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.     

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.

Microstructure and performance of AZO thin films prepared by sol–gel processing

Al-doped zinc oxide (AZO) films were prepared by a wet-chemical coating technique, their microstructure and crystal growth were characterized as a function of the single layer thickness. When similar final thicknesses are attained by more multiple subsequent coating-firing cycles, film porosity is reduced from over 14 to 2 %. Simultaneously the AZO crystallite size is increased from approximately 23 to 60 nm, a preferential c-axis oriented growth is observed. Different substrates (soda-lime glass, soda-lime glass with a SiO₂ barrier coating, borosilicate glass and alkali-free display glass) were used and the resulting AZO films were compared. It is found that the substrate composition primarily affects grain growth and subsequently the electrical performance of the AZO films.     

Structural and electrosurface characteristics of titanium dioxide xerogel prepared by the sol–gel method

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 (S_sp = 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.     

Investigation of structural,morphological, optical,and magnetic properties of Sm-doped LaFeO3 nanopowders prepared by sol–gel method

Journal of Sol-Gel Science and Technology - Pure orthorhombic phase of La1?xSmxFeO3 (x?=?0, 0.1, 0.2, and 0.3) nanoparticles can be obtained by sol–gel method after...     

Carbon supported electrocatalysts prepared by the sol–gel method and their utilization for the oxidation of methanol in acid media

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.     

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.     

High transparent thermal curable hybrid polycarbonate films prepared by the sol–gel method

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.     

Thermal and luminescent properties of Eu2+-doped aluminates prepared by the sol–gel method

Alkaline earth aluminates with the overall nominal compositions Ca_0.5Sr_0.5Al₂O₄, Ca_0.5Mg_0.5Al₂O₄ and Mg_0.5Sr_0.5Al₂O₄ doped with 1 mol% of Eu²⁺ ions were prepared by the modified aqueous sol–gel method. The thermal behaviour of the xerogels was studied by the TG/DSC-MS technique under an argon and a reductive atmosphere (Ar/H₂–5 %). Appropriate luminescent efficiency of the materials was achieved after annealing at temperatures lower than those in conventional solid state reactions. All three aluminates are mixtures of at least two phases; the monoclinic phase of CaAl₂O₄, the hexagonal phase of SrAl₂O₄ and the cubic phase of MgAl₂O₄ were identified. Solid solubility was recognised in the Ca_0.5Sr_0.5Al₂O₄:Eu²⁺ composition due to the similar ionic radii of Ca²⁺ and Sr²⁺. UV excited luminescence was observed in the blue region (λ_max = 441 nm) in the aluminates containing the monoclinic phase of CaAl₂O₄ and in the green region (λ_max = 520 nm) in the Mg_0.5Sr_0.5Al₂O₄:Eu²⁺ composition.     

Synthesis and characterization of nitrogen-doped TiO2 nanoparticles prepared by sol–gel method

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 N^3? 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 N^3? 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.     

Antibacterial glass films prepared on metal surfaces by sol–gel method

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.     

Structural characterization and electrical conductivity studies of BaMoO4 nanofibers prepared by sol–gel and electrospinning techniques

Scheelite type BaMoO₄ nanofibers were prepared by using acrylamide assisted sol–gel process and electrospinning technique. The prepared Scheelite BaMoO₄ nanofibers were characterized by using TG/DTA, XRD, FTIR, FT-Raman and SEM–EDX techniques. Thermal behavior, crystalline phase and structure of the prepared BaMoO₄ nanofibers samples were confirmed from the analysis of the obtained results of TG/DTA, XRD, FTIR and FT-Raman respectively. SEM micrographs along with EDX showed the formation of one dimensional (1D) nanofibers 100–350 nm diameters and existence of Ba, Mo and O elements in the BaMoO₄ nanofibers sample. The electrical conductivity of BaMoO₄ nanofibers as a function of temperature 200–400 °C under air was evaluated by analyzing the measured impedance data using the winfit software. The newly prepared Scheelite type BaMoO₄ nanofibers showed electrical conductivity of 0.92 × 10^?3 S/cm at 400 °C.     

Compound-induced changes in thermal,structural and optical properties of indium–gallium–zinc oxides prepared by sol–gel method

In this study, IZO/IGZO powders and films of different composition ratios were fabricated by sol–gel method. The influences of the composition ratio on the decomposition temperature, crystallization behavior, structural and optical properties of multi-component oxides were thoroughly examined. Thermogravimetric/differential scanning calorimetric results revealed that in contrast to zinc and indium oxides, the high crystallization temperature and low crystallinity of gallium oxide were attributed to the high dehydroxylation temperature of gallium hydroxide, which led to the high decomposition and crystallization temperatures of IGZO compound. The XRD analysis of the IGZO films confirmed that the addition of Ga amount made the films turn into amorphous easily. However, TEM analysis suggested that the IZO film (In:Zn = 1:2) and the IGZO (In:Ga:Zn = 1:1:1) film consisted of short-range-order nanostructure although the selected area diffraction of both samples indicated that they are amorphous. The transmittance measurements agreed well with the XRD results; that is, the band gaps of the IZO/IGZO films obviously depend on the composition ratio and are closely related to the change of the structural properties.     

Study on the crack mechanism of SiO2 anti-reflective layer prepared by sol–gel method

Journal of Sol-Gel Science and Technology - SiO2 anti-reflective (AR) layers have been prepared via sol–gel dip-coating technique and the mechanism study of crack formation has been then...