Individual Carbon Fibers Research Articles

Enhanced mechanical and electrical properties of nylon‐6 composite by using carbon fiber/graphene multiscale structure as additive

ABSTRACTIn order to improve the mechanical properties and electrical conductivity of nylon‐6 (PA6) composites, a highly effective multiscale structure filler comprising poly(diallyldimethylammonium chloride) (PDDA)‐modified graphene and negatively surface‐charged carbon fiber was synthesized in this study. For this, the graphene used a top‐down method for synthesis by exfoliating graphite oxide (GO) through focused solar radiation on it and then modified its surface by using a polyelectrolyte. The carbon fiber (CF) surface was functionalized by an acid oxidation method. The multiscale structure was manufactured via the electrostatic interaction between the positively charged solar graphene (SG) and oppositely charged CF by homogeneous mixing. Scanning electron microscopy (SEM) images of the fracture surface of the PA6 composites exhibited that the carbon fiber/graphene multiscale structure possessed better dispersion and compatibility than those of individual CF and SG did. Thus, the impact strength, bending properties, and electrical conductivity of the PA6 composites were enhanced. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2015,132, 41968.

Preparation and hydrothermal corrosion behavior of Cf/SiCN and Cf/SiHfBCN ceramic matrix composites

Cf/SiCN and Cf/SiHfBCN-based ceramic matrix composites (CMC) were fabricated using the precursor infiltration and pyrolysis technique (PIP). Their behavior in subcritical hydrothermal conditions was investigated at 150–250°C using exposition times of 48, 96 and 240h and shown to rely on active corrosion.The data of the mass loss as a function of the corrosion time and temperature at S/V of 0.075 were used to rationalize the corrosion kinetics of the CMCs. Both materials have been shown to exhibit excellent stability in subcritical hydrothermal conditions. The corrosion rates of Cf/SiHfBCN were lower than those determined for Cf/SiCN; furthermore, SEM investigation indicates that spallation occurred in the Cf/SiCN samples; whereas the ceramic matrix was still attached on the individual carbon fibers in Cf/SiHfBCN. The results indicate that the incorporation of Hf and B into SiCN matrix leads to a significant improvement of its hydrothermal corrosion performance.

Conversion of Lignin Precursors to Carbon Fibers with Nanoscale Graphitic Domains

Lignin is one of the most abundant and inexpensive natural biopolymers. It can be efficiently converted to low cost carbon fiber, monolithic structures, or powders that could be used directly in the production of anodes for lithium-ion batteries. In this work, we report thermomechanical processing methods relevant for the conversion of lignin precursors into carbon fiber-based anode materials, the impact of lignin precursor modification on melt processing, and the microstructure of the final carbon material. Modification of softwood lignin produced functionalities and rheological properties that more closely resemble hardwood lignin thereby enabling the melt processing of softwood lignin in oxidative atmospheres (air). The conversion process encompasses melt spinning of the lignin precursor, oxidative stabilization, and a low temperature carbonization step in a nitrogen/hydrogen atmosphere. We determined resistivities of individual carbon fiber samples and characterized the microstructure by scanning electron microscopy. Neutron diffraction reveals nanoscale graphitic domains embedded in an amorphous carbon matrix. These unique structural characteristics make biomass-derived carbon fibers a suitable material for energy storage applications with enhanced electrochemical performance.

Oxidative Treatment to Improve Coating and Electrochemical Stability of Carbon Fiber Paper with Niobium Doped Titanium Dioxide Sols for Potential Applications in Fuel Cells

Regular hydrophobized carbon paper cannot be used for unitized regenerative fuel cell applications as it corrodes at high potentials on the oxygen electrode side. Reported here are the oxidative treatment and dip-coating of carbon paper (Spectracarb™ 2050A-0850) with Nb-doped TiO2 sols (anatase phase) to increase the corrosion resistance of the carbon paper at the interface between catalyst layer and gas diffusion backing layer. Coating of carbon paper with Nb-doped TiO2 sols generates a reasonably uniform layer of TiO2 and covers the individual carbon fibers well only if the carbon paper is oxidatively functionalized prior to coating. This can be reasoned with a better wetting of the functionalized carbon paper by the sol-gel and the formation of covalent bonds between Ti and the large number of functional groups on the surface of oxidized carbon paper, which is in good agreement with previous observation for carbon nanotubes. The resistance towards oxidation of coated and uncoated samples of untreated and functionalized carbon paper was probed by cyclic voltammetry in 0.5M aqueous H2SO4 at 1.2V versus Ag/AgCl for up to 72hours to mimic the conditions in a unitized regenerative fuel cell. Among these four cases studied here, functionalized carbon paper coated with a layer of Nb-doped TiO2 shows the highest stability towards electrochemical oxidation while uncoated functionalized carbon paper is the least stable due to the large number of available oxidation sites. These results clearly demonstrate that a coating of carbon fibers with TiO2 generates a lasting protection against oxidation under conditions encountered at the oxygen electrode side of unitized regenerative fuel cells.

Electrospinning of "Welded" Carbon Fiber Paper for Lithium Ion Battery Current Collectors

An approach for electrospinning interconnected (“welded”) carbon fiber mats for improved electronic conduction in 3D porous positive electrode current collectors for lithium ion batteries is presented. Although individual carbon fibers have high axial electronic conductivity, when used as current collectors in lithium ion batteries and other electrochemical storage/conversion systems, their electronic conductivity is largely limited by the interconnectivity of the carbon fibers. Active electrode materials for lithium ion batteries have low electronic conductivity and can block the carbon fiber interconnectivity when loaded onto the fibers. Interconnectivity in commercial carbon fiber paper (CFP) (d ≈ 10μm) is achieved by bonding of individual carbon fibers using additional polymer precursor and subsequent carbonization. In some reports of CFP current collectors in electrochemical devices additional carbon additives are mixed with the active material slurry and then pressed into the CFP in order to improve interconnectivity and electronic conductivity [1]. When carbon fiber paper is used directly in an electrode without an addition of carbon additives, the electrode is reported to suffer from low electronic conductivity due to low interconnectivity of carbon fibers [2]. Additionally, for application in lithium ion battery electrodes, CFP should be composed of small diameter fibers. Decreasing carbon fiber diameter can improve mass loadings for active material coated carbon fiber current collectors, and reduces the path length for ionic conductivity, however this also increases the number of junction points of carbon fibers in the CFP and decreases interconnectivity. In a typical carbon fiber paper (CFP) electrode, hundreds of fiber-to-fiber contact points are encountered along the path of the electron to the external circuit. A multitude of junction points creates a tortuous electronic pathway, decreasing the interconnectivity of the fibers. In order to improve electronic conductivity in small diameter CFP based LIB electrodes we have used an electrospinning method that allows us to weld the carbon fiber junctions together, increasing the conductivity and maintaining the integrity of the connections during coating of ceramic active materials. In this study, welded CFP paper was created by electrospinning polyacyrlonitrile (PAN) precursor solution into fiber mats followed by carbonization to create carbon fiber paper. LiMn2O4 active materials were grown directly on the welded CFP using a hydrothermal synthesis technique. The individual fibers were approximately 1 μm diameter and the fibers were loaded with approximately 60wt% active material. The LiMn2O4 loaded electrodes were used directly as positive electrodes in lithium ion batteries without additional binder or carbon additive. The improvement in electronic conductivity of the welded fibers dramatically improved the performance of the lithium ion battery (Li metal / 1 M LiPF6 in 1:1 EC:DMC / LiMn2O4) at intermediate rates.[1] Kercher, Andrew K., J. O. Kiggans, and Nancy J. Dudney. "Carbon Fiber Paper Cathodes for Lithium Ion Batteries." Journal of The Electrochemical Society157.12 (2010): A1323-A1327.[2] Kim, Chan, et al. "Fabrication of Electrospinning‐Derived Carbon Nanofiber Webs for the Anode Material of Lithium‐Ion Secondary Batteries." Advanced Functional Materials 16.18 (2006): 2393-2397.

Electrodeposited polyethylenedioxythiophene with infiltrated gel electrolyte interface: a close contest of an all-solid-state supercapacitor with its liquid-state counterpart

We report the design of an all-solid-state supercapacitor, which has charge storage characteristics closely matching that of its liquid-state counterpart even under extreme temperature and humidity conditions. The prototype is made by electro-depositing polyethylenedioxythiophene (PEDOT) onto the individual carbon fibers of a porous carbon substrate followed by intercalating the matrix with polyvinyl alcohol-sulphuric acid (PVA-H2SO4) gel electrolyte. The electrodeposited layer of PEDOT maintained a flower-like growth pattern along the threads of each carbon fiber. This morphology and the alignment of PEDOT led to an enhanced surface area and electrical conductivity, and the pores in the system enabled effective intercalation of the polymer-gel electrolyte. Thus, the established electrode-electrolyte interface nearly mimics that of its counterpart based on the liquid electrolyte. Consequently, the solid device attained very low internal resistance (1.1 Ω cm(-2)) and a high specific capacitance (181 F g(-1)) for PEDOT at a discharge current density of 0.5 A g(-1). Even with a high areal capacitance of 836 mF cm(-2) and volumetric capacitance of 28 F cm(-3), the solid device retained a mass-specific capacitance of 111 F g(-1) for PEDOT. This is in close agreement with the value displayed by the corresponding liquid-state system (112 F g(-1)), which was fabricated by replacing the gel electrolyte with 0.5 M H2SO4. The device also showed excellent charge-discharge stability for 12 000 cycles at 5 A g(-1). The performance of the device was consistent even under wide-ranging humidity (30-80%) and temperature (-10 to 80 °C) conditions. Finally, a device fabricated by increasing the electrode area four times was used to light an LED, which validated the scalability of the process.

Solid polymer electrolyte-coated carbon fibres for structural and novel micro batteries

We report a method to deposit a thin solid polymer electrolyte (SPE) coating around individual carbon fibres for the realization of novel battery designs. In this study an electrocoating method is used to coat methacrylate-based solid polymer electrolytes onto carbon fibres. By this approach a dense uniform, apparently pinhole-free, poly(methoxy polyethylene glycol (350) monomethacrylate) coating with an average coating thickness of 470. nm was deposited around carbon fibres. Li-triflate, used as supporting electrolyte remained in the coating after the electrocoating operation. The Li-ion content in the solid polymer coating was found to be sufficiently high for battery applications. A battery device was built employing the SPE coated carbon fibres as negative electrode demonstrating reversible specific capacity of 260. mA. h/g at low currents (C/10), suggesting that these coated carbon fibres can be employed in future structural composite batteries.

Fracture behavior of individual carbon fibers in tension using nano-fabricated notches

Abstract The fracture toughness of single Toray T700 polyacrylonitrile (PAN) carbon fibers is measured using focused ion beam (FIB) nano-fabrication techniques to induce controlled geometry of end notches with lengths 100 nm to 1 μm. These fibers were subjected to axial loading with a nano-tensile testing system for evaluating mode I fracture behavior. The test data indicates the mode-I fracture toughness (KIC) for these PAN based carbon fibers is 1.73 MPa m1/2 for notch sizes larger than 300 nm, which compares well with limited previous studies. However, measurement scatter in the current study is significantly reduced by using a FIB artificial notch opposed to the native flaw distribution for fracture initiation. In addition, improved fiber mounting and alignment procedures coupled with the precision of the nano-tensile testing system assist in unprecedented resolution in single fiber fracture toughness. For notch sizes less than 0.3 μm, the KIC fracture toughness increases with decreasing notch size, confirming PAN carbon fibers sheath/core microstructure hypothesis. The softer core and harder shell due to synthesis and processing steps suggest the measured data has important implications to single carbon fiber structure–mechanical property relationship.

Lithium manganese aluminum oxide-based full Li-ion battery using carbon fibers as current collectors

Herein, Li-ion battery using carbon fibers instead of conventional aluminum/copper foils as the current collectors is assembled. To achieve the binder-free environment, LiMn0.97Al0.03O2-based fiber type cathode is prepared directly via a two-step strategy involving electroplating and hydrothermal method by forming active materials on the individual carbon fiber. Cu6Sn5-based fiber type anode is prepared directly via electroplating and subsequent heat treatment. The resulting LiMn0.97Al0.03O2|Cu6Sn5 Li-ion battery using carbon fiber as the current collector functions at about 3 V, with an initial capacity of 180 mAh g−1 (based on the cathode). The capacity retention is 90 % after 150 cycles. In particular, the battery using phosphate-modified LiMn0.97Al0.03O2-based fiber type electrode demonstrates a better cycling and high rate performance compared to the unmodified counterpart.

In situ study of copper electrodeposition on a single carbon fiber

Copper metallization on carbon surface can improve physicochemical performances of carbon based materials and introduce multi-functionalities. This paper reports on the combined electrochemical characterization, in situ X-ray diffraction and fluorescence research, and scanning electron microscopic studies of nucleation and growth of Cu on individual carbon fibers. Compared to the flat glassy carbon substrates and Au thin film substrates, the onset potential of Cu electrodeposition on individual carbon microfiber is more negative with lower efficiencies, indicating the difficulty of Cu nucleation on carbon fiber surface. Utilizing the capability of synchrotron X-ray microbeam diffraction and fluorescence spectroscopy techniques, real time Cu crystalline structure and composition evolvement information during the electrochemical reaction processes have been studied. In situ study reveals random Cu grain formation and anisotropic growth. Dynamic Cu growth and dissolution were found to occur simultaneously during deposition. Cu nuclei density and size can be effectively controlled, in addition to the grain morphology and stability, indicating the possibility of electrochemical manipulation of microstructure thus the properties of Cu coated carbon materials.

The effect of grain size on the lattice thermal conductivity of an individual polyacrylonitrile-based carbon fiber

The lattice thermal conductivity (λL) of general purpose grade polyacrylonitrile (PAN)-based carbon fibers with a crystallite size (La) of several nanometers was examined. Using a modified 3ω method, the λL of the fibers with different heat-treatment temperatures were detected, and it was found that the λL was linearly dependent on −1/La. Based on phonon scattering theory, this observation can be attributed to the combined effect of boundary scattering and point-defect scattering. The constant for point-defect scattering (A) was evaluated and a formula was derived.

Hygrothermal effects on painted carbon fibre composite surfaces

In this article, the effect of hygrothermal aging on the painted surface finish of unidirectional and fabric carbon fibre composite laminates, with and without surfacing film was investigated. The results highlighted the importance of ensuring that the composite surface directly beneath the paint layer is made from a uniform material with a consistent thickness in order to minimise surface defects from occurring during aging. The surfacing film was found to minimise the print through development on the painted unidirectional and twill composite surfaces. However, the surfacing film layer was found to intermingle with the carbon fibre plies during cure, which resulted in an uneven film thickness that caused increased levels of orange peel. The twill laminate painted surface produced high levels of print through and surface waviness that was caused by the large resin rich regions located within the tow intersections at the surface which enlarged due to thermal expansion and swelling of the matrix with hygrothermal aging. It was also noted that the small resin rich regions between the individual carbon fibres on the unidirectional composite surface were sufficiently large to print through the painted surface.

Interfacial Microstructure and Properties of Carbon Fiber Composites Modified with Graphene Oxide

The performance of carbon fiber-reinforced composites is dependent to a great extent on the properties of fiber-matrix interface. To improve the interfacial properties in carbon fiber/epoxy composites, we directly introduced graphene oxide (GO) sheets dispersed in the fiber sizing onto the surface of individual carbon fibers. The applied graphite oxide, which could be exfoliated to single-layer GO sheets, was verified by atomic force microscope (AFM). The surface topography of modified carbon fibers and the distribution of GO sheets in the interfacial region of carbon fibers were detected by scanning electron microscopy (SEM). The interfacial properties between carbon fiber and matrix were investigated by microbond test and three-point short beam shear test. The tensile properties of unidirectional (UD) composites were investigated in accordance with ASTM standards. The results of the tests reveal an improved interfacial and tensile properties in GO-modified carbon fiber composites. Furthermore, significant enhancement of interfacial shear strength (IFSS), interlaminar shear strength (ILSS), and tensile properties was achieved in the composites when only 5 wt % of GO sheets introduced in the fiber sizing. This means that an alternative method for improving the interfacial and tensile properties of carbon fiber composites by controlling the fiber-matrix interface was developed. Such multiscale reinforced composites show great potential with their improved mechanical performance to be likely applied in the aerospace and automotive industries.

3-D pore-scale resolved model for coupled species/charge/fluid transport in a vanadium redox flow battery

The vanadium redox flow battery (VRFB) has emerged as a viable grid-scale energy storage technology that offers cost-effective energy storage solutions for renewable energy applications. In this paper, a novel methodology is introduced for modeling of the transport mechanisms of electrolyte flow, species and charge in the VRFB at the pore scale of the electrodes; that is, at the level where individual carbon fiber geometry and electrolyte flow are directly resolved. The detailed geometry of the electrode is obtained using X-ray computed tomography (XCT) and calibrated against experimentally determined pore-scale characteristics (e.g., pore and fiber diameter, porosity, and surface area). The processed XCT data is then used as geometry input for modeling of the electrochemical processes in the VRFB. The flow of electrolyte through the pore space is modeled using the lattice Boltzmann method (LBM) while the finite volume method (FVM) is used to solve the coupled species and charge transport and predict the performance of the VRFB under various conditions. An electrochemical model using the Butler–Volmer equations is used to provide species and charge coupling at the surfaces of the carbon fibers. Results are obtained for the cell potential distribution, as well as local concentration, overpotential and current density profiles under galvanostatic discharge conditions. The cell performance is investigated as a function of the electrolyte flow rate and external drawing current. The model developed here provides a useful tool for building the structure–property–performance relationship of VRFB electrodes.

Measurement Methods and Applications for Thermophysical Properties at Micro/nanoscales

The effect of thermal contact resistance (TCR) on the measurement of thermal properties of micro/nanowires is investigated using the changing length T type probe and the 3ω-T type probe. For the junction established by two crossed platinum microwires, the TCR is found to decrease as temperature increases, which can be possibly explained by the plastic deformation of the microscopic contacts. The same value of thermal effusivity of the test wire is obtained in the presence of different interstitial materials, and the one with small thermal impedance will give a decrease in the temperature oscillation of the hot wire. Based on this fact, the thermal conductivity and thermal effusivity of individual carbon fibers heat treated at 2800 and 1000 °C are measured, and the calculated specific heat is found to decrease with increasing heat-treatment temperature and to approach the value of graphite.

Fiber‐Based Hybrid Nanogenerators for/as Self‐Powered Systems in Biological Liquid

Fiber‐Based Hybrid Nanogenerators for/as Self‐Powered Systems in Biological Liquid

Simultaneous Measurements of Thermal Properties of Individual Carbon Fibers

Combining the steady-state and quasi-steady-state T type probes, the longitudinal thermal conductivity and thermal effusivity of individual mesophase pitch-based carbon fiber heat treated at 2800 °C and 1000 °C have been measured from 100 K to 300 K. The present method allows simultaneous measurements of thermal properties using the same instrument, by simply changing the applied direct current to alternating current. The specific heat is found to decrease with increasing heat-treatment temperature and to approach the value of graphite. The highly graphitized carbon fiber has a maximum thermal conductivity of 410 W · m−1 · K−1 at about 250 K, and its thermal diffusivity decreases with increasing temperature. Comparatively, the thermal conductivity of the fiber heat treated at 1000 °C is much smaller, with the peak shifting to high temperature due to a large defect density, and its thermal diffusivity is nearly temperature independent.

Hierarchical graphene nanocones over 3D platform of carbon fabrics: A route towards fully foldable graphene based electron source

A three dimensional field emitter comprising hierarchical nanostructures of graphene over flexible fabric substrate is presented. The nanostructuring is realized through plasma treatment of graphene, coaxially deposited over individual carbon fiber by means of simple aqueous phase electrophoretic deposition technique. Hierarchical graphene nanocone, acting as a cold electron emitter, exhibits outstanding electron emission performance with a turn-on field as low as 0.41 V μm(-1) and a threshold field down to 0.81 V μm(-1). Electric field modification around the special woven like geometry of the underlying base fabric substrate serves as the booster to the nanostructured graphene related field amplification at the electron emission site. Superb robustness in the emission stability can be attributed to suppressed joule heating on behalf of higher inborn accessible surface area of graphene nanocone as well as excellent electrical and thermal conductivity of both the graphene and carbon fabrics. Superior flexibility of this high-performance graphene based emitter ensures their potential use in completely foldable and wearable field emission devices.

Multi‐scale modeling of moving interface problems with flux and field jumps: Application to oxidative degradation of ceramic matrix composites

AbstractProblems involving reaction and species diffusion involve field and flux jumps at a moving reaction front. In multi‐scale problems such as carbon fiber composite oxidation, these effects need to be tracked at the microscopic scale of individual carbon fibers. A multi‐scale model is derived in this paper for predicting species distribution in such problems using a fully coupled multi‐scale homogenization approach. The homogenized fluxes from the micro‐scale are derived using Hill's macro‐homogeneity condition accounting for both flux jumps and species density field jumps at the reacting interface in the micro‐scale unit cell. At the macro‐scale, the competition between the transport of reacting species (oxygen) and the reaction product (carbon dioxide) is modeled using homogenized mass conservation equations. The moving reaction front in carbon fibers at the micro‐scale is tracked using level set method and an adaptive meshing strategy. The macroscopic weight loss of the composite when exposed to oxygen is simulated as a function of time using a coupled finite element methodology at various locations in a validated macroscopic model. Copyright © 2010 John Wiley & Sons, Ltd.

Temperature dependence of the thermal conductivity of individual pitch-derived carbon fibers

Temperature dependence of the thermal conductivity of individual pitch-derived carbon fibers