A method for preparing spherical aluminum nitride powder

Abstract

This application relates to the field of ceramic powder processing, specifically disclosing a method for preparing spherical aluminum nitride powder, comprising the following steps: S1, dissolving a water-soluble organic carbon source in water by stirring to obtain a mixed solution; then adding alumina, mixing and stirring evenly, with the mass ratio of the water-soluble organic carbon source to alumina being 1:1-2, to obtain a reaction precursor; S2, subjecting the reaction precursor to spray drying and dry pressing to obtain a block; S3, subjecting the block to degreasing, carbonization, and nitriding reduction treatments to obtain a semi-finished product; S4, subjecting the semi-finished product to decarbonization, cooling, and pulverization to obtain the finished aluminum nitride powder; which has the advantages of high sphericity, high purity, and good thermal conductivity.

Description

Technical Field

[0001] This application relates to the field of ceramic powder processing, and more specifically, it relates to a method for preparing spherical aluminum nitride powder. Background Technology

[0002] Aluminum nitride powder has high purity, small particle size, and high activity, making it the main raw material for manufacturing high thermal conductivity aluminum nitride ceramic substrates.

[0003] Aluminum nitride ceramic substrates need to have advantages such as high thermal conductivity, low coefficient of expansion, high strength, high temperature resistance, chemical corrosion resistance, high resistivity, and low dielectric loss. Therefore, aluminum nitride powder needs to have high sphericity and high purity to ensure that the aluminum nitride ceramic substrate has advantages such as high thermal conductivity, good heat resistance, corrosion resistance, and low coefficient of expansion.

[0004] In existing technologies, the production method of spherical aluminum nitride powder is generally as follows: high-purity aluminum nitride powder is ball-milled together with sintering aids, resin dispersants, solvents, etc., and then spray-granulated to form spherical aluminum nitride particles (D50: 20-200 micrometers). The particles are then passed through a high-temperature degreasing furnace to remove organic resin, and then the degreased spherical particles are sintered at high temperature to form spherical ceramic particles. These particles contain aluminum nitride grains and liquid-phase sintering aids, and strictly speaking, they are polycrystalline compounds of aluminum nitride, which affects the purity of aluminum nitride and thus affects the thermal conductivity of aluminum nitride powder.

[0005] Therefore, the question is how to prepare an aluminum nitride powder with high sphericity and high purity, which also has the advantage of good thermal conductivity. Summary of the Invention

[0006] In order to prepare an aluminum nitride powder with high sphericity and high purity, and to give it the advantage of thermal conductivity, this application provides a method for preparing spherical aluminum nitride powder.

[0007] This application provides a method for preparing spherical aluminum nitride powder, which adopts the following technical solution:

[0008] A method for preparing spherical aluminum nitride powder includes the following steps:

[0009] S1. Dissolve the water-soluble organic carbon source in water by stirring to obtain a mixed solution; then add alumina, mix and stir evenly, the mass ratio of water-soluble organic carbon source to alumina is 1:1-2, to obtain the reaction precursor;

[0010] S2. The reaction precursor is spray-dried and dry-pressed to obtain a bulk product;

[0011] S3. The block is subjected to degreasing, carbonization, and nitriding reduction treatment to obtain a semi-finished product;

[0012] S4. After decarbonization, cooling, and pulverization, the semi-finished product is obtained as finished aluminum nitride powder.

[0013] By adopting the above technical solution, the water-soluble organic carbon source is stirred and dispersed in water, allowing the water-soluble organic carbon source to dissolve directly. After adding alumina, it can be ensured that the alumina is uniformly dispersed in the mixed solution, increasing the contact area and contact uniformity between the organic carbon source and alumina, so that the organic carbon source is uniformly bonded to the surface of alumina. This not only promotes the reaction formation of aluminum nitride, but also improves the sphericity of aluminum nitride. After spray drying to remove moisture, combined with dry pressing, the block structure is relatively stable, with microporous channels to ensure the flow and transfer of nitrogen and oxygen, promoting the reaction formation of aluminum nitride and facilitating the removal of residual carbon in aluminum nitride. At the same time, it can also discharge excess gas during the carbonization process to the semi-finished product, ensuring the purity and sphericity of the aluminum nitride powder, thereby giving aluminum nitride high thermal conductivity.

[0014] Preferably, the water-soluble organic carbon source is composed of sucrose ester, citric acid and low-viscosity white oil in a mass ratio of 1:2.5-6:0.5-1.

[0015] By adopting the above technical solution, sucrose ester, citric acid, and low-viscosity white oil are combined. First, citric acid dissolves in water, and its viscosity does not easily increase after dissolving in water. Alumina utilizes its surface hydroxyl groups to crosslink with the carboxyl groups in the citric acid aqueous solution, so that the alumina is uniformly dispersed in the citric acid aqueous solution while the citric acid is uniformly attached to the alumina surface. Utilizing the hydrophilic and lipophilic properties of sucrose ester, the citric acid and low-viscosity white oil on the alumina surface are connected, allowing the sucrose ester and low-viscosity white oil to disperse on the alumina surface. The dispersion effect of sucrose ester and low-viscosity white oil improves the dispersion uniformity of alumina in the mixed solution and prevents the alumina powder from agglomerating and sticking in the mixed solution.

[0016] As carbonization proceeds, citric acid, sucrose esters, and low-viscosity white oil on the alumina surface are gradually carbonized, producing carbon. The cross-linked network channels formed by citric acid, sucrose esters, and low-viscosity white oil facilitate the discharge of excess gas during carbonization. Furthermore, the resulting microporous channels ensure the injection of nitrogen during the nitriding reduction process, thereby promoting the formation of aluminum nitride. Combined with the uniform contact of carbon source materials around the alumina surface, this improves the sphericity of aluminum nitride. If alumina powder agglomeration occurs, the contacting alumina particles will not come into contact with nitrogen, thus affecting the formation of aluminum nitride at the contact points and consequently impacting the sphericity of the aluminum nitride powder.

[0017] Preferably, in step S1, citric acid is dissolved in water by stirring, then alumina powder is added, and after mixing and stirring evenly, sucrose ester is added and mixing and stirring are continued. Then, the temperature is raised to 60-70℃, and low-viscosity white oil is added and mixed and stirred evenly to obtain the reaction precursor.

[0018] By adopting the above technical solution, citric acid is first dissolved in water, and then alumina is dispersed in the citric acid solution, so that citric acid is uniformly attached to the surface of the alumina. The carbon generated by the carbonization of citric acid promotes the formation of aluminum nitride. Then, sucrose ester is added and heated to dissolve the sucrose ester. Finally, low-viscosity white oil is added. The emulsifying and dispersing effect of sucrose ester is used to bind the alumina and low-viscosity white oil together. The low-viscosity white oil has a good dispersing effect, so that the alumina is not prone to agglomeration in the viscous sucrose ester solution. This ensures the dispersion effect of alumina while ensuring the bonding stability of the block. The uniformly dispersed alumina can be uniformly carbonized and nitrided on the surface, so that the finished aluminum nitride has good sphericity.

[0019] Preferably, the sucrose ester is made from high-fat pectin, sucrose ester microparticles, and polyethylene glycol solution in a mass ratio of 1:1-2:0.5-1.

[0020] By adopting the above technical solution, high-fat pectin, sucrose ester, and polyethylene glycol solution are combined. The adhesive effect of polyethylene glycol solution facilitates the bonding of high-fat pectin and sucrose ester. During the pressing process, the high-fat pectin is flexible and can be deformed by extrusion, which improves the structural density of the block. During carbonization and nitriding, the high-fat pectin can be carbonized, and the generation of micropores can ensure gas flow, thereby ensuring the formation of silicon nitride. The extrusion of high-fat pectin can reduce the size of micropores. If the pore size is high, the aluminum nitride will have a higher contact degree with carbon on one side and a lower contact degree on the other side, which can easily lead to poor sphericity in the finished aluminum nitride.

[0021] Preferably, the low-viscosity white oil is made from nitrogen-doped graphene and low-viscosity white oil in a mass ratio of 1:1-2.

[0022] By adopting the above technical solution, nitrogen-doped graphene and low-viscosity white oil are combined. The low-viscosity white oil on the surface of nitrogen-doped graphene can make nitrogen-doped graphene adhere to the surface of alumina. The pyridine nitrogen on the outer surface of nitrogen-doped graphene can intercalate and overlap with the carbon of the carbonization product. Combined with the porous structure of nitrogen-doped graphene, it is convenient for nitrogen to react with alumina and carbon. At the same time, pyridine nitrogen can catalyze the nitridation reduction reaction, thereby further promoting the formation of aluminum nitride and reducing the impurity content in aluminum nitride.

[0023] Preferably, the spray drying temperature is 100-200℃.

[0024] By adopting the above technical solution, the spray drying temperature is limited, ensuring that moisture is removed while maintaining the particle size of the product, so that the finished aluminum nitride has good sphericity.

[0025] Preferably, the degreasing and carbonization temperature is 600-1000℃, the time is 5-15h, and the heating rate is 2-5℃ / min.

[0026] By adopting the above technical solution, the temperature, time and heating rate of degreasing and carbonization are limited, so that the material on the outer surface of the block is carbonized first, creating gas flow channels, while the material near the center of the block is gradually carbonized. The gas generated by carbonization flows out with the gas flow channels on the outer surface, ensuring the micropore connectivity effect and reducing the size of the micropores inside the semi-finished product. This ensures that there is an equal amount of carbon around the alumina, thereby giving the finished aluminum nitride a high degree of sphericity.

[0027] Preferably, the pressure of the dry pressing process is 30-45 MPa.

[0028] By adopting the above technical solutions, the molding effect of the block is guaranteed, and the structural density is ensured. During the carbonization and nitriding process, interconnected micropores are generated to ensure gas flow while avoiding excessively large pores, thus giving the finished silicon nitride high sphericity and thermal conductivity.

[0029] Preferably, the specific steps of the nitridation reduction treatment are as follows:

[0030] The temperature for the first nitriding reaction is 1300-1400℃, and the reaction time is 2-4 hours. The temperature for the second nitriding reaction is 1400-1650℃, and the reaction time is 5-10 hours.

[0031] By adopting the above technical solutions, the sphericity and thermal conductivity of aluminum nitride can be improved.

[0032] Preferably, the specific steps of the carbon removal treatment are as follows:

[0033] The semi-finished product is soaked and dispersed in hydrogen peroxide, then pressure treated for 2-5 minutes under a pressure of 0.2-0.6 MPa, heated to 100-150℃ at a heating rate of 1-3℃ / min and treated for 20-60 minutes, and then heated to 600-800℃ and treated for 2-12 hours.

[0034] By adopting the above technical solution, the permeation effect of hydrogen peroxide during the soaking process, combined with pressurization, allows hydrogen peroxide to easily penetrate into the interior of the semi-finished product. Since the micropores inside the semi-finished product are interconnected, the permeation effect of hydrogen peroxide is achieved throughout the semi-finished product, thus ensuring that the hydrogen peroxide is evenly distributed within it. As the temperature rises, the hydrogen peroxide decomposes to produce oxygen, allowing the carbon in the semi-finished product to come into uniform contact with the oxygen, improving the carbon removal effect and thereby increasing the purity of aluminum nitride.

[0035] In summary, this application has the following beneficial effects:

[0036] 1. Water-soluble organic carbon sources are dispersed in water by stirring, allowing the water-soluble organic carbon sources to dissolve directly. The addition of alumina ensures that the alumina is uniformly dispersed in the aqueous solution of the organic carbon sources, increasing the contact area and uniformity between the organic carbon sources and alumina. This allows the organic carbon sources to adhere evenly to the surface of the alumina, facilitating the formation of aluminum nitride and improving the sphericity of the aluminum nitride. After spray drying to remove moisture and dry pressing, the bulk structure is relatively stable, with micropores for the flow and transfer of nitrogen and oxygen, ensuring the formation of aluminum nitride and the removal of excess carbon. It also facilitates the discharge of excess gas from the semi-finished product during carbonization, ensuring the purity and sphericity of the aluminum nitride powder, thus giving aluminum nitride high thermal conductivity.

[0037] 2. First, citric acid is added to ensure uniform dispersion of alumina. Then, sucrose ester and low-viscosity white oil are added, along with heating. This allows for a more stable adhesion of water-soluble organic carbon source materials to the alumina surface, while preventing alumina agglomeration. During the pressing process, the uniform adhesion of sucrose ester and low-viscosity white oil to alumina improves the molding stability of the block, making it less prone to disintegration and breakage during sintering. This results in higher purity and sphericity of aluminum nitride, thus giving it the advantage of high thermal conductivity.

[0038] 3. Citric acid, sucrose esters and low-viscosity white oil are combined to form a cross-linked network inside the block, ensuring the connectivity of the pores. During carbonization and nitriding, the interconnected micropores facilitate the discharge and injection of gas, thereby ensuring the formation of aluminum nitride and giving the finished aluminum nitride high sphericity and thermal conductivity. Detailed Implementation

[0039] The present application will be further described in detail below with reference to the embodiments.

[0040] Example of sucrose ester preparation: High-fat pectin in the following raw materials was purchased from Guangzhou Tianjia Biotechnology Co., Ltd.; sucrose ester microparticles were purchased from Hefei Shengrun Biological Products Co., Ltd.; other raw materials were commercially available.

[0041] Preparation Example 1: Sucrose esters were prepared by the following method:

[0042] 0.7 kg of polyethylene glycol solution was uniformly sprayed onto the surface of 1 kg of high-fat pectin, and then 1.5 kg of sucrose ester microparticles were added. After drying and dispersion, the finished sucrose ester was obtained with an average particle size of 10 μm. The high-fat pectin had an average particle size of 3 μm. The polyethylene glycol solution was a 2% (w / w) aqueous solution of polyethylene glycol, and the polyethylene glycol was polyethylene glycol 8000. The sucrose ester microparticles had an average particle size of 4 μm.

[0043] Preparation Example 2: The difference between this preparation example and Preparation Example 1 is that:

[0044] 0.5 kg of polyethylene glycol solution was evenly sprayed onto the surface of 1 kg of high-fat pectin, and then 1 kg of sucrose ester microparticles were added. After drying and dispersion, the finished sucrose ester was obtained.

[0045] Preparation Example 3: The difference between this preparation example and Preparation Example 1 is that:

[0046] 1 kg of polyethylene glycol solution was evenly sprayed onto the surface of 1 kg of high-fat pectin, and then 2 kg of sucrose ester microparticles were added. After drying and dispersion, the finished sucrose ester was obtained.

[0047] Example of preparation of low viscosity white oil

[0048] All of the following ingredients are commercially available.

[0049] Preparation Example 4: Low-viscosity white oil was prepared by the following method:

[0050] Flake graphite was dispersed in water at a mass ratio of 1:9 and stirred at 3000 r / min for 30 min. The mixture was then homogenized in a high-pressure homogenizer for 60 min and freeze-dried for 24 h to obtain graphene. 100 mg of graphene was ultrasonically dispersed in 20 mL of water at 20 kHz for 10 min to obtain a graphene solution. 40 mg of melamine was placed in 20 mL of water, heated to 65 °C, and stirred until the melamine was completely dissolved to obtain a melamine solution. The graphene solution and melamine solution were mixed and stirred, then vacuum-sealed and reacted at 130 °C for 24 h. After cooling to room temperature and filtration, when the pH of the composite solution was neutral, it was placed in a drying oven and dried at 65 °C for 18 h to obtain nitrogen-doped graphene with an average particle size of 3 μm. The nitrogen content of the nitrogen-doped graphene was 6.25%, of which the pyridine nitrogen content was 2.85%.

[0051] Weigh 1 kg of nitrogen-doped graphene and 1.5 kg of low-viscosity white oil, mix and stir evenly to obtain low-viscosity white oil; the viscosity of the low-viscosity white oil is 8 mm. 2 / s.

[0052] Preparation Example 5: The difference between this preparation example and Preparation Example 4 is that:

[0053] Weigh 1 kg of nitrogen-doped graphene and 1 kg of low-viscosity white oil, mix and stir evenly to obtain low-viscosity white oil.

[0054] Preparation Example 6: The difference between this preparation example and Preparation Example 4 is that:

[0055] Weigh 1 kg of nitrogen-doped graphene and 2 kg of low-viscosity white oil, mix and stir evenly to obtain low-viscosity white oil.

[0056] Example

[0057] All of the following ingredients are commercially available.

[0058] Example 1: A method for preparing spherical aluminum nitride powder:

[0059] S1. 4.3 kg of citric acid was placed in 100 kg of water and stirred until the citric acid was completely dissolved to obtain a citric acid solution. Then, 9 kg of alumina with a sphericity of 85%-88% was added at a rate of 120 g / min. During the addition process, the citric acid solution was stirred at a rate of 200 r / min. After mixing and stirring evenly, 1 kg of sucrose ester prepared in Preparation Example 1 was added and the mixture was stirred evenly at a rate of 120 g / min. Then, the temperature was raised to 65°C and stirred for 10 min. Finally, 0.7 kg of low-viscosity white oil prepared in Preparation Example 4 was added and stirred evenly to obtain the reaction precursor.

[0060] S2. The reaction precursor was spray-dried at 120°C and then dry-pressed at 35 MPa for 30 min to obtain a bulk material.

[0061] S3. The block is degreased and carbonized at 800℃ for 10 hours, with a heating rate of 3℃ / min. Then it undergoes nitriding reduction treatment, with the first nitriding reaction at 1350℃ for 3 hours and the second nitriding reaction at 1450℃ for 8 hours, yielding a semi-finished product. The nitriding reaction gas volume is 10m³. 3 / h;

[0062] S4. The semi-finished product is soaked and dispersed in hydrogen peroxide, then pressure treated for 3 minutes under a pressure of 0.5 MPa, heated to 130℃ at a heating rate of 2℃ / min and treated for 40 minutes, then heated to 750℃ and treated for 3 hours. After decarbonization, it is cooled and pulverized to obtain the finished aluminum nitride powder. The finished product has an oxygen content of ≤1.0%, a nitrogen content of ≤500ppm, and a D50 of 10μm.

[0063] Example 2: The difference between this example and Example 1 is that:

[0064] S1. 2.5 kg of citric acid was placed in 100 kg of water and stirred until the citric acid was completely dissolved to obtain a citric acid solution. Then, 4 kg of alumina was added at a rate of 120 g / min. During the addition process, the citric acid solution was stirred at a rate of 200 r / min. After mixing and stirring evenly, 1 kg of sucrose ester prepared in Preparation Example 2 was added and the mixture was stirred evenly at a rate of 120 g / min. Then, the temperature was raised to 60 °C and stirred for 10 min. Finally, 0.5 kg of low-viscosity white oil prepared in Preparation Example 5 was added and the mixture was stirred evenly to obtain the reaction precursor.

[0065] S2. The reaction precursor was spray-dried at 100°C and then dry-pressed at 30 MPa for 40 min to obtain a bulk material.

[0066] S3. The block is degreased and carbonized at 600℃ for 15 hours, with a heating rate of 2℃ / min. Then it undergoes nitriding reduction treatment, with the first nitriding reaction at 1300℃ for 4 hours and the second nitriding reaction at 1400℃ for 4 hours, yielding a semi-finished product. The nitriding reaction gas volume is 10m³. 3 / h;

[0067] S4. The semi-finished product is soaked and dispersed in hydrogen peroxide, then pressurized at 0.2 MPa for 5 min, heated to 100℃ at a rate of 1℃ / min for 60 min, and then heated to 600℃ for 12 h. After decarbonization, it is cooled and pulverized to obtain the finished aluminum nitride powder.

[0068] Example 3: The difference between this example and Example 1 is that:

[0069] S1. 6 kg of citric acid was placed in 120 kg of water and stirred until the citric acid was completely dissolved to obtain a citric acid solution. Then, 16 kg of alumina was added at a rate of 120 g / min. During the addition process, the citric acid solution was stirred at a rate of 200 r / min. After mixing and stirring evenly, 1 kg of sucrose ester prepared in Preparation Example 3 was added and the mixture was stirred evenly at a rate of 120 g / min. Then, the temperature was raised to 70 °C and stirred for 10 min. Finally, 1 kg of low-viscosity white oil prepared in Preparation Example 6 was added and the mixture was stirred evenly to obtain the reaction precursor.

[0070] S2. The reaction precursor was spray-dried at 200℃ and then dry-pressed at 45MPa for 20min to obtain a bulk material.

[0071] S3. The block is degreased and carbonized at 1000℃ for 5 hours, with a heating rate of 5℃ / min. Then it undergoes nitriding reduction treatment, with the first nitriding reaction at 1400℃ for 2 hours and the second nitriding reaction at 1650℃ for 5 hours, yielding a semi-finished product. The nitriding reaction gas volume is 10m³. 3 / h;

[0072] S4. The semi-finished product is soaked and dispersed in hydrogen peroxide, then pressurized at 0.6 MPa for 2 minutes, heated to 150°C at a rate of 3°C / min for 20 minutes, and then heated to 800°C for 2 hours. After decarbonization, it is cooled and pulverized to obtain the finished aluminum nitride powder.

[0073] Example 4: The difference between this example and Example 1 is that:

[0074] S1. Place 6 kg of citric acid in 100 kg of water and stir until the citric acid is completely dissolved to obtain a citric acid solution; then add 9 kg of alumina at a rate of 120 g / min. During the addition process, the citric acid solution is stirred at a rate of 200 r / min; after mixing and stirring evenly, the reaction precursor is obtained.

[0075] Example 5: The difference between this example and Example 1 is that:

[0076] No low-viscosity white oil was added to the water-soluble organic carbon source.

[0077] Example 6: The difference between this example and Example 1 is that:

[0078] S1. Place 4.3 kg of citric acid, 1 kg of sucrose ester and 0.7 kg of low-viscosity white oil in 100 kg of water, heat to 65 °C and stir until completely dissolved; then add 9 kg of alumina at a rate of 120 g / min and stir at 200 r / min during the addition process to obtain the reaction precursor.

[0079] Example 7: The difference between this example and Example 1 is that:

[0080] No high-fat pectin or polyethylene glycol solution was added during the preparation of sucrose ester.

[0081] Example 8: The difference between this example and Example 1 is that:

[0082] No nitrogen-doped graphene was added during the preparation of the low-viscosity white oil.

[0083] Example 9: The difference between this example and Example 1 is that:

[0084] S4. The semi-finished product is treated at 750℃ for 3 hours to remove carbon. After cooling and crushing, the finished aluminum nitride powder is obtained.

[0085] Comparative Example

[0086] Comparative Example 1: The difference between this comparative example and Example 1 is that:

[0087] 0.5 kg of phenolic resin and 10 kg of ethanol were mixed and stirred until the phenolic resin was completely dissolved to obtain a resin solution. 1 kg of graphite, 1 kg of alumina and 0.5 kg of resin solution were mixed and spheroidized for 2 h to obtain a precursor. Then, the precursor was carbonized at 700 °C, nitrided at 1400 °C for 8 h, and then decarbonized at 800 °C to obtain the finished product.

[0088] Performance testing

[0089] 1. Sphericity testing

[0090] Aluminum nitride powder was prepared using the methods described in Examples 1-8 and Comparative Example 1, respectively. The sphericity of the aluminum nitride powder was observed using scanning electron microscopy, and the average sphericity data was recorded.

[0091] 2. Purity testing

[0092] Aluminum nitride powder was prepared using the methods of Examples 1-9 and Comparative Example 1, and its purity was tested and the data were recorded.

[0093] 3 Thermal conductivity test

[0094] Finished aluminum nitride powders were prepared using the preparation methods of Examples 1-8 and Comparative Example 1, respectively. The thermal conductivity was tested and recorded using a laser thermal conductivity meter.

[0095] Table 1 Performance Test Table (In the table, " / " indicates that there is no data for the corresponding embodiment)

[0096]

[0097] As can be seen from Examples 1-3 and Table 1, the aluminum nitride powder prepared in this application has high sphericity, purity, and good thermal conductivity.

[0098] Combining Examples 1 and 4-9 with Table 1, it can be seen that the water-soluble organic carbon source in Example 4 is citric acid. Compared with Example 1, the aluminum nitride powder prepared in Example 4 has lower sphericity, lower purity, and worse thermal conductivity than that in Example 1. This indicates that although citric acid can carbonize to form aluminum nitride, the hydrophilic groups on the surface of alumina are prone to particle aggregation in citric acid solution, affecting the uniform contact between alumina and the carbon source, thus affecting the sphericity of aluminum nitride. Furthermore, the alumina aggregated in the bulk does not easily form uniform micro-gap channels, affecting the contact between nitrogen, oxygen, alumina, and carbon, thereby affecting the purity of aluminum nitride and impacting the thermal conductivity of the finished alumina.

[0099] In Example 5, no low-viscosity white oil was added to the water-soluble organic carbon source. Compared with Example 1, the sphericity, purity, and thermal conductivity of the aluminum nitride powder prepared in Example 5 were all lower than those in Example 1. This indicates that the addition of low-viscosity white oil can improve the dispersion uniformity of aluminum oxide. As aluminum oxide and carbon come into uniform contact during the carbonization process, the formation of aluminum nitride is guaranteed, and the sphericity is improved, thus giving aluminum nitride the advantage of high thermal conductivity.

[0100] In Example 6, citric acid, sucrose ester, and low-viscosity white oil were added together. Compared with Example 1, the aluminum nitride powder prepared in Example 6 had lower sphericity, purity, and thermal conductivity. This indicates that adding them together can easily affect the dispersion of alumina due to viscosity issues. Adding citric acid first ensures uniform dispersion of alumina, while adding sucrose ester and low-viscosity white oil then improves the uniformity of alumina dispersion, prevents agglomeration, and ensures uniform carbon adhesion on the alumina surface, thereby improving the sphericity, purity, and thermal conductivity of the aluminum nitride powder.

[0101] In Example 7, no high-fat pectin or polyethylene glycol solution was added during the preparation of sucrose ester. Compared to Example 1, the sphericity, purity, and thermal conductivity of the aluminum nitride powder prepared in Example 7 were all lower than those in Example 1. This indicates that during the pressing process, high-fat pectin has flexibility and can be deformed by extrusion, increasing the structural density of the bulk. During carbonization and nitriding, high-fat pectin can carbonize, and the generation of micropores can ensure gas flow, thereby ensuring the formation of silicon nitride. While ensuring the existence of micropores, the size of the micropores is reduced. Uniform contact between carbon and alumina promotes the formation of spherical alumina. If the pore size is high, the contact degree between aluminum nitride and carbon will be higher on one side and lower on the other side, which can easily lead to poor sphericity in the finished aluminum nitride.

[0102] In Example 8, no nitrogen-doped graphene was added during the preparation of the low-viscosity white oil. Compared with Example 1, the sphericity, purity, and thermal conductivity of the aluminum nitride powder prepared in Example 8 were all lower than those in Example 1. This indicates that the pyridine nitrogen on the outer surface of nitrogen-doped graphene can intercalate and overlap with the carbon in the carbonization product. Combined with the porous structure of nitrogen-doped graphene, it facilitates the reaction of nitrogen with alumina and carbon. At the same time, pyridine nitrogen can catalyze the nitride reduction reaction, thereby further promoting the formation of aluminum nitride, reducing the impurity content in aluminum nitride, and improving the sphericity, purity, and thermal conductivity of aluminum nitride powder.

[0103] In Example 9, no hydrogen peroxide was added during the decarbonization process. Compared to Example 1, the purity of the aluminum nitride powder prepared in Example 9 was lower than that in Example 1. This indicates that the hydrogen peroxide penetration effect is achieved in the semi-finished product, thereby making the hydrogen peroxide evenly distributed in the semi-finished product. As the temperature is increased, the hydrogen peroxide decomposes to produce oxygen, which allows the carbon in the semi-finished product to come into uniform contact with oxygen, improving the decarbonization effect and giving the aluminum nitride a higher purity.

[0104] Combining Example 1 and Comparative Example 1 with Table 1, it can be seen that the sphericity, purity, and thermal conductivity of the aluminum nitride powder prepared in Comparative Example 1 are all lower than those in Example 1. This indicates that although the resin binder can ensure the bonding between graphite and alumina, it affects the dispersion uniformity of alumina and graphite, and also affects the carbonization and nitriding reactions. At the same time, it is easy for residual polycrystalline compounds of aluminum nitride to appear, affecting the purity, sphericity, and thermal conductivity of aluminum nitride.

[0105] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing spherical aluminum nitride powder, characterized in that, Includes the following steps: S1. Dissolve the water-soluble organic carbon source in water by stirring to obtain a mixed solution; then add alumina and mix thoroughly. The mass ratio of the water-soluble organic carbon source to alumina is 1:1-2 to obtain the reaction precursor. The water-soluble organic carbon source is composed of sucrose ester, citric acid, and low-viscosity white oil in a mass ratio of 1:2.5-6:0.5-1. The sucrose ester is made from high-fat pectin, sucrose ester microparticles, and polyethylene glycol solution in a mass ratio of 1:1-2:0.5-1. The low-viscosity white oil is made from nitrogen-doped graphene and low-viscosity white oil in a mass ratio of 1:1-2. S2. The reaction precursor is spray-dried and dry-pressed to obtain a bulk product; S3. The block is subjected to degreasing, carbonization, and nitriding reduction treatment to obtain a semi-finished product; S4. After decarbonization, cooling, and pulverization, the semi-finished product is obtained as finished aluminum nitride powder.

2. The method for preparing spherical aluminum nitride powder according to claim 1, characterized in that, S1. Dissolve citric acid in water by stirring, then add alumina powder, mix and stir evenly, then add sucrose ester and continue mixing and stirring. Then heat to 60-70℃, add low viscosity white oil and mix and stir evenly to obtain the reaction precursor.

3. The method for preparing spherical aluminum nitride powder according to claim 1, characterized in that, The spray drying temperature is 100-200℃.

4. The method for preparing spherical aluminum nitride powder according to claim 1, characterized in that, The degreasing and carbonization process is carried out at a temperature of 600-1000℃ for 5-15 hours, with a heating rate of 2-5℃ / min.

5. The method for preparing spherical aluminum nitride powder according to claim 1, characterized in that, The pressure for the dry pressing process is 30-45 MPa.

6. The method for preparing spherical aluminum nitride powder according to claim 1, characterized in that, The specific steps of the nitridation reduction treatment are as follows: The temperature for the first nitriding reaction is 1300-1400℃, and the reaction time is 2-4 hours. The temperature for the second nitriding reaction is 1400-1650℃, and the reaction time is 5-10 hours.

7. The method for preparing spherical aluminum nitride powder according to claim 1, characterized in that, The specific steps of the carbon removal process are as follows: The semi-finished product is soaked and dispersed in hydrogen peroxide, then pressure treated for 2-5 minutes under a pressure of 0.2-0.6 MPa, heated to 100-150℃ at a heating rate of 1-3℃ / min for 20-60 minutes, and then heated to 600-800℃ for 2-12 hours.

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