Anticorrosion behavior of superhydrophobic particles reinforced epoxy coatings for long-time in the high salinity liquid

doi:10.1016/j.porgcoat.2020.105867

Progress in Organic Coatings

Volume 147, October 2020, 105867

https://doi.org/10.1016/j.porgcoat.2020.105867 Get rights and content

Highlights

•
Superhydrophobic Al₂O₃ particles reinforced epoxy coatings using simple mechanical dispersion method.
•
SF-Al₂O₃-epoxy coatings showed good protection resistance under long-time exposure to solution of seawater salinity.
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SF-Al₂O₃-epoxy coatings showed higher |Z|0.01Hz value (6.5×10⁹ Ω·cm₂) after 144 d of immersion.
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Hydrophilic Al₂O₃ particles led to the obvious degradation in corrosion resistance.

Abstract

The low cost and excellent properties make Al₂O₃ particles a great potential in developing advanced epoxy composites. However, it’s a big challenge to disperse the particles into epoxy matrixes in molecular-level. In this work, superhydrophobic Al₂O₃ particles, which was dispersed with mechanical method, were developed as reinforced particles for epoxy coating to develop the anti-corrosion under long-time exposure to solution of seawater salinity. The silane functionalized Al₂O₃ (SF-Al₂O₃) particles exhibited a water contact angle of 156.5°. Electrochemical testing including open circuit potential, impedance and phase angle measurements showed that SF-Al₂O₃ epoxy has better corrosion resistance in high salinity solution than original epoxy, while the unfunctionalized Al₂O₃ (UF-Al₂O₃) coating got failure after 36 days (d) of immersion. Scanning electron microscope analysis revealed a very good condition of the SF-Al₂O₃ epoxy coating after 144 d of immersion. It is clearly observed that silane-modified particles were very effective on the anti-corrosion protection property of composites in high salinity solution. There may be profound implication to design organic coatings reinforced by particles using simple mechanical stirring method.

Graphical abstract

Comparison of the effects of using hydrophilic and superhydrophobic micro-Al₂O₃ as reinforced particles on the protection property of epoxy coating.

Introduction

One of the most serious problems faced by various industries is the damage of equipment and pipelines due to fouling, corrosion and erosion. Not only is corrosion and erosion the cause of some of the industry’s biggest accidents, it also brings about significant economic burden to companies. The corrosive species (ions, water and oxygen) can penetrate all polymeric coatings over time to reach the substrate and make the protective coating fail [1]. Epoxy coatings are considered to be one of the best protective method for metals because of their good anti-corrosion performance [2,3]. However, the application of epoxy coatings has been limited in many cases due to their other poor physical property [4,5]. Meanwhile, the pure epoxy coatings can be easily damaged caused by the physical wear and hydrolytic degradation [[6], [7], [8], [9]].

In recent years, second phase particles for toughening the epoxy matrix have attracted a lot of attention [[10], [11], [12], [13], [14], [15]]. The conventional agents in the field of epoxy toughening have been replaced by many new materials such as rubber, micro-fillers and block copolymers [[16], [17], [18], [19]]. Many kinds of particles for example TiO₂ [20,21], Al₂O₃ [22,23], and SiO₂ [[24], [25], [26]] were used to improve the property of epoxy coatings. This can be attributed to their excellent hardness and toughness. Ling et al. [27] researched the reinforcement of adhesion strength of epoxy coating using alumina particles on steel. The adhesion strength of the epoxy was greatly improved by the Al₂O₃ doping. Attar et al. [28] claimed the protection property of epoxy can be reinforced by pre-dispersed nano-Al₂O₃ particles. Galdino et al. [29] indicated that the micro-Al₂O₃ powder (26 % doping) can increase durability and adhesion of epoxy about 30 % and 50 % respectively. Papini et al. [1] also found that micro-Al₂O₃ can increase the corrosion protection of epoxy significantly. However, it was found afterwards that the interfacial effects between solid phase and liquid phase make it hard to disperse particles into resin. The silane-modification of the particle surface is very important in order to solve the interfacial effects between particles and epoxy [30]. Meanwhile, an obviously enhancement in both shear force and adhesive peel strength appeared because of the effect of silane coupling agents. Other studies have reached similar conclusions [31,32]. Such as the alkoxy silane has been widely used as surface modification of graphene oxide (GO) sheets to improve the anti-corrosion property of epoxy. Sepideh et al. [33] reported that the silane containing amine group can enhance the compatibilities of GO with epoxy.

So far, there are many reports that the inorganic particles as a second phase can reinforce the protection property of the epoxy coatings, and the electrochemical characterization of those particle-reinforced epoxy coatings was normally studied for short exposure time. However, relatively few researches examined the anti-corrosion properties of superhydrophobic particle-reinforced epoxy coatings with long exposure time in corrosive solution. In this work, the surface of Al₂O₃ particles was modified with methyltriethoxysilane (MTES) and diethoxydimethylsilane (DMDES) to prepare superhydrophobic particles which were used to reinforce epoxy resin. The silane on the particle surface was shown to be able to improve the bonding performance between Al₂O₃ and epoxy resin. Protection of Al₂O₃-epoxy coatings (Al-ECs) for AZ31 magnesium alloy in high salinity solution for a long time were evaluated. In addition, the influence of hydrophilic and superhydrophobic Al₂O₃ particles on the anti-corrosion behavior of epoxy coatings was compared.

Section snippets

Synthesis of silane functionalized Al₂O₃ particles (SF- Al₂O₃)

The functionalization of Al₂O₃ particles was conducted using the following procedure which was adapted from our previous work [34]. First, the mixture of H₂O, isopropyl alcohol and ethanol was added in a round-bottomed flask. Then 1 g of Al₂O₃ particles was added. Meanwhile, MTES (2 mL) and DMDES (2 mL) were added dropwise. The reaction was reacted under condensation reflux for 2 h (h) at 90 °C. The cooled mixture then continues to react under stirring at 25 °C for 10 h. Subsequently, the

Reaction mechanism

Siloxanes are the most commonly used chemical materials, which are used to construct appropriate surface morphology, reduce surface energy, and act as adhesives, or combine low surface energy materials with particles [35]. The alkoxy group on siloxanes, such as single bond OCH₂CH₃ and OCH₃, can hydrolyze in the presence of water to produce silanol. After that, the formed SiOH can be covalently coupled to the OH on the alumina particles via polycondensation reaction [34]. MTES and DMDES were used as

Conclusions

In this study, pure, SF-Al₂O₃ and UF-Al₂O₃ epoxy coatings were successfully prepared to study the influence of silane and the corresponding modified Al₂O₃ on the protection property of particle-reinforced epoxy coatings on AZ31 magnesium alloys for long-time immersion in high salinity solution. The siloxane modified Al₂O₃ particles are superhydrophobic (water contact angle of 156.5°). Electrochemical measurements indicated that SF-Al₂O₃ epoxy coatings showed higher |Z|_0.01Hz value (6.5 × 10⁹

Data availability

The raw/processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study.

CRediT authorship contribution statement

Mingdong Yu: Conceptualization, Methodology, Formal analysis, Investigation, Writing - original draft, Supervision. Caiquan Fan: Validation, Software, Validation, Formal analysis. Sike Han: Formal analysis, Software. Feng Ge: Resources, Project administration. Zhongyu Cui: Methodology, Resources, Supervision. Qingye Lu: Conceptualization, Resources, Writing - review & editing, Visualization. Xin Wang: Supervision, Funding acquisition.

Declaration of Competing Interest

The authors declare that they have no conflict of interest.

Acknowledgements

The authors wish to acknowledge the financial support of National Natural Science Foundation of China (No. 51601182), Natural Science Foundation of Shandong Province (ZR2016EMB12), the Fundamental Research Funds for the Central Universities (No. 201762008), the National Environmental Corrosion Platform, CSC scholarship201806330026, the Discovery Grant from the Natural Sciences and Engineering Research Council of Canada (NSERC, Q. Lu), and the Start-up Fund from the University of Calgary (Q. Lu).

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Anticorrosion behavior of superhydrophobic particles reinforced epoxy coatings for long-time in the high salinity liquid

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Synthesis of silane functionalized Al2O3 particles (SF- Al2O3)

Reaction mechanism

Conclusions

Data availability

CRediT authorship contribution statement

Declaration of Competing Interest

Acknowledgements

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Synthesis of silane functionalized Al₂O₃ particles (SF- Al₂O₃)