Different Types Of Carbon Fibers Research Articles

Determination of the longitudinal thermal conductivity of low‐ordered carbon fibers by using an optothermal Raman technique

AbstractThe usage of carbon fibers (CFs) for high‐temperature applications has been increasing in recent years. However, the determination of thermal properties at high temperatures is a challenging task. In this study, the thermal conductivity of two different types of CF having a diameter in the range from 5–7 m, as a function of temperature, was examined by using the optothermal Raman method. Raman spectroscopy was first used to obtain the structural organization and structural homogeneity of the fibers. Then, owing to the fact that Raman spectra are sensitive to laser excitation power and external temperature, Raman spectroscopy was used as a contactless thermometer to determine the local temperature rise of the fibers. A formula was derived by solving the heat diffusion equation for cylindrical fibers and a set of boundary conditions, similar to the experimental conditions, which allows accurate estimation of longitudinal thermal conductivity. The results are discussed in relation with the phonon scattering theory and can be attributed to the combined effect of scattering from defects. The radiative and convective heat losses were estimated, and their influence on thermal conductivity was also determined.

Study on the mechanical properties of C/C composites reinforced by different types of carbon fibers

With the aim of selecting suitable carbon fibers as reinforcement material for carbon/carbon composites, needled carbon fiber felt preforms are fabricated by T300 carbon fibers and TZ300 carbon fibers as raw material respectively. The industrial CT results of prepared deposited carbon/carbon (C/C) composites show that the porosity of the composites fabricated by T300 is higher than that of TZ300. The mechanical properties of C/C composites after deposition and heat treatment are comparatively investigated. The results show that the difference between two deposited composites is small, while the difference at high temperature is large. After 2100 °C and 2450 °C heat treatment, the mechanical properties of T300-C/C composites show a gradual decline, while the TZ300-C/C composites decrease sharply, indicating that the high-temperature properties of TZ300 carbon fiber is inferior to T300 carbon fiber. The fracture mechanisms of two composites are investigated through microscopic fracture observation. T300 carbon fibers are still attached to the pyrolysis carbon layer while TZ300 fibers are completely stripped from the fracture surface. The interfacial bonding between T300 and pyrolytic carbon is higher than that of TZ300.

Investigation of the Tendency of Carbon Fibers to Disintegrate into Respirable Fiber-Shaped Fragments

Recent reports of the release of large numbers of respirable and critically long fiber-shaped fragments from mesophase pitch-based carbon fiber polymer composites during machining and tensile testing have raised inhalation toxicological concerns. As carbon fibers and their fragments are to be considered as inherently biodurable, the fiber pathogenicity paradigm motivated the development of a laboratory test method to assess the propensity of different types of carbon fibers to form such fragments. It uses spallation testing of carbon fibers by impact grinding in an oscillating ball mill. The resulting fragments were dispersed on track-etched membrane filters and morphologically analyzed by scanning electron microscopy. The method was applied to nine different carbon fiber types synthesized from polyacrylonitrile, mesophase or isotropic pitch, covering a broad range of material properties. Significant differences in the morphology of formed fragments were observed between the materials studied. These were statistically analyzed to relate disintegration characteristics to material properties and to rank the carbon fiber types according to their propensity to form respirable fiber fragments. This tendency was found to be lower for polyacrylonitrile-based and isotropic pitch-based carbon fibers than for mesophase pitch-based carbon fibers, but still significant. Although there are currently only few reports in the literature of increased respirable fiber dust concentrations during the machining of polyacrylonitrile-based carbon fiber composites, we conclude that such materials have the potential to form critical fiber morphologies of WHO dimensions. For safe-and-sustainable carbon fiber-reinforced composites, a better understanding of the material properties that control the carbon fiber fragmentation is imperative.

Effect of carbon fibers crystallinity on the formation and growth of TiC coating in molten salt

To improve the application of molten salt method in carbon fibers (CFs) surface modification, the work explores the effect of the CFs-itself crystallinity on the formation and growth mechanism of TiC coating in the molten salt reaction. Three different types of CFs were used to prepare TiC coatings at 850°C, and the formation and growth mechanisms were studied. The results showed that CFs surface defects could preferentially initiate nucleation and cause inhomogeneity of TiC particles in the initial stage of TiC coating formation. The CFs surface with high crystallinity could obtain a finer and more uniform TiC coating because the growth rate of TiC particles is slower and the particles do not accumulate with each other during the coating growth. At the same time, the growth rate of TiC coating decreased with increasing CFs crystallinity during the TiC coating growth, which reason is that CFs with higher crystallinity require more activation energies of carbon atom counter diffusion. Therefore, the surface of CFs with higher crystallinity and fewer surface defects is easier to obtain a uniform and particle size TiC coating during the molten salt reaction.

Preparation, thermal stability and deflection of a density gradient thermally-conductive carbon foam material derived from phenolic resin

A density (ρ) gradient thermally-conductive (λ) phenolic foam material was initially prepared and it was used as a precursor to prepare a carbon foam (CF) material (ρ-λ-CF). The precursor was carbonized at the temperature between 900 and 1100 °C under the protection of N2 gas and graphitized between 2100 and 2500 °C under the protection of Ar gas, respectively. The thermogravimetric analysis was carried out to investigate the influence of temperature on the thermal stability of the achieved ρ-λ-CF during carbonization and graphitization. The deflection of ρ-λ-CF reinforced with different types of carbon fibers by mass fractions of 0 wt%, 3 wt%, 6 wt%, and 9 wt% was investigated. The microstructure of the composites was observed and analyzed by scanning electron microscopy. The results show that the prepared ρ-λ-CF consisted of three parts: reticulated carbon, carbon microspheres, and voids. It had the graphite structure and exhibited a well structured obturator microsphere shape. The toughening mechanism of ρ-λ-CF reinforced with carbon fibers was preliminarily discussed.

Investigation of the fibre type influence on the energy density of the induction heating process through a semi-analytic method

The study investigated the induction welding of carbon fibre-reinforced Polyamide 66 with different types of carbon fibres and fabrics. The major scope of the study was the plastification of the thermoplastic matrix as the first process step of the continuous induction welding. A new semi-analytic method was created to simulate the dependence of the plastification parameters (induction coil, power, weld velocity and coil-workpiece distance) on the fibre and fabric. Numerical and physical methods of Duhovic [1] and Velthuis [2] were used to investigate the complete process of plastification and consolidation. This kind of simulation uses the principle of the finite element method (FEM) [1]. The calculated results are strongly influenced on the one hand by the simplification of the thermal conductivity of the fibre and the matrix in the composite material (constant shape value, constant beam value) and on the other hand by the parameterization of the heat source.The semi-analytic method uses the radial basic function and the physical correlation between the thermal losses and the induced eddy currents at the electric conductive carbon fibers for the calculations. The calibration of the tool was done by testing a series of plastification parameters for different kinds of fibre and fabrics. In-situ temperature measurements through thermocouples and pyrometer were carried out for the melt zone in addition to destructive testing of the resulting joint. Yarlagadda [3] and Ahmed [4] have investigated the induction heating of carbon fibres and have shown three kinds of heating mechanisms: Joule loss/fibre heating, junction heating/dielectric hysteresis heating and junction heating/contact resistance heating. The simulation model investigated the amount of heating based on these three mechanisms.The semi-analytic model was created to use it for weldability check of material combinations and the pre-parameter setup for induction welding at a fully automated production system of composite automotive structural parts [5].

Analysis of the tensile moduli affected by microstructures among seven types of carbon fibers

Abstract A two-phase micromechanical model composed of crystallites and amorphous components can be employed to address the relationship between the microstructure and the tensile modulus of carbon fibers. It turns out that the tensile modulus increases with the increase of three factors: the aspect ratio of crystallites, volume fraction of crystallites and degree orientation of crystallites. Subsequently, seven types of carbon fibers are compared, and their differences of the tensile moduli affected by the three factors are calculated. The results show that the differences of the tensile moduli affected by the factors of microstructures between different types of carbon fibers can be discussed using the two-phase micromechanical model.

Factors controlling the strength of carbon fibres in tension

We have investigated the fracture mechanisms of different types of carbon fibres, in terms of skin-core differences in single fibres, flaw size and fracture toughness. The fibre strength distribution was measured precisely using the fragmentation test for single-fibre composites. The failure probability for intermediate/high modulus types fibres was found to be constant with fibre strength in the range 2–4GPa, but in contrast the strength scatter for high modulus type fibres was reduced. The fracture toughness of the carbon fibres, determined by introducing notches with lengths in range 60–200nm, was found to be about 1.1MPam1/2. The average flaw size of the carbon fibres increased with increasing fibre modulus, suggesting that the crack growth of surface flaws on the tens-of-nm scale occurred. This appears to be the main reason for the reduction in tensile strength during the carbonisation treatment.

Dependence of the mechanical properties, morphology, and structural characteristics of different types of carbon fibers on treatment temperature

A comparative study was made of three types of carbon fibers subjected to high-temperature treatment at 2000, 2400, and 2800°C in the static regime. The mechanical properties of the initial and heat-treated fibers were studied by scanning electron microscopy, x-ray diffraction, and laser mass spectrometry. Analysis of the surface morphology and structural characteristics of the fibers showed that the two types of fibers obtained with the use of an organic solvent as the precursor have similar structural and mechanical characteristics. Their treatment at 2400°C was accompanied by a slight decrease in strength characteristics and a change in the morphology of the surface. At the same time, the carbon fibers that were made based on a precursor obtained with the use of sodium rhodanide had a more distinct morphology and underwent a marked reduction in strength at temperatures >2000°C. This result might be related to the differences in the conditions under which these fibers were formed, the type of solvent used, and the fibers’ chemical composition.

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.

Influence of carbon fibre on the through‐the‐thickness NPR behaviour of composite laminates

AbstractThis work is concerned with the influence of carbon fibre, resin types and fibre volume fraction on the through the thickness Poisson's ratio of composite laminates. Different types of carbon fibres in various resins with several fibre volume fractions ranging between 65 and 80% are analysed to show the effect of each parameters on the values of the Poisson's ratios ν13 of the laminates balanced of the type [±θ]2S.

Carbon fibre composite for ventilation air methane (VAM) capture

Coal mine methane (CMM) is not only a hazardous greenhouse gas but is also a wasted energy resource, if not utilised. This paper evaluates a novel adsorbent material developed for capturing methane from ventilation air methane (VAM) gas in underground coal mines. The adsorbent material is a honeycomb monolithic carbon fibre composite (HMCFC) consisting of multiple parallel flow-through channels and the material exhibits unique features including low pressure drop, good mechanical properties, ability to handle dust-containing gas streams, good thermal and electrical conductivity and selective adsorption of gases. During this study, a series of HMCFC adsorbents (using different types of carbon fibres) were successfully fabricated. Experimental data demonstrated the proof-of-concept of using the HMCFC adsorbent to capture methane from VAM gas. The adsorption capacity of the HMCFC adsorbent was twice that of commercial activated carbon. Methane concentration of 0.56% in the inlet VAM gas stream is reduced to about 0.011% after it passes through the novel carbon fibre composite adsorbent material at ambient temperature and atmospheric pressure. This amounts to a maximum capture efficiency of 98%. These encouraging laboratory scale studies have prompted further large scale trials and economic assessment.

A comparative study of carbon fiber-based microelectrodes for the measurement of nitric oxide in brain tissue

The measurement of Nitric oxide ( NO) in real-time has been a major concern due to the involvement of this ubiquitous free radical modulator in several physiological and pathological pathways in tissues. Here we performed a study aiming at evaluating different types of carbon fibers, namely Textron, Amoco, Courtaulds and carbon nanotubes (University of Kentucky) covered with Nafion ®/ o-phenylenediamine ( o-PD) for NO measurement in terms of sensitivity, LOD, response time and selectivity against major potential interferents in the brain (ascorbate, nitrite and dopamine). The results indicate that, as compared with the other carbon fibers and nanotubes, Textron carbon fiber microelectrodes coated with two layers of Nafion ® and o-PD exhibited better characteristics for NO measurement as they are highly selective against ascorbate (>30,000:1), nitrite (>2000:1) and dopamine (>80:1). These coated Textron microelectrodes showed an average sensitivity of 341 ± 120 pA/μM and a detection limit of 16 ± 11 nM. The better performance of the Textron fibers is likely related to a stronger adhesion or more uniform coating of the Nafion ® and o-PD polymers to the fiber surface. In addition, the background current of the Textron carbon fibers is low, contributing to the excellent signal-to-noise for detection of NO.

Self-Diagnosis of Hybrid CFRP Rods and As-Strengthened Concrete Structures

A literature survey reveals that extensive studies have been published on the hybridization of composite and self-diagnosis of carbon fiber reinforced polymer (CFRP) composites. In these researches, not more than one type of carbon fibers or powders is used as active materials. This article addresses a new class of smart hybrid CFRP (HCFRP) rods consisting of at least two types of carbon fibers of different strength and moduli as active materials and their applications to concrete structures. The carbon fibers function as both structural and sensing materials by virtue of their good mechanical properties, electrical conductivity, and piezoresistivity. The hybridization focuses on two aspects: to better the electrical behavior of the HCFRP rods in order to obtain a stage-based sensing function, and to upgrade their mechanical properties. The self-diagnosis and damage detection functions of the HCFRP rods and/or the as-strengthened concrete structures are realized through measuring the change in electrical resistance. The sensing principles are based on the electrical resistance change with the strain change and sudden jumps in electrical resistance due to the gradual fractures of different types of carbon fibers. The results show that the electrical resistance of the HCFRP rods changes with strain in a stepwise manner. The sudden jumps in electrical resistance at different strain amplitudes are associated with the ruptures of different types of carbon fibers. Thus, the step-based sensing of HCFRP rods-selves or strengthened structures is realized. Moreover, the initiation and propagation of cracks in the HCFRP rod-strengthened concrete beams are also measured by means of clip gages and distributed fiber optic sensors (FOS).

Characterization of PEMFCs gas diffusion layers properties

Experiments have been carried out on different gas diffusion layer (GDL) materials in order to better understand the influence of this component on fuel cell performance. The study, focused on the mechanical behaviour of the GDL, shows the effect of the stress caused both by the hot-pressing and the compression in a cell on different types of carbon fibres based supports: a cloth, a felt and a paper. It has been observed that decreasing the stress applied on the GDL, which is of high interest for the durability of the MEAs, has moreover a positive effect on their performance.

Electrical and Mechanical Characterization of Hybrid CFRP Sheets

This study brings forth the electrical and mechanical models of a new kind of hybrid carbon fiber-reinforced polymer (HCFRP) composites consisting of several types of carbon fibers with different strengths and Young’s moduli. Then, an experimental program with some main variables including the carbon fiber types and their volume fractions has been carried out. Six types of specimens have been fabricated to investigate the mechanical properties and self-health monitoring function of the HCFRP sheets with different types of carbon fiber and volume fractions. The experimental results indicate that the hybridization of several types of carbon fibers is an effective method for upgrading the mechanical properties of the HCFRP sheets. The electrical resistance of the HCFRP sheets changes with the strain in a stepwise manner due to the gradual macro-fracture of different types of carbon fibers. The number of steps is related to the number of carbon fiber types. It has also been shown that the ruptured carbon fibers can still contribute to the current conduction through transverse electrical conduction. The good correlations between the mechanical and electrical behaviors reveal the self-health monitoring function of the HCFRP sheets.

Self-diagnosis of structures strengthened with hybrid carbon-fiber-reinforced polymersheets

The correlation of mechanical and electrical properties of concrete beams strengthened withhybrid carbon-fiber-reinforced polymer (HCFRP) sheets is studied in this paper. Two typesof concrete beams, with and without reinforcing bars, are strengthened with externallybonded HCFRP sheets, which have a self-structural health monitoring function due to theelectrical conduction and piezoresistivity of carbon fibers. Parameters investigated includethe volume fractions and types of carbon fibers. According to the investigation, it isfound that the hybridization of uniaxial HCFRP sheets with several differenttypes of carbon fibers is a viable method for enhancing the mechanical propertiesand obtaining a built-in damage detection function for concrete structures. Thechanges in electrical resistance during low strain ranges before the rupture of carbonfibers are generally smaller than 1%. Nevertheless, after the gradual ruptures ofcarbon fibers, the electrical resistance increases remarkably with the strain ina step-wise manner. For the specimens without reinforcing bars, the electricalbehaviors are not stable, especially during the low strain ranges. However, theelectrical behaviors of the specimens with reinforcing bars are relatively stable,and the whole range of self-sensing function of the HCFRP-strengthened RCstructures has realized the conceptual design of the HCFRP sensing models andis confirmed by the experimental investigations. The relationships between thestrain/load and the change in electrical resistance show the potential self-monitoringcapacity of HCFRP reinforcements used for strengthening concrete structures.

High-Temperature Oxidation Resistance of Ceramic Matrix Composites Si3N4– Cf

We have studied the behavior of ceramic matrix composites in the system Si3N4 – Cf, reinforced with different types of carbon fibers, at moderate (1100°C) and maximum (1500°C) service temperatures. We have studied the effect of the composition of ceramic matrix composites and the oxidation temperature conditions on their strength properties and microstructure.

Decreased functions of astrocytes on carbon nanofiber materials

Carbon nanofibers possess excellent conductivity properties, which may be beneficial in the design of more effective neural prostheses; however, limited evidence on their cytocompatibility properties currently exists. The objective of the present in vitro study was to determine cytocompatibility properties of formulations containing carbon nanofibers pertinent to neural implant applications. Substrates were prepared from four different types of carbon fibers, two with nanoscale diameters (nanophase, or less than or equal to 100 nm) and two with conventional diameters (or greater than 100 nm). Within these two categories, both a high and a low surface energy fiber were investigated and tested. Carbon fibers were compacted in a manual hydraulic press via a uniaxial loading cycle. Astrocytes (glial scar tissue-forming cells) were seeded onto the substrates for adhesion, proliferation, and long-term function studies (such as total intracellular protein and alkaline phosphatase activity). Results provided the first evidence that astrocytes preferentially adhered and proliferated on carbon fibers that had the largest diameter and the lowest surface energy. Based on these results, composite substrates were also formed using different weight percentages (0–25 wt%) of the nanophase, high surface energy fibers in a polycarbonate urethane matrix. Results provided the first evidence of decreased adhesion of astrocytes with increasing weight percents of the high surface energy carbon nanofibers in the polymer composite; this further demonstrates that formulations containing carbon fibers in the nanometer regime may limit astrocyte functions leading to decreased glial scar tissue formation. Positive interactions with neurons, and, at the same time, limited astrocyte functions leading to decreased gliotic scar tissue formation are essential for increased neuronal implant efficacy.

Cytocompatibility of Carbon Nanofiber Materials for Neural Applications

AbstractSince the cytocompatibility of carbon nanofibers with respect to neural applications remains largely uninvestigated, the objective of the present in vitro study was to determine cytocompatibility properties of formulations containing carbon nanofibers. Carbon fiber substrates were prepared from four different types of carbon fibers, two with nanoscale diameters (nanophase, or less than or equal to 100 nm) and two with conventional diameters (or greater than 200 nm). Within these two categories, both a high and a low surface energy fiber were investigated and tested. Astrocytes (glial scar tissue-forming cells) and pheochromocytoma cells (PC-12; neuronal-like cells) were seeded separately onto the substrates. Results provided the first evidence that astrocytes preferentially adhered on the carbon fiber that had the largest diameter and the lowest surface energy. PC-12 cells exhibited the most neurites on the carbon fiber with nanodimensions and low surface energy. These results may indicate that PC-12 cells prefer nanoscale carbon fibers while astrocytes prefer conventional scale fibers. A composite was formed from poly-carbonate urethane and the 60 nm carbon fiber. Composite substrates were thus formed using different weight percentages of this fiber in the polymer matrix. Increased astrocyte adherence and PC-12 neurite density corresponded to decreasing amounts of the carbon nanofibers in the poly-carbonate urethane matrices. Controlling carbon fiber diameter may be an approach for increasing implant contact with neurons and decreasing scar tissue formation.