Aluminum nitride powder, its preparation method and use

Abstract

The application discloses aluminum nitride powder and a preparation method and application thereof. The preparation method comprises the following steps: taking alumina particles to perform surface activation to obtain activated alumina particles; performing molecular layer deposition treatment on the activated alumina particles to form an aluminoxane film on the surface to obtain coated alumina particles; sintering the coated alumina particles at 600-800 DEG C under an oxidizing atmosphere to obtain alumina particles coated with a porous alumina layer; mixing the alumina particles coated with the porous alumina layer with carbon black uniformly, and then introducing nitrogen to perform a carbothermic reduction reaction, so that the aluminum nitride powder is obtained. The application can synthesize spherical aluminum nitride powder with high purity and low oxygen content at a lower reaction temperature and a shorter holding time.

Description

Technical Field

[0001] This invention relates to the technical field of ceramic material synthesis, and more specifically, to an aluminum nitride powder, its preparation method, and its applications. Background Technology

[0002] Aluminum nitride (AlN) ceramics possess high thermal conductivity, low coefficient of thermal expansion, high strength, high temperature resistance, chemical corrosion resistance, high resistivity, and low dielectric loss, making them ideal heat dissipation substrates and packaging materials for large-scale integrated circuits. Aluminum nitride powder, with its high purity, small particle size, and high activity, is the primary raw material for manufacturing high thermal conductivity aluminum nitride ceramic materials.

[0003] The main methods for synthesizing aluminum nitride powder include carbothermal reduction, direct nitridation of aluminum powder, self-propagating high-temperature synthesis, and chemical vapor deposition. Among these, carbothermal reduction is one of the most commonly used methods in large-scale industrial production due to its wide availability of raw materials, low cost, insensitivity to process conditions, and good stability. The synthesis route of aluminum nitride powder produced by carbothermal reduction is: 3C (solid) + Al2O3 (solid) + N2 (gaseous) → 2AlN (solid) + 3CO (gaseous). Because alumina powder and carbon black have significantly different physical properties, they are difficult to mix uniformly. To ensure a complete reaction, an excess of carbon source is usually added, and a decarbonization process is added later to remove unreacted carbon. The high concentration of CO generated during the synthesis reaction coats the surface of the resulting aluminum nitride. If this CO is not removed in time, it will affect the penetration of N2 into the unreacted alumina region. This not only prolongs the reaction time (often requiring more than 10 hours in production) but also leads to coarsening of the resulting aluminum nitride particles, reducing the specific surface area and sintering activity of the powder.

[0004] Patent CN108793102A discloses a method for preparing aluminum nitride powder under high pressure. In the process of preparing AlN powder using the carbothermic reduction method, flowing nitrogen is used for the nitriding reaction. By increasing the partial pressure of nitrogen in the furnace, the reaction temperature can be reduced and the reaction time shortened. The final AlN powder is spherical with a uniform particle size distribution. While this method of increasing the partial pressure of nitrogen in the furnace to promote the reaction can shorten the reaction time to 3 hours, the D50 particle size of the product reaches 1.1-1.34 μm, failing to effectively prevent particle coarsening. Furthermore, the carbon content in the product is 310-430 ppm, and the oxygen content is 0.87-0.95%, indicating that the purity of the product needs improvement. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects and shortcomings of existing aluminum nitride powder preparation methods, such as long reaction time, low purity of aluminum nitride particles, large particle size, low specific surface area and sintering activity of the powder, and to provide a method for preparing aluminum nitride powder.

[0006] Another object of the present invention is to provide an aluminum nitride powder prepared by a method for preparing aluminum nitride powder.

[0007] Another object of the present invention is to provide an application of the above-mentioned aluminum nitride powder in the manufacture of aluminum nitride ceramic substrates.

[0008] This invention protects a method for preparing aluminum nitride powder, comprising the following steps:

[0009] S1, take alumina particles and perform surface activation to obtain activated alumina particles;

[0010] S2, the activated alumina particles are subjected to molecular layer deposition treatment to form an aluminoxane film on the surface, thus obtaining coated alumina particles.

[0011] S3, the coated alumina particles are sintered at 600-800℃ in an oxidizing gas atmosphere to obtain alumina particles coated with a porous alumina layer.

[0012] S4. After the alumina particles coated with the porous alumina layer are mixed evenly with carbon black, nitrogen gas is introduced to carry out a carbothermic reduction reaction to obtain the aluminum nitride powder.

[0013] The present invention discloses a method for preparing aluminum nitride powder, wherein a porous alumina coating layer is formed on the surface of alumina particles. This alumina coating layer has a porous structure, which can effectively inhibit grain growth during the carbothermic reduction reaction. Its specific effects are mainly reflected in the following aspects:

[0014] 1. Providing reaction sites and promoting reaction: The porous structure of alumina provides abundant reaction sites for the carbothermic reduction reaction. These pores can serve as transport channels between reactants and products, accelerating the reaction process and thus promoting grain formation and growth. In the carbothermic reduction reaction, the reactant N2 and the product CO need to move within a certain space to continue the reaction, and the porous structure of alumina provides just such space, thus allowing the nitriding reaction to continue and shortening the reaction time.

[0015] 2. Controlling AlN particle size: After porous alumina is nitrided to form aluminum nitride, it obtains a porous aluminum nitride structure. The porous structure increases the diffusion resistance between particles, and the pores may act as pinning points of grain boundaries, thereby slowing down the diffusion and migration of atoms or ions between grain boundaries. Particle growth is inhibited, and the particle size is effectively controlled.

[0016] 3. Influence on Grain Growth Direction: In the carbothermic reduction reaction, the porous structure of alumina ceramics can alter the stress distribution within the particles by changing the contact mode between the grains and the reaction medium. Furthermore, the uniform pore distribution obtained using ALD (Alternating Current Deposition) results in a relatively consistent grain growth rate in all directions, leading to aluminum nitride particles with predominantly spherical morphology. The smoother surface of these spherical particles provides a larger specific surface area, enhancing the material's reactivity and adsorption capacity. Simultaneously, their sphericity and good chemical homogeneity contribute to excellent formability and superior dispersibility. Moreover, the porous structure of the aluminum nitride powder effectively prevents particle agglomeration, further improving particle dispersibility in conjunction with its spherical particle structure.

[0017] In some embodiments, the surface activation is ball milling activation or plasma activation; the plasma surface activation process involves injecting N2 into a vacuum chamber, generating nitrogen plasma through a high-frequency electric field, and then reacting the nitrogen plasma with alumina at 40-60°C to form aluminum nitride compounds on the surface of the alumina particles. These aluminum nitride compounds increase the surface roughness of the alumina particles, improving wettability and adhesion to the coating material for subsequent coating treatment; they also form nucleation sites for aluminum nitride, facilitating its formation.

[0018] In some embodiments, in step S2, the density of the aluminoxane film is 1.5-1.8 g / cm³. 3 The density of conventional alumina particles is approximately 3.9-4.0 g / cm³. 3 Controlling the density of the aluminoxane film to be close to half that of alumina is beneficial for controlling the formation of an open-pore structure with a certain porosity in the sintered alumina layer.

[0019] In some embodiments, in step S2, the thickness of the aluminoxane film is 10-50 nm.

[0020] In some embodiments, step S2 of the molecular layer deposition process includes:

[0021] S201, the activated alumina particles are placed in the chamber of the molecular layer deposition apparatus, and the chamber temperature is controlled at 85-95℃ and the carrier gas flow rate is 80-100 sccm.

[0022] S202, pulse injection of oxygen-containing compound, injection time 0.01-0.02s, wait 3-5s;

[0023] S203, pulse injection of trimethylaluminum, injection time 0.05-0.15s, wait 3-5s;

[0024] S204, repeat steps S202 and S203 for 20-150 cycles.

[0025] Preferably, the oxygen-containing compound is an organic molecule with a homogeneous bifunctional group, including but not limited to ethylene glycol, glycerol, 1,4-benzenehydrin, succinic acid, terephthalic acid, and trimalonic acid. More preferably, the oxygen-containing compound is ethylene glycol. The reaction process of ethylene glycol and trimethylaluminum is as follows: the -OH groups on the particle surface release CH4 byproducts under a trimethylaluminum pulse. The resulting surface is exposed to ethylene glycol vapor, releasing CH4 byproducts and coating the particle surface with -OH groups. This process is repeated to form an aluminum oxane film.

[0026] Preferably, in step S204, the cycle is repeated 25-125 times to obtain an aluminum oxane film with a thickness of 10-50 nm.

[0027] In some embodiments, the carrier gas is an inert gas, including but not limited to nitrogen and argon, and the carrier gas is used to transport the reactant precursor into the reaction chamber.

[0028] In some embodiments, in step S3, the oxygen content in the oxidizing gas is not less than 10%, preferably, the oxygen content is 15-25%.

[0029] In some embodiments, in step S3, the porosity of the porous alumina layer in the alumina particles coated by the porous alumina layer is 15-32%.

[0030] In some embodiments, in step S4, the alumina particles coated with the porous alumina layer are mixed with carbon black and loaded onto a graphite plate, and nitrogen gas is introduced from bottom to top to carry out a carbothermic reduction reaction; the graphite plate is tilted upward along the gas outlet direction.

[0031] In some embodiments, in step S4, the conditions for the carbothermic reduction reaction are: reaction temperature 1450-1650℃, reaction time 3-6h.

[0032] In some embodiments, step S4 of the carbothermic reduction reaction includes:

[0033] S401, the alumina particles coated with the porous alumina layer, carbon black, dispersant and suspending agent are mixed evenly to obtain a mixed powder;

[0034] S402, after drying the mixed powder, spread it evenly on a graphite plate, then insert the graphite plate into a graphite furnace and introduce nitrogen gas, and carry out a carbothermic reduction reaction at 1450-1650℃ to obtain the aluminum nitride powder.

[0035] In some embodiments, step S401 includes mixing the alumina particles coated with the porous alumina layer and carbon black uniformly by high-frequency vibration, and then adding a dispersant and a suspending agent under continuous stirring and mixing uniformly to obtain a mixed powder; by combining dry and wet processing, the viscosity of the slurry can be reduced and the dispersibility increased.

[0036] In some embodiments, step S401 includes adding a suspending agent and a portion of a dispersant to the alumina particles coated with the porous alumina layer and mixing them evenly. The portion of the dispersant accounts for 30-70 wt% of the total amount. Then, the remaining dispersant and carbon black are added and mixed evenly to obtain a mixed powder. By adding the dispersant in batches, the dispersion state of the carbon black particles can be controlled more effectively. When the dispersant is added for the first time, it is dispersed on the surface of the alumina particles or mixed in the suspending agent and coated on the surface of the alumina particles together with the suspending agent. When added for the second time, it is evenly distributed on the surface of the carbon black, thereby reducing the agglomeration between particles and improving the overall dispersibility of the material.

[0037] In addition, the alumina surface is first coated with a suspending agent, which can effectively adsorb carbon black; at the same time, the outer layer of carbon black covers the suspending agent, which is protected by the carbon black during the carbothermic reaction. The suspending agent is further protected from the sintering atmosphere and can self-decompose to form nano-sized amorphous carbon. The reactivity of this nano-sized amorphous carbon is better than that of carbon black, which effectively promotes the carbothermic reaction.

[0038] Preferably, the dispersant is polyethylene glycol (PEG) and / or acrylic acid. The dispersant accounts for 0.5-5 wt% of the mass of the alumina particles.

[0039] Preferably, the suspending agent is at least one selected from PVA, PVB, epoxy resin, acrylic resin and phenolic resin; the amount used is 1-10 wt% of the mass of the alumina particles.

[0040] In some embodiments, the mass ratio of alumina particles to carbon black coated by the porous alumina layer is 1:(3.25-5.0).

[0041] In some embodiments, with a 500L furnace, the nitrogen flow rate is 125-250L / min.

[0042] In some embodiments, in step S402, the graphite plate is inserted into the graphite furnace at an upward tilt. Preferably, the angle between the graphite plate and the horizontal direction is 15-60°, and the nitrogen gas flows from bottom to top, with the nitrogen gas inlet direction parallel to the graphite plate. Existing methods of placing graphite plates involve horizontally stacking them layer by layer in the graphite furnace. This can easily lead to uneven airflow between layers, preventing timely removal of CO and affecting further nitriding. Furthermore, even with horizontal inlet and outlet, the airflow direction is upward, resulting in less nitrogen at the bottom and more at the top, which is detrimental to nitriding at the bottom. Therefore, this invention modifies the graphite plate to be tilted, with nitrogen entering from the bottom and exiting from the top. The parallel position of the graphite plate and the nitrogen inlet direction facilitates preferential and sufficient contact between nitrogen and the powder. The tilted placement of the graphite plate also facilitates the removal of the reaction product CO. This synergistic effect ensures sufficient contact between nitrogen and reactants, resulting in complete carbothermic nitriding, while the generated CO is promptly removed, improving the reaction conversion rate. In some embodiments, in step S1, the alumina particles have a particle size of 0.1-1 μm, preferably 0.3-0.7 μm, and more preferably 0.4-0.6 μm.

[0043] This invention protects an aluminum nitride powder, prepared by the method described above. The aluminum nitride powder has a near-spherical structure, uniform size, and a primary crystal D50 particle size between 0.1-1 μm, preferably 0.3-0.8 μm.

[0044] This invention protects the use of aluminum nitride powder in the manufacture of aluminum nitride ceramic substrates.

[0045] Compared with the prior art, the beneficial effects of the present invention are:

[0046] This invention provides a method for preparing aluminum nitride powder, which has a simple preparation process and is suitable for large-scale production. A porous alumina coating layer is formed on the surface of alumina particles. This porous coating layer effectively inhibits grain growth, provides reaction sites, and promotes the reaction during carbothermic reduction. The method can synthesize high-purity spherical aluminum nitride powder with an oxygen content of less than 0.71%, a nitridation rate of more than 99.32%, and an average particle size of less than 0.65 μm by conducting a carbothermic reaction at a temperature below 1600℃ and a holding time of 5 minutes. When the aluminum nitride powder is used to make a ceramic substrate, its thermal conductivity is above 213 W / (m·K), and its strength is above 428 MPa. Attached Figure Description

[0047] Figure 1 The image shows the XRD pattern of a product prepared by a method for preparing aluminum nitride powder according to Example 1 of the present invention.

[0048] Figure 2The image shows a SEM image of a product prepared by a method for preparing aluminum nitride powder according to Example 1 of the present invention.

[0049] Figure 3 This is a schematic diagram of the carbothermic reduction reaction process of an aluminum nitride powder preparation method according to Example 5 of the present invention. Detailed Implementation

[0050] The present invention will be further described below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise stated, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.

[0051] Example 1

[0052] A method for preparing aluminum nitride powder includes the following steps:

[0053] S1, take alumina particles with a D50 particle size of 0.56μm and ball mill them for 5h to break up hard agglomerates and activate the surface to obtain pretreated alumina particles;

[0054] S2, the pretreated alumina particles are subjected to molecular layer deposition treatment to form an aluminoxane film on the surface, the density of the aluminoxane film being 1.6 g / cm³. 3 Coated alumina particles were obtained;

[0055] Specifically, the steps of the molecular layer deposition process include:

[0056] The activated alumina particles are placed in the chamber of the molecular layer deposition apparatus, and the following procedure is performed:

[0057] Step 1, wait 5 seconds;

[0058] Step 2, carrier gas flow rate 90 sccm;

[0059] Step 3, chamber temperature 90℃;

[0060] Step 4, wait for the temperature to stabilize for 200 seconds;

[0061] Step 5, ethylene glycol pulse injection time 0.015s, wait 4s;

[0062] Step 6, TMA pulse injection time 0.1s, wait 4s;

[0063] Step 7, repeat steps 5 and 6 for 25 cycles;

[0064] Step 8, carrier gas flow rate 5 sccm;

[0065] Step 9: The chamber temperature returns to room temperature.

[0066] S3, the coated alumina particles are sintered at 700°C in an oxygen atmosphere to obtain alumina particles coated with a porous alumina layer; S4, the alumina particles coated with the porous alumina layer are mixed evenly with carbon black and then nitrogen is introduced to carry out a carbothermic reduction reaction.

[0067] The steps of the carbothermic reduction reaction include:

[0068] 1) Add polyethylene glycol as a first dispersant and PVB as a suspending agent to the alumina particles coated with the porous alumina layer and mix evenly. The first dispersant accounts for 50 wt% of the total amount. Then add the remaining second dispersant and carbon black and mix evenly to obtain a mixed powder.

[0069] 2) After drying the mixed powder in an oven at 120°C for 10 hours, spread it evenly on a graphite plate. Then, insert the graphite plate at an angle into a graphite furnace and introduce nitrogen gas. The angle between the graphite plate and the horizontal direction is 15°. The nitrogen gas inlet is tilted synchronously with the graphite plate, that is, the nitrogen gas inlet direction is kept parallel to the graphite plate and the nitrogen gas is introduced from below. Carbothermic reduction reaction is carried out at 1600°C for 3 hours to obtain the aluminum nitride powder.

[0070] S5. The powder obtained in step S4 is placed in a decarbonization furnace, and a mixture of high-purity N2 and dry O2 gas is introduced to remove carbon, and aluminum nitride powder is obtained after decarbonization.

[0071] Example 2

[0072] A method for preparing aluminum nitride powder differs from Example 1 in that:

[0073] In this embodiment, step S1 involves taking alumina particles with a D50 particle size of 0.56 μm and treating them with nitrogen plasma at 50°C to obtain pretreated alumina particles.

[0074] Example 3

[0075] A method for preparing aluminum nitride powder includes the following steps:

[0076] S1, take alumina particles with a D50 particle size of 0.56μm and ball mill them for 5h to break up hard agglomerates and activate the surface to obtain pretreated alumina particles;

[0077] S2, the pretreated alumina particles are subjected to molecular layer deposition treatment to form an aluminoxane film on the surface, the density of the aluminoxane film being 1.6 g / cm³. 3 Coated alumina particles were obtained;

[0078] Specifically, the steps of the molecular layer deposition process include:

[0079] The activated alumina particles are placed in the chamber of the molecular layer deposition apparatus, and the following procedure is performed:

[0080] Step 1, wait 5 seconds;

[0081] Step 2, carrier gas flow rate 90 sccm;

[0082] Step 3, chamber temperature 90℃;

[0083] Step 4, wait for the temperature to stabilize for 200 seconds;

[0084] Step 5, glycerin pulse injection time 0.015s, wait 4s;

[0085] Step 6, TMA pulse injection time 0.1s, wait 4s;

[0086] Step 7, repeat steps 5 and 6 for 50 cycles;

[0087] Step 8, carrier gas flow rate 5 sccm;

[0088] Step 9: The chamber temperature returns to room temperature.

[0089] S3, the coated alumina particles are sintered at 700°C and in an oxygen atmosphere to obtain alumina particles coated with a porous alumina layer.

[0090] S4, after the alumina particles coated with the porous alumina layer are mixed evenly with carbon black, nitrogen gas is introduced to carry out a carbothermic reduction reaction.

[0091] The steps of the carbothermic reduction reaction include:

[0092] 1) Add the first dispersant acrylic acid and the suspending agent PVA to the alumina particles coated with the porous alumina layer and mix evenly. The first dispersant accounts for 40 wt% of the total amount. Then add the remaining second dispersant and carbon black and mix evenly to obtain a mixed powder.

[0093] 2) After drying the mixed powder in an oven at 120°C for 10 hours, spread it evenly on a graphite plate. Then, insert the graphite plate at an angle into a graphite furnace and introduce nitrogen gas. The angle between the graphite plate and the horizontal direction is 30°. The nitrogen gas inlet is tilted synchronously with the graphite plate, that is, the nitrogen gas inlet direction is kept parallel to the graphite plate and the nitrogen gas is introduced from below. Carbothermic reduction reaction is carried out at 1580°C for 3 hours to obtain the aluminum nitride powder.

[0094] S5. The powder obtained in step S4 is placed in a decarbonization furnace, and a mixture of high-purity N2 and dry O2 gas is introduced to remove carbon, and aluminum nitride powder is obtained after decarbonization.

[0095] Example 4

[0096] A method for preparing aluminum nitride powder includes the following steps:

[0097] S1, take alumina particles with a D50 particle size of 0.56μm and ball mill them for 5h to break up hard agglomerates and activate the surface to obtain pretreated alumina particles;

[0098] S2, the pretreated alumina particles are subjected to molecular layer deposition treatment to form an aluminoxane film on the surface, the density of the aluminoxane film being 1.6 g / cm³. 3 Coated alumina particles were obtained;

[0099] Specifically, the steps of the molecular layer deposition process include:

[0100] The activated alumina particles are placed in the chamber of the molecular layer deposition apparatus, and the following procedure is performed:

[0101] Step 1, wait 5 seconds;

[0102] Step 2, carrier gas flow rate 90 sccm;

[0103] Step 3, chamber temperature 90℃;

[0104] Step 4, wait for the temperature to stabilize for 200 seconds;

[0105] Step 5, 0.015s pulse injection time for tricorniolic acid, wait 4s;

[0106] Step 6, TMA pulse injection time 0.1s, wait 4s;

[0107] Step 7, repeat steps 5 and 6 for 75 cycles;

[0108] Step 8, carrier gas flow rate 5 sccm;

[0109] Step 9: The chamber temperature returns to room temperature.

[0110] S3, the coated alumina particles are sintered at 700°C and in an oxygen atmosphere to obtain alumina particles coated with a porous alumina layer.

[0111] S4, after the alumina particles coated with the porous alumina layer are mixed evenly with carbon black, nitrogen gas is introduced to carry out a carbothermic reduction reaction.

[0112] The steps of the carbothermic reduction reaction include:

[0113] 1) Add polyethylene glycol as a first dispersant and PVA as a suspending agent to the alumina particles coated with the porous alumina layer and mix evenly. The first dispersant accounts for 60 wt% of the total amount. Then add the remaining second dispersant and carbon black and mix evenly to obtain a mixed powder.

[0114] 2) After drying the mixed powder in an oven at 120°C for 10 hours, spread it evenly on a graphite plate. Then, insert the graphite plate at an angle into a graphite furnace and introduce nitrogen gas. The angle between the graphite plate and the horizontal direction is 45°. The nitrogen gas inlet is tilted synchronously with the graphite plate, that is, the nitrogen gas inlet direction is kept parallel to the graphite plate and the nitrogen gas is introduced from below. Carbothermic reduction reaction is carried out at 1560°C for 4 hours to obtain the aluminum nitride powder.

[0115] S5. The powder obtained in step S4 is placed in a decarbonization furnace, and a mixture of high-purity N2 and dry O2 gas is introduced to remove carbon, and aluminum nitride powder is obtained after decarbonization.

[0116] Example 5

[0117] A method for preparing aluminum nitride powder includes the following steps:

[0118] S1, take alumina particles with a D50 particle size of 0.56μm and ball mill them for 5h to break up hard agglomerates and activate the surface to obtain pretreated alumina particles;

[0119] S2, the pretreated alumina particles are subjected to molecular layer deposition treatment to form an aluminoxane film on the surface, the density of the aluminoxane film being 1.6 g / cm³. 3 Coated alumina particles were obtained;

[0120] Specifically, the steps of the molecular layer deposition process include:

[0121] The activated alumina particles are placed in the chamber of the molecular layer deposition apparatus, and the following procedure is performed:

[0122] Step 1, wait 5 seconds;

[0123] Step 2, carrier gas flow rate 90 sccm;

[0124] Step 3, chamber temperature 90℃;

[0125] Step 4, wait for the temperature to stabilize for 200 seconds;

[0126] Step 5, ethylene glycol pulse injection time 0.015s, wait 4s;

[0127] Step 6, TMA pulse injection time 0.1s, wait 4s;

[0128] Step 7, repeat steps 5 and 6 for 100 cycles;

[0129] Step 8, carrier gas flow rate 5 sccm;

[0130] Step 9: The chamber temperature returns to room temperature.

[0131] S3, the coated alumina particles are sintered at 700°C and in an oxygen atmosphere to obtain alumina particles coated with a porous alumina layer.

[0132] S4, after the alumina particles coated with the porous alumina layer are mixed evenly with carbon black, nitrogen gas is introduced to carry out a carbothermic reduction reaction.

[0133] The steps of the carbothermic reduction reaction include:

[0134] 1) Add polyethylene glycol as a first dispersant and PVA as a suspending agent to the alumina particles coated with the porous alumina layer and mix evenly. The first dispersant accounts for 50 wt% of the total amount. Then add the remaining second dispersant and carbon black and mix evenly to obtain a mixed powder.

[0135] 2) After drying the mixed powder in an oven at 120°C for 10 hours, spread it evenly on a graphite plate. Then, insert the graphite plate at an angle into a graphite furnace and introduce nitrogen gas. The angle between the graphite plate and the horizontal direction is 60°. The nitrogen gas inlet is tilted synchronously with the graphite plate, that is, the nitrogen gas inlet direction is kept parallel to the graphite plate and the nitrogen gas is introduced from below. Carbothermic reduction reaction is carried out at 1530°C for 4 hours to obtain the aluminum nitride powder.

[0136] S5. The powder obtained in step S4 is placed in a decarbonization furnace, and a mixture of high-purity N2 and dry O2 gas is introduced to remove carbon, and aluminum nitride powder is obtained after decarbonization.

[0137] Example 6

[0138] A method for preparing aluminum nitride powder differs from Example 5 in that:

[0139] Step S4, the carbothermic reduction reaction includes the following steps:

[0140] 1) The alumina particles coated with the porous alumina layer and the carbon black are mixed evenly by high-frequency vibration at a frequency of 40Hz. Z Then, under continuous stirring, slowly add the ethanol solution of dispersant polyethylene glycol and suspending agent PVB and mix evenly to obtain a mixed powder.

[0141] 2) After drying the mixed powder in an oven at 120°C for 10 hours, spread it evenly on a graphite plate, then insert the graphite plate at an angle into a graphite furnace and introduce nitrogen gas. The angle between the graphite plate and the horizontal direction of the water is 60°. Carbothermic reduction reaction is carried out at 1530°C for 5 hours to obtain the aluminum nitride powder.

[0142] Example 7

[0143] A method for preparing aluminum nitride powder includes the following steps:

[0144] S1, take alumina particles with a D50 particle size of 0.56μm and ball mill them for 5h to break up hard agglomerates and activate the surface to obtain pretreated alumina particles;

[0145] S2, the pretreated alumina particles are subjected to molecular layer deposition treatment to form an aluminoxane film on the surface, the density of the aluminoxane film being 1.6 g / cm³. 3 Coated alumina particles were obtained;

[0146] Specifically, the steps of the molecular layer deposition process include:

[0147] The activated alumina particles are placed in the chamber of the molecular layer deposition apparatus, and the following procedure is performed:

[0148] Step 1, wait 5 seconds;

[0149] Step 2, carrier gas flow rate 90 sccm;

[0150] Step 3, chamber temperature 90℃;

[0151] Step 4, wait for the temperature to stabilize for 200 seconds;

[0152] Step 5, succinic acid pulse injection time 0.015s, wait 4s;

[0153] Step 6, TMA pulse injection time 0.1s, wait 4s;

[0154] Step 7, repeat steps 5 and 6 for 125 cycles;

[0155] Step 8, carrier gas flow rate 5 sccm;

[0156] Step 9: The chamber temperature returns to room temperature.

[0157] S3, the coated alumina particles are sintered at 700°C and in an oxygen atmosphere to obtain alumina particles coated with a porous alumina layer.

[0158] S4, after the alumina particles coated with the porous alumina layer are mixed evenly with carbon black, nitrogen gas is introduced to carry out a carbothermic reduction reaction.

[0159] The steps of the carbothermic reduction reaction include:

[0160] 1) The alumina particles coated with the porous alumina layer and the carbon black are mixed evenly by high-frequency vibration at a frequency of 40Hz. Z Then, under continuous stirring, slowly add the dispersant polyethylene glycol and the suspending agent PVB ethanol solution and mix evenly to obtain a mixed powder.

[0161] 2) After drying the mixed powder in an oven at 120°C for 10 hours, spread it evenly on a graphite plate. Then, insert the graphite plate at an angle into a graphite furnace and introduce nitrogen gas. The angle between the graphite plate and the horizontal direction is 30°. The nitrogen gas inlet is tilted synchronously with the graphite plate, that is, the nitrogen gas inlet direction is kept parallel to the graphite plate and the nitrogen gas is introduced from below. Carbothermic reduction reaction is carried out at 1500°C for 5 hours to obtain the aluminum nitride powder.

[0162] S5. The powder obtained in step S4 is placed in a decarbonization furnace, and a mixture of high-purity N2 and dry O2 gas is introduced to remove carbon, and aluminum nitride powder is obtained after decarbonization.

[0163] Example 8

[0164] A method for preparing aluminum nitride powder includes the following steps:

[0165] S1, take alumina particles with a D50 particle size of 0.56μm and ball mill them for 5h to break up hard agglomerates and activate the surface to obtain pretreated alumina particles;

[0166] S2, the pretreated alumina particles are subjected to molecular layer deposition treatment to form an aluminoxane film on the surface, the density of the aluminoxane film being 1.6 g / cm³. 3 Coated alumina particles were obtained;

[0167] Specifically, the steps of the molecular layer deposition process include:

[0168] The activated alumina particles are placed in the chamber of the molecular layer deposition apparatus, and the following procedure is performed:

[0169] Step 1, wait 5 seconds;

[0170] Step 2, carrier gas flow rate 90 sccm;

[0171] Step 3, chamber temperature 90℃;

[0172] Step 4, wait for the temperature to stabilize for 200 seconds;

[0173] Step 5, ethylene glycol pulse injection time 0.015s, wait 4s;

[0174] Step 6, TMA pulse injection time 0.1s, wait 4s;

[0175] Step 7, repeat steps 5 and 6 for 125 cycles;

[0176] Step 8, carrier gas flow rate 5 sccm;

[0177] Step 9: The chamber temperature returns to room temperature.

[0178] S3, the coated alumina particles are sintered at 700°C and in an oxygen atmosphere to obtain alumina particles coated with a porous alumina layer.

[0179] S4, after the alumina particles coated with the porous alumina layer are mixed evenly with carbon black, nitrogen gas is introduced to carry out a carbothermic reduction reaction.

[0180] The steps of the carbothermic reduction reaction include:

[0181] 1) Add dispersant polyethylene glycol and a portion of suspending agent PVB to the alumina particles coated with the porous alumina layer and mix evenly. The portion of suspending agent accounts for 50 wt% of the total amount. Then add the remaining suspending agent and carbon black and mix evenly to obtain a mixed powder.

[0182] 2) After drying the mixed powder in an oven at 120°C for 10 hours, spread it evenly on a graphite plate. Then, insert the graphite plate at an angle into a graphite furnace and introduce nitrogen gas. The angle between the graphite plate and the horizontal direction is 30°. The nitrogen gas inlet is tilted synchronously with the graphite plate, that is, the nitrogen gas inlet direction is kept parallel to the graphite plate and the nitrogen gas is introduced from below. Carbothermic reduction reaction is carried out at 1500°C for 4 hours to obtain the aluminum nitride powder.

[0183] S5. The powder obtained in step S4 is placed in a decarbonization furnace, and a mixture of high-purity N2 and dry O2 gas is introduced to remove carbon, and aluminum nitride powder is obtained after decarbonization.

[0184] Comparative Example 1

[0185] A method for preparing aluminum nitride powder differs from Example 8 in that:

[0186] Step S4, the carbothermic reduction reaction includes the following steps:

[0187] 1) Add dispersant polyethylene glycol and a portion of suspending agent PVB to the alumina particles coated with the porous alumina layer and mix evenly. The portion of suspending agent accounts for 50 wt% of the total amount. Then add the remaining suspending agent and carbon black and mix evenly to obtain a mixed powder.

[0188] 2) After drying the mixed powder in an oven at 120°C for 10 hours, spread it evenly on a graphite plate, then insert the graphite plate horizontally into a graphite furnace and introduce nitrogen gas. The nitrogen gas is introduced in a direction parallel to the graphite plate. Carbothermic reduction reaction is carried out at 1500°C for 4 hours to obtain the aluminum nitride powder.

[0189] Comparative Example 2

[0190] A method for preparing aluminum nitride powder includes the following steps:

[0191] S1, take alumina particles with a D50 particle size of 0.56μm and ball mill them for 5h to break up hard agglomerates and activate the surface to obtain pretreated alumina particles;

[0192] S2, after the pretreated alumina particles and carbon black are mixed evenly, nitrogen gas is introduced to carry out a carbothermic reduction reaction.

[0193] The steps of the carbothermic reduction reaction include:

[0194] 1) The alumina particles and carbon black are mixed evenly by high-frequency vibration at a frequency of 40Hz. Z Then, under continuous stirring, slowly add the dispersant polyethylene glycol and the suspending agent PVB ethanol solution and mix evenly to obtain a mixed powder.

[0195] 2) After drying the mixed powder in an oven at 120°C for 10 hours, spread it evenly on a graphite plate. Then, insert the graphite plate at an angle into a graphite furnace and introduce nitrogen gas. The angle between the graphite plate and the horizontal direction is 30°. The nitrogen gas inlet is tilted synchronously with the graphite plate, that is, the nitrogen gas inlet direction is kept parallel to the graphite plate and the nitrogen gas is introduced from below. Carbothermic reduction reaction is carried out at 1500°C for 5 hours to obtain the aluminum nitride powder.

[0196] S3. The powder obtained in step S2 is placed in a decarbonization furnace, and a mixture of high-purity N2 and dry O2 gas is introduced to remove carbon, and aluminum nitride powder is obtained after decarbonization.

[0197] Comparative Example 3

[0198] A method for preparing aluminum nitride powder includes the following steps:

[0199] S1, take alumina particles with a D50 particle size of 0.56μm and ball mill them for 5h to break up hard agglomerates and activate the surface to obtain pretreated alumina particles;

[0200] S2, after the pretreated alumina particles and carbon black are mixed evenly, nitrogen gas is introduced to carry out a carbothermic reduction reaction.

[0201] The steps of the carbothermic reduction reaction include:

[0202] 1) Add dispersant polyethylene glycol and a portion of suspending agent PVB to the alumina particles and mix evenly. The portion of suspending agent accounts for 50 wt% of the total amount. Then add the remaining suspending agent and carbon black and mix evenly to obtain a mixed powder.

[0203] 2) After drying the mixed powder in an oven at 120°C for 10 hours, spread it evenly on a graphite plate. Then, insert the graphite plate at an angle into a graphite furnace and introduce nitrogen gas. The angle between the graphite plate and the horizontal direction is 30°. The nitrogen gas inlet is tilted synchronously with the graphite plate, that is, the nitrogen gas inlet direction is kept parallel to the graphite plate and the nitrogen gas is introduced from below. Carbothermic reduction reaction is carried out at 1680°C for 5 hours to obtain the aluminum nitride powder.

[0204] S3. The powder obtained in step S2 is placed in a decarbonization furnace, and a mixture of high-purity N2 and dry O2 gas is introduced to remove carbon, and aluminum nitride powder is obtained after decarbonization.

[0205] Comparative Example 4

[0206] A method for preparing aluminum nitride powder includes the following steps:

[0207] S1, take alumina particles with a D50 particle size of 0.56μm and ball mill them for 5h to break up hard agglomerates and activate the surface to obtain pretreated alumina particles;

[0208] S2, after the pretreated alumina particles and carbon black are mixed evenly, nitrogen gas is introduced to carry out a carbothermic reduction reaction.

[0209] The steps of the carbothermic reduction reaction include:

[0210] 1) Add dispersant polyethylene glycol and a portion of suspending agent PVB to the pretreated alumina particles and mix evenly. The portion of suspending agent accounts for 50 wt% of the total amount. Then add the remaining suspending agent and carbon black and mix evenly to obtain a mixed powder.

[0211] 2) After drying the mixed powder in an oven at 120°C for 10 hours, spread it evenly on a graphite plate. Then, insert the graphite plate at an angle into a graphite furnace and introduce nitrogen gas. The angle between the nitrogen gas inlet direction and the graphite plate is 30°. The nitrogen gas inlet is tilted synchronously with the graphite plate, that is, the nitrogen gas inlet direction is kept parallel to the graphite plate and the nitrogen gas is introduced from below. Carbothermic reduction reaction is carried out at 1680°C for 10 hours to obtain the aluminum nitride powder.

[0212] S3. The powder obtained in step S2 is placed in a decarbonization furnace, and a mixture of high-purity N2 and dry O2 gas is introduced to remove carbon, and aluminum nitride powder is obtained after decarbonization.

[0213] Performance testing

[0214] 1. XRD characterization

[0215] The aluminum nitride powder obtained in Example 1 was subjected to XRD analysis, and the results are as follows: Figure 1 As shown.

[0216] The results showed that the aluminum nitride powder synthesized in Example 1 was synthesized into a pure aluminum nitride phase.

[0217] 2. SEM characterization

[0218] The aluminum nitride powder obtained in Example 1 was analyzed by SEM, and the results are as follows: Figure 2 As shown.

[0219] The results showed that the aluminum nitride powder synthesized in Example 1 was generally spherical with obvious edges and corners, no obvious agglomeration, and uniform size, with the primary crystal size between 0.4 and 0.7 μm.

[0220] 3. Comprehensive performance characterization experiment

[0221] The porous alumina layers and aluminum nitride powder products obtained during the preparation processes of Examples 1-8 and Comparative Examples 1-3 were tested for their oxygen content, nitriding rate and average particle size. The results are shown in Table 1.

[0222] Aluminum nitride powders from Examples 1-8 and Comparative Examples 1-3 were ball-milled and mixed evenly with sintering aid (Y2O3), dispersant, binder, plasticizer and solvent to obtain a slurry; the slurry was degassed under vacuum and then cast into a film, followed by debinding (debinding temperature 550℃, holding time 2h) and sintering (sintering temperature 1800℃, holding time 6h) to obtain a ceramic substrate with a final thickness of 0.5mm.

[0223] The ceramic substrate was subjected to thermal conductivity and strength tests. The thermal conductivity was tested using the planar heat flow method, with a sample size of 100*100*0.5mm. The strength was tested using a universal testing machine, with a sample size of 13*80*0.5mm. The results are shown in Table 1.

[0224] Table 1

[0225]

[0226] As can be seen from Table 1, the greater the thickness of the porous alumina layer, the higher the porosity. The oxygen content of the aluminum nitride powder prepared by this invention is less than 0.71%, the nitriding rate is more than 99.32%, the thermal conductivity of the ceramic substrate is more than 213 W / (m·K), and the strength is more than 428 MPa. All performance indicators exceed the industry standards.

[0227] In Comparative Example 1, the graphite plate was laid flat and inserted into the graphite furnace, with the graphite plate parallel to the nitrogen gas. Under the carbothermic reaction with a relatively low reaction temperature and reaction time, the nitridation reaction and carbon removal were not fully achieved, resulting in a high oxygen content and a decrease in the nitridation rate.

[0228] Compared to Example 7, Comparative Example 2 did not coat the alumina particles to form a porous alumina layer, resulting in excessively high oxygen content in the powder, a decreased nitriding rate, and a decline in substrate performance. Comparative Example 3 increased the reaction temperature, which improved the nitriding rate but still failed to meet requirements, and also led to an increase in the D50 particle size of the aluminum nitride grains.

[0229] In Comparative Example 4, the alumina particles were not coated to form a porous alumina layer. The aluminum nitride powder prepared by the carbothermic reduction reaction at 1680℃ for 10 h had a low oxygen content, but its nitridation rate was low, the D50 particle size was large, and the thermal conductivity of the prepared ceramic substrate was too low.

[0230] The above embodiments of the present invention are merely examples for clearly illustrating the present invention and are not intended to limit the implementation of the present invention. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all possible implementations here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing aluminum nitride powder, characterized in that, Includes the following steps: S1, take alumina particles and perform surface activation to obtain activated alumina particles; S2, the activated alumina particles are subjected to molecular layer deposition treatment to form an aluminoxane film on the surface, thus obtaining coated alumina particles. S3, the coated alumina particles are sintered at 600-800℃ in an oxidizing atmosphere to obtain alumina particles coated with a porous alumina layer; S4. After the alumina particles coated with the porous alumina layer are mixed evenly with carbon black, nitrogen gas is introduced to carry out a carbothermic reduction reaction to obtain the aluminum nitride powder. In step S4, the alumina particles coated with the porous alumina layer are mixed with carbon black and loaded onto a graphite plate. Nitrogen gas is introduced from bottom to top to carry out a carbothermic reduction reaction. The graphite plate is tilted upward along the gas outlet direction.

2. The method for preparing aluminum nitride powder according to claim 1, characterized in that, In step S2, the density of the aluminoxane film is 1.5-1.8 g / cm³.

3. The method for preparing aluminum nitride powder according to claim 1 or 2, characterized in that, In step S2, the molecular layer deposition process includes: S201, the activated alumina particles are placed in the chamber of the molecular layer deposition apparatus, and the chamber temperature is controlled at 85-95℃ and the carrier gas flow rate is 80-100 sccm. S202, pulse injection of oxygen-containing compound, injection time 0.01-0.02 s, wait 3-5 s; S203, pulse injection of trimethylaluminum, injection time 0.05-0.15 s, wait 3-5 s; S204, repeat steps S202 and S203 for 20-150 cycles.

4. The method for preparing aluminum nitride powder according to claim 1, characterized in that, In step S4, the conditions for the carbothermic reduction reaction are: reaction temperature 1450-1650℃, reaction time 3-6h.

5. The method for preparing aluminum nitride powder according to claim 1, characterized in that, In step S4, the carbothermic reduction reaction includes the following steps: S401, the alumina particles coated with the porous alumina layer, carbon black, dispersant and suspending agent are mixed evenly to obtain a mixed powder; S402, after drying the mixed powder, spread it evenly on a graphite plate, then insert the graphite plate into a graphite furnace and introduce nitrogen gas, and carry out a carbothermic reduction reaction at 1450-1650℃ to obtain the aluminum nitride powder.

6. The method for preparing aluminum nitride powder according to claim 5, characterized in that, In step S402, the graphite plate is inserted into the graphite furnace at an upward tilt, with the angle between the graphite plate and the horizontal direction being 15-60°, and the nitrogen gas inlet direction being parallel to the graphite plate.

7. The method for preparing aluminum nitride powder according to claim 5, characterized in that, In step S1, the alumina particles have a particle size of 0.1-1 μm.

8. An aluminum nitride powder, characterized in that, It is prepared by the method for preparing aluminum nitride powder according to any one of claims 1-7.

9. The use of the aluminum nitride powder according to claim 8 in the manufacture of aluminum nitride ceramic substrates.

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