Fabrication of superhydrophobic aluminium alloy surface with excellent corrosion resistance by a facile and environment-friendly method
Graphical abstract
The superhydrophobic surface with excellent corrosion resistance takes on a micro- and nanoscale hierarchical rough structure with lots of 3D flower-like clusters growing on the nanoporous substrate.
Introduction
In recent years, the development of new materials based on bionic science has been widely carried out in various fields [1], [2]. As one of bionic materials, the artificial superhydrophobic surfaces with water contact angles larger than 150°, inspired by the lotus effect, have also been developed and researched extensively [3], [4]. Due to the outstanding water repellent property, the superhydrophobic surfaces have attracted significant interest from both fundamental research and industrial applications [5], [6]. Such a unique wettability for superhydrophobic surfaces has shown wide potential applications, such as self-cleaning, anti-icing, corrosion resistance, drag-reduction, anti-bioadhesion, and so on [7], [8], [9].
Wettability at the solid surface is a very important property which is governed by both chemical composition and geometric microstructure [10], [11], [12]. Generally, the superhydrophobic surfaces can be produced in two types of technology ways: on one hand, modifying of an appropriate rough surface with the low surface energy molecules or coatings. On the other hand, creation of a rough micro- and nanostructure at hydrophobic surfaces [13], [14], [15]. Up to now, artificial superhydrophobic surfaces have been fabricated by various techniques, such as sol–gel process, chemical etching, layer-by-layer assembly, electrostatic spinning, chemical vapor deposition, lithographic process, etc. [16], [17], [18]. Hydrophobicity is usually explained by the theories of Wenzel and Cassie–Baxter [19], [20]. In Wenzel's model, the liquid fully penetrates the surface grooves, so-called homogeneous wetting, and the larger contact angle results from the increase of the hydrophobic surface roughness. While in the Cassie–Baxter model, the water rests on the structured air/solid interface, so the water droplets on the rough surface are easy to roll.
As we all know, the aluminium and its alloy is an important category of materials owing to its abundant in nature, easy to handle, and high technological value. Consequently, the aluminium and its alloy have wide range of industrial applications, especially in aerospace and household industries [21]. In dry and non-salty environments, aluminium develops a thin aluminium oxide layer (on the order of 20 Å), which can inhibit the further corrosion. Aluminium and its alloys, however, are reactive materials and are prone to corrosion in wet, salty environments for the oxide layer will be penetrated and further corrosion ensues [22], [23]. This corrosion behavior prevents aluminium and its alloys from being widely used in wet, water, and salty environments.
The corrosion resistance can be improved by introducing the anticorrosive coatings on the surface of aluminium and its alloys. E.g., preparing the chromate-based coatings or anodizing the surfaces [24], [25]. Chromate-based coatings can provide highly effective corrosion protection, but environmental regulations are increasingly restricting their use, while the anodization will increase the weight of the aluminium and its alloys. Given the strong water repulsive property of the superhydrophobic surfaces, it may be a promising technology for slowing the breakdown of the native aluminium oxide layer and thereby retarding corrosion of the aluminium layer underneath by fabricating the superhydrophobic coatings or surfaces on the aluminium and its alloys. As a result, the anticorrosion performance of aluminium and its alloys may be improved because the superhydrophobic surfaces can inhibit the contact of a surface with water, environmental humidity, and corrosive medium.
Up to now, a few methods have been reported for preparing the superhydrophobic surface on aluminium alloy with the outstanding corrosion resistance. Zhang and co-worker reported a hierarchical micro/nanostructured superhydrophobic film on a PAO/Al substrate, and which provides a very effective corrosion-resistant coating for the underlying aluminium [26]. Yin et al. fabricated a superhydrophobic coating applied in corrosion protection on the surface of aluminium alloy by chemical etching and surface modification [27]. Barkhudarov obtained a superhydrophobic films as corrosion inhibitors on aluminium surfaces from a precursor solution containing mixed alkoxides 3,3,3-trifluoropropyl-trimethoxysilane and tetramethyl orthosilicate [28].
However, in these cases, either special equipment/complex process control is required, or caustic or costly reagents, for instance, HNO3, HF, H2O2 or fluoride, etc., are needed. Consequently, these methods/procedures may concern problem as environment pollution, high cost, and so on. Therefore, a simple, inexpensive, and environment-friendly fabrication method is quite needed since it is very advantageous for industrial large-scale production. Herein, we report a novel method for the fabrication of superhydrophobic surfaces on the aluminium alloy by treating the aluminium alloy in the boiling water and ethanol–water solution containing stearic acid, respectively. The procedure was fairly facile to carry out and no special technique or equipment is required. Moreover, only the ordinary reagents, such as the boiling water, ethanol, stearic acid, etc., are used in the procedure. Therefore, the method is also environment-friendly and inexpensive, while the as-fabricated superhydrophobic aluminum alloy surface has excellent corrosion resistance.
Section snippets
Materials
Aluminium alloy sheet (brand LD6063, commercially available engineering materials) with a size of 20 mm × 10 mm × 2 mm was purchased from the market. Stearic acid (STA) was purchased from Sinopharm Group Chemical Reagent Co., Ltd. Ethanol and acetone, were from Tianjin Benchmark Chemical Reagent Co., Ltd. (China).
Fabrication of the superhydrophobic aluminium alloy surface
The superhydrophobic aluminium alloy surface was fabricated by a facile and environment-friendly method. Firstly, the aluminium alloy sheet was polished with 800#, 1200#, and 1500# sandpaper
Fabrication of the superhydrophobic aluminium alloy surface
The superhydrophobic aluminium alloy surface was fabricated by the treatment of the aluminium alloy sheet with sandpaper, boiling water, and STA modification in turn. No caustic reagents were used in the preparation procedure, and the fabrication work is very easy to put in practice. So the method for the fabrication is quite facile and environment-friendly.
The whole fabrication procedure is monitored by evaluating the surface wettability and morphology, and Fig. 1, Fig. 2 show changes of the
Conclusions
A superhydrophobic aluminium alloy surface with outstanding corrosion resistance is fabricated by treating in the boiling water and immersing in STA–ethanol–H2O solution. Results show that a porous and rough structure is resulted at the aluminium alloy surface upon the boiling water treatment, while the long hydrophobic alkyl chains are chemically grafted onto the surface successfully by immersing the porous and rough aluminium alloy in STA–ethanol–H2O solution. Meanwhile, both the treatment
Acknowledgements
This research is supported by National Natural Science Foundation of China (Grant No. 21161012) and Natural Science Foundation of Gansu Province, China (Grant No. 1107RJZA184).
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