Electrochemical impedance spectroscopy characteristic of degradation process for carbon fiber/vinyl ester composites in salt water

Abstract

The Electrochemical impedance spectroscopy of the T700/VE (vinyl ester) carbon fiber composite in 3.5% NaCl solution under open circuit potential (OCP) and cathodic polarization (−0.6 V_SCE and −1.2 V_SCE) conditions were studied, the moisture absorption was evaluated by weight gain test, and the degradation process was analyzed combined with scanning electron microscope. The T700/VE composite has very good resistance to degradation under OCP condition for long time (205 days) immersion, with about 0.38% moisture uptake and a slight decrease of low-frequency impedance (|Z|_0.01 Hz). Cathodic polarization remarkably promotes the diffusion of moisture and ions in the resin matrix, the de-bonding between resin and carbon fibers, and characteristic of a porous electrode occurrence with a very quick decrease in |Z|_0.01 Hz value. The variation of |Z|_0.01 Hz is negatively correlated with the moisture absorption under OCP and −0.6 V_SCE polarization conditions. So, |Z|_0.01Hz may be used to monitor the water absorption and degradation process of the composite.