Polypyrrole/Aluminum Flake Hybrids as Corrosion Inhibitors for Aluminum 2024-T3
By Vetter, Christopher; Gohmann, Katherine; Harper, Alice C. & Gelling, Victoria Johnston
2010
Abstract
The aluminum alloy 2024-T3 (AA 2024-T3) used in aircraft has localized corrosion issues such as pitting and intergranular corrosion. This susceptibility to localized corrosion is caused by the inherent nature of the copper-rich 2024-T3 aluminum alloy. Chromate surface treatments and chromate-containing epoxy primers are often used for the corrosion control of such aluminum alloys as 2024-T3. However, due to environmental concerns and adverse health effects surrounding such use of chromates, there is an intensive effort to find suitable replacements for chromate-based coatings. Electroactive conducting polymers (ECPs) continue to be of considerable interest as components of corrosion-resistant coating systems due to their conductivity and redox properties. One of the most studied of these conducting polymers is polypyrrole (PPy). PPy films have been shown to act as corrosion inhibitors for various metal substrates. Since the pyrrole monomer has moderate solubility in water (~1M), many groups have been investigating the aqueous electropolymerization of pyrrole onto surfaces. The use of an aqueous solution lowers the cost of waste disposal and the technique is able to be done under mild conditions. In this paper, the synthesis of polypyrrole/aluminum flake hybrids under aqueous conditions is investigated. The polymer-coated flakes were then incorporated, at high pigment volume concentrations, into epoxy primers. The resulting coatings were investigated for any corrosion inhibiting characteristics via long-term immersion in dilute Harrison's solution. This was accomplished by utilizing electrochemical impedance spectroscopy. Additionally, surface analysis and elemental analysis was performed utilizing scanning electron microscopy (SEM) and x-ray photoelectron spectroscopy (XPS). Density tests were also performed to determine the extent of polypyrrole attachment to the aluminum flake.