Different-conductivity rGO-epoxy resin anticorrosive paint and preparation method thereof

Abstract

The invention discloses rGO-epoxy resin anticorrosive paint with different conductivity and a preparation method thereof, and belongs to the technical field of anticorrosive coating preparation. The conductivity of graphene is reduced by controlling the reduction condition, the electron transmission efficiency can be reduced, so that the activity of a corrosion battery is weakened, after the rGO160 with the conductivity of 1.51 S / cm is added to the epoxy coating, the rGO160 graphene serves as an electron channel, electrons generated by metal corrosion are transmitted to the surface of the coating, and the corrosion resistance of the corrosion battery is improved. The cathode reaction occurs on the surface of the coating and the surface of the non-metal substrate, so that the electrochemical corrosion speed is reduced. By regulating and controlling the conductivity of the reduced graphene oxide, the shielding performance and the corrosion inhibition capability of the reduced graphene oxide can be effectively balanced, so that the optimization of the corrosion resistance of the coating is realized.

Description

Technical Field

[0001] This invention relates to the field of anti-corrosion coating preparation technology, and in particular to an anti-corrosion coating of rGO-epoxy resin with different electrical conductivity and its preparation method. Background Technology

[0002] Metallic materials possess excellent mechanical properties and are widely used in industrial fields. However, metal corrosion often leads to safety accidents and causes significant economic losses. Applying organic coatings to metal surfaces can prevent and slow down metal corrosion, offering advantages such as low cost, easy application, and good protective effect.

[0003] Epoxy-based coatings are among the most widely used polymer coatings applied to metal surfaces to mitigate corrosion. These promising polymer coatings offer excellent properties, including significant thermomechanical stability, low cost, and superior adhesion. However, during the curing process of epoxy coatings, microscopic defects such as microcracks and micropores easily form within the coating due to its inherent brittleness and solvent evaporation. Corrosive media tend to utilize these microscopic defects to diffuse to the metal substrate surface, causing corrosion. This also indicates that simple epoxy resin coatings cannot provide stable protection for the substrate over long periods and in harsh environments. Therefore, researchers often add fillers to epoxy coatings to achieve highly efficient corrosion and wear resistance.

[0004] Currently, graphene and its derivatives have been extensively studied as two-dimensional nanofillers for corrosion-resistant and wear-resistant coatings. As graphene derivatives, graphene oxide (GO) and reduced graphene oxide (rGO) not only inherit the large specific surface area and two-dimensional structure of graphene, but also possess advantages in low cost and corrosion resistance. Their large specific surface area and two-dimensional layered structure allow them to be uniformly dispersed and stacked layer by layer in coatings, forming a dense physical barrier layer, enabling large-area protection even with relatively thin coatings. Small-sized nanomaterials can fill and repair coating defects, improve coating density and water resistance, further enhance physical barrier performance, and effectively prevent corrosive media from penetrating to the substrate. Only trace amounts are needed to significantly improve the mechanical properties of the coating, thereby enhancing its friction-reducing and wear-resistant characteristics. Furthermore, graphene and its derivatives exhibit significant hydrophobic properties. Organic coatings incorporating graphene can effectively inhibit the penetration of water molecules into the coating's internal structure. The presence of graphene in the coating matrix significantly prolongs the diffusion path of corrosive substances, thus forming a "maze effect" that hinders their contact with the metal surface.

[0005] In existing technologies, Daradmare obtained few-layer graphene (FLG) via electrochemical exfoliation and uniformly dispersed it in epoxy resin (EP) to prepare a graphene / EP composite coating. When the graphene content was 1 wt%, this composite coating showed approximately 20 times better corrosion resistance, 30% higher hardness, and 35% higher elastic modulus compared to the pure EP coating. Yu et al. prepared functionalized graphene using tea polyphenols as a reducing agent and graphene oxide as a precursor via a green and simple method. The corrosion resistance of polyphenol-reduced graphene oxide (T-rGO) in waterborne epoxy coatings was evaluated using electrochemical impedance spectroscopy, polarization curves, water absorption rate, and salt spray tests. The results showed that the T-rGO / epoxy coating had the highest impedance modulus and corrosion potential, and its corrosion current density was an order of magnitude lower than that of the pure epoxy coating. This coating exhibited excellent corrosion resistance in a continuous high salt spray environment. Due to its good dispersibility and intrinsic properties, T-rGO significantly improved the corrosion resistance of waterborne epoxy coatings.

[0006] The π-π chemical bonds in the graphene sheet structure endow electrons with extremely strong migration capabilities and excellent electrical conductivity. When the substrate metal loses electrons through an anodic reaction, graphene, acting as an electron transport channel, can transfer electrons generated by metal corrosion to the coating surface, thereby achieving separation of the anode and cathode reactions. The generated OH... - Ions remain trapped on the coating surface, making it difficult for them to react with the Fe generated at the anode. 3+ Ions combine to form Fe(OH)3, thereby preventing Fe from being released. 3+ Precipitation. Meanwhile, Fe... 3+ The continuous accumulation of Fe can hinder the anodic reaction process and reduce the electrochemical corrosion rate. Furthermore, the accumulated Fe... 3+It can also promote metal passivation and significantly reduce the solubility of iron. These two synergistic effects significantly extend the service life of the coating, thus achieving corrosion protection. However, this view remains controversial. Some researchers believe that due to graphene's high conductivity, in the later stages of corrosion, the conductive graphene in contact with the metal substrate acts as a cathode, greatly promoting anodic metal corrosion, thereby accelerating coating aging, blistering, and peeling. Professor Alex Zetter published an article in the journal *ACS Nano* criticizing this application, stating that using graphene as a long-term anti-corrosion coating is "worse than not using it at all." Researchers using chemical vapor deposition (CVD) to prepare graphene films only provided temporary corrosion protection on copper surfaces. After a longer period (6 months), its corrosion level even exceeded that of bare copper. The article explains that although graphene has excellent physical barrier properties, its high conductivity accelerates the electrochemical corrosion rate of the copper surface, leading to the formation of oxides and other corrosion products, thus making the corrosion more severe than that of bare copper. Some researchers have refuted these views. Xie Yaping et al. pointed out that nanostructural defects in graphene grown by chemical vapor deposition are the main cause of corrosion effects. These defects can be reduced using atomic layer deposition (ALD) technology, achieving a corrosion resistance rate exceeding 99%. Huang Jiaxing, in a commentary published in *Nature Nanotechnology*, while acknowledging graphene's excellent barrier properties, also emphasized from an electrochemical potential perspective that graphene acts as a cathode during corrosion. Therefore, even very small cracks or scratches on the coating can accelerate localized electrochemical corrosion, significantly increasing the corrosion rate in exposed areas and reducing the strength and toughness of the metal.

[0007] In summary, although numerous studies have explored the application of reduced graphene oxide in epoxy resin coatings, the mechanism by which its high conductivity induces accelerated / inhibited corrosion in the coating remains unclear, and the long-term corrosion resistance of the prepared coatings requires further investigation. Summary of the Invention

[0008] To address the problems existing in the prior art, this invention provides an anti-corrosion coating of rGO-epoxy resin with different electrical conductivity and its preparation method. This invention obtains reduced graphene oxide with different electrical conductivity through different reduction times and applies it to the epoxy resin system, significantly improving the well-known anti-corrosion performance.

[0009] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0010] On one hand, the present invention provides an anti-corrosion coating of rGO-epoxy resin with different electrical conductivity, which is prepared by the following components in parts by weight: 6 parts by weight of reduced graphene oxide, 125 parts by weight of mullite, 125 parts by weight of nano zirconium dioxide, 100 parts by weight of epoxy resin, 100 parts by weight of curing agent, and 700-800 parts by weight of ethanol.

[0011] The reduced graphene oxide has an electrical conductivity of 7 × 10⁻⁶. -2 The particle size of the mullite is 1-1.5 μm, and the particle size of the nano-zirconia is 50-100 nm. The mullite has a particle size of 1-1.5 μm.

[0012] On the other hand, the present invention also provides a method for preparing rGO-epoxy resin anti-corrosion coatings with different electrical conductivity, comprising:

[0013] Step 1: Preparation of graphene oxide (GO) dispersion using the modified Hummers method: 1 g of graphite, 6 g of potassium permanganate, and 50 mL of concentrated sulfuric acid were placed in a 250 mL Erlenmeyer flask and heated in a 55°C water bath with continuous stirring for 2 hours. After the system cooled to room temperature, deionized water and hydrogen peroxide were added sequentially to obtain a graphene oxide slurry. The slurry was then washed with deionized water by centrifugation until neutral and diluted to a concentration of 2 mg / mL to obtain a graphene oxide dispersion. After ultrasonic exfoliation, a monolayer GO dispersion was obtained.

[0014] Step 2: Transfer the GO dispersion to a reaction vessel and carry out a hydrothermal reduction reaction at 140-180℃ for 3-12 hours, followed by freeze-drying to obtain reduced graphene oxide (rGO); specifically:

[0015] Without adding other reducing agents, the GO dispersion was transferred to a polytetrafluoroethylene-lined reactor and subjected to hydrothermal reduction reactions at four temperatures: 140, 160, and 180 °C, with reaction times of 6, 9, and 12 hours, respectively, to prepare a series of reduced graphene oxide (rGO) dispersions. Finally, the dispersions were freeze-dried for 48 hours.

[0016] Step 3: Place 5 grams of mullite, 5 grams of nano-zirconia, and 31.6 grams (40 ml) of ethanol into a ball mill container. Then add zirconia grinding balls with a mass ratio of 1:1 and diameters of 3 mm and 0.5 mm, respectively, for a ball-to-material ratio of 10:1. Perform ball milling at 300 rpm for 7 hours to obtain an MZr mixed slurry.

[0017] Step 4: First, 0.24 g of rGO with different reduction degrees was dispersed in MZr slurry and ultrasonically treated to obtain a uniform dispersion system; then, 4 g of epoxy resin was added to the mixture under continuous stirring and stirred for 60 minutes to form a homogeneous solution.

[0018] Step 5: Then add 4 grams of curing agent and continue stirring for 20 minutes to obtain the coating slurry.

[0019] Step 6: Apply the mixture evenly to the surface of the Q235 electrode substrate using a scraping method, with a coating amount of 1-2 g / cm³.2 The coating is formed after 24 hours of curing at room temperature.

[0020] To further improve the anti-corrosion performance of the coating, the prepared rGO was modified as follows: The rGO prepared in step 2 was ultrasonically dispersed in DMF at a concentration of 1 mg / mL; a solution of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) was added and stirred for 1-6 h; then γ-aminopropyltriethoxysilane (KH-792) was added and stirred at 40-80℃ for 2-8 h; the mixture was centrifuged, washed, and dried to obtain the modified rGO. The molar ratio of the rGO dispersion, EDC, NHS, and KH-792 was 100 mg: 5 mmol: 6 mmol: 6 mmol.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] This invention employs a hydrothermal method to prepare reduced graphene oxide with different electrical conductivities, and then composites it with epoxy resin to prepare a coating. The anti-corrosion performance of the coating is tested using methods such as electrochemical impedance spectroscopy and salt spray testing. The influence of the size effect and conductivity effect of reduced graphene oxide with different degrees of reduction on the anti-corrosion performance of the epoxy resin coating is investigated. This invention reduces the electrical conductivity of graphene by controlling the reduction conditions, thereby reducing electron transport efficiency and weakening the activity of the corrosion cell. Furthermore, rGO with a conductivity of 1.51 S / cm is added to the epoxy-based coating. 160 After that, at this time rGO 160 Graphene, acting as an electron channel, transfers electrons generated by metal corrosion to the coating surface, causing the cathodic reaction to occur on the coating surface rather than the metal substrate surface, thus reducing the electrochemical corrosion rate. This invention, by controlling the conductivity of reduced graphene oxide, can effectively balance its shielding performance and corrosion inhibition capability, thereby optimizing the coating's anti-corrosion performance.

[0023] The rGO surfaces of the present invention contain a certain amount of oxygen-containing functional groups such as carboxyl groups, which can be activated by the EDC / NHS system to form a semi-stable NHS ester intermediate. Then, KH-792 (N-(2-aminoethyl)-3-aminopropyltrimethoxysilane) is used as a bifunctional coupling agent. One end forms an amide bond with the activated carboxyl group on the rGO surface through an amino group, and the other end of the trimethoxysilane group can react with epoxy resin to form a covalent bond, thereby improving the dispersibility and interfacial bonding strength of rGO in epoxy resin and further improving the anti-corrosion performance. Attached Figure Description

[0024] Figure 1 (a) Infrared spectra of graphene oxide reduced to different degrees of reduction; (b) XRD images of graphene oxide reduced to different degrees of reduction;

[0025] Figure 2 The conductivity of reduced graphene oxide at different degrees of reduction;

[0026] Figure 3 TEM image of rGO (a1) rGO 120 ;(b1)rGO 140 ;(c1)rGO 160 ;(d1)rGO 180 ; rGO size statistics (a2) rGO 120 (b2)rGO 140 (c2)rGO 160 ;(d2)rGO 180 ;

[0027] Figure 4 (a) Infrared spectra of MZrE and MZrE-rGO; (b) X-ray diffraction images of MZrE and MZrE-rGO;

[0028] Figure 5 For (a) MZrE; (b) MZrE-rGO 120 (c)MZrE-rGO 140 (d)MZrE-rGO 160 (e)MZrE-rGO 180 Scanning electron microscope images;

[0029] Figure 6 For (a) MZrE; (b) MZrE-rGO 120 (c)MZrE-rGO 140 (d)MZrE-rGO 160 (e)MZrE-rGO 180 Surface roughness;

[0030] Figure 7 For MZrE, MZrE-rGO 120 MZrE-rGO 140 MZrE-rGO 160 MZrE-rGO 180 Nyquist plots after soaking in 3.5 wt% NaCl solution for 3 days (a), 7 days (b), 14 days (c), and 30 days (d);

[0031] Figure 8 For MZrE, MZrE-rGO 120 MZrE-rGO 140 MZrE-rGO 160MZrE-rGO 180 Bode modulus plots of MzrE, MZrE-rgo after soaking in 3.5 wt% NaCl solution for 3 d (a), 7 d (b), 14 d (c) and 30 d (d);

[0032] Figure 9 For MZrE, MZrE-rGO 120 MZrE-rGO 140 MZrE-rGO 160 MZrE-rGO 180 Tafel polarization curves and corrosion inhibition rate histograms for (a1) 3 days, (b1) 7 days, (c1) 14 days, and (d1) 30 days after immersion in 3.5 wt% sodium chloride solution;

[0033] Figure 10 For MZrE, MZrE-rGO 120 MZrE-rGO 140 MZrE-rGO 160 MZrE-rGO 180 Digital comparison photos of scratch-coated samples before and after a 900-hour neutral salt spray test;

[0034] Figure 11 (a) Optical microscope image of the MZrE scratch-coated sample (the selected location in the image is used to calculate the average width of the scratch); (b) MZrE and MZrE-rGO 120 MZrE-rGO 140 MZrE-rGO 160 MZrE-rGO 180 (a) Optical microscope images of the corrosion on the carbon steel surface after the coating was peeled off from the carbon steel surface after 900 hours of neutral salt spray test (the selected locations in the figure are used to calculate the average width of the scratches); (c) is a graph showing the average width of the scratches as statistically analyzed in Figures (a) and (b).

[0035] Figure 12 Scanning electron microscope (SEM) images of the coating at the substrate interface and elemental distribution of the corresponding region after immersion in salt water for 10 days: (a) MZrE; (b) MZrE-rGO 120 (c)MZrE-rGO 140 (d)MZrE-rGO 160 (e)MZrE-rGO 180 . Detailed Implementation

[0036] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0037] Unless otherwise specified, all materials and reagents used in this invention are commercially available. The graphite size is 10-20 micrometers, the concentrated sulfuric acid concentration is 98%, and the hydrogen peroxide concentration is 30%. All reagents were purchased directly without special treatment. The mullite was fused mullite from a certain company, with a particle size of 1-1.5 μm, and the nano-zirconia particle size was 50-100 nm. The epoxy resin was epoxy resin 6101 supplied by Shanghai Maclean Biochemical Technology Co., Ltd. (Shanghai, China). The Q235 steel plate substrate with dimensions of 20×20×0.3 mm was successively polished with 150-grit, 600-grit, and 800-grit sandpaper, then ultrasonically cleaned with ethanol and dried at room temperature.

[0038] This invention provides an anti-corrosion coating of rGO-epoxy resin with different electrical conductivity and its preparation method, and specific embodiments are as follows.

[0039] Example 1

[0040] A method for preparing rGO-epoxy resin anti-corrosion coatings with different electrical conductivity, comprising:

[0041] Step 1: Preparation of graphene oxide (GO) dispersion using the modified Hummers method: 1 g of graphite, 6 g of potassium permanganate, and 50 mL of concentrated sulfuric acid were placed in a 250 mL Erlenmeyer flask and heated in a 55°C water bath with continuous stirring for 2 hours. After the system cooled to room temperature, 150 mL of deionized water and 60 mL of concentrated hydrogen peroxide were added sequentially to obtain a graphene oxide slurry. The slurry was then washed with deionized water by centrifugation until neutral and diluted to a concentration of 2 mg / mL to obtain a graphene oxide dispersion. After ultrasonic exfoliation (400 W power, 40 min), a monolayer GO dispersion was obtained.

[0042] Step 2: The GO dispersion was transferred to a polytetrafluoroethylene-lined reactor and subjected to a hydrothermal reduction reaction at 140°C for 6 hours. Then, it was freeze-dried for 48 hours to obtain reduced graphene oxide (rGO). 140 ;

[0043] Step 3: Place 5 grams of mullite, 5 grams of nano-zirconia and 31.6 grams of ethanol into a ball mill container, then add zirconia grinding balls with diameters of 3 mm and 0.5 mm respectively at a mass ratio of 1:1, with a ball-to-material ratio of 10:1, and ball mill at a speed of 300 rpm for 7 hours to obtain MZr mixed slurry.

[0044] Step 4: Add 0.24 grams of rGO 120The epoxy resin was dispersed in MZr slurry and ultrasonically treated to obtain a uniform dispersion system. Subsequently, 4 grams of epoxy resin were added to the mixture under continuous stirring and stirred for 60 minutes to form a homogeneous solution.

[0045] Step 5: Then add 4 grams of curing agent and continue stirring for 20 minutes to obtain the coating slurry;

[0046] Step 6: Apply the mixture evenly to the surface of the Q235 electrode substrate using a scraping method, with a coating amount of 1.5 g / cm³. 2 After curing at room temperature for 24 hours, a coating MZrE-rGO is formed. 140 .

[0047] Example 2

[0048] In this embodiment, step 2 is as follows: the GO dispersion is transferred to a polytetrafluoroethylene-lined reactor and subjected to a hydrothermal reduction reaction at 160°C for 9 hours, followed by freeze-drying for 48 hours to obtain reduced graphene oxide (rGO). 160 The remaining conditions are the same as in Example 1, resulting in the coating MZrE-rGO. 160 .

[0049] Example 3

[0050] In this embodiment, step 2 is as follows: the GO dispersion is transferred to a polytetrafluoroethylene-lined reactor and subjected to a hydrothermal reduction reaction at 180°C for 12 hours, followed by freeze-drying for 48 hours to obtain reduced graphene oxide (rGO). 180 The remaining conditions are the same as in Example 1, resulting in the coating MZrE-rGO. 180 .

[0051] Comparative Example 1

[0052] rGO is omitted in this comparative example. 160 Under the same conditions as in Example 2, the coating MZrE was obtained.

[0053] Comparative Example 2

[0054] In this comparative example, step 2 involves transferring the GO dispersion into a polytetrafluoroethylene-lined reactor and subjecting it to a hydrothermal reduction reaction at 120°C for 3 hours. This is followed by freeze-drying for 48 hours to obtain reduced graphene oxide (rGO). 120 The remaining conditions are the same as in Example 2, resulting in the coating MZrE-rGO. 120 .

[0055] Among them, MZrE-rGO 120 MZrE-rGO 140 MZrE-rGO 160 MZrE-rGO180 Collectively referred to as MZrE-rGO coating.

[0056] The reduced graphene oxide prepared in Examples 1-3 and Comparative Example 2 was tested, and the results are shown in the figure. Figure 1 As shown in Figure 1(a), the changes in graphene functional groups depend on the temperature and time of the reduction treatment. Studies have shown that the functional groups of reduced graphene oxide (rGO) change significantly under different degrees of reduction. 120 At 3441 cm -1 The OH stretching vibration peak at this location is the strongest and the peak shape is significantly broadened, indicating a high hydroxyl content and the formation of hydrogen bonds between hydroxyl groups. (1596 cm⁻¹) -1 The absorption peak at that location and the sp in graphene 2 The stretching vibration peaks of hybrid C=C are consistent. Conversely, the peak at 1133 cm⁻¹ is... -1 and 932 cm -1 The peak at [location] is attributed to the COC skeletal vibration of the epoxy groups in rGO. With increasing processing temperature and time, [the peak from rGO]... 140 To rGO 180 3441 cm -1 The OH stretching vibration peak at 1596 cm⁻¹ gradually narrows and decreases in intensity. This indicates a decrease in hydroxyl content and an increase in the degree of reduction, which is insufficient to form hydrogen bonds, leading to a sharper peak. Furthermore, with increasing reduction, the peak initially at 1596 cm⁻¹... -1 The peak at that location splits at 1639 cm. -1 and 1536 cm -1 The two peaks at 1133 cm⁻¹ indicate that the π-electron network within graphene oxide (GO) has undergone reorganization. The vibrational peak associated with the epoxy groups is at 1133 cm⁻¹. -1 and 932 cm -1 At this point, a ring-opening reaction occurs after reduction, causing the corresponding vibrational peak to disappear.

[0057] like Figure 1 As shown in (b), reduced graphene oxide (rGO) prepared at different hydrothermal temperatures was characterized by X-ray diffraction (XRD). The diffraction peaks near 10° and 25° correspond to the characteristic peaks of graphene oxide and graphite, respectively. In the rGO sample prepared at 120°C, the diffraction peak at 10.8°C was weak and had a large half-width. When the temperature was increased to 140°C, the characteristic peak of graphene oxide disappeared significantly; at 160°C, the graphitization characteristic peak began to appear; and when the temperature reached 180°C, the intensity of this characteristic peak further increased. The study shows that increasing the temperature has a significant effect on the decomposition of oxygen-containing functional groups and the recovery of the conjugated system in rGO. Experiments confirmed that when rGO is reduced to a certain extent, the interlayer structure will recover sp.2 The hybridization state induces a π-π stacking effect. The enhanced van der Waals forces ultimately lead to the appearance of characteristic peaks in graphite.

[0058] The electrical properties of rGO are determined by its functional group composition and structure. The conductivity of rGO with different functional group contents can be characterized using a four-probe technique. As shown in Figure 2, the conductivity of rGO prepared at different hydrothermal temperatures for 3, 6, 9, and 12 hours exhibits a clear columnar distribution. This figure shows that as the hydrothermal temperature increases from 120°C to 180°C, the conductivity of the obtained rGO increases from 4 × 10⁻⁶. −4 The conductivity of rGO increased to 22.72 S / cm. This phenomenon is mainly attributed to the fact that low temperatures cannot provide the energy required for the decomposition of oxygen-containing functional groups, thus a large number of oxygen-containing functional groups remain on the rGO surface. As the reaction temperature gradually increased to 140°C and 160°C, the conductivity of the obtained rGO first increased rapidly, and then gradually increased. This phenomenon can be attributed to the fact that high temperatures provide the necessary energy for the decomposition of oxygen-containing functional groups, thereby significantly increasing the decomposition rate. Therefore, the conductivity of rGO can reach a high value in a relatively short time. Comparison of the conductivity of rGO prepared at different hydrothermal temperatures shows that high temperatures are more conducive to the decomposition of oxygen-containing functional groups and the improvement of reduction efficiency.

[0059] Figure 3 shows that the reduced graphene oxide samples prepared at different reduction temperatures exhibit significant differences in size. At a reduction temperature of 120°C, the average length of the reduced graphene oxide sheets is approximately 4 micrometers. With increasing temperature and reduction time, the size gradually decreases; when the reduction temperature reaches 160°C, the average length of the reduced graphene oxide sheets drops to approximately 2 micrometers. Further increasing the reduction temperature to 180°C, the average length of the graphene sheets ranges from 1.6 to 1.8 micrometers.

[0060] The inventors also tested the prepared anti-corrosion coating, and the results are as follows.

[0061] Figure 4(a) The infrared spectra of MZrE / MZrE-rGO are shown. In all samples, the peak at 3300 cm⁻¹ corresponds to the OH stretching vibration of the hydroxyl group, and the peak at 1651 cm⁻¹ corresponds to the C=O group in the epoxy resin. Conjugation with the benzene ring causes a wavenumber redshift. The double peaks observed at 1604 cm⁻¹ and 1504 cm⁻¹ are attributed to the vibrational peaks of the benzene ring skeleton in the epoxy resin. The peak at 1238 cm⁻¹ is attributed to the Ar-O stretching vibration of the aromatic ether, with an increased wavenumber due to the p-π conjugation effect. The peak at 1177 cm⁻¹ is attributed to the asymmetric stretching vibration of the COC bond in the epoxy group. The peak at 1032 cm⁻¹ is attributed to the stretching vibration of the Si-OC bond. The peaks observed at 822 and 562 cm⁻¹ are attributed to the stretching and bending vibrations of the Si-O-Al bond, respectively. The peak at 732 cm⁻¹ is attributed to the stretching vibration of the Zr-O bond in zirconium oxide. After incorporation of reduced graphene oxide, it is evident that the absorption peak at 562 cm⁻¹ gradually weakens with increasing reduction, while the absorption peak at 732 cm⁻¹ correspondingly strengthens. This finding indicates that the oxygen-containing groups in the reduced graphene oxide significantly alter the crystal structure of zirconium oxide and mullite in the original coating. This change is reflected in the weakening of the 562 cm⁻¹ absorption peak, suggesting a decrease in the crystallinity of mullite.

[0062] Figure 4 (b) shows the XRD pattern, with the peak at 2θ ≈ 35° corresponding to the tetragonal phase of zirconia. The intensity of this peak gradually increases with the addition of reduced graphene oxide, indicating that the interfacial stress introduced by the reduced graphene oxide promotes phase stability. The (002) peak of the reduced graphene oxide, indicating its crystallinity, is typically located in the 20–30° range (corresponding to approximately 2θ ≈ 24°). Its intensity is relatively weak in the composite coating, indicating that it is uniformly dispersed in the matrix, thus masking the diffraction signal.

[0063] The surface morphology of the prepared coating was characterized, and the results are shown in the figure. Figure 5 Comparison of samples showed that the coating prepared without the addition of reduced graphene oxide had more cracks. Figure 5 (a) The addition of reduced graphene oxide (rGO) increases the density of the coating, thereby extending the corrosion path of corrosive media such as H2O, O2, and Cl⁻, and thus enhancing the corrosion resistance of the coating. As shown in the figure, the coating contains rGO. 120 and rGO 140 The coating surface exhibits a rough texture, which can be attributed to its large size and insufficient dispersion. Containing rGO 180The appearance of fine cracks on the surface of the composite coating is likely due to its high degree of reduction, resulting in fewer residual epoxy groups on the surface. This phenomenon has been shown to weaken the interfacial interaction between graphene and epoxy resin, thereby reducing the coating's corrosion resistance. MZrE-rGO 160 The coating has the highest density and a smooth surface.

[0064] like Figure 6 As shown, MZrE-rGO 120 and MZrE-rGO 140 The surfaces exhibit a rough texture, attributed to their large size and insufficient dispersion, corresponding to roughnesses of 2.45 μm and 2.36 μm. MZrE-rGO 180 The surface roughness is 1.508 micrometers, slightly higher than that of MZrE-rGO. 160 The surface roughness was 1.31 μm, a difference that can be attributed to the inhomogeneity of the prepared rGO layer thickness. This surface roughness further indicates the presence of MZrE-rGO. 160 The coating has a relatively smooth and flat surface, which may improve the coating's density and corrosion resistance.

[0065] This invention uses an AC signal frequency of 10 4 Hertz to 10 -1 Electrochemical impedance spectroscopy (EIS) measurements in the Hertz range were used to compare and analyze the anti-corrosion effects of MzrE and MZrE-rGO composite coatings on steel substrates. Figure 7 As shown in (a), (b), (c), and (d), Nyquist plots were obtained after immersion in a 3.5% (mass fraction) sodium chloride solution for 3, 7, 14, and 30 days, respectively. The Nyquist plots exhibit semicircles of varying sizes. Generally, an increase in the diameter of the semicircle correlates with an increase in impedance, indicating enhanced corrosion resistance of the coating. See [see attached table]. Figure 7 See Table 1.

[0066] like Figure 7 As shown in (a), after soaking for 3 days, MZrE-rGO 160 The coating exhibits the largest semi-circular diameter and the highest impedance value, indicating optimal corrosion resistance. Even after immersion for 30 days, the MZrE-rGO coating shows excellent corrosion resistance with prolonged immersion time. 160 The coating still exhibits the largest semicircular diameter, with a corresponding impedance value of 3.585 × 10⁻⁶. 7 Ω·cm 2 After soaking for 180 days, its corresponding impedance value still reached 7.51 × 10⁻⁶. 6 Ω·cm 2 Compared to MZrE and MZrE-rGO120 Coating, MZrE-rGO 140 The coating improved corrosion resistance by 1-2 orders of magnitude. Specific impedance data are shown in Table 1.

[0067] Table 1

[0068]

[0069] like Figure 8 Figures (a), (b), (c), and (d) show the Bode modulus plots of the MZrE / MZrE-rGO coatings with different immersion times. Generally, the larger the stable value of log|Z| at low frequencies, the better the impedance-based electronic conductivity of the coating. Figure 8 As shown in (a), in the low-frequency region, the modulus value of the coating initially increases and then decreases. MZrE-rGO 160 The coating exhibits the highest modulus value, approximately 10. 8 Ω·cm 2 It also possesses optimal corrosion resistance. For example... Figure 8 As shown in (d), even after soaking for 30 days, MZrE-rGO 160 The coating maintains its advantage in |Z| values ​​in the low-frequency region. This result is confirmed by the Nyquist plot and is consistent with experimental results.

[0070] Tafel polarization curves play a crucial role in evaluating the corrosion resistance of anti-corrosion coatings. Using Cview fitting software, the Tafel polarization curves of all coatings can be accurately determined, thereby obtaining key parameters such as corrosion potential (Ecorr) and corrosion current density (Icorr). Coatings with higher corrosion potentials and lower corrosion current densities generally exhibit superior corrosion resistance. The corrosion current and corrosion potential of the original Q235 steel are 9.40 × 10⁻⁶. −6 A·cm −2 and −631.36 mV. After a 30-day immersion experiment, MZrE-rGO 160 The polarization curve of the coating showed a significant shift, confirming its characteristics as an anodic corrosion inhibitor. The coating maintained a high corrosion inhibition rate (η) even after long-term immersion (180 days), as detailed in Table 2, demonstrating its continued high corrosion resistance.

[0071] Table 2

[0072]

[0073] Recent research indicates that adding rGO to epoxy resin can significantly extend the diffusion path of corrosive substances, thereby effectively improving the barrier properties of epoxy coatings. However, over time, the corrosive effects of the medium can gradually compromise the structural integrity of the coating. Notably, although the substrate itself is not substantially damaged, the highly conductive rGO can induce galvanic corrosion at micropore defects in the metal substrate and coating. This corrosion can spread along the conductive coating to more reactive areas, and if left uncontrolled, it can cause irreparable damage in a short period. To address this, the inventors created artificial scratches with a width of 600±50 micrometers on the surface of MZrE and MZrE-rGO coatings and continuously tested the samples in a salt spray chamber containing 3.5% sodium chloride for 900 hours. Figure 10 As shown in Table 3, digital photos of the scratched coating before and after the salt spray test were obtained, and the average width of the artificial scratches after corrosion was calculated.

[0074] Table 3

[0075]

[0076] Depend on Figure 10 It can be seen that the corrosion diffusion range around the scratches on the MZrE sample is larger than that of the MZrE-rGO coating. This finding indicates that carbon steel protected by the unreinforced rGO coating suffers more severe corrosion. This phenomenon is attributed to the layered structure of rGO in the coating, which elongates the path of the corrosive medium to the metal surface, thus creating a labyrinth effect. The MZrE-rGO... 120 and MZrE-rGO 140 The coated carbon steel sample not only showed severe corrosion at the scratches, but also obvious blistering in other areas. Meanwhile, MZrE-rGO... 160 With MZrE-rGO 180 The corrosion status of the coatings is difficult to distinguish with the naked eye. To further investigate the corrosion process of these two coatings, the coatings were peeled off the carbon steel surface, and the degree of corrosion on the carbon steel surface under different coating protection was observed using an optical microscope. Figure 11 As shown, MZrE-rGO 160 Only negligible corrosion was observed near the scratch, with a scratch extension width of 1061.8925 micrometers; in contrast, MZrE-rGO... 180 Significant corrosion was observed around the scratches, causing the scratch edges to become blurred. This indicates that rGO... 180 The high conductivity of the galvanic corrosion effect spreads from the scratch to other parts.

[0077] To further investigate the corrosion behavior and results of carbon steel electrodes with different coatings, MzrE and MZrE-rGO were immersed in a 3.5% (mass fraction) sodium chloride (NaCl) solution for 15 days. Afterward, the coatings were carefully peeled off the carbon steel surface. The samples were then thoroughly cleaned with alcohol to ensure sterility. The interface between the coating and carbon steel was rigorously analyzed using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). It is well known that the corrosion of carbon steel involves a series of chemical and electrochemical reactions when exposed to a corrosive environment, involving oxygen, water molecules, and chloride ions. The main corrosion products are ferrous hydroxide (Fe(OH)2) and small amounts of hematite (Fe2O3) and magnetite (Fe3O4). Therefore, this invention focuses primarily on the accumulation of iron and oxygen elements at the interface between different coatings and carbon steel. The more complete the coating morphology, the stronger its resistance to penetration.

[0078] like Figure 12 As shown in (a)-(c), MZrE and MZrE-rGO 120 The interface between the coating and carbon steel exhibited significant damage and penetration. Furthermore, EDS analysis revealed a marked enrichment of iron and oxygen in this interfacial region. In contrast, MZrE-rGO... 160 The interface structure between the coating and carbon steel remained intact, with uniform distribution of ferrite elements and no obvious aggregation. Experimental results show that MZrE-rGO... 160 The coating exhibits excellent corrosion resistance.

[0079] To further illustrate the beneficial effects of the present invention, the following comparative examples were constructed.

[0080] Comparative Example 3

[0081] In this comparative example, steps 1-3 are omitted, and the epoxy resin is directly mixed with the curing agent and applied. The remaining conditions are the same as in Example 2.

[0082] Comparative Example 4

[0083] In this comparative example, step 3 is omitted, and rGO is directly used. 160 It was dispersed in 4 grams of epoxy resin, and the remaining conditions were the same as in Example 2.

[0084] Comparative Example 5

[0085] In this comparative example, mullite is omitted, and the other conditions are the same as in Example 2.

[0086] Comparative Example 6

[0087] In this comparative example, nano-zirconia was omitted, and the other conditions were the same as in Example 2.

[0088] The impedance values ​​of the above coating after immersing in 3.5% (mass fraction) sodium chloride solution for 3, 7, 14, 30, 90 and 180 days are shown in Table 4.

[0089] Table 4

[0090]

[0091] As shown in Table 4, the addition of reduced graphene oxide can improve the corrosion resistance of epoxy resin coatings; the addition of mullite or nano-zirconia further enhances its corrosion resistance, but there is still a gap in corrosion resistance compared with the examples. This is because mullite constructs the basic reinforcing skeleton of the coating; while nano-zirconia fills the voids in the skeleton and the resin matrix, making the coating structure exceptionally dense and significantly enhancing its corrosion resistance.

[0092] To further improve the long-term corrosion resistance of the prepared coating, the prepared reduced graphene oxide was modified, and specific embodiments are as follows.

[0093] Example 4

[0094] A method for preparing rGO-epoxy resin anti-corrosion coatings with different electrical conductivity, comprising:

[0095] Steps 1-2 are the same as steps 1-2 in Example 1;

[0096] Step 3: The rGO prepared in step 2... 140 The rGO was ultrasonically dispersed in DMF to obtain a concentration of 1 mg / mL. 100 mL of the rGO dispersion was taken, and 5 mmol of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) and 6 mmol of N-hydroxysuccinimide (NHS) solution were added, followed by stirring for 4 h. Then, 6 mmol of γ-aminopropyltriethoxysilane (KH-792) was added, and the mixture was stirred at 60 °C for 5 h. The mixture was then centrifuged at 6000 rpm for 30 min, washed three times with deionized water, and dried at 60 °C to obtain MrGO. 140 ;

[0097] Step 4 is the same as step 3 in Example 1;

[0098] Step 5: Add 0.024 grams of modified rGO 140 The mixture was dispersed in 4 ml of MZr slurry and ultrasonically treated to obtain a uniform dispersion system. Subsequently, 0.4 g of epoxy resin was added to the mixture under continuous stirring and stirred for 60 minutes to form a homogeneous solution.

[0099] Steps 6-7 are the same as steps 5-6 in Example 1, resulting in the MZrE-MrGO coating. 140 .

[0100] Example 5

[0101] In this embodiment, rGO 140 Replace with rGO 160 The remaining conditions are the same as in Example 4, resulting in the MZrE-MrGO coating. 160 .

[0102] Example 6

[0103] In this embodiment, rGO 140 Replace with rGO 180 The remaining conditions are the same as in Example 4, resulting in the MZrE-MrGO coating. 180 .

[0104] Comparative Example 7

[0105] In this comparative example, rGO will be used. 160 Replace with rGO 120 The remaining conditions are the same as in Example 5, resulting in the MZrE-MrGO coating. 120 .

[0106] Comparative Example 8

[0107] Step 2 is omitted, and the remaining conditions are as described in Example 5, resulting in the coating MZrE-GO.

[0108] Comparative Example 9

[0109] In this comparative example, step 4 is omitted, and MrGO is directly used. 160 It was dispersed in 4 grams of epoxy resin, and the remaining conditions were the same as in Example 5.

[0110] Comparative Example 10

[0111] In this comparative example, mullite is omitted, and the other conditions are the same as in Example 5.

[0112] Comparative Example 11

[0113] In this comparative example, nano-zirconia was omitted, and the other conditions were the same as in Example 5.

[0114] Among them, MZrE-MrGO 120 MZrE-MrGO 140 MZrE-MrGO 160 MZrE-MrGO 180 Collectively referred to as MZrE-MrGO coating.

[0115] The anti-corrosion performance of the coatings prepared in Examples 4-6 and Comparative Examples 7-11 was tested, and the results are shown in Tables 3-4.

[0116] The impedance values ​​of the above coating after immersion in a 3.5% (mass fraction) sodium chloride solution for 3, 7, 14, 30, 90, and 180 days are shown in Table 5. The above coating was then placed in a salt spray chamber containing 3.5% sodium chloride for 180 days for continuous testing, and the corrosion of the surface coating was observed. The results are shown in Table 6.

[0117] Table 5

[0118]

[0119] As shown in Table 5, the modified reduced graphene oxide of this invention significantly enhances the anti-corrosion performance of the epoxy resin coating. After prolonged immersion, the impedance value of the coating is increased by one to two orders of magnitude compared to unmodified reduced graphene oxide. For MZrE-GO, the modification of graphene oxide improves its dispersibility in epoxy resin, thereby enhancing its anti-corrosion performance. MZrE-MrGO 140 The coating impedance also reached 10. 7 Ω·cm 2 Compared to unmodified reduced graphene oxide, it is two orders of magnitude higher. Compared to Comparative Example 7-11, the long-term corrosion resistance value is also increased by one to two orders of magnitude.

[0120] Table 6

[0121]

[0122] As shown in Table 6, the corrosion inhibition rate of the MZrE-MrGO coating remained high after 180 days of immersion testing.

[0123] The inventors also created artificial scratches with a width of 600±50 micrometers on the MZrE-GO and MZrE-MrGO coating surfaces and continuously tested the samples in a salt spray chamber containing 3.5% sodium chloride for 900 hours. The average width of the artificial scratches after corrosion was calculated, and the results are shown in Table 7.

[0124] Table 7

[0125]

[0126] As shown in Table 7, when modified reduced graphene oxide is used in epoxy resin anti-corrosion coatings, the width of the scratches after corrosion is significantly reduced compared to the unmodified version.

[0127] In summary, this invention effectively balances the shielding performance and corrosion inhibition capability of reduced graphene oxide by controlling its electrical conductivity, thereby optimizing the anti-corrosion performance of the coating. Furthermore, by modifying the reduced graphene oxide, its dispersibility in the epoxy resin matrix is ​​improved, further enhancing the anti-corrosion performance.

[0128] The above description is a preferred embodiment of the present invention. For those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A rGO-epoxy resin anti-corrosion coating with different electrical conductivity, characterized in that, It is prepared from the following components by weight: 6 parts reduced graphene oxide, 125 parts mullite, 125 parts nano zirconium dioxide, 100 parts epoxy resin, 100 parts curing agent, and 700-800 parts ethanol. The reduced graphene oxide has an electrical conductivity of 7 × 10⁻⁶. -2 The particle size of the mullite is 1-1.5 μm, and the particle size of the nano-zirconia is 50-100 nm.

2. The method for preparing rGO-epoxy resin anti-corrosion coatings with different electrical conductivities as described in claim 1, characterized in that, include: Step 1: Prepare graphene oxide (GO) dispersion using the modified Hummers method; Step 2: Transfer the GO dispersion to a reaction vessel and carry out a hydrothermal reduction reaction at 140-180℃ for 6-12 hours, then freeze-dry to obtain reduced graphene oxide (rGO). Step 3: Weigh each component according to claim 1, and then mix and ball-mill the mullite, nano-zirconium dioxide, and ethanol to obtain a mullite-zirconium dioxide (MZr) mixed slurry; Step 4: Disperse rGO in MZr mixed slurry, ultrasonically mix until uniform, add epoxy resin under stirring condition, and stir until uniform; Step 5: Add curing agent to the system from step 4, stir well, and obtain coating slurry. Step 6: Apply the coating paste to the substrate surface using a scraper, with a coating amount of 1-2 g / cm². 2 The anti-corrosion coating can be obtained by curing at room temperature.

3. The preparation method according to claim 2, characterized in that, Step 1 specifically involves placing 1 g of graphite, 6 g of potassium permanganate, and 50 mL of concentrated sulfuric acid in a 250 mL Erlenmeyer flask, heating and stirring continuously for 2 hours in a 55°C water bath; after the system cools to room temperature, adding deionized water and hydrogen peroxide sequentially to obtain graphite oxide slurry; then washing with deionized water by centrifugation until neutral, and diluting to a concentration of 2 mg / mL to obtain graphite oxide dispersion; and obtaining a monolayer GO dispersion after ultrasonic exfoliation.

4. The preparation method according to claim 2, characterized in that, Step 3 specifically involves placing mullite, nano-zirconia, and ethanol into a ball milling container, then adding zirconia grinding balls with diameters of 3 mm and 0.5 mm respectively at a mass ratio of 1:1, resulting in a ball-to-material ratio of 10:

1. The mixture is then ball-milled at a speed of 300 rpm for 7 hours to obtain a MZr mixed slurry.

5. The preparation method according to claim 2, characterized in that, The preparation method further includes the modification of rGO: the rGO prepared in step 2 is ultrasonically dispersed in DMF to obtain an rGO dispersion with a concentration of 1 mg / mL; a solution of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) is stirred for 1-6 h; then γ-aminopropyltriethoxysilane (KH-792) is added and stirred at 40-80℃ for 2-8 h; after centrifugation, washing, and drying, the modified rGO is obtained.

6. The preparation method according to claim 5, characterized in that, The mass molar ratio of the rGO dispersion, EDC, NHS and KH-792 was 100 mg: 5 mmol: 6 mmol: 6 mmol.

7. The preparation method according to claim 6, characterized in that, The KH-792 has the same molar ratio as NHS.

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