Fibers electrical resistivity values

This semp can also be used to measure the electrical resistance values of fibers during their production. The sample holder should be placed just before the final winding of fiber on the bobbin. With the movement of the fibrous sample, the wheels would also rotate thus, the surface morphology of the object would not be affected because of its friction with the surface of the wheels. 

The high electrical resistivity of asbestos fibers is weU-known, and has been widely exploited in electrical insulation appHcations. In general, the resistivity of chrysotile is lower than that of the amphiboles, particularly in high humidity environments (because of the availabiHty of soluble ions). For example, the electrical resistivity of chrysotile decreases from 1 to 2100 MQ/cm in a dry environment to values of 0.01 to 0.4 MQ/cm at 91% relative humidity. Amphiboles, on the other hand, exhibit resistivity between 8,000 and 900,000 MQ/cm. 

The electrical conductivity of PET fibers as compared with other main synthetic fibers is relatively low. This explains why PET fibers are often utilized in the manufacture of textiles as electroisolating materials. The value of the electrical resistivity characterizing reciprocal conductivity is of the order 10 (/2 cm). The mechanism of the electrical conductivity of PET fibers is still a matter of controversy. According to results attained [57], there are convincing arguments that in the case of PET objects the electrical conductivity is due to the ionic mechanism. 

Use For apparatus and equipment (such as vacuum tubes) where its high melting point, ability to withstand large and rapid temperature changes, chemical inertness and transparency (including UV radiation), and electrical resistance are valuable. Produced as fibers and fabrics for heat resistance, low expansion coefficient, and insulating value. 

The electrical resistivity of the fibers as a function of carbonizing temperature are shown in Figure 14. The resistivity drops from a value of several hundred thousand micro ohm centimeters at low carbonization temperatures to about 675p ohm cm at 2200 C carbonization temperatures. 

Piezoresistivity [66] was observed in cement matrix composites with 2.6-7.4 vol% unidirectional continuous carbon fibers. The dc electrical resistance in the fiber direction increased upon tensile loading in the same direction, such that the effect was mostly reversible when the stress was below that required for the tensile modulus to decrease. The gage factor was up to 60. The resistance increase was due to the degradation of the interface of the fiber and matrix, which was mostly reversible. Above the stress at which the modulus started to decrease, the resistance abruptly increased with stress/strain, due to fiber breakage. The tensile strength and modulus of the composites were 88% and 84%, respectively, of the calculated values based on the rule of mixtures. 

Carbon fiber has been found to be an effective thermistor [192-194], such as a cement paste reinforced with chopped carbon fiber (about 5 mm long) with silica fume (15 wt% cement). Its electrical resistivity decreased reversibly with increasing temperature (1-45°C), with activation energy of electrical conduction (electron hopping) of 0.4 eV. This value is comparable to semiconductors (typical thermistor materials) and is higher than that of carbon fiber polymer matrix composites. The current-voltage characteristics of carbon fiber reinforced silica fume cement paste were linear up to 8 V at 20°C. 

In practical terms, the electrical resistance measurements on conductive fibers/yams is always problematic due to their soft, flexible, and poor dimensional stabilities. Very few publications have reported research regarding electrical measurements on fibrous stmctures. Usually, the conventional method, in which crocodile clips are attached with a voltmeter, is used for this purpose. Crocodile clips hold the conductive fibers/yarns of specific length and then electrical resistance is measured on particular voltage values. However, the hard grip of crocodile clips damages any conductive coatings or creates internal cracks in the fibrous stmctures, which cause the permanent loss in electrical properties of conductive threads. Consequently, consistent results with crocodile clips cannot be obtained. 

Surface resistivity is one factor that can be controlled by the incorporation of a reinforcing agent or a filler into a polymer formulation. Thus, the incorporation of natural fiber into high-density polyethylene composites decreases the surface resistivity of the composite. Reinforcing agents can also affect the electrical resistance. The incorporation of Kevlar fibers in polyaniline increases the tracking resistance threefold over the value for the base polymer. 

Typical thermal conductivity values (all in W/mK) are 0.2 to 0.3 for pol5Tners, 1 to 2 for carbon black, 10 to 20 for polyacrylonitrile (PAN) based carbon fiber, 100 to 800 (depends on the heat treatment temperature) for petrolaim pitch-based carbon fiber, 400 for copper, and 600 for graphite. Electrical resistivity (1/electrical conductivity) values (all in ohm-cm) for various materials are lO to 10 for polymers, 10" for electrically conductive carbon black, 10 for PAN-based carbon fiber, 10" for pitch based carbon fiber, 10 for graphite, and lO" for metals such as aluminum and copper. One proach to inqjroving the conductivity of a polymer is through the addition of conductive filler, such as carbon and metal [1, 2]. Typically for a bipolar plate, the desired thermal and electricM conductivity are 20 W/mK and 50 S/cm (0.02 ohm-cm). 

Electrical Behavior. The resistivity of acetate varies significantly with humidity with typical values ranging from 10 ohm-cm at 45% rh to 10 ohm-cm at 95% rh (16). Because of the high resistivity both acetate and triacetate yams readily develop static charges and an antistatic finish is usually apphed to aid in fiber processing. Both yams have also been used for electrical insulation after lubricants and other finishing agents are removed. 

Tests for Fire Resistance of Roof Covering Materials, 1983. (similar to ASTM E 108) Tests for Flame Propagation and Smoke Density Values for Electrical and Optical Fiber Cables in Spaces Transporting Environmental Air, 1991. 

Through assumptions and the use of values for known resistances of the materials used in the apparatus, the actual bulk resistance of the DL material could be calculated. This resistance was then used so that the electrical conductivity could be solved. Nitta and colleagues noted that the in-plane conductivities of the DL materials were a linear fxmction of the compressed thickness (i.e., the conductivity increased when the thickness decreased with increased compression pressure). This resulted from a decrease in thickness that led to a loss of porosity in the DL materials and higher contact between fibers. 

This paper describes some recently completed work on the electrical conductivity of paper. A reliable method of measuring bulk conductivity of paper, where the contact resistance is reduced to negligible values, has been developed. A study of the effect of some papermaking variables, such as the type of pulp, the degree of refining and the fiber orientation, on the bulk conductivity of paper is reported. Finally, an investigation has been made into the current transient phenomena exhibited by paper upon the application of an electric field. These transient currents were interpreted as the transport of ionic species within a water associated fibrous network making up the paper. 

Studies on MWCNT electronic properties have shown that they behave like an ultimate carbon fiber [77] at high temperature their electrical conductivity can be described by the semiclassical models already used for graphite, while at low temperature they reveal two-dimensional quantum transport features. A reliable prediction of their electronic properties is even more difficult than in the case of SWCNTs, due to the higher complexity of their structure, and experimental measurements on MWCNT resistivity have not given reliable values (Table 9.2), due to different CNT purities and measuring conditions. 

Fibers with specific resistance ( )ofabout 10 cm or less are called conductive fibers and those of 10 to 10 cm are called antistatic fibers. Since ordinary manmade fibers have values of of 10 to 10 cm, agents must be added to increase conductivity ofa fiber and reduce specific resistance. The reduced specific resistance allows articles formed from the fibers to dissipate electrical charge and reduces static sparkling. 

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