Optimization of hybrid sol-gel coatings by combination of layers with complementary properties for corrosion protection of AA2024 (original) (raw)
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Hybrid sol–gel coatings doped with cerium nanocontainers for active corrosion protection of AA2024
Progress in Organic Coatings
This work presents a new approach to develop protective pre-treatment for AA2024 based on the inhibitor efficiency of cerium ions which are considered as a promising alternative to replace chromate compounds. The inhibition properties of cerium salts for improving the anti-corrosion performance of AA2024 have been characterized by polarization curves and EIS measurements. Cerium ions were inserted into nanoclays platelets by cationic-exchange reactions (CeMMT). XRD analysis proved the presence of cerium ions intercalated into clay structure. EIS measurements and polarization curves highlighted a high corrosion inhibition effect of ceriummodified nanoclays. This effectiveness can be related to the release of 60% of cerium ions from CeMMT structure in sodium chloride as determined by UV-vis measurements. Salt spray test made on scratched sol-gel samples indicated a self-healing effect of cerium ions which provide an active corrosion protection to aluminum substrate. EIS measurements revealed that hybrid sol-gel films doped with CeMMT improve barrier properties and anticorrosion protection of aluminum 2024 substrate.
This study reports the application of sol-gel coatings on aluminium alloy 2024-T3 substrates under electrochemical regimes and dip-coating process. Cerium-titanium oxide nanocontainers loaded with corrosion inhibitors 2-mercaptobenzothiazole and 8-hydroxyquinoline were incorporated into the coatings in order to improve the corrosion protection properties. Various silanes and silicones were used as precursors. The electro-deposited coatings were compared to coatings developed by dip coating process. Electrochemical impedance spectroscopy measurements were carried out in order the corrosion protection properties of the films to be evaluated. It was found that 3-glycidoxypropyltrimethoxysilane based films provided better protection against corrosion. The presence of nanocontainers improved the corrosion protection.
Advancement in corrosion resistance of AA 2024-T3 through sol-gel coatings including nanocontainers
Manufacturing Review, 2017
The current study investigates the effect of nanocontainers incorporation into sol-gel coatings for the protection improvement of aluminium alloys 2024-T3 against corrosion. The nanocontainers were synthesized via a combination of radical polymerization process and sol-gel technique. They consist of cerium and molybdenum oxides and loaded with the anodic corrosion inhibitor 2-mercaptobenzothiazole (MBT). The preparation of the coating matrix was accomplished using (3-glycidoxypropyl)trimethoxysilane as precursor. These organic modified silicate based sol-gel films were evaluated for their corrosion behaviour as well as nanomechanical properties using electrochemical and nanoindentation techniques, respectively. The results reveal that the presence of loaded nanocontainers improved the corrosion protection of the coatings; outcome that can be attributed to either the increase coherence of the coating or the simultaneously inhibition action of cerium and molybdate ions together with the corrosion inhibitor MBT. Moreover, the addition of nanocontainers empty or loaded with inhibitor amount strengthens (increase of wear resistance) the coating and decreases the coefficient of friction.
Journal of Sol-Gel Science and Technology, 2017
Hybrid sol-gel materials have been extensively studied as viable alternatives to toxic chromate (VI)-based coatings for the corrosion protection of AA2024-T3 in the aerospace industry, due to the wide range of available chemistries they offer and the tremendous development potential of innovative functional coatings. However, so far, little work has been performed in identifying the effect of the employed chemistries on the structure and anticorrosion properties of the coatings. This work proposes to contribute to a better understanding of the relationship existing between the structure, morphology and anticorrosion properties of hybrid sol-gel coatings deposited on AA2024-T3 aluminium surfaces, the most widely used alloy in the aerospace industry. The sol-gels are prepared employing two hybrid precursors; an organosilane, 3-trimethoxysilylpropylmethacrylate, and a zirconium complex prepared from the chelation of zirconium n-propoxide, and methacrylic acid. The structure of the hybrid sol-gel formulation is modified by altering the concentration of the transition metal complex. The structure and morphology of the coatings are characterised by dynamic light scattering, fourier transform infrared spectroscopy, silicon nuclear magnetic resonance spectroscopy, differential scanning calorimetry, scanning electron microscopy, atomic-force microscopy and the anticorrosion barrier properties characterised by electrochemical impedance spectroscopy and neutral salt-spray. It is found that the transition metal concentration affected the morphology and structure, as well as the anticorrosion performances of the hybrid sol-gel coatings. A direct correlation between the morphology of the coatings and their final anticorrosion barrier properties is demonstrated, and the optimum material amongst this series is determined to be comprised of a concentration of between 20 and 30% of transition metal.
Inhibition effect of cerium in hybrid sol-gel films on aluminium alloy AA2024
Surface and Interface Analysis, 2010
Aluminium alloys such as AA2024 are susceptible to severe corrosion attack in aggressive solutions (e.g. chlorides). Conversion coatings, like chromate, or rare earth conversion coatings are usually applied in order to improve corrosion behaviour of aluminium alloys. Methacrylate-based hybrid films deposited with sol–gel technique might be an alternative to conversion coatings. Barrier properties, paint adhesion and possibly self-healing ability are important aspects for replacement of chromate-based pre-treatments. This work evaluates the behaviour of cerium as corrosion inhibitor in methacrylate silane-based hybrid films containing SiO2 nano-particles on AA2024. Hybrid films were deposited on aluminium alloy AA2024 by means of dip-coating technique. Two different types of coating were applied: a non-inhibited film consisting of two layers (non-inhibited system) and a similar film doped with cerium nitrate in an intermediate layer (inhibited system). The film thickness was 5 µm for the non-inhibited system and 8 µm for the inhibited system. Film morphology and composition were investigated by means of GDOES (glow discharge optical emission spectroscopy). Moreover, GDOES qualitative composition profiles were recorded in order to investigate Ce content in the hybrid films as a function of immersion time in 0.05 M NaCl solution. The electrochemical behaviour of the hybrid films was studied in the same electrolyte by means of EIS technique (electrochemical impedance spectroscopy). Electrochemical measurements provide evidence that the inhibited system containing cerium displays recovery of electrochemical properties. This behaviour is not observed for the non-inhibited coating. GDOES measurements provide evidence that the behaviour of inhibited system can be related to migration of Ce species to the substrate/coating interface. Copyright © 2010 John Wiley & Sons, Ltd.
Nanostructured sol–gel coatings doped with cerium nitrate as pre-treatments for AA2024-T3
Electrochimica Acta, 2005
Nanostructured hybrid sol-gel coatings doped with cerium ions were investigated in the present work as pre-treatments for the AA2024-T3 alloy. The sol-gel films have been synthesized from tetraethylorthosilicate (TEOS) and 3-glycidoxypropyltrimethoxysilane (GPTMS) precursors. Additionally the hybrid sol was doped with zirconia nanoparticles prepared from hydrolyzed tetra-n-propoxyzirconium (TPOZ). Cerium nitrate, as corrosion inhibitor, was added into the hybrid matrix or into the oxide nanoparticles.