Electrical conductivity improvement of aeronautical carbon fiber reinforced polyepoxy composites by insertion of carbon nanotubes

An increase and homogenization of electrical conductivity is essential in epoxy carbon fiber laminar aeronautical composites. Dynamic conductivity measurements have shown a very poor transversal conductivity. Double wall carbon nanotubes have been introduced into the epoxy matrix to increase the electrical conductivity. The conductivity and the degree of dispersion of carbon nanotubes in epoxy matrix were evaluated. The epoxy matrix was filled with 0.4 wt.% of CNTs to establish the percolation threshold. A very low value of carbon nanotubes is crucial to maintain the mechanical properties and avoid an overload of the composite weight. The final carbon fiber aeronautical composite realized with the carbon nanotubes epoxy filled was studied. The conductivity measurements have shown a large increase of the transversal electrical conductivity. The percolative network has been established and scanning electron microscopy images confirm the presence of the carbon nanotube conductive pathway in the carbon fiber ply. The transversal bulk conductivity has been homogenized and improved to 10^? 1 S·m^? 1 for a carbon nanotubes loading near 0.12 wt.%.     

Selective area molecular beam epitaxy of InAs on GaAs (110) masked substrates for direct fabrication of planar nanowire field-effect transistors

We have synthesized InAs nanowires (NWs) by selective area molecular beam epitaxy (SA-MBE) on GaAs masked substrates. In particular, we have obtained in-plane-oriented NWs on the (110) plane, and then directly applied the NWs to planar nanowire field-effect transistors (NWFETs) using conventional electron beam lithography without a NW dispersion process. We have measured output and transfer characteristics of the NWFETs at room temperature, and obtained a current swing but no turning off, and a field-effect mobility peak of 150 cm²/V-s. We have also observed almost no temperature influence on field-effect mobility between 2 K and 300 K, suggesting a high-dense surface accumulation layer even at low temperatures.     

Silicon nanowire solar cells grown by PECVD

Silicon nanowires offer an opportunity to improve light trapping in low-cost silicon photovoltaic cells. We have grown radial junctions of hydrogenated amorphous silicon over p-doped crystalline silicon nanowires in a single pump-down plasma enhanced chemical vapor deposition process on glass substrates. By using Sn catalysts and boosting p-type doping in the nanowires, the open-circuit voltage of the devices increased from 200 to 800 mV. Light trapping was optimized by extending the length of nanowires in these devices from 1 to 3 μm, producing currents in excess of – 13 mA cm^? 2 and energy conversion efficiencies of 5.6%. The advantages of using thinner window layers to increase blue spectral response were also assessed.     

Preparation of optical axial GRIN components through migration of charged amorphous ZrO2 nanoparticles inside an organic–inorganic hybrid matrix by electrophoresis

A novel sol–gel synthesis route for the preparation of a transparent organic–inorganic nanocomposite was developed by combining methacrylic acid (MA) stabilized, amorphous ZrO₂ nanoparticles, which were synthesized by the sol–gel process, with an organic–inorganic dodecandioldimethacrylate (DDDMA)/3-methacryloxypropyl trimethoxysilane (MPTS) hybrid matrix. The average hydrodynamic particle size was determined to be approximately 6 nm by photon correlation spectroscopy. HR-TEM micrographs present irregular shaped zirconia particles with diameters up to 3 nm. Nearly solvent-free nanocomposites with zirconium (Zr) contents up to 15.2 mol% were synthesized and photochemically cured to transparent crack-free bulks. The surface charged nanoparticles in 1-propanol had an electrophoretic mobility of 0.017 (μm cm)/(V s), measured by Laser Doppler Anemometry (LDA) and a refractive index n_e of ⩾1.648 ± 0.007 determined by spectroscopic ellipsometry. After filling the nanocomposite into a linear electrophoresis cell (1 × 1.6 × 0.8 cm³), positively charged high refractive nanoparticles migrated through the low refractive hybrid matrix toward the cathode by the application of an electric potential difference of 2 kV/cm for 96 h. A 67% increase in Zr over a distance of 8 mm between the cathode and anode was observed by high-resolution scanning electron microscopy (HR-SEM) and energy dispersive X-ray spectroscopy (EDXS).     

Effect of dehydration techniques on the fluorescence spectral features and OH absorption of heavy metals containing fluoride tellurite glasses

Heavy metal containing fluoride tellurite glasses were prepared by different dehydration techniques and the effects of dehydration techniques on fluorescence spectral features, OH content and volatilization of the glass compositions were systematically studied by means of fluorescence spectral measurements FTIR and energy-dispersive X-ray spectrometer. Experimental results indicated that different dehydration induced difference in actual compositions of the glasses that resulted in the variation of their fluorescence spectral features, and melting the glass frits in close environment with mechanical stirring and simultaneous bubbling dry O₂ + CCl₄ mixture in a O₂-rich environment was much more effective to remove the OH groups in the glass matrix, through which an OH absorption coefficient and absorption concentration could be efficiently reduced to as low as 1.09 cm^? 1 and 1.17 × 10¹⁹ cm^? 3, respectively. The low OH content contributed to the increase in fluorescence lifetime, and resulted in the improvement of gain characteristic. The bubbling time of dry O₂ + CCl₄ mixture was optimized via OH absorption concentration investigation.     

Development of quaternary Fe-based bulk metallic glasses with high saturation magnetization above 1.6 T

Quaternary Fe-based ferromagnetic bulk metallic glasses (BMGs) with saturation magnetization above 1.6 T were successfully fabricated in Fe–Si–B–P alloy system by copper mold casting. These BMGs exhibit low coercive force of 1.6–1.9 A/m, high effective permeability of 16,500–17,200 and low core loss. In additional, these BMGs exhibit good mechanical properties as well, i.e., high strength of 3200 MPa and plasticity of 1.1%. They are promising to be used as magnetic functional and structural materials in the future.     

Electrochemical properties of conductive filler/carbon aerogel composites as electrodes of supercapacitors

Carbon black, multi-walls carbon nanotube (CNT) and vapor grown carbon nano-fiber with different contents were added to the carbon aerogels (CAs) electrodes as conductive fillers to improve their capacitive properties. The results show that maximum capacitance exists when the content of the conductive filler gets to its percolation threshold. CNT is the most ideal conductive filler. The CA with 1 wt% content of CNT has the best electrochemical performance; its specific capacitances are 141.3 F g^?1 at 5 mV s^?1 and 127.1 F g^?1 at 100 mV s^?1, 1.4 times and 2.2 times as high as that of CA electrode, respectively.     

Crystal-field spectroscopy of Eu3+ doped silica glasses

Fourier transform absorption spectroscopy in the 500–6000 cm^? 1 and 9–300 K ranges is applied to monitor the effects produced by Eu³⁺ incorporation into sol–gel silica samples doped with concentration increasing from 0.001 to 10 mol%. The aim is to investigate the formation of aggregates by exploiting the Eu³⁺ crystal-field transitions. Complementary microreflectance and Raman spectra are also measured in the range of silica intrinsic vibrational modes to confirm the hypothesis of matrix modification induced by increasing doping levels. Evidences of clustering are found for high Eu³⁺ concentrations. Up to 3 mol% the crystal-field line intensities gradually increase and the OH^? content smoothly decreases. A further increase to 10 mol% causes drastic, remarkable changes, i.e. sharp crystal-field lines appear which narrow by lowering the temperature. Furthermore, the OH^? related bands are no longer detectable. For concentrations up to 3 mol% the aggregates are amorphous as the silica matrix, while for the Eu³⁺ 10 mol% sample they show a rather ordered structure.     

Low-temperature growth of tetragonal tungsten nanowire arrays on tungsten substrate using Ni solid catalysts

Tetragonal tungsten nanowire arrays were successfully fabricated on tungsten substrate using Ni catalysts by chemical vapor deposition (CVD) at 950 °C. The synthesized tungsten nanowires grew along [100] direction, with a high aspect ratio more than 50 and sharp tips. The Ni catalyst was found to be located at the wire's bottom and assisted the nucleation of the tungsten nanowire. Samples were characterized in detail by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) technologies. Based on the analysis of the experimental results, the possible formation mechanism of nanowires was proposed as well.     

Structural impact of iron ions on BaBiBO4 glasses: Spectroscopic and dielectric investigations

Transparent glasses of composition 10BaO.20Bi₂O₃.(70 ? x)B₂O₃.xFe₂O₃ (wt.%) where 0 ≤ x ≤ 2.0, were characterized by XRD and SEM. Physical, spectroscopic and dielectric properties were investigated. At higher dopant of Fe₂O₃, EPR results revealed that, the number of Fe³⁺ ions participate in the resonance is decreased by forming a new signal at g ≈ 3.015 due to increase of antiferromagnetic interaction of Fe³⁺ ions and/or formation of low spin Fe³⁺ ions in the glass matrix. With initial 0.5 wt.% doping of Fe₂O₃, less dense glass is formed with colloids of metallic Bi⁰ atoms. The absorption bands at 604 and 712 nm in F5 glass are ascribed to Bi⁰ and Bi⁺ radicals respectively. No characteristic Fe³⁺ absorption bands (spin-forbidden) are found. Fe²⁺ ions are increased at higher concentration of Fe₂O₃. Higher concentration of Fe₂O₃ is favorable for BO₂O^?, BO₃, BiO₆ and FeO₆ symmetry unit leads to low band gap and high Urbach energy. By doping of Fe₂O₃ the dielectric parameters like dielectric constant (ε′), loss (tanδ and ac electrical conductivity (σ_ac) are found to increase.     

EPR and magnetic susceptibility studies of B2O3–Bi2O3–Gd2O3 glasses

Glasses of the xGd₂O₃ · (100 − x)[B₂O₃ · Bi₂O₃] system with 0.5 ⩽ x ⩽ 10 mol% were studied by electron paramagnetic resonance (EPR) and magnetic susceptibility measurements. Data obtained show that for low gadolinium oxide contents of the samples (x ⩽ 3 mol%) the Gd³⁺ ions are randomly distributed in the host glass matrix and are present as isolated and dipole–dipole coupled species. For higher gadolinium oxide contents of the samples (x > 3 mol%) the Gd³⁺ ions appear as both isolated and antiferromagnetically coupled species. The EPR spectra of the glasses reveal resonance sites with an unexpected high crystalline field in addition to the ‘U’ spectrum, typical for Gd³⁺ ions in disordered systems. This absorption line is due to Gd³⁺ ions that replace Bi³⁺ ions from the host glass matrix and could play the network unconventional former role in the studied glasses.     

Lightweight Ti–Zr–Be–Al bulk metallic glasses with improved glass-forming ability and compressive plasticity

A series of lightweight Ti–Zr–Be–Al bulk metallic glasses (BMGs) have been developed through the addition of Al to Ti–Zr–Be ternary glassy alloy. By replacing Be with Al, the critical size of the glassy rod has been increased from 5 mm for Ti₄₁Zr₂₅Be₃₄ alloy to 7 mm for Ti₄₁Zr₂₅Be₂₉Al₅ alloy, while the yield strength of Ti₄₁Zr₂₅Be_34 ? xAl_x (x = 2–10) has been greatly enhanced, resulting in a significant increase of the specific strength which is defined as yield strength/density. Among these newly developed Ti–Zr–Be–Al BMGs, Ti₄₁Zr₂₅Be₂₆Al₈ glassy alloy exhibits a high specific strength of 4.33 × 10⁵ Nm/kg and a very large compressive plastic strain of 47.0%, which are much larger than those (3.69 × 10⁵ Nm/kg and 2.9%, respectively) for Ti₄₁Zr₂₅Be₃₄ glassy alloy. The present results show that Al is an effective alloying element for improving the glass-forming ability (GFA) and mechanical properties of Ti-Zr-Be glassy alloy.     

Toughness of Zr55Cu30Al10Ni5 bulk metallic glass for two oxygen levels

This paper demonstrates the embrittlement of a Zr-based bulk metallic glass caused by the presence of very low oxygen traces during its synthesis. Toughness studies are conducted both at room and low (77 K) temperatures. Samples with 2000 appm of oxygen contain crystalline defects (trapping all oxygen) while those with 300 appm are completely glassy. Toughness results clearly indicate that these defects embrittle the glass. Therefore, careful attention must be paid during synthesis with respect to the oxygen content to get a completely glassy alloy. This issue is of paramount importance when dealing with mechanical properties such as toughness.     

Microstructure and stored energy evolutions during rolling of Cu60Zr20Ti20 bulk metallic glass

The microstructure and stored energy of Cu₆₀Zr₂₀Ti₂₀ bulk metallic glass rolled at cryogenic temperature in a wide strain rate range 1.0 × 10^?4 ? 5.0 × 10^?1 s^?1 have been investigated. As the specimen is rolled to be thinner, the stored energy first increases linearly, and then saturates above a critical thickness reduction at lower strain rates, or decreases at high strain rates. At the initial stage of rolling, no phase transformation except shear bands appears in the glass. Phase transformation occurs only when the specimen is severely deformed at strain rates higher than 1.0 × 10^?4 s^?1. As strain rate increases, the critical strain for the stored energy to saturate increases, but the critical strain for phase separation to occur decreases, and meanwhile the type of the phase transformation changes from phase separation to nanocrystallization. The stored energy does not change with the occurrence of phase separation, but decreases due to nanocrystallization. It is proposed that coalescence of more free volume in shear bands into nano-voids should be principally responsible for the saturation of the stored energy, which balances the results from the increase in shear band number at higher strains.     

Preparation and growth mechanism of clustered one-dimensional SiOx amorphous nanowires by catalytic pyrolysis of a polymer precursor

Large-scale synthesis of clustered one-dimensional amorphous silica nanowires was achieved by simple thermal pyrolysis of an amorphous preceramic powder from perhydropolysilazane on alumina wafers coated with catalyst FeCl₂. Scanning electron microscopy and transmission electron microscopy observations showed that the silica nanowires had smooth surface, and lengths of hundreds of micrometers and diameters in the range of 30–40 nm. Energy dispersive X-ray spectroscopy revealed that these nanowires consisted of Si and O elements in an atomic ratio of approximately 1:2, consistent with the stoichiometric formula SiO₂. The two amorphous bulges in Raman spectrum at the centers of around 260 cm^?1 and 800 cm^?1 were identified to be those of amorphous silica. The growth mechanism of the as-produced silica nanowires could be attributed to vapor–liquid–solid mechanism. These results provide an alternative and simple preparation procedure for nanostructures with controlled morphology, and it will be helpful to understand the growth mechanism of one-dimensional SiO₂ nanostructures.     

Epitaxial ZnS/Si core–shell nanowires and single-crystal silicon tube field-effect transistors

Epitaxial single-crystal ZnS/Si core–shell nanowires have been synthesized via a two-step thermal evaporation method. The epitaxial growth is due to the close match of crystal structure between zinc blende ZnS and diamond-like cubic Si. The nanowires have a uniform diameter of 80–200 nm and a length of several to several tens of micrometers. Single-crystal Si nanotubes can be obtained by chemical etching of the ZnS/Si core–shell structure. Characteristics of field-effect transistors (FETs) fabricated from the Si nanotubes suggests that the Si tubes show weak n-type semiconductivity with a mobility of about 3.7×10^?2 cm²/(V s), which is 1 order larger than that of intrinsic Si.     

Effect of P incorporation on aggregation of nanocrystallites in amorphous and nanocrystalline mixed-phase silicon thin films

We report the effects of P incorporation on the nanometer-scale structural and electrical properties of amorphous and nanocrystalline mixed-phase Si:H films. In the intrinsic and weakly P-doped (3 × 10¹⁸ at/cm³) films, the nanocrystallites aggregate to cone-shaped structures. Conductive atomic force microscopy images showed high current flows through the nanocrystalline cones and a distinct two-phase structure in the micrometer range. Adding PH₃ into the processing gas moved the amorphous/nanocrystalline transition to a higher hydrogen dilution ratio required for achieving a similar Raman crystallinity. In a heavily P-doped (2 × 10²¹ at/cm³) film, the nanocrystalline aggregation disappeared, where isolated grains of nanometer sizes were distributed throughout the amorphous matrix. The heavily doped mixed-phase film with 5–10% crystal volume fraction showed a dramatic increase in conductivity. We offer an explanation for the nanocrystalline cone formation based on atomic hydrogen enhanced surface diffusion model, and propose that the coverage of P-related radicals on the existing nanocrystalline surface during film growth and the P segregation in grain boundaries are responsible for preventing new nucleation on the surface of the existing nanocrystallites, resulting in nanocrystallites dispersed throughout the amorphous matrix.     

Synthesis,characterization and local changes induced by a cw argon laser in silica glass xerogel doped with transition metal ions

We report on the synthesis, characterization and local changes induced by a cw argon laser in SiO₂ xerogel doped with low metal ion concentrations, and obtained by the sol–gel process. The V, Mn and Cr metal ions were introduced into the SiO₂ matrix as inorganic salts and as an oxide in the case of Mo. The characterization of these materials showed that an amorphous system with high porosity was obtained; the metals were incorporated as ions with several different oxidation states, and the thermal diffusivity was around 10⁻⁹ m²/s. In these xerogel monoliths it is possible to induce local changes in the refractive index with the incidence of a focused laser beam at 488 nm, about 80 μm in diameter, with power intensities from 1 to 48 mW and an incidence time from 0.5 to 5 min. After this process, a high contrast in the transmitted light between the processed area and the homogenous matrix is obtained, resulting in an optical memory effect.     

Exploration on nano-composite fumed silica-based composite polymer electrolytes with doping of ionic liquid

Fumed silica (SiO₂)-based composite polymer electrolytes were prepared by means of solution casing technique. Horizontal attenuated total reflectance-Fourier Transform Infrared (HATR-FTIR) study shows the complexation between polymer matrix and SiO₂. The highest ionic conductivity of (4.11 ± 0.01) × 10^? 3 Scm^? 1 is achieved upon inclusion of 8 wt.% of SiO₂. Three different regions have been observed in the frequency dependence–ionic conductivity study. The conductivity rises sharply with frequency at low frequency regime. It is followed by a frequency independent plateau region and sharp decrease in the conductivity at high frequency range. The dielectric permittivity (ε^') and dielectric loss (ε^") are decreased with increasing the frequency. This phenomenon is mainly attributed to the electrode polarization effect. The formation of electrical double layer has been proven in these dielectric permittivity studies. This indicates the non-Debye properties of the nano-composite polymer electrolytes.     

Effect of OH-content on thermal and chemical properties of SnOP2O5 glasses

Glasses with 55–60 mol% SnO and 40–45 mol% P₂O₅ have shown extremely large differences in the chemical and thermal properties depending on the temperature at which they were melted. Glasses prepared at low melting temperature, 450–550 °C, had low T_g, 150–200 °C, and low chemical stability. Glasses prepared at high melting temperature, 800–1200 °C, had much higher T_g, 250–300 °C, and much higher chemical stability. No significant differences were found by ¹¹⁹Sn Mössbauer and ³¹P Nuclear Magnetic Resonance spectroscopy. Large differences in the OH-content could be detected as the reason by infrared absorption spectroscopy, thermal analyses, and ¹H Nuclear Magnetic Resonance spectroscopy. In samples with low T_g, a broad OH – vibration band around 3000 nm with an absorption intensity >20 cm^?1, bands at 2140 nm with intensity ～5 cm^?1, at 2038 nm with intensity ～2.7 cm^?1, and at 1564 nm with intensity ～0.4 cm^?1 were measured. These samples have shown a mass loss of 3–4 wt% by thermal gravimetric analyses under argon in the temperature range 400–1000 °C. No mass loss and only one broad OH-band with a maximum at 3150 nm and low absorption intensity <4 cm^?1 could be detected in samples melted at high temperature, 1000–1200 °C, which have much higher T_g, ～300 °C, and much higher chemical stability.