Corrosion Resistance of Superhydrophobic Layered Double Hydroxide Films on Aluminum

Abstract

The costs of metal corrosion amount to several percent of the GDP of an industrialized country. [1] In the case of aluminum, chromate-based coatings [2] provide highly effective corrosion protection, but environmental regulations are increasingly restricting their use. Anodization [3] increases the thickness of the oxide layer, but it retains its porous nature.[4] Layered materials such as anionic clays (e.g., layered double hydroxides ) [5,6] and cationic clays (e.g., montmorillonite) [7] have been widely investigated as additives in organic anticorrosion coatings or as polymer-clay nanocomposite corrosion-resistant coatings. Zeolites [8,9] have also been explored as corrosion-resistant coating materials. Hydrophobic self-assembled monolayers (SAMs) [10] of surfactant molecules on the surface have recently been proposed as corrosion inhibitors but suffer from the drawbacks that the layers have limited stability and molecule-sized defects which allow water to reach the underlying surface. These problems should be mitigated if the surfactant could be incorporated in an inorganic host matrix, a thin film of which has been previously strongly bonded to the aluminum surface.Layered double hydroxides (LDHs) are one such potential inorganic host. They can be expressed by the generalwhere the cations M 2+ and M 3+ occupy the octahedral holes in a brucite-like layer and the anion A nÀ is located in the hydrated interlayer galleries.[11] The ability to vary the composition over a wide range allows materials with a wide variety of properties to be prepared. We recently showed [12] that an NiAl-LDH-CO 3 2Àfilm can be formed directly on porous anodic alumina/ aluminum (PAO/Al) substrates; since PAO/Al is the only source of Al 3+ , the thin film grows directly on the substrate and thus exhibits good adhesion and mechanical stability. [13] Treatment with sodium laurate (n-dodecanoate) results in surface-bonded laurate films showing superhydrophobicity with water contact angles (CA) greater than 1608. Here we show that intercalation of laurate anions by ion exchange with ZnAl-LDH-NO 3 À film precursors on a PAO/Al substrate leads to a hierarchical micro/nanostructured superhydrophobic film which provides a very effective corrosion-resistant coating for the underlying aluminum.The aluminum substrate was first coated with a layer of porous anodic alumina by conventional anodization and subsequently treated with an alkaline solution of zinc nitrate in the presence of an excess of nitrate anions. In addition to the peaks of the PAO/Al substrate, the XRD pattern of the film shows two low-angle reflections at 8.874 and 4.462 (Figure 1 a), which can be assigned to the [003] and [006] reflections of an LDH phase with a basal spacing of 0.887 nm, consistent with the literature for ZnAl-LDH-NO 3 À .[14] The presence of NO 3 À in the interlayer galleries of the LDH film was confirmed by the characteristic peak at 1384 cm À1 in the FTIR spectrum. It is well known that LDHs in their usual powder form readily exchange NO 3 À ions for oth...

Large-area fabrication of superhydrophobic surfaces for practical applications: an overview

“…Given their strong water repulsion properties, superhydrophobic coatings are ideal for slowing the breakdown of the native metal oxide layer of metal substrates, and thus the corrosion of the aluminum layer underneath [65]. Zhang et al [66] utilized the intercalation of laurate anions by ion exchange with ZnAl-(layered double hydroxides)-NO − 3 film precursors on a porous anodic alumina/aluminum substrate to fabricate a hierarchical micro/nanostructured superhydrophobic film, which provided a very effective corrosion-resistant coating for the underlying aluminum. Liu et al [67] prepared stable superhydrophobic films with a contact angle of 151…”

Hydrodesulfurization of 4,6-DMDBT on a multi-metallic sulfide catalyst with layered structure

“…Specific ides and exchangeable anions located in the interlayer gallery for charge balance [28][29][30]. The synthesized multi-metallic catalyst was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD).…”

Controlled anisotropic wetting behaviour of multi-scale slippery surface structure of non fluoro polymer composite

“…Superhydrophobic surfaces have received great interest due to their multifunctional applications in different areas such as self-cleaning, anticorrosion, drag reduction, ice-mitigation, window glasses, antiicing textile, micro/macro fluid channels, optical devices, electronic and photonic material chemical sensors etc. [6][7][8][9][10][11]. Slippery surfaces are generally obtained by a combination of low surface energy materials and hierarchal structures, with trapped air pockets on which water droplets forms a liquid ball [12][13][14][15][16][17].…”