Durable Hydrophobic Coating Based on Cerium phosphate nanorod

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Durable Hydrophobic Coating Based on Cerium phosphate nanorod-Siliconized Epoxy for Corrosion Protection Nithyaa Jayakumar, Krishnapriya Karattu Veedu, and Nishanth Karimbintherikkal Gopalan ACS Appl. Nano Mater., Just Accepted Manuscript • DOI: 10.1021/acsanm.9b00172 • Publication Date (Web): 03 May 2019 Downloaded from http://pubs.acs.org on May 6, 2019

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ACS Applied Nano Materials

Durable Hydrophobic Coating Based on Cerium Phosphate NanorodSiliconized Epoxy for Corrosion Protection Nithyaa Jayakumar †, Krishnapriya Karattu Veedu †§ and Nishanth Karimbintherikkal Gopalan †, §, * † Materials

Science and Technology Division, CSIR-National Institute for Interdisciplinary

Science and Technology (NIIST), Thiruvananthapuram 695019, India. §

Academy of Scientific and Innovative Research (AcSIR), Ghaziabad- 201002, India. * Corresponding author. Tel.: +91471 2515508; Fax: +91471 2491712 E-mail address: [email protected]

Abstract Here, we present a new eco-friendly cerium phosphate (CP) nanorod system can be utilized as an anti-corrosive pigment to protect steel from corrosive environment. Among the various formulations studied, CP nanorod (10wt%) loaded epoxy exhibited the best corrosion resistance efficiency. The anti-corrosion property of the coating was further improved by the introduction of hydrophobicity through siliconization process. This enhanced the average surface roughness (Ra = 0.4 to 11 nm) and consequently generated hydrophobic contact angle of 121°. A three-fold increase of the corrosion resistance of epoxy is attributed to the synergistic effect of the hydrophobic surface and nanorod morphology. The durability of the coating was also studied by an electrochemical method for the duration of two months. The enhanced corrosion inhibition efficiency and durability of the developed coating can be of significant importance for industrial applications.

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Keywords: Corrosion, coating, cerium phosphate, siliconized epoxy, hydrophobicity, EIS.

Introduction Epoxy-based coatings have been used over the past several decades for the protection of metals from the corrosive media owing to their chemical stability and processability. However, the usage was limited due to the porous nature of the coating, hydrophilicity and less impact strength.1 Meanwhile, filler loaded epoxy composite coats yielded an advantage by filling pores.2 Especially, nano-fillers with unique morphology provide homogeneous dispersion thereby restricting the pathways of corrosive species attack.3–6 Such nano pigments usually interconnect the monomer and increase the density of the cured coating. The usage of chromate-based pigments has been restricted due to the environmental issues associated with them. Recently, zinc phosphate pigments gathered more attention owing to its ability to protect metal surface from the corrosive environment by the formation of an effective protective layer of secondary phosphate ions.7–10 However, the zinc phosphate pigments are also restricted due to their toxic nature to aquatic organisms.11,12 The cerium-based anti-corrosive coatings are established as some of the most suitable alternatives of the existing toxic pigments owing to its eco-friendly nature.13–16 The microstructure and morphology of cerium phosphate (CP) can be varied by employing suitable processing techniques.17–21 In the present work, we have synthesized CP nanorods by a wet chemical reaction method and incorporated with epoxy for fabricating metal protective coating for a saline medium. We observed that, 2 ACS Paragon Plus Environment

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the CP-epoxy interaction not only increased the crosslinking density but also decreased the porosity of the coating very effectively. Further, realizing the scientific and technological importance of siliconized epoxy, the present research is directed to its utilization as an additional hydrophobic barrier to increase the durability of the coating.15–18 Efficient epoxy/polydimethylsiloxane (PDMS) hybrid polymer systems are known for various engineering applications.1,22–25 Specifically, the epoxy/PDMS polymer network for corrosion resistance with zinc powder and zinc oxide nanorods are described previously.26,27 Ivanou et al. evaluated the sealing of anodic layers with hybrid epoxy-silane coating.28 Combination of PDMS and octadecyl amine (ODA) for super-hydrophobicity has been reported by Xue et al.29 In the present work, the three-dimensional interlock structure of interpenetrating epoxy/PDMS polymer network along with ODA was utilized to enhance the barrier performance of CP nanorods. CP/siliconized epoxy coating exhibited remarkable improvement in hydrophobicity and corrosion resistance which is suitable to prevent corrosion of steel in saline media.

Experimental section Materials Cerium

nitrate

hexahydrate,

ammonium

dihydrogen

phosphate,

polydimethylsiloxane, SYLGARD 184, γ– aminopropyl triethoxy silane (APS) and octadecyl amine purchased from Sigma-Aldrich, tertiary butyl alcohol, sodium chloride from Merck, epoxy and polyamide hardener from Aditya, India, steel by local purchase.



Pigment preparation CP pigment was prepared via wet chemical method using cerium nitrate hexahydrate (0.5 M) and ammonium dihydrogen phosphate (0.5 M) as precursors (shown in Scheme-1). The precursor solution was mixed dropwise under stirring, and the pH of the reaction mixture was adjusted to 10 by adding ammonium hydroxide. A white precipitate was obtained, which had been kept in room temperature for 24 hrs. Then the precipitate was centrifuged and washed with distilled water to attain neutral pH and dried at 60 ºC.

Scheme-1. Schematic illustration of CP preparation.

Coating preparation Steel coupons (4 × 3 cm) were polished with silicon carbide papers (grit size220, 320, 400, 600, 800 and 1000). Coupons were rinsed in distilled water, degreased with acetone, dried at room temperature and kept in a vacuum desiccator.

CP-epoxy coating


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The as synthesized CP (5, 10 and 15 wt%) was well dispersed in tert-butyl alcohol using probe sonicator for 10 min, followed by the successive addition of commercial epoxy and polyamide curing agent. The ratio of epoxy, hardener and solvent was fixed at 2:1:2. Subsequently, the obtained solutions were coated on polished degreased metal coupons by dip coating with the dipping rate of 80 mm/min and 1 min immersion time. Coated coupon was allowed to cure for 48 hrs at room temperature, and then stored in a vacuum desiccator till the electrochemical experiment.

CP-siliconized epoxy coating The active sites for PDMS were generated in epoxy by stirring with 1wt% APS coupling agent for 1 hr at 60 °C. Low wt% of APS was used to avoid excessive consumption of epoxide group.30 The CP- siliconized epoxy coating preparation on a steel coupon is shown in Scheme-2. The APS treated epoxy and the stoichiometric equivalent of PDMS along with 3 wt% of ODA (with respect to PDMS) were added to 10 wt% CP dispersed tertiary butyl alcohol. After dissolving ODA and swelling APS treated epoxy and PDMS, their respective curing agents polyamide and sylgard (10 wt% of PDMS) added and sonicated for 10 minutes. Mechanism of formation of siliconized epoxy was reported previously.22,31,27 Monomers of epoxy and PDMS added in the same solvent and simultaneously curing process induced by the respective curing agent to achieve a greater extent of molecular mixing and avoid the phase separation.32, 33



Scheme-2. Schematic illustration of coating preparation. (S-Epoxy denotes APS treated epoxy) Then, the obtained solution was coated on metal coupons as mentioned in CPepoxy coating. Siliconization of epoxy may be explained as in the Scheme-3. NH2 O Epoxy

+

N

O Si(OC2H5)3 Epoxy

Si(OC2H5)3 APS treated epoxy OH 3 HO Si O H n PDMS

-3 Si O Si

N OH

OH

Si

O

Si O

O

m Sylgard 184

N

Si O

OH

OH

O

O

Si O

O

Si

O

Si O Si O Si

Si

O

O

OH

OH

+

APS

Si

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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O

Siliconized Epoxy


Si

O

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Scheme-3. Formation of siliconized epoxy

Techniques Pigment Characterization Synthesized CP was characterized by X-ray diffraction (XRD), Philips X’ pert Pro diffractometer, Ni-filtered Cu-Kα (λ=0.154060 nm) radiation was used to reveal the phase crystalline structure of CP. Field emission scanning electron microscopy (FESEM) JEOL JSM-5600 model and high-resolution transmission electron microscopy (HRTEM) FEI (Tecnai 30 G2 S- TWIN microscope, The Netherlands) were utilized to study morphology.

Coat characterization Cured coatings were characterized using Fourier transform infrared (FT-IR) Bruker Alfa-E, to reveal the bonding between PDMS and epoxy. The thermaldecomposition nature of coatings was studied using Thermogravimetric analysis in SII Nanotechnology Inc., TG-DTA 6200. Thickness and morphology of the coating were measured using SEM and AFM respectively. The contact angle was measured using the sessile drop method. Electrochemical impedance spectroscopy (EIS), and Tafel studies used to measure the corrosion resistance of coatings in 3.5% NaCl, were carried out using the Autolab M204 (Metrhom) instrument.

Results and discussion Characterization of Pigment and Optimization of Pigment Loading



Powder XRD pattern of the prepared CP shown in Figure-S1. The phase purity and crystallinity of the material can be recognized from the XRD pattern, which is further indexed with JCPDS card number 32-0199 and confirms the monoclinic phase of the CP.34-36 The TEM analysis confirms the rod morphology, as shown in Figure-1a-d. The particle size of CP is calculated to be 12 nm in width and ~200 nm in length. Based on the aspect ratio, the pigment particles are confirmed to be nanorods. In agreement with the XRD patterns, the crystallinity of the synthesized pigment is also confirmed from the fringes in high-resolution TEM image (Figure-1d). The elemental analysis of CP nanorods, studied using energy-dispersive X-ray analysis, shown in Figure-1f. As seen from the SAED image, the continuous rings reveal that the synthesized CP pigment is polycrystalline in nature with finer grain size. Additionally, the high intense rings in the SAED pattern are also indexed using PXRD, and shown in Figure-1e.


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Figure-1 TEM images of CP with different resolution (a-d), e) SAED pattern f) TEMEDS of CP Nanorods. Non-destructive in situ EIS analysis is utilized to study, the electrical properties like coating resistance, polymer capacitance and charge transfer process occurring on the metal coat interface. EIS studies have been performed in an autolab potentiostat with standard calomel reference electrode, graphite counter electrode and coated steel coupon as the working electrode in a flat cell having 3.5% sodium chloride solution as an electrolyte. The EIS was performed within an area of 1 cm2 within the frequency 9 ACS Paragon Plus Environment


range of 10-2 to 105 Hz and amplitude of 0.005 V. OCP runs until it attained a steady state.

Figure-2 a) Nyquist plot of bare steel, pristine epoxy and different wt% of CP loaded epoxy coatings. b) The electrochemical equivalent circuit for coated steel coupons. The equivalent circuit consists of solution resistance of electrolyte (Rs), capacitance of intact polymer coating (Qdl), pore resistance (Rp) and charge transfer resistance (Rct). The constant phase element (Q) was utilized by considering current density distribution along the inhomogeneous electrode surface.37 The impedance function of CPE can be represented as:

where Y is the constant phase element (CPE) constant, n is the CPE exponent which can be used to represent the heterogeneity or roughness of the surface, j2 = −1 is an imaginary number and ω is the angular frequency in rad s−1. Depending on n, CPE can represent a resistance (ZCPE = R, n =0); capacitance (ZCPE = C, n = 1), Warburg impedance (ZCPE = W, n = 0.5), and inductance (ZCPE = L, n = −1). 10 ACS Paragon Plus Environment

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The CP nanorods of different wt% (5, 10 and 15) are incorporated into the epoxypolyamide matrix, and the optimized pigment loading has been evaluated from EIS plots. Figure-2a shows the Nyquist plot of bare steel, pristine epoxy coat, 5, 10 and 15 wt% CP nanorod loaded epoxy composite coat. Impedance spectral data fitted with a most probable equivalent circuit, to evaluate the quantitative estimation of anti-corrosion performance of the coating, shown in Figure-2b. Bare steel impedance data fitted with simple Randel circuit. All coatings exhibit capacitive semi-circle, signifying that coatings are capable of protecting steel surface from the penetration of H2O, O2 and Cl .38 The overlap of pigments in the epoxy matrix increased the density of the cured coat, and subsequently prevent the penetration of aggressive ions, offering barrier protection. Under long term exposure, the CP pigment may facilitate phosphatization layer to prevent the corrosion. The ‘n’ value listed in Table-1 indicates the non-homogeneity of the coated metal surface. Table-1 Summarized the electrochemical impedance parameters of bare steel and coated coupons. The decrease in Qcoat achieved by the incorporation of pigment into epoxy coat.



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Table-1 Electrochemical fitted parameters of bare metal and different coatings. Sample

Bare

Rcoat

Qcoat

R ct

Qdl

(Ω cm2)

(F)

(Ω cm2)

(F)

4.03×103

0.15×10-6

0.7

1.83×106

1.17×104

0.64×10-9

0.9

7.06×104

5.59×10-9

3.30×104

0.97×10-9

n

χ2

0.97×10-6

0.5

0.1

2.12×106

0.76×10-6

0.6

0.1

0.8

1.09×107

0.59 ×10-6

0.6

0.4

0.9

2.94×106

0.46×10-6

0.6

0.2

n

Epoxy 5% CPEpoxy 10% CPEpoxy 15% CPEpoxy

The pigment loading by 10 wt% gives a higher impedance value, whereas for 15 wt% of the pigment the impedance value decreases. Nevertheless, the impedance value is decreased for 15 wt% loading of the pigment probably due to the aggregation of CP nanorod which acted as pores in the polymer matrix. Consequently, the efficiency upgradation was performed with 10 wt% pigment loaded epoxy coat by siliconization.

Characterization of siliconized epoxy Coating The FT–IR spectra of commercial uncured epoxy, APS treated epoxy and siliconized epoxy, shown in Figure-3a. The vibrational band around 3500 cm-1 (Figure-3a(i)) is attributed to -OH stretching. While the vibrational peaks at around 1240 and 920 cm-1 denote symmetric and asymmetric stretching vibration of oxirane rings, respectively.27,39 The peak intensity of hydroxyl group 3370 cm-1 decreased in APS treated epoxy owing 12 ACS Paragon Plus Environment

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to the

consumption of -OH group during APS treatment (Figure-3a(ii)).

The

disappearance of a peak at 920 cm-1 in Figure-3a(iii) confirms the ring opening of the epoxied group on reaction with curing agent to form a polymer network. The subsequent formation of band at 803 cm-1 (shown in Figure-3a(iii)) corresponds to Si-C stretching vibration.31,27 Meanwhile, the elevation in the intensities of peaks at 2800-3100 and 1360 cm-1 attributed to the asymmetric methyl group stretching of Si-O-CH3 and Si-C, which indicates the PDMS incorporation into the epoxy system.27,1 The FT-IR results confirm the formation of epoxy/PDMS hybrid polymer through interpenetrating polymer mechanism.

Figure-3 a) FT-IR spectra of coatings: i) uncured epoxy, ii) cured APS treated epoxy and iii) cured siliconized epoxy b) TGA curves of cured 10 wt% CP nanorod loaded epoxy and siliconized epoxy. The TG curves of pigment loaded epoxy and siliconized epoxy systems are shown in Figure-3b. The thermal stability of CP-siliconized epoxy is improved appreciably over CP-epoxy probably due to the intercross linking of PDMS with epoxy and partial ionic nature of stable Si-O-Si inorganic silicone moiety, which can also be recognized from the FT-IR study.22,27 The thermal degradation temperature is enhanced 13 ACS Paragon Plus Environment


due to the high bond dissociation energy of Si-O bond (443.7 KJ/mol). The inorganic nature of Si-O-Si bond stabilized epoxy polar hydroxyl group, siloxane moiety and highly cross-linked interpenetrated polymer producing dense layer resulting in a lower rate of decomposition. Decomposition of 50% of the cured epoxy polymer and siliconized polymer appeared at 357.42 and 374.75 ˚C, respectively, shows the substantial thermal stability of the siliconized epoxy. The huge weight loss in the initial stage is attributed to the presence of high moisture content in the epoxy coating, owing to its hydrophilic nature.

The absence of char in epoxy coating shows low residue than siliconized

epoxy. The cross-sectional SEM image of the siliconized coating, presented in FigureS2, shows the uniform thickness of the siliconized epoxy coat over the steel coupon. No significant crack and defects are observed at the interface of the coating and steel coupon. From the SEM results, the thickness of the coating is calculated to be around 9±1 µm. Sessile drop method was utilized to optically measure the contact angle between distilled water and coating. The neat epoxy coat on the steel coupons provides the water contact angle θ = 43° indicating the hydrophilicity of the coating. On the addition of CP nanorods (10 wt%), the value was increased to θ = 66° due to surface roughness induced by the incorporation of the CP nanorods. The CP-siliconized epoxy coating further increased the water contact angle due to the alkyl group, which hold the water droplet (θ = 121°), as shown in Figure-4. Impermeability of corrosive media into the metal-coating interface and reduced kinetics of the electrochemical corrosion process of hydrophobic protective coating (90° < θ < 150°) was well-established.40-41 CP nanorod


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loaded siliconized epoxy coat shows the highest contact angle designating the lowest wettability, which has been directly influenced by the surface roughness.

Figure-4 AFM Topographic 3D images of epoxy, CP loaded epoxy and siliconized CP loaded epoxy and corresponding contact angle. The AFM images illustrate the homogeneousness and pinhole free protective coating. Tapping mode 3D-AFM images of neat epoxy, CP nanorod-epoxy, CP nanorodsiliconized epoxy given in Figure-4 exhibit the morphology of the coatings. The average surface roughness of neat epoxy, CP nanorod-epoxy, CP nanorodsiliconized epoxy was found to be 0.4, 0.5 and 11 nm respectively. The AFM indicates



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the phase of PDMS domain with few nanometer scales in an epoxy matrix. Nano surface roughness on CP nanorod-siliconized epoxy provides the hydrophobicity.40–42 Anti-corrosive performance of 10%CP-siliconized epoxy The improvement in corrosion efficiency of the epoxy coating has been achieved by making it hydrophobic. The enhancement of the efficiency of the coating is evaluated using EIS. Siliconization of epoxy leads to the achievement of a two order raise in impedance value, which shows the barrier nature of hydrophobic coating as shown in Figure-5a. The electrochemical parameters were tabulated in Table-2. The Resistance of pigment incorporated siliconized epoxy exhibits one order higher than bare siliconized epoxy as shown in Figure-S3 and data tabulated in Table- S1. Table-2 Electrochemical fitted parameters of 10 wt% CP loaded epoxy and siliconized epoxy.

Sample

Rcoat (Ω

10% CP-epoxy

cm2)

Qcoat

R ct

n

(F)

(Ω

cm2)

Qdl

n

χ2

(F)

7.07×104

5.59×10-9

0.8

1.09×107

0.59 ×10-6

0.6

0.8

6.75×107

0.29×10-9

0.9

2.29×109

0.11×10-9

0.6

0.6

10%CP-siliconized epoxy A three order decreases in Qdl suggests a maximum protection against the corrosive medium. Herein, Qcoat represents the density of conducting pathway of the coating. The value of Qcoat decreases by the incorporation of pigment into the epoxy coat, which is further decreased by the siliconization. Moreover, Qdl and Qcoat values show the outstanding protection of siliconized epoxy coat. Figure-5b shows the wide


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range of frequency, phase angle value 90° which proposed the better barrier property of coating.43

Figure-5 a) Nyquist plot b) Bode plot of 10% CP loaded siliconized epoxy coat c) Tafel plot of bare steel, pristine epoxy, 10% CP-epoxy coat and 10% CP-siliconized epoxy coat d) Time-dependent electrochemical impedance modulus of 10% CPsiliconized epoxy. Potentiodynamic polarization semi-log plots corresponding to different coatings shown in Figure-5c. Tafel plots drawn by polarising coated and uncoated coupons about 250 mv anodically and cathodically. Corrosion potential (Ecorr) calculated from the intersection of anodic and cathodic curves, Icorr obtained by extrapolating the Ecorr to Y axis. Corrosion current density (Icorr) proportional to the rate of corrosion and corrosion 17 ACS Paragon Plus Environment


potential shows the propensity towards corrosion. Corrosion potential of steel coupon increased from -0.8034 to -0.5651 V for epoxy coating. Siliconized pigment loaded coating substantially shifted to -0.0542 V, showing the high positive potential shift. From the observed results (Table-3) corrosion current density of epoxy coated steel exhibited one order of magnitude less than uncoated steel. The Icorr value improved by the incorporation of pigment by two order shows the significance of CP nanorods. 10% CPepoxy coat has Icorr 4.6049×10-9 μA/cm2 whereas 10% CP-siliconized epoxy reduced the Icorr to 2.0902×10-11 μA/cm2 due to dual protection of pigment and barrier hydrophobic surface. Pigment loaded siliconized epoxy exhibits enhanced positive corrosion potential shift and negative shift in corrosion current density, showing the greater protection of the coating.44–46 High polarizations resistance obtained for 10% CP incorporated siliconized epoxy which in turn reduces the corrosion rate to 2.1×10-7 mm/year. Superior protection towards corrosive medium obtained by the synergetic effect of the hydrophobic surface as well as the CP nanorod pigment well defined from EIS and Tafel studies.


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Table-3 Electrochemical polarization parameters of steel coupon, epoxy, CP nanorod loaded epoxy, siliconized epoxy and CP nanorod loaded siliconized epoxy Sample

3.5% NaCl solution Ecorr

Icorr

ba

bc

Polarization

Corrosion

(V/

(μA/cm2)

(mV/ dec-1)

(mV/ dec-1)

Resistance

rate

(Ω)

(mm/year)

SCE) Bare Steel

-0.80

5.34×10-6

7.7

4.9

9.8×102

0.1

Epoxy coat

-0.57

1.60×10-7

13.2

12.6

1.1×105

0.02

10% CP-

-0.45

4.60×10-9

26.9

28.9

2.7×107

3.5×10-5

-0.05

2.0×10-11

34.2

30.8

3.3×109

2.1×10-7

epoxy 10%CPsiliconized epoxy

Tafel extrapolation technique provides highly useful information by analyzing the electrochemical activity at pores on coatings. From SEM & AFM morphologies, the coating was found to be pinhole free. Polarisation studies also justified the absences of pores, breakdown and water uptake of the coating and onset of corrosion of base metal. To estimate the durability of the siliconized epoxy coating, the coupon was continuously immersed in 3.5% sodium chloride solution and impedance modulus was measured. Figure-5d shows that after 2 months of continuous immersion impedance modulus at a low frequency is higher than 108 Ω cm2. High Impedance modulus at a lower frequency (0.01 Hz) even after two months of immersion, illustrates that weakening of the coating takes place at much slower rate due to combined effect of CP



nanorods and hydrophobic surface.27 A contact angle of 107o has been retained even after exposure to corrosive medium for two months. Electrochemical studies justify the efficiency of CP nanorod loaded siliconized epoxy coating formulation for maximum barrier protection of steel in saline environment. Mechanism of coating protection Strong affinity of epoxy to adhere on material surfaces is well known. Addition of APS silane coupling agent behaves as both cross linker for PDMS as well as it produces effective adhesion by forming metal siloxane interphase. The CP nanorods form a dense coating and restrict the path of corrodent attack. Interpenetrated epoxyPDMS hybrid polymer produces a highly cross-linked hydrophobic surface, which prevents the penetration of corrodents. Higher impedance value at a lower frequency even after exposure of 2 months shows the effective adhesion of the coating.

Figure-6. schematic representation of coating protection of a) Epoxy b) CP- epoxy c) CP- siliconized epoxy. Figure-6a shows that the micro pore in epoxy provides a permissive path for corrosive species to the metal surface upon exposure to the corrosive medium. CP nanorods incorporated epoxy polymer decreases the porosity and increases the density of the coating. The CP nanorods effectively restrict the attack of corrodent as shown in 20 ACS Paragon Plus Environment

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Figure-6b. Further siliconization process contributes to the nano roughness, which result in the hydrophobic surface as shown in Figure-6c. Hydrophobic surface prevents the penetration of water into the metal surface. The combined effect of CP nanorods and hydrophobic surface can restrict the access of corrosive species to the metal surface, resulting in the improved corrosion resistance. Conclusion Eco-friendly cerium phosphate nanorod pigment with the dimension of ~200 nm length was successfully synthesized by wet chemical method. We observed that cerium phosphate nanorods loaded (10 wt%) epoxy-polyamide exhibited the maximum efficiency. Unique nanorod morphology of the pigment helped to ramble the corrodent attack, thereby reducing the kinetics of corrosion process. Further, nano-roughness was introduced by siliconization in order to enhance the efficiency of the coating. The average surface roughness of 11 nm generated a hydrophobic surface with a contact angle of 121° contributed to barrier property. The EIS studies indicate a high resistance of more than three orders of magnitude for siliconized CP/epoxy over pristine epoxy and Tafel analysis also revealed the high positive potential shift and a negative current density shift. The very large effect is attributed to the synergistic effect of CP nanorods and siliconization. Thus, we formulated an efficient eco-friendly durable anti-corrosive coating based on CP-siliconized epoxy for steel in a saline environment. Author Information Corresponding Author *E-mail- [email protected] Tel: +91471 2515508; Fax: +91471 2491712 21 ACS Paragon Plus Environment


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Note The authors declare no competing financial interest Acknowledgment Financial support from the DST-Science & Engineering Research Board (SERB), Government of India (Grant no. EEQ// 2016/000342) is gratefully acknowledged. The author Krishnapriya K. V. also acknowledges CSIR, New Delhi for the award of Junior Research Fellowship. We thank Mr. Kiran Mohan for TEM analysis. Supporting Information Figures of XRD of CP, Nyquist plot of siliconized epoxy and cross-sectional SEM of the coating. References (1)

Thanikai Velan, T. V; Bilal, I. M. Aliphatic Amine Cured PDMS–epoxy Interpenetrating

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High

Performance

Engineering

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Bahrami Panah, N.; Payehghadr, M.; Danaee, I.; Nourkojouri, H.; Sharbatdaran, M. Investigation of Corrosion Performance of Epoxy Coating Containing Polyaniline Nanoparticles. Iran. Polym. J. 2012, 21, 747–754.

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Shi, X.; Nguyen, T. A.; Suo, Z.; Liu, Y.; Avci, R. Effect of Nanoparticles on the Anticorrosion and Mechanical Properties of Epoxy Coating. Surf. Coatings Technol. 2009, 204, 237–245.

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Sharifi Golru, S.; Attar, M. M.; Ramezanzadeh, B. Studying the Influence of Nano-


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Durable Hydrophobic Coating Based on Cerium phosphate nanorod

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