Corrosion resistance properties of Ormosil coatings on 2024-T3 aluminum alloy |
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Authors: | Tammy L Metroke Jaspreet S Gandhi Allen Apblett |
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Affiliation: | a Department of Chemistry, 107 Physical Sciences, Oklahoma State University, Stillwater, OK 74078, USA b Department of Chemical and Materials Engineering, University of Cincinnati, Cincinnati, OH 45221-0012, USA |
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Abstract: | The corrosion resistance behavior of organically modified silane (Ormosil) thin films on 2024-T3 aluminum alloy substrates was investigated using electrochemical impedance spectroscopy (EIS) and accelerated salt spray analysis techniques. Coatings were prepared containing 0–16.6 vol.% alkyl-modified silane, Xn---Si(OR)4?n, where X=methyl, dimethyl, n-propyl, n-butyl, i-butyl, n-hexyl, n-octyl, or i-octyl. Coating thicknesses were measured to be in the 6–16 μm range, with the thickest coatings being observed for the highest concentrations of alkyl-modified silane. Contact angle measurements showed an enhancement in hydrophobicity of the Ormosil film imparted by increasing size and concentration of the alkyl-modifiers in the coating. In general, corrosion resistance characteristics, as determined using EIS and salt spray techniques, were found to increase with increasing alkyl-modified silane concentration and alkyl chain length. The best overall corrosion resistance was observed for coating systems containing ≥10.4 vol.% alkyl-modified silane; the hexyl-modified films exhibited corrosion resistance properties superior to the other Ormosil coatings. Immersion studies conducted in 0.5 M K2SO4 indicated that coating degradation occurs via hydration of the dense linear chain silicate network leading to the formation of porous cyclic structures. |
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Keywords: | Ormosil coating Corrosion resistance Electrochemical impedance spectroscopy Salt spray Infrared spectroscopy |
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