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

Spectroscopical and Electrochemical Characterisation of a (3-Mercaptopropyl)trimethoxysilane - Based Protective Coating on Aluminium Alloy 2024

“…In a sense, this is a follow up from a previous paper in which in situ electrochemical AFM study of another protective coating -based on 1,2-bis(trimethoxysilyl)ethane (BTMSE) -was carried out. [13] That study revealed a decrease in the surface roughness during immersion of the coating at open circuit potential conditions, followed by very similar values during application of the chronocoulometric pulses. This indicated a reasonably stable structure of the coating during anodic polarisation.…”

“…The longitudinal optical (LO) modes are obtained in IR RA spectra, usually being shifted towards the higher wavelengths compared to transversal optical (TO) modes obtained in IR absorbance spectra. [10,13] These shifts occur due to the intrinsic dielectric properties of the materials. Consequently, the assignment of the LO modes in IR RA spectra of MPTMS protective coatings can be carried out on the basis of previously developed knowledge on trialkoxysilanes.…”

“…Consequently, the assignment of the LO modes in IR RA spectra of MPTMS protective coatings can be carried out on the basis of previously developed knowledge on trialkoxysilanes. [13,[14][15][16] The eventual changes in topography of the MPTMS coatings during the corrosion process can be effectively monitored using in situ electrochemical atomic force microscopy (AFM). [17,18] AFM enables the investigation of conductive and non-conductive surfaces, which is a great advantage when studying corrosion processes.…”

“…For example, conventional IR absorbance measurements can help understand the reactions of hydrolysis and condensation that start to occur already in sols. [6,13] The insight into the structure of the coating, however, can be obtained using IR reflectionabsorption (IR RA) measurements at a near-grazing incidence angle conditions (80°). The longitudinal optical (LO) modes are obtained in IR RA spectra, usually being shifted towards the higher wavelengths compared to transversal optical (TO) modes obtained in IR absorbance spectra.…”

“…[13,19,24] However, in prolonged in situ AFM measurements a certain drift of the laser during scanning is inherent. [25] Among the successful attempts where this problem was overcome were in situ AFM measurements of tungsten monocarbidebased coatings [24] and a study on the early stages of nucleation and growth of electrodeposited cerium oxide.…”