Tuning F-doped degree of rGO: Restraining corrosion-promotion activity of EP/rGO nanocomposite coating
Lu Shena, b, Yong Lib, Wenjie Zhaoa, *, Kui Wangb, *, Xiaojing Cia, Yangmin Wua, Gang Liua, Chao Liuc, Zhiwen Fangc
a Key Laboratory of Marine Materials and Related Technologies, Zhejiang Key Laboratory of Marine Materials and Protective Technologies, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Science, Ningbo, 315201, Chinab Public Technology Service Center, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Science, Ningbo, 315201, Chinac Engineering Technology Research Center of Fluorocarbon Materials, Shandong Zhongshan Photoelectric Materials Co., Ltd., Zibo, 255138, China
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2020 Editorial board of Journal of Materials Science & Technology Copyright reserved, Editorial board of Journal of Materials Science & Technology
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Abstract
Given that graphene features high electrical conductivity, it is a kind of material with corrosion-promotion activity. This study aimed to inhibit the corrosion-promotion activity of graphene in coatings. Here, we report an exciting application of epoxy matrix (EP)/F-doped reduced graphene oxide (rGO) coatings for the long-term corrosion protection of steel. The synthesized F-doped rGO (FG) did not reduce the utilization of rGO by a wide margin and possessed distinctive electrically insulating nature. The electrical conductivity of rGO was approximately 1500 S/m, whereas those of FG-1, FG-2 and FG-3 were 1.17, 5.217 × 10-2 and 3.643 × 10-11 S/m, respectively. FG and rGO were then dispersed into epoxy coatings. The chemical structures of rGO and FG were investigated by transmission electron microscopy (TEM), scanning probe microscopy (SPM), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD). EP/FG coatings exhibited outstanding corrosion protection in comparison with blank EP and EP/rGO coatings mainly because the corrosion-promotion effect of rGO was eliminated. The anticorrosion ability of EP/FG coatings was improved with increased F-doped degree of FG. In addition, electrochemical impendance spectroscopy (EIS) results indicated that the Rc values of EP/FG-2 and EP/FG-3 were four orders of magnitude higher than those of EP/rGO in diluent NaCl solution (3.5 wt.%) after immersion for 90 days.
With the development of material science, many new and effective methods to fabricate anticorrosive materials have been developed [1]. Graphene is a kind of two-dimensional carbon material composed of sp2-bonded carbon atoms that form a one-atom-thick planar sheet. Given its unique physical and chemical properties, graphene has attracted considerable attention within the scientific community since its discovery. Recent studies demonstrated that graphene could provide new chances for anticorrosion barriers for metals [2]. In addition, graphene has been named as “the thinnest corrosion-resistant coating” [3,4].
One mode of graphene in anticorrosion application is to synthesis graphene-reinforced composite coatings [[5], [6], [7], [8]]. Gu et al. found that the addition of well-dispersed graphene through an π-π interaction with a carboxylated aniline trimer derivative could remarkably enhance the anticorrosion performance of graphene-based epoxy composite coating [9]. Shen et al. found that the addition of 0.3 wt.% graphene in zinc-rich coatings could effectively reduce the zinc content in the coatings due to the excellent electronic conductivity of graphene [10]. Yang and co-workers synthesized 3,4,9,10-perylene tetracarboxylic acid-graphene (PTCA-G) composite material. They found that the corrosion resistance of the PTCA-G/epoxy coating was remarkably improved because PTCA-G dispersed well and it acted as a physical barrier in the coating [11]. Parhizkar et al. modified cerium film via graphene oxide (GO) nanosheets, which were covalently functionalized with a silane coupling agent. They found that the cathodic disbonding, corrosion protection and adhesion properties of the epoxy coating were improved by fabricating cerium nanofilm on the steel substrate [12].
In addition, the preparation of graphene through CVD method has attracted considerable attention [13]. Multilayer graphene can effectively act as the anti-oxidation barrier to protect Ni foils from oxdation [14]. Chen and co-workers demonstrated that graphene prepared using the CVD method could inhibit oxidation on the surface of Cu and Cu/Ni alloys [15]. Dong et al. found that graphene films provided better protection to polished Cu than ground Cu for short durations [16]. Nayak and co-workers demonstrated that CVD-graphene could protect Ni substrate against air oxidation at 500 °C for 3 h and exposure to H2O2 solution [17]. Wu et al. also investigated the anticorrosion performance of Cu coated with graphene and found that multi-layered graphene with high density of defects could accelerate the process of corrosive agents reaching the substrate [18]. On one hand, graphene presents advantages over traditional anticorrosion materials. On the other hand, it also presents some disadvantages in corrosion protection. Schriver and co-workers demonstrated that graphene could promote Cu corrosion from one month to two years at room temperature. It is the conductive path existing between Cu and graphene that resulted in the nonuniform corrosion at graphene defects [19]. Zhou and co-workers also confirmed the corrosion-promotion activity of graphene film, which was related to the existence of defects on the graphene film and its high electrical conductivity [20]. Hence, the effective application of graphene in corrosion protection must be taken into consideration.
Sun et al. encapsulated graphene in low-electrical-conductivity pernigraniline, nanosized SiO2, or (3-aminopropyl)-triethoxysilane (APTES) to inhibit the corrosion-promotion activity of graphene. These work revealed that embedding synthesized graphene/pernigraniline, rGO@APTES, or graphene@SiO2 into a coating could effectively enhance the anticorrosion ability of a coating [[21], [22], [23]]. However, the applied amount of these composites was large (>5 wt.%), suggesting that these methods of encapsulating graphene considerably reduced the utilizition of graphene. Therefore, eliminating the corrosion-promotion activity of graphene is a remarkable challenge for the further development of graphene application in corrosion protection.
Becides the encapsulation strategy of graphene with high electrical conductivity, another effective method to eliminate the corrosion-promotion activity of graphene is doping heteroatoms in graphene, which could tailor graphene’s electronic structures and electrochemical properties by changing the electronic density within graphene [24,25]. The electronegativity of N atom is higher than that of C atom, and its radius is similar to that of the C atom. Moreover, the introduction of N atom could change the local electronic structures of graphene. Therefore, chemical reactivity of graphene changed. Recently, N-doped graphene (NG) has attracted considerable attention from researchers. Ren et al. found that the corrosion resistance of NG film with large doping concentration was poorer compared with those of others due to the discontinuity of the film [26]. Hence, preparing NG with ideal chemical structures and chemical properties is very important in industrial applications. F-doped graphene (FG) could also eliminate the corrosion-promotion activity of graphene because F atom is more electronegative than C atom. Liu and co-workers reported that fluorographene was incorporated into polyvinyl butyral coating to enhance its corrosion protection performances [27]. They also found that superhydrophobic epoxy coating modified by fluorographene could be used for anti-corrosion and self-cleaning [28]. FG not only possesses a distinctive feature of electrical insulation but also does not change the utilization of graphene by a wide margin. Therefore, we selected FG as the additive of epoxy coatings in the present work. FG was obtained by reacting reduced GO (rGO) with fluorine gas (F2) in a special Teflon autoclave instead of exfoliation of fluorographite or fluorination of GO. This method allows rGO and F2 to come in full contact. Moreover, varying degrees of F-doped FG could be prepared. To the best of our knowledge, contrastive study of FG addition with different F-doped degrees in epoxy matrix (EP) has not been systematically investigated. The difference in corrosion resistance between FG and rGO should also be discussed. The addition of FG to EP could provide new possibilities for eliminating the corrosion-promotion activity of graphene.
2. Experimental
2.1. Materials
Exfoliated rGO was provided by Shandong Zhongshan Photoelectricity Materials Industry Co., Ltd., China. Epoxy resin 601 and curing agent (650-polyamide) were supplied by SM Chemical Industry Co., Ltd., China. Sodium chloride and xylene were purchased from Sinopharm Chemical Reagent Co., Ltd. All chemical reagents were used as received without purification. Q235 mild steel was acquired from Sheng Xin Technology Co., Ltd.
2.2. Preparation of few-layered FG nanosheets
Multilayer FGi materials were synthesized by reacting exfoliated rGO powder with F2 in a Teflon autoclave. First, 0.05 g of rGO was placed in the Teflon autoclave, and N2-F2 mixture gas (80 vol% N2, 20 vol% F2) was introduced at 300 °C for 6, 12, and 24 h. Hence, the FGi materials with various F-doped degrees were obtained by controlling the reaction time. With the increase of F-doped degrees, the color of FGi materials changed from black to white, as shown in Fig. 1. We adopted the modified method proposed in the literature via a one-pot sonochemical exfoliation method under ambient conditions (Fig. 1) to obtain the few-layered FG nanosheets [29]. The procedure for preparing the few-layered FG dispersion was as follows. Approximately 75 mg of multilayer FGi was added to 18 mL of chloroform solvent. Subsequently, the system was ultrasonicated in an ice-bath under ambient conditions for 3 h to obtain a stabilized FG dispersion. Graphene dispersion was prepared in a similar method.
Before coating, Q235 mild carbon steel (1 cm × 1 cm × 1 cm) was used as a work electrode. First, it was degreased via ultrasonication in acetone for 30 min. Then, the steel was welded with copper wire, and one side of the steel was fixed in a PVC tube by injecting AB glue into the tube. The AB glue in the PVC tube should be cured for 72 h at room temperature. The side of the Q235 steel electrode exposed to air was ground using #400, #800, and #1200 sandpapers successively. Subsequently, the electrode surface was dried using a blow dryer. A certain amount of FG or rGO (0.6 wt.%) was added into the chloroform solvent (as shown in Section 2.2). Then, 13 g of epoxy 601 was mixed into the dispersion and stirred for 30 min. The excess solvent was removed by rotary evaporation and heating. Subsequently, 3.9 g of curing agent (30 wt.% of epoxy 601) was added to the uniform mixture and equably stirred for 10 min. The composite coatings contained 0.6 wt.% of FG or rGO. Finally, degassing was conducted in a vaccum oven at room temperture for approximately 10 min. The paint was coated on the electrode surfaces by using a wire bar coater (25 μm). The coatings had a thickness of approximately 25 ± 2 μm. Finally, the coatings were dried in air at room temperature for 3 days to obtain the EP/FG or EP/rGO composite coatings. A blank EP coating was also prepared for comparison.
2.4. Characterization techniques
A Veeco MultiMode/NanoScope IIIa SPM was used to confirm the thickness of FG. Electrical conductivity of FG was measured using an ST-2722 semiconductor powder resistivity tester with an ST2255 ultra-high resistance test module. The morphologies and crystalline structures of FG and rGO nanosheets were estimated by Tecnai F20 TEM (USA). XPS (Axis Ultra Dld, Shimadzu, UK) was conducted to evaluate the chemical composition of FG and rGO. Additionally, XPS data in this work were analyzed using the Casa 2273 software. The crystal structures of FG and rGO were measured by XRD with a Bruker AXS X-ray diffractometer. Infrared spectrometer (Nicolet 6700, Thermo, USA) was utilized to characterize the molecular structure of FG and rGO. The FEI QUANTA 250 SEM and LSM 700 confocal laser scanning microscope were employed to characterize the surface and fracture surface of the coatings and coating-exfoliated steels. The rust layers formed on the working electrode were characterized using a Renishaw inVia Reflex Raman microscope. The electrochemical behaviors of the prepared specimens were measured using CHI-660E electrochemical workstation with Pt plate (2.5 cm2 area), saturated calomel electrode, and a working electrode. Three parallel samples were performed for each test to ensure reproducibility. The open-circuit potential (OCP) results of the coatings during immersion were collected. EIS measurements of the prepared coatings were in the frequency range of 105-10-2 Hz, and the sinusoidal perturbation was 20 mV. Scanning vibrating electrode technique (SVET) was employed to examine the inhibition effect of the prepared samples in a VersaSCAN micro-scanning electrochemical workstation (AMETEK, USA). Before testing, an artificial defect (with a length of 2 mm) was made in the coated samples. The corrosion current density was detected on an area of 2000 μm × 2000 μm and 21 × 21 points X and Y axes. The microelectrode had a diameter of 10 μm, and the vibration amplitude was 30 μm at a frequency of 80 Hz. The salt spray test was employed to investigate the corrosion protection performance of the as-prepared coatings in accordance with the ASTM B117 standard. The thickness of the paint films was 200 μm.
3. Results and discussion
3.1. Morphology and structure of rGO and FG
Fig. 2(a-d) show the TEM images of exfoliated rGO and FG materials. As shown in Fig. 2(a), the wrinkled rGO nanosheets exhibited a typical exfoliated layer structure, indicating the well-dispersed rGO. In addition, the inset of Fig. 2(a) shows the selected area electron diffraction (SAED) pattern of rGO. It presented a clear hexagonal spot pattern, indicating a well-crystallized graphene structure. The SAED results suggested that FG displayed an enhanced polycrystalline ring structure with the increase of F-doped degree, revealing that the FG materials presented a polycrystalline structure.
Fig. 2. TEM images and corresponding SAED of (a) rGO, (b) FG-1, (c) FG-2, (d) FG-3. AFM images of (e) rGO, (f) FG-1, (g) FG-2, (h) FG-3.
AFM was then employed to evaluate the thickness of rGO and FG. As shown in Fig. 2(e), the thickness of a rGO sheet was approximately 3.50 nm. The thickness of the FG sheets in Fig. 2(f-h) was approximately 3-4 nm. Considering that the thickness of a single-layer FG is 0.8-1.0 nm [30,31], the layer number of the obtained FG sheets was approximately 3-5.
XPS elemental analysis was conducted on rGO, FG-1, FG-2, and FG-3. The chemical composition of the samples is listed in Table 1. Fig. 3(a-d) show the full spectra of rGO, FG-1, FG-2, and FG-3, respectively. The atomic percentage of F increased from FG-1 to FG-3 (FG-1: 12.56 %, FG-2: 33.98 %, and FG-3: 43.36 %). All samples contained a certain amount of oxygen because rGO was reacted with F2 to prepare FG samples. In Fig. 3(e-h), the peaks centered at 284.5 and 285.2 eV corresponded to C=C (sp2) and C—C (sp3) from rGO, respectively. The peaks at approximately 289.2, 289.9, and 291.3 eV corresponded to C—F semi-ionic, C—F, and -CF2 bonds, respectively. The content of C=C and C—C decreased with the increase of C—F content.
Table 1
Table 1 Chemical composition of rGO, FG-1, FG-2 and FG-3.
Fig. 3. Full spectrum of (a) rGO, (b) FG-1, (c) FG-2, (d) FG-3. High-resolution XPS spectra of (e) rGO, (f) FG-1, (g) FG-2, (h) FG-3.
The FTIR results of rGO and FG materials are presented in Fig. 4(a). The plot of rGO exhibited the C—O ether group stretching at 1285 cm-1, C—O anhydride group stretching at 1057 cm-1, C—OH stretching at 1400 cm-1, C=C stretching at 1645 cm-1, and carbon skeletons at 1572 cm-1 [32]. FG displayed an obvious peak at 1215 cm-1, which corresponded to the stretching vibration mode of C—F bonds in the structures [33]. This peak became stronger with the increase of F-doped degree of FG materials. In the case of FG-3, the C—F streching vibration situated at the nanosheet margin was located at 1324 cm-1 [34]. However, the bond was not evident from FG-1 and FG-2. The absorption peaks of the carbon skeletons appeared at 1523, 1625 (FG-3), and 1555 cm-1 (FG-1 and FG-2).
Fig. 4. (a) FTIR spectra of rGO, FG-1, FG-2 and FG-3. (b) XRD spectra of rGO, FG-1, FG-2 and FG-3.
The structures of rGO, FG-1, FG-2, and FG-3 were also confirmed by XRD measurements. In Fig. 4(b), rGO exhibited a [002] peak at 2θ = 26.36°, suggesting that the high reduction degree of rGO could lead to rGO aggregation and a structure similar to that of graphite. However, the [002] peak gradually disappeared with the increase of F-doped degree of the FG samples; by contrast, a new peak of [001] at 2θ = 13.33° appeared, and the intensity increased with the increase in F-doped degree. As shown in Fig. 4(b), the [100] peak located at approximately 40°-45° was related to the in-plane crystallite size of the samples [35,36]. In accordance with the change of the [100] peak position and the change of the full width at half maximum, we deduced that the in-plane crystallite size of FG samples decreased along with the increase of F-doped degree.
Fig. 5 shows the fracture surface morphologies of the composite coatings before immersion. Before the fracture surfaces of the coatings were observed, all coatings experienced breaking process in liquid nitrogen. F element uniformly dispersed in epoxy matrix according to the fracture surface morphologies of the coatings (Fig. S1 in the Supplementary Material). As shown in Fig. 5(a), the blank EP presented a typical brittle fractured surface with evident directional long cracks, presenting a smooth fracture surface. Nevertheless, the addition of rGO or FG in epoxy coatings resulted in different fracture surfaces in comparison with the blank EP (Fig. 5(b-e)). The addition of rGO or FG in the composite coatings disturbed the directional fracture patterns and effectively inhibited the crack propagation. In the case of the composite coatings, the fracture surfaces became denser than those of the blank EP.
Fig. 5. SEM images for fracture surfaces of (a) blank EP, (b) EP/rGO, (c) EP/FG-1, (d) EP/FG-2 and (e) EP/FG-3.
3.2. EIS measurements
EIS was used to evaluate and compare the anticorrosion performance of the prepared coatings during immersion in the diluent NaCl solution. The OCP results of the five kinds of coatings were measured at different periods. With prolonged immersion time, the OCP values of all coatings presented a downward trend (Fig. 6). Owing to the penetration of abundant corrosive agents into the coatings with prolonged immersion time, the OCP values gradually decreased. The OCP values of EP/FG-1, EP/FG-2, and EP/FG-3 coatings were more positive than those of blank EP and EP/rGO coatings. The OCP results suggested the blank EP and EP/rGO coatings showed a stronger corrosion tendency. The essence of corrosion promote activity of rGO was galvanic corrosion, so the OCP of Fe coated EP/FG coating was more positive than that of Fe coated EP/rGO and blank EP coatings. Compared with rGO nanosheets, FG featured an impermeable property and electrical insulation, thereby inhibiting galvanic corrosion.
Fig. 6. Trend of OCP values of five kinds of coatings in period of immersion in diluent NaCl solution.
Impedance plots (bode and Nyquist plots) of the five coatings are shown in Fig. 7. In addition, some frequencies were marked in Fig. 7 of Nyquist plots (for example, 0.01 Hz, 0.0316 Hz and 0.0618 Hz were marked in Fig. 7(c1)). The enlarged image of Fig. 7(c1) was shown in Fig. S1 in the Supplementary Material. Impedance modulus at the lowest frequency (Zf=0.01Hz) is one of the electrochemical parameters for evaluating the corrosion resistance of the coatings. After immersion for 5 days, the Zf=0.01Hz values of the total coatings exceeded 109 Ω cm2 except for EP/rGO coating. The Zf=0.01Hz results of EP/FG-2 and EP/FG-3 coatings exceeded 1011 Ω cm2. After 50 days of immersion, the Zf=0.01Hz results of blank EP and EP/rGO coatings decreased to 6.20 × 107 and 5.63 × 107 Ω cm2, respectively. However, the Zf=0.01Hz values of EP/FG-1, EP/FG-2, and EP/FG-3 coatings decreased slightly to 1.47 × 109, 5.25 × 1010, and 6.81 × 1010 Ω cm2, respectively. In the case of the blank EP coating, the phase angle curve presented one time constant, indicating the response of coating resistance. Additionally, the phase angle of blank EP coating was 85° within the range of 102.5-105 Hz after 40 days of immersion (Fig. 7(b1)). Subsequently, the phase angle curves of the coating showed two time constants from 50 days to 90 days of immersion. The time constant existing at high frequencies corresponded to the barrier property of a coating. The emergence of the second time constant at the middle-low frequencies suggested that the corrosive agents diffused to the metal substrate and that corrosion reactions occurred [37,38]. With regard to EP/rGO, the second time constant at low frequency after immersion for 5 days indicated that the corrosive medium could easily penetrate the metallic substrate because rGO with high electrical conductivity could promote corrosion. The phase angle of EP/FG-1 coating was near 85° in the range of 101-105 Hz. It was lower than 10° at 10-2 Hz. The phase angles of EP/FG-2 and EP/FG-3 coatings were close to 85° within the range of 10°-105 and 10-0.5-105 Hz, respectively. At 0.01 Hz, the phase angle of EP/FG-2 coating was approximately 20°, whereas that of EP/FG-3 coating was approximately 30°. At 90 days of immersion, the Zf=0.01Hz values of blank EP and EP/rGO decreased to 1.36 × 106 and 5.46 × 107 Ω cm2, respectively. However, the Zf=0.01Hz results of EP/FG-1, EP/FG-2, and EP/FG-3 maintained at 2.97 × 108, 2.92 × 1010, and 3.15 × 1010 Ω·cm2, suggesting that the coatings featured long-term anticorrosion ability. The phase angle of EP/FG-2 and EP/FG-3 coatings reached 85° within a frequency range of 10°-105 Hz (Fig. 7 (b4 and b5)). Thus, the EP/FG composite coatings presented better corrosion protection in comparison with the blank EP and EP/rGO coatings.
Fig. 7. EIS results of the steels coated with different coatings. (a1-c1) bland EP, (a2-c2) EP/rGO, (a3-c3) EP/FG-1, (a4-c4) EP/FG-2 and (a5-c5) EP/FG-3.
The EIS results of the coatings were fitted by Zview software using the equivalent electrical circuits in Models I, II, and III (Fig. 8(a)). In Fig. 8(a), Rs is the solution resistance, Rc is the coating resistance, and Cc is the coating capacitance. Qdl is the double-layer capacitance, and Rct is the charge-transfer resistance. With regard to the blank EP coating, the Model I equivalent electrical circuit (Fig. 8(a)) was used before 30 days of immersion. In this process, the corrosive agents did not diffuse to the steel substrate. Subsequently, the Model II equivalent electrical circuit was used, indicating that the corrosive agents diffused to the steel substrate and corrosion reaction occurred. After 50 days, Warburg impedance (Zw) was included in the equivalent electric circuit, which could be assigned to the diffusion-controlled process at the corroding interface (Model III). For the EP/rGO coating, the Model II equivalent electrical circuit was used before 40 days of immersion. Then, it was expressed as Model III. With regard to EP/FG-1, the Model I equivalent electrical circuit was employed within 80 days of immersion. Thereafter, the Model II equivalent electrical circuit was used. However, the equivalent electrical circuit was expressed as Model I for EP/FG-2 and EP/FG-3 during the whole immersion process, revealing that FG-2 and FG-3 could effectively extend the time for corrosive agents diffusing to the steel substrate. The variation of Cc values with the immersion time for the five coatings is shown in Fig. 8(b). Generally speaking, water absorption of the coatings can be presented by the variation of Cc results [39]. As the diffusion of water into the coating increased, Cc showed a tendency to increase. For EP and EP/rGO, Cc fluctuated within 50 days of immersion. Then, the values increased markedly after immersion for 50 days, suggesting that the absorption of water did not reach saturation state. In case of EP/FG-1, EP/FG-2, and EP/FG-3 coatings, Cc increased slowly within 80 days of immersion, revealing the diffusion of water into the coating matrix. By contrast, after 80 days of immersion, the Cc values of EP/FG-1, EP/FG-2, and EP/FG-3 maintained at 1.705 × 10-10, 1.303 × 10-10, and 1.132 × 10-10 F·cm2, respectively. Overall, the EP/FG coatings had lower Cc values than the other two coatings, implying that EP/FG coatings adsorbed less water than EP and EP/rGO coatings.
Fig. 8. (a) Equivalent electric circuits models (Model I, Model II and Model III) of coatings. (b) Cc results as a function of immersion time of the five coatings. (c) The coating resistance Rc as a function of the immersion of the five coatings.
The anticorrosion performance of all coatings was also discussed in terms of Rc values. Rc usually decreases as the immersion time of the coatings increases because the electrolytes could penetrate through the coating pores. Rc reflects the barrier capacity of the coatings toward electrolytes [40]. Fig. 8(c) shows the trend of Rc values of the five coatings with prolonged immersion time. The Rc values of blank EP coating markedly decreased from 3.58 × 109 Ω cm2 to 9.27 × 105 Ω cm2 within 80 days of immersion. Thereafter, it stabilized near 1 × 106 Ω cm2. The Rc of EP/rGO slowly varied from 3.297 × 107 Ω cm2 to 1.45 × 107 Ω cm2 during immersion. The Rc values of EP/FG-1 slowly decreased within 80 days of immersion and decreased to 5.48 × 107 Ω cm2 at the end of immersion. However, the Rc values of EP/FG-2 and EP/FG-3 coatings dropped by an order of magnitude during the whole immersion time. The findings verified that EP coatings with F-doped rGO presented superior corrosion resistance than blank EP and EP/rGO coatings. Furthermore, the steady Rc values of EP/FG-2 and EP/FG-3 coatings revealed that they exhibited optimal barrier function and effectively reduced the diffusion of corrosion agents into the coatings due to the impermeable and electrically insulating FG nanosheets added in the coatings.
3.3. Salt spray test
Salt spray test was also carried out to assess the corrosion resistance of the as-prepared coatings and support the electrochemical results. As shown in Fig. 9 and Table 2, a salt spray investigation of the samples at exposure time of 48, 114, 240, and 336 h was conducted. The anticorrosion performance of EP was affected remarkably by the addition of FG nanosheets. After 48 h of spray exposure, brown rusting appeared on the scratches of the blank EP and EP/rGO coatings, whereas in the case of EP/FG coatings, rusting formation was negligible. After 240 h, a wide range of rusting coupled with small blisters appeared around the scribes of the blank EP and EP/rGO coatings, indicating that the coatings no longer protected the steel substrate against corrosion. With prolonged time, rusting progressed after 336 h for the EP/rGO coating. A great deal of blisters appeared on the surface of the steel substrates of the blank EP and EP/rGO coatings, suggesting that the steel substrates were severely corroded. By contrast, rust on the EP/FG coatings was less evident than that on the blank EP and EP/rGO coatings within 114 h. In the case of the EP/FG-1 and EP/FG-2 coatings, the corrosion area enlarged after 240 h. Small blisters appeared on the steel substrate of the EP/FG-1 coating after 240 h, whereas blisters were not evident on the surfaces of the EP/FG-2 and EP/FG-3 coatings. In comparison with other coatings, the EP/FG-3 coating displayed remarkably improved corrosion resistance with less rusting on the steel substrate even after 336 h. In conclusion, the blank EP coating containing a small amount of FG could remarkably enhance the anticorrosion property of the coatings.
Fig. 9. Optical images of salt spray tests steel substrates coated by blank EP, EP/rGO, EP/FG-1, EP/FG-2 and EP/FG-3 coatings after 48, 114, 240 and 336 h (Test length of the artificial scribes was 2 cm).
Artificial defects with a length of 2 mm were carefully scratched on the prepared coatings using a knife, and the coatings were exposed in the diluent NaCl solution. The current density transformed from the potential signals around the defects is shown in Fig. 10. In the case of the blank EP, the variation of anodic current density was approximately 0-0.27 μA cm-2, implying that anodic dissolution occurred on the artificial scratch after immersion for 6 h in the NaCl solution. The variation of anodic current density of EP/rGO was similar to that of blank EP after 6 h of immersion. With increasing immersion time (12-36 h), the anodic current density (around 0.2-0.5 μA cm-2) of blank EP and EP/rGO coatings increased as indicated by the current density maps (Fig. 10). By contrast, anodic dissolution did not evidently occur until immersion for 6-12 h for the EP/FG-1 coating, and the variation of anodic current density was maintained at 0-0.25 μA cm-2 with prolonged time (12-36 h). With regard to EP/FG-2 and EP/FG-3 coatings, anodic dissolution occured evidently after 12 h immersion. The coatings possessed a low anodic current density during 36 h of immersion. The results revealed that FG added to the EP coating could retard corrosion of defects on the coatings. Of note, FG with a high F-doped degree in the coatings could retard the corrosion of defects effectively. Blank EP was easily corroded because the defects existed on the coating, and corrosive agents could rapidly penetrate into the internal coating and reach the steel substrate. As for EP/rGO, rGO was likely to promote the corrosion of steel, which was caused by the excellent electrical conductivity of rGO and the uniform dispersion of rGO nanosheets in the coating when a large number of corrosive agents penetrated into the coatings.
Fig. 10. SVET results of current density for blank EP (a), EP/rGO (b), EP/FG-1 (c), EP/FG-2 (d) and EP/FG-3 (e) immersed in diluent NaCl solution.
After 90 days of immersion, the coatings were mechanically peeled off from Q235 steel surfaces, and they were characterized using a confocal laser scanning microscope. The micrographs confirmed that corrosion products were generated on the steel surfaces with blank EP and EP/rGO coatings. By contrast, the morphologies of the steel surfaces coated with EP/FG-1, EP/FG-2, and EP/FG-3 were not evidently corroded after immersion in diluent NaCl solution for 90 days (Fig. 11(c1-e1)) and were similar to that of ground steel (inset of Fig. 11(d1)). The morphology and element composition of the steel surfaces were analyzed using SEM and EDS, respectively. The steel surfaces coated with blank EP or EP/rGO with corrosive region were rough. However, the steel surfaces coated with EP/FG without corrosive products only showed evident scratches after the surfaces were rubbed with sandpaper (Fig. 11(c2-e2)). The corresponding EDS results in Fig. 11(a3-c3) indicate that Cl exists on the surface of steel coated with blank EP or EP/rGO, thereby indicating that corrosive medium penetrated the coatings and reached the steel substrates. By contrast, only C and Fe were found on the surfaces of steel with EP/FG coating, revealing that the substrates were not corroded. The results confirmed that the electronically insulating FG added in the coatings could efficiently slow down the corrosion of the coatings, whereas the electrically conductive rGO could promote their corrosion.
Fig. 11. Micrographs of coating-exfoliated steel surfaces after 90 days immersion in 3.5 wt.% NaCl solution: (a1) blank EP, (b1) EP/rGO, (c1) EP/FG-1, (d1) EP/FG-2 and (e1) EP/FG-3. SEM images of coating-exfoliated steel surfaces coated by blank EP (a2), EP/rGO (b2), EP/FG-1 (c2), EP/FG-2 (d2) and EP/FG-3 (e2). (a3-e3) EDS results corresponded to areas selected in (a2-e2).
Raman spectroscopy, a reliable non-destructive technique, has been employed for identifying pure iron oxides and steel corrosive products [41,42]. The Raman results of the rusting layers formed on the Q235 steel substrates coated by the five kinds of coatings are shown in Fig. 12. The major components of the corrosion products that formed on the corrosive atmosphere of steel were goethite (α-FeOOH), akaganeite (β-FeOOH), lepidocrocite (γ-FeOOH), and feroxyhite (δ-FeOOH) [43]. Among them, β-FeOOH is formed only in saline conditions and is often found in marine environments and chloride-rich solutions [44]. EP displayed bands at 310, 328, 392, 419, 540, and 723 cm-1, and EP/rGO showed bands at 313, 392, 421, 538, and 721 cm-1, which could likely represent β-FeOOH. In the case of EP/FG-1, EP/FG-2, and ER/FG-3 coated steels, the characteristic bands of iron oxides were not observed, which confirmed that they were not corroded.
Fig. 12. Raman results of rusting layers formed on steel substrate coated by the five kinds of coatings.
3.5. Corrosion resistance mechanism of the prepared coatings
The corrosion resistance mechanism of the blank EP, EP/rGO, and EP/FG coatings are shown in Fig. 13. For blank EP, the corrosion media easily penetrated the defects in the coating and started to corrode the substrate. In case of the EP/rGO coating, the steel substrate was corroded after the coating was saturated by corrosive agents. After the coating lost effectiveness, rGO could accelerate the corrosion of the substrate due to the excellent electrical conductivity of rGO. The electrode potential of rGO was more positive than that of Fe. Therefore, rGO in the coating acted as cathode. Moreover, the rGO nanosheets in the coating served as a link between the coating and metal interface. The corrosion of steel could generate large numbers of electrons in the anode sites. On one hand, a portion of electrons was transmitted through the steel and reached the surface of the substrate. Then, they carried out redox reactions. On the other hand, another part of electrons moved to the rGO cathode site along the conductive rGO to participate in redox reactions. With regard to EP/FG coatings, FG did not possess corrosion-promotion effects because they cut off the electronic transmission path. Redox reactions only occurred on the surface of the steel. Given that FG was electronically insulating, the redox reactions were considerably inhibited, resulting in the excellent corrosion protection of EP/FG coatings.
Fig. 13. Schematic of corrosion protection mechanism of EP coating (a), composite coatings enhanced via rGO or FG (b); (c) Coating was exaggerated to clearly show the electron transfer in EP/rGO coating; (d) Coating was exaggerated to clearly show the electron transfer in EP/FG coatings.
4. Conclusion
Low-electrical-conductive and flake-like FG materials with different F-doped degrees were synthesized and added into epoxy coatings to improve the corrosion resistance of the coatings. FG featured not only impermeable property inherited from rGO but also electrical insulating property. OCP, EIS, and salt spray tests revealed that EP coatings presented a long-term anticorrosion effect when 0.6 wt.% FG was used as a filler. The well-dispersed FG nanosheets with impenetrable and electrically insulating properties enhanced the physical barrier of the EP and extended the time of corrosion protection. Graphene is a kind of two-dimensional carbon material composed of sp2-bonded carbon atoms that form a one-atom-thick planar sheet. Partial of sp2 C atoms were converted to sp3 C atoms in FG. Doping F atom in graphene could destroy the electron conduction pathway in graphene since continuous π-π bond was converted to isolated π-π bonds in FG. Moreover, the electrical conductivity of FG decreased with the F-doped degree. Hence, FG could inhibit the corrosion-promotion activity of graphene. Compared with graphene, FG has less surface energy and better hydrophobic performance. Hence, the corrosion resistance of EP/FG coatings was enhanced with the progressing of F-doping degree of FG materials in the composite coatings. Interestingly, we also found that the corrosion resistance of EP/FG coatings was enhanced with increased F-doped degree of FG materials in the composite coatings. This study may provide an effective strategy for restraining the corrosion-promotion activity of rGO and achieving long-term anticorrosive coating in industrial applications.
Acknowledgment
This work was financially supported by the National Natural Science Foundation of China (No. 51775540), the Youth Innovation Promotion Association, CAS (No. 2017338), the Nature Science Foundation of Zhejiang (No. LQ19E030007) and the Natural Science Foundation of Ningbo (No. 2018A610114).
We report on the exceptional application of polyaniline/graphene composites (PAGCs) for corrosion protection of steel. The composites display outstanding barrier properties against O-2 and H2O compared with neat polyaniline and polyaniline/clay composites (PACCs). The conductive filler, 4-aminobenzoyl group-functionalized graphene-like sheets (ABF-G) with a relatively higher aspect ratio than organophilic clay nonconductive fillers, is a versatile platform for polymer grafting that promotes better dispersion of the graphite within the polymer matrix and lengthens the diffusion pathway that gases should effectively encounter. This concept can be used for other polymer/graphene composites. (c) 2012 Elsevier Ltd.
[8]
R.Maurya, A.R.Siddiqui, P.K.Katiyar, K.Balani, J. Mater. Sci. Technol.35(2019) 1767-1778.
Dispersion of graphene in solvents is of crucial importance toward its practical applications. In this study, using a water-soluble carboxylated aniline trimer derivative (CAT(-)) as a stabilizer, the commercial graphene can be stably dispersed in water at high concentration (>1 mg/mL) via strong π-π interaction that was proved by Raman and UV-vis spectra. Moreover, the CAT(-)-functionalized graphene sheets (G-CAT(-) hybrid) exhibited high conductivity (∼1.5 S/cm), good electroactivity and improved electrochemical stability. The addition of well-dispersed graphene into waterborne epoxy system (G-CAT(-)/epoxy) remarkably improved corrosion protection compared with pure waterborne epoxy coating, based on a series of electrochemical measurements performed under 3.5% NaCl solution. This significantly enhanced anticorrosion performance is mainly due to the improved water barrier properties derived from highly dispersed graphene nanosheets in the epoxy coating.
In this paper, the 3, 4, 9, 10-perylene tetracarboxylic acid-graphene (PTCA-G) composite was synthesized and the corrosion protection property of epoxy coating-coated Q235 steel containing PTCA-G composite was investigated. The results of Fourier transform infrared spectroscopy (FT-IR) proved that 3, 4, 9, 10-perylene tetracarboxylic acid (PTCA) and graphene (G) were combined via π-π interactions and hydrophobic forces between PTCA and G. The results of electrochemical tests indicated that with additives of sole PTCA, sole G and PTCA-G composite, the corrosion resistance of epoxy coating was increased compared with pure epoxy coating. And the most significant improved corrosion resistance of PTCA-G/epoxy coating might be attributed to the good dispersion and barrier performance of PTCA-G composite in the epoxy coating. Besides, compared with the corrosion protection property of PTCA-G/epoxy coating with other volume ratios, the corrosion resistance of epoxy coating containing PTCA-G composite with 10:4 vol ratio of PTCA and G was the best. It might be attributed to the excellent barrier and dispersion properties of PTCA-G composite with 10:4 vol ratio of PTCA and G.
[12]
N.Parhizkar, B.Ramezanzadeh, T.Shahrabi, J. Ind. Eng. Chem.64(2018) 402-419.
The ability to protect refined metals from reactive environments is vital to many industrial and academic applications. Current solutions, however, typically introduce several negative effects, including increased thickness and changes in the metal physical properties. In this paper, we demonstrate for the first time the ability of graphene films grown by chemical vapor deposition to protect the surface of the metallic growth substrates of Cu and Cu/Ni alloy from air oxidation. In particular, graphene prevents the formation of any oxide on the protected metal surfaces, thus allowing pure metal surfaces only one atom away from reactive environments. SEM, Raman spectroscopy, and XPS studies show that the metal surface is well protected from oxidation even after heating at 200 °C in air for up to 4 h. Our work further shows that graphene provides effective resistance against hydrogen peroxide. This protection method offers significant advantages and can be used on any metal that catalyzes graphene growth.
Anticorrosion and antioxidation surface treatments such as paint or anodization are a foundational component in nearly all industries. Graphene, a single-atom-thick sheet of carbon with impressive impermeability to gases, seems to hold promise as an effective anticorrosion barrier, and recent work supports this hope. We perform a complete study of the short- and long-term performance of graphene coatings for Cu and Si substrates. Our work reveals that although graphene indeed offers effective short-term oxidation protection, over long time scales it promotes more extensive wet corrosion than that seen for an initially bare, unprotected Cu surface. This surprising result has important implications for future scientific studies and industrial applications. In addition to informing any future work on graphene as a protective coating, the results presented here have implications for graphene's performance in a wide range of applications.
This paper reports the enhancement of long-term oxidation of copper at room temperature by a graphene coating. Previous studies showed that graphene is an effective anticorrosion barrier against short-term thermal and electrochemical oxidation of metals. Here, we show that a graphene coating can, on the contrary, accelerate long-term oxidation of an underlying copper substrate in ambient atmosphere at room temperature. After 6 months of exposure in air, both Raman spectroscopy and energy-dispersive X-ray spectroscopy indicated that graphene-coated copper foil had a higher degree of oxidation than uncoated foil, although X-ray photoelectron spectroscopy showed that the surface concentration of Cu(2+) was higher for the uncoated sample. In addition, we observed that the oxidation of graphene-coated copper foil was not homogeneous and occurred within micrometer-sized domains. The corrosion enhancement effect of graphene was attributed to its ability to promote electrochemical corrosion of copper.
Graphene can be a corrosion-promotion material because of its high electrical conductivity. This paper aims at eliminating the undesired corrosion-promotion effect of graphene, and reports a promising application of graphene/pernigraniline composites (GPCs) for the corrosion protection of copper. The composites were synthesized by an in situ polymerization-reduction/dedoping process. The synthesized composites have a flake-like structure, and their conductivity is as low as 2.3 x 10(-7) S/cm. The GPCs are then embedded into polyvinylbutyral coating (PVBc) to modify the coating. Potentiodynamic polarization and electrochemical impedance spectroscopy measurements reveal that the GPC-modified PVBc is an outstanding barrier against corrosive media compared with pernigraniline or reduced graphene oxide (rGO) modified PVBc. Scratch tests also show that the corrosion-promotion effect of rGO in GPCs is inhibited. The enhanced corrosion protection performance is observed because on the one hand the pernigraniline growing on rGO surface avoids graphene-graphene/metal connections increasing the electrical resistance of coating; on the other hand the as-prepared GPCs are less flexible than polymer-free rGO and they are more likely to unfold during the coating process, which can greatly prolong the diffusion pathway of corrosive media in the coating matrix. (C) 2014 Elsevier Ltd.
Graphane, the fully hydrogenated analogue of graphene, and its partially hydrogenated counterparts are attracting increasing attention. We review here its structure and predicted material properties, as well as the current methods of preparation. Graphane and hydrogenated graphenes are far more complex materials than graphene, expected to have a tuneable band gap via the extent of hydrogenation, as well as exhibit ferromagnetism. The methods for hydrogenated graphene characterization are discussed. We show that hydrogenation methods based on low or high pressure gas hydrogenation lead to less hydrogen saturation than wet chemistry methods based on variations of Birch reduction. The special cases of patterning of hydrogenated graphene strips in a graphene lattice are discussed.
3AuOTf and Pd2dba3, separately (i.e., only Au or only Pd) results in zero conversion to product at all monitored time points compared to quantitative conversion to product when both are present in cocatalytic reactions.]]>
As the youngest in the graphene family, fluorographene has received numerous expectations from the scientific community. Investigation of fluorographene is similar to graphene and graphene oxide, wherein fabrication is an importance subject in the infancy stage. Fluorographene produced by the currently existing protocols, however, could only disperse in a limited number of solvents, and the dispersions generally exhibit short-term stability, restricting its manipulation and processing. To address this formidable challenge, we herein report that fluorographene nanosheets, most of which have a single-layered structure, could be easily formulated from commercially available graphite fluoride via a one-pot chloroform-mediated sonochemical exfoliation under ambient conditions without any pretreatment, special protection or stabilizers. Significantly, owing to the exceptional volatility of chloroform, our fluorographene originally dispersed in chloroform, could be facilely transferred into other 24 kinds of solvents via a volatilization-redispersion process, wherein dispersions of extremely long-term stability (more than six months) could be obtained. As an example to demonstrate the merit of the as-formulated fluorographene and its potential application possibilities, we further show that our fluorographene could be easily assembled as a modified layer in pentacene-based organic field-effect transistors simply by a spin-coating method, wherein distinctly increased mobility and positively shifted threshold voltage could be achieved. Considering the excellent popularity of chloroform in the scientific community, the remarkable volatility of chloroform, the broad solvent dispersibility of our fluorographene, and together with the long-term stability of the dispersions, our chloroform-mediated sonochemical exfoliation protocol likely endow fluorographene with new and broad opportunities for fabrication of graphene-based advanced functional films and nanocomposites via liquid-phase manipulation or solution-processing strategies.
Stoichoimetric graphene fluoride monolayers are obtained in a single step by the liquid-phase exfoliation of graphite fluoride with sulfolane. Comparative quantum-mechanical calculations reveal that graphene fluoride is the most thermodynamically stable of five studied hypothetical graphene derivatives; graphane, graphene fluoride, bromide, chloride, and iodide. The graphene fluoride is transformed into graphene via graphene iodide, a spontaneously decomposing intermediate. The calculated bandgaps of graphene halides vary from zero for graphene bromide to 3.1 eV for graphene fluoride. It is possible to design the electronic properties of such two-dimensional crystals.
The liquid-phase extraction of graphene fluoride by exfoliation of graphite fluoride in dimethylformamide and subsequent reduction with triethylsilane or zinc particles yields the corresponding chemically converted graphene, namely reduced graphene fluoride. The formation of either graphene fluoride (fluorographene) or graphene monolayers in the course of the reaction was demonstrated by several microscopy techniques. Fluorine elimination after reduction was verified by elemental analysis and infrared/Raman spectroscopy. (C) 2011 Elsevier Ltd.
The commercial graphene oxide (FL-GOc) shows a stacking nanostructure of about 22 x 6 nm average diameter by height with the distance of 0.9 nm between 6-7 graphene layers, whereas the respective reduced graphene oxide (FL-RGOc)-about 8 x 1 nm average diameter by height stacking nanostructure with the distance of 0.4 nm between 2-3 graphene layers (XRD). The REELS results are consistent with those by the XRD indicating 8 (FL-GOc) and 4 layers (FL-RGOc). In graphene oxide and reduced graphene oxide prepared from the graphite the REELS indicates 8-11 and 7-10 layers. All graphene oxide samples show the C/O ratio of 2.1-2.3, 26.5-32.1 at% of C sp(3) bonds and high content of functional oxygen groups (hydroxyl C-OH, epoxy-C-O-C, carbonyl-C=O, carboxyl-C-OOH, water) (XPS). Reduction increases the C/O ratio to 2.8-10.3, decreases C sp(3) content to 11.4-20.3 at% and also the content of C-O-C and C=O groups, accompanied by increasing content of C-OH and C-OOH groups. Formation of additional amount of water due to functional oxygen group reduction leads to layer delamination. Removing of functional oxygen groups and water molecules results in decreasing the distance between the graphene layers. (C) 2014 Published by Elsevier B.V.]]>
Recently, two-dimensional, layered materials such as graphene and hexagonal boron nitride (h-BN) have been identified as interesting materials for a range of applications. Here, we demonstrate the corrosion prevention applications of h-BN in marine coatings. The performance of h-BN/polymer hybrid coatings, applied on stainless steel, were evaluated using electrochemical techniques in simulated seawater media [marine media]. h-BN/polymer coating shows an efficient corrosion protection with a low corrosion current density of 5.14 × 10(-8) A/cm(2) and corrosion rate of 1.19 × 10(-3) mm/year and it is attributed to the hydrofobic, inert and dielectric nature of boron nitride. The results indicated that the stainless steel with coatings exhibited improved corrosion resistance. Electrochemical impedance spectroscopy and potentiodynamic analysis were used to propose a mechanism for the increased corrosion resistance of h-BN coatings.
Homogeneous, 50-mu m-thick, epoxy coatings and composite epoxy coatings containing 2 wt% of 130-nm silica particles were successfully synthetized on austenitic stainless steel of the type AISI 316L. The surface morphology and mechanical properties of these coatings were compared and characterized using a profilometer, defining the average surface roughness and the Vickers hardness, respectively. The effects of incorporating the silica particles on the surface characteristics and the corrosion resistance of the epoxy-coated steel were additionally investigated with contact-angle measurements as well as by potentiodynamic polarization and electrochemical impedance spectroscopy in a 3.5 wt% NaCl solution. The silica particles were found to significantly improve the microstructure of the coating matrix, which was reflected in an increased hardness, increased surface roughness and induced hydrophobicity. Finally, the silica/epoxy coating was proven to serve as a successful barrier in a chloride-ion-rich environment with an enhanced anticorrosive performance, which was confirmed by the reduced corrosion rate and the increased coating resistance due to zigzagging of the diffusion path available to the ionic species. (C) 2013 Elsevier B.V.
... With the development of material science, many new and effective methods to fabricate anticorrosive materials have been developed [1]. Graphene is a kind of two-dimensional carbon material composed of sp2-bonded carbon atoms that form a one-atom-thick planar sheet. Given its unique physical and chemical properties, graphene has attracted considerable attention within the scientific community since its discovery. Recent studies demonstrated that graphene could provide new chances for anticorrosion barriers for metals [2]. In addition, graphene has been named as “the thinnest corrosion-resistant coating” [3,4]. ...
1
2019
... With the development of material science, many new and effective methods to fabricate anticorrosive materials have been developed [1]. Graphene is a kind of two-dimensional carbon material composed of sp2-bonded carbon atoms that form a one-atom-thick planar sheet. Given its unique physical and chemical properties, graphene has attracted considerable attention within the scientific community since its discovery. Recent studies demonstrated that graphene could provide new chances for anticorrosion barriers for metals [2]. In addition, graphene has been named as “the thinnest corrosion-resistant coating” [3,4]. ...
1
2014
... With the development of material science, many new and effective methods to fabricate anticorrosive materials have been developed [1]. Graphene is a kind of two-dimensional carbon material composed of sp2-bonded carbon atoms that form a one-atom-thick planar sheet. Given its unique physical and chemical properties, graphene has attracted considerable attention within the scientific community since its discovery. Recent studies demonstrated that graphene could provide new chances for anticorrosion barriers for metals [2]. In addition, graphene has been named as “the thinnest corrosion-resistant coating” [3,4]. ...
1
2014
... With the development of material science, many new and effective methods to fabricate anticorrosive materials have been developed [1]. Graphene is a kind of two-dimensional carbon material composed of sp2-bonded carbon atoms that form a one-atom-thick planar sheet. Given its unique physical and chemical properties, graphene has attracted considerable attention within the scientific community since its discovery. Recent studies demonstrated that graphene could provide new chances for anticorrosion barriers for metals [2]. In addition, graphene has been named as “the thinnest corrosion-resistant coating” [3,4]. ...
1
2019
... One mode of graphene in anticorrosion application is to synthesis graphene-reinforced composite coatings [[5], [6], [7], [8]]. Gu et al. found that the addition of well-dispersed graphene through an π-π interaction with a carboxylated aniline trimer derivative could remarkably enhance the anticorrosion performance of graphene-based epoxy composite coating [9]. Shen et al. found that the addition of 0.3 wt.% graphene in zinc-rich coatings could effectively reduce the zinc content in the coatings due to the excellent electronic conductivity of graphene [10]. Yang and co-workers synthesized 3,4,9,10-perylene tetracarboxylic acid-graphene (PTCA-G) composite material. They found that the corrosion resistance of the PTCA-G/epoxy coating was remarkably improved because PTCA-G dispersed well and it acted as a physical barrier in the coating [11]. Parhizkar et al. modified cerium film via graphene oxide (GO) nanosheets, which were covalently functionalized with a silane coupling agent. They found that the cathodic disbonding, corrosion protection and adhesion properties of the epoxy coating were improved by fabricating cerium nanofilm on the steel substrate [12]. ...
1
2016
... One mode of graphene in anticorrosion application is to synthesis graphene-reinforced composite coatings [[5], [6], [7], [8]]. Gu et al. found that the addition of well-dispersed graphene through an π-π interaction with a carboxylated aniline trimer derivative could remarkably enhance the anticorrosion performance of graphene-based epoxy composite coating [9]. Shen et al. found that the addition of 0.3 wt.% graphene in zinc-rich coatings could effectively reduce the zinc content in the coatings due to the excellent electronic conductivity of graphene [10]. Yang and co-workers synthesized 3,4,9,10-perylene tetracarboxylic acid-graphene (PTCA-G) composite material. They found that the corrosion resistance of the PTCA-G/epoxy coating was remarkably improved because PTCA-G dispersed well and it acted as a physical barrier in the coating [11]. Parhizkar et al. modified cerium film via graphene oxide (GO) nanosheets, which were covalently functionalized with a silane coupling agent. They found that the cathodic disbonding, corrosion protection and adhesion properties of the epoxy coating were improved by fabricating cerium nanofilm on the steel substrate [12]. ...
1
2012
... One mode of graphene in anticorrosion application is to synthesis graphene-reinforced composite coatings [[5], [6], [7], [8]]. Gu et al. found that the addition of well-dispersed graphene through an π-π interaction with a carboxylated aniline trimer derivative could remarkably enhance the anticorrosion performance of graphene-based epoxy composite coating [9]. Shen et al. found that the addition of 0.3 wt.% graphene in zinc-rich coatings could effectively reduce the zinc content in the coatings due to the excellent electronic conductivity of graphene [10]. Yang and co-workers synthesized 3,4,9,10-perylene tetracarboxylic acid-graphene (PTCA-G) composite material. They found that the corrosion resistance of the PTCA-G/epoxy coating was remarkably improved because PTCA-G dispersed well and it acted as a physical barrier in the coating [11]. Parhizkar et al. modified cerium film via graphene oxide (GO) nanosheets, which were covalently functionalized with a silane coupling agent. They found that the cathodic disbonding, corrosion protection and adhesion properties of the epoxy coating were improved by fabricating cerium nanofilm on the steel substrate [12]. ...
1
2019
... One mode of graphene in anticorrosion application is to synthesis graphene-reinforced composite coatings [[5], [6], [7], [8]]. Gu et al. found that the addition of well-dispersed graphene through an π-π interaction with a carboxylated aniline trimer derivative could remarkably enhance the anticorrosion performance of graphene-based epoxy composite coating [9]. Shen et al. found that the addition of 0.3 wt.% graphene in zinc-rich coatings could effectively reduce the zinc content in the coatings due to the excellent electronic conductivity of graphene [10]. Yang and co-workers synthesized 3,4,9,10-perylene tetracarboxylic acid-graphene (PTCA-G) composite material. They found that the corrosion resistance of the PTCA-G/epoxy coating was remarkably improved because PTCA-G dispersed well and it acted as a physical barrier in the coating [11]. Parhizkar et al. modified cerium film via graphene oxide (GO) nanosheets, which were covalently functionalized with a silane coupling agent. They found that the cathodic disbonding, corrosion protection and adhesion properties of the epoxy coating were improved by fabricating cerium nanofilm on the steel substrate [12]. ...
1
2015
... One mode of graphene in anticorrosion application is to synthesis graphene-reinforced composite coatings [[5], [6], [7], [8]]. Gu et al. found that the addition of well-dispersed graphene through an π-π interaction with a carboxylated aniline trimer derivative could remarkably enhance the anticorrosion performance of graphene-based epoxy composite coating [9]. Shen et al. found that the addition of 0.3 wt.% graphene in zinc-rich coatings could effectively reduce the zinc content in the coatings due to the excellent electronic conductivity of graphene [10]. Yang and co-workers synthesized 3,4,9,10-perylene tetracarboxylic acid-graphene (PTCA-G) composite material. They found that the corrosion resistance of the PTCA-G/epoxy coating was remarkably improved because PTCA-G dispersed well and it acted as a physical barrier in the coating [11]. Parhizkar et al. modified cerium film via graphene oxide (GO) nanosheets, which were covalently functionalized with a silane coupling agent. They found that the cathodic disbonding, corrosion protection and adhesion properties of the epoxy coating were improved by fabricating cerium nanofilm on the steel substrate [12]. ...
1
2019
... One mode of graphene in anticorrosion application is to synthesis graphene-reinforced composite coatings [[5], [6], [7], [8]]. Gu et al. found that the addition of well-dispersed graphene through an π-π interaction with a carboxylated aniline trimer derivative could remarkably enhance the anticorrosion performance of graphene-based epoxy composite coating [9]. Shen et al. found that the addition of 0.3 wt.% graphene in zinc-rich coatings could effectively reduce the zinc content in the coatings due to the excellent electronic conductivity of graphene [10]. Yang and co-workers synthesized 3,4,9,10-perylene tetracarboxylic acid-graphene (PTCA-G) composite material. They found that the corrosion resistance of the PTCA-G/epoxy coating was remarkably improved because PTCA-G dispersed well and it acted as a physical barrier in the coating [11]. Parhizkar et al. modified cerium film via graphene oxide (GO) nanosheets, which were covalently functionalized with a silane coupling agent. They found that the cathodic disbonding, corrosion protection and adhesion properties of the epoxy coating were improved by fabricating cerium nanofilm on the steel substrate [12]. ...
1
2018
... One mode of graphene in anticorrosion application is to synthesis graphene-reinforced composite coatings [[5], [6], [7], [8]]. Gu et al. found that the addition of well-dispersed graphene through an π-π interaction with a carboxylated aniline trimer derivative could remarkably enhance the anticorrosion performance of graphene-based epoxy composite coating [9]. Shen et al. found that the addition of 0.3 wt.% graphene in zinc-rich coatings could effectively reduce the zinc content in the coatings due to the excellent electronic conductivity of graphene [10]. Yang and co-workers synthesized 3,4,9,10-perylene tetracarboxylic acid-graphene (PTCA-G) composite material. They found that the corrosion resistance of the PTCA-G/epoxy coating was remarkably improved because PTCA-G dispersed well and it acted as a physical barrier in the coating [11]. Parhizkar et al. modified cerium film via graphene oxide (GO) nanosheets, which were covalently functionalized with a silane coupling agent. They found that the cathodic disbonding, corrosion protection and adhesion properties of the epoxy coating were improved by fabricating cerium nanofilm on the steel substrate [12]. ...
1
2018
... One mode of graphene in anticorrosion application is to synthesis graphene-reinforced composite coatings [[5], [6], [7], [8]]. Gu et al. found that the addition of well-dispersed graphene through an π-π interaction with a carboxylated aniline trimer derivative could remarkably enhance the anticorrosion performance of graphene-based epoxy composite coating [9]. Shen et al. found that the addition of 0.3 wt.% graphene in zinc-rich coatings could effectively reduce the zinc content in the coatings due to the excellent electronic conductivity of graphene [10]. Yang and co-workers synthesized 3,4,9,10-perylene tetracarboxylic acid-graphene (PTCA-G) composite material. They found that the corrosion resistance of the PTCA-G/epoxy coating was remarkably improved because PTCA-G dispersed well and it acted as a physical barrier in the coating [11]. Parhizkar et al. modified cerium film via graphene oxide (GO) nanosheets, which were covalently functionalized with a silane coupling agent. They found that the cathodic disbonding, corrosion protection and adhesion properties of the epoxy coating were improved by fabricating cerium nanofilm on the steel substrate [12]. ...
1
2019
... In addition, the preparation of graphene through CVD method has attracted considerable attention [13]. Multilayer graphene can effectively act as the anti-oxidation barrier to protect Ni foils from oxdation [14]. Chen and co-workers demonstrated that graphene prepared using the CVD method could inhibit oxidation on the surface of Cu and Cu/Ni alloys [15]. Dong et al. found that graphene films provided better protection to polished Cu than ground Cu for short durations [16]. Nayak and co-workers demonstrated that CVD-graphene could protect Ni substrate against air oxidation at 500 °C for 3 h and exposure to H2O2 solution [17]. Wu et al. also investigated the anticorrosion performance of Cu coated with graphene and found that multi-layered graphene with high density of defects could accelerate the process of corrosive agents reaching the substrate [18]. On one hand, graphene presents advantages over traditional anticorrosion materials. On the other hand, it also presents some disadvantages in corrosion protection. Schriver and co-workers demonstrated that graphene could promote Cu corrosion from one month to two years at room temperature. It is the conductive path existing between Cu and graphene that resulted in the nonuniform corrosion at graphene defects [19]. Zhou and co-workers also confirmed the corrosion-promotion activity of graphene film, which was related to the existence of defects on the graphene film and its high electrical conductivity [20]. Hence, the effective application of graphene in corrosion protection must be taken into consideration. ...
1
2014
... In addition, the preparation of graphene through CVD method has attracted considerable attention [13]. Multilayer graphene can effectively act as the anti-oxidation barrier to protect Ni foils from oxdation [14]. Chen and co-workers demonstrated that graphene prepared using the CVD method could inhibit oxidation on the surface of Cu and Cu/Ni alloys [15]. Dong et al. found that graphene films provided better protection to polished Cu than ground Cu for short durations [16]. Nayak and co-workers demonstrated that CVD-graphene could protect Ni substrate against air oxidation at 500 °C for 3 h and exposure to H2O2 solution [17]. Wu et al. also investigated the anticorrosion performance of Cu coated with graphene and found that multi-layered graphene with high density of defects could accelerate the process of corrosive agents reaching the substrate [18]. On one hand, graphene presents advantages over traditional anticorrosion materials. On the other hand, it also presents some disadvantages in corrosion protection. Schriver and co-workers demonstrated that graphene could promote Cu corrosion from one month to two years at room temperature. It is the conductive path existing between Cu and graphene that resulted in the nonuniform corrosion at graphene defects [19]. Zhou and co-workers also confirmed the corrosion-promotion activity of graphene film, which was related to the existence of defects on the graphene film and its high electrical conductivity [20]. Hence, the effective application of graphene in corrosion protection must be taken into consideration. ...
1
2011
... In addition, the preparation of graphene through CVD method has attracted considerable attention [13]. Multilayer graphene can effectively act as the anti-oxidation barrier to protect Ni foils from oxdation [14]. Chen and co-workers demonstrated that graphene prepared using the CVD method could inhibit oxidation on the surface of Cu and Cu/Ni alloys [15]. Dong et al. found that graphene films provided better protection to polished Cu than ground Cu for short durations [16]. Nayak and co-workers demonstrated that CVD-graphene could protect Ni substrate against air oxidation at 500 °C for 3 h and exposure to H2O2 solution [17]. Wu et al. also investigated the anticorrosion performance of Cu coated with graphene and found that multi-layered graphene with high density of defects could accelerate the process of corrosive agents reaching the substrate [18]. On one hand, graphene presents advantages over traditional anticorrosion materials. On the other hand, it also presents some disadvantages in corrosion protection. Schriver and co-workers demonstrated that graphene could promote Cu corrosion from one month to two years at room temperature. It is the conductive path existing between Cu and graphene that resulted in the nonuniform corrosion at graphene defects [19]. Zhou and co-workers also confirmed the corrosion-promotion activity of graphene film, which was related to the existence of defects on the graphene film and its high electrical conductivity [20]. Hence, the effective application of graphene in corrosion protection must be taken into consideration. ...
1
2015
... In addition, the preparation of graphene through CVD method has attracted considerable attention [13]. Multilayer graphene can effectively act as the anti-oxidation barrier to protect Ni foils from oxdation [14]. Chen and co-workers demonstrated that graphene prepared using the CVD method could inhibit oxidation on the surface of Cu and Cu/Ni alloys [15]. Dong et al. found that graphene films provided better protection to polished Cu than ground Cu for short durations [16]. Nayak and co-workers demonstrated that CVD-graphene could protect Ni substrate against air oxidation at 500 °C for 3 h and exposure to H2O2 solution [17]. Wu et al. also investigated the anticorrosion performance of Cu coated with graphene and found that multi-layered graphene with high density of defects could accelerate the process of corrosive agents reaching the substrate [18]. On one hand, graphene presents advantages over traditional anticorrosion materials. On the other hand, it also presents some disadvantages in corrosion protection. Schriver and co-workers demonstrated that graphene could promote Cu corrosion from one month to two years at room temperature. It is the conductive path existing between Cu and graphene that resulted in the nonuniform corrosion at graphene defects [19]. Zhou and co-workers also confirmed the corrosion-promotion activity of graphene film, which was related to the existence of defects on the graphene film and its high electrical conductivity [20]. Hence, the effective application of graphene in corrosion protection must be taken into consideration. ...
1
2013
... In addition, the preparation of graphene through CVD method has attracted considerable attention [13]. Multilayer graphene can effectively act as the anti-oxidation barrier to protect Ni foils from oxdation [14]. Chen and co-workers demonstrated that graphene prepared using the CVD method could inhibit oxidation on the surface of Cu and Cu/Ni alloys [15]. Dong et al. found that graphene films provided better protection to polished Cu than ground Cu for short durations [16]. Nayak and co-workers demonstrated that CVD-graphene could protect Ni substrate against air oxidation at 500 °C for 3 h and exposure to H2O2 solution [17]. Wu et al. also investigated the anticorrosion performance of Cu coated with graphene and found that multi-layered graphene with high density of defects could accelerate the process of corrosive agents reaching the substrate [18]. On one hand, graphene presents advantages over traditional anticorrosion materials. On the other hand, it also presents some disadvantages in corrosion protection. Schriver and co-workers demonstrated that graphene could promote Cu corrosion from one month to two years at room temperature. It is the conductive path existing between Cu and graphene that resulted in the nonuniform corrosion at graphene defects [19]. Zhou and co-workers also confirmed the corrosion-promotion activity of graphene film, which was related to the existence of defects on the graphene film and its high electrical conductivity [20]. Hence, the effective application of graphene in corrosion protection must be taken into consideration. ...
1
2019
... In addition, the preparation of graphene through CVD method has attracted considerable attention [13]. Multilayer graphene can effectively act as the anti-oxidation barrier to protect Ni foils from oxdation [14]. Chen and co-workers demonstrated that graphene prepared using the CVD method could inhibit oxidation on the surface of Cu and Cu/Ni alloys [15]. Dong et al. found that graphene films provided better protection to polished Cu than ground Cu for short durations [16]. Nayak and co-workers demonstrated that CVD-graphene could protect Ni substrate against air oxidation at 500 °C for 3 h and exposure to H2O2 solution [17]. Wu et al. also investigated the anticorrosion performance of Cu coated with graphene and found that multi-layered graphene with high density of defects could accelerate the process of corrosive agents reaching the substrate [18]. On one hand, graphene presents advantages over traditional anticorrosion materials. On the other hand, it also presents some disadvantages in corrosion protection. Schriver and co-workers demonstrated that graphene could promote Cu corrosion from one month to two years at room temperature. It is the conductive path existing between Cu and graphene that resulted in the nonuniform corrosion at graphene defects [19]. Zhou and co-workers also confirmed the corrosion-promotion activity of graphene film, which was related to the existence of defects on the graphene film and its high electrical conductivity [20]. Hence, the effective application of graphene in corrosion protection must be taken into consideration. ...
1
2013
... In addition, the preparation of graphene through CVD method has attracted considerable attention [13]. Multilayer graphene can effectively act as the anti-oxidation barrier to protect Ni foils from oxdation [14]. Chen and co-workers demonstrated that graphene prepared using the CVD method could inhibit oxidation on the surface of Cu and Cu/Ni alloys [15]. Dong et al. found that graphene films provided better protection to polished Cu than ground Cu for short durations [16]. Nayak and co-workers demonstrated that CVD-graphene could protect Ni substrate against air oxidation at 500 °C for 3 h and exposure to H2O2 solution [17]. Wu et al. also investigated the anticorrosion performance of Cu coated with graphene and found that multi-layered graphene with high density of defects could accelerate the process of corrosive agents reaching the substrate [18]. On one hand, graphene presents advantages over traditional anticorrosion materials. On the other hand, it also presents some disadvantages in corrosion protection. Schriver and co-workers demonstrated that graphene could promote Cu corrosion from one month to two years at room temperature. It is the conductive path existing between Cu and graphene that resulted in the nonuniform corrosion at graphene defects [19]. Zhou and co-workers also confirmed the corrosion-promotion activity of graphene film, which was related to the existence of defects on the graphene film and its high electrical conductivity [20]. Hence, the effective application of graphene in corrosion protection must be taken into consideration. ...
1
2013
... In addition, the preparation of graphene through CVD method has attracted considerable attention [13]. Multilayer graphene can effectively act as the anti-oxidation barrier to protect Ni foils from oxdation [14]. Chen and co-workers demonstrated that graphene prepared using the CVD method could inhibit oxidation on the surface of Cu and Cu/Ni alloys [15]. Dong et al. found that graphene films provided better protection to polished Cu than ground Cu for short durations [16]. Nayak and co-workers demonstrated that CVD-graphene could protect Ni substrate against air oxidation at 500 °C for 3 h and exposure to H2O2 solution [17]. Wu et al. also investigated the anticorrosion performance of Cu coated with graphene and found that multi-layered graphene with high density of defects could accelerate the process of corrosive agents reaching the substrate [18]. On one hand, graphene presents advantages over traditional anticorrosion materials. On the other hand, it also presents some disadvantages in corrosion protection. Schriver and co-workers demonstrated that graphene could promote Cu corrosion from one month to two years at room temperature. It is the conductive path existing between Cu and graphene that resulted in the nonuniform corrosion at graphene defects [19]. Zhou and co-workers also confirmed the corrosion-promotion activity of graphene film, which was related to the existence of defects on the graphene film and its high electrical conductivity [20]. Hence, the effective application of graphene in corrosion protection must be taken into consideration. ...
1
2014
... Sun et al. encapsulated graphene in low-electrical-conductivity pernigraniline, nanosized SiO2, or (3-aminopropyl)-triethoxysilane (APTES) to inhibit the corrosion-promotion activity of graphene. These work revealed that embedding synthesized graphene/pernigraniline, rGO@APTES, or graphene@SiO2 into a coating could effectively enhance the anticorrosion ability of a coating [[21], [22], [23]]. However, the applied amount of these composites was large (>5 wt.%), suggesting that these methods of encapsulating graphene considerably reduced the utilizition of graphene. Therefore, eliminating the corrosion-promotion activity of graphene is a remarkable challenge for the further development of graphene application in corrosion protection. ...
1
2015
... Sun et al. encapsulated graphene in low-electrical-conductivity pernigraniline, nanosized SiO2, or (3-aminopropyl)-triethoxysilane (APTES) to inhibit the corrosion-promotion activity of graphene. These work revealed that embedding synthesized graphene/pernigraniline, rGO@APTES, or graphene@SiO2 into a coating could effectively enhance the anticorrosion ability of a coating [[21], [22], [23]]. However, the applied amount of these composites was large (>5 wt.%), suggesting that these methods of encapsulating graphene considerably reduced the utilizition of graphene. Therefore, eliminating the corrosion-promotion activity of graphene is a remarkable challenge for the further development of graphene application in corrosion protection. ...
1
2015
... Sun et al. encapsulated graphene in low-electrical-conductivity pernigraniline, nanosized SiO2, or (3-aminopropyl)-triethoxysilane (APTES) to inhibit the corrosion-promotion activity of graphene. These work revealed that embedding synthesized graphene/pernigraniline, rGO@APTES, or graphene@SiO2 into a coating could effectively enhance the anticorrosion ability of a coating [[21], [22], [23]]. However, the applied amount of these composites was large (>5 wt.%), suggesting that these methods of encapsulating graphene considerably reduced the utilizition of graphene. Therefore, eliminating the corrosion-promotion activity of graphene is a remarkable challenge for the further development of graphene application in corrosion protection. ...
1
2013
... Becides the encapsulation strategy of graphene with high electrical conductivity, another effective method to eliminate the corrosion-promotion activity of graphene is doping heteroatoms in graphene, which could tailor graphene’s electronic structures and electrochemical properties by changing the electronic density within graphene [24,25]. The electronegativity of N atom is higher than that of C atom, and its radius is similar to that of the C atom. Moreover, the introduction of N atom could change the local electronic structures of graphene. Therefore, chemical reactivity of graphene changed. Recently, N-doped graphene (NG) has attracted considerable attention from researchers. Ren et al. found that the corrosion resistance of NG film with large doping concentration was poorer compared with those of others due to the discontinuity of the film [26]. Hence, preparing NG with ideal chemical structures and chemical properties is very important in industrial applications. F-doped graphene (FG) could also eliminate the corrosion-promotion activity of graphene because F atom is more electronegative than C atom. Liu and co-workers reported that fluorographene was incorporated into polyvinyl butyral coating to enhance its corrosion protection performances [27]. They also found that superhydrophobic epoxy coating modified by fluorographene could be used for anti-corrosion and self-cleaning [28]. FG not only possesses a distinctive feature of electrical insulation but also does not change the utilization of graphene by a wide margin. Therefore, we selected FG as the additive of epoxy coatings in the present work. FG was obtained by reacting reduced GO (rGO) with fluorine gas (F2) in a special Teflon autoclave instead of exfoliation of fluorographite or fluorination of GO. This method allows rGO and F2 to come in full contact. Moreover, varying degrees of F-doped FG could be prepared. To the best of our knowledge, contrastive study of FG addition with different F-doped degrees in epoxy matrix (EP) has not been systematically investigated. The difference in corrosion resistance between FG and rGO should also be discussed. The addition of FG to EP could provide new possibilities for eliminating the corrosion-promotion activity of graphene. ...
1
2012
... Becides the encapsulation strategy of graphene with high electrical conductivity, another effective method to eliminate the corrosion-promotion activity of graphene is doping heteroatoms in graphene, which could tailor graphene’s electronic structures and electrochemical properties by changing the electronic density within graphene [24,25]. The electronegativity of N atom is higher than that of C atom, and its radius is similar to that of the C atom. Moreover, the introduction of N atom could change the local electronic structures of graphene. Therefore, chemical reactivity of graphene changed. Recently, N-doped graphene (NG) has attracted considerable attention from researchers. Ren et al. found that the corrosion resistance of NG film with large doping concentration was poorer compared with those of others due to the discontinuity of the film [26]. Hence, preparing NG with ideal chemical structures and chemical properties is very important in industrial applications. F-doped graphene (FG) could also eliminate the corrosion-promotion activity of graphene because F atom is more electronegative than C atom. Liu and co-workers reported that fluorographene was incorporated into polyvinyl butyral coating to enhance its corrosion protection performances [27]. They also found that superhydrophobic epoxy coating modified by fluorographene could be used for anti-corrosion and self-cleaning [28]. FG not only possesses a distinctive feature of electrical insulation but also does not change the utilization of graphene by a wide margin. Therefore, we selected FG as the additive of epoxy coatings in the present work. FG was obtained by reacting reduced GO (rGO) with fluorine gas (F2) in a special Teflon autoclave instead of exfoliation of fluorographite or fluorination of GO. This method allows rGO and F2 to come in full contact. Moreover, varying degrees of F-doped FG could be prepared. To the best of our knowledge, contrastive study of FG addition with different F-doped degrees in epoxy matrix (EP) has not been systematically investigated. The difference in corrosion resistance between FG and rGO should also be discussed. The addition of FG to EP could provide new possibilities for eliminating the corrosion-promotion activity of graphene. ...
1
2018
... Becides the encapsulation strategy of graphene with high electrical conductivity, another effective method to eliminate the corrosion-promotion activity of graphene is doping heteroatoms in graphene, which could tailor graphene’s electronic structures and electrochemical properties by changing the electronic density within graphene [24,25]. The electronegativity of N atom is higher than that of C atom, and its radius is similar to that of the C atom. Moreover, the introduction of N atom could change the local electronic structures of graphene. Therefore, chemical reactivity of graphene changed. Recently, N-doped graphene (NG) has attracted considerable attention from researchers. Ren et al. found that the corrosion resistance of NG film with large doping concentration was poorer compared with those of others due to the discontinuity of the film [26]. Hence, preparing NG with ideal chemical structures and chemical properties is very important in industrial applications. F-doped graphene (FG) could also eliminate the corrosion-promotion activity of graphene because F atom is more electronegative than C atom. Liu and co-workers reported that fluorographene was incorporated into polyvinyl butyral coating to enhance its corrosion protection performances [27]. They also found that superhydrophobic epoxy coating modified by fluorographene could be used for anti-corrosion and self-cleaning [28]. FG not only possesses a distinctive feature of electrical insulation but also does not change the utilization of graphene by a wide margin. Therefore, we selected FG as the additive of epoxy coatings in the present work. FG was obtained by reacting reduced GO (rGO) with fluorine gas (F2) in a special Teflon autoclave instead of exfoliation of fluorographite or fluorination of GO. This method allows rGO and F2 to come in full contact. Moreover, varying degrees of F-doped FG could be prepared. To the best of our knowledge, contrastive study of FG addition with different F-doped degrees in epoxy matrix (EP) has not been systematically investigated. The difference in corrosion resistance between FG and rGO should also be discussed. The addition of FG to EP could provide new possibilities for eliminating the corrosion-promotion activity of graphene. ...
1
2016
... Becides the encapsulation strategy of graphene with high electrical conductivity, another effective method to eliminate the corrosion-promotion activity of graphene is doping heteroatoms in graphene, which could tailor graphene’s electronic structures and electrochemical properties by changing the electronic density within graphene [24,25]. The electronegativity of N atom is higher than that of C atom, and its radius is similar to that of the C atom. Moreover, the introduction of N atom could change the local electronic structures of graphene. Therefore, chemical reactivity of graphene changed. Recently, N-doped graphene (NG) has attracted considerable attention from researchers. Ren et al. found that the corrosion resistance of NG film with large doping concentration was poorer compared with those of others due to the discontinuity of the film [26]. Hence, preparing NG with ideal chemical structures and chemical properties is very important in industrial applications. F-doped graphene (FG) could also eliminate the corrosion-promotion activity of graphene because F atom is more electronegative than C atom. Liu and co-workers reported that fluorographene was incorporated into polyvinyl butyral coating to enhance its corrosion protection performances [27]. They also found that superhydrophobic epoxy coating modified by fluorographene could be used for anti-corrosion and self-cleaning [28]. FG not only possesses a distinctive feature of electrical insulation but also does not change the utilization of graphene by a wide margin. Therefore, we selected FG as the additive of epoxy coatings in the present work. FG was obtained by reacting reduced GO (rGO) with fluorine gas (F2) in a special Teflon autoclave instead of exfoliation of fluorographite or fluorination of GO. This method allows rGO and F2 to come in full contact. Moreover, varying degrees of F-doped FG could be prepared. To the best of our knowledge, contrastive study of FG addition with different F-doped degrees in epoxy matrix (EP) has not been systematically investigated. The difference in corrosion resistance between FG and rGO should also be discussed. The addition of FG to EP could provide new possibilities for eliminating the corrosion-promotion activity of graphene. ...
1
2017
... Becides the encapsulation strategy of graphene with high electrical conductivity, another effective method to eliminate the corrosion-promotion activity of graphene is doping heteroatoms in graphene, which could tailor graphene’s electronic structures and electrochemical properties by changing the electronic density within graphene [24,25]. The electronegativity of N atom is higher than that of C atom, and its radius is similar to that of the C atom. Moreover, the introduction of N atom could change the local electronic structures of graphene. Therefore, chemical reactivity of graphene changed. Recently, N-doped graphene (NG) has attracted considerable attention from researchers. Ren et al. found that the corrosion resistance of NG film with large doping concentration was poorer compared with those of others due to the discontinuity of the film [26]. Hence, preparing NG with ideal chemical structures and chemical properties is very important in industrial applications. F-doped graphene (FG) could also eliminate the corrosion-promotion activity of graphene because F atom is more electronegative than C atom. Liu and co-workers reported that fluorographene was incorporated into polyvinyl butyral coating to enhance its corrosion protection performances [27]. They also found that superhydrophobic epoxy coating modified by fluorographene could be used for anti-corrosion and self-cleaning [28]. FG not only possesses a distinctive feature of electrical insulation but also does not change the utilization of graphene by a wide margin. Therefore, we selected FG as the additive of epoxy coatings in the present work. FG was obtained by reacting reduced GO (rGO) with fluorine gas (F2) in a special Teflon autoclave instead of exfoliation of fluorographite or fluorination of GO. This method allows rGO and F2 to come in full contact. Moreover, varying degrees of F-doped FG could be prepared. To the best of our knowledge, contrastive study of FG addition with different F-doped degrees in epoxy matrix (EP) has not been systematically investigated. The difference in corrosion resistance between FG and rGO should also be discussed. The addition of FG to EP could provide new possibilities for eliminating the corrosion-promotion activity of graphene. ...
1
2013
... Multilayer FGi materials were synthesized by reacting exfoliated rGO powder with F2 in a Teflon autoclave. First, 0.05 g of rGO was placed in the Teflon autoclave, and N2-F2 mixture gas (80 vol% N2, 20 vol% F2) was introduced at 300 °C for 6, 12, and 24 h. Hence, the FGi materials with various F-doped degrees were obtained by controlling the reaction time. With the increase of F-doped degrees, the color of FGi materials changed from black to white, as shown in Fig. 1. We adopted the modified method proposed in the literature via a one-pot sonochemical exfoliation method under ambient conditions (Fig. 1) to obtain the few-layered FG nanosheets [29]. The procedure for preparing the few-layered FG dispersion was as follows. Approximately 75 mg of multilayer FGi was added to 18 mL of chloroform solvent. Subsequently, the system was ultrasonicated in an ice-bath under ambient conditions for 3 h to obtain a stabilized FG dispersion. Graphene dispersion was prepared in a similar method. ...
1
2010
... AFM was then employed to evaluate the thickness of rGO and FG. As shown in Fig. 2(e), the thickness of a rGO sheet was approximately 3.50 nm. The thickness of the FG sheets in Fig. 2(f-h) was approximately 3-4 nm. Considering that the thickness of a single-layer FG is 0.8-1.0 nm [30,31], the layer number of the obtained FG sheets was approximately 3-5. ...
1
2012
... AFM was then employed to evaluate the thickness of rGO and FG. As shown in Fig. 2(e), the thickness of a rGO sheet was approximately 3.50 nm. The thickness of the FG sheets in Fig. 2(f-h) was approximately 3-4 nm. Considering that the thickness of a single-layer FG is 0.8-1.0 nm [30,31], the layer number of the obtained FG sheets was approximately 3-5. ...
1
2017
... The FTIR results of rGO and FG materials are presented in Fig. 4(a). The plot of rGO exhibited the C—O ether group stretching at 1285 cm-1, C—O anhydride group stretching at 1057 cm-1, C—OH stretching at 1400 cm-1, C=C stretching at 1645 cm-1, and carbon skeletons at 1572 cm-1 [32]. FG displayed an obvious peak at 1215 cm-1, which corresponded to the stretching vibration mode of C—F bonds in the structures [33]. This peak became stronger with the increase of F-doped degree of FG materials. In the case of FG-3, the C—F streching vibration situated at the nanosheet margin was located at 1324 cm-1 [34]. However, the bond was not evident from FG-1 and FG-2. The absorption peaks of the carbon skeletons appeared at 1523, 1625 (FG-3), and 1555 cm-1 (FG-1 and FG-2). ...
1
2003
... The FTIR results of rGO and FG materials are presented in Fig. 4(a). The plot of rGO exhibited the C—O ether group stretching at 1285 cm-1, C—O anhydride group stretching at 1057 cm-1, C—OH stretching at 1400 cm-1, C=C stretching at 1645 cm-1, and carbon skeletons at 1572 cm-1 [32]. FG displayed an obvious peak at 1215 cm-1, which corresponded to the stretching vibration mode of C—F bonds in the structures [33]. This peak became stronger with the increase of F-doped degree of FG materials. In the case of FG-3, the C—F streching vibration situated at the nanosheet margin was located at 1324 cm-1 [34]. However, the bond was not evident from FG-1 and FG-2. The absorption peaks of the carbon skeletons appeared at 1523, 1625 (FG-3), and 1555 cm-1 (FG-1 and FG-2). ...
1
2011
... The FTIR results of rGO and FG materials are presented in Fig. 4(a). The plot of rGO exhibited the C—O ether group stretching at 1285 cm-1, C—O anhydride group stretching at 1057 cm-1, C—OH stretching at 1400 cm-1, C=C stretching at 1645 cm-1, and carbon skeletons at 1572 cm-1 [32]. FG displayed an obvious peak at 1215 cm-1, which corresponded to the stretching vibration mode of C—F bonds in the structures [33]. This peak became stronger with the increase of F-doped degree of FG materials. In the case of FG-3, the C—F streching vibration situated at the nanosheet margin was located at 1324 cm-1 [34]. However, the bond was not evident from FG-1 and FG-2. The absorption peaks of the carbon skeletons appeared at 1523, 1625 (FG-3), and 1555 cm-1 (FG-1 and FG-2). ...
1
2014
... The structures of rGO, FG-1, FG-2, and FG-3 were also confirmed by XRD measurements. In Fig. 4(b), rGO exhibited a [002] peak at 2θ = 26.36°, suggesting that the high reduction degree of rGO could lead to rGO aggregation and a structure similar to that of graphite. However, the [002] peak gradually disappeared with the increase of F-doped degree of the FG samples; by contrast, a new peak of [001] at 2θ = 13.33° appeared, and the intensity increased with the increase in F-doped degree. As shown in Fig. 4(b), the [100] peak located at approximately 40°-45° was related to the in-plane crystallite size of the samples [35,36]. In accordance with the change of the [100] peak position and the change of the full width at half maximum, we deduced that the in-plane crystallite size of FG samples decreased along with the increase of F-doped degree. ...
1
1941
... The structures of rGO, FG-1, FG-2, and FG-3 were also confirmed by XRD measurements. In Fig. 4(b), rGO exhibited a [002] peak at 2θ = 26.36°, suggesting that the high reduction degree of rGO could lead to rGO aggregation and a structure similar to that of graphite. However, the [002] peak gradually disappeared with the increase of F-doped degree of the FG samples; by contrast, a new peak of [001] at 2θ = 13.33° appeared, and the intensity increased with the increase in F-doped degree. As shown in Fig. 4(b), the [100] peak located at approximately 40°-45° was related to the in-plane crystallite size of the samples [35,36]. In accordance with the change of the [100] peak position and the change of the full width at half maximum, we deduced that the in-plane crystallite size of FG samples decreased along with the increase of F-doped degree. ...
1
2013
... Impedance plots (bode and Nyquist plots) of the five coatings are shown in Fig. 7. In addition, some frequencies were marked in Fig. 7 of Nyquist plots (for example, 0.01 Hz, 0.0316 Hz and 0.0618 Hz were marked in Fig. 7(c1)). The enlarged image of Fig. 7(c1) was shown in Fig. S1 in the Supplementary Material. Impedance modulus at the lowest frequency (Zf=0.01Hz) is one of the electrochemical parameters for evaluating the corrosion resistance of the coatings. After immersion for 5 days, the Zf=0.01Hz values of the total coatings exceeded 109 Ω cm2 except for EP/rGO coating. The Zf=0.01Hz results of EP/FG-2 and EP/FG-3 coatings exceeded 1011 Ω cm2. After 50 days of immersion, the Zf=0.01Hz results of blank EP and EP/rGO coatings decreased to 6.20 × 107 and 5.63 × 107 Ω cm2, respectively. However, the Zf=0.01Hz values of EP/FG-1, EP/FG-2, and EP/FG-3 coatings decreased slightly to 1.47 × 109, 5.25 × 1010, and 6.81 × 1010 Ω cm2, respectively. In the case of the blank EP coating, the phase angle curve presented one time constant, indicating the response of coating resistance. Additionally, the phase angle of blank EP coating was 85° within the range of 102.5-105 Hz after 40 days of immersion (Fig. 7(b1)). Subsequently, the phase angle curves of the coating showed two time constants from 50 days to 90 days of immersion. The time constant existing at high frequencies corresponded to the barrier property of a coating. The emergence of the second time constant at the middle-low frequencies suggested that the corrosive agents diffused to the metal substrate and that corrosion reactions occurred [37,38]. With regard to EP/rGO, the second time constant at low frequency after immersion for 5 days indicated that the corrosive medium could easily penetrate the metallic substrate because rGO with high electrical conductivity could promote corrosion. The phase angle of EP/FG-1 coating was near 85° in the range of 101-105 Hz. It was lower than 10° at 10-2 Hz. The phase angles of EP/FG-2 and EP/FG-3 coatings were close to 85° within the range of 10°-105 and 10-0.5-105 Hz, respectively. At 0.01 Hz, the phase angle of EP/FG-2 coating was approximately 20°, whereas that of EP/FG-3 coating was approximately 30°. At 90 days of immersion, the Zf=0.01Hz values of blank EP and EP/rGO decreased to 1.36 × 106 and 5.46 × 107 Ω cm2, respectively. However, the Zf=0.01Hz results of EP/FG-1, EP/FG-2, and EP/FG-3 maintained at 2.97 × 108, 2.92 × 1010, and 3.15 × 1010 Ω·cm2, suggesting that the coatings featured long-term anticorrosion ability. The phase angle of EP/FG-2 and EP/FG-3 coatings reached 85° within a frequency range of 10°-105 Hz (Fig. 7 (b4 and b5)). Thus, the EP/FG composite coatings presented better corrosion protection in comparison with the blank EP and EP/rGO coatings. ...
1
2014
... Impedance plots (bode and Nyquist plots) of the five coatings are shown in Fig. 7. In addition, some frequencies were marked in Fig. 7 of Nyquist plots (for example, 0.01 Hz, 0.0316 Hz and 0.0618 Hz were marked in Fig. 7(c1)). The enlarged image of Fig. 7(c1) was shown in Fig. S1 in the Supplementary Material. Impedance modulus at the lowest frequency (Zf=0.01Hz) is one of the electrochemical parameters for evaluating the corrosion resistance of the coatings. After immersion for 5 days, the Zf=0.01Hz values of the total coatings exceeded 109 Ω cm2 except for EP/rGO coating. The Zf=0.01Hz results of EP/FG-2 and EP/FG-3 coatings exceeded 1011 Ω cm2. After 50 days of immersion, the Zf=0.01Hz results of blank EP and EP/rGO coatings decreased to 6.20 × 107 and 5.63 × 107 Ω cm2, respectively. However, the Zf=0.01Hz values of EP/FG-1, EP/FG-2, and EP/FG-3 coatings decreased slightly to 1.47 × 109, 5.25 × 1010, and 6.81 × 1010 Ω cm2, respectively. In the case of the blank EP coating, the phase angle curve presented one time constant, indicating the response of coating resistance. Additionally, the phase angle of blank EP coating was 85° within the range of 102.5-105 Hz after 40 days of immersion (Fig. 7(b1)). Subsequently, the phase angle curves of the coating showed two time constants from 50 days to 90 days of immersion. The time constant existing at high frequencies corresponded to the barrier property of a coating. The emergence of the second time constant at the middle-low frequencies suggested that the corrosive agents diffused to the metal substrate and that corrosion reactions occurred [37,38]. With regard to EP/rGO, the second time constant at low frequency after immersion for 5 days indicated that the corrosive medium could easily penetrate the metallic substrate because rGO with high electrical conductivity could promote corrosion. The phase angle of EP/FG-1 coating was near 85° in the range of 101-105 Hz. It was lower than 10° at 10-2 Hz. The phase angles of EP/FG-2 and EP/FG-3 coatings were close to 85° within the range of 10°-105 and 10-0.5-105 Hz, respectively. At 0.01 Hz, the phase angle of EP/FG-2 coating was approximately 20°, whereas that of EP/FG-3 coating was approximately 30°. At 90 days of immersion, the Zf=0.01Hz values of blank EP and EP/rGO decreased to 1.36 × 106 and 5.46 × 107 Ω cm2, respectively. However, the Zf=0.01Hz results of EP/FG-1, EP/FG-2, and EP/FG-3 maintained at 2.97 × 108, 2.92 × 1010, and 3.15 × 1010 Ω·cm2, suggesting that the coatings featured long-term anticorrosion ability. The phase angle of EP/FG-2 and EP/FG-3 coatings reached 85° within a frequency range of 10°-105 Hz (Fig. 7 (b4 and b5)). Thus, the EP/FG composite coatings presented better corrosion protection in comparison with the blank EP and EP/rGO coatings. ...
1
2011
... The EIS results of the coatings were fitted by Zview software using the equivalent electrical circuits in Models I, II, and III (Fig. 8(a)). In Fig. 8(a), Rs is the solution resistance, Rc is the coating resistance, and Cc is the coating capacitance. Qdl is the double-layer capacitance, and Rct is the charge-transfer resistance. With regard to the blank EP coating, the Model I equivalent electrical circuit (Fig. 8(a)) was used before 30 days of immersion. In this process, the corrosive agents did not diffuse to the steel substrate. Subsequently, the Model II equivalent electrical circuit was used, indicating that the corrosive agents diffused to the steel substrate and corrosion reaction occurred. After 50 days, Warburg impedance (Zw) was included in the equivalent electric circuit, which could be assigned to the diffusion-controlled process at the corroding interface (Model III). For the EP/rGO coating, the Model II equivalent electrical circuit was used before 40 days of immersion. Then, it was expressed as Model III. With regard to EP/FG-1, the Model I equivalent electrical circuit was employed within 80 days of immersion. Thereafter, the Model II equivalent electrical circuit was used. However, the equivalent electrical circuit was expressed as Model I for EP/FG-2 and EP/FG-3 during the whole immersion process, revealing that FG-2 and FG-3 could effectively extend the time for corrosive agents diffusing to the steel substrate. The variation of Cc values with the immersion time for the five coatings is shown in Fig. 8(b). Generally speaking, water absorption of the coatings can be presented by the variation of Cc results [39]. As the diffusion of water into the coating increased, Cc showed a tendency to increase. For EP and EP/rGO, Cc fluctuated within 50 days of immersion. Then, the values increased markedly after immersion for 50 days, suggesting that the absorption of water did not reach saturation state. In case of EP/FG-1, EP/FG-2, and EP/FG-3 coatings, Cc increased slowly within 80 days of immersion, revealing the diffusion of water into the coating matrix. By contrast, after 80 days of immersion, the Cc values of EP/FG-1, EP/FG-2, and EP/FG-3 maintained at 1.705 × 10-10, 1.303 × 10-10, and 1.132 × 10-10 F·cm2, respectively. Overall, the EP/FG coatings had lower Cc values than the other two coatings, implying that EP/FG coatings adsorbed less water than EP and EP/rGO coatings. ...
1
2017
... The anticorrosion performance of all coatings was also discussed in terms of Rc values. Rc usually decreases as the immersion time of the coatings increases because the electrolytes could penetrate through the coating pores. Rc reflects the barrier capacity of the coatings toward electrolytes [40]. Fig. 8(c) shows the trend of Rc values of the five coatings with prolonged immersion time. The Rc values of blank EP coating markedly decreased from 3.58 × 109 Ω cm2 to 9.27 × 105 Ω cm2 within 80 days of immersion. Thereafter, it stabilized near 1 × 106 Ω cm2. The Rc of EP/rGO slowly varied from 3.297 × 107 Ω cm2 to 1.45 × 107 Ω cm2 during immersion. The Rc values of EP/FG-1 slowly decreased within 80 days of immersion and decreased to 5.48 × 107 Ω cm2 at the end of immersion. However, the Rc values of EP/FG-2 and EP/FG-3 coatings dropped by an order of magnitude during the whole immersion time. The findings verified that EP coatings with F-doped rGO presented superior corrosion resistance than blank EP and EP/rGO coatings. Furthermore, the steady Rc values of EP/FG-2 and EP/FG-3 coatings revealed that they exhibited optimal barrier function and effectively reduced the diffusion of corrosion agents into the coatings due to the impermeable and electrically insulating FG nanosheets added in the coatings. ...
1
2008
... Raman spectroscopy, a reliable non-destructive technique, has been employed for identifying pure iron oxides and steel corrosive products [41,42]. The Raman results of the rusting layers formed on the Q235 steel substrates coated by the five kinds of coatings are shown in Fig. 12. The major components of the corrosion products that formed on the corrosive atmosphere of steel were goethite (α-FeOOH), akaganeite (β-FeOOH), lepidocrocite (γ-FeOOH), and feroxyhite (δ-FeOOH) [43]. Among them, β-FeOOH is formed only in saline conditions and is often found in marine environments and chloride-rich solutions [44]. EP displayed bands at 310, 328, 392, 419, 540, and 723 cm-1, and EP/rGO showed bands at 313, 392, 421, 538, and 721 cm-1, which could likely represent β-FeOOH. In the case of EP/FG-1, EP/FG-2, and ER/FG-3 coated steels, the characteristic bands of iron oxides were not observed, which confirmed that they were not corroded. ...
1
1999
... Raman spectroscopy, a reliable non-destructive technique, has been employed for identifying pure iron oxides and steel corrosive products [41,42]. The Raman results of the rusting layers formed on the Q235 steel substrates coated by the five kinds of coatings are shown in Fig. 12. The major components of the corrosion products that formed on the corrosive atmosphere of steel were goethite (α-FeOOH), akaganeite (β-FeOOH), lepidocrocite (γ-FeOOH), and feroxyhite (δ-FeOOH) [43]. Among them, β-FeOOH is formed only in saline conditions and is often found in marine environments and chloride-rich solutions [44]. EP displayed bands at 310, 328, 392, 419, 540, and 723 cm-1, and EP/rGO showed bands at 313, 392, 421, 538, and 721 cm-1, which could likely represent β-FeOOH. In the case of EP/FG-1, EP/FG-2, and ER/FG-3 coated steels, the characteristic bands of iron oxides were not observed, which confirmed that they were not corroded. ...
1
1974
... Raman spectroscopy, a reliable non-destructive technique, has been employed for identifying pure iron oxides and steel corrosive products [41,42]. The Raman results of the rusting layers formed on the Q235 steel substrates coated by the five kinds of coatings are shown in Fig. 12. The major components of the corrosion products that formed on the corrosive atmosphere of steel were goethite (α-FeOOH), akaganeite (β-FeOOH), lepidocrocite (γ-FeOOH), and feroxyhite (δ-FeOOH) [43]. Among them, β-FeOOH is formed only in saline conditions and is often found in marine environments and chloride-rich solutions [44]. EP displayed bands at 310, 328, 392, 419, 540, and 723 cm-1, and EP/rGO showed bands at 313, 392, 421, 538, and 721 cm-1, which could likely represent β-FeOOH. In the case of EP/FG-1, EP/FG-2, and ER/FG-3 coated steels, the characteristic bands of iron oxides were not observed, which confirmed that they were not corroded. ...
1
2004
... Raman spectroscopy, a reliable non-destructive technique, has been employed for identifying pure iron oxides and steel corrosive products [41,42]. The Raman results of the rusting layers formed on the Q235 steel substrates coated by the five kinds of coatings are shown in Fig. 12. The major components of the corrosion products that formed on the corrosive atmosphere of steel were goethite (α-FeOOH), akaganeite (β-FeOOH), lepidocrocite (γ-FeOOH), and feroxyhite (δ-FeOOH) [43]. Among them, β-FeOOH is formed only in saline conditions and is often found in marine environments and chloride-rich solutions [44]. EP displayed bands at 310, 328, 392, 419, 540, and 723 cm-1, and EP/rGO showed bands at 313, 392, 421, 538, and 721 cm-1, which could likely represent β-FeOOH. In the case of EP/FG-1, EP/FG-2, and ER/FG-3 coated steels, the characteristic bands of iron oxides were not observed, which confirmed that they were not corroded. ...
, Kui Wang
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