Polyacrylonitrile-based Carbon Fibers Research Articles

Tensile Strength of Carbon Fiber Reinforced Cement Composites

ABSTRACTThe effect of carbon fibers on the uniaxial tensile strength of cement paste matrix is studied. The tensile strength values are obtained using the novel Cementitious Composites Axial Tensile Technique (CCATT) described previously [1]. The addition of 1.0, 1.5 and 2.0 volume percent of Polyacrylonitrile-based (PAN) carbon fiber results in an increase in tensile strength of 32, 41 and 48 percent respectively, as compared to the unreinforced matrix. A model based on the rule of mixtures is used to predict the tensile strength of the carbon fiber reinforced composites. Results are discussed with respect to fiber, interface bond, and cementitious matrix characteristic.

Heat Transfer during Heat-treatment of Carbon Fibers by Direct Currenting

A polyacrylonitrile-based carbon fiber tow was heat-treated by directly passing electric current through the tow. The relation between the surface temperature of the tow and supplied electric power was analyzed by an energy balance equation. The rediation became the dominant factor for the heat-loss at high temperatures. The apparent heatconductivity of tow increased with increasing temperature. Temperature distribution in the crosssection of tow was analyzed by considering the temperature dependences of heat-conductivity and specific resistivity. The calculated temperature difference between the center and the surface of the tow increased with increasing surface temperature. The temperature distribution was reduced by installing a reflector around the tow. It is expected that the temperature distribution in a tow gives rise to a certain distribution of the structure of carbon fibers. This subject was also studied by analysing the intensity profiles of wide-angle x-ray diffraction. The integral width of 002 reflection for the tow heat-treated by direct currenting was calculated by using the analyzed temperature distribution and the heat-treatment temperature versus layer thickness relation obtained for the carbon fibers heat-treated with a conventional furnace. The estimated values agreed well with the experimental ones.

Heat-treatment of Carbon Fibers by Direct Currenting

A continuous process for heat-treating a carbon fiber tow by directly passing electric curren through the tow was developed, and by this process a polyacrylonitrile-based carbon fiber tow which was prepared at a highest temperature of about 1250°C was heat-treated. Heat-treatments of two types were made; one employing a reflector covering the heat-radiating zone of a tow, and the other without a reflector. The structural parameters characterizing the stacks of carbon layer, such as interlayer spacing, sizes and orientation, and the mechanical propertie of the carbon fibers heat-treated by direct currenting were evaluated as a function of surfac temperature of tow during heat treatment over the range of 1000 to 2000°C. A considerable heat-loss by radiation from the tow surface is expected during heat-treatment by direct currenting. Therefore an effective heat-treatment temperature in the inside of tow will be lower for the heat-treatment with a reflector than that without a reflector if the surface temperature of tow is constant. The structural parameters versus surface temperature relations for the tow heat-treated with a reflector differed from those for the tow heat-treated without a reflector. These results were explained by considering an effective heat-treatment temperature of tow. Differences in density and linear density between the tows heat-treated with and without a reflector could not be explained by the effective heat-treatment temperature, and seemed to be caused by a certain factor proper to the present heat-treatment method. The tensile modulus after making a correction on density increased almost linearly with increasing orientation of the stacks. The tensile strength decreased with increasing heat-treatment temperature in a similar manner reported for carbon fibers heat-treated by a conventional method.

Total energy distribution of field-emitted electrons from polyacrylonitrile-based high-modulus carbon fibres

Abstract The total energy distribution of field-emitted electrons from polyacrylonitrile carbon fibres and reactor graphite was investigated. Two peaks appeared in the total energy-distribution spectrum of the carbon fibre pyrolysed at 2500°C. In contrast, only one energy peak resulted from the carbon fibre re-pyrolysed at 3000°C and from the reactor graphite. The peak with a high energy is attributed to π electrons of graphite, while the other is attributed to σ electrons. This finding corresponds well with the results obtained by soft X-ray spectroscopy of carbon fibres. Re-pyrolysation of carbon fibres at 3000°C provides high graphitization which results in a disappearance of a electrons. Field-ion microscopical observations of highly graphitized carbon fibres showed the agglomeration of fibrils even at the central area of the fibre where electrons were field-emitted.

The Surface Characterization of Polyacrylonitrile-based Carbon Fibres by Electrochemical Techniques

Carbon fibre surface properties have been studied by measuring the electrochemical behaviour of the hexacyano ferrate (III)/ferrate(II) couple using carbon fibre brush electrodes. Courtaulds Grafil polyacrylonitrile (PAN) based fibres have been studied that have been subjected to different extents of a proprietary wet oxidative surface treatment varying from 0 to 500% of the standard treatment. Analysis of the cyclic voltammograms gives information on the electroactive surface area, a parameter related to the conductivity perpendicular to the fibre surface and rate of electron transfer across the surface of the fibres. The electrochemical data are correlated with other surface properties such as the surface area determined by oxygen chemisorption, surface energy components and some adhesion parameters, such as interlaminar shear strength and critical fragment aspect ratio of epoxy matrix composites.

The temperature dependence of the electrical resistivity of celion carbon fibres

The dependence of the electrical resistivity of Celion polyacrylonitrile-based carbon fibres on test temperature is characterized by a two-stage electrical conduction process and a semiconductor type of behaviour with a low activation energy. It was found that annealing affects the elastic moduli. The electrical conductivity increases with increasing elastic moduli. This behaviour was analysed in terms of the electrical anisotropy and the reorientation of the c axes of the graphite crystallites existing in the fibre during the heat treatment process.

4590055 Pitch-based carbon fibers and pitch compositions and precursor fibers therefor

The invention provides carbon fibers having mechanical properties equival to or even better than those of the polyacrylonitrile-based carbon fibers from a bituminous material, e.g. coal tar pitch, as the starting material. The starting pitch is first partially hydrogenated in tetrahydroquinoline under specific conditions followed by a heat treatment to give a pitch composition suitable for spinning which can be characterized by several parameters including the proportions of the carbons and hydrogens having different chemical shifts in the NMR analysis. The pitch composition for spinning is then subjected to spinning under specific conditions including the temperature condition for controlling the viscosity behavior of the molten pitch composition determined by use of the Andrade's equation and the pitch filament is then infusibilized in an oxidative atmosphere and carbonized in an inert atmosphere into carbon fibers having a tensile strength of at least 200 kg/mm2 and a tensile modulus of at least 10 tons/mm2.

Characterization of microvoids in polyacrylonitrile-based carbon fibres

The microvoids in PAN-based carbon fibres covering a wide range of crystallite size were measured by the method using small-angle X-ray scattering on fibre bundles, and the fractional content of voids and the parameters representing the cross-sectional size of voids perpendicular to the fibre axis were determined. The variation in the shape and size distribution of voids with crystallite thickness was considered by introducing an elliptical crosssection model and a cross-sectional size distribution model. The electron density distribution in the inside of a void was also considered. It is concluded that the electron density difference between a void and the solid surrounding the void is relatively larger in the periphery than in the inner part of a void, and that the electron density in the inner part of a void decreases with increasing crystallite thickness.

Carbon fibres, manufacture, use and economy

More than a decade has passed since carbon fibre has been introduced into market. At the beginning, carbon fibre was appreciated bacause of its degree of freedom of form and its flexibility compared with solid carbon/graphite block. Main applications were: heat resistant, refractory or ablative materials. In 1959, rayon based carbon fibre with high strength and high modulus properties was introduced under a tradename of Thornel 25 by Union Carbide Corp. USA. Since then carbon fibre has come into the spotlight as a reinforcing material in the composite for structural usage.Then an intensive research work has been carried out to find the more suitable raw materials for carbon fibre (precursor) in UK and in Japan, Dr. Shindo, Osaka Industrial Institute of Japan has succeded in making carbon fibre from acrylic fibre in 1961. The scientists of RAE (Royal Aircraft Establishment, U. K.) have invented the manufacturing technology of carbon fibre based on PAN (polyacrylonitrile) in 1964. The mechanical properties of them were far excellent compared with that of rayon based carbon fibre. Since then, PAN has established the position of precursor and still the most important precursor for structural use carbon fibre.On the other hand in order to reduce the cost, a number of extensive work has been done to develop carbon fibre based on petroleum pitch or on coal pitch. Nowadays high performance carbon fibre based on pitch is industrialized by Union Carbide and also general purpose carbon fibre based on pitch has been commercialized by Kureha Chemical Co, Japan.With regards to the applications, high performance PAN based carbon fibre paves the way for reinforced resin structural materials for aerospace applications. With an increasing performance requirements from aerospace industry, carbon fibre is moving to the second phase in terms of its properties to meet these requirements. A new generation type of carbon fibre is now under development by a number of manufacturers.In this paper, the trend of carbon fibre including its characteristics applications and market estimation are reviewed.

Characterization of polyacrylonitrile based carbon fibers

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Surface topography and mechanical properties of carbon fibres

AbstractSurface topography of polyacrylonitrile based carbon fibres preoxidized under a variety of conditions has been studied in detail. Only those carbon fibres processed under optimum conditions are found to possess defect free surface topography. Changes in surface topography and the tensile strength of carbon fibres with processing conditions have been discussed.

Magnetoresistance and Microstructure of Stress-graphitized Carbon Fibers

The microstructure of stress-graphitized polyacrylonitrile-based carbon fibers has been studied through the measurements of magnetoresistance at 77K and by scanning electron microscopy. The carbon fibers were stretched throughout oxcidation, carbonization and graphitization (at 2700°C). The fibers were then annealed at 3000°C. The transverse magnetoresistance of the fibers was positive. The magnetoresistance changes linearly with increasing magnetic field strength above 3kG. The low field behavior of the magnetoresistance suggested the existence of the light minority carriers in the samples. The maximum transverse magnetoresistance at 10kG is 10.45%, which indicates the presence of the extensively grown crystallites with three dimensional crystallinity. Preferred orientation of the samples was determined by the anisotropy of the magnetoresistance as follows: (1) The c-axes of the crystallites are perpendicular to the fiber axis.(2) The c-axes of the crystallites are parallel to the radial direction in the cross-section of the fibers. The preferred orientation of the crystallites in the cross-section was confirmed by scanning electron microscopy. The average crystallite size of the samples was estimated by the scanning electron micrographs of the cross-section to be about 0.6-1.2μm in width and 500-700A in thickness.

Some electronic properties of polyacrylonitrile-based carbon fibres

The resistivity, thermoelectric power and magnetoresistance of carbon fibres derived from a polyacrylonitrile-based precursor heat treated to between 1000°C and 2800°C have been examined. The resistivity ratio as a function of heat treatment temperature exhibits a broad minimum roughly at about a heat treatment temperature (HTT) of 1750°C, and both the thermoelectric power and the magnetoresistance undergo a change of sign at that temperature. The importance of the temperature 1750°C, at which fundamental structural changes are believed to take place, is examined in the light of existing band models in the carbon and amorphous semiconductor fields.

Direct lattice resolution of layer planes in polyacrylonitrile based carbon fibres

THE microstructure of polyacrylonitrile (PAN) based carbon fibres has been investigated by several techniques including high and low angle X-ray diffraction and electron microscopy. The results obtained with high-modulus (400 GNm−2) RAE carbon fibres1,2 and high-modulus Rolls-Royce carbon fibres3 are essentially similar; crystallites, the widths of which have a distribution of values with a mean about 65 A, enclose sharp-edged microvoids of mean width about 10 A. There is little three-dimensional order in the crystallites and the graphite layer planes are essentially turbostratic. The length of the crystallite seems to be limited by lattice defects to less than 100 A although individual layers may well be much longer. Studies of rayon-based carbon fibres4 have yielded similar evidence and recently Fourdeux, Herinckx, Perret and Ruland5 reported that the layer planes in these materials can be resolved directly by high-resolution electron microscopy following the phase-contrast method described by Heidenreich, Hess and Ban6 for carbon black specimens.

Direct Lattice Resolution of Layer Planes in Polyacrylonitrile Based Carbon Fibres

THE microstructure of polyacrylonitrile (PAN) based carbon fibres has been investigated by several techniques including high and low angle X-ray diffraction and electron microscopy. The results obtained with high-modulus (400 GNm−2) RAE carbon fibres1,2 and high-modulus Rolls-Royce carbon fibres3 are essentially similar; crystallites, the widths of which have a distribution of values with a mean about 65 A, enclose sharp-edged microvoids of mean width about 10 A. There is little three-dimensional order in the crystallites and the graphite layer planes are essentially turbostratic. The length of the crystallite seems to be limited by lattice defects to less than 100 A although individual layers may well be much longer. Studies of rayon-based carbon fibres4 have yielded similar evidence and recently Fourdeux, Herinckx, Perret and Ruland5 reported that the layer planes in these materials can be resolved directly by high-resolution electron microscopy following the phase-contrast method described by Heidenreich, Hess and Ban6 for carbon black specimens.

Stress Graphitization of Polyacrylonitrile Based Carbon Fibre

CARBON fibre can be made by the pyrolysis of organic polymer fibre precursors. Up to now, cellulose1 and polyacrylonitrile (PAN)2 have been found to produce carbon fibre of good strength and modulus. Preliminary details of the structure of PAN based carbon fibre, similar to that prepared and used by us, have been published by Johnson and Watt3 and Badami, Joiner and Jones4. One of us5 has reported that the strength of PAN carbon fibre declines when heated above 1,200° C. It is therefore of interest to report that increasing strength with Young's modulus can be obtained if stress is applied to the fibre at graphitizing temperatures.