BaBi2Nb2O9 powder and their ceramics prepared by aqueous solution–gel method

BaBi₂Nb₂O₉ powders and their ceramics were prepared by aqueous solution?Cgel method. The phase evolution and microstructure of samples including powders and ceramics were determined by X-rays, SEM. An homogenous BaBi₂Nb₂O₉ powder was observed after thermal treatment at the temperature as low as 400?°C. The texture phenomena has been observed in the ceramics during the process of sintering, the size and area of oriented grains increased with increase the sintering temperature, and the grain growth occurs in preferential direction which is parallel to the plane of the ceramic plate. The density of this ceramics has been determined, the study revealed that the density increases with sintering temperature and reached a maximum at 1,000?°C and then decreases gradually. The characteristic diffuse phase transition of the BaBi₂Nb₂O₉ ceramics was observed at about 200?°C.     

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.     

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.     

Dielectric and energy storage properties of barium strontium titanate based glass–ceramics prepared by sol–gel method

Ba_0.6Sr_0.4TiO₃ based glass–ceramics were prepared by sol–gel process. Influences of B–Si–O glass content on the microstructure, dielectric, and energy storage properties of the BST based glass–ceramics have been investigated. Perovskite barium strontium titanate phase was found at annealing temperature 800 °C. A secondary phase Ba₂TiSi₂O₈ was detected and lowered by declining the mole ratio of element Si (from 50 to 25 mol%) in glass additive. Microstructural observation indicated that the microstructure homogeneity can be improved by glass addition till 2 mol%, while worsened by excessive glass concentrations. Due to relatively homogeneous microstructure, the maximum discharged energy density and breakdown strength were also obtained in samples with 2 mol% glass additive, which were found to be 0.553 J/cm³ and 43.2 kv/mm, respectively. Microscopic observation of the breakdown area was performed and the mechanical failure, including the formation and accumulation of micro-cracks during the dielectric breakdown process, was considered to be the main cause of dielectric breakdown. Results of the charging and discharging energy densities show that the BST based glass–ceramics prepared by sol–gel method has a potential for pulse power 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.     

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.

Structure and voltage tunable dielectric properties of sol–gel derived Bi1.5MgNb1.5O7 thin films

Bi_1.5MgNb_1.5O₇ (BMN) thin films were fabricated on Au/Ti/SiO₂/Si(100) substrates using a sol?Cgel spin coating process. Thermo decomposition of the BMN precursor gel was discussed. The structures, morphologies, dielectric properties and voltage tunable dielectric properties were investigated. The deposited films showed a cubic pyrochlore structure after annealing at 550?°C or higher temperatures. With the annealing temperature increased from 500 to 800?°C, the root-mean-square surface roughness of the films increased from 0.6 to 6.8?nm. Additional phase, MgNb₂O₆, emerged after annealing at 800?°C due to the volatilization of Bi element. The dielectric properties and tunability of the films were annealing temperature dependent. BMN thin films annealed at 750?°C had a high dielectric constant of 135 and low dielectric loss of 0.002 at 1?MHz. The high tunability of 31.3?% and figure of merit of 156.5 were obtained under an applied electric field of 1?MV/cm at room temperature.     

Improved electrochemical performance of sol–gel method prepared Na4Mn9O18 in aqueous hybrid Na-ion supercapacitor

The rod-like Na₄Mn₉O₁₈ material was prepared by sol–gel method and compared with a similar material produced by solid-state method. Their electrochemical properties were examined in aqueous sodium-ion electrolyte cells. The resulting Na₄Mn₉O₁₈ materials were characterized by SEM, TGA, and XRD techniques. The analysis shows that the rod-like Na₄Mn₉O₁₈ has a small particle diameter ranging from 0.2 to 1 μm. The electrochemical performance was characterized by cyclic voltammetry and galvanostatic charge–discharge test in aqueous Na-ion cells with active carbon (AC) as counter electrode. The Na₄Mn₉O₁₈ materials prepared at 800 °C show a high specific capacity of about 200 F g^?1 at a current density of 200 mA g^?1. The Na₄Mn₉O₁₈/Na₂SO₄/AC Na-ion hybrid supercapacitor exhibits excellent cycle performance through 4,000 cycles with 84 % capacity remaining at 500 mA g^?1 charge–discharge current density (an 18 C rate).     

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.     

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.     

Cu–ZnO nanocrystallites by aqueous thermolysis method

ZnO and different atomic percentages of Cu-doped ZnO nanocrystallites have been prepared by aqueous thermolysis method using Glycine as a fuel and encapsulating agent. Mechanism and formation of intermediate products have been given for the first time. All the findings given are for samples annealed at 800?°C. XRD of nanocrystalline ZnO and Cu?CZnO has been indexed to hexagonal wurtzite structure. Influence of temperature on thermal properties of gel precursor and Cu-doped ZnO nanoparticles have been investigated using thermogravimetric and differential thermal analysis. Accordingly, samples have been annealed at different temperatures. Infrared studies revealed formation of Cu?CZnO nanoparticles and removal of organic matter at higher temperature.     

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.