Study on the aging behavior of waterborne silicone coating by EIS in a 400°C high-temperature environment

Purpose This paper aims to use electrochemical impedance spectroscopy (EIS) as a quantitative tool to monitor the performance changes of waterborne silicone coatings on Q235 substrates during 400 °C high-temperature aging. Design/methodology/approach A waterborne silicone coating was subjected to oxidation at 400 °C. EIS was used to monitor the aging process, and Fourier transform infrared spectroscopy and scanning electron microscopy analyzes were conducted to verify the corresponding structural and morphological changes, confirmed that it can monitor the coating aging process through EIS. Findings The waterborne silicone coating significantly reduced the oxidation kinetics of Q235 substrate at 400 °C and improved the high-temperature oxidation resistance of Q235 substrate by approximately 1.8 times. The oxidation rate constant was from 0.0110–0.00596 mg-2·cm-4·h-1. During the initial oxidation stage (within 10 h), the coating impedance rapidly decreased from 2.060 × 107O to 2.39 × 105O·cm2, accompanied by a significant reduction in the CPE1-P value from 0.90–0.323. With increasing oxidation time (10–100 h), the impedance exhibited a transient recovery followed by a gradual decline and eventual stabilization, which was attributed to a partial sintering of the porous structure or interface reconstruction within the coating. This phenomenon results in a transient improvement in barrier performance, contrary to the conventional expectation of monotonic degradation under thermal aging conditions. Originality/value This provides a new idea for the quantitative analysis of the high-temperature oxidation behavior of waterborne silicone coatings using the impedance method.