Fluorocarbon lubricant impregnated nanoporous oxide for omnicorrosion-resistant stainless steel

doi:10.1016/j.jcis.2019.09.117

Journal of Colloid and Interface Science

Volume 558, 15 January 2020, Pages 301-309

https://doi.org/10.1016/j.jcis.2019.09.117 Get rights and content

Abstract

Corrosion protection coatings have been required for long-term uses of metallic materials applied in various environments incorporating liquid and/or vapor phase corrosion reactants. In this study, we introduce a fluorocarbon lubricant impregnated nanoporous oxide (FLINO) coating on stainless steel for realizing effective resistances against corrosive media in both liquid and vapor phases. The FLINO layer on stainless steel significantly enhances corrosion resistances with superior durability and self-healing capability. The combination of nanoporous structure and fluorocarbon lubricant layer provides an outstanding atmospheric corrosion resistance, which has been a serious issue to be overcome on corrosion-resistant coatings. Therefore, the FLINO coating exhibiting stable and remarkable corrosion resistance against both liquid and vaporized corrosive media, called omnicorrosion-resistance, gives a new route for the versatile protection of metallic materials in various environments encompassing both underwater and atmospheric applications.

Graphical abstract

Introduction

Corrosion causes many serious problems precluding satisfactory lifetime of metallic materials. Therefore, corrosion-resistant surfaces of metallic materials are of great importance in a broad range of engineering systems and applications. For long decades, various strategies have been employed to prevent the corrosion of metallic materials regarding the service environments. For example, thin organic (or polymer) coatings, such as simple painting, spraying and shrink-wrapping [1], [2], [3], [4], [5], [6], have been convenient and widely used ways to form passive layers on metals. Although these organic coatings inhibit the mass transfer of corrosion reactant (e.g., water, oxygen and chloride) they can be easily degraded by UV exposure and temperature change, so that the corrosion reactants are allowed to be transported to the interface of metal/polymer resulting in crevice corrosion and the delamination of coating from a metal surface [7]. Hard ceramic protective layers by thermal spraying and passive oxide layers by sol–gel coating have also been employed for anti-corrosion of metals [8], [9], [10]. However inhomogeneous coatings with surface cracks by poor adhesion are still hurdles to be overcome [11], [12].

Recently it has been studied that hydrophobic or superhydrophobic surfaces have a potential to enhance the corrosion resistance on metallic surfaces [13], [14], [15], [16]. Especially, the superhydrophobic passivation has shown the prevention of corrosion in wet environments accompanied with corrosive water by harbouring air layer within the surface structures [16], [17], [18], [19]. However, it should be noted that the corrosive media can be airborne (e.g., in sea coast and chemical plants) and transported via a vapor phase [20], [21], so that the superhydrophobic passivation fails to inhibit the penetration of corrosive gas into the underlying metallic substrate. Therefore, an alternative strategy to realize omnicorrosion-resistant passivation, which protects the metallic substrate from corrosive media in both liquid and gas phases, is required.

A lubricant-impregnated surface, which is one of representative liquid repellent surfaces, has also been studied for corrosion-resistant coating of metals. Due to the mobile and low surface tension lubricant layer, most liquids including water and aqueous corrosive media can effectively be repelled from the surface resulting in the protection of the metal surface against corrosive liquids. Although the lubricant-impregnated surface shows good corrosion resistance, the protection efficacy against atmospheric corrosion in a vapor phase has not yet been investigated. In addition, a meniscus (or wetting ridge) of lubricant surrounding a liquid drop can be rinsed off when a liquid drop slides on the lubricant-impregnated surface, which is a serious issue on durability of conventional lubricant impregnated surfaces [22], [23], [24].

In this study, we design a method to fabricate a highly stable fluorocarbon lubricant impregnated nanoporous oxide (FLINO) surface on metals as an omnicorrosion resistant coating (i.e., corrosion protection against corrosive media in both liquid and vapor phases). The effect of FLINO is investigated especially on stainless steel. Stainless steel, employed in many applications such as chemical plants, heat exchangers, seawater desalination and marine systems, is exposed to severe corrosive environments where the corrosive media can be transported via both liquid and vapor phases. The anodic oxidation (or anodizing) process is adapted to realize disconnected high-aspect-ratio and dead-end nanopore structures [25], [26], which have not yet been examined for stainless steel to realize omniphobic de-wetting property. Such nanoporous geometry has advantages in immobilizing a lubricant liquid within the structures and allows superior durability along with a unique self-healing capability [27]. The surface featured with a nanoporous oxide layer composited with polytetrafluoroethylene (PTFE) coating and water-immiscible lubricant liquid physically precludes the penetration of aqueous corrosive media into the oxide and inhibits the corrosion of metallic substrates [27], [28], [29]. In addition, the lubricant perfectly covering the surface also blocks vaporized media in corrosive atmospheres. This combination of nanoporous oxide and lubricant exhibits highly durable and effective anti-corrosivity against both aqueous and vaporized media, which opens a new door to develop an omnicorrosion coating on metals.

Section snippets

Pretreatment of stainless steel

For stainless steel substrate, AISI 304 (Fe-18Cr-8Ni, Alfa Aesar) sheet with 0.1 mm in thickness was employed. It was cut into 45 mm × 20 mm in size and used for a specimen. The specimen was degreased in acetone with ultrasonication for 3 min. Before anodizing, the surface of stainless steel was electropolished in a mixture of percholoric acid and ethylene glycol (1:19 volumetric ratio) under voltage of 40 V for 5 min at 10 °C.

Anodization of stainless steel

Ethylene glycol based electrolyte was employed for anodizing to

Nanoporous anodic oxide of stainless steel

For the fluorocarbon lubricant impregnated nanoporous oxide (FLINO) coating, a stable nanoporous oxide should be first prepared on the surface of stainless steel followed by the surface modification with low surface energy polytetrafluoroethylene and the impregnation of fluorocarbon lubricant (Fig. 1a). The stainless steel plate can be anodized in ethylene glycol-based solution (7.5 g L⁻¹ NH₄F + 2.0 g L⁻¹ water) resulting in a yellowish film (Fig. 1b). Since the as-anodized structure of

Conclusions

Various technologies creating porous surface structures have been applied to realize the omniphobic lubricant impregnated surfaces on commercial materials [43], [47], [48]. Such lubricant impregnated porous surfaces show multifunctional properties, such as anti-bacterial adhesion [49], [50], [51], anti-wetting transparency [43], [52], anti-corrosion [53], enhanced condensation [54] and anti-icing [55]. Among the porous structures, the disconnected high-aspect-ratio dead-end nanopore structures

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was supported by the US Office of Naval Research (ONR) Award N00014-14-1-0502. J. Lee acknowledges the support from the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT, Ministry of Science and ICT) (No. 2018R1C1B6006156) and the local industry promotion business linked with public institutions (Gyeongnam) (P0004798) funded by the Ministry of Trade, Industry & Energy (MOTIE, Korea). This research was also supported by a grant (19CTAP-C151876-01)

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Li et al. [90] found that their coating can repair itself within 2 h after being damaged. And Choi et al. [84] reported that the corrosion current density of their coating did not increase more than 8 times after physical damages, but the anodized stainless steel corrosion current density increased more than 36 times after physical damages. The above results indicate that good self-healing properties can be found in the fluorocarbons lubricating layer.
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Fluorocarbon lubricant impregnated nanoporous oxide for omnicorrosion-resistant stainless steel

Abstract

Graphical abstract

Introduction

Section snippets

Pretreatment of stainless steel

Anodization of stainless steel

Nanoporous anodic oxide of stainless steel

Conclusions

Declaration of Competing Interest

Acknowledgements

Surf. Coat. Technol.

Electrochim. Acta

Electrochim. Acta

Electrochim. Acta

Surf. Coat. Technol.

Surf. Coat. Technol.

Surf. Coat. Technol.

Prog. Org. Coat.

Coatings

Appl. Surf. Sci.

Mater. Des.

Appl. Surf. Sci.

Electrochem. Commun.

J. Colloid Interf. Sci.

J. Colloid Interf. Sci.

Corros. Sci.

Colloids Surf., A

Chem. Eng. J.

Appl. Surf. Sci.

Water transport in multilayer organic coatings

J. Electrochem. Soc.

Investigation of corrosion and container integrity in metal food containers using scanning electron microscopy-x-ray microanalysis

Scanning

Anticorrosion coatings with self-healing effect based on nanocontainers impregnated with corrosion inhibitor

Chem. Mater.

Sol–gel coatings for corrosion protection of metals

J. Mater. Chem.

Nanoengineered superhydrophobic surfaces of aluminum with extremely low bacterial adhesivity

ACS Appl. Mater. Inter.

Drag reduction using superhydrophobic sanded Teflon surfaces

Exp. Fluids

Air-impregnated nanoporous anodic aluminum oxide layers for enhancing the corrosion resistance of aluminum

Langmuir

Applications of bio-inspired special wettable surfaces

Adv. Mater.

Superhydrophobic CuO nanoneedle-covered copper surfaces for anticorrosion

J. Mater. Chem. A