Nanometer sized tantalum pentoxide fibers prepared by electrospinning

Novel, porous tantalum pentoxide (Ta₂O₅) nanofibers with 150–250 nm diameter were obtained by high temperature calcination of the as-electrospun tantalum pentoxide/poly(vinyl acetate) (PVAc) composite fibers prepared by sol–gel processing and electrospinning technique. Surface analysis, structure and elemental composition of these as-electrospun and as-calcinated Ta₂O₅ nanofibers have been studied by scanning electron microscope (SEM) equipped with an energy dispersive X-ray analysis (EDX), high resolution field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), X-ray diffraction patterns (XRD) and FT-IR. High-resolution FE-SEM images showed the porous nature of Ta₂O₅ nanofibers. EDX analysis revealed the perfect stoichiometry of the nanofibers as Ta₂O₅. A linear correlation was noted between the calcination temperature and orthorhombic crystalline phase evolution of Ta₂O₅.     

Fabrication of room temperature H2 gas sensor using pure and La: ZnO with novel nanocorn morphology prepared by sol–gel dip coating method

Nanostructured ZnO thin films with different lanthanum concentration (0, 1, 3, 5 and 10 wt%) were fabricated by sol–gel dip coating method on glass substrates. The effect of La incorporation on structural, morphological and H₂ gas sensing (room temperature) properties of the ZnO thin films was studied. Thermal behaviour of the xerogel of pure ZnO was studied by thermo gravimetric analysis/differential thermal analysis. The structural property of the films was analyzed by powder X-ray diffraction method and which revealed the presence of hexagonal structure. It emphasized that the film became (002) textured upon the 3 wt% of La incorporation onwards. The surface morphology was examined by field emission scanning electron microscopy equipped with energy dispersive X-ray spectroscopy (EDX) and it substantiated that all the films have uniform distribution of particles with novel corn like morphology. Obviously, the length of nanocorn increases with the increase of La. The elemental composition was studied by EDX spectroscopy. Photoluminescence (PL) spectra revealed that La: ZnO thin films showed a blue shift and an enhanced PL intensity over that of the pure ZnO. The H₂ gas sensitivity of the pure and La: ZnO thin films were studied towards the concentration of 1,000 ppm. 1 wt% of La incorporated ZnO thin film showed a high sensitivity (51 %) than the pure and the higher La concentration. The increase and decrease of H₂ gas sensitivity of pure ZnO upon La incorporation is also discussed in this paper.     

Examination of the concrete from an old Portuguese dam: Texture and composition of alkali–silica gel

Exudations and pop-outs were identified in the interior galleries of a large dam built in the 1960s. The samples collected were examined by a Scanning Electron Microscope. A dense material with a smooth surface and drying shrinkage cracks or a spongy texture were observed in the samples. The semi-quantitative composition was obtained by energy dispersive spectrometry (EDS) and it was concluded that this material corresponds to alkali–silica gel, composed of SiO₂–Na₂O–K₂O–CaO. A viscous white product in contact with an aggregate particle in a cone sampled from a pop-out was observed through use of the scanning electron microscope and it has characteristics similar to the gel present in the exudations and cavities. Reference is made to the potential alkali reactivity of the aggregate present in the concrete. The texture and composition of the products probably resulting from an alkali–silica reaction are presented, set out in ternary diagrams, and discussed.     

A facile route to synthesis of AgInS2 nanostructures

AgInS₂ nanoparticles have been synthesized via a facile one-step process using AgNO₃, thiosemicarbazid (TSC) and InCl₃·4H₂O as starting reagents from propylene glycol solution. The effects of concentration of precursors, reaction time and type of sulfur sources on the morphology and particle size were also studied. X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX), scanning electron microscope (SEM), transmission electron microscope (TEM), ultraviolet-visible spectroscopy (UV-Vis) and photoluminescence (PL) spectroscopy were used to characterize the obtained products.     

Performance of ground clay brick in ASR-affected concrete: Effects on expansion, mechanical properties and ASR gel chemistry

The effects of ground clay brick (GCB) on alkali-silica reaction (ASR) expansion as well as on mechanical properties of ASR-affected concrete are investigated. Crushed red clay brick originated from demolished masonry was ground in a laboratory ball mill and replaced for portland cement at levels of 15% and 25% by weight in concrete mixes produced with alkali reactive sand. ASR expansion, compressive strength, flexural strength, and modulus of elasticity of the concrete mixes were evaluated. Effect of GCB on ASR gel chemistry was also studied on Pyrex glass-paste specimens using SEM/EDS (scanning electron microscope equipped with energy dispersive X-ray spectroscopy). The results indicate that GCB effectively reduces ASR expansion in concrete: associated cracking and loss on mechanical properties are also significantly reduced. SEM study suggests that GCB alters alkali silica gel chemistry thus resulting in a less expansive product.     

Capability of mechanical alloying and SPS technique to develop nanostructured high Cr,Al alloyed ODS steels

Abstract

Oxide dispersion strengthened (ODS) Fe alloys were produced by mechanical alloying (MA) with the aim of developing a nanostructured powder. The milled powders were consolidated by spark plasma sintering (SPS). Two prealloyed high chromium stainless steels (Fe–14Cr–5Al–3W) and (Fe–20Cr–5Al+3W) with additions of Y₂O₃ and Ti powders are densified to evaluate the influence of the powder composition on mechanical properties. The microstructure was characterised by scanning electron microscope (SEM) and electron backscattering diffraction (EBSD) was used to analyse grain orientation, grain boundary geometries and distribution grain size. Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) equipped with energy dispersive X-ray spectrometer (EDX) were used to observe the nanostructure of ODS alloys and especially to observe and analyse the nanoprecipitates. Vickers microhardness and tensile tests (in situ and ex situ) have been performed on the ODS alloys developed in this work.     

The stability of hydroxyapatite in an optimized bioactive glass matrix at sintering temperatures

The stability of sintered hydroxylapatite particles was studied in glass matrices of the system SiO₂-CaO-P₂O₅-Na₂O-Al₂O₃-B₂O₃ at sintering temperatures between 700 and 1000 °C. The results from X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDX) analysis, transmission electron microscopy (TEM) and electron diffraction showed that above 700 °C the Na⁺ ions diffuse into the hydroxylapatite particles which then transform into rhenanite. The glass matrix undergoes crystallization yielding wollastonite crystals and a silica rich matrix.     

Studies in structural characterization of silica–heteropolyacids composites prepared by sol–gel method

Heteropolyacids (HPAs) which are included in mesoporous silica, H₃PMo₁₂O₄₀/SiO₂ and H₄PMo₁₁VO₄₀/SiO₂ have been synthesized by a sol–gel technique that involves hydrolysis of ethyl orthosilicate. The effect of incorporation of heteropolyacids species on silica matrix was studied by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and Raman spectroscopy, thermo gravimetric analysis (TGA) and differential thermal analysis (DTA), N₂ adsorption–desorption, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS).     

Synthesis of stable spherical platinum diphosphide, PtP2/carbon nanocomposite by reacting Pt(PPh3)4 at elevated temperature under autogenic pressure

The synthesis of microsized carbon spheres supporting the semiconductor platinum diphosphide, PtP₂, was conducted by the thermal decomposition of an organometallic precursor. This novel reaction was carried out using the reaction under autogenic pressure at elevated temperature (RAPET) method by dissociating Pt(PPh₃)₄ at 1000 °C. The product was characterized using methods of electron microscopy (scanning electron microscope (SEM), transmission electron microscope (TEM), selected area energy dispersive spectroscopy (SAEDS), elemental analyzer (EA) and energy dispersive X-ray analysis (EDX)) and powder-XRD. Transmission electron microscope images indicate that the particle size of the nanoparticles of PtP₂ coated on the carbon spheres is 50 nm.     

Composition and Structure of Block-Type Ferrospheres Isolated from Calcium-Rich Power Plant Ash

Polished sections of individual ferrospheres 30 to 40 μm in size, with single-block and blocky structures and a variable glass phase content, have been studied using a scanning electron microscope equipped with an energy dispersive X-ray spectrometer system. The results demonstrate that the single-block globules consist of sintered magnetite crystallites containing Al₂O₃, MgO, and CaO as impurities and are formed from the pyrite of the initial coal. Characteristically, the ferrospheres with a variable glass phase content differ in the composition of local areas on polished sections of the globules, which attests to inhomogeneity of the melt droplets they formed from. We have identified groups of globules whose overall composition, as well as the composition of their local areas, meet general equations for the interrelation between the concentrations of their components: SiO₂ = f(FeO) and SiO₂ = f(Al₂O₃). Comparison of the coefficients of the SiO₂ = f(Al₂O₃) dependence for the globules with the silicate modulus (SiO₂/Al₂O₃) of the aluminosilicate mineral components of the coal indicates that the formation of this type of globules involves pyrite–anorthite or pyrite–albite associates containing quartz impurities. The composition of the spinel ferrite in the globules produced with the participation of anorthite comprises FeO, Al₂O₃, MgO, and CaO in concentrations of 85–96, 1.7–10, 0.1–1.8, and 0.3–2.8 wt %, respectively. In the albite-based globules, the respective concentrations are 81–92, 0.7–5.9, 1.0–5.7, and 2.2–5.6 wt %. The crystallite size and shape are determined by the size of the local melt areas where the total concentration of spinel-forming oxides exceeds 85 wt %.     

Preparation of silica coated iron oxide nanoparticles using non-transferred arc plasma

Silica coated iron oxide nanoparticles were prepared using non-transferred arc plasma. The plasma was discharged with argon. Vapors of iron pentacarbonyl (Fe(CO)₅) and tetraethyl orthosilicate (TEOS, Si(OC₂H₅)₄) were injected into a plasma torch with carrier gas and reacted in the plasma chamber. In addition, two types of reaction chambers that are a hot wall reactor and a cold wall reactor were used to investigate the effect of temperature gradient on the synthesis of silica coated iron oxide nanoparticles. The synthesized nanoparticles were collected on the chamber wall and bottom. Phase compositions of the obtained nanoparticles were characterized by X-ray diffractometer (XRD) and the morphologies and the size distributions of the synthesized particles were analyzed by scanning electron microscopy (SEM) and transmission electron microscope (TEM). Additionally, elements mapping of the coated particles was performed by energy dispersive spectroscopy (EDS). The phase composition of the prepared particles was mainly composed of amorphous silica and polycrystalline Fe₃O₄. It was confirmed that the silica was adsorbed on iron oxide particles or encapsulated iron oxide particles. Furthermore, the mechanism of the formation of silica coated iron oxide in the plasma chamber was predicted.     

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.     

Excimer laser and electron beam irradiation effects in iron-doped lithium niobate

Excimer laser (=308 nm, =10 ns) and electron beam (W=7 MeV) irradiation effects in⁵⁷Fe:LiNbO₃ have been studied on samples of two crystallographic orientations. Complementary information regarding radiation induced changes to the optical absorbance of the crystal, valence states of Fe, phase composition and morphology of the irradiated regions was obtained by optical absorption measurements, Mössbauer spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, microRaman and Read thin film camera analysis. The relationship between irradiation treatment conditions and induced property modifications in iron-doped lithium niobate is reported within the frame of available defect models.     

Synthesis of metastable silver-nickel alloys by a novel laser-liquid-solid interaction technique

Metastable silver-nickel alloys have been synthesized by chemical wetness and laser-liquid-solid interaction techniques from nitrate and acetate precursors of silver and nickel. Ethylene glycol and 2-ethoxyethanol were used as reductants in the synthesis reactions. Rotating niobium substrates immersed in the liquid precursor were irradiated by a continuos wave CO₂ and Nd-YAG laser ( = 1064 nm). The powders were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and high-resolution transmission electron microscopy (HRTEM). Two-phase alloys containing silver, nickel, and oxygen were fabricated, and the shape of the particles was found to be dependent on laser parameters and the chemical composition of the precursor solution. The synthesis mechanism of non-equilibrium Ag-Ni alloy nanoparticles has been proposed to occur primarily at the laser-liquid-solid interface by a nucleation and growth mechanism.     

Preparation of flexible,hydrophobic, and oleophilic silica aerogels based on a methyltriethoxysilane precursor

We report the synthesis of flexible, hydrophobic, and oleophilic silica aerogels through a two-step acid–base sol–gel reaction followed by supercritical drying, in which methyltriethoxysilane (MTES) is used as a precursor, ethanol (EtOH) as a solvent, and hydrochloric acid (HCl) and ammonia (NH₃·H₂O) as catalysts. At the optimal molar ratio of MTES:EtOH:H₂O:HCl:NH₃·H₂O is 1:18:3.5:1.44 × 10^?4:1.2, MTES-based silica aerogels show the minimum density of 0.046 g/cm³ and the maximum compression ratio of 80 % with 15.09 kPa stress. They are superhydrophobic with a water contact angle of 157° and thermally stable up to 350 °C. We also find that they show the excellent adsorption for ethanol with a ratio of 1400 %.     

Te纳米线模板法加工Bi_2Te_3-Te片式棒热电材料(英文)

以碲纳米线为模板,采用简便的回流法大规模合成了Bi2Te3-Te片式棒一维材料,产量达到90%.利用X射线衍射、扫描电镜、X射线能谱、透射电镜对样品进行了分析.系统的研究了KOH、EDTA以及反应时间对产物结构的影响,提出了这种异质结构的形成机制.本制备方法可以推广到合成其它金属和半导体的一维特殊纳米结构.     

A novel method for synthesis of α-Si3N4 nanowires by sol–gel route

Silicon nitride (Si₃ N₄) nanowires have been prepared by carbothermal reduction followed by the nitridation (CTRN) of silica gel containing ultrafine excess carbon obtained by the decomposition of dextrose over the temperature range of 1200–1350 °C. This innovative process involves repeated evacuation followed by purging of nitrogen gas so that the interconnected nanopores of the gel are filled with nitrogen gas prior to heat treatment. During heat treatment at higher temperatures, the presence of nitrogen gas in the nanopores of the gel starts the CTRN reaction simultaneously throughout the bulk of the gel, leading to the formation of Si₃ N₄ nanowires. The in situ generated ultrafine carbon obtained by the decomposition of dextrose decreases the partial pressure of oxygen in the system to stabilize the nanowires. The nanowires synthesized by this process are of ∼500 nm diameter and ∼0.2 mm length. The product was characterized by scanning electron microscope (SEM), energy dispersive x-ray analysis (EDX), x-ray diffraction (XRD) and infrared (IR) spectra.     

Diffusion bonding between Ti‐6Al‐4V alloy and interstitial free steel

This work deals with diffusion bonded joints between Ti–6Al–4V alloy and interstitial free (IF) steel at different temperatures under a pressure of 5 MPa for 30 min. The effect of bonding temperature on the microstructure and mechanical properties of the joint interface was investigated using optic microscopy, a scanning electron microscope (SEM) equipped with X‐ray energy dispersive spectrometer (EDS) and shear strength measurements. The intermetallic phases such as FeTi and Fe₂Ti occurred at the interface of bonded specimens. In addition, it was seen that shear strength of bonded specimens decreased with increasing temperature due to growing intermetallics.     

Corrosion behaviour of copper in LiBr solutions – surface examination

Optical microscope (O.M) and scanning electron microscope (SEM) equipped with energy dispersive X‐ray (EDX) were used to follow the changes that occurred on the surfaces of copper after treated electrochemically in concentrated solutions of LiBr (up to 9 M). Results showed the existence of protective film of CuO and Cu(OH)₂ which are recorded during the passive film formation in 5 × 10^–1 M LiBr at 200 mV. At 1 M LiBr and during the partial passive region (600 mV) a porous film of Cu₂O with a small ratio of CuOH and Cu(OH)₂ were detected which confirmed the higher current density recorded. On the other hand and at the same concentration (1 M LiBr at 1000 mV), surface examination confirmed the detection of CuBr₂ with small ratio of CuO which explain the deleterious effect of bromide and the autocatalytic dissolution of Cu at this higher potential. At higher concentrations from 4 to 9 M, the film formed is non homogeneous with a more porous structure which is mainly CuBr and some area of the film suffered from cracking. This proves the general dissolution through the complexing formation of soluble CuBr₂^–.     

A novel method for synthesis of α-Si3N4 nanowires by sol–gel route

Abstract

Silicon nitride (Si₃ N₄) nanowires have been prepared by carbothermal reduction followed by the nitridation (CTRN) of silica gel containing ultrafine excess carbon obtained by the decomposition of dextrose over the temperature range of 1200–1350 °C. This innovative process involves repeated evacuation followed by purging of nitrogen gas so that the interconnected nanopores of the gel are filled with nitrogen gas prior to heat treatment. During heat treatment at higher temperatures, the presence of nitrogen gas in the nanopores of the gel starts the CTRN reaction simultaneously throughout the bulk of the gel, leading to the formation of Si₃ N₄ nanowires. The in situ generated ultrafine carbon obtained by the decomposition of dextrose decreases the partial pressure of oxygen in the system to stabilize the nanowires. The nanowires synthesized by this process are of ～500 nm diameter and ～0.2 mm length. The product was characterized by scanning electron microscope (SEM), energy dispersive x-ray analysis (EDX), x-ray diffraction (XRD) and infrared (IR) spectra.