A comparative study on reactions of n-alkylamines with tungstic acids with various W–O octahedral layers: Novel evidence for the “dissolution–reorganization” mechanism

The aim of this paper was to provide a convincing experimental research to demonstrate a dissolution–reorganization mechanism for the formation of tungstate-based inorganic–organic hybrid nanobelts by comparatively investigating the reaction behaviors of H₂WO₄ and H₂W₂O₇·xH₂O with n-alkylamines (C_mH_2m+1NH₂, m = 4–10). The formation of tungstate-based hybrid nanobelts derived from the reactions between n-alkylamines and H₂WO₄ with single-octahedral W–O layers was investigated with a detailed comparison with those between n-alkylamines and H₂W₂O₇·xH₂O with double-octahedral W–O layers. H₂WO₄ and H₂W₂O₇·xH₂O reacted with n-alkylamines, respectively, in reverse-microemulsion-like media. The obtained products were characterized by XRD, FT-IR, TG–DTA and SEM. The results indicated that the products derived from H₂WO₄ and those from H₂W₂O₇·xH₂O were similar in compositions, microstructures and morphologies. The structural analysis indicated the products were tungstate-based inorganic–organic hybrid one-dimensional belts with highly ordered lamellar structures by alternately stacking organic n-alkylammonium bilayers and inorganic single-octahedral W–O layers. The n-alkyl chains in the above hybrid nanobelts from H₂WO₄ and H₂W₂O₇·xH₂O took on a bilayer arrangement with tilt angles of 65° and 74°, respectively. The similarities in the microstructures of the products from H₂W₂O₇·xH₂O and H₂WO₄ demonstrated that the double-octahedral W–O layers of H₂W₂O₇·xH₂O were decomposed during the reactions. The changes of inorganic W–O layers and the morphologic changes of the tungstic-acid precursors before and after the reactions corroborated the dissolution–reorganization mechanism.     

Fabrication of DNA-antibody–apatite composite layers for cell-targeted gene transfer

Surface-mediated gene transfer systems using apatite (Ap)-based composite layers have received increased attention in tissue engineering applications owing to their safety, biocompatibility and relatively high efficiency. In this study, DNA-antibody–apatite composite layers (DA–Ap layers), in which DNA and antibody molecules are immobilized within a matrix of apatite nanocrystals, were fabricated using a biomimetic coating process. They were then assayed for their gene transfer capability for application in a specific cell-targeted gene transfer. A DA–Ap layer that was fabricated with an anti-CD49f antibody showed a higher gene transfer capability to the CD49f-positive CHO-K1 cells than a DNA–apatite composite layer (D–Ap layer). The antibody facilitated the gene transfer capability of the DA–Ap layer only to the specific cells that were expressing corresponding antigens. When the DA–Ap layer was fabricated with an anti-N-cadherin antibody, a higher gene transfer capability compared with the D–Ap layer was found in the N-cadherin-positive P19CL6 cells, but not in the N-cadherin-negative UV♀2 cells or in the P19CL6 cells that were pre-blocked with anti-N-cadherin. Therefore, the antigen–antibody binding that takes place at the cell–layer interface should be responsible for the higher gene transfer capability of the DA–Ap than D–Ap layer. These results suggest that the DA–Ap layer works as a mediator in a specific cell-targeted gene transfer system.     

Fabrication of DNA-antibody–apatite composite layers for cell-targeted gene transfer

Abstract

Surface-mediated gene transfer systems using apatite (Ap)-based composite layers have received increased attention in tissue engineering applications owing to their safety, biocompatibility and relatively high efficiency. In this study, DNA-antibody–apatite composite layers (DA–Ap layers), in which DNA and antibody molecules are immobilized within a matrix of apatite nanocrystals, were fabricated using a biomimetic coating process. They were then assayed for their gene transfer capability for application in a specific cell-targeted gene transfer. A DA–Ap layer that was fabricated with an anti-CD49f antibody showed a higher gene transfer capability to the CD49f-positive CHO-K1 cells than a DNA–apatite composite layer (D–Ap layer). The antibody facilitated the gene transfer capability of the DA–Ap layer only to the specific cells that were expressing corresponding antigens. When the DA–Ap layer was fabricated with an anti-N-cadherin antibody, a higher gene transfer capability compared with the D–Ap layer was found in the N-cadherin-positive P19CL6 cells, but not in the N-cadherin-negative UV♀2 cells or in the P19CL6 cells that were pre-blocked with anti-N-cadherin. Therefore, the antigen–antibody binding that takes place at the cell–layer interface should be responsible for the higher gene transfer capability of the DA–Ap than D–Ap layer. These results suggest that the DA–Ap layer works as a mediator in a specific cell-targeted gene transfer system.     

NOT and NAND logic circuits composed of top-gate ZnO nanowire field-effect transistors with high-k Al(2)O(3) gate layers

Electrical characteristics of NOT and NAND logic circuits fabricated using top-gate ZnO nanowire field-effect transistors (FETs) with high-k?Al(2)O(3) gate layers were investigated in this study. To form a NOT logic circuit, two identical FETs whose I(on)/I(off) ratios were as high as ～10(8) were connected in series in a single ZnO nanowire channel, sharing a common source electrode. Its voltage transfer characteristics exhibited an inverting operation and its logic swing was?98%. In addition, the characteristics of a NAND logic circuit composed of three top-gate FETs connected in series in a single nanowire channel are discussed in this paper.     

Fabrication and characterization of microcapsules with polyamide–polyurea as hybrid shell

Well-defined microcapsules with polyamide–polyurea as a hybrid shell have been described for biomedical applications. Interfacial polymerization method with surfactant and cosurfactant was developed for the preparation of the hybrid microcapsules. After reaction, centrifugation, and freeze drying processes, the polyamide–polyurea hybrid microcapsules with porous membranes were successfully fabricated. Compared with previous researches of the single polyamide or polyurea microcapsules, experimental data showed that the hybrid microcapsules have a thicker shell and excellent mechanical property. Various diameters and morphologies for the hybrid microcapsules can be obtained by changing the stirring rate, drying method, and surfactant content.     

Mechanics and mechanisms of fatigue in a WC–Ni hardmetal and a comparative study with respect to WC–Co hardmetals

There is a major interest in replacing cobalt binder in hardmetals (cemented carbides) aiming for materials with similar or even improved properties at a lower price. Nickel is one of the materials most commonly used as a binder alternative to cobalt in these metal-ceramic composites. However, knowledge on mechanical properties and particularly on fatigue behavior of Ni-base cemented carbides is relatively scarce. In this study, the fatigue mechanics and mechanisms of a fine grained WC–Ni grade is assessed. In doing so, fatigue crack growth (FCG) behavior and fatigue limit are determined, and the attained results are compared to corresponding fracture toughness and flexural strength. An analysis of the results within a fatigue mechanics framework permits to validate FCG threshold as the effective fracture toughness under cyclic loading. Experimentally determined data are then used to analyze the fatigue susceptibility of the studied material. It is found that the fatigue sensitivity of the WC–Ni hardmetal investigated is close to that previously reported for Co-base cemented carbides with alike binder mean free path. Additionally, fracture modes under stable and unstable crack growth conditions are inspected. It is evidenced that stable crack growth under cyclic loading within the nickel binder exhibit faceted, crystallographic features. This microscopic failure mode is rationalized on the basis of the comparable sizes of the cyclic plastic zone ahead of the crack tip and the characteristic microstructure length scale where fatigue degradation phenomena take place in hardmetals, i.e. the binder mean free path.     

Impact of insulator layer thickness on the performance of metal–MgO–ZnO tunneling diodes

The performance of metal–insulator–semiconductor (MIS) type tunneling diodes based on ZnO nanostructures is investigated through modeling. The framework used in this work is the Schrödinger equation with an effective-mass approximation. The working mechanism of the MIS type tunneling diode is investigated by examining the electron density, electric field, electrostatic potential, and conduction band edge of the device. We show that a valley in the electrostatic potential is formed at the ZnO/MgO interface, which induces an energy barrier at the ZnO side of this interface. Therefore, electrons need to overcome two barriers: the high and narrow MgO barrier, and the barrier from the depletion region induced at the ZnO side of the ZnO/MgO interface. As the MgO layer becomes thicker, the valley in electrostatic potential becomes deeper. At the same time, the barrier induced at the ZnO/MgO interface becomes higher and wider. This leads to a fast decrease in the current passing through the MIS diode. We optimize the thickness of the MgO insulating layer, sandwiched between a ZnO film (in this work we use a single ZnO nanowire) and a metal contact, to achieve maximum performance of the diode, in terms of rectification ratio. An optimal MgO layer thickness of 1.5 nm is found to yield the highest rectification ratio, of approximately 169 times that of a conventional metal–semiconductor–metal Schottky diode. These simulated results can be useful in the design and optimization of ZnO nanodevices, such as light emitting diodes and UV photodetectors.

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Fabrication and properties of titanium–hydroxyapatite nanocomposites

Titanium–hydroxyapatite nanocomposites with different HA contents (3, 10, 20 vol%) were produced by the combination of mechanical alloying (MA) and powder metallurgical process. The structure, mechanical and corrosion properties of these materials were investigated. Microhardness test showed that the obtained material exhibits Vickers microhardness as high as 1030 and 1500 HV_0.2, which is more than 4–6 times higher than that of a conventional microcrystalline titanium. Titanium nanocomposite with 10 vol% of HA was more corrosion resistant (i_C = 1.19 × 10⁻⁷ A cm⁻², E_C = −0.41 V vs. SCE) than microcrystalline titanium (i_C = 1.31 × 10⁻⁵ A cm⁻², E_C = −0.36 V vs. SCE). Additionally, the electrochemical treatment in phosphoric acid electrolyte results in porous surface, attractive for tissue fixing and growth. Mechanical alloying and powder metallurgy process for the fabrication of titanium–ceramic nanocomposites with a unique microstructure are developed.     

Fabrication of Mn–ZnO photoanodes for photoelectrochemical water splitting applications

Journal of Materials Science: Materials in Electronics - A photoelectrochemical (PEC) water splitting ability of pure ZnO and manganese-incorporated ZnO thin films fabricated via a simple...     

ECAP processing and mechanical milling of Mg and Mg–Ti powders: a comparative study

A study was carried out into the possibility of employing ECAP processing in lieu of mechanical milling for the purpose of developing powder-based hydrogen storage alloys. Mg and Mg–Ti powder compacts were encapsulated in a copper block and were subjected to ECAP deformation to an apparent strain of ε = 4. This resulted in the consolidation of the compacts as well as in the refinement of their structures. The values of coherently diffracting volume size were as small as 70–80 nm, quite comparable to those achieved with mechanical milling. It is, therefore, concluded that ECAP processing can be employed successfully for the purpose of structural refinement. As for material synthesis, however, the ECAP is less efficient in expanding the interfacial area. Therefore, it is necessary to impose relatively heavy strains to able to achieve comparable expansion in the interfacial area. It appears that an advantage of ECAP deformation is the development of structures which have improved ability for milling. It is, therefore, recommended that in the processing of hydrogen storage alloys, the powder mixtures may be first processed with ECAP in open atmosphere and then by mechanical milling of a short duration carried out under protective atmosphere.     

Fabrication of spherical CaO–SrO–ZnO–SiO2 particles by sol–gel processing

This study was concerned with the fabrication of ceramic CaO–SrO–ZnO–SiO₂ spherical particles, which are novel candidates for the glass phase in glass polyalkenoate cements (GPCs). GPCs made from these glasses have potential as bone cements because, unlike conventional GPCs, they do not contain aluminum ions, which inhibit the calcification of hydroxyapatite in the body. The glass phase of GPCs require a controllable glass morphology and particle size distribution. Sol–gel processing can potentially be used to fabricate homogenous ceramic particles with controlled morphology. However, a thorough study on preparation conditions of spherical CaO–SrO–ZnO–SiO₂ particles by sol–gel processing has, to date, not been reported. In this study, gels were prepared by hydrolysis and polycondensation of tetraethoxysilane (TEOS) in an aqueous solution containing polyethylene glycol and nitrates of calcium, strontium and zinc. It was possible to control the morphology and size of the gels by varying the H₂O/TEOS molar ratio and the metal ion content in the starting compositions. An aliquot of 3–5 μm homogenous spherical particles were obtained at a H₂O/TEOS molar ratio of 42.6 when the starting composition molar ratios were Sr(NO₃):Ca(NO₃)₂:Zn(NO₃)₂:Si(OC₂H₅)₄ = x:0.12:(0.40 − x):0.48 (0 ≤ x ≤ 0.8). Starting composition limitations are caused by the low solubility of strontium ions in the minimal amount of water used and the acceleration of hydrolysis as well as polycondensation at higher water content.     

A comparative study of standard and elegant Hermite–Gaussian beams propagating through turbulent atmosphere

Based on the extended Huygens–Fresnel principle and the definition of the second-order moments of the Wigner distribution function (WDF), the analytical expressions for the root-mean-square (rms) beam width and far-field divergence angle, curvature radius and M ²-factor of standard Hermite–Gaussian (SHG) and elegant Hermite–Gaussian (EHG) beams passing through turbulent atmosphere are derived and compared. It is shown that in turbulent atmosphere the far-field divergence angle of SHG and EHG beams is equal under the same conditions, but the rms beam width, curvature radius and the M ²-factor of SHG and EHG beams are different except for beam orders m?=?0 and m?=?1. The relative rms beam width, relative curvature radius and relative M ²-factor of SHG beams are less than those of EHG beams. Therefore, the conclusion that SHG beams are less influenced by turbulence than EHG beams can be drawn if we examine one of the above three relative beam parameters.     

Fabrication of PANI–ZnO nanocomposite thin film for room temperature methanol sensor

In the recent past, polymer–metal oxide nanocomposites have been identified as one of the key and new class of materials for fabricating gas sensors owing to their swift redox characteristics. In this line of thought, chemical oxidative process was employed to synthesize zinc oxide (ZnO) and polyaniline (PANI) nanocomposite thin films with different mass concentrations of ZnO to explore their gas sensing signatures. X-ray diffraction patterns and Fourier transform infrared spectra confirmed the formation of pure ZnO and PANI–ZnO composites. Field emission scanning electron micrographs revealed the leaf like structure of ZnO, porous nature of PANI and the uniformly distributed blend of these two structures for the composite films. Further, the room temperature gas/vapour sensing characteristics revealed the selective nature of nanocomposite films towards methanol vapour in the presence of other vapours with better response, swift response and recovery times of 7 and 20 s respectively.     

A comparative study on erosion characteristics of red mud filled bamboo–epoxy and glass–epoxy composites

Bamboo fiber reinforced epoxy matrix composites filled with different weight proportions of red mud (a solid waste generated in alumina plants) are fabricated. The mechanical properties of these composites are evaluated and are then compared with those of a similar set of glass–epoxy composites. The solid particle erosion characteristics of the bamboo–epoxy composites have been studied and the experimental results are compared with those for glass–epoxy composites under similar test conditions available in the published literature. For this, an air jet type erosion test rig and Taguchi orthogonal arrays have been used. The methodology based on Taguchi’s experimental design approach is employed to make a parametric analysis of erosion wear process. This systematic experimentation has led to determination of significant process parameters and material variables that predominantly influence the wear rate of the particulate filled composites reinforced with bamboo and glass fiber, respectively. The comparative study indicates that although the bamboo based composites exhibit relatively inferior mechanical properties, their erosion wear performance is better than that of the glass fiber reinforced composites. It further indicates that the incorporation of red mud particulates results in improvement of erosion wear resistance of both the bamboo and glass fiber composites.     

Comparative photocatalytic performance and therapeutic applications of zinc oxide (ZnO) and neodymium-doped zinc oxide (Nd–ZnO) nanocatalysts against Acid Yellow-3 dye: kinetic and thermodynamic study of the reaction and effect of various parameters

Zinc oxide (ZnO) nanoparticles (NPs) were synthesized hydrothermally and doped with 4% Neodymium (Nd). The produced NPs were characterized using UV–Vis spectroscopy, X-ray diffraction (XRD), Energy dispersive X-ray analysis, Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Thermogravimetric analysis (TGA) and Photoluminescence (PL) spectroscopy. With the addition of 4% Nd, the bandgap reduced from 3.20 to 3.00 eV which confirmed successful doping with Nd which also evident from FTIR study. The XRD study showed hexagonal structure of the synthesized material, while SEM study confirmed that Nd-doped ZnO (Nd–ZnO) NPs are well dispersed as compare to ZnO. TGA study revealed that synthesized NPs were much stable to temperature and only 11.3% and 7.2% the total loss occurred during heating range (40–600 °C) in case of ZnO and Nd–ZnO NPs, respectively. The PL intensity of the visible peaks of ZnO reduced after doping with Nd. The degradation of Acid yellow-3 over both the catalysts followed first-order kinetics. The activation energy calculated for the photodegradation reaction was 43.8 and 33.7 kJ/mol using pure ZnO and Nd–ZnO NPs, respectively. About 91% and 80% dye was degraded at the time interval of 160 min using Nd–ZnO and ZnO NPs, respectively. High percent degradation of dye was found at low concentration (10 ppm) and at optimal dosage (0.035 g) of the catalyst. The rate of Acid yellow-3 dye degradation was found to increase with increase in temperature (up to 50 °C) and pH(8) of the medium. The recyclability study showed that both pure ZnO and Nd–ZnO NPs could be reused for the degradation of the given dye. With the addition of H₂O₂ up to 5 µL, the rate of reaction increased clearly indicating the effect of OH^· generation during photocatalysis. When compared with Nd–ZnO NPs at low concentrations, ZnO NPs at higher concentrations were found to be less hazardous. Both the NPs showed best antibacterial activities against Staphylococcus aureus. The hemolytic study indicated that at low concentration, pure ZnO was non-hemolytic as compared to Nd–ZnO.

     

A comparative study on the electrical,thermal and mechanical properties of ethylene–octene copolymer based composites with carbon fillers

Conducting polymer composites (CPC) were prepared with an ethylene–octene copolymer (EOC) matrix and with either carbon fibers (CFs) or multiwall carbon nanotubes (MWCNTs) as fillers. Their electrical and thermal conductivities, mechanical properties and thermal stabilities were evaluated and compared. CF/EOC composites showed percolation behavior at a lower filler level (5 wt.%) than the MWCNT/EOC composites (10 wt.%) did. Alternating current (AC) conductivity and real part of permittivity (dielectric constant) of these composites were found to be frequency-dependent. Dimensions and electrical conductivities of individual fillers have a great influence on the conductivities of the composites. CF/EOC composites possessed higher conductivity than the MWCNT-composites at all concentrations, due to the higher length and diameter of the CF filler. Both electrical and thermal conductivities were observed to increase with increasing filler level. Tensile moduli and thermal stabilities of both (CF/EOC and MWCNT/EOC) composites increase with rising filler content. Improvements in conductivities and mechanical properties were achieved without any significant increase in the hardness of the composites; therefore, they can be potentially used in pressure/strain sensors. Thermoelectric behavior of the composites was also studied. Accordingly, CF and MWCNT fillers are versatile and playing also other roles in their composites than just being conducting fillers.     

A comparative study of microstructure and mechanical behavior of CO2 and diode laser deposited Cu–38Ni alloy

Cu–38Ni alloy was deposited on C71500 (Cu–30Ni) substrates by a laser-aided direct metal deposition technique using CO₂ and diode lasers. Structure–property relationships of deposited specimens were investigated by optical microscopy, electron microscopy, X-ray diffraction techniques, and microhardness and tensile measurements. Laser-deposited specimens’ microstructures were primarily dendritic, forming columnar grains growing epitaxially from the substrate and subsequent layers along the preferred crystallographic growth. The grain growth pattern and grain size distribution was significantly different in both specimens. The lattice parameter of the solid solution phase was relatively larger in diode laser-formed specimen; CO₂ laser-formed specimens showed relatively higher but non-uniform hardness distribution whereas a very uniform hardness distribution was observed in diode laser formed specimens. Diode laser formed specimens showed higher tensile properties compared to CO₂ laser formed specimens which were comparable to C71500 substrates. Microstructure and mechanical behavior were explained based on laser processing parameters.     

Microstructure and corrosion behaviour of additively manufactured Ti–6Al–4V with various post-heat treatments

This paper presents the results of an experimental investigation into the effects of solution treatment, age and stress relief on the corrosion behaviour of direct metal laser sintered Ti–6Al–4V. The evidence of microstructural change and phase evolution, as affected by heat-treatment temperature, was characterised through scanning electron microscopy and X-ray diffraction. The corrosion behaviour was evaluated electrochemically in Ringer's solution, at 37°C. It was determined that the non-equilibrium α’ phase, with a small amount of β nuclei, formed in the as-printed sample. Enhancement in the resistance of the passive oxide layer on the alloy was observed after solution treatment and age, as well as after high-temperature stress relief. The structure of the passive layer of the surface showed a heat-treatment temperature dependency.     

A comparative study of Ni–Ti and Ni–Ti–Cu shape memory alloy processed by plasma melting and injection molding

Shape memory alloys (SMA) are smart materials that present potential applications in such diverse areas as aeronautics, automotive, electronics, biomedicine and others. This work aimed at comparing some physical and functional properties of a Ni–Ti–Cu and equiatomic Ni–Ti SMA. Therefore, Ni–50Ti and Ni–50Ti–5Cu (at.%) were manufactured using plasma melting followed by injection in metallic mold, named Plasma Skull Push–Pull (PSPP) process. Afterwards, samples of both Ni–Ti based SMA were annealed at 1113 K during 2400 s and water quenched. The obtained specimens were analyzed by optical microscopy, microhardness, differential scanning calorimetry, electrical resistance as a function of temperature, and force generation tests. The results showed that Ni–Ti alloy presented higher levels of hardness and lower generated recover forces during heating when compared to the Ni–Ti–Cu SMA. Moreover, the Ni–Ti alloy holds hysteresis larger than the Ni–Ti–Cu SMA as a result of the presence of the R-phase transformation. There was also a better stability under thermal cycling of NiTiCu SMA compared with the equiatomic NiTi.