The effect of wettability on corrosion resistance of oxide films produced by SILAR method on magnesium, aluminum and copper substrates

Highlights

• Oxide films on the Mg, Al and Cu were enlarged by the SILAR methods.

• Properties of wettability for oxide films that were enlarged by the SILAR methods were viewed.

• Wettability effects of corrosion were investigated.

Abstract

The CuO, MgO and Al₂O₃ films were deposited on Cu, Mg and Al substrates by the Successive Ionic Layer Adsorption and Reaction (SILAR) method. While the MgO thin film showed hydrophilic behavior with contact angle of 75°, the Al₂O₃ film was hydrophobic with the contact angle of 117°. The best enhancement in terms of the wetting behavior was obtained from the copper oxide films. For these films, maximum static water contact angle was 164°. Results showed super-hydrophobic property and unique shape of form. Moreover, the superhydrophobic surface of CuO film exhibited higher corrosion resistance than MgO and Al₂O₃ films.

Introduction

Light metals are especially used in the area of high strength to weight ratio as well as aeronautical industry, transportation, defense, automotive, electric and electronic industry, etc. and these metals can be exposed to corrosion depending on their application areas. Therefore, it is necessary the corrosion resistance in order to extend the usage life of materials. If the contact area and the contact period of the surfaces in the solution decrease, the possibility of exposing electrochemical decomposition decreases too. [1], [2] Therefore, it is thought that it might be useful if the surface of such metals has hydrophobic property. One of the methods which improvethe corrosion resistance of these metals is to coat the surface with oxide films. Several different methods are used so as to produce oxide films such as thermal decomposition of metal hydroxide or carbonate [3], sol–gel [4], hydrothermal [5], chemical gas phase deposition [6], combustion aerosol synthesis [7], chemical methods [8], PVD [9], [10], [11], plasma spraying [12], [13], [14], and PEO methods [15].

The coating methods involving the film growth from chemical solution are called as chemical methods [8], [9]. The solutions containing precursor molecules are found in thin film. Chemical deposition methods have many advantageous as inexpensive and enable to synthesis of thin film materials. The chemical deposition methods are electroless deposition, spray pyrolysis, electrodeposition, successive ionic layer adsorption and reaction (SILAR), chemical bath deposition (CBD), anodization, liquid phase epitaxy, etc. The prominent properties of these methods are:

1. Proposing no limitations on substrate material. 2. Proposing extremely easy way to dope film. 3. Usually having low operating temperature. 4. Proposing better adaptation and improved grain structure, since the basic particles are ions instead of atoms. 5. Proposing enigmatical morphology of the films which can be easily controlled by preparative parameters. 6. Containing different physical deposition methods, they do not require high quality objective and/or substrates [8], [16], [17], [18].

Among these thin film preparation processes, successive ionic layer adsorption and reaction (SILAR) has many superior properties such as simple application, low cost, and synthesis at room temperature. Also, SILAR can be used to deposit the compound materials on a variety of substrates such as insulators, semiconductors, and metals [19], [20], [21].

SILAR method is based on the dipping of substrate into the solution including anionic and cationic precursors separately. Then it is fined in distilled water after every dipping. When substrate is dipped in cationic precursor, cations are adsorbed on the substrate surface. Fining the substrate in distilled water can separate the unadsorbed or excess ions out and avoid homogeneous precipitation. When the substrate is dipped in anionic precursor solution, anions react with preadsorbed cations. The unreacted or powdery material can be removed by fining the substrate in distilled water. These operations can be called as cycle. Multilayer films form on material surfaces after repeating the cycles. Quality and thickness of the film depend mainly upon preparative parameters. [8], [20], [21], [22], [23]. Pathan and Lokhande [19] reported the advantages of SILAR method. In SILAR method, deposition of thick film requires many hours and hence it can be operated with microprocessor or computer. Dubal et al. [24] prepared the Mn₃O₄ thin films by SILAR method. It is reported that the supercapacitive property of Mn₃O₄ thin film showed maximum supercapacitance of 314 F g^− 1 at a scan rate of 5 mV s^− 1. Giner et al. [25] investigated the corrosion behavior of single crystalline MgO surfaces in simulated body fluid (SBF). In this study square etch pits for the first time have been obtained at the physiological pH-value. Fan et al. [26] achieved superhydrophobic films via hydrothermally synthesized CuO film on copper substrate and investigated the corrosion behavior of the films. They measured the water contact angle as 157° and reported the anticorrosion properties in detail. Another study, cationic doping of MgO surfaces was investigated to build corrosion protection in Mg alloys. It was shown that increased dissociation barrier for water adsorbed on the same doped surfaces indicates the incorporation of such impurities that will effectively block the dissolution of oxide films and potentially enhance the film's resistivity to water [27]. Kumar et al. [28] deposited hydrophobic ZnO thin films on the glass substrate by SILAR method. They investigated the morphology and hydrophobicity of thin film. More et al. [29] fabricated titanium dioxide (TiO₂) films on fluorine doped tin oxide (FTO) coated glass substrate by SILAR method. The surface morphological, optical and surface wettability properties of the as-deposited and annealed TiO₂ films were investigated by them. Ubale et al. [30] deposited the (PbS)_x(CuS)_1 − x thin films on glass substrates via SILAR method. They studied the structural, morphological and optical characterizations of the films. The films were nanocrystalline in nature and the mixed phase of cubic PbS and hexagonal CuS has been observed. The dc dark electrical resistivity of PbS film decreased when content of Cu in composite increased. The films were n-type and films were in hydrophilic property. The main of this study indicate that can be enlarged of different oxide films with SILAR methods as easy, economic and investigate to corrosion resistance which depend on properties wettability of these oxide films. For this purpose, the surfaces of copper, aluminum and magnesium metals were coated with their oxide films by SILAR method. The relationship between the hydrophobic properties and the corrosion behaviors of these films was investigated. Also, the structural and morphological properties of these films were examined using SEM and XRD analyses.