ZnO coated on passivated low nickel stainless steel

The PE results discovered that the P(Popd-co- Ani)/Zno copolymer coating on passivated LN SS metal more effectively protects the substrate with enhanced the corrosion resistance down to [r]

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Original Article

Poly(ophenylenediaminecoaniline)/ZnO coated on passivated low nickel stainless steel

P Karthikeyan, M Malathy, R Rajavel*

Department of Chemistry, Periyar University, Salem, 636 011, Tamilnadu, India

a r t i c l e i n f o

Article history: Received 19 August 2016 Received in revised form November 2016 Accepted 13 November 2016 Available online 19 November 2016 Keywords:

LN SS

Copolymer composite Electrochemical techniques Anti-corrosion

a b s t r a c t

Iron and its alloys are broadly used in many applications, which have strengthened the research in corrosion resistance in various neutral and provoking environments Almost powerful corrosion in-hibitors have negative effects on both environment and health Therefore, there is a need for a primer that provides outstanding adherence and corrosion resistance, and is environmentally safer The con-ducting polymer coating on metals was found to offer the anti-corrosion In this work, the aniline) copolymers (P(Popd-co-Ani)) and Poly(o-phenylenediamine-co-aniline)/ZnO (P(Popd-co-Ani)/ZnO) composite were synthesized using the electrochemical techniques on borate passivated low nickel stainless steel (LN SS) electrodes from lithium perchlorate in acetonitrile solutions containing aﬁxed concentration of monomer and different concentrations of zinc oxide (ZnO) The structural and morphological analyses of the copolymer and composite coatings were conducted by Fourier transform-infrared spectroscopy (FT-IR), X-ray diffraction (XRD),ﬁeld emission scanning electron microscopy (FE-SEM), elemental mapping and energy dispersion X-ray spectroscopy (EDX) The surface topography was assessed with using an atomic force microscope (AFM), and the corrosion protection behavior of these copolymer-coated stainless steels was investigated in a 0.5 M H2SO4solution by the potentiodynamic polarization (Tafel) and electrochemical impedance spectroscopy methods Among the as developed protective copolymer coatings, the P(Popd-co-Ani)/ZnO composite exhibited the best corrosion protection

© 2016 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)

1 Introduction

Stainless steel is of great interest in industrial applications owing to the union of exceptional resistance to corrosion, good mechanical properties, intrinsic durability, ductility and good workability[1e5] Anti-corrosion is essential by many industries via, oil and gas exploration and production, chemical manufacture, petroleum reﬁning and product additives[6e8] For this reason, the stainless steel, in which the nickel content is partly replaced with other elements (low-nickel stainless steel (LN SS)), is being evalu-ated as a possible alternative to traditional carbon steel This LN SS could mean a saving of about 15e20% in contrast to the conven-tional austenitic stainless steel[9e11]

Although the inﬂuence of chemical and atmosphere can be negligible, LN SS is susceptible to corrosion in the aggressive environment To tailor the corrosion rate of LN SS, different ap-proaches have been developed such as use of inhibitors, protective coatings, etc One of the ideal ways to improve the corrosion resistance of LN SS is to apply the protective coatings[12e14] To protect the metals from corrosion, organic conducting polymer coatings were found to be more effective than other protective coatings[15e18] Additionally, polymers are with the aim of they can be evenly and electrochemically deposited the metal surface with easiness of control over the extent of the polymer coatings and irrespective of the surface roughness and shape[19]

Phenylenediamine (Popd) is inspect as one of the most examine conducting polymers and also advantages much interest in several studies with a choice of practical applications for the reason that of its high conductivity, outstanding air stability[20,21], and special physical and chemical properties compared to other conducting polymers [22] Also, the rigid backbone structure of o-aniline * Corresponding author

E-mail address:drrajavelpu@gmail.com(R Rajavel)

Peer review under responsibility of Vietnam National University, Hanoi

Contents lists available atScienceDirect

Journal of Science: Advanced Materials and Devices

j o u r n a l h o m e p a g e : w w w e l s e v i e r c o m / l o c a t e / j s a m d

http://dx.doi.org/10.1016/j.jsamd.2016.11.003

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attributed[23e26]to the extensive delocalization ofpeelectrons The copolymers have a stand of special properties for instance enhanced chemical, thermostability and good barrier properties etc

[27,28]

Conducting polymer/inorganic oxide nanocomposites have a little while back attracted great attention caused by their unique micro and nano shape, electrooptical, physiochemical properties and a wide-range of their potential treatment in battery cathodes and in the structure of nanoscopic assemblies in sensors and mi-croelectronics It is believed that, with the development of material science, ZnO has found applications in many ﬁelds such as the chemical industry, electronics, optics, and number of areas because of its catalysis, optical, magnetic, and mechanical special features

[29] The nanocomposites consisting of polymers and ZnO have attracted lots of interest in their magniﬁcent properties and po-tential applications The Numerous researches investigated con-ducting polymer/ZnO nano-composites, and a number of research groups have focused their research on the investigation of PVC/ZnO nanocomposites and their applications [30] To the best of our knowledge, there are no reports on the electrochemical synthesis of nanocomposite coating consisting of PoPd, PAni and ZnO by CV technique on borate passivated LN SS material In the present work the structure and properties of P(Popd-co-Ani)/Zno nanocomposite coating were studied and the anticorrosive property of P(Popd-co-Ani)/Zno nanocomposite coating on metal sample was investigated in 0.5 M H2SO4at room temperature

2 Experimental

In this work, The LN SS (size of cm cm 0.3 cm) samples were embedded in epoxy resin with suitable electrical make con-tact with to have an exposed area of cm2 The substrates were polished with a 200 to 1500 series of emery papers, the specimens were cleaned by ultrasonication and followed by thorough rinsing in acetone and DI-water and dried in air[1] Passivation of LN SS surface was done in the borate buffer solution [31] and under potentiostatic conditions for h at potentials of 0.64 V according to procedure declared by our previous work The polymer composite coatings were electrosynthesized on the passivated LN SS by using cyclic voltammetry[32,33] The Ani, Popd and ZnO monomers were double distilled prior to their use The electrochemical polymeri-zation was complete in a one compartment three electrode chamber with working electrode (LN SS), reference electrode (SCE) and counter electrode (platinum) The cyclic voltammetric setting were maintained using a CHI Electrochemical Workstation (CHI 760C, CH Instruments, USA) After deposition, the working elec-trode (LN SS metal) was removed from the electrolyte and rinsed with DI water and dried in air

3 Result and discussion

3.1 Preparation of P(Popd-co-Ani)/Zno composite

The cyclic voltammetric (CV) curves recorded for P(Popd-co-Ani)/Zno copolymer composite coating on passivated LN SS from ACN-LiClO4containing solution (Fig 1) The equal ratio of monomer

in the presence and absence of ZnO nanoparticles were taken in arrange to compare the morphology, shape and corrosion resis-tance of composite coating with P(Popd-co-Ani) theﬁgure repre-sents (CV) between0.8 to 2.0 V at a scan rate of 100 mV s1at

room temperature (28± 1C) and for 20 cycles In CV studies well

deﬁned oxidation and reduction peaks of P(Popd-co-Ani)/Zno copolymer composite between0.4 and ỵ 2.0 V vs SCE appear to indicating the formation of homogenous and strong adherent

P(Popd-co-Ani)/Zno copolymer composite coating occurs over the passivated LN SS surface

3.2 Phase structure and morphological characterization

The electropolymerized P(Popd-co-Ani) in the presence and absence of ZnO on the passivated steel surface was scraped off and their Fourier transform infrared spectroscopy (FT-IR) spectrum were recorded (Fig 2) TheFig 2a,b gives the FT-IR spectra of pure P(Popd-co-Ani) and P(Popd-co-Ani)/ZnO composite [23] The P(Popd-co-Ani) peaks are present in the composite and the peak appeared at 578 cm1 conﬁrms the presence of ZnO composite coating formed on LN SS surface.Fig 3shows the XRD patterns for P(Popd-co-Ani) and P(Popd-co-Ani)/ZnO nanocomposite The peaks for P(Popd-co-Ani) (Fig 3a) is found around the 2qvalues of 20e25, respectively Similarly the XRD pattern of nanocomposite (Fig 3b) shows the corresponding peaks for copolymer along with the peaks for ZnO (31, 34, 36, 47, 56, 62, and 67) Hence, the XRD pattern supports for the formation of P(Popd-co-Ani)/ZnO nano-composite[30]

The FE-SEM morphological study of CV electrodeposited P(Popd-co-Ani) and P(Popd-co-Ani)/Zno composite coatings ob-tained at 20 segments above condition shown inFig TheFig 4a shows the non-uniform structure for P(Popd-co-Ani) coating whereas aﬂower-like morphology is obtained for the P(Popd-co-Ani)/Zno coating (Fig 4b) which covers the entire surface of the anticorrosion P(Popd-co-Ani)/Zno composite coating consisted reveals that the ZnO particles were distributed randomly into the net lines among P(Popd-co-Ani) The morphologies of the obtained Fig Cyclic voltammograms of P(Popd-co-Ani)/ZnO copolymer nanocomposite coating on passivated LN SS for cycle numbers 1e20 at a scan rate of 100 mV s1.

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coatings are well evident from the higher magnification of the figure, which have specified as the inset to the SEM imageFig 4b The morphological changes may be due to the substitution of ZnO in monomer at the prolonged polymer This indicates that the CV electrodeposition system seems to be favorable for the develop-ment of resultant coatings on LN SS The eledevelop-mental mapping of P(Popd-co-Ani)/Zno composite coating indicated they found everywhere presence of C, N, Zn, O and Cl at areas of differential concentration (Fig 5aee) The C and N distribution correspond well to the Zn and O distributions, confirming the substitution of the Zno ions into the copolymer lattice In addition to these, the distribution of Cl in the composite coating was found which revealed the oxidation of copolymer in P(Popd-co-Ani)/Zno composite The EDS spectrum of the P(Popd-co-Ani)/Zno composite coating shows the presence of C, N, Zn, O and Cl (Fig 5f), indicating the existence of ZnO and copolymer composite coating Thus, the homogenously distributed ZnO and the in P(Popd-co-Ani) particles can be observed upon EDS mapping analysis[6,21]

The surface topography of P(Popd-co-Ani) and P(Popd-co-Ani)/ ZnO composite coatings on LN SS samples was studied using AFM and theFig 6a,b shows the experimental topographic images The

AFM topographical image for P(Popd-co-Ani) coating with opti-mum feed ratios of monomers on LN SS sample (Fig 6a) clearly showed that the coating surface is more compact, dense, contin-uous and non-uniform in nature (Fig 6a) The P(Popd-co-Ani)/ZnO composite coated LN SS topography is presented inFig 6b The topographical image of the composite coatingsFig 6b, revealed the uniform distribution of non-porous network conﬁguration on the compact polymer layer The average root mean squared roughness value for the P(Popd-co-Ani) compact layer measured value for 151.61 nm whereas for the P(Popd-co-Ani)/ZnO composite coatings measuring the value was found to be 28.72 nm, respectively This low value of surface roughness provides the information about quality of ZnO dispersion in the P(Popd-co-Ani) coatings which represents good homogeneity of ZnO deposition on the composite layer This information reveals the formation of uniform and pores free ZnO composite P(Popd-co-Ani) coating Smooth and homo-geneousﬁlm coating act as a good barrier and forms a non-porous layer without depletion of grain boundaries thus favorably affecting the corrosion protection of the coatings

3.3 Electrochemical investigation of the composite

The corrosion protection performance of uncoated P(Popd-co-Ani) copolymer and P(Popd-co-P(Popd-co-Ani)/Zno composite coatings on passivated LN SS was studied by potentiodynamic polarization system The polarization curves of uncoated P(Popd-co-Ani) copolymer coated LN SS samples immersed in 0.5 M H2SO4

solu-tion is shown in Fig The resultant corrosion parameters for instance corrosion potential (Ecorr) and corrosion current density (icorr) derived from these curves are given inTable The Ecorr and icorr value for the bare LN SS sample was found to be449 mV vs SCE and 0.72 mA cm2, respectively[1,31] An investigation of the polarization curves showed positive shift in the Ecorrand

consid-erable decrease in the Icorrof the LN SS (Fig 7a) due to the

elec-trosynthesized P(Popd-co-Ani) copolymer and P(Popd-co-Ani)/Zno coatings, which indicates the corrosion (PE%) protection efﬁciency of the P(Popd-co-Ani) copolymer and composites[20,31]

This implied that the P(Popd-co-Ani)/Zno copolymer coating provides an effective protection for LN SS against corrosion in 0.5 M H2SO4 This is due to the formation of more compact layer with

uniform arrangement of randomly structure likeﬂower and this result is in good agreement with FESEM results The protection

Fig FESEM images of (a) P(Popd-co-Ani) coating (b) P(Popd-co-Ani)/ZnO composite coating (inset: high magniﬁcation of P(Popd-co-Ani)/ZnO composite coating on passivated LN SS, respectively)

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efﬁciency (PE) of the P(Popd-co-Ani) coating and P(Popd-co-Ani)/ Zno is calculated from the icorr values using the following expression

PE%¼icorr i0corr icorr 100

where, i0corr and icorrare the corrosion current density (mA cm2)

values of bare and coated specimens, respectively

The PE of P(Popd-co-Ani) coating and P(Popd-co-Ani)/Zno is calculated from potentiodynamic polarization data and is found to be 93.1% and 98.8% for P(Popd-co-Ani) and P(Popd-co-Ani)/Zno, respectively[1,20] The PE results discovered that the P(Popd-co-Ani)/Zno copolymer coating on passivated LN SS metal more effectively protects the substrate with enhanced the corrosion resistance down to its homogeneous and more compact morphology when compared to the P(Popd-co-Ani) copolymer coating Electrochemical impedance spectroscopic studies[1,31]

The impedance technique studies more information on both capacitive and resistive capability of the sample in 0.5 M H2SO4

medium which showed an admirable agreement between the conduct experiment andﬁtting The equivalent circuit, Rs (R1Cdl)

(R2Cdl1) is used forﬁtting the impedance spectrum of

P(Popd-co-Ani)/Zno coating on passivated LN SS and is shown inFig 7b The primary element Rs in the equivalent circuit constitute the solution resistance which similarity to the ohmic resistance of the system and R1and Cd1represent the resistance by oxidation of the alloy

and dual layer capacitance of the bare LN SS, respectively[20,31] The second subsystem corresponds to the resistance (R2), the

double layer capacitance of the P(Popd-co-Ani)/Zno coating in the case of bare LN SS These different elements were characterized by two equivalent combinations of resistance and capacitance in cycle with Rs

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sample when compared with the bare LN SS These results point out that P(Popd-co-Ani)/Zno copolymer coating acts as barrier between the substrate and atmosphere to increase the corrosion resistance Additionally, the comparison of EIS parameters for the P(Popd-co-Ani) copolymer coated substrate exposed the highest value of to-tal impedance and coating resistance Also, the lowest value of capacitance for the LN SS sample coated with P(Popd-co-Ani)/Zno copolymer

The EIS studies in the form of Bode and phase plots for the uncoated (bare LN SS), Ani) copolymers and P(Popd-co-Ani)/Zno coated LN SS samples in 0.5 M H2SO4solution at an OCP

condition are shown inFig 7c,d An analysis of these EIS results showed upper values for Rp andjZj of the LN SS due to the elec-trochemically synthesized copolymer composites, which indicates the corrosion PE of the P(Popd-co-Ani) and P(Popd-co-Ani)/Zno, respectively These results exposed that the higher Rp and jZj values of P(Popd-co-Ani)/Zno copolymer coated LN SS has veriﬁed its better corrosion protection efﬁciency than other copolymers

[19,31]as a result of the more compact and effective barrier nature of the copolymer composite coating which was even conﬁrmed by FESEM (Fig 4b) Moreover, the higher Rp and jZj values of the P(Popd-co-Ani)/Zno copolymer coating on passivated LN SS is possible because of an area effect where the P(Popd-co-Ani)/Zno copolymer coating is hindering the access of the forceful electro-lyte to the metal surface[21] From then on top of results, it could be well ascertained that the P(Popd-co-Ani)/Zno copolymer coating on passivated LN SS is higher in corrosion protection

Fig AFM images of (a) P(Popd-co-Ani) coating (b) P(Popd-co-Ani)/ZnO composite coating on passivated LN SS

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3.4 Mechanical properties of the composite (P(Popd-co-Ani)/ZnO) coatings

3.4.1 Adhesion tests

Adhesion of the composite coating on the LN SS specimen is one of the important properties for in industrial Here, the adhesion strength (Fig 8a) of the P(Popd-co-Ani), ZnO and composite P(Popd-co-Ani)/ZnO coatings on LN SS was evaluated The adhesive strength of the composite P(Popd-co-Ani)/ZnO LN SS is 13.1± 1.1 MPa whereas the individual coatings of P(Popd-co-Ani) and ZnO on LN SS exhibited values of 12.6 ± 1.0 MPa and 13.5 ± 1.0 MPa, respectively This adhesion strength of the as-formed composite coating will make it suitable for industrial applications

3.4.2 Hardness tests

The Vickers micro-hardness (Hv) values for the uncoated LN SS and P(Popd-co-Ani), ZnO and composite P(Popd-co-Ani)/ZnO coatings on LN SS samples are shown inFig 7b For the P(Popd-co-Ani), ZnO and-coated LN SS specimens, the Vickers micro-hardness values were found to be 96.9 ± 10.5, 112.5 ± 12 Hv, respectively The Hv value (137.7± 11.3) obtained for the composite coated LN SS was higher than those of the P(Popd-co-Ani) and ZnOcoated LN SS specimens

4 Conclusion

Pure P(Popd-co-Ani) coating and P(Popd-co-Ani)/ZnO nano-composite coating were successfully electrodeposited on passiv-ated LN SS, respectively by cyclic voltammetric method SEM and AFM show characteristic results that ZnO incorporated in polymer matrix affect the polymer morphology The existence of ZnO nano-particles inside the coating increases the anti-corrosion effect on metal In other words, the comparison between corrosion perfor-mances of pure P(Popd-co-Ani) coating and P(Popd-co-Ani)/ZnO nanocomposite coating has shown that P(Popd-co-Ani)/ZnO nanocomposite coating provided much better protection to LN SS in 0.5 M H2SO4solution

Acknowledgements

One of the authors R Rajavel acknowledges the majorﬁnancial support from the Council of Scientiﬁc and Industrial Research, New Delhi, India, (CSIR) (01(2835)/15/EMR-II) P Karthikeyan acknowl-edges the support received from Periyar University in the form of University Research FellowShip (URF)

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Electrochemical parameters of the uncoated LN SS, P(Popd-co-Ani) copolymers and P(Popd-co-Ani)/ZnO composite coating on passivated LN SS in 0.5 M H2SO4solution

Sample Ecorr[mV] icorr[mA cm2] Rp[Ucm2] jZj [Ucm2] PE%

Bare LN SS 449 0.72 147 166 e

(Popd-co-Ani) copolymer

327 0.05 1819 1977 93.1

(Popd-co-Ani)/ZnO composite

230 0.008 2696 2833 98.8

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