Magnesium oxide coated aluminum nitride high-thermal-conductivity spherical powder and preparation method thereof

Abstract

The invention provides magnesium oxide coated aluminum nitride high-thermal-conductivity spherical powder and a preparation method thereof, and belongs to the field of coated aluminum nitride high-thermal-conductivity spherical powder. The preparation method comprises the following steps: preparing modified aluminum nitride powder, preparing magnesium salt nano micro-precipitation sol, performing spray granulation and calcining. The step of preparing the modified aluminum nitride powder comprises the following steps: carrying out ball milling treatment on aluminum nitride, absolute ethyl alcohol, yttrium oxide, lanthanum oxide and a modified aluminum nitride powder additive, and washing and drying to obtain the modified aluminum nitride powder; the modified aluminum nitride powder admixture is a mixture of phosphoric acid, aluminum dihydrogen phosphate, gamma-aminopropyltriethoxysilane and polyoxyethylene stearate; according to the magnesium oxide coated aluminum nitride high-thermal-conductivity spherical powder prepared by the preparation method disclosed by the invention, on the premise of ensuring the thermal conductivity, the hydrolysis resistance is improved, the surface density is enhanced, and the stability is improved.

Description

Technical Field

[0001] The invention belongs to the field of aluminum nitride coated high thermal conductivity spherical powder, and specifically relates to magnesium oxide coated aluminum nitride high thermal conductivity spherical powder and a preparation method thereof. Background Art

[0002] Aluminum nitride is a covalent bond compound that belongs to the hexagonal system and has a lead-zinc ore-type crystal structure. It has high strength at room temperature, and its strength decreases slowly with increasing temperature. It has good thermal conductivity and a small thermal expansion coefficient. It is a good heat shock-resistant material, and has strong resistance to erosion by molten metals, good dielectric properties, and a very wide range of applications.

[0003] Although aluminum nitride powder has high thermal conductivity (theoretical value 320 W / (m·K)), it has the following problems: it is easy to hydrolyze, which is not convenient for daily use and storage, and aluminum nitride reacts with water to form aluminum hydroxide, which will reduce the thermal conductivity to a certain extent; poor interface bonding: low surface activity, weak bonding with polymer substrate, high interface thermal resistance; uncontrollable morphology, traditional powder morphology is irregular (sphericity <90%), and low filling rate (<60wt%). Therefore, it is very necessary to coat aluminum nitride without affecting its thermal conductivity.

[0004] At present, aluminum nitride-coated spherical powders are mostly coated with alumina or silicon dioxide; The alumina coating method usually uses aluminum nitrate or aluminum sulfate as the aluminum source and ammonia water as the precipitant. Under heating conditions, aluminum hydroxide colloid is generated and coated on the surface of aluminum nitride. After high-temperature calcination, aluminum hydroxide is dehydrated to form aluminum oxide, thereby achieving the coating of aluminum oxide on aluminum nitride. However, the thermal expansion coefficients of alumina and aluminum nitride are quite different, which can easily lead to interfacial stress cracking at high temperatures. In addition, the thermal conductivity of alumina is relatively low. The use of alumina coating will reduce the overall thermal conductivity of aluminum nitride powder to a certain extent.

[0005] The silica coating method usually adopts the sol-gel method or the vapor deposition method to form a silica layer on the surface of aluminum nitride. However, the thickness of the coating layer is difficult to control, and the thermal conductivity of silica is lower, only 1.4 W / (m·K), which has a great influence on the thermal conductivity of aluminum nitride powder.

[0006] It can be seen that it is of great significance to find a suitable coating material to improve the hydrolysis resistance and stability of spherical powders without affecting the thermal conductivity.

[0007] Magnesium oxide or magnesium salt materials are inexpensive, have high thermal conductivity, good chemical stability, and have a thermal expansion coefficient close to that of aluminum nitride, which can reduce interfacial stress. However, the prior art does not have a mature solution for using magnesium oxide to coat aluminum nitride to produce high thermal conductivity spherical powders. During the research and development process, the applicant discovered that magnesium oxide and aluminum nitride have poor surface wettability, which easily leads to agglomeration of aluminum nitride particles, uneven coating of aluminum nitride powder, and low interfacial bonding strength between magnesium oxide and aluminum nitride. The magnesium oxide layer easily falls off, resulting in poor temperature resistance of the resulting product.

[0008] Therefore, providing a magnesium oxide-coated aluminum nitride high thermal conductivity spherical powder and a preparation method thereof, while ensuring thermal conductivity, improving hydrolysis resistance, strong surface density, good stability, and excellent high temperature resistance is a technical problem that needs to be urgently solved in the prior art. Summary of the invention

[0009] In order to solve the technical problems existing in the prior art, the present invention provides a magnesium oxide-coated aluminum nitride high thermal conductivity spherical powder and a preparation method thereof, which improves the hydrolysis resistance, enhances the surface density and improves the stability while ensuring the thermal conductivity.

[0010] In view of the above technical problems, the present invention adopts the following technical solutions: A method for preparing a magnesium oxide-coated aluminum nitride high thermal conductivity spherical powder includes the steps of preparing modified aluminum nitride powder, preparing a magnesium salt nano-microprecipitation sol, spray granulation and calcination. The specific operations are as follows: 1. Preparation of modified aluminum nitride powder Aluminum nitride, anhydrous ethanol, yttrium oxide, lanthanum oxide and modified aluminum nitride powder additives are placed in a ball mill, the grinding balls are zirconium oxide balls with a diameter of 2.5-3.5 mm, the ball-to-material ratio is 2-5:1, and the ball milling is carried out at a speed of 280-320 r / min for 9.5-10.5 hours, and the ball-milled slurry is washed with anhydrous ethanol, and then centrifuged with a centrifuge after washing, and then the centrifuged material is placed in an oven, and dried at 78-82° C. for 22-26 hours to obtain modified aluminum nitride powder; The mass ratio of the aluminum nitride, anhydrous ethanol, yttrium oxide and lanthanum oxide is 10-40:40-60:10-15:10-15; The modified aluminum nitride powder additive is 10-30wt% of the aluminum nitride mass; The modified aluminum nitride powder additive is a mixture of phosphoric acid, aluminum dihydrogen phosphate, γ-aminopropyl triethoxysilane, and polyoxyethylene stearate; The mass ratio of the phosphoric acid, aluminum dihydrogen phosphate, γ-aminopropyl triethoxysilane and polyoxyethylene stearate is 2-5:1-2:0.5-1:0.1-0.5.

[0011] 2. Preparation of Magnesium Salt Nano-precipitation Sol Deionized water, magnesium chloride, magnesium sulfate, basic magnesium carbonate and magnesium salt nano-micro precipitation sol additive are mixed, stirred at a speed of 480-520 r / min for 55-65 minutes, and then the solution is placed in a sealed tank and kept in an oven at 115-126° C. for 23-25 ​​hours to obtain a magnesium salt nano-micro precipitation sol with a viscosity of 80-120 mPa·S; The mass ratio of the deionized water, magnesium chloride, magnesium sulfate and basic magnesium carbonate is 20-70:5-15:20-40:5-25; The amount of the magnesium salt nano-micro-precipitation sol additive added to the magnesium salt nano-micro-precipitation sol is 3-10wt%; The magnesium salt nano-microprecipitation sol additive is a mixture of polyvinyl pyrrolidone, methyl cellulose and oxalic acid; The mass ratio of the polyvinyl pyrrolidone, methyl cellulose and oxalic acid is 1-5:0.5-2:1-5.

[0012] 3. Spray granulation Deionized water, modified aluminum nitride powder and magnesium salt nano-microprecipitation sol are mixed, and then ultrasonic dispersion is performed, the ultrasonic time is controlled to be 25-35 minutes, the ultrasonic frequency is controlled to be 36-44kHz, and after the ultrasonication is completed, stirring is performed at room temperature for 1.0-1.3 hours at a speed of 780-820r / min to obtain a slurry to be sprayed; the slurry to be sprayed is sprayed and granulated through a spray tower, and the inlet temperature is controlled to be 215-225°C, the outlet temperature is controlled to be 95-105°C, the atomization pressure is controlled to be 1.3-1.6MPa, the centrifugal disk speed is controlled to be 18000-21000r / min, the nozzle aperture is controlled to be 0.6-1.0mm, and the feed rate is controlled to be 8-12mL / min to obtain a spherical powder; The mass ratio of the deionized water, the modified aluminum nitride powder, and the magnesium salt nano-micro-precipitation sol is 30-60:20-40:20-30.

[0013] 4. Calcination The spherical powder is calcined in an argon atmosphere, first the temperature is increased to 780-820°C at a rate of 4.5-5.5°C / min, and kept warm for 25-35 minutes, then the temperature is increased to 1450-1550°C at a rate of 9.0-12.0°C / min, and kept warm for 2.8-3.4 hours to obtain magnesium oxide-coated aluminum nitride high thermal conductivity spherical powder.

[0014] Compared with the prior art, the present invention has achieved the following beneficial effects: 1. In the step of preparing the modified aluminum nitride powder of the present invention, the rare earth oxides yttrium oxide and lanthanum oxide can effectively inhibit the hydrolysis of aluminum nitride, and combined with additives such as phosphoric acid, aluminum dihydrogen phosphate, and γ-aminopropyltriethoxysilane, a dense protective layer is formed on the surface of the aluminum nitride particles through Al-OP bond connection and surface modification of the silane modifier, which effectively prevents aluminum nitride from contacting with water and improves the hydrolysis resistance of the aluminum nitride powder; under the action of additives such as oxalic acid, a certain proportion of nano magnesium salt particles is formed in the magnesium salt solution, and under the action of methyl cellulose, the magnesium salt solution has a certain viscosity to reach a similar In the state of sol; in the process of fully mixing and stirring the modified aluminum nitride powder and the magnesium salt nano-micro-precipitation sol in water for spray granulation, the nano-magnesium salt particles are filled in the gaps after the aluminum nitride powder is combined, and the magnesium salt sol is coated on the surface of the aluminum nitride spherical powder to form a uniform and dense surface structure. After sintering, a magnesium oxide-coated aluminum nitride high thermal conductivity spherical powder is obtained, and the magnesium oxide is uniformly coated on the aluminum nitride surface, and the surface is smooth and crack-free. Under the premise of not affecting its thermal conductivity, the hydrolysis resistance is enhanced, and the interface bonding between magnesium oxide and aluminum nitride is strong, and the high temperature stability is excellent; 2. The magnesium oxide-coated aluminum nitride high thermal conductivity spherical powder obtained by the present invention has a particle size of 30um-100um; 3. The magnesium oxide-coated aluminum nitride high thermal conductivity spherical powder obtained by the present invention has a sphericity of ≥98.2%, a density of >99.0%, and a thermal conductivity of 285-300W / (m·K); 4. The magnesium oxide-coated aluminum nitride high thermal conductivity spherical powder obtained by the present invention has a mass loss rate of 0.22-0.30% after being immersed in deionized water of 4 times the mass at 80°C for 72 hours; 5. The magnesium oxide-coated aluminum nitride high thermal conductivity spherical powder obtained by the present invention is heat-treated at 1400° C. for 25 hours in an air atmosphere, and the mass change rate is 0.37-0.54%. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a SEM image of the magnesium oxide-coated aluminum nitride high thermal conductivity spherical powder obtained in Example 3 at a magnification of 950; Figure 2 This is a SEM image of the magnesium oxide-coated aluminum nitride high thermal conductivity spherical powder prepared in Example 3 at 150 times magnification. DETAILED DESCRIPTION

[0016] In order to more clearly understand the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described.

[0017] Example 1 1. Preparation of modified aluminum nitride powder Aluminum nitride, anhydrous ethanol, yttrium oxide, lanthanum oxide and modified aluminum nitride powder additives are placed in a ball mill, the grinding balls are zirconium oxide balls with a diameter of 2.5 mm, the ball-to-material ratio is 2:1, and the ball milling is performed at a speed of 280 r / min for 9.5 hours. The ball-milled slurry is washed with anhydrous ethanol, and then centrifuged with a centrifuge. The centrifuged material is then placed in an oven and dried at 78° C. for 26 hours to obtain modified aluminum nitride powder. The mass ratio of the aluminum nitride, anhydrous ethanol, yttrium oxide and lanthanum oxide is 10:40:10:10; The modified aluminum nitride powder additive is 10wt% of the aluminum nitride mass; The modified aluminum nitride powder additive is a mixture of phosphoric acid, aluminum dihydrogen phosphate, γ-aminopropyl triethoxysilane, and polyoxyethylene stearate; The mass ratio of the phosphoric acid, aluminum dihydrogen phosphate, γ-aminopropyl triethoxysilane and polyoxyethylene stearate is 2:1:0.5:0.1.

[0018] 2. Preparation of Magnesium Salt Nano-precipitation Sol Deionized water, magnesium chloride, magnesium sulfate, basic magnesium carbonate and magnesium salt nano-micro precipitate sol additive were mixed, stirred at a speed of 480 r / min for 55 minutes, and then the solution was placed in a sealed tank and kept in an oven at 115° C. for 25 hours to obtain a magnesium salt nano-micro precipitate sol with a viscosity of 80 mPa·S; The mass ratio of deionized water, magnesium chloride, magnesium sulfate and basic magnesium carbonate is 20:5:20:5; The amount of the magnesium salt nano-micro-precipitation sol additive added to the magnesium salt nano-micro-precipitation sol is 3wt%; The magnesium salt nano-microprecipitation sol additive is a mixture of polyvinyl pyrrolidone, methyl cellulose and oxalic acid; The mass ratio of the polyvinyl pyrrolidone, methyl cellulose and oxalic acid is 1:0.5:1.

[0019] 3. Spray granulation Deionized water, modified aluminum nitride powder and magnesium salt nano-microprecipitation sol are mixed, and then ultrasonic dispersion is performed, the ultrasonic time is controlled to be 25 minutes, the ultrasonic frequency is controlled to be 44kHz, and after the ultrasonication is completed, stirring is performed at room temperature for 1.3 hours at a speed of 780r / min to obtain a slurry to be sprayed; the slurry to be sprayed is sprayed and granulated through a spray tower, and the inlet temperature is controlled to be 215°C, the outlet temperature is controlled to be 95°C, the atomization pressure is controlled to be 1.3MPa, the centrifugal disk speed is controlled to be 18000r / min, the nozzle aperture is controlled to be 0.6mm, and the feed rate is controlled to be 8mL / min to obtain a spherical powder; The mass ratio of the deionized water, the modified aluminum nitride powder, and the magnesium salt nano-micro-precipitation sol is 30:20:20.

[0020] 4. Calcination The spherical powder was calcined in an argon atmosphere, firstly the temperature was increased to 780°C at a rate of 4.5°C / min, kept at this temperature for 35 minutes, then the temperature was increased to 1450°C at a rate of 90.0°C / min, kept at this temperature for 3.4 hours, to obtain magnesium oxide-coated aluminum nitride high thermal conductivity spherical powder.

[0021] The magnesium oxide-coated aluminum nitride high thermal conductivity spherical powder obtained by the method of Example 1 has a sphericity of 98.2%, a density of 99.0%, and a thermal conductivity of 285W / (m·K); after being immersed in 4 times the mass of deionized water at 80°C for 72 hours, the mass loss rate is 0.30%; in an air atmosphere, after heat treatment at 1400°C for 25 hours, the mass change rate is 0.54%.

[0022] Example 2 1. Preparation of modified aluminum nitride powder Aluminum nitride, anhydrous ethanol, yttrium oxide, lanthanum oxide and modified aluminum nitride powder additives are placed in a ball mill, the grinding balls are zirconium oxide balls with a diameter of 3.5 mm, the ball-to-material ratio is 5:1, and the ball milling is performed at a speed of 320 r / min for 10.5 hours, and the ball-milled slurry is washed with anhydrous ethanol, and then centrifuged with a centrifuge after washing, and then the centrifuged material is placed in an oven, and dried at 82° C. for 22 hours to obtain modified aluminum nitride powder; The mass ratio of the aluminum nitride, anhydrous ethanol, yttrium oxide and lanthanum oxide is 40:60:15:15; The modified aluminum nitride powder additive is 30wt% of the aluminum nitride mass; The modified aluminum nitride powder additive is a mixture of phosphoric acid, aluminum dihydrogen phosphate, γ-aminopropyl triethoxysilane, and polyoxyethylene stearate; The mass ratio of the phosphoric acid, aluminum dihydrogen phosphate, γ-aminopropyltriethoxysilane and polyoxyethylene stearate is 5:2:1.0:0.5.

[0023] 2. Preparation of Magnesium Salt Nano-precipitation Sol Deionized water, magnesium chloride, magnesium sulfate, basic magnesium carbonate and magnesium salt nano-micro precipitate sol additive were mixed, stirred at a speed of 520 r / min for 65 minutes, and then the solution was placed in a sealed tank and kept in an oven at 126° C. for 23 hours to obtain a magnesium salt nano-micro precipitate sol with a viscosity of 120 mPa·S; The mass ratio of the deionized water, magnesium chloride, magnesium sulfate and basic magnesium carbonate is 70:15:40:25; The amount of the magnesium salt nano-micro-precipitation sol additive added to the magnesium salt nano-micro-precipitation sol is 10wt%; The magnesium salt nano-microprecipitation sol additive is a mixture of polyvinyl pyrrolidone, methyl cellulose and oxalic acid; The mass ratio of the polyvinyl pyrrolidone, methyl cellulose and oxalic acid is 5:2:5.

[0024] 3. Spray granulation Deionized water, modified aluminum nitride powder and magnesium salt nano-microprecipitation sol are mixed, and then ultrasonic dispersion is performed, the ultrasonic time is controlled to be 35 minutes, the ultrasonic frequency is controlled to be 36kHz, and after the ultrasonication is completed, stirring is performed at room temperature for 1.0 hour at a speed of 820r / min to obtain a slurry to be sprayed; the slurry to be sprayed is sprayed and granulated through a spray tower, and the inlet temperature is controlled to be 225°C, the outlet temperature is 105°C, the atomization pressure is 1.6MPa, the centrifugal disk speed is 21000r / min, the nozzle aperture is 1.0mm, and the feed rate is 12mL / min to obtain a spherical powder; The mass ratio of the deionized water, the modified aluminum nitride powder and the magnesium salt nano-micro-precipitation sol is 60:40:30.

[0025] 4. Calcination The spherical powder was calcined in an argon atmosphere, first the temperature was increased to 820°C at a rate of 5.5°C / min, kept warm for 25 minutes, then the temperature was increased to 1550°C at a rate of 12.0°C / min, kept warm for 2.8 hours, to obtain magnesium oxide-coated aluminum nitride high thermal conductivity spherical powder.

[0026] The magnesium oxide-coated aluminum nitride high thermal conductivity spherical powder obtained by the method of Example 2 has a sphericity of 99.1%, a density of 99.4%, and a thermal conductivity of 294W / (m·K); after being immersed in 4 times the mass of deionized water at 80°C for 72 hours, the mass loss rate is 0.26%; in an air atmosphere, after heat treatment at 1400°C for 25 hours, the mass change rate is 0.47%.

[0027] Example 3 1. Preparation of modified aluminum nitride powder Aluminum nitride, anhydrous ethanol, yttrium oxide, lanthanum oxide and modified aluminum nitride powder additives are placed in a ball mill, the grinding balls are zirconium oxide balls with a diameter of 3.0 mm, the ball-to-material ratio is 4:1, and the ball milling is performed at a speed of 300 r / min for 10 hours. The ball-milled slurry is washed with anhydrous ethanol, and then centrifuged with a centrifuge after washing. The centrifuged material is then placed in an oven and dried at 80° C. for 24 hours to obtain modified aluminum nitride powder. The mass ratio of the aluminum nitride, anhydrous ethanol, yttrium oxide and lanthanum oxide is 28:50:12:13; The modified aluminum nitride powder additive is 20wt% of the aluminum nitride mass; The modified aluminum nitride powder additive is a mixture of phosphoric acid, aluminum dihydrogen phosphate, γ-aminopropyl triethoxysilane, and polyoxyethylene stearate; The mass ratio of the phosphoric acid, aluminum dihydrogen phosphate, γ-aminopropyl triethoxysilane and polyoxyethylene stearate is 3.4:1.5:0.8:0.3.

[0028] 2. Preparation of Magnesium Salt Nano-precipitation Sol Deionized water, magnesium chloride, magnesium sulfate, basic magnesium carbonate and magnesium salt nano-micro precipitate sol additive were mixed, stirred at a speed of 500 r / min for 60 minutes, and then the solution was placed in a sealed tank and kept in an oven at 120° C. for 24 hours to obtain a magnesium salt nano-micro precipitate sol with a viscosity of 100 mPa·S; The mass ratio of the deionized water, magnesium chloride, magnesium sulfate and basic magnesium carbonate is 50:10:28:16; The amount of the magnesium salt nano-micro-precipitation sol additive added to the magnesium salt nano-micro-precipitation sol is 6wt%; The magnesium salt nano-microprecipitation sol additive is a mixture of polyvinyl pyrrolidone, methyl cellulose and oxalic acid; The mass ratio of the polyvinyl pyrrolidone, methyl cellulose and oxalic acid is 3:1.4:2.6.

[0029] 3. Spray granulation Deionized water, modified aluminum nitride powder and magnesium salt nano-microprecipitation sol are mixed, and then ultrasonic dispersion is performed, the ultrasonic time is controlled to be 30 minutes, the ultrasonic frequency is controlled to be 40kHz, and after the ultrasonication is completed, stirring is performed at room temperature for 1.0 hour at a speed of 800r / min to obtain a slurry to be sprayed; the slurry to be sprayed is sprayed and granulated through a spray tower, and the inlet temperature is controlled to be 220°C, the outlet temperature is 100°C, the atomization pressure is 1.5MPa, the centrifugal disk speed is 20000r / min, the nozzle aperture is 0.8mm, and the feed rate is 10mL / min to obtain a spherical powder; The mass ratio of the deionized water, the modified aluminum nitride powder, and the magnesium salt nano-micro-precipitation sol is 45:30:26.

[0030] 4. Calcination The spherical powder was calcined in an argon atmosphere, firstly the temperature was increased to 800°C at a rate of 5.0°C / min, kept at this temperature for 30 minutes, then the temperature was increased to 1500°C at a rate of 10.0°C / min, kept at this temperature for 3.0 hours, to obtain magnesium oxide-coated aluminum nitride high thermal conductivity spherical powder.

[0031] The SEM image of the magnesium oxide coated aluminum nitride high thermal conductivity spherical powder obtained in Example 3 at 950 times is shown in the attached figure of the specification. Figure 1 ; The SEM image of the magnesium oxide coated aluminum nitride high thermal conductivity spherical powder obtained in Example 3 at 150 times is shown in the attached figure of the specification. Figure 2 .

[0032] The magnesium oxide-coated aluminum nitride high thermal conductivity spherical powder obtained by the method of Example 3 has a sphericity of 99.5%, a density of 99.6%, and a thermal conductivity of 300 W / (m·K); after being immersed in 4 times the mass of deionized water at 80°C for 72 hours, the mass loss rate is 0.22%; in an air atmosphere, after heat treatment at 1400°C for 25 hours, the mass change rate is 0.37%.

[0033] Comparative Example Based on Example 3, the following changes are made: 1. In the step of preparing modified aluminum nitride powder, an equal amount of the modified aluminum nitride powder additive is replaced with aluminum nitride; 2. In the step of preparing the magnesium salt nano-micro-precipitation sol, an equal amount of the magnesium salt nano-micro-precipitation sol additive is replaced with magnesium chloride; The remaining operations are exactly the same as those in Example 3.

[0034] The magnesium oxide-coated aluminum nitride high thermal conductivity spherical powder obtained by the comparative example method has a sphericity of 90.3%, a density of 95.6%, and a thermal conductivity of 241W / (m·K); after being immersed in 4 times the mass of deionized water at 80°C for 72 hours, the mass loss rate is 1.45%; in an air atmosphere, after heat treatment at 1400°C for 25 hours, the mass change rate is 3.68%.

[0035] In the comparative example, the modified aluminum nitride powder additive is replaced with aluminum nitride during the preparation process, and the surface functionalization treatment is missing, resulting in the inability to form a dense protective layer on the aluminum nitride surface. After contacting with water, a hydrolysis reaction occurs to generate aluminum hydroxide and ammonia. The interface compatibility between aluminum nitride and yttrium oxide and lanthanum oxide dispersants is poor, resulting in agglomeration. After the magnesium salt nano-microprecipitation sol is replaced with magnesium chloride, the magnesium ions are only coated by physical adsorption, lacking the chemical bonding effect of the sol-gel method, the density and coverage of the coating layer are reduced, and the agglomeration defects of the aluminum nitride powder cannot be effectively repaired, resulting in a decrease in sphericity, which ultimately affects the product's hydrolysis resistance and thermal conductivity, and weakens its high-temperature stability.

[0036] Unless otherwise specified, all ratios and percentages described in the present invention are by mass ratios and percentages are by mass percentages.

[0037] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing magnesium oxide-coated aluminum nitride high thermal conductivity spherical powder, characterized in that: The method comprises the steps of preparing modified aluminum nitride powder, preparing magnesium salt nano-micro precipitation sol, spray granulation and calcination; The step of preparing the modified aluminum nitride powder is to ball-mill aluminum nitride, anhydrous ethanol, yttrium oxide, lanthanum oxide and an additive for modified aluminum nitride powder, and then wash and dry to obtain the modified aluminum nitride powder; The modified aluminum nitride powder additive is a mixture of phosphoric acid, aluminum dihydrogen phosphate, γ-aminopropyl triethoxysilane, and polyoxyethylene stearate; The step of preparing the magnesium salt nano-micro precipitate sol is to mix deionized water, magnesium chloride, magnesium sulfate, basic magnesium carbonate and a magnesium salt nano-micro precipitate sol additive, stir them, and then place them in a sealed tank and keep them warm at 115-126° C. to obtain a magnesium salt nano-micro precipitate sol with a viscosity of 80-120 mPa·S; The magnesium salt nano-micro-precipitation sol additive is a mixture of polyvinyl pyrrolidone, methyl cellulose and oxalic acid.

2. The method for preparing a magnesium oxide-coated aluminum nitride high thermal conductivity spherical powder according to claim 1, characterized in that: The step of preparing the modified aluminum nitride powder is as follows: aluminum nitride, anhydrous ethanol, yttrium oxide, lanthanum oxide and an additive for modified aluminum nitride powder are loaded into a ball mill, the grinding balls are zirconium oxide balls with a diameter of 2.5-3.5 mm, the ball-to-material ratio is 2-5:1, the ball milling is performed at a speed of 280-320 r / min for 9.5-10.5 hours, the ball-milled slurry is washed with anhydrous ethanol, and after washing, it is centrifuged with a centrifuge, and then the centrifuged material is placed in an oven, and dried at 78-82° C. for 22-26 hours to obtain the modified aluminum nitride powder.

3. The method for preparing a magnesium oxide-coated aluminum nitride high thermal conductivity spherical powder according to claim 1, characterized in that: In the step of preparing the modified aluminum nitride powder, the mass ratio of the aluminum nitride, anhydrous ethanol, yttrium oxide, and lanthanum oxide is 10-40:40-60:10-15:10-15; The modified aluminum nitride powder additive is 10-30wt% of the mass of aluminum nitride.

4. The method for preparing a magnesium oxide-coated aluminum nitride high thermal conductivity spherical powder according to claim 1, characterized in that: In the modified aluminum nitride powder additive, the mass ratio of the phosphoric acid, aluminum dihydrogen phosphate, γ-aminopropyl triethoxysilane, and polyoxyethylene stearate is 2-5:1-2:0.5-1:0.1-0.

5.

5. The method for preparing a magnesium oxide-coated aluminum nitride high thermal conductivity spherical powder according to claim 1, characterized in that: In the step of preparing the magnesium salt nano-precipitation sol, the mass ratio of the deionized water, magnesium chloride, magnesium sulfate, and basic magnesium carbonate is 20-70:5-15:20-40:5-25; The amount of the magnesium salt nano-micro-precipitation sol additive added to the magnesium salt nano-micro-precipitation sol is 3-10wt%.

6. The method for preparing a magnesium oxide-coated aluminum nitride high thermal conductivity spherical powder according to claim 1, characterized in that: In the magnesium salt nano-microprecipitation sol additive, the mass ratio of polyvinyl pyrrolidone, methyl cellulose and oxalic acid is 1-5:0.5-2:1-5.

7. The method for preparing a magnesium oxide-coated aluminum nitride high thermal conductivity spherical powder according to claim 1, characterized in that: Deionized water, modified aluminum nitride powder and magnesium salt nano-microprecipitation sol are mixed, and then ultrasonic dispersion is performed, the ultrasonic time is controlled to be 25-35 minutes, the ultrasonic frequency is controlled to be 36-44kHz, and after the ultrasonication is completed, stirring is performed at room temperature for 1.0-1.3 hours at a speed of 780-820r / min to obtain a slurry to be sprayed; the slurry to be sprayed is sprayed and granulated through a spray tower, and the inlet temperature is controlled to be 215-225°C, the outlet temperature is controlled to be 95-105°C, the atomization pressure is controlled to be 1.3-1.6MPa, the centrifugal disk speed is controlled to be 18000-21000r / min, the nozzle aperture is controlled to be 0.6-1.0mm, and the feed rate is controlled to be 8-12mL / min to obtain a spherical powder; The mass ratio of the deionized water, the modified aluminum nitride powder, and the magnesium salt nano-micro-precipitation sol is 30-60:20-40:20-30.

8. The method for preparing a magnesium oxide-coated aluminum nitride high thermal conductivity spherical powder according to claim 1, characterized in that: The calcination step comprises calcining the spherical powder in an argon atmosphere, firstly raising the temperature to 780-820° C. at a rate of 4.5-5.5° C. / min, keeping the temperature for 25-35 minutes, then raising the temperature to 1450-1550° C. at a rate of 9.0-12.0° C. / min, keeping the temperature for 2.8-3.4 hours, to obtain magnesium oxide-coated aluminum nitride high thermal conductivity spherical powder.

9. A magnesium oxide-coated aluminum nitride high thermal conductivity spherical powder, prepared by the preparation method according to any one of claims 1 to 8.

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