The anti-corrosion performance of the epoxy coating enhanced via 5-Amino-1,3,4-thiadiazole-2-thiol grafted graphene oxide at ambient and low temperatures

Highlights

• The neat EP, GO/EP and AMT-GO/EP coatings were synthesized, and their anti-corrosion performance at ambient and low temperatures were estimated.

• At low temperature, the failure of coatings is promoted by freezing.

• AMT-GO sheets could enhance the anticorrosion performance of the coatings.

Abstract

In this study, the 5-Amino-1,3,4-thiadiazole-2-thiol grafted graphene oxide (AMT-GO) composite was synthesized and the corrosion protection properties of the neat EP, GO/EP and AMT-GO/EP coatings at the ambient and low temperatures were comparatively studied. Based on the experimental results, AMT is anchored on GO mainly via the reactions between -NH₂ and -SH of AMT and -COOH and -CH(O)CH- of GO. After modification, the dispersity of the GO nanosheets is significantly improved. As the filler, both of the GO and AMT-GO nano-platforms could enhance the protective ability of the polymer coating, the latter possessing the more remarkable effect because of its better dispersity and the beneficial impact provided by exposed -NH₂ and -SH. All of the three coatings exhibit worse anti-corrosion performance at the low temperature than the ambient temperature, because the diffusion of corrosive media across the polymer matrix and along the substrate/coating interface could be accelerated by freezing.

Introduction

With the rapid development of science and technology, the research about the environments with low temperatures such as the south and north poles has become a hot topic at present [1,2]. Although the electrochemical reaction rate is significantly reduced at the low temperature according to the Arrhenius equation [3,4], this doesn't mean that the metallic materials are immune to corrosion in this kind of environment. A series of strategies including the design of metal substrate, use of corrosion inhibitor, cathodic protection, and the coverage of surface coating have been proposed to control or delay the metal corrosion [5]. Among all the strategies, the application of organic coatings is regarded as an economical and effective method to protect metals from corrosion. In general, the protective properties of nearly all the organic coatings will be degraded due to the occurrence of embrittlement at low temperatures [[7], [8], [9], [10]]. Therefore, it is urgently necessary to develop an anti-corrosion coating that can work effectively in low-temperature environments.

Graphene, which is a single layer of carbon atoms, has attracted rapidly increasing attention in the field of corrosion protection, due to its excellent chemical stability, high specific surface area, and superior barrier properties against aggressive media such as oxygen, water, chloride, and so on [[11], [12], [13]]. Numerous studies proved that graphene coatings prepared by chemical vapor deposition (CVD) and electrochemical deposition could provide effective corrosion protection for Cu and Ni [[14], [15], [16]]. However, there is also some research reporting that the service life may be reduced by the galvanic corrosion caused by the grain boundaries and defects existing in the graphene coating because of its electrical conductivity [17,18]. To avoid galvanic corrosion, an alternating route for the fabrication of graphene-based anti-corrosion coatings is the incorporation of graphene nanosheets into a polymer matrix to inhibit the diffusion of corrosive media through the “labyrinth effect” [18,19]. However, the producing routes to prepare graphene-like cleavage, CVD and epitaxial growth are not really practical and cheap enough for the mass production needed for the polymer composites preparations [20].

In recent years, the graphene oxide (GO), which is a precursor for graphene, is considered as the best alternating solution to graphene as a filler in the anti-corrosion coating, because GO not only has similar properties to graphene especially the enormous surface-to-mass ratio and superior barrier performance, but also possesses the cheaper and more reliable production procedure [[20], [21], [22], [23]]. The experimental results reported by Bahadur et al. elucidated that the graphene oxide coatings could exhibit excellent protectiveness for the metallic materials [21,22,24]. Additionally, the functional groups containing hydroxyl, carbonyl, carboxyl, and epoxy groups in GO as the active sites make the covalent and/or noncovalent functionalization more easily, thus leading to the enhancement in dispersion and compatibility of the nanosheets in the organic coating [5,25]. In the work of Ramezanzadeh et al., the GO was functionalized with the polyaniline (PAni), polypyrrole (PPy), and the polyamidoamine (PAMAM), and the corrosion resistance of the epoxy coating where the synthesized nano-platforms were well dispersed was enhanced to a large extent [[26], [27], [28]]. Wang et al. prepared the newfangled cationic dopamine-reduced GO nanosheets via simple dopamine oxidative self-polymerization and ionization reaction, the water-based epoxy reinforced by the obtained fillers exhibited extraordinary corrosion resistance [29]. Although the studies about the corrosion resistance of the GO/epoxy composites have been documented in previous reports, few of them were conducted in low-temperature conditions, and the failure mechanism of the anti-corrosion coating is still unclear up to now.

5-amino-1,3,4-thiadiazole-2-thiol (AMT) is composed of an amino, a thiol, and a thiazole ring [[30], [31], [32], [33], [34]]. The amino could react with the epoxide and carboxyl groups, resulting in the formation of strong chemical bonds between the GO and AMT [26]. The thiol group that has a high chemical reactivity could bond with the carboxyl groups in the GOs through esterification reaction to graft AMT on the GO surfaces [35]. The π-π interaction should exist between the thiazole ring and the aromatic rings of GO. Above all, it could be speculated that the functional groups containing in AMT are conductive to dispersion and compatibility of GO in the anti-corrosion coating consisted of the epoxy resin, which could enhance the corrosion resistance of the composite coating.

In this study, the anti-corrosion coating was fabricated via incorporating the GO modified with AMT (AMT-GO) into epoxy, which was called AMT-GO/EP coating here, and then the corrosion resistance of the coating was evaluated at ambient and low temperatures. The structures, functional groups, and morphologies of the AMT-GO nanocomposites and AMT-GO/EP coating were characterized with Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), energy disperse spectroscopy (EDS), scanning electron microscope (SEM), and transmission electron microscope (TEM). The corrosion protection performance of the AMT-GO/EP coating at ambient and low temperatures was also investigated by electrochemical impedance spectroscopy (EIS), salt spray test, and scanning vibration electrochemical technology (SVET). Besides, the pull-off adhesion and water uptake of the anti-corrosion coating were also analyzed to better understand the failure mechanism of the anti-corrosion coating and the effect of the AMT-GO nanocomposites at ambient and low temperatures.