Kaolin-graphene composite aqueous slurry and preparation method thereof

Abstract

The invention discloses kaolin-graphene composite aqueous slurry and a preparation method thereof. The preparation method comprises the following steps: S1, proportioning and mixing: mixing kaolin and amorphous carbon powder to obtain a solid mixture; s2, conductive networking and forming: adding a conductive auxiliary agent into the solid mixture obtained in the step S1, uniformly mixing, and then tabletting or granulating the mixture to obtain a to-be-treated blank; s3, ultrafast carbon heat treatment: carrying out ultrafast carbon heat treatment on two ends of the to-be-treated blank obtained in the step S2 in a negative pressure environment to obtain a composite filler; and S4, wet dispersion pulping: adding the composite filler obtained in the step S3 into a water-phase dispersion medium, and carrying out high-speed shearing dispersion, so as to obtain the kaolin-graphene composite water-based slurry. The waterborne epoxy anticorrosive coating has the advantages that stable dispersion and constructability can be realized in a waterborne system, and a multi-scale layered shielding network is constructed in a coating film, so that the barrier property and durability of the waterborne epoxy anticorrosive coating are improved.

Description

Technical Field

[0001] This invention relates to the field of functional coating materials technology, and in particular to a kaolin-graphene composite aqueous slurry and its preparation method. Background Technology

[0002] Metal components are susceptible to corrosion in marine, salt spray, humid, and industrial environments. Using coatings to isolate and protect metal surfaces is a common corrosion prevention method. With increasingly stringent requirements for volatile organic compound (VOC) emission control, waterborne epoxy and other waterborne anti-corrosion coatings have been widely adopted. However, waterborne coating systems generally suffer from problems such as residual moisture during film formation, high porosity, or high water absorption. Media such as water, oxygen, and chloride ions can easily diffuse along the micropores of the coating and reach the metal interface, reducing the shielding effect and affecting the coating's salt spray and immersion resistance.

[0003] To improve the barrier properties of coatings, existing technologies typically employ sheet-like inorganic fillers to create a "maze effect," extending the diffusion path of the medium within the coating. On the other hand, graphene and its derivatives, with their high aspect ratio and barrier properties, have attracted attention as shielding fillers in anti-corrosion coatings. However, in aqueous systems, graphene materials are prone to aggregation and sedimentation, making it difficult to form a stable dispersion. Furthermore, their interfacial compatibility with aqueous resins is insufficient, easily forming micro-defect channels at the filler-resin interface, leading to unstable barrier performance improvements. In addition, some graphene preparation or modification methods involve oxidation, reduction, or multi-step separation and purification processes, easily introducing soluble salts, metallic impurities, or residual small molecules. Aqueous systems are more sensitive to these impurities, and coatings are prone to pinholes, blistering, and decreased adhesion, thus affecting the consistency and durability of anti-corrosion performance.

[0004] Kaolin, a widely available and low-cost aluminosilicate mineral, possesses a certain layered structure and can be used as a filler in coating systems. After heat treatment to convert kaolin into metakaolin, its surface activity and interfacial interaction with resin may be enhanced, which is beneficial for improving the density of the coating film. Therefore, combining kaolin / metakaolin with graphene-based carbon materials at the micro-nano scale and achieving stable dispersion in the form of an aqueous slurry that is both storable and applicable is expected to simultaneously improve the barrier properties and application adaptability of waterborne anti-corrosion coatings.

[0005] However, current technologies still lack a simplified and scalable preparation method for a kaolin-graphene composite aqueous slurry that can simultaneously ensure the dispersion stability of the aqueous system, reduce the content of soluble salts and impurities, inhibit the aggregation of nanomaterials, and balance the density and workability of the coating film. Therefore, there is an urgent need to provide a new kaolin-graphene composite aqueous slurry and its preparation method to solve problems such as the difficulty in dispersing nano-shielding fillers, unstable barrier enhancement, and early failure due to coating defects in aqueous anti-corrosion coatings. Summary of the Invention

[0006] To address the problems in existing waterborne anti-corrosion coating systems, such as insufficient shielding capacity, rapid medium penetration rate, poor dispersion stability due to the easy aggregation and sedimentation of nano-shielding fillers in waterborne systems, and pinholes, blistering, and fluctuations in corrosion resistance caused by impurities / soluble salts / hard agglomerates, the present invention aims to provide a kaolin-graphene composite waterborne slurry and its preparation method. This slurry can achieve stable dispersion and workability in waterborne systems and construct a multi-scale layered shielding network in the coating film, thereby improving the barrier performance and durability of waterborne epoxy anti-corrosion coatings.

[0007] The above-mentioned technical objective of the present invention is achieved through the following technical solution:

[0008] A method for preparing a kaolin-graphene composite aqueous slurry includes the following steps: S1, Ingredients and Mixing: Kaolin and amorphous carbon powder are mixed to obtain a solid mixture; S2, Conductive network construction and molding: Add conductive additives to the solid mixture obtained in step S1 and mix evenly. Then, press the mixture into tablets or granules to obtain the blank to be processed. S3, Ultrafast carbon heat treatment: The two ends of the blank obtained in step S2 are subjected to ultrafast carbon heat treatment under negative pressure to obtain composite filler. S4, Wet dispersion slurry preparation: The composite filler obtained in step S3 is added to the aqueous dispersion medium for high-speed shear dispersion to obtain kaolin-graphene composite aqueous slurry.

[0009] Preferably, in step S1, the kaolinite content in the kaolin is ≥85%, and the kaolin is dried before mixing at a temperature of 80~150℃ for 1~24h, with a particle size of less than 75μm.

[0010] Preferably, in step S1, the amorphous carbon powder is selected from one or more of carbon black, pyrolytic carbon, coal-based amorphous carbon, phenolic resin carbonized carbon, petroleum coke powder, pitch coke powder, and biomass carbon powder, and the particle size of the amorphous carbon powder is less than 10 μm.

[0011] Preferably, the mass ratio of kaolin to amorphous carbon powder in step S1 is 60:40 to 90:10.

[0012] Preferably, in step S2, the amount of conductive additive added is 0.5~5wt% of the total mass of the solid mixture, and the conductive additive is selected from one or more of conductive carbon black, carbon nanotubes, graphite powder, and chopped carbon fibers, and the particle size of the conductive additive is less than 20μm.

[0013] Preferably, the forming pressure of tableting or granulation in step S2 is 5~20MPa, wherein the tablet thickness is 1~20mm and the granulation particle size is 0.5~10mm.

[0014] Preferably, the specific parameters of the ultrafast carbon heat treatment in step S3 are as follows: the negative pressure environment is a vacuum degree greater than 0.07MPa, voltage is applied to both ends of the blank to be treated, and current is passed through it to generate Joule heat, the peak temperature is 2000~4000℃, the holding time is 0.01~1s, and the heat is applied in a pulse manner 2~5 times.

[0015] Preferably, the aqueous dispersion medium in step S4 includes deionized water and additives. The additives are selected from one or more of wetting and dispersing agents, defoamers, thickeners or anti-settling thixotropic agents, leveling agents, pH adjusters, and preservatives and mildew inhibitors. The solid content of the kaolin-graphene composite aqueous slurry is 10~70wt%.

[0016] Preferably, in step S4, the shear line velocity of the high-speed shear dispersion is 5~30m / s, and the dispersion time is 5~60min.

[0017] A kaolin-graphene composite aqueous slurry is prepared using a method for preparing kaolin-graphene composite aqueous slurries.

[0018] In summary, the present invention has the following beneficial effects: 1. Constructing a multi-scale shielding structure to improve barrier performance: The metakaolinite phase provides a micron-scale rigid framework structure, while the graphene-like carbon material provides a nano-scale sheet-like sealing structure. The two form a multi-scale layered shielding network in the coating, which significantly prolongs the diffusion path of water, oxygen, and chloride ions in the coating, thereby improving the barrier performance of the water-based anti-corrosion coating.

[0019] 2. Improve the dispersion stability of nanofillers: In-situ composite is achieved during ultrafast carbothermal processes, allowing carbon sheets to disperse and adhere to the surface of the silicon-aluminum phase, reducing the agglomeration tendency of carbon materials in aqueous systems. Combined with wet shear dispersion and auxiliary agent systems, a stable slurry is formed, reducing sedimentation and agglomeration.

[0020] 3. Improve coating density and interfacial stability: The metakaolin activated phase enhances the interfacial interaction with the resin matrix, and the graphene-like carbon material improves the continuity and density of the coating, thereby reducing the probability of interfacial defects and the formation of permeation channels, and improving the stability of the coating's salt spray resistance and immersion resistance.

[0021] 4. Simplified process, suitable for large-scale production: This invention uses an in-situ ultrafast carbothermal conversion method to prepare composite fillers, with a wide range of raw material sources and a simple process; the obtained fillers are directly converted into water-based slurry products, which are convenient for industrial storage, transportation and metering addition, and have good engineering application prospects. Detailed Implementation

[0022] The specific embodiments of the present invention will be further described below. These embodiments do not constitute a limitation on the present invention.

[0023] A method for preparing a kaolin-graphene composite aqueous slurry includes the following steps: S1, Ingredients and Mixing: Kaolin and amorphous carbon powder are mixed in a mass ratio of 60:40 to 90:10 to obtain a solid mixture.

[0024] The kaolin contains ≥85% kaolinite and is dried before mixing at a temperature of 80~150℃ for 1~24h, with a particle size of less than 75μm. The amorphous carbon powder is selected from one or more of carbon black, pyrolytic carbon, coal-based amorphous carbon, phenolic resin carbonized carbon, petroleum coke powder, pitch coke powder, and biomass carbon powder, with a particle size of less than 10μm.

[0025] By controlling the ratio and particle size of the two phases, the silicon-aluminum phase and the carbon phase can form a sufficient contact interface during subsequent processing.

[0026] S2, Conductive mesh building and molding: Add conductive additives to the solid mixture obtained in step S1 and mix evenly. The amount of conductive additives added is 0.5~5wt% of the total mass of the solid mixture. The conductive additives are selected from one or more of conductive carbon black, carbon nanotubes, graphite powder, and chopped carbon fibers. The particle size of the conductive additives is less than 20μm.

[0027] The mixture is then compressed or granulated to obtain the blank to be processed. The forming pressure of the compression or granulation is 5~20MPa, the thickness of the compressed tablet is 1~20mm, and the particle size of the granulation is 0.5~10mm.

[0028] This step is used to establish a continuous conductive network, which allows the subsequent ultrafast carbothermal treatment to proceed uniformly.

[0029] S3, Ultrafast Carbothermal Treatment: The two ends of the blank obtained in step S2 are subjected to ultrafast carbothermal treatment under a negative pressure environment with a vacuum degree greater than 0.07MPa. Voltage is applied to both ends of the blank to generate Joule heat by allowing current to pass through it. The peak temperature is 2000~4000℃, and the holding time is 0.01~1s. The treatment is applied in a pulse manner 2~5 times to obtain the composite filler.

[0030] Under this ultrafast carbothermic effect: Kaolin undergoes dehydroxylation and structural rearrangement to form a metakaolinite phase; Amorphous carbon undergoes a sheet-like / graphitization transformation to form graphene-like carbon materials; The two form a micro-nano composite structure in close contact under transient high temperature conditions.

[0031] This step enables the simultaneous activation of the silicon-aluminum phase and the layering of the carbon phase, resulting in a composite filler formed by the intercalation of metakaolinite phase and graphene-like carbon material.

[0032] S4, Wet dispersion pulping: The composite filler obtained in step S3 is added to an aqueous dispersion medium for high-speed shear dispersion. The aqueous dispersion medium includes deionized water and additives. The additives are selected from one or more of wetting and dispersing agents, defoamers, thickeners or anti-settling thixotropic agents, leveling agents, pH adjusters, and preservatives and mildew inhibitors. The solid content of the kaolin-graphene composite aqueous slurry is 10~70wt%, the shear line velocity of the high-speed shear dispersion is 5~30m / s, and the dispersion time is 5~60min, thus obtaining the kaolin-graphene composite aqueous slurry.

[0033] By combining the above-mentioned additive system with high-speed shear dispersion, the composite filler forms a stable dispersion system in the aqueous dispersion medium, thereby improving storage stability and construction adaptability.

[0034] Example 1 S1. Ingredients and Mixing Kaolin: Kaolinite content ≥85%, D90=45μm; Amorphous toner: carbon black, D90=5μm; Conductive additive: Conductive carbon black, D90=10μm; Weigh the raw materials according to a mass ratio of 80:20 (kaolin: amorphous carbon).

[0035] Kaolin was first dried at 100℃ for 12 hours. The dried kaolin was then mixed with amorphous carbon in a high-speed mixer for 15 minutes to obtain a uniform solid mixture.

[0036] S2. Conductive mesh formation and molding Add 2 wt% conductive carbon black to the mixture and continue mixing for 10 min; The mixture is then compressed into tablets. Molding pressure: 10MPa; Tablet thickness: 10mm; A uniform and dense billet is obtained.

[0037] S3. Ultrafast carbon heat treatment The billet is placed in a sealed reaction chamber and evacuated to a vacuum level of 0.085 MPa; A voltage is applied across the material, causing current to flow through it and generating Joule heat. Ultrafast carbothermal treatment is then performed: peak temperature: 2800℃, single holding time: 0.1s, number of pulses: 3, followed by natural cooling to obtain a black composite filler.

[0038] S4. Wet Dispersion Pulping The aqueous dispersion system consists of: 0.8 wt% polycarboxylate dispersant, 0.2 wt% silicone defoamer, 0.5 wt% polyurethane associative thickener, pH adjusted to 8.5 with ammonia, 0.1 wt% isothiazolinone preservative, and the remainder is deionized water. The black composite filler is added to the above aqueous dispersion system to make the slurry solid content 40 wt%.

[0039] High-speed shear dispersion was employed: linear velocity: 20 m / s, dispersion time: 30 min, to obtain a uniform and stable kaolin-graphene composite aqueous slurry.

[0040] The slurry showed no obvious sedimentation or stratification after standing for 7 days.

[0041] Example 2 The difference from Example 1 is as follows: In step S1, the mass ratio of kaolin to amorphous carbon is 70:30.

[0042] In step S2: the amount of conductive additive added is 3wt%, and the molding pressure is 15MPa.

[0043] In step S3: peak temperature: 3200℃, single heat preservation time: 0.05s, number of pulses: 4, vacuum degree: 0.09MPa.

[0044] In step S4: slurry solid content: 60wt%, shear line speed: 25m / s, dispersion time: 20min.

[0045] The resulting slurry is uniformly blackish-gray and exhibits good storage stability.

[0046] Example 3 The difference from Example 1 is as follows: In step S1, the mass ratio of kaolin to amorphous carbon is 90:10.

[0047] In step S2: the amount of conductive additive added is 1wt%, the molding method is granulation, and the granulation particle size is 5mm.

[0048] In step S3: peak temperature: 2400℃, holding time: 0.2s, number of pulses: 2, vacuum degree: 0.075MPa.

[0049] In step S4: slurry solid content: 30wt%, shear line speed: 10m / s, dispersion time: 45min.

[0050] The resulting slurry has good workability.

[0051] Comparative Example 1 Steps S1 and S2 are the same as in Example 1.

[0052] The ultrafast carbon heat treatment in step S3 was not performed; the mixed powder was directly added to the aqueous dispersion system for dispersion.

[0053] result: The material showed obvious agglomeration during the dispersion process, and sedimentation occurred within 7 days.

[0054] Note: Without ultrafast carbon heat treatment, a micro-nano composite structure was not formed, and the shielding structure is incomplete.

[0055] Comparative Example 2 The difference from Example 1 is that no conductive additive is added, but the rest of the steps are the same.

[0056] result: The uneven temperature distribution during ultrafast carbon heat treatment results in inconsistent filler color and poor subsequent dispersion stability.

[0057] Note: Conductive mesh construction helps address uniformity and the formation of composite structures.

[0058] The slurries obtained in Examples 1-3 and Comparative Examples 1-2 were added to an aqueous epoxy system at a filler content of 5 wt% of the resin solids to prepare coatings. Q235 steel plates were sandblasted, and the dry film thickness was 100 ± 5 μm. The coatings were then cured at 25°C for 7 days. The comparison of the coatings' salt spray corrosion resistance and shielding performance is shown in Tables 1 and 2, respectively.

[0059] Table 1 Salt spray test (GB / T 1771-2007, 5% NaCl, 500h)

[0060] Table 2 Electrochemical impedance spectroscopy (0.01 Hz low-frequency impedance, Ω·cm) 2 )

[0061] The results show that the coating of the present invention exhibits significantly improved salt spray corrosion resistance and shielding performance compared to the comparative example. The metakaolinite phase in this invention provides a micron-scale rigid framework structure, while the graphene-like carbon material provides a nanoscale sheet-like sealing structure. Together, they form a multi-scale layered shielding network in the coating, significantly extending the diffusion paths of water, oxygen, and chloride ions, thereby improving the barrier performance of the water-based anti-corrosion coating. Simultaneously, the activated metakaolinite phase enhances the interfacial interaction with the resin matrix, and the graphene-like carbon material improves the continuity and density of the coating, thereby reducing the probability of interfacial defects and permeation channels, and improving the stability of the coating's salt spray and immersion resistance.

[0062] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art can make various modifications or equivalent substitutions to the present invention within the scope of its essence and protection. Such modifications or equivalent substitutions should also be considered to fall within the protection scope of the present invention.

Claims

1. A method for preparing a kaolin-graphene composite aqueous slurry, characterized in that, Includes the following steps: S1, Ingredients and Mixing: Kaolin and amorphous carbon powder are mixed to obtain a solid mixture; S2, Conductive network construction and molding: Add conductive additives to the solid mixture obtained in step S1 and mix evenly. Then, press the mixture into tablets or granules to obtain the blank to be processed. S3, Ultrafast carbon heat treatment: The two ends of the blank obtained in step S2 are subjected to ultrafast carbon heat treatment under negative pressure to obtain composite filler. S4, Wet dispersion slurry preparation: The composite filler obtained in step S3 is added to the aqueous dispersion medium for high-speed shear dispersion to obtain kaolin-graphene composite aqueous slurry.

2. The method for preparing a kaolin-graphene composite aqueous slurry according to claim 1, characterized in that: In step S1, the kaolinite content in the kaolin is ≥85%, and the kaolin is dried before mixing at a temperature of 80~150℃ for 1~24h, with a particle size of less than 75μm.

3. The method for preparing a kaolin-graphene composite aqueous slurry according to claim 1, characterized in that: In step S1, the amorphous carbon powder is selected from one or more of carbon black, pyrolytic carbon, coal-based amorphous carbon, phenolic resin carbonized carbon, petroleum coke powder, pitch coke powder, and biomass carbon powder, and the particle size of the amorphous carbon powder is less than 10 μm.

4. The method for preparing a kaolin-graphene composite aqueous slurry according to claim 1, characterized in that: In step S1, the mixing mass ratio of kaolin and amorphous carbon powder is 60:40 to 90:

10.

5. The method for preparing a kaolin-graphene composite aqueous slurry according to claim 1, characterized in that: In step S2, the amount of conductive additive added is 0.5~5wt% of the total mass of the solid mixture. The conductive additive is selected from one or more of conductive carbon black, carbon nanotubes, graphite powder, and chopped carbon fibers. The particle size of the conductive additive is less than 20μm.

6. The method for preparing a kaolin-graphene composite aqueous slurry according to claim 1, characterized in that: In step S2, the forming pressure for tableting or granulation is 5~20MPa, wherein the tablet thickness is 1~20mm and the granulation particle size is 0.5~10mm.

7. The method for preparing a kaolin-graphene composite aqueous slurry according to claim 1, characterized in that: The specific parameters for the ultrafast carbon heat treatment in step S3 are as follows: the negative pressure environment is a vacuum degree greater than 0.07MPa, voltage is applied to both ends of the blank to be treated, and current is passed through it to generate Joule heat, with a peak temperature of 2000~4000℃, a holding time of 0.01~1s, and applied in a pulse manner 2~5 times.

8. The method for preparing a kaolin-graphene composite aqueous slurry according to claim 1, characterized in that: In step S4, the aqueous dispersion medium includes deionized water and additives. The additives are selected from one or more of wetting and dispersing agents, defoamers, thickeners or anti-settling thixotropic agents, leveling agents, pH adjusters, and preservatives and mildew inhibitors. The solid content of the kaolin-graphene composite aqueous slurry is 10~70wt%.

9. The method for preparing a kaolin-graphene composite aqueous slurry according to claim 1, characterized in that: In step S4, the shear line velocity of the high-speed shear dispersion is 5~30m / s, and the dispersion time is 5~60min.

10. A kaolin-graphene composite aqueous slurry, characterized in that: It was prepared using the preparation method of any one of claims 1 to 9 for the kaolin-graphene composite aqueous slurry.

Images