Mark B. Jensen

Tungstate and vanadate-doped polypyrrole/aluminum flake composite coatings for the corrosion protection of aluminum 2024-T3

Polypyrrole (PPy) doped with either tungstate or vanadate as counter anions was synthesized by chemical oxidative polymerization on the surface of aluminum (Al) flakes. This resulted in the deposition of PPy on the surface of the Al flakes leading to the formation of doped PPy/Al flake composite pigments. These composite pigments were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive spectroscopy, conductive-atomic force microscopy, four-point probe conductivity, and X-ray photoelectron spectroscopy. Furthermore, these composites were incorporated in an epoxy-amide binder system in order to formulate a primer for an aluminum 2024-T3 substrate. The coatings were exposed to the Prohesion test conditions and corrosion resistance properties were monitored by electrochemical impedance spectroscopy, DC polarization, galvanic coupling, and scanning electrochemical microscopy measurements. It was found that the doped PPy/Al flake coatings provided sacrificial protection to the underlying aluminum 2024-T3 substrate. Additionally, the release of dopants from PPy backbone resulted in the passivation in the defect areas improving the corrosion protection ability.

Scanning electrochemical microscopy and video microscopy investigations of Tiron-mediated polypyrrole nucleation on AA2024-T3

Scanning electrochemical microscopy (SECM) and video microscopy have been used to examine the mediated electrodeposition of polypyrrole on AA2024-T3. Of particular interest is the role of surface heterogeneity (namely, copper-rich secondary phase particles) on electrodeposition mediated by 4,5-dihydroxy-1,3-benzenedisulfonic acid (Tiron). SECM shows that polymer nucleation occurs exclusively on the aluminum matrix of the alloy. Video microscopy shows this to be true on a model alloy (a pure Al substrate with an embedded Cu wire) as well, and also suggests that polymer growth is directional toward the copper-rich sites in the absence of sulfate in the deposition solution. A model is presented in which polymer deposition on the copper-rich sites is inhibited either by CuSO4-induced passivation or by the loss of mediator due to Cu–Tiron complex formation.