- Email: [email protected]
functionalized multiwall carbon nanotubes composites
Progress in Organic Coatings xxx (xxxx) xxxx
Contents lists available at ScienceDirect
Progress in Organic Coatings journal homepage: www.elsevier.com/locate/porgcoat
Advanced anticorrosive coatings based on epoxy/functionalized multiwall carbon nanotubes composites M.A. Deyab*, Ahmed E. Awadallah Egyptian Petroleum Research Institute (EPRI), Nasr City, Cairo, Egypt
A R T I C LE I N FO
A B S T R A C T
Keywords: Epoxy coating Corrosion CNTs Petroleum tanks Formation water
Anti-corrosion epoxy coatings are extensively used to protect the petroleum tanks. For anti-corrosion applications of such epoxy coatings, it is necessary to decrease the defects that are commonly observed in conventional epoxy coatings. Herein we report the new anti-corrosive coatings based on epoxy/functionalized multiwall carbon nanotubes (f-MWCNTs) composites. The electrochemical impedance spectroscopy (EIS), nanoindenter tests, transmission electron microscopy (TEM), Raman spectra, X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FT-IR) were conducted to investigate the performance of prepared composites. The results revealed that anti-corrosion performance of epoxy/ f-MWCNTs nanocomposite film was significantly improved compared to those of pure epoxy and epoxy/ p-MWCNTs. Our results confirm also that f-MWCNTs are able to promote the epoxy coating hardness and reduced modulus.
1. Introduction The corrosion of storage tanks in the petroleum field causes a large economic loss [1,2]. Storage tanks function as assembly points to collect formation water from various production fields. The formation water contains sodium and chloride as the dominant ions [3]. The corrosion in the storage tanks occurs due to the presence of corrosive ions in the formation water [4]. The internal coating using epoxy resin protects the surface of the storage tanks from corrosion [5–9]. The porosity and low adhesion of the epoxy resins are the major defects stumbling block to their used widespread [10–12]. Therefore, many efforts are undertaken to improve the efficiency of the epoxy coatings by incorporating nanoparticles (e.g. SiO2, CNTs, phosphates, and M-phthalocyanines) into epoxy resin [13–18]. Carbon nanotubes (CNTs) have a wide variety of applications [19–21]. They have mild chemical stability, high electrical conductivity, and special thermal conductivity [22]. These characteristics are expected to be valuable in organic coatings technology. In light of this, greater improvement in the CNTs properties by functionalization the surface of CNTS has garnered more attention [23–25]. The functionalization of CNTs has a great impact on the barrier properties of nanocomposites coatings [26]. In this study, we introduce new advanced anticorrosive coatings based on epoxy/ f-MWCNTs composites. We hypothesize that f-
⁎
MWCNTs can not only improve the anti-corrosion performance of epoxy resin but also enhance the mechanical properties of epoxy. 2. Methods 2.1. Materials and chemicals For the tests, plates (130 mm × 50 mm × 2.0 mm) from a storage tank (QPC Company, Egypt) filled with formation water were used as substrates. The cleaning processes for these substrates were carried out using procedures published before by Deyab et al. [27]. The corrosive solution is formation water (pH = 6.5) from QPC Company, Egypt. It contains 46,337 ppm of chloride ions. TDS of the solution is 55,258 mg l−1. Bisphenol-based epoxy resins (DY-128) and the hardener (dimethylaminopropylamine) were obtained from Eric & Deyuan Co. Xylene, acetone and butanol were purchased from Sigma-Aldrich. 2.2. Synthesis of p-MWCNTs and f-MWCNTs MWCNTs were supplied from EPRI Nanotechnology Center, Cairo, Egypt. The MWCNTs sample was refluxed with concentrated H2SO4 and HNO3 (ratio 3:1) for 3.0 h at 353 K. The obtained powder was filleted and dried at 373 for 24 h.
Corresponding author. E-mail address: [email protected] (M.A. Deyab).
https://doi.org/10.1016/j.porgcoat.2019.105423 Received 3 July 2019; Received in revised form 22 October 2019; Accepted 27 October 2019 0300-9440/ © 2019 Elsevier B.V. All rights reserved.
Please cite this article as: M.A. Deyab and Ahmed E. Awadallah, Progress in Organic Coatings, https://doi.org/10.1016/j.porgcoat.2019.105423
Progress in Organic Coatings xxx (xxxx) xxxx
M.A. Deyab and A.E. Awadallah
2.3. Characterization of p-MWCNTs and f-MWCNTs The Powder X-ray Diffraction (XRD) was carried out using X’Pert PRO PANalytical apparatus. The internal and morphology structure of p-MWCNTs and fMWCNTs were detected by transmission electron microscopy (TEM, Model JEM-200CX, JEOL, Japan). The graphitization and crystallinity of carbon samples were observed by SENTERRA Dispersive Raman Microscope (Bruker Co.). The functional groups in the f-MWCNTs were identified by FT-IR (PERKIN ELMER). 2.4. Preparation of nanocomposites coatings The nanocomposites coatings were prepared by dispersing pMWCNTs and f-MWCNTs (1.0%) inside the epoxy resin. Solvents mixture (xylene, acetone and butanol) and hardener agent were used to disperse the nano-particles into the resin. All these ingredients were mixed using magnetic stirrer for 2.0 h at 298 K. The homogeneous solution was then sonicated for 0.5 h. The clean carbon steel substrates were coated by new nanocomposites coatings using film applicator. Finally, the curing process occurred in the oven for 2.0 h at 353 K. The coating thickness for dry samples is about 52 ± 3 μm.
Fig. 2. Raman spectra of (a) p-MWCNTs and (b) f-MWCNTs samples.
2.5. Electrochemical and mechanical tests
openings. Moreover, MWCNTs have curved shapes with hollow openings. Its length nearly is several microns (see Fig.1a). According to Fig. 1b, there are large numbers of imperfections were clearly seen in the sidewalls of the MWCNTs after treating it with strong acids (H2SO4 and HNO3). These intrinsic defects could be attributed to the oxidative harm by strong acids [28]. Raman spectra of the p-MWCNTs and f-MWCNTs are presented in Fig. 2. In both cases, we got two separate peaks. The first peak (D-band at 1345 cm−1) is due to the presence of some defects in graphite layers. The second peak (G-band at 1565 cm−1) is due to graphitized MWCNTs [29]. The presence of D band confirms the framework of MWCNTs. The ratio between the intensities of the D and G bands (ID/IG) is used as a direct measure for sample quality due to its relative response of graphite carbon to defective carbon. The ratio of ID/IG for p-MWCNTs is significantly less than that for fMWCNTs (0.64 and 0.92, respectively). The increase in the value of ID after acid functionalization of MWCNTs reveals the attachment of functional groups on the MWCNTs surface. This demonstrates that the incorporation of functional groups on the sidewall of CNTs causes a large number of defects.
The EIS measurements (Gill AC potentiostat) were used to evaluate the anti-corrosion effectiveness of new nanocomposites. All experiments were measured after 5 days immersion at open circuit potential (OCP) in a frequency ranges 105–10−2 Hz using current amplitude of 10 mV. The electrochemical cell contains a glass cell with three electrodes (coated substrates, pt electrode, and reference saturated calomel electrode (SCE)). The mechanical properties were investigated by measuring the elastic modulus and the hardness of coatings layers using nanoindenter tests (nano-indenter: NanoTest Vantage, Micro Materials instruments). 3. Results and discussion 3.1. Characterization studies The morphological structures of the p-MWCNTs and f-MWCNTs were inspected by transmission electron microscope (TEM) (see Fig. 1). In all case, we got multi-walled carbon nanotubes (MWCNTs diameters ≈ 10–40 nm). Moreover, MWCNTs have curved shapes with hollow
Fig. 1. TEM images of (a) p-MWCNTs and (b) f-MWCNTs samples. 2
Progress in Organic Coatings xxx (xxxx) xxxx
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Fig. 5. Nyquist plot for carbon steel substrates covered with neat epoxy, epoxy/ p-MWCNTs and epoxy/f-MWCNTs nanocomposites coatings immersed in formation water at 303 K.
Fig. 3. XRD patterns of (a) p-MWCNTs and (b) f-MWCNTs samples. Table 1 XRD data of CNTs materials.
3.2. Corrosion studies
Carbon materials
2Theta
FWHM
d-spacing (nm)
Relative Intensity (%)
p-MWCNTs f-MWCNTs
25.8 26.2
0.4723 0.0010
0.3444 0.3404
100 100
The response of the impedance (Nyquist shape) for carbon steel substrates covered with various coatings immersed in the formation water at 303 K is displayed in Fig. 5. The Nyquist Plot for neat epoxy (Fig. 5) results from the electrical circuit of Fig. 6(a). Neat epoxy coating deteriorates with time, giving the more complex behavior. The Nyquist plot is characterized by two time constants. Long immersion in corrosive solution led to the corrosive ions penetration through the epoxy coating matrix. This leads to the creation of the corrosion cell under epoxy layers. Essentially, carbon steel is oxidized to produce rust [34,35]. In this case, the 1st loop in Nyquist plot represents the coating layer and the 2nd loop represents the corrosion process under the epoxy layer [36,37]. The presence of p-MWCNTs and f-MWCNTs led to the disappearing of the 2nd loop. Thus the Nyquist plot, in this case, contains one time constant. The equivalent circuit for epoxy/p-MWCNTs and epoxy/fMWCNTs nanocomposites is shown in Fig. 6(b). The resistance (Repoxy) and capacitance (Cepoxy) for neat epoxy are 123 kΩ cm2 and 36 × 10−9 F cm-2, respectively. This indicates that the neat epoxy film has low resistance for corrosion. In this case, the severe corrosion products can be observed on the substrate. The presence of chloride ions in formation water increases the general corrosion of steel substrates and induces pitting corrosion [38,39]. The hydrogen gas evolution due to cathodic reaction causes coating de-bonding [40,41].
Fig. 3 displays the XRD models of p-MWCNTs and f-MWCNTs. It observed the presence of the intense sharp peak located at 2θ = 25.7°. This is an indication for (002) plane in hexagonal graphite. This was observed for both p-MWCNTs and f-MWCNTs samples [30]. Moreover, a weak shoulder peak appeared at 2θ = 23.4° in case of f-MWCNTs sample. This is due to the oxygenated function groups in the sidewalls (Fig. 3b). The changes in the interlayer d-spacing of graphite (002) at 2θ = ∼26° for both purified and functionalized samples are not significant (see Table 1). Their values are close to 0.3354 nm which reflects the higher graphitization degree and better crystallinity [30,31]. FT-IR spectrum of the f-MWCNTs confirms the successful synthesis of functionalized MWCNTs as shown in Fig. 4. Different types of oxygenated functional groups were clearly appeared in the spectrum. The broad band at 3450 cm−1 is due to the OeH groups [32]. The band at 1590 cm−1 is assigned to the C]C of benzene rings [33]. The peak centered at 1420 cm−1 is due to C–O stretching vibration.
Fig. 4. FT-IR spectrum of f-MWCNTs sample. 3
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Fig. 6. Equivalent electric circuits for (a) neat epoxy, (b) epoxy/p-MWCNTs and epoxy/f-MWCNTs nanocomposites coatings.
in the case of the epoxy/f-MWCNTs layer. These results confirm that the epoxy/f-MWCNTs coating is consistent layer with high mechanical performance.
In the case of steel covered with epoxy/p-MWCNTs nanocomposite, only one semicircle is observed with the increase in Repoxy value to 1379 kΩ cm2 and the decrease in Cepoxy value to 5.4 × 10−9 F cm-2. This suggests that the presence of p-MWCNTs particles leads to the improvement in the epoxy texture and anti-corrosion performance [42]. In the case of steel covered with epoxy/f-MWCNTs nanocomposite, it is evident that the Nyquist plot shows one semicircle with very high Repoxy value (2567 kΩ cm2) and very low Cepoxy value (1.2 × 10−9 F cm-2). From the results of Repoxy and Cepoxy, it can be concluded that the epoxy/f-MWCNTs nanocomposite coating exhibits the best anti-corrosion property.
3.4. The mechanism of action of nanocomposites The use of epoxy coatings is an effective way to protect petroleum tanks from corrosion. They provide a tangible barrier between the tanks surface and the corrosive circumference [43]. In order to produce sufficient corrosion protection, the epoxy layers must be uniform, well-adhered and pore-free [44,45]. The above information indicates that the neat epoxy is not effective to protect the carbon steel substrates from the corrosion. This is due to the high porosity of the epoxy layer and low adhesion between the metal surface and coating layers. This leads to the passage of the corrosion ions from an electrolyte to a metal surface through the epoxy layer and formation of corrosion cell under coating layers [46–48]. Notably, the corrosion of coated carbon steel seemed to be even more suppressed by adding p-MWCNTs into the epoxy matrix. Here, the p-MWCNTs decrease the porosity of the epoxy resin matrix and increase the coating adhesion [49–51]. In addition, the incorporation of pMWCNTs improves the mechanical strength of the epoxy coating [51]. The results confirm that the epoxy/f-MWCNTs nanocomposites coating is more effective than epoxy/p-MWCNTs nanocomposites. The high Repoxy and the low Cepoxy values for epoxy/f-MWCNTs nanocomposites indicate that they have a durable layer [52–54]. The presence of functional groups on CNTs surfaces decreases the agglomeration tendency of CNTs and increases the interactions with solvent molecules [55,56]. This improves CNTs dispersion in epoxy resin and leads to a uniform distribution in the epoxy matrix. The dispersion of particles besides the strong interactions of f-MWCNTs with the epoxy matrix is the key factor for promoting the mechanical properties of nanocomposites coating [57]. In addition, it was confirmed that the f-MWCNTs gave the better tensile strength than the p-MWCNTs. This is due to the interactions
3.3. Mechanical studies The Mechanical behavior of the neat epoxy and the new nanocomposites coatings were investigated by nano-indentation tests. The load-displacement curves can be used to extract mechanical parameters of the coating such as hardness and reduced modulus. These parameters are summarized in Table 2. In this case, the fixed load was applied on the coated samples and the resultant displacements were recorded. The steel covered with the neat epoxy showed low hardness and low reduced modulus values (see Table 2). Interestingly, the epoxy/pMWCNTs layer exhibited higher values of hardness and reduced modulus. The best results for hardness and reduced modulus were achieved Table 2 The hardness and reduced modulus for neat epoxy, epoxy/p-MWCNTs and epoxy/f-MWCNTs nanocomposites coatings. Reduced modulus (GPa (
Hardness (GPa)
Coating type
2.95 3.87 5.32
0.15 0.57 0.89
Neat epoxy Epoxy/p-MWCNTs Epoxy/f-MWCNTs
4
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between the functional groups on CNTs and the epoxy matrix [58]. The functional groups on CNTs result in the increase in cross-link density of epoxy matrix and this leads to the reducing in the porosity of the epoxy layer [59,60].
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4. Conclusion In this research work, we have developed new advanced anticorrosive coatings based on epoxy/f-MWCNTs composites. The new nanocomposites are used to protect the petroleum tanks filled by the formation water from corrosion. The new coatings were successfully synthesized and investigated for their anti-corrosion and mechanical effectiveness. The results indicated that the neat epoxy coating exhibited anticorrosion protection impairment. However, when the incorporation of p-MWCNTs and f-MWCNTs particles with the neat epoxy coating occurred, it formed protective, adherent and uniform coating layers that significantly reduced the corrosion rates. The insert of functional groups on CNTs (f-MWCNTs) enhances the performance of nanocomposites coating. Collectively, the incorporation of f-MWCNTs particles with the neat epoxy coating are promising for anti-corrosion applications and should be further studied in the long-term using various functional groups. Declaration of Competing Interest The authors declare that there are no conflicts of interest. References [1] W. Renpu, Advanced Well Completion Engineering (Third Edition(, Gulf Professional Publishing Books, Elsevier, 2011. [2] M.A. Deyab, S.S. Abd El-Rehim, J. Taiwan Inst. Chem. Eng. 45 (2014) 1065–1072. [3] M.A. Deyab, Khadija Eddahaoui, Rachid Essehli, Tarik Rhadfi, Said Benmokhtar, Giuseppe Mele, Desalination 383 (2016) 38–45. [4] M.A. Deyab, B. El Bali, R. Essehli, R. Ouarsal, M. Lachkar, H. Fuess, J. Mol. Liq. 216 (2016) 636–640. [5] Y. Mei, J. Xu, L. Jiang, Q. Tan, Prog. Org. Coat. 134 (2019) 288–296. [6] M. Ramezanzadeh, G. Bahlakeh, B. Ramezanzadeh, J. Alloys Compd. 792 (2019) 375–388. [7] S. Pourhashem, A. Rashidi, M.R. Vaezi, Z. Yousefian, E. Ghasemy, J. Alloys Compd. 764 (2018) 530–539. [8] I. Mohammadi, M. Izadi, T. Shahrabi, D. Fathi, A. Fateh, Prog. Org. Coat. 131 (2019) 119–130. [9] M.A. Deyab, R. Ouarsal, A.M. Al-Sabagh, M. Lachkar, B. El Bali, Prog. Org. Coat. 107 (2017) 37–42. [10] Z.T. Khodair, A.A. Khadom, H.A. Jasim, J. Mater. Res. Technol. 8 (2019) 424–435. [11] C. Lou, R. Zhang, X. Lu, C. Zhou, Z. Xin, Colloids Surf. A Physicochem. Eng. Asp. 562 (2019) 8–15. [12] M.A. Deyab, K. Eddahaoui, R. Essehli, S. Benmokhtar, T. Rhadfi, G.M. Alberto De Riccardis, J. Mol. Liq. 216 (2016) 699–703. [13] M.A. Deyab, A.D. Riccardis, G. Mele, J. Mol. Liq. 220 (2016) 513–517. [14] Y. Xia, Y. He, C. Chen, Y. Wu, J. Chen, Prog. Org. Coat. 132 (2019) 316–327. [15] X. Li, B. Chen, Y. Jia, X. Li, J. Yang, C. Li, F. Yan, Surf. Coat. Technol. 344 (2018)
5
Contents lists available at ScienceDirect
Progress in Organic Coatings journal homepage: www.elsevier.com/locate/porgcoat
Advanced anticorrosive coatings based on epoxy/functionalized multiwall carbon nanotubes composites M.A. Deyab*, Ahmed E. Awadallah Egyptian Petroleum Research Institute (EPRI), Nasr City, Cairo, Egypt
A R T I C LE I N FO
A B S T R A C T
Keywords: Epoxy coating Corrosion CNTs Petroleum tanks Formation water
Anti-corrosion epoxy coatings are extensively used to protect the petroleum tanks. For anti-corrosion applications of such epoxy coatings, it is necessary to decrease the defects that are commonly observed in conventional epoxy coatings. Herein we report the new anti-corrosive coatings based on epoxy/functionalized multiwall carbon nanotubes (f-MWCNTs) composites. The electrochemical impedance spectroscopy (EIS), nanoindenter tests, transmission electron microscopy (TEM), Raman spectra, X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FT-IR) were conducted to investigate the performance of prepared composites. The results revealed that anti-corrosion performance of epoxy/ f-MWCNTs nanocomposite film was significantly improved compared to those of pure epoxy and epoxy/ p-MWCNTs. Our results confirm also that f-MWCNTs are able to promote the epoxy coating hardness and reduced modulus.
1. Introduction The corrosion of storage tanks in the petroleum field causes a large economic loss [1,2]. Storage tanks function as assembly points to collect formation water from various production fields. The formation water contains sodium and chloride as the dominant ions [3]. The corrosion in the storage tanks occurs due to the presence of corrosive ions in the formation water [4]. The internal coating using epoxy resin protects the surface of the storage tanks from corrosion [5–9]. The porosity and low adhesion of the epoxy resins are the major defects stumbling block to their used widespread [10–12]. Therefore, many efforts are undertaken to improve the efficiency of the epoxy coatings by incorporating nanoparticles (e.g. SiO2, CNTs, phosphates, and M-phthalocyanines) into epoxy resin [13–18]. Carbon nanotubes (CNTs) have a wide variety of applications [19–21]. They have mild chemical stability, high electrical conductivity, and special thermal conductivity [22]. These characteristics are expected to be valuable in organic coatings technology. In light of this, greater improvement in the CNTs properties by functionalization the surface of CNTS has garnered more attention [23–25]. The functionalization of CNTs has a great impact on the barrier properties of nanocomposites coatings [26]. In this study, we introduce new advanced anticorrosive coatings based on epoxy/ f-MWCNTs composites. We hypothesize that f-
⁎
MWCNTs can not only improve the anti-corrosion performance of epoxy resin but also enhance the mechanical properties of epoxy. 2. Methods 2.1. Materials and chemicals For the tests, plates (130 mm × 50 mm × 2.0 mm) from a storage tank (QPC Company, Egypt) filled with formation water were used as substrates. The cleaning processes for these substrates were carried out using procedures published before by Deyab et al. [27]. The corrosive solution is formation water (pH = 6.5) from QPC Company, Egypt. It contains 46,337 ppm of chloride ions. TDS of the solution is 55,258 mg l−1. Bisphenol-based epoxy resins (DY-128) and the hardener (dimethylaminopropylamine) were obtained from Eric & Deyuan Co. Xylene, acetone and butanol were purchased from Sigma-Aldrich. 2.2. Synthesis of p-MWCNTs and f-MWCNTs MWCNTs were supplied from EPRI Nanotechnology Center, Cairo, Egypt. The MWCNTs sample was refluxed with concentrated H2SO4 and HNO3 (ratio 3:1) for 3.0 h at 353 K. The obtained powder was filleted and dried at 373 for 24 h.
Corresponding author. E-mail address: [email protected] (M.A. Deyab).
https://doi.org/10.1016/j.porgcoat.2019.105423 Received 3 July 2019; Received in revised form 22 October 2019; Accepted 27 October 2019 0300-9440/ © 2019 Elsevier B.V. All rights reserved.
Please cite this article as: M.A. Deyab and Ahmed E. Awadallah, Progress in Organic Coatings, https://doi.org/10.1016/j.porgcoat.2019.105423
Progress in Organic Coatings xxx (xxxx) xxxx
M.A. Deyab and A.E. Awadallah
2.3. Characterization of p-MWCNTs and f-MWCNTs The Powder X-ray Diffraction (XRD) was carried out using X’Pert PRO PANalytical apparatus. The internal and morphology structure of p-MWCNTs and fMWCNTs were detected by transmission electron microscopy (TEM, Model JEM-200CX, JEOL, Japan). The graphitization and crystallinity of carbon samples were observed by SENTERRA Dispersive Raman Microscope (Bruker Co.). The functional groups in the f-MWCNTs were identified by FT-IR (PERKIN ELMER). 2.4. Preparation of nanocomposites coatings The nanocomposites coatings were prepared by dispersing pMWCNTs and f-MWCNTs (1.0%) inside the epoxy resin. Solvents mixture (xylene, acetone and butanol) and hardener agent were used to disperse the nano-particles into the resin. All these ingredients were mixed using magnetic stirrer for 2.0 h at 298 K. The homogeneous solution was then sonicated for 0.5 h. The clean carbon steel substrates were coated by new nanocomposites coatings using film applicator. Finally, the curing process occurred in the oven for 2.0 h at 353 K. The coating thickness for dry samples is about 52 ± 3 μm.
Fig. 2. Raman spectra of (a) p-MWCNTs and (b) f-MWCNTs samples.
2.5. Electrochemical and mechanical tests
openings. Moreover, MWCNTs have curved shapes with hollow openings. Its length nearly is several microns (see Fig.1a). According to Fig. 1b, there are large numbers of imperfections were clearly seen in the sidewalls of the MWCNTs after treating it with strong acids (H2SO4 and HNO3). These intrinsic defects could be attributed to the oxidative harm by strong acids [28]. Raman spectra of the p-MWCNTs and f-MWCNTs are presented in Fig. 2. In both cases, we got two separate peaks. The first peak (D-band at 1345 cm−1) is due to the presence of some defects in graphite layers. The second peak (G-band at 1565 cm−1) is due to graphitized MWCNTs [29]. The presence of D band confirms the framework of MWCNTs. The ratio between the intensities of the D and G bands (ID/IG) is used as a direct measure for sample quality due to its relative response of graphite carbon to defective carbon. The ratio of ID/IG for p-MWCNTs is significantly less than that for fMWCNTs (0.64 and 0.92, respectively). The increase in the value of ID after acid functionalization of MWCNTs reveals the attachment of functional groups on the MWCNTs surface. This demonstrates that the incorporation of functional groups on the sidewall of CNTs causes a large number of defects.
The EIS measurements (Gill AC potentiostat) were used to evaluate the anti-corrosion effectiveness of new nanocomposites. All experiments were measured after 5 days immersion at open circuit potential (OCP) in a frequency ranges 105–10−2 Hz using current amplitude of 10 mV. The electrochemical cell contains a glass cell with three electrodes (coated substrates, pt electrode, and reference saturated calomel electrode (SCE)). The mechanical properties were investigated by measuring the elastic modulus and the hardness of coatings layers using nanoindenter tests (nano-indenter: NanoTest Vantage, Micro Materials instruments). 3. Results and discussion 3.1. Characterization studies The morphological structures of the p-MWCNTs and f-MWCNTs were inspected by transmission electron microscope (TEM) (see Fig. 1). In all case, we got multi-walled carbon nanotubes (MWCNTs diameters ≈ 10–40 nm). Moreover, MWCNTs have curved shapes with hollow
Fig. 1. TEM images of (a) p-MWCNTs and (b) f-MWCNTs samples. 2
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Fig. 5. Nyquist plot for carbon steel substrates covered with neat epoxy, epoxy/ p-MWCNTs and epoxy/f-MWCNTs nanocomposites coatings immersed in formation water at 303 K.
Fig. 3. XRD patterns of (a) p-MWCNTs and (b) f-MWCNTs samples. Table 1 XRD data of CNTs materials.
3.2. Corrosion studies
Carbon materials
2Theta
FWHM
d-spacing (nm)
Relative Intensity (%)
p-MWCNTs f-MWCNTs
25.8 26.2
0.4723 0.0010
0.3444 0.3404
100 100
The response of the impedance (Nyquist shape) for carbon steel substrates covered with various coatings immersed in the formation water at 303 K is displayed in Fig. 5. The Nyquist Plot for neat epoxy (Fig. 5) results from the electrical circuit of Fig. 6(a). Neat epoxy coating deteriorates with time, giving the more complex behavior. The Nyquist plot is characterized by two time constants. Long immersion in corrosive solution led to the corrosive ions penetration through the epoxy coating matrix. This leads to the creation of the corrosion cell under epoxy layers. Essentially, carbon steel is oxidized to produce rust [34,35]. In this case, the 1st loop in Nyquist plot represents the coating layer and the 2nd loop represents the corrosion process under the epoxy layer [36,37]. The presence of p-MWCNTs and f-MWCNTs led to the disappearing of the 2nd loop. Thus the Nyquist plot, in this case, contains one time constant. The equivalent circuit for epoxy/p-MWCNTs and epoxy/fMWCNTs nanocomposites is shown in Fig. 6(b). The resistance (Repoxy) and capacitance (Cepoxy) for neat epoxy are 123 kΩ cm2 and 36 × 10−9 F cm-2, respectively. This indicates that the neat epoxy film has low resistance for corrosion. In this case, the severe corrosion products can be observed on the substrate. The presence of chloride ions in formation water increases the general corrosion of steel substrates and induces pitting corrosion [38,39]. The hydrogen gas evolution due to cathodic reaction causes coating de-bonding [40,41].
Fig. 3 displays the XRD models of p-MWCNTs and f-MWCNTs. It observed the presence of the intense sharp peak located at 2θ = 25.7°. This is an indication for (002) plane in hexagonal graphite. This was observed for both p-MWCNTs and f-MWCNTs samples [30]. Moreover, a weak shoulder peak appeared at 2θ = 23.4° in case of f-MWCNTs sample. This is due to the oxygenated function groups in the sidewalls (Fig. 3b). The changes in the interlayer d-spacing of graphite (002) at 2θ = ∼26° for both purified and functionalized samples are not significant (see Table 1). Their values are close to 0.3354 nm which reflects the higher graphitization degree and better crystallinity [30,31]. FT-IR spectrum of the f-MWCNTs confirms the successful synthesis of functionalized MWCNTs as shown in Fig. 4. Different types of oxygenated functional groups were clearly appeared in the spectrum. The broad band at 3450 cm−1 is due to the OeH groups [32]. The band at 1590 cm−1 is assigned to the C]C of benzene rings [33]. The peak centered at 1420 cm−1 is due to C–O stretching vibration.
Fig. 4. FT-IR spectrum of f-MWCNTs sample. 3
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Fig. 6. Equivalent electric circuits for (a) neat epoxy, (b) epoxy/p-MWCNTs and epoxy/f-MWCNTs nanocomposites coatings.
in the case of the epoxy/f-MWCNTs layer. These results confirm that the epoxy/f-MWCNTs coating is consistent layer with high mechanical performance.
In the case of steel covered with epoxy/p-MWCNTs nanocomposite, only one semicircle is observed with the increase in Repoxy value to 1379 kΩ cm2 and the decrease in Cepoxy value to 5.4 × 10−9 F cm-2. This suggests that the presence of p-MWCNTs particles leads to the improvement in the epoxy texture and anti-corrosion performance [42]. In the case of steel covered with epoxy/f-MWCNTs nanocomposite, it is evident that the Nyquist plot shows one semicircle with very high Repoxy value (2567 kΩ cm2) and very low Cepoxy value (1.2 × 10−9 F cm-2). From the results of Repoxy and Cepoxy, it can be concluded that the epoxy/f-MWCNTs nanocomposite coating exhibits the best anti-corrosion property.
3.4. The mechanism of action of nanocomposites The use of epoxy coatings is an effective way to protect petroleum tanks from corrosion. They provide a tangible barrier between the tanks surface and the corrosive circumference [43]. In order to produce sufficient corrosion protection, the epoxy layers must be uniform, well-adhered and pore-free [44,45]. The above information indicates that the neat epoxy is not effective to protect the carbon steel substrates from the corrosion. This is due to the high porosity of the epoxy layer and low adhesion between the metal surface and coating layers. This leads to the passage of the corrosion ions from an electrolyte to a metal surface through the epoxy layer and formation of corrosion cell under coating layers [46–48]. Notably, the corrosion of coated carbon steel seemed to be even more suppressed by adding p-MWCNTs into the epoxy matrix. Here, the p-MWCNTs decrease the porosity of the epoxy resin matrix and increase the coating adhesion [49–51]. In addition, the incorporation of pMWCNTs improves the mechanical strength of the epoxy coating [51]. The results confirm that the epoxy/f-MWCNTs nanocomposites coating is more effective than epoxy/p-MWCNTs nanocomposites. The high Repoxy and the low Cepoxy values for epoxy/f-MWCNTs nanocomposites indicate that they have a durable layer [52–54]. The presence of functional groups on CNTs surfaces decreases the agglomeration tendency of CNTs and increases the interactions with solvent molecules [55,56]. This improves CNTs dispersion in epoxy resin and leads to a uniform distribution in the epoxy matrix. The dispersion of particles besides the strong interactions of f-MWCNTs with the epoxy matrix is the key factor for promoting the mechanical properties of nanocomposites coating [57]. In addition, it was confirmed that the f-MWCNTs gave the better tensile strength than the p-MWCNTs. This is due to the interactions
3.3. Mechanical studies The Mechanical behavior of the neat epoxy and the new nanocomposites coatings were investigated by nano-indentation tests. The load-displacement curves can be used to extract mechanical parameters of the coating such as hardness and reduced modulus. These parameters are summarized in Table 2. In this case, the fixed load was applied on the coated samples and the resultant displacements were recorded. The steel covered with the neat epoxy showed low hardness and low reduced modulus values (see Table 2). Interestingly, the epoxy/pMWCNTs layer exhibited higher values of hardness and reduced modulus. The best results for hardness and reduced modulus were achieved Table 2 The hardness and reduced modulus for neat epoxy, epoxy/p-MWCNTs and epoxy/f-MWCNTs nanocomposites coatings. Reduced modulus (GPa (
Hardness (GPa)
Coating type
2.95 3.87 5.32
0.15 0.57 0.89
Neat epoxy Epoxy/p-MWCNTs Epoxy/f-MWCNTs
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between the functional groups on CNTs and the epoxy matrix [58]. The functional groups on CNTs result in the increase in cross-link density of epoxy matrix and this leads to the reducing in the porosity of the epoxy layer [59,60].
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4. Conclusion In this research work, we have developed new advanced anticorrosive coatings based on epoxy/f-MWCNTs composites. The new nanocomposites are used to protect the petroleum tanks filled by the formation water from corrosion. The new coatings were successfully synthesized and investigated for their anti-corrosion and mechanical effectiveness. The results indicated that the neat epoxy coating exhibited anticorrosion protection impairment. However, when the incorporation of p-MWCNTs and f-MWCNTs particles with the neat epoxy coating occurred, it formed protective, adherent and uniform coating layers that significantly reduced the corrosion rates. The insert of functional groups on CNTs (f-MWCNTs) enhances the performance of nanocomposites coating. Collectively, the incorporation of f-MWCNTs particles with the neat epoxy coating are promising for anti-corrosion applications and should be further studied in the long-term using various functional groups. Declaration of Competing Interest The authors declare that there are no conflicts of interest. References [1] W. Renpu, Advanced Well Completion Engineering (Third Edition(, Gulf Professional Publishing Books, Elsevier, 2011. [2] M.A. Deyab, S.S. Abd El-Rehim, J. Taiwan Inst. Chem. Eng. 45 (2014) 1065–1072. [3] M.A. Deyab, Khadija Eddahaoui, Rachid Essehli, Tarik Rhadfi, Said Benmokhtar, Giuseppe Mele, Desalination 383 (2016) 38–45. [4] M.A. Deyab, B. El Bali, R. Essehli, R. Ouarsal, M. Lachkar, H. Fuess, J. Mol. Liq. 216 (2016) 636–640. [5] Y. Mei, J. Xu, L. Jiang, Q. Tan, Prog. Org. Coat. 134 (2019) 288–296. [6] M. Ramezanzadeh, G. Bahlakeh, B. Ramezanzadeh, J. Alloys Compd. 792 (2019) 375–388. [7] S. Pourhashem, A. Rashidi, M.R. Vaezi, Z. Yousefian, E. Ghasemy, J. Alloys Compd. 764 (2018) 530–539. [8] I. Mohammadi, M. Izadi, T. Shahrabi, D. Fathi, A. Fateh, Prog. Org. Coat. 131 (2019) 119–130. [9] M.A. Deyab, R. Ouarsal, A.M. Al-Sabagh, M. Lachkar, B. El Bali, Prog. Org. Coat. 107 (2017) 37–42. [10] Z.T. Khodair, A.A. Khadom, H.A. Jasim, J. Mater. Res. Technol. 8 (2019) 424–435. [11] C. Lou, R. Zhang, X. Lu, C. Zhou, Z. Xin, Colloids Surf. A Physicochem. Eng. Asp. 562 (2019) 8–15. [12] M.A. Deyab, K. Eddahaoui, R. Essehli, S. Benmokhtar, T. Rhadfi, G.M. Alberto De Riccardis, J. Mol. Liq. 216 (2016) 699–703. [13] M.A. Deyab, A.D. Riccardis, G. Mele, J. Mol. Liq. 220 (2016) 513–517. [14] Y. Xia, Y. He, C. Chen, Y. Wu, J. Chen, Prog. Org. Coat. 132 (2019) 316–327. [15] X. Li, B. Chen, Y. Jia, X. Li, J. Yang, C. Li, F. Yan, Surf. Coat. Technol. 344 (2018)
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