Temperature-dependent dielectric measurements of polyacrylonitrile fibers during air oxidation

Simple direct-current (DC) electrical conductivity measurements are widely used to measure the degree of carbon fiber processing during the latter stages of the carbonization, and during the graphitization, of polyacrylonitrile (PAN) fiber. Unfortunately, DC conductivity measurements are not possible for the oxidation stage and for the early stages of carbonization because the PAN conductivity is too low. Herein is described a simple microwave cavity technique for a continuous, non-contacting, in-situ, real-time measurement of the complex dielectric constant of PAN during the oxidation and early carbonization stages of carbon fiber manufacturing. The real and imaginary parts of the dielectric constant are good indicators of the degree of thermal processing in the PAN oxidation/stabilization process.