Carbon fibers conductivity

Conductive fibers Stainiess steei fiber, carbon fiber, conductive coated fibers Permanent, nonmigratory Used for internal EMI shielding... 

Antistatic additives are capable of modifying properties of plastics in such a way that they become antistatic, conductive, and/or improve electromagnetic interference shielding (EMI). Carbon fibers, conductive carbon powders, and other electrically conductive materials are used for this purpose. 

Yang and Butkus, Carbon Fibers Conductivity Studies", NASA Contractor Report 166302, Aug 1980. 

Process. Any standard precursor material can be used, but the preferred material is wet spun Courtaulds special acrylic fiber (SAF), oxidized by RK Carbon Fibers Co. to form 6K Panox B oxidized polyacrylonitrile (PAN) fiber (OPF). This OPF is treated ia a nitrogen atmosphere at 450—750°C, preferably 525—595°C, to give fibers having between 69—70% C, 19% N density less than 2.5 g/mL and a specific resistivity under 10 ° ohm-cm. If crimp is desired, the fibers are first knit iato a sock before heat treating and then de-knit. Controlled carbonization of precursor filaments results ia a linear Dow fiber (LDF), whereas controlled carbonization of knit precursor fibers results ia a curly carbonaceous fiber (EDF). At higher carbonizing temperatures of 1000—1400°C the fibers become electrically conductive (22). 

Excellent insulating properties, along with the abiUty to be stmctural components, make plastics the ideal candidate materials for electrical appHcations. Although generally used as insulators, carbon black or carbon fiber can be added to make plastic materials electrically conductive, thereby expanding their usefulness in the electronics area. 

Fig. 8. Comparison of electrical and thermal conductivity of PAN- and pitch-based carbon fiber to metals, where P = pitch, T = Thornel, and...

Electrical Hazards. Because carbon fibers are conductive, the airborne filaments can create serious problems shorting out electrical equipment. The best option is to locate sensitive equipment in clean rooms outside of areas where carbon fiber is being processed. If this is not possible, electrical cabinets must be effectively sealed to prevent contact with carbon fibers. A filtered air-positive purge provides additional protection for sensitive equipment. 

Pitch-based fibers generally have higher moduh but lower strengths than theh PAN-based counterparts. The specific properties of the various types of carbon fibers are compared in Figure 4. Pitch-based fibers also have higher electrical conductivity, which can be an important consideration in certain circumstances, for example, for use in electromagnetic inductance (EMI) shielding. 

Because of their unique blend of properties, composites reinforced with high performance carbon fibers find use in many structural applications. However, it is possible to produce carbon fibers with very different properties, depending on the precursor used and processing conditions employed. Commercially, continuous high performance carbon fibers currently are formed from two precursor fibers, polyacrylonitrile (PAN) and mesophase pitch. The PAN-based carbon fiber dominates the ultra-high strength, high temperature fiber market (and represents about 90% of the total carbon fiber production), while the mesophase pitch fibers can achieve stiffnesses and thermal conductivities unsurpassed by any other continuous fiber. This chapter compares the processes, structures, and properties of these two classes of fibers. 

In contrast, there is also current interest in investigating PAN-based fibers in low thermal conductivity composites [62], Such fibers are carbonized at low temperature and offer a substitute to rayon-based carbon fibers in composites designed for solid rocket motor nozzles and exit cones. 

Duffy, D.R., Ting, J.-M., Guth, J.R. and Lake, M.L., Carbon fiber reinforced lightweight composites with ultra high thermal conductivities, Proc. Int. JEPC, Atlanta, GA, Sept., 1994, pp. 442 448. 

Ting, J.M. and Lake, M.L., Vapor grown carbon fiber reinforced aluminum composites with very high thermal conductivity J. Mat. Res., 1995, 10(2), 247 250. 

Fig. 18. The temperature dependence of the thermal conductivity of hybrid carbon fiber monoliths measured in the to fibers direction at two densities.

Dinwiddie, R.B., Nelson, G.E., and Weaver, C.E., The effect of sub-minute high temperature heat treatments on the thermal conductivity of carbon-bonded carbon fiber (CBCF) insulation. In Proc. Thermal Conductivity 23, ed. K.E. Wilkes, R.B. Dinwiddie and R.S. Graves, Technomic Pub. Co., Inc., Lancaster, PA, 1996, pp. 466 477. 

Because direct calculation of thermal conductivity is difficulty 1], experimental measurements on composites with nanotubes aligned in the matrix could be a first step for addressing the thermal conductivity of carbon nanotubes. High on-axis thermal conductivities for CCVD high-temperature treated carbon fibers have been obtained, but have not reached the in-plane thermal conductivity of graphite (ref. [3], Fig. 5.11, p. 115). We expect that the radial thermal conductivity in MWNTs will be very low, perhaps even lower than the c-axis thermal conductivity of graphite. 

---