Galvanic blistering in carbon fiber polymer composites
Carbon fiber reinforced polymer composites form blisters when galvanically coupled to metals in sea water or salt water. This blistering process is termed 'galvanic blistering'. Galvanic blisters nucleate and grow along the fiber/matrix interface. The blisters were filled with liquids with pH of 14. Carbon fiber reinforced vinyl esters, polyesters and epoxies were found to blister galvanically.^ Chemical analysis revealed that the galvanic blister fluids were essentially aqueous solutions of sodium hydroxide and sodium carbonate. Based upon these results, the following galvanic blistering mechanism was proposed: Galvanic coupling produces a surface charge on the fibers which results in modification of the polymer/fiber bonding. This makes possible a water clustering at the interface which starts the delamination process. Oxygen reduction takes place at these zones producing hydroxyl ions and a sodium hydroxide solution is formed. The sodium hydroxide solution creates an osmotic pressure which causes the blister to grow.^ It was proved that almost certainly the oxygen reduction to hydroxyl ions occurs on carbon fibers that are cathodically polarized. The corrosion currents were limited by diffusion rates of oxygen. Time for blister appearance decreased with greater cathodic potentials and higher oxygen concentrations.^ Electrochemical impedance was measured and the data was modeled using equivalent electrical circuit. Pore resistance decreases with time after application of cathodic potentials. This was due to creation of holes in the polymer layer over the fibers by rupture of blisters. The predicted charge transfer resistances were lower for increasing oxygen concentrations and greater cathodic potentials.^ The effect of galvanic blistering on the apparent interlaminar shear strength of the composite was investigated. The results revealed little or no change in the ILSS due to galvanic blistering because the inner layers of the composite were protected from blistering by the consumption of oxygen on the surface carbon fibers.^ A complete analytical approach to predict the galvanic blister rates was presented. A semi-empirical model was developed to predict blister growth rates. ^
Engineering, Chemical|Engineering, Mechanical|Plastics Technology
Shravan Kumar Miriyala,
"Galvanic blistering in carbon fiber polymer composites"
Dissertations and Master's Theses (Campus Access).