Article www.acsanm.org
Cite This: ACS Appl. Nano Mater. 2019, 2, 2689−2696
Durable Hydrophobic Coating Based on Cerium Phosphate Nanorod-Siliconized 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
Downloaded via NOTTINGHAM TRENT UNIV on July 25, 2019 at 05:58:03 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.
S Supporting Information *
ABSTRACT: Here, we present a new eco-friendly cerium phosphate (CP) nanorod system that can be utilized as an anticorrosive pigment to protect steel from corrosive environment. Among the various formulations studied, CP nanorod (10 wt %) loaded epoxy exhibited the best corrosion resistance efficiency. The anticorrosion property of the coating was further improved by the introduction of hydrophobicity through siliconization process. This enhanced the average surface roughness (Ra = 0.4−11 nm) and consequently generated hydrophobic contact angle of 121°. A 3-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. 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, fillerloaded epoxy composite coats yielded an advantage by filling pores.2 Especially, nanofillers with unique morphology provide homogeneous dispersion thereby restricting the pathways of corrosive species attack.3−6 Such nanopigments 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 anticorrosive 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 the CP−epoxy interaction not only increased the © 2019 American Chemical Society
cross-linking 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 superhydrophobicity 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 triethoxysilane (APS), and octadecyl amine were purchased from Received: January 29, 2019 Accepted: May 3, 2019 Published: May 3, 2019 2689
DOI: 10.1021/acsanm.9b00172 ACS Appl. Nano Mater. 2019, 2, 2689−2696
Article
ACS Applied Nano Materials Sigma-Aldrich, tertiary butyl alcohol and sodium chloride were purchased from Merck, and epoxy and polyamide hardener were purchased 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).
simultaneously curing process induced by the respective curing agent to achieve a greater extent of molecular mixing and avoid the phase separation.32,33 Then, the obtained solution was coated on metal coupons as mentioned in CP−epoxy coating. Siliconization of epoxy may be explained as in the Scheme 3.
Scheme 1. Schematic Illustration of CP Preparation
Scheme 3. Formation of Siliconized Epoxy
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 h. Then the precipitate was centrifuged and washed with distilled water to attain neutral pH and dried at 60 °C. Coating Preparation. Steel coupons (4 × 3 cm) were polished with silicon carbide papers (grit size: 220, 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. 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 h at room temperature and then stored in a vacuum desiccator until the electrochemical experiment. CP−Siliconized Epoxy Coating. The active sites for PDMS were generated in epoxy by stirring with 1 wt % APS coupling agent for 1 h 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
■
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 JSM5600 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 scanning electron microscopy (SEM) and atomic force microscopy (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.
Scheme 2. Schematic Illustration of Coating Preparationa
■
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. On the basis of 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, are 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
a
S-epoxy denotes APS treated epoxy.
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) were added and sonicated for 10 min. Mechanism of formation of siliconized epoxy was reported previously. 22,31,27 Monomers of epoxy and PDMS added in the same solvent and 2690
DOI: 10.1021/acsanm.9b00172 ACS Appl. Nano Mater. 2019, 2, 2689−2696
Article
ACS Applied Nano Materials
optimized pigment loading has been evaluated from EIS plots. Figure 2a shows the Nyquist plot of bare steel, pristine epoxy
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.
coat, and 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 anticorrosion performance of the coating, shown in Figure 2b. Bare steel impedance data fitted with simple Randel circuit. All coatings exhibit capacitive semicircle, 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 prevented 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 nonhomogeneity 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. 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. However, 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 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 SiC 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 SiOCH3 and SiC, 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 1. (a−d) TEM images of CP with different resolution, (e) SAED pattern, and (f) TEM-EDS of CP nanorods.
grain size. Additionally, the high intense rings in the SAED pattern are also indexed using PXRD and shown in Figure 1e. Nondestructive 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 range of 10−2 to 105 Hz and amplitude of 0.005 V. Open circuit potential (OCP) ran until it attained a steady state. 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 ZCPE = Y −1(jw)−n
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). The CP nanorods of different wt % (5, 10, and 15) are incorporated into the epoxy−polyamide matrix, and the 2691
DOI: 10.1021/acsanm.9b00172 ACS Appl. Nano Mater. 2019, 2, 2689−2696
Article
ACS Applied Nano Materials Table 1. Electrochemical Fitted Parameters of Bare Metal and Different Coatings sample
Rcoat (Ω cm2)
bare epoxy 5% CP−epoxy 10% CP−epoxy 15% CP−epoxy
4.03 × 10 1.17 × 104 7.06 × 104 3.30 × 104 3
Qcoat (F) −6
0.15 × 10 0.64 × 10−9 5.59 × 10−9 0.97 × 10−9
n
Rct (Ω cm2)
0.7 0.9 0.8 0.9
1.83 × 10 2.12 × 106 1.09 × 107 2.94 × 106 6
Qdl (F) −6
0.97 × 10 0.76 × 10−6 0.59 × 10−6 0.46 × 10−6
n
χ2
0.5 0.6 0.6 0.6
0.1 0.1 0.4 0.2
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.
Figure 4. AFM topographic 3D images of epoxy, CP loaded epoxy, and siliconized CP-loaded epoxy and corresponding contact angle.
The TG curves of pigment loaded epoxy and siliconized epoxy systems are shown in Figure 3b. The thermal stability of CPsiliconized epoxy is improved appreciably over CP−epoxy probably due to the intercross linking of PDMS with epoxy and
partial ionic nature of stable SiOSi inorganic silicone moiety, which can also be recognized from the FT-IR study.22,27 The thermal degradation temperature is enhanced due to the high bond dissociation energy of SiO bond (443.7 kJ/mol). 2692
DOI: 10.1021/acsanm.9b00172 ACS Appl. Nano Mater. 2019, 2, 2689−2696
Article
ACS Applied Nano Materials
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% CP-siliconized epoxy.
Table 2. Electrochemical Fitted Parameters of 10 wt % CP Loaded Epoxy and Siliconized Epoxy sample
Rcoat (Ω cm2)
10% CP−epoxy 10% CP−siliconized epoxy
7.07 × 10 6.75 × 107 4
Qcoat (F) −9
5.59 × 10 0.29 × 10−9
n
Rct (Ω cm2)
0.8 0.9
1.09 × 10 2.29 × 109 7
Qdl (F) −6
0.59 × 10 0.11 × 10−9
n
χ2
0.6 0.6
0.8 0.6
holds 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 loaded siliconized epoxy coat shows the highest contact angle designating the lowest wettability, which has been directly influenced by the surface roughness. The AFM images illustrate the homogeneousness and pinhole free protective coating. Tapping mode 3D-AFM images of neat epoxy, CP nanorod−epoxy, and CP nanorod−siliconized epoxy given in Figure 4 exhibit the morphology of the coatings. The average surface roughness of neat epoxy, CP nanorod-epoxy, CP nanorod−siliconized epoxy was found to be 0.4, 0.5, and 11 nm, respectively. The AFM indicates the phase of PDMS domain with few nanometer scales in an epoxy matrix. Nanosurface roughness on CP nanorod−siliconized epoxy provides the hydrophobicity.40−42 Anticorrosive 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
The inorganic nature of SiOSi 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 Figure S2, 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. With 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 2693
DOI: 10.1021/acsanm.9b00172 ACS Appl. Nano Mater. 2019, 2, 2689−2696
Article
ACS Applied Nano Materials
Table 3. Electrochemical Polarization Parameters of Steel Coupon, Epoxy, CP Nanorod Loaded Epoxy, Siliconized Epoxy, and CP Nanorod Loaded Siliconized Epoxy 3.5% NaCl solution sample bare steel epoxy coat 10% CP−epoxy 10%CP-siliconized epoxy
Ecorr (V/SCE) −0.80 −0.57 −0.45 −0.05
Icorr (μA/cm2) −6
5.34 × 10 1.60 × 10−7 4.60 × 10−9 2.0 × 10−11
ba (mV/dec−1)
bc (mV/dec−1)
polarization resistance (Ω)
corrosion rate (mm/year)
7.7 13.2 26.9 34.2
4.9 12.6 28.9 30.8
9.8 × 102 1.1 × 105 2.7 × 107 3.3 × 109
0.1 0.02 3.5 × 10−5 2.1 × 10−7
Figure 6. Schematic representation of coating protection of (a) epoxy, (b) CP−epoxy, (c) CP−siliconized epoxy.
coatings. From SEM and AFM morphologies, the coating was found to be pinhole free. Polarization 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, the 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 the combined effect of CP nanorods and hydrophobic surface.27 A contact angle of 107° has been retained even after exposure to corrosive medium for two months. Electrochemical studies justify the efficiency of the 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 epoxy− PDMS hybrid polymer produces a highly cross-linked hydrophobic surface, which prevents the penetration of corrodents. Higher impedance value at a lower frequency even after an exposure of 2 months shows the effective adhesion of the coating. Figure 6a shows that the micropore in epoxy provides a permissive path for corrosive species to the metal surface upon exposure to the corrosive medium. CP nanorods that incorporated epoxy polymer decrease the porosity and increase the density of the coating. The CP nanorods effectively restrict the attack of corrodent as shown in Figure 6b. A further siliconization process contributes to the nanoroughness, which results 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.
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. 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 valuesshow the outstanding protection of siliconized epoxy coat. Figure 5b shows the wide range of frequency with a phase angle value 90° which was proposed as the better barrier property of coating.43 Potentiodynamic polarization semilog plots corresponding to different coatings shown in Figure 5c. Tafel plots are drawn by polarizing coated and uncoated coupons at about 250 mV anodically and cathodically. Corrosion potential (Ecorr) is calculated from the intersection of anodic and cathodic curves, and Icorr is obtained by extrapolating the Ecorr to Y-axis. Corrosion current density (Icorr) proportional to the rate of corrosion and corrosion potential shows the propensity toward corrosion. Corrosion potential of steel coupon increased from −0.8034 to −0.5651 V for epoxy coating. Siliconized pigmentloaded 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 1 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. Ten percent CP−epoxy coat has Icorr of 4.6049 × 10−9 μA/cm2 whereas 10% CP−siliconized epoxy reduced the Icorr to 2.0902 × 10−11μA/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-polarization resistance obtained for 10% CP incorporated siliconized epoxy which in turn reduces the corrosion rate to 2.1 × 10−7 mm/year. Superior protection toward corrosive medium obtained by the synergetic effect of the hydrophobic surface as well as the CP nanorod pigment are well-defined from EIS and Tafel studies. Tafel extrapolation technique provides highly useful information by analyzing the electrochemical activity at pores on 2694
DOI: 10.1021/acsanm.9b00172 ACS Appl. Nano Mater. 2019, 2, 2689−2696
Article
ACS Applied Nano Materials
■
(5) Xiao, X.; Wang, D.; Li, Y.; Jackson, E.; Fang, Y.; Zhang, Y.; Xie, N.; Shi, X. Investigation into the Synergistic Effect of Nano-Sized Materials on the Anti-Corrosion Properties of a Waterborne Epoxy Coating. Int. J. Electrochem. Sci. 2016, 11, 6023−6042. (6) Torknezhad, Y.; Khosravi, M.; Assefi, M. Corrosion Protection Performance of Nanoparticle Incorporated Epoxy Paint Assessed by Linear Polarization and Electrochemical Impedance Spectroscopy. Mater. Corros. 2018, 69, 472−480. (7) Prosek, T.; Thierry, D. A Model for the Release of Chromate from Organic Coatings. Prog. Org. Coat. 2004, 49, 209−217. (8) Bethencourt, M.; Botana, F. J.; Calvino, J. J.; Marcos, M.; Rodriguez-Chacon, M. A. Lanthanide Compounds as EnvironmentallyFriendly Corrosion Inhibitors of Aluminium Alloys: A Review. Corros. Sci. 1998, 40, 1803−1819. (9) Selvaraj, K.; et al. Removal of Hexavalent Chromium Using Distillery Sludge. Bioresour. Technol. 2003, 89, 207−211. (10) Wu, F.; Wu, W.; Kuo, H.; Liu, C.; et al. Effect of Genotoxic Exposure to Chromium among Electroplating Workers in Taiwan. Sci. Total Environ. 2001, 279, 21−28. (11) Buxbaum, G.; Pfaff, G. Industrial Inorganic Pigments, third ed.; Wiley-VCH: Weinheim, Germany, 2005. (12) Kirmaier, L.; Bender, S.; Heyn, A. The Path to New Zinc-Free Anti-Corrosive Pigments. PPCJ. Polym. Paint Colour J. 2014, 204, 48− 51. (13) Fan, F.; Zhou, C.; Wang, X.; Szpunar, J. Layer-by-Layer Assembly of a Self-Healing Anticorrosion Coating on Magnesium Alloys. ACS Appl. Mater. Interfaces 2015, 7, 27271−27278. (14) Shi, H.; Han, E.; Lamaka, S. V.; Zheludkevich, M. L.; Liu, F.; Ferreira, M. G. S. Progress in Organic Coatings Cerium Cinnamate as an Environmentally Benign Inhibitor Pigment for Epoxy Coatings on AA 2024-T3. Prog. Org. Coat. 2014, 77, 765−773. (15) Danaee, I.; Darmiani, E.; Rashed, G. R.; Zaarei, D. Self-Healing and Anticorrosive Properties of Ce (III)/ Ce (IV) in Nanoclay - Epoxy Coatings. Iran. Polym. J. 2014, 23, 891−898. (16) Darmiani, E.; Danaee, I.; Rashed, G. R.; Zaarei, D. Formulation and Study of Corrosion Prevention Behavior of Epoxy Cerium Nitrate Montmorillonite Nanocomposite Coated Carbon Steel. J. Coatings Technol. Res. 2013, 10, 493−502. (17) Doull, C. Toxicology: The Basic Science Of Poisons, sixth ed.; Klaassen, C. D., Ed.; McGraw-Hill, 2001. (18) Haley, J. T. Pharmaceutical Sciences. J. Pharm. Sci. 1965, 54, 663−670. (19) Li, Z.; Yue, Y.; Hao, Y.; Feng, S.; Zhou, X. A Glassy Carbon Electrode Modified with Cerium Phosphate Nanotubes for the Simultaneous Determination of Hydroquinone, Catechol and Resorcinol. Microchim. Acta 2018, 185, 1−9. (20) Lima, J. F.; De Sousa Filho, P. C.; Serra, O. A. Single Crystalline Rhabdophane-Type CePO4nanoparticles as Efficient UV Filters. Ceram. Int. 2016, 42, 7422−7431. (21) Parangi, T.; Wani, B.; Chudasama, U. Sorption and Separation Study of Heavy Metal Ions Using Cerium Phosphate: A Cation Exchanger. Desalin. Water Treat. 2016, 57, 6443−6451. (22) Ananda Kumar, S.; Sankara Narayanan, T. S. N. Thermal Properties of Siliconized Epoxy Interpenetrating Coatings. Prog. Org. Coat. 2002, 45, 323−330. (23) Alagar, M.; Velan, T. V. T.; Kumar, A. A.; Mohan, V. Synthesis and Characterization of High Performance Polymeric Hybrid Siliconized Epoxy Composites for Aerospace Applications. Mater. Manuf. Processes 1999, 14, 67−83. (24) Sung, P.-H.; et al. Chien-Yang li. Polysiloxane Modified Epoxy Polymer Networks-I. Graft Interpenetrating Polymeric Networks. Eur. Polym. J. 1997, 33, 903−906. (25) Wu, X.; Zhao, X.; Ho, J. W. C.; Chen, Z. Design and Durability Study of Environmental-Friendly Room-Temperature Processable Icephobic Coatings. Chem. Eng. J. 2019, 355, 901−909. (26) Kumar, S. A.; Alagar, M.; Mohan, V. Studies on CorrosionResistant Behavior of Siliconized Epoxy Interpenetrating Coatings over Mild Steel Surface by Electrochemical Methods. J. Mater. Eng. Perform. 2002, 11, 123−129.
CONCLUSION Eco-friendly cerium phosphate nanorod pigment with the dimension of ∼200 nm in 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, nanoroughness 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 3 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 anticorrosive coating based on CP−siliconized epoxy for steel in a saline environment.
■
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsanm.9b00172.
■
Figures of XRD of CP, Nyquist plot of siliconized epoxy, and cross-sectional SEM of the coating (PDF)
AUTHOR INFORMATION
Corresponding Author
*Tel.: +91471 2515508. Fax: +91471 2491712. E-mail:
[email protected]. ORCID
Nithyaa Jayakumar: 0000-0002-6161-196X Krishnapriya Karattu Veedu: 0000-0002-7417-1502 Nishanth Karimbintherikkal Gopalan: 0000-0001-7293-5946 Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS Financial support from the DST-Science and Engineering Research Board (SERB), Government of India (Grant EEQ// 2016/000342) is gratefully acknowledged. K.K.V. also acknowledges CSIR, New Delhi for the award of Junior Research Fellowship. We thank Mr. Kiran Mohan for TEM analysis.
■
REFERENCES
(1) Thanikai Velan, T. V.; Bilal, I. M. Aliphatic Amine Cured PDMSepoxy Interpenetrating Network System for High Performance Engineering ApplicationsDevelopment and Characterization. Bull. Mater. Sci. 2000, 23, 425−429. (2) 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. (3) Shi, X.; Nguyen, T. A.; Suo, Z.; Liu, Y.; Avci, R. Effect of Nanoparticles on the Anticorrosion and Mechanical Properties of Epoxy Coating. Surf. Coat. Technol. 2009, 204, 237−245. (4) Sharifi Golru, S.; Attar, M. M.; Ramezanzadeh, B. Studying the Influence of Nano-Al2O3 particles on the Corrosion Performance and Hydrolytic Degradation Resistance of an Epoxy/Polyamide Coating on AA-1050. Prog. Org. Coat. 2014, 77, 1391−1399. 2695
DOI: 10.1021/acsanm.9b00172 ACS Appl. Nano Mater. 2019, 2, 2689−2696
Article
ACS Applied Nano Materials (27) Ammar, S.; Ramesh, K.; Vengadaesvaran, B.; Ramesh, S.; Arof, A. K. Amelioration of Anticorrosion and Hydrophobic Properties of Epoxy/PDMS Composite Coatings Containing Nano ZnO Particles. Prog. Org. Coat. 2016, 92, 54−65. (28) Ivanou, D. K.; Starykevich, M.; Lisenkov, A. D.; Zheludkevich, M. L.; Xue, H. B.; Lamaka, S. V.; Ferreira, M. G. S. Plasma Anodized ZE41 Magnesium Alloy Sealed with Hybrid Epoxy-Silane Coating. Corros. Sci. 2013, 73, 300−308. (29) Xue, C. H.; Bai, X.; Jia, S. T. Robust, Self-Healing Superhydrophobic Fabrics Prepared by One-Step Coating of PDMS and Octadecylamine. Sci. Rep. 2016, 6, 1−11. (30) Ji, W. G.; Hu, J. M.; Liu, L.; Zhang, J. Q.; Cao, C. N. Water Uptake of Epoxy Coatings Modified with γ-APS Silane Monomer. Prog. Org. Coat. 2006, 57, 439−443. (31) Ahmad, S.; Gupta, A. P.; Sharmin, E.; Alam, M.; Pandey, S. K. Synthesis, Characterization and Development of High Performance Siloxane-Modified Epoxy Paints. Prog. Org. Coat. 2005, 54, 248−255. (32) Jia, L.-Y.; Zhang, C.; Du, Z.-J.; Li, C.-J.; Li, H.-Q. Preparation of Interpenetrating Polymer Networks of Epoxy/Polydimethylsiloxane in a Common Solvent of the Precursors. Polym. J. 2007, 39, 593−597. (33) Yang, J.; Winnik, M. A.; Ylitalo, D.; DeVoe, R. J. PolyurethanePolyacrylate Interpenetrating Networks. 1. Preparation and Morphology. Macromolecules 1996, 29, 7047−7054. (34) Verma, S.; Bamzai, K. K. Preparation of Cerium Orthophosphate Nanosphere by Coprecipitation Route and Its Structural, Thermal, Optical and Electrical Characterization. J. Nanopart. 2014, 2014, 1. (35) Ekthammathat, N.; Thongtem, T.; Phuruangrat, A.; Thongtem, S. Facile Hydrothermal Synthesis and Optical Properties of Monoclinic CePO4 Nanowires with High Aspect Ratio. J. Nanomater. 2012, 2012, 1−7. (36) Verma, S.; Singh, V.; Raina, B.; Bamzai, K. K. Structural, Optical, Electrical Characteristics of Synthesized Nanoparticles of Cerium Orthophosphate. Int. J. Chem. Tech Res. 2014, 6, 3297−3299. (37) Sutter, E.; Albrecht, P.; Camino, F. E.; Sutter, P. Monolayer Graphene as Ultimate Chemical Passivation Layer for Arbitrarily Shaped Metal Surfaces. Carbon 2010, 48, 4414−4420. (38) Koenig, S. P.; Boddeti, N. G.; Dunn, M. L.; Bunch, J. S. Ultrastrong Adhesion of Graphene Membranes. Nat. Nanotechnol. 2011, 6, 543−546. (39) Duraibabu, D.; Ganeshbabu, T.; Manjumeena, R.; Ananda Kumar, S.; Dasan, P. Unique Coating Formulation for Corrosion and Microbial Prevention of Mild Steel. Prog. Org. Coat. 2014, 77, 657−664. (40) Metroke, T. L.; Kachurina, O.; Knobbe, E. T. Spectroscopic and Corrosion Resistance Characterization of GLYMO-TEOS Ormosil Coatings for Aluminum Alloy Corrosion Inhibition. Prog. Org. Coat. 2002, 44, 295−305. (41) Mohamed, A. M. A.; Abdullah, A. M.; Younan, N. A. Corrosion Behavior of Superhydrophobic Surfaces: A Review. Arabian J. Chem. 2015, 8, 749−765. (42) Abdolah Zadeh, M.; Van Der Zwaag, S.; Garcia, S. J. Adhesion and Long-Term Barrier Restoration of Intrinsic Self-Healing Hybrid Sol-Gel Coatings. ACS Appl. Mater. Interfaces 2016, 8, 4126−4136. (43) Chen, G.; Feng, J.; Qiu, W.; Zhao, Y. Eugenol-Modified Polysiloxanes as Effective Anticorrosion Additives for Epoxy Resin Coatings. RSC Adv. 2017, 7, 55967−55976. (44) Caldona, E. B.; De Leon, A. C. C.; Pajarito, B. B.; Advincula, R. C. Novel Anti-Corrosion Coatings from Rubber-Modified Polybenzoxazine-Based Polyaniline Composites. Appl. Surf. Sci. 2017, 422, 162− 171. (45) Ruhi, G.; Bhandari, H.; Dhawan, S. K. Corrosion Resistant Polypyrrole/Flyash Composite Coatings Designed for Mild Steel Substrate. Am. J. Polym. Sci. 2015, 5, 18−27. (46) Taghavikish, M.; Dutta, N.; Roy Choudhury, N. Emerging Corrosion Inhibitors for Interfacial Coating. Coatings 2017, 7, 217.
2696
DOI: 10.1021/acsanm.9b00172 ACS Appl. Nano Mater. 2019, 2, 2689−2696
