Article pubs.acs.org/IECR
Ceria/Acrylic Polymer Microgel Composite: Synthesis, Characterization, and Anticorrosion Application for API 5L X70 Substrate in Chloride-Enriched Medium Ubong Eduok,* Ericmoore Jossou, Ahmed Tiamiyu, Joseph Omale, and Jerzy Szpunar Department of Mechanical Engineering, College of Engineering, University of Saskatchewan, 57 Campus Drive, Saskatoon, S7N 5A9, Saskatchewan Canada S Supporting Information *
ABSTRACT: Ceria/poly(acrylic acid) microgel composite with anticorrosion potential has been synthesized via an in situ polymerization method. This polymer composite matrix has demonstrated significant reduction in API 5L X70 steel corrosion in 0.5 M HCl. In-depth studies of the anticorrosion properties of this microgel have been conducted by corrosion electrochemistry, and its adsorption on steel altered both anodic dissolution and cathodic hydrogen evolution in the acid medium. Increment of CeO2 content within the PAA/CeO2 hybrid composite improved its surface protective performance; 1 and 5 g of CeO2 within the composite recorded 82 and 90% inhibition efficiency, respectively, compared to PAA alone (62%), at equal concentration. PAA formed a protective polymeric film on steel upon molecular adsorption, but in the presence of the PAA/CeO2, the metal surface protection was enhanced by the adhesion of compact hybrid films. PAA/CeO2 microgel composite may have a future as an anticorrosive paint component for metal surface treatments.
1. INTRODUCTION The gradual degradation of materials deployed in transport (e.g., steel pipelines) and storage facilities (e.g., steel-based sewage plants) is directly linked with corrosion. Wearing of the inner and outer walls of pipelines may lead to corrosion-related spillages, serious economic losses, and negative impact on the environment.1 In line with the effects of corrosion on flow assurance, most multinationals are investing more on mitigation strategies and methods against pipeline corrosion menace.2 Techniques not limited to the use of surface coatings have been widely reported, but the application of industrial corrosion inhibitor formulations on metal surfaces is one of the most applicable anticorrosion tools since it involves the formation of physical barriers against the migration of corrosion species at metal/solution interfaces.3 The use of film-forming polymer systems is effective against corrosion within the inner walls of ferrous-based transport pipelines. According to Olverá Martinez et al.,3 though the effectiveness of chemical compounds (like polymers) deployed as corrosion inhibitors depends on compositional and shear-related factors associated with the constant fluidic motions within the pipes, these compounds function widely by adsorbing and blocking metal surfaces from corrosive species, hence reducing corrosion rates. To control internal corrosion in closed systems, these chemicals are injected within mixtures of anticorrosive agents into pipelines during transportation of gas and crudes.3 Chemicals of this class are also widely used to suppress rates of © 2017 American Chemical Society
degradation processes related to pickling, cleaning, and descaling during precleaning operations of industrial metals.4−7 Organic compounds like high molecular weight polymers with heteroatoms (e.g., nitrogen, sulfur, and oxygen) have been considered better corrosion inhibitors, since these atoms serve as anchor sites on metal surfaces upon adsorption in the liquid phase. The protective films formed by these polymers are known to distort cathodic or anodic reactions at the metal surfaces as they adsorb at various active sites.8,9 The use of various forms of polymers, including composites and blends, is advantageous since their spontaneous adsorption on metal surfaces results in the displacement of a sufficient number of water molecules to initiate corrosion inhibition. This unique surface property of polymers is also promoted by the presence of multiple bonding sites within their C−C macromolecular chains, which makes subsequent desorption almost irreversible.8,10 Compared to their monomer analogues, polymers possess greater coverage on surfaces due to their unique molecular sizes; hence, they are better corrosion inhibitors. Over the years, the use of polymers like poly(acrylic acid) (PAA) and its derivatives has attracted much attention toward metal protection in various media: Al in bicarbonate buffer,8 Received: Revised: Accepted: Published: 5586
February April 13, April 25, April 25,
19, 2017 2017 2017 2017 DOI: 10.1021/acs.iecr.7b00714 Ind. Eng. Chem. Res. 2017, 56, 5586−5597
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Industrial & Engineering Chemistry Research Scheme 1. Proposed Formation Scheme for PAA/CeO2 Microgel Composite from Acrylic Acid Monomer (AA)a
a
The globulelike macromolecular network structure of the composite is modelled from its SEM morphology.
copper and brass pigments in desalinated water at pH 8.5−10,11 bulk nanocrystalline ingot iron in sulfuric acid,12 pure iron (99.99% Fe) in sulfuric acid,13 Au and Au/Au2O3 interfaces in neutral medium,14 natural graphite negative electrode in Li ion battery solutions,15 and mild steel in chloride solution.16 In all, corrosion inhibition by PAA has been ascribed to the adsorption and subsequent formation of spatially ordered surface films on metal surfaces, thereby providing uniform coverage against corrosion. Umoren et al.9 have illustrated its mechanism of corrosion inhibition by in situ atomic force microscopy. These authors discovered a uniform PAA film coverage on the surface of iron substrate at a range of potential below and above the potential of zero charge (pzc) while also demonstrating a synergistic protective action in the presence of KI within an acidic corrosive medium. PAA is a green polymer, easy to synthesize from cheap sources, and a benign macromolecular compound that readily adsorbs on metals via the O-heteroatom attached to its surface-active acrylic acid functional group.12 PAA adsorption of metal surfaces is widely successful by virtue of interaction of its π/unshared electron pairs with the empty d-orbitals of Fe (on ferrous metals) to form coordinate bonds.12,13 However, the use of pure PAA derivatives as corrosion inhibitors for metal substrates is limited by the structural flexibility and solution properties within the polymer matrices. Since most of them are colloidal gels in solutions, they could be significantly modified to form organic− inorganic hybrid composites with novel and tunable physical and chemical properties not limited to thermomechanical, thermoelectrical conductivity, and solution stability.17 Recent applications of some of these organic−inorganic hybrid composites have centered on the modification of their matrices using inorganic metal nano- and microscaled particles via chemical methods, featuring new synthetic routes.17−19 Zhu et al.20 have reported the in situ polymerization of acrylic acid (AA) on flaky Al particles; the resultant PAA/Al composite was observed to be resistant against corrosion. Its corrosion inhibition efficiency was also observed to be dependent on the initial amount of the AA monomer in the reaction mixture. Wang et al.21 have also investigated the design and synthesis of PAA/nanotubes and metal oxide composite films for protective
purposes via an electrophoretic deposition technique. The gradual adsorption of PAA molecules in the presence of these inorganic metal particles was observed to alter the suspension stability and film thickness. Particulate cerium (Ce) pigments are an outstanding class of inorganic metal compounds with anticorrosion potentials capable of being used for the fabrication of organic−inorganic hybrid composites with polymers. Since all toxic trivalent (Cr3+) and hexavalent (Cr6+) chromate compounds have been banned from industrial anticorrosive formulations,22 in a view of this legislative order, the need to replace chromium compounds with better and safer alternatives has necessitated the deployment of various CeO2 pigments.17 CeO2 pigments are a cheap class of rare earth compounds that act as active site blockers for metal substrates. The synergistic corrosion inhibitive effects of Ce compounds with polymers has also been mentioned in the literature.23−25 Unfortunately, there are no available reports on anticorrosive composites synthesized from PAA and CeO2 pigments being utilized in metal surface treatments or deployed within corrosion inhibitor formulations for ferrous alloys in acid medium. In this work, we designed an in situ polymerization route for acrylic acid monomer in the presence of CeO2 pigments using a combined sodium bisulfite/ ammonium persulfate redox initiator system; the new PAA/ CeO2 hybrid microgel composite product formed is characterized accordingly and utilized as a corrosion retarder for steel. This study also presents in-depth studies of the anticorrosion properties of the PAA/CeO2 hybrid composite on API 5L X70 steel in 0.5 M HCl medium using various electrochemical and surface analytical techniques. The effect of CeO2 content on the barrier properties of this polymeric hybrid composite adsorbed on steel upon exposure to corrosive medium is also investigated to correlate compositional changes (within the film) with corrosion protective behaviors of composite content. The morphological and interfacial features of the metallic substrates, during and after polymer film removal, are vividly evaluated by means of scanning electron microscopy (SEM) in the presence of the microgel composite. PAA derivatives are corrosion inhibitors as well as antiflocculants/antiscalant agents due to their unique solution chemistries with dissolved salts in 5587
DOI: 10.1021/acs.iecr.7b00714 Ind. Eng. Chem. Res. 2017, 56, 5586−5597
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monitored at intervals from the onset of the reaction until 1 h. The polymerization reaction was accompanied by increased viscosity of the medium; solution thickening within the reaction medium signifies PAA formation.28 At the end of the test, Raman measurement was also conducted on both CeO2modified and unmodified PAA powdery composites with 16 scans on a 514 nm edge laser using an extended grating scan type on a Renishaw Raman InVia reflex microscope (Renishaw). In the quest to further analyze the structures of as-synthesized composites, X-ray diffraction (XRD) analyses was conducted on both microgel composite and the PAA reference using a Bruker D8 Discover XRD diffractometer operating with Cr Kα radiation from 10° to 110°. Diffraction data were fitted using the Philips X′Pert High Score software. Thermogravimetric analysis was also conducted on both systems under Ar atmosphere up to 800 °C at varying heating rates. The morphologies of PAA and PAA/CeO2 composite powders were observed using SEM (Hitachi SU6600 scanning electron microscope) prior to the corrosion tests. SEM analyses were conducted at 1 kV acceleration voltage since the dispersed amorphous polymer composite powders on the sample holder were not coated with any conductive layer; surface analysis at this acceleration voltage aided direct visualization without external influences of any adsorbed layer. 2.4. Corrosion Tests. Electrochemical corrosion tests were conducted using a ParaCell electrochemical cell kit connected to a potentiostat/galvanostat/ZRA (Interface 1000, Gamry Instruments) bearing Ag/AgCl (sat. KCl) and a graphite rod as reference and counter electrodes, respectively. The series of corrosion tests carried out in this work aimed at assessing the anticorrosion properties of both CeO2-modified and unmodified PAA microgels on X70 substrates (working electrodes) in 0.5 M HCl electrolyte solution using potentiodynamic polarization and electrochemical impedance spectroscopic (EIS) techniques. An exposure area of 1 cm2 was defined on the X70 working electrodes with the aid of PortHoles electrochemical sample mask/tape and maintained throughout the tests. For the Tafel polarization experiments, a potential sweep in the range ±0.25 V relative to Eoc was applied with a 1 mV s−1 sweep rate. Impedance measurements were also conducted on the same X70 coupon with a minute amplitude perturbation of 10 mV over a frequency range of 0.1 to 105 Hz. The EChem Analyst software (Garmy Instruments) was then deployed to evaluate appropriate parameters by fitting respective Tafel and impedance curves of applicable microgel composite systems. The morphologies of the metal surfaces exposed to the corrosive acid electrolyte containing different concentrations of PAA/CeO2 composites were investigated prior to and after 72 h. It is also worthy of note that the chosen concentrations of PAA/1.0 g CeO2 composites (100−500 ppm) were comparatively studied with 500 ppm PAA (without CeO2), while the corrosion-inhibiting properties of these PAA/ CeO2 composites on X70 substrate with 2.5 and 5.0 g of CeO2 particles were also evaluated in order to probe the corrosion protective behaviors of the organic−inorganic hybrid composites at higher CeO2 particulate concentrations. Evidence of protective film formation on the metal surfaces was revealed using SEM, while quantitative element-specific compositional information were obtained using an energy dispersive X-ray (EDX) analyzer.
aqueous systems. Some are also used as ion exchange resins and adhesives and as thickeners, dispersants, or emulsifiers in paints and cosmetics.26,27
2. EXPERIMENTAL PROCEDURES 2.1. Materials and Material Pretreatment. All the reagents deployed within this study were used directly as purchased without further purification. Acrylic acid (AA) monomer, nanopowder cerium(IV) oxide ( PAA/2.5 g CeO2 > PAA/1.0 g CeO2 > PAA. The Nyquist curves as well as their respective EIS parameters showing the effect of increasing concentrations of CeO2 within the conjugate polymeric composite are also represented in Figure 7b and Table 1. Wider Nyquist semicircle loops at higher CeO2 concentrations denote superior protective performance against steel corrosion due to the formation of stronger organic−inorganic hybrid surface film clusters.17,39 The magnitudes of Rct for the adsorbed film with 1, 2.5, and 5 g of CeO2 pigments are 300.9, 337.6, and 484.1 Ω cm2, respectively, as compared to 210.7 Ω cm2 recorded at the same PAA concentration (500 ppm). A decrease in CPE values with the increasing CeO2 content within the micorgel composite is also indicative of corrosion protection. The magnitudes of Zphz from the phase angle curves are more negative for more resistive systems due to the presence of CeO2, as revealed in Figure S1 (SI). Increment in CeO2 within the composite also contributed to the observed increase in Zmod between 0.1 and 10 Hz (see Figure S1c,d, SI). The values of IE% obtained from this technique follow a similar trend as the values obtained from the dc test for the same metal substrate and are in good agreement. 3.4.3. Surface Morphology. The corrosion electrochemical results of API 5L X70 steel were correlated with the microstructural morphologies of each metal substrate exposed to the acidified inhibitor systems to attempt an in-depth understanding of surface protection by means of electron microscopy. Upon 72 h exposure of prepolished and clean X70 substrates exposed to 0.5 M HCl solutions containing the assynthesized PAA and PAA/CeO2 composites, their surfaces were analyzed for evidence of corrosion inhibition, as illustrated in Figure 8. According to the presented SEM micrographs, corrosion inhibition by these microgel conjugates is accompanied by the formation of protective polymeric films at the metal surface, initiated by associated mass and charge transfer actions.44,45 The presence of these insulating films are observed for PAA and PAA/CeO2 (1.0 and 5.0 g of CeO2) systems,
inorganic CeO2 particles compared to PAA alone. This unique inhibition property of the PAA/CeO2 composites has been attributed to molecular adsorption of these polymer conjugates at metal surfaces and the subsequent retardation of anodic dissolution within the acid electrolyte. However, since most cerium compounds have been widely reported 48−51 to precipitate as insoluble cerium hydroxide capable of blocking diffusion pathways at the metal/solution interface, it was pertinent to test the effect of CeO2 content on the corrosion efficiency of the hybrid microgel. In this test, the additional two sets of microgels synthesized from 2.5 and 5.0 g of CeO2 pigments within the same PAA polymer matrix were also comparatively tested for their anticorrosive properties for X70 in 0.5 M HCl. The Tafel curves and the dc parameters for X70 steel substrates in 0.5 M HCl corrosive medium containing different concentrations of CeO2 within the PAA/CeO2 hybrid composites relative to PAA are displayed in Figure 7a and Table 1, respectively. As revealed, the magnitudes of jcorr for X70 substrate decrease with CeO2 content, and this is indicative of an improved corrosion resistance in 0.5 M HCl acid. The observed corrosion-protective behaviors of the organic− inorganic hybrid composites at higher CeO2 particulate concentrations could have been due to the formation of stable
Figure 7. (a) Tafel and (b) Nyquist curves for X70 steel substrates in 0.5 M HCl corrosive medium containing PAA/CeO2 composite with varying concentrations of CeO2 compared to 500 ppm PAA at room temperature. 5593
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Figure 8. SEM micrographs of X70 surfaces exposed to 0.5 M HCl medium modified with (a) 500 ppm PAA, (b) 500 ppm PAA/1.0 g CeO2, and (c) 500 ppm PAA/5.0 g CeO2, respectively. (d) Corresponding Ce elemental map of each surface.
Figure 9. SEM images of precleaned X70 surfaces (a) before and (b) after exposure within the corrosive medium. X70 surfaces upon removal of adhering PAA/CeO2 composite film/corrosion product aggregates after 72 h exposure to 0.5 M HCl containing (c) 500 ppm PAA, (d) 500 ppm PAA/1.0 g CeO2, and (e) 500 ppm PAA/5.0 g CeO2 at room temperature.
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Scheme 2. A Proposed Corrosion Inhibition Mechanism by the Synthesized PAA/CeO2 Composite Adsorbed on X70 Substrate in 0.5 M HCl Corrosive Medium at Room Temperaturea
a
The corrosion of X70 is observed to reduce to a great extent in the presence of the polymer/CeO2 aggregate. The enhanced surface protective potential of this PAA/CeO2 composite could be linked with its molecular adsorption at the X70/HCl interface and subsequent formation of multiple layers of insulating PAA/CeO2 composite, in turn, reducing the percolation of corrosive ions toward the metal.
respectively, being the first line of defense against chlorideinduced corrosion attack at the metal/solution interface. It is noteworthy to mention that the observed surface film degradation is due to the action of heat after hot-air treatment prior to SEM imaging. Polymer film degradation appears in the form of surface fissures/cracks (a−c). Within the composites, CeO2 nanopigments appear to serve as an anchor within the microstructure of the PAA film; hence, the reduced crack formation for the PAA/5.0 g CeO2 film on X70 (c) compared to others; this inhibitor matrix is also observed to possess the most Ce content (25%), as revealed by the elemental map in Figure 8d. After this round of studies, these metal surfaces were also passed through a mild acid pickling scrub in order to remove the adhering protective film and corrosion products using 10% HNO3. This later test was designed to reveal possible evidence of underfilm pitting in comparison to the bare X70 substrate exposed to the same acid medium without the polymeric inhibitors. Figure 9 represents the SEM images of precleaned X70 surfaces upon removal of adhering PAA composite film aggregates from the metal surfaces after 72 h exposure to 0.5 M HCl containing (b) 500 ppm PAA, (c) 500 ppm PAA/1.0 g CeO2 and (d) 500 ppm PAA/5.0 g CeO2 at room temperature compared to the bare/unimmersed metal surface (a). The surface morphology of the X70 surface reveals the presence of slanted polishing marks prior to corrosion (Figure 9a). After exposure to 0.5 M HCl, without the polymers, the metal surface is pitted by chloride ion attack (Figure 9b). Subcrevices and detached grains are revealed within the pits as well as adhering corroded ferrous aggregates sparsely distributed within the pit depth (white arrows/ markings). Mild corrosion is revealed as uneven protrusions from X70 substrates exposed to 0.5 M HCl containing 500 ppm PAA (c), 500 ppm PAA/1.0 g CeO2 (d), and 500 ppm PAA/ 5.0 g CeO2 (e). The metal surfaces with the superior inhibitor systems are less corroded, without distinct pits or damage since the adhering protective polymeric films had impeded metallic
dissolution of these surfaces. It is also evident that the presence of the inorganic CeO2 particles within the composite has enhanced the anticorrosion potency of PAA polymer against X70 metal dissolution in 0.5 M HCl. 3.5. Proposed Corrosion Inhibition Mechanism by PAA/CeO2 Hybrid Microgel Composite. In corrosive media, the electrolyte ionic/molecular diffusion rate toward the metal surface is reduced when there is an established mechanical interlocking and/or physical barrier impeding these motions, usually an interfacial oxide layer.52 However, surface adhesion at the metal/solution interfaces could be destroyed depending on the type and concentration of inherent corrosive species. API 5L X70 is susceptible to pitting damage in chloride-enriched media independent of its alloying elements; extended exposure of metal surface could lead to severe material loss (Figure 9b). In the presence of corrosion inhibitors, like the modified polymer composite used in this study, the rate of anodic dissolution is reduced to a great extent and corrosion is delayed. Scheme 2 illustrates a proposed corrosion inhibition mechanism for the synthesized PAA/CeO2 composite adsorbed on X70 substrate in 0.5 M HCl corrosive medium. PAA alone must have inhibited the corrosion of the metal substrate by molecular adsorption, but in the presence of the PAA/CeO2 microgel composite, adsorption must have been followed by subsequent formation of multiple layers of insulating hybrid PAA/CeO2 composite, in turn, reducing the percolation of corrosive ions toward the metal.17,39 Increment in CeO2 content within the microgel also facilitated the formation of oxide/hydroxides of Ce within the protective film, in turn reducing chloride-induced attack, hence improving corrosion inhibition.48,49 As illustrated, the uniformly distributed globular PAA/CeO2 composites are water-soluble and have improved anticorrosion properties at higher CeO2 concentrations. The enhanced metal surface coverage due to the presence of the polymer must have also been facilitated by a secondary reaction, leading to the formation of a cerium−iron5595
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type complex at the metal/solution interface.17,25 In a recent study, Hu et al.53 have opined that inherent inhibiting effects in the presence of Ce compounds at metal/solution interfaces are determined by the type of insoluble precipitates formed. These compounds gradually grow into oxide/hydroxide barriers capable of impeding ionic current flow (eqs 5−7). Ce+3 + 3OH− → Ce(OH)3 ↓
(5)
4Ce+3 + O2 + 4OH− + 2H 2O → 4Ce(OH)2+2
(6)
Ce(OH)2+2 + 2OH− → CeO2 ↓ + 2H 2O
(7)
ASSOCIATED CONTENT
* Supporting Information S
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.7b00714. Bode impedance and phase angle plots for X70 steel substrate exposed to the corrosive medium containing PAA/CeO2 composites at room temperature (PDF)
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REFERENCES
(1) Feng, Y.; Cheng, Y. F. An intelligent coating doped with inhibitor-encapsulated nanocontainers for corrosion protection of pipeline steel. Chem. Eng. J. 2017, 315, 537−551. (2) Obanijesu, E. O.; Gubner, R.; Barifcani, A.; Pareek, V.; Tade, M. O. The influence of corrosion inhibitors on hydrate formation temperature along the subsea natural gas pipelines. J. Pet. Sci. Eng. 2014, 120, 239−252. (3) Olvera-Martínez, M. E.; Mendoza-Flores, J.; Genesca, J. CO2 corrosion control in steel pipelines. Influence of turbulent flow on the performance of corrosion inhibitors. J. Loss Prev. Process Ind. 2015, 35, 19−28. (4) Quraishi, M. A.; Sardar, R. Aromatic triazoles as corrosion inhibitors for mild steel in acidic environments. Corrosion 2002, 58, 748−755. (5) Soror, T. Y.; El Dahan, H. A.; Ammer, N. G. E. Corrosion inhibition of carbon steel in hot hydrochloric acid solutions. J. Mater. Sci. Technol. 1999, 15, 559−562. (6) Dhawan, S. K.; Trivedi, D. C. Synthesis and properties of polyaniline obtained using sulfamic acid. J. Appl. Electrochem. 1992, 22, 563−570. (7) Ali, S. A.; Saeed, M. T.; Rahman, S. U. The isoxazolidines: a new class of corrosion inhibitors of mild steel in acidic medium. Corros. Sci. 2003, 45, 253−266. (8) Amin, M. A.; Abd EI-Rehim, S. S.; El-Sherbini, E. E. F.; Hazzazi, O. A.; Abbas, M. N. Polyacrylic acid as a corrosion inhibitor for aluminium in weakly alkaline solutions. Part I: Weight loss, polarization, impedance EFM and EDX studies. Corros. Sci. 2009, 51, 658−667. (9) Umoren, S. A.; Pan, C.; Li, Y.; Wang, F. H. Elucidation of mechanism of corrosion inhibition by polyacrylic acid and synergistic action with iodide ions by in-situ AFM. J. Adhes. Sci. Technol. 2014, 28, 31−37. (10) Geethanjali, R.; Sabirneeza, A. A. F.; Subhashini, S. WaterSoluble and Biodegradable Pectin-Grafted Polyacrylamide and PectinGrafted Polyacrylic Acid: Electrochemical Investigation of CorrosionInhibition Behaviour on Mild Steel in 3.5% NaCl Media. Indian J. Mater. Sci. 2014, 2014, 356075. (11) Müller, B.; Triantafillidis, D. Polymeric corrosion inhibitors for copper and brass pigments. J. Appl. Polym. Sci. 2001, 80, 475−483. (12) Umoren, S. A.; Li, Y.; Wang, F. H. Influence of iron microstructure on the performance of polyacrylic acid as corrosion inhibitor in sulfuric acid solution. Corros. Sci. 2011, 53, 1778−1785. (13) Umoren, S. A.; Li, Y.; Wang, F. H. Synergistic effect of iodide ion and polyacrylic acid on corrosion inhibition of iron in H2SO4 investigated by electrochemical techniques. Corros. Sci. 2010, 52, 2422−2429. (14) Grchev, T.; Cvetkovska, M.; Schultze, J. W. The electrochemical testing of polyacrylic acid and its derivatives as inhibitors of corrosion. Corros. Sci. 1991, 32, 103−112. (15) Lee, J. H.; Paik, U.; Hackley, V. A.; Choi, Y. M. Effect of poly(acrylic acid) on adhesion strength and electrochemical performance of natural graphite negative electrode for lithium-ion batteries. J. Power Sources 2006, 161, 612−616. (16) Dharmalingam, V.; Sahayaraj, P. A.; Amalraj, A. J.; Prema, A. A. Poly(acrylic acid) and Potassium Sodium Tartrate as Effective Corrosion Inhibitors for Mild Steel in Aqueous Environment. J. Adv. Electrochem. 2016, 2, 37−41. (17) Sasikumar, Y.; Kumar, A. M.; Gasem, Z. M.; Ebenso, E. E. Hybrid nanocomposite from aniline and CeO2 nanoparticles: Surface protective performance on mild steel in acidic environment. Appl. Surf. Sci. 2015, 330, 207−215. (18) He, D.; Zeng, C.; Xu, C.; Cheng, N.; Li, H.; Mu, S.; Pan, M. Polyaniline-functionalized carbon nanotube supported platinum catalysts. Langmuir 2011, 27, 5582−5588. (19) Kumar, R.; Ansari, M. O.; Barakat, M. A. DBSA doped polyaniline/multi-walled carbon nanotubes composite for high efficiency removal of Cr (VI) from aqueous solution. Chem. Eng. J. 2013, 228, 748−755.
4. CONCLUSIONS Water-soluble and anticorrosive PAA/CeO2 microgel composite has been synthesized via an in situ polymerization method for steel. Judging from the potentiodynamic polarization experiments, PAA/CeO2 microgel is a mixed-type inhibitor system; its adsorption on API 5L X70 affected both anodic dissolution and cathodic hydrogen evolution in 0.5 M HCl without altering the acid-induced corrosion mechanism of the metal substrate. The adsorbed PAA is observed to shield the metal surface against pitting, while corrosion inhibition is enhanced in the presence of the PAA/CeO2 microgel composite by virtue of dense hybrid inhibitor film coverage at the metal surface. SEM/EDX has revealed evidence of polymer-type films on X70 with different CeO2 content. Enhanced metal surface protection has also been established for the PAA/CeO2 composite with more CeO2 content; up to 90% protection efficiency is recorded for 5 g of CeO2. Increment in CeO2 content within the microgel composite facilitated the formation of passive oxide/hydroxides of Ce within the adhering protective film, in turn reducing chloride-induced attack, hence improving corrosion protection. On the basis of these results, PAA/CeO2 composite has demonstrated promising potential as an effective corrosion inhibitor for X70 in acidic medium.
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AUTHOR INFORMATION
Corresponding Author
*Tel: +1 (306) 966 7752. Fax: +1 (306) 966 5427. E-mail:
[email protected] or
[email protected]. ORCID
Ubong Eduok: 0000-0002-4476-4841 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS Authors wish to acknowledge the financial support/research grant from The Canada Research Chairs Program; The Saskatchewan Structural Sciences Centre (SSSC) is also acknowledged for providing some of the facilities for this research. 5596
DOI: 10.1021/acs.iecr.7b00714 Ind. Eng. Chem. Res. 2017, 56, 5586−5597
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Industrial & Engineering Chemistry Research (20) Zhu, H.; Chen, Z.; Sheng, Y.; Thi, T. T. L. Flaky polyacrylic acid/aluminium composite particles prepared using in-situ polymerization. Dyes Pigm. 2010, 86, 155−160. (21) Wang, Y.; Deen, I.; Zhitomirsky, I. Electrophoretic deposition of polyacrylic acid and composite films containing nanotubes and oxide particles. J. Colloid Interface Sci. 2011, 362, 367−374. (22) Schem, M.; Schmidt, T.; Gerwann, J.; Wittmar, M.; Veith, M.; Thompson, G. E.; Molchan, I. S.; Hashimoto, T.; Skeldon, P.; Phani, A. R.; Santucci, S.; Zheludkevich, M. L. CeO2-filled sol−gel coatings for corrosion protection of AA2024-T3 aluminium alloy. Corros. Sci. 2009, 51, 2304−2315. (23) Jeyaprabha, C.; Sathiyanarayanan, S.; Venkatachari, G. Effect of cerium ions on corrosion inhibition of PANI for iron in 0.5 M H2SO4. Appl. Surf. Sci. 2006, 253, 432−438. (24) Abd El-Lateef, H. M. Synergistic effect of polyethylene glycols and rare earth Ce4+ on the corrosion inhibition of carbon steel in sulfuric acid solution: electrochemical, computational, and surface morphology studies. Res. Chem. Intermed. 2016, 42, 3219−3240. (25) Umoren, S. A.; Madhankumar, A. Effect of addition of CeO2 nanoparticles to pectin as inhibitor of X60 steel corrosion in HCl medium. J. Mol. Liq. 2016, 224, 72−82. (26) Orwoll, R. A.; Yong, C. S. Poly(acrylic acid). In Polymer Data Handbook; Mark, J. E., Ed.; Oxford University Press Inc.: Oxford, 1999; pp 252−253. (27) Moulay, S.; Boukherissa, M.; Abdoune, F.; Benabdelmoumene, F. Z. Low molecular weight poly(acrylic acid) as a salt scaling inhibitor in oilfield operations. J. Iran. Chem. Soc. 2005, 2, 212−219. (28) Omidian, H.; Zohuriaan-Mehr, M. J.; Bouhendi, H. Aqueous solution polymerization of neutralized acrylic acid using Na2S2O5/ (NH4)2S2O8 redox pair system under atmospheric conditions. Int. J. Polym. Mater. 2003, 52, 307−321. (29) Wang, X.; Wang, T.; Liu, D.; Guo, J.; Liu, P. Synthesis and Electrochemical Performance of CeO2/PPy Nanocomposites: Interfacial Effect. Ind. Eng. Chem. Res. 2016, 55, 866−874. (30) Yu, J.; Liu, H.; Chen, J. FT-Raman spectroscopy for monitoring the polymerization of acrylic in aqueous medium. Chin. J. Polym. Sci. 1999, 17, 603−606. (31) Wang, S.; Wang, W.; Zuo, J.; Qian, Y. Study of the Raman spectrum of CeO2 nm thin films. Mater. Chem. Phys. 2001, 68, 246− 248. (32) Sudarsanam, P.; Mallesham, B.; Durgasri, D. N.; Reddy, B. M. Physicochemical characterization and catalytic CO oxidation performance of nanocrystalline Ce−Fe mixed oxides. RSC Adv. 2014, 4, 11322−11330. (33) Todica, M.; Pop, C. V.; Udrescu, L.; Stefan, T. Spectroscopy of a Gamma Irradiated Poly(Acrylic Acid)-Clotrimazole System. Chin. Phys. Lett. 2011, 28, 128201−128201−4. (34) Sánchez-Márquez, J. A.; Fuentes-Ramírez, R.; Cano-Rodríguez, I.; Gamiño-Arroyo, Z.; Rubio-Rosas, E.; Kenny, J. M.; Rescignano, N. Membrane Made of Cellulose Acetate with Polyacrylic Acid Reinforced with Carbon Nanotubes and Its Applicability for Chromium Removal. Int. J. Polym. Sci. 2015, 2015, 320631. (35) Wang, W.; Liao, Q.; Chen, K.; Pan, S.; Lu, M. Glass formation and FTIR spectra of CeO2-doped 36Fe2O3−10B2O3−54P2O5 glasses. J. Non-Cryst. Solids 2015, 409, 76−82. (36) He, X.; Zhang, D.; Li, H.; Fang, J.; Shi, L. Shape and size effects of ceria nanoparticles on the impact strength of ceria/epoxy resin composites. Particuology 2011, 9, 80−85. (37) Huang, J.; Wan, S.; Guo, M.; Yan, H. Preparation of narrow or mono-disperse crosslinked poly((meth)acrylic acid)/iron oxide magnetic microspheres. J. Mater. Chem. 2006, 16, 4535−4541. (38) Tai, Z.; Yang, J.; Qi, Y.; Yan, X.; Xue, Q. Synthesis of a graphene oxide−polyacrylic acid nanocomposite hydrogel and its swelling and electroresponsive properties. RSC Adv. 2013, 3, 12751−12757. (39) Syed, J. A.; Tang, S.; Lu, H.; Meng, X. Water-Soluble Polyaniline−Polyacrylic Acid Composites as Efficient Corrosion Inhibitors for 316SS. Ind. Eng. Chem. Res. 2015, 54, 2950−2959.
(40) Eduok, U.; Faye, O.; Szpunar, J. Corrosion inhibition of X70 sheets by a film-forming imidazole derivative at acidic pH. RSC Adv. 2016, 6, 108777−108790. (41) Gerengi, H.; Sahin, H. I. Schinopsis lorentzii Extract As a Green Corrosion Inhibitor for Low Carbon Steel in 1 M HCl Solution. Ind. Eng. Chem. Res. 2012, 51, 780−787. (42) Popova, A.; Sokolova, E.; Raicheva, S.; Christov, M. AC and DC study of the temperature effect on mild steel corrosion in acid media in the presence of benzimidazole derivatives. Corros. Sci. 2003, 45, 33− 58. (43) Eduok, U. M.; Khaled, M. M. Corrosion protection of nonalloyed AIAI 316L concrete steel metal grade in aqueous H2SO4: Electroanalytical and surface analyses with Metiamide. Constr. Build. Mater. 2014, 68, 285−290. (44) Avci, G. E. Corrosion inhibition of indole-3-acetic acid on mild steel in 0.5 M HCl. Colloids Surf., A 2008, 317, 730−736. (45) Bentiss, F.; Lebrini, M.; Vezin, H.; Lagrenée, M. Experimental and theoretical study of 3-pyridyl-substituted 1,2,4-thiadiazole and 1,3,4-thiadiazole as corrosion inhibitors of mild steel in acidic media. Mater. Chem. Phys. 2004, 87, 18−23. (46) Riazi, H. R.; Danaee, I.; Peykari, M. Influence of ultraviolet light irradiation on the corrosion behavior of carbon steel AISI 1015. Met. Mater. Int. 2013, 19, 217−224. (47) Kraljić Rokovic, M.; Kvastek, K.; Horvat-Radosevic, V.; Duic, L. Poly(ortho-ethoxyaniline) in corrosion protection of stainless steel. Corros. Sci. 2007, 49, 2567−2580. (48) Schem, M.; Schmidt, T.; Gerwann, J.; Wittmar, M.; Veith, M.; Thompson, G. E.; Molchan, I. S.; Hashimoto, T.; Skeldon, P.; Phani, A. R.; Santucci, S.; Zheludkevich, M. L. CeO2-filled sol−gel coatings for corrosion protection of AA2024-T3 aluminium alloy. Corros. Sci. 2009, 51, 2304−2315. (49) Aldykewicz, A. J.; Isaacs, H. S.; Davenport, A. J. The investigation of cerium as a cathodic inhibitor for aluminum−copper alloys. J. Electrochem. Soc. 1995, 142, 3342−3350. (50) Hinton, B. R. W.; Arnott, D. R.; Ryan, N. E. Inhibition of aluminum alloy corrosion by cerous cations. Met. Forum 1984, 7, 211− 217. (51) Bethencourt, M.; Botana, F. J.; Calvino, J. J.; Marcos, M.; RodrIǵ uez-Chacón, M. A. Lanthanide compounds as environmentallyfriendly corrosion inhibitors of aluminium alloys: a review. Corros. Sci. 1998, 40, 1803−1819. (52) Ramezanzadeh, B.; Rostami, M. The effect of cerium-based conversion treatment on the cathodic delamination and corrosion protection performance of carbon steel-fusion-bonded epoxy coating systems. Appl. Surf. Sci. 2017, 392, 1004−1016. (53) Hu, T.; Shi, H.; Fan, S.; Liu, F.; Han, E. H. Cerium tartrate as a pigment in epoxy coatings for corrosion protection of AA 2024-T3. Prog. Org. Coat. 2017, 105, 123−131.
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DOI: 10.1021/acs.iecr.7b00714 Ind. Eng. Chem. Res. 2017, 56, 5586−5597
