The influence of titania content on structure and properties of spherical mixed silica/titania particles

Spherical mixed silica/titania particles are prepared from silica/titania sol by an ultrasonic vibrator. The titania content of the samples varies from pure silica to a titania mole fraction of 0.31. Narrow size distributions with most frequent particle diameter of about 1 μm are obtained. Specific surface area and pore volume, mean pore radius as well as the meso pore size distribution are influenced by titania content. The spheres are composed of both silica and titania homogeneous distributed as it is indicated by scanning electron microscopy. X-ray diffraction studies show that the particles must be considered amorphous. Structural modifications of the framework are detected. Samples with varying refractive index may be prepared.     

Development of nanosized oxide composites for catalytic CO oxidation

Abstract

Effect of composition and morphology on the catalytic activity in CO oxidation of Co-, Cu-, Ce-containing oxide materials prepared by citrate method has been studied. It was shown that composites consist of well-dispersed oxides Со₃O₄, CuO and CeO₂ with average crystallite sizes 13–24?nm, 14–26?nm and 3–7?nm, respectively. It was established that Co-, Cu-, Ce-oxide nanocomposites demonstrated higher catalytic activity in CO oxidation in comparison with individual oxides. The ternary oxide system Со₃O₄–CuO–СеO₂ (Со:Cu:Се=10:1:1) was found to possess the highest catalytic activity due to formation finely dispersed particles of CuO and СеO₂ oxides simultaneously with nanosized Со₃O₄ species and formation of large quantity of mobile oxygen at the interfaces between the oxide nanoparticles.     

Synthesis and physico-chemical properties of composites based on nanostructured zinc oxide and polyaniline

Composites based on polyaniline and nanostructured zinc oxide were synthesized by mechanical mixing and the method of in situ polymerization and their physicochemical properties were studied. The electrical conductivity, surface structure and morphology of composites have been investigated. It is shown that the method of synthesis and quantity of filler affects the morphology and physicochemical properties of composite materials. An addition of various quantities of mineral filler to composite allows controlling conductivity of obtained materials. XRD-analysis of composite materials synthesized by in situ polymerization confirms the interaction of the components of the composite.     

Effect of boron addition on the structure and properties of iron phosphate glasses

Effects of boron addition on the glass forming characteristics, structure and properties of iron phosphate glasses with nominal compositions of xB₂O₃-(40−x)Fe₂O₃-60P₂O₅ (x = 2-20, mol%) and xB₂O₃-(100−x)[Fe₂O₃-60P₂O₅] (x = 2-20, mol%) have been investigated by DTA, XRD, IR and Mössbauer spectroscopy. Although there were some weak local surface crystallizations on especially most of the glasses in group B, all of the compositions formed glass. DTA spectra showed two exothermic peaks corresponding to crystallizations along with an endothermic glass transition peak. T_g increased with increasing B₂O₃ content for the glasses in the first series which indicates that the addition of B₂O₃ increases the thermal stability of glasses in this series while the opposite is observed in the second series. The dissolution rates of boron containing bulk glasses were found to be around 10⁻⁹ gr/cm² min which are comparable to that of the base iron phosphate glass. When the B₂O₃ content was above 14%, new bands related to BO₄ tetrahedral groups have been observed in the IR spectra. The Mössbauer isomer shift values of boron doped glasses were found to be a little lower than that of base glass but both iron ions had distorted octahedral coordination in all glasses. The fraction of Fe²⁺ ions in glasses (Fe²⁺/∑(Fe²⁺ + Fe³⁺)) was found to be 23% for the base glass while it was 10-22% for the boron doped glasses.     

Effect of synthesis method on the structure and properties of AgPO3-based glasses

The relation between ionic conductivity, glass transition temperature and structure has been investigated in silver-metaphosphate, AgPO₃, glasses synthesized under varying conditions. The key finding of this work concerns the AgPO₃ doping with up to 3 mol.% Al₂O₃ when melting is done in alumina crucibles, a practice used widely for the synthesis of fast ion conducting glasses. Vibrational spectroscopy showed that Al₂O₃-doping increases the phosphate network connectivity by P-O-Al-O-P cross-links. This effect causes a drastic enhancement in ionic conductivity and glass transition temperature relative to Al₂O₃-free AgPO₃ glasses obtained by melting in Pt crucibles.     

Effect of growth temperature on the structure and optical properties of ZnO nanorod arrays grown on ITO substrate

ZnO nanorod arrays have been successfully prepared on ITO substrate by a chemical‐bath deposition method at different growth temperatures. The influence of the growth temperature on the morphology and microstructure of the ZnO nanorods was investigated by scanning electron microscopy (SEM) and X‐ray diffraction (XRD). The results showed that the diameter of the ZnO nanorods decreased and the size of the nanocrystals increased with increasing growth temperature. Optical absorption measurements showed the absorption band edge has shifted to a lower‐energy region due to the quantum size effect. Green emission and UV emission bands were observed and they are found to be temperature dependent, which indicates that the deep‐level emission and band‐edge emission of ZnO nanorods is closely related to the rod diameter, and the related mechanism is discussed.     

Investigation of the hydrogen capacity of composites based on ZnOCu

The composites ZnOCuH(D) saturated with hydrogen (deuterium) to a content of ～1 wt % are investigated by the neutron scattering methods. Upon cooling of the samples (the ZnO matrix containing Cu crystals ～10 nm in size) from 300 to 4 K, hydrogen (deuterium) is condensed on the cluster surface and penetrates inside the clusters in which the atomic hydrogen content with respect to copper can be as high as 30% at 20 K. Simultaneously, hydrogen fills nanopores of the ZnO matrix. It is revealed that, at temperatures of 90–300 K, approximately one-third of the hydrogen amount participates in the fast diffusion (the diffusion constant is approximately equal to 8 × 10^?5 cm²/s) and the other two-thirds are immobilized. At 20 K, the fraction of mobile hydrogen decreases to ～10%. An analysis of the results obtained demonstrates that the energy barriers retaining hydrogen in defect regions are relatively low.     

Effect of super-heat treatment and quenching wheel speed on the structure and magnetic properties of Fe-Si-Nb-Cu-B-Al-Ge melt spun ribbons

In this work an attempt is made to study the effect of super-heat temperature and quenching wheel speed on the structure and magnetic properties of the Al/Ge substituted FINEMET alloy. In this respect, various as-spun ribbons were prepared at two different super-heat temperatures (150 and 250 °C) and various quenching wheel speeds (20, 30 and 40 m/s). Based on the results obtained, it was shown that both the super-heat temperature and wheel speed play an important role in the control of the level of amorphicity and of magnetic properties of the as-spun ribbons. Further, it was seen that the higher was the super-heat temperature/quenching wheel speed the higher was the degree of amorphicity giving rise to a lower magnetic saturation induction/magnetic permeability and higher coercivity for the ribbons prepared.     

Preparation and analysis of multilayer composites based on polyelectrolyte complexes

A method for preparing multilayer film composites based on chitosan has been developed by the example of polymer pairs: chitosan–hyaluronic acid, chitosan–alginic acid, and chitosan–carrageenan. The structure of the composite films is characterized by X-ray diffractometry and scanning electron microscopy. It is shown that the deposition of a solution of hyaluronic acid, alginic acid, or carrageenan on a chitosan gel film leads to the formation of a polyelectrolyte complex layer at the interface, which is accompanied by the ordering of chitosan chains in the surface region; the microstructure of this layer depends on the nature of contacting polymer pairs.     

Effect of strontium substitution on the structure,ionic diffusion and dynamic properties of 45S5 Bioactive glasses

Strontium ions can promote bone growth and enhance bioactivity in bioactive glasses that find critical biomedical applications. In this paper, the effect of SrO/CaO substitution on the structure, ionic diffusion, and dynamic properties of 45S5 bioactive glasses has been studied using constant pressure molecular dynamics simulations with a set of effective partial charge potentials. The simulated structure models were validated by comparing with experimental neutron diffraction results. It was found that the SrO/CaO substitution leads to an increase of glass density and decrease of oxygen density, a measure of compactness of the glass, in excellent agreement with available experimental data. On the other hand, the substitution does not significantly change of the medium range glass structures as characterized by silicon and phosphorous Q_n distributions, network connectivity, and ring size distributions. The diffusion and dynamic behavior of these glasses and their melts were also determined by calculating the mean square displacements and velocity autocorrelation functions. It was found that the diffusion energy barriers of sodium, calcium and strontium ions remain nearly constant with respect to the level of substitution. However, strontium ions do influence the diffusion behaviors of calcium and sodium ions at high temperature, as evidenced from their velocity autocorrelation functions. Like calcium and sodium, strontium ions only contribute to the lower frequency (around 100 cm^? 1) of the vibrational spectra the substitution has little effect on high frequency features and the general shape of the vibrational density of states. These results suggest that the increase of the dissolution rate in strontium containing glasses are mainly due to the increase of free volume and the non-local effect that weakens the silicon-oxygen network due to strontium ions.     

Effect of grain size on the electrical properties of ultraviolet photodetector with ZnO/diamond film structure

Highly c-axis-oriented ZnO films were successfully deposited on the nucleation sides of freestanding diamond films by RF reactive magnetron sputtering. I–V characteristics of ultraviolet (UV) photodetectors with ZnO/diamond structure were studied and a significant photoresponse was observed under UV light illumination. The dark-current and the photocurrent of the ZnO photodetectors were relative to the grain size and the quality of ZnO films. For the photodetector with a bigger grain size, a weaker dark current and a stronger photocurrent were obtained under 10 V bias voltage. The photocurrent rise and decay process confirmed the carrier-trapping effect.     

Prediction of piezoelectric properties of crystal-ceramic composites

In the framework of the model of a piezoelectrically active ferroelectric crystal-ceramic composite of the 0–3 type, the concentration dependences of the effective piezoelectric properties of this composite are determined. Two examples of such composites are discussed: the single-domain PbTiO₃ crystal (Pb_{1 ? x}Ca _itx)TiO₃ ceramic and the polydomain PbTiO₃ crystal (Pb_{1 ? x}Ca_x)TiO₃ ceramic. Based on these examples, we analyzed the effect of the 90° domain structure, the form of crystalline inclusions, the remanent polarization of the ceramics, molar Ca concentration (x), and other factors of the effective piezoelectric coefficients e _3j ^* and d _3j ^* and and their anisotropy. The relation between the piezoelectric polarization of the composite to single-domain inclusions and the anisotropy of its piezoelectric coefficients is also studied.     

Growth,structure, and some transport properties of topological insulators based on bismuth chalcogenide single crystals

Single crystals of topological insulators—bismuth chalcogenides Bi₂Te₃, Bi_{2 ? x} Sn _x Te₃, Bi₂Se₃, and Bi_{2 ? x} Cu _x Se₃ with different charge-carrier densities—are grown by the modified Bridgman method. Their composition and structure are investigated and temperature dependences of the electric resistance and magnetic field dependences of the Hall voltage are obtained.     

Influence of thermal history on the structure and properties of silicate glasses

We studied a set of float glass samples prepared with different fictive temperatures by previous annealing around the glass transition temperature. We compared the results to previous measurements on a series of amorphous silica samples, also prepared with different fictive temperatures. We showed that the modifications on the structure at a local scale are very small, the changes of physical properties are moderate but the changes on density fluctuations at a nanometer scale are rather large: 12% and 20% in float glass and silica, for relative changes of fictive temperature equal to 13% and 25% respectively. Local order and mechanical properties of silica vary in the opposite way compared to float glass (anomalous behavior) but the density fluctuations in both glasses increase with temperature and fictive temperature.     

Preparation and characterization of nickel based catalysts on silica,alumina and titania obtained by sol–gel method

This work reports the investigation of the characteristics of catalysts produced by the sol gel process. Our analysis focuses on the properties related to heterogeneous catalysis, such as methane steam reforming, dry reforming, hydrogenation of organic compositions. Alumina, silica and titania based materials doped with Ni were synthesized. The characterization techniques used were: temperature programmed reduction, thermogravimetric analysis, specific surface area and X-ray powder diffraction. The specific surface area values obey the following sequence: Ni–SiO₂ > Ni–Al₂O₃ > Ni–TiO₂. The temperature programmed reduction indicated that in the Ni–SiO₂ sample, the nickel oxide is present in two different forms on the surface; the Ni–Al₂O₃ material presented one peak at high temperature, suggesting the presence of a nickel aluminate form. However, Ni–TiO₂ did not present reduction peaks. The thermogravimetric analysis, which was performed under inert atmosphere, showed the decomposition of the organic residues adsorbed on surface. The X-ray powder diffraction patterns of calcined materials showed two crystalline forms for TiO₂ in Ni–TiO₂ rutile and anatase. In Ni–Al₂O₃, crystalline areas composed of α-Al₂O₃, γ-Al₂O₃ and NiO were observed and finally for Ni–SiO₂, amorphous areas and NiO were found.     

Electrosynthesis and properties of poly(3-methylthiophene-pyrrole) composites

Poly(3-methylthiophene/overoxidized pyrrole) (PMT/OPPy) composites were electrochemically prepared by simultaneous polymerization of 3-methylthiophene and pyrrole, which were added together at a 10:1 concentration ratio into a non-aqueous medium (acetonitrile). The films were characterized by cyclic voltammetry, spectroscopic (FTIR, UV-VIS, and photocurrent) and current-voltage measurements, and with atomic force microscopy (AFM). The PMT/OPPy films exhibited intermediate characteristics than those seen for the homopolymers, OPPy and PMT, but with PMT as the predominant element of the PMT/OPPy composition. Optical, morphological, and electrical properties of the OPPy, PMT, and PMT/OPPy films were compared aiming toward application in optoelectronic devices and sensors.     

Characteristics of composites based on PMMA modified gel silica glasses

Gel silica glass prepared by the sol-gel process can be modified by incorporating an organic phase into the intrinsically porous inorganic gel matrix, which results in a composite material with much improved mechanical and optical properties. Characterisation of PMMA modified gel silica glass prepared by the in situ polymerisation method using FT-Raman spectroscopy, gel permeation chromatography and the nitrogen adsorption technique are reported. Some essential problems encountered in the preparation are discussed.     

Effects of addition of nitrogen on bioglass properties and structure

Bioglasses have been developed for use in surgery because of their ability to form a hydroxy-carbonate apatite (HCA) layer on their surface which facilitates bonding to natural bone. However, they do not have sufficient strength for use in load-bearing situations and therefore improving their mechanical properties would allow their use in more robust applications. The purpose of this work was to study the effects of nitrogen addition on the physical and mechanical properties and the structure of oxynitride bioglasses based on the system Na₂O–CaO–SiO₂–Si₃N₄. The density, glass transition temperature, hardness and elastic modulus were measured and observed to increase linearly with nitrogen content. These increases are consistent with the incorporation of N into the glass structure in three-fold coordination with silicon which results in extra cross-linking of the glass network. The characterization of these oxynitride bioglasses using solid state nuclear magnetic resonance ²⁹Si MAS NMR and infrared spectroscopy have shown firstly that all the N atoms are bonded to Si atoms and secondly that this increase in rigidity of the glass network can be explained by the formation of SiO₃N, SiO₂N₂ tetrahedra and Q⁴ units with extra bridging anions at the expense of Q³ units. The oxynitride bioglasses in simulated body fluid form a hydroxy-carbonate apatite (HCA) layer on their surfaces showing that bioactivity is retained.     

Influence of sodium dodecylbenzene sulfonate on the structure and properties of carbon aerogels

This letter describes the effects that the surfactant, sodium dodecylbenzene sulfonate (SDBS), has on the structure and electrical properties of monolithic carbon aerogels (CA). Using organic sol-gel chemistry, a series of novel CA materials prepared with different concentrations of SDBS were characterized to evaluate the influence the surfactant had on the network structure of the resultant material. Addition of the SDBS surfactant to the sol-gel reaction mixture was shown to generate CA structures that had different pore sizes, higher densities and improved electrical conductivity than those prepared without the surfactant. These results are discussed in comparison with relevant sol-gel literature and theory.