CA SELECTS Carbon & Graphite fibers

该文研究了注塑成型短切碳纤维填充聚合物基复合材料的电导性,应用渗透理论和比例法分析了纤维尺寸以及体积分数对电导的影响。渗透开始点的纤维体积分数被测得而且实现了三维计算机模拟,介绍了一种在临界点电导率下可以减小预算体积分数和实验体积分数差异的假想纤维壳体模型,按照模拟所得的临界体积分数Vc通过实验发现是由纤维的长径比来决定的,而纤维的表面化学性质对其影响很小。实验电导数据随着     

Development of niobiumtin conductors at SLE

Superconductors Lips ECN is a recently formed company which produces NbTi and Nb₃Sn multifilament wires as well as superconducting cables. Multifilamentary Nb₃Sn wire, produced by the powder route, is developed commercially. About 30 km of strand material has been produced for the SULTAN 12 T project. These wires showed good performance. Developments are underway to reduce gradually the filament diameter at the same current performance to meet the full requirements for the NET and LHC conductors.     

Preparation of tin ferrite–tin oxide by hydrothermal,precipitation and auto-combustion: photo-catalyst and magnetic nanocomposites for degradation of toxic azo-dyes

In this work, tin ferrite nanoparticles were first synthesized by simple chemical procedures such as co precipitation, sol–gel auto combustion and hydrothermal methods. In general, all three methods were compared in the synthesis of nanoparticles. Then tin ferrite–tin oxide (50%:50%) nanocomposites were prepared using co precipitation method. Crystal structures of nanoparticles and nanocomposite were studied using X-ray diffraction pattern. The particle size was determined by Scanning Electron Microscopy. Vibrating sample magnetometer was used to study the magnetic property of the products. And also, by applying Fourier transform infrared spectrometer, the purity of the material was determined. Photocatalytic activity of nanoparticles and nanocomposites was investigated under ultra-violet and visible spectroscopy (UV–Vis). The results show that prepared nanocomposites are applicable for magnetic and photocatalytic performance and they were able to degrade azo dyes (organic dyes) under UV–Vis radiation.     

Preparation of nanocrystalline tin powders by the γ-radiation method

The γ-radiation method has been successfully used to prepare nanocrystalline tin powders. X-ray powder diffraction reveals that the product is single phase of tin with a tetragonal structure. Electron microscopy shows that the average particle size is about 28 nm. The mechanism of Sn²⁺ ion reduction during γ-irradiation is discussed.     

In–vitro calcium phosphate growth over functionalized cotton fibers

Biomimetic growth of calcium phosphate compound on cotton sheets treated with tetraethoxy silane and soaked in simulated body fluid solution was studied using scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), micro-Fourier transform infrared spectroscopy (FTIR) and X-ray diffractometry (XRD). Micro-FTIR and EDAX results show that silicon was coupled to the cotton fiber when cotton was treated with tetra-ethoxy silane (TEOS) at 125°C for 1 h. Calcium phosphate nucleation started to occur on the surface of TEOS-treated cotton fibers upon immersion in 1.5×SBF (simulated body fluid solution) within 3 days and after 20 days, all the fiber surfaces were found covered with a thick and porous coating of calcium phosphate. The Ca and P determined by inductively coupled plasma spectroscopy (ICP) analysis revealed that the Ca/P ratio as well as the amount of calcium phosphate coating depends on the soaking time in SBF solution. © 1999 Kluwer Academic Publishers     

Structure–property relationships for high thermal conductivity carbon fibers

Previous work at Clemson University has shown that ribbon-shaped mesophase pitch-based carbon fibers graphitized at only 2400°C can develop thermal conductivities comparable with those of commercial round-shaped pitch-based carbon fibers graphitized at temperatures above 3000°C. The thermal and electronic transport properties (i.e. thermal conductivity and electrical resistivity) of ribbon-shaped carbon fibers produced at Clemson University are being studied. In addition, the structure of these fibers is being analyzed by electron microscopy and X-ray diffraction techniques. This paper will discuss the relationships between processing conditions, fiber structure and fiber properties.     

Graphitization of polyacrylonitrile carbon fibers and graphite irradiated by γ rays

To investigate the effect of γ-ray radiation on the microstructure of carbon fibers (CF) and graphite, the carbon fibers and graphite were irradiated by ⁶⁰Co source at room temperature. X-ray diffraction results indicate that the interlayer spacing d₀₀₂ of CF and graphite decreased after irradiation. The intensity of (002) peak in CF decreased while the peak of the (002) plane in graphite becomes sharper after irradiation. Scanning electron microscopy combined with energy dispersive X-ray spectroscopy determines that γ-ray irradiation slightly improves the carbon content of CF surface layer. Compton scattering effect and heating caused by γ-ray are proposed to be responsible for the graphitization of CF and graphite.     

Melt-processable acrylonitrile–methyl acrylate copolymers and melt-spun fibers containing MicroPCMs

Acrylonitrile–methyl acrylate (AN–MA molar ratio 85/15) copolymer and copolymers containing 5–25 wt% of microencapsulated phase change materials (MicroPCMs) were synthesized by aqueous redox initiated polymerization. MicroPCMs were incorporated into the copolymer at the step of polymerization. The copolymers were processed by environment friendly, solvent-free melt-spinning. The structures and properties of the copolymers and as-spun fibers containing MicroPCMs were characterized by Nuclear Magnetic Resonance (¹H NMR), Gel Permeation Chromatography (GPC), Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TG), Scanning Electronic Microscope (SEM), X-ray Diffraction (XRD), and Melting Index (MI). The results show that the composition of AN–MA copolymer agrees well with the feeding ratio of AN and MA. The copolymers containing MicroPCMs can be processed at 200 °C. The crystalline enthalpies of the fibers containing 20 and 25 wt% of MicroPCMs are 21 and 25 J/g, respectively; and they increase steadily as the contents of MicroPCMs increase. Tensile strengths of the as-spun fibers are in the range of 1.0–3.2 cN/dtex. The fibers are potentially used as raw materials to fabricate thermo-regulated fabric for comfort clothing.     

Optical properties of tin in the 2.5 to 40μm region

The optical constantsn andk of evaporated tin deposited on different substrates (potassium bromide and mica-sheet discs) were determined in the 2.5 to 40m region by measuring its transmittance. From these values a second step vveacarried out to determine other physical parameters of tin films. These were the density of conduction electrons,N, the effective collision frequency of the electrons ₀ the plasma frequency, ₀, the velocity on the Fermi surface,V ₀ the effective area of the Fermi surface,A _eff, and the absorption coefficient,A. The energy-loss functions for surface and volume plasmons show sharp peak at 7.69m. These values are compared with those found in earlier work.     

Strengthening of basalt fibers with nano-SiO2–epoxy composite coating

Coatings, which were made from pure epoxy and SiO₂ nanoparticle modified epoxy composite, respectively, were applied onto the basalt fiber rovings. The SiO₂ nanoparticles were synthesized using a sol–gel method and modified using coupling agent. Fourier transform infrared spectroscopy (FT-IR) and Differential Scanning Calorimetry (DSC) analyses indicated the formation of modified SiO₂ nanoparticles. The SiO₂ nanoparticle–epoxy composite coating gave rise to a significant increase in the tensile strength of the basalt fibers as compared with the pure epoxy coating, and also the coating endowed the basalt fiber with a promising interfacial property in the basalt fiber reinforced resin matrix composite. The coating modification was an effective way in improving the mechanical properties of basalt fibers and the properties of basalt fiber/epoxy resin composites.     

Composites with piezoelectric thin fibers – first evidence of piezoelectric behavior

 The integration of functional components into composite materials is still a challenge for materials science. The integrated components themselves acting as sensor and/or as actuator should not interfere with the excellent mechanical properties of fiber-reinforced composite materials. Using this approach the implementation of ”one-dimensional”geometries – like fibers with small diameters – is recommended. Thin fibers consisting of piezoelectric materials like PZT are among the promising candidates offering the sensor/actuator coupling. Sol-gel processing is useful for fabricating PZT fibers thin enough to behave flexibly. Therefore, they offer the opportunity to make composite materials adaptive while maintaining the structural conformity. Sol-gel derived high-quality PZT fibers with diameters smaller than 30 μm have been successfully integrated into planar fiber architectures. Within them the fibers are oriented uni-directionally. These architectures are embedded with interdigital electrodes. After embedding the fiber/electrode architectures within glass fiber-reinforced polymers the fibers can be poled and become piezoelectric. The resulting structures were suitable to be tested as adaptive components. It has been demonstrated that such structures can detect impacts and tensions. They can also be driven actively leading to a vibration of the structure. Received: 21 July 1998 / Reviewed and accepted: 22 October 1998     

Determination of diffusivity of sodium in liquid tin using Na-ß″ alumina

Diffusivity of sodium in molten tin was determined using an electrochemical cell of the type Na/Na-β″-Al₂O₃/(Na)Sn where Na-β″-Al₂O₃, which is a sodium-ion conductor, was the solid electrolyte. Using the above cell in which a small amount of sodium dissolved in tin was transported through β″-Al₂O₃ upon application of an external voltage, and using a known solution to Fick's second law for appropriate boundary conditions, the diffusivity was determined to be $$D{\text{ = 4}}{\text{.4 }}\left( {\begin{array}{*{20}c} {{\text{ + 1}}{\text{.0}}} \\ {{\text{ - 0}}{\text{.5}}} \\ \end{array} } \right){\text{ x 10}}^{{\text{ - 4}}} {\text{ exp }}\left( {{\text{ - }}\frac{Q}{{RT}}} \right){\text{ cm}}^{\text{2}} {\text{ sec}}^{{\text{ - 1}}} $$ withQ = 16320 J mol^?1 over a range of temperatures from 240 to 440° C. From the solution to Fick's second law, it was shown that first term approximations, which have often been used in the past, lead to an estimate of diffusivity which is about a factor of 2 too high indicating that more terms should be considered. The diffusivity was also determined using a transient technique in which the decay in voltage upon removal of externally applied voltage was recorded as a function of time. The diffusivity so determined, in which it was assumed that the only polarization was the concentration polarization, was higher than the previous method. The difference between the two diffusivities became smaller with increasing temperature. These experiments thus suggested that interfacial or activation polarization must also be present.     

Processing and characterization of TLCP fibers reinforced by 1?wt% MWCNT

A thermotropic liquid crystalline polymer (TLCP) blend with 1?wt% multiwall carbon nanotubes (MWCNTs) was prepared by melt compounding. Morphological observations of the blend show that the chemical-treated MWCNTs were well dispersed in the TLCP matrix with a good interface. MWCNTs have little effects on the thermal and rheological properties of pure TLCP. TLCP fibers with and without MWCNTs were prepared at certain drawing ratios by a melt spinning method. The degree of orientation of TLCP chains is enhanced by MWCNT micro-clusters during the fiber formation. The mechanical properties of TLCP/MWCNT fibers are significantly increased by 34.5?% for tensile strength and 38.0?% for tensile modulus in comparison with those of pristine TLCP fibers, due to the synergistic effects of MWCNT and TLCP.     

Preparation and high-temperature properties of skin–core structure SiC ceramic fibers

Journal of Materials Science - A new type of skin–core structure SiC ceramic fibers was prepared from polycarbosilane by employing the curing process of alternating air and vacuum atmosphere...     

Effect of addition of tin on the microstructure and machinability of α-brass

This study was aimed at developing lead-free brass alloys with the goal of substituting lead element with tin. For this purpose, lead-free alloys with tin were developed and the microstructure, hardness and machining behaviour of the Cu–30%Zn alloy was compared with Cu–30%Zn–x%Sn (x?= 1.2, 3.2, 5.4, 8, 11.4, 13.9, 17.4). The results showed that the addition of Sn to single-α phase brass led to the formation of duplex (α?+?β′) brass and then the formation of (β′?+?? ) brass both with increased hardness. In addition, the addition of Sn to Cu–30%Zn alloy led to the decrement of equivalent machining forces (F_m), surface roughness and also the promotion of chip fragmentation due to the formation of the β′ phase, which is an improvement in machinability.     

In-situ observations of novel single-atom thick 2D tin membranes embedded in graphene

There is ongoing research in freestanding single-atom thick elemental metal patches,including those suspended in a two-dimensional(2D)material,due to their utility in providing new structural and energetic insight into novel metallic 2D systems.Graphene pores have shown promise as support systems for suspending such patches.This study explores the potential of Sn atoms to form freestanding stanene and/or Sn patches in graphene pores.Sn atoms were deposited on graphene,where they formed novel single-atom thick 2D planar clusters/patches(or membranes)ranging from 1 to 8 atoms within the graphene pores.Patches of three or more atoms adopted either a star-like or close-packed structural configuration.Density functional theory(DFT)calculations were conducted to look at the cluster configurations and energetics(without the graphene matrix)and were found to deviate from experimental observations for 2D patches larger than five atoms.This was attributed to interfacial interactions between the graphene pore edges and Sn atoms.The presented findings help advance the development of single-atom thick 2D elemental metal membranes.     

Rapid oxidation of liquid tin and its alloys at 600 to 800°C

The behavior of liquid tin and its alloys in oxygen at temperature range 600 to 800°C were investigated. Rapid and nearly linear reaction kinetics were observed for pure tin at temperature higher than 700°C. Marker experiments, which determine the mode of mass transport through the scale, and wetting phenomena between the oxide and melts were studied to delineate the reaction mechanism of oxide growth. Moreover, the rates of oxidation of tin were markedly changed by alloying it with small amount of foreign elements. Significantly increased oxidation rates for binary tin alloys containing Mg, Ba, La or Ca were observed. TEM studies indicated that additional growth stresses were introduced into the SnO₂ scales by these additions.     

Mössbauer lattice parameters of mixed tin fluoride α-Sn2F6

Mössbauer resonance measurements using the 23.8 keV γ-transition in ^II9Sn have been carried out on the mixed tin fluoride Sn^IISn^IVF₆ over the temperature range 4.2 ⩽ T ⩽ 378 K.From the temperature dependence of the isomer shift it is possible to extract the effective vibrating masses, i.e. M_eff = 178 amu for Sn(II) and M_eff = 298 amu for Sn(IV). The lattice temperatures calculated from the temperature dependence of the area of the resonance peak are 166 K and 211 K for Sn(II) and Sn(IV) respectively. Using M_eff leads to lattice temperatures of 139K (Sn(II)) and 133 K (Sn(IV)). The recoilless fractions at 293 K are 0.15 for Sn(II) and 0.31 for Sn(IV).     

Optimization of fully aligned bioactive electrospun fibers for “in vitro” nerve guidance

Complex architecture of natural tissues such as nerves requires the use of multifunctional scaffolds with peculiar topological and biochemical signals able to address cell behavior towards specific events at the cellular (microscale) and macromolecular (nanoscale) level. In this context, the electrospinning technique is useful to generate fiber assemblies having peculiar fiber diameters at the nanoscale and patterned by unidirectional ways, to facilitate neurite extension via contact guidance. Following a bio-mimetic approach, fully aligned polycaprolactone fibers blended with gelatin macromolecules have been fabricated as potential bioactive substrate for nerve regeneration. Morphological and topographic aspects of electrospun fibers assessed by SEM/AFM microscopy supported by image analyses elaboration allow estimating an increase of fully aligned fibers from 5 to 39 % as collector rotating rate increases from 1,000 to 3,000 rpm. We verify that fully alignment of fibers positively influences in vitro response of hMSC and PC-12 cells in neurogenic way. Immunostaining images show that the presence of topological defects, i.e., kinks—due to more frequent fiber crossing—in the case of randomly organized fiber assembly concurs to interfere with proper neurite outgrowth. On the contrary, fully aligned fibers without kinks offer a more efficient contact guidance to direct the orientation of nerve cells along the fibers respect to randomly organized ones, promoting a high elongation of neurites at 7 days and the formation of bipolar extensions. So, this confirms that the topological cue of fully alignment of fibers elicits a favorable environment for nerve regeneration.