In addition, the peaks that were centered at 1202 and 923 cm1 were assigned to the doping states of PPy [33]. Its corrosion rate was about 100 times lower than that of neat epoxy coating. Hence, the EPPyNG2 also exhibited better anticorrosion performance than those of EPPyN (4.5 106 cm2) and EPPyNG1 (5.4 106 cm2). Figure 6 shows the Nyquist and Bode plots of the coated mild steels during different immersion days. PMC legacy view Liu S., Gu L., Zhao H., Chen J., Yu H. Corrosion Resistance of Graphene-Reinforced Waterborne Epoxy Coatings. Rp is the polarization resistance calculated by the slope of the polarization curve at the Ecorr according to the SternGeary Equation (2) [45]: Here, ba and bc are the anodic and cathodic Tafel slopes, Icorr is the corrosion current density. Rpore modeled ionically conducting paths across the coating, which could be used to evaluate the barrier performance of the coatings [54]. It could be observed that the Rpore of neat epoxy coating gradually decreased from 7.3 105 cm2 to a much lower value (1.3 104 cm2). An official website of the United States government. ); moc.361@ljwcnxj (J.W. Qiu S., Chen C., Cui M., Li W., Zhao H., Wang L. Corrosion protection performance of waterborne epoxy coatings containing self-doped polyaniline nanofiber. Applications of conducting polymer composites to electrochemical sensors: A review. The electrolyte was 3.5 wt % NaCl solution. 657-678. https://doi.org/10.1108/IJBPA-12-2018-0099, Copyright 2019, Emerald Publishing Limited. HHS Vulnerability Disclosure, Help You can join in the discussion by joining the community or logging in here.You can also find out more about Emerald Engage. After that, the PPyNG nanocomposites were incorporated into waterborne epoxy coatings to study their anticorrosion performance for mild steel. Knife-peel test was performed to assess the adhesion between epoxy and underlying steel after two years of exposure. The potential dynamic polarization curves of blank epoxy, EPPyN, and EPPyNG coatings were performed with a sweep rate of 2 mV/s from the cathodic direction to the anodic direction. The electroactive nature of PPy allows for it to oxidize the metal substrate, which results in the formation of a passive oxide layer at the interface between the PPy and underlying metal substrate [14]. ; resources, W.Z. Polypyrrole nanowires/graphene (PPyNG) nanocomposites as anticorrosive fillers were prepared by in situ polymerization in order to improve the anticorrosion performance of waterborne epoxy coatings. For the EPPyNG2 coatings, the Icorr was lowest than other coatings, which indicated the best anticorrosion performance in all of the studied samples, which corresponded to results of OCP tests. The statements made herein are solely the responsibility of the authors and do not necessarily reflect the opinions of the Sponsor. PPy with one-dimensional nanostructure, such as nanotube [24], nanorod [25], and nanowire [26], are used in various applications including sensors, supercapacitors and battery electrodes [13,27,28]. Learn more Achieving high performance corrosion and wear resistant epoxy coatings via incorporation of noncovalent functionalized graphene. Hao Y., Sani L.A., Ge T., Fang Q. Phytic acid doped polyaniline containing epoxy coatings for corrosion protection of Q235 carbon steel. Grundmeier G., Schmidt W., Stratmann M. Corrosion protection by organic coatings: Electrochemical mechanism and novel methods of investigation. It would not only result in economic losses, but also threaten the safety of industrial production. ; writingreview and editing, J.Z. In the initial immersion, the OCP values exhibited a less negative potential for the Blank, EPPyN, and EPPyNG3 coatings, (0.3 to 0.45 V), but the EPPyNG2 showed a more noble OCP value of around 0.14 V. This relative high potential demonstrated that EPPyNG2 provided excellent protective performance. Chen C., Qiu S., Cui M., Qin S., Yan G., Zhao H., Wang L., Xue Q. Despite these advantages, the aggregation tendency of PPy particles is a major restriction of the processing and application of epoxy/PPy coating. Huang Y., Li H., Wang Z., Zhu M., Pei Z., Xue Q., Huang Y., Zhi C. Nanostructured Polypyrrole as a flexible electrode material of supercapacitor. Nyquist and Bode plots of the coatings: (a,b) blank, (c,d) EPPyN, (e,f) EPPyNG1, (g,h) EPPyN2, and (i,j) EPPyNG3. Among the available ICPs, polypyrrole (PPy) is the most promising polymer due to its easy polymerization, mechanical stability, and better biocompatibility, as well as tunable electrical property [13]. 1Jiangxi Engineering Laboratory of Waterborne Coating, Department of Coatings and Polymeric Materials, Jiangxi Science and Technology Normal University, Nanchang 330013, China; moc.361@8210ygnid (Y.D. The Martin-Gallego M., Verdejo R., Lopez-Manchado M.A., Sangermano M. Epoxy-Graphene UV-cured nanocomposites. Yeh J.-M., Chin C.-P., Chang S. Enhanced corrosion protection coatings prepared from soluble electronically conductive polypyrrole-clay nanocomposite materials. Lei W., He P., Wang Y., Zhang S., Dong F., Liu H. Soft template interfacial growth of novel ultralong polypyrrole nanowires for electrochemical energy storage. Among them, polymer coatings are the most common approach for protecting metal surface from corrosion due to their low cost and high anticorrosion performance. Pretreated graphite was then dispersed in the alkali water (pH = 14) under ultrasonication while using a sonic vibra-cell VC505 processor in 60% power for 1 h, resulting in black graphene slurry. Consequently, it could be concluded that the EPPyNG2 composite coating showed the outstanding corrosion resistance, which was in agreement with the potentiodynamic polarization results. The preparation procedure was as follows. Lei Y., Qiu Z., Liu J., Li D., Tan N., Liu T., Zhang Y., Chang X., Gu Y., Yin Y. was added in batches into concentrated H2SO4 (2 L, 98%) over a period of 45 min. Parameters of Tafel polarization curve for coated Q235 substrates. However, the lower rate of declination was observed in EPPyN, EPPyNG1, EPPyNG2, and EPPyNG3 when compared to the blank epoxy coating after immersion 20 days. The Icorr values of EPPyNG1 and EPPyNG2 coated mild steel considerably decreased when compared with EPPyN. The bare mild steels or mild steels with coatings were sealed while using sealant (paraffin: Rosin = 1:1) and Teflon to leave 1 cm2 area opening to the electrolytic solution. Federal government websites often end in .gov or .mil. The wet powders of pretreated graphite were obtained after filtering and washing. Qiu S., Li W., Zheng W., Zhao H., Wang L. Synergistic Effect of Polypyrrole-Intercalated Graphene for Enhanced Corrosion Protection of Aqueous Coating in 3.5% NaCl Solution. The reaction was allowed to proceed under stirring for 4 h at about 05 C. 51563011 and 2170436). Loading PPy can also enhance the corrosion inhibiting properties of zinc-filled epoxy coatings [16,17]. (a) Rpore and (b) Cc values with immersion in 3.5 wt % NaCl solution. National Library of Medicine 8600 Rockville Pike The Ecorr of the neat epoxy resin coated mild steel was 784 mV. ; funding acquisition, J.Z., F.G. and L.S. Evolution of open circuit potential (OCP) value for the samples with continuous immersion. Although EPPyNG3 possessed longer conjugation length, its excess graphene content might increase the defects due to influence of polypyrrole nanowires, and probably generated micro galvanic corrosion that showed the corrosion-promotion activity [53]. A significantly positive shift Ecorr of 565 mV was obtained for the composites coating with PPyN, confirming that EPPyN engaged in redox reactions, resulting in the formation of metal oxide passive layer [20,42]. Hexion Inc. (Columbus, Ohio, US) provided waterborne epoxy resin (Epikote 6520-WH-53) and curing agent (Epikur 8538-Y-68). Meanwhile, the well-dispersed PPyNG could block the coating pores and decrease the corrosive medias diffusion toward the substrate. Integration with montmorillonite and graphene turns out to be an effective method for avoiding aggregations and improve dispersion of PPy in the polymer matrix, which contributes to a great corrosion protection enhancement [6,19,20]. All of the chemicals were of analytical reagent grade and used without further purification. Conjugation length of PPy was increased with the addition of graphene. However, from Figure 3d, the granular morphology of PPyNG3 was observed. In the anticorrosion field, the ICPs can be used to form a protective barrier layer and release inhibitors in the coating [12]. 37 No. Firstly, the PPy nanowires and PPyNG nanocomposites were completely dispersed in 10 mL of deionized water with a high-speed dispersion and then added into 30 g waterborne epoxy resin. ; writingoriginal draft preparation, J.Z. The radius of capacitive impedance loop in high-frequency domain diminished during the immersion, which implied declined corrosion protective properties for mild steel. Nguyen Thi T., Dinh Thi Mai T., Pham Thi N., Nguyen Thu P., Vu Thi Hai V., Ngo Quang M. Enhanced Anti-Corrosion Protection of Carbon Steel with Silica-Polypyrrole-Dodecyl Sulfate Incorporated into Epoxy Coating. This research was funded by Natural Science Foundation of Jiangxi Education Department (Contract No. For instance, especially, epoxy coatings have attracted many researchers due to their strong adhesion to substrates and excellent mechanical properties. in an ice-water bath. Figure 5 shows the Tafel curves of the as prepared coatings immersion in corrosive solutions. Scanning electron microscopy (SEM) images of the (a) PPyN, (b)PPyNG1, (c)PPyNG2, and (d) PPyNG3. and then repeatedly washed by a large amount of water (46 times) until pH approached 10. The purpose of this paper is to present the results of a two-year long study carried out in order to evaluate the corrosion performance of mild steel bare bars (BB) and epoxy-coated rebar (ECR) in concrete under a simulated harsh environment of chlorides. The electrochemical impedance spectroscopy (EIS) measurements were collected in the frequency range of 100 kHz to 0.01 Hz while using an alternating current signal with the amplitude of 5 mV. In a typical process, 0.31 mL pyrrole monomer and 0.91 g CTAB were added in a mixture of 125 mL 0.2 M hydrochloric acid and graphene-NMP dispersion and stirred for 2 h at ambient temperature, and then cooled to 05 C. Table 1 shows the electrochemical parameters that were obtained from Tafel curves. The broad band at 30003500 cm1 arose from NH stretching vibrations [30]. Models (a) and (b) were fitted with the EIS data of pure epoxy coating and composites coatings, respectively. Zhang L.L., Zhao S., Tian X.N., Zhao X.S. The Fourier transform infrared spectrometer (FTIR) spectra of PPyNG films were collected by a Bruker-Veretex70 spectrometer (Bruker Company, Karlsruhe, Germany) while using KBr pellets. Gu H., Ma C., Gu J., Guo J., Yan X., Huang J., Zhang Q., Guo Z. The dry coating thickness was around 37 m. Open circuit potential (OCP) measurements, Tafel polarization curves, and electrochemical impedance spectroscopy (EIS) using an electrochemical workstation evaluated the anticorrosion properties of the waterborne epoxy/PPyNG coatings (EPPyNG). Electrochemical behaviour of LiMn2O4PPy composite cathodes in the 4-V region. and J.W. The .gov means its official. Before You may be able to access teaching notes by logging in via your Emerald profile. The following are available online at https://www.mdpi.com/2073-4360/11/12/1998/s1, Figure S1: t Water absorption of epoxy/polypyrrole nanowires coatings filled with 0%, 0.3%, 0.5% and 0.7% polypyrrole nanowires., Figure S2: Tafel curves of mild steel with coatings of epoxy/polypyrrole nanowires coatings filled with 0%, 0.3%, 0.5% and 0.7% polypyrrole nanowires in 3.5% sodium chloride solution after 20 days. Results of electrochemical impedance spectroscopy (EIS) for coated Q235 substrates. The effect of polymer morphology on the performance of a corrosion inhibiting polypyrrole/aluminum flake composite pigment. A study on the anticorrosion performance of epoxy nanocomposite coatings containing epoxy-silane treated nano-silica on mild steel substrate. Field emission scanning electron microscope (FESEM) and Fourier transform infrared spectroscopy (FTIR) characterized the morphologies and structures of the synthesized PPyNG. Li J., Xie H., Li Y. However, the coating with excess graphene (EPPyNG3) exhibited lower Ecorr than EPPyNG2, probably because larger fraction of graphene affected the growth of PPy nanowires and induced the defects in PPyNG3 composites [38], which was in agreement with the results of SEM. The Cc of pure epoxy coating continuously increased from 3.1 109 F/cm2 to 1.1 108 F/cm2. The investigated coatings in this study consisted of the epoxy without the addition of filler as well as with the incorporation of PPy nanowires and PPy nanowires/graphene as the functional additives. Study on Enhancement Mechanism of Conductivity Induced by Graphene Oxide for Polypyrrole Nanocomposites. Moreover, the ratio between the peak area of the skeletal band 1478 cm1 and oxidization state sensitive 1558 cm1 band (I1478/I1558) could be used to calculate the conjugation length [35,36]. sharing sensitive information, make sure youre on a federal The https:// ensures that you are connecting to the The PPyN/graphene (PPyNG) nanocomposites were synthesized through in situ polymerization. The isolated graphene nanosheets could also be seen due to increasing concentration of graphene nanosheets. Navarchian A.H., Joulazadeh M., Karimi F. Investigation of corrosion protection performance of epoxy coatings modified by polyaniline/clay nanocomposites on steel surfaces. Liu C., Bi Q., Matthews A. EIS comparison on corrosion performance of PVD TiN and CrN coated mild steel in 0.5 N NaCl aqueous solution. (Department of Chemical Engineering, College of Engineering, Infrastructure durability in harsh climate, https://doi.org/10.1108/IJBPA-12-2018-0099. Ma Z., Chen P., Cheng W., Yan K., Pan L., Shi Y., Yu G. Highly Sensitive, Printable Nanostructured Conductive Polymer Wireless Sensor for Food Spoilage Detection. Many researchers have investigated polymer composites incorporating various functional fillers [5], such as montmorillonite [6], carbon nanotubes [7], graphene [8], and intrinsically conducting polymers (ICPs) [9], to overcome this problem. Shchukin D.G., Zheludkevich M., Yasakau K., Lamaka S., Ferreira M.G.S., Mhwald H. Layer-by-Layer Assembled Nanocontainers for Self-Healing Corrosion Protection. Designing a dual-functional epoxy composite system with self-healing/barrier anti-corrosion performance using graphene oxide nano-scale platforms decorated with zinc doped-conductive polypyrrole nanoparticles with great environmental stability and non-toxicity. The ratio was 0.1304, 0.1328, 0.1427, and 0.1515 for PPy, PPyNG1, PPyNG2, and PPyNG3, respectively, which suggested that the conjugation length increased with further incorporation of the graphene. Kalendov A., Vesel D., Kohl M., Stejskal J. Anticorrosion efficiency of zinc-filled epoxy coatings containing conducting polymers and pigments. All of the electrochemical tests were conducted at room temperature. ; data curation, Y.D. Zhang Y., Shao Y., Zhang T., Meng G., Wang F. High corrosion protection of a polyaniline/organophilic montmorillonite coating for magnesium alloys. The SEM image (Figure 3a) revealed the uniform nanowire structure with an average diameter of about 50 nm and length of several micrometers. Generally, a higher Rpore and lower Cc suggested that a small amount of corrosive media penetrated into the coatings [55]. and H.H. Ding J., Zhao H., Xu B., Zhao X., Su S., Yu H. Superanticorrosive Graphene Nanosheets through Deposition of Boron Nitride Nanodots. government site. Arefinia R., Shojaei A., Shariatpanahi H., Neshati J. Anticorrosion properties of smart coating based on polyaniline nanoparticles/epoxy-ester system. 100 g graphite (1 wt % equiv., 325 mesh) was then added in batches under stirring at 35 C for 2 h. The black flakes were filtered through a 200-mesh sieve and poured into 2 L of ice water after reaction. The graphene slurry was centrifuged at 10,000 rpm for 10 min. For comparison, neat PPy nanowires (PPyN) were fabricated by similar method absence of graphene dispersion. By addition of PPyNG, the Ecorr dramatically increased to 537 mV with 1 wt % graphene and 482 mV with 2 wt % graphene. The blocks are subjected to Southern Exposure testing. The synergistic effect of PPy/graphene greatly enhances the anticorrosion performance of epoxy coating [23]. Williams G., Geary S., McMurray H.N. The potentiodynamic polarization tests were carried out to study the anticorrosion performance of EPPyNG composites coatings. Fabrication of graphene oxide/polypyrrole nanowire composite for high performance supercapacitor electrodes. ), 2Department of Applied Physics, School of Science, East China Jiaotong University, Nanchang 330013, China; moc.621@tpo_gnehcqz. Bethesda, MD 20894, Web Policies An overview of multifunctional epoxy nanocomposites. The bands at 1048 and 1321 cm1 were attributed to CH deformation vibrations and CN stretching vibrations, respectively [32]. ); nc.moc.untsxj@6102oagief (F.G.); nc.moc.untsxj@7240fheh (H.H. The polypyrrole nanowires with about 50 nm in diameter were obtained. The protection efficiency (PE, %) was calculated via Equation (3) [46]: where Rp(bare) and Rp(coated) denote the polarization resistance of bare and coated steel, respectively. Subsequently, 30 wt % H2O2 was added to decompose the insoluble manganese dioxide. Gharibi R., Yousefi M., Yeganeh H. Synthesis, characterization and assessment of poly(urethane-co-pyrrole)s derived from castor oil as anticorrosion coatings for stainless steel. Kumar A., Ghosh P.K., Yadav K.L., Kumar K. Thermo-mechanical and anti-corrosive properties of MWCNT/epoxy nanocomposite fabricated by innovative dispersion technique. The impedance modulus at low frequency (|Z|0.01Hz) was used as a semi-quantitative standard of coatings protective performance for the Bode patterns [49], as summarized in Table 2. Figure 3 shows the morphologies of pure PPyN and the PPyNG nanocomposites. Investigation, Y.D. In the case of protection efficiency, the highest PE value from EPPyNG2 (99.9%) described that PPyNG2 loading in the epoxy coating can provide superior inhibition corrosion performance. Fourier transform infrared spectroscopy (FTIR) spectrum of the PPyN, PPyNG1, PPyNG2, and PPyNG3. The electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR) and Tafel plot are performed to measure the polarization resistance and corrosion current densities of these rebars. Zhong W., Liu S., Chen X., Wang Y., Yang W. High-Yield Synthesis of Superhydrophilic Polypyrrole Nanowire Networks. The electrochemical measurements were carried out to characterize the anticorrosive properties of blank epoxy, EPPyN and EPPyNG coatings using a CHI 660E electrochemical workstation (Chinstruments Co., Ltd., Shanghai, China) that was equipped with a conventional three-electrode cell with a saturated calomel electrode (SCE) as reference, a platinum counter electrode with 1 cm2 area, and a working electrode. In this study, the PPy nanowires were synthesized while using CTAB as soft template, and combined with graphene nanosheets by in situ oxidation polymerization. Gnana kumar G., Kirubaharan C.J., Udhayakumar S., Ramachandran K., Karthikeyan C., Renganathan R., Nahm K.S. Dong L., Chen Z., Zhao X., Ma J., Lin S., Li M., Bao Y., Chu L., Leng K., Lu H., et al. Therefore, the EPPyNG3 (1.6 106 cm2) displayed worse anticorrosive property when compared with EPPyNG2. The resulting coating was obtained after curing for 48 h at room temperature. Kalendov A., Vesel D., Kohl M., Stejskal J. Ma G., Wen Z., Wang Q., Shen C., Peng P., Jin J., Wu X. Contri G., Barra G.M.O., Ramoa S.D.A.S., Merlini C., Ecco L.G., Souza F.S., Spinelli A. Epoxy coating based on montmorillonite-polypyrrole: Electrical properties and prospective application on corrosion protection of steel. will also be available for a limited time. For comparison, the neat epoxy coating was also prepared through a similar method without loadings, which was named Blank. Potentiodynamic polarization plots, impedance measurements, and fitted Rpore and Cc were used to study the anticorrosion performance of the coatings. When comparing to the FTIR spectra of PPyN, all peaks had also appeared in the PPyNG nanocomposites. Zhong J., Gao S., Xue G., Wang B. For neat epoxy coating (Figure 6a), the Nyquist plots displayed two capacitive arcs after 15 days immersion, which indicated that the electrolyte was in contact with the metal surface. A precooled aqueous solution of 10 mL 0.2 M HCl containing 4 mmol APS was added into above solution in batches. The corrosion current density (Icorr), corrosion potential (Ecorr), anodic Tafel slope (ba), and cathodic Tafel slope (bc) were estimated from the Tafel extrapolation of anodic and cathodic lines to the point of intersection. Similar phenomenon was observed in others research [38]. Yeh T.-C., Huang T.-C., Huang H.-Y., Huang Y.-P., Cai Y.-T., Lin S.-T., Wei Y., Yeh J.-M. Electrochemical investigations on anticorrosive and electrochromic properties of electroactive polyurea. Polypyrrole Nanowire Actuators. Smart release corrosion inhibitor pigments based on organic ion-exchange resins. The Rpore of coatings with EPPyN, EPPyNG1, and EPPyNG3 decreased to some extent, while the EPPyNG2 coating always maintained much higher values. and J.Z. In this paper, the PPy nanowires (PPyN) were prepared by a soft template method. The characteristic polypyrrole peaks located at 1558 and 1478 cm1 were due to the asymmetric and symmetric ring-stretching modes, respectively [31]. The new PMC design is here! Figure 4 shows the evolution of open circuit potential (OCP) for coatings on mild steels in a 3.5% NaCl corrosive solution. After two years of immersion in 3.89 percent NaCl solution, the mild steel BB were severely corroded and a considerable weight loss was observed, whereas under heavy chloride attack, ECR showed no deterioration of epoxy coating and neither any corrosion of underlying steel. The impedance modulus dramatically decreased after 15 days and then progressively reduced with the increasing immersion time for all studied coatings, probably owing to the penetration of water and movement of ions through the coatings [50]. Figure S4. Optical microscopic images of epoxy/polypyrrole nanowires coatings filled with 0%, 0.3%, 0.5% and 0.7% polypyrrole nanowires. Wei H., Ding D., Wei S., Guo Z. Anticorrosive conductive polyurethane multiwalled carbon nanotube nanocomposites. Tken T., Arslan G., Yazc B., Erbil M. The corrosion protection of mild steel by polypyrrole/polyphenol multilayer coating. official website and that any information you provide is encrypted Lee J.I., Cho S.H., Park S.-M., Kim J.K., Kim J.K., Yu J.-W., Kim Y.C., Russell T.P. Figure S3 shows the Tafel curve of bare steel. Moreover, ZSimpWin software further fitted the EIS measurements while using the equivalent electric circuits, as shown in Figure 7. Revisiting graphenepolymer nanocomposite for enhancing anticorrosion performance: A new insight into interface chemistry and diffusion model. A non-dispersion strategy for large-scale production of ultra-high concentration graphene slurries in water. The EPPyNG3 coating also exhibited lower Rpore and higher Cc than EPPyNG2, which confirmed that excess graphene induced the defect coating and reduced corrosion protection. Finally, the product was dried in a vacuum oven at 40 C for 24 h. The weight ratio of pyrrole to graphene varied as 99:1, 98:2, 97:3, and the resulting black composites were named as PPyNG1, PPyNG2, and PPyNG3, respectively. Effect of Conducting Polyaniline/Graphene Nanosheet Content on the Corrosion Behavior of Zinc-Rich Epoxy Primers in 3.5% NaCl Solution. ; supervision, Z.C. The |Z|0.01Hz of EPPyNG2 (Figure 6h), in the early immersion time, was up to 7.7 106 cm2, higher than those of neat epoxy (1.0 106 cm2). Therefore, PPy nanowires/graphene nanocomposite would be used as a promising anticorrosion pigment. The studied nanocomposite coating possessed superior corrosion protection performance when the graphene content of the filler was 2 wt %. Effect of surface treatment of pigment particles with polypyrrole and polyaniline phosphate on their corrosion inhibiting properties in organic coatings. Advanced corrosion protection effect of EPPyNG coating compared to EPPyN might arose from dispersing graphene nanosheets to increase the tortuosity of the diffusion pathway of H2O, O2, and Cl [43]. Ammonium persulfate (APS), potassium permanganate (KMnO4), sulfuric acid (H2SO4), hydrogen peroxide (H2O2), N-methyl pyrrolidone (NMP), Sodium chloride (NaCl), and cetyltrimethylammonium bromide (CTAB) were obtained from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). The incorporation of PPy nanowires/graphene into waterborne epoxy on mild steel substrate was performed. The passivation effect of the PPy nanowires contributed to the effective inhibiting corrosive effect. However, for the EPPyNG2 coating, the radius of capacitive impedance arc at low frequency region in the immersion seven days suddenly expanded beyond that of three days, which suggested that PPy might react to passivate the metal substrate [23]. The 0.5% additive based on the total formulation was finally determined. The calculated vcorr value of 8.9 105 mm/year for EPPyNG2 was about 100 times lower than that for blank epoxy coating. The corrosion rate, vcorr (mm/year) was obtained from Equation (1) [44]: where the molecular weight (M) is 55.85 g/mol for Q235, Icorr is the corrosion current density (A/cm2), n is 2 for the oxidation of steel, and the density () is 7.85 g/cm3 for Q235, 3270 is a constant. The monitoring of OCP allowed for the assessment of the inclination of corrosion [39].
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