Influence of Hydrostatic Pressure on the Corrosion Behavior of Superhydrophobic Surfaces on Bare and Oxidized Aluminum Substrates

Abstract

It is generally recognized that superhydrophobic surfaces in water may be used for corrosion resistance due to the entrapped air in the solid/liquid interface and could find potential applications in the protection of ship hull. For a superhydrophobic surface, as its immersion depth into water increases, the resultant hydrostatic pressure is also increased, and the entrapped air can be squeezed out much more easily. It is therefore predicted that high hydrostatic pressure would cause an unexpected decrease in corrosion resistance for the vessels in deep water (e.g., submarines) because of the unstable entrapped air. In this work, in order to clarify the role of hydrostatic pressure in the corrosion behavior of superhydrophobic surfaces, two typical superhydrophobic surfaces (SHSs) were prepared on bare and oxidized aluminum substrates, respectively, and then were immersed into the NaCl aqueous solutions with different depths of ∼0 cm (hydrostatic pressure ∼0 kPa), 10 cm (1 kPa), and 150 cm (15 kPa). It was found out for the SHSs on the oxidized Al, as the hydrostatic pressure increased, the corrosion behavior became severe. However, for the SHSs on the bare Al, their corrosion behavior was complex due to hydrostatic pressure. It was found that the corrosion resistance under 1 kPa was the highest. Further mechanism analysis revealed that this alleviated corrosion behavior under 1 kPa resulted from suppressing the oxygen diffusion through the liquid and reducing the subsequent corrosion rate as compared with 0 kPa, whereas the relatively low hydrostatic pressure (HP) could stabilize the entrapped air and hence enhance the corrosion resistance, compared with 15 kPa. The present study therefore provided a fundamental understanding for the applications of SHSs to prevent the corrosion, especially for various vessels in deep water.

Micro‐/Nanostructured Interface for Liquid Manipulation and Its Applications

“…The anticorrosion capability of micro‐/nanostructured surface can be attributed to the entrapped air pocket between corrosive liquid and rough surface, which can be illustrated by the Cassie superhydrophobic state. The protective air layer can effectively block the diffusion of corrosive species, such as Cl − ( Figure a) . Besides surface micro‐/nanostructure, lowering of surface energy is also required.…”

“…a) Schematic illustration showing the anticorrosion mechanism of superhydrophobic surfaces . Copyright 2018, American Chemical Society.…”

The challenges, achievements and applications of submersible superhydrophobic materials

“…Ou et al used superhydrophobic aluminium samples immersed at varying depths in aqueous NaCl to observe the corrosion behaviour. 130 The results indicated that, as hydrostatic pressure increased, the degradation of superhydrophobicity increased and more severe corrosion was observed for nonoxidised samples. The air layer acting as a protective barrier was lost at increased pressures allowing corrosive species, such as Cl À ions, to reach the surface.…”

“…Fig.18Schematic of the oxygen corrosion of the aluminium substrate and proposed corrosion mechanism. Reproduced with permission from ref 130…”

One-Step Preparation of Super-Hydrophobic Micro-Nano Dendrites on Al Alloy for Enhanced Corrosion Resistance

“…Al alloys have been extensively used as engineering components, parts and plates in shipbuilding and oceanic engineering areas because of their easy accessibility, good workability, high specific strength and low price [1,2]. Usually, Al alloys are easily oxidized to protect themselves from corrosion [3]. However, reactive anions can erode metallic substrates thereby leading to corrosion failures in wet conditions [4].…”