Preparation and characterization of epoxy/γ-aluminum oxide nanocomposites

Epoxy/γ-Al₂O₃ nanocomposites were prepared with a homogenizer and followed by a stepwise thermal curing process in this study. The dispersion of γ-Al₂O₃ nanoparticles was examined with a transmission electron microscopy (TEM). Meanwhile, the effects of γ-Al₂O₃ nanoparticles on thermal, dynamic mechanical and tensile properties of epoxy/γ-Al₂O₃ nanocomposites were also investigated and discussed. When the γ-Al₂O₃ content was increased from 1phr to 5phr, results revealed that γ-Al₂O₃ nanoparticles were effective to enhance both the stiffness and toughness of epoxy resin. Meanwhile, the maximum properties of glass transition temperature (T_g), T_d5%, storage modulus, tensile modulus, and elongation at break were observed in the epoxy/5phr γ-Al₂O₃ nanocomposite.     

Effects of environment on creep behavior of two oxide/oxide ceramic–matrix composites at 1200 °C

The tensile creep behavior of two oxide/oxide ceramic–matrix composites (CMCs) was investigated at 1200 °C in laboratory air, in steam, and in argon. The composites consist of a porous oxide matrix reinforced with laminated, woven mullite/alumina (Nextel™720) fibers, have no interface between the fiber and matrix, and rely on the porous matrix for flaw tolerance. The matrix materials were alumina and aluminosilicate. The tensile stress–strain behavior was investigated and the tensile properties were measured at 1200 °C. Tensile creep behavior of both CMCs was examined for creep stresses in the 80–150 MPa range. Creep run-out defined as 100 h at creep stress was achieved in air and in argon for stress levels ≤100 MPa for both composites. The retained strength and modulus of all specimens that achieved run-out were evaluated. The presence of steam accelerated creep rates and reduced creep life of both CMCs. In the case of the composite with the aluminosilicate matrix, no-load exposure in steam at 1200 °C caused severe degradation of tensile strength. Composite microstructure, as well as damage and failure mechanisms were investigated. Poor creep performance of both composites in steam is attributed to the degradation of the fibers and densification of the matrix. Results indicate that the aluminosilicate matrix is considerably more susceptible to densification and coarsening of the porosity than the alumina matrix. The views expressed are those of the authors and do not reflect the official policy or position of the United States Air Force, Department of Defense or the U.S. Government.     

An AlGaAs/GaAs oxide‐stripe double‐heterostructure laser

Abstract

An AlGaAs/GaAs oxide‐stripe double‐heterostructure (DH) laser is fabricated by liquid‐phase epitaxy (LPE) successfully. This laser consists of four epilayers, i.e., (N) Al_0.35Ga_0.65As cladding layer, (p) Al_0.05Ga_0.95As active layer, (P) Al_0.35Ga_0.65As cladding layer and (p) Al_0.05Ga_0.95As contact layer, and a top SiO₂ insulating layer. The stripe window opened through the SiO₂ layer is either 5 or 10 μm wide. The emission properties of the laser diodes were all measured under pulse mode. The lowest threshold current measured is 95 mA for a 10, μm‐wide stripe laser which corresponds to a threshold current density of 3,200 A/cm². The best power output is more than 30 mW per facet with a differential quantum efficiency of 10% per facet. In addition, the single filament operation is also observed in a 5 μm‐wide stripe laser. The lasing wavelength is centered around 8,500 Å.     

Reaction of tantalum oxide with calcium chloride–calcium oxide melts

Tantalum oxide is a suitable precursor for electro-deoxidation, where a cathodic potential is applied to the oxide, immersed in a molten salt, to remove oxygen from the oxide leaving tantalum metal. The electro-deoxidation reactions take place in a melt of CaCl₂–CaO and, unlike the reduction of other metal oxides where little or no reaction occurs between the melt and oxide until the application of a cathodic potential, tantalum oxide readily reacts with the calcium oxide to form CaTa₄O₁₁, CaTa₂O₆ and Ca₂Ta₂O₇. These phases have completely different morphologies which convert a robust pellet into a collection of poorly connected particles.     

Preparation and tribological properties of polyurethane/α-aluminum oxide hybrid films

This study focused on the preparation and tribological properties of polyurethane/α-aluminum oxide (PU/α-Al₂O₃) hybrid films. PU/α-Al₂O₃ hybrid films containing various nanoscaled α-Al₂O₃ contents were prepared by an effectively mechanical stirring method. The tribological properties of PU/α-Al₂O₃ hybrid films were investigated by a TABER type abrasion tester after 2000 cycles. The results of abrasion tests showed the abrasion resistance of the PU/α-Al₂O₃ hybrid film was increased as the α-Al₂O₃ content was increased. The abrasion resistance of the PU/α-Al₂O₃ hybrid film was significantly improved up to 27.4% by adding 2 wt.% nanoscaled α-Al₂O₃ particles. The surface morphologies of PU/α-Al₂O₃ hybrid films, before and after abrasion tests, were examined by scanning electron microscopy (SEM). For the loading of 2 wt.% α-Al₂O₃ particles, the SEM image of the worn surface of the PU/α-Al₂O₃ hybrid film showed much smoother than those of pure PU film and other PU/α-Al₂O₃ hybrid films.     

Tribological performance of carbon nanotube–graphene oxide hybrid/epoxy composites

An investigation is conducted on the effect of the hybrid of multi-wall carbon nanotubes (MWCNTs) and graphene oxide (GO) nanosheets on the tribological performance of epoxy composites at low GO weight fractions of 0.05–0.5 phr. The MWCNT amount is kept constant at 0.5 phr, which is typical for CNT/epoxy composites with enhanced mechanical properties. Friction and wear tests against smooth steel show that the introduction of 0.5 phr MWCNTs into the epoxy matrix increases the friction coefficient and decreases the specific wear rate. When testing the tribological performance of MWCNT/GO hybrids, it is shown that at a high GO amount of 0.5 phr, the friction coefficient is decreased below that of the neat matrix whereas the wear rate is increased above that of the neat matrix. At an optimal hybrid formulation, i.e., 0.5 phr MWCNTs and 0.1 phr GO, a further increase in the friction coefficient and a further reduction in the specific wear rate are observed. The specific wear rate is reduced by about 40% down to a factor of 11 relative to the neat epoxy when the GO content is 0.1 phr.     

One step synthesis of β-FeOOH nanowire bundles/graphene oxide nanocomposites

A nanocomposite of graphene oxide (GO) and β-ferric oxyhydroxide (β-FeOOH) nanowire bundles is synthesized by in situ hydrolysis of the precursor ferric chloride and GO nanosheets. Characterization by X-ray diffraction, transmission electron microscopy, and thermogravimetric analysis established the composite structure of the synthesized sample. The results revealed that the surface of GO nanosheets was uniformly assembled by numerous nanowire bundles with diameters in the range of 30–50 nm and lengths of 100–150 nm. Furthermore, β-FeOOH/GO nanocomposites showed a very high adsorption capacity of Congo red and thus these nanocomposites can be used as good adsorbents and can be used for the removal of organic dye from the waste water system.     

Reduced graphene oxide–nickel oxide composites with high electrochemical capacitive performance

Reduced graphene oxide (RGO)–NiO composites have been fabricated by a simple solvothermal route starting with graphite oxide (GO). The morphology, composition and microstructure of the as-obtained samples are systematically characterized by thermogravimetric (TG) analysis, X-ray diffraction (XRD), and field emission scanning electron microscopy (FESEM). Moreover, the electrochemical performances of composites were evaluated by cyclic voltammogram (CV) and galvanostatic charge–discharge. Interestingly, it was found that the electrochemical performance of the composites could be affected by the mass ratio between RGO and NiO. The composite with the mass ratio up to 79:21 (NiO:RGO) exhibits the highest specific capacitance of 576 F g⁻¹ at 1 A g⁻¹, which is much higher than that of pure NiO (240 F g⁻¹) and pure RGO (98 F g⁻¹). In addition, the cycling measurements showed that RGO–NiO composite exhibited excellent cycling stability with no decay in the available capacity over 1100 cycles. The enhancement in specific capacitance and cycling stability may be attributed to the increased electrode conductivity owing to RGO network, the increased effective interfacial area between NiO and the electrolyte, as well as the contact area between NiO and RGO.     

Na2O对MoSi2/oxide发热元件特性的影响

为了克服半导体热处理炉中MoSi2发热元件的低温氧化问题，通过添加高Na2O粘土获得了由MoSi2/oxide复合材料制成的发热元件，考查了脱Na工艺前后MoSi2/oxide发热元件使用特性的变化。研究结果表明，脱Na工艺较好地解决了半导体制品热处理装置中石英玻璃管的失透问题，使发热元件的弯曲强度和高温蠕变特性有了明显地改善，提高了发热元件的使用寿命。     

Synthesis, characterization and oxide ionic conductivity of β-type solid solution in bismuth oxide doped with ytterbium oxide binary system

In this study, after doping Yb₂O₃ substance to α -Bi₂O₃ substance in the range of 1% ≤ n ≤ 8% in a series of different mole ratios, heat treatment was performed by applying a cascade temperature rise in the range of 700–790 °C for 48 and 120 h and new phases were obtained in the (Bi₂O₃)_1???x (Yb₂O₃) _x system. After 48 h of heat treatment at 750 °C and 120 h of heat treatment at 790 °C, mixtures containing 1–8% mole Yb₂O₃ formed a tetragonal phase. With the help of XRD, crystal systems and lattice parameters of the solid solutions were obtained and their characterization was carried out. Thermal measurements were made by using a simultaneous DTA/TG system. The total conductivity (σ _T) in the β-Bi₂O₃ doped with Yb₂O₃ system was measured using four-probe d.c. method.     

Mesoporous titanium dioxide@ zinc oxide–graphene oxide nanocarriers for colon-specific drug delivery

In this project, TiO₂@ZnO nanoparticles core–shell nanostructured and titanium dioxide@ mesoporous zinc oxide–graphene oxide (TiO₂@ZnO–GO) hybrid nanocomposites as controlled targeted drug delivery systems were synthesized by a facile sono-chemical method. We prepared a novel mesoporous and core–shell structure as a drug nanocarrier (NCs) for the loading and pH-responsive characteristics of the chemotherapeutic curcumin. The structure, surface charge, and surface morphology of NCs were studied using with X-ray diffraction, Fourier transform infrared spectroscopy, dynamic light scattering, brunauer–emmett–teller, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The SEM and TEM images of NCs show the uniform hexagonal mesoporous morphology with average grain size of about ～ 190 nm. The drug loading was very high about 16 and 19 for TiO₂@ZnO and TiO₂@ZnO–GO, respectively. The NCs showed pH-dependent drug release behavior. Drug release from TiO₂@ZnO–GO in neutral pH were higher than in acidic medium, due to anionic charge of GO nanosheet. MTT assay results showed that the curcumin-loaded NCs showed significant toxicity due to which cell viability reduced to below 50% at 140 μg/mL concentration, thereby confirming its anticancer effects. The goal of this study is the application of water-dispersed TiO₂@ZnO–GO with pH-dependent release properties for design a new drug delivery carrier.     

Synthesis and characterization of nanofiber-structured Ba0.5Sr0.5Co0.8Fe0.2O3−δ perovskite oxide used as a cathode material for low-temperature solid oxide fuel cells

Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF) was synthesized in two forms: as a powder (by the sol-gel combined citrate-EDTA complexing (CC-EDTA) method) and as nanofibers (by electrospinning). Both forms were sintered at 950 °C for 5 h in air before their morphology and structure were characterized by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and specific surface area analysis based on the BET theory. Moreover, the mass loss and heat flow of as-electrospun BSCF nanofibers were analyzed by differential thermal analysis (DTA) and thermogravimetric analysis (TG). The results showed that these materials had a perovskite oxide crystal structure. The CC-EDTA method yielded BSCF in powder form, with a particle size of 1-10 μm and a specific surface area of 1.0 m²/g. On the other hand, BSCF obtained by the electrospinning technique was in the form of highly porous nanofibers with diameters in the range of 100-200 nm and a specific surface area of 2.4 m²/g. To demonstrate the potential applications of BSCF as a cathode material in low-temperature solid oxide fuel cells (LT-SOFCs), the electrochemical properties of the samples were determined using electrochemical impedance spectroscopy (EIS). The area specific resistance (ASR) of the BSCF nanofiber cathode was determined to be 0.094 Ω cm² at 600 °C, whereas that of the BSCF powder cathode was 0.468 Ω cm² under similar conditions.     

Effect of zinc oxide concentration on the core–shell ZnS/ZnO nanocomposites

In this work, synthesis and characterization of core–shell zinc sulphide (ZnS)/zinc oxide (ZnO) nanocomposites has been reported to see the effect of ZnO concentration in core–shell combination. The nascent as well as core–shell nanostructures were prepared by a chemical precipitation method starting with the synthesis of nascent ZnS nanoparticles. The change in morphological and optical properties of core–shell nanoparticles was studied by changing the concentration of ZnO for a fixed amount of ZnS. The nascent ZnS nanoparticles were of 4–6 nm in diameter as seen from TEM, each containing primary crystallites of size 1.8 nm which was estimated from the X-ray diffraction patterns. However, the particle size increases appreciably with the increase in ZnO concentration leading to the well known ZnO wurtzite phase coated with FCC phase of ZnS. Band gap studies were done by UV–visible spectroscopy and it shows that band gap tunability can be achieved appreciably in case of ZnS/ZnO core–shell nanostructures by varying the concentration of ZnO. Fourier transform infrared analysis also proves the formation of core–shell nanostructures. Photoluminescence studies show that emission wavelength blue shifts with the increase in ZnO concentration. These core–shell ZnS/ZnO nanocomposites will be a very suitable material for any type of optoelectronic application as we can control various parameters in this case in comparison to the nascent nanostructures.     

Effect of gadolinia addition on varistor characteristics of vanadium oxide–doped zinc oxide ceramics

The effect of gadolinia addition on microstructure, electrical and dielectric characteristics, and aging behavior of vanadium oxide–doped zinc oxide varistor ceramics was systematically investigated. The average grain size decreased from 5.6 to 5.2 μm with an increase in the amount of Gd₂O₃ up to 0.1 mol%, whereas a further increase caused it to increase to 5.7 μm at 0.25 mol%. The sintered densities decreased from 5.51 to 5.44 g/cm³ with an increase in the amount of Gd₂O₃. With increasing the amount of Gd₂O₃, the breakdown field increased from 4,800 to 5,365 V/cm up to 0.05 mol%, whereas a further increase decreased it to 4,781 V/cm at 0.25 mol%. The varistor ceramics modified with 0.05 mol% Gd₂O₃ exhibited excellent nonlinear properties, with 66.1 in the nonlinear coefficient, whereas a further increase caused it to decrease to 17.6 at 0.25 mol%. The gadolinium acted like a donor, based on the electron concentration increasing from 4.20 × 10¹⁷/cm³ to 7.38 × 10¹⁷/cm³ with an increase in the amount of Gd₂O₃.     

Ascorbic acid-mediated synthesis and characterisation of iron oxide/gold core–shell nanoparticles.

The current article reports on providing surface modification of magnetic nanoparticles with gold to provide stability against aggregation. Gold-coated magnetite nanoparticles were synthesised to combine both magnetic as well as surface plasma resonance (SPR) properties in a single moiety. The nanocomposites were produced by reduction (using ascorbic acid) of gold chloride on to the surface of iron oxide nanoparticles. Ascorbic acid not only acts as a reducing agent, but also the oxidised form of ascorbic acid i.e. Dehydro-ascorbic acid acts as a capping agent to impart stability to as synthesised gold-coated iron oxide nanocomposites. The synthesised nanocomposite was monodispersed with a mean particle size of around 16 nm and polydispersity index of 0.190. X-ray diffraction analysis confirms presence of gold on the surface of magnetite nanoparticles. The synthesised nanocomposites had a total organic content of around 3.2% w/w and also showed a shifted SPR peak at 546 nm as compared to gold nanoparticles (528 nm). Both uncoated and gold-coated magnetite exhibited superparamagnetic behaviour at room temperature. Upon coating with gold shell, saturation magnetisation of iron oxide nanoparticles decreases from 42.806 to 3.54 emu/gram.     

Metal nanocrystal memory with sol-gel derived HfO2 high-κ tunnel oxide

An all-solution processed metal-oxide-semiconductor (MOS) capacitor structure containing gold (Au) nanoparticles (NPs) within HfO₂ high-κ oxide was fabricated. The ultra-thin (~ 10 nm) HfO₂ high-κ tunnel oxide layer was prepared by sol-gel process and showed good electrical properties, which were critical to superior memory property of the MOS structure. Au NPs with particle size of about 3.3 nm were synthesized by chemical reduction method and then self-assembled onto HfO₂ tunnel oxide. Finally, a Si/HfO₂/Au NPs/HfO₂ memory structure was constructed after the substrate had been covered with a sol-gel-derived HfO₂ control oxide layer (~ 13 nm). By utilizing high-quality HfO₂ as tunnel oxide, the MOS structure containing Au NPs showed memory effect even at a low voltage of ± 3 V. Although its memory window was only 0.8 V by a swapping voltage between ± 5 V, the MOS showed desirable retention characteristics. Therefore, we have fabricated nanocrystal memory device with sol-gel derived HfO₂ high-k tunnel oxide which are attractive for low operation voltage non-volatile memory applications.     

Adsorptive removal of trinitrophenol using nano α-Fe2O3/reduced graphene oxide

Abstract

2,4,6-Trinitrophenol (TNP), an explosive utilized for artillery munitions, ends up polluting water and soil. This study targets the treatment of TNP contaminated water via adsorption technique. A comparative adsorption study using pristine rGO (reduced graphene oxide), α-Fe₂O₃/rGO, bare α-Fe₂O₃ and physical mixture of α-Fe₂O₃ & rGO has been carried to select the most suitable adsorbent. To understand the mechanism of adsorption of TNP on α-Fe₂O₃/rGO adsorption isotherms were applied on adsorption data. The adsorption kinetics followed pseudo second order kinetic model. The mechanism of adsorption changed significantly with change in pH. The maximum adsorption capacity was found to be 769.23?mg?·?g^?1. Regeneration studies indicated that the adsorbent can be used up to 3 times without significant decrease in adsorption efficiency. Magnetic nature of adsorbent allowed its easy segregation from the contaminant solution upon application of external magnetic field. To assess the adsorption efficacy of α-Fe₂O₃/rGO in real water under ambient condition, TNP was spiked in ground water samples collected from adjoining district that had high TDS (Total dissolved solids). The Langmuir adsorption capacity of 164.24?mg?·?g^?1 was attained with substantial decrease in TDS. Thus α-Fe₂O₃/rGO proves to be an efficient adsorbent for nitrophenols and can be used commercially for waste water treatment.     

The photo-electrochemical studies of Eu doped yttrium orthovanadate–zinc oxide–reduced graphene oxide nanohybrid

A new class of nanostructured photo-electrocatalyst Eu³⁺ doped yttrium orthovanadate–zinc oxide–reduced graphene oxide (YVO₄:Eu³⁺–ZnO–RGO) nanohybrid was developed by a simple electrostatic self-assembly at room temperature, using ZnO, YVO₄:Eu³⁺ and RGO as building blocks. Interaction among YVO₄:Eu³⁺, ZnO and RGO is indicated by variation in hydrodynamic diameter (H_D) and zeta potentials of the products as compared to their individual components, thus suggesting that YVO₄:Eu³⁺–ZnO–RGO is a nanohybrid and not a physical mixture. Electrochemical response of this nanohybrid towards the redox couple of Fe(CN)₆^3−/4− was investigated before and after UV irradiation. Apart from quenching of the green emission of ZnO in photoluminescence spectrum, which serves as a probe to monitor the interfacial electron transfer from excited ZnO to RGO, degradation in electrochemical redox process provides an additional path to monitor interfacial electron transfer.     

Magnetic properties and Mössbauer spectra of gamma ferric oxide and doped gamma ferric oxide

Magnetic hysteresis, Mössbauer spectra and temperature variation of initial magnetic susceptibility of thirteen samples of doped -Fe₂O₃ containing cobalt or gadolinium are determined. The samples containing more than 1.0% cobalt are found to have a multi-domain configuration, and undoped -Fe₂O₃, gadolinium-doped -Fe₂O₃ and doped -Fe₂O₃ containing less than 1.0% (except 0.3%) cobalt have a single domain configuration. Mössbauer spectra of gadoliniumdoped samples suggest that gadolinium occupies A and B sites. In cobalt-doped samples, the effective magnetic fields at A and B sites are different at room temperature and liquid nitrogen temperature. The samples which have a multi-domain configuration display an additional central doublet in Mössbauer spectra indicating that these samples contain multi-domain clusters. The saturation magnetization of gadolinium-doped -Fe₂0₃ is much lower, and the coercive force of cobalt-doped samples is much higher than of gadolinium-doped and undoped samples.     

Nanoscale epitaxial growth control of oxide thin films by laser molecular beam epitaxy—towards oxide nanoelectronics

The nanoscale growth control of oxide thin films, such as ferroelectric and magnetic materials, were explored by a novel technique based on nanoscale substrate engineering as well as atomic layer control via laser molecular beam epitaxy (laser-MBE). Atomic-scale analysis of the terminating layer of perovskite oxide films was performed by in situ coaxial impact-collision ion scattering spectroscopy. The novel heteroepitaxies that could be attained were: (1) the termination-regulated molecular layer-by-layer epitaxy of BaTiO₃ and La_0.7Sr_0.3MnO₃ thin films and (2) the step-decoration epitaxy resulting in the nanowire or nanodot structures of magnetic oxides such as (Mn, Zn) ferrite on ultrasmooth sapphire substrates with straight atomic steps.