Conductive Carbon Fiber Research Articles

An electron microscopy study of high-thermal-conductivity ribbon-shape carbon fibers

In an effort to develop a low-cost high thermal conductivity carbon fiber, ribbon-shaped fibers were meltspun from a liquid crystalline, mesophase pitch precursor. Initial tests indicated that the ribbon-shaped fibers could be processed more easily and exhibited improved thermal conductivities when compared to commercial round fibers. Evidently, it is the more linear, polycrystalline structure within these fibers that accounts for their improved thermal conductivities. Thus, studies using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were conducted to fully analyze the transverse and longitudinal structure of these high thermal conductivity fibers.Ribbon-shaped fibers, melt-spun from a synthetic mesophase pitch and then heat treated, were tested to determine their tensile strengths, tensile moduli and thermal conductivities. A Jeol JSM-I C848 SEM at an accelerating voltage of 20 kV was used to obtain general structural information, such as extent and texture of lamellar organization of the graphitic layers within the fibers, and the microstructure of the fibers was studied by TEM.

A local theory of heating in cross‐ply carbon fiber thermoplastic composites by magnetic induction

AbstractFor joining and repair of continuous fiber thermoplastic composites, induction heating has been viewed a strong candidate. Induction heating employs an applied alternating magnetic field, which induces a rotational emf in a grid of conductive carbon fibers, which are then used to carry resulting currents. In continuous carbon fiber crossply composites the available paths for “eddy current” loops are along the network of conductive carbon fibers. For this to occur, an electrical transfer must take place between crossing fibers in adjacent plies. Tests involving variable thicknesses of interply neat film layers have been performed to provide insight into the mechanisms taking place. These tests indicate that the primary mechanism for heating in such laminates is dielectric losses in the polymeric region between fibers in adjacent planes that form the conductive loop. Therefore, heating is not uniform in such composites despite a uniform magnetic flux. Heating patterns were viewed using liquid crystal materials and E‐type thermocouples. Several factors leading to nonhomogeneous thermal distributions have been considered, including current density effects, internal emf cancellation, and rotational field effects. Global and local considerations are addressed, a localized model is proposed, and the corresponding theory is developed qualifying the early results. Additional testing has supported the theory.

A New Approach Towards Defibrillation Electrodes: Highly Conductive Isotropic Carbon Fibers

A new carbon fiber material was studied for its potential benefit in defibrillation electrodes. Miniaturization of the fiber production can result in small strands with extremely large surface areas. Two carbon fiber patches and a single carbon fiber bundle were used for the purposes of this study, and the results were compared to those obtained with conventional titanium/mesh patch electrodes. Tests performed in a saline filled tank revealed considerably lower resistances through the carbon material when compared to standard mesh electrodes. There was also a higher peak current flow with lower voltage. The carbon fibers exhibited lower impedance for defibrillation and this may be related to low polarization known to occur with carbon materials. This new carbon material may prove to be useful and further research is required.

Preparation and properties of vapor grown graphite

Carbon films with various electrical conductivities have been prepared by plasma CVD in various preparation conditions. Especially, carbon films prepared on stainless steel showed good electrical conductivity. Conductive carbon films and fibers prepared by plasma CVD became high quality graphite materials comparable to HOPG after heat-treatment at over 3000°C. These graphite materials show electrical conductivity over 1×10 5 S/cm by intercalation of various acceptors; HNO 3, AsF 5, Br 2, ICl and CuCl 2. The electrical conductivity and structure of these intercalated films and fibers were hardly changed for almost 1.5 years. These films and fibers except intercalated with HNO 3 are stable in the air atmosphere at room temperature. Stable structure of AsF 5, ICl- and CuCl 2-intercalated films and fibers are supposed to be 4th, 6th and 2nd stage, respectively, from X-ray diffraction patterns. Both CuCl 2- and ICl-GIC were stable up to 350°C in the air and the conductivities of both rose in proportion to the temperature until 350°C. The limiting current density of plasma CVD graphite fibers and ICI-intercalated graphite fibers are measured to 5×10 4 and 7×10 4A/cm 2, respectively.

Grilles n�gatives composites pour accumulateurs au plomb

A new manufacturing process of negative composite grids for lead acid accumulators is described and discussed. In this process long grid preforms are woven with both conductive carbon fibres and nonconductive glass or polypropylene fibres. Then, lead is selectively deposited on to the conductive carbon fibres by continuous electroplating and, after rinsing and drying, the composite grids are stamped out of the impregnated preforms. In these grids, the carbon fibres, embedded with lead, form the connector and the grid-bars. The non-conductive glass or polypropylene fibres provide the necessary cohesion of the woven preform before electroplating, and retension of the active material pasted into the grids. These negative composite grids are about four times lighter than the classical lead-alloy grids of similar size. They exhibit the excellent corrosion resistance and hydrogen overpotential of pure lead. Negative plates made from these grids have been subjected to CEI-type charge-discharge cycles (12 h cycles, 75% discharge depth): they have undergone more than 250 cycles without deterioration.

Resistivity behavior of filled electrically conductive crosslinked polyethylene

AbstractThe electrical resistivity of crosslinked high‐density polyethylene loaded with conductive blacks and carbon fibers was studied as a function of filler concentration and temperature. A thermoelectric switching phenomenon (a sudden resistivity increase in the vicinity of the polyethylene melting point) in such semicrystalline conductive systems was investigated. Significant switching behavior was exhibited by compounds containing very low concentrations of carbon fibers. Some crosslinked compounds filled with mixtures of carbon black and carbon fibers were also studied.

Assessment of the potential for release of conductive fibers from advanced composites by means of thermogravimetric analysis and scanning electron microscopy

AbstractRecently, there has been concern over the effects of accidentally released conductive carbon and graphite fibers on unprotected electrical circuits. Because of their thermal stability, such fibers could be released by the involvement of a resin matrix composite in a fire. A simple method based on thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) has been developed which permits the assessment of release potential from such composites. Dynamic TGA is used to determine temperatures at which significant events such as onset of resin matrix decomposition occur. Isothermal TGA permits a determination of the time required to produce releasable fibers at a given temperature. SEM examination of residues from TGA experiments serves to characterize their physical state which, in turn, permits a more precise assessment of release potential. This method has been used to examine a large number of materials composed of several different fibers in a variety of thermoset and thermoplastic matrices. It is concluded that release potential varies inversely with resin thermal‐oxidative stability and directly with fiber stability. The matching of matrix resin char and fiber stabilities is especially effective in suppressing fiber release.