Manufacturing of ceramic nanomaterials in Ti–Si–C–N system by sol–gel method

Problems concerning sol–gel synthesis of ceramic nanomaterials, methods of investigation of these materials and of processes proceeding with their participation have been presented. One-component nc-TiC, nc-TiN and multi-component TiC + SiC + C and Ti(C,N) + Si(C,N) + Si₃N₄, powders have been investigated. The sol–gel synthesis is carried out in two stages: low-temperature, in which the raw nc-TiC_x product is obtained, and high-temperature one. In the high-temperature stage carbonization of carbides and elimination of excessive organic compounds, being the source of carbon in carbonization process, take place. It has been demonstrated that the oxygen, present at trace level in argon, can react with components of the system in certain range of temperature, influencing the quality of obtained product. High-temperature oxidation resistance of investigated materials in dry air was also determined, applying kinetic methods. TG-DSC measurement data were used as the basis of kinetic analysis. The method of investigation has been presented at the example of TiC + SiC + C powder oxidation. Is has been demonstrated, that in case of multi-component materials, components were oxidized in temperature ranges characteristic for pure phases.     

Fluorescent organic nanocrystal confined in sol–gel matrix for bio-imaging

The sol–gel chemistry combined to a spray-drying process allowed us to control the formation of original hybrid core–shell nanoparticles constituted by molecular nanocrystals of rubrene embedded in biocompatible silicate spheres. With a good management of all the physical (gas flows, temperatures) and chemical (dye, solvent and alkoxide natures, concentrations, and hydrolysis and condensation conditions) parameters, we optimized a one-step and self-assembly process allowing to obtain nanoparticles exhibiting promising optical properties such as highly fluorescent labels (two-photon excitation) for medical imaging. Moreover, the presence of Si–OH functions on the silicate shell surface make easy to functionalize these fluorescent nanoparticles by grafting biomolecules for targeting properties. The confined nucleation and growth of rubrene nanocrystals in sol–gel silicate spheres during their drying in the air laminar flows, prevents any phase segregation or particle coalescence and stabilizes mechanically and chemically the organic cores. The first particle sizes obtained in these first experiments are ranging between 80 and 600 nm, but lower diameters will be easily prepared by increasing the solvent amount. Transmission electron microscopy was used to characterize the rubrene organic cores. The electron diffraction patterns performed at 100 K, under low-dose illumination to avoid amorphization of the samples during electron irradiation, have shown the good crystallinity of the NP rubrene cores that seem to be constituted by single rubrene nanocrystals. Finally, optical confocal microscopy, used in reflection and fluorescence modes, showed that all the core–shell particles are strongly fluorescent. This high fluorescence intensity arises from the high molecule numbers of rubrene nanocrystals, which enhance the absorption and emission cross sections.     

Synthesis of nanostructural Yttrium fluorosilicate glass ceramic via sol–gel method

Journal of Sol-Gel Science and Technology - The yttrium fluorosilicate glass ceramic pieces were prepared by sol–gel method starting from yttrium acetate, trifluoroacetic acid, and...     

Review of mullite synthesis routes by sol–gel method

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.     

Anticorrosive cerium-based coatings prepared by the sol–gel method

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.     

Polymeric organic–inorganic proton-exchange membranes for fuel cells produced by the sol–gel method

Approaches to the production of polymeric organic–inorganic hybrid proton-exchange membranes for fuel cells by the sol–gel method are summarized, and a classification is proposed for them. Features of the mechanism of conduction in the proton-conducting membranes are considered. Characteristics of the hybrid membranes and of fuel cells using them are presented. The main directions of research in this field are discussed.     

Deposition of silica thin films formed by sol–gel method

Deposition of silica thin films on silicon wafer was investigated by in situ mass measurements with a microbalance configured for dip coating. Mass change was recorded with respect to deposition time when the substrate was fully immersed in the silica sol. Mass gain during deposition was higher than predicted from monolayer coverage of silica nano particles. This implied that deposition was facilitated by gelling of the nanoparticles on the substrate. The rate of deposition was enhanced by increasing the particle concentration in the sol and by decreasing the particle size from 12 to 5 nm. Increasing the salt concentration of the silica sol at constant pH enhanced the deposition of the silica particles. Reducing the pH of the sol from 10 to 6 decreased the deposition rate due to aggregation of the primary silica particles.     

Synthesis of SnO2 nanostructures by ultrasonic-assisted sol–gel method

Fluorine doped SnO₂ nanostructures were grown using ultrasonic assisted sol–gel method. The gel was obtained by dissolving stannous chloride in methanol with ammonium fluoride as dopant followed by irradiation with ultrasonic vibrations. Obtained samples were characterized by structural, morphological and optical studies. All the peaks in the X-ray diffractograms are identified and indexed as tetragonal cassiterite structure. Negative slope of Williamson–Hall plots indicates compressive strain. Particle size of SnO₂ nanostructures is decreases with increases in concentration of fluorine doping. Atomic force microscopy, scanning electron microscopy and transmission electron microscopy studies confirm the formation of ring like porous structures and then hollow tube like growth with increase in the fluorine concentration. Peaks in Raman spectra also indicate strong confinement in SnO₂ particles. Distinct peaks in the PL spectra make the structure suitable for photovoltaic applications.     

Study of tri-layer antireflection coatings prepared by sol–gel method

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.     

Synthesis of high-temperature resistant monolithic zirconia-based aerogel via facile water glass assisted sol–gel method

Zirconia aerogel monolith was prepared by a facile co-hydrolysis method, which adopts ZrOCl₂ as the precursor and water glass (Na₂SiO₃) as the gel initiator. ZrO₂ aerogel was formed by rational controlling of the hydrolysis rate of Zr⁴⁺ ions by Na₂SiO₃. The obtained aerogel consists of ZrO₂ nanoparticles surrounded by amorphous SiO₂ nano shell. The density and the surface area can be well tuned by adjusting the ratio of ZrOCl₂ to Na₂SiO₃. The in-situ introduced SiO₂ nano shell layer acts as the particle boundary reinforcement phase, which not only strengths the ZrO₂ particle connections to form monolith, but also significantly mitigates the sintering of ZrO₂ nanoparticles at high temperature. As a result, the zirconia aerogel prepared by such method could maintain its nanoporous microstructure up to 1000?°C.

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Electrochemical oxidation of aniline in a silica sol–gel matrix

Electrochemical oxidation of aniline encapsulated in a silica solid electrolyte prepared by a sol–gel process yielded products that were dependent on the pore size. An acid-catalyzed process that used tetramethyl orthosilicate as the precursor and aniline as a dopant yielded the silica. When the aging time was limited to one day so that a mesoporous solid was obtained, the potentiodynamic oxidation of aniline at a carbon fiber electrode resulted in the formation of polyaniline. With aging times of 3–5 days, microporous silica was obtained. In this electrolyte, the formation of dimers and other oligomers was observed by cyclic voltammetry. Evidence for these products was the presence of a quasi-reversible redox couple at 0.2 V vs Ag/AgCl that was previously related to oligomeric aniline by Raman spectroscopy. The results supported the hypothesis that the pore structure of sol–gel electrolytes can influence the pathways of electrode reactions therein.     

Preparation of Cyanex 272-containing silica composite by sol–gel method for neodymium adsorption

A kind of silica composite containing bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex 272) was prepared via a in situ sol–gel approach. ³¹P solid-state NMR and FT–IR spectra were employed to analyze the structure of the composite. The thermal stability and surface properties were characterized, and the adsorption ability towards trivalent neodymium (Nd(III)) was evaluated by batch experiments. The Cyanex 272 loaded silica composite showed the advantage of an effective adsorption of Nd(III) from low acidic or neutral solutions with a capacity of ~50 mg/g. The influence of contact time, acidity and initial metal concentration of the stock solutions on the adsorption were comprehensively investigated.     

Effect of CaO additive on sintering and crystallization behavior of cordierite glass–ceramic prepared by sol–gel method

In the present work, cordierite glass–ceramic was prepared via sol–gel method using TEOS, AlCl₃·6H₂O, MgCl₂·6H₂O as starting materials. Different steps of phase transformations to cordierite have been studied by DSC and XRD. Various phases have been formed at different heat-treatment temperatures. Addition of CaO led to an increase in both the formation rate and the intensity of α-cordierite. Sinterability of the samples was determined too. The results showed that high content of CaO improved sintering. Morphology of hexagonal prism for α-cordierite was displayed by SEM.     

Synthesis and characterization of nanocrystalline tin oxide by sol–gel method

Nanocrystalline SnO₂ particles have been synthesized by a sol–gel method from the very simple starting material granulated tin. The synthesis leads a sol–gel process when citric acid is introduced in the solution obtained by dissolving granulated tin in HNO₃. Citric acid has a great effect on stabilizing the precursor solution, and slows down the hydrolysis and condensation processes. The obtained SnO₂ particles range from 2.8 to 5.1 nm in size and 289–143 m² g⁻¹ in specific surface area when the gel is heat treated at different temperatures. The particles show a lattice expansion with the reduction in particle size. With the absence of citric acid, the precursor hydrolyzes and condenses in an uncontrollable manner and the obtained SnO₂ nanocrystallites are comparatively larger in size and broader in size distribution. The nanocrystallites have been characterized by means of TG-DSC, FT-IR, XRD, BET and TEM.     

Synthesis and characterization of lead oxide nano-powders by sol–gel method

Our goal in this research was to obtain lead oxide nano-powders by sol–gel method. In this method, lead oxide nano-powders were synthesized through the reaction of citric acid (C₆H₇O₈·H₂O) solution and lead acetate [Pb(C₂H₃O₂)₂] solution as stabilizer and precursor, respectively. The effect of different parameters including calcination temperature, (molar ratio of citric acid to lead acetate) and drying conditions were investigated. The prepared lead oxide nano-powders were characterized by FT-IR spectroscopy, X-ray diffraction, thermogravimetric analysis and scanning electron microscopy. The prepared PbO samples consist of the particles in the range of 50–120 nm or the thick plate like structures with thickness of 53 nm depending on the drying conditions.     

Nano/macroporous monolithic scaffolds prepared by the sol–gel method

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.

Synthesis and characterization of nanostructured aluminum borate by sol–gel method

Nanostructured aluminum borate was synthesized using sol?Cgel technique. X-ray diffraction study revealed that the synthesized aluminum borate was single crystal. These nanorods have very uniform diameter. High-resolution transmission electron microscope images indicate that aluminum borate is well crystallized. The alternating current (AC) conductivity of the aluminum borate was studied as a function of temperature and frequency. The AC conductivity mechanism of the aluminum borate was found to be proportional to ??^s. The exponent s is almost independent with temperature. This suggests that AC conductivity mechanism of the aluminum borate can be interpreted by localized hopping model.