Hot wet aging of glass syntactic foam coatings monitored by impedance spectroscopy

This paper examined both short and long term behaviors of glass-epoxy syntactic foam coatings containing various types of microspheres while exposed to hot deionized water. Electrochemical impedance spectroscopy (EIS) was used to monitor in situ the water uptake of the coating in complement to gravimetry but also to investigate the degradation phenomenon occurring after the matrix had reached saturation (monitoring over 420 days). Diffusion properties were discussed from capacitance measurements in comparison to classical gravimetric data. In addition, attention was paid to the increase of ionic conductivity suggesting the creation of water paths through the material and/or the occurrence of ionic extraction from the microsphere glass due to water leaching. Possible degradation mechanisms were discussed from the modeling of the results obtained by in situ monitoring. The interest of EIS for the investigation of composite coating aging was highlighted.