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silane composite films
Colloids and Surfaces A 562 (2019) 247–254
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Corrosion resistance performance of the self-assembled reduction of graphene/silane composite films
T
Yuqing Wen , Dan Kong, Wei Shang , Mingming Ma, Xiaoqiang Zhan, Yuqing Li ⁎
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Guangxi Key Laboratory of Electrochemical and Magnetochemical Functional Materials, Guilin University of Technology, Guilin, 541004, China
GRAPHICAL ABSTRACT
ARTICLE INFO
ABSTRACT
Keywords: Aluminum alloy Hydrophobicity Self-assembled Corrosion resistance
To improve the corrosion resistance of an aluminium alloy, a bis [3- (triethoxysilyl) propyl] tetrasulfide (BTESPT) - reduced graphene (rGO) etching self-assembly composite film (CE-SAMs-rGO) was fabricated by a method that combinies chemical etching with self-assembly. The surface morphology, composition and structure of the CE-SAMs-rGO were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). At the same time, the hydrophobicity of the film was also tested using a contact angle tester. Finally, the corrosion resistance of the CE-SAMs-rGO film was studied by polarization curve, AC impedance and soaking measurements. The results showed that the corrosion current density of the CE-SAMs-rGO was 2.274×10−9 A/cm−2, and the AC impedance was 2.402×106 Ω cm2. The CE-SAMs-rGO samples were more resistant to corrosion than bare aluminium and the CE-SAMs samples. These results indicated that graphene helps to enhance the ability of the film to prevent corrosive ions from invading the metal matrix, and further indicates that graphene aids the corrosion resistance of metals.
1. Introduction
conductivity and thermal conductivity, and easy processing [1–3]. However, these aluminium materials are prone to pitting, intergranular corrosion, stress corrosion cracking and exfoliation corrosion. Therefore, the necessary protection and treatment of an aluminium alloy must be carried out. To improve the bonding durability of the
Aluminium and aluminium alloys are widely used in electronics, ships, and the aerospace, automotive and other industries because of their low density, high specific strength, good ductility, good electrical
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Corresponding authors. E-mail addresses: [email protected] (Y. Wen), [email protected] (W. Shang).
https://doi.org/10.1016/j.colsurfa.2018.11.044 Received 18 September 2018; Received in revised form 17 November 2018; Accepted 17 November 2018 Available online 19 November 2018 0927-7757/ © 2018 Elsevier B.V. All rights reserved.
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protective film and aluminium alloy substrate, the surface of aluminium alloy is usually pre-treated by phosphating, chromate and anodizing. The traditional chromate treatment process, due to Cr+6 in the passivation solution, exhibits great toxicity to the environment and the human body, and its application has been strictly limited. Therefore, it is urgent to develop an environmentally friendly pre-treatment method for the corrosion protection of aluminium alloys. Some surface treatment techniques have been developed, of which silane pre-treatment is a promising and effective method. Silane coupling agents are becoming increasingly more attractive because of the adhesive properties of the coatings, good corrosion inhibition and environmental friendliness. The treatment of metal surfaces with organic silanes is a new type of surface protection treatment developed in recent years. Because of its unique structure, the silane coupling agent can obviously improve the interfacial bonding properties between the metal and the inorganic and organic phases [4–6]. The surface treatment steps with graphene and silane are combined to form a silane-graphene composite film on the substrate surface, which is expected to meet the corrosion resistance and environmental protection requirements. Graphene is a new carbon material, which is tightly packed by a single-layer of carbon atoms to form a two-dimensional honeycomb lattice structure through sp2 hybridization [7–10]. Graphene is also a basic unit for constructing other dimensional carbonaceous materials, such as zero-dimensional fullerene, one-dimensional carbon nanotubes and three-dimensional graphite [11,12]. Graphene has ultra-high mechanical properties, a low density, high thermal conductivity, high anisotropy, high electron mobility, high specific surface area and high barrier properties [13–15]. Graphene materials have unique physical and electronic properties and have great application prospects in nanodevices, composite materials, sensors, lithium batteries [16], hydrogen storage materials and other fields [17–19]. In addition, this material exhibits good transmittance and gas barrier properties. The preparation of graphene-polymer composites with graphene and polymer materials is an effective means to fully demonstrate the excellent properties of graphene. In addition, graphene derivatives, such as graphene oxide, lose the excellent conductivity of graphene, but the rich oxygen groups on their lamellae are helpful for preparing the graphene and polymer composites. Graphene not only improves the physical and mechanical properties of the composite but also provides its functionality. Therefore, it is necessary to prepare a homogeneous composite coating of graphene to make full use of the large surface area of graphene and its derivatives. The flexible surface chemical properties of graphene with these useful properties provide a favourable research basis for the realization of advanced properties in protective coatings. Recent studies indicate that graphene can be used as a corrosion inhibitor because of its unique and impermeable two-dimensional structure, which provides barrier to reactive corrosive ions. The functionalization of graphene has been widely studied and applied because of its compatibility with the matrix material as follows. Zhu et al. [20] investigated the self-assembled graphene oxide/silane coatings for corrosion resistance by immersion experiments in 3.5% NaCl solution. The result indicated that the composite film has good resistance to penetration by corrosive ions. Li et al. [21] prepared a silanized graphene oxide (SGO) reinforced organofunctional silane composite coating on a galvanized steel substrate. The composite coating exhibited the highest protection of 0.2% by weight of SGO. It was believed that Silylated graphene provides a physical barrier to corrosive molecules. Naghdi et al. [22] examined reversible wettability conversion of electrodeposited graphene oxide/titania nanocomposite coatings. Ramezanzadeh et al. [23] proposed a facile route of making silica nanoparticles-covered graphene oxide nanohybrids (SiO2-GO) in the fabrication of a SiO2-GO/epoxy composite coatings with superior barrier and corrosion protection performance. Finally, Chen et al. [24] reported on stable aqueous dispersions of polymer-functionalized graphene sheets from electrochemical exfoliation for anticorrosion applications. The enhanced corrosion protection is primarily due to the
longer and roundabout diffusion path from the corrosive medium of the highly dispersed self-assembly film-graphene sheets in the composite coating. Based on the above discussion and the large specific surface area of reduced graphene(rGO), because of its good penetration resistance, the self-assembled film of the bis-(g-triethoxysilylpropyl)-tetrasulfide (BTESPT)-doped rGO had exhibit better corrosion resistance [25–27]. During the preparation of the rGO and BTESPT composite films, the strong interaction between the rGO and BTESPT weakens the van der Waals forces between the graphene sheets, which inhibits agglomeration [28–30]. On the other hand, the motion of the BTESPT molecules can be restricted, and the interaction between them can be enhanced, thus improving the performance of the composite films [31,32]. In this paper, the surface of the aluminium alloy was treated by acid etching and the self-assembly method. The electrochemical impedance spectroscopy (EIS) and dynamic potential polarization methods were used to test the corrosion properties of the composite membrane by soaking in a 3.5 wt% NaCl solution. The durability of the composite membrane was studied. 2. Experiments 2.1. Materials The AA 6061 substrate was cut into a 30 mm × 40 mm × 2 mmsized specimen. The samples were ground from a 600 # to 800 # to 1200 # granularity of sand SiC sand paper, and ultrasonic cleaning was carried out with ethanol and deionized water solution for 10 min. Bis(3-triethoxysilylpropyl)-tetrasulfide (BTESPT, AR, Jiangxi Xinyi Agricultural Chemical Co., Ltd.), potassium permanganate (KMnO4), hydrochloric acid (HCl, 37%), sulphuric acid (H2SO4, 98%), potassium sulphate(K2SO4), polyethanol 200 (AR) and hydrogen peroxide (H2O2, 30%) were purchased from Chinese Xilong Chemical Co., Ltd. The clean aluminium alloy substrates were treated with 3.75 mol/L HF for 10 min and 4 mol/L HCl for 12 min. Finally, the substrates were cleaned with deionized water and dried with a blast dryer at 70–100 °C. An improved Hummer method was used to synthesize the graphene oxide (GO). A total volume of 50 mL of the BTESPT solution was prepared as follows: 37.5 mL anhydrous ethanol, 2.5 mL BTESPT, 5 mL polyethylene glycol 200, and 5 mL potassium sulphate (with acetic acid to adjust the pH to 4.0) were stirred in a 35 °C magnetic stirrer for 1 h, and immediately the next step deal was addressed. GO (40 mg) weighed on a nanoscale was dispersed in a 100 mL silane solution by a 1 h ultrasonic treatment. The pre-treated 6061 aluminium alloy was placed in a well-prepared BTESPT solution at a temperature of 35 °C. The alloy was removed and placed into a self-contained system for 1 h. The sample was washed with deionized water several times to remove the unreacted small molecules and solvents on the surface. Then the alloy was heated to 100 °C and held for several hours. Finally, a variety of testing methods were used to test the morphology, structure and properties of the samples. The fabrication route was shown in Fig. 1. 2.2. Measurement methods Scanning electron microscopy (SEM) images were acquired with a Hitachi SU5000 emission scanning electron microscope. The SEM acceleration voltage was 10.0 kV at a working distance ranging from 5.00 μm to 10.00 μm. The Holmarc contact angle metre model was used for contact angle (WCA) testing to show the super-hydrophobic properties at room temperature and atmospheric pressure. Deionized water with a volume of approximately 5 μL was dropped onto the aluminium alloy substrate. At least five parallel points were tested on the substrate surface to obtain the mean value of the contact angle. The crystalline structures of the CE-SAMs-rGO composite films were investigated by Xray diffraction, which were performed on an X'Pert3 powder diffractometer (XRD, PANalytical) with a Cu Kα radiation source at a 248
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Fig. 1. Fabrication route for the SAMs.
scanning range of 5-90° (2θ). Raman spectra were collected using a LabRam HR Raman system, and the excitation source was a 532 nm laser with extended scanning between 100 and 3200 wavenumbers (10 s). To evaluate the content and elemental mapping of the CE-SAMsrGO composite films, energy dispersive spectrometry (EDS) mapping analysis was conducted using a Bruker Quantax system (XFlash 6|10) attached to an FESEM system. The chemical characteristics of the BTESPT SAMs were characterized by X-ray photoelectron spectroscopy (XPS, Thermo Electron Corp, ESCALAB 250Xi) with monochromic Al Kα (1486.6 eV)) radiation. The AC impedance and potentiodynamic polarization curves were acquired in 3.5 wt% NaCl at room temperature via an electrochemical workstation with an exposed sample area of 1.0 × 1.0 cm2 (CH, Instruments, Model 760E Co., Ltd.). The electrochemical performance test system was three-electrode system consisting of a working electrode, an auxiliary electrode and a reference electrode. The self-assembled aluminium alloy sheet was used as the working electrode (WE), the platinum (Pt) sheet was used as the auxiliary electrode (CE) and the saturated calomel electrode (SCE) was utilized as the reference electrode. All the experiments were carried out at room temperature. The frequency range of the AC impedance tests was 10−2 Hz to 105 Hz, and the applied sinusoidal applied voltage was 10 mV.
[33]. The contact angle of the CE-SAMs-rGO film reached 159°, which is greater than the contact angle of the other films. It was shown that the chemical etching self-assembled reduced graphene composite films have better hydrophobic properties, and the surface of the film was dense. This may be due to the formation of step structure with a certain distribution on the metal surface after etching and self-assembly. With the addition of graphene, the surface roughness of the composite film increases after high temperature curing. In addition, the superhydrophobic properties of graphene. Therefore, the composite film has superhydrophobic properties. The superhydrophobic properties can improve the corrosion resistance of the metal surface. Based on these explanations, the rGO and the BTESPT formed a composite film. The microstructure of the composite film will contribute to improve the hydrophobicity and corrosion resistance of the metal surface [34–36]. Fig. 3 presents the XRD pattern of aluminium alloy samples, the CESAMs and CE-SAMs-rGO composite coating materials. The XRD pattern of the BTESPT-containing rGO shows a diffraction peak at 2θ = 25.2°, which represents the peak of the reduced graphene. With the aluminium alloy substrate and the self -assembled films, the reduced graphene crystal peaks appeared on the CE-SAMs-rGO films. Four strong peaks were observed at 38.21°, 44.68°, 64.90° and 78.30°, which correspond to the crystalline planes of (111), (200), (220) and (311) for Al, respectively. These peaks not only confirmed the existence of CE-SAMsrGO in the composite films but also proved that the self-assembly of the CE-SAMs-rGO on the base of the aluminium alloy was successful. Raman spectroscopy is an effective tool for characterizing the structural and chemical properties of carbon nanomaterials. Therefore, this method was used to characterize the graphene oxide in the composite membrane (Fig. 4). Compared with the Raman spectrum of the CE-SAMs films, two main peaks are observed in the spectrum of the CESAMs-rGO film, such as the D peak (1352 cm−1) and G peak (1584 cm−1). Located at 1352 cm−1, the D peak is attributed to lattice vibration from the Brillouin zone centre caused by a reduction in graphene samples and can be characterized by an irregular and disordered structure. This irregular and disordered structure reduced the surface of the graphene by a small amount of oxygen-containing functional groups. The G peak at 1584 cm−1 was caused by the intraplane vibration of the sp2 hybrid carbon atoms. The appearance of the Raman peaks of typical graphene shows that graphene microplates were embedded in the BTESPT films, and the CE-SAMs -rGO composite films
3. Results and discussion 3.1. The morphologies of the SAMs Fig. 2 was the SEM morphology of the self-assembled monolayers under different conditions. Fig. 2(a–d) represent the bare aluminium alloy substrate, self-assembled reduced graphene composite films (CESAMs-rGO), chemically etched self-assembled film (CE-SAMs), and chemically etched self-assembled reduced graphene composite films (CE-SAMs-rGO). Compared with the bare aluminium alloy substrate (Fig. 2a), there was reductive graphene on the BTESPT coating on the substrate (Fig. 2b). Moreover, from Fig. 2(c and d), the chemical etching self-assembled film was compared with the chemical etching self-assembly reduction graphene films, and the reduced graphene evenly covered the chemically etched self-assembled graphene film. This may be due to the formation of multilayer graphene films on metal surface by the aggregation of intermolecular forces on metal surface 249
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Fig. 2. SEM and static contact angle of different samples.
Fig. 3. XRD of samples.
Fig. 4. Raman spectra of CE-SAMs and CE-SAMs-rGO.
were successfully made on the aluminium alloy substrate. To demonstrate that the CE-SAMs-rGO was successfully applied to the surface, the chemical composition of the modified and unmodified samples was analysed by EDS. The results are shown in Fig. 5 and Table 1. Compared with the bare aluminium alloy, carbon, oxygen sulfur and silicon elements appear on the surfaces of the CE-SAMs and CE-SAMs-rGO films, indicating that the BTESPT films were on the substrate. The chemical composition depends greatly on the process at the surface. Table 1 summarizes the EDS data of the CE-SAMs- rGO coating layer. Five elements were found in the CE-SAMs and CE-SAMsrGO composite films. However, the content of C, O, Si and S in the CESAMs-rGO composite films were higher than that of the CE-SAMs composite films. The increase in the content of C and O further illustrated the combination of rGO and the self-assembled monolayers. The EDS map shows that the membrane was mainly composed of S, O, Si, Al
and C, and the reduced graphene was successfully covered in the selfassembled composite films. To explore the bonding structure of the composite films on the aluminium alloy substrate, the interaction between rGO and BTESPT silane was characterized by XPS. Fig. 6a shows the XPS spectrum of the sample, indicating the existence of C, Si, S and O in the rGO composite films. Fig. 6b shows the C1s spectrum, and the original C1s spectrum was fitted to the three peaks centred on 284.82 eV, 286.44 eV, and 287.78 eV, which were CeC, CeO and C]O [37–39], respectively, confirming that rGO and BTESPT were found in the membrane. Fig. 6c depicts the O1s XPS spectrum, which indicates that the four peaks at 531.54 eV, 531.82 eV, 532.10 eV and 532.22 eV belong to C]O, Si-O (including Si-O-Si and SieOH) CeO and AleOeSi, respectively. According to Fig. 5d, the Si 2p spectrum was fitted to show the SieOH, SieOeSi and SieOeC keys at 101.32 eV, 102.08 eV and 102.83 eV, respectively. Meanwhile, the XPS analysis showed that CE250
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Fig. 5. EDS of samples.
corrosion resistance of the base metal and blocking the corrosive medium. The results showed that the prepared the CE-SAMs-rGO composite films had better corrosion resistance than other films. The Bode plot for the phase angle also showed the differences between the bare aluminium alloy, the CE-SAMs and the CE-SAMs-rGO coated surfaces. The phase angle of the CE-SAMs-rGO in the high frequency range was generally higher than that of the bare aluminium alloy and CESAMs, which indicated a better protective effect of the metal matrix. The potentiodynamic polarization curves of samples in a 3.5% NaCl solution under different conditions are shown in Fig. 8. The corrosion current density and corrosion voltage were calculated by an extrapolation method. As seen from Fig. 8, the bare aluminium, the CE-SAMs and the CE-SAMs-rGO corrosion potentials were −1.107 V, −0.646 V and −0.525 V, respectively. The prepared composite film was obviously moved to the positive potential. The corrosion current densities were 1.326 × 10−5 A/cm2, 1.140 × 10−7 A/cm2 and 2.402 × 10−9 A/ cm2. Compared with bare aluminium, the corrosion current density of the CE-SAMs films and the CE-SAMs-rGO composite films were decreased by 2 orders of magnitude. In addition, the corrosion current density of the CE-SAMs-rGO composite films was 2 orders of magnitude lower than that of the CE-SAMs films. The corrosion current of the composite film decreased, and the corrosion potential was moved forward. The corrosion inhibition efficiency [31,40] (ŋp) was calculated by the following formula.
Table 1 EDS data of the surface composition of samples. Sample
Al (weight %)
C (weight %)
O (weight %)
Si (weight %)
S (weight %)
Bare CE-SAMs CE-SAMs-rGO
93.82 76.19 59.75
3.85 14.45 22.22
1.86 6.82 12.05
0.47 1.75 3.19
– 0.78 2.78
SAMs-rGO composite films were formed on the surface of the aluminium alloy, and the formation of Si-O-Al and Si-O-C increased the strength and compactness of the composite films. The corrosion resistance of the bare aluminium alloy, CE-SAMs and CE-SAMs-rGO were investigated by electrochemical impedance spectroscopy in 3.5% NaCl solution at room temperature. Fig. 7 shows the EIS characteristics of the bare aluminium, the CE-SAMs and the CESAMs-rGO composite films. Compared with the other composite films, the impedance values of the CE-SAMs-rGO composite coatings were significantly improved after the formation of the layers of the self-assembled monolayers. Fig. 7a shows the Bode plots of the measured electrochemical impedance. The impedance (∣Z∣) of the CE-SAMs-rGO composite films (6.28 × 105 Ω) were almost three times higher (2.67 × 105 Ω) than that of the CE-SAMs composite films in the low frequency range (0.01 Hz), which is an order of magnitude higher than that of the bare aluminium alloy (2.794 × 104 Ω). The CE-SAMs-rGO had a relatively higher impedance value in the low frequency region, which showed that the silane films played a role in improving the
P%
251
=
0 icoor icoor × 100% 0 icoor
(1)
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Fig. 6. XPS spectra of CE-rGO-SAMs (a) and high resolution of the atoms C (b), O (c), Si (d).
Fig. 8. Potentiodynamic polarization curves of samples in 3.5% NaCl solution. Table 2 Electrochemical parameters of potentiodynamic polarization curves for samples in 3.5% NaCl solutions. Samples
Ecoor(V)
Icoor(A/cm2)
Rp(Ω·cm2)
ηp(%)
Bare CE-SAMs CE-SAMs-rGO
−1.107 −0.646 −0.525
1.326 × 10−5 1.140 × 10−7 2.402 × 10−9
2700 2.205 × 105 2.274 × 106
– 99.19% 99.98%
The icorr and i°corr are the corrosion current density values of the bare aluminium and the composite films samples, respectively. As presented in Table 2, the corrosion rate of the CE-SAMs and the CESAMs-rGO protection films were lower than the bare aluminium, especially the preparation of the CE-SAMs-rGO composite films. It was shown that the CE-SAMs-rGO composite layer can effectively inhibit the
Fig. 7. EIS of different samples in 3.5 wt.% NaCl solution. 252
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Fig. 9. SEM of different samples after immersion test in 3.5 wt% NaCl solution.
corrosion current density of the CE-SAMs-rGO was 2.274 × 10−9 A/ cm2, and the AC impedance was 2.402 × 106 Ω cm2. In addition, the results of the 120 h soaking experiment showed that the CE-SAMs-rGO film was more resistant to corrosion than the bare aluminium and the CE-SAMs samples in 3.5% NaCl solution. These findings show that the CE-SAMs-rGO films had good anti-penetration ability to corrosive ions, and reduced graphene is beneficial for improving the corrosion resistance of aluminium alloys.
infiltration of corrosive ions into the substrate, and the inhibition efficiency was the highest (99.98%). This high efficiency was because these SiOH groups easily adsorb onto the metal surface by forming hydrogen bonds between the SiOH group and the surface metal hydroxyl group (MOH) and form excess SiOH groups and corrosion resistant species showing the chemical stability of the siloxane network (Si-O-Si). It was considered that the composite film was composed of SiOSi and SiOAl bonds formed by the condensation reaction between SiOH groups themselves and between SiOH and AlOH groups. Thus, the metal surface no longer favours water adsorption, thereby suppressing the tendency of the aqueous metal solution to corrode the surface while suppressing the infiltration of the corrosive ions. Therefore, the composite film has excellent corrosion resistance, indicating that the self-assembled composite layer structure effectively hinders and extends the corrosive electrolyte penetration path. To explore the corrosion resistance, the bare aluminium, the CESAMs and the CE-SAMs-rGO were immersed in aqueous NaCl for 120 h. Afterwards, the samples were taken out of the solution, flushed with distilled water and then dried at 50℃ for 2 h. The surface morphology of the corroded sample is shown in Fig. 9. For the bare aluminium samples, surface cracks and many particles were generated as the immersion time increased, as shown in Fig. 9a. The CE-SAMs samples also showed cracks on the surface. However, the corrosion of the CE-SAMsrGO samples, and the change in the surface topography was not obvious. These observations indicate that the corrosion of the CE-SAMsrGO samples was minor. In other words, the CE-SAMs-rGO samples were more resistant to corrosion than the bare aluminium and the CESAMs samples.
Conflict of interest The authors declare no conflict of interest. Acknowledgements The authors thank the financial supports from the National Natural Science Foundation of China (No. 51665010 and No. 51664011), and the Guangxi Key Laboratory of Electrochemical and Magnetochemical Functional Materials (No. EMFM20181106). References [1] J.L. Qi, Z.Y. Wang, J.H. Lin, T.Q. Zhang, A.T. Zhang, J. Cao, L.X. Zhang, J.C. Feng, Graphene-enhanced Cu composite interlayer for contact reaction brazing aluminum alloy 6061, Vacuum 136 (2017) 142–145. [2] S. Naghdi, B. Jaleh, A. Ehsani, Electrophoretic deposition of graphene oxide on aluminum: characterization, low thermal annealing, surface and anticorrosive properties, Bull. Chem. Soc. Jpn. 88 (2015) 722–728. [3] A. Sharma, S. Sagar, R.P. Mahto, B. Sahoo, S.K. Pal, J. Paul, Surface modification of Al6061 by graphene impregnation through a powder metallurgy assisted friction surfacing, Surf. Coat. Technol. 337 (2018) 12–23. [4] L. Li, B. Li, J. Dong, J. Zhang, Roles of silanes and silicones in forming superhydrophobic and superoleophobic materials, J. Mater. Chem. A 4 (2016) 13677–13725. [5] A. Ahmadi, B. Ramezanzadeh, M. Mahdavian, Hybrid silane coating reinforced with silanized graphene oxide nanosheets with improved corrosion protective performance, RSC Adv. 6 (2016) 54102–54112. [6] M. Mrad, Y. Ben Amor, L. Dhouibi, M.F. Montemor, Corrosion prevention of AA2024-T3 aluminum alloy with a polyaniline/poly(γ-glycidoxypropyltrimethoxysilane) bi-layer coating: comparative study with polyaniline mono-layer feature, Surf. Coat. Technol. 337 (2018) 1–11. [7] M.J. Nine, M.A. Cole, D.N.H. Tran, D. Losic, Graphene: a multipurpose material for
4. Conclusions CE-SAMs-rGO composite films were prepared on the surface of an aluminium alloy by a method of combining chemical etching with selfassembly. The SEM, XRD, Raman spectra, EDS and XPS results indicated that the CE-SAMs-rGO film was successfully prepared on the surface of the aluminium alloy. The contact angle between the film and water was 159°, as determined by a contact angle tester, indicating the superhydrophobicity of the film. The electrochemical results show that the 253
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Colloids and Surfaces A journal homepage: www.elsevier.com/locate/colsurfa
Corrosion resistance performance of the self-assembled reduction of graphene/silane composite films
T
Yuqing Wen , Dan Kong, Wei Shang , Mingming Ma, Xiaoqiang Zhan, Yuqing Li ⁎
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Guangxi Key Laboratory of Electrochemical and Magnetochemical Functional Materials, Guilin University of Technology, Guilin, 541004, China
GRAPHICAL ABSTRACT
ARTICLE INFO
ABSTRACT
Keywords: Aluminum alloy Hydrophobicity Self-assembled Corrosion resistance
To improve the corrosion resistance of an aluminium alloy, a bis [3- (triethoxysilyl) propyl] tetrasulfide (BTESPT) - reduced graphene (rGO) etching self-assembly composite film (CE-SAMs-rGO) was fabricated by a method that combinies chemical etching with self-assembly. The surface morphology, composition and structure of the CE-SAMs-rGO were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). At the same time, the hydrophobicity of the film was also tested using a contact angle tester. Finally, the corrosion resistance of the CE-SAMs-rGO film was studied by polarization curve, AC impedance and soaking measurements. The results showed that the corrosion current density of the CE-SAMs-rGO was 2.274×10−9 A/cm−2, and the AC impedance was 2.402×106 Ω cm2. The CE-SAMs-rGO samples were more resistant to corrosion than bare aluminium and the CE-SAMs samples. These results indicated that graphene helps to enhance the ability of the film to prevent corrosive ions from invading the metal matrix, and further indicates that graphene aids the corrosion resistance of metals.
1. Introduction
conductivity and thermal conductivity, and easy processing [1–3]. However, these aluminium materials are prone to pitting, intergranular corrosion, stress corrosion cracking and exfoliation corrosion. Therefore, the necessary protection and treatment of an aluminium alloy must be carried out. To improve the bonding durability of the
Aluminium and aluminium alloys are widely used in electronics, ships, and the aerospace, automotive and other industries because of their low density, high specific strength, good ductility, good electrical
⁎
Corresponding authors. E-mail addresses: [email protected] (Y. Wen), [email protected] (W. Shang).
https://doi.org/10.1016/j.colsurfa.2018.11.044 Received 18 September 2018; Received in revised form 17 November 2018; Accepted 17 November 2018 Available online 19 November 2018 0927-7757/ © 2018 Elsevier B.V. All rights reserved.
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protective film and aluminium alloy substrate, the surface of aluminium alloy is usually pre-treated by phosphating, chromate and anodizing. The traditional chromate treatment process, due to Cr+6 in the passivation solution, exhibits great toxicity to the environment and the human body, and its application has been strictly limited. Therefore, it is urgent to develop an environmentally friendly pre-treatment method for the corrosion protection of aluminium alloys. Some surface treatment techniques have been developed, of which silane pre-treatment is a promising and effective method. Silane coupling agents are becoming increasingly more attractive because of the adhesive properties of the coatings, good corrosion inhibition and environmental friendliness. The treatment of metal surfaces with organic silanes is a new type of surface protection treatment developed in recent years. Because of its unique structure, the silane coupling agent can obviously improve the interfacial bonding properties between the metal and the inorganic and organic phases [4–6]. The surface treatment steps with graphene and silane are combined to form a silane-graphene composite film on the substrate surface, which is expected to meet the corrosion resistance and environmental protection requirements. Graphene is a new carbon material, which is tightly packed by a single-layer of carbon atoms to form a two-dimensional honeycomb lattice structure through sp2 hybridization [7–10]. Graphene is also a basic unit for constructing other dimensional carbonaceous materials, such as zero-dimensional fullerene, one-dimensional carbon nanotubes and three-dimensional graphite [11,12]. Graphene has ultra-high mechanical properties, a low density, high thermal conductivity, high anisotropy, high electron mobility, high specific surface area and high barrier properties [13–15]. Graphene materials have unique physical and electronic properties and have great application prospects in nanodevices, composite materials, sensors, lithium batteries [16], hydrogen storage materials and other fields [17–19]. In addition, this material exhibits good transmittance and gas barrier properties. The preparation of graphene-polymer composites with graphene and polymer materials is an effective means to fully demonstrate the excellent properties of graphene. In addition, graphene derivatives, such as graphene oxide, lose the excellent conductivity of graphene, but the rich oxygen groups on their lamellae are helpful for preparing the graphene and polymer composites. Graphene not only improves the physical and mechanical properties of the composite but also provides its functionality. Therefore, it is necessary to prepare a homogeneous composite coating of graphene to make full use of the large surface area of graphene and its derivatives. The flexible surface chemical properties of graphene with these useful properties provide a favourable research basis for the realization of advanced properties in protective coatings. Recent studies indicate that graphene can be used as a corrosion inhibitor because of its unique and impermeable two-dimensional structure, which provides barrier to reactive corrosive ions. The functionalization of graphene has been widely studied and applied because of its compatibility with the matrix material as follows. Zhu et al. [20] investigated the self-assembled graphene oxide/silane coatings for corrosion resistance by immersion experiments in 3.5% NaCl solution. The result indicated that the composite film has good resistance to penetration by corrosive ions. Li et al. [21] prepared a silanized graphene oxide (SGO) reinforced organofunctional silane composite coating on a galvanized steel substrate. The composite coating exhibited the highest protection of 0.2% by weight of SGO. It was believed that Silylated graphene provides a physical barrier to corrosive molecules. Naghdi et al. [22] examined reversible wettability conversion of electrodeposited graphene oxide/titania nanocomposite coatings. Ramezanzadeh et al. [23] proposed a facile route of making silica nanoparticles-covered graphene oxide nanohybrids (SiO2-GO) in the fabrication of a SiO2-GO/epoxy composite coatings with superior barrier and corrosion protection performance. Finally, Chen et al. [24] reported on stable aqueous dispersions of polymer-functionalized graphene sheets from electrochemical exfoliation for anticorrosion applications. The enhanced corrosion protection is primarily due to the
longer and roundabout diffusion path from the corrosive medium of the highly dispersed self-assembly film-graphene sheets in the composite coating. Based on the above discussion and the large specific surface area of reduced graphene(rGO), because of its good penetration resistance, the self-assembled film of the bis-(g-triethoxysilylpropyl)-tetrasulfide (BTESPT)-doped rGO had exhibit better corrosion resistance [25–27]. During the preparation of the rGO and BTESPT composite films, the strong interaction between the rGO and BTESPT weakens the van der Waals forces between the graphene sheets, which inhibits agglomeration [28–30]. On the other hand, the motion of the BTESPT molecules can be restricted, and the interaction between them can be enhanced, thus improving the performance of the composite films [31,32]. In this paper, the surface of the aluminium alloy was treated by acid etching and the self-assembly method. The electrochemical impedance spectroscopy (EIS) and dynamic potential polarization methods were used to test the corrosion properties of the composite membrane by soaking in a 3.5 wt% NaCl solution. The durability of the composite membrane was studied. 2. Experiments 2.1. Materials The AA 6061 substrate was cut into a 30 mm × 40 mm × 2 mmsized specimen. The samples were ground from a 600 # to 800 # to 1200 # granularity of sand SiC sand paper, and ultrasonic cleaning was carried out with ethanol and deionized water solution for 10 min. Bis(3-triethoxysilylpropyl)-tetrasulfide (BTESPT, AR, Jiangxi Xinyi Agricultural Chemical Co., Ltd.), potassium permanganate (KMnO4), hydrochloric acid (HCl, 37%), sulphuric acid (H2SO4, 98%), potassium sulphate(K2SO4), polyethanol 200 (AR) and hydrogen peroxide (H2O2, 30%) were purchased from Chinese Xilong Chemical Co., Ltd. The clean aluminium alloy substrates were treated with 3.75 mol/L HF for 10 min and 4 mol/L HCl for 12 min. Finally, the substrates were cleaned with deionized water and dried with a blast dryer at 70–100 °C. An improved Hummer method was used to synthesize the graphene oxide (GO). A total volume of 50 mL of the BTESPT solution was prepared as follows: 37.5 mL anhydrous ethanol, 2.5 mL BTESPT, 5 mL polyethylene glycol 200, and 5 mL potassium sulphate (with acetic acid to adjust the pH to 4.0) were stirred in a 35 °C magnetic stirrer for 1 h, and immediately the next step deal was addressed. GO (40 mg) weighed on a nanoscale was dispersed in a 100 mL silane solution by a 1 h ultrasonic treatment. The pre-treated 6061 aluminium alloy was placed in a well-prepared BTESPT solution at a temperature of 35 °C. The alloy was removed and placed into a self-contained system for 1 h. The sample was washed with deionized water several times to remove the unreacted small molecules and solvents on the surface. Then the alloy was heated to 100 °C and held for several hours. Finally, a variety of testing methods were used to test the morphology, structure and properties of the samples. The fabrication route was shown in Fig. 1. 2.2. Measurement methods Scanning electron microscopy (SEM) images were acquired with a Hitachi SU5000 emission scanning electron microscope. The SEM acceleration voltage was 10.0 kV at a working distance ranging from 5.00 μm to 10.00 μm. The Holmarc contact angle metre model was used for contact angle (WCA) testing to show the super-hydrophobic properties at room temperature and atmospheric pressure. Deionized water with a volume of approximately 5 μL was dropped onto the aluminium alloy substrate. At least five parallel points were tested on the substrate surface to obtain the mean value of the contact angle. The crystalline structures of the CE-SAMs-rGO composite films were investigated by Xray diffraction, which were performed on an X'Pert3 powder diffractometer (XRD, PANalytical) with a Cu Kα radiation source at a 248
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Fig. 1. Fabrication route for the SAMs.
scanning range of 5-90° (2θ). Raman spectra were collected using a LabRam HR Raman system, and the excitation source was a 532 nm laser with extended scanning between 100 and 3200 wavenumbers (10 s). To evaluate the content and elemental mapping of the CE-SAMsrGO composite films, energy dispersive spectrometry (EDS) mapping analysis was conducted using a Bruker Quantax system (XFlash 6|10) attached to an FESEM system. The chemical characteristics of the BTESPT SAMs were characterized by X-ray photoelectron spectroscopy (XPS, Thermo Electron Corp, ESCALAB 250Xi) with monochromic Al Kα (1486.6 eV)) radiation. The AC impedance and potentiodynamic polarization curves were acquired in 3.5 wt% NaCl at room temperature via an electrochemical workstation with an exposed sample area of 1.0 × 1.0 cm2 (CH, Instruments, Model 760E Co., Ltd.). The electrochemical performance test system was three-electrode system consisting of a working electrode, an auxiliary electrode and a reference electrode. The self-assembled aluminium alloy sheet was used as the working electrode (WE), the platinum (Pt) sheet was used as the auxiliary electrode (CE) and the saturated calomel electrode (SCE) was utilized as the reference electrode. All the experiments were carried out at room temperature. The frequency range of the AC impedance tests was 10−2 Hz to 105 Hz, and the applied sinusoidal applied voltage was 10 mV.
[33]. The contact angle of the CE-SAMs-rGO film reached 159°, which is greater than the contact angle of the other films. It was shown that the chemical etching self-assembled reduced graphene composite films have better hydrophobic properties, and the surface of the film was dense. This may be due to the formation of step structure with a certain distribution on the metal surface after etching and self-assembly. With the addition of graphene, the surface roughness of the composite film increases after high temperature curing. In addition, the superhydrophobic properties of graphene. Therefore, the composite film has superhydrophobic properties. The superhydrophobic properties can improve the corrosion resistance of the metal surface. Based on these explanations, the rGO and the BTESPT formed a composite film. The microstructure of the composite film will contribute to improve the hydrophobicity and corrosion resistance of the metal surface [34–36]. Fig. 3 presents the XRD pattern of aluminium alloy samples, the CESAMs and CE-SAMs-rGO composite coating materials. The XRD pattern of the BTESPT-containing rGO shows a diffraction peak at 2θ = 25.2°, which represents the peak of the reduced graphene. With the aluminium alloy substrate and the self -assembled films, the reduced graphene crystal peaks appeared on the CE-SAMs-rGO films. Four strong peaks were observed at 38.21°, 44.68°, 64.90° and 78.30°, which correspond to the crystalline planes of (111), (200), (220) and (311) for Al, respectively. These peaks not only confirmed the existence of CE-SAMsrGO in the composite films but also proved that the self-assembly of the CE-SAMs-rGO on the base of the aluminium alloy was successful. Raman spectroscopy is an effective tool for characterizing the structural and chemical properties of carbon nanomaterials. Therefore, this method was used to characterize the graphene oxide in the composite membrane (Fig. 4). Compared with the Raman spectrum of the CE-SAMs films, two main peaks are observed in the spectrum of the CESAMs-rGO film, such as the D peak (1352 cm−1) and G peak (1584 cm−1). Located at 1352 cm−1, the D peak is attributed to lattice vibration from the Brillouin zone centre caused by a reduction in graphene samples and can be characterized by an irregular and disordered structure. This irregular and disordered structure reduced the surface of the graphene by a small amount of oxygen-containing functional groups. The G peak at 1584 cm−1 was caused by the intraplane vibration of the sp2 hybrid carbon atoms. The appearance of the Raman peaks of typical graphene shows that graphene microplates were embedded in the BTESPT films, and the CE-SAMs -rGO composite films
3. Results and discussion 3.1. The morphologies of the SAMs Fig. 2 was the SEM morphology of the self-assembled monolayers under different conditions. Fig. 2(a–d) represent the bare aluminium alloy substrate, self-assembled reduced graphene composite films (CESAMs-rGO), chemically etched self-assembled film (CE-SAMs), and chemically etched self-assembled reduced graphene composite films (CE-SAMs-rGO). Compared with the bare aluminium alloy substrate (Fig. 2a), there was reductive graphene on the BTESPT coating on the substrate (Fig. 2b). Moreover, from Fig. 2(c and d), the chemical etching self-assembled film was compared with the chemical etching self-assembly reduction graphene films, and the reduced graphene evenly covered the chemically etched self-assembled graphene film. This may be due to the formation of multilayer graphene films on metal surface by the aggregation of intermolecular forces on metal surface 249
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Fig. 2. SEM and static contact angle of different samples.
Fig. 3. XRD of samples.
Fig. 4. Raman spectra of CE-SAMs and CE-SAMs-rGO.
were successfully made on the aluminium alloy substrate. To demonstrate that the CE-SAMs-rGO was successfully applied to the surface, the chemical composition of the modified and unmodified samples was analysed by EDS. The results are shown in Fig. 5 and Table 1. Compared with the bare aluminium alloy, carbon, oxygen sulfur and silicon elements appear on the surfaces of the CE-SAMs and CE-SAMs-rGO films, indicating that the BTESPT films were on the substrate. The chemical composition depends greatly on the process at the surface. Table 1 summarizes the EDS data of the CE-SAMs- rGO coating layer. Five elements were found in the CE-SAMs and CE-SAMsrGO composite films. However, the content of C, O, Si and S in the CESAMs-rGO composite films were higher than that of the CE-SAMs composite films. The increase in the content of C and O further illustrated the combination of rGO and the self-assembled monolayers. The EDS map shows that the membrane was mainly composed of S, O, Si, Al
and C, and the reduced graphene was successfully covered in the selfassembled composite films. To explore the bonding structure of the composite films on the aluminium alloy substrate, the interaction between rGO and BTESPT silane was characterized by XPS. Fig. 6a shows the XPS spectrum of the sample, indicating the existence of C, Si, S and O in the rGO composite films. Fig. 6b shows the C1s spectrum, and the original C1s spectrum was fitted to the three peaks centred on 284.82 eV, 286.44 eV, and 287.78 eV, which were CeC, CeO and C]O [37–39], respectively, confirming that rGO and BTESPT were found in the membrane. Fig. 6c depicts the O1s XPS spectrum, which indicates that the four peaks at 531.54 eV, 531.82 eV, 532.10 eV and 532.22 eV belong to C]O, Si-O (including Si-O-Si and SieOH) CeO and AleOeSi, respectively. According to Fig. 5d, the Si 2p spectrum was fitted to show the SieOH, SieOeSi and SieOeC keys at 101.32 eV, 102.08 eV and 102.83 eV, respectively. Meanwhile, the XPS analysis showed that CE250
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Fig. 5. EDS of samples.
corrosion resistance of the base metal and blocking the corrosive medium. The results showed that the prepared the CE-SAMs-rGO composite films had better corrosion resistance than other films. The Bode plot for the phase angle also showed the differences between the bare aluminium alloy, the CE-SAMs and the CE-SAMs-rGO coated surfaces. The phase angle of the CE-SAMs-rGO in the high frequency range was generally higher than that of the bare aluminium alloy and CESAMs, which indicated a better protective effect of the metal matrix. The potentiodynamic polarization curves of samples in a 3.5% NaCl solution under different conditions are shown in Fig. 8. The corrosion current density and corrosion voltage were calculated by an extrapolation method. As seen from Fig. 8, the bare aluminium, the CE-SAMs and the CE-SAMs-rGO corrosion potentials were −1.107 V, −0.646 V and −0.525 V, respectively. The prepared composite film was obviously moved to the positive potential. The corrosion current densities were 1.326 × 10−5 A/cm2, 1.140 × 10−7 A/cm2 and 2.402 × 10−9 A/ cm2. Compared with bare aluminium, the corrosion current density of the CE-SAMs films and the CE-SAMs-rGO composite films were decreased by 2 orders of magnitude. In addition, the corrosion current density of the CE-SAMs-rGO composite films was 2 orders of magnitude lower than that of the CE-SAMs films. The corrosion current of the composite film decreased, and the corrosion potential was moved forward. The corrosion inhibition efficiency [31,40] (ŋp) was calculated by the following formula.
Table 1 EDS data of the surface composition of samples. Sample
Al (weight %)
C (weight %)
O (weight %)
Si (weight %)
S (weight %)
Bare CE-SAMs CE-SAMs-rGO
93.82 76.19 59.75
3.85 14.45 22.22
1.86 6.82 12.05
0.47 1.75 3.19
– 0.78 2.78
SAMs-rGO composite films were formed on the surface of the aluminium alloy, and the formation of Si-O-Al and Si-O-C increased the strength and compactness of the composite films. The corrosion resistance of the bare aluminium alloy, CE-SAMs and CE-SAMs-rGO were investigated by electrochemical impedance spectroscopy in 3.5% NaCl solution at room temperature. Fig. 7 shows the EIS characteristics of the bare aluminium, the CE-SAMs and the CESAMs-rGO composite films. Compared with the other composite films, the impedance values of the CE-SAMs-rGO composite coatings were significantly improved after the formation of the layers of the self-assembled monolayers. Fig. 7a shows the Bode plots of the measured electrochemical impedance. The impedance (∣Z∣) of the CE-SAMs-rGO composite films (6.28 × 105 Ω) were almost three times higher (2.67 × 105 Ω) than that of the CE-SAMs composite films in the low frequency range (0.01 Hz), which is an order of magnitude higher than that of the bare aluminium alloy (2.794 × 104 Ω). The CE-SAMs-rGO had a relatively higher impedance value in the low frequency region, which showed that the silane films played a role in improving the
P%
251
=
0 icoor icoor × 100% 0 icoor
(1)
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Fig. 6. XPS spectra of CE-rGO-SAMs (a) and high resolution of the atoms C (b), O (c), Si (d).
Fig. 8. Potentiodynamic polarization curves of samples in 3.5% NaCl solution. Table 2 Electrochemical parameters of potentiodynamic polarization curves for samples in 3.5% NaCl solutions. Samples
Ecoor(V)
Icoor(A/cm2)
Rp(Ω·cm2)
ηp(%)
Bare CE-SAMs CE-SAMs-rGO
−1.107 −0.646 −0.525
1.326 × 10−5 1.140 × 10−7 2.402 × 10−9
2700 2.205 × 105 2.274 × 106
– 99.19% 99.98%
The icorr and i°corr are the corrosion current density values of the bare aluminium and the composite films samples, respectively. As presented in Table 2, the corrosion rate of the CE-SAMs and the CESAMs-rGO protection films were lower than the bare aluminium, especially the preparation of the CE-SAMs-rGO composite films. It was shown that the CE-SAMs-rGO composite layer can effectively inhibit the
Fig. 7. EIS of different samples in 3.5 wt.% NaCl solution. 252
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Fig. 9. SEM of different samples after immersion test in 3.5 wt% NaCl solution.
corrosion current density of the CE-SAMs-rGO was 2.274 × 10−9 A/ cm2, and the AC impedance was 2.402 × 106 Ω cm2. In addition, the results of the 120 h soaking experiment showed that the CE-SAMs-rGO film was more resistant to corrosion than the bare aluminium and the CE-SAMs samples in 3.5% NaCl solution. These findings show that the CE-SAMs-rGO films had good anti-penetration ability to corrosive ions, and reduced graphene is beneficial for improving the corrosion resistance of aluminium alloys.
infiltration of corrosive ions into the substrate, and the inhibition efficiency was the highest (99.98%). This high efficiency was because these SiOH groups easily adsorb onto the metal surface by forming hydrogen bonds between the SiOH group and the surface metal hydroxyl group (MOH) and form excess SiOH groups and corrosion resistant species showing the chemical stability of the siloxane network (Si-O-Si). It was considered that the composite film was composed of SiOSi and SiOAl bonds formed by the condensation reaction between SiOH groups themselves and between SiOH and AlOH groups. Thus, the metal surface no longer favours water adsorption, thereby suppressing the tendency of the aqueous metal solution to corrode the surface while suppressing the infiltration of the corrosive ions. Therefore, the composite film has excellent corrosion resistance, indicating that the self-assembled composite layer structure effectively hinders and extends the corrosive electrolyte penetration path. To explore the corrosion resistance, the bare aluminium, the CESAMs and the CE-SAMs-rGO were immersed in aqueous NaCl for 120 h. Afterwards, the samples were taken out of the solution, flushed with distilled water and then dried at 50℃ for 2 h. The surface morphology of the corroded sample is shown in Fig. 9. For the bare aluminium samples, surface cracks and many particles were generated as the immersion time increased, as shown in Fig. 9a. The CE-SAMs samples also showed cracks on the surface. However, the corrosion of the CE-SAMsrGO samples, and the change in the surface topography was not obvious. These observations indicate that the corrosion of the CE-SAMsrGO samples was minor. In other words, the CE-SAMs-rGO samples were more resistant to corrosion than the bare aluminium and the CESAMs samples.
Conflict of interest The authors declare no conflict of interest. Acknowledgements The authors thank the financial supports from the National Natural Science Foundation of China (No. 51665010 and No. 51664011), and the Guangxi Key Laboratory of Electrochemical and Magnetochemical Functional Materials (No. EMFM20181106). References [1] J.L. Qi, Z.Y. Wang, J.H. Lin, T.Q. Zhang, A.T. Zhang, J. Cao, L.X. Zhang, J.C. Feng, Graphene-enhanced Cu composite interlayer for contact reaction brazing aluminum alloy 6061, Vacuum 136 (2017) 142–145. [2] S. Naghdi, B. Jaleh, A. Ehsani, Electrophoretic deposition of graphene oxide on aluminum: characterization, low thermal annealing, surface and anticorrosive properties, Bull. Chem. Soc. Jpn. 88 (2015) 722–728. [3] A. Sharma, S. Sagar, R.P. Mahto, B. Sahoo, S.K. Pal, J. Paul, Surface modification of Al6061 by graphene impregnation through a powder metallurgy assisted friction surfacing, Surf. Coat. Technol. 337 (2018) 12–23. [4] L. Li, B. Li, J. Dong, J. Zhang, Roles of silanes and silicones in forming superhydrophobic and superoleophobic materials, J. Mater. Chem. A 4 (2016) 13677–13725. [5] A. Ahmadi, B. Ramezanzadeh, M. Mahdavian, Hybrid silane coating reinforced with silanized graphene oxide nanosheets with improved corrosion protective performance, RSC Adv. 6 (2016) 54102–54112. [6] M. Mrad, Y. Ben Amor, L. Dhouibi, M.F. Montemor, Corrosion prevention of AA2024-T3 aluminum alloy with a polyaniline/poly(γ-glycidoxypropyltrimethoxysilane) bi-layer coating: comparative study with polyaniline mono-layer feature, Surf. Coat. Technol. 337 (2018) 1–11. [7] M.J. Nine, M.A. Cole, D.N.H. Tran, D. Losic, Graphene: a multipurpose material for
4. Conclusions CE-SAMs-rGO composite films were prepared on the surface of an aluminium alloy by a method of combining chemical etching with selfassembly. The SEM, XRD, Raman spectra, EDS and XPS results indicated that the CE-SAMs-rGO film was successfully prepared on the surface of the aluminium alloy. The contact angle between the film and water was 159°, as determined by a contact angle tester, indicating the superhydrophobicity of the film. The electrochemical results show that the 253
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