Electrical and mechanical properties of copper chloride-intercalated pitch-based carbon fibers

Using chlorine vapor transport we have intercalated pitch-based fibers, highly oriented pyrolytic graphite (HOPG), and natural single crystals of graphite with CuCl₂. In this paper we report mainly on the electrical properties of pitch-based fibers heat treated to 2500, 2750 and 3000 °C and then intercalated. The electrical resistivity both above and below room temperature, the tensile strength, and Young's modulus are reported. In very high magnetic fields at 4 K the fibers exhibit Shubnikov-de Haas oscillations, which means this powerful technique is now available as a diagnostic tool for intercalated fibers.     

Tensile Properties of Polyimide Composites Incorporating Carbon Nanotubes-Grafted and Polyimide-Coated Carbon Fibers

The tensile properties and fracture behavior of polyimide composite bundles incorporating carbon nanotubes-grafted (CNT-grafted) and polyimide-coated (PI-coated) high-tensile-strength polyacrylonitrile (PAN)-based (T1000GB), and high-modulus pitch-based (K13D) carbon fibers were investigated. The CNT were grown on the surface of the carbon fibers by chemical vapor deposition. The pyromellitic dianhydride/4,4′-oxydianiline PI nanolayer coating was deposited on the surface of the carbon fiber by high-temperature vapor deposition polymerization. The results clearly demonstrate that CNT grafting and PI coating were effective for improving the Weibull modulus of T1000GB PAN-based and K13D pitch-based carbon fiber bundle composites. In addition, the average tensile strength of the PI-coated T1000GB carbon fiber bundle composites was also higher than that of the as-received carbon fiber bundle composites, while the average tensile strength of the CNT-grafted T1000GB, K13D, and the PI-coated K13D carbon fiber bundle composites was similar to that of the as-received carbon fiber bundle composites.     

The oxidative intercalation of selected carbon fibers by bis(fluorosulfuryl)peroxide,S2O6F2

Oxidative intercalation of two selected PAN- and pitch-based carbon fibers by bis(fluorosulfuryl)peroxide, S₂O₆F₂, results in materials with enhanced electrical conductivities. The nature and the extent of intercalation show some differences in both systems. Pitch-based fibers can be intercalated up to a composition of C_7·5SO₃F. PAN-based fibers lose some of the lattice nitrogen atoms during intercalation and a lower degree of intercalation is noted. Conductance enhancements up to 14 and 17 times were observed for intercalated tows of pitch- and PAN-based fibers respectively. Specific resistivity measurements on intercalated filaments showed metallic behaviour of these materials up to 300 K. The observed conductance values are discussed, together with the structural data obtained on them.     

Synthesis of ternary intercalation compounds of carbon fiber

Ternary intercalation compounds of carbon fiber (ICCF) were successfully synthesized by soaking pitch-based carbon fibers in solvents such as 1,2-dimethoxyethane (DME) or tetrahydrofuran (THF) containing dissolved alkali metals (lithium, sodium, or potassium). ICCF with stage-1 and random stage was synthesized in alkali metal–DME and potassium–THF systems using different types of carbon fibers. However, ICCF with stage-1 could not be synthesized in lithium– or sodium–THF systems using carbon fibers with a low graphitization degree. Furthermore, the influence of the graphitization degree in the synthesis of ICCF was discussed. The graphitization degree of the host carbon fiber, in addition to the dimensions and steric structure of the intercalated complex affected the formation of TICCF.     

Electrospun camphorsulfonic acid doped poly(o-toluidine)–polystyrene composite fibers: Chemical vapor sensing

The electrospinning technique was utilized to produce camphorsulfonic acid (HCSA) doped poly(o-toluidine) (POT)–polystyrene (PS) composite fibers in the non-woven mat form. HCSA doped POT–PS composite fibers were fabricated on an interdigited gold (Au) substrate for use as a chemical vapor sensor. The composite fiber sensor responded to volatile chemicals in different ways, depending on the polarity of sensing chemicals. The surface morphology of the non-woven composite fiber mat after chemical vapor sensing was unchanged. This study highlights that composite fibers comprised of polyaniline derivative and a spinnable polymer do have potential for use as chemical sensors due to their good solubility in common solvents and detectable electrical changes at low fiber contents.     

Self-Diagnosis of GFRP composites containing carbon powder and fiber as electrically conductive phases

The electrical characteristics of glass fiber reinforced plastic (GFRP) composites have been investigated in order to incorporate a self-diagnosis function suitable for monitoring the health of structural materials. The electrical conductivity was introduced by adding carbon powder (CP) or carbon fibers (CF) into GFRP rods and sheets. The self-diagnosis ability of the composites was evaluated by measuring the change in electrical resistance as a function of stress (or strain) in tensile tests. The resistance of CFGFRP changed only slightly at small strain levels and increased nonlinearly with the applied stress due to cutting of the fibers at higher levels. CPGFRP showed high sensitivity to stress and the resistance changed linearly over a wide strain range. During cyclic loading tests, a residual resistance was also observed in CPGFRP composites after unloading. The residual resistance increased with maximum applied strain, showing that it can be used as an indicator of previously applied strain or stress. It is concluded that the CPGFRP composite is a promising material for simple diagnosis of dynamic damage and cumulative strain.     

Toughening of carbon fiber/pitch-based carbon matrix composites by microspace control

A relation between the pore structure and the fracture resistance is examined on carbon fiber/pitch-based carbon matrix composites since pores are considered an important microspace component affecting the fracture behavior in the composites. A part of the pores may lie on a fiber surface so that the bonding force at the fiber/matrix interface is varied depending on the size and the spatial distributions of the pores. The change in the bonding force distribution brings a large-scale fiber pullout process into the composites. Therefore, the fracture resistance can be improved by controlling the microspace of the composites.     

Electrodic characteristics of various carbon materials for lithium rechargeable batteries

Electrodic characteristics of various carbon materials have been investigated to study the correlation between structures of carbon materials and performances of negative electrodes of lithium rechargeable batteries. In the case of highly graphitized carbon materials, the discharge capacity was determined mainly by their crystallinity with no dependence on textures and natural graphite; the highest graphitization at about 360 mAh/g was stage-1 lithium-intercalated graphite, C₆Li (theoretical maximum 372 mAh/g). The coulombic efficiency at the first cycle was strongly dependent on the textures of the carbon materials, and pitch-based carbon fiber of a radial structure showed an excellent coulombic efficiency over 96% by selecting appropriate electrolytes. The performances of the pitch-based carbon fiber were also excellent in the electrolytes consisting of mixed solvents containing propylene carbonate. On the other hand, the pitch coke heat-treated at 550 °C had an initial capacity over 550 mAh/g, which was beyond the theoretically maximum capacity of 372 mAh/g for C₆Li, although the capacity decreased rapidly to less than 250 mAh/g within ten cycles. Polyacrylonitrile (PAN)-based carbon fiber showed a stable capacity with cycling over 350 mAh/g in spite of low graphitization. The initial coulombic efficiency seemed to increase in accordance with decrease of hydrogen and oxygen in the pitch coke, and oxygen and nitrogen in the polyacrylonitrile (PAN) fibers. These phenomena seemed to suggest that carbon materials of disordered structure would have higher capacity than that of the graphitic carbon materials.     

Conductive fibers from enzymatically synthesized polyaniline

Conducting polyaniline (PANI) fibers have been spun from a water-soluble form of PANI which was enzymatically synthesized. The enzyme, horseradish peroxidase (HRP) was used to polymerize aniline in the presence of sulfonated polystyrene (SPS) to directly form a water-soluble, conducting, PANI/SPS complex which combines moderate electrical conductivity with appreciable processability. The PANI/SPS complex was spun into fibers from aqueous solution using a dry-spinning technique. Thermal studies which included thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and DMA show that the complex has very good thermal stability and a T_g at 150°C. Mechanical properties of the fibers show a tenacity of 0.34 cN/dtex for the as-spun fibers with an increase to 0.56 cN/dtex after thermal stretch alignment. Wide angle X-Ray diffraction shows the presence of two weak peaks at d values of 4.16 Å and 2.95 Å for the drawn fibers, while no crystalline reflections were observed for cast films. The drawn fibers also show an order of magnitude improvement in conductivity. These results show that some degree of fiber orientation and crystallinity may be induced during processing.     

Preparation of continuous Si-Fe-C-O functional ceramic fibers

A new polymer named polyferrocarbosilane（PFCS） was prepared from polydimethylsilane and ferrocene. The spinnability of this polymer can be tailored by controlling the content of ferrocene in the polymer. The prepared polymer was spun into a continuous polymer fiber that was subsequently cured in air and heat-treated finally in N2 up to 1 350 ℃ for conversion into Si-Fe-C-O fibers. The resulted Si-Fe-C-O fibers display low specific resistance and magnetic property due to the existence of Fe, which also reduces the specific resistance significantly to 10^-2Ω·cm at room temperature when the amount of ferrocene in feed is as low as 3.0% （mass fraction）. The resulted Si-Fe-C-O fibers, with C/Si molar ratio of about 1.3 and the maximum Fe content of about 2.0% （mole fraction）, are composed ofβ-SiC and small amount of Fe3Si-like crystalline and have an average tensile strength of about 2.0 GPa.     

Chemical and mechanical alterations of SiC Nicalon fiber properties during the CVD/CVI process for boron nitride

To improve the interfacial properties in SiC/SiC composites, BN is an appropriate interphase material to control the fiber/matrix bond. Unfortunately, the gaseous phase (NH₃,BF₃,HF,Ar) used to deposit BN acts aggressively upon Si–C–O (ex-PCS) Nicalon fiber surfaces, and weakens that bond through the formation of a complex interfacial sequence (SiO₂/C), which actually controls the localization of debonds. The reactions between each gas involved and the fiber surface have been studied. Further, if the fiber surface consists of SiC or any silicon-containing compound, the BF₃ gas reacts through a substitution of the silicon by boron in the initial fiber composition. Then, the surface evolves from a (C,O,Si) composition to a (B,C,O,Si) glassy layer. Such a reaction occurs mainly before the BN nucleation, and it alters the reinforcing potential of fibers in composites. This boron-containing glass is shown to be very unstable in the presence of HF gas (the main reaction product).     

Effect of applied pressure on mechanical properties of squeeze cast mg matrix composites

The present study aims at investigating the correlation of microstructure and fracture properties of two AZ91 Mg matrix composites fabricated by squeeze casting technique with a variation of the applied pressure. The composites were reinforced with Kaowool alumino-silicate short fibers and Saffil alumina short fibers, respectively. Microstructural observation, fractographic observation, andin situ fracture tests were conducted on these composites to identify the microfracture process. From thein situ fracture observation of the Kaowool reinforced composites, microcracks were initiated at the short fiber/matrix interfaces for the composite processed with the lower applied pressure, whereas microcracks were initiated easily at short fibers already cracked during squeeze casting at the very low stress intensity level for the composite processed with the higher applied pressure. Thus in this case. the effect of the applied pressure on mechanical properties could be explained using a competing mechanism; the detrimental effect of fiber breakage might override the beneficial effect of the grain refinement and the densification as the applied pressure was increased. On the other hand, for the composites reinforced with Saffil short fibers, microcracks were initiated mainly at the fiber/matrix interfaces at the considerably high stress intensity factor level while the degradation of fibers was hardly observed even in the case of the highest applied pressure. This finding indicated that the higher applied pressure yielded the better mechanical properties on the basis of the reinforcing effect of Saffil short fibers having excellent resistance to cracking.     

An assessment of graphitized carbon fiber use for electrical power transmission

Significant progress has been made in the last few years toward the production of a highly conductive carbon filament. Graphitized carbon fibers, made from a variety of precursor materials such as rayon, polyacrylonitrile (PAN), pitch, mesophase pitch and benzene, have electrical conductivities in the range $\text{10}{}^6\text{? 10}{}^7\text{(Ω}\text{m}\text{)}{}^{\mathrm{?1}}$, tensile strengths in the range 1–3 GPa, tensile moduli in the range 100–700 GPa and densities in the range 1.8 ?2 2.2 × 10³ kg/m³. These properties suggest that graphitized fibers may have potential as current carriers for electrical power transmission. This paper examines the physical reasons for the electrical and mechanical properties and evaluates prospects for fibers with better electrical conductivity without degradation of mechanical properties. Chemical doping (intercalation) of the highly graphitized carbon fibers is found to be capable of achieving increases in conductivity of 5 to 15 times with some degradation in tensile strength. Various applications for electrical power transmission usage are examined, i.e., underground and overhead conductors, underground pipe, overhead towers and submarine cable. Near-term usage is most probable in towers and submarine cable, where high strength-to-weight advantages may offset the present failure of fiber electrical conductivity to equal aluminum or copper values.     

Electrospinning PVDF/PPy/MWCNTs conducting composites

Conducting PVDF/PPy composites (PPy composites) were prepared by using the highly porous electrospun (e-spun) nonwoven web as a host polymer. E-spun nonwoven web was made by electrospinning a solution of PVDF and CuCl₂·2H₂O in solvent of N,N-dimethylacetamide (DMAc). The PPy composites were fabricated by exposing a nonwoven web containing oxidant to pyrrole vapors. Field-emission scanning electron microscopy (FE-SEM) analysis was conducted to show the microstructure of the nonwoven webs and the uniform coating of PPy on the e-spun fiber surfaces of the PPy composite. The information of PPy on the e-spun fibers surface was confirmed by attenuated Fourier-transform infrared spectrometer (ATR FT-IR) and X-ray photoelectron spectroscope (XPS). The thermal property of PPy composites was also investigated by differential scanning calorimeter (DSC) and thermogravimetric analyzer (TGA). The electrical conductivity of the PPy composites was affected by the fabrication method and oxidant content in the nonwoven web. The electrical conductivity and mechanical strength of the PPy composites were improved when surface-modified multi-walled carbon nanotubes (MWCNTs) were added to the e-spun fibers. Energy-filtered transmission electron microscopy (EF-TEM) results confirmed that the MWCNTs were well arranged and embedded in the e-spun fibers. The observed conductivity of the conducting PPy-MWCNTs composite was 10^?1 S/cm.     

Mats and fabrics for electromagnetic interference shielding

Fabrics (with continuous electrically conductive fibers) are more effective than mats (with discontinuous conductive fibers) for electromagnetic interference shielding. Conductive fibers in the form of metal-coated polymer fibers or metal-coated carbon fibers are more effective than those in the form of bare carbon fibers. The highest shielding effectiveness of 53 dB at 1.0 GHz was attained by a metal-coated polymer fabric. The shielding is due mainly to reflection. A higher shielding effectiveness correlates with a higher reflectivity and a lower electrical resistivity. Both shielding effectiveness and reflectivity decrease with increasing frequency from 300 kHz to 1.5 GHz. The shielding effectiveness increases with thickness, as shown for bare carbon fiber mats. A nickel-coated carbon fiber mat of areal weight 9 g/m² is similar to a bare carbon fiber mat of areal weight 17 g/m² in shielding effectiveness.     

Tribology characteristics of in-situ laser deposition of Fe-TiC

In this paper, the effects of TiC morphology and TiC volume fraction on wear resistance of the laser deposited Fe-TiC were studied. In-situ Fe-TiC clad layers were deposited on an AISI 1030 steel substrate with a fiber laser using dynamic blow technique. Two laser conditions along with two atomic percent ratios, 45:55 and 55: 45, were selected for C:Ti, and Fe percentages were explored with 70, 60,50 and 10 wt.%. Results showed that TiC morphology was affected by laser process parameters and powder composition. Optimum wear resistance was found among the samples by conducting wear tests with the ASTM G65-04, dry sand/rubber wheel, low-stress, coarse and abrasive (three-body) test methods. The abrasive characteristics of TiC were compared to WC-12wt.% Ni deposited on a similar substrate measured under identical test conditions. Results showed excellent wear resistance of in-situ TiC. The clad layer's abrasive wear resistance was a factor of 50–70 and 1.2 times higher than that of AISI 1030 steel and WC-12% Ni, respectively.     

Interface and thermal expansion of carbon fiber reinforced aluminum matrix composites

Two kinds of unidirectional PAN M40 carbon fiber(55%,volume fraction) reinforced 6061Al and 5A06Al composites were fabricated by the squeeze-casting technology and their interface structure and thermal expansion properties were investigated.Results showed that the combination between aluminum alloy and fibers was well in two composites and interface reaction in M40/5A06Al composite was weaker than that in M40/6061Al composite.Coefficients of thermal expansion(CTE) of M40/Al composites varied approximately from(1.45-2.68)×10-6 K-1 to(0.35-1.44)×10-6 K-1 between 20 °C and 450 °C,and decreased slowly with the increase of temperature.In addition,the CTE of M40/6061Al composite was lower than that of M40/5A06Al composite.It was observed that fibers were protruded significantly from the matrix after thermal expansion,which demonstrated the existence of interface sliding between fiber and matrix during the thermal expansion.It was believed that weak interfacial reaction resulted in a higher CTE.It was found that the experimental CTEs were closer to the predicted values by Schapery model.     

Evolution of the health of concrete structures by electrically conductive GFRP (glass fiber reinforced plastic) composites

The function and performance of self-diagnostic composites embedded in concrete blocks and piles were investigated by bending tests and electrical resistance measurement. Carbon powder (CP) and carbon fiber (CF) were introduced into glass fiber reinforced plastic (GFRP) composites to provide electrical conductivity. The CPGFRP composite displays generally good performance in various bending tests of concrete block and piles compared to the CFGFRP composite. The electrical resistance of the CPGFRP composite increases remarkably at small strains in response to microcrack formation at about 200 μm strain, and can be used to detect smaller deformations before crack formation. The CPGFRP composite shows continuous change in resistance up to a large strain level just before the final fracture for concrete structures reinforced by steel bars. It is concluded that self-diagnostic composites can be used to predict damage and fracture in concrete blocks and piles.     

Hot-pressed electrospun PAN nano fibers: An idea for flexible carbon mat

Fibers on the nano scale are characterized by its high surface area per unit mass which is associated with high surface free energy. It seems to be an interesting idea to take advantage of this high free surface energy in electrospun in-plane randomly oriented (quasi-isotropic) multi-layered PAN fibrous mat by stabilizing the as electrospun structure at 220 °C under suitable pressure in oxygen environment; such treatment not only activates its high surface energy but also allows the contribution of larger number of molecules on the nano fiber surfaces as well as enhances the bonding between fibers. Mechanical examination of the hot pressed electrospun PAN Nano fibers mat showed higher flexibility than commercial carbon fiber as well as 2-D structure that can be advantageous in applications where the forces are equal in all directions and no specific orientation are required. Stress–strain curves of the hot pressed electro-spun PAN mats showed ductile behavior. The absolute values for tensile strength ranged from 55 to 63 MPa similar to some ductile pure metals such as aluminum, with much larger strain (6.5–8.25%). The modulus value for the fabric was found to be a measure for the enhanced surface free energy (nano size bond) and not the measure for single nano fiber properties, which was proved by preliminary examination for the fracture pattern of the fabric mat. This revealed de-lamination between the mat's layers breaking the bond in between within a value approximately equal or slightly larger than the modulus for bulk PAN polymer (2.80–3.04 GPa) with measured Poisson's ratio of 0.33. Raman analysis for the hot pressed samples showed a formation of disordered carbon structure at 1360 cm^?1 and ordered carbon structure at 1580 cm^?1.     

Tribological properties of brake friction materials with steel fibers

The tribological properties of brake friction materials with and without steel fibers were investigated. The focus of this study was determining the effect of steel fibers on the speed sensitivity of the friction coefficient. The speed sensitivity of the friction coefficient is closely associated with the stick-slip phenomenon. The results indicate that the friction material containing steel filbers was more sensitive to sliding speed, exhibiting a highly negative μ-ν relation. In particular, the friction material with steel fibers showed a larger vibration amplitude during brake applications, suggesting that the μ-ν relation was strongly related to the friction-induced vibration. On the other hand, the wear resistance of the friction materials containing steel was significantly better than that without steel fibers, suggesting longer service life. A possible mechanism of the stick-slip by the steel fibers is discussed in terms of the physical properties of the steel fiber and the gray iron rotor.