Synergistic effect of hydrophobic film and porous MAO membrane containing alkynol inhibitor for enhanced corrosion resistance of magnesium alloy

Accepted Manuscript Synergistic effect of hydrophobic film and porous MAO membrane containing alkynol inhibitor for enhanced corrosion resistance of magnesium alloy

Zhaoxia Li, Qiangliang Yu, Chaoyang Zhang, Yupeng Liu, Jun Liang, Daoai Wang, Feng Zhou PII: DOI: Reference:

S0257-8972(18)31161-7 doi:10.1016/j.surfcoat.2018.10.054 SCT 23917

To appear in:

Surface & Coatings Technology

Received date: Revised date: Accepted date:

5 September 2018 16 October 2018 19 October 2018

Please cite this article as: Zhaoxia Li, Qiangliang Yu, Chaoyang Zhang, Yupeng Liu, Jun Liang, Daoai Wang, Feng Zhou , Synergistic effect of hydrophobic film and porous MAO membrane containing alkynol inhibitor for enhanced corrosion resistance of magnesium alloy. Sct (2018), doi:10.1016/j.surfcoat.2018.10.054

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT

Synergistic effect of hydrophobic film and porous MAO membrane containing alkynol inhibitor for enhanced corrosion resistance of magnesium alloy

PT

Zhaoxia Lia,b, Qiangliang Yua, Chaoyang Zhanga, Yupeng Liua,c, Jun Lianga, Daoai Wanga,c*, Feng

State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese

SC

a

RI

Zhoua

Academy of Sciences, Lanzhou 730000, China.

University of Chinese Academy of Sciences, Beijing, 100049, China

c

Qingdao Center of Resource Chemistry and New Materials, Qingdao 266100, China

MA

NU

b

AC

CE

PT E

* E-mail: [email protected].

D

Corresponding Author

ACCEPTED MANUSCRIPT Abstract Magnesium and magnesium alloys have important applications in aviation, electronic devices, medical equipment, and automotive industries, while the corrosion is a common and real problem

PT

that must be solved for these applications. In this paper, a novel and effective anti-corrosive composite coating on AZ31 Mg alloys was prepared by the combination of micro-arc oxidation

RI

(MAO) layer, corrosion inhibitor and hydrophobic wax film technologies. And among these, the

SC

MAO treated micro- and nanopores as the container of corrosion inhibitor and the solid hydrophobic

NU

wax as the multifunctional sealing isolating agent. The morphology and phase composition of the resulting composite coatings were investigated by field emission scanning electron microscopy

MA

(FESEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD), respectively,

D

indicating the successful synthesis of the organic-inorganic composite coating. The potentiodynamic

PT E

polarization and electrochemical impedance spectroscopy measurements showed that compared with the MAO membrane covered Mg alloys, the organic-inorganic composite coating has superior

CE

corrosion resistance with the a lower corrosion current (5.764×10-9 A/cm2) and a higher protection efficiency (99.7 %) after immersion in 3.5 wt % NaCl solution, attributing to the synergistic effect of

AC

effective inhibition of inhibitor and the physical barrier ability of hydrophobic film and MAO membrane. This simple and low cost strategy to fabricate organic-inorganic composite anticorrosion coatings would have promising applications in the corrosion protection of the light metals and their alloys.

Key words: AZ31 Mg alloy; Micro-arc oxidation layer; Corrosion inhibitor; EIS; Tafel; Synergistic effect

ACCEPTED MANUSCRIPT 1. Introduction In recent years, magnesium and its alloys have attracted more and more attention owing to their high specific strength, high thermal conductivity, good machinability and easy recyclability, which are deemed as one of the most promising green engineering materials [1]. Nevertheless, magnesium

PT

and its alloys possess a low standard potential, which usually results in the oxidation and corrosion in

RI

the humid atmosphere or corrosive aqueous solution especially containing the aggressive ions of Cl−.

SC

This common corrosion problem seriously hinders their applications in aerospace, biomedical engineering, automobile and other fields.

NU

In the past few years, numerous anticorrosion techniques have been developed to solve the

MA

problem of corrosion damage of the magnesium and magnesium alloys. Among these approaches, chemical conversion coating[2-4], micro-arc oxidation (MAO)[5-7], surface chemical modification[8,

D

9], as well as inhibitor[10, 11] were widely studied and applied in the protection of magnesium and

PT E

magnesium alloys materials. For example, micro-arc oxidation technology is a commonly used treatment strategy to enhance the corrosion resistance and wear resistance of the light metal surfaces

CE

by fabricating a hard ceramic structure coating with some porous structures [12-14]. While the

AC

presence of the micro-pores and micro-cracks in the MAO films might increase the opportunity for penetration of aggressive substance in the corrosion process, thus weakening the protective performance for the substrate material [13, 15]. Some researches turned to study how to reduce or seal these micro-pores and micro-cracks to improve the corrosion resistance of MAO film of the Mg alloys [16, 17], which is still a systematic and arduous challenge from the basic principle of micro arc oxidation. On the other hand, adding inhibitor to the organic coating is another effective strategy to improve

ACCEPTED MANUSCRIPT the corrosion resistance of metal materials, which could adsorb on the metal surface by the some functional groups to form a complex to insulate water and the protected metals, thus improving the corrosion resistance of the metals [18, 19]. Generally, the adsorption of organic inhibitor mainly depends on the electronic properties (ie. electron density of donor atoms, steric effects and π orbital

PT

character) and physicochemical of the molecule [20, 21]. Thus, design the organic inhibitors

RI

containing sulphur, oxygen, nitrogen and aromatic rings or multiple bonds anticorrosive functional

SC

group in their molecular structure with strong absorption force between the protected metals and inhibitor is particularly important [21], which would contribute to further improvement of

NU

anticorrosion performance. In the practical applications, adding corrosion inhibitor directly to

MA

organic coating is one of the most commonly used methods to suppress metal corrosion. The amount of corrosion inhibitors, the adding methods and the distribution of the inhibitors in the coating have

D

great influence on the corrosion resistance and mechanical properties of the coatings, which should

PT E

be carefully balanced in the practical use. To solve this problem, some researchers introduced the micro- /nano-containers in this coating system, for instance, the layered double hydroxides (LDH)

CE

[22, 23], MSNs [24, 25], capsule [26], halloysite [27] and so on, to control the release process of the

AC

corrosion inhibitor and increase its content. However, it is still a challenge to resolve the new problems of high cost, incompatibility, poor binding force and small scale. Herein, we introduced a novel method to fabricate an effective anti-corrosive composite coating on AZ31 Mg alloys by the combination of micro-arc oxidation, corrosion inhibitor and hydrophobic wax technologies. MAO film with micro- and nanopore structures was firstly formed on the surface of AZ31 Mg alloy, which was used as both the new container of corrosion inhibitor and the inorganic anticorrosion layer. Then, a quaternary ammonium salt with long alkyl chain was synthesized and

ACCEPTED MANUSCRIPT filled into the porous MAO layer as the corrosion inhibitor. Last, a thin hydrophobic wax film was coated on the top surface to seal the corrosion inhibitor and to further isolate the protected metal from aggressive medium. The wax layer is chosen as the sealing material because it is a low cost, transparent, hydrophobic, flexible and easy processing material, and is different from the normal

PT

organic coatings for fabricating a thin film on the protected metal surfaces. Furthermore, the

RI

micro-pores and micro-cracks structures in MAO membrane could not only act as the new type of

SC

reservoir for inhibitor but also the mechanical tongs, which can provide more mechanical interlocking sites so as to improve the continued adhesion of organic coating to the substrate. The

NU

electrochemical and salt spray experiments showed that the obtained composite coating possessed

MA

remarkable corrosion resistance property, which would be ascribed to the synergistic effect of the inhibitory action of ammonium salt with long alkyl chain, and the isolation effect of the inorganic

PT E

2. Experiment section

D

ceramic MAO membrane and organic hydrophobic layer.

2.1 Materials and Chemicals

CE

Magnesium alloy plates, 30 mm×20 mm×5 mm (AZ31 composition, wt.%: 3.21 Al, 0.82 Zn,

AC

0.42 Mn, 0.012 Si, 0.0011Fe, 0.0012 Cu, 0.00063 Ni, and Mg balance), were commercial available and used as the metal substrates in this study. Prior to micro-oxidation treatment, the AZ31 Mg plates were grinded with 200#, 600#, 800#,1000# and 1500# abrasives papers, followed by degreasing with acetone, ethanol and rinsed with deionized water (DI), and finally dried in nitrogen. NaH (99%), anhydrous tetrahydrofuran (THF, 99%), acetonitrile (99%), sodium silicate, and potassium

hydroxide

were

purchased

from

Tianjin Kermel Chemical Reagent Co.,

Ltd.

1,2-dibromoethane, propargyl alcohol(99%) and N,N-dimethyloctadecylamine were used as received

ACCEPTED MANUSCRIPT from the Chemical Reagent Co. of J&K Chemical Ltd (Beijing, China). Other reagent and solvents were used as received without further treatment. 2.2 Synthesis of inhibitor of N-16 The molecular formula and molecular structure of the synthesized inhibitor of [N-

PT

（5-hydroxypent-3-yl）-N,N-dimethylhexadecan-1-aminium bromide] are shown in Fig. 1. Firstly,

RI

NaH (0.5 mol, 12.6081 g) was dissolved in anhydrous tetrahydrofuran (THF), and propynyl alcohol

SC

(0.5 mol, 28.0332 g) was added dropwise, followed the solution was heated to 55 °C. After the reaction mixture being stirred for 2 h under N 2 atmosphere, 1,2-dibromoethane (0.45 mol, 86.8633 g)

NU

was added dropwise. After the reaction was carried out for 12 hours, 30

g of

MA

N,N-dimethyloctadecylamine dissolved in acetonitrile was added to the reaction system, and the mixture was refluxed at 85 °C. After recrystallization, the product was obtained by vacuum drying,

AC

CE

PT E

D

and marked as N-16.

Fig. 1. The molecular formula and optimized molecular structure of N-16.

2.3 Preparation of micro-arc oxidation layer AZ31 Mg alloy samples were used as anodes and a stainless steel bi-pass cylinder container with

ACCEPTED MANUSCRIPT a volume of 1 L was used as cathode during the MAO process. Na2SiO3 and KOH were dissolved in distilled water and then were poured into the cylinder container as electrolytes (10.0 g/L of Na 2SiO3 and 1.0 g/L of KOH). The micro-arc oxidation technique was performed using WHYH-20 equipment (Low Energy Nuclear Physics Institute, China). Besides, the circulating system of cooling water

PT

(kept around 0 °C) and the magnetic stirring were necessarily needed. All the MAO treatments were

RI

performed at a constant current of 16.6 A/dm2 and the negative constant voltage of 125 V, and the

SC

oxidation time was 10 minutes.

2.4. Fabrication of hydrophobic wax/ N-16/ MAO composite coating

NU

The preparation of N-16/MAO sample as follows: firstly, 5 mg of N-16 inhibitor was dissolved

MA

into the 50 mL of distilled water. Then the MAO specimens were put into the above mixed solution, and were pumped to a certain negative pressure so as to inject the N-16 inhibitor into the micro-pores

D

and micro-cracks of MAO membrane. This process was repeated for three times to ensure the

PT E

successful embedment of N-16 inhibitor.

To fabricate the hydrophobic wax film on the surface of N-16/MAO layer, the wax was firstly

CE

melted and then was coated on the top surface of N-16/ MAO in an oven at 80 °C to form the

AC

organic/inorganic composite coating. Last, after erasing the excess wax solution by filter paper, the sample was kept in an oven at 60 ° C for 2 h and cooled naturally to room temperature to form a thin and uniform hydrophobic wax film on the top surface of N-16/ MAO composite coating. 2.5. Characterization 1

H and

13

C NMR spectra were recorded on a 400 MHz spectrometer (Bruker AM-400) using

CDCl3 as solvent. HRMS spectrum was obtained on a Bruker mico TOF-QⅡ mass spectrometer. The thermal ability was determined with a thermogravimetric analyzer (TGA) (Netzsch, STA 449C) over

ACCEPTED MANUSCRIPT a temperature range of 30-1000 °C at a heating rate of 10 °C min-1 under N2 atmosphere. Morphologies of the prepared coatings were observed by scanning electron microscope (SEM, 5601L). Prior to scanning, all coating samples were sputtered with Au to improve their conductivity. The elemental distribution of coating samples was examined using an energy dispersive X-ray

PT

spectroscopy (EDS) elemental mapping and content analysis. The phase constituents of coating were

RI

investigated by an X-Ray diffraction (XRD, X’PERT PRO) with a scanning rate of 0.02° /min and

SC

scanning scale of 5-80 °. Search match software was used to identify the diffraction peaks with reference to standard cards. Meanwhile, the water contact angle (WCA) was acquired using a

NU

DSA-100 optical contact angle meter (Kruss Company, Ltd., Germany) at room temperature (25 °C).

MA

The average contact angle values were obtained by measuring five points on the substrate surface. In order to investigate the corrosion resistance of coatings, electrochemical impedance

D

spectroscopy (EIS) and potentiodynamic polarization curve measurement were conducted in 3.5 wt%

PT E

NaCl solution at 25 °C through the electrochemical workstation (CHI660E, Chenhua, SHANGHAI). In experiment, the AZ31 Mg alloy substrate and coating specimens were used as working electrodes

CE

(1 cm×1 cm, the exposed area), the saturated calomel electrode (SCE) as reference electrode and a

AC

platinum plate as auxiliary electrode. The EIS studies were performed in the open circuit potential after 30 minutes immersion in the NaCl solution. The scan frequency ranged from 100 kHz to 10 mHz with an amplitude of 10 mV. The obtained EIS plots were analyzed using ZsimpWin software, and they were fitted to the appropriate equivalent circuit models. Potentiodynamic polarization tests were performed from appropriately -2000 to -1000 mV/SCE at a scanning rate of 1 mV/s. All electrochemical parameters (corrosion current density (icorr), corrosion potential (Ecorr) and Tafel slops (βa and βc) were fitted using the Tafel extrapolation method. According to relevant literatures,

ACCEPTED MANUSCRIPT the polarization resistance (Rp) and the protection efficiency (Eprotection, %) were calculated from

PT

expressions below (1) (2) [28, 29], respectively.

The salt spray test was further conducted to measure the durability. The test specimens are

RI

placed in an enclosed chamber at an angle of 45° firstly, then exposed to a continuous indirect spray

SC

of salt water solution (5 % NaCl and 95 % water, by weight), which the fog falls out on to the

NU

specimens at a rate of 1.0 mL/80 cm2/hour, in a chamber temperature of 35 °C. The chamber climate is maintained under constant steady state conditions, and the test duration is 24 h, 5 days and 15 days,

MA

respectively.

3. Results and discussions

PT E

D

The organic/inorganic composite coating on the surface of AZ31 Mg alloy is schematically shown in Fig. 2. First, the micro- and nanoporous structured inorganic ceramic membrane was

CE

fabricated on AZ31 Mg alloy surface by micro-arc oxidation technique. Subsequently, by using the micro- and nanopores on the surface of MAO film as the corrosion inhibitor reservoirs, the

AC

as-prepared inhibitor of N-16 was deposited into the micro-pores and micro-cracks. Finally, a hydrophobic wax film as the top-coating sealant on the sample was prepared to further improve the anti-corrosion performance by isolation effect. Among them, the detailed preparation process of the corrosion inhibitor N-16 could be seen in experimental section, and the 1HNMR, 13CNMR and mass spectrum of N-16 inhibitor are shown in Fig. S 1, S 2 and S 3. In addition, the thermogravimetric curves of N-16 inhibitor showed it has good thermal stability below 200 °C as shown in Fig. S 4.

PT

ACCEPTED MANUSCRIPT

Fig. 2. Schematic diagram of the as-prepared anticorrosion composite coating on the AZ31 Mg alloy

RI

Fig. 3 shows the typical SEM images of the morphologies of blank AZ31 Mg, MAO, MAO/N-16

SC

and MAO/N-16/wax film. It was found that compared with the MAO treated samples, the top surface

NU

of bare AZ31 Mg is very smooth, only with some light scratches formed during the polish process as shown in Fig. 3a. After MAO treatment, the surface of AZ31 Mg turned rough with some micro- and

MA

nanopores formed as seen in Fig. 3b. Most of the pores with the size between 0.5 to 2 μm, which are disorderly arranged on the sample surface. And the micro-pore did not interconnect each other. From

PT E

D

the cross-sectional images of the MAO film as shown in Fig. 3c, the thickness of the ceramic membrane is about 44.6 μm, and the sufficient hole depth is conducive to the embedding of the

CE

corrosion inhibitor. And meanwhile, the irregular pore structure also provides a certain mechanical interlocking sites for the wax film. After the corrosion inhibitor of N-16 being deposited into the pore,

AC

the size of micro- and nanopores gradually decreased and the surface became more compact as shown in Fig. 3d. After coating the wax film with the thickness of 24 μm, the rough MAO membrane surface became smooth with most of the micro- and nanopore structures being covered as shown in Fig. 3e and 3f.

MA

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

Fig. 3. The SEM morphology of (a) AZ31; (b) MAO; (c) the cross section of MAO coating; (d)

PT E

D

MAO/N-16; (e) MAO/N-16/wax film; (f) the cross section of MAO/N-16/wax film.

Energy-dispersive spectroscopy (EDS) was used to identify the elemental composition of the as-

CE

prepared composite coatings. The elemental mapping and EDS analysis results of as-prepared MAO

AC

coating were shown in Fig. 4a-e. It is evident that the distributions of Si and O were extraordinary uniform and distinguishable. Moreover, the EDS results revealed 10.64 wt % C, 33.11 wt % O, 4.49 wt % Na, 29.14 wt % Mg, 21.58 wt % Si, and 1.04 wt % K on the as-prepared MAO coating, which came from the AZ31 My alloy and the micro arc oxidation electrolyte containing Na2SiO3 and KOH. To characterize whether the inhibitor is successfully embedded in the MAO micro-pores and micro-cracks, the composition of the as-prepared MAO/N-16 coating were also conducted by the element mapping EDS. From Fig. 4g and h, we can find the MAO/N-16 coating was rich in N and Br,

ACCEPTED MANUSCRIPT and the distribution was very even, which were accordance in the element composition of inhibitor N-16. Meanwhile, it is obvious to see the N, Br elements were distributed in cross-section of MAO/N-16, as shown in Fig. S7. From the above results, it can be concluded that the alkynol

AC

CE

PT E

D

MA

NU

SC

RI

PT

inhibitor N-16 was successfully incorporated into the porors of MAO membrane.

Fig. 4. SEM microscopy image (a), O and Si elemental mapping images (b, c), the energy depersive spectroscopy (EDS) and content analysis of MAO(d,e); SEM microscopy image (f), N and Br

ACCEPTED MANUSCRIPT elemental mapping images (g, h) and the EDS of MAO/N-16 (i, j) .

To further study the elements and phases in the coatings, the XRD patterns of bare Mg alloy and Mg alloy with MAO coatings, MAO/N-16 coating and MAO/N-16 /Wax coating are shown in Fig. 5.

PT

From these results we can see that most of the sharp peaks attributes to AZ31 magnesium alloy. After

RI

MAO treatment, new peaks of MgO and MgSiO4 appeared, which can also be certified in the Fig. b

SC

(the magnification of the b area in the Fig. 5a), indicating the MAO coatings are mainly composed of MgO and MgSiO4. Besides, in order to demonstrate the presence of inhibitor N-16, we compared the

NU

XRD patterns of bare inhibitor N-16 and N-16 coated MAO/Mg alloy in Fig. 5c and Fig. S8, in

MA

which can verify the existence of inhibitor N-16 with an amorphous phase in MAO/N-16 coating. In addition, the XRD patterns of MAO/N-16 /Wax was also compared with the blank wax film as

D

shown in Fig. 5d, and the peak positions are nearly identical, indicating the successful preparation of

AC

CE

PT E

wax film on the surface of MAO/N-16 sample.

MA

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

Fig. 5. (a) X-ray diffraction patterns of (1) AZ31, (2) MAO coated AZ31, (3) MAO/N-16 coated

PT E

D

AZ31 and (4) MAO/N-16/wax film coated AZ31. (b-d) Comparative X-ray patterns of (b) bare AZ31 Mg alloy and MAO coatings, (c) N-16 corrosion inhibtor and MAO/N-16 composite, (d) bare wax

CE

film and MAO/N-16/wax coating.

AC

The wettability of the surface of the material also has an important effect on the corrosion resistance of the composite coating. Generally, the hydrophilic surfaces make water molecules or chloride ions more easily to permeate to the metal surface, resulting in the corrosion or oxidation of materials. While the hydrophobic and superhydrophobic surfaces make water molecules or chloride ions more difficult to penetrate into the metal surface because of isolation effect, thus inhibiting the occurrence of metal corrosion or oxidation. Fig. 6 shows the water contact angles photos on the Mg alloys before and after post treatments, wherein the contact angle photographs were taken after the

ACCEPTED MANUSCRIPT water droplets stayed stable on the surface of the sample. The bare AZ31 has a water contact angle of ca. 68.7o as shown in Fig. 6a. The water contact angle decreases after micro-arc oxidation treatment, which was ascribe to the formation of porous and hydrophilic oxide structures (Fig. 6b). After loading the corrosion inhibtor of N-16, the contact angle has slightly decrease as shown in Fig. 6c,

PT

owing to the hydrophilicity of inhibitor N-16 by which the corrosion inhibtor molecules could

RI

transfer from MAO membrane to the metal bare surface to form the anticorrosion layer. After coating

SC

the wax film as sealing coating on the top surface, the water contact angle of sample increased to more than 90o, which became hydrophobic coating to isolate the water molecules or other corrosion

NU

ions to penetrate to the metal surface for anticorrosion. Besides in order to vertify the effect of the

MA

introduction of the wax film on the mechanical properties of the entire coating, a scratch test was performed, as shown in Fig. S5. Here, the critical load Lc is defined as the minimum normal force

D

that caused whole film detachment from the substrate, which marked as Lc2 (Fig. S5). Especially for

PT E

the critical loads of partial delamination (Lc1) have direct relation with mechanical properties of coatings. In Fig. S5 (a), the partial delamination occurred when the applied load of 1.7 N, and cracks

CE

gradually propagate to the substrate under compressive stress. Eventually the critical load of full

AC

delamination (Lc2) is about 4.9 N. However, for the MAO/N-16/wax films specimen, the Lc1 and Lc2 are approximately 6.8 N, 8.9 N, respectively. These results manifested the hardness of MAO is low and oxide ceramic structure is very fragile, and the introduction of corrosion inhibitor and wax film does not have much influence on the loss of mechanical properties of the entire coating, but rather increases the bonding strength of the composite coating and the substrate to some extent.

SC

RI

PT

ACCEPTED MANUSCRIPT

Fig. 6. The water contact angles of various samples: (a) AZ31 Mg alloy; (b) MAO; (c) MAO/N-16;

MA

NU

(d) MAO/N-16/wax film.

The anti-corrosion ability of the composite coatings was evaluated by the measurement of

D

potentiodynamic polarization curves in 3.5 wt % NaCl solution, as shown in Fig. 7. It is found that

PT E

the corrosion potential of the bare AZ31 Mg alloy is about -1.495 V vs. SCE, indicating the bare AZ31 Mg sample is very vulnerable to corrosion with a large current density in 3.5 wt % NaCl

CE

solution. Compared with the bare AZ31 Mg sample, the micro-arc oxidation treated sample shows

AC

more positive corrosion potential (-1.493 V vs. SCE) and lower current density (4.612×10-8 A/cm2). This result suggests that the inorganic ceramics structure was helpful to improve the corrosion resistance of Mg alloy. Meanwhile, the anticorrosion performance of micro-pores as reservoir of inhibitor N-16 was investigated. Compared with bare AZ31 Mg, the corrosion potential of MAO/N-16 sample shifted more positive and the corrosion current density decreased by nearly two order of magnitude, in which probably owing to the formation of adsorption film of alkynol inhibitor N-16 to form the anticorrosion layer. Moreover, after fabricating the outside hydrophobic coating,

ACCEPTED MANUSCRIPT the MAO/N-16/Wax film sample presented more positive corrosion potential (Ecorr is -1.412 V vs. SCE) and lower current density (5.764×10-9 A/cm2) during the process of cathode or anode polarization than that of MAO/N-16 film coated AZ31 Mg. The coverage of films largely reduced the corrosion rete of the AZ31 Mg, especially for the hydrophobic wax film covered

PT

MAO/N-16/Wax composite coating. According to the Stern-Geary equation and protection efficiency

RI

formula [28, 29], the polarization resistance (Rp) and protection efficiency (Eprotection) of the

SC

specimens were summarized in Table 1. It can be concluded that the polarization resistance and protection efficiency increase gradually by successive treatments of forming MAO membrane,

NU

loading N-16 inhibitor and coating hydrophobic wax film, respectively. More significantly, the

MA

composite coating consisted of porous oxide structure, the inhibitor and hydrophobic wax film enabled the protection efficiency of MAO/N-16/Wax film up to 99.7%, and the polarization

AC

CE

PT E

D

resistance increased to 3.96×106 Ω·cm2.

Fig. 7. Potentiodynamic curves for bare Mg, MAO, MAO/N-16 and MAO/N-16 /Wax coating samples immersion in 3.5 wt % NaCl solution.

ACCEPTED MANUSCRIPT

Table 1 Electrochemical kinetic parameters obtained by potentiodynamic polarization curves of different treatments samples in 3.5 wt % NaCl solution at room temperature.

(vs. SCE)

icorr

-βc

βａ

Rp

Eprotection

/A·cm2

/mV dec-1

/mV dec-1

/Ω·cm2

/%

259

-1.495

1.936×10-6

123.2

MAO

-1.493

4.612×10-8

148.8

MAO/N-16

-1.476

2.340×10-8

155.6

MAO/N-16/wax film

-1.412

5.764×10-9

183.5

1.87×104

―

6.81×105

97.6

235.6

1.74×106

98.7

73.5

3.96×106

99.7

140.5

MA

NU

SC

AZ31 Mg

PT

Ecorr/V

RI

Samples

As a means of nondestructive detection, EIS measurement was further performed for studying the

D

corrosion resistance properties of bare AZ31 alloy and the influence of MAO, inhibitor and

PT E

hydrophobic wax film on the anticorrosion performance of AZ31 alloy substrate. The EIS spectra (Nyquist and Bode plots) of blank AZ31 Mg alloy, the MAO coating, the MAO/N-16 and wax coated

CE

MAO/N-16 in 3.5 wt % NaCl solution are presented in Fig. 8. It is evident that electrochemical

AC

impedance spectra for different samples immersed in 3.5 wt % NaCl solution contained a depressed semicircle. Generally, the lager axial radius of the semi-elliptical arc, the better anticorrosive property of the coating[30]. In Fig. 8a, the Nyquist diagrams show that the diameter of the capacitance looping of MAO/N-16/Wax was much larger than the MAO and MAO/N-16 samples, suggesting that the hydrophobic film has good corrosion resistance in 3.5 wt % NaCl solution. After MAO treatment, the capacitive loop of MAO inorganic ceramic coating sample has larger axial radius than the blank AZ31 Mg alloy, indicating that the corrosion resistance improved distinctly

ACCEPTED MANUSCRIPT through the formation of ceramic and porous oxidation layer on AZ31 Mg alloy, as shown in the inset of Fig. 8a. In addition, the embedment of corrosion inhibitor to the micro- and nanopores of MAO membrane has a positive influence on the protection of substrate, which shows a larger axial radius than the MAO coating.

PT

Generally, the AC impedance at high frequency reflects the properties of coating, and at low

RI

frequency the parameters represent the Faraday reaction resistance Rct and double layer capacitance

SC

[31]. And the materials with a higher Z modulus at lower frequencies exhibit better corrosion resistance on metal substrates[32]. The Bode plots of the AZ31 Mg with and withou the anticorrosion

NU

coatings in 3.5 wt % NaCl solution are shown in Fig. 8b and Fig. 8c. In Fig. 8b, the impedance

MA

modulus of the bare AZ31 Mg without any treatment at low frequency is about 10 4 Ω ·cm2. The impedance modulus of MAO membrane coated AZ31 Mg alloy is about 106 Ω ·cm2 at low frequency,

D

which is two orders of magnitude higher than that of bare AZ31 Mg. This result indicates that the

PT E

formation of inorganic ceramic MAO film has better anticorrosion ability than bare AZ31 Mg. After the embedment of inhibitor N-16 into the micro-pores and micro-cracks of MAO membrane, the

CE

impedance modulus has no significant change compared with MAO membrane coated Mg alloy.

AC

Nevertheless, the impedance modulus of the MAO/N-16/Wax film at low frequency significantly improved after coating the hydrophobic wax film. The impedance modulus is about 107Ω· cm2, which is three orders of magnitude higher than that of bare AZ31 Mg. It is well known that high impedance in the specimen is usually ascribed to an area effect wherein the coating blocks the aggressive electrolyte from reaching the reactive metal surface[33]. This result shows MAO/N-16/Wax film has favorable corrosion resistance, which would be ascribed to the existence of adsorption film between porous oxide layer structure and inhibitor, on the other hand the air trapped

ACCEPTED MANUSCRIPT in the micro-pores and micro-cracks surface acts as a barrier and prevents corrosive ions from

PT E

D

MA

NU

SC

RI

PT

penetrating the Mg alloy substrate.

Fig. 8. The EIS results for bare Mg, MAO, MAO/N-16 and MAO/N-16/Wax film in 3.5 wt % NaCl

CE

solution: (a) Nyquist plots, (b) Bode curves and (c) Bode-phase angle versus frequency plots. The inset in Figure 8a corresponds to the enlarged impedance spectra in the higher frequency range with

AC

red rectangle region.

The Bode-phase angle diagrams in Fig. 8c show the bare AZ31 Mg has one peak, whereas MAO, MAO/N-16 and MAO/N-16/Wax film have two peaks. Therefore, according to these characteristics, models of equivalent circuits for EIS results are shown in Fig. 9, where Qct and Qc represent the constant phase element (CPE) used to replace capacitance. Usually, the CPE is defined by admittance Y and power index number n through the formula Y = Y0(jω)n （0＜n≤1）, when the value of n is

ACCEPTED MANUSCRIPT close to 1, which reflects the capacitive properties of the interface[34]. The bare AZ31 Mg displays one time constant and low phase angle in high frequency zone. The equivalent circuit of bare AZ31 Mg can be described as Rs(QdlRct) in Fig. 9a, which is a typical circuit for a passive oxide layer resulting from the Mg passivation effect. In the equivalent circuits, Rs is the solution resistance, and

PT

Rct and Qdl represent resistance and capacitive reactance produced by charge transfer, respectively.

RI

Besides, the MAO coating and MAO/N-16 coating have an outer porous layer and an inner

SC

compactness layer, it is found that they show two phase angles in the high frequency and low frequency, respectively. Therefore, the equivalent circuits of MAO and MAO/N-16 coating are

NU

interpreted using a model with two time constants as Rs(QdlRct)( QcRc) in Fig. 9b, values of Rc and Qc

MA

correspond to the adsorption layer resistances and capactive reactance of between MAO film and inhibitor. The equivalent circuit of MAO/N-16/Wax film composite coating is defined as L

D

Rs(QdlRct)( QcRc) ,where L represents inductance in Fig. 9c. In Fig. 9c, Rc is the total of all coating,

PT E

including the adsorption layer resistances between MAO and inhibitor, and hydrophobic wax film

AC

CE

resistances, and Qc is the capacitive reactance of above systems.

ACCEPTED MANUSCRIPT Fig. 9. Schematic of equivalent circuit obtained by EIS result fitting: (a) bare AZ31 Mg, (b) MAO and MAO/N-16, (c) MAO/N-16/Wax. Rs: solution resistance, Qc: constant phase element corresponding to coating, Rc: coating resistance, Qdl: constant phase element corresponding to

PT

double-layer, Rct: charge transfer resistance, L:inductance.

RI

The fitting results of different electrochemical elements of the equivalent circuits, as listed in

SC

Table 2. It is well known that Rct directly reflects the anticorrosion ability of coating, and Qct can be used to evaluate the degree of penetration of the electrolyte in the membrane layer, which is related

NU

to the thickness, density, and defect structures of the as-prepared coating. It is found that

MA

MAO/N-16/Wax has low capacitance (CPEc and CPEdl) and high resistance (Rc and Rct), thereby demonstrating the composite coating effectively protect the substrate from corrosion. Different from

D

MAO/N-16, the MAO/N-16/Wax with hydrophobic layer is obviously pronounced because the

PT E

presence of wax film effectively prolongs the diffusion distance of corrosive particles, which lead to the permeability of the corrosive particles to membrane layer decreases. In this experiment,

CE

micro-porous MAO structures were employed as reservoir of inhibitor N-16 to effectively improve

AC

the corrosion resistance. Besides, for the anticorrosion coating, the mechanical property, especially the wear-resisting property is very important. So we conducted the anti-wear performance of composite coating consisted of MAO, N-16 inhibitor and wax film, as shown in Fig. S6. By comparing with bare AZ31 Mg alloy, it is evident that MAO/N-16/Wax film has favorable anti-wear property.

ACCEPTED MANUSCRIPT Table 2 Electrochemical impedance parameters for bare AZ31 Mg, MAO, MAO/N-16 and MAO/N-16/Wax film in 3.5 wt % NaCl solution at room temperature. Rs Ydl(Scm-2ndl

Rct

Qc

(Ω·cm2)

ndl

Yc(Scm-2

s-n×10-6)

Rc nc

(Ω·cm2)

s-n×10-6)

24.05

9.349

0.9829

4.31×103

MAO

16.71

0.726

0.7594

1.06×104

MAO/N-16

12.26

0.5583

0.7106

1.63×104

MAO/N-16/

15.36

0.1384

0.4775

4.93×104

NU

(H·cm2 )

-

-

-

0.7492

1.36×106

-

1.253

0.8029

1.22×106

-

0.000147

1

2.25×107

0.0102

1.937

MA

Wax

L

-

SC

bare Mg

PT

(Ω·cm2)

Qdl

RI

Samples

D

In order to test the corrosion durability of the samples, the salt spray tests were carried out for the

PT E

samples via different treatments after 24 h, 5 days and 15 days test duration, respectively, as shown in Fig. 10. It is observed that the bare AZ31 Mg has been attacked severely by corrosive species after

CE

24 h, which lead to the formation of corrosion product of Mg(OH)2. In comparison, the MAO coated

AC

sample only had slight boundary corrosion, and the N-16/MAO coated sample displayed a small number of pitting corrosion, while the MAO/N-16/Wax composite film coated sample nearly had no change. However, after 5 days, a lower amount of pits were observed on the MAO/N-16 sample than on the MAO sample, and the MAO/N-16/Wax film sample was still nearly intact. After 15 days of exposure, the enhancement of the barrier properties of the composite coatings is more pronounced when the N-16 inhibitor was incorporated into the porous MAO coating and the formation of hydrophobic wax film. Interestingly, the surface of bare AZ31 Mg has more fragments owing to the

ACCEPTED MANUSCRIPT invasion of most of corrosive ions. The salt spray test results are in consistent with the barrier

AC

CE

PT E

D

MA

NU

SC

RI

PT

properties studied by EIS and Tafel test.

Fig. 10. The salt spray photos for AZ31; MAO; MAO/N-16; MAO/N-16/wax film.

The schematic representation of long-term anticorrosion mechanism of the composite coating is shown in Fig. 11, which are mainly based on the passivation of metal surface or formation an isolative physical barrier by sealants or corrosion inhibitor. In this protecting strategy, the

ACCEPTED MANUSCRIPT as-prepared composite coating consisted of porous MAO inorganic ceramic layer, alkynol inhibitor with long alkyl chains and hydrophobic wax film, which would highly improve the corrosion resistance of substrate ascribing to the synergistic effect of the composite coating. When corrosive ions attack the integrated composite coating without damage, the hydrophobic top sealing wax

PT

coating would firstly provide corrosion protection for the substrate materials by the isolation effect

RI

firstly [36]. Herein, according to the Cassie model [37, 38], it would reduce the opportunity of the

SC

corrosion ion and water molecule approaching the substrate of AZ31 Mg owing to the water repellent characteristic of the hydrophobic wax film. Secondly, the hard inorganic ceramic layer of MAO

NU

membrane also plays an important role in the protecting of AZ31 Mg alloy from corrosion. Besides,

MA

the incorporated N-16 alkynol inhibitor in the pores of MAO membrane could form a special passivation layer on the surface of the protected metal due to its own characteristics of inhibition

D

effect, as shown in Fig. 11a. Nevertheless, when the composite coating was damaged after suffering

PT E

from an attack of external force, the exposed inhibitor molecules with long alkyl chains would played remarkable inhibition function, on the one hand the N-16 inhibitors with long hydrocarbon

CE

tails also prevented the penetration of aggressive ions and water, on the other hand, the micro- and

AC

nanopores in the MAO membrane could be used as the containers to load more corrosion inhibitor of N-16, which can penetrate and spread to form a passivation or adsorption layer on the surface of AZ31 Mg alloy substrate to inhibit the occurrence of corrosion [35], as shown in Fig. 11 b. So it can be concluded that the anticorrosion ability was significantly improved by the synergistic effect of MAO/N-16/wax composite coating.

MA

NU

SC

RI

PT

ACCEPTED MANUSCRIPT

Fig. 11. The schematic diagrams of corrosion protection of MAO/N-16/Wax composite coating in 3.5

D

wt % NaCl solution: (a) composite coating was undamaged after suffering from corrosion attack; (b)

CE

4. Conclusions

PT E

composite coating was damaged after suffering from corrosion attack.

AC

In this work, the organic/inorganic composite coatings were successfully fabricated on the surface of AZ31 Mg alloy by the combination of a micro-arc oxidation ceramic layer, alkynol type corrosion inhibitor N-16 and hydrophobic wax layer. The EIS results indicated the prepared coating exhibited superior performance in preventing corrosive species such as ions and water in contact with the underlying metallic substrate (Magnesium alloy) in 3.5 wt % NaCl aqueous solution with high inhibition efficiency and long- term protectiveness. Meanwhile, the composite coating is more salt spray resistant, in which could be attributed to the synergistic effect of MAO membrane

ACCEPTED MANUSCRIPT embedded with inhibitor N-16 and the hydrophobic wax film. Therefore, it is anticipated that this composite anticorrosion coating with superior anticorrosion performance would have a promising application prospect in light metal industry.

PT

Acknowledgments

RI

This work was supported by National Natural Science Foundation of China (No.51722510,

SC

21573259), Key research project of Frontier Science of the Chinese Academy of Sciences (QYZDY-SSW-JSC013), the outstanding youth fund of Gansu Province (1606RJDA31), Qingdao

NU

science and technology plan application foundation research project (17-1-1-70-JCH) and the

AC

CE

PT E

D

MA

“Hundred Talents Program” of Chinese Academy of Sciences (D. Wang).

ACCEPTED MANUSCRIPT References

[1] L. Shi, J. Hu, X. Lin, L. Fang, F. Wu, J. Xie, F. Meng, A robust superhydrophobic PPS-PTFE/SiO2 composite coating on AZ31 Mg alloy with excellent wear and corrosion resistance

PT

properties, Journal of Alloys and Compounds, 721 (2017) 157-163.

RI

[2] S.-H. Chang, L. Niu, Y. Su, W. Wang, X. Tong, G. Li, Effect of the pretreatment of silicone

Materials Chemistry and Physics, 171 (2016) 312-317.

SC

penetrant on the performance of the chromium-free chemfilm coated on AZ91D magnesium alloys,

NU

[3] S. Chen, J. Zhang, Y. Chen, S. Zhao, M. Chen, X. Li, M.F. Maitz, J. Wang, N. Huang, Application

MA

of Phenol/Amine Copolymerized Film Modified Magnesium Alloys: Anticorrosion And Surface Biofunctionalization, ACS Applied Materials & Interfaces, 7 (2015) 24510-24522.

D

[4] Q. Zong, L. Wang, W. Sun, G. Liu, Active deposition of bis (8-hydroxyquinoline) magnesium

PT E

coating for enhanced corrosion resistance of AZ91D alloy, Corrosion Science 89 (2014) 127-136. [5] P. Liu, X. Pan, W. Yang, K. Cai, Y. Chen, Improved anticorrosion of magnesium alloy via

AC

(2012) 118-121.

CE

layer-by-layer self-assembly technique combined with micro-arc oxidation, Materials Letters 75

[6] X.-j. Cui, X.-z. Lin, C.-h. Liu, R.-s. Yang, X.-w. Zheng, M. Gong, Fabrication and corrosion resistance of a hydrophobic micro-arc oxidation coating on AZ31 Mg alloy, Corrosion Science 90 (2015) 402-412. [7] L. Chang, L. Tian, W. Liu, X. Duan, Formation of dicalcium phosphate dihydrate on magnesium alloy by micro-arc oxidation coupled with hydrothermal treatment, Corrosion Science 72 (2013) 118-124.

ACCEPTED MANUSCRIPT [8] L. Wang, Q. Zong, W. Sun, Z. Yang, G. Liu, Chemical modification of hydrotalcite coating for enhanced corrosion resistance, Corrosion Science 93 (2015) 256-266. [9] Y. Li, H. Li, Q. Xiong, X. Wu, J. Zhou, J. Wu, X. Wu, W. Qin, Multipurpose surface functionalization on AZ31 magnesium alloys by atomic layer deposition: tailoring the corrosion

PT

resistance and electrical performance, Nanoscale 9 (2017) 8591-8599.

RI

[10] M.L. Zheludkevich, J. Tedim, M.G.S. Ferreira, “Smart” coatings for active corrosion protection

SC

based on multi-functional micro and nanocontainers, Electrochimica. Acta 82 (2012) 314-323. [11] N. Pirhady Tavandashti, M. Ghorbani, A. Shojaei, J.M.C. Mol, H. Terryn, K. Baert, Y.

NU

Gonzalez-Garcia, Inhibitor-loaded conducting polymer capsules for active corrosion protection of

MA

coating defects, Corrosion Science 112 (2016) 138-149.

[12] X.-J. Cui, C.-H. Liu, R.-S. Yang, M.-T. Li, X.-Z. Lin, Self-sealing micro-arc oxidation coating

D

on AZ91D Mg alloy and its formation mechanism, Surface and Coatings Technology 269 (2015)

PT E

228-237.

[13] K. Dong, Y. Song, D. Shan, E.-H. Han, Corrosion behavior of a self-sealing pore micro-arc

CE

oxidation film on AM60 magnesium alloy, Corrosion Science 100 (2015) 275-283.

AC

[14] Y.H. Xia, B.P. Zhang, C.X. Lu, L. Geng, Improving the corrosion resistance of Mg-4.0Zn-0.2Ca alloy by micro-arc oxidation, Materials science & engineering. C 33 (2013) 5044-5050. [15] F. Liu, D. Shan, Y. Song, E.-H. Han, Effect of additives on the properties of plasma electrolytic oxidation coatings formed on AM50 magnesium alloy in electrolytes containing K2ZrF6, Surface and Coatings Technology 206 (2011) 455-463. [16] F. Liu, D. Shan, Y. Song, E.-H. Han, W. Ke, Corrosion behavior of the composite ceramic coating containing zirconium oxides on AM30 magnesium alloy by plasma electrolytic oxidation,

ACCEPTED MANUSCRIPT Corrosion Science 53 (2011) 3845-3852. [17] X. Lu, C. Blawert, Y. Huang, H. Ovri, M.L. Zheludkevich, K.U. Kainer, Plasma electrolytic oxidation coatings on Mg alloy with addition of SiO2 particles, Electrochimica Acta 187 (2016) 20-33.

PT

[18] W.-h. Li, Q. He, S.-t. Zhang, C.-l. Pei, B.-r. Hou, Some new triazole derivatives as inhibitors for

RI

mild steel corrosion in acidic medium, Journal of Applied Electrochemistry, 38 (2008) 289-295.

SC

[19] M. Bouklah, A. Ouassini, B. Hammouti, A.E. Idrissi, Corrosion inhibition of steel in 0.5M H2SO4 by [(2-pyridin-4-ylethyl)thio]acetic acid, Applied Surface Science, 250 (2005) 50-56. F.

Bentiss,

M.

Traisnel,

M.

NU

[20]

Lagrenee,

Influence

of

MA

2,5-bis(4-dimethylaminophenyl)-1,3,4-thiadiazole on corrosion inhibition of mild steel in acidic media, Journal of Applied Electrochemistry, 31 (2001) 41-48.

D

[21] B. Hammouti, A. Aouniti, M. Taleb, M. Brighli, S. Kertit, L-Methionine Methyl Ester

PT E

Hydrochloride as a Corrosion Inhibitor of Iron in Acid Chloride Solution, Corrosion 51 (1995) 411-416.

CE

[22] X. Zhang, G. Wu, X. Peng, L. Li, H. Feng, B. Gao, K. Huo, P.K. Chu, Mitigation of Corrosion

AC

on Magnesium Alloy by Predesigned Surface Corrosion, Scientific Reports 5 (2015) 17399. [23] F. Peng, H. Li, D. Wang, P. Tian, Y. Tian, G. Yuan, D. Xu, X. Liu, Enhanced Corrosion Resistance and Biocompatibility of Magnesium Alloy by Mg-Al-Layered Double Hydroxide, ACS Applied Materials & Interfaces, 8 (2016) 35033-35044. [24] Z.H. Xie, D. Li, Z. Skeete, A. Sharma, C.J. Zhong, Nanocontainer-Enhanced Self-Healing for Corrosion-Resistant Ni Coating on Mg Alloy, ACS Applied Materials & Interfaces, 9 (2017) 36247-36260.

ACCEPTED MANUSCRIPT [25] C. Ding, J. Xu, L. Tong, G. Gong, W. Jiang, J. Fu, Design and Fabrication of a Novel Stimulus-Feedback Anticorrosion Coating Featured by Rapid Self-Healing Functionality for the Protection of Magnesium Alloy, ACS Applied Materials & Interfaces, 9 (2017) 21034-21047. [26] D.G. Shchukin, H. Mohwald, Smart nanocontainers as depot media for feedback active coatings,

PT

Chem Commun (Camb) 47 (2011) 8730-8739.

RI

[27] K.A. Zahidah, S. Kakooei, M.C. Ismail, P. Bothi Raja, Halloysite nanotubes as nanocontainer

SC

for smart coating application: A review, Progress in Organic Coatings, 111 (2017) 175-185. [28] S.J. Lee, D.L.H. Toan, Effects of copper additive on micro-arc oxidation coating of LZ91

NU

magnesium-lithium alloy, Surface and Coatings Technology, 307 (2016) 781-789.

MA

[29] S.S. Abd El-Rehim, M.A.M. Ibrahim, K.F. Khaled, 4-Aminoantipyrine as an inhibitor of mild steel corrosion in HCl solution, Journal of Applied Electrochemistry, 29 (1999) 593-599.

D

[30] D. Yu, J. Tian, J. Dai, X. Wang, Corrosion resistance of three-layer superhydrophobic composite

PT E

coating on carbon steel in seawater, Electrochimica Acta 97 (2013) 409-419. [31] G.X. Shen, Y.C. Chen, L. Lin, C.J. Lin, D. Scantlebury, Study on a hydrophobic nano-TiO2

AC

5083-5089.

CE

coating and its properties for corrosion protection of metals, Electrochimica Acta 50 (2005)

[32] L. Guo, F. Zhang, L. Song, R.-C. Zeng, S.-Q. Li, E.-H. Han, Corrosion resistance of ceria/polymethyltrimethoxysilane modified magnesium hydroxide coating on AZ31 magnesium alloy, Surface and Coatings Technology, 328 (2017) 121-133. [33] Y. Liu, H. Cao, S. Chen, D. Wang, Ag Nanoparticle-Loaded Hierarchical Superamphiphobic Surface on an Al Substrate with Enhanced Anticorrosion and Antibacterial Properties, The Journal of Physical Chemistry C 119 (2015) 25449-25456.

ACCEPTED MANUSCRIPT [34] S. Cui, X. Yin, Q. Yu, Y. Liu, D. Wang, F. Zhou, Polypyrrole nanowire/TiO2 nanotube nanocomposites as photoanodes for photocathodic protection of Ti substrate and 304 stainless steel under visible light, Corrosion Science, 98 (2015) 471-477. [35] H. Wei, Y. Wang, J. Guo, N.Z. Shen, D. Jiang, X. Zhang, X. Yan, J. Zhu, Q. Wang, L. Shao, H.

PT

Lin, S. Wei, Z. Guo, Advanced micro/nanocapsules for self-healing smart anticorrosion coatings,

RI

Journal of Materials Chemistry A, 3 (2015) 469-480.

SC

[36] H. Zhang, J. Yang, B. Chen, C. Liu, M. Zhang, C. Li, Fabrication of superhydrophobic textured steel surface for anti-corrosion and tribological properties, Applied Surface Science 359 (2015)

NU

905-910.

MA

[37] N. A. Patankar, On the Modeling of Hydrophobic Contact Angles on Rough Surfaces, Langmuir 19 (2003) 1249-1253.

AC

CE

PT E

D

[38] A. Lafuma, D. Quere, Superhydrophobic states, Nature Materials 2 (2003) 457-460.

ACCEPTED MANUSCRIPT

Highlights:  In-situ growth of porous oxide coating as an inhibitor micro/ nano-containers.  Synthesis of a new type of effective corrosion inhibitor with long alkyl chain.

PT

 Fabricating a new integrated anti-corrosion coating.

RI

 Lower corrosion current density and high protection efficiency were obtained by the

AC

CE

PT E

D

MA

NU

SC

synergistic effect of hydrophobic film and porous oxide layer with alkynol inhibitor.