In situ deposition reduced graphene oxide-silica for improving the corrosion resistance of organic epoxy coatings: A comparative study

In situ deposition reduced graphene oxide-silica for improving the corrosion resistance of organic epoxy coatings: A comparative study | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article In situ deposition reduced graphene oxide-silica for improving the corrosion resistance of organic epoxy coatings: A comparative study Jiaqi Huang, Meiping Wu, Xiaojin Miao, Jianyu Wang, Yiwen Chen, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4022694/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract In this study, two facile routes for in situ construction and characterization of silica particles decorated with reduced graphene oxide (rGO-SiO 2 ) based on the sol-gel principle are reported and incorporated into epoxy resins to prepare coatings for comparative testing of their corrosion protection and mechanical properties. The microstructure, phase identification and composition of the hybrid materials were characterized by SEM, XRD, and FT-IR, respectively. The results demonstrated that both two methods can successfully generate silica on the surface of reduced graphene oxide, but the silica generated by method I had lower content and finer size. And this trend was more obvious with the increase of reaction time. The mechanical properties and anticorrosion behavior of the epoxy coatings were investigated by coating adhesion automated scratch test, contact angle, salt spray test and EIS test. The results were shown that incorporation of rGO-SiO 2 hybrids (produced in both methods I and II) into the epoxy coating notably enhanced its bongding strength, dispersion performance, barrier properties and corrosion resistance. It was also indicated that the hybrid material prepared by method I after 48h had the best mechanical and anti-corrosion properties. Silica particles-decorated reduced graphene oxide hybrids (rGO-SiO2) TEOS epoxy coatings corrosion Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 1. Introduction Corrosion of metals and alloys is a key problem in industrial areas around the world, causing huge economic losses and risks to security and the environment [ 1 ]. So far, epoxy coatings have been the main corrosion protection strategy, which provides a strong barrier to metal from penetration by aggressive agents [ 2 ]. However, in the curing process of epoxy resin, there are some problems such as high brittleness caused by cross-linking and curing, and large amounts of micro-pores are easily generated by the release of solvent [ 3 ]. Recent research has shown that the addition of nanofillers to the epoxy coatings improves their barrier and corrosion resistance [ 4 ]. Nanofillers are capable of blocking the micro-pores and cavities existed in the coating matrix and reducing the electrolyte diffusion to the coating/metal interface through zigzagging the electrolyte pathway [ 5 – 6 ]. Also, surface functional nanoparticles can increase the crosslink density of the coating and improve its barrier properties [ 7 – 8 ]. Graphene and its derivatives, due to their lightweight two-dimensional structure, possess unique properties such as hydrophobicity, impermeability to small molecules, and high chemical inertness [ 9 ]. Therefore, they have great potential for application in the field of anti-corrosion coatings and are ideal filling materials for anti-corrosion coatings [ 10 ]. However, the high specific surface area and strong π-π interactions between graphene layers make it highly prone to agglomeration, affecting its uniform dispersion in coating media. Moreover, the high conductivity of structurally intact graphene can promote corrosion activity [ 11 ]. Reduced graphene oxide (rGO) has been reported to have poor conductivity, good hydrophobicity and low production cost [xx], which is suitable to used as filling material. Besides, corrosion protection coatings functionalized with rGO are proven to possess excellent shielding effects [ 12 ]. In recent studies it has been reported that chemical and/or physical grafting of nanoparticles i.e. platinum [ 13 ], silver [ 14 ], zinc oxide [ 15 ], titanium dioxide [ 16 ] on the basal planes of GO sheet as spacer could prevent it from aggregation in polymer coating and a higher degree of exfoliation can be obtained. Yu et al. [ 17 ] reported the effect of graphene oxide sheets modified by titanium dioxide (GO-TiO 2 ) and alumina nanoparticles (GO-Al 2 O 3 ) on the corrosion protection performance of epoxy coating. Results showed that decorating GO sheets by TiO 2 and Al 2 O 3 nanoparticles significantly enhanced their exfoliation and dispersion in the epoxy coating. GO-Al 2 O 3 and GO-TiO 2 nanoparticles could enhance the corrosion resistance of epoxy coating through plugging its micro-pores. Kou et al. [ 18 ] used TEOS for synthesis of silica nanoparticles on the GO surface for producing super hydrophilic coatings. They employed a one-step sol-gel route for this purpose and achieved proper enhancement. To the best of our knowledge there is no systematic report on the synthesis of rGO-SiO 2 nanohybrids using mixture of silanes and its effect on the barrier performance and corrosion resistance of the polymeric coating. In this study, we aimed at the synthesis of rGO-SiO 2 hybrids through a two-step sol-gel method using TEOS in a water-alcohol solution. rGO-SiO 2 hybrids were synthesized by two different methods. The properties of two routes of synthesis rGO-SiO 2 hybrids were compared by employing FTIR, XRD, and SEM analysis. The rGO-SiO 2 hybrids produced by two methods (I and II) were incorporated into the epoxy coating. The effect of rGO-SiO 2 hybrids on the barrier and corrosion protection performance of the coating was investigated by SEM and EIS analysis. 2. Experimental 2.1 Raw materials The rGO sheets was purchased from SZGraphene Nanotechnology Co. (China). The Tetraethylorthosilicate (TEOS, C 8 H 20 O 4 Si) were purchased from Aldrich Co. (Germany). Acetic acid (C 2 H 4 O 2 ), ethanol (C 2 H 5 OH, 98%), and sodium hydroxide (NaOH) were purchased from HUSHI. Epoxy lotion (6520) was prepared from CNOOC Changzhou Coating and Chemical Research Institute Co.. The polyamine hardener (8538-Y-68) was purchased from HEXION (America). The sodium nitrite (NaNO 2 , 99%), leveling agent and defoamer (902W) were purchased from Shanghai LingFeng Chemical Reagent Co., BYK and Nanjing Hanbao Co., respectively. 2.2 Preparation of rGO-SiO 2 hybrids synthesis Method I : Functionalization of rGO sheets was achieved by in-situ hydrolysis of TEOS silane. For this purpose 25 mg rGO sheets was dispersed in 100 mL solution of alcohol – water-silane (75: 10: 15, v/v) through 30 min sonication. The pH of the mixture was then adjusted on 4.5 with acetic acid, and the mixture was left at room temperature (25℃) for 24, 48, and 72 hours. After 24 hours, 48 hours and 72 hours, the pH of the reaction mixture was raised to 8.5 with a solution of sodium hydroxide (5 wt.%). The mixture was kept at 65℃ for 1 hour to condense silanes which were physically adsorbed on rGO surface. The rGO-SiO 2 suspension was centrifuged and washed 5 times with 100 mL mixture of alcohol-water (3:1, v/v) and finally one time with 100 mL water. The final product was stored in alcohol for further characterizations. The hybrids were named as rGO-SiO 2 -I/24h, rGO-SiO 2 -I/48h and rGO-SiO 2 -I/72h, respectively. Method II : In this method the SiO 2 particles were deposited on the rGO sheets by an in situ hydrolysis of TEOS silane. For this purpose, a mixture of alcohol-water-silane (80:15:5, v/v) was prepare. The pH of the mixture was then adjusted on 4.5 with acetic acid, and the mixture was left at room temperature (25℃) for 24, 48, and 72 hours. In this step the hydrolysis and self-condensation of silane occur simultaneously resulting in the creation of oligomeric silanes. Finally, 25 mg rGO sheets were added to the reaction mixture, and they were sonicated for 15 minutes and kept on a stirrer for 3 hours. The reaction mixture was then raised to 8.5 with a solution of sodium hydroxide (5 wt.%). The mixture was stored at 65℃for 1 hour. In this way the oligomeric silane condensation on the rGO surface resulted in SiO 2 particles deposition. The rGO sheets were centrifuged and washed 5 times with a 100 mL alcohol-water mixture (3:1, v/v) and finally with water once. The final product was stored in alcohol for further characterization. The hybrids were named as rGO-SiO 2 -II/24h, rGO-SiO 2 -II/48h and rGO-SiO 2 -II/72h, respectively. 2.3 Preparation of anti-corrosion epoxy coatings To prepare the anti-corrosion epoxy coating, 1.5 wt.% rGO-SiO 2 hybrids obtained through method I and II was dispersion in 15 wt.% deionized water and sonicated for 5min, then add the hybrid aqueous solution to the 60 wt.% 6520 epoxy resin, which was named as wet transfer migration (WTM). This method can help hybrid particles disperse better in epoxy resin. The rGO-SiO 2 /EP resin was then mixed with 8535-Y-68 curing agent and other residual additives in a mixing ration of 9:1.7:1 (wt.%). The steel (150mm×70mm×3mm) was sandblasted on the steel plate using a pressure box sandblasting machine. The tinplate (120mm×50mm×1mm) was abraded with 400 and 800 grit abrasive papers and cleaned with ethanol, degreased with acetone. Finally, the plate was sprayed using the air spraying method, and the coating samples were kept at room temperature for 24h and then transferred into the oven (80℃ for 6h). The dry thickness of the coatings after curing was 100 ± 5 µm (Q235 carbon steel) and 50 ± 2 (tinplate) µm, respectively. The coatings were named as EP, rGO-SiO 2 -I/24h@EP, rGO-SiO 2 -I/48h@EP, rGO-SiO 2 -I/72h@EP, rGO-SiO 2 -II/24h@EP, rGO-SiO 2 -II/48h@EP, rGO-SiO 2 -II/72h@EP, respectively. 2.4 Characterization The amount of silane grafted and silica nanoparticles precipitated on the rGO surface were investigated by FT-IR analysis (Vertex-70, Bruker) in the range of 4000 − 400 cm − 1 . The surface morphology and structure of hybrids and epoxy coatings were characterized by SEM. The crystal phases of hybrids were performed by X-ray power diffractometer (APEX II DUO) with Cu-Kα radiation working in the Bragg-Brentano (θ-2θ) geometry utilizing a para-focusing geometry to increase intensity and angular resolution in the angle range of 5-130 o . The bond between the coating and the substrate was measured with a coating adhesion automated scratch tester model WS2005. The applied load range was 0–20 N, the scratch length was 5 mm, and the inflection point was the maximum bond. The hydrophilicity of the coating was tested with a contact angle tester model JC2000CS. 2.5 Corrosion resistance The opposite surface of the sample was glued with waterproof adhesive glue, and the exposed area was 10×30 mm 2 . Then, the samples were placed in the 3.5 wt.% NaCl aqueous solution open to the air, simulating the seawater environment. According to the national Standard GB/T 1771–2007 ‘color paint and varnish-neutral salt fog performance test’, the composite coatings were placed in the salt spray test box (BGD881, Biuged, Guangzhou). The corrosion conditions were: 5 wt.% NaCl aqueous solution, chamber temperature of 35℃, saturation temperature of 47℃, pH of 6.5–7.2 and spray volume of 1–2 mL/80cm 2 /h. The angle between thetested surface of the sample and the vertical direction was fixed at 20°. The exposed area of the composite coatings was around 120×50 mm 2 . The samples used as a working electrode was bonded with a conductive wire by a conductive adhesive and then covered with acrylic resin leaving a square surface area of 1 cm 2 exposed to 3.5 wt.% NaCl aqueous solution. The electrochemical workstation (CHE 660E) was used to test the open circuit potential (OCP) and polarization curves of the samples. A standard three-compartment cell was used with an Ag/AgCl 3M KCl electrode and a Pt electrode as a reference and counter electrodes, respectively. The potentiodynamic current–potential curves were recorded at a sweep rate of 20 mV·min − 1 . Before the polarization test, the electrochemical impedance spectroscopic (EIS) measurements were carried out at the measured steady-state OCP value of the corresponding working electrode in the frequency range of 10 − 2 -10 5 Hz. All the experiments were conducted at room temperature. All impedance measurements were made in Faraday cages to minimize external disturbances and the experimental data were fitted by ZsimDemo software. According to formula (1), the corrosion protection efficiency (CPE) can be calculated, and the protective effects of different coatings on metals can be directly compared: $$\text{C}\text{P}\text{E}=\frac{{i}_{ccor}^{0}-{i}_{ccor}^{c}}{{i}_{ccor}^{0}}\times 100\%$$ 1 where \({i}_{ccor}^{0}\) indicates the corrosion current density (A/cm 2 ) of the working electrode in the test blank epoxy coating, \({i}_{ccor}^{c}\) indicates the corrosion current density (A/cm 2 ) of the working electrodes of other coating samples. 3. Results and discussion 3.1 FT-IR analysis The rGO particles were modified with SiO 2 nanoparticles through methods I and II. The FT-IR analysis was performed on the rGO nanosheets dispersed in silica matrix through method I) and II at different reaction times (24h, 48h and 72 h). The FT-IR spectra of various samples are presented in Fig. 2 . According to Fig. 2 there are various peaks in the FT-IR spectrum of rGO including -OH (3700 cm − 1 ), C = C (1636 cm − 1 ), C-O (918 cm − 1 ), and C-O-C (670 cm − 1 ), indicating the presence of hydroxyl, carboxyl, and epoxide groups on the surface of rGO, respectively. Three new intensive peaks appeared in the FT-IR spectra of rGO nanosheets dispersed in silica matrix at all silanization times. These are Si-O-Si- (asymmetric vibration at 1090 cm − 1 and bending vibration at 465 cm − 1 ), Si-O-C (asymmetric vibration at 1124 and bending vibration at 694 cm − 1 ) and -NH 2 (3260 cm − 1 ). These all confirm the presence of silane moieties on the rGO surface [ 19 – 20 ]. Observation of an intensive peak corresponded to -Si-O-Si- bond at 1090 cm − 1 in all samples indicates the significant self-condensation of silane precursors forming silica clusters on the rGO surface. In addition, Si-O-C bond at 1124 and 694 cm − 1 confirms chemical grafting of silanes on the rGO surface through reaction with carboxylic groups. Results show disappearance of the carboxyl and epoxide groups of the rGO located at 1708 cm − 1 indicating the reaction of silanes with the rGO surface [ 21 ]. It can be seen from Fig. 2 (a) that the carboxyl and epoxy groups on rGO-SiO 2 -II/24h completely disappear, while there are still some unreacted carboxyl and epoxy groups on rGO-SiO 2 -I/24h. These confirm the more silane groups reaction with the rGO surface in the second method when the mixture of silanes were hydrolyzed for 24 h and then the rGO nanosheets were added to the hydrolyzed solution [ 22 – 23 ]. The above results indicated that the silylation method can significantly affect the way SiO 2 generated by TEOS hydrolysis was grafted onto the surface of rGO. In method I, SiO 2 was mainly grafted with functional groups on the surface of rGO while SiO 2 particles were covered on the surface of rGO in method II. 3.2 XRD analysis It can be seen from Fig. 3 that rGO is a lamellar structure, and the sharp and strong diffraction peak appeared at near 2θ = 26°, which corresponds to the diffraction peak of graphene (002) crystal plane [ 24 ], indicating that the spatial arrangement of graphene microcrystals is very neat. According to the Prague formula [ 25 ]: 2dsinθ = nλ (2) where d is the interlayer spacing between crystal planes, θ is the diffraction angle, n is the diffraction order (n = 1), λ is the wavelength of the X-ray (λ = 0.15406), the interlayer spacing of rGO can be calculated to 0.3424nm. The weak diffraction peak near 2θ = 54.6° corresponds to the graphene (004) crystal plane [ 24 ]. In addition, although the diffraction intensity of 43.3° and 44.4° is very weak, the diffraction peak also appears, which corresponds to graphene (100) and (101) crystal planes [ 26 ]. This may be caused by graphene destroying its lamellar structure or breaking some layered blocks during the processing. On the diffraction pattern of rGO-SiO 2 , an additional diffraction peak appears at 2θ = 22.26°, which corresponds to the diffraction of SiO 2 [ 27 ]. However, in the rGO-SiO 2 hybrid material, the diffraction peak of graphene becomes wider and the strength is obviously weakened, the diffraction peak position of rGO-SiO 2 prepared by method I is more left compared with that of method II, the interlayer spacing can be calculated to 0.4298nm (method I) and 0.3935nm (method II), which is because after coating SiO 2 , the size of graphene lamella shrinks, the integrity of crystal structure decreases, and the degree of disorder increases. According to the peak position of rGO-SiO 2 hybrid material and the PDF standard card, it can be concluded that SiO 2 can be successfully coated on the surface of graphene [ 28 ] due to the presence of hydroxyl, carboxyl and other oxygen containing groups on the graphene sheet. 3.3 SEM analysis The surface morphology of pristine rGO sheets before and after silanization thorough methods I and II (rGO-SiO 2 ) microcapsules were studied by SEM analysis. The SEM micrographs of the rGO and rGO-SiO 2 48h are compared in Fig. 4 . In Fig. 4 (a) , the lamellar structure of rGO is clearly visible and the surface is smooth, but there are large agglomerations. After 48h of silylation, silicon spheres precipitate on the surface of rGO, mostly spherical or nearly spherical. Moreover, rGO-SiO 2 presents a fluffy form, indicating that silica particles as spacers can prevent Gr from agglomeration due to intermolecular van der Waals force during drying to some extent [ 29 ]. In Fig. 4(b) , some spherical particles can be seen on the surface of rGO, which indicates that the powder prepared by method I is chemically grafted silane on the surface of rGO to generate SiO 2 , rather than the precipitation of silica clusters. However, in Fig. 4(c) , the lamellar structure of rGO is almost invisible, and the silicon sphere completely encloses rGO. Based on these explanations the pristine rGO sheets successfully covered with silica nanoparticles and nanohybrids were obtained. 3.4 Bonding strength analysis The bonding strength between the coating and the substrate, an essential index for evaluating the mechanical properties of the coating, was related to the reliability of the coatings. In this paper, the pulling method was used to test the adhesion of the coatings, and the test results were shown in Fig. 5 (a) . The adhesion of the coatings with the addition of the hybrid materials has been improved to different degrees depending on the test results, among which the adhesion of the coating with rGO-SiO 2 -I/48h hybrid materials had the best performance, reaching 6.2 MPa, which is 180% higher than the bond strength of the EP coating. rGO and SiO 2 have large specific surface area, which can easily produce strong interaction with epoxy resin to form a dense lattice structure [ 30 – 31 ]. In addition, there are still some oxygen-containing functional groups on the surface of the lamellar rGO, which can produce van der Waals force interaction with the substrate, and epoxy resin to form an excellent compatibility and bonding surface structure, which further enhances the bonding strength between the coating and the substrate [ 32 ]. 3.5 Contact angle analysis Test the effect of adding hybrid materials on the hydrophilicity of epoxy coatings by measuring the size of the contact angle, as shown in Fig. 5 (b) . As shown in Fig. 5 (b) , the contact angle of the EP coating was 46.61°, indicating that the EP coating is hydrophilic. After adding different hybrid materials, the contact angle of the coating increased to 59.85°, 64.31°, 66.56°, 57.93°, 52.09°, and 60.78°, respectively. This indicated that the hydrophobicity of rGO-SiO 2 @EP was stronger than that of EP, which helps to slow down the corrosion of steel substrate by corrosive media in the environment [ 33 – 34 ]. 3.6 EIS analysis The effect of rGO-SiO 2 hybrids produced through method I and method II on the corrosion and ionic resistances of the epoxy coating was studied by EIS technique. The polarization curve, Nyquist and Bode plots of different samples after 24h immersion were displayed in Fig. 6– 7 . In addition, the experimental results were fitted with suitable electrical equivalent circuits. Figure 6 showed polarization curve of the EP coating with or without rGO-SiO 2 hybrids. It can be obviously seen that the corrosion potential and current density of EP were − 0.670V and 2.01×10 − 6 A·cm − 2 , respectively, with a corrosion impedance value of 5911.6 Ω· cm 2 , and a passivation plateau appeared in the range of -0.40V to -0.35V, indicating the formation of oxide films on the metal surface [ 35 ]. After adding rGO-SiO 2 to the coating, there was no passivation plateau on the polarization curve, and I ccor significantly decreased, while the impedance value significantly increased. According to the data analysis in Table 2 , the rGO-SiO 2 -I/48h@EP coating had the highest impedance value (154121.0 Ω· cm 2 ), and the CPE of this coating was also the largest among the six coatings, up to 90.15%. The above data all indicate that the addition of rGO-SiO 2 can greatly enhance the protective effect on the steel substrate, improving a more effective anti-corrosion barrier for the steel substrate. This is because rGO-SiO 2 has good hydrophobicity and barrier performance [ 36 ]. After adding the coating, it can effectively fill the pores and cracks on the surface of the coating, effectively blocking the penetration channel of the corrosive medium, and playing a role in protecting the metal. According to the corrosion protection efficiency CPE, these coatings are sorted in the following order: rGO-SiO 2 -I/48h@EP > rGO-SiO 2 -I/72h@EP > rGO-SiO 2 -I/24h@EP > rGO-SiO 2 -II/24h@EP > rGO-SiO 2 -II/72h@EP > rGO-SiO 2 -II/48h@EP. The rGO-SiO 2 @EP coating prepared by Method I has better corrosion resistance than Method II, with the best corrosion resistance still being the rGO-SiO 2 -I/48h@EP coating.. Figure 6 Polarization curves of EP and rGO-SiO 2 @EP coatings Table 2 Potentiodynamic polarization parameters Coatings E ccor /V I ccor /A·cm − 2 R p /Ω·cm 2 CPE(%) EP -0.670 2.012×10 − 6 5911.6 / rGO-SiO 2 -I/24h@EP -0.478 2.683×10 − 7 144640.1 86.89 rGO-SiO 2 -I/48h@EP -0.477 1.909×10 − 7 154121.0 90.51 rGO-SiO 2 -I/72h@EP -0.526 2.268×10 − 7 124202.0 88.73 rGO-SiO 2 -II/24h@EP -0.538 3.209×10 − 7 110846.3 84.05 rGO-SiO 2 -II/48h@EP -0.478 4.028×10 − 7 111133.8 79.98 rGO-SiO 2 -II/72h@EP -0.652 3.414×10 − 7 104213.8 83.03 From Fig. 7 , it can be seen that the EP coating exhibits a characteristic impedance spectrum controlled by charge transfer in the high-frequency region, with a semi-circular shape. The impedance spectrum appearing in the low-frequency region was the diffusion impedance of the solution, which corresponds to the Bode diagram with two time constants. This indicated that the corrosive electrolyte gradually diffuses towards the coating substrate through defects such as micro pores and cavities generated during the coating and curing process within 24 hours of immersion, leading to coating damage, loss of barrier performance [ 29 ], as shown in Table 2 , the R c and R ct of the EP coating were 7487 Ω cm 2 and 1678 Ω·cm 2 , respectively. At this time, the corrosion process of the EP coating was mainly controlled by two factors: R c and R ct . The radius of the arc represents the size of the resistance, and the larger the radius of the arc, the better the protective effect of the coating. It can be clearly observed that the arc radius of the rGO-SiO 2 -I/48h@EP coating was much larger than that of all other coatings, indicating that the rGO-SiO 2 -I/48h@EP coating had the highest resistance and the best protective effect on metals. From Table 2 , it can be seen that compared with EP, the Rc of rGO-SiO 2 @EP significantly increased, indicating that the coating had good barrier performance, with the most significant improvement being the rGO-SiO 2 -I/48h@EP coating, with an Rc of 2.405×10 4 Ω·cm 2 . However, further increasing the silylation time (rGO-SiO 2 -I/72h@EP) will actually lead to a decrease in the protective effect of the coating. Except for the Bode diagram of rGO-SiO 2 -II/24h@EP coating where two time constants can be observed, all other coatings had only one time constant. Usually, oxygen, water, and corrosive ions (Cl − ) enter the interior of the coating through cracks or pores, causing corrosion and detachment under the coating. Among them, the time constant in the high-frequency region reflects the response between the electrolyte and coating interface, while the time constant in the low-frequency region reflects the corrosion process between the electrolyte and substrate interface [ 37 ]. Although the impedance value of the rGO-SiO 2 -I/48h@EP coating was at a high level, the electrolyte solution had gradually begun to penetrate. However, the layered structure of rGO-SiO 2 is two-dimensional, which can extend the time for corrosive electrolyte solution to reach the middle of the coating and metal substrate, and reduce the corrosion rate. 3.8 Salt spray analysis Salt spray corrosion refers to an accelerated corrosion method that simulates the seawater environment, and its resistance time determines the quality of corrosion resistance. Fig. S1 shows the optical photos of the coatings with or without hybrid materials at placed in a salt spray box with 5 wt.% NaCl solution for 180 hours. The surface topography and surface elements of the coatings are analyzed by SEM and EDS, which is shown in Fig. S2 . From Fig. S1 , it can be seen that there were varying degrees of corrosion at the scratches on the coating surface, and some plate surfaces had obvious rust spots. The width of the expansion marks at the scratch on the surface of EP coated board were about 3mm, and there were large corrosion products and rust spots in the lower left corner of the board, with a large corrosion area and a small amount of bubbles. In contrast, after adding the hybrid materials to the EP coating, the corrosion propagation area at the scratch of the coatings decreased, and the propagation width was generally around 1.5 mm-2 mm. The number of rust spots was also significantly reduced compared to EP. According to the analysis of the number of rust spots, it can be observed that rGO-SiO 2 -I@EP coatings had better corrosion resistance than rGO-SiO 2 -II@EP coatings. Among them, the rGO-SiO 2 -I/48h@EP had the best surface condition and almost no rust spots. And the surface of rGO-SiO 2 @EP coatings did not show any blistering phenomenon, and the adhesion of the coatings above the scratch were still good, indicating that the physical barrier performance of the coating surface and the bonding strength between the coating and the steel substrate were effectively enhanced by the addition of rGO-SiO 2 hybrid materials, greatly improving the protective performance of the coating on the steel substrate [ 38 ]. Additionally, it can be shown in Fig. S2 that Fe, Cl, C and Si elements were present within EP coating after salt spray test, which means the corrosive medium had reached the surface of the substrate. Compared with it, the surface of the rGO-SiO 2 -I/48h@EP coating and rGO-SiO 2 -II/48h@EP coating had only Fe, O, C and Si element but not Cl element, which indicated that the coating formed a good shielding effect on the corrosive medium and protected the metal substrate perfectly [ 39 – 40 ]. The corrosion mechanism of the coating is shown in Fig. 8 . Due to its large structural gaps and small adhesion between particles, epoxy coatings can only provide a certain degree of protection [ 41 ], so the corrosion resistance performance of EP coating was the weakest. In conjunction with the other experiments described above, the better dispersion of rGO-SiO 2 hybrids prepared by method I than the one obtained in method II is responsible for the higher corrosion resistance of the former. The silane molecules grafted on the rGO surface and SiO 2 nanoparticles increased the interlayer distance of rGO sheets preventing them from agglomerations in the epoxy matrix. The rGO dispersion improvement in this case would cause significant improvement of the coating barrier properties [ 29 ]. The rGO nanosheets are impermeable against the electrolyte diffusion and could block the electrolyte pathways and increase the diffusion length of oxygen and water diffusion. In addition the rGO-SiO 2 hybrids could resist against Cl − ions diffusion. This is due to the negative surface charge of rGO-SiO 2 in the EP [ 38 ]. These mean that rGO-SiO 2 nanosheets can enhance the barrier properties of EP against oxygen, water and corrosive Cl − ions. However, these are not the only favorites of using SiO2-GO nanosheets in the epoxy coating. There are NH 2 groups on the rGO-SiO 2 surface which are reactive sites that can react with epoxide groups of EP resin through a SN2 nucleophilic substitution ring opening reaction [ 42 ]. This can result in the increase of EP cross-linking density around rGO-SiO 2 hybrids. In addition, a portion of the fillers in the coating shows a tendency of lateral arrangement, constructing a labyrinth shielding structure, extending the penetration and diffusion path of the road corrosion medium, further improving the anti-permeability and service life of the coatings. 4. Conclusion An amine functional rGO-SiO 2 hybrid was prepared by sol-gel method. The properties of the rGO-SiO 2 hybrids were studied, and they were added to the epoxy coating. Then, the barrier performance and anti-corrosion properties of rGO-SiO 2 /epoxy composite have been studied. The main results obtained are listed below: (1) The synthesis of silica nanoparticles on rGO sheets was successful. It was found that adding rGO sheets to the water-alcohol/silane mixture had significant influence on the formation of SiO 2 particles. When the rGO sheet is incorporated into the water-alcohol silane mixture, lower and finer particles are synthesized and hydrolyzed for a specified time (24, 48, 72 hours). In addition, in this method the silanes mostly tend to be grafted on the rGO surface through reaction with carboxylic and hydroxyl groups. However, a larger amount of SiO 2 particles with a larger size were formed on the rGO sheets when the rGO sheets were added to the water-alcohol/silane mixture after a certain pre-hydrolyzing time (24, 48, 72 hours). The FT-IR analysis showed that the reaction with TEOS led to the formation of SiO 2 particles with amine function on the surface of rGO. Also the increase of reaction time led to greater SiO 2 particles creation over the rGO surface. (2) The incorporation of the rGO-SiO 2 hybrid (manufactured by Methods I and II) into the epoxy coating has been demonstrated to significantly improve its dispersion, barrier and corrosion resistance. The improvement was more remarkable when the rGO-SiO 2 hybrid produced by Method I was used. In addition, a 48 hour response time resulted in the greatest improvement. The SiO 2 particles acted as spacer between rGO sheets, and their dispersion and exfoliation were enhanced. Also the amine functional groups existed on the SiO 2 particles provides proper interaction of rGO sheets with the epoxy coating matrix and steel substrate. Declarations CRediT authorship contribution statement Jiaqi Huang: Writing and correction of the paper, sample preparation, experiment designing and analysis. Meiping Wu, Xiaojin Miao and Yiwen Chen: Monitor and check, provide guidance. Jianyu Wang and Yiyao Wang: Proofread the paper, provide advice. Wangping Wu: Proofread the paper and platform support. Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Data availability Data will be made available on request. References E. Matin, M. M. Attar, B. Ramezanzadeh, Prog. Org. Coat. 78, 395 (2015) Y J Wan, L C Tang, L X Gong, D Yan, Y B Li, L B Wu, J X Jiang, G Q Lai, Carbon 69, 467 (2014) H Yi, C Chen, F Zhong, Z Xu, High Perform. Polym. 26, 255 (2014) A. Ghazi, E. Ghasemi, M. Mahdavian, B. Ramezanzadeh, M. Rostami, Corros. Sci. 94, 207 (2015) M. K. Sahnesarayi, H. Sarpoolaky, S. Rastegari, Surf. Coat. Technol. 258, 861 (2014) J Q Huang, K M Liu, X L Song, G C Zheng, Q Chen, J D Sun, H Z Jin, L L Jiang, Y S Jiang, Y Zhang, P Jiang, W P Wu, RSC Adv. 12, 24804 (2022) M. G. Sari, B. Ramezanzadeh, M. Shahbazi, Corros. Sci. 92, 162 (2015) M. A. Deyab, S. T. Keera, Mater. Chem. Phys. 146,406 (2014) S Y Tian, S W Yang, T Huang, J Sun, H S Wang, X P Pu, L F Tian, P He, Carbon 111, 617 (2017) G Cui, Z Bi, R Zhang, J Liu, X Yu, Z Li, Chem. Eng. J. 373, 104 (2019) D. S. Chauhan, M. A. Quraishi, K. R. Ansari, T. A. Saleh, Prog. Org. Coat. 147, 105741 (2020) B Kulyk, M. A. Freitas, N. F. Santos, F Mohseni, A. F. Carvalho, K Yasakau, António J. S. Fernandes, A. Bernardes, B. Figueiredo, R. Silva, J. Tedim, F. M. Costa, Crit. Rev. Solid State Mater. Sci. 47, 309 (2022) Y Si, E. T. Samulski, Chem. Mater. 20, 6792 (2008) I. V. Lightcap, T. H. Kosel, P. V. Kamat, Nano lett. 10, 577 (2010) G Williams, P. V. Kamat, Langmuir 25, 13869 (2009) G Williams, B Seger, P. V. Kamat, ACS nano 2, 1487 (2008) Z Yu, H Di, Y Ma, L Lv, Y Pan, C Zhang, Y He, Appl. Surf. Sci. 351, 986 2015) L Kou, C Gao, Nanoscale 2011, 3, 19 (2011) Y. L. Khung, S. H. Ngalim, L Meda, D. Narducci, Chem. - Eur. J. 20, 15151 (2014) A Maio, S Agnello, R Khatibi, L Botta, A Alessi, A Piazza, G Buscarino, A Mezzi, G Pantaleo, R Scaffaro, J. Alloys Compd. 664, 428 (2016) C Y Lee, J H Bae, T Y Kim, S H Chang, S Y Kin, Composites, Part A 75, 11 (2015) L Kou, C Gao, Nanoscale 3, 519 (2011) Y Yang, S Qiu, W Cui, Q Zhao, X J Cheng, R. K. Y. Li, X L Xie, Y W Mai, J. Mater. Sci. 44, 4539 (2009) N. H. Othman, M. C. Ismail, M Mustapha, N Sallih, Prog. Org. Coat. 135, 82 (2019) X Li, C Guo, H Wang, Y Chen, J Zhou, J Lin, Ceram. Int. 46, 5863 (2020) G Jena, J Philip, Prog. Org. Coat. 173, 107208 (2022) S Larumbe, C Gomez-Polo, J. I. Pérez-Landazábal, J. M. Pastor, J. Phys.: Condens. Matter 24, 266007 (2012) N Li, M Cao, C Hu, Nanoscale 4, 6205 (2012) B Ramezanzadeh, Z Haeri, M Ramezanzadeh, Chem. Eng. J. 303: 511 (2016) M Ma, H Li, Y Xiong, F Dong, Mater. Des. 198, 109367 (2021) J R Ma, J C Shu, W Q Cao, M Zhang, X X Wang, J Yuan, M S Cao, Composites, Part B 166, 187 (2019) C Qiu, L Jiang, Y Gao, L Sheng, Mater. Des. 230, 111952 (2023) L Wang, L Deng, D Zhang, D W Zhang , H C Qian, C W Du, X G Li , J. M. C. Mol, H. A. Terryn, Prog. Org. Coat. 97, 261 (2016) D Zhao, D Liu, Z Hu, J. Coat. Technol. Res. 14, 85 (2017) X Wang, W W Wu, D K Xie, J W Liu, P Jiang, J J Huang, Y Zhang, M Liu, L Xin, Y F Chen, Surf. Eng. Appl. Electrochem 57, 75 (2021) S Z Haeri, B Ramezanzadeh, M Asghari, J. Colloid Interface Sci. 493, 111 (2017) J Y Wang, M P Wu, X J Miao, D Bian, Y Y Wang, Y W Zhao, Surf. Coat. Technol. 473, 129987 (2023) B Ramezanzadeh, E Ghasemi, M Mahdavian, E Changizi, M. H. Mohamadzadeh Moghadam, Carbon 93, 555 (2015) K. I.Bolotin, K. J. Sikes, Z Jiang, M Klima , G Fudenberg, J Hone, P Kim, H. L. Stormer, Solid State Commun. 146, 351 (2008) J F Shen, Y Z Hu, M Shi, H W Ma, M X Ye, J. Phys. Chem. C 114, 1498 (2010) Y Y Wang, M P Wu, P P Lu, W Zhou, X J Shi, K Yang, X J Miao, Colloids Surf., A 632, 127824 (2022) B Ramezanzadeh, S Niroumandrad, A Ahmadi, M. Mahdavian, M. H. Mohamadzadeh Moghadam, Corros. Sci. 103, 283 (2016) Additional Declarations No competing interests reported. Supplementary Files Fig.S1andFig.S2.docx Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4022694","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":276989897,"identity":"fb9714f5-b775-443e-865e-61654fa5bf14","order_by":0,"name":"Jiaqi Huang","email":"","orcid":"","institution":"Jiangnan University","correspondingAuthor":false,"prefix":"","firstName":"Jiaqi","middleName":"","lastName":"Huang","suffix":""},{"id":276989898,"identity":"ccd74aa0-0db7-4dc1-9174-1c06d2764b5b","order_by":1,"name":"Meiping Wu","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA40lEQVRIiWNgGAWjYLCCBAYJBgZm5sMPPhjY2JGghZ0tzXBGQVoyCVbx8yhI83w4xNhASKHBjezEBw93WOTJO/MwGNsYHGBmYD98dAN+LbmbDRLPSBQbHuY98DjH4A4fA09a2g18Wsxu5G6TSGyTSNzYzJdgnGPwjJlBgseMkJbtPyBaeAykLQwOMzYQoWUbA0jLfGagFgZitNifebtZAuiXxA3MwEDuMUhLZiPkF8n23I0ff+6oS5zff/jwgx9/bOz42Q8fw6sFDEBxYXAAymEjqBymRb6BKKWjYBSMglEwEgEAgkJNxSDKVjgAAAAASUVORK5CYII=","orcid":"","institution":"Jiangnan University","correspondingAuthor":true,"prefix":"","firstName":"Meiping","middleName":"","lastName":"Wu","suffix":""},{"id":276989899,"identity":"8ff0ac29-b280-4a59-b164-bf22120771b2","order_by":2,"name":"Xiaojin Miao","email":"","orcid":"","institution":"Jiangnan University","correspondingAuthor":false,"prefix":"","firstName":"Xiaojin","middleName":"","lastName":"Miao","suffix":""},{"id":276989900,"identity":"bf5fc7e4-a49e-4893-a353-1ae26c495a6f","order_by":3,"name":"Jianyu Wang","email":"","orcid":"","institution":"Jiangnan University","correspondingAuthor":false,"prefix":"","firstName":"Jianyu","middleName":"","lastName":"Wang","suffix":""},{"id":276989901,"identity":"8465e7a8-4187-4305-9f88-eb13f3376ab1","order_by":4,"name":"Yiwen Chen","email":"","orcid":"","institution":"State Key Laboratory of Clean and Efficient Turbomachinery Power Equipment","correspondingAuthor":false,"prefix":"","firstName":"Yiwen","middleName":"","lastName":"Chen","suffix":""},{"id":276989902,"identity":"1b9f0c15-21a8-4a2d-ba82-d9a80449536f","order_by":5,"name":"Yiyao Wang","email":"","orcid":"","institution":"Jiangnan University","correspondingAuthor":false,"prefix":"","firstName":"Yiyao","middleName":"","lastName":"Wang","suffix":""},{"id":276989903,"identity":"705e2cd8-2eb1-47fb-bfd9-66e56e02e63f","order_by":6,"name":"Wangping Wu","email":"","orcid":"","institution":"Changzhou University","correspondingAuthor":false,"prefix":"","firstName":"Wangping","middleName":"","lastName":"Wu","suffix":""}],"badges":[],"createdAt":"2024-03-07 03:14:59","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4022694/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4022694/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":52418454,"identity":"c37c7e3d-444c-4a32-8d86-fce61b8f3ef9","added_by":"auto","created_at":"2024-03-11 12:37:24","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":673093,"visible":true,"origin":"","legend":"\u003cp\u003erGO-SiO\u003csub\u003e2\u003c/sub\u003e hybrid material preparation process (a) Method I, (b) Method II\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-4022694/v1/cae50873cf55aa7f3d24550e.png"},{"id":52418452,"identity":"a4338c1d-7b0a-48bf-9f12-97a6d5e8dfdf","added_by":"auto","created_at":"2024-03-11 12:37:21","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":590908,"visible":true,"origin":"","legend":"\u003cp\u003eFT-IR spectra of rGO and rGO-SiO\u003csub\u003e2\u003c/sub\u003e hybrids fabricated by method I and II after (a) 24h, (b) 48h and (c) 72h reaction times\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-4022694/v1/9e7f1c08554393e12d8d3dfb.png"},{"id":52418456,"identity":"cb78131e-14bb-4904-84d2-b4b5c075df91","added_by":"auto","created_at":"2024-03-11 12:37:30","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":147179,"visible":true,"origin":"","legend":"\u003cp\u003eXRD patterns of rGO and rGO-SiO\u003csub\u003e2\u003c/sub\u003e hybrids fabricated by method I and II after 48h reaction times\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-4022694/v1/bbfd17b5229b5fb8933e6005.png"},{"id":52418457,"identity":"05818307-7f47-49ca-a4b9-83dceea5fd56","added_by":"auto","created_at":"2024-03-11 12:37:31","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":534159,"visible":true,"origin":"","legend":"\u003cp\u003eSEM micrographs of (a) rGO, (b) rGO-SiO\u003csub\u003e2\u003c/sub\u003e-I/48h and (c) S rGO-SiO\u003csub\u003e2\u003c/sub\u003e-II/48h\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-4022694/v1/2b2ca553b11db3f34df27d4e.png"},{"id":52418453,"identity":"2a58eec0-1178-4def-bcba-cbd9889cc358","added_by":"auto","created_at":"2024-03-11 12:37:22","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":96531,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(a) \u003c/strong\u003eBonding strength between coating and substrate, (b) the contact angles of EP and rGO-SiO\u003csub\u003e2\u003c/sub\u003e@EP coatings\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-4022694/v1/112ab786e96742248bce2786.png"},{"id":52418450,"identity":"c9fddbf3-3c6a-4aae-a6a1-88c429f7bd56","added_by":"auto","created_at":"2024-03-11 12:37:12","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":153868,"visible":true,"origin":"","legend":"\u003cp\u003ePolarization curves of\u003cstrong\u003e \u003c/strong\u003eEP and rGO-SiO\u003csub\u003e2\u003c/sub\u003e@EP coatings\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-4022694/v1/ab3440bb68f73f2a96db0126.png"},{"id":52418451,"identity":"a53257b0-0630-4814-8324-5c2f233b8537","added_by":"auto","created_at":"2024-03-11 12:37:13","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":531311,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Nyquist and (b)(c) Bode plots obtained from EIS analysis for the coatings immersed in 3.5 wt.% NaCl solution for 24h, (d) electrical equivalent circuits\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-4022694/v1/df6973229eb874649615b317.png"},{"id":52418460,"identity":"499117c7-b188-4df0-94d2-ca6e1b19bc06","added_by":"auto","created_at":"2024-03-11 12:37:31","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":431139,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of corrosion mechanism of epoxy coating\u003c/p\u003e","description":"","filename":"floatimage9.png","url":"https://assets-eu.researchsquare.com/files/rs-4022694/v1/e69c80d01ca2a069b042e1f5.png"},{"id":52418668,"identity":"7adb3af8-cc40-4ea6-b911-1d14d57d4184","added_by":"auto","created_at":"2024-03-11 12:45:01","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2174754,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4022694/v1/887adb9a-9efd-47af-915e-3f04b12de864.pdf"},{"id":52418458,"identity":"160bc315-f3dc-4570-8eaf-faa371cc9944","added_by":"auto","created_at":"2024-03-11 12:37:31","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":7854199,"visible":true,"origin":"","legend":"","description":"","filename":"Fig.S1andFig.S2.docx","url":"https://assets-eu.researchsquare.com/files/rs-4022694/v1/ca7fe5ddb7af1536dae91d73.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"In situ deposition reduced graphene oxide-silica for improving the corrosion resistance of organic epoxy coatings: A comparative study","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eCorrosion of metals and alloys is a key problem in industrial areas around the world, causing huge economic losses and risks to security and the environment [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. So far, epoxy coatings have been the main corrosion protection strategy, which provides a strong barrier to metal from penetration by aggressive agents [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. However, in the curing process of epoxy resin, there are some problems such as high brittleness caused by cross-linking and curing, and large amounts of micro-pores are easily generated by the release of solvent [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Recent research has shown that the addition of nanofillers to the epoxy coatings improves their barrier and corrosion resistance [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Nanofillers are capable of blocking the micro-pores and cavities existed in the coating matrix and reducing the electrolyte diffusion to the coating/metal interface through zigzagging the electrolyte pathway [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Also, surface functional nanoparticles can increase the crosslink density of the coating and improve its barrier properties [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eGraphene and its derivatives, due to their lightweight two-dimensional structure, possess unique properties such as hydrophobicity, impermeability to small molecules, and high chemical inertness [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Therefore, they have great potential for application in the field of anti-corrosion coatings and are ideal filling materials for anti-corrosion coatings [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. However, the high specific surface area and strong π-π interactions between graphene layers make it highly prone to agglomeration, affecting its uniform dispersion in coating media. Moreover, the high conductivity of structurally intact graphene can promote corrosion activity [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Reduced graphene oxide (rGO) has been reported to have poor conductivity, good hydrophobicity and low production cost [xx], which is suitable to used as filling material. Besides, corrosion protection coatings functionalized with rGO are proven to possess excellent shielding effects [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. In recent studies it has been reported that chemical and/or physical grafting of nanoparticles i.e. platinum [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e], silver [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e], zinc oxide [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e], titanium dioxide [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e] on the basal planes of GO sheet as spacer could prevent it from aggregation in polymer coating and a higher degree of exfoliation can be obtained. Yu et al. [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e] reported the effect of graphene oxide sheets modified by titanium dioxide (GO-TiO\u003csub\u003e2\u003c/sub\u003e) and alumina nanoparticles (GO-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e) on the corrosion protection performance of epoxy coating. Results showed that decorating GO sheets by TiO\u003csub\u003e2\u003c/sub\u003e and Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e nanoparticles significantly enhanced their exfoliation and dispersion in the epoxy coating. GO-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and GO-TiO\u003csub\u003e2\u003c/sub\u003e nanoparticles could enhance the corrosion resistance of epoxy coating through plugging its micro-pores. Kou et al. [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e] used TEOS for synthesis of silica nanoparticles on the GO surface for producing super hydrophilic coatings. They employed a one-step sol-gel route for this purpose and achieved proper enhancement. To the best of our knowledge there is no systematic report on the synthesis of rGO-SiO\u003csub\u003e2\u003c/sub\u003e nanohybrids using mixture of silanes and its effect on the barrier performance and corrosion resistance of the polymeric coating.\u003c/p\u003e \u003cp\u003eIn this study, we aimed at the synthesis of rGO-SiO\u003csub\u003e2\u003c/sub\u003e hybrids through a two-step sol-gel method using TEOS in a water-alcohol solution. rGO-SiO\u003csub\u003e2\u003c/sub\u003e hybrids were synthesized by two different methods. The properties of two routes of synthesis rGO-SiO\u003csub\u003e2\u003c/sub\u003e hybrids were compared by employing FTIR, XRD, and SEM analysis. The rGO-SiO\u003csub\u003e2\u003c/sub\u003e hybrids produced by two methods (I and II) were incorporated into the epoxy coating. The effect of rGO-SiO\u003csub\u003e2\u003c/sub\u003e hybrids on the barrier and corrosion protection performance of the coating was investigated by SEM and EIS analysis.\u003c/p\u003e"},{"header":"2. Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Raw materials\u003c/h2\u003e \u003cp\u003eThe rGO sheets was purchased from SZGraphene Nanotechnology Co. (China). The Tetraethylorthosilicate (TEOS, C\u003csub\u003e8\u003c/sub\u003eH\u003csub\u003e20\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003eSi) were purchased from Aldrich Co. (Germany). Acetic acid (C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e), ethanol (C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e5\u003c/sub\u003eOH, 98%), and sodium hydroxide (NaOH) were purchased from HUSHI. Epoxy lotion (6520) was prepared from CNOOC Changzhou Coating and Chemical Research Institute Co.. The polyamine hardener (8538-Y-68) was purchased from HEXION (America). The sodium nitrite (NaNO\u003csub\u003e2\u003c/sub\u003e, 99%), leveling agent and defoamer (902W) were purchased from Shanghai LingFeng Chemical Reagent Co., BYK and Nanjing Hanbao Co., respectively.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Preparation of rGO-SiO\u003csub\u003e2\u003c/sub\u003e hybrids synthesis\u003c/h2\u003e \u003cp\u003e \u003cb\u003eMethod I\u003c/b\u003e:\u003c/p\u003e \u003cp\u003eFunctionalization of rGO sheets was achieved by in-situ hydrolysis of TEOS silane. For this purpose 25 mg rGO sheets was dispersed in 100 mL solution of alcohol \u0026ndash; water-silane (75: 10: 15, v/v) through 30 min sonication. The pH of the mixture was then adjusted on 4.5 with acetic acid, and the mixture was left at room temperature (25℃) for 24, 48, and 72 hours. After 24 hours, 48 hours and 72 hours, the pH of the reaction mixture was raised to 8.5 with a solution of sodium hydroxide (5 wt.%). The mixture was kept at 65℃ for 1 hour to condense silanes which were physically adsorbed on rGO surface. The rGO-SiO\u003csub\u003e2\u003c/sub\u003e suspension was centrifuged and washed 5 times with 100 mL mixture of alcohol-water (3:1, v/v) and finally one time with 100 mL water. The final product was stored in alcohol for further characterizations. The hybrids were named as rGO-SiO\u003csub\u003e2\u003c/sub\u003e-I/24h, rGO-SiO\u003csub\u003e2\u003c/sub\u003e-I/48h and rGO-SiO\u003csub\u003e2\u003c/sub\u003e-I/72h, respectively.\u003c/p\u003e \u003cp\u003e \u003cb\u003eMethod II\u003c/b\u003e:\u003c/p\u003e \u003cp\u003eIn this method the SiO\u003csub\u003e2\u003c/sub\u003e particles were deposited on the rGO sheets by an in situ hydrolysis of TEOS silane. For this purpose, a mixture of alcohol-water-silane (80:15:5, v/v) was prepare. The pH of the mixture was then adjusted on 4.5 with acetic acid, and the mixture was left at room temperature (25℃) for 24, 48, and 72 hours. In this step the hydrolysis and self-condensation of silane occur simultaneously resulting in the creation of oligomeric silanes. Finally, 25 mg rGO sheets were added to the reaction mixture, and they were sonicated for 15 minutes and kept on a stirrer for 3 hours. The reaction mixture was then raised to 8.5 with a solution of sodium hydroxide (5 wt.%). The mixture was stored at 65℃for 1 hour. In this way the oligomeric silane condensation on the rGO surface resulted in SiO\u003csub\u003e2\u003c/sub\u003e particles deposition. The rGO sheets were centrifuged and washed 5 times with a 100 mL alcohol-water mixture (3:1, v/v) and finally with water once. The final product was stored in alcohol for further characterization. The hybrids were named as rGO-SiO\u003csub\u003e2\u003c/sub\u003e-II/24h, rGO-SiO\u003csub\u003e2\u003c/sub\u003e-II/48h and rGO-SiO\u003csub\u003e2\u003c/sub\u003e-II/72h, respectively.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Preparation of anti-corrosion epoxy coatings\u003c/h2\u003e \u003cp\u003eTo prepare the anti-corrosion epoxy coating, 1.5 wt.% rGO-SiO\u003csub\u003e2\u003c/sub\u003e hybrids obtained through method I and II was dispersion in 15 wt.% deionized water and sonicated for 5min, then add the hybrid aqueous solution to the 60 wt.% 6520 epoxy resin, which was named as wet transfer migration (WTM). This method can help hybrid particles disperse better in epoxy resin. The rGO-SiO\u003csub\u003e2\u003c/sub\u003e/EP resin was then mixed with 8535-Y-68 curing agent and other residual additives in a mixing ration of 9:1.7:1 (wt.%).\u003c/p\u003e \u003cp\u003eThe steel (150mm\u0026times;70mm\u0026times;3mm) was sandblasted on the steel plate using a pressure box sandblasting machine. The tinplate (120mm\u0026times;50mm\u0026times;1mm) was abraded with 400 and 800 grit abrasive papers and cleaned with ethanol, degreased with acetone. Finally, the plate was sprayed using the air spraying method, and the coating samples were kept at room temperature for 24h and then transferred into the oven (80℃ for 6h). The dry thickness of the coatings after curing was 100\u0026thinsp;\u0026plusmn;\u0026thinsp;5 \u0026micro;m (Q235 carbon steel) and 50\u0026thinsp;\u0026plusmn;\u0026thinsp;2 (tinplate) \u0026micro;m, respectively. The coatings were named as EP, rGO-SiO\u003csub\u003e2\u003c/sub\u003e-I/24h@EP, rGO-SiO\u003csub\u003e2\u003c/sub\u003e-I/48h@EP, rGO-SiO\u003csub\u003e2\u003c/sub\u003e-I/72h@EP, rGO-SiO\u003csub\u003e2\u003c/sub\u003e-II/24h@EP, rGO-SiO\u003csub\u003e2\u003c/sub\u003e-II/48h@EP, rGO-SiO\u003csub\u003e2\u003c/sub\u003e-II/72h@EP, respectively.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Characterization\u003c/h2\u003e \u003cp\u003eThe amount of silane grafted and silica nanoparticles precipitated on the rGO surface were investigated by FT-IR analysis (Vertex-70, Bruker) in the range of 4000\u0026thinsp;\u0026minus;\u0026thinsp;400 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The surface morphology and structure of hybrids and epoxy coatings were characterized by SEM. The crystal phases of hybrids were performed by X-ray power diffractometer (APEX II DUO) with Cu-Kα radiation working in the Bragg-Brentano (θ-2θ) geometry utilizing a para-focusing geometry to increase intensity and angular resolution in the angle range of 5-130\u003csup\u003eo\u003c/sup\u003e. The bond between the coating and the substrate was measured with a coating adhesion automated scratch tester model WS2005. The applied load range was 0\u0026ndash;20 N, the scratch length was 5 mm, and the inflection point was the maximum bond. The hydrophilicity of the coating was tested with a contact angle tester model JC2000CS.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Corrosion resistance\u003c/h2\u003e \u003cp\u003eThe opposite surface of the sample was glued with waterproof adhesive glue, and the exposed area was 10\u0026times;30 mm\u003csup\u003e2\u003c/sup\u003e. Then, the samples were placed in the 3.5 wt.% NaCl aqueous solution open to the air, simulating the seawater environment. According to the national Standard GB/T 1771\u0026ndash;2007 \u0026lsquo;color paint and varnish-neutral salt fog performance test\u0026rsquo;, the composite coatings were placed in the salt spray test box (BGD881, Biuged, Guangzhou). The corrosion conditions were: 5 wt.% NaCl aqueous solution, chamber temperature of 35℃, saturation temperature of 47℃, pH of 6.5\u0026ndash;7.2 and spray volume of 1\u0026ndash;2 mL/80cm\u003csup\u003e2\u003c/sup\u003e/h. The angle between thetested surface of the sample and the vertical direction was fixed at 20\u0026deg;. The exposed area of the composite coatings was around 120\u0026times;50 mm\u003csup\u003e2\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe samples used as a working electrode was bonded with a conductive wire by a conductive adhesive and then covered with acrylic resin leaving a square surface area of 1 cm\u003csup\u003e2\u003c/sup\u003e exposed to 3.5 wt.% NaCl aqueous solution. The electrochemical workstation (CHE 660E) was used to test the open circuit potential (OCP) and polarization curves of the samples. A standard three-compartment cell was used with an Ag/AgCl 3M KCl electrode and a Pt electrode as a reference and counter electrodes, respectively. The potentiodynamic current\u0026ndash;potential curves were recorded at a sweep rate of 20 mV\u0026middot;min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Before the polarization test, the electrochemical impedance spectroscopic (EIS) measurements were carried out at the measured steady-state OCP value of the corresponding working electrode in the frequency range of 10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e-10\u003csup\u003e5\u003c/sup\u003e Hz. All the experiments were conducted at room temperature. All impedance measurements were made in Faraday cages to minimize external disturbances and the experimental data were fitted by ZsimDemo software. According to formula (1), the corrosion protection efficiency (CPE) can be calculated, and the protective effects of different coatings on metals can be directly compared:\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\text{C}\\text{P}\\text{E}=\\frac{{i}_{ccor}^{0}-{i}_{ccor}^{c}}{{i}_{ccor}^{0}}\\times 100\\%$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({i}_{ccor}^{0}\\)\u003c/span\u003e\u003c/span\u003e indicates the corrosion current density (A/cm\u003csup\u003e2\u003c/sup\u003e) of the working electrode in the test blank epoxy coating, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({i}_{ccor}^{c}\\)\u003c/span\u003e\u003c/span\u003e indicates the corrosion current density (A/cm\u003csup\u003e2\u003c/sup\u003e) of the working electrodes of other coating samples.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\n \u003ch2\u003e3.1 FT-IR analysis\u003c/h2\u003e\n \u003cp\u003eThe rGO particles were modified with SiO\u003csub\u003e2\u003c/sub\u003e nanoparticles through methods I and II. The FT-IR analysis was performed on the rGO nanosheets dispersed in silica matrix through method I) and II at different reaction times (24h, 48h and 72 h). The FT-IR spectra of various samples are presented in Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e\n \u003cp\u003eAccording to Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e there are various peaks in the FT-IR spectrum of rGO including -OH (3700 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), C\u0026thinsp;=\u0026thinsp;C (1636 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), C-O (918 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), and C-O-C (670 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), indicating the presence of hydroxyl, carboxyl, and epoxide groups on the surface of rGO, respectively. Three new intensive peaks appeared in the FT-IR spectra of rGO nanosheets dispersed in silica matrix at all silanization times. These are Si-O-Si- (asymmetric vibration at 1090 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and bending vibration at 465 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), Si-O-C (asymmetric vibration at 1124 and bending vibration at 694 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and -NH\u003csub\u003e2\u003c/sub\u003e (3260 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). These all confirm the presence of silane moieties on the rGO surface [\u003cspan class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e20\u003c/span\u003e].\u003c/p\u003e\n \u003cp\u003eObservation of an intensive peak corresponded to -Si-O-Si- bond at 1090 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e in all samples indicates the significant self-condensation of silane precursors forming silica clusters on the rGO surface. In addition, Si-O-C bond at 1124 and 694 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e confirms chemical grafting of silanes on the rGO surface through reaction with carboxylic groups. Results show disappearance of the carboxyl and epoxide groups of the rGO located at 1708 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e indicating the reaction of silanes with the rGO surface [\u003cspan class=\"CitationRef\"\u003e21\u003c/span\u003e]. It can be seen from Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e \u003cstrong\u003e(a)\u003c/strong\u003e that the carboxyl and epoxy groups on rGO-SiO\u003csub\u003e2\u003c/sub\u003e-II/24h completely disappear, while there are still some unreacted carboxyl and epoxy groups on rGO-SiO\u003csub\u003e2\u003c/sub\u003e-I/24h. These confirm the more silane groups reaction with the rGO surface in the second method when the mixture of silanes were hydrolyzed for 24 h and then the rGO nanosheets were added to the hydrolyzed solution [\u003cspan class=\"CitationRef\"\u003e22\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e23\u003c/span\u003e].\u003c/p\u003e\n \u003cp\u003eThe above results indicated that the silylation method can significantly affect the way SiO\u003csub\u003e2\u003c/sub\u003e generated by TEOS hydrolysis was grafted onto the surface of rGO. In method I, SiO\u003csub\u003e2\u003c/sub\u003e was mainly grafted with functional groups on the surface of rGO while SiO\u003csub\u003e2\u003c/sub\u003e particles were covered on the surface of rGO in method II.\u003c/p\u003e\n \u003cp\u003e\u003c/p\u003e\n \u003cp\u003e\u003cimg src=\"https://myfiles.space/user_files/122228_c8a1650c59388082/122228_custom_files/img1710160469.png\"\u003e\u003c/p\u003e\n \u003cp\u003e\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\n \u003ch2\u003e3.2 XRD analysis\u003c/h2\u003e\n \u003cp\u003eIt can be seen from Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e that rGO is a lamellar structure, and the sharp and strong diffraction peak appeared at near 2\u0026theta;\u0026thinsp;=\u0026thinsp;26\u0026deg;, which corresponds to the diffraction peak of graphene (002) crystal plane [\u003cspan class=\"CitationRef\"\u003e24\u003c/span\u003e], indicating that the spatial arrangement of graphene microcrystals is very neat.\u003c/p\u003e\n \u003cp\u003eAccording to the Prague formula [\u003cspan class=\"CitationRef\"\u003e25\u003c/span\u003e]:\u003c/p\u003e\n\u003c/div\u003e\n\u003ch3\u003e2dsin\u0026theta;\u0026thinsp;=\u0026thinsp;n\u0026lambda; (2)\u003c/h3\u003e\n\u003cp\u003ewhere d is the interlayer spacing between crystal planes, \u0026theta; is the diffraction angle, n is the diffraction order (n\u0026thinsp;=\u0026thinsp;1), \u0026lambda; is the wavelength of the X-ray (\u0026lambda;\u0026thinsp;=\u0026thinsp;0.15406), the interlayer spacing of rGO can be calculated to 0.3424nm. The weak diffraction peak near 2\u0026theta;\u0026thinsp;=\u0026thinsp;54.6\u0026deg; corresponds to the graphene (004) crystal plane [\u003cspan class=\"CitationRef\"\u003e24\u003c/span\u003e]. In addition, although the diffraction intensity of 43.3\u0026deg; and 44.4\u0026deg; is very weak, the diffraction peak also appears, which corresponds to graphene (100) and (101) crystal planes [\u003cspan class=\"CitationRef\"\u003e26\u003c/span\u003e]. This may be caused by graphene destroying its lamellar structure or breaking some layered blocks during the processing.\u003c/p\u003e\n\u003cp\u003eOn the diffraction pattern of rGO-SiO\u003csub\u003e2\u003c/sub\u003e, an additional diffraction peak appears at 2\u0026theta;\u0026thinsp;=\u0026thinsp;22.26\u0026deg;, which corresponds to the diffraction of SiO\u003csub\u003e2\u003c/sub\u003e [\u003cspan class=\"CitationRef\"\u003e27\u003c/span\u003e]. However, in the rGO-SiO\u003csub\u003e2\u003c/sub\u003e hybrid material, the diffraction peak of graphene becomes wider and the strength is obviously weakened, the diffraction peak position of rGO-SiO\u003csub\u003e2\u003c/sub\u003e prepared by method I is more left compared with that of method II, the interlayer spacing can be calculated to 0.4298nm (method I) and 0.3935nm (method II), which is because after coating SiO\u003csub\u003e2\u003c/sub\u003e, the size of graphene lamella shrinks, the integrity of crystal structure decreases, and the degree of disorder increases. According to the peak position of rGO-SiO\u003csub\u003e2\u003c/sub\u003e hybrid material and the PDF standard card, it can be concluded that SiO\u003csub\u003e2\u003c/sub\u003e can be successfully coated on the surface of graphene [\u003cspan class=\"CitationRef\"\u003e28\u003c/span\u003e] due to the presence of hydroxyl, carboxyl and other oxygen containing groups on the graphene sheet.\u003c/p\u003e\n\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\n \u003ch2\u003e3.3 SEM analysis\u003c/h2\u003e\n \u003cp\u003eThe surface morphology of pristine rGO sheets before and after silanization thorough methods I and II (rGO-SiO\u003csub\u003e2\u003c/sub\u003e) microcapsules were studied by SEM analysis. The SEM micrographs of the rGO and rGO-SiO\u003csub\u003e2\u003c/sub\u003e 48h are compared in \u003cstrong\u003eFig.\u0026nbsp;4\u003c/strong\u003e. In \u003cstrong\u003eFig.\u0026nbsp;4 (a)\u003c/strong\u003e, the lamellar structure of rGO is clearly visible and the surface is smooth, but there are large agglomerations. After 48h of silylation, silicon spheres precipitate on the surface of rGO, mostly spherical or nearly spherical. Moreover, rGO-SiO\u003csub\u003e2\u003c/sub\u003e presents a fluffy form, indicating that silica particles as spacers can prevent Gr from agglomeration due to intermolecular van der Waals force during drying to some extent [\u003cspan class=\"CitationRef\"\u003e29\u003c/span\u003e]. In \u003cstrong\u003eFig.\u0026nbsp;4(b)\u003c/strong\u003e, some spherical particles can be seen on the surface of rGO, which indicates that the powder prepared by method I is chemically grafted silane on the surface of rGO to generate SiO\u003csub\u003e2\u003c/sub\u003e, rather than the precipitation of silica clusters. However, in \u003cstrong\u003eFig.\u0026nbsp;4(c)\u003c/strong\u003e, the lamellar structure of rGO is almost invisible, and the silicon sphere completely encloses rGO. Based on these explanations the pristine rGO sheets successfully covered with silica nanoparticles and nanohybrids were obtained.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\n \u003ch2\u003e3.4 Bonding strength analysis\u003c/h2\u003e\n \u003cp\u003eThe bonding strength between the coating and the substrate, an essential index for evaluating the mechanical properties of the coating, was related to the reliability of the coatings. In this paper, the pulling method was used to test the adhesion of the coatings, and the test results were shown in Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e\u003cstrong\u003e(a)\u003c/strong\u003e. The adhesion of the coatings with the addition of the hybrid materials has been improved to different degrees depending on the test results, among which the adhesion of the coating with rGO-SiO\u003csub\u003e2\u003c/sub\u003e-I/48h hybrid materials had the best performance, reaching 6.2 MPa, which is 180% higher than the bond strength of the EP coating. rGO and SiO\u003csub\u003e2\u003c/sub\u003e have large specific surface area, which can easily produce strong interaction with epoxy resin to form a dense lattice structure [\u003cspan class=\"CitationRef\"\u003e30\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e31\u003c/span\u003e]. In addition, there are still some oxygen-containing functional groups on the surface of the lamellar rGO, which can produce van der Waals force interaction with the substrate, and epoxy resin to form an excellent compatibility and bonding surface structure, which further enhances the bonding strength between the coating and the substrate [\u003cspan class=\"CitationRef\"\u003e32\u003c/span\u003e].\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\n \u003ch2\u003e3.5 Contact angle analysis\u003c/h2\u003e\n \u003cp\u003eTest the effect of adding hybrid materials on the hydrophilicity of epoxy coatings by measuring the size of the contact angle, as shown in Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e\u003cstrong\u003e(b)\u003c/strong\u003e. As shown in Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e\u003cstrong\u003e(b)\u003c/strong\u003e, the contact angle of the EP coating was 46.61\u0026deg;, indicating that the EP coating is hydrophilic. After adding different hybrid materials, the contact angle of the coating increased to 59.85\u0026deg;, 64.31\u0026deg;, 66.56\u0026deg;, 57.93\u0026deg;, 52.09\u0026deg;, and 60.78\u0026deg;, respectively. This indicated that the hydrophobicity of rGO-SiO\u003csub\u003e2\u003c/sub\u003e@EP was stronger than that of EP, which helps to slow down the corrosion of steel substrate by corrosive media in the environment [\u003cspan class=\"CitationRef\"\u003e33\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e34\u003c/span\u003e].\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e\n \u003ch2\u003e3.6 EIS analysis\u003c/h2\u003e\n \u003cp\u003eThe effect of rGO-SiO\u003csub\u003e2\u003c/sub\u003e hybrids produced through method I and method II on the corrosion and ionic resistances of the epoxy coating was studied by EIS technique. The polarization curve, Nyquist and Bode plots of different samples after 24h immersion were displayed in Fig. 6\u0026ndash;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e. In addition, the experimental results were fitted with suitable electrical equivalent circuits.\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eFigure\u0026nbsp;6\u003c/strong\u003e showed polarization curve of the EP coating with or without rGO-SiO\u003csub\u003e2\u003c/sub\u003e hybrids. It can be obviously seen that the corrosion potential and current density of EP were \u0026minus;\u0026thinsp;0.670V and 2.01\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003eA\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, respectively, with a corrosion impedance value of 5911.6 Ω\u0026middot; cm\u003csup\u003e2\u003c/sup\u003e, and a passivation plateau appeared in the range of -0.40V to -0.35V, indicating the formation of oxide films on the metal surface [\u003cspan class=\"CitationRef\"\u003e35\u003c/span\u003e]. After adding rGO-SiO\u003csub\u003e2\u003c/sub\u003e to the coating, there was no passivation plateau on the polarization curve, and I\u003csub\u003eccor\u003c/sub\u003e significantly decreased, while the impedance value significantly increased.\u003c/p\u003e\n \u003cp\u003eAccording to the data analysis in Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e, the rGO-SiO\u003csub\u003e2\u003c/sub\u003e-I/48h@EP coating had the highest impedance value (154121.0 Ω\u0026middot; cm\u003csup\u003e2\u003c/sup\u003e), and the CPE of this coating was also the largest among the six coatings, up to 90.15%. The above data all indicate that the addition of rGO-SiO\u003csub\u003e2\u003c/sub\u003e can greatly enhance the protective effect on the steel substrate, improving a more effective anti-corrosion barrier for the steel substrate. This is because rGO-SiO\u003csub\u003e2\u003c/sub\u003e has good hydrophobicity and barrier performance [\u003cspan class=\"CitationRef\"\u003e36\u003c/span\u003e]. After adding the coating, it can effectively fill the pores and cracks on the surface of the coating, effectively blocking the penetration channel of the corrosive medium, and playing a role in protecting the metal. According to the corrosion protection efficiency CPE, these coatings are sorted in the following order: rGO-SiO\u003csub\u003e2\u003c/sub\u003e-I/48h@EP\u0026thinsp;\u0026gt;\u0026thinsp;rGO-SiO\u003csub\u003e2\u003c/sub\u003e-I/72h@EP\u0026thinsp;\u0026gt;\u0026thinsp;rGO-SiO\u003csub\u003e2\u003c/sub\u003e-I/24h@EP\u0026thinsp;\u0026gt;\u0026thinsp;rGO-SiO\u003csub\u003e2\u003c/sub\u003e-II/24h@EP\u0026thinsp;\u0026gt;\u0026thinsp;rGO-SiO\u003csub\u003e2\u003c/sub\u003e-II/72h@EP\u0026thinsp;\u0026gt;\u0026thinsp;rGO-SiO\u003csub\u003e2\u003c/sub\u003e-II/48h@EP. The rGO-SiO\u003csub\u003e2\u003c/sub\u003e@EP coating prepared by Method I has better corrosion resistance than Method II, with the best corrosion resistance still being the rGO-SiO\u003csub\u003e2\u003c/sub\u003e-I/48h@EP coating..\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eFigure\u0026nbsp;6\u003c/strong\u003e Polarization curves of EP and rGO-SiO\u003csub\u003e2\u003c/sub\u003e@EP coatings \u0026nbsp;\u003c/p\u003e\n \u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003ePotentiodynamic polarization parameters\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCoatings\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eE\u003csub\u003eccor\u003c/sub\u003e/V\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eI\u003csub\u003eccor\u003c/sub\u003e/A\u0026middot;cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eR\u003csub\u003ep\u003c/sub\u003e/Ω\u0026middot;cm\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCPE(%)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eEP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-0.670\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.012\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;6\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5911.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003erGO-SiO\u003csub\u003e2\u003c/sub\u003e-I/24h@EP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-0.478\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.683\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;7\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e144640.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e86.89\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003erGO-SiO\u003csub\u003e2\u003c/sub\u003e-I/48h@EP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-0.477\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.909\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;7\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e154121.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e90.51\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003erGO-SiO\u003csub\u003e2\u003c/sub\u003e-I/72h@EP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-0.526\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.268\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;7\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e124202.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e88.73\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003erGO-SiO\u003csub\u003e2\u003c/sub\u003e-II/24h@EP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-0.538\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.209\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;7\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e110846.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e84.05\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003erGO-SiO\u003csub\u003e2\u003c/sub\u003e-II/48h@EP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-0.478\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.028\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;7\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e111133.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e79.98\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003erGO-SiO\u003csub\u003e2\u003c/sub\u003e-II/72h@EP\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e-0.652\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.414\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;7\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e104213.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e83.03\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003c/p\u003e\n \u003cp\u003eFrom Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003e, it can be seen that the EP coating exhibits a characteristic impedance spectrum controlled by charge transfer in the high-frequency region, with a semi-circular shape. The impedance spectrum appearing in the low-frequency region was the diffusion impedance of the solution, which corresponds to the Bode diagram with two time constants. This indicated that the corrosive electrolyte gradually diffuses towards the coating substrate through defects such as micro pores and cavities generated during the coating and curing process within 24 hours of immersion, leading to coating damage, loss of barrier performance [\u003cspan class=\"CitationRef\"\u003e29\u003c/span\u003e], as shown in Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e, the R\u003csub\u003ec\u003c/sub\u003e and R\u003csub\u003ect\u003c/sub\u003e of the EP coating were 7487 Ω cm\u003csup\u003e2\u003c/sup\u003e and 1678 Ω\u0026middot;cm\u003csup\u003e2\u003c/sup\u003e, respectively. At this time, the corrosion process of the EP coating was mainly controlled by two factors: R\u003csub\u003ec\u003c/sub\u003e and R\u003csub\u003ect\u003c/sub\u003e.\u003c/p\u003e\n \u003cp\u003eThe radius of the arc represents the size of the resistance, and the larger the radius of the arc, the better the protective effect of the coating. It can be clearly observed that the arc radius of the rGO-SiO\u003csub\u003e2\u003c/sub\u003e-I/48h@EP coating was much larger than that of all other coatings, indicating that the rGO-SiO\u003csub\u003e2\u003c/sub\u003e-I/48h@EP coating had the highest resistance and the best protective effect on metals. From Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e, it can be seen that compared with EP, the Rc of rGO-SiO\u003csub\u003e2\u003c/sub\u003e@EP significantly increased, indicating that the coating had good barrier performance, with the most significant improvement being the rGO-SiO\u003csub\u003e2\u003c/sub\u003e-I/48h@EP coating, with an Rc of 2.405\u0026times;10\u003csup\u003e4\u003c/sup\u003e Ω\u0026middot;cm\u003csup\u003e2\u003c/sup\u003e. However, further increasing the silylation time (rGO-SiO\u003csub\u003e2\u003c/sub\u003e-I/72h@EP) will actually lead to a decrease in the protective effect of the coating. Except for the Bode diagram of rGO-SiO\u003csub\u003e2\u003c/sub\u003e-II/24h@EP coating where two time constants can be observed, all other coatings had only one time constant. Usually, oxygen, water, and corrosive ions (Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e) enter the interior of the coating through cracks or pores, causing corrosion and detachment under the coating. Among them, the time constant in the high-frequency region reflects the response between the electrolyte and coating interface, while the time constant in the low-frequency region reflects the corrosion process between the electrolyte and substrate interface [\u003cspan class=\"CitationRef\"\u003e37\u003c/span\u003e]. Although the impedance value of the rGO-SiO\u003csub\u003e2\u003c/sub\u003e-I/48h@EP coating was at a high level, the electrolyte solution had gradually begun to penetrate. However, the layered structure of rGO-SiO\u003csub\u003e2\u003c/sub\u003e is two-dimensional, which can extend the time for corrosive electrolyte solution to reach the middle of the coating and metal substrate, and reduce the corrosion rate.\u003c/p\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec16\" class=\"Section2\"\u003e\n \u003ch2\u003e3.8 Salt spray analysis\u003c/h2\u003e\n \u003cp\u003eSalt spray corrosion refers to an accelerated corrosion method that simulates the seawater environment, and its resistance time determines the quality of corrosion resistance. \u003cstrong\u003eFig. S1\u003c/strong\u003e shows the optical photos of the coatings with or without hybrid materials at placed in a salt spray box with 5 wt.% NaCl solution for 180 hours. The surface topography and surface elements of the coatings are analyzed by SEM and EDS, which is shown in \u003cstrong\u003eFig. S2\u003c/strong\u003e.\u003c/p\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003cp\u003eFrom \u003cstrong\u003eFig. S1\u003c/strong\u003e, it can be seen that there were varying degrees of corrosion at the scratches on the coating surface, and some plate surfaces had obvious rust spots. The width of the expansion marks at the scratch on the surface of EP coated board were about 3mm, and there were large corrosion products and rust spots in the lower left corner of the board, with a large corrosion area and a small amount of bubbles. In contrast, after adding the hybrid materials to the EP coating, the corrosion propagation area at the scratch of the coatings decreased, and the propagation width was generally around 1.5 mm-2 mm. The number of rust spots was also significantly reduced compared to EP. According to the analysis of the number of rust spots, it can be observed that rGO-SiO\u003csub\u003e2\u003c/sub\u003e-I@EP coatings had better corrosion resistance than rGO-SiO\u003csub\u003e2\u003c/sub\u003e-II@EP coatings. Among them, the rGO-SiO\u003csub\u003e2\u003c/sub\u003e-I/48h@EP had the best surface condition and almost no rust spots. And the surface of rGO-SiO\u003csub\u003e2\u003c/sub\u003e@EP coatings did not show any blistering phenomenon, and the adhesion of the coatings above the scratch were still good, indicating that the physical barrier performance of the coating surface and the bonding strength between the coating and the steel substrate were effectively enhanced by the addition of rGO-SiO\u003csub\u003e2\u003c/sub\u003e hybrid materials, greatly improving the protective performance of the coating on the steel substrate [\u003cspan class=\"CitationRef\"\u003e38\u003c/span\u003e].\u003c/p\u003e\n \u003cp\u003eAdditionally, it can be shown in \u003cstrong\u003eFig. S2\u003c/strong\u003e that Fe, Cl, C and Si elements were present within EP coating after salt spray test, which means the corrosive medium had reached the surface of the substrate. Compared with it, the surface of the rGO-SiO\u003csub\u003e2\u003c/sub\u003e-I/48h@EP coating and rGO-SiO\u003csub\u003e2\u003c/sub\u003e-II/48h@EP coating had only Fe, O, C and Si element but not Cl element, which indicated that the coating formed a good shielding effect on the corrosive medium and protected the metal substrate perfectly [\u003cspan class=\"CitationRef\"\u003e39\u003c/span\u003e\u0026ndash;\u003cspan class=\"CitationRef\"\u003e40\u003c/span\u003e].\u003c/p\u003e\n \u003cp\u003eThe corrosion mechanism of the coating is shown in Fig. \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003e. Due to its large structural gaps and small adhesion between particles, epoxy coatings can only provide a certain degree of protection [\u003cspan class=\"CitationRef\"\u003e41\u003c/span\u003e], so the corrosion resistance performance of EP coating was the weakest. In conjunction with the other experiments described above, the better dispersion of rGO-SiO\u003csub\u003e2\u003c/sub\u003e hybrids prepared by method I than the one obtained in method II is responsible for the higher corrosion resistance of the former. The silane molecules grafted on the rGO surface and SiO\u003csub\u003e2\u003c/sub\u003e nanoparticles increased the interlayer distance of rGO sheets preventing them from agglomerations in the epoxy matrix. The rGO dispersion improvement in this case would cause significant improvement of the coating barrier properties [\u003cspan class=\"CitationRef\"\u003e29\u003c/span\u003e]. The rGO nanosheets are impermeable against the electrolyte diffusion and could block the electrolyte pathways and increase the diffusion length of oxygen and water diffusion. In addition the rGO-SiO\u003csub\u003e2\u003c/sub\u003e hybrids could resist against Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e ions diffusion. This is due to the negative surface charge of rGO-SiO\u003csub\u003e2\u003c/sub\u003e in the EP [\u003cspan class=\"CitationRef\"\u003e38\u003c/span\u003e]. These mean that rGO-SiO\u003csub\u003e2\u003c/sub\u003e nanosheets can enhance the barrier properties of EP against oxygen, water and corrosive Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e ions. However, these are not the only favorites of using SiO2-GO nanosheets in the epoxy coating. There are NH\u003csub\u003e2\u003c/sub\u003e groups on the rGO-SiO\u003csub\u003e2\u003c/sub\u003e surface which are reactive sites that can react with epoxide groups of EP resin through a SN2 nucleophilic substitution ring opening reaction [\u003cspan class=\"CitationRef\"\u003e42\u003c/span\u003e]. This can result in the increase of EP cross-linking density around rGO-SiO\u003csub\u003e2\u003c/sub\u003e hybrids. In addition, a portion of the fillers in the coating shows a tendency of lateral arrangement, constructing a labyrinth shielding structure, extending the penetration and diffusion path of the road corrosion medium, further improving the anti-permeability and service life of the coatings.\u003c/p\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eAn amine functional rGO-SiO\u003csub\u003e2\u003c/sub\u003e hybrid was prepared by sol-gel method. The properties of the rGO-SiO\u003csub\u003e2\u003c/sub\u003e hybrids were studied, and they were added to the epoxy coating. Then, the barrier performance and anti-corrosion properties of rGO-SiO\u003csub\u003e2\u003c/sub\u003e/epoxy composite have been studied. The main results obtained are listed below:\u003c/p\u003e\n\u003cp\u003e(1) The synthesis of silica nanoparticles on rGO sheets was successful. It was found that adding rGO sheets to the water-alcohol/silane mixture had significant influence on the formation of SiO\u003csub\u003e2\u003c/sub\u003e particles. When the rGO sheet is incorporated into the water-alcohol silane mixture, lower and finer particles are synthesized and hydrolyzed for a specified time (24, 48, 72 hours). In addition, in this method the silanes mostly tend to be grafted on the rGO surface through reaction with carboxylic and hydroxyl groups. However, a larger amount of SiO\u003csub\u003e2\u003c/sub\u003e particles with a larger size were formed on the rGO sheets when the rGO sheets were added to the water-alcohol/silane mixture after a certain pre-hydrolyzing time (24, 48, 72 hours). The FT-IR analysis showed that the reaction with TEOS led to the formation of SiO\u003csub\u003e2\u003c/sub\u003e particles with amine function on the surface of rGO. Also the increase of reaction time led to greater SiO\u003csub\u003e2\u003c/sub\u003e particles creation over the rGO surface.\u003c/p\u003e\n\u003cp\u003e(2) The incorporation of the rGO-SiO\u003csub\u003e2\u003c/sub\u003e hybrid (manufactured by Methods I and II) into the epoxy coating has been demonstrated to significantly improve its dispersion, barrier and corrosion resistance. The improvement was more remarkable when the rGO-SiO\u003csub\u003e2\u003c/sub\u003e hybrid produced by Method I was used. In addition, a 48 hour response time resulted in the greatest improvement. The SiO\u003csub\u003e2\u003c/sub\u003e particles acted as spacer between rGO sheets, and their dispersion and exfoliation were enhanced. Also the amine functional groups existed on the SiO\u003csub\u003e2\u003c/sub\u003e particles provides proper interaction of rGO sheets with the epoxy coating matrix and steel substrate.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eCRediT authorship contribution statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eJiaqi Huang: Writing and correction of the paper, sample preparation, experiment designing and analysis. Meiping Wu, Xiaojin Miao and Yiwen Chen: Monitor and check, provide guidance. Jianyu Wang and Yiyao Wang: Proofread the paper, provide advice. Wangping Wu: Proofread the paper and platform support.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDeclaration of competing interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eData will be made available on request.\u003c/p\u003e\n"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eE. Matin, M. M. Attar, B. Ramezanzadeh, Prog. Org. Coat. 78, 395 (2015)\u003c/li\u003e\n\u003cli\u003eY J Wan, L C Tang, L X Gong, D Yan, Y B Li, L B Wu, J X Jiang, G Q Lai, Carbon 69, 467 (2014)\u003c/li\u003e\n\u003cli\u003eH Yi, C Chen, F Zhong, Z Xu, High Perform. Polym. 26, 255 (2014)\u003c/li\u003e\n\u003cli\u003eA. Ghazi, E. Ghasemi, M. Mahdavian, B. Ramezanzadeh, M. Rostami, Corros. Sci. 94, 207 (2015)\u003c/li\u003e\n\u003cli\u003eM. K. Sahnesarayi, H. Sarpoolaky, S. Rastegari, Surf. Coat. Technol. 258, 861 (2014)\u003c/li\u003e\n\u003cli\u003eJ Q Huang, K M Liu, X L Song, G C Zheng, Q Chen, J D Sun, H Z Jin, L L Jiang, Y S Jiang, Y Zhang, P Jiang, W P Wu, RSC Adv. 12, 24804 (2022)\u003c/li\u003e\n\u003cli\u003eM. G. Sari, B. Ramezanzadeh, M. Shahbazi, Corros. Sci. 92, 162 (2015)\u003c/li\u003e\n\u003cli\u003eM. A. Deyab, S. T. Keera, Mater. Chem. Phys. 146,406 (2014)\u003c/li\u003e\n\u003cli\u003eS Y Tian, S W Yang, T Huang, J Sun, H S Wang, X P Pu, L F Tian, P He, Carbon 111, 617 (2017)\u003c/li\u003e\n\u003cli\u003eG Cui, Z Bi, R Zhang, J Liu, X Yu, Z Li, Chem. Eng. J. 373, 104 (2019)\u003c/li\u003e\n\u003cli\u003eD. S. Chauhan, M. A. Quraishi, K. R. Ansari, T. A. Saleh, Prog. Org. Coat. 147, 105741 (2020)\u003c/li\u003e\n\u003cli\u003eB Kulyk, M. A. Freitas, N. F. Santos, F Mohseni, A. F. Carvalho, K Yasakau, Ant\u0026oacute;nio J. S. Fernandes, A. Bernardes, B. Figueiredo, R. Silva, J. Tedim, F. M. Costa, Crit. Rev. Solid State Mater. Sci. 47, 309 (2022)\u003c/li\u003e\n\u003cli\u003eY Si, E. T. Samulski, Chem. Mater. 20, 6792 (2008)\u003c/li\u003e\n\u003cli\u003eI. V. Lightcap, T. H. Kosel, P. V. Kamat, Nano lett. 10, 577 (2010)\u003c/li\u003e\n\u003cli\u003eG Williams, P. V. Kamat, Langmuir 25, 13869 (2009)\u003c/li\u003e\n\u003cli\u003eG Williams, B Seger, P. V. Kamat, ACS nano 2, 1487 (2008)\u003c/li\u003e\n\u003cli\u003eZ Yu, H Di, Y Ma, L Lv, Y Pan, C Zhang, Y He, Appl. Surf. Sci. 351, 986 2015)\u003c/li\u003e\n\u003cli\u003eL Kou, C Gao, Nanoscale 2011, 3, 19 (2011)\u003c/li\u003e\n\u003cli\u003eY. L. Khung, S. H. Ngalim, L Meda, D. Narducci, Chem. - Eur. J. 20, 15151 (2014)\u003c/li\u003e\n\u003cli\u003eA Maio, S Agnello, R Khatibi, L Botta, A Alessi, A Piazza, G Buscarino, A Mezzi, G Pantaleo, R Scaffaro, J. Alloys Compd. 664, 428 (2016)\u003c/li\u003e\n\u003cli\u003eC Y Lee, J H Bae, T Y Kim, S H Chang, S Y Kin, Composites, Part A 75, 11 (2015)\u003c/li\u003e\n\u003cli\u003eL Kou, C Gao, Nanoscale 3, 519 (2011)\u003c/li\u003e\n\u003cli\u003eY Yang, S Qiu, W Cui, Q Zhao, X J Cheng, R. K. Y. Li, X L Xie, Y W Mai, J. Mater. Sci. 44, 4539 (2009)\u003c/li\u003e\n\u003cli\u003eN. H. Othman, M. C. Ismail, M Mustapha, N Sallih, Prog. Org. Coat. 135, 82 (2019)\u003c/li\u003e\n\u003cli\u003eX Li, C Guo, H Wang, Y Chen, J Zhou, J Lin, Ceram. Int. 46, 5863 (2020)\u003c/li\u003e\n\u003cli\u003eG Jena, J Philip, Prog. Org. Coat. 173, 107208 (2022)\u003c/li\u003e\n\u003cli\u003eS Larumbe, C Gomez-Polo, J. I. P\u0026eacute;rez-Landaz\u0026aacute;bal, J. M. Pastor, J. Phys.: Condens. Matter 24, 266007 (2012)\u003c/li\u003e\n\u003cli\u003eN Li, M Cao, C Hu, Nanoscale 4, 6205 (2012)\u003c/li\u003e\n\u003cli\u003eB Ramezanzadeh, Z Haeri, M Ramezanzadeh, Chem. Eng. J. 303: 511 (2016)\u003c/li\u003e\n\u003cli\u003eM Ma, H Li, Y Xiong, F Dong, Mater. Des. 198, 109367 (2021)\u003c/li\u003e\n\u003cli\u003eJ R Ma, J C Shu, W Q Cao, M Zhang, X X Wang, J Yuan, M S Cao, Composites, Part B 166, 187 (2019)\u003c/li\u003e\n\u003cli\u003eC Qiu, L Jiang, Y Gao, L Sheng, Mater. Des. 230, 111952 (2023)\u003c/li\u003e\n\u003cli\u003eL Wang, L Deng, D Zhang, D W Zhang , H C Qian, C W Du, X G Li , J. M. C. Mol, H. A. Terryn, Prog. Org. Coat. 97, 261 (2016)\u003c/li\u003e\n\u003cli\u003eD Zhao, D Liu, Z Hu, J. Coat. Technol. Res. 14, 85 (2017)\u003c/li\u003e\n\u003cli\u003eX Wang, W W Wu, D K Xie, J W Liu, P Jiang, J J Huang, Y Zhang, M Liu, L Xin, Y F Chen, Surf. Eng. Appl. Electrochem 57, 75 (2021)\u003c/li\u003e\n\u003cli\u003eS Z Haeri, B Ramezanzadeh, M Asghari, J. Colloid Interface Sci. 493, 111 (2017)\u003c/li\u003e\n\u003cli\u003eJ Y Wang, M P Wu, X J Miao, D Bian, Y Y Wang, Y W Zhao, Surf. Coat. Technol. 473, 129987 (2023)\u003c/li\u003e\n\u003cli\u003eB Ramezanzadeh, E Ghasemi, M Mahdavian, E Changizi, M. H. Mohamadzadeh Moghadam, Carbon 93, 555 (2015)\u003c/li\u003e\n\u003cli\u003eK. I.Bolotin, K. J. Sikes, Z Jiang, M Klima , G Fudenberg, J Hone, P Kim, H. L. Stormer, Solid State Commun. 146, 351 (2008)\u003c/li\u003e\n\u003cli\u003eJ F Shen, Y Z Hu, M Shi, H W Ma, M X Ye, J. Phys. Chem. C 114, 1498 (2010)\u003c/li\u003e\n\u003cli\u003eY Y Wang, M P Wu, P P Lu, W Zhou, X J Shi, K Yang, X J Miao, Colloids Surf., A 632, 127824 (2022)\u003c/li\u003e\n\u003cli\u003eB Ramezanzadeh, S Niroumandrad, A Ahmadi, M. Mahdavian, M. H. Mohamadzadeh Moghadam, Corros. Sci. 103, 283 (2016)\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Silica particles-decorated reduced graphene oxide hybrids (rGO-SiO2), TEOS, epoxy coatings, corrosion","lastPublishedDoi":"10.21203/rs.3.rs-4022694/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4022694/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIn this study, two facile routes for in situ construction and characterization of silica particles decorated with reduced graphene oxide (rGO-SiO\u003csub\u003e2\u003c/sub\u003e) based on the sol-gel principle are reported and incorporated into epoxy resins to prepare coatings for comparative testing of their corrosion protection and mechanical properties. The microstructure, phase identification and composition of the hybrid materials were characterized by SEM, XRD, and FT-IR, respectively. The results demonstrated that both two methods can successfully generate silica on the surface of reduced graphene oxide, but the silica generated by method I had lower content and finer size. And this trend was more obvious with the increase of reaction time. The mechanical properties and anticorrosion behavior of the epoxy coatings were investigated by coating adhesion automated scratch test, contact angle, salt spray test and EIS test. The results were shown that incorporation of rGO-SiO\u003csub\u003e2\u003c/sub\u003e hybrids (produced in both methods I and II) into the epoxy coating notably enhanced its bongding strength, dispersion performance, barrier properties and corrosion resistance. It was also indicated that the hybrid material prepared by method I after 48h had the best mechanical and anti-corrosion properties.\u003c/p\u003e","manuscriptTitle":"In situ deposition reduced graphene oxide-silica for improving the corrosion resistance of organic epoxy coatings: A comparative study","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-03-11 12:36:54","doi":"10.21203/rs.3.rs-4022694/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"2d62d6d6-2fe9-4479-b46e-0f37da76a7c0","owner":[],"postedDate":"March 11th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-03-11T12:36:57+00:00","versionOfRecord":[],"versionCreatedAt":"2024-03-11 12:36:54","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4022694","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4022694","identity":"rs-4022694","version":["v1"]},"buildId":"J0_U0BvcaRcwD8yVFaRlm","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}