Preparation method of magnesium pyrophosphate coated magnesium oxide

Abstract

The invention provides a preparation method of magnesium pyrophosphate coated magnesium oxide. The preparation method comprises the following steps: firstly, sequentially carrying out ball-milling pretreatment on magnesium oxide, an ethanol-water mixed solution and a silane coupling agent, and forming a magnesium hydroxide layer and a silane hydrophobic protection layer on the surface of magnesium oxide to obtain pre-hydrolyzed magnesium oxide particles; and then mixing and ball-milling with a phosphorus-containing mineralizing agent, and carrying out high-temperature melting and calcining, so that the mineralizing agent reacts with the magnesium hydroxide layer to generate a compact magnesium pyrophosphate coating layer, namely the magnesium pyrophosphate-coated magnesium oxide is prepared. According to the preparation method disclosed by the invention, effective coating of magnesium pyrophosphate on magnesium oxide is successfully realized through a simple ball-milling and calcining process, the hydrolysis resistance is remarkably improved, and meanwhile, the obtained powder is good in dispersity and uniform in particle size, and has a wide application prospect in the field of high-thermal-conductivity composite materials.

Description

Technical Field

[0001] This invention belongs to the field of inorganic non-metallic powder material preparation technology, specifically relating to a method for preparing magnesium oxide coated with magnesium pyrophosphate. Background Technology

[0002] In the field of high-power electronic devices, efficient heat dissipation is crucial to ensuring their reliability and lifespan, making the demand for high thermal conductivity fillers increasingly urgent. Alumina, due to its good chemical stability, has long been widely used as a conventional thermally conductive filler. However, its relatively low thermal conductivity (approximately 30 W / m·K) is insufficient to meet the heat dissipation requirements of next-generation high-heat-generating electronic devices.

[0003] Compared to polycrystalline alumina, cubic magnesium oxide has twice the thermal conductivity, and its lower hardness and production cost make it a promising candidate to become a new mainstay in thermally conductive fillers. However, the high hygroscopicity of magnesium oxide severely limits its practical application. Magnesium oxide readily absorbs moisture from the air, reacting to form magnesium hydroxide, which has relatively low thermal conductivity. This hygroscopic reaction not only significantly reduces the thermal conductivity of the filler itself, but the accompanying volume expansion can also lead to stress cracks within the composite material, ultimately causing device failure.

[0004] To address the moisture absorption problem of magnesium oxide, researchers have employed organic or inorganic coating and surface modification methods to further improve its hydrolysis resistance. For example, Chinese invention patent CN106702489A discloses a method for preparing iron-coated magnesium oxide fixed whiskers. This method involves high-temperature calcination of a mixture of carbonyl iron powder and magnesium carbonate to obtain iron-coated magnesium oxide fixed whiskers. While the whiskers prepared by this method exhibit good dispersibility, their moisture resistance is poor. Chinese patent CN109095482A discloses a method for manufacturing spherical magnesium oxide. This method uses irregular magnesium oxide as raw material and spheroidizes it using a flame melting method. The spherical magnesium oxide prepared by this method has high sphericity and good dispersibility. However, this technology mainly focuses on morphology control and does not address surface passivation treatment to reduce moisture absorption, thus failing to improve the moisture resistance defect of the spherical magnesium oxide. Summary of the Invention

[0005] Based on the problems described in the background art, the purpose of this invention is to provide a method for preparing magnesium oxide coated with magnesium pyrophosphate. Through ball milling and heat treatment processes, a dense and stable magnesium pyrophosphate coating layer is constructed on the surface of magnesium oxide, fundamentally solving the technical problem of poor hydrolysis resistance of magnesium oxide powder. At the same time, the coated magnesium oxide has uniform particle size and narrow distribution, smooth surface and no agglomeration, and has excellent dispersibility and filling properties in composite materials.

[0006] To achieve the above objectives, this invention provides a method for preparing magnesium oxide coated with magnesium pyrophosphate. The core of this method lies in achieving in-situ coating through a two-step ball milling and one-step calcination process. The specific formation process and principle are as follows: (1) First, in the first ball milling step, a mixture of ethanol and distilled water is added to cause slight hydrolysis of the magnesium oxide surface, forming a layer of magnesium hydroxide; subsequently, the added silane coupling agent is hydrolyzed and can crosslink with the hydroxyl groups on the magnesium oxide surface to form a hydrophobic silica layer to prevent further hydrolysis of magnesium oxide. (2) Then, the pretreated magnesium oxide particles are mixed with a phosphorus-containing mineralizer and ball-milled for a short time to ensure uniform adhesion of the mineralizer. High-temperature melting and calcination are then used to coat magnesium oxide with magnesium pyrophosphate. During the high-temperature process, the outermost silica layer melts, cracks, and volatilizes. Simultaneously, the phosphorus-containing mineralizer reacts with the magnesium hydroxide layer to generate a magnesium pyrophosphate layer, thus obtaining magnesium oxide powder material coated with magnesium pyrophosphate.

[0007] This invention provides a method for preparing magnesium oxide coated with magnesium pyrophosphate, comprising the following steps: (1) Step 1: Add magnesium oxide powder, ethanol and distilled water mixture to a ball mill jar in a certain proportion, and place it in a planetary ball mill. Ball mill reaction at room temperature and speed of 100-600 r / min for 0.5-2 h. Then add silane coupling agent to the ball mill jar in a certain proportion, and continue ball mill reaction at room temperature and speed of 100-600 r / min for 0.5-2 h to obtain pre-hydrolyzed magnesium oxide particles. (2) Step 2: Add the phosphorus mineralizing agent to the ball mill jar containing pre-hydrolyzed magnesium oxide in step (1) according to a certain proportion and continue ball milling. After mixing for 5 minutes at room temperature and a speed of 300 r / min, pour it into a crucible and place the crucible in a muffle furnace for melting and calcination. The calcination temperature is 800-1500℃ and the holding time is 1-12h. After the sintered body cools naturally to room temperature, put it into a planetary ball mill and ball mill for 5-30 minutes to obtain magnesium oxide powder coated with magnesium pyrophosphate.

[0008] In step (1), the median diameter D50 of the magnesium oxide powder is 1-300 μm.

[0009] In step (1), the mass ratio of magnesium oxide powder, ethanol, distilled water, and silane coupling agent is 100-300:0.5-3:0.01-0.03:0.5-3.

[0010] In step (1), the silane coupling agent is one or more of dodecyltrimethoxysilane, γ-chloropropylmethyldiethoxysilane, and 3-aminopropyltrimethoxysilane.

[0011] In step (1), the concentration of ethanol is 95.0% to 99.8%. This refers to the concentration of the ethanol raw material.

[0012] In step (2), the amount of phosphorus mineralizing agent added is 0.5% to 10% of the mass of pre-hydrolyzed magnesium oxide.

[0013] The phosphorus mineralizing agent in step (2) is one or more of phosphoric acid, phosphate, and phosphate ester.

[0014] Compared with the prior art, the present invention has the following advantages: (1) The present invention achieves effective coating of magnesium oxide with magnesium pyrophosphate through ball milling and heat treatment. The magnesium pyrophosphate layer with stable surface structure fundamentally blocks the contact between water molecules and magnesium oxide core material, thereby significantly improving its hydrolysis resistance. (2) The magnesium pyrophosphate coated magnesium oxide particles prepared by the present invention have uniform particle size, narrow distribution range, smooth surface and no hard agglomerates. They have good dispersibility and filling properties in composite materials, which further improves the thermal conductivity of magnesium pyrophosphate coated magnesium oxide in composite materials. Attached Figure Description

[0015] Figure 1 This is a SEM image of magnesium oxide coated with magnesium pyrophosphate prepared in Example 2.

[0016] Figure 2 SEM image of the product prepared for Comparative Example 1.

[0017] Figure 3 SEM images of the product prepared for Comparative Example 2.

[0018] Figure 4 SEM image of the product prepared for Comparative Example 3.

[0019] Figure 5 SEM image of the product prepared for Comparative Example 4. Detailed Implementation

[0020] The following embodiments provide a detailed description of the above-mentioned content of the present invention. In particular, it should be noted that several adjustments and improvements can be made based on the principles of the present invention, and these adjustments and improvements are also considered to be within the protection scope of the embodiments of the present invention.

[0021] Example 1 (1) Step 1: Add 1000g of 1μm magnesium oxide powder, 5g of ethanol and 0.1g of distilled water mixture into a ball mill jar and place it in a planetary ball mill. Ball mill the mixture at 100r / min at room temperature for 0.5h. Then add 5g of dodecyltrimethoxysilane into the ball mill jar and continue ball milling the mixture at 100r / min at room temperature for 0.5h to obtain pre-hydrolyzed magnesium oxide particles. (2) Step 2: Add 1g of phosphoric acid to the ball mill jar containing 200g of pre-hydrolyzed magnesium oxide in step (1) and continue ball milling. After mixing for 5 minutes at room temperature and a speed of 300r / min, pour it into a crucible and place the crucible in a muffle furnace for melting and calcination at a temperature of 800℃ and a holding time of 1h. After the sintered body cools naturally to room temperature, place it in a planetary ball mill and ball mill for 5 minutes to obtain magnesium oxide powder coated with magnesium pyrophosphate.

[0022] Example 2 (1) Step 1: Add 2000g of 50μm magnesium oxide powder, 15g of ethanol and 0.2g of distilled water mixture into a ball mill jar and place it in a planetary ball mill. Ball mill the mixture at 300r / min at room temperature for 1h. Then add 15g of dodecyltrimethoxysilane into the ball mill jar and continue ball milling the mixture at 300r / min at room temperature for 1h to obtain pre-hydrolyzed magnesium oxide particles. (2) Step 2: Add 10g of sodium dihydrogen phosphate to the ball mill jar containing 200g of pre-hydrolyzed magnesium oxide in step (1) and continue ball milling. After mixing for 5 minutes at room temperature and a speed of 300r / min, pour it into a crucible and place the crucible in a muffle furnace for melting and calcination at a temperature of 1200℃ and a holding time of 6h. After the sintered body cools naturally to room temperature, place it in a planetary ball mill and ball mill for 15 minutes to obtain magnesium oxide powder coated with magnesium pyrophosphate.

[0023] Example 3 (1) Step 1: Add 3000g of 300μm magnesium oxide powder, 30g of ethanol and 0.3g of distilled water mixture into a ball mill jar and place it in a planetary ball mill. Ball mill the mixture at 600r / min at room temperature for 2h. Then add 30g of 3-aminopropyltrimethoxysilane into the ball mill jar and continue ball milling the mixture at 600r / min at room temperature for 2h to obtain pre-hydrolyzed magnesium oxide particles. (2) Step 2: Add 20g of phosphate ester to the ball mill jar containing 200g of pre-hydrolyzed magnesium oxide in step (1) and continue ball milling. After mixing for 5 minutes at room temperature and a speed of 300r / min, pour it into a crucible and place the crucible in a muffle furnace for melting and calcination at a temperature of 1500℃ and a holding time of 12h. After the sintered body cools naturally to room temperature, place it in a planetary ball mill and ball mill for 30 minutes to obtain magnesium oxide powder coated with magnesium pyrophosphate.

[0024] Comparative Example 1 The methods and procedures of Comparative Example 1 and Example 2 are basically the same, except that the pre-hydrolysis step is not included. The 50μm magnesium oxide powder raw material in Example 2 is directly put into a planetary ball mill and ball-milled for 15 minutes.

[0025] Comparative Example 2 The methods and steps of Comparative Example 2 and Example 2 are basically the same, the only difference being that step (1) in Example 2 is removed and dodecyltrimethoxysilane is not added in Comparative Example 2.

[0026] Comparative Example 3 The methods and steps of Comparative Example 3 are basically the same as those of Example 2, except that sodium dihydrogen phosphate is removed in step (2) of Example 2 and sodium dihydrogen phosphate is not added in Comparative Example 3.

[0027] Comparative Example 4 The methods and steps of Comparative Example 4 and Example 2 are basically the same, except that magnesium oxide, ethanol, distilled water and dodecyltrimethoxysilane from step (1) of Example 2 are added together to the ball mill jar for the experiment.

[0028] The performance testing methods and standards are as follows: Maximum filler content test: 30g of 500cP vinyl silicone oil, 0.76g of hydrogen-containing silicone oil, 0.1g of ethynylcyclohexanol, and 0.15g of 3000ppm chloroplatinic acid were mixed evenly, and a certain amount of the powder filler from the present invention and comparative examples was added. After initial dispersion, the mixture was placed in a vacuum stirrer and degassing machine with a speed of 800r / min and stirred for 6min. Then, it was calendered and shaped into a 2mm thick cured sheet using a molding machine. The cured sheet was placed in a 120℃ oven and dried for 0.5h. After the cured sheet was removed and allowed to cool naturally to room temperature, the maximum filler content was achieved if the cured sheet did not shed powder and the surface did not crack. Moisture resistance test: 30g of 500cP vinyl silicone oil, 0.76g of hydrogen-containing silicone oil, 0.1g of ethynylcyclohexanol, and 0.15g of 3000ppm chloroplatinic acid were mixed evenly, and a certain amount of the powder filler of the present invention and comparative examples was added. After preliminary dispersion, the mixture was placed in a vacuum stirrer and degassing machine with a speed of 800r / min and stirred for 6min. Then, it was calendered and shaped into a 2mm thick cured sheet using a molding machine. The hardness of the cured sheet was uniformly 50HD. Finally, the obtained gasket was stirred in boiling water at 100℃ for a period of time, and the mass gain rate was measured to evaluate the moisture resistance. Thermal conductivity test: 10g of 350cP vinyl silicone oil was added to a certain amount of the powder filler of the present invention embodiment, as well as alumina powder with the same particle size as the powder of the embodiment. After initial dispersion, it was placed in a vacuum stirrer and degassing machine with a speed of 800r / min and stirred for 6min. Then, it was calendered and shaped into a 2mm thick cured sheet using a molding machine. The hardness of the cured sheet was uniformly 50HD. Finally, the thermal conductivity was tested using a thermal conductivity meter in Xiangtan.

[0029] Table 1: Maximum filling amount of magnesium oxide powder prepared in each example serial number Maximum number of fillers Example 1 600 copies Example 2 650 copies Example 3 650 copies Comparative Example 1 180 copies Comparative Example 2 300 copies Comparative Example 3 200 copies Comparative Example 4 300 copies

[0030] Table 2: Mass gain rate of magnesium oxide powder prepared in each example:

[0031] Table 3: Thermal conductivity of different powders with the same filler content and particle size serial number D50 / μm Number of fillers Thermal conductivity W / m·K Example 1 30 600 2.3 Example 2 30 600 2.5 Example 3 30 600 2.3 Alumina 30 600 1.7

[0032] As can be seen from the attached figures and the data in Table 1: (1) Scanning electron microscope image ( Figures 1-4 Analysis, comparative example 1 ( Figure 2 In Comparative Example 2, experiments were conducted using unhydrolyzed magnesium oxide raw materials, and the resulting product particles had a rough surface morphology; Figure 3 In Comparative Example 3, without the addition of a silane coupling agent, the product particle morphology was an irregularly shaped aggregate; Figure 4 In the experiment without the addition of phosphorus-containing mineralizing agents, the product particle morphology was an irregularly shaped agglomerate; Comparative Example 4 ( Figure 5 In an experiment, distilled water and a coupling agent were added together to the product. The resulting product had irregularly shaped aggregates; while the magnesium pyrophosphate-coated magnesium oxide powder prepared according to Example 2 of this invention (…) Figure 1 Its product morphology is a spherical shape with a smooth surface and no particle aggregation. (2) Analysis of the maximum filling amount of magnesium oxide powder coated with magnesium pyrophosphate prepared in each example (Table 1) shows that compared with comparative examples 1 to 4, the magnesium oxide powder coated with magnesium pyrophosphate in examples 1 to 3 of the present invention has better dispersibility. The filling amount in 500 cP vinyl silicone oil can be increased by 100 to 260%, indicating that magnesium oxide powder coated with magnesium pyrophosphate significantly improves the dispersibility of magnesium oxide and its compatibility with organosilicon, and greatly improves the thermal conductivity of magnesium oxide materials. (3) Analysis of the mass increase rate of magnesium oxide powder coated with magnesium pyrophosphate prepared in each example (Table 2) shows that compared with comparative examples 1 to 4, the magnesium oxide powder coated with magnesium pyrophosphate of the present invention in examples 1 to 3 has better moisture resistance. After a water bath time of 1 hour, the mass increase rate of comparative examples 1 to 3 is about 3 to 9%, indicating that the magnesium oxide in comparative examples 1 to 3 undergoes a hydrolysis reaction and has strong hygroscopicity. After a water bath time of 48 hours, the mass increase rate of examples 1 to 3 is about 0.1 to 0.3%, indicating that the magnesium oxide coated with magnesium pyrophosphate in examples 1 to 3 does not undergo a hydrolysis reaction and has excellent moisture resistance. (4) Analysis of the thermal conductivity of different powders with the same filler content and particle size (Table 3) shows that, under the same filler content and particle size, the thermal conductivity of the embodiment of the present invention is 2.3 to 2.5 W / m·K, the thermal conductivity of alumina is 1.7 W / m·K, and the thermal conductivity of magnesium oxide coated with magnesium pyrophosphate is 0.6 to 0.7 W / m·K higher than that of alumina, indicating that the magnesium oxide coated with magnesium pyrophosphate in Examples 1 to 3 has excellent thermal conductivity.

[0033] As demonstrated by the above embodiments, this invention successfully prepares magnesium oxide powder coated with magnesium pyrophosphate, overcoming the shortcomings of poor moisture resistance and poor dispersibility of magnesium oxide in existing technologies. Furthermore, this method is simple, rapid, environmentally friendly, and suitable for large-scale production, facilitating process promotion.

[0034] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, any equivalent changes or modifications made to the structure, features and principles described in the claims of the present invention without departing from the principles of the present invention are included within the protection scope of the present invention.

Claims

1. A method for producing magnesium pyrophosphate-coated magnesium oxide, characterized by, The method comprises the following steps: (1) Step one: magnesium oxide powder, ethanol and distilled water mixture are added into a ball mill tank in a certain proportion, and placed in a planetary ball mill, and ball milled at a speed of 100-600 r / min at room temperature for 0.5-2 h, then silane coupling agent is added into the ball mill tank in a certain proportion, and continuously ball milled at a speed of 100-600 r / min at room temperature for 0.5-2 h, to obtain pre-hydrolyzed magnesium oxide; (2) Step two: phosphorus-containing mineralizer is added into the ball mill tank containing pre-hydrolyzed magnesium oxide in step (1) and continuously ball milled, and then poured into a crucible after ball milling and mixing at a speed of 300 r / min at room temperature for 5 min, and then the crucible is placed in a muffle furnace for melting and calcination, the calcination temperature is 800-1500℃, the holding time is 1-12 h, and after the sintered body is naturally cooled to room temperature, it is put into a planetary ball mill and ball milled for 5-30 min, to obtain magnesium pyrophosphate coated magnesium oxide powder.

2. The method for preparing magnesium oxide coated with magnesium pyrophosphate according to claim 1, characterized in that, In step (1), the median diameter D50 of the magnesium oxide powder is 1-300 μm.

3. The method for preparing magnesium oxide coated with magnesium pyrophosphate according to claim 1, characterized in that, In step (1), the mass ratio of magnesium oxide powder, ethanol, distilled water and silane coupling agent is 100-300: 0.5-3: 0.01-0.03: 0.5-3.

4. The method for preparing magnesium oxide coated with magnesium pyrophosphate according to claim 1, characterized in that, In step (1), the silane coupling agent is one or more of dodecyltrimethoxysilane, γ-chloropropylmethyldiethoxysilane and 3-aminopropyltrimethoxysilane.

5. The method for preparing magnesium oxide coated with magnesium pyrophosphate according to claim 1, characterized in that, In step (1), the concentration of ethanol is 95.0%-99.8%.

6. The method for preparing magnesium oxide coated with magnesium pyrophosphate according to claim 1, characterized in that, In step (2), the addition amount of phosphorus-containing mineralizer is 0.5%-10% of the mass of pre-hydrolyzed magnesium oxide.

7. The method for preparing magnesium oxide coated with magnesium pyrophosphate according to claim 1, characterized in that, In step (2), the phosphorus-containing mineralizer is one or more of phosphoric acid, phosphate and phosphorus-containing ester.

Images