Flux growth of silicates with vapour transported silicon

As a result of a proposed vapour transport mechanism, silicate crystals have been grown from fluxed melts which originally contained only trace amounts of silicon. The melts were contained in platinum crucibles in a sillimanite, Al₂SiO₅, muffle, and the flux consisted of PbF₂, or PbF₂ + PbO, occasionally with additional MoO₃. It is postulated that a volatile siliceous species resulted from the reaction of PbF₂ vapour with the muffle and that this species transported Si into the fluxed melts. The silicate crystals produced include Er₂SiO₅, Dy₂SiO₅, Mg₂SiO₄·MgF₂, a new material of formula Dy₄SiO₈, and several new rare earth compounds with the apatite structure.     

An infrared spectroscopic study of vacuum-evaporated SiO-CeO2 thin films

Infrared spectra of vacuum-evaporated SiO-CeO₂ thin films are reported for a series of thin films of varying compositions. They show a systematic shift of the SiO “O stretch” frequency from a value of 1040 cm^?1 in the pure (100 mol %) SiO film to 950 cm^?1 in the 16 mol % SiO84 mol % CeO₂ film, as well as a gradual diminishing of the band at 876 cm^?1 with increasing CeO₂ concentration. After introducing the general perspective for the analysis of the infrared spectra of amorphous solids, and tetrahedrally bonded compounds in particular, it is proposed that the first two features of the spectra result from a chemical association between nonbridging oxygen atoms of the SiO network and cerium atoms. This entails the interpretation of the band at 876 cm^?1 as being due to the stretching vibrations of the non-bridging oxygen atoms. The effect of annealing on the spectra is also presented and explained in terms of creation of new Si-O-Si linkages.     

Synthesis,structural and optical characterization of ZrO2 core–ZnO@SiO2 shell nanoparticles prepared using co-precipitation method for opto-electronic applications

Nanocrystalline Zirconia (ZrO₂) and Zinc oxide (ZnO) as well as Silica (SiO₂) coated ZrO₂ core–shell structures were synthesized by both Co-precipitation and seeded polymerization technique. The phase analysis and the core–shell structure formation were confirmed by X-ray diffraction (XRD), FESEM and high resolution transmission electron microscopy (HRTEM) analysis. The existence of SiO₂ on ZrO₂@ZnO was characterized by FT-IR measurement. UV–Vis study reveals coating of ZnO over Zirconia shows red shift in the absorption spectra. Photoluminescence studies show the non-monotonous variation in luminescence behavior of these core–shell nanoparticles. This investigation explains that the interfacial effect between the core (ZrO₂) and the shell materials (ZnO and SiO₂) can be exploited to tune the optical properties of the material. This implies that we can envisage the core–shell materials as potential candidates for optical–electronic devices.     

Enhancing the antifouling property of poly(vinylidene fluoride)/SiO2 hybrid membrane through TIPS method

PVDF/SiO₂ hybrid membranes with outstanding antifouling property were prepared from PVDF/glycerol triacetate system via thermally induced phase separation method, and characterized by scanning electron microscope, energy dispersive X-ray spectrometer analyses, differential scanning calorimeter, and wide angle X-ray diffraction. Their properties such as permeability, porosity, pore size distribution, and mechanical performance were also determined. The results show that SiO₂ nanoparticles modified by 3-aminopropyltriethoxysilane can be uniformly dispersed in membranes due to improved compatibility between PVDF solution and nanoparticles. The addition of SiO₂ particles to PVDF/glycerol triacetate mixture has a strong effect on crystallinity of the resulting hybrid membrane, which does not affect the type of PVDF crystal structure. Water flux recovery ratio is significantly increased from 11.7 % for pure PVDF membrane to 93.8 % for PVDF/SiO₂ hybrid membrane with addition of 8 wt% modified SiO₂. This remarkable promotion is related to the implantation of SiO₂ nanoparticles into the inner surface of membrane, which effectively restrains the adsorption of bovine serum albumin on the pore walls and improves antifouling property of the final membranes. Additionally, pure water flux of the hybrid membrane is increased by 276 %, i.e., from 85 to 320 L m^?2 h^?1, tensile strength is increased by 26.5 %, and elongation at break is increased by 85.4 % compared with that of pure membrane.     

Effect of pressure on the phase composition of Li(Na)/W/Mn/SiO2 composites and their catalytic activity for oxidative coupling of methane

The phase state of Li/W/Mn/SiO₂ and Na/W/Mn/SiO₂ composites after exposure to high pressures (2.5 GPa at 500°C) and subsequent exploitation in oxidative coupling of methane (OCM) was studied. Comparison of the catalytic activity of the composites before and after exposure to high pressures indicates that the formation of Li(Na)/W/Mn/SiO₂ composites catalytically active for OCM is significantly influenced by high pressures.     

Deposition of ZnO thin films on Si by RF magnetron sputtering with various substrate temperatures

Undoped ZnO thin films were successfully deposited on Si substrates by RF magnetron sputtering with different substrate temperatures. The dependence was systematically investigated the structural, morphology, chemical state and optical properties of ZnO thin films. Crystal quality, growth orientation and optical properties of ZnO thin films were improved at proper substrate temperature (450 °C) whereas were deteriorated at higher temperature (600 °C). X-ray photoelectron spectroscopy showed that proper substrate temperature promoted the formation of Zn–O bonding, resulting in an improvement of film quality, while higher temperature decreased the formation of the Zn–O bonding and increased the oxygen vacancy due to formation of an amorphous SiO₂ layer at the interface of ZnO and Si, resulting in a degradation of film quality. Moreover, the amorphous SiO₂ layer is formed by oxygen related to the Zn–O bonding, mainly. Therefore, the experimental results indicate that the substrate temperature plays an important role in the deposition of ZnO film on Si substrate and needs to be carefully selected to suppress a formation of an amorphous SiO₂ layer.     

Maximum SiO2 layer thickness by utilizing polyethylene glycol as the surfactant in synthesis of core/shell structured TiO2–SiO2 nano-composites

TiO₂–SiO₂ nano-composites with the core/shell structure have been prepared by means of a technique based on an extension of well-known Stöber process. In this way, the silica coating of TiO₂ nano-particles in the presence of various commercially available surfactants of cationic, anionic and nonionic has been conducted with the aim to increase barrier properties against UV (UV blocking) radiation, in order to optimize photo-killing ability of the TiO₂ nano-particles and decline of the high photo-catalytic property of titania. The influences of varying coating parameters such as time and temperature on the silica content of nano-composites have been studied and optimum conditions for attaining a thick layer of SiO₂ have been determined. Electro-phoretic mobility measurements indicated that the silica coating shifted the iso-electric point of titania toward that of a typical pure colloidal silica. Surface elemental composition of core/shell structured TiO₂–SiO₂ nano-composites was verified by using energy dispersive X-ray analysis. It was found that maximum silica shell thickness can be obtained in the presence of polyethylene glycol as a nonionic surfactant at 80 °C for 360 min. The photo-catalytic activities were evaluated by the degradation of an aqueous solution of methylene blue under UV light irradiation. In addition, the resultant optimum nano-composites have been characterized by FESEM, TEM, BET, FTIR and UV–Vis spectroscopy.     

Highly oriented single-phase blend films of high- and low-density polyethylene

The microstructures of highly oriented drawn films of blends of high-density polyethylene (HDPE) and low-density polyethylene (LDPE) were investigated by transmission electron microscopy, electron diffraction, X-ray diffraction, and differential scanning calorimetry (DSC). The average crystal size, as well as long period, crystalline content, and melting endotherm peak, decreased as LDPE was added to the blend. When the LDPE content exceeded ～ 50%, the film texture changed from a single crystal texture to fibre symmetric. Segregation of the two polyethylenes was not detected at low LDPE contents in as-drawn or melted and recrystallized films. In the as-drawn films, a low temperature tail began to appear on endotherm melting peaks at LDPE contents ?70%, indicating the onset of segregation. In meltcrystallized films, however, two distinct melting endotherm peaks were visible for LDPE contents ?50%. An equilibrium melting point of 141° C and end surface free energy of 101 erg cm^?2 (101 × 10^?7 J cm^?2) were determined by use of the Thomson equation. The close agreement between these values and literature values for HDPE suggested that the crystals present in HDPE/LDPE blends were thermodynamically equivalent to HDPE crystals of equal size, implying that branches were excluded from the crystalline phase.     

Effects of SEBS-g-MA copolymer on non-isothermal crystallization kinetics of polypropylene

The non-isothermal crystallization kinetics of pure PP and PP/SEBS-g-MA blends up to volume fraction, Φ _d (0–0.50) was studied by differential scanning calorimetry at four different cooling rates. Crystallization parameters were analyzed by Ozawa and Liu models. The Ozawa model fits in the PP/SEBS-g-MA blends and indicates the effect of SEBS-g-MA copolymer on the crystallization process of polypropylene. Augis–Bennet model has been used to calculate activation energy, ?E, during non-isothermal crystallization process. The value of ?E decreased with SEBS-g-MA due to flexibility of SEBS-g-MA by which movements of chains of PP become easier.     

Asphalt concrete modification with waste PMMA/ATH

This paper presents recycling of waste PMMA/ATH powder in asphalt concrete mixture. Waste PMMA/ATH is generated in large amounts during shaping process of acrylic sheets. Recycling waste polymers rationally and efficiently has become one of the priorities of road pavement industry in recent years. Therefore, in this study waste PMMA/ATH powder was incorporated in an asphalt mixture. In one case waste PMMA/ATH was used as an asphalt binder modifier and in other case as a partial replacement for fine aggregate fraction. Basic performance characteristics of asphalt mixtures were evaluated by measuring material properties such as rutting potential and stripping resistance. Binder characteristics were determined also on artificially aged samples. With both modification methods, improved performance characteristics of asphalt mixture were achieved which can increase road pavement durability. Finally, waste PMMA/ATH allowed us to prepare an asphalt mixture that had strongly enhanced mechanical properties regarding to the wheel tracking test and could also have less negative effects on the environment as indicated by moisture susceptibility test results.     

New rare earth silicate crystals: Dy2MoSi2Al4O16, compounds in the systems R2O3-SiO2-PbO,and a new form of R2SiO5

The growth of crystals of a new cubic compound, Dy₂MoSi₂Al₄O₁₆, and of R₂SiO₅ (R=Dy, Tb, Gd) with a new structure is reported. Flux growth studies in the systems R₂O₃-SiO₂-PbO are also described. These have yielded single crystals of two new families of compounds: PbR₄Si₅O₁₇, with a monoclinic structure, and apatite-related phases of composition between Pb_1.4Er_2.93Si_3.6O₁₃ and Pb_1.8Er_2.5Si_3.7O₁₃ for R=Er. The compounds are characterized by X-ray powder patterns, single crystal X-ray data, and EPMA.     

Low temperature crystallization of glasses in the H2O-NaCl-dimethyl sulphoxide ternary system

The determination and application of ternary H₂O-NaCl-cryoprotective agent phase diagram information appears to offer materials scientists and biologists a unique opportunity for co-operative research. Dimethyl sulphoxide (DMSO) is a widely used cryoprotective agent and in this investigation the H₂O-NaCl-DMSO system appears to develop a glassy phase even at relatively low cooling rates (25°C min^?1) for those water-rich compositions where the ratio of DMSO to NaCl varies from 2 to 1/2. This glassy phase is relatively unstable and the kinetics of the glass-to-crystalline phase transition have been investigated and shown to be first order. Activation energies (Q) and the times required for the completion of this first order transformation have been evaluated by differential thermal analysis. Such information may be useful in interpreting the effects of long term storage on rapidly frozen biological materials perfused with DMSO.     

Porous asymmetric SiO2-g-PMMA nanoparticles produced by phase inversion

A new kind of asymmetric organic–inorganic porous structure has been proposed. Asymmetric lattices of polymer grafted silica nanoparticles were manufactured by casting and phase inversion in water. Silica nanoparticles were first functionalized with 3-(dimethylethoxysilyl)propyl-2-bromoisobutyrate, followed by grafting of poly(methylmethacrylate) (PMMA) segments, performed by atom-transfer radical polymerization. Mechanically stable self-standing films were prepared by casting a dispersion of functionalized nanoparticles in different solvents and immersion in water. The resulting asymmetrically porous morphology and nanoparticle assembly was characterized by scanning electron and atomic force microscopy. The PMMA functionalized SiO₂ hybrid material in acetone or acetone/dioxane led to the best-assembled structures. Porous asymmetric membranes were prepared by adding free PMMA and PMMA terminated with hydrophilic hydroxyl group. Nitrogen flow of 2800 L m^?2 h^?1 was measured at 1.3 bar demonstrating the porosity and potential application for membrane technology.     

Magnetic and Structural Study of FeNi3 Nanoparticles: Effect of Calcination Temperature

Bimetallic Fe–Ni alloy nanoparticles (NPs) with molar ratio of Fe to Ni 1:3 were synthesized via chemical reduction using hydrazine in aqueous solution and then calcined at different temperatures. The prepared NPs have been characterized utilizing X-ray diffraction (XRD), energy-dispersive X-ray (EDS) spectroscopy, and vibrating sample magnetometer (VSM). XRD results show that FeNi₃ NPs with face-centered cubic (FCC) crystalline structure were formed. FeNi₃ phase completely disappeared and pure NiO and NiFe₂O₄ phases observed on further heating at 550° C. VSM results reveal a superparamagnetic characteristic for the synthesized NPs when calcined at 50° C. An increased coercivity and decreased saturation magnetization has been observed with increasing calcination temperature up to 550° C.     

Phase states of Na/W/Mn/SiO2 composites at temperatures of catalytic oxidative coupling of methane

This paper analyzes phase states in the Na₂O-WO₃-MnO-Mn₂O₃ and Na₂O-WO₃-Mn₂O₃-SiO₂ systems at temperatures of oxidative coupling of methane (OCM). The results indicate that, in the case of effective OCM, Na/W/Mn/SiO₂ composite catalysts are in melt-Mn₂O₃ -tridymite (cristobalite) equilibrium.     

Effect of phenolic resin infiltration content on the structural and electrochemical properties of hierarchical porous carbons

Hierarchical porous (micro-, meso- and macro-porous) carbons (HPCs) are synthesized by a facile replica template method with phenolic resin (PR) as a carbon source and hollow mesoporous silica as a hard template. The morphology of the HPCs can be easily controlled by altering the mass ratio of PR to SiO₂ spheres. Structural characterizations reveal that a well-defined HPC with a large surface area of 1141 m² g^?1 is formed when PR/SiO₂ is 1:1. With further increasing PR infiltration content, macropores of carbons disappear while solid structures appear. A possible formation mechanism for the morphological transformation of HPCs is proposed. The effect of phenolic resin infiltration content on the electrochemical properties of HPCs-based materials as supercapacitor electrodes is further evaluated. The HPCs-1(PR/SiO₂ = 1) electrode exhibits the highest specific capacitance of 256 F g^?1 due to its faster diffusion of electrolyte ions and lower charge transfer resistance. The relationship between the morphology and the electrochemical behavior of HPCs is also elucidated.     

Structure of reconstituted collagen hollow fibre membranes

Small- and wide-angle X-ray scattering (SAXS and WAXS) methods were employed to study the structure of reconstituted collagen hollow fibre membranes and the changes that ensue upon entry of water. The tails of the SAXS curves were analysed and were shown to obey Porod's Law. WAXS and water absorption measurements as a function of relative humidity were combined with density measurements to determine the relative volume fractions of water in the “free” and “bound” states. Treating the hollow fibre as a two phase system and employing Porod's Law, average length parameters transverse to the fibre axis were extracted for the collagen fibrils and the water filled pores. All this information was synthesized to yield a model of the structural changes in the hollow fibre caused by water. Implications of such a model for qualitative and quantitative prediction of changes in properties were studied.     

Nanoscale structuration and optical properties of thin gold films on textured FTO

In this work, we propose a methodology to synthesize metallic nanoparticles on textured Fluorine Tin Oxide (FTO) surface by laser irradiations of deposited Au films. In particular, the breakup of the Au films into nanoparticles (NPs) is observed as a consequence of the melting and solidification processes induced by laser irradiations. The mean Au NPs size and surface density evolution are analyzed as a function of the laser fluence. Optical characterizations of the glass/FTO/Au NPs multilayer show, in the absorption spectra, plasmonic peaks due to the Au NPs and an improvement of the light absorption efficiency from the sample with larger Au NPs. The simulated trends of the ratio between the scattering and absorption cross section suggest that the absorption efficiency dominates over the scattering efficiency in the spectral range between 200 and 600 nm. The simulation shows that, by varying the NPs radius from about 18 to 24 nm, the radiation-scattered intensity remains symmetric in forward and reverse directions. These results indicate that the surface coverage size distribution of Au NPs is the key parameter to correlate the structural and optical properties of the glass/FTO/Au NPs multilayer. Furthermore, electrical characterizations highlight a reduction in the sheet resistance of the textured FTO due to the presence of the NPs. We compare these results with those obtained for the same systems when standard furnace annealing processes are used to obtain the Au NPs on the textured FTO surface.     

Performance improvement of pentacene organic field-effect transistor through introducing polymer buffer layers

Pentacene organic field-effect transistors (OFETs) employing poly(methyl methacrylate) (PMMA), polystyrene and polyvinylidene fluoride as the electrode buffer layers by simple spray-coating fabrication process were systematically investigated. Significant performance enhancement of the OFETs was obtained. By analyzing the morphologies of pentacene films grown on gold electrodes and the electrical characteristics of these OFETs, the performance improvement was attributed to the uniform and hydrophobic properties of polymer surface, leading to a remarkable reduction of contact resistance at the pentacene/electrodes interface. Moreover, the results showed that the device employing PMMA as the electrode buffer layer exhibited the highest hole mobility of 0.59 cm²/Vs, which was almost five times of the control one. Such effect was ascribed to the optimal surface energy and appropriate dielectric constant of PMMA, which were favorable for the growth of pentacene crystal and responsible for the highest performance of OFET using PMMA as the electrode buffer layer.     

Influence of Al2O3/SiO2 ratio on the microstructure and properties of low temperature co-fired CaO–Al2O3–SiO2 based ceramics

In this work, in order to obtain the materials for low temperature co-fired ceramics applications, CaO–Al₂O₃–SiO₂ (CAS) based ceramics were synthesized at a low sintering temperature of 900 °C. The influences of Al₂O₃/SiO₂ ratio on the microstructure, mechanical, electrical and thermal properties were studied. According to the X-ray diffractomer and scanning electron microscopy results, the addition of the Al₂O₃ is advantageous for the formation of the desired materials. Anorthite(CaAl₂Si₂O₈) is the major crystal phase of the ceramics, and the SiO₂ phase is identified as the secondary crystal phase. No new crystal phase appears in the ceramics with the increasing Al₂O₃ content. More or less Al₂O₃ addition would all worsen the sintering, mechanical and dielectric properties of CAS based ceramics. The ceramic specimen (Al₂O₃/SiO₂ = 20/18.5) sintered at 900 °C shows good properties: high bending strength = 145 MPa, low dielectric constant = 5.8, low dielectric loss = 1.3 × 10^?3 and low coefficient of thermal expansion value = 5.3 × 10^?6 K^?1. The results indicate that the prepared CAS based ceramic is one of the candidates for low temperature co-fired ceramic applications.