Impedance spectroscopy was performed on adhesive joints formed of aluminum or stainless steel adherends and one of two commercial epoxy adhesives exposed to a humid environment, and correlated with gravimetric measurements. The impedance spectrum followed the Cole-Cole relations, and the dependence of the apparent dielectric constant of the adhesive with water content was found to follow a simple constant volume rule-of-mixtures relation. Absorption of water appeared Fickian, with a semi-infinite body relation. Values are reported for the diffusivity and apparent dielectric constant of absorbed water. Impedance spectroscopy was also performed on samples of three commercial paints immersed in ersatz seawater. Short-time behavior was described by the Cole-Cole relations, with diffusion apparently following finite body behavior. A correlation was seen between water uptake as reflected in capacitance and early paint failure.

Subject
Circuits, Water, Adhesives, Substrates, Impedance, Dielectric constant, Weight gain, Joints, Capacitance, Impedance measurements, Polymers, Epoxies, Paints
Keywords:
adhesives, epoxy, impedance, paint
National Association of Corrosion Engineers
1989
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