Electrochemical properties and corrosion protection of organosilane self-assembled monolayers on aluminum 2024-T3

Aluminum 2024-T3 surfaces were modified by the deposition of organosilane self-assembled monolayers (SAMs) and studied by surface characterization and electrochemical measurements. The SAMs were hydrophobic and had infrared spectral trends consistent with a densely packed hydrocarbon SAM. Electrochemical testing indicated that anodic dissolution was suppressed on the SAM modified surfaces while cathodic reduction of oxygen was not. Polarization resistance and capacitance values from EIS measurements were used to evaluate the corrosion protection of the SAMs. On exposure to 0.5 M NaCl, the polarization resistance values of the SAM modified surfaces quickly converge to values similar to the bare surface even though the capacitance values indicate the continued presence of the SAM. There are a large number of defects on SAM modified 2024-T3 relative to SAMs on pure substrates. The defects probably occur over copper enriched particles found on the 2024-T3 surface. The copper enriched particles must be protected by a coating since localized corrosion originates on the particles.