Impedance spectroscopy and circuit modeling of Southern pine above 20% moisture content

Abstract Impedance spectra were collected from Southern pine (Pinus spp.) equilibrated to a moisture content 20% and a saturated condition. Cylindrical graphite electrodes were embedded in the wood so that they met nearly end-to-end along a line parallel to the grain, and impedance properties were characterized as functions of electrode spacing and electrode contact pressure at frequencies between 1×10^-1 and 3×10⁵ Hz. The data exhibit a low-frequency tail that can be fit with a Warburg element, indicative of a diffusive motion of charge carriers. Values of the Warburg impedance were compared with previously published data on molar conductivities of endogenous mineral ions in wood. The data suggest that mineral ions are the predominant charge carriers in wood at low frequencies and high moisture contents based on the strong correlation between the Warburg impedance and molar conductivities.