Simplified approach to assess water uptake in protective organic coatings by parallel plate capacitor method

Abstract

Water uptake in organic coatings is often determined from changes in coating capacitance obtained by analyzing electrochemical impedance spectroscopy (EIS) data. However, the method has been criticized for providing inconsistent results poorly correlating to gravimetry measurements, which may arise from the absence of a straightforward approach to treat impedance data. A simple method based on forming a parallel plate capacitor (PPC) and measuring the capacitance using commercial inductance (L), capacitance (C) and resistance (R) meter is proposed. Water content in commercial coil coated steel specimens was determined by the Brasher-Kingsbury equation from coating capacitance measured by both PPC and EIS methods. A good correlation was observed between the reference gravimetric results and water uptake measured by the PPC approach. The new method can be considered as an industrial technique applicable also for on-site determination of water content in protective coatings applied on metallic structures.