Graphite nanoplatelets filled silicone composites with novel electrical and dielectric properties

In the design of medium and low voltage equipment such as cable accessories, generator, motor end windings or bushings, issues with electrical field enhancement occur at interfaces between insulators and conductors, resulting in accelerated material ageing. The purpose of this paper is to present a novel dielectric composite material which has the properties to mitigate this local amplification. It is a functional dielectric which resistivity decreases by several orders with electric field from 10¹⁴ to 10⁹ Ωm up to 1 kV?mm^?1 while the dielectric constant decreases from 15 to 12 in the 10^–2–10⁶ Hz range. This novel material is made with graphite nanoplatelets. It may be used as a resistive or capacitive field grading material in electrical applications.

     

Experimental studies and space charge mechanism for the conductivity/mobility enhancement due to SnO2 dispersion in Ag+ ion conducting borate glass

The enhancement in ionic conductivity of a Ag⁺ ion conducting borate glass of molar % composition 55.5 Agl-22.25 Ag₂0-22.25 B₂O₃ is reported with the dispersion of SnO₂. X-ray diffraction (XRD), i.r. and optical microscopy reveals that the SnO₂ addition yields a dispersed phase material and not a new glass. The material is essentially a Ag⁺ ion conducting (Agl+Ag₂O+B₂O₃) glass in which Sn_O2 is dispersed. The direct measurement of mobility of the mobile ions reveals that the enhancement in conductivity is controlled by the enhancement in mobility. A space charge model based on the mechanism of adsorption-desorption of mobile ions near/at the interface in the space charge region creating a certain type of mobile ion concentration gradient is introduced to explain the results.     

Method for microwave radiation enhancement using elongated nanotubes dispersed in a gaseous medium

A new method is proposed to enhance microwave radiation with a wavelength of λ ∼ 1 cm in an active medium comprising elongated conducting nanotubes dispersed in air, which is energy pumped by a nonstationary electric field. For a volume fraction of nanoparticles c ₀ ≈ 10⁻³ in air at atmospheric pressure, the necessary value of the nonstationary pumping electric field (generated by a high-power nanosecond pulsed voltage source) is estimated at ∼ 200 J/m³ and the weak signal gain is estimated at Γ₀ = 0.055 m⁻¹. One possible mechanism of microwave radiation enhancement in a spatial resonator is considered.     

POSS-based luminescent hybrid material for enhanced photo-emitting properties

In this present work, we have developed a novel POSS type monomer ligand “2,6-pyridinediamine-bis-(propanylheptaisobutyl POSS)” (PDC-POSS) and utilized in the preparation of potential luminescent hybrid complex Eu-PDC-POSS with an inner transition metal ion Eu³⁺. The solubility and photo-emitting properties of new Eu-PDC-POSS hybrid material were studied. The precursor PDC-POSS was synthesized by treating (3-aminopropyl)heptaisobutyl POSS with PDC (2,6-pyridinedicarboxylic acid chloride), and then coordinated with Eu³⁺ using europium nitrate to afford Eu-PDC-POSS hybrid material. The europium-doped hybrid material was characterized using fourier transform infrared spectroscopy, and scanning electron microscopy along with energy dispersive X-ray analysis. The photo emitting properties were studied using a fluorescence spectrophotometer in which, the results showed enhancement in red emission peak at 618 nm for Eu-PDC-POSS, when compared to that of a known solgel-based material Eu-PDC-solgel.     

High-energy sensitivity enhancement in panchromatic photopolymers for holography using a mixture of visiblelight photoinitiators

Abstract

A new aqueous photopolymer containing the monomers acrylamide, N,N'-methylenbisacrylamide and zinc acrylate, the initiators 4,5-diiodosuccinylfluorescein (2ISF) and methylene blue (MB), and the coinitiator sodium p-toluenesulphinate is described. This formulation exhibits a clear enhancement of the high-energy sensitivity upon irradiation with 514 or 633 nm light (Ar⁺ laser or He–Ne laser respectively), with respect to the same mixture but with only one of the two dyes, reaching maximum diffraction efficiencies of 15–20% with 15–60 mJ cm^?2. This enhancement is explained by the more efficient photogeneration of initiator radicals by the ground-state formation of an ion-pair complex between cationic (MB) and anionic (2ISF) chromophores. This must compensate the observed decrease in the absorbance of the mixture of the two dyes at 514 nm, with respect to the absorbance of the same medium but with only 2ISF (maximum absorption at 490 nm). A clear absorbance increase at 633 nm, with respect to the absorbance of this system with only MB (maximum absorption at 660 nm), must also favour photopolymerization.     

Damped second-order Rayleigh-Timoshenko semi-infinite beam vibration—an exact complex dynamic member stiffness matrix

A uniform linear semi-infinite beam in a uniform linear ambient medium is studied. The beam performs stationary harmonic damped non-synchronous space vibration in simultaneous tension, torsion, bending and shear. Hysteretic and viscous dampings of the beam material and ambient medium are considered. Four new generalized complex Kolousek functions are derived. A 6 × 6 complex symmetric stiffness matrix is established for a semi-infinite beam member excited at its end by prescribed harmonic translations and rotations which have the same frequency but may be out of phase. This matrix extends the range of application of the so called ‘exact analysis’ of non-proportionally damped built-up beam structures as described in a previous paper by Lundén and Åkesson.¹ Numerical examples are given, including applications of the computer program SFVIBAT-DAMP. Power flows are studied.     

Toxicological Profiling of Highly Purified Single‐Walled Carbon Nanotubes with Different Lengths in the Rodent Lung and Escherichia Coli

Carbon nanotubes (CNTs) exhibit a number of physicochemical properties that contribute to adverse biological outcomes. However, it is difficult to define the independent contribution of individual properties without purified materials. A library of highly purified single‐walled carbon nanotubes (SWCNTs) of different lengths is prepared from the same base material by density gradient ultracentrifugation, designated as short (318 nm), medium (789 nm), and long (1215 nm) SWCNTs. In vitro screening shows length‐dependent interleukin‐1β (IL‐1β) production, in order of long > medium > short. However, there are no differences in transforming growth factor‐β1 production in BEAS‐2B cells. Oropharyngeal aspiration shows that all the SWCNTs induce profibrogenic effects in mouse lung at 21 d postexposure, but there are no differences between tube lengths. In contrast, these SWCNTs demonstrate length‐dependent antibacterial effects on Escherichia coli, with the long SWCNT exerting stronger effects than the medium or short tubes. These effects are reduced by Pluronic F108 coating or supplementing with glucose. The data show length‐dependent effects on proinflammatory response in macrophage cell line and antibacterial effects, but not on collagen deposition in the lung. These data demonstrate that over the length scale tested, the biological response to highly purified SWCNTs is dependent on the complexity of the nano/bio interface.     

Impact of carbon fibre/epoxy corrugated cores

The dynamic compressive response of corrugated carbon-fibre reinforced epoxy sandwich cores has been investigated using a Kolsky-bar set-up. Compression at quasi-static rates up to v₀ = 200 ms⁻¹ have been tested on three different slenderness ratios of strut. High speed photography was used to capture the failure mechanisms and relate these to the measured axial compressive stress. Experiments show significant strength enhancement as the loading rate increases. Although material rate sensitivity accounts for some of this, it has been shown that the majority of the strength enhancement is due to inertial stabilisation of the core members. Inertial strength enhancement rises non-linearly with impact velocity. The largest gains are associated with a shift to buckle modes composed of 2–3 half sine waves. The loading rates tested within this study are similar to those that are expected when a sandwich core is compressed due to a blast event.     

Ultrathin Hierarchical Porous Carbon Nanosheets for High‐Performance Supercapacitors and Redox Electrolyte Energy Storage

The design of advanced high‐energy‐density supercapacitors requires the design of unique materials that combine hierarchical nanoporous structures with high surface area to facilitate ion transport and excellent electrolyte permeability. Here, shape‐controlled 2D nanoporous carbon sheets (NPSs) with graphitic wall structure through the pyrolysis of metal–organic frameworks (MOFs) are developed. As a proof‐of‐concept application, the obtained NPSs are used as the electrode material for a supercapacitor. The carbon‐sheet‐based symmetric cell shows an ultrahigh Brunauer–Emmett–Teller (BET)‐area‐normalized capacitance of 21.4 µF cm^?2 (233 F g^?1), exceeding other carbon‐based supercapacitors. The addition of potassium iodide as redox‐active species in a sulfuric acid (supporting electrolyte) leads to the ground‐breaking enhancement in the energy density up to 90 Wh kg^?1, which is higher than commercial aqueous rechargeable batteries, maintaining its superior power density. Thus, the new material provides a double profits strategy such as battery‐level energy and capacitor‐level power density.     

Development of a new device to perform torsional ultrasonic fatigue testing

The interest in gaining experimental knowledge on fatigue strength of materials over 10⁹ cycles is rapidly increasing as evidenced for the large amount of investigations on this subject presented at the last very high cycle fatigue meeting (VHCF-3), held on September 2004. Most of the fatigue results presented at this conference were obtained under tension-compression, rotating bending, flexion and bending cyclic loading (some attaining 10¹⁰ cycles), using ultrasonic devices whose design was based on the natural frequency principles. In general, very little literature concerning the metallic alloys behavior under torsion cyclic loading using ultrasonic is available; however, in order to perform an accurate component design under multi-axial loading and VHCF, the material behavior under torsion cyclic loading is required. This investigation presents the development of a new mechanical device for testing and characterizing metallic alloys in the range of 10⁹–10¹⁰ cycles in torsional cyclic loading and the first experimental results for medium carbon steel (38MnSV5S). The new device was designed to excite the components under testing with pure torsional vibration mode at a frequency of 20 kHz.     

Enhancement of Raman scattering signals from gaseous medium near the surface of a holographic aluminum diffraction grating

The possibility of applying surface-enhanced Raman scattering (RS) for amplification of RS intensity in gaseous media is investigated. A more than sixfold enhancement of the RS signal is detected experimentally from the main atmospheric air components during interaction of continuous-wave laser radiation with a holographic aluminum diffraction grating. The averaged value of the RS signals’ amplification factor in the near-surface 30-nm-thick layer at the boundary between the diffraction grating and gaseous medium amounted to ~3 × 10³.     

Microwave radiation enhancement and self-focusing using quasi-stationary electric field in a medium with elongated nanoparticles

It is shown that a mechanism of microwave radiation enhancement and self-focusing can be operative in a wave channel and spatial cavity filled with air containing elongated (dumbbell-shaped) nanoparticles at a volume fraction of c ₀ ∼ 10⁻³. This nonlinear medium can be pumped using a quasi-stationary electric field. At an oscillation frequency of Ω ∼ 10¹⁰−10¹¹s⁻¹, the radiation enhancement and self-focusing in a wave channel is possible over a length of Δz ∼ 50−200 m, while that in a spatial cavity can take place within a period of time Δt ∼ (2−7) × 10⁻⁷ s.     

A Binder‐Free and Free‐Standing Cobalt Sulfide@Carbon Nanotube Cathode Material for Aluminum‐Ion Batteries

Rechargeable aluminum‐ion batteries (AIBs) are considered as a new generation of large‐scale energy‐storage devices due to their attractive features of abundant aluminum source, high specific capacity, and high energy density. However, AIBs suffer from a lack of suitable cathode materials with desirable capacity and long‐term stability, which severely restricts the practical application of AIBs. Herein, a binder‐free and self‐standing cobalt sulfide encapsulated in carbon nanotubes is reported as a novel cathode material for AIBs. The resultant new electrode material exhibits not only high discharge capacity (315 mA h g⁻¹ at 100 mA g⁻¹) and enhanced rate performance (154 mA h g⁻¹ at 1 A g⁻¹), but also extraordinary cycling stability (maintains 87 mA h g⁻¹ after 6000 cycles at 1 A g⁻¹). The free‐standing feature of the electrode also effectively suppresses the side reactions and material disintegrations in AIBs. The new findings reported here highlight the possibility for designing high‐performance cathode materials for scalable and flexible AIBs.     

Ellipsometrical characterization of complex refractive index depth profile of 50 keV silicon ion implanted PMMA

Multiangle reflection ellipsometry is applied to characterize the refractive index change of the material in the subsurface layer produced by ion implantation of polymethylmethacrylate (PMMA) with low-energy (50 keV) silicon ions at fluences ranging from 10¹⁴ to 10¹⁷ cm⁻². By employing an effective medium approximation, the in-depth distribution of both real and imaginary parts of the complex refractive index of ion-modified material near the surface was modeled. The degree of in-depth modification of the target PMMA material upon ion implantation was established. A distinct fluence level was found that produced a maximum efficiency of the ion-induced change of the optical properties of the material. The ellipsometrical depth profiling of the refractive index of silicon ion implanted PMMA was proved with data obtained by reflectance spectroscopy and X-ray photoelectron spectroscopy.     

The effect of high temperature carburization upon the ambient temperature ductility of Alloy 800H

This paper presents the results of a series of tests designed to assess the changes in ambient temperature ductility of Alloy BOOH, a 20%Cr-32%Ni austenitic steel, resulting from exposure to an aggressive carburizing environment at 10000°C. A gas mixture of H₂-CH₄ with 0.8 carbon activity has been used as the corrosive medium and postexposure compression testing of the carburized tubular specimens has enabled the significant reduction in ductility accompanying the uptake of carbon to be demonstrated and understood.     

A new class of electrorheological material: synthesis and electrorheological performance of rare earth complexes of phosphate cellulose

A new class of electrorheological (ER) material, rare earth (RE = Ce, Gd, Er and Y) complexes of phosphate cellulose, has been synthesized using microcrystalline cellulose, phosphoric acid, urea and RE(NO₃)₃ solutions as starting materials. The ER properties of suspensions of microcrystalline cellulose, phosphate cellulose [cellulose-P-ONH₄] and the [cellulose(-P-O)₃RE] complex particle materials in silicon oil have been investigated under DC electric field. The formation of rare earth complexes helps to decrease the shear stress and viscosity at zero electric field, and to enhance the ER effect of the materials. The shear stress (τ_E) of the ER fluid (20% weight fraction) of a typical yttrium complex [cellulose(-P-O)₃Y], the yttrium content of which is 0.04 mol/100 g, is 2.3 kPa at 4.2 kV/mm and 300 s⁻¹ with a τ_r value (τ_r = τ_E/τ₀, where τ₀ is the shear stress at no electric field and 300 s⁻¹) of 34.3, which is 18 times higher than that of pure microcrystalline cellulose suspensions. The improvement of dielectric loss tangent of the material, due solely to the formation of rare earth complexes, resulted in an enhancement in the ER effect of the material. In addition, the cellulose(-P-O)₃RE materials possess better thermal stability, and their suspensions are more stable in the anti-sedimentation than that of the cellulose-P-ONH₄ material.     

New Strategy: Molten Salt-Assisted Synthesis to Enhance Lanthanide Upconversion Luminescence

Lanthanide-doped upconversion luminescent materials (LUCMs) have attracted much attention in diverse practical applications because of their superior features. However, the relatively weak luminescence intensity and low efficiency of LUCMs are the bottleneck problems that seriously limit their development. Unfortunately, most of the current major strategies of luminescence enhancement have some inherent shortcomings in their implementation. Here, a new and simple strategy of molten salt-assisted synthesis is proposed to enhance lanthanide upconversion luminescence for the first time. As a proof-of-concept, a series of rare earth oxides with obvious luminescence enhancement are prepared by a one-step method, utilizing molten NaCl as the high-temperature reaction media and rare earth chlorides as the precursors. The enhancement factors at different reaction temperatures are systematically investigated by taking Yb³⁺/Er³⁺ co-doped Y₂O₃ as an example, which can be enhanced up to more than six times. In addition, the molten salts are extended to all alkali chlorides, indicating that it is a universal strategy. Finally, the potential application of obtained UCL materials is demonstrated in near-infrared excited upconversion white light-emitting diodes (WLEDs) and other monochromatic LEDs.     

Focusing Plasmons in Nanoslits for Surface‐Enhanced Raman Scattering

The focusing of plasmons to obtain a strong and localized electromagnetic‐field enhancement for surface‐enhanced Raman scattering (SERS) is increasing the interest in using plasmonic devices as molecular sensors. In this Full Paper, we report the successful fabrication and demonstration of a solid‐state plasmonic nanoslit–cavity device equipped with nanoantennas on a freestanding thin silicon membrane as a substrate for SERS. Numerical calculations predict a strong and spatially localized enhancement of the optical field in the nanoslit (6 nm in width) upon irradiation. The predicted enhancement factor of SERS was 5.3 × 10⁵, localized in an area of just 6 × 1.5 nm². Raman spectroscopy and imaging confirm an enhancement factor of ≈10⁶ for SERS from molecules chemisorbed at the nanoslit, and demonstrate the electromagnetic‐field‐enhancing function of the plasmonic nanoantennas. The freestanding membrane is open on both sides of the nanoslit, offering the potential for through‐slit molecular translocation studies, and opening bright new perspectives for SERS applications in real‐time (bio)chemical analysis.     

N,S co-doped lignin-based carbon microsphere functionalized graphene hydrogel with ‘‘sphere-in-layer” interconnection as electrode materials for supercapacitor and molecularly imprinted electrochemical sensors

This work reports a three-dimensional N, S co-doped lignin-based carbon microsphere/graphene composite hydrogel (GH-NSCMS) as an electrode material for supercapacitors and a signal enhancement material for tetracycline molecularly imprinted electrochemical sensors (MIECS). As a supercapacitor electrode, GH-NSCMS electrode has a specific capacitance of 434.6 F g^?1 at 0.5 A g^?1, which can still maintain 94.15% after 5,000 cycles. In addition, a highly sensitive MIP electrochemical sensor for tetracycline detection is prepared based on GH-NSCMS composite material due to the synergistic effects of the high recognition accuracy of the imprinting method, and excellent conductivity of the composite hydrogel material. The sensor has a wide linear range (0.1–50 μM) and a significant detection limit (5 × 10^?8 mol L^?1). Therefore, the 3D GH-NSCMS composites described herein have potential application prospects in supercapacitor electrode materials and tetracycline molecular imprinting detection.     

About the dynamic uniaxial tensile strength of concrete-like materials

Experimental methods for determining the tensile strength of concrete-like materials over a wide range of strain-rates from 10⁻⁴ to 10² s⁻¹ are examined in this paper. Experimental data based on these techniques show that the tensile strength increases apparently with strain-rate when the strain-rate is above a critical value of around 10⁰-10¹ s⁻¹. However, it is still not clear that whether the tensile strength enhancement of concrete-like materials with strain-rate is genuine (i.e. it can be attributed to only the strain-rate effect) or it involves “structural” effects such as inertia and stress triaxility effects. To clarify this argumentation, numerical analyses of direct dynamic tensile tests, dynamic splitting tests and spalling tests are performed by employing a hydrostatic-stress-dependent macroscopic model (K&C concrete model) without considering strain-rate effect. It is found that the predicted results from these three types of dynamic tensile tests do not show any strain-rate dependency, which indicates that the strain-rate enhancement of the tensile strength observed in dynamic tensile tests is a genuine material effect. A micro-mechanism model is developed to demonstrate that microcrack inertia is one of the mechanisms responsible for the increase of dynamic tensile strength with strain-rate observed in the dynamic tensile tests on concrete-like materials.