An Impedance Study of a Carbon Fiber/Vinyl Ester Composite

The electrochemical behavior of a carbon fiber/vinyl ester composite in 3.5% NaCI solution was investigated. The technique chosen for the study was electrochemical impedance spectroscopy (EIS), which enables time-dependent data to be acquired nondestructively on single samples. The data from the measurement technique is also amenable to modeling by passive electrical circuit elements. Negative potentials were applied to the composite material to simulate galvanic coupling of metals. The impedance of the material as a function of time and applied negative potential was measured. The data was adequately modeled by passive circuit elements. It was found that increased damage to the composite was induced by more applied negative potentials as cathodic reactions were increased with decreasing potential. At a potential of −1.2 V (SCE), holes were found in the composite surface after 90 h of exposure. The pore resistance determined from the model used to fit the impedance data offered a damage-monitoring criteria for the composite material.