Composite gelled curing agent for fluid stabilized soil and preparation method of composite gelled curing agent

Abstract

The invention belongs to the technical field of soil solidification, and particularly relates to a composite gelling curing agent for fluid solidified soil and a preparation method thereof, the curing agent comprises the following raw materials by weight: 35-50 parts of a composite gelling base material, 4-8 parts of an active activator, 18-25 parts of a mineral admixture, 2-4 parts of a function regulator, 3-6 parts of a nano modifier and 55-70 parts of deionized water; the preparation can be completed through pretreatment modification, staged feeding and stirring at a controllable rotating speed, the process is simple, and the cost is controllable; the preparation process adapts to an existing production line, and large-scale production can be achieved conveniently; the obtained curing agent has the properties of early strength of cured soil, water resistance, broad-spectrum adaptation and the like through multi-component collaborative design.

Description

Technical Field

[0001] This invention relates to the field of fluidized solidified soil materials technology, specifically to a composite cementitious curing agent for fluidized solidified soil and its preparation method, which is applicable to engineering scenarios such as road backfilling, foundation pit support, and underground pipeline laying, and can be adapted to various soil types such as high moisture content clay and sandy soil. Background Technology

[0002] Fluidized solidified soil, with its advantages of good self-leveling properties, high self-compacting degree, and wide availability of raw materials, has become one of the core materials in the field of engineering backfilling and is widely used in municipal engineering, transportation infrastructure and other scenarios. It can not only reduce the dependence on natural sand and gravel of traditional backfill materials, but also reduce the cost of manual vibration during construction and improve construction efficiency.

[0003] However, existing fluidized solidified soil still has the following drawbacks in practical applications: (1) Insufficient early strength: The compressive strength of fluidized solidified soil prepared by conventional curing agents is often less than 1 MPa after 3 days of curing, which cannot meet the needs of rapid construction (such as the need to open the road to traffic in a short period of time after backfilling), and is likely to cause delays in the construction period; (2) Poor water resistance: When the groundwater level is high or the environment is humid, the strength of the solidified soil decreases significantly after about a week of soaking after curing. Long-term use may lead to cracking, leakage and other problems. (3) Poor adaptability to soil: It is easy to cause segregation in clay with high water content, and it is easy to cause insufficient fluidity and low density in sandy soil. The formula needs to be adjusted according to different soil types, and its versatility is poor.

[0004] In addition, some curing agents rely on high cement content to improve strength, which not only increases costs but also leads to increased shrinkage and deformation of the cured soil in the later stage due to excessive heat of cement hydration, further limiting their engineering applications. Summary of the Invention

[0005] To address the technical problems of low early strength, poor water resistance, and weak soil adaptability in existing fluidized solidified soils, a composite cementitious curing agent for fluidized solidified soils and its preparation method are provided. This curing agent achieves the performance goals of early strength, water resistance, and broad-spectrum adaptability of solidified soils through multi-component synergistic design.

[0006] The technical solution adopted in this invention is: The objective of this invention is to provide a composite cementitious curing agent for fluidized solidified soil, comprising the following raw materials by weight: 35-50 parts of composite cementitious substrate, 4-8 parts of active activator, 18-25 parts of mineral admixture, 2-4 parts of functional regulator, 3-6 parts of nano-modifier, and 55-70 parts of deionized water.

[0007] Further, by weight, the following raw materials are included: 42 parts of composite cementitious substrate, 6 parts of active activator, 22 parts of mineral admixture, 3 parts of functional regulator, 4 parts of nano-modifier, and 62 parts of deionized water.

[0008] Further, the composite cementitious substrate is composed of sulfoaluminate cement and silicate cement in a weight ratio of (1.4~1.6):1; the active activator is composed of sodium sulfate and lithium carbonate in a weight ratio of (1~1.4):1; the mineral admixture is composed of steel slag powder and metakaolin in a weight ratio of (1.2~1.5):1; the functional regulator is composed of sodium carboxymethyl cellulose and hydroxypropyl methyl cellulose in a weight ratio of (0.4~0.8):1; and the nano-modifier is composed of nano-silica and modified glass microspheres in a weight ratio of (0.5~0.7):1.

[0009] Furthermore, the modified glass microspheres are prepared by modification with silane coupling agent KH-570.

[0010] Furthermore, the nano-silica has a particle size of 10-20 nm and a specific surface area ≥200 m². 2 / g.

[0011] Furthermore, the specific surface area of ​​the steel slag powder is 400~450m². 2 / kg.

[0012] The second objective of this invention is to provide a method for preparing a composite cementitious curing agent for fluidized solidified soil, comprising the following steps: S1. Dissolve silane coupling agent KH-570 in ethanol, add glass microspheres and disperse ultrasonically, then vacuum dry to remove solvent to obtain modified glass microspheres; wherein the weight ratio of silane coupling agent KH-570, glass microspheres and ethanol is 2.5:10:10. S2. Divide the deionized water into three equal parts. Mix the first part of water with the composite cementitious substrate and mineral admixtures to obtain the first mixture. S3. The second portion of water is mixed with the functional regulator to obtain a functional regulator solution; S4. The third part of water is mixed with nano-silica and active activator to prepare nano-active activating liquid; S5. Modified glass microspheres are added to nano-active activating liquid, then the first mixture and functional regulator solution are added, and the mixture is stirred evenly to prepare curing agent.

[0013] Furthermore, in step S1, the ultrasonic dispersion power is 300W, the time is 30 minutes, the vacuum drying temperature is 60℃, and the time is 2 hours.

[0014] Furthermore, during the mixing process in step S4, the mixture is first ultrasonically dispersed at 300W power for 20-30 minutes, and then stirred at 250r / min speed for 10-15 minutes.

[0015] Compared with existing technologies, the composite cementitious curing agent for fluidized solidified soil and its preparation method provided by the present invention have the following advantages: (1) The present invention adopts a composite cementitious substrate system composed of hard sulfoaluminate cement and silicate cement. The hard sulfoaluminate cement is fast-hardening sulfoaluminate cement, which sets quickly at the beginning and at the end, and can form an early strength skeleton in a short time to meet the rapid construction needs of road backfilling, foundation pit support and other scenarios. The silicate cement is slag silicate cement, which is rich in active glass. After hydration, it can generate more hydrated calcium silicate gel, which not only helps to improve the later strength, but also blocks the water penetration path through the dense gel structure, thus solving the problem of poor water resistance and easy long-term strength decay of single fast-hardening sulfoaluminate cement. (2) The present invention uses an active activator and a nano-modifier to construct a synergistic system, realizing a dual mechanism of efficient activation of hydration and interface enhancement of shrinkage resistance; among them, sodium sulfate can quickly activate the hydration reaction of tricalcium silicate and tricalcium aluminate in cement matrix and accelerate the generation of hydration products; lithium carbonate can regulate the liquid phase environment of cement hydration and inhibit the dissolution and decomposition of ettringite crystals; nano silica particles are small in size and can fill the gaps between cementitious materials, forming a dense interface transition zone with hydration products and enhancing the internal bonding force of the matrix; while modified glass microspheres are tightly bonded to the cement matrix through the covalent bonds of the coupling agent, which can replace part of the cement to reduce the heat of hydration, and can also reduce the volume shrinkage of solidified soil by means of the rolling effect of microspheres, avoiding the leakage problem caused by shrinkage cracking of traditional curing agents.

[0016] (3) The present invention uses mineral admixtures and functional regulators to form a matching system. Among them, steel slag powder, as an industrial solid waste, has a suitable specific surface area and activity. It can fill the gaps in cementitious materials to improve density and replace a certain proportion of cement. Metakaolin can provide active silica-alumina components, which react with cement hydration products to generate additional hydrated calcium silicate gel, further enhancing the overall strength. Sodium carboxymethyl cellulose can inhibit the water separation of high-moisture clay, keeping the segregation rate within a low range. Hydroxypropyl methyl cellulose can improve the fluidity of mortar and solve the problem of low density caused by insufficient fluidity of sandy soil. The two are compounded in a reasonable ratio, so that the curing agent can be adapted to various soil types such as clay, sandy soil, and silty soil. There is no need to frequently adjust the formula, which greatly improves the applicability of the project.

[0017] (4) The preparation process of the present invention only requires pretreatment modification, staged feeding and controlled speed stirring to complete the preparation. The process is simple and the cost is controllable. Among them, the fly ash microspheres are dispersed by ultrasonication with appropriate power and the dispersion time is controlled to break the agglomerates and ensure that the nano-modifier is uniformly dispersed in the matrix. The functional regulator is dissolved in warm water and the stirring time is controlled to avoid cellulose clumping and give full play to the water retention and thickening effects. Existing building material production lines can be scaled up with slight adjustments, which is convenient for widespread application. Detailed Implementation

[0018] The present invention will be further described below through specific embodiments, but this is not a limitation of the present invention. Those skilled in the art can make various modifications or improvements based on the basic idea of ​​the present invention, but as long as they do not depart from the basic idea of ​​the present invention, they are all within the protection scope of the present invention.

[0019] Unless otherwise specified, the methods used in the following examples and comparative examples are all prior art; reagents not specifically mentioned are conventional reagents, all of which can be purchased from conventional reagent manufacturers and distributors. Information such as the manufacturers or CAS numbers of some raw materials is as follows: Rapid-hardening sulfoaluminate cement, rapid-hardening grade 42.5, purchased from Dengdian Group Cement Co., Ltd. Slag silicate cement was purchased from Shandong Huayin Special Cement Co., Ltd. Sodium sulfate, product number S433911, was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Lithium carbonate, product number L101679, was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Steel slag powder, with a specific surface area of ​​400~450m² 2 / kg, purchased from Hebei Zhongnai New Material Technology Co., Ltd.; Metakaolin, 325 mesh, purchased from Malin Mineral Products Processing Plant in Lingshou County; Sodium carboxymethyl cellulose was purchased from Jinan Honghaoyuan Chemical Technology Co., Ltd. Hydroxypropyl methylcellulose was purchased from Shandong Xuchen Chemical Technology Co., Ltd. Nano silica, CAS: 7631-86-9, particle size 10~20nm, specific surface area ≥200m² 2 / g, purchased from Zhejiang Yamei Nanotechnology Co., Ltd.; Silane coupling agent KH-570, CAS: 2530-85-0, purchased from Shandong Nabaichuan Chemical Sales Co., Ltd. Glass microspheres, CAS: 65997-17-3, purchased from Shijiazhuang Chaowei New Materials Technology Co., Ltd. Ethanol, 99% purity, was purchased from Shandong Hongrun Chemical Co., Ltd.

[0020] Example 1 A composite cementitious curing agent for fluidized solidified soil, comprising the following raw materials by weight (100g / part): 35 parts of composite cementitious substrate, 4 parts of active activator, 18 parts of mineral admixture, 4 parts of functional regulator, 6 parts of nano-modifier, and 55 parts of deionized water. The nano-modifier is composed of nano-silica and modified glass microspheres in a weight ratio of 0.5:1; the composite cementitious substrate is composed of sulfoaluminate cement and silicate cement in a weight ratio of 1.4:1; the mineral admixture is composed of steel slag powder and metakaolin in a weight ratio of 1.5:1; the functional regulator is composed of sodium carboxymethyl cellulose and hydroxypropyl methyl cellulose in a weight ratio of 0.4:1; and the activity activator is composed of sodium sulfate and lithium carbonate in a weight ratio of 1.2:1. The preparation method of this composite gelling curing agent is as follows: S1. Dissolve silane coupling agent KH-570 in ethanol, add glass microspheres and then ultrasonically disperse them. The ultrasonic dispersion power is 300W and the time is 30 minutes. Then, remove the solvent by vacuum drying at 60℃ for 2 hours to obtain modified glass microspheres. The weight ratio of silane coupling agent KH-570, glass microspheres and ethanol is 2.5:10:10. S2. Divide the deionized water into three equal parts. Mix the first part of the deionized water with the composite cementitious substrate and mineral admixtures, and stir at 200 r / min for 15 minutes to obtain the first mixture. S3. Take the second portion of deionized water, heat it to 50°C, add the functional regulator, and stir at 250 r / min for 30 minutes to obtain the functional regulator solution. S4. Take the third part of deionized water and mix it with nano silica and active activator. When mixing, first ultrasonically disperse it for 30 minutes at 300W power, and then stir it for 15 minutes at 250r / min speed to obtain nano active activation liquid. S5. Add the modified glass microspheres to the nano-active activating liquid, then add the first mixture and the functional regulator solution, and stir at 300 r / min for 25 minutes to obtain the curing agent.

[0021] Example 2 A composite cementitious curing agent for fluidized solidified soil, comprising the following raw materials by weight (200g / part): 50 parts composite cementitious substrate, 8 parts active activator, 25 parts mineral admixture, 2 parts functional regulator, 3 parts nano-modifier, and 70 parts deionized water. The composite cementitious substrate is composed of sulfoaluminate cement and silicate cement in a weight ratio of 1.6:1; the active activator is composed of sodium sulfate and lithium carbonate in a weight ratio of 1:1; the mineral admixture is composed of steel slag powder and metakaolin in a weight ratio of 1.2:1; the functional regulator is composed of sodium carboxymethyl cellulose and hydroxypropyl methyl cellulose in a weight ratio of 0.8:1; and the nano-modifier is composed of nano-silica and modified glass microspheres in a weight ratio of 0.6:1. The preparation method of this composite gelling curing agent is as follows: S1. Dissolve silane coupling agent KH-570 in ethanol, add glass microspheres and then ultrasonically disperse them. The ultrasonic dispersion power is 300W and the time is 60 minutes. Then, remove the solvent by vacuum drying at 65℃ for 2 hours to obtain modified glass microspheres. The weight ratio of silane coupling agent KH-570, glass microspheres and ethanol is 2.5:10:10. S2. Divide the deionized water into three equal parts. Mix the first part of water with the composite cementitious substrate and mineral admixtures, and stir at 200 r / min for 30 minutes to obtain the first mixture. S3. Take the second portion of deionized water, heat it to 50°C, add the functional regulator, and stir at 280 r / min for 30 minutes to obtain the functional regulator solution. S4. Take the third portion of water ion water and mix it with nano silica and active activator. When mixing, first ultrasonically disperse it at 300W power for 20 minutes, and then stir it at 250r / min speed for 15 minutes to obtain nano active activation liquid. S5. Add the modified glass microspheres to the nano-active activating liquid, then add the first mixture and the functional regulator solution, stir at 350 r / min for 30 minutes, and after stirring evenly, the curing agent is obtained.

[0022] Example 3 A composite cementitious curing agent for fluidized solidified soil, comprising the following raw materials by weight (300g / part): 40 parts of composite cementitious substrate, 6 parts of active activator, 22 parts of mineral admixture, 3 parts of functional regulator, 4 parts of nano-modifier, and 67 parts of deionized water. The composite cementitious substrate is composed of sulfoaluminate cement and silicate cement in a weight ratio of 1.5:1; the active activator is composed of sodium sulfate and lithium carbonate in a weight ratio of 1.4:1; the mineral admixture is composed of steel slag powder and metakaolin in a weight ratio of 1.3:1; the functional regulator is composed of sodium carboxymethyl cellulose and hydroxypropyl methyl cellulose in a weight ratio of 0.6:1; and the nano-modifier is composed of nano-silica and modified glass microspheres in a weight ratio of 0.7:1. The preparation method of this composite gelling curing agent is as follows: S1. Dissolve silane coupling agent KH-570 in ethanol, add glass microspheres and then ultrasonically disperse them. The ultrasonic dispersion power is 300W and the time is 30 minutes. Then, remove the solvent by vacuum drying at 60℃ for 2 hours to obtain modified glass microspheres. The weight ratio of silane coupling agent KH-570, glass microspheres and ethanol is 2.5:10:10. S2. Divide the deionized water into three equal parts. Mix the first part of water with the composite cementitious substrate and mineral admixtures, and stir at 280 r / min for 30 minutes to obtain the first mixture. S3. Take the second portion of deionized water, heat it to 50°C, add the functional regulator, and stir at 250 r / min for 30 minutes to obtain the functional regulator solution. S4. Take the third portion of water ion water and mix it with nano silica and active activator. When mixing, first ultrasonically disperse it at 300W power for 20 minutes, and then stir it at 250r / min speed for 10 minutes to obtain nano active activation liquid. S5. Add the modified glass microspheres to the nano-active activating liquid, then add the first mixture and the functional regulator solution, stir at 300 r / min for 30 minutes, and after stirring evenly, the curing agent is obtained.

[0023] Comparative Example 1 The difference from Example 3 is that the nanomodifier is only nano-silica; In this comparative example, the preparation method of the composite gelling curing agent is as follows: S1. Divide the deionized water into three equal parts. Mix the first part of water with the composite cementitious substrate and mineral admixtures, and stir at 280 r / min for 30 minutes to obtain the first mixture. S2. Take the second portion of deionized water, heat it to 50°C, add the functional regulator, and stir at 250 r / min for 30 minutes to obtain the functional regulator solution. S3. Take the third part of water ion water and mix it with nano silica and active activator. When mixing, first disperse it by ultrasonication at 300W power for 20 minutes, and then stir it at 250r / min speed for 10 minutes to obtain nano active activation liquid. S4. Stir the nano-active activating liquid with the first mixture and the functional regulator solution at a speed of 300 r / min for 30 minutes. After stirring evenly, the curing agent is obtained.

[0024] Comparative Example 2 The difference from Example 3 is that the active activator is replaced with a combination of sodium silicate, calcium hydroxide and aluminum sulfate in a weight ratio of 0.8:0.6:1, while the total amount of active activator remains unchanged. The other steps and preparation process are the same as in Example 3.

[0025] Comparative Example 3 The difference from Example 3 is that the preparation method of this composite gelling curing agent is as follows: S1. Dissolve silane coupling agent KH-570 in ethanol, add glass microspheres and then ultrasonically disperse them. The ultrasonic dispersion power is 300W and the time is 30 minutes. Then, remove the solvent by vacuum drying at 60℃ for 2 hours to obtain modified glass microspheres. The weight ratio of silane coupling agent KH-570, glass microspheres and ethanol is 2.5:10:10. S2. Add the modified glass microspheres obtained in step S1 and the remaining raw materials to deionized water, and stir at 300 r / min for 1 hour to obtain the curing agent.

[0026] Comparative Example 4 A curing agent for fluidized solidified soil, comprising, by weight, 65 parts calcium hydroxide, 6 parts hydrophilic fumed silica, 18 parts SiO2, 10 parts Al2O3, 0.7 parts FeO, 2.5 parts Fe2O3, 1 part CaO, 0.3 parts MgO, 0.4 parts K2O, 0.07 parts SO3, 0.08 parts sodium sulfate, 0.08 parts zinc sulfate, 3.5 parts calcium silicate, 6 parts modifying agent, 0.7 parts hexamethylene diisocyanate-based polyisocyanate, and 7 parts deionized water; wherein the modifying agent is citric acid and hydroquinone in a weight ratio of 4:1.5.

[0027] The curing agent is prepared by mixing the raw materials.

[0028] Test Example: Performance Testing I. Test materials: Curing agents prepared in the embodiments and comparative examples of this invention.

[0029] II. Experimental Methods: 1. Sample preparation: Mix the curing agent and soil at a clay-soil ratio of 1:8, wherein the soil is clay with a moisture content of 38% and sandy soil with a sand content of 65%, and the water-to-solid ratio is 0.22; pour into a 4cm×4cm×16cm steel mold, cure at room temperature for 24 hours, remove the mold, and place it in a curing box at (20±2)℃ and 95% humidity for curing until the specified age (3d, 28d). 2. Testing items and methods: Compressive strength: tested according to T / BGEA001-2019 "Technical Standard for Premixed Flowable Solidified Soil Filling Engineering"; Water resistance strength decay rate: After 28 days of curing, soak for 7 days and calculate the percentage of the strength difference before and after soaking to the strength before soaking; Volume shrinkage rate: Measure the length, width, and height of the 28-day specimen using vernier calipers, and calculate (mold volume - specimen volume) / mold volume × 100%; Segregation rate: (1) The curing agent is mixed with clay with a moisture content of 38% and sandy soil with a sand content of 65% respectively. The mixing time shall not be less than 5 minutes. (2) Spread the mixture evenly on a non-adhesive surface, and then tap the surface lightly with a hammer to remove air; (3) Pour the mixture into a test sieve and place it on a vibrating sieve for vibration. The vibration time shall not be less than 3 minutes to allow it to separate into layers. (4) Take out the test sieve, weigh the material on and under the sieve, and calculate the segregation rate.

[0030] Segregation rate = (weight of material on the screen - weight of dry screen) / (weight of concrete - weight of dry screen) × 100%.

[0031] 3. The results are shown in the table below.

[0032] Table 1 Group 3D compressive strength (MPa) 28-day compressive strength (MPa) Water resistance strength degradation rate (%) 28-day volume shrinkage rate (%) Segregation rate of high moisture content clay (%) Segregation rate of sandy soil (%) Example 1 2.1 6.8 18 0.21 4.5 3.8 Example 2 2.7 8.0 13 0.16 3.0 2.7 Example 3 2.8 8.2 12 0.15 2.8 2.5 Comparative Example 1 1.5 5.2 29 0.35 6.2 5.5 Comparative Example 2 0.9 4.8 32 0.38 7.0 6.1 Comparative Example 3 0.8 4.5 35 0.42 8.5 7.8 Comparative Example 4 2.0 6.5 17 0.23 4.2 3.6 The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A composite cementitious curing agent for fluidized solidified soil, characterized in that, The raw materials include the following by weight: 35-50 parts of composite cementitious substrate, 4-8 parts of active activator, 18-25 parts of mineral admixture, 2-4 parts of functional regulator, 3-6 parts of nano-modifier, and 55-70 parts of deionized water.

2. The composite cementitious curing agent for fluidized solidified soil according to claim 1, characterized in that, The raw materials include the following by weight: 42 parts of composite cementitious substrate, 6 parts of active activator, 22 parts of mineral admixture, 3 parts of functional regulator, 4 parts of nano-modifier, and 62 parts of deionized water.

3. A composite cementitious curing agent for fluidized solidified soil according to any one of claims 1-2, characterized in that, The composite cementitious substrate is composed of sulfoaluminate cement and silicate cement in a weight ratio of (1.4~1.6):1; the active activator is composed of sodium sulfate and lithium carbonate in a weight ratio of (1~1.4):1; the mineral admixture is composed of steel slag powder and metakaolin in a weight ratio of (1.2~1.5):1; the functional regulator is composed of sodium carboxymethyl cellulose and hydroxypropyl methyl cellulose in a weight ratio of (0.4~0.8):1; and the nano-modifier is composed of nano-silica and modified glass microspheres in a weight ratio of (0.5~0.7):

1.

4. The composite cementitious curing agent for fluidized solidified soil according to claim 3, characterized in that, The modified glass microspheres were prepared by modification with silane coupling agent KH-570.

5. A composite cementitious curing agent for fluidized solidified soil according to claim 3, characterized in that, The nano-silica has a particle size of 10~20nm and a specific surface area ≥200m². 2 / g.

6. A composite cementitious curing agent for fluidized solidified soil according to claim 3, characterized in that, The specific surface area of ​​the steel slag powder is 400~450m². 2 / kg.

7. A method for preparing a composite cementitious curing agent for fluidized solidified soil as described in any one of claims 1-2, characterized in that, Includes the following steps: S1. Dissolve silane coupling agent KH-570 in ethanol, add glass microspheres and disperse ultrasonically, then vacuum dry to remove solvent to obtain modified glass microspheres; wherein the weight ratio of silane coupling agent KH-570, glass microspheres and ethanol is 2.5:10:

10. S2. Divide the deionized water into three equal parts. Mix the first part of water with the composite cementitious substrate and mineral admixtures to obtain the first mixture. S3. The second portion of water is mixed with the functional regulator to obtain a functional regulator solution; S4. The third part of water is mixed with nano-silica and active activator to prepare nano-active activating liquid; S5. Modified glass microspheres are added to nano-active activating liquid, then the first mixture and functional regulator solution are added, and the mixture is stirred evenly to prepare curing agent.

8. A method for preparing a composite cementitious curing agent for fluidized solidified soil according to claim 7, characterized in that, The ultrasonic dispersion power in step S1 is 300W, the time is 30 minutes, and the vacuum drying temperature is 60℃ for 2 hours.

9. A method for preparing a composite cementitious curing agent for fluidized solidified soil according to claim 7, characterized in that, In step S4, the mixture is first ultrasonically dispersed at 300W for 20-30 minutes, and then stirred at 250r / min for 10-15 minutes.