An ultrafine magnesium oxide powder and its preparation method

Abstract

This invention discloses an ultrafine magnesium oxide powder and its preparation method, belonging to the field of alkaline earth metal oxide powders. The steps include: preparing a dispersion of magnesium oxide to be treated; adding a polyethyleneimine solution under stirring; centrifuging; collecting the insoluble matter to obtain magnesium oxide for the next step; washing the magnesium oxide with water; using the magnesium oxide obtained in the previous step to prepare a new dispersion of magnesium oxide to be treated; adding a sodium polyacrylate solution under stirring; centrifuging; collecting the insoluble matter to obtain new magnesium oxide to be treated; washing the magnesium oxide with water; repeating the above steps several times to obtain a magnesium oxide semi-finished product; and vacuum drying the washed magnesium oxide semi-finished product to obtain ultrafine magnesium oxide powder. The ultrafine magnesium oxide prepared by this method has a core-shell structure. Under the protection of the shell, the magnesium oxide in the core is not easily dissolved, and its acid and alkali resistance is improved.

Description

Technical Field

[0001] This invention relates to an ultrafine magnesium oxide powder and its preparation method, belonging to the field of alkaline earth metal oxide powders. Background Technology

[0002] Ultrafine magnesium oxide powder has wide applications in catalysis, adsorption, flame retardancy, and medicine due to its excellent properties, such as high specific surface area, good adsorption capacity, and non-toxicity. However, magnesium oxide is an alkaline oxide, which easily dissolves in acidic or alkaline environments to form corresponding magnesium salts or hydroxides, leading to structural damage, performance degradation, and limited application range. Summary of the Invention

[0003] To overcome the shortcomings of the prior art, the present invention provides an ultrafine magnesium oxide powder and its preparation method, which can improve the acid and alkali resistance of the ultrafine magnesium oxide powder.

[0004] The technical solution adopted by this invention to solve its technical problem is:

[0005] In a first aspect, this application provides a method for preparing ultrafine magnesium oxide powder, which includes the following steps in sequence:

[0006] To prepare a dispersion of magnesium oxide to be treated, a polyethyleneimine solution was added while stirring.

[0007] Centrifuge to separate and collect the insoluble matter to obtain the magnesium oxide to be treated for the next step, and wash the magnesium oxide to be treated with water;

[0008] The magnesium oxide to be treated obtained in the previous step was used to reconstitute the dispersion of the magnesium oxide to be treated, and sodium polyacrylate solution was added while stirring.

[0009] Centrifuge to separate and collect insoluble matter to obtain new magnesium oxide to be treated, and wash the magnesium oxide to be treated with water;

[0010] Repeat the above steps several times to obtain magnesium oxide semi-finished product;

[0011] The magnesium oxide semi-finished product after vacuum drying and washing is used to obtain the ultrafine magnesium oxide powder.

[0012] The ultrafine magnesium oxide powder prepared by the method provided in this application has a core-shell structure. Under the protection of the shell, the magnesium oxide in the core is not easily dissolved, and its acid and alkali resistance is improved.

[0013] Furthermore, the number of rounds refers to 2 to 5 rounds.

[0014] Fewer rounds may result in an excessively thin shell, insufficient barrier effect; too many rounds may result in an excessively thick shell, increasing preparation costs and potentially masking the high specific surface area advantage of the MgO core. Two to five rounds can balance corrosion resistance and material activity. Within this range, the shell thickness is moderate (approximately tens of nanometers), effectively protecting MgO without significantly reducing its original properties and avoiding excessive agglomeration.

[0015] Furthermore, the solvent used in the dispersion of magnesium oxide to be treated, the solvent used in the polyethyleneimine solution, and the solvent used in the sodium polyacrylate solution are all 60wt%-75wt% ethanol-water mixtures.

[0016] Mixing ethanol with water reduces surface tension, improves the wettability of magnesium oxide, and reduces agglomeration. At a 60-75% ethanol ratio, the solubility of PEI and PAA-Na is moderate, which helps to avoid polymer precipitation or uneven adsorption. At the same time, ethanol can partially inhibit the hydrolysis of magnesium oxide during dispersion.

[0017] Further, by mass, the dispersion of magnesium oxide to be treated comprises 800 parts solvent and 90-100 parts magnesium oxide to be treated; the concentration of the polyethyleneimine solution is 2wt%-3wt%; and the concentration of the sodium polyacrylate solution is 2wt%-3wt%.

[0018] A high solvent ratio helps prevent particle collision and aggregation due to excessive concentration, promoting the formation of monodisperse particles. A moderate polyelectrolyte concentration provides sufficient charge for adsorption while preventing the formation of bridging bonds in the solution by free polyelectrolytes at excessively high concentrations, which would lead to particle flocculation. After monolayer adsorption saturation, excess polyelectrolytes are easily washed away, ensuring the orderly construction of multilayer shells.

[0019] Further, the step of adding the polyethyleneimine solution under stirring includes:

[0020] While stirring at 200-300 rpm, the polyethyleneimine solution was added dropwise. After the addition was complete, stirring was continued at 200-300 rpm for 20-30 minutes.

[0021] The step of adding sodium polyacrylate solution under stirring includes:

[0022] While stirring at 200-300 rpm, the sodium polyacrylate solution is added dropwise. After the addition is complete, stirring continues at 200-300 rpm for 20-30 minutes. This facilitates the full diffusion of PEI or PAA-Na molecules to the particle surface and completes adsorption, forming a uniform coating.

[0023] Further, the step of preparing the dispersion of the magnesium oxide to be treated includes:

[0024] The dispersion is first pre-dispersed in a shear disperser, and then transferred to an ultrasonic disperser for ultrasonic dispersion. This combination of two dispersion methods balances efficiency and dispersion effect.

[0025] Furthermore, the pre-dispersion requirements are: above 6000 rpm, 15-20 min.

[0026] Furthermore, the requirements for ultrasonic dispersion are: power 300W, 30-60min.

[0027] Furthermore, before the step of vacuum drying and washing the magnesium oxide semi-finished product, the method further includes the following steps: preparing a dispersion of the magnesium oxide semi-finished product, adding 1-ethyl-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide to the semi-finished product dispersion, adjusting the pH to 5.8, stirring for 1-2 hours, centrifuging, collecting the insoluble matter, and obtaining the new magnesium oxide semi-finished product.

[0028] The combination of 1-ethyl-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide covalently links the carboxyl groups (-COOH) of sodium polyacrylate with the amino groups (-NH2) of PEI via amide bonds. This upgrades the multilayer shell from "electrostatic adsorption" to a dual effect of "electrostatic + covalent bonding," significantly improving the shell's mechanical strength and chemical stability. Even in strong acidic or alkaline environments, the shell is less prone to detachment due to electrostatic shielding, continuously protecting the MgO core.

[0029] Secondly, this application provides an ultrafine magnesium oxide powder, which is prepared by the ultrafine magnesium oxide powder preparation method described in the first aspect.

[0030] The beneficial effects of this invention are as follows: The method for preparing ultrafine magnesium oxide powder of this invention is a layer-by-layer self-assembly method. It utilizes electrostatic interactions to construct a multilayer shell structure of polyelectrolytes on the surface of ultrafine magnesium oxide powder. Ultrafine magnesium oxide serves as the core, providing a high specific surface area and active sites. Polyethylene imine carries a positive charge in solution and is adsorbed onto the magnesium oxide surface through electrostatic interactions. Sodium polyacrylate carries a negative charge in solution and is adsorbed onto the PEI layer surface through electrostatic interactions. By alternately adsorbing PEI and PAA-Na, a multilayer shell structure can be constructed, ultimately improving the acid and alkali resistance of ultrafine magnesium oxide powder. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure are described clearly and completely below. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the described embodiments of this disclosure without creative effort are within the scope of protection of this invention.

[0032] It should be understood that, without conflict, any and all embodiments of the present invention can be combined with technical features of any other embodiment or multiple other embodiments to obtain other embodiments. The present invention includes such combinations to obtain other embodiments.

[0033] In this specification, groups and their substituents may be selected by those skilled in the art to provide stable structural moieties and compounds. When a substituent is described by a conventional chemical formula written from left to right, the substituent also includes chemically equivalent substituents obtained when the structural formula is written from right to left.

[0034] Unless otherwise specified, all technical and scientific terms used herein have the standard meaning in the field to which the claimed subject matter pertains. Where multiple definitions exist for a term, the definition herein shall prevail.

[0035] Ultrafine magnesium oxide powder is prone to dissolution in acidic or alkaline environments, which limits its application. For example, in the improvement of acidic soils, magnesium oxide powder easily reacts with acidic substances in the soil, leading to magnesium loss and short-lived improvement effects.

[0036] Therefore, this application provides a method for preparing ultrafine magnesium oxide powder, which includes the following steps in sequence:

[0037] S1: Prepare a dispersion of magnesium oxide to be treated by adding a polyethyleneimine solution while stirring.

[0038] S2: Centrifuge to separate and collect the insoluble matter to obtain magnesium oxide to be treated for step S3. Wash the magnesium oxide to be treated with water.

[0039] S3: Use the magnesium oxide obtained in step S2 to reconstitute the magnesium oxide dispersion, and add sodium polyacrylate solution while stirring.

[0040] S4: Centrifuge to separate and collect the insoluble matter to obtain new magnesium oxide to be treated. Wash the magnesium oxide to be treated with water.

[0041] Repeat steps S1 to S4 several times to obtain magnesium oxide semi-finished product.

[0042] S5: The semi-finished magnesium oxide product after vacuum drying and washing is used to obtain ultrafine magnesium oxide powder.

[0043] It should be noted that the purpose of this application is not to produce finer magnesium oxide, but to modify the surface of ultrafine magnesium oxide to give it acid and alkali resistance. Because of the shell, the actual particle size of the magnesium oxide produced will be larger than that of the raw material. However, the ultrafine magnesium oxide powder produced by this application is less likely to agglomerate into larger particles than the untreated raw material when used in the future.

[0044] In the embodiments of this application, the combination of PEI (polyethyleneimine) and PAA-Na (sodium polyacrylate) has the following advantages: First, both PEI and PAA-Na have good solubility and film-forming properties, making it easy to form a uniform shell on the surface of magnesium oxide; second, the amine groups in PEI and the carboxyl groups in PAA-Na can form hydrogen bonds, enhancing the stability of the shell; third, the multi-layer shell structure can effectively prevent acidic or alkaline substances from directly contacting the magnesium oxide core, thereby improving its acid and alkali resistance.

[0045] The core-shell structured ultrafine magnesium oxide powder prepared in this application exhibits significantly improved acid and alkali resistance. The polyelectrolyte shell effectively prevents acidic or alkaline substances from directly contacting the magnesium oxide core, thus slowing down the dissolution rate. The polyelectrolyte shell can reduce van der Waals forces between powder particles, improving their dispersibility in aqueous media. By adjusting the molecular weight, dosage, and number of shell layers of the polyelectrolyte, the surface properties and functions of the powder can be flexibly controlled.

[0046] Preferably, steps S1 to S4 are repeated 2 to 5 times. The solvents used for the dispersion of magnesium oxide to be treated, the polyethyleneimine solution, and the sodium polyacrylate solution are all 60wt%-75wt% ethanol-water mixtures. By mass, the dispersion of magnesium oxide to be treated comprises 800 parts solvent and 90-100 parts magnesium oxide to be treated; the concentration of the polyethyleneimine solution is 2wt%-3wt%; and the concentration of the sodium polyacrylate solution is 2wt%-3wt%. Specific examples include:

[0047] Raw material composition: ultrafine magnesium oxide powder (core), 100 parts by weight, particle size 50nm-100nm; polyethyleneimine (PEI, positively charged polyelectrolyte), molecular weight range 10000-70000, 1-5 parts by weight; sodium polyacrylate (PAA-Na, negatively charged polyelectrolyte), molecular weight range 2000-10000, 1-5 parts by weight; deionized water; ethanol.

[0048] Specific preparation steps:

[0049] 1. Magnesium oxide dispersion: 100 parts by weight of ultrafine magnesium oxide powder were dispersed in 800 parts by weight of the first solvent. To ensure sufficient dispersion, the mixture was first pre-dispersed for 15 minutes using a high-speed shear disperser at 8000 rpm. Then, the mixture was transferred to an ultrasonic disperser and ultrasonically dispersed for 30 minutes at a power of 300W to ensure the formation of a uniform and stable suspension.

[0050] 2. PEI Adsorption: Slowly add PEI solution (3 parts by weight of polyethyleneimine dissolved in 100 parts by weight of the first solvent) to the magnesium oxide suspension. Control the dropping rate at 3 mL per minute using a peristaltic pump for precise control. After the addition is complete, stir continuously at 300 rpm for 1 hour at room temperature to ensure that PEI is fully adsorbed on the magnesium oxide surface.

[0051] 3. First centrifugal washing: The PEI-modified magnesium oxide suspension was centrifuged at 8000 rpm for 10 minutes. The supernatant was discarded, and the precipitate was redispersed with 200 parts by weight of deionized water. The precipitate was ultrasonically dispersed for 5 minutes, and then centrifuged again. This process was repeated 3 times to completely remove unadsorbed PEI.

[0052] 4. PAA-Na Adsorption: The washed PEI-modified magnesium oxide was redispersed in 800 parts by weight of the first solvent and ultrasonically dispersed for 5 minutes. PAA-Na solution (3 parts by weight of sodium polyacrylate dissolved in 100 parts by weight of the first solvent) was slowly added dropwise to the suspension at a rate of 3 mL per minute. After the addition was complete, the mixture was stirred continuously at 300 rpm for 1 hour at room temperature to ensure that PAA-Na was fully adsorbed onto the PEI layer surface.

[0053] 5. Second centrifugal washing: The PAA-Na modified magnesium oxide suspension was centrifuged at 8000 rpm for 10 minutes. The supernatant was discarded, and the precipitate was redispersed with 200 parts by weight of deionized water. The precipitate was ultrasonically dispersed for 5 minutes and then centrifuged again. This process was repeated 3 times to completely remove unadsorbed PAA-Na.

[0054] 6. Layer Construction: Repeat steps 2-5 according to actual needs to construct the required number of polyelectrolyte shell layers. Each repetition must include thorough washing to remove any unadsorbed polyelectrolytes.

[0055] 7. Drying: Transfer the final washed powder to a vacuum drying oven and dry it under vacuum at 60°C for 12 hours to ensure complete evaporation of moisture. The dried powder is a core-shell structured ultrafine magnesium oxide powder.

[0056] Although PEI and PAA-Na can form a stable shell structure at room temperature, the shell structure is easily destroyed at high temperatures, exposing the magnesium oxide core and reducing its acid and alkali resistance. For example, in some high-temperature catalytic reactions or in materials requiring high-temperature processing, this stability issue can affect the application performance of magnesium oxide.

[0057] Preferably, crosslinking is introduced using EDC (1-ethyl-(3-dimethylaminopropyl)carbodiimide) and NHS (N-hydroxysuccinimide), with specific examples as follows:

[0058] Raw material composition: Ultrafine magnesium oxide powder (core), 100 parts by weight, particle size 50nm-100nm; Polyethylene imine (PEI, positively charged polyelectrolyte), molecular weight range 10000-70000, 1-5 parts by weight; Sodium polyacrylate (PAA-Na, negatively charged polyelectrolyte), molecular weight range 2000-10000, 1-5 parts by weight; EDC, 0.1-0.5 parts by weight; NHS, 0.05-0.25 parts by weight; Deionized water; Ethanol.

[0059] Specific preparation steps:

[0060] 1. Magnesium oxide dispersion: 100 parts by weight of ultrafine magnesium oxide powder were dispersed in 800 parts by weight of the first solvent. To ensure sufficient dispersion, the mixture was first pre-dispersed for 15 minutes using a high-speed shear disperser at 8000 rpm. Then, the mixture was transferred to an ultrasonic disperser and ultrasonically dispersed for 30 minutes at a power of 300W to ensure the formation of a uniform and stable suspension.

[0061] 2. PEI Adsorption: Slowly add PEI solution (3 parts by weight of polyethyleneimine dissolved in 100 parts by weight of the first solvent) to the magnesium oxide suspension. Control the dropping rate at 3 mL per minute using a peristaltic pump for precise control. After the addition is complete, stir continuously at 300 rpm for 1 hour at room temperature to ensure that PEI is fully adsorbed on the magnesium oxide surface.

[0062] 3. First centrifugal washing: The PEI-modified magnesium oxide suspension was centrifuged at 8000 rpm for 10 minutes. The supernatant was discarded, and the precipitate was redispersed with 200 parts by weight of deionized water. The precipitate was ultrasonically dispersed for 5 minutes, and then centrifuged again. This process was repeated 3 times to completely remove unadsorbed PEI.

[0063] 4. PAA-Na Adsorption: The washed PEI-modified magnesium oxide was redispersed in 800 parts by weight of the first solvent and ultrasonically dispersed for 5 minutes. PAA-Na solution (3 parts by weight of sodium polyacrylate dissolved in 100 parts by weight of the first solvent) was slowly added dropwise to the suspension at a rate of 3 mL per minute. After the addition was complete, the mixture was stirred continuously at 300 rpm for 1 hour at room temperature to ensure that PAA-Na was fully adsorbed onto the PEI layer surface.

[0064] 5. Second centrifugal washing: The PAA-Na modified magnesium oxide suspension was centrifuged at 8000 rpm for 10 minutes. The supernatant was discarded, and the precipitate was redispersed with 200 parts by weight of deionized water. The precipitate was ultrasonically dispersed for 5 minutes and then centrifuged again. This process was repeated 3 times to completely remove unadsorbed PAA-Na.

[0065] 6. Multilayer Construction: Repeat steps 2-5 as needed to construct the required number of polyelectrolyte shell layers. During each repetition, ensure thorough washing to remove unadsorbed polyelectrolytes and crosslinking agents.

[0066] 7. EDC-NHS crosslinking: The washed magnesium oxide was redispersed in 800 parts by weight of the first solvent and ultrasonically dispersed for 5 minutes. A mixed solution of EDC (0.3 parts by weight) and NHS (0.15 parts by weight) was added (EDC and NHS were dissolved in 50 parts by weight of deionized water), and stirring was continued for 2 hours to allow PAA-Na and PEI to undergo a crosslinking reaction.

[0067] 8. Third centrifugal washing: The cross-linked magnesium oxide suspension is centrifuged at 8000 rpm for 10 minutes. The supernatant is discarded, and the precipitate is redispersed with 200 parts by weight of deionized water. The precipitate is ultrasonically dispersed for 5 minutes and then centrifuged again. This process is repeated 3 times to thoroughly remove unadsorbed EDC and NHS.

[0068] 9. Drying: Transfer the final washed powder to a vacuum drying oven and dry it under vacuum at 60°C for 12 hours to ensure complete evaporation of moisture. The dried powder is a cross-linked core-shell structured ultrafine magnesium oxide powder.

[0069] After adding EDC and NHS, the pH of the reaction system is adjusted to 5.5-6.0. Within this pH range, EDC can more effectively activate the carboxyl groups in PAA-Na, promoting the reaction with the amine groups in PEI and improving crosslinking efficiency. Simultaneously, this pH range also facilitates the stable presence of NHS, reducing the occurrence of side reactions. By precisely controlling the pH, the quality of the crosslinked network can be improved, further enhancing the product's thermal stability and acid and alkali resistance.

[0070] Example 1: Product formulation:

[0071] Ultrafine magnesium oxide powder: 100 parts by weight (Shijiazhuang Gengcheng Chemical Technology Co., Ltd.);

[0072] Polyethyleneimine (PEI): 3 parts by weight (Guangzhou Meigu Chemical Co., Ltd., molecular weight approximately 10,000);

[0073] Sodium polyacrylate (PAA-Na): 3 parts by weight (416029, Sigma-Aldrich, molecular weight approximately 8000).

[0074] Deionized water;

[0075] Ethanol is used to prepare a first solvent containing 75 wt% ethanol.

[0076] Product preparation method:

[0077] 1. Disperse the ultrafine magnesium oxide powder in the first solvent, pre-disperse it for 15 minutes using a high-speed shear disperser at 8000 rpm, and then ultrasonically disperse it for 30 minutes using an ultrasonic disperser at 300W to form a uniform suspension.

[0078] 2. Slowly add PEI solution (PEI dissolved in 100 parts by weight of the first solvent) to the magnesium oxide suspension, controlling the dropping rate at 3 mL per minute, using a peristaltic pump for precise control. After the addition is complete, stir continuously at 300 rpm for 1 hour at room temperature.

[0079] 3. Centrifuge the PEI-modified magnesium oxide suspension at 8000 rpm for 10 minutes. Discard the supernatant, redisperse the precipitate with 200 parts by weight of deionized water, sonicate for 5 minutes, and centrifuge and wash again. Repeat this process three times.

[0080] 4. Redisperse the washed PEI-modified magnesium oxide in 800 parts by weight of the first solvent and sonicate for 5 minutes. Slowly add PAA-Na solution (PAA-Na dissolved in 100 parts by weight of the first solvent) to the suspension, controlling the adding rate at 3 mL per minute. After the addition is complete, stir continuously at 300 rpm for 1 hour at room temperature.

[0081] 5. Centrifuge the PAA-Na modified magnesium oxide suspension at 8000 rpm for 10 minutes. Discard the supernatant, redisperse the precipitate with 200 parts by weight of deionized water, sonicate for 5 minutes, and centrifuge and wash again. Repeat this process three times.

[0082] Repeat steps 2-5 for a total of 3 rounds.

[0083] The washed powder was transferred to a vacuum drying oven and vacuum dried at 60°C for 12 hours.

[0084] Perform performance testing on the product:

[0085] Acid and alkali resistance test: Weigh 0.1g of sample and place it in 50mL of acetic acid solution with pH=2.5, and let it stand at 20℃ for 5 minutes. Then take the supernatant and determine the concentration of magnesium ions in the supernatant by inductively coupled plasma optical emission spectrometry (ICP-OES). Calculate the solubility of magnesium oxide.

[0086] Dispersibility test: Disperse 0.5g of sample in 0.9% sodium chloride solution and sonicate for 5 minutes. Measure the particle size distribution in the dispersion using a laser particle size analyzer (model: Malvern Zetasizer Nano ZS). Record the D50 value; the smaller the D50 value, the better the dispersibility (if particles clump together and are difficult to disperse, the particle size is larger).

[0087] Thermal stability test: The sample was placed in an oven and heated at 180°C for 2 hours, and then the above-mentioned acid and alkali resistance test and dispersibility test were performed.

[0088] Performance data results:

[0089] The unheated sample showed a magnesium oxide solubility of 30.9 mg / L in acid and alkali resistant conditions; the D50 value in the dispersibility test was 125 nm. The heated sample showed a magnesium oxide solubility of 98.2 mg / L in acid and alkali resistant conditions; the D50 value in the dispersibility test was 163 nm.

[0090] Example 2: Product formulation:

[0091] Ultrafine magnesium oxide powder: 100 parts by weight (Shijiazhuang Gengcheng Chemical Technology Co., Ltd.);

[0092] Polyethyleneimine (PEI): 3 parts by weight (Guangzhou Meigu Chemical Co., Ltd., molecular weight approximately 10,000);

[0093] Sodium polyacrylate (PAA-Na): 3 parts by weight (416026, Sigma-Aldrich, molecular weight approximately 8000).

[0094] 1-Ethyl-(3-dimethylaminopropyl)carbodiimide (EDC): 0.3 parts by weight (N807578, Shanghai Maclean Reagent Co., Ltd.);

[0095] N-hydroxysuccinimide (NHS): 0.15 parts by weight (56480, Shanghai Maclean Reagent Co., Ltd.).

[0096] Deionized water;

[0097] Ethanol is used to prepare a 70 wt% first solvent.

[0098] Product preparation method:

[0099] 1. Disperse the ultrafine magnesium oxide powder in the first solvent, pre-disperse it for 15 minutes using a high-speed shear disperser at 8000 rpm, and then ultrasonically disperse it for 30 minutes using an ultrasonic disperser at 300W to form a uniform suspension.

[0100] 2. Slowly add PEI solution (PEI dissolved in 100 parts by weight of the first solvent) to the magnesium oxide suspension, controlling the dropping rate at 3 mL per minute, using a peristaltic pump for precise control. After the addition is complete, stir continuously at 300 rpm for 1 hour at room temperature.

[0101] 3. Centrifuge the PEI-modified magnesium oxide suspension at 8000 rpm for 10 minutes. Discard the supernatant, redisperse the precipitate with 200 parts by weight of deionized water, sonicate for 5 minutes, and centrifuge and wash again. Repeat this process three times.

[0102] 4. Redisperse the washed PEI-modified magnesium oxide in 800 parts by weight of the first solvent and sonicate for 5 minutes. Slowly add PAA-Na solution (PAA-Na dissolved in 100 parts by weight of the first solvent) to the suspension, controlling the adding rate at 3 mL per minute. After the addition is complete, stir continuously at 300 rpm for 1 hour at room temperature.

[0103] 5. Centrifuge the PAA-Na modified magnesium oxide suspension at 8000 rpm for 10 minutes. Discard the supernatant, redisperse the precipitate with 200 parts by weight of deionized water, sonicate for 5 minutes, and centrifuge and wash again. Repeat this process 3 times. Repeat steps 2-5 for two rounds.

[0104] 6. Redisperse the washed magnesium oxide in 800 parts by weight of the first solvent and sonicate for 5 minutes. Add a mixed solution of EDC and NHS (EDC and NHS dissolved in 50 parts by weight of deionized water) to adjust the pH of the reaction system to 5.8, and continue stirring for 2 hours to allow PAA-Na and PEI to undergo a cross-linking reaction.

[0105] 7. Centrifuge the cross-linked magnesium oxide suspension at 8000 rpm for 10 minutes. Discard the supernatant, redisperse the precipitate with 200 parts by weight of deionized water, sonicate for 5 minutes, and centrifuge and wash again. Repeat this process three times.

[0106] The washed powder was transferred to a vacuum drying oven and dried under vacuum at 60°C for 12 hours.

[0107] Perform performance testing on the product:

[0108] Acid and alkali resistance test: Weigh 0.1g of sample and place it in 50mL of acetic acid solution with pH=2.5, and let it stand at 20℃ for 5 minutes. Then take the supernatant and determine the concentration of magnesium ions in the supernatant by inductively coupled plasma optical emission spectrometry (ICP-OES). Calculate the solubility of magnesium oxide.

[0109] Dispersibility test: Disperse 0.5g of sample in 0.9% sodium chloride solution and sonicate for 5 minutes. Measure the particle size distribution in the dispersion using a laser particle size analyzer (model: Malvern Zetasizer Nano ZS). Record the D50 value; the smaller the D50 value, the better the dispersibility (if particles clump together and are difficult to disperse, the particle size is larger).

[0110] Thermal stability test: The sample was placed in an oven and heated at 180°C for 2 hours, and then the above-mentioned acid and alkali resistance test and dispersibility test were performed.

[0111] Performance data results:

[0112] The unheated sample showed a magnesium oxide solubility of 22.5 mg / L in acid and alkali tests; the D50 value in the dispersibility test was 135 nm. The heated sample showed a magnesium oxide solubility of 45.1 mg / L in acid and alkali tests; the D50 value in the dispersibility test was 143 nm.

[0113] Comparison Example

[0114] The ultrafine magnesium oxide raw material was tested for performance directly using the same test method as in Example 1 without any further treatment.

[0115] Performance data results:

[0116] The unheated sample showed a magnesium oxide solubility of 118.3 mg / L in acid and alkali resistant conditions; the D50 value in the dispersibility test was 239 nm. The heated sample showed a magnesium oxide solubility of 117.9 mg / L in acid and alkali resistant conditions; the D50 value in the dispersibility test was 253 nm.

[0117] The test results from the above examples and control groups show that the core-shell structured ultrafine magnesium oxide powder prepared by this invention exhibits superior acid and alkali resistance, thermal stability, and dispersibility compared to commercially available unmodified nano-magnesium oxide powder. Specifically, the magnesium oxide powder prepared by this invention dissolves more slowly in acetic acid solution at pH 2.5, indicating a significant improvement in its acid resistance. These results demonstrate that this invention can effectively improve the acid and alkali resistance of ultrafine magnesium oxide powder, expanding its application areas.

[0118] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0119] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A method for preparing ultrafine magnesium oxide powder, characterized in that, The steps are included in sequence: To prepare a dispersion of magnesium oxide to be treated, a polyethyleneimine solution was added while stirring. Centrifuge to separate and collect the insoluble matter to obtain the magnesium oxide to be treated for the next step, and wash the magnesium oxide to be treated with water; The magnesium oxide to be treated obtained in the previous step was used to reconstitute the dispersion of the magnesium oxide to be treated, and sodium polyacrylate solution was added while stirring. Centrifuge to separate and collect insoluble matter to obtain new magnesium oxide to be treated, and wash the magnesium oxide to be treated with water; Repeat the above steps several times to obtain magnesium oxide semi-finished product; To prepare a dispersion of the magnesium oxide semi-finished product, 1-ethyl-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide are added to the semi-finished product dispersion, the pH is adjusted to 5.8, the mixture is stirred for 1-2 hours, centrifuged, and the insoluble matter is collected to obtain the new magnesium oxide semi-finished product. The magnesium oxide semi-finished product after vacuum drying and washing is used to obtain the ultrafine magnesium oxide powder.

2. The method for preparing ultrafine magnesium oxide powder according to claim 1, characterized in that, The number of rounds refers to 2 to 5 rounds.

3. The method for preparing ultrafine magnesium oxide powder according to claim 1, characterized in that, The solvents used in the dispersion of magnesium oxide to be treated, the solvents used in the polyethyleneimine solution, and the solvents used in the sodium polyacrylate solution are all 60wt%-75wt% ethanol-water mixtures.

4. The method for preparing ultrafine magnesium oxide powder according to claim 3, characterized in that, The dispersion of magnesium oxide to be treated comprises 800 parts solvent and 90-100 parts magnesium oxide to be treated by weight; the concentration of the polyethyleneimine solution is 2wt%-3wt%; and the concentration of the sodium polyacrylate solution is 2wt%-3wt%.

5. The method for preparing ultrafine magnesium oxide powder according to claim 4, characterized in that, The step of adding the polyethyleneimine solution under stirring includes: While stirring at 200-300 rpm, the polyethyleneimine solution was added dropwise. After the addition was complete, stirring was continued at 200-300 rpm for 20-30 minutes. The step of adding sodium polyacrylate solution under stirring includes: While stirring at 200-300 rpm, add the sodium polyacrylate solution dropwise. After the addition is complete, continue stirring at 200-300 rpm for 20-30 minutes.

6. The method for preparing ultrafine magnesium oxide powder according to claim 1, characterized in that, The steps for preparing the dispersion of the magnesium oxide to be treated include: First, pre-disperse in a shear disperser, then transfer to an ultrasonic disperser for ultrasonic dispersion.

7. The method for preparing ultrafine magnesium oxide powder according to claim 6, characterized in that, The pre-dispersion requirements are: above 6000 rpm, 15-20 min.

8. The method for preparing ultrafine magnesium oxide powder according to claim 6, characterized in that, The requirements for ultrasonic dispersion are: power 300W, 30-60min.

9. An ultrafine magnesium oxide powder, characterized in that, It is prepared by the method for preparing ultrafine magnesium oxide powder according to any one of claims 1 to 8.