Preparation method of submicron aluminum nitride powder

Abstract

The invention relates to a preparation method of submicron AlN powder, which mainly comprises the following steps: taking alpha-Al2O3 and an organic carbon source as raw materials, stirring slurry or rotating a reaction kettle while performing hydrothermal treatment to avoid alpha-Al2O3 particles to sink to the bottom due to gravity so as to obtain a uniform Al2O3-C precursor, carbonizing, and performing carbon thermal reduction and nitridation at 1500-1650 DEG C to obtain high-purity AlN powder. According to the method, the required raw materials are cheap and easy to obtain, the process is simple, submicron AlN powder with various average particle sizes can be synthesized according to requirements, and the powder can well maintain the original morphology, is less in agglomeration, narrow in particle size distribution, low in oxygen content and carbon content, high in sintering activity and suitable for preparing large-size and high-thermal-conductivity ceramic substrates. The method can be easily combined with a granulation technology to realize large-batch production, and the product is high in uniformity and stability.

Description

TECHNICAL FIELD

[0001] The present application relates to a preparation method of submicron AlN powder, and belongs to the field of ceramic powder preparation. BACKGROUND

[0002] Due to its high thermal conductivity (theoretical value is 319 W / m·K), ultra-wide band gap, low dielectric constant and dielectric loss, high strength, non-toxicity, and excellent performance of matching thermal expansion coefficient with semiconductor materials (silicon and gallium nitride), etc., aluminum nitride ceramic has become one of the ideal semiconductor substrates and electronic packaging materials, and has been widely used in high-power LEDs, IGBT power modules, 5G communications, semiconductor processes, etc. in recent years, and the use of high-quality AlN powder is a prerequisite for preparing AlN ceramic with excellent thermal conductivity.

[0003] Currently, the main methods for preparing AlN powder include direct nitridation, carbothermal reduction nitridation, chemical vapor deposition, etc. Among them, carbothermal reduction nitridation is the main method for industrial production of AlN powder, which has the advantages of wide raw material sources, low oxygen content, less agglomeration, high sintering activity, etc. The key to synthesizing high-quality AlN powder by this method is to uniformly mix the aluminum source and the carbon source. Traditional carbothermal reduction nitridation usually uses various crystal forms of Al2O3 and inorganic carbon such as carbon black as raw materials for mechanical ball milling mixing, but the distribution of raw materials is often uneven. The addition of dispersants can significantly improve the wettability and dispersibility of carbon black, thereby improving the uniform mixing degree of Al2O3 and carbon black [Qiao Liang et al., CN202110558017.9, 2021], but Al2O3 self-sintering may still occur.

[0004] When organic materials such as sucrose are used instead of carbon black as the carbon source, a carbon layer of a certain thickness is deposited on the surface of Al2O3 particles, which can not only make closer and more complete contact with Al2O3, but also effectively inhibit the sintering of Al2O3 and AlN through the inert carbon layer. This precursor of carbon-coated Al2O3 particles can improve the shortcomings of traditional inorganic carbon to a certain extent [Song Xibin et al., CN201810350588.1. 2018]. The porous structure obtained by combining this precursor with foaming technology is beneficial to gas exchange during high-temperature synthesis [Mao Qianqian et al., CN201610289195.5, 2016]. Compared with traditional precursor preparation methods, the hydrothermal method makes it relatively easy to prepare Al2O3@C precursors with good dispersibility due to the spatial effect of liquid water. The synthesized AlN powder has a uniform particle size, generally not greater than 150 nm, and excellent sintering activity [M. Xiang, et al., Journal of American Ceramics Society, 2017, 100(6): 2482-2491]. Currently, in order to form a uniformly coated Al2O3@C precursor during hydrothermal processes, the aluminum source often used is water-soluble Al(NO3)3 (which transforms into γ-Al2O3 upon calcination), with relatively low density and small particle size (generally <50nm), or even lower density alumina hydroxide (which also transforms into γ-Al2O3 upon calcination) [XN Sun, et al., Ceramics International, 2023, 49(13): 22128-22138; Feng Guanzheng et al., CN202510235281.7, 2025]. However, the AlN powder prepared by using such ultrafine γ-Al2O3 as a raw material or intermediate is often still a dull gray color after decarbonization, with serious residual carbon, which severely hinders ceramic sintering and reduces thermal conductivity, while also increasing dielectric loss. More importantly, although this nano-AlN powder has high sintering activity, its easy hydrolysis and high oxygen content actually offer no advantages in storage, molding, or the production of large-size AlN ceramics with high thermal conductivity (such as electrostatic chucks). Currently, the industry benchmark for AlN powder used in the production of high thermal conductivity substrates is generally considered to be the E powder produced by Tokuyama Soda Co., Ltd. of Japan, with an average particle size of 0.96-1.07µm. Therefore, the preparation of submicron AlN powder is more practically significant. The prerequisite for preparing a uniform Al2O3@C precursor using the hydrothermal method is that the Al2O3 particles must be uniformly suspended. This has little impact on γ-Al2O3 with a particle size of only tens of nanometers and water-soluble Al(NO3)3. However, when the original Al2O3 particles (especially α-Al2O3) are larger than 100nm, the uneven settling phenomenon caused by gravity sedimentation becomes severe, and even suspension by Brownian motion of particles in aqueous solution and the addition of a small amount of organic dispersant is difficult to solve well. SUMMARY

[0005] Considering that the particle size of AlN raw material powder used for industrial production of high-thermal-conductivity ceramic substrates is usually submicron or even micron level, and that the preparation of uniform Al2O3@C precursor by hydrothermal method only stays at the synthesis of nanoscale AlN powder (generally not more than 150 nm), aiming at the problem, the purpose of the present application is to provide a method for preparing a hydrothermally uniform Al2O3@C precursor and submicron AlN powder.

[0006] In order to achieve the above-mentioned purpose, the technical scheme of the present application is: a preparation method of submicron AlN powder, characterized by comprising the following steps: (1) A proper amount of Al2O3, water-soluble organic carbon source and dispersant are weighed and added into deionized water for ball milling to obtain a slurry, wherein the mass ratio of Al2O3 to the organic carbon source is 1:2.0-3.5, the dispersant is 0.1-2% of the mass of Al2O3, and the mass ratio of Al2O3 to deionized water is 1:4.0-6.0; (2) The slurry obtained in step (1) is filtered, diluted and stirred to form a uniform slurry, and a proper amount of the slurry is added into a reaction kettle. The temperature is raised to 160-220℃ and kept for 4-8h, and the slurry is stirred or the hydrothermal kettle is rotated during the temperature rising and keeping stages, the stirring speed is 50-200r / min, the rotation speed is 20-100r / min, and the temperature is naturally lowered to obtain a black or dark brown precursor; (3) The precursor obtained in step (2) is filtered, dried and lightly ground, and then further carbonized at 700-900℃ under nitrogen for 1-3h to obtain an Al2O3@C precursor; (4) The precursor obtained in step (3) is high-temperature synthesized at 1500-1650℃ under nitrogen in a high-temperature furnace, the nitrogen flow is 100-500ml / min, the temperature is kept for 2-5h and then naturally lowered to obtain a gray-black powder; (5) The AlN powder obtained in step (4) is treated to remove carbon at 650℃ in air for 2-5h to obtain the submicron AlN powder.

[0007] According to the above scheme, the Al2O3 in step (1) is α-Al2O3, the average particle size is greater than 100nm and less than 1μm.

[0008] According to the above scheme, the water-soluble organic carbon source in step (1) is one of glucose, sucrose and starch.

[0009] According to the above scheme, the dispersant in step (1) is one of polyacrylic acid, polyacrylammonium and polymethacrylammonium.

[0010] The principle of the present application is that in the hydrothermal process, the Al2O3 particles can be effectively prevented from sinking to the bottom due to gravity by stirring the slurry or rotating the reaction kettle, which is beneficial to the non-uniform nucleation of the organic carbon source on the surface of each Al2O3 particle and the formation of a layer of hydrothermal carbon, thereby obtaining an Al2O3@C precursor with good dispersity. In addition, using α-Al2O3 as the raw material, the selection of the particle size of the raw material is widened, and because the diffusion of carbon in the α-Al2O3 lattice or the neck of the particle is slower than that of other active Al2O3, it is beneficial to reduce the residual carbon in the lattice or the neck.

[0011] The beneficial results of the present application are: 1. The Al2O3 particles can be effectively prevented from sinking to the bottom by stirring the slurry or rotating the reaction kettle during hydrothermal process, thereby obtaining an Al2O3@C precursor with good dispersity and uniform coating, which can effectively inhibit the sintering of Al2O3 and AlN, and is also beneficial to the diffusion and exchange of gas; 2. Using α-Al2O3 as the raw material, the phase transition during the reaction is avoided, and the isolation effect of the hydrothermal carbon layer can better maintain the original morphology, so that AlN powders with various particle sizes can be synthesized according to the needs, and the powders have less agglomeration, narrow particle size distribution, low oxygen content and carbon content, and high sintering activity; 3. The submicron AlN powder prepared has high green body density, and is suitable for sintering large-size and high-thermal-conductivity AlN ceramic substrates; 4. The surface of the Al2O3@C precursor is hydrophilic, and batch production can be easily realized by combining with the granulation technology, and the product has high uniformity and stability. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 FIG. 4 is an XRD pattern of the AlN powder prepared in Comparative Example 1 of the present application.

[0013] Figure 2 FIG. 5 is a scanning electron microscope photograph of the AlN powder prepared in Example 1 of the present application.

[0014] Figure 3 FIG. 4 is an XRD pattern of the AlN powder prepared in Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0015] In order to better understand the present application, the content of the present application will be further illustrated below in combination with the drawings and examples, but the content of the present application is not limited to the following examples.

[0016] Example 1: 10 g of α-Al2O3 powder with an average particle size of about 100 nm and serious agglomeration, 0.01 g of ammonium polymethacrylate, 20 g of sucrose, and 30 g of deionized water were weighed into a planetary ball mill, and ball-milled for 10 h at a rotation speed of 350 r / min. After ball-milling, the mixture was filtered, diluted with deionized water to a solid content of 5% of α-Al2O3, and stirred magnetically for 1 h. Then, 50 ml of the slurry was taken and added to a 100-ml reaction kettle, which was heated to 220 ℃ and kept for 8 h. During heating, the reaction kettle was rotated at a rotation speed of 100 r / min. The slurry obtained by hydrothermal treatment was filtered, and dried at 80 ℃ for 24 h. The dried product was gently ground, and carbonized at 800 ℃ in nitrogen for 2 h to obtain a precursor of Al2O3@C. An appropriate amount of the precursor was placed in a tube furnace, heated at a rate of 5 ℃ / min to 1500 ℃, kept for 3 h, and cooled with nitrogen at a flow rate of 300 ml / min to obtain a gray-black powder. The powder was decarburized at 650 ℃ in a muffle furnace for 2 h to obtain a gray-white AlN powder. The AlN powder obtained in this example was subjected to XRD testing (see FIG. 1) and SEM testing (see FIG. 2), and the AlN powder prepared was a pure phase. The average particle size of the AlN powder prepared was about 150 nm, and the particle size distribution was narrow. Figure 1 Figure 2

[0017] Example 2: 10 g of α-Al2O3 powder with an average particle size of about 200 nm and slight agglomeration, 0.2 g of ammonium polyacrylate, and 35 g of glucose were weighed into a drum ball mill, and ball-milled for 2 h at a rotation speed of 100 r / min. After ball-milling, the mixture was filtered, diluted with deionized water to a solid content of 5% of α-Al2O3, and stirred magnetically for 1 h. Then, 50 ml of the slurry was taken and added to a 100-ml reaction kettle, which was heated to 200 ℃ and kept for 6 h. During heating, the reaction kettle was rotated at a rotation speed of 20 r / min. The slurry obtained by hydrothermal treatment was filtered, and dried at 80 ℃ for 24 h. The dried product was gently ground, and carbonized at 900 ℃ in nitrogen for 1 h to obtain a precursor of Al2O3@C. An appropriate amount of the precursor was placed in a tube furnace, heated at a rate of 5 ℃ / min to 1600 ℃, kept for 2 h, and cooled with nitrogen at a flow rate of 500 ml / min to obtain a gray-black powder. The powder was decarburized at 650 ℃ in a muffle furnace for 5 h to obtain a gray-white AlN powder. It was determined that the AlN powder prepared in this example was a pure phase, and the average particle size was about 280 nm, and the particle size distribution was narrow.

[0018] ​​Example 3: 10 g of α-Al2O3 powder with an average particle size of about 1 μm and moderate agglomeration, 0.1 g of polyacrylic acid, and 25 g of starch were weighed into 50 g of deionized water, and planetary ball milling was performed for 10 h at a rotation speed of 250 r / min. After the ball milling, the mixture was filtered, diluted with deionized water to a solid content of 5% for α-Al2O3, and stirred magnetically for 1 h. Then, 70 ml of the slurry was taken and added to a 200 ml reactor, heated to 160°C and maintained for 4 h, and mechanically stirred at a stirring speed of 200 r / min during the heating. The slurry obtained after the hydrothermal treatment was filtered, air-dried at 80°C for 24 h, and then lightly ground. The resulting precursor of Al2O3@C was carbonized in nitrogen at 700°C for 3 h. An appropriate amount of the precursor was placed in a tube furnace, heated at a rate of 5°C / min to 1650°C, maintained for 2 h, and cooled with the furnace at a nitrogen flow rate of 300 ml / min to obtain a gray-black powder. The powder was decarburized in a muffle furnace at 650°C for 2 h to obtain a gray-white AlN powder. The AlN powder prepared in this example was determined to be a pure phase with an average particle size of about 0.9 μm and a narrow particle size distribution.

[0019] Example 4: 10 g of α-Al2O3 powder with an average particle size of about 500 nm and slight agglomeration, 0.1 g of polyacrylic acid, and 25 g of sucrose were weighed into 30 g of deionized water, and drum ball milling was performed for 3 h at a rotation speed of 120 r / min. After the ball milling, the mixture was filtered, diluted with deionized water to a solid content of 4% for α-Al2O3, and stirred magnetically for 1 h. Then, 70 ml of the slurry was taken and added to a 200 ml reactor, heated to 180°C and maintained for 6 h, and mechanically stirred at a stirring speed of 50 r / min during the heating. The slurry obtained after the hydrothermal treatment was filtered, air-dried at 80°C for 24 h, and then lightly ground. The resulting precursor of Al2O3@C was carbonized in nitrogen at 900°C for 2 h. An appropriate amount of the precursor was placed in a tube furnace, heated at a rate of 5°C / min to 1650°C, maintained for 5 h, and cooled with the furnace at a nitrogen flow rate of 100 ml / min to obtain a gray-black powder. The powder was decarburized in a muffle furnace at 650°C for 5 h to obtain a gray-white AlN powder. The AlN powder prepared in this example was determined to be a pure phase with an average particle size of about 500 nm and a narrow particle size distribution.

[0020] Example 5: 10 g of α-Al2O3 powder with an average particle size of about 200 nm and severe agglomeration, 0.05 g of poly-methyl-acrylic-ammonium, 20 g of glucose, and 40 g of deionized water were weighed and put into a planetary ball mill for 20 h at a rotation speed of 300 r / min. After ball milling, the mixture was filtered and diluted with deionized water to a solid content of 5% of α-Al2O3. The mixture was stirred magnetically for 1 h. 80 ml of the slurry was taken and put into a 200 ml reactor. The reactor was heated to 200 °C and kept for 6 h. During the heating, the reactor was mechanically stirred at a speed of 100 r / min. The slurry obtained after the hydrothermal treatment was filtered and dried at 80 °C for 24 h. The dried product was lightly ground and carbonized at 800 °C for 3 h in nitrogen. A suitable amount of the precursor was put into a carbon tube furnace and heated to 1600 °C at a heating rate of 10 °C / min. The nitrogen flow was 200 ml / min. After the furnace was cooled, a gray-black powder was obtained. The powder was decarburized at 650 °C for 3 h in a muffle furnace to obtain a gray-white AlN powder. It was determined that the AlN powder prepared in this example was a pure phase with an average particle size of about 260 nm and a narrow particle size distribution.

[0021] Example 6: 30 g of α-Al2O3 powder with an average particle size of about 200 nm and severe agglomeration, 0.15 g of poly-methyl-acrylic-ammonium, 60 g of glucose, and 120 g of deionized water were weighed and put into a planetary ball mill for 20 h at a rotation speed of 300 r / min. After ball milling, the mixture was filtered and diluted with deionized water to a solid content of 5% of α-Al2O3. 100 ml of the slurry was taken and put into a 200 ml reactor. The reactor was heated to 200 °C and kept for 6 h. During the heating, the reactor was rotated at a speed of 50 r / min. The slurry obtained after the hydrothermal treatment was filtered. The precursor obtained after the filtration, 0.15 g of poly-methyl-acrylic-ammonium, a solution containing 0.6 g of polyvinyl alcohol, and 120 g of deionized water were put into a drum ball mill for 1 h at a rotation speed of 80 r / min. The obtained slurry was spray granulated. The granulated powder was carbonized at 800 °C for 3 h in nitrogen. A suitable amount of the precursor was put into a carbon tube furnace and heated to 1600 °C at a heating rate of 10 °C / min. The nitrogen flow was 200 ml / min. After the furnace was cooled, a gray-black powder was obtained. The powder was decarburized at 650 °C for 3 h in a muffle furnace to obtain a gray-white AlN powder. It was determined that the AlN powder prepared in this example was a pure phase with an average particle size of about 220 nm and a narrow particle size distribution.

[0022] Comparative Example 1: 10 g of α-Al2O3 powder with an average particle size of about 200 nm and slight agglomeration, 0.1 g of ammonium polyacrylate, 20 g of glucose, and 40 g of deionized water were weighed into a roller ball mill, and ball-milled at a speed of 100 r / min for 2 h. After ball-milling, the mixture was filtered, diluted with deionized water to a solid content of 5% for α-Al2O3, and stirred magnetically for 1 h. 50 ml of the slurry was taken and added to a 100 ml reactor, heated to 220°C and maintained for 8 h. The slurry obtained after hydrothermal treatment was filtered, dried at 80°C for 24 h, and then lightly ground. The resulting product was carbonized at 800°C in nitrogen for 2 h to obtain a precursor of Al2O3@C. An appropriate amount of the precursor was placed in a tube furnace, heated at a rate of 5°C / min to 1550°C, maintained for 4 h, and cooled with nitrogen at a flow rate of 400 ml / min to obtain a gray-black powder. The powder was decarburized at 650°C in a muffle furnace for 5 h to obtain a gray-white AlN powder. It was determined that the powder prepared in this comparative example was impure, still containing a small amount of α-Al2O3 phase (see Figure 3 ), and was severely agglomerated.

[0023] Comparative Example 2: 10 g of α-Al2O3 powder with an average particle size of about 200 nm and slight agglomeration, 0.1 g of ammonium polyacrylate, 20 g of sucrose, and 30 g of deionized water were weighed into a roller ball mill, and ball-milled at a speed of 100 r / min for 3 h. After ball-milling, the mixture was filtered, dried at 80°C for 24 h, and then microwave-dried for 10 min. The resulting product was carbonized at 900°C in nitrogen for 2 h to obtain a precursor of Al2O3@C. An appropriate amount of the precursor was placed in a tube furnace, heated at a rate of 5°C / min to 1600°C, maintained for 2 h, and cooled with nitrogen at a flow rate of 300 ml / min to obtain a gray-black powder. The powder was decarburized at 650°C in a muffle furnace for 3 h to obtain a gray AlN powder. It was determined that the AlN powder prepared in this comparative example was impure, still containing a small amount of α-Al2O3 phase, and was severely agglomerated.

Claims

1. A method for preparing submicron AlN powder, characterized by The method comprises the following steps: (1) a certain amount of Al2O3, water-soluble organic carbon source and dispersant are weighed and added into deionized water for ball milling to obtain a slurry, wherein the mass ratio of Al2O3 to the organic carbon source is 1:2.0-3.5, the dispersant is 0.1-2% of the mass of Al2O3, and the mass ratio of Al2O3 to deionized water is 1:4.0-7.0; (2) the slurry obtained in step (1) is filtered, diluted and stirred to obtain a uniform slurry, and a certain amount of the slurry is added into a reaction kettle. The temperature is increased to 160-220°C and kept for 4-8h. The slurry is stirred or the hydrothermal kettle is rotated during the temperature increasing and keeping stages, the stirring speed is 50-200 r / min, the rotating speed is 20-100 r / min, and the natural cooling is performed to obtain a black or dark brown precursor; (3) the precursor obtained in step (2) is filtered, dried, lightly ground and further carbonized at 700-900°C for 1-3h under nitrogen to obtain an Al2O3@C precursor; (4) the precursor obtained in step (3) is high-temperature synthesized at 1500-1650°C under nitrogen, the nitrogen flow is 100-500ml / min, the temperature is kept for 2-5h, and then the natural cooling is performed to obtain a gray-black powder; (5) the AlN powder obtained in step (4) is treated for 2-5h at 650°C in air to remove carbon, and the submicron AlN powder is obtained.

2. The method according to claim 1, wherein the method is characterized by: The Al2O3 in step (1) is α-Al2O3, the average particle size is greater than 100nm and less than 1μm.

3. The method according to claim 1, wherein the method is characterized by: The water-soluble organic carbon source in step (1) is one of glucose, sucrose and starch.

4. The method according to claim 1, wherein the method is characterized by: The dispersant in step (1) is one of polyacrylic acid, polyacrylammonium and polymethacrylammonium.

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