Photoluminescence of ZnO layer on commercial glass substrate prepared by sol–gel process

Amorphous ZnO thin film on soda–lime–silica glass substrate was prepared by the sol–gel process at low-temperature processing, i.e., 100 °C. No distinct grain structure was observable in the surface of the film. The photoluminescence spectrum of the ZnO thin film with an intense near band edge emission was observed while the defect-related broad green emission was nearly quenched.     

Ultrahydrophobic silica films by sol–gel process

Wettability of solid surfaces is a crucial concern in our daily life as well as in engineering and science. The present research work describes the room temperature (27 °C) synthesis of adherent and water repellent silica films on glass substrates using vinyltrimethoxysilane (VTMS) as a hydrophobic reagent by a single step sol–gel process. The silica sol was prepared by keeping the molar ratio of tetraethoxysilane (TEOS), methanol (MeOH), water (H₂O) constant at 1:14.69:5, respectively, with 0.01 M NH₄F throughout the experiments and the VTMS/TEOS molar ratio (M) was varied from 0 to 0.97. The effects of M on the surface structure and hydrophobicity have been researched. The static water contact angle as high as 144° and water sliding angle as low as 14° was obtained for silica film prepared from M = 0.97. The hydrophobic silica films retained their hydrophobicity up to a temperature of 255 °C and above this temperature the films became superhydrophilic. The prepared silica films were characterized by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), Fourier Transform Infrared (FT-IR) spectroscopy, humidity test and static and dynamic water contact angle measurements.     

Photocatalytic evolution of hydrogen over nanocrystalline mesoporous titania prepared by surfactant-assisted templating sol–gel process

Nanocrystalline mesoporous titania was synthesized via a combined sol–gel process with surfactant-assisted templating route and evaluated for photocatalytic activity of hydrogen evolution from an aqueous methanol solution. In this proposed method, applied surfactant template molecules advantageously behaved as both mesopore-forming and gel formation-assisting agent. The activity of the mesoporous titania thermally treated under appropriate conditions, i.e., at calcination temperature of 600 °C for 4 h, was considerably higher than that of commercial titania powders, Ishihara ST-01 and Degussa P-25. It is clearly revealed that introducing mesoporous framework into TiO₂ by this synthetic system provided much better photocatalytic performance.     

Complex permittivity andpermeability of Zn–Co substituted Z type hexaferrite prepared by citrate sol–gel process

Abstract

A series of Z type hexaferrite samples with composition Ba₃Co_xZn_{2 -x}Fe₂₄O₄₁ (x varying from 0·0 to 2·0 in steps of 0·4) were prepared by a citrate sol-gel process. Samples were characterised by TG-DSC, X-ray diffraction, and scanning electron microscopy. Complex permittivity and permeability, and dielectric and magnetic losses were studied as a function of measurement frequency, composition, and annealing temperature. The dependence of natural resonant frequency on annealing temperature as well as on cobalt content was investigated in the range 100 MHz to 6 GHz. Reflection loss has been calculated as a function of frequency according to transmission line theory.     

Hydrophilization by coating of silylated polyoxazoline using sol–gel process

Hybrid films prepared from TEOS and polyoxazolines (Si–POx–Si) crosslinking agents were coated on different substrates in order to modify their surface properties. The film cohesion and adhesion on substrates were expected through the hydrogen bonding of the polyoxazoline crosslinked network. Low molecular-weight α,ω-unsaturated polyoxazolines (DA-PMOx)s were synthesized by a one step cationic ring-opening polymerization (CROP) of 2-methyl-2-oxazoline (MOx) with a good control over the molecular weight. Based on double thiol-ene coupling (d-TEC) a post-functionalization of DA-PMOx end chains gave in good yield polyoxazoline cross linker (Si–POx–Si). Glass and various polymer substrates (PP, PEI, POM, etc.) were spin coated by the organic–inorganic hybrid films through sol–gel process. AFM, SEM, visible reflectance spectroscopy and contact angle experiments allowed the full characterization of targeted surfaces and demonstrated the efficiency of the polyoxazoline coating.     

Dielectric relaxation properties of PbTiO3-multiwalled carbon nanotube composites prepared by a sol–gel process

Dielectric composites fabricated by combining multi-walled carbon nanotubes (MWCNT) and PbTiO₃ (PTO) powder were prepared using a sol–gel process. Well-dispersed PTO powder with various volume ratios of MWCNT was compressed to form a pellet, and then silver electrodes were coated on both sides for electrical measurements. The PTO–MWCNT composite with 0.4 vol% MWCNT showed the highest dielectric constant (912 at 1 kHz), which is approximately 25 times larger than that (37 at 1 kHz) of a pure PbTiO₃ pellet. Furthermore, a strong frequency dependence of the dielectric constant in the low frequency range was shown for the PTO–MWCNT composites. Interfacial effects related to dielectric relaxation in composite materials were used to explain an observed increase of the dielectric constant near the percolation threshold.     

Re-crystallization of silica-based calcium phosphate glass prepared by sol–gel technique

Bioactive glass (BG) is a potential material for treating dentin hypersensitivity owing to its high solubility. In this study, we synthesized 80S-BG bioactive glass samples using a sol–gel technique and mixed with various hardening agents. The obtained material could be used in human dentinal dentinal tubule occlusions. X-ray diffraction (XRD), scanning electronic microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) measurements were employed to investigate the physiochemical properties and dentinal dentinal tubule occlusion efficiency by mixing the 80S bioactive glass (80S-BG) with various hardening agents.The major crystallite phase obtained on mixing 80S-BG with phosphoric acid (PA) was Ca(H₂PO₄)₂·H₂O. The mixture of 80S-BG powders and 20, 30, or 40 wt% PA acted as a hardening agent and achieved a dentinal tubule penetration depth of 30.7–62.6 µm.80S-BG on mixing with suitable PA agents exhibited a short reaction time and good operability, making it feasible for use in occluding dentinal tubules. 80S-BG mixed with hardening agents exhibited a greater potential for treating dentin hypersensitivity as compared to the 80S-BG not mixed with any hardening agents.     

Effect of yttria on crystallization and microstructure of an alumina–YAG fiber prepared by aqueous sol–gel process

Continuous fiber development is needed for high performance and high temperature composites. Various methods have been used to make ceramic fibers. In this research, composite fibers (yttrium aluminum garnet (YAG)/Al₂O₃) were prepared by a sol–gel method using aqueous solution. They were synthesized from aluminum salt, aluminum metal, yttrium oxide and water used as solvent. Transparent gel fibers were obtained by immersing a thin wire into the viscous sol, then pulling it out by hand. The obtained fibers contained very fine grains with diameter ranging from 10 to 80 μm after heat treatment. When yttria content was increased, the crystallization of YAG shifted to a lower temperature, whereas the transformation temperature to α-Al₂O₃ shifted to a higher temperature. Nevertheless, the fibers with different amounts of yttria contained alumina and YAG after heat treatment at 1400 °C. The composite fibers had vermicular structure and were denser than alumina fibers. The yttria percent concerning the limits of this study (≤10 wt%) effected on fiber diameter. As the yttria content was increased, the fiber diameter increased, whereas grain size and densification of the composite fibers decreased.     

Preparation of LaNiO3/SrTiO3/LaNiO3 capacitor structure through sol–gel process

In this paper, SrTiO₃/LaNiO₃ (STO/LNO) bilayer films were prepared on lanthanum aluminate (LAO) substrates by use of the sol–gel technique. An array of LNO electrodes with diameters of 200 μm was prepared on the surface of STO/LNO bilayer films. Therefore, LaNiO₃/SrTiO₃/LaNiO₃ (LNO/STO/LNO), a capacitor structure with symmetrical top and bottom electrodes, was obtained. The XRD analysis showed that the obtained capacitor structure has a biaxial texture. The dielectric test suggested that the relative dielectric constant of the LNO/STO/LNO structure is symmetric, has a high tunability, and has a low dielectric dissipation factor (tan δ) in response to varying electric field bias. As the temperature decreased, the relative dielectric constant of the STO film increased, the tunability increased, and the tan δ decreased. At test conditions of 80 K and 100 kH, the tunability and the figure of merit (FOM) reached 56% and 107, respectively.     

Preparation of scratch resistant superhydrophobic hybrid coatings by sol–gel process

Organic–inorganic hybrid coatings on glass substrates with superhydrophobic properties and with improved scratch resistance were obtained by means of applying a multilayer approach including multiple sol–gel processes. The coatings exhibited a water contact angle (WCA) higher than 150°. Ultraviolet (UV)-curable vinyl ester resins and vinyltriethoxysilane (VTEOS) as coupling agent were employed to increase the adhesion between substrate and the inorganic layers. The surfaces were characterized by means of dynamic contact angle and roughness measurements. Indeed, the occurrence of superhydrophobic behavior was observed. The scratch resistance of the hybrid coatings was tested to evaluate the adhesion of the coatings to the glass substrate. The proposed preparation method for scratch resistant, mechanically stable, superhydrophobic coatings is simple and can be applied on large areas of different kinds of substrates.     

Non-fluorinated,room temperature curable hydrophobic coatings by sol–gel process

Non-fluorinated hydrophobic silica surfaces were generated on soda lime glass (SLG) substrates using hexamethyldisilazane (HMDS) as a surface modifying agent. Silica coatings were fabricated by dip coating of a sol derived from base catalyzed hydrolysis and condensation of tetraethoxysilane (TEOS). Two methodologies were adopted to generate the hydrophobic surface; one where the hydrophilic silica coated surface was treated by immersion into different concentrations of alcoholic solutions of HMDS varying from 2.5 wt% to 15 wt%. In the other method, HMDS was directly added to a mixture of TEOS, water, ethanol, and ammonium hydroxide and coatings were deposited using this sol by dip coating and spray coating. Water contact angles (WCA) were measured to study the effect of HMDS treatment times and concentrations on hydrophobicity in the first case, and in the second case, WCA were measured for dip and spray coated samples. UV–visible transmission, scratch resistance, and thermal stability of the coatings were determined. The WCA increased from 66 ± 2° to 125 ± 4° after the treatment of the silica coatings with HMDS. In case of coatings generated from direct addition of HMDS to silica sol, WCA varied from 145 ± 2° to 166 ± 4° for dip and spray coated surfaces respectively. Surface morphology was studied to explain the difference in hydrophobicity of coatings generated using the two methods.     

Effect of peptiser species on crystallisation of alumina gel produced by sol–gel process

The present work reports a study on the effect that a peptiser species has on the crystallisation of alumina gel produced by a sol–gel process to help develop a method for producing α-Al₂O₃ at low temperature. The white precipitate of aluminium hydroxide, which was prepared with a homogeneous precipitation method using aluminium nitrate and urea in an aqueous solution, was peptised using various peptisers at room temperature to form a transparent alumina sol. The alumina gel obtained from the alumina sol, which was produced using formic acid as the peptiser, was most dominantly crystallised into α-Al₂O₃ by annealing at 900°C. The optimal [peptiser]/[Al³⁺] (P/A) molar ratio for the crystallisation into α-Al₂O₃ was 0.2. The alumina gel began to crystallise into α-Al₂O₃ with annealing at as low as 500°C when formic acid and a P/A ratio of 0.2 were used.     

Multilayer zirconium titanate thin films prepared by a sol–gel deposition method

Zirconium titanate multilayer thin films were prepared by an aqueous particulate sol–gel process followed by spin coating. The obtained structures were studied by transmission electron microscope, scanning electron microscope, atomic force microscope, and spectroscopic reflection analyses. According to the results, sound thin films up to three layers were developed, accompanied by an increase in thickness and roughness by increasing the number of the layers. It was also found that the coatings consist of globular nanoparticles with an average diameter of 50 nm. Considering the contribution of roughness to biological responses, the optimization of the surface characteristics to meet an optimal performance seems to be a challenging issue, which demands future studies.     

Structural characterisation and electrical conductivity studies of BaMoO4 nanorods prepared by modified acrylamide assisted sol–gel process

Abstract

Scheelite type BaMoO₄ nanorods have been synthesised by modified acrylamide assisted sol–gel process. The prepared samples were characterised by X-ray diffraction (XRD), Fourier transform infrared (FTIR), Fourier transform Raman (FT-Raman), scanning electron microscope–energy dispersive X-ray (SEM–EDX) and transmission electron microscope (TEM) techniques. The crystalline phase and structure of the prepared samples were confirmed from the analysis of the obtained results of XRD, FTIR and FT-Raman respectively. The average crystallite size calculated using Scheeer’s formula and XRD data is found to be 98 nm. SEM images showed the formation one dimensional nanorods of diameter <300 nm. EDX spectra showed the existence of Ba, Mo and O elements of the prepared samples. From the TEM images, diameter and length of the rod are found to be 80 and 2070 nm respectively. The ac conductivities by impedance spectroscopy of the prepared BaMoO₄ samples were evaluated as a function of temperature ranging from 500 to 800°C in the air. The newly prepared BaMoO₄ nanorods showed electrical conductivity of 3·14×10^?3 S cm^?1.     

Catalytic performance of NO oxidation over LaMeO3 (Me = Mn,Fe, Co) perovskite prepared by the sol–gel method

The catalytic performance of LaMeO₃ (Me = Mn, Fe, Co) perovskite prepared by a sol–gel method was studied. These catalysts were characterized by X-ray diffraction (XRD), N₂ adsorption (BET), H₂ temperature programmed reduction (TPR), NO temperature programmed desorption (TPD) and CO–O₂ pulse. LaCoO₃ exhibited the best activity than that of LaFeO₃ and LaMnO₃ even after hydrothermal ageing. The activity sequence is in accordance with the reducibility of the samples. The activated oxygen species and adsorbed NO play key roles in the NO oxidation reaction.     

Mechanical properties and thermal stability of ambient-cured thick polysiloxane coatings prepared by a sol–gel process of organoalkoxysilanes

Ambient-curable polysiloxane coatings were prepared by pre-hydrolysis/condensation of phenyltrimethoxysilane (PTMS) and dimethyldimethoxysilane (DMDMS) in the presence of ammonia solution and subsequently mixing with aminopropyltriethoxysilane (APS). The mechanical properties of coatings were thoroughly examined at both macro- and micro-level and the thermal stability of coatings was characterized by thermogravimetic analysis, both of which were correlated with coating composition and the hydrolysis/condensation degree of polysiloxane oligomer. It was found that pro-hydrolysis step is essential for fabrication of thick crack-free coatings (18–35 μm). Higher DMDMS molar ratio, more APS dosage and lower hydrolysis/condensation degree of polysiloxane oligomer favor enhancing the hardness. Excellent impact resistance (50 cm kg) of coatings was obtained at 5% and 10% APS dosage, despite of the type and structure of polysiloxane oligomer. Whatever, the best scratch resistance of coatings was attained using the polysiloxane oligomer, prepared at PTMS-to-DMDMS molar ratio of 2:8 and water-to-precursor molar ratio of 1:1, and 5% APS dosage. The polysiloxane coatings exhibit high thermal stability, however, which strongly depends on the coating composition.     

Crystal structure and mixed ionic–electronic conductivity of La1−xCaxMnO3 (0 ≤ x ≤ 0.8) produced by mechanosynthesis

The aim of this work was to study the relationship between the crystalline structure, the mixed ionic–electronic conductivity and the calcium content in calcium-doped lanthanum manganites (CLM, La_1?xCa_xMnO₃) synthesized by reactive ball milling. Mechanosynthesis was employed to produce nanocrystalline CLM with varying calcium content (x = 0–0.8 in increments of 0.1). Powders of Mn₂O₃, La₂O₃ and CaO mixed in the stoichiometric ratio were used as raw materials. The mechanosynthesis was carried out using a high-energy shaker mixer/mill. X-ray powder diffraction and Rietveld refinement were used to determine the crystalline structure as a function of calcium content. The four-point probe resistivity test was used to measure the electrical resistivity of the compacted and sintered powders using a DC milli-ohm meter. The results showed that the substitution of the La³⁺ ion by the Ca²⁺ ion during mechanosynthesis only changed the lattice parameters but not the orthorhombic Pnma structure. The mixed ionic–electronic conductivity increased with the Ca²⁺ content. The best conductivity was observed for the composition of La_0.2Ca_0.8MnO₃.     

Highly conductive coatings of carbon black/silica composites obtained by a sol–gel process

Conductive submicronic coatings of carbon black (CB)/silica composites have been prepared by a sol–gel process and deposited by spray-coating on glazed porcelain tiles. Stable CB dispersions with surfactant were rheologically characterized to determine the optimum CB-surfactant ratio. The composites were analyzed by Differential Thermal and Thermogravimetric Analysis and Hg-Porosimetry. Thin coatings were thermally treated in the temperature range of 300–500 °C in air atmosphere. The microstructure of the coatings was determined by scanning electron microscopy and the structure evaluated by confocal Raman spectroscopy. The electrical characterization of the samples was carried out using dc intensity–voltage curves. The coatings exhibit good adhesion, high density and homogeneous distribution of the conductive filler (CB) in the insulate matrix (silica) that protects against the thermal degradation of the CB nanoparticles during the sintering process. As consequence, the composite coatings show the lowest resistivity values for CB-based films reported in the literature, with values of ～7 × 10^?5 Ωm.     

Optical properties of Nb-doped TiO2 thin films prepared by sol–gel method

In this work, we studied optical properties of pure and Nb-doped TiO₂ synthesized using a sol–gel method and deposited as thin films by spin-coating followed by annealing in air at 500 °C for 1 h. The surface elemental composition was derived from X-ray photoelectron spectra, while structure and surface morphology were investigated using X-ray diffraction and atomic force/scanning electron microscopy. Finally, the optical properties were investigated by means of UV–vis spectrophotometry and spectroscopic ellipsometry.The Nb content was determined from XPS measurements to vary between 1.8 and 4.3 at%. The XRD patterns of the deposited thin films, with a maximum thickness of about 56 nm, showed no diffraction peaks. As proven both by microscopy and spectroscopic ellipsometry studies doping TiO₂ with Nb modified the surface morphology of the samples; the grain size is increasing while the surface roughness decreases with the increase in Nb content. This is accompanied by a decrease in the refractive index and an increase of the extinction coefficient.