A Structural and Corrosion Study of Triethoxysilyl Functionalized POSS Coatings on AA 2024 Alloy

Abstract

A novel bifunctional polyhedral oligomeric silsesquioxane (POSS) based silane precursor R(x)R'(y)(SiO(3/2))(8), (x + y = 8), bearing 3-(N-(3-triethoxysilylpropyl)ureido)propyl (ureasil - U) and isooctyl (IO) groups (i.e., U(2)IO(6) POSS) was synthesized, and the corresponding coatings, prepared under the acid hydrolysis conditions, were studied in order to assess their corrosion inhibition of the AA 2024-T3 alloy. The U(2)IO(6) POSS precursor was made in two steps: in the first, an appropriate stoichiometric (2:6) mixture of 3-aminopropyltriethoxysilane (AP(2)) and isooctyltrimethoxysilane (IO(6)) was autoclaved under basic hydrolysis conditions giving AP(2)IO(6)(SiO(3/2))(8) cubes, which were reacted in the second step with 3-isocyanatopropyltriethoxysilane (ICPTES), leading to the bis end-capped sol-gel precursor U(2)IO(6) POSS having a cube-like structure. Coatings were made from sols catalyzed with acidified water. IR and (29)Si NMR spectroscopic studies combined with mass spectrometric measurements were employed to confirm the cube-like structure of AP(2)IO(6) and U(2)IO(6) POSS. The structure and morphology of the U(2)IO(6) POSS coatings were studied with the help of infrared reflection-absorption (IR RA) spectroscopic measurements combined with XPS and AFM measurements, providing information about the formation of partially self-assembled coatings. The degree of corrosion inhibition was assessed from the potentiodynamic measurements showing around 10 times smaller current densities for the coatings only 30-40 nm thick. Ex situ IR RA spectroelectrochemical measurements were performed by consecutive measurements of the IR RA spectra of U(2)IO(6) POSS coatings which were chronocoulometrically charged at different potentials. At potentials more positive than the corrosion potential (E(corr) approximately -0.5 V), the amide I bands shifted, indicating the formation of new urea-urea aggregations and associations, with the newly formed strong band at 1680-1690 cm(-1) suggesting the formation of amidonium ions. These results showed that the urea groups represented the weakest part of the coatings due to their tendency to protonation.

Corrosion protection of AA 2024-T3 aluminium alloys using 3, 4-diaminobenzoic acid chelated zirconium–silane hybrid sol–gels

“…However in the interest of human health [2,3] and environmental concerns, alternative solutions are being pursued. For engineering applications organic polymers (polyesters, polyamides, alkyds, and polyurethane) [4], conductive polymers (polyaniline and polypyrrole) [5] and sol-gel derived organicinorganic hybrid materials have emerged as promising Cr 6+ alternatives [6].…”

Modified bis-(3-(3-(3-triethoxysilyl)propyl)thioureido)propyl terminated poly(dimethylsiloxane)/POSS protective coatings on AA 2024

“….). Surface passivating coatings that form on aluminium alloys under atmospheric conditions are composed essentially of an aluminium oxide Al 2 O 3 with eventually some admixed oxyhydroxide/hydroxide phases [3][4][5]. When such surface was exposed to electrolytic or highly humid environments it was shown by Raman spectroscopy that various oxyhydroxides/hydroxides co-exist and could not be identified unambiguously due to the overlapping of their bands.…”

Bacteriostatic photocatalytic properties of cotton modified with TiO2 and TiO2/aminopropyltriethoxysilane

“…The sol-gel TiP/APTES hybrid finishes resemble aminofunctionalized polymeric systems in many aspects. Namely, TiP/APTES hybrids belong to a class of organic-inorganic hybrid materials that have been extensively studied in our laboratory in the past (Vince et al 2006;Fir et al 2007;Jerman et al 2008;Vilčnik et al 2009;Koželj et al 2009;Č olović et al 2011;Jerman et al 2012;Simončič et al 2014;Vasiljević et al 2014). In the TiP/APTES hybrids studied here, the TiP and APTES acted as sol-gel network formers, while the amino groups of the APTES (the organic part of the hybrid) imparted the hybrid with bactericidal properties.…”