SiO2 / MgO composite powder with core-shell structure and preparation method of SiO2 / MgO composite powder

Abstract

The invention relates to SiO2 / MgO composite powder with a core-shell structure and a preparation method of the SiO2 / MgO composite powder, and belongs to the field of nano materials. The invention relates to a preparation method of SiO2 / MgO composite powder with a core-shell structure, which is a sol-gel method and specifically comprises the following steps: simultaneously and respectively dropwise adding a sodium silicate solution with the mass concentration of 2% and a diluted hydrochloric acid or diluted nitric acid solution with the mass concentration of 0.5 mol / L into a magnesium oxide powder suspension at the temperature of 60-75 DEG C, keeping the pH value of the suspension at 8-11 all the time, stirring and reacting for 5-8 hours, naturally cooling to room temperature, filtering and drying to obtain the SiO2 / MgO composite powder with the core-shell structure. The SiO2 / MgO composite powder with the core-shell structure is obtained. Sodium silicate is hydrolyzed under a certain condition by adopting a sol-gel method to generate SiO2, the SiO2 is adsorbed on the surfaces of magnesium oxide powder particles under the action of electrostatic field force and Van der Waals force, a polycondensation phenomenon is generated, a gel reaction is generated, the magnesium oxide particles are tightly coated, and a core-shell structure is formed, so that the magnesium oxide powder with high stability and good dispersity is obtained.

Description

Technical Field

[0001] The invention relates to a SiO2 / MgO composite powder with a core-shell structure and a preparation method thereof, belonging to the field of nano materials. Background Art

[0002] With the continuous progress of science and technology in today's society, industrial technology is also constantly innovating. The application of high-tech technology has improved industrial production efficiency and quality, and inorganic powder plays a very important role in industrial production. It is widely used in many industries and is an indispensable material in modern industrial production. Among them, magnesium oxide is an important inorganic material with a series of excellent properties, such as high temperature resistance, excellent insulation performance, antibacterial and antibacterial properties, good flame retardancy, good thermal conductivity, and excellent mechanical properties. my country's magnesium oxide production scale is small, and the equipment is outdated and cannot meet the needs of foreign markets. The Chinese patent of publication number CN116282092A discloses a method of desulfurizing and removing impurities from magnesium nitrate, concentrating it, and roasting it to obtain high-yield, high-purity magnesium oxide, which solves the problem of magnesium oxide purity, but consumes acid and alkali raw materials in the preparation process, which is not only low in recycling but also pollutes the environment. However, traditional magnesium oxide powder is easy to agglomerate in water due to the combined action of surface electrostatic force and intermolecular force, and cannot be evenly dispersed in the sol system and other problems, which limits the application of magnesium oxide in production. Therefore, if the sol-gel method can be used to hydrolyze sodium silicate under certain temperature and pH conditions to generate SiO2 coating film coated on the surface of magnesium oxide powder, its dispersibility can be improved, agglomeration can be reduced, and the use depth of magnesium oxide powder in high-end fields can be deepened, which is of great significance. Although the technical solution described in the Chinese patent "CN116282092 Method for preparing magnesium oxide using magnesium sulfate as raw material" improves the yield and purity of magnesium oxide, the preparation process contains a large amount of acid and alkali raw materials, which cannot be recycled, and the problems existing in the application of magnesium oxide powder, such as uneven particle size distribution, low surface activity, poor fluidity, easy agglomeration, poor dispersibility, etc., also exist. Summary of the invention

[0003] The present invention aims to solve the defects of the prior art, and aims to reduce the easy agglomeration and uneven dispersion of magnesium oxide powder. At the same time, the influencing factors of the dispersibility of magnesium oxide powder are explored, and a low-cost and green method for preparing SiO2 / MgO composite powder with a core-shell structure is specifically provided. A product with high dispersibility, good stability and uniform particle size distribution is obtained by using a sol-gel method.

[0004] A method for preparing a SiO2 / MgO composite powder with a core-shell structure is a sol-gel method, specifically: at 60-75°C, equal volumes of a sodium silicate solution with a mass concentration of 2% and a 0.5 mol / L dilute hydrochloric acid or dilute nitric acid solution are added dropwise to a magnesium oxide powder suspension at the same time, respectively, so that the pH value of the suspension is always maintained at 8-11, the reaction is stirred for 5-8 hours, and the SiO2 / MgO composite powder is filtered and dried after naturally cooling to room temperature to obtain the core-shell structured SiO2 / MgO composite powder.

[0005] In the above technical solution, equal volumes of sodium silicate solution with a mass concentration of 2% and 0.5 mol / L dilute hydrochloric acid or dilute nitric acid solution are added to the magnesium oxide powder suspension simultaneously and separately. When adding, preferably two peristaltic pumps are used to simultaneously add the sodium silicate solution and the acid solution to the magnesium oxide powder suspension, and the dropping speed of the two is controlled to be the same and the dropping end time is the same, so as to ensure that the volume ratio of the sodium silicate solution and the 0.5 mol / L dilute hydrochloric acid or dilute nitric acid solution is 1:1.

[0006] In the above technical solution, the sodium silicate is 1-5% of the mass of magnesium oxide.

[0007] In the above technical solution, the mass concentration of the magnesium oxide powder suspension is 10-20%, and the average particle size of the magnesium oxide powder is 1-10 microns.

[0008] In the above technical solution, the pH value of the suspension can be adjusted by adding 1.0 mol / L sodium hydroxide solution into the reaction solution, so that the pH value of the suspension is always maintained at 8-11.

[0009] In the above technical solution, the pH value of the suspension is always maintained at 9.5-11.5.

[0010] In the above technical solution, the product is naturally cooled to room temperature, vacuum filtered and then placed in an oven at 100°C for 36 hours for drying.

[0011] In the above technical scheme, the magnesium oxide powder suspension is prepared according to the following method: the magnesium oxide powder washed and dried with anhydrous ethanol is placed in a ball mill for wet ball milling, zirconium oxide grinding balls are used as grinding media, and anhydrous ethanol is added to assist grinding, and high-energy ball milling is performed at a speed of 300r / min for 2h; the suspension after ball milling is dried, the dried magnesium oxide powder is dispersed in deionized water, sodium pyrophosphate is added to make the added mass fraction 1% to 1.5%, the pH of the suspension system is adjusted to 9 to 12 with 0.5mol / L dilute hydrochloric acid / dilute nitric acid or 1.0mol / L sodium hydroxide solution, and the magnesium oxide suspension is ultrasonically dispersed for 10 to 20min to obtain the product.

[0012] Another object of the present invention is to provide a core-shell structured SiO2 / MgO composite powder prepared by the above method, wherein the SiO2 / MgO composite powder is spherical, with SiO2 as the shell and MgO powder coated in the shell.

[0013] Furthermore, the size of the composite powder is 40-80 μm, and the specific surface area of ​​the powder is 500-1100 m 2 / kg. The sedimentation accumulation of the powder after 24h is minimal, and the particles have good dispersion in the suspension system.

[0014] The beneficial effects of the present invention are as follows: the present invention adopts the sol-gel method to hydrolyze sodium silicate under certain conditions to produce SiO2, and under the action of electrostatic field force and van der Waals force, SiO2 is adsorbed on the surface of magnesium oxide powder particles, polycondensation occurs, and a gel reaction occurs, which tightly coats the magnesium oxide particles to form a core-shell structure, thereby obtaining magnesium oxide powder with high stability and good dispersibility. It has been detected that the surface morphology of the SiO2 / MgO composite powder prepared by the present invention changes from an irregular flaky angular shape to a spherical shape, the powder particle size reaches 40 to 80 μm, and the powder specific surface area is reduced to 500 to 1100 m 2 / kg, the sedimentation accumulation of the powder after 24 hours is the smallest and the dispersion stability in water is improved. The dispersants used in the preparation method of the present invention are safe and non-toxic, with little harm to operators and the environment; the operation method is simple, the process is simple, and the manufacturing cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 SEM photos of the uncoated and modified sample (a, c) and the coated and modified sample (b, d) prepared in Example 1 of the present invention; it can be seen from the figure that the uncoated original magnesium oxide powder particles are irregular flakes, the particles have relatively clear edges and corners, and the surface has scaly protrusions. The particles are closely spaced from each other, resulting in an agglomeration effect, and the dispersion is poor; the agglomeration effect between the particles is significantly improved after the coating modification, the particles are evenly distributed and the distance between them is moderate; the particle structure changes from the original flake-shaped angular type to a spherical rough type, the particle surface is significantly covered with particulate matter of different sizes, and the shape is rough and uneven with protrusions.

[0016] Figure 2 This is the microscopic morphology of the coated and modified magnesium oxide powder prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0017] The following non-limiting embodiments may enable a person skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0018] The test methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0019] One of the specific implementations:

[0020] The magnesium oxide powder pretreatment method is specifically as follows: (1) impurity removal: a commercial magnesium oxide powder anhydrous ethanol mixed solution is placed in an ultrasonic cleaning machine for dispersion for 15 minutes and aging for 30 minutes; (2) filtration + drying: the obtained solution is placed in a filter for vacuum filtration, and the precipitate obtained after filtration is placed in an oven for drying at 100°C for 24 hours to obtain the treated magnesium oxide powder. (3) ball milling: the magnesium oxide powder obtained after treatment is placed in a ball mill for wet ball milling, using zirconium oxide beads as the grinding medium, and adding anhydrous ethanol to assist grinding, and high-energy ball milling is performed at a speed of 300r / min for 2 hours; the suspension after ball milling is placed in an oven for drying at 100°C for 24 hours, wherein the mass ratio of zirconium oxide beads: magnesium oxide: anhydrous ethanol is 5:3:3.

[0021] The preparation method of magnesium oxide suspension comprises the following steps: dispersing dried magnesium oxide powder in deionized water, adding sodium pyrophosphate to make the added mass fraction 1-1.5%, adjusting the pH value of the suspension system with 0.5 mol / L dilute hydrochloric acid / dilute nitric acid and 1.0 mol / L sodium hydroxide solution to make the pH value range 9-12, and then ultrasonically dispersing the magnesium oxide suspension for 10-20 minutes, so that the mass concentration of the obtained magnesium oxide powder suspension is 10-20%, and the average particle size of the magnesium oxide powder is 1-10 microns.

[0022] The method for preparing SiO2 / MgO composite powder with core-shell structure is as follows: at 60-75°C, 2% sodium silicate solution and 0.5 mol / L dilute hydrochloric acid / dilute nitric acid solution are added to the above-obtained magnesium oxide suspension in a slow dripping manner using two peristaltic pumps, so that the pH value of the suspension is always maintained at 8-11 (if necessary, it can be adjusted using sodium hydroxide solution), and stirred at 260 r / min. The coating reaction is carried out for 5-8 hours, and the obtained magnesium oxide suspension is allowed to stand to room temperature, and after vacuum filtration, it is placed in a 100°C oven for drying for 36 hours.

[0023] Example 1

[0024] The pretreatment method of magnesium oxide powder is specifically as follows: (1) impurity removal: the magnesium oxide anhydrous ethanol mixed solution is placed in an ultrasonic cleaning machine for dispersion for 15 minutes and aging for 30 minutes; (2) filtration + drying: the obtained solution is placed in a filter for vacuum filtration, and the precipitate obtained after filtration is placed in an oven and dried at 100°C for 24 hours to obtain the treated magnesium oxide powder. (3) ball milling: the magnesium oxide powder obtained after treatment is placed in a ball mill for wet ball milling, using zirconium oxide beads as the grinding medium, and adding anhydrous ethanol to assist grinding, and high-energy ball milling is performed at a speed of 300r / min for 2 hours; the suspension after ball milling is placed in an oven and dried at 100°C for 24 hours.

[0025] The preparation method of magnesium oxide suspension is as follows: magnesium oxide powder is dispersed in deionized water at a solid-liquid ratio of 2:8, and sodium pyrophosphate (1.5% of the mass of magnesium oxide) is added. The pH of the suspension system is adjusted with a 1.0 mol / L sodium hydroxide solution to a pH value of 11.5, and the magnesium oxide suspension is ultrasonically dispersed for 20 minutes to obtain a magnesium oxide powder suspension, wherein the average particle size of the magnesium oxide powder is 7.39 microns.

[0026] The preparation method of SiO2 / MgO composite powder with core-shell structure is as follows: at 65°C, 5% sodium silicate solution and 0.5 mol / L dilute hydrochloric acid solution are added to the above-obtained magnesium oxide suspension by two peristaltic pumps in a slow dripping manner, and 1.0 mol / L sodium hydroxide solution is added at the same time to keep the pH value of the suspension at 10.5, and the mixture is stirred at 260 r / min for 7 hours for coating reaction. The obtained magnesium oxide suspension is allowed to stand and cool to room temperature, and then vacuum filtered and dried in a 100°C oven for 36 hours. The obtained coated powder system has excellent stability and dispersibility, with a particle size of 70.5 μm and a specific surface area of ​​792 m 2 / kg, after 24 hours of sedimentation, the powder sedimentation accumulation was 20%, and the upper clear liquid became more turbid.

[0027] Example 2

[0028] The pretreatment method of magnesium oxide powder is specifically as follows: (1) impurity removal: the magnesium oxide anhydrous ethanol mixed solution is placed in an ultrasonic cleaning machine for dispersion for 15 minutes and aging for 30 minutes; (2) filtration + drying: the obtained solution is placed in a filter for vacuum filtration, and the precipitate obtained after filtration is placed in an oven and dried at 100°C for 24 hours to obtain the treated magnesium oxide powder. (3) ball milling: the magnesium oxide powder obtained after treatment is placed in a ball mill for wet ball milling, using zirconium oxide beads as the grinding medium, and adding anhydrous ethanol to assist grinding, and high-energy ball milling is performed at a speed of 300r / min for 2 hours; the suspension after ball milling is placed in an oven and dried at 100°C for 24 hours.

[0029] The preparation method of magnesium oxide suspension is as follows: magnesium oxide powder is dispersed in deionized water at a solid-liquid ratio of 2:8, and sodium pyrophosphate (1.5% of the mass of magnesium oxide) is added. The pH of the suspension system is adjusted with a 1.0 mol / L sodium hydroxide solution to a pH value of 11.5, and the magnesium oxide suspension is ultrasonically dispersed for 20 minutes to obtain a magnesium oxide powder suspension, wherein the average particle size of the magnesium oxide powder is 7.39 microns.

[0030] The preparation method of SiO2 / MgO composite powder with core-shell structure is as follows: at 60°C, 2% sodium silicate solution and 0.5 mol / L dilute hydrochloric acid solution are added to the above-obtained magnesium oxide suspension in a slow dripping manner using two peristaltic pumps, and 1.0 mol / L sodium hydroxide solution is added at the same time to keep the pH value of the suspension at 8, and the mixture is stirred at 260 r / min for 5 hours for coating reaction. The obtained magnesium oxide suspension is allowed to stand and cool to room temperature, and is vacuum filtered and placed in a 100°C oven for 36 hours for drying. The obtained coated powder system has good stability and good dispersibility, a particle size of 45.8 μm, and a specific surface area of ​​the powder reduced to 995 m 2 / kg, after 24 hours of sedimentation, the powder sedimentation accumulation was 72%, and the upper clear liquid was turbid.

[0031] Comparative Example 1

[0032] The magnesium oxide powder pretreatment method is specifically as follows: (1) impurity removal: the magnesium oxide anhydrous ethanol mixed solution is placed in an ultrasonic cleaning machine for dispersion for 15 minutes and aging for 30 minutes; (2) filtration + drying: the obtained solution is placed in a filter for vacuum filtration, and the precipitate obtained after filtration is placed in an oven and dried at 100°C for 24 hours to obtain the treated magnesium oxide powder. (3) ball milling: the magnesium oxide powder obtained after treatment is placed in a ball mill for wet ball milling, using zirconium oxide beads as the grinding medium, and adding anhydrous ethanol to assist grinding, and high-energy ball milling is performed at a speed of 300r / min for 2 hours; the suspension after ball milling is placed in an oven and dried at 100°C for 24 hours to obtain the magnesium oxide powder after ball milling.

[0033] The preparation method of magnesium oxide suspension is as follows: magnesium oxide powder is dispersed in deionized water at a solid-liquid ratio of 2:8, and sodium pyrophosphate (1.5% of the mass of magnesium oxide) is added. The pH of the suspension system is adjusted with a 1.0 mol / L sodium hydroxide solution to a pH value of 11.5, and the magnesium oxide suspension is ultrasonically dispersed for 20 minutes to obtain a magnesium oxide powder suspension, wherein the average particle size of the magnesium oxide powder is 7.39 microns.

[0034] The composite powder preparation method is specifically as follows: at 55°C, two peristaltic pumps are used to slowly add 2% sodium silicate solution and 0.5 mol / L dilute nitric acid solution to the above-mentioned magnesium oxide suspension, and 1.0 mol / L sodium hydroxide solution is added at the same time to keep the pH value of the suspension at 9.5, and the mixture is stirred at 260 r / min. The coating reaction is carried out for 1 hour, and the obtained magnesium oxide suspension is allowed to stand and cool to room temperature, and then vacuum filtered and placed in a 100°C oven for 36 hours. The obtained coated powder system is very unstable and has poor dispersibility. The particle size is 25.6 μm, and the specific surface area of ​​the powder is reduced to 1246 m 2 / kg, after 24h of sedimentation, the powder sedimentation accumulation was 85%, and the supernatant was clear.

[0035] Comparative Example 2

[0036] The pretreatment method of magnesium oxide powder is specifically as follows: (1) impurity removal: the magnesium oxide anhydrous ethanol mixed solution is placed in an ultrasonic cleaning machine for dispersion for 15 minutes and aging for 30 minutes; (2) filtration + drying: the obtained solution is placed in a filter for vacuum filtration, and the precipitate obtained after filtration is placed in an oven and dried at 100°C for 24 hours to obtain the treated magnesium oxide powder. (3) ball milling: the magnesium oxide powder obtained after treatment is placed in a ball mill for wet ball milling, using zirconium oxide beads as the grinding medium, and adding anhydrous ethanol to assist grinding, and high-energy ball milling is performed at a speed of 300r / min for 2 hours; the suspension after ball milling is placed in an oven and dried at 100°C for 24 hours.

[0037] The preparation method of magnesium oxide suspension is as follows: magnesium oxide powder is dispersed in deionized water at a solid-liquid ratio of 2:8, and sodium pyrophosphate (1.5% of the mass of magnesium oxide) is added. The pH of the suspension system is adjusted with a 1.0 mol / L sodium hydroxide solution to a pH value of 11.5, and the magnesium oxide suspension is ultrasonically dispersed for 20 minutes to obtain a magnesium oxide powder suspension, wherein the average particle size of the magnesium oxide powder is 7.39 microns.

[0038] The composite powder preparation method is specifically as follows: at 60°C, two peristaltic pumps are used to slowly add 2% sodium silicate solution and 0.5 mol / L dilute nitric acid solution to the magnesium oxide suspension, and 1.0 mol / L sodium hydroxide solution is added at the same time to keep the pH value of the suspension at 10.5, and the mixture is stirred at 260 r / min for 3 hours for coating reaction. The obtained magnesium oxide suspension is allowed to stand and cool to room temperature, and then vacuum filtered and placed in a 100°C oven for 36 hours for drying. The obtained coated powder system is generally stable, but has poor dispersibility, a particle size of 35.5 μm, and a specific surface area of ​​the powder is reduced to 1116 m 2 / kg, after 24h of sedimentation, the powder sedimentation accumulation is 60%, and the upper clear liquid is relatively clear.

Claims

1. A method for preparing a core-shell structured SiO2 / MgO composite powder, characterized in that: The method is a sol-gel method, specifically, at 60-75° C., equal volumes of a 2% sodium silicate solution and a 0.5 mol / L dilute hydrochloric acid or dilute nitric acid solution are added dropwise to a magnesium oxide powder suspension at the same time, so that the pH value of the suspension is always maintained at 8-11, and the reaction is stirred for 5-8 hours. After naturally cooling to room temperature, the mixture is filtered and dried to obtain a SiO2 / MgO composite powder with a core-shell structure.

2. The method according to claim 1, characterized in that: The sodium silicate accounts for 1-5% of the mass of magnesium oxide.

3. The method according to claim 1, characterized in that: The mass concentration of the magnesium oxide powder suspension is 10-20%, and the average particle size of the magnesium oxide powder is 1-10 microns.

4. The method according to claim 1, characterized in that: The pH value of the suspension was adjusted with 1.0 mol / L sodium hydroxide solution so that the pH value of the suspension was always maintained at 8-11.

5. The method according to claim 1 or 2, characterized in that: The pH value of the suspension was always maintained at 9.5-11.

5.

6. The method according to claim 1, characterized in that: The mixture was cooled naturally to room temperature, vacuum filtered and dried in an oven at 100°C for 36 h.

7. The method according to claim 1, characterized in that: The magnesium oxide powder suspension is prepared according to the following method: placing magnesium oxide powder washed with anhydrous ethanol and dried in a ball mill for wet ball milling, using zirconium oxide grinding balls as grinding media, adding anhydrous ethanol to assist grinding, and performing high-energy ball milling at a speed of 300 r / min for 2 hours; drying the suspension after ball milling, dispersing the dried magnesium oxide powder in deionized water, adding sodium pyrophosphate so that the added mass fraction is 1% to 1.5%, adjusting the pH of the suspension system to 9 to 12 with 0.5 mol / L dilute hydrochloric acid / dilute nitric acid or 1.0 mol / L sodium hydroxide solution, and then ultrasonically dispersing the magnesium oxide suspension for 10 to 20 minutes to obtain the magnesium oxide suspension.

8. The SiO2 / MgO composite powder with a core-shell structure obtained by the method according to any one of claims 1 to 7, characterized in that: The SiO2 / MgO composite powder is spherical, with SiO2 as a shell and MgO powder coated in the shell.

9. The SiO2 / MgO composite powder according to claim 8, characterized in that: The size of the composite powder is 40-80 μm, and the specific surface area of ​​the powder is 500-1100 m 2 / kg.

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