Electric poling of carbon fiber with and without nickel coating

This paper reports for the first time electric poling in a carbon material. The material is carbon fiber (polyacrylonitrile-based, 12,000-fiber tow, 40-mm inter-electrode distance) with/without nickel coating. The poling involves passing a fixed DC current. The resulting polarization causes an electric field that opposes the applied field, thus increasing the apparent direct-current electrical resistance. For the uncoated fiber, at 80 s of 10.000-mA current application, the apparent resistance or effective electric permittivity is increased by 1.3%, corresponding to 2800 electrons participating in the polarization (5.3 × 10⁻¹⁶) of the carriers, which include the inherent carriers and injected electrons. The nickel coating enhances the polarization, but decreases the fraction of carriers that participate. This fraction increases monotonically with increasing current application time for the nickel-coated fiber, but increases and then decreases for the uncoated fiber. Upon instantaneous polarity reversal, the apparent resistance decreases instantaneously, with the values immediately before and after the reversal being asymmetrical about the true resistance. The electrical asymmetry is due to an inherent electret (without poling). The polarization associated with the electret is much higher than the additional polarization that the poling provides. Nevertheless, the poling increases the polarization through the interaction of the injected electrons with the atoms.