Ex situ IR reflection–absorption (IR RA) and Raman spectroscopic measurements were performed on sol–gel anticorrosion coatings to take advantage of the complementarity of the two vibrational techniques. The coatings were prepared on the basis of (3-glycidoxypropyl)trimethoxysilane, (3-aminopropyl)trimethoxysilane and amino-heptaisooctyl-functionalised polyhedral oligomeric silsesquioxane and their protective efficiency evaluated in terms of the hydrophobic poly(dimethylsiloxane) (PDMS) content. The results of IR absorbance and rheology measurements of sols showed that coatings should be deposited 30 min after the addition of acetic acid sol–gel catalyst and thermally treated at 150 C. The surface energy values of coatings decreased with increasing amounts of PDMS chains, from 29.6 to 22.6 mJ/m2. Potentiodynamic polarisation revealed that the concentration of PDMS chains in coatings should be optimised to depict the lowest corrosion current density, of the order of magnitude 10(E-)9 A/cm2. Extensive ex situ IR RA studies of the degradation of coatings during polarisation indicated that breakage of siloxane bonds occurred through the formation of lower cyclosiloxanes and hydration, while conformational changes of methylene groups were noted in coatings without PDMS chains. Ex situ confocal Raman images of coatings with PDMS recorded after anodic polarisation mainly revealed bands of PDMS chains of decreasing intensity, while no signal was found in areas of pitting corrosion.
COBISS.SI-ID: 5262362
Due to its non-destructive character and high spatial resolution, confocal Raman spectroscopy was found to be a good technique for detecting spray-deposited sol-gel coatings on electronic boards (EBs). EBs are demanding substrates to cover because of their non-flat surfaces, containing various metals, alloys, pins and other elements. Nanocomposite coatings were made on the basis of bis end-capped organic-inorganic hybrid precursors, bis-(3-(3-(3-triethoxysilyl)propyl)thioureido)propyl terminated polydimethylsiloxane (PDMSTU) and bis-[3-(triethoxysilyl)propyl]tetrasulphide (BTESPT), imparting a hydrophobic character to the produced anticorrosion coatings. Reactions of hydrolysis and condensation were initiated with an addition of the 0.1 M HCl catalyst. Nanoparticles were introduced in the sols as trisilanol-heptaisooctyl-polyhedral oligomeric silsesquioxanes (up to 5 nm). The obtained sols were spray deposited on the test substrate, i.e., the aluminium alloy AA 2024, and also on EB. The coatings on AA 2024 were used for potentiodynamic electrochemical and surface (SEM, AFM) characterisation of the prepared coatings. Extensive Raman spectroscopy measurements of the uncovered and covered EBs revealed that the sol-gel coatings on various elements and pins of EBs are clearly visible in the Raman spectra and that this is an appropriate technique for detecting the coatings on such demanding substrates.
COBISS.SI-ID: 36654085