Investigating the Effect of Hydrophobic Nanofillers on Corrosion Protection Performance of Epoxy Coatings on Aluminum Alloy (AA-2219) for Application in Marine Environment

Abstract

Corrosion is a universal issue that impacts many industries, particularly for ships and submarines in oceanic environments. The present study examines the influence of adding hydrophobic nanofillers into epoxy coatings on aluminum alloy (AA-2219) surfaces to improve their corrosion protection performance in seawater. The aim of the research is to find out the impact of a series of Zeolitic Imidazole Framework (ZIFs) nanofillers and their composites with Tetraethyl orthosilicate (TEOS) which is a hydrophobic and crosslinking agent in augmenting the coating's capacity to resist corrosion that sustain the harsh conditions encountered in maritime environments. In the present work, we have prepared a series of hydrophobic nanofiller epoxy-based coatings namely (a) Pure epoxy, (b) ZIF 67+Epoxy, (c) ZIF-67@TEOS+Epoxy(6w%), (d) ZIF-67@TEOS+Epoxy(10w%). The material was analyzed using various techniques including Fourier-transformed infrared spectroscopy (FT-IR) confirming the characteristics vibrational modes ascertaining the formation of ZIF-67 nanoparticles. The peak at 423 cm-1 is associated with the Co-N stretching vibration that confirms the Co-N bond formation within the ZIF-67 architecture. The crystallinity, purity and average crystallite size of the synthesized material are confirmed by XRD. The unique diffraction peaks of ZIF-67 reveal its high purity and crystallinity. Scherrer's equation is used to calculate the average crystallite size of the ZIF 67 NPs. The average crystallite size is measured to be 0.0984 nm. The comparison of ZIF 67 with a series of different coated coupons indicates that its crystallinity transforms into an amorphous state. The elemental composition, chemical, and electronic state of atoms in a material was analyzed through XPS. The spectrum predominantly exhibits peaks at binding energies of 284 eV (C1s), 399 eV (N1s), 532 eV (O1s), and 791 eV (Co 2p), which provide further evidence for the successful formation of ZIF-67. SEM images combined with EDX analysis provide information regarding the surface properties of the material, including its composition, morphology, and topography. Average particle size was also calculated through SEM by using Image J which is 310.85 nm as reported. Employing electrochemical impedance spectroscopy (EIS) and Tafel, electrochemical techniques on the bare aluminum alloy (AA-2219), and a series of different coated samples were carried out to evaluate the corrosion resistance (Rcorr), pore resistance (Rpo), solution resistance xii (Rsoln), corrosion current (Icorr), corrosion potential (Ecorr) and corrosion rate at a different time interval. Electrochemical studies revealed that ZIF-67@TEOS+Epoxy(6w%) is the best composite anticorrosive coating having superior corrosion resistance amounting up to 27,780 ohms for two weeks of immersion in 3M NaCl solution compared to the other coated samples. ZIF-67@TEOS+Epoxy (6w%) has greater corrosion resistance throughout the time interval from one week to three months. The Tafel scan demonstrated a significant decrease in corrosion rate for ZIF-67@TEOS+Epoxy(6w%) which is 0.2334 mpy for two weeks of immersion in 3M NaCl solution. This is because ZIF-67 possesses the ability to adsorb corrosive species due to their high surface area and adjustable pore sizes. ZIF-67 containing coatings have the ability to reduce the concentration of species at the metal surface, which slows down or prevents the corrosion process. It also accelerates the curing reaction of epoxy which increases its corrosion protection performance. The employment of TEOS facilitates effective bonding between the organic and inorganic phases, thereby preventing phase separation. ZIF-67 has a high surface area and adjustable pore size that provides channels to TEOS which is a cross-linking agent that increases corrosion resistance. This research will boost corrosion protection technology by improving epoxy coatings for aluminum structures in marine settings.