.4 m2/g) and the high open porosity (0.7 cm3/g) of the obtained RGO(5 wt%)/Al2O3 nanocomposite. This is also the first study with a detailed discussion of the reactions expected to occur during the synthesis of an RGO/Al2O3 nanocomposite. 相似文献
The study explored the compatibility between the main product of Portland cement hydration and the main product of the alkali
activation of fly ash: C–S–H and N–A–S–H gels, respectively. Both gels were synthesized with laboratory reagents at different
pH values. Blends of the two were synthesized as well, using the sol–gel procedure. All the gels were characterized with Fourier
transform IR spectroscopy (FTIR). The gels synthesized with this procedure were shown to precipitate together with a silica-rich
gel. In addition, the pH level was found to play a determinant role in both C–S–H and N–A–S–H gel synthesis. The C–S–H gel
is the major phase formed at pH > 11 and N–A–S–H gel for pH > 12. The results relating to the joint synthesis of the two (C–S–H
and N–A–S–H) gels were not conclusive. Technique used for the characterization failed to differentiate between them in the
blended material.