Cerium salt modified graphene / epoxy powder coating and preparation and application thereof

Abstract

The application belongs to the technical field of coating, and discloses a cerium salt modified graphene / epoxy powder coating and a preparation and application thereof.The coating is mainly prepared from the following components by weight fraction: 100 parts of epoxy resin, 0.025-0.2 parts of cerium salt modified graphene, 10-50 parts of curing agent, 10-100 parts of pigment and filler, and 2-20 parts of additive.The application also discloses a preparation method of the coating.The application realizes liquid phase shearing on natural graphite in a water and ethanol mixed solution of polyvinyl alcohol, realizes surface modification of graphene by polyvinyl alcohol while peeling off graphene, obtains cerium salt modified graphene, and then adds the cerium salt modified graphene into the epoxy powder coating according to a certain ratio, so as to give the coating a double function of barrier protection and corrosion inhibition, and realize stronger and more durable corrosion resistance of the coating.The method is simple, environment-friendly and effective, and has a wide application prospect.The coating can be used for metal corrosion prevention.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of coating, in particular to a cerium salt modified graphene / epoxy powder coating and its preparation and application in metal corrosion protection. BACKGROUND

[0002] Metal corrosion as a spontaneous natural process, brings huge losses to human society every year, for which various metal corrosion strategies have been developed, coating protection is a direct and effective method, among which organic coating has been widely used due to its high plasticity and diversified functions. In recent years, organic powder coating has the advantages of environmental protection and high moisture resistance due to the avoidance of the use of a large amount of solvent, and occupies an increasing share in the coating market.

[0003] Among many organic polymers, thermosetting epoxy resin is outstanding due to its easy processability, excellent mechanical properties and strong adhesion, and is often used as the matrix of organic coating. However, due to insufficient crosslinking reaction between epoxy molecules during curing and the brittleness of the cured coating, many structural defects such as pores and cracks exist in the epoxy coating, which become diffusion channels for corrosion medium, and are not conducive to the long-term corrosion protection of the coating to the substrate.

[0004] Nano fillers have been proved to effectively improve the corrosion resistance of the coating, among which carbon nano fillers, due to their light density, can achieve significant enhancement effect with a very low content (below 1wt%) compared with other nano fillers, avoiding the "mass loss" caused by high addition amount.

[0005] Graphene, as a two-dimensional carbon nano filler, has a large specific surface area and can effectively block the diffusion of corrosion medium in the coating. In addition, graphene can also be used as a carrier for grafting or loading various functional groups, organic molecules or corrosion inhibitors, thereby improving the dispersion in the coating and the interfacial bonding between the coating matrix, and endowing the coating with more functions.

[0006] There are various methods for preparing graphene, however, the graphene prepared by many processes often has surface defects, which is not conducive to play a blocking role in the coating. In addition, due to the existence of interlayer π-π interaction, graphene sheets are prone to agglomeration in the coating matrix, thereby introducing defects such as pores or cracks, reducing the corrosion resistance of the coating. SUMMARY

[0007] In order to realize stronger and more durable corrosion resistance of the epoxy powder coating, the application provides a cerium salt modified graphene / epoxy powder coating and a preparation method thereof. The application realizes the surface modification of graphene by liquid phase shearing of natural graphite in a water and ethanol mixed solution of polyvinyl alcohol, realizes the peeling of graphene and the surface modification of graphene by polyvinyl alcohol at the same time, thereby improving the dispersibility of graphene sheets in the base epoxy powder, and the hydroxyl groups on the polyvinyl alcohol molecular chain provide more active sites, which is conducive to the loading of cerium ions on the graphene sheets through hydrogen bond interaction and cation-π interaction between the graphene, and the cerium salt modified graphene is obtained, and then the cerium salt modified graphene is added into the epoxy powder coating according to a certain ratio, so as to endow the coating with barrier protection and corrosion inhibition double functions, and realize stronger and more durable corrosion resistance of the coating. The method is simple, environment-friendly and effective, and has a wide application prospect. Another purpose of the application is to provide the application of the coating. The coating is used for metal corrosion prevention.

[0008] The technical scheme of the application is as follows:

[0009] A cerium salt modified graphene / epoxy powder coating is prepared from the following components by weight fraction:

[0010] 100 parts of epoxy resin;

[0011] 0.025-0.2 parts of cerium salt modified graphene, preferably 0.04-0.06 parts;

[0012] 10-50 parts of curing agent, preferably 15-25 parts;

[0013] 10-100 parts of color filler, preferably 30-60 parts;

[0014] 2-20 parts of auxiliary agent, preferably 2-10 parts.

[0015] The epoxy resin is at least one of bisphenol A type epoxy resin, bisphenol F type epoxy resin and phenolic epoxy resin.

[0016] The curing agent is at least one of dicyandiamide curing agent, phenolic curing agent and acid anhydride curing agent.

[0017] The color filler is at least one of titanium dioxide, barium sulfate powder, wollastonite powder and mica powder.

[0018] The auxiliary agent includes one or more than one of brightener, leveling agent, degassing agent, antioxidant, ultraviolet light absorber, light stabilizer, adhesion promoter and the like, wherein the leveling agent can be at least one of acrylic acid and nano white carbon black; the degassing agent can be at least one of polysiloxane and benzoin; and the adhesion promoter is amino silicone oil.

[0019] The preparation method of the cerium salt modified graphene comprises the following steps:

[0020] S1: dispersing the graphite powder in a mixed solution of water and ethanol of polyvinyl alcohol, shearing and centrifuging to obtain a graphene supernatant, then performing ultracentrifugation, freeze-drying and crushing and sieving the precipitated graphene to obtain a graphene powder;

[0021] S2: ultrasonic dispersing the graphene powder in a mixed solution of water and ethanol to obtain a graphene dispersion; dissolving cerium salt in water to obtain a cerium salt solution; stirring and treating the cerium salt solution and the graphene dispersion to obtain a cerium salt modified graphene solution, then performing ultracentrifugation, freeze-drying, crushing and sieving to obtain a cerium salt modified graphene powder.

[0022] The mesh number of the graphite powder in step S1 is 325-3000.

[0023] The volume ratio of water to ethanol in the mixed solution in step S1 is (5-7):(5-3), preferably 6:4.

[0024] The mass ratio of the graphite to the polyvinyl alcohol is 10:(0.5-2). The concentration of the polyvinyl alcohol in the mixed solution is 0.5-1 mg / ml.

[0025] The viscosity of the polyvinyl alcohol is 60-75 mPa·s.

[0026] The rotation speed of the shearing is 10000-12000 rpm, and the shearing time is 30-70 min. Cooling is performed every 20-30 min of shearing, and then the shearing is continued. The shearing is performed in an ice water bath.

[0027] The rotation speed of the centrifugation is 400-600 rpm, and the centrifugation time is 40-60 min.

[0028] The ultracentrifugation condition is 9500-10500 rpm for 25-35 min.

[0029] The volume ratio of water to ethanol in the mixed solution in step S2 is (5-7):(5-3), preferably 6:4.

[0030] The concentration of the graphene dispersion is 0.5-1.5 mg / ml. The mass ratio of the graphene to the cerium salt is 1:(1-3).

[0031] The concentration of the cerium salt solution is 2-4 mg / ml.

[0032] The stirring and treating time is 1.5-4 h.

[0033] The ultracentrifugation condition is 9500-10500 rpm for 10-20 min.

[0034] The freeze-drying condition is freeze-drying at a temperature of -30 to -40 DEG C for 20 to 36 hours.

[0035] The cerium salt is one or more of cerium nitrate, cerium chloride and cerium sulfate.

[0036] The preparation method of the cerium salt modified graphene / epoxy powder coating comprises the following steps:

[0037] (1) uniformly mixing epoxy resin, curing agent, pigment and filler and additive, then adding cerium salt modified graphene powder, and uniformly mixing, followed by extrusion, tabletting, powdering and sieving to obtain cerium salt modified graphene / epoxy powder coating;

[0038] (2) electrostatically spraying the powder coating obtained in step (1) to the surface of a metal substrate, baking and curing, and cooling to obtain cerium salt modified graphene / epoxy powder coating.

[0039] In step (2), the process parameters of the electrostatic spraying are as follows: electrostatic voltage is 60 kV to 70 kV, the distance between the nozzle of the spraying gun and the metal substrate is 10 cm to 20 cm, the powder spraying angle is 70 DEG to 90 DEG, and the powder spraying pressure is 0.4 MPa to 0.7 MPa.

[0040] In step (2), the baking and curing is carried out at 180 DEG C to 220 DEG C for 5 min to 20 min.

[0041] The present application has the following advantages:

[0042] (1) The present application prepares graphene by shearing and exfoliating graphite in a clean and environmentally friendly polyvinyl alcohol and ethanol mixed solution system, wherein the polyvinyl alcohol is adsorbed on the surface of graphene through CH-π interaction to realize surface modification of graphene, and the steric hindrance between polymer chains prevents the agglomeration of graphene sheets, thereby improving the dispersibility of graphene powder;

[0043] (2) The present application further modifies the exfoliated graphene with environmentally friendly corrosion inhibitor cerium salt, wherein the cerium ions are adsorbed on the graphene sheets through hydrogen bond interaction between the hydroxyl groups on the polyvinyl alcohol molecular chains adsorbed on the graphene and the cation-π interaction between the π electrons on the graphene, realizing the loading of cerium ions on the graphene;

[0044] (3) The present application uniformly mixes cerium salt modified graphene powder with epoxy resin and curing agent to prepare cerium salt modified graphene / epoxy powder coating, and then prepares cerium salt modified graphene / epoxy powder coating on a metal substrate through electrostatic spraying and baking and curing, which is simple and fast in the preparation process, avoids the use of a large amount of solvent, and meets the development concept of saving and environmental protection;

[0045] (4) The graphene / epoxy powder coating provided by the present application has barrier protection and corrosion inhibition dual functions, as indicated by open circuit potential monitoring, electrochemical impedance spectrum testing and scratch salt spray testing, so that stronger and more durable corrosion protection performance can be achieved. BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 Atomic force microscope images of graphene obtained by liquid phase shear exfoliation in Examples 1-5;

[0047] Figure 2 Scanning electron microscope images of graphite powder and graphene powder obtained by liquid phase shear exfoliation in Examples 1-5;

[0048] Figure 3 Open circuit potential change diagrams of the coatings of Example 2 and the comparative example after immersion in 3.5% NaCl solution for 168h, 336h, 504h, 720h, 1008h and 1440h;

[0049] Figure 4 Bode diagrams of the coatings of Examples 1-5 and the comparative example after immersion in 3.5% NaCl solution for 168h;

[0050] Figure 5 Series bode diagrams of the coating of Example 2 after immersion in 3.5% NaCl solution for 168h, 336h, 504h, 720h, 1008h and 1440h;

[0051] Figure 6 Photos of the coatings of Example 2 and the comparative example after placement in a 5% NaCl solution salt spray chamber for 240h. DETAILED DESCRIPTION

[0052] The present application will be further described in conjunction with specific examples, but the embodiments of the present application are not limited thereto. The materials and instrument information involved in the embodiments of the present application are as follows:

[0053] Graphite powder (325 mesh), purchased from Shanghai Aldrin Biochemical Technology Co., Ltd.;

[0054] Polyvinyl alcohol (hydrolysis degree 98.0%-98.8%, viscosity 62.0-72.0 mPa·s, extra pure), purchased from China National Pharmaceutical Group Chemical Reagent Co., Ltd.;

[0055] Cerium nitrate hexahydrate (99.95%), purchased from Shanghai Aldrin Biochemical Technology Co., Ltd.;

[0056] Epoxy resin 804, provided by China Petroleum Chemical Co., Ltd.;

[0057] Phenolic curing agent 410M, provided from Huangshan Xingjia Fine Material Co., Ltd.;

[0058] Q235 standard steel (150 mm x 70 mm x 0.8 mm), purchased from Jiangsu Guoqiang Galvanized Industry Co., Ltd.;

[0059] High-speed shear dispersion emulsifier (FA40), purchased from Shanghai Fruitec Technology Development Co., Ltd.;

[0060] Tabletop high-speed centrifuge (H1850), purchased from Hunan Xiangyi Laboratory Instrument Development Co., Ltd.;

[0061] Vacuum freeze dryer (LGJ-12), purchased from Beijing Songyuan Huaxing Technology Development Co., Ltd.

[0062] Example 1

[0063] (1) First, polyvinyl alcohol was dissolved in a mixed solution of water and ethanol with a volume ratio of 6:4, and 325 mesh graphite powder was added. The concentration of polyvinyl alcohol in the obtained mixed system was 0.83 mg / ml, and the concentration of graphite powder was 8.33 mg / ml;

[0064] (2) The mixed system obtained in step (1) was high-speed sheared in an ice water bath at a speed of 11000 rpm for 30 min. After the system was cooled, it was sheared at a speed of 11000 rpm for another 30 min, and then centrifuged at a speed of 500 rpm (26 g) for 45 min. The supernatant of graphene was separated;

[0065] (3) The supernatant of graphene in step (2) was centrifuged at a speed of 10000 rpm (10744 g) for 30 min. The obtained graphene precipitate was freeze-dried, crushed and passed through a 200 mesh sieve to obtain graphene powder;

[0066] (4) 1 part by mass of the graphene powder obtained in step (3) was dispersed in a mixed solution of water and ethanol with a volume ratio of 6:4 at a concentration of 1 mg / ml, and ultrasonic was applied for 5 min to obtain a graphene dispersion liquid again. 1.5 parts by mass of cerium nitrate hexahydrate was dissolved in water at a concentration of 3 mg / ml to obtain a cerium nitrate solution, which was added to the graphene dispersion liquid (the mass ratio of graphene powder to cerium nitrate hexahydrate was 1:1.5). After stirring at room temperature for 2 h, a cerium salt modified graphene dispersion liquid was obtained;

[0067] (5) The cerium salt modified graphene dispersion liquid obtained in step (4) was centrifuged at a speed of 10000 rpm (10744 g) for 15 min. The obtained precipitate was freeze-dried at a temperature of -36℃ for 24 h, crushed and passed through a 200 mesh sieve to obtain cerium salt modified graphene powder;

[0068] (6) The cerium salt modified graphene powder obtained in step (5), epoxy resin, curing agent, and pigment and filler components are mixed in the following mass ratio:

[0069]

[0070] (7) The epoxy resin 804, phenolic curing agent 410M, titanium white, nano white carbon black, benzoin, and amino silicone oil in the above mass ratio are stirred and mixed uniformly, and then the cerium salt modified graphene powder is added and stirred uniformly, and then extruded, pressed into a sheet, ground, and sieved to obtain a cerium salt modified graphene / epoxy powder coating;

[0071] (8) The powder coating obtained in step (7) is electrostatically sprayed onto the surface of a carbon steel, and the process parameters for electrostatic spraying are as follows: electrostatic voltage 60 kV, distance between the spray gun nozzle and the metal substrate 15 cm, powder spraying angle 80°, powder spraying pressure 0.5 MPa, baking and curing at 180°C for 10 min, and natural cooling to obtain a cerium salt modified graphene / epoxy powder coating.

[0072] Example 2

[0073] (1) First, polyvinyl alcohol is dissolved in a mixed solution of water and ethanol in a volume ratio of 6:4, and 325 mesh graphite powder is added to obtain a mixed system with a polyvinyl alcohol concentration of 0.83 mg / ml and a graphite powder concentration of 8.33 mg / ml;

[0074] (2) The mixed system obtained in step (1) is high-speed sheared in an ice water bath at a speed of 11000 rpm for 30 min, and then sheared at a speed of 11000 rpm for another 30 min after cooling. Subsequently, centrifugation is performed at a speed of 500 rpm (26 g) for 45 min to separate the graphene supernatant;

[0075] (3) The graphene supernatant in step (2) is centrifuged at a speed of 10000 rpm (10744 g) for 30 min, and the obtained graphene precipitate is freeze-dried, crushed, and sieved through a 200 mesh sieve to obtain a graphene powder;

[0076] (4) 1 mass part of the graphene powder obtained in step (3) is dispersed in a mixed solution of water and ethanol in a volume ratio of 6:4 at a concentration of 1 mg / ml, and ultrasonic treatment is performed for 5 min to obtain a graphene dispersion. 1.5 mass parts of cerium nitrate hexahydrate is dissolved in water at a concentration of 3 mg / ml to obtain a cerium nitrate solution, which is added to the graphene dispersion and stirred at room temperature for 2 h to obtain a cerium salt modified graphene dispersion;

[0077] (5) Centrifuge the cerium salt modified graphene dispersion obtained in step (4) at a speed of 10000 rpm (10744 g) for 15 min, freeze-dry the obtained precipitate at a temperature of -36°C for 24 h, crush and sieve through a 200 mesh sieve to obtain cerium salt modified graphene powder;

[0078] (6) Mix the cerium salt modified graphene powder obtained in step (5), epoxy resin, curing agent, and pigment and filler, etc. according to the following mass ratio:

[0079]

[0080] (7) Mix the above mass of epoxy resin 804, phenolic curing agent 410M, titanium white, nano white carbon black, benzoin, and amino silicone oil uniformly by stirring, then add the cerium salt modified graphene powder, uniformly stir, then extrude, press into tablets, crush and sieve to obtain cerium salt modified graphene / epoxy powder coating;

[0081] (8) Electrostatically spray the powder coating obtained in step (7) onto the surface of carbon steel, and the process parameters of electrostatic spraying are as follows: electrostatic voltage is 60 kV, the distance between the spray gun nozzle and the metal substrate is 15 cm, the powder spraying angle is 80°, the powder spraying pressure is 0.5 MPa, then bake and cure at 180°C for 10 min, and naturally cool to obtain a cerium salt modified graphene / epoxy powder coating.

[0082] Example 3

[0083] (1) First, dissolve polyvinyl alcohol in a mixed solution of water and ethanol in a volume ratio of 6:4, and add 325 mesh graphite powder to obtain a mixed system with a polyvinyl alcohol concentration of 0.83 mg / ml and a graphite powder concentration of 8.33 mg / ml;

[0084] (2) High-speed shear the mixed system obtained in step (1) in an ice water bath at a speed of 11000 rpm for 30 min, then shear at a speed of 11000 rpm for another 30 min after the system cools, then centrifuge at a speed of 500 rpm (26 g) for 45 min to separate the graphene supernatant;

[0085] (3) Centrifuge the graphene supernatant in step (2) at a speed of 10000 rpm (10744 g) for 30 min, freeze-dry the obtained graphene precipitate, crush and sieve through a 200 mesh sieve to obtain graphene powder;

[0086] (4) Take 1 part by mass of the graphene powder obtained in step (3) and disperse it in a mixed solution of water and ethanol at a volume ratio of 6:4 at a concentration of 1 mg / ml, and ultrasonic for 5 min to obtain a graphene dispersion; take 1.5 parts by mass of cerium nitrate hexahydrate and dissolve it in water at a concentration of 3 mg / ml to obtain a cerium nitrate solution, and add it to the graphene dispersion, and stir at room temperature for 2 h to obtain a cerium salt modified graphene dispersion;

[0087] (5) Centrifuge the cerium salt modified graphene dispersion obtained in step (4) at a speed of 10,000 rpm (10,744 g) for 15 min, freeze-dry the obtained precipitate at a temperature of -36°C for 24 h, crush and pass through a 200 mesh sieve to obtain cerium salt modified graphene powder;

[0088] (6) The components of cerium salt modified graphene powder, epoxy resin, curing agent, and pigment and filler, etc. obtained in step (5) are mixed according to the following mass ratio:

[0089]

[0090] (7) The epoxy resin 804, phenolic curing agent 410M, titanium white, nano white carbon black, benzoin, and amino silicone oil of the above mass parts are stirred and mixed uniformly, then the cerium salt modified graphene powder is added, and after stirring uniformly, it is extruded, pressed into a sheet, ground and sieved to obtain a cerium salt modified graphene / epoxy powder coating;

[0091] (8) The powder coating obtained in step (7) is electrostatically sprayed onto the surface of a carbon steel, and the process parameters of the electrostatic spraying are: electrostatic voltage of 60 kV, distance between the spray gun mouth and the metal substrate of 15 cm, powder spraying angle of 80°, powder spraying pressure of 0.5 MPa, and baking and curing at 180°C for 10 min, and natural cooling to obtain a cerium salt modified graphene / epoxy powder coating.

[0092] Example 4

[0093] (1) First, polyvinyl alcohol is dissolved in a mixed solution of water and ethanol at a volume ratio of 6:4, and 325 mesh graphite powder is added to obtain a mixed system with a polyvinyl alcohol concentration of 0.83 mg / ml and a graphite powder concentration of 8.33 mg / ml;

[0094] (2) The mixed system obtained in step (1) is high-speed sheared at a speed of 11,000 rpm in an ice water bath for 30 min, and after the system is cooled, it is sheared at a speed of 11,000 rpm for another 30 min, and then centrifuged at a speed of 500 rpm (26 g) for 45 min to obtain a graphene supernatant;

[0095] (3) centrifuge the supernatant of graphene in step (2) at 10000 rpm (10744 g) for 30 min, freeze-dry the obtained graphene precipitate, crush and sieve through a 200-mesh sieve to obtain graphene powder;

[0096] (4) take 1 part by mass of the graphene powder obtained in step (3) and disperse in a mixed solution of water and ethanol at a volume ratio of 6:4 at a concentration of 1 mg / ml, ultrasonic for 5 min to obtain a graphene dispersion; take 1.5 parts by mass of cerium nitrate hexahydrate and dissolve in water at a concentration of 3 mg / ml to obtain a cerium nitrate solution, add to the graphene dispersion, stir at room temperature for 2 h to obtain a cerium salt modified graphene dispersion;

[0097] (5) centrifuge the cerium salt modified graphene dispersion obtained in step (4) at 10000 rpm (10744 g) for 15 min, freeze-dry the obtained precipitate at a temperature of -36℃ for 24 h, crush and sieve through a 200-mesh sieve to obtain cerium salt modified graphene powder;

[0098] (6) the components of cerium salt modified graphene powder, epoxy resin, curing agent, and pigment and filler in step (5) are mixed according to the following mass ratio:

[0099]

[0100] (7) the above mass of epoxy resin 804, phenolic curing agent 410M, titanium dioxide, nano white carbon black, benzoin and amino silicone oil are stirred and mixed uniformly, then the cerium salt modified graphene powder is added, stirred uniformly, then extruded, pressed into tablets, ground and sieved to obtain cerium salt modified graphene / epoxy powder coating;

[0101] (8) the powder coating obtained in step (7) is electrostatically sprayed on the surface of carbon steel, and the process parameters of electrostatic spraying are as follows: electrostatic voltage is 60 kV, the distance between the nozzle of the spray gun and the metal substrate is 15 cm, the powder spraying angle is 80°, the powder spraying pressure is 0.5 MPa, and then the coating is baked and cured at 180℃ for 10 min, and then naturally cooled to obtain a cerium salt modified graphene / epoxy powder coating.

[0102] Example 5

[0103] (1) first, polyvinyl alcohol is dissolved in a mixed solution of water and ethanol at a volume ratio of 6:4, and 325-mesh graphite powder is added, the concentration of polyvinyl alcohol in the obtained mixed system is 0.83 mg / ml, and the concentration of graphite powder is 8.33 mg / ml;

[0104] (2) The mixed system obtained in step (1) is sheared at a high speed of 11000 rpm in an ice water bath for 30 min, and after the system is cooled, it is sheared at a speed of 11000 rpm for another 30 min, and then centrifuged at a speed of 500 rpm (26 g) for 45 min, and the supernatant of graphene is separated;

[0105] (3) The supernatant of graphene in step (2) is centrifuged at a speed of 10000 rpm (10744 g) for 30 min, the obtained graphene precipitate is freeze-dried, crushed and passed through a 200 mesh sieve to obtain graphene powder;

[0106] (4) 1 part by mass of the graphene powder obtained in step (3) is dispersed in a mixed solution of water and ethanol at a volume ratio of 6:4 at a concentration of 1 mg / ml, and ultrasonic treatment is performed for 5 min to obtain a graphene dispersion liquid again; 1.5 parts by mass of cerium nitrate hexahydrate is dissolved in water at a concentration of 3 mg / ml to obtain a cerium nitrate solution, which is added to the graphene dispersion liquid, and stirred at room temperature for 2 h to obtain a cerium salt modified graphene dispersion liquid;

[0107] (5) The cerium salt modified graphene dispersion liquid obtained in step (4) is centrifuged at a speed of 10000 rpm (10744 g) for 15 min, and the obtained precipitate is freeze-dried at a temperature of -36℃ for 24 h, crushed and passed through a 200 mesh sieve to obtain cerium salt modified graphene powder;

[0108] (6) The cerium salt modified graphene powder, epoxy resin, curing agent, pigment and filler and other components obtained in step (5) are mixed according to the following mass ratio:

[0109]

[0110] (7) The epoxy resin 804, phenolic curing agent 410M, titanium white, nano white carbon black, benzoin and amino silicone oil of the above mass parts are mixed and stirred uniformly, and then the cerium salt modified graphene powder is added, stirred uniformly, and then extruded, pressed into a sheet, ground and sieved to obtain a cerium salt modified graphene / epoxy powder coating;

[0111] (8) The powder coating obtained in step (7) is electrostatically sprayed onto the surface of a carbon steel, and the process parameters of the electrostatic spraying are as follows: the electrostatic voltage is 60 kV, the distance between the spray gun nozzle and the metal substrate is 15 cm, the powder spraying angle is 80°, the powder spraying pressure is 0.5 MPa, and the powder coating is baked and cured at 180℃ for 10 min, and then naturally cooled to obtain a cerium salt modified graphene / epoxy powder coating.

[0112] Comparative Example

[0113] (1) The epoxy resin, curing agent, pigment and filler and other components are mixed according to the following mass ratio:

[0114]

[0115] (2) The epoxy resin 804, phenolic curing agent 410M, titanium white, nano white carbon black, benzoin and amino silicone oil in the above amounts were stirred and mixed uniformly, then extruded, pressed into tablets, ground and sieved to obtain an epoxy powder coating;

[0116] (3) The powder coating obtained in step (2) was electrostatically sprayed onto the surface of a carbon steel, and the process parameters of the electrostatic spraying were as follows: electrostatic voltage 60 kV, distance between the spraying gun and the metal substrate 15 cm, powder spraying angle 80°, powder spraying pressure 0.5 MPa, baking and curing at 180 ℃ for 10 min, and natural cooling to obtain an epoxy powder coating.

[0117] Performance test:

[0118] Figure 1 The images of the graphene obtained by liquid-phase shear exfoliation in step (2) of Examples 1-5 under an atomic force microscope. The left arrow measures the edge thickness of the graphene sheet to be about 1.68 nm, and the right arrow measures the edge thickness of the graphene sheet to be about 1.91 nm, indicating that the number of layers is 5-6.

[0119] Figure 2 The scanning electron microscope images of the graphite powder and the graphene powder prepared in step (3) of Examples 1-5. The graphite sheets aggregate to form large agglomerates, while the graphene sheets are in a loose accumulation state, indicating that the graphene powder has good dispersibility.

[0120] The samples of Example 2 and the comparative example were immersed in a 3.5% NaCl solution, and the open circuit potential and electrochemical impedance spectrum were tested at regular intervals. The change in open circuit potential is shown in Figure 3 When the immersion time reached 168 h, the open circuit potential of the pure epoxy powder coating sample of the comparative example had dropped to about -0.63 V, which is the corrosion potential of iron in a 3.5% NaCl solution, indicating that the steel substrate had been corroded. Thereafter, the open circuit potential of the sample of the comparative example fluctuated at -0.6 V, indicating the continuation of the corrosion process and the deepening of the corrosion degree. In comparison, the open circuit potential of the coating sample of Example 2 remained above -0.5 V, which may be due to the participation of cerium ions on the graphene in the cathodic reaction of steel corrosion, generating a cerium hydroxide protective film on the surface of the steel substrate, preventing further corrosion. The Bode plots obtained by electrochemical testing of Examples 1-5 and the comparative example after immersion in a 3.5% NaCl solution for 168 h are shown in Figure 4As shown in the figures, the impedance value of the coating sample of Example 2 at 0.01 Hz is always higher than that of the comparative example and other examples, which is due to the effective barrier effect of the appropriate amount of two-dimensional graphene sheets in the coating matrix, which significantly enhances the barrier performance of the coating. Further, a series of Bode plots of the coating sample of Example 2 immersed in 3.5% NaCl solution for different times are shown in Figure 5 As shown in the figures, as the immersion time is extended to 1440h, the impedance value of the coating has no significant decrease, and the logarithmic value remains at about 6.75-7, indicating that the cerium hydroxide protective film formed continues to play a barrier protection role on the steel substrate, forming long-term protection for the steel substrate.

[0121] Figure 6 The photos of the scratch of the coating samples of Example 2 and the comparative example after being placed in a 5% NaCl salt spray chamber for 240h show that the pure epoxy powder coating sample of the comparative example has a large accumulation of red rust corrosion products at the scratch, indicating that the substrate has suffered severe corrosion. In comparison, the corrosion of the coating sample of Example 2 is much less, which is due to the cerium hydroxide protective film generated at the scratch, which provides good protection for the steel substrate.

Claims

1. A cerium salt modified graphene / epoxy powder coating, characterized in that: It is mainly prepared from the following components in parts by weight: 100 parts epoxy resin 0.04-0.06 parts of cerium salt modified graphene 15-25 parts of curing agent 30-60 parts of pigments and fillers 2-10 parts of auxiliary agent; The preparation method of the cerium salt modified graphene includes the following steps: S1: Graphite powder is dispersed in a mixed solution of polyvinyl alcohol and water and ethanol, sheared and centrifuged to obtain graphene supernatant, then ultracentrifuged, freeze-dried and pulverized and sieved to obtain graphene powder. S2: Graphene powder is ultrasonically dispersed in a mixed solution of water and ethanol to obtain a graphene dispersion; cerium salt is dissolved in water to obtain a cerium salt solution; the cerium salt solution and the graphene dispersion are stirred to obtain a cerium salt modified graphene solution, which is then ultracentrifuged, freeze-dried, pulverized, and sieved to obtain cerium salt modified graphene powder. In step S1, the volume ratio of water to ethanol in the mixed solution is (5~7):(5~3); the mass ratio of graphite powder to polyvinyl alcohol is 10:(0.5~2); the concentration of polyvinyl alcohol in the mixed solution is 0.5~1 mg / ml; and the viscosity of polyvinyl alcohol is 60-75 mPa·s. In step S1, the shearing speed is 10000~12000 rpm, the shearing time is 30~70 min, and cooling is performed every 20~30 min before continuing the shearing; the shearing is carried out in an ice-water bath; the centrifugation speed is 400~600 rpm, the centrifugation time is 40~60 min; the ultracentrifugation conditions are 9500~10500 rpm for 25~35 min. In step S2, the mass ratio of graphene to cerium salt is 1:(1~3); the volume ratio of water to ethanol in the mixed solution in step S2 is (5~7):(5~3); the concentration of the graphene dispersion is 0.5-1.5 mg / ml; the concentration of the cerium salt solution is 2~4 mg / ml; the stirring time is 1.5~4 h; the ultracentrifugation conditions are 9500~10500 rpm for 10~20 min; the freeze-drying conditions are freeze-drying at -30~-40 ℃ for 20~36 h; the cerium salt is one or more of cerium nitrate, cerium chloride, and cerium sulfate. The graphite powder mentioned in step S1 has a mesh size of 325-3000 mesh; The preparation method of the cerium salt modified graphene / epoxy powder coating includes the following steps: (1) Mix epoxy resin, curing agent, pigments and fillers and additives evenly, then add cerium salt modified graphene powder, mix evenly and then extrude, press, grind and sieve to obtain cerium salt modified graphene / epoxy powder coating. (2) The powder coating obtained in step (1) is electrostatically sprayed onto the surface of the metal substrate, baked and cured, and cooled to obtain the cerium salt modified graphene / epoxy powder coating.

2. The cerium salt modified graphene / epoxy powder coating according to claim 1, characterized in that: The epoxy resin is at least one of bisphenol A type epoxy resin, bisphenol F type epoxy resin, and phenolic epoxy resin; The curing agent is at least one of dicyandiamide curing agent, phenolic curing agent, and acid anhydride curing agent; The pigments and fillers are selected from at least one of titanium dioxide, barium sulfate powder, wollastonite powder, and mica powder; The additives include one or more of the following: brighteners, leveling agents, degassing agents, antioxidants, ultraviolet light absorbers, light stabilizers, and adhesion promoters.

3. The cerium salt modified graphene / epoxy powder coating according to claim 1, characterized in that: In step (2), the electrostatic spraying process parameters are: electrostatic voltage of 60kV to 70kV, distance between the spray gun nozzle and the metal substrate of 10cm to 20cm, powder spraying angle of 70° to 90°, and powder spraying pressure of 0.4MPa to 0.7MPa.

4. The cerium salt modified graphene / epoxy powder coating according to claim 1, characterized in that: In step (2), the baking and curing is carried out at 180 ℃~220 ℃ and the curing time is 5 min~20 min.

5. The application of the cerium salt modified graphene / epoxy powder coating according to any one of claims 1 to 4, characterized in that: The cerium salt modified graphene / epoxy powder coating is used for metal corrosion protection.

Images