Preparation method of melamine-modified graphene oxide anti-corrosion coating

Abstract

The application discloses a preparation method of melamine modified graphene oxide anticorrosive paint, and the method comprises the following steps: preparing graphene oxide; dispersing the graphene oxide in a solvent to obtain graphene oxide dispersion; dispersing melamine in a solvent to obtain melamine dispersion; mixing the graphene oxide dispersion and the melamine dispersion to react; drying and grinding after the reaction is completed to obtain modified graphene oxide; adding the modified graphene oxide into an epoxy resin solvent, uniformly dispersing through ultrasonic, adding epoxy resin, stirring until the epoxy resin is completely dissolved, and finally adding a curing agent, and uniformly mixing to obtain the melamine modified graphene oxide anticorrosive paint. The graphene oxide prepared under weak acid conditions is more conducive to activating carboxyl and carbonyl of the graphene oxide, more activated carboxyl and carbonyl are obtained, the reaction of the melamine and the graphene oxide is facilitated, and therefore the corrosion resistance of the coating is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of anti-corrosion coatings, and more particularly to a method for preparing a melamine-modified graphene oxide anti-corrosion coating. Background Art

[0002] Metal materials are used in many fields, and the corrosion problem of metal materials has caused losses to the application of metals. In order to reduce the losses caused by corrosion, many anti-corrosion measures have been taken. So far, the most commonly used method is to coat the surface of metal materials with anti-corrosion materials. For example, in the field of marine ships, since ships are in contact with saline-alkali water environments for a long time, the requirements for anti-corrosion coatings on the surface of ships are high, and the anti-corrosion coatings are required to have good high temperature resistance, corrosion resistance, wear resistance and other excellent properties. Epoxy resin (EP) is widely used in the fields of electronics and electrical, machinery manufacturing, aerospace, etc. Researchers have been committed to the modification research of epoxy resin in order to obtain epoxy resins that can be used in multiple ways and applied to special fields. Summary of the Invention

[0003] To this end, the technical problem to be solved by the present invention is to provide a method for preparing a melamine-modified graphene oxide anti-corrosion coating with better corrosion resistance.

[0004] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0005] A method for preparing a melamine-modified graphene oxide anti-corrosion coating comprises the following steps:

[0006] (1) preparing graphene oxide;

[0007] (2) dispersing graphene oxide in a solvent to obtain a graphene oxide dispersion;

[0008] (3) dispersing melamine in a solvent to obtain a melamine dispersion;

[0009] (4) mixing the graphene oxide dispersion and the melamine dispersion to react, and drying and grinding after the reaction is completed to obtain modified graphene oxide;

[0010] (5) Add the modified graphene oxide to the epoxy resin solvent, disperse it evenly by ultrasonication, then add the epoxy resin, stir until the epoxy resin is completely dissolved, and finally add the curing agent. After mixing evenly, the melamine-modified graphene oxide anti-corrosion coating is obtained.

[0011] In the above-mentioned method for preparing a melamine-modified graphene oxide anti-corrosion coating, in step (1), the preparation method of graphene oxide is as follows:

[0012] (1-1) Weigh graphite, add sulfuric acid, phosphoric acid, and potassium permanganate in an ice bath, and mix thoroughly;

[0013] (1-2) Carry out the reaction in a water bath;

[0014] (1-3) After the reaction is complete, add ice water to dilute;

[0015] (1-4) Add hydrogen peroxide dropwise until the solution turns golden yellow;

[0016] (1-5) filtering, washing the filter residue with water, and centrifuging the filter residue, testing the pH of the last washing solution of the filter residue to obtain graphene oxide at different pH values;

[0017] (1-6) Freeze-dry, grind, and collect graphene oxide.

[0018] The preparation method of the above-mentioned melamine-modified graphene oxide anti-corrosion coating,

[0019] In step (1-1), the amount of graphite added is 1.2-1.8 g, the amount of sulfuric acid added is 120-180 mL, the mass concentration of sulfuric acid is 98%, the amount of phosphoric acid added is 40-60 mL, the concentration of phosphoric acid is 85%, and the amount of potassium permanganate added is 12-18 g;

[0020] In step (1-2): the reaction temperature is 50-70°C, and the reaction time is 10-14 minutes;

[0021] In step (1-3): the amount of ice water added is: 180-250 mL;

[0022] In step (1-4): the concentration of the hydrogen peroxide solution is: 6%.

[0023] The preparation method of the above-mentioned melamine-modified graphene oxide anti-corrosion coating comprises the following steps: in step (2): dispersing graphene oxide in water to obtain a graphene oxide aqueous dispersion, wherein the amount of graphene oxide and water is: adding 0.1 to 0.5 g of graphene oxide per 10 mL of water.

[0024] The preparation method of the above-mentioned melamine-modified graphene oxide anti-corrosion coating comprises the following steps: in step (3): dispersing melamine in water to obtain a melamine aqueous dispersion, wherein the amount of melamine and water used is: adding 0.02 to 0.08 g of melamine per 10 mL of water.

[0025] The method for preparing the melamine-modified graphene oxide anti-corrosion coating comprises the following steps: in step (4): the volume ratio of the graphene oxide dispersion to the melamine dispersion is 4 to 6:1, the reaction temperature is 70 to 90° C., and the reaction time is 20 to 40 minutes.

[0026] The preparation method of the above-mentioned melamine-modified graphene oxide anti-corrosion coating comprises the following steps: in step (5): the amounts of modified graphene oxide and epoxy resin solvent are 0.01-0.05 g and 10-15 mL respectively; the epoxy resin solvent is a mixture of xylene and n-butanol, the volume ratio of xylene to n-butanol is 7:3; the amount of epoxy resin added is 3.0-3.5 g; and the curing agent is polyamide, the amount of curing agent added is 4-8 g.

[0027] The method for preparing the melamine-modified graphene oxide anti-corrosion coating comprises the following steps: in step (2): dispersing graphene oxide in water in an ice bath environment to obtain a graphene oxide aqueous dispersion; then adding polyphosphoric acid to the graphene oxide aqueous dispersion, and stirring and mixing the mixture to obtain a graphene oxide-polyphosphoric acid aqueous solution.

[0028] The method for preparing the melamine-modified graphene oxide anti-corrosion coating comprises the following steps: in step (3): dispersing melamine in ethanol to obtain a melamine ethanol dispersion; and in step (4): adding a graphene oxide-polyphosphoric acid aqueous solution dropwise to the melamine ethanol dispersion under stirring.

[0029] The preparation method of the above-mentioned melamine-modified graphene oxide anti-corrosion coating,

[0030] In step (2), the mass ratio of graphene oxide to water is 3-4:100; the mass ratio of graphene oxide to polyphosphoric acid in the graphene oxide-polyphosphoric acid aqueous solution is 1:2-3; the mass content of P2O5 in the polyphosphoric acid is 80-85%;

[0031] In step (3), the mass ratio of melamine to ethanol is 4-8:40; during the stirring process, the temperature is controlled at 40-45° C. and the stirring time is 1-2 hours;

[0032] In step (4), the volume ratio of the melamine ethanol dispersion to the graphene oxide-polyphosphoric acid aqueous solution is 1:1-2.5; the graphene oxide-polyphosphoric acid aqueous solution is added dropwise to the melamine ethanol dispersion while stirring at 70-80° C. for 1-2 hours, and then yttrium vanadate is added during stirring to carry out a catalytic reaction, the reaction temperature is maintained at 70-80° C., the stirring time is 4-5 hours, the mixture is filtered, and vacuum dried at 90° C. for 10-12 hours to obtain modified graphene oxide; the amount of yttrium vanadate added is 3-4wt% of the amount of melamine added;

[0033] In step (5): the amounts of modified graphene oxide and epoxy resin solvent are 0.01-0.05 g and 10-15 mL respectively, the epoxy resin solvent is a mixture of xylene and n-butanol, the volume ratio of xylene to n-butanol is 7:3, the amount of epoxy resin added is 3.0-3.5 g, the curing agent is polyamide, and the amount of curing agent added is 4-8 g.

[0034] The technical solution of the present invention achieves the following beneficial technical effects:

[0035] 1. Acidic conditions are generally considered to be detrimental to corrosion resistance. The applicant accidentally discovered that the anti-corrosion coating prepared by modified graphene oxide prepared under acidic conditions without thorough washing also has good corrosion resistance.

[0036] Experiments show that under salt spray tests of 300-500 hours, only minor corrosion occurs under different pH conditions, and the low-frequency impedance modulus remains high. Graphene oxide prepared under weakly acidic conditions is more conducive to the activation of its carboxyl and carbonyl groups, resulting in more activated carboxyl and carbonyl groups, which facilitates the reaction between melamine and graphene oxide, thereby improving the corrosion resistance of the coating.

[0037] 2. However, the applicant also found that the graphene oxide sheet structure has a high degree of disorder. The overlapping sheets easily cause agglomeration and shield the active sites, which is not conducive to the reaction between melamine and graphene oxide. The resulting melamine-modified graphene oxide sheet has a high degree of disorder.

[0038] By adding polyphosphoric acid and utilizing its long-chain structure, the amino group -NH2 of melamine reacts with the carboxyl group -COOH of graphene oxide to form an -NH3...OOC- bond. On the other hand, the remaining amino group -NH2 of melamine reacts with the hydroxyl group -OH of polyphosphoric acid to form an -O...NH3- bond. As a result, the long chain of polyphosphoric acid can be used to fix multiple melamine-modified graphene oxides, reducing the disorder of the overlapping graphene oxide sheets, thereby exposing more active sites, facilitating the full reaction between melamine and graphene oxide, and further improving the corrosion resistance of the coating.

[0039] During the experiment, considering the problem of hydrolysis of polyphosphoric acid, graphene oxide and polyphosphoric acid were dispersed in an ice bath environment; dispersing melamine in ethanol can, on the one hand, increase the solubility of melamine, and on the other hand, reduce the hydrolysis of polyphosphoric acid during the process of adding the graphene oxide-polyphosphoric acid aqueous solution to the melamine ethanol dispersion.

[0040] The graphene oxide-polyphosphoric acid aqueous solution is dropped into the melamine ethanol dispersion liquid, which is beneficial to the dispersion of the polyphosphoric acid and the graphene oxide in the ethanol; the yttrium vanadate is used as the catalyst, the active site of the reaction can be activated, and the reaction is promoted; the cooperation of the ethanol solvent and the yttrium vanadate can slowly release heat in the reaction process, reduce the local overheating, on one hand, the slow heat release can increase the active site of the graphene oxide, on the other hand, the slow heat release is beneficial to the reaction of the melamine and the polyphosphoric acid, and the local overheating can cause the overlapping of the layers of the graphene oxide. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 Preparation flow chart of the graphene oxide in the application;

[0042] Figure 2 Preparation flow chart of the melamine modified graphene oxide from the graphene oxide in the application;

[0043] Figure 3 Preparation flow chart of the anticorrosion coating from the melamine modified graphene oxide in the application;

[0044] Figure 4 Infrared spectrum of the graphene oxide under different pH values;

[0045] Figure 5a Raman spectrum of the graphene oxide under different pH values; Figure 5b Raman spectrum of the melamine graphene oxide under different pH values;

[0046] Figure 6 Morphology comparison of the coating of the melamine modified graphene oxide under different pH values after 300h salt spray corrosion, (a) pH=1, (b) pH=2, (c) pH=3, (d) pH=4, (e) pH=5, (f) pH=6;

[0047] Figure 7 Morphology comparison of the coating of the melamine modified graphene oxide under different pH values after 500h salt spray corrosion, (a) pH=1, (b) pH=2, (c) pH=3, (d) pH=4, (e) pH=5, (f) pH=6;

[0048] Figure 8 Low-frequency impedance modulus value comparison of the coating of the melamine modified graphene oxide under different pH values after 72h salt water immersion;

[0049] Figure 9 Structure diagram of the polyphosphoric acid-melamine-graphene oxide;

[0050] Figure 10a Surface photo of the coating of the melamine modified graphene epoxy resin after 500h salt spray corrosion after adding the long-chain structure polyphosphoric acid;

[0051] Figure 10b Surface photo of the coating of melamine-modified graphene epoxy resin coating with long-chain polyphosphoric acid added after 700h salt spray corrosion. DETAILED DESCRIPTION

[0052] 1. Preparation of melamine-modified graphene oxide anti-corrosion coating

[0053] Example 1

[0054] The preparation method of the melamine-modified graphene oxide anti-corrosion coating of this embodiment comprises the following steps:

[0055] (1) preparing graphene oxide; Figure 1 Shown is the preparation flow chart of graphene oxide.

[0056] (1-1) Weigh graphite, add sulfuric acid, phosphoric acid, and potassium permanganate in an ice bath, and mix thoroughly. The graphite is added in an amount of 1.5 g, the sulfuric acid is added in an amount of 150 mL (the concentration of the sulfuric acid is 98%), the phosphoric acid is added in an amount of 50 mL (the concentration of the phosphoric acid is 85%), and the potassium permanganate is added in an amount of 15 g.

[0057] (1-2) The reaction was carried out in a water bath at a temperature of 60°C and a reaction time of 12 min.

[0058] (1-3) After the reaction is complete, add ice water to dilute; the amount of ice water added is: 200 mL;

[0059] (1-4) Add hydrogen peroxide dropwise until the solution turns golden yellow; the concentration of hydrogen peroxide in the solution is: the amount added is: 6%

[0060] (1-5) filtering, washing the filter residue with water, and centrifuging the filter residue. The pH of the last washing liquid of the filter residue was tested to obtain graphene oxide with pH values ​​of 1, 2, 3, 4, 5, and 6, respectively.

[0061] (1-6) Freeze-dry, grind, and collect graphene oxide.

[0062] (2) Dispersing 6 groups of graphene oxide with different pH values ​​in water to obtain graphene oxide dispersed aqueous solutions; dispersing 0.4 g of graphene oxide in 10 mL of water; Figure 2 shown.

[0063] (3) dispersing 0.05 g of melamine in 10 mL of deionized water to obtain a melamine dispersion aqueous solution;

[0064] (4) mixing a graphene oxide dispersion aqueous solution and a melamine dispersion aqueous solution for reaction, wherein the volume ratio of the graphene oxide dispersion to the melamine dispersion is 5:1, reacting in a water bath at 80° C. for 30 minutes, and drying and grinding after the reaction to obtain melamine-modified graphene oxide;

[0065] (5) Figure 3 As shown, melamine-modified graphene oxide is added to an epoxy resin solvent and ultrasonically dispersed to obtain a uniform coating. The epoxy resin is then added and stirred until the epoxy resin is completely dissolved. Finally, a curing agent is added and mixed to obtain a melamine-modified graphene oxide anti-corrosion coating. The amounts of melamine-modified graphene oxide and epoxy resin solvent are 0.01 g and 12 mL, respectively. The epoxy resin solvent is a mixture of xylene and n-butanol in a volume ratio of 7:3. The amount of epoxy resin added is 3.3 g, and the curing agent is polyamide, with an amount of 6 g added.

[0066] Example 2

[0067] The preparation method of the graphene oxide in this embodiment is the same as that in Example 1, except that the method for preparing the modified graphene oxide is different.

[0068] Since the melamine-modified graphene oxide sheet in Example 1 has a high degree of disorder, the dispersion effect of the melamine-modified graphene oxide in the epoxy resin is poor, resulting in poor spraying effect of the spray coating, which in turn affects the anti-corrosion performance of the coating.

[0069] In this embodiment, polyphosphoric acid is added and the long chain structure in the polyphosphoric acid is utilized to reduce the disorder of the melamine-modified graphene oxide flakes, thereby improving the anti-corrosion effect of the coating.

[0070] In step (2), 4 g of graphene oxide prepared in Example 1 is dispersed into 100 mL of water in an ice bath environment to obtain a graphene oxide aqueous dispersion; 12 g of polyphosphoric acid is added to the graphene oxide aqueous dispersion, wherein the mass content of P2O5 in the polyphosphoric acid is 82%, and the mixture is stirred and mixed to obtain a graphene oxide-polyphosphoric acid aqueous solution.

[0071] In step (3), 12 g of melamine is dispersed in 40 g of ethanol to obtain a melamine ethanol dispersion, the temperature is controlled at 40-45° C., and the stirring time is 1-2 h.

[0072] In step (4), the graphene oxide-polyphosphoric acid aqueous solution was added dropwise to the melamine ethanol dispersion while stirring at 80°C for 1 hour. Yttrium vanadate was then added during stirring to catalyze the reaction. The reaction temperature was maintained at 80°C and the stirring time was 4 hours. The mixture was filtered and vacuum-dried at 90°C for 10 hours to obtain modified graphene oxide. The amount of yttrium vanadate added was 0.36 g. [Melamine is insoluble in water, while graphene oxide and polyphosphoric acid have a certain solubility in ethanol, so back-drip is not possible.] The hydroxyl groups (OH) of the polyphosphoric acid react with the remaining amino groups (NH2) of melamine to form -O…NH3- bonds. Especially under the catalysis of yttrium vanadate and with ethanol as the medium, the reaction slowly releases heat without localized overheating. Simultaneously, the amino groups (NH2) of melamine react with the carboxyl groups (COOH) of graphene oxide to form -NH3…OOC- bonds. This allows the long chains of polyphosphoric acid to be used to fix multiple melamine-modified graphene oxides, reducing the disorder of the graphene oxide sheets.

[0073] In step (5), the modified graphene oxide is added to the epoxy resin solvent, ultrasonically dispersed uniformly, then the epoxy resin is added, stirred until the epoxy resin is completely dissolved, and finally the curing agent is added and mixed uniformly to obtain a melamine-modified graphene oxide anti-corrosion coating; the amounts of modified graphene oxide and epoxy resin solvent are 0.01 g and 12 mL respectively, the epoxy resin solvent is a mixture of xylene and n-butanol, the amount of epoxy resin added is 3.3 g, and the amount of curing agent added is 6 g.

[0074] 2. Results and Characterization

[0075] (1) 6 groups of graphene oxide prepared under different pH conditions were characterized by infrared spectroscopy.

[0076] like Figure 4 The following are FTIR spectra of graphene oxide at different pH values. The low-pH graphene oxide exhibits a high number of impurity peaks, indicating a high level of impurities in the sample, likely due to insufficient water washing. As the number of washes increases and the pH rises, the infrared spectra become smoother and the impurity peaks significantly decrease.

[0077] (2) Raman spectral characterization of graphene oxide and modified graphene oxide prepared under 6 groups of different pH conditions.

[0078] like Figure 5a and Figure 5b As shown, there are 6 groups of Raman spectra of graphene oxide and modified graphene oxide under different pH conditions. pH has almost no effect on the position and intensity ratio of the D peak and G peak of graphene oxide and modified graphene oxide.

[0079] 3. Salt spray corrosion test

[0080] As shown in Figure 6 Figure 3, the morphology comparison chart of the coating layer added with MGO of different pH values after 300h salt spray corrosion, the cross-cut marks on the surface of the coating layer under each condition were not eroded.

[0081] As shown in Figure 7 Figure 4, the morphology comparison chart of the coating layer added with MGO of different pH values after 500h salt spray corrosion, the cross-cut marks on the surface of the coating layer under the conditions of pH=3 and pH=5 were not eroded.

[0082] 4、Electrochemical performance

[0083] Figure 8 The low-frequency impedance modulus value comparison of the coating layer added with MGO of different pH values after 72h salt water immersion.

[0084] 5、In Example 2, the corrosion resistance of the epoxy resin coating layer of melamine modified graphene added with long chain structure polyphosphoric acid is better, experiments show that the cross-cut marks on the surface of the coating layer after 500h and 700h salt spray corrosion are not eroded, and the morphology comparison chart is shown in Figure 10a and Figure 10b .

[0085] 6、Summary

[0086] (1) Infrared spectroscopy shows that there are more spurious peaks in the infrared spectrum of low-pH GO;

[0087] (2) Raman spectroscopy shows that the position and intensity ratio of D peak and G peak of GO and MGO of different pH values have no obvious change, which shows that pH value does not affect the disorder degree of MGO sheet;

[0088] (3) After 300h salt spray corrosion treatment, the coating layer samples added with MGO of different pH values only have slight corrosion marks;

[0089] (4) After 72h salt water immersion treatment, the low-frequency impedance modulus value of the coating layer samples added with MGO of different pH values remains at a high level.

[0090] (5) When polyphosphoric acid and melamine are used together to modify graphene oxide, the disorder degree of the modified graphene oxide sheet is greatly reduced, and the corrosion resistance is further improved.

[0091] In summary, in the process of preparing GO and MGO by improved Hummers method, the number of water washing is reduced, and the acid MGO prepared can still exhibit good corrosion resistance in the epoxy resin coating layer.

[0092] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the claims of this patent application.

Claims

1. A method for preparing a melamine-modified graphene oxide anti-corrosion coating, characterized in that: The steps include: (1) Preparation of graphene oxide; (2) dispersing graphene oxide in water in an ice bath environment to obtain a graphene oxide aqueous dispersion; then adding polyphosphoric acid to the graphene oxide aqueous dispersion and stirring and mixing uniformly to obtain a graphene oxide-polyphosphoric acid aqueous solution; (3) dispersing melamine in ethanol to obtain a melamine ethanol dispersion; (4) During the stirring process at 70-80°C, the graphene oxide-polyphosphoric acid aqueous solution is added dropwise to the melamine ethanol dispersion for a reaction time of 1-2 hours, and then yttrium vanadate is added during the stirring process to carry out a catalytic reaction, the reaction temperature is maintained at 70-80°C, the stirring time is 4-5 hours, the mixture is filtered, and the mixture is vacuum dried at 90°C for 10-12 hours to obtain modified graphene oxide; the amount of yttrium vanadate added is 3-4wt% of the amount of melamine added; the volume ratio of the melamine ethanol dispersion to the graphene oxide-polyphosphoric acid aqueous solution is 1:1-2.5; (5) Add the modified graphene oxide to the epoxy resin solvent, disperse it evenly by ultrasonication, then add the epoxy resin, stir until the epoxy resin is completely dissolved, and finally add the curing agent. After mixing evenly, the melamine-modified graphene oxide anti-corrosion coating is obtained.

2. The method for preparing a melamine-modified graphene oxide anti-corrosion coating according to claim 1, wherein: In step (1), the preparation method of graphene oxide is as follows: (1-1) Weigh graphite, add sulfuric acid, phosphoric acid, and potassium permanganate in an ice bath, and mix thoroughly; (1-2) Carry out the reaction in a water bath; (1-3) After the reaction is complete, add ice water to dilute; (1-4) Add hydrogen peroxide dropwise until the solution turns golden yellow; (1-5) Filtration, washing the filter residue with water and centrifuging, testing the pH of the last washing liquid of the filter residue to obtain graphene oxide at different pH values; (1-6) Freeze-dry, grind, and collect graphene oxide.

3. The method for preparing a melamine-modified graphene oxide anti-corrosion coating according to claim 2, wherein: In step (1-1), the amount of graphite added is 1.2-1.8 g, the amount of sulfuric acid added is 120-180 mL, the mass concentration of sulfuric acid is 98%, the amount of phosphoric acid added is 40-60 mL, the concentration of phosphoric acid is 85%, and the amount of potassium permanganate added is 12-18 g. In step (1-2): the reaction temperature is 50-70°C, and the reaction time is 10-14 minutes; In steps (1-3): the amount of ice water added is: 180-250 mL; In steps (1-4): the concentration of the hydrogen peroxide solution is: 6%.

4. The method for preparing a melamine-modified graphene oxide anti-corrosion coating according to claim 1, wherein: In step (2): the mass ratio of graphene oxide to water is 3-4:100; the mass ratio of graphene oxide to polyphosphoric acid in the graphene oxide-polyphosphoric acid aqueous solution is 1:2-3; the mass content of P2O5 in the polyphosphoric acid is 80-85%; In step (3): the mass ratio of melamine to ethanol is 4-8:40; during the stirring process, the temperature is controlled at 40-45°C and the stirring time is 1-2 hours; In step (5): the amounts of modified graphene oxide and epoxy resin solvent are 0.01-0.05 g and 10-15 mL, respectively; the epoxy resin solvent is a mixture of xylene and n-butanol, the volume ratio of xylene to n-butanol is 7:3; the amount of epoxy resin added is 3.0-3.5 g; the curing agent is polyamide, and the amount of curing agent added is 4-8 g.

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