Ex situ IR reflection–absorption and in situ AFM electrochemical characterisation of the 1,2-bis(trimethoxysilyl)ethane-based protective coating on AA 2024 alloy

• Protective coating for AA 2024 based on organic–inorganic hybrid.
• Extensive IR spectroscopic assignment.
• Ex situ IR reflection–absorption measurements during anodic polarisation.
• IR evidence for hydration and cleavage of some bonds.
• In situ electrochemical AFM measurements on the protective coating.

The organic–inorganic protective coatings for the aluminium alloy AA 2024-T3 were produced from a precursor 1,2-bis(trimethoxysilyl)ethane. The structural properties of the coatings were analysed using SEM, EDS, contact angles and IR reflection–absorption at the near grazing incidence angle conditions. Moreover, the forced degradation of the protective coatings at the anodic potentials was studied by various means of the ex situ and in situ analytical approaches with the aim to verify their applicability. The ex situ IR reflection–absorption spectroscopy revealed the prominent changes in the bands like hydration of coatings, cleavage of some siloxane bonds, changes in the regions of CH vibrations and breaking of some SiOAl bonds. The in situ electrochemical AFM approach revealed a decrease in the surface roughness during immersion of the coating, followed by the pretty similar values during application of the chronocoulometric pulses. The impedance spectroscopy indirectly confirmed a gradual dissolution/degradation of the coating.

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