Elsevier

Corrosion Science

Volume 85, August 2014, Pages 482-487
Corrosion Science

Short Communication
Corrosion protection of mild steel by one-step electrodeposition of superhydrophobic silica film

https://doi.org/10.1016/j.corsci.2014.04.026Get rights and content

Abstract

Superhydrophobic silica films were deposited onto mild steel substrate for the purpose of corrosion protection. The superhydrophobicity was obtained by one-step electrodeposition of inorganic/organic hybrid sol–gel films from tetraethoxysilane and dodecyltriethoxysilane mixed sol–gel precursors, as a result of simultaneous generation of high roughness and low-energy surface. The corrosion performance was investigated by monitoring the change of water contact angle, by the electrochemical impedance spectroscopy measurements and by iron dissolution test over the whole immersion time. The results show that the superhydrophobic film provides an effective barrier coating for the mild steel interface.

Introduction

Traditionally, phosphating and chromating are commonly used strategies for metal protection. However, both the two methods are not environmentally compliant. Phosphorous pollution is the major factor contributing to water eutrophication and chromium (VI) is well-known for its high toxicity and carcinogenic effects on humans [1], [2]. Therefore, the use of chromate and phosphate compounds is becoming stricter and is even forbidden in many countries in corrosion protection industry. Various types of alternative materials, based on the use of self-assembled layers [3], sol–gel-derived films [4], [5], [6], [7], [8], and the films of rare-earth compounds [9], [10], [11] etc. have been shown their potentiality using for corrosion protection.

Recently, superhydrophobic materials, which are defined when the water contact angle is larger than 150°, have emerged as a new method to improve the corrosion performance of metals. Materials with such superhydrophobicity property possess the capacity as physical barrier to prevent corrosion electrolyte from penetrating onto metal substrate. Superhydrophobic films have been successfully prepared on lots of metals and their alloys, such as aluminum [12], [13], [14], magnesium [15], [16], copper [17], [18] and zinc [19], [20] for corrosion protection. The preparation procedure of superhydrophobic films described in previous literature, however, is relatively complicated [21], [22]. Two-step method was commonly used. A surface with sufficient roughness is constructed by a variety of physical and chemical methods, then further modified with low-surface-energy materials. Therefore, it is much more attractive to use simple one-step methodologies, by which high roughness and low-energy surfaces are obtained simultaneously. Successful examples of one-step procedures include the use of phase-separated [23] or nanofiller-added polymers [24], strongly corrosive solutions containing hydrophobic agents [25], reactive metal salts and low-surface-energy materials [26]. Conventionally, fluorinated chemicals were often used as the low-surface-energy materials in either one- or two-step techniques [27], [28], [29], which is not essentially environmentally friendly.

In our recent work, we have reported one-step fabrication of superhydrophobic surface on ITO glass and stainless steel substrates [30]. The superhydrophobicity was achieved as a result of simultaneous generation of high roughness and low energy surface by electrodeposition of organic/inorganic hybrid sol–gel film. In the hybrid film, inorganic silica component ensures the formation of highly porous and rough framework, and the environmentally compliant organosilanes, e.g. dodecyltriethoxysilane, DTMS, provide low surface energy. Noting that electrodeposition plays a key role for the acceleration growth of sol–gel films and for the eventual achievement of superhydrophobicity. Such acceleration is based on the enhancing sol–gel condensation process due to the increased pH in solution near the substrate when applying cathodic potentials on metallic substrates [1], [31], [32], [33]. The benign preparation conditions and low-cost and environmentally compliant chemicals used ensure its wide application in constructing superhydrophobic surfaces on conducting substrates.

In the present communication, we have borrowed the same strategy to prepare electrodeposited SiO2/DTMS superhydrophobic films (E-SiO2/DTMS films) on mild steel (MS) substrate, the majority of metallic materials used in industry and are highly susceptible to corrosive attack [34], [35], for the purpose of corrosion inhibition. Noting that although as described above, superhydrophobic film has been used for corrosion protection of various metallic materials, it has not yet been applied for corrosion protection of steels. It should also be noted that unlike some other traditional surface treatments, such as phosphate or chromate conversion layers, which are often used with the combination of organic coatings for long-term corrosion protection, superhydrophobic thin film is usually applied for temporary (short-term) protection of metals. Experimental results show that the as-prepared superhydrophobic film provides an effective barrier layer against the attacking of corrosion medium for MS interface.

Section snippets

Materials and chemicals

Mild steel (MS) sheets (kindly supplied by Pentatomic Science & Technology, Hangzhou, China, wt.%: C 0.01, Si 0.35, P 0.018, Cr 0.04, Mo 0.03, Ni 0.017, Cu 0.02, Al 0.06; Fe balance) were cut into 3.0 cm × 4.0 cm plates (0.1 cm thickness). The plates were abraded consecutively finner emery papers to 400 grade, degreased with home-made alkaline solution (composition: Na2CO3 8 g/L, Na2SiO3·9H2O 5 g/L, Na5P3O10 8 g/L, C12H25NaO3S 1 g/L, Triton X-100 5 mL/L) for 10 min at 60 °C under sonication, then

Results and discussion

One major advantage of electrochemically assisted deposition technique, comparing with the conventional dip-coating or spin-coating methods, lies in the fact that it offers a feasible way to control the growth kinetics of sol–gel film by varying electrochemical parameters, such as deposition potential and duration time. SEM observation shows that only some discrete silica particles can be found on the substrate after deposition for a short time (Fig. 1a, 20 s). Prolonging the deposition time

Conclusions

In conclusion, we have fabricated environmentally compliant superhydrophobic SiO2/DTMS hybrid films by one-step electrochemical deposition for the corrosion protection of mild steel. The thickness, roughness and hydrophobicity of the hybrid films can be regulated easily by adjusting the deposition potential and duration time. The combination of highly porous silica component and hydrophobic DTMS makes the derived hybrid silica film turns to be superhydrophobic, which effectively prevents the

Acknowledgments

This work was supported by the NSFC (Nos. 21173187, 51371159), NCET, and the Fundamental Research Funds for the Central Universities.

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