A kind of magnesium oxide coated aluminum nitride high thermal conductivity spherical powder and preparation method thereof

Abstract

The invention provides a magnesium oxide-coated aluminum nitride high-thermal-conductivity spherical powder and a preparation method thereof, belonging to the field of coated aluminum nitride high-thermal-conductivity spherical powders; the preparation method comprises the steps of preparing modified aluminum nitride powder, preparing a magnesium salt nano-microprecipitation sol, spray granulation, and calcination; the step of preparing the modified aluminum nitride powder comprises the steps of ball-milling aluminum nitride, anhydrous ethanol, yttrium oxide, lanthanum oxide, and an external additive for the modified aluminum nitride powder, and washing and drying to obtain the modified aluminum nitride powder; the external additive for the modified aluminum nitride powder is a mixture of phosphoric acid, aluminum dihydrogen phosphate, γ-aminopropyltriethoxysilane, and polyoxyethylene stearate; the magnesium oxide-coated aluminum nitride high-thermal-conductivity spherical powder prepared by the invention has improved hydrolysis resistance, enhanced surface density, and improved stability while ensuring thermal conductivity.

Description

Technical Field

[0001] The invention belongs to the field of aluminum nitride-coated high-thermal-conductivity spherical powder, and particularly 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 molten metal corrosion. It has 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 easily hydrolyzed, making it inconvenient for daily use and storage. In addition, aluminum nitride reacts with water to form aluminum hydroxide, which can reduce thermal conductivity to a certain extent. It also has poor interfacial bonding: low surface activity, weak bonding with the polymer substrate, and high interfacial thermal resistance. Its morphology is uncontrollable, and traditional powders have irregular morphology (sphericity <90%) and low filling rate (<60wt%). Therefore, it is very necessary to coat aluminum nitride without affecting its thermal conductivity.

[0004] At present, most of the coated aluminum nitride spherical powders are coated with alumina or silica;

[0005] The alumina coating method usually uses aluminum nitrate or aluminum sulfate as the aluminum source and ammonia as the precipitant. Under heating conditions, aluminum hydroxide colloid is generated and coated on the surface of aluminum nitride. After high-temperature calcination, the aluminum hydroxide is dehydrated to form aluminum oxide, thereby achieving the coating of aluminum nitride with aluminum oxide.

[0006] 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.

[0007] The silica coating method usually uses a sol-gel method or a 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 even lower, at only 1.4 W / (m·K), which has a significant impact on the thermal conductivity of aluminum nitride powder.

[0008] 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.

[0009] 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, there is no mature solution in the existing technology to use magnesium oxide to coat aluminum nitride to produce high thermal conductivity spherical powders.

[0010] During the research and development process, the applicant discovered that the surface wettability of magnesium oxide and aluminum nitride was poor, which easily led to the agglomeration of aluminum nitride particles, resulting in uneven coating of aluminum nitride powder. In addition, the interfacial bonding strength between magnesium oxide and aluminum nitride was not high, and the magnesium oxide layer easily fell off, resulting in poor temperature resistance of the resulting product.

[0011] 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 solved urgently in the existing technology. Summary of the Invention

[0012] 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.

[0013] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0014] A method for preparing magnesium oxide-coated aluminum nitride high thermal conductivity spherical powder includes the steps of preparing modified aluminum nitride powder, preparing magnesium salt nano-microprecipitation sol, spray granulation, and calcination. The specific operations are as follows:

[0015] 1. Preparation of modified aluminum nitride powder

[0016] Aluminum nitride, anhydrous ethanol, yttrium oxide, lanthanum oxide and modified aluminum nitride powder additives are placed in a ball mill, and zirconium oxide balls with a diameter of 2.5-3.5 mm are used as grinding balls, and the ball-to-material ratio is 2-5:1. The ball mill 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 centrifuged in a centrifuge after washing. The centrifuged material is then placed in an oven and dried at 78-82° C. for 22-26 hours to obtain modified aluminum nitride powder.

[0017] The mass ratio of the aluminum nitride, anhydrous ethanol, yttrium oxide, and lanthanum oxide is 10-40:40-60:10-15:10-15;

[0018] The modified aluminum nitride powder additive is 10-30wt% of the mass of aluminum nitride;

[0019] The modified aluminum nitride powder additive is a mixture of phosphoric acid, aluminum dihydrogen phosphate, γ-aminopropyltriethoxysilane, and polyoxyethylene stearate;

[0020] The mass ratio of the phosphoric acid, aluminum dihydrogen phosphate, γ-aminopropyltriethoxysilane and polyoxyethylene stearate is 2-5:1-2:0.5-1:0.1-0.5.

[0021] 2. Preparation of Magnesium Salt Nano-precipitation Sol

[0022] Deionized water, magnesium chloride, magnesium sulfate, basic magnesium carbonate and a magnesium salt nano-microprecipitation 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-microprecipitation sol with a viscosity of 80-120 mPa·s;

[0023] The mass ratio of the deionized water, magnesium chloride, magnesium sulfate and basic magnesium carbonate is 20-70:5-15:20-40:5-25;

[0024] The amount of the magnesium salt nano-micro precipitate sol additive added to the magnesium salt nano-micro precipitate sol is 3-10wt%;

[0025] The magnesium salt nano-microprecipitation sol additive is a mixture of polyvinyl pyrrolidone, methyl cellulose and oxalic acid;

[0026] The mass ratio of the polyvinyl pyrrolidone, methyl cellulose and oxalic acid is 1-5:0.5-2:1-5.

[0027] 3. Spray granulation

[0028] 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 spherical powder;

[0029] The mass ratio of the deionized water, the modified aluminum nitride powder, and the magnesium salt nano-microprecipitation sol is 30-60:20-40:20-30.

[0030] 4. Calcination

[0031] The spherical powder is calcined in an argon atmosphere, first increasing the temperature to 780-820°C at a rate of 4.5-5.5°C / min, keeping it warm for 25-35 minutes, then increasing the temperature to 1450-1550°C at a rate of 9.0-12.0°C / min, keeping it warm for 2.8-3.4 hours, to obtain magnesium oxide-coated aluminum nitride high thermal conductivity spherical powder.

[0032] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0033] 1. In the step of preparing the modified aluminum nitride powder of the present invention, rare earth oxides yttrium oxide and lanthanum oxide can effectively inhibit the hydrolysis of aluminum nitride. 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 viscosity. 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 and spray granulating, the nano-magnesium salt particles fill 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, forming a uniform and dense surface structure. After sintering, a magnesium oxide-coated aluminum nitride high thermal conductivity spherical powder is obtained. The magnesium oxide is evenly coated on the surface of the aluminum nitride, and the surface is smooth and crack-free. Without affecting its thermal conductivity, the hydrolysis resistance is enhanced, and the interface bonding between the magnesium oxide and the aluminum nitride is strong, and the high temperature stability is excellent.

[0034] 2. The magnesium oxide-coated aluminum nitride high thermal conductivity spherical powder obtained by the present invention has a particle size of 30um-100um;

[0035] 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 285-300 W / (m·K);

[0036] 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 4 times its mass at 80°C for 72 hours;

[0037] 5. The magnesium oxide-coated aluminum nitride high thermal conductivity spherical powder obtained by the present invention is heat-treated at 1400°C in an air atmosphere for 25 hours, and the mass change rate is 0.37-0.54%. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1This is a SEM image of the magnesium oxide-coated aluminum nitride high thermal conductivity spherical powder prepared in Example 3 at 950 times magnification;

[0039] 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

[0040] 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.

[0041] Example 1

[0042] 1. Preparation of modified aluminum nitride powder

[0043] Aluminum nitride, anhydrous ethanol, yttrium oxide, lanthanum oxide and modified aluminum nitride powder additives are placed in a ball mill jar, and the grinding balls are zirconia balls with a diameter of 2.5 mm, and the ball-to-material ratio is 2:1. The ball mill is carried out at a speed of 280 r / min for 9.5 hours. The ball-milled slurry is washed with anhydrous ethanol and then centrifuged in 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.

[0044] The mass ratio of the aluminum nitride, anhydrous ethanol, yttrium oxide, and lanthanum oxide is 10:40:10:10;

[0045] The modified aluminum nitride powder additive is 10wt% of the aluminum nitride mass;

[0046] The modified aluminum nitride powder additive is a mixture of phosphoric acid, aluminum dihydrogen phosphate, γ-aminopropyltriethoxysilane, and polyoxyethylene stearate;

[0047] The mass ratio of the phosphoric acid, aluminum dihydrogen phosphate, γ-aminopropyltriethoxysilane and polyoxyethylene stearate is 2:1:0.5:0.1.

[0048] 2. Preparation of Magnesium Salt Nano-precipitation Sol

[0049] Deionized water, magnesium chloride, magnesium sulfate, basic magnesium carbonate, and a magnesium salt nano-microprecipitation sol additive were mixed and stirred at a speed of 480 r / min for 55 minutes. The solution was then placed in a sealed jar and kept in an oven at 115°C for 25 hours to obtain a magnesium salt nano-microprecipitation sol with a viscosity of 80 mPa·s.

[0050] The mass ratio of the deionized water, magnesium chloride, magnesium sulfate, and basic magnesium carbonate is 20:5:20:5;

[0051] The amount of the magnesium salt nano-micro precipitate sol additive added to the magnesium salt nano-micro precipitate sol is 3wt%;

[0052] The magnesium salt nano-microprecipitation sol additive is a mixture of polyvinyl pyrrolidone, methyl cellulose and oxalic acid;

[0053] The mass ratio of the polyvinyl pyrrolidone, methyl cellulose and oxalic acid is 1:0.5:1.

[0054] 3. Spray granulation

[0055] Deionized water, modified aluminum nitride powder and magnesium salt nano-microprecipitate sol were mixed, and then ultrasonic dispersion was performed, with the ultrasonic time controlled at 25 minutes and the ultrasonic frequency at 44 kHz. After the ultrasonication, the mixture was stirred at room temperature at a speed of 780 r / min for 1.3 hours to obtain a slurry to be sprayed; the slurry to be sprayed was sprayed and granulated through a spray tower, with the inlet temperature controlled at 215° C., the outlet temperature controlled at 95° C., the atomization pressure controlled at 1.3 MPa, the centrifugal disk speed controlled at 18,000 r / min, the nozzle aperture controlled at 0.6 mm, and the feed rate controlled at 8 mL / min to obtain spherical powder;

[0056] The mass ratio of the deionized water, the modified aluminum nitride powder, and the magnesium salt nano-microprecipitation sol is 30:20:20.

[0057] 4. Calcination

[0058] 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 warm for 35 minutes, then the temperature was increased to 1450°C at a rate of 90.0°C / min, kept warm for 3.4 hours, to obtain magnesium oxide-coated aluminum nitride high thermal conductivity spherical powder.

[0059] 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 285 W / (m·K); after immersion in 4 times the mass of deionized water at 80°C for 72 hours, the mass loss rate is 0.30%; after heat treatment at 1400°C for 25 hours in an air atmosphere, the mass change rate is 0.54%.

[0060] Example 2

[0061] 1. Preparation of modified aluminum nitride powder

[0062] Aluminum nitride, anhydrous ethanol, yttrium oxide, lanthanum oxide and modified aluminum nitride powder additives are placed in a ball mill jar. Zirconia balls with a diameter of 3.5 mm are used as grinding balls. The ball-to-material ratio is 5:1. The ball milling is carried out at a speed of 320 r / min for 10.5 hours. The ball-milled slurry is washed with anhydrous ethanol and then centrifuged in a centrifuge. The centrifuged material is then placed in an oven and dried at 82°C for 22 hours to obtain modified aluminum nitride powder.

[0063] The mass ratio of the aluminum nitride, anhydrous ethanol, yttrium oxide, and lanthanum oxide is 40:60:15:15;

[0064] The modified aluminum nitride powder additive is 30wt% of the aluminum nitride mass;

[0065] The modified aluminum nitride powder additive is a mixture of phosphoric acid, aluminum dihydrogen phosphate, γ-aminopropyltriethoxysilane, and polyoxyethylene stearate;

[0066] The mass ratio of the phosphoric acid, aluminum dihydrogen phosphate, γ-aminopropyltriethoxysilane and polyoxyethylene stearate is 5:2:1.0:0.5.

[0067] 2. Preparation of Magnesium Salt Nano-precipitation Sol

[0068] Deionized water, magnesium chloride, magnesium sulfate, basic magnesium carbonate, and a magnesium salt nano-microprecipitation sol additive were mixed and stirred at a speed of 520 r / min for 65 minutes. The solution was then placed in a sealed jar and kept in an oven at 126°C for 23 hours to obtain a magnesium salt nano-microprecipitation sol with a viscosity of 120 mPa·s.

[0069] The mass ratio of the deionized water, magnesium chloride, magnesium sulfate, and basic magnesium carbonate is 70:15:40:25;

[0070] The amount of the magnesium salt nano-micro precipitate sol additive added to the magnesium salt nano-micro precipitate sol is 10wt%;

[0071] The magnesium salt nano-microprecipitation sol additive is a mixture of polyvinyl pyrrolidone, methyl cellulose and oxalic acid;

[0072] The mass ratio of the polyvinyl pyrrolidone, methyl cellulose and oxalic acid is 5:2:5.

[0073] 3. Spray granulation

[0074] Deionized water, modified aluminum nitride powder and magnesium salt nano-microprecipitation sol were mixed, and then ultrasonic dispersion was performed, with the ultrasonic time controlled at 35 minutes and the ultrasonic frequency at 36 kHz. After the ultrasonication, the mixture was stirred at room temperature at a speed of 820 r / min for 1.0 hour to obtain a slurry to be sprayed; the slurry to be sprayed was sprayed and granulated through a spray tower, with the inlet temperature controlled at 225° C., the outlet temperature controlled at 105° C., the atomization pressure controlled at 1.6 MPa, the centrifugal disk speed controlled at 21000 r / min, the nozzle aperture controlled at 1.0 mm, and the feed rate controlled at 12 mL / min to obtain spherical powder;

[0075] The mass ratio of the deionized water, the modified aluminum nitride powder, and the magnesium salt nano-microprecipitation sol is 60:40:30.

[0076] 4. Calcination

[0077] The spherical powder was calcined in an argon atmosphere, firstly 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.

[0078] 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 294 W / (m·K); after immersion in 4 times the mass of deionized water at 80°C for 72 hours, the mass loss rate is 0.26%; after heat treatment at 1400°C for 25 hours in an air atmosphere, the mass change rate is 0.47%.

[0079] Example 3

[0080] 1. Preparation of modified aluminum nitride powder

[0081] Aluminum nitride, anhydrous ethanol, yttrium oxide, lanthanum oxide and modified aluminum nitride powder additives are placed in a ball mill jar, and the grinding balls are zirconia balls with a diameter of 3.0 mm, and the ball-to-material ratio is 4:1. The ball milling is carried out at a speed of 300 r / min for 10 hours. The ball-milled slurry is washed with anhydrous ethanol and then centrifuged in a centrifuge. The centrifuged material is then placed in an oven and dried at 80°C for 24 hours to obtain modified aluminum nitride powder.

[0082] The mass ratio of the aluminum nitride, anhydrous ethanol, yttrium oxide, and lanthanum oxide is 28:50:12:13;

[0083] The modified aluminum nitride powder additive is 20wt% of the aluminum nitride mass;

[0084] The modified aluminum nitride powder additive is a mixture of phosphoric acid, aluminum dihydrogen phosphate, γ-aminopropyltriethoxysilane, and polyoxyethylene stearate;

[0085] The mass ratio of the phosphoric acid, aluminum dihydrogen phosphate, γ-aminopropyltriethoxysilane and polyoxyethylene stearate is 3.4:1.5:0.8:0.3.

[0086] 2. Preparation of Magnesium Salt Nano-precipitation Sol

[0087] Deionized water, magnesium chloride, magnesium sulfate, basic magnesium carbonate, and a magnesium salt nano-microprecipitation sol additive were mixed and stirred at a speed of 500 r / min for 60 minutes. The solution was then placed in a sealed jar and kept in an oven at 120°C for 24 hours to obtain a magnesium salt nano-microprecipitation sol with a viscosity of 100 mPa·s.

[0088] The mass ratio of the deionized water, magnesium chloride, magnesium sulfate, and basic magnesium carbonate is 50:10:28:16;

[0089] The amount of the magnesium salt nano-micro precipitate sol additive added to the magnesium salt nano-micro precipitate sol is 6wt%;

[0090] The magnesium salt nano-microprecipitation sol additive is a mixture of polyvinyl pyrrolidone, methyl cellulose and oxalic acid;

[0091] The mass ratio of the polyvinyl pyrrolidone, methyl cellulose and oxalic acid is 3:1.4:2.6.

[0092] 3. Spray granulation

[0093] Deionized water, modified aluminum nitride powder and magnesium salt nano-microprecipitation sol were mixed, and then ultrasonic dispersion was performed, with the ultrasonic time controlled at 30 minutes and the ultrasonic frequency at 40 kHz. After the ultrasonication, the mixture was stirred at room temperature at a speed of 800 r / min for 1.0 hour to obtain a slurry to be sprayed; the slurry to be sprayed was sprayed and granulated through a spray tower, with the inlet temperature controlled at 220° C., the outlet temperature controlled at 100° C., the atomization pressure controlled at 1.5 MPa, the centrifugal disk speed controlled at 20,000 r / min, the nozzle aperture controlled at 0.8 mm, and the feed rate controlled at 10 mL / min to obtain spherical powder.

[0094] The mass ratio of the deionized water, the modified aluminum nitride powder, and the magnesium salt nano-microprecipitation sol is 45:30:26.

[0095] 4. Calcination

[0096] 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 warm for 30 minutes, then the temperature was increased to 1500°C at a rate of 10.0°C / min, kept warm for 3.0 hours, to obtain magnesium oxide-coated aluminum nitride high thermal conductivity spherical powder.

[0097] 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 accompanying figure of the specification. Figure 1 ;

[0098] The SEM image of the magnesium oxide coated aluminum nitride high thermal conductivity spherical powder obtained in Example 3 at 150 times magnification is shown in the accompanying figure of the specification. Figure 2 .

[0099] 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 immersion in 4 times the mass of deionized water at 80°C for 72 hours, the mass loss rate is 0.22%; after heat treatment at 1400°C for 25 hours in an air atmosphere, the mass change rate is 0.37%.

[0100] Comparative Example

[0101] Based on Example 3, the following changes are made:

[0102] 1. In the step of preparing modified aluminum nitride powder, the modified aluminum nitride powder additive is replaced with aluminum nitride in equal amounts;

[0103] 2. In the step of preparing the magnesium salt nano-micro-precipitation sol, the magnesium salt nano-micro-precipitation sol additive is replaced with magnesium chloride in equal amounts;

[0104] The remaining operations are exactly the same as those in Example 3.

[0105] 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 immersion in 4 times the mass of deionized water at 80°C for 72 hours, the mass loss rate is 1.45%; after heat treatment at 1400°C for 25 hours in an air atmosphere, the mass change rate is 3.68%.

[0106] In the comparative example, the modified aluminum nitride powder additive was replaced with aluminum nitride during the preparation process, and the surface functionalization treatment was missing, resulting in the inability to form a dense protective layer on the aluminum nitride surface. After contact with water, a hydrolysis reaction occurred to generate aluminum hydroxide and ammonia. The interface compatibility between aluminum nitride and yttrium oxide and lanthanum oxide dispersants was poor, resulting in agglomeration. After the magnesium salt nano-microprecipitation sol was replaced with magnesium chloride, the magnesium ions were only coated by physical adsorption, lacking the chemical bonding effect of the sol-gel method. The density and coverage of the coating layer were reduced, and the agglomeration defects of the aluminum nitride powder could not be effectively repaired, resulting in a decrease in sphericity, which ultimately affected the product's hydrolysis resistance and thermal conductivity, and weakened its high-temperature stability.

[0107] Unless otherwise specified, all ratios and percentages described in the present invention are by mass.

[0108] 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, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or 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 scope of protection 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-microprecipitation sol, spray granulation and calcination; The step of preparing the modified aluminum nitride powder comprises ball milling aluminum nitride, anhydrous ethanol, yttrium oxide, lanthanum oxide and modified aluminum nitride powder additives, and washing and drying to obtain the modified aluminum nitride powder; The modified aluminum nitride powder additive is a mixture of phosphoric acid, aluminum dihydrogen phosphate, γ-aminopropyltriethoxysilane, 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 the mixture, and then place the mixture in a sealed tank and keep the mixture warm at 115-126° C. to obtain a magnesium salt nano-micro precipitate sol having a viscosity of 80-120 mPa·s; The magnesium salt nano-microprecipitation sol additive is a mixture of polyvinyl pyrrolidone, methyl cellulose and oxalic acid; The spray granulation step comprises: mixing deionized water, modified aluminum nitride powder and magnesium salt nano-microprecipitation sol, and then performing ultrasonic dispersion; after the ultrasonic dispersion is completed, stirring at room temperature for 1.0-1.3 hours to obtain a slurry to be sprayed; and spraying the slurry to be sprayed through a spray tower to obtain spherical powder; The calcination step comprises calcining the spherical powder in an argon atmosphere and keeping the temperature at 1450-1550° C. for 2.8-3.4 hours to obtain magnesium oxide-coated aluminum nitride high thermal conductivity spherical powder.

2. The method for preparing a magnesium oxide-coated aluminum nitride high thermal conductivity spherical powder according to claim 1, characterized in that: The modified aluminum nitride powder is prepared by placing aluminum nitride, anhydrous ethanol, yttrium oxide, lanthanum oxide and an additive for modified aluminum nitride powder into a ball mill, using zirconium oxide balls with a diameter of 2.5-3.5 mm and a ball-to-material ratio of 2-5:1, ball milling at a speed of 280-320 r / min for 9.5-10.5 hours, washing the milled slurry with anhydrous ethanol, centrifuging it in a centrifuge after washing, and then placing the centrifuged material in an oven and drying it 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 10-30 wt% of the mass of the 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 admixture, the mass ratio of the phosphoric acid, aluminum dihydrogen phosphate, γ-aminopropyltriethoxysilane, 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 precipitate sol additive added to the magnesium salt nano-micro precipitate sol is 3-10 wt %.

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: In the spray granulation step, the mass ratio of the deionized water, the modified aluminum nitride powder, and the magnesium salt nano-microprecipitation sol is 30-60:20-40:20-30.

8. A magnesium oxide-coated aluminum nitride high thermal conductivity spherical powder, prepared by the preparation method according to any one of claims 1 to 7.

Images