A method for preparing self-propagating synthesis of micro-sized aluminum nitride powder

Abstract

The application relates to the technical field of aluminum nitride synthesis, and provides a preparation method of self-propagating combustion synthesis micron-level aluminum nitride powder, which solves the problems of poor controllability, high impurity content, high energy consumption, high cost and coarse and uneven product crystal grains in the traditional aluminum nitride combustion synthesis process; the method comprises the following steps: S1, dosing: the first mixture, the second mixture and the third mixture are all composed of 30-35 parts by weight of mixed aluminum powder, 65-70 parts by weight of aluminum nitride powder and ammonium salt; S2, gradient dosing: the third mixture, the second mixture and the first mixture are sequentially layered and laid into a material frame; S3, combustion reaction: the material frame is placed into a high-pressure reaction kettle, and a current is introduced to trigger a self-propagating combustion synthesis reaction; and S4, post-treatment: after the reaction is completed, the initially prepared micron-level aluminum nitride powder is used as an aluminum nitride diluent, steps S1 to S4 are repeated, 6-8 times of iterative nitriding are carried out, and the self-propagating combustion synthesis micron-level aluminum nitride powder is obtained.

Description

Technical Field

[0001] This invention relates to the field of aluminum nitride synthesis technology, and in particular to a method for preparing micron-sized aluminum nitride powder through self-propagating combustion synthesis. Background Technology

[0002] AlN ceramics, with their superior mechanical, thermal, and dielectric properties, demonstrate immense potential for applications in numerous technological fields. Currently, aluminum nitride ceramics are widely used in the metallurgical industry, serving as key materials such as refractory bricks and crucibles for smelting pure iron, aluminum, and aluminum alloys. Simultaneously, with continuous innovation and breakthroughs in AlN powder synthesis technology and ceramic preparation processes, particularly the maturing development of aluminum nitride ceramic substrate casting technology, its application areas are continuously expanding into high-tech industries such as electronic packaging, semiconductor substrates, and high-frequency communications, indicating a very broad market prospect. As the core raw material for preparing aluminum nitride ceramics, high-purity, high-performance aluminum nitride powder is fundamental to driving its technological upgrades and industrial expansion.

[0003] Currently, the main methods for preparing aluminum nitride powder include carbothermal reduction, direct nitriding, and combustion synthesis. Carbothermal reduction uses Al₂O₃ powder as raw material, reducing and nitriding it with C powder at high temperature under a nitrogen atmosphere, followed by decarburization at 600℃-700℃ to obtain aluminum nitride powder. Direct nitriding involves placing Al powder in a mixed gas stream of nitrogen and ammonia, and directly nitriding it at high temperature to generate aluminum nitride powder. While these two methods are technologically mature, they generally suffer from long reaction cycles, high energy consumption, low efficiency, and high costs, necessitating technological improvements to enhance their economic viability.

[0004] Most of the publicly available patents related to the gas-phase synthesis of aluminum nitride focus on the preparation of aluminum nitride thin films, while the publicly available patents related to the combustion synthesis of aluminum nitride all have some limitations.

[0005] Chinese Patent Publication No. CN121085227A discloses a method for preparing silicon nitride and aluminum nitride powders, comprising: mixing aluminum powder and aluminum nitride raw powder to obtain a first mixture; mixing silicon powder, silicon nitride raw powder, and ammonium salt to obtain a second mixture; spreading the first and second mixtures in a material frame lined with carbon felt, and using the carbon felt to separate the first and second mixtures; placing the material frame in a self-propagating reactor, evacuating it, and then introducing nitrogen gas to ignite the first mixture to induce a combustion synthesis reaction in the second mixture; after the combustion synthesis reaction, cooling to room temperature, releasing the pressure in the self-propagating reactor, removing the synthesized product, and grinding the synthesized product to obtain silicon nitride powder and aluminum nitride powder. This disclosure can improve the purity of powder materials. However, this method requires maintaining a high nitrogen pressure (4-6 MPa), resulting in correspondingly high energy consumption and cost; and the simultaneous synthesis of two powders may lead to cross-contamination, such as silicon potentially diffusing into aluminum nitride, which is not conducive to obtaining ultra-high purity single-component powders.

[0006] Chinese Patent Publication No. CN121321202A discloses a method for preparing high-purity aluminum nitride single crystal powder. The method involves mixing raw aluminum powder and aluminum nitride powder in a specific ratio, placing the mixture in a pressure sintering furnace, evacuating the furnace, introducing high-pressure argon gas, heating to a set temperature, and then introducing nitrogen gas to induce a combustion and explosion reaction. The mixture is then cooled to room temperature and crushed to obtain high-purity aluminum nitride single crystal powder with a D50 of 20-200 μm. This invention utilizes the rapid nitridation and combustion reaction of aluminum powder in high-temperature, high-pressure nitrogen gas to synthesize coarse-particle high-purity aluminum nitride single crystal powder. It features a simple process and low preparation cost, and the prepared high-purity aluminum nitride single crystal powder can be used as a high thermal conductivity filler for electronic packaging. However, the aluminum nitride powder prepared by this method suffers from uneven particle size; and the high-temperature, high-pressure combustion and explosion reaction has poor controllability and high energy consumption. Summary of the Invention

[0007] Therefore, in view of the above problems, the present invention provides a method for preparing micron-sized aluminum nitride powder by self-propagating combustion synthesis, which solves the problems of poor reaction controllability, high impurity content, high energy consumption, high cost and large and uneven product grains in the traditional aluminum nitride combustion synthesis process.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing micron-sized aluminum nitride powder synthesized by self-propagating combustion includes the following steps: S1. Ingredients: Prepare a first mixture, a second mixture, and a third mixture, each of which consists of 30-35 parts by weight of mixed aluminum powder, 65-70 parts by weight of aluminum nitride powder, and ammonium salt; the mixed aluminum powder is prepared by mixing fine aluminum powder with a particle size of 5-25 μm and coarse aluminum powder with a particle size of 25-80 μm in a mass ratio of (5-9):(1-5); the ratio of fine aluminum powder to coarse aluminum powder in the mixed aluminum powder of the first mixture, the second mixture, and the third mixture is different; S2, Gradient Fabrication: Carbon felt is laid at the bottom and around the material frame, and a layer of aluminum nitride diluent is laid on the surface of the carbon felt; the first mixture, the second mixture and the third mixture obtained in step S1 are vacuum dried respectively, and then laid into the material frame in the order of the third mixture, the second mixture and the first mixture. After each layer is laid, a loosening treatment is performed. After the three layers are laid, an ignition wire and an ignition agent are set at the end of the material frame and covered with carbon felt. S3. Combustion reaction: The layered material frame is placed into a high-pressure reactor, vacuumed, and then filled with nitrogen to a pressure of 1.0-2.0 MPa. An electric current is then applied to trigger the self-propagating combustion synthesis reaction. S4. Post-processing: After the reaction is completed, cool to room temperature, take out the product, crush and grind it to obtain the initial micron-sized aluminum nitride powder. Use the initial micron-sized aluminum nitride powder as an aluminum nitride diluent, repeat steps S1 to S4, and perform 6-8 iterative nitriding to obtain self-propagating synthetic micron-sized aluminum nitride powder.

[0009] The material employs a dual-gradient particle size-pore size distribution structure. Compared to previous single-ratio powder distribution methods, the gradually increasing pore density from the inside out promotes better contact between nitrogen and the internal reactants, allowing for complete reaction even with a high proportion of aluminum powder. The particle size gradient distribution also enables the use of aluminum powder with larger particle sizes without altering the performance of the synthesized product, reducing raw material costs compared to using aluminum powder with a single particle size.

[0010] The finished product is crushed using a two-roll mill. The initial micron-sized aluminum nitride powder is finely ground into micron-sized powder, which is then used as a diluent to repeat the S1 to S4 iterations approximately 6-8 times. Compared to the medium-high pressure nitrogen experimental environment (10MPa) required for the self-propagation synthesis of ammonium salts in traditional preparation methods, the nitrogen experimental environment of this technology is only 1.0-2.0MPa. Furthermore, the resulting structure is more porous and less dense than that of the self-propagation reaction without ammonium salts, resulting in higher purity, more uniform morphology, easier post-processing, and lower oxygen content. The micron-sized aluminum nitride powder obtained by this technology, after refinement, exhibits excellent particle size uniformity and high purity. Simultaneously, the process is simple, energy-efficient, rapid, and highly controllable, significantly reducing production costs and possessing industrial application value.

[0011] Furthermore, the self-propagating synthesized micron-sized aluminum nitride powder has an average particle size of 1.2μm-3μm, an oxygen content of <1.0ppm, and a purity of ≥99.5%.

[0012] Furthermore, the mass percentage of coarse aluminum powder in the mixed aluminum powder is as follows: the mass percentage of fine aluminum powder in the mixed aluminum powder is as follows: the proportion of fine aluminum powder in the mixed aluminum powder of the first mixture > the proportion of fine aluminum powder in the mixed aluminum powder of the second mixture > the proportion of fine aluminum powder in the mixed aluminum powder of the third mixture.

[0013] Furthermore, in step S1, the aluminum nitride powder undergoes a drying process, which is vacuum drying at 110°C for 1 hour; the ammonium salt is ammonium chloride, and its addition amount is 1%-6% of the total mass of the mixed aluminum powder and aluminum nitride powder.

[0014] Furthermore, in step S2, the loosening process involves inserting a long spoon handle along the depth direction of the material frame and performing longitudinal sweeping and lateral swinging.

[0015] Furthermore, in step S2, the vacuum drying conditions are: vacuum degree -0.5MPa to -0.1MPa, temperature 75℃ to 85℃, and time 60min to 90min.

[0016] Furthermore, in step S2, the ignition wire is a spiral tungsten wire, and the ignition agent is a mixture of aluminum powder and aluminum nitride in a molar ratio of 1:1.

[0017] Furthermore, in step S3, the current applied is 10A-20A, and the energizing time is 10s-15s.

[0018] By adopting the aforementioned technical solution, the beneficial effects of the present invention are as follows: 1. This technical solution uses mixed aluminum powder, aluminum nitride powder and ammonium salt as raw materials. The mixed aluminum powder is formed by mixing fine aluminum powder and coarse aluminum powder, which reduces costs compared with using aluminum powder of a single particle size as raw material. 2. After the self-propagating combustion synthesis reaction is completed, the initial micron-sized aluminum nitride powder is used as an aluminum nitride diluent. Steps S1 to S4 are repeated for 6-8 iterations of nitriding. The nitriding is more complete, and micron-sized aluminum nitride powder with better oxygen content is obtained. 3. Vacuum drying pretreatment of raw aluminum nitride powder effectively reduces the impurity content caused by water absorption in aluminum nitride powder; 4. Loosen the material during gradient feeding to ensure full contact between the raw material and nitrogen, and avoid insufficient nitrogen penetration due to rapid melting and agglomeration of aluminum powder, resulting in defects such as low nitrogen content, uneven composition, and severe agglomeration in the product powder. 5. The self-ignition synthesis method is simple, has a short production cycle, and low energy consumption. Except for a small amount of energy input required to start the combustion reaction, the synthesis process is maintained by the exothermic reaction system itself, which saves energy. The nitrogen pressure required for the reaction is extremely low, which can significantly reduce production costs. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the gradient fabric structure in Embodiment 1 of the present invention; Figure 2 This is a SEM image of the micron-sized aluminum nitride powder synthesized by self-propagation in Example 1 of the present invention; Figure 3 This is a graph showing the relationship between the number of AlN powder iterations and oxygen content in Example 1 of the present invention. Detailed Implementation Example 1

[0020] refer to Figures 1 to 3 A method for preparing micron-sized aluminum nitride powder through self-propagating combustion includes the following steps: S1. Ingredients: Prepare the first mixture, the second mixture, and the third mixture respectively; S1-1. Weigh 30 parts of mixed aluminum powder and 70 parts of aluminum nitride powder by weight, and add ammonium chloride at 4% of the total weight of the mixed aluminum powder and aluminum nitride powder. Mix them evenly to obtain the first mixture. The mixed aluminum powder is a mixture of fine aluminum powder with a particle size of 15μm and coarse aluminum powder with a particle size of 50μm, with a weight ratio of fine aluminum powder to coarse aluminum powder of 7:3. S1-2. Weigh 32.5 parts of mixed aluminum powder and 67.5 parts of aluminum nitride powder by weight, and add ammonium chloride at 3% of the total weight of the mixed aluminum powder and aluminum nitride powder. Mix them evenly to obtain a second mixture. The mixed aluminum powder is a mixture of fine aluminum powder with a particle size of 10 μm and coarse aluminum powder with a particle size of 60 μm, with a weight ratio of fine aluminum powder to coarse aluminum powder of 6.5:3.5. S1-3. Weigh 30 parts of mixed aluminum powder and 70 parts of aluminum nitride powder by weight. The amount of ammonium chloride added is 3% of the total weight of the mixed aluminum powder and aluminum nitride powder. Mix them evenly to obtain a second mixture. The mixed aluminum powder is a mixture of fine aluminum powder with a particle size of 5μm and coarse aluminum powder with a particle size of 80μm. The weight ratio of fine aluminum powder to coarse aluminum powder is 6:4. S2, Gradient Material Distribution: Carbon felt is laid at the bottom and around the material frame, and a layer of aluminum nitride diluent is laid on the surface of the carbon felt to prevent the mixture from directly contacting the carbon felt, which could lead to problems such as material sticking, contamination of the mixture, or increased impurities. The first mixture, the second mixture, and the third mixture obtained in step S1 are vacuum dried respectively, and then layered into the material frame in the order of the third mixture, the second mixture, and the first mixture. After each layer is laid, a loosening treatment is performed. After the three layers are laid, an ignition wire and ignition agent are set at the end of the material frame and covered with carbon felt. The purpose is to keep the reactants warm and prevent impurities in the reactor from entering the material frame. S3. Combustion reaction: The layered material frame is placed into a high-pressure reactor, vacuumed, and then filled with nitrogen to a pressure of 2.0 MPa. A 20A pulse current is applied for 10 seconds to heat the spiral tungsten wire to the temperature at which aluminum reacts with nitrogen. Then the pulse power is turned off, and the chemical reaction proceeds layer by layer in a self-propagating manner to carry out the self-propagating combustion synthesis reaction. S4. Post-processing: After the reaction is completed, a uniform product without any sandwich structure is obtained. The product is cooled to room temperature, taken out, and crushed using a two-roll mill. After crushing and grinding, a preliminary micron-sized aluminum nitride powder is obtained. The preliminary micron-sized aluminum nitride powder is used as an aluminum nitride diluent. Steps S1 to S4 are repeated for 6 iterations of nitriding to obtain self-propagating synthetic micron-sized aluminum nitride powder.

[0021] The chemical equation for the synthesis of the self-propagating combustion micron-sized aluminum nitride powder is as follows:

[0022] The chemical equation for the decomposition of ammonium chloride is:

[0023] The mass percentage of coarse aluminum powder in the mixed aluminum powder is as follows: the percentage of coarse aluminum powder in the first mixture > the percentage of coarse aluminum powder in the second mixture > the percentage of coarse aluminum powder in the third mixture.

[0024] In step S1, the aluminum nitride powder undergoes a drying process, which is vacuum drying at 110°C for 1 hour.

[0025] In step S2, the loosening process is as follows: insert a long spoon handle along the depth direction of the material frame and perform longitudinal stroking and lateral swinging.

[0026] In step S2, the vacuum drying conditions are: vacuum degree -0.5MPa, temperature 75℃, and time 60min.

[0027] In step S2, the ignition wire is a spiral tungsten wire, and the ignition agent is a mixture of aluminum powder and aluminum nitride in a molar ratio of 1:1. Example 2

[0028] A method for preparing micron-sized aluminum nitride powder synthesized by self-propagating combustion includes the following steps: S1. Ingredients: Prepare the first mixture, the second mixture, and the third mixture respectively; S1-1. Weigh 33 parts of mixed aluminum powder and 67 parts of aluminum nitride powder by weight, and add ammonium chloride at 4% of the total weight of the mixed aluminum powder and aluminum nitride powder. Mix them evenly to obtain the first mixture. The mixed aluminum powder is a mixture of fine aluminum powder with a particle size of 25μm and coarse aluminum powder with a particle size of 30μm, with a weight ratio of fine aluminum powder to coarse aluminum powder of 8:2. S1-2. Weigh 32.5 parts of mixed aluminum powder and 67.5 parts of aluminum nitride powder by weight, and add ammonium chloride at 3.5% of the total weight of the mixed aluminum powder and aluminum nitride powder. Mix them evenly to obtain a second mixture. The mixed aluminum powder is a mixture of fine aluminum powder with a particle size of 15μm and coarse aluminum powder with a particle size of 55μm, with a weight ratio of fine aluminum powder to coarse aluminum powder of 7:3. S1-3. Weigh 30 parts of mixed aluminum powder and 70 parts of aluminum nitride powder by weight. The amount of ammonium chloride added is 6% of the total weight of the mixed aluminum powder and aluminum nitride powder. Mix them evenly to obtain a second mixture. The mixed aluminum powder is a mixture of fine aluminum powder with a particle size of 20μm and coarse aluminum powder with a particle size of 30μm, with a weight ratio of fine aluminum powder to coarse aluminum powder of 6:4. S2, Gradient Material Distribution: Carbon felt is laid at the bottom and around the material frame, and a layer of aluminum nitride diluent is laid on the surface of the carbon felt to prevent the mixture from directly contacting the carbon felt, causing material adhesion, contamination of the mixture, or increase of impurities; The first mixture, the second mixture, and the third mixture obtained in step S1 are vacuum dried respectively, and then layered into the material frame in the order of the third mixture, the second mixture, and the first mixture. After each layer is laid, a loosening treatment is performed. After the three layers are completed, an ignition wire and ignition agent are set at the end of the material frame and covered with carbon felt. The purpose is to keep the reactants warm and prevent impurities in the reactor from entering the material frame. S3. Combustion reaction: The layered material frame is placed into a high-pressure reactor, vacuumed, and then filled with nitrogen to a pressure of 2.0 MPa. A 20A pulse current is applied for 10 seconds to heat the spiral tungsten wire to the temperature at which aluminum reacts with nitrogen. Then the pulse power is turned off, and the chemical reaction proceeds layer by layer in a self-propagating manner to carry out the self-propagating combustion synthesis reaction. S4. Post-processing: After the reaction is completed, a uniform product without sandwich is obtained. The product is cooled to room temperature, taken out, and crushed using a two-roll mill. After crushing and grinding, a preliminary micron-sized aluminum nitride powder is obtained. The preliminary micron-sized aluminum nitride powder is used as an aluminum nitride diluent. Steps S1 to S4 are repeated for 7 iterations of nitriding to obtain self-propagating synthetic micron-sized aluminum nitride powder.

[0029] The mass percentage of coarse aluminum powder in the mixed aluminum powder is as follows: the percentage of coarse aluminum powder in the first mixture > the percentage of coarse aluminum powder in the second mixture > the percentage of coarse aluminum powder in the third mixture.

[0030] In step S1, the aluminum nitride powder undergoes a drying process, which is vacuum drying at 110°C for 1 hour.

[0031] In step S2, the loosening process is as follows: insert a long spoon handle along the depth direction of the material frame and perform longitudinal stroking and lateral swinging.

[0032] In step S2, the vacuum drying conditions are: vacuum degree -0.5MPa, temperature 75℃, and time 60min.

[0033] In step S2, the ignition wire is a spiral tungsten wire, and the ignition agent is a mixture of aluminum powder and aluminum nitride in a molar ratio of 1:1.

[0034] Comparative Example 1 The difference from Example 1 is that the first mixture, the second mixture, and the third mixture are uniformly mixed and laid into the material frame in a single layer. Other technical solutions are the same as in Example 1.

[0035] Comparative Example 2 The difference from Example 1 is that the first mixture, the second mixture, and the third mixture are uniformly mixed and laid into the material frame in a single layer; and only one iteration of nitriding is performed in step S4. Other technical solutions are the same as in Example 1.

[0036] The test results of the aluminum nitride powders prepared in Examples 1, 2, Comparative Example 1, and 2 are shown in Table 1.

[0037] Table 1

[0038] This technical solution addresses the problems of lengthy reaction times, excessively rapid reaction rates leading to process loss of control, and coarsening of product grains in traditional combustion synthesis of aluminum nitride. It also addresses the drawbacks of complex additives causing increased impurity content and limitations on large-scale production. By innovatively reducing the pressure of the reaction system and simplifying the types and amounts of additives, high-purity, uniformly morphological, and finely grained aluminum nitride powder is synthesized. This technological breakthrough effectively resolves the contradiction between poor reaction controllability and impurity accumulation in traditional processes, significantly improving product quality and production economics, and laying a technological foundation for the large-scale, high-quality production of aluminum nitride materials.

[0039] Although the invention has been specifically shown and described in conjunction with preferred embodiments, those skilled in the art should understand that various changes in form and detail may be made to the invention without departing from the spirit and scope of the invention as defined in the appended claims, all of which shall be within the scope of protection of the invention.

Claims

1. A method for preparing micron-sized aluminum nitride powder through self-propagating combustion, characterized in that, Includes the following steps: S1. Ingredients: Prepare a first mixture, a second mixture, and a third mixture, each of which consists of 30-35 parts by weight of mixed aluminum powder, 65-70 parts by weight of aluminum nitride powder, and ammonium salt; the mixed aluminum powder is prepared by mixing fine aluminum powder with a particle size of 5-25 μm and coarse aluminum powder with a particle size of 25-80 μm in a mass ratio of (5-9):(1-5); the ratio of fine aluminum powder to coarse aluminum powder in the mixed aluminum powder of the first mixture, the second mixture, and the third mixture is different; S2, Gradient Fabrication: Carbon felt is laid at the bottom and around the material frame, and a layer of aluminum nitride diluent is laid on the surface of the carbon felt; the first mixture, the second mixture and the third mixture obtained in step S1 are vacuum dried respectively, and then laid into the material frame in the order of the third mixture, the second mixture and the first mixture. After each layer is laid, a loosening treatment is performed. After the three layers are laid, an ignition wire and an ignition agent are set at the end of the material frame and covered with carbon felt. S3. Combustion reaction: The layered material frame is placed into a high-pressure reactor, vacuumed, and then filled with nitrogen to a pressure of 1.0-2.0 MPa. An electric current is then applied to trigger the self-propagating combustion synthesis reaction. S4. Post-processing: After the reaction is completed, cool to room temperature, take out the product, crush and grind it to obtain the initial micron-sized aluminum nitride powder. Use the initial micron-sized aluminum nitride powder as an aluminum nitride diluent, repeat steps S1 to S4, and perform 6-8 iterative nitriding to obtain self-propagating synthetic micron-sized aluminum nitride powder.

2. The method for preparing micron-sized aluminum nitride powder by self-propagating combustion according to claim 1, characterized in that, The self-propagating combustion synthesized micron-sized aluminum nitride powder has an average particle size of 1.2μm-3μm, an oxygen content of <1.0ppm, and a purity of ≥99.5%.

3. The method for preparing micron-sized aluminum nitride powder by self-propagating combustion according to claim 1, characterized in that, The mass percentage of fine aluminum powder in the mixed aluminum powder is as follows: the percentage of fine aluminum powder in the first mixture > the percentage of fine aluminum powder in the second mixture > the percentage of fine aluminum powder in the third mixture.

4. The method for preparing micron-sized aluminum nitride powder by self-propagating combustion according to claim 1, characterized in that, In step S1, the aluminum nitride powder is dried, and the drying process is: vacuum drying at 110°C for 1 hour; the ammonium salt is ammonium chloride, and its addition amount is 1%-6% of the total mass of the mixed aluminum powder and aluminum nitride powder.

5. The method for preparing self-propagating combustion-synthesized micron-sized aluminum nitride powder according to claim 1, characterized in that, In step S2, the loosening process is as follows: insert a long spoon handle along the depth direction of the material frame and perform longitudinal stroking and lateral swinging.

6. The method for preparing micron-sized aluminum nitride powder by self-propagating combustion according to claim 1, characterized in that, In step S2, the vacuum drying conditions are: vacuum degree -0.5MPa to -0.1MPa, temperature 75℃ to 85℃, and time 60min to 90min.

7. The method for preparing micron-sized aluminum nitride powder by self-propagating combustion according to claim 1, characterized in that, In step S2, the ignition wire is a spiral tungsten wire, and the ignition agent is a mixture of aluminum powder and aluminum nitride in a molar ratio of 1:

1.

8. The method for preparing micron-sized aluminum nitride powder by self-propagating combustion according to claim 1, characterized in that, In step S3, the current is 10A-20A and the energizing time is 10s-15s.

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