Light-weighting vehicular components through adoption of light-metal structural alloys holds promise for reducing the fuel consumption of internal combustion engine vehicles and increasing the range of battery electric vehicles. However, the alloyed microstructure and surface precipitates of aluminum alloys render these materials susceptible to corrosion under modest excursions from neutral pH. Traditional chromium-based anodic passivation layers are subject to increasingly stringent environmental regulations, whereas options for sacrificial cathodic films are sparse for electropositive metals. While hybrid nanocomposite coatings have shown initial promise, mechanistic underpinnings remain poorly understood. Here, a fully imidized polyetherimide (PEI) resin is utilized as the continuous phase with inclusion of unfunctionalized exfoliated graphite (UFG). A comprehensive investigation of the mechanisms of corrosion protection reveals key fundamental design principles underpinning corrosion inhibition. First, strong interfacial adhesion, which for PEI is facilitated by binding of imide carbonyl moieties to Lewis acidic sites on Al surfaces. Second, the miscibility of ion-impervious nanoscopic UFG fillers and stabilization of a substantial interphase region at UFG/PEI boundaries that result in minimizing the free volume at the filler/polymer interface. Finally, extended tortuosity of ion diffusion pathways imbued by the below-percolation-threshold 2D fillers. These three design principles help govern and modulate ion transport from electrolyte/coating interfaces to the coating/metal interface and are crucial for the extended preservation of barrier properties. The results suggest an approach to systematically activate multiple modes of corrosion inhibition through rational design of hybrid nanocomposite coatings across hard-to-abate sectors where light metal alloys are likely to play an increasingly prominent role.
Multi-functional low-cost epoxy based nanocomposite corrosion resistant coatings
Corrosion is a significant global issue, resulting in high maintenance and repair costs. Long term structural integrity of metal and its products is directly dependent on its anti-corrosive properties. Surfaces exposed to marine environments are prone to microbial attachment followed by biofilm formation, resulting in bio-fouling. Hence coatings are used to protect the surfaces against corrosion and biofilm formation. Currently various organic coatings are used to protect metals and the cost of these coatings is directly dependent upon the cost of the fillers used to impart specific properties. Conventionally fillers such as zinc, Titanium and Silver based compounds are used in coatings for corrosion and/or microbial protection of surfaces, which are expensive. The underlying issue with using these compounds as fillers is that they can adversely effect mechanical and barrier properties, due to which they are used as a base coat and additional fillers are used to compensate for such property losses. Most of these coatings need an enhanced anti-microbial surface and improvement in their barrier efficacy against water/moisture, oxygen, and chloride ions. Hence it is imperative to develop low-cost fillers that will enhance both active & passive corrosion resistance properties, prevent microbial attachment on the surfaces and will not degrade any polymeric properties. In this work, ASL is developing a multi-functional low cost epoxy-clay nanocomposite coating, for microbial and corrosion resistance. Multi-functional coatings are developed using a multi-component approach, where the innovation lays in deriving the benefits of various fillers through a combinatorial approach to synergistic harvesting of functionality and vigor. The primary filler is a naturally abundant clay material and, owing to their sheet like morphology and layered structures, their surface can be modified to achieve the desired property enhancements. Sheet like morphology enhances polymer filler interactions, resulting in enhanced mechanical and reduced barrier properties. The presence of clay in the coating materials will mitigate the impact of moisture and chloride ions (in marine environment) providing passive protection to the coated surface. Modification of clay with transition metal ions (TMI) enhances corrosion resistance properties of coatings.
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- Award ID(s):
- 1648922
- NSF-PAR ID:
- 10061870
- Date Published:
- Journal Name:
- MegaRust 2017 Organized by the American Society of Naval Engineers
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Multifunctional coatings with simultaneous antibacterial and anticorrosive properties are essential for marine environments, oil and gas industry, medical settings, and domestic/public appliances to preserve integrity and functionality of pipes, instruments, and surfaces. In this work, we developed a simple and effective method to prepare graphene oxide (GO)-hybridized waterborne epoxy (GOWE) coating to simultaneously improve anticorrosive and antibacterial properties . The effects of different GO filler ratios (0.05, 0.1, and 0.5, 1 wt%) on the electrochemical and antibacterial behaviors of the waterborne epoxy coating were investigated over short- and long-term periods. The electrochemical behavior was analyzed with salt solution for 64 days. The antibacterial effect of GOWE coating was evaluated with Shewanella oneidensis (MR-1), which is a microorganism that can be involved in corrosion. Our results revealed that concentrations as low as 0.1 wt% of the GO was effective performance than the waterborne epoxy coating without graphene oxide. This result is due to the high hydrophilicity of the graphene oxide fillers, which allowed great dispersion in the waterborne epoxy coating matrix. Furthermore, this study used a corrosion relevant bacterium as a model organism, that is, Shewanella oneidensis (MR-1), which is more relevant for real-word applications. This as-prepared GO-hybridized waterborne polymeric hybrid film provides new insight into the application of 2D nanomaterial polymer composites for simultaneous anticorrosive and antibacterial applications.more » « less
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Abstract While hexagonal boron nitride (hBN) has been widely used as a buffer or encapsulation layer for emerging electronic devices, interest in utilizing it for large‐area chemical barrier coating has somewhat faded. A chemical vapor deposition process is reported here for the conformal growth of hBN on large surfaces of various alloys and steels, regardless of their complex shapes. In contrast to the previously reported very limited protection by hBN against corrosion and oxidation, protection of steels against 10% HCl and oxidation resistance at 850 °C in air is demonstrated. Furthermore, an order of magnitude reduction in the friction coefficient of the hBN coated steels is shown. The growth mechanism is revealed in experiments on thin metal films, where the tunable growth of single‐crystal hBN with a selected number of layers is demonstrated. The key distinction of the process is the use of N2gas, which gets activated exclusively on the catalyst's surface and eliminates adverse gas‐phase reactions. This rate‐limiting step allowed independent control of activated nitrogen along with boron coming from a solid source (like elemental boron). Using abundant and benign precursors, this approach can be readily adopted for large‐scale hBN synthesis in applications where cost, production volume, and process safety are essential.
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