Preparation of zirconium diboride ultrafine hollow spheres by a combined sol–gel and boro/carbothermal reduction technique

In this work, we introduce a modified novel silica sol–gel process to synthesize hexagonal close-packed (hcp) and face-centered cubic (fcc) nickel (Ni) nanoparticles supported on amorphous carbon and silica matrix. The supporting of amorphous carbon and silica can prevent the Ni nanoparticles from aggregating and being oxided which would result in the loss of their magnetism and dispersibility. The phase structure of the Ni nanoparticles which were obtained from the gels pyrolyzed from 250 to 350 °C is hcp structure, whereas that of the Ni nanoparticles pyrolyzed at 750 °C is fcc structure. The grain sizes of the hcp Ni nanoparticles calcined at 250 °C range from 5 to 20 nm in diameter, and that of the fcc Ni nanoparticles calcined at 750 °C range in 7–35 nm. The studies of magnetic properties of the hcp and fcc Ni nanoparticles show that both have quite different magnetic behaviors.     

Synthesis of zirconium diboride nano-powders by novel complex sol–gel technology at low temperature

Zirconium diboride nano-powders were synthesized by novel complex sol–gel technology at low temperature. Zirconium oxychloride as source of zirconium was complexed via adding propylene oxide that could form the stable zirconium sol by protonation and ring-opening reactions and boric acid as source of boron was dissolved effectively using glycerol that acted as complexing agent to create the boron network through forming stable coordination compound. Additionally, glycerol could be carbonized as source of carbon, which could replace the conventional carbon source additives. Then the mixed sols were gelated, dried, and exposed to 1,450 °C for 2 h with flowing argon in the furnace. High purity of ZrB₂ nano-powders with spherical shape of ca. 200 nm were synthesized via carbothermal reduction. The mechanism of two complexing agents were discussed combining with the infrared spectroscopy analysis results, and the powder characteristics were performed by using X-ray diffraction and transmission electron microscopy.     

Optical and structural properties of aluminium oxide thin films prepared by a non-aqueous sol–gel technique

Clear aluminium oxide sols without precipitation were synthesized via a non-aqueous sol–gel technique using three different alcohols (ethanol, isopropanol and n-butyl alcohol) as solvent, aluminium sec-butoxide as a precursor and acetyl acetone as a chelating agent. Although all sols could be successfully used to prepare thin films, the most stable one was prepared with n-butyl alcohol. Highly transparent, homogenous and amorphous aluminium oxide thin films were obtained on Si substrates after a heat treatment at 500 °C. X-Ray photoelectron spectroscopy (XPS) and Fourier transform infrared absorption (FT-IR) spectroscopy revealed all films were hydroxide free. The optical and structural properties of the films were particularly investigated. Any significant difference except from thickness on the film properties was not observed by changing the alcohol. Refractive index was used as an indication of the porosity of the films and ranged from 1.54 to 1.60.     

Polydimethylsiloxane/silica/titania composites prepared by solvent-free sol–gel technique

Composites based on polydimethylsiloxane incorporating silica and titania were prepared by mixing polydimethylsiloxane with proper oxides precursors, tetraethyl-orthosilicate and tetrabutyl-orthotitanate. In the presence of environmental humidity and in acid catalysis, hydrolysis/condensation processes take place with formation of oxides and concomitantly polymer crosslinking. Partial replacement of SiO₂ in a polydimethylsiloxane/silica composite with titania (both generated in situ by sol–gel process) affects surface hydrophilicity (evaluated by dynamic contact angle), water vapor sorption ability (determined by dynamic vapor sorption) and thermal stability. The dielectric properties are also controlled by composition.     

Photocathodic protection properties of three-dimensional titanate nanowire network films prepared by a combined sol–gel and hydrothermal method

A combined sol–gel and hydrothermal method was developed for preparing a three-dimensional titanate nanowire network film on titanium substrates to achieve an especial photocathodic protection effect for 403 stainless steel. Photopotential measurements were performed to study the protection effect of the film. The results indicated that the titanate film exhibited a special all-dimensional uniform porous structure composed of branched titanate nanowires. When we coupled the steel in a 0.5 M NaCl solution to the titanate film photoanode in a 1.0 M NaOH solution under illumination, its potential decreased by 560 mV. Especially after the light source was cut off, the photopotential of the steel increased by only 50–145 mV, and kept at the lower values than the corrosion potential under dark conditions for over 10 h, indicating that the titanate nanowire network film could produce a striking photocathodic protection effect for 403 stainless steel under illumination and dark conditions.     

Titanium dioxide fibers prepared by sol–gel process and centrifugal spinning

A new study of the preparation of nanocrystalline titanium dioxide (TiO₂) fibers is reported in the paper, which were prepared by sol–gel process with titanium acetate [Ti(CH₃COO)₄] as precursor. After that, centrifugal spinning and steam atmosphere heat-treatment were used to obtain final fibers. Here, the molecule structure of precursor was analyzed and the TiO₂ fibers obtained were characterized. Additionally, the effects of the silica (SiO₂) doping were discussed in this paper. By the Fourier transformation infrared spectrum analysis, the chain structure of –O–Ti–O–Ti–O– was confirmed in the Ti(CH₃COO)₄ precursor, as a result the precursor spinning solution showed a good spinning performance. And the pyrolysis process of precursor fibers was analyzed with the help of DSC–TG method. The phase of TiO₂ fibers obtained after heat-treatment with steam atmosphere was characterized mainly by the X-ray diffractometer (XRD), from the XRD curves, the result that the SiO₂ doping can efficiently inhibit the grain growth of TiO₂ fibers could also be verified. The microstructure of the TiO₂ fibers was observed by scanning electron microscope, which showed that diameter of TiO₂ fibers obtained with excellent continuity are from 5 to 10 μm. At last, the photocatalytic property of TiO₂ fibers was also tested.     

Borate,lithium borate,and borophosphate powders by sol–gel precipitation

Borate, lithium borate and borophosphate powders were synthesized by the sol–gel method. Triethyl borate, lithium methoxide, and orthophosphoric acid were used as precursors for B₂O_3, Li₂O, and P₂O₅, respectively. Powders were characterized by FTIR, DTA, XRD and SEM techniques. Powders from the Li₂O–B₂O₃ system exhibited glassy features while borate and borophosphate powders contained mainly crystalline B₂O₃ according to XRD analysis. However, a 500 °C heat treatment transformed these crystalline powders into glass powders. Conversely, heat treatment of Li₂O–B₂O₃ powders transformed their structure from glassy to crystalline (Li₂B₄O₇). Chemical durability studies conducted in water at 60 °C showed that minor additions of P₂O₅ into borate and lithium borate powders improved their chemical durability significantly. Furthermore, Li₂O and P₂O₅ acted synergistically on the chemical durability when added simultaneously to borate compositions.     

Evaluation of a novel silica-supported sol–gel sorbent prepared by a surface molecular imprinting technique for the selective separation of estazolam from human plasma

A molecular imprinting polymer (MIP) based on surface modification of silica gel was prepared via the sol–gel process with 3-aminopropyltriethoxysilane and phenyltrimethoxysilane as functional monomers, and estazolam as the template. The imprinted silica sorbent was characterized by Fourier Transform Infrared Spectroscopy, surface elemental analysis, and scanning electron microscopy (SEM). An MIP of agglomerated nano-particles with multi-pores was grafted onto the surface of the silica gel after hydrolytic condensation of the siloxane. The imprinted silica sorbent was used for solid phase extraction (SPE). Using water as loading solvent, the extraction efficiency for estazolam was higher compared to the use of an organic solvent. The imprinted silica sorbent was selective not only for the template, but also for the analogue. Compared to C₁₈-SPE and liquid–liquid extraction, the MIP-SPE was the most feasible technique for extraction of estazolam from human plasma; up to 98.7?±?1.2% recovery was achieved.     

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.     

Sensing abilities of materials prepared by sol–gel technology

The advantages of the sol–gel technology are undoubtedly simplicity and versatility. It enables to obtain for example oxides in the form of layers, powders, monoliths or fibers. These materials can be successfully applied for sensing purposes due to their properties such as transparency, porosity, and high surface areas. In this article, the basis of operation of mainly optical and semiconductor sensors are presented. A brief overview of various kinds of sensors is submitted. The utility of optical fibers and planar waveguides in these systems is discussed. The paper contains also some results obtained by the authors in the field of thin film-based sensors.     

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.     

Structural and optical characterization of Ag-doped TiO2 nanoparticles prepared by a sol–gel method

Undoped and silver-doped TiO₂ nanoparticles (Ti_1?x Ag _x O₂, where x?=?0.00?C0.10) were synthesized by a sol?Cgel method. The synthesized products were characterized by X-ray diffraction (XRD), particle size analyzer (PSA), scanning electron microscope (SEM), and UV?CVisible spectrophotometer. XRD pattern confirmed the tetragonal structure of synthesized samples. Average crystallite size of synthesized nanoparticles was determined from X-ray line broadening using the Debye?CScherrer formula. The crystallite size was varied from 8 to 33?nm as the calcination temperature was increased from 300 to 800?°C. The incorporation of 3 to 5% Ag⁺ in place of Ti⁴⁺ provoked a decrease in the size of nanocrystals as compared to undoped TiO₂. The SEM micrographs revealed the agglomerated spherical-like morphology of particles. SEM, PSA, and XRD measurements show that the particles size of the powder is in nanoscale. Optical absorption measurements indicated a red shift in the absorption band edge upon silver doping. Direct allowed band gap of undoped and Ag-doped TiO₂ nanoparticles measured by UV?CVis spectrometer were 3.00 and 2.80?eV, respectively, at 500?°C.     

Physical and optical properties of organo-modified silica nanoparticles prepared by sol–gel

A comparative study on the physical and optical properties of silica nanoparticles prepared by sol–gel has been carried out. Post-modification of as-synthesized silica nanoparticles produced organo-functionalized silica nanoparticles slightly increased in size (~20%) and relatively high aggregation. However, in situ method produced sixfold bigger functionalized particles with good dispersion and less aggregation. Higher organic content was observed for in situ modified nanosilica, leading to a higher surface hydrophobicity that improved compatibility and dispersion in preparation of silica-polymer nanocomposite. Furthermore, in situ and post-modified nanosilica demonstrated a distinct optical activity, photoluminescence and UV compared to the unmodified nanoparticles.     

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.     

Preparation and microstructure evolution of diboride ultrafine powder by sol–gel and microwave carbothermal reduction method

Titanium diboride ultrafine powder was prepared from sucrose, tetrabutyl titanate and boric acid by the sol–gel and microwave carbothermal reduction method. The influence of reaction temperature, ratio of Ti to C and Ti to B on the synthesis of titanium diboride was studied. The results indicated that the carbothermal temperature, the content of carbon and the amount of H₃BO₃ show obvious effects on the formation of TiB₂. 1,300 °C was the optimum synthesis temperature and pure TiB₂ could be prepared. The microstructure of prepared TiB₂ was investigated by field emission-scanning electron microscopy (FE-SEM), which results showed that the crystalline size of the prepared titanium diboride at 1,300 °C was about 3–5 μm. The quantities of the crystalline phases of the powders prepared at different temperatures were analyzed by Rietveld refinement method. An erratum to this article can be found at     

Optical,mechanical and electrical properties of LSCF–SDC composite cathode prepared by sol–gel assisted rotary evaporation technique

Journal of Sol-Gel Science and Technology - La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) is a perovskite-type oxide that exhibits excellent mixed ionic–electronic conducting properties and is a...