Etching and heating treatment combined approach for superhydrophobic surface on brass substrates and the consequent corrosion resistance

Accepted Manuscript Title: Etching and heating treatment combined approach for superhydrophobic surface on brass substrates and the consequent corrosion resistance Author: Han Jie Qunjie Xu Liu Wei YuLin Min PII: DOI: Reference:

S0010-938X(15)30112-8 http://dx.doi.org/doi:10.1016/j.corsci.2015.10.013 CS 6509

To appear in: Received date: Accepted date:

18-8-2015 12-10-2015

Please cite this article as: Han Jie, Qunjie Xu, Liu Wei, YuLin Min, Etching and heating treatment combined approach for superhydrophobic surface on brass substrates and the consequent corrosion resistance, Corrosion Science http://dx.doi.org/10.1016/j.corsci.2015.10.013 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.

Etching and heating treatment combined approach for superhydrophobic surface on brass substrates and the consequent corrosion resistance

Han Jie, Qunjie Xu*, Liu Wei, YuLin Min

(Shanghai Key Laboratory of Materials Protection and Advanced Materials in Electric Power,

Shanghai Engineering Research Center of Energy-Saving in Heat Exchange Systems,

Shanghai University of Electric Power, Shanghai 200090, China)

* Corresponding author. Tel./fax: +86 021 35304734,

E-mail address: [email protected](Q J Xu)

17

HIGHLIGHTS 

The superhydrophobic surfaces on brass substrates were prepared by etching and heat treatment combination approach.



The achieved superhydrophobic surface has a contact angle as high as 153.6°.



The superhydrophobic surface exhibited excellent and persistent corrosion resistance in 3.5wt% NaCl aqueous solution.

18

Abstract Designing micro-nano structure is one of promising method to fabricate hydrophobic surfaces. In this paper, we demonstrated a combining etching and heat treatment approach to achieve a superhydrophobic surface on brass. Following by simple modification using stearic acid, the water contact angle on micro-nano structured brass was 153.6°, along which exhibited good and persistent corrosion resistance in 3.5 wt% NaCl aqueous solutions. This method could provide an effective route to fabricate superhydrophobic surface with corrosion resistance and self-cleaning properties for applications in the metal alloys materials.

Keywords: etching; heat treatment; superhydrophobic; corrosion resistance

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1. Introduction Superhydrophobic, which is the surface with a contact angle greater than 150°, has attracted great attention of researchers[1]. Due to its importance in fundamental research and industrial application [2], these superhydrophobic surfaces can potentially be used in corrosion inhibition [3-6], self-cleaning [7], anti-sticking of snow or ice, oil-water separation, microfluidic devices [8] and many others. Generally, the superhydrophobic surface can be obtained by coating a low energy hydrophobic surface onto a rough structure with special micro-nano structure [9]. It is well-known that the wettability of surface is influenced by surface roughness. Thus the special micro-nano structure would be the key to build superhydrophobic surface, as described by Wenzel [10] and Cassie-Baxter [11]. In recent years, researchers have attempted to design the micro-nano structures via various techniques [12-13], such as template methods [13], chemical etching [14], oxidation [15], electrodeposited sol-gel methods [16], and solution-immersion approaches [17]. However, the fabrication methods above somewhat are costly and complicated, therefore, to find a simple, low cost and appropriate method is still challenging towards the superhydrophobic surfaces. Brass is widely used in chemical and marine industry due to its good thermal and electrical conductivities. However, brass is an active alloy, which does not resist corrosion well [18]and seriously restricts its practical applications in industry. To overcome this drawback, researchers have applied many methods to protect brass[19]. Generally, the traditional corrosion inhibition methods applied to the brass could not achieve good performance in high corrosive seawater and furthermore cause environmental pollutions [20]. As a new corrosion inhibition technology, superhydrophobic has been applied for corrosion inhibition of many metals. Liu et al [21] used chemical etching method to construct superhydrophobic surface, which greatly improved the corrosion resistance of copper in the seawater. Zhao et al[22] also constructed superhydrophobic surface on magnesium alloy to improve its corrosion resistance. Although the superhydrophobic surfaces can get good corrosion 20

protection in a short time [23], the stability and durability of corrosion resistance still remained a challenging task, as documented in previous reports that some of superhydrophobic surfaces are easily fragile even by the finger contact [24]. In this work, we report a facile and novel method for the fabrication of superhydrophobic surfaces on brass. By combining chemical etching and thermal treatment method, the micro-nano structures on brass surface could be constructed. After this combined methods treatment, the brass surface was further modified with an ethanol solution of stearic acid [25]. Interestingly, it was found that the time of the stearic acid modification to form strong superhydrophobic film with flower structure was 10 s. Moreover, this kind of superhydrophobic surface had stable and persistent corrosion resistance in the seawater. In addition, the effect of etching, heating and modification time had been studied in the paper. On the basis of the experiment results,

the

formation

process

and

corrosion

resistance

mechanism

of

superhydrophobic surface are also discussed.

2. Experiment 2.1 Materials Brass alloy H85 plates (2mm thick; composition: 84wt% Cu, 15.5wt% Zn, 1wt%Ni) were purchased from Xiangwei Machinery Co., LTD., China. Ferric chloride, hydrochloric acid and stearic acid were purchased from Shanghai Chemical Reagent Co., LTD., China. All reagents were of analytical grade and used as received without further purification.

2.2 Specimen preparation Brass samples (30mm×10mm×2mm) and electrodes (10mm×10mm) were a braded with different grades of emery paper (1#, 3#, 6#), cleaned ultrasonically with alcohol and deionized water respectively, and dried in air. The cleaned brass and brass electrode were etched with 30mL aqueous solution of FeCl3 (10 wt%) contained100uL HCl (35-37 wt%) at room temperature for about 45 min, and then 21

these samples and electrodes were washed with alcohol and deionized water and dried again. Subsequently, these samples and electrodes were heated in air at 350oC for 25 min. Finally, the brass surfaces were modified in an ethanol solution of stearic acid at room temperature for a controlled period of time. The obtained samples were washed with alcohol and deionized water, and then dried for pending test.

2.3 Characterization The surface morphologies and chemical composition of the samples were investigate with a scanning electron microscopy (SEM, SU-1500, Hitachi, Japan), and an X-ray diffraction (XRD, Cu Kα radiation, Bruker, D8 Advance, and Germany). The contact angle (CA) was measured by K100-MK2 Almighty Tension Meter (KRUSS Germany), and the shape of water drops placed on sample surface was tested with a JC2000C1 CA system at ambient temperature. With an electrochemical workstation (CHI 660E, CH Instruments Inc.) equipped with a standard three-electrode system with a Pt electrode as the counter electrode, a calomel electrode (SCE) as the reference electrode and the sample as the working electrode, the electrochemical properties were conducted in 3.5wt% NaCl aqueous solution at room temperature. The potentiodynamic polarization curves were measured between -0.15 and 0.15 V (vs OCP) with the scanning rate of 1 mV/s. The electrochemical impedance spectroscopy (EIS) measurements were conducted in the frequency range from 100 kHz to 0.05Hz at open circuit potential with amplitude of perturbation voltage 5mV. All samples without specification about immersion time are characterized after only 1 day immersion time in 3.5wt% NaCl aqueous solution.

3. Result and Discussion 3.1 Wettability characterization The wettability of the prepared brass surfaces were characterized by measuring the static contact angle (CA). Fig.1 showed the static CAs of the brass etched with 22

different time of 15min, 30min, 45min, 60 min and 75min in the etching solution before they were heated for 45min and modified with 10% stearic acid for 10s. The CAs of the surfaces with different etching time were137.6°, 145.6°, 153.6°, 141.7° and 136.5°, respectively. Obviously, the values of CAs rose to a peak and then reduced, as the etching time increasing. And for 45 min etching one, the CA was at the peak of 153.6°, which indicated that 45min is the optimal etching time. The heating effects were also investigated using 45 min etching sample with different heat time of 5 min, 10 min, 15 min, 20 min, 25 min, at 350 oC. The corresponding CAs were 141.8°, 143.5°, 150.1°, 153.6°and 144.5° respectively. It could conclude that 20min was the most appropriate heating time to achieve the best superhydrophobicity. Taking into account of bothFig.1 and Fig.2, as listed at Tab 1 and Tab 2, it could be seen that the procedure composed of 45 min etching and then 20 min heating was the best condition to construct the superhydrophobic surface. In order to figure out the relationship between modified time and superhydrophobic surfaces, the CA of copper substrates treated with the same method at the same time points were measured. Fig.3 compared the different CAs for brass surfaces etched for 45min, heated for 20 min and modified with stearic acid for 10 s, 20 s, 30 s, 40 s, 50 s and 60 s. The fluctuations of CAs were very small, suggesting the CAs weren’t strongly dependent on the treated time of stearic acid. However, if either etching or heating processes was ignored, the surface properties would be greatly inhibited. As shown in Fig.4 and Fig. 5, without heating treatment, the CAs for the brass surfaces with stearic acid treatment for 10, 20, 30, 40, 50 and 60 s were 120.5°. 122.3°, 124.5°, 124.6°, 125.3°,124.5° respectively. While without etching, they would be 111.6°, 113.5°, 112.6°, 112.3°, 112.6° and 112.1°respectively. The results indicated that both etching and heating treatment played an important influence for superhydrophobicity. In summary, the superhydrophobicity could be realized by 45min etching, 20min 23

heating, and 10s steric acid treatment (Fig.6). In the meanwhile, it has little relationship between superhydrophobic surfaces and each treating times. Significantly, etching and heating processes play two important roles to achieve the superhydrophobic surface. The combined approach could lead to a good superhydrophobic surface with large contact angle on brass (Table 3) because surface structures are strongly dependent on the etching and heating factors, hence affecting superhydrophobic behaviors. The understanding should be based on the changes of morphology and micro structure in brass surface during the etching and heating processes.

3.2 Surface morphology and Composition The geometrical characteristics of the surfaces after etching, heating and modification were investigated by SEM images. As a controlled group, Fig. 7a showed the morphology on the surface of brass samples without any treatment, and the morphology of surface was very smooth with the CA of 77°. After being etched for 45 min, heated for 20 min and modified for 10 s, there were many holes with several micrometers depth on the surface with CA nearly 0°. The whole surface had no regular texture (Fig.7b). It indicated Zn and Cu in brass (Cu-Zn alloy) surface were dissolved from brass surface in the FeCl3 solution [26-28]. During this process, the dissolution of Zn must be a prior reaction since Zn in brass is known as an active metal relative to Cu. This was named as “priority dissolution mechanism” [29]. Therefore, brass etching process by FeCl3 solution could be expressed by the combined equations of (1) and (2) [30-31].

2FeCl3 + Zn = 2FeCl2 + ZnCl2

(1)

2FeCl3 + Cu = 2FeCl2 + CuCl2

(2)

After being heated, much rougher structures at both micro and nano-scale were achieved on the substrate. Vertically oriented lamellae appeared to be the etched structure (Fig.8a). Under higher magnification(Fig.8b), The details were quite clear under higher magnification, where lamellae or sheets-similar structures have nearly 24

uniform size with clear nano-scale thickness in the vertical direction and rough microscale in the other two directions. The Cu and Zn oxides were believed to be main contributor to the micro-nano lamellas or sheets, because the Cu and Zn ion diffusion through the grain boundaries could promote the growth of both Cu oxides and Zn oxides layers due to the presence of compressive stress in the copper film. The results in this study also supported the compressive stress relaxation mechanism. As the oxygen atoms diffused into the brass substrate, tensile stress and compressive stress were generated in the outer convex surface and inner concave surface, respectively. Hence, Cu and Zn oxides grew in the inner surface due to the relaxation of compressive stress [32]. When the surfaces were treated in an ethanol solution of stearic acid, radial structure with diameter of 15μm could be indistinctly observed on brass surface (Fig.9a). In the enlarged picture (Fig.9b), radial structure grew in flower-like framework distributed over the brass substrate with the CA of 153.6°. The flower-like structure has nano-scale thickness and micro-scale width. It could be ascribed to the formation of copper (zinc) carboxylate [21, 33] via rapid reaction with stearic acid on the surface of zinc and copper oxides composed surface. Since the reaction belongs to the Metathesis reaction [34], which could be performed sharply, thus, 10s was enough to form micro-nano flower-like structure. XRD analyses were carried out to study the composition and crystal structure on the brass substrate. Fig.10 showed the XRD patterns of the bare, etched, etched-heat treatment brass substrates. The sharp and intensive peak located at 2θ=43.47° is assigned to the (110) diffraction lattice plane of brass. The weak ones located at 2θ=50.47° and 79.62° are attributed to (422) and (211) facets of brass, respectively. The results confirm that the brass substrates before and after being etched are both pure brass without the presence of chloride. Interesting, the peak intensities of (110) and (422) facets for the bare brass are stronger than the etched brass, which means that the brass basal surface is grown along the oriented (110) and (422). The (211) facet appeared after etching strongly indicates that a part of (221) facet exposes gradually on the brass surface during the etching process, 25

implying there is a selective etching of (211) facet. In the XRD patterns of etched-heat treatment brass shows the (110) and (101) facets of Cu2O and ZnO. It indicates that micro-nano lamellae or sheets structures are the Cu2O and ZnO crystals, which also demonstrate the SEM changes of brass substrate. In the XRD analysis, it can be concluded that the micro-nano structure on the brass substrate is composed of Cu2O and ZnO crystals, which is consist with SEM characterization.

3.3 Corrosion resistance The corrosion inhibition of the superhydrophobic surface in 3.5wt% NaCl solution

was

electrochemical

investigated impedance

from

potentiodynamic

spectroscopy (EIS).

polarization

curves

and

Fig.11showedpotentiodynamic

polarization curves of bare brass, superhydrophobic brass, etched and heat treatment brass before modified. The treated substrates were performed by immersing in 3.5wt% NaCl aqueous solution for 1day. Fig.12 shows potentiodynamic polarization curves of superhydrophobic surface formed on the brass after immersion in 3.5wt% NaCl aqueous with the different time of5day, 10day, 15day, and 20day.Table 4shows the polarization parameters (corrosion potential, Ecorr; anodic Tafel slope, βa; corrosion current density, icorr) obtained from simulation of these polarization curves. In a typical polarization curve, a lower corrosion current density (icorr) or a higher corrosion potential (Ecorr) corresponds to a lower corrosion rate and a better corrosion resistance [35-37]. From Fig. 11, Ecorr positively increase from -0.278V vs. SCE for the bare brass to -0.214V vs. SCE for the superhydrophobic one. The positive shift of the Ecorr could be regarded to be an improvement in protective properties of brass [38-39]. The Ecorr of etched and heat treatment brass were also increased in a certain range. But they were still lower than superhydrophobic one. The icorr of the superhydrophobic brass substrate (5.40×10-9Acm-2) decreases by nearly 3 orders of magnitude as compared with the untreated one (9.55×10-7Acm-2), compared with the icorr of etched one (4.18×10-6Acm-2) and heat treatment one (6.76×10-7 Acm-2). The icorr of superhydrophobic brass is much lower than either etched or heat treatment one. 26

And the icorr of etched one is even higher than brass one. It is believed that the air trapped in micro and nanoscale surface cavities behave as a dielectric for a pure parallel plate capacitor [15, 40]. The air dielectric can inhibit the electron transfer between the electrolyte and the brass substrate and greatly improve the corrosion resistance of the brass substrate [5, 41]. In Fig.12 the icorr of the superhydrophobic surface formed on the brass after immersion in the 3.5wt% NaCl aqueous solution for 5, 10, 15 and 20 day were estimated to be 3.13×10-8 Acm-2, 4.68×10-8Acm-2, 5.37×10-8Acm-2, 7.59×10-8 Acm-2, respectively. The icorr of the superhydrophobic samples rise as the immersion time increased. But all superhydrophobic sample values were much lower than the untreated brass (the corrosion current density values is 9.55×10-7 Acm-2). It indicated that the superhydrophobic surface is effective for improving the corrosion resistance of brass. As the immersion time increased, the superhydrophobic sample values decreased slightly, which were caused by permeation of Cl- through cracks in the film. However, after immersion in 3.5wt% NaCl aqueous solution for 20day, the corrosion current density is still much lower than the untreated brass, which could demonstrate that the superhydrophobic surface is very stable and strong. The corrosion resistance of superhydrophobic surface was also examined by EIS studies. Because plots at low frequency are messy and illogical for poor conductivity, EIS plots within a frequency (10-1 Hz to 105 Hz). Fig.13presents EIS results of bare brass, superhydrophobic, etched and heat treatment surface formed on brass. The treated substrates have been immersed in NaCl aqueous solution for one day. Fig. 13a shows the Nyquist plots of etched, heat treatment and superhydrophobic simples are composed of a capacitive loop in high frequency and Warburg impedance in low frequency range. The presence of Warburg impedance reflect anodic diffusion of CuCl2 from brass electrode surface to bulk solution, and cathodic diffusion of

dissolved oxygen from bulk solution to brass electrode surface[3].It is clear that diameter of capacitive arc of brass covered with superhydrophobic layer is much higher than that of bare brass. As shown in Fig. 13b and Fig. 13c, for the treated brass, 27

there are two peaks at approximately 103 and 10 Hz exist within testing frequency range in Bode–phase angle versus Log (f/Z) plots. These peaks correspond to formation of corrosion layers at higher frequency and corroding interface at lower frequency on the treated substrates surfaces respectively. Fig. 14 presents Nyquist plots of bare brass and superhydrophobic brass immersed in 3.5wt% NaCl aqueous solutions for 5, 10, 15, 20 day. The Nyquist plots are also composed of a capacitive loop in high frequency and Warburg impedance in low frequency range. The diameters of capacitive arc of the brasses with superhydrophobic surface are followed gradually smaller. For the bare brass, the EIS result can be analyzed with the circuit shown in Fig.15a, where Rs is solution resistance, Rtis charge-transfer resistance and CPEdl is constant phase elements modeling the capacitance of the double. The EIS results of treated and immersed substrates can be analyzed with circuit in Fig. 15b, in which Rs donates solution resistance, Rt donates charge-transfer resistance, Rf donates resistance of corrosion layer, and CPEdl and CPEf are constant phase elements modeling the capacitance of the double and corrosion layers, respectively. The impedance of CPE is given by equation (1):

ZCPE 

1 Y 0( J  ) n

(3)

Where Y 0 is the modulus,  is angular frequency, and n is the phase [6]. Table 4 presents electrochemical parameters. The listed inhibition efficiency (η) was calculated with the following formula [42]:

 (%)  (1-

Rt0 ) 100 Rt

(4)

Where Rt0 is the charge transfer resistance of bare brass, Rt is the charge transfer resistance of treated and superhydrophobic immersed brass substrates. From the electrochemical parameters of brass in 3.5 wt% NaCl solution (Table 5), it can be found that Rf of superhydrophobic surfaceis37.92 kΩcm2, and its inhibition efficiency is 98.7%. The inhibition efficiency of etched substrate is 11.8% and heat 28

treatment one is 86.4%. It indicates the corrosion resistance of superhydrophobic one is better than etched and heat treatment ones. When the superhydrophobic surface was immersed for 20day, Rf decreased to 5.319 kΩ cm2, and its inhibition efficiency also decreased to 81.4%. It was the result of Cl- attacking the superhydrophobic surface. However, Rt at this time is still higher than bare brass, and the superhydrophobic surface can also inhibit corrosion process to some extent.

4. Conclusions Superhydrophobic film was fabricated on brass via chemical etching and thermal oxidation surface combined methods. The brass substrate etched for 45 min, then heated in air at 350 oC for 25 min and modified with an ethanol solution of stearic acid, which formed the micro-nano flower-like structure superhydrophobic film with a contact angle of 153.6°. The superhydrophobic film exhibited an improved performance of corrosion resistance when immersed in 3.5 wt% NaCl aqueous solution, as demonstrated by measurement result from potentiodynamic polarization curves and EIS characterizations. In addition, even if the superhydrophobic film immersed in 3.5 wt% NaCl aqueous for 20 day, it still showed good corrosion inhibitive properties, compared to the bare brass. It was confirmed that superhydrophobic film improved the corrosion resistance of brass. In this paper, etching and heating treatment combined approach is relatively facile, which provides a new idea to fabricate functional superhydrophobic film with corrosion inhibitive properties on metals.

Acknowledgments This work was financially supported by National Science Foundation of China (No.21473039), Innovation Program of Shanghai Municipal Education Commission (No. 14ZZ152) and Science and Technology Commission of Shanghai Municipality. (No: 14DZ2261000).

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Contact Angle(degree)

155

150

145

140

135 20

40

60

80

Etching time(min) Fig.1.CA of brass surface with different etching time (15min, 30min, 45min, 60min

and 75min) in etching solution at room temperature then heat for 20min and modified with stearic acid for 10s.

Contact Angle(degree)

155

150

145

140 5

10

15

20

25

Heat time(min) Fig.2.CA of brass surface treated in the same method with different heat treatment time (5min, 10min, 15min, 20min and 25min) at 350℃ in the air.

34

Contact Angle(degree)

155

150

145 10

20

30

40

50

60

Modifiacation time(s) Fig.3.CA of brass surface etched for 45min, heat for 20min at 350℃ in the air with different modification time (10s, 20s, 30s, 40s, 50s, 60s) in the stearic acid.

Contact Angle(degree)

130

125

120 10

20

30

40

50

60

Modifacation time(s) Fig.4.CA of brass surface only etched for 45min then modified with stearic acid with different time (10s, 20s, 30s, 40s, 50s, 60s).

35

Contact Angle(degree)

120

115

110 10

20

30

40

50

60

Modifacation time(s) Fig.5.CA of brass surface only heat for 20min at 350℃then modified with stearic acid with different time (10s, 20s, 30s, 40s, 50s, 60s).

Fig.6.Photograph of the water droplets (a) and (b) on the superhydrophobic surfaces

36

Fig.7.SEM images of bare brass (a) and etched brass (b).

Fig.8.SEM images of brass (a) and (b) after thermal treatment.

37

Fig.9.SEM images of brass with (a) and (b) superhydropobic surface.

(110)

Indensity(a.u)

(422)

Bare (110) (422)

Etched

(211)

(110) (422)

(110)Cu2O (101)ZnO

20

40

Etched-heat

(211)

60

80

2 theta/degree Fig.10.XRD patterns of bare brass surface, etched brass surface and etched-heat treatment brass surface.

38

Fig.11.Potentiodynamic polarization curves of bare brass, superhydrophobic brass, etched and heat treatment brass in 3.5 wt% NaCl solution.

Fig. 12.Potentiodynamic polarization curves of bare brass,superhydrophobic brass

39

Fig. 13.EIS results of bare brass, superhydrophobic, etched and heat treatment surface formed on brass in 3.5wt% NaCl aqueous solution. (a) Nyquistplots, (b) Bode Log|Z| versus Log(f/Hz)plots, (c) Bode-phase angle versus Log(f/Hz) plots.

40

Fig. 14.Nyquist plots of bare brass,superhydrophobic brassand superhydrophobic brass after immersion in 3.5wt% NaCl aqueoussolutionwith different time of 5 day, 10 day, 15 day and 20 day respectively.

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Fig. 15.Equivalent circults for (a) Bare brass, (b) Treated brass,superhydrophobicbrassand superhydrophobic brass after immersion in 3.5wt% NaCl aqueous solution with different time of 5 day, 10 day, 15 day and 20 day respectively.

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Table 1 Contact angles of brass substrates with the different etched time. Etched time 15

30

45

60

75

137.8

145.6

153.6

147.1

136.5

(minute) Contact angle （degree）

Table 2 Contact angles of brass substrates with the different heat time. Heat time 5

10

15

20

25

141.8

143.5

150.1

153.6

144.5

(minute) Contact angle (degree)

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Table 3 Contact angles of brass substrates with different treat methods at the same modified time (10 s, 20 s, 30 s, 40 s, 50 s, 60 s). Modified time(second)

10

20

30

40

50

60

CA (degree) of combined method

153.6

152.1

150.6

151.5

153.1

144.5

CA (degree) of etched method

122.5

122.3

124.6

124.8

125.3

124.5

CA (degree) of heat method

111.8

113.5

112.6

112.3

112.6

112.1

andsuperhydrophobic brass after immersion in 3.5wt% NaCl aqueous solutionwith different time of 5 day, 10 day, 15 day and 20day respectively.

Table 4 Polarization parameters of brass substrates in 3.5 wt% NaCl solution. Samples Ecorr(mV vs. SCE) βa(mV dec-1 ) icorr (Acm-2) Bare -278 53.6 9.55×10-7 Etched -226 61.7 4.18×10-6 Heat -279 67.9 6.76×10-7 Superhydrophobic -214 76.2 5.40×10-9 Immersed 5 day -225 91.2 3.13×10-8 Immersed 10 day -221 77.1 4.68×10-8 Immersed 15 day -249 71.2 5.37×10-8 Immersed 20 day -256 78.5 7.59×10-8

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Table 5 Electrochemical parameters obtained from simulation of EIS results of brass substrates

Samples

Rs

Cf

Rf

Cdl

Rt

η(﹪)

(Ωcm ) (μF cm ) (kΩcm ) (μF cm ) (kΩcm ) 2

-2

2

-2

2

Bare

9.061

20.78

\

\

6.817

\

Etched

8.892

38.15

12.19

58.48

7.73

11.8

Heat

9.591

5.86

17.48

1.51

50.4

86.4

Superhydrophobic

9.161

0.0158

37.91

0.153

533.9

98.7

Immersed 5 day

9.189

2.596

26.16

0.124

221.6

96.9

Immersed 10 day

9.201

42.98

23.45

0.097

180.41

96.2

Immersed 15 day

9.263

4.255

20.26

0.079

110.17

93.8

Immersed 20 day

9.875

0.032

18.32

0.0106

36.54

81.4

45