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 VSCE and -1.2 VSCE) conditions were studied, the moisture absorption was evaluated by weight gain test, and the degradation process was analyzed combined with scanning electron microscope (SEM). The T700/VE composite has very good resistance to degradation under OCP condition for long time (205 d) immersion, with about 0.38% moisture uptake and a slight decreasing of low frequency impedance (|Z|0.01Hz). 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 very quickly decrease in |Z|0.01Hz value. The variation of |Z|0.01Hz is negatively correlated with the moisture absorption under OCP and -0.6 VSCE polarization conditions. So, |Z|0.01Hz may be used to monitor the water absorption and degradation process of the composite.

The one-step preparation and corrosion resistance of a Ca–Mn–Zn ternary phosphate conversion coating on magnesium alloy AZ91D

“…From the results of Figures 7 (f)–(j) and 8(b), no obvious localized corrosion occurs on the surface of Ca-Mn-Zn@TPCC-coated AZ91D sample when it is immersed in the NaCl solution, implying that the appearance of inductive semicircle is because of species adsorption rather than localized corrosion. From Figure 9, with the extension of immersion time, from 1 to 8 days, the semicircle radius of EIS decreases obviously, indicating the gradual degradation of Ca-Mn-Zn@TPCC; over 8 days, the change of EIS is slight, implying the total degradation of Ca-Mn-Zn@TPCC (Tang et al , 2022).…”