Blistering of Graphite/Polymer Composites Galvanically Coupled with Metals in Sea Water

The effects of bulk oxygen partial pressures on the galvanic blister growth in carbon fiber vinyl ester composites were studied. Varying oxygen concentrations significantly affected the corrosion currents when the samples were subjected to a cathodic potential of -900 mV (SCE). An increase in oxygen concentration proportionately increased the corrosion currents which is an almost certain evidence that oxygen reduction reaction occurs on carbon fibers in the composite. The blister detectability times decreased or the blister growth rates increased with increasing oxygen concentration. Comparison of short beam apparent interlaminar shear strength test results of virgin, water saturated, electrolyte saturated and cathodically polarized (until blistered) samples of carbon fiber vinyl ester (CFVE) composite, revealed little changes in the interlaminar shear strength. The results indicated that galvanic blistering of CFVE samples subjected to galvanic conditions (applied potential: -900 mV (SCE) for 7 days did not affect the apparent interlaminar shear strength of the composite. The implication of this result is that only galvanic blisters form only at surface layers for the given electrochemical conditions and the interior layers are protected from blistering because interior layers were depleted from oxygen. This depletion of oxygen in the inner layers is as a result of entire consumption of available dissolved oxygen at the surface carbon layer (as evidenced by the diffusion controlled current). This must be further verified by conducting strength tests of samples subjected to cathodic potentials for longer periods (several months). A modification to the blister nucleation theory was suggested following the ILSS test results.