Enhancement of Anticorrosion Properties of Epoxy Based Primer Coating by Bis[[3,4-Dihydroxyphenylmethylene] carbonothioi
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nhancement of Anticorrosion Properties of Epoxy Based Primer Coating by Bis[[3,4-Dihydroxyphenylmethylene] carbonothioicdihydrazide] on AA2024-T3 Alloy B. G. Prakashaiaha, b, A. Nityananda Shettya, *, and B. E. Amitha Ranib aDepartment b
of Chemistry, National Institute of Technology Karnataka, Surathkal, Karnataka, Srinivasnagar, 575025 India Surface Engineering Division, CSIR-National Aerospace Laboratories, Bengaluru, Karnataka, India *e-mail: [email protected] Received September 23, 2019; revised December 5, 2019; accepted January 3, 2020
Abstract—A corrosion inhibitor bis[[3,4-dihydroxyphenylmethylene]carbonothioicdihydrazide] (DCT) was synthesized and used to improve the corrosion resistance of an epoxy based primer coating on AA2024-T3 alloy in NaCl solution. The ability of DCT to inhibit the corrosion was evaluated by electrochemical studies. The compound exhibited an inhibition efficiency of 99%. The surfaces of the corroded specimens were characterized by field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. The anticorrosion nature of the substrate coated with a commercial epoxy-based primer doped with DCT was evaluated by electrochemical impedance spectroscopy and a salt spray test. The results established not only the ability of DCT to improve the anticorrosion property of the epoxy based primer coating on AA2024-T3 alloy but also a sustained corrosion protection (1000 h) of the alloy. Keywords: epoxy coating, primer, corrosion protection, inhibitor, inhibition efficiency DOI: 10.3103/S1068375520050129
Aluminum alloys of the type AA2024-T3 find their uses in aerospace industry, they contain inclusions of additional elements as copper, silicon, chromium, manganese, zinc, and magnesium to impart better mechanical properties, e.g. specific strength. The presence of these elements in aluminum alloys is responsible for the higher corrosion susceptibility of the alloy than that of pure aluminum [1–8]. Therefore, aluminum alloys used in aircraft applications are usually protected with a three-layered coating. The first thin layer of 10–60 nm is the pre-treated surface conversion coating that protects the metal surface from corrosion and also enhances the adhesion of the next layer of the coating on the substrate surface. The second layer consists of an epoxy-based primer coating with a thickness ranging from 5 to 200 μm, as per the requirement of the application [9, 10]. The primer layer is generally doped with hexavalent chromate pigments to provide corrosion protection. The topcoat of a polyurethane layer most often functions as a barrier against environmental influences and ultra-violet rays, with the coating thickness of 50 to 200 μm [11, 12]. Strontium chromate is doped as an inhibitive pigment in primer coatings. However, the usage of chromate particles is restricted due to their carcinogenicity [13, 14], therefore, there is a need for non-chrome alternatives as a replacement. Some of the promising environmentally friendly organic a
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