A method for preparing a high thermal conductivity aluminum nitride ceramic

Abstract

The application relates to the technical field of ceramic preparation, and provides a preparation method of high-thermal-conductivity aluminum nitride ceramic, which solves the problems of relatively poor thermal conductive performance and bending strength of the aluminum nitride ceramic prepared by the prior art; the method comprises the following preparation steps: 1) raw material preparation; 2) ball milling mixing; 3) preheating reduction; and 4) hot-pressing sintering.

Description

Technical Field

[0001] This invention relates to the field of ceramic preparation technology, and in particular to a method for preparing aluminum nitride ceramics with high thermal conductivity. Background Technology

[0002] Aluminum nitride (AlN) is a new generation of advanced heat dissipation material with high thermal conductivity (theoretically up to 320 W·m). -1 ·K -1 It possesses advantages such as good insulation (>10¹⁴ Ω cm), certain mechanical properties (bending strength 300~650 MPa), a coefficient of thermal expansion comparable to silicon, and non-toxicity. It is commonly used as a substrate material, capable of resisting thermal stress shocks caused by circuits and effectively dissipating heat.

[0003] Chinese Patent Application No. 202110920742.6 discloses an aluminum nitride ceramic casting slurry, an aluminum nitride ceramic substrate, and a preparation method thereof. The aluminum nitride ceramic casting slurry is made from the following raw materials in parts by weight: 100 parts aluminum nitride powder, 3-10 parts sintering aid, 1-6 parts dispersant, 50-100 parts organic solvent, 10-50 parts binder, 1-15 parts plasticizer, and 0.5-2 parts defoamer. The sintering aid consists of component A and component B. Component A is at least one of yttrium trioxide and calcium oxide, and component B is at least one of niobium pentoxide, cerium oxide, and samarium oxide. Therefore, the sintering temperature of the aluminum nitride ceramic substrate does not exceed 1800℃, the sintering heating rate is higher than 5℃ / min, and the sintering holding time can be less than 3 hours, improving the efficiency of the preparation process without degrading the ceramic properties. However, the aluminum nitride ceramic prepared by this invention has poor thermal conductivity, only 175-184 W·m. -1 ·K -1 .

[0004] Chinese Patent Application No. 202410606989.4 discloses an aluminum nitride ceramic sintered body, its preparation method, and an aluminum nitride ceramic substrate. The sintering body comprises pure aluminum nitride powder and a composite sintering aid. The composite sintering aid includes a Li-containing compound, a Ca-containing compound, and a Y-containing compound. The mass ratio of each component in the composite sintering aid is: Y-containing compound > Ca-containing compound > Li-containing compound. The mass of the Y-containing compound is calculated as Y₂O₃, the mass of the Ca-containing compound as CaF₂, and the mass of the Li-containing compound as Li₂O. The aluminum nitride ceramic substrate of this invention possesses both high thermal conductivity and high flexural strength, with a thermal conductivity of 198-249 W·m. -1 ·K -1 It has a high flexural strength greater than 500 MPa. However, its thermal conductivity still cannot exceed 250 W·m. -1 ·K -1 . Summary of the Invention

[0005] Therefore, in view of the above problems, the present invention provides a method for preparing aluminum nitride ceramics with high thermal conductivity, which solves the problem that the aluminum nitride ceramics prepared by the prior art have relatively poor thermal conductivity and bending strength.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing high thermal conductivity aluminum nitride ceramics includes the following preparation steps:

[0008] S1. Preparation of raw materials: including AlN powder, Y2O3 powder, BN powder and anhydrous ethanol;

[0009] S2. Ball milling and mixing: Weigh 96-98 parts by weight of the AlN powder and 2-4 parts by weight of Y2O3 powder, add them to a ball mill jar, mix them to obtain a first mixed powder, add Al2O3 particles according to the mass ratio of the first mixed powder to Al2O3 particles of 1:6-7, and add anhydrous ethanol according to the solid-liquid ratio of the first mixed powder to anhydrous ethanol of 1:1-1.5, purge with nitrogen for protection, seal, and ball mill for 6-8 hours to obtain a slurry;

[0010] S3. Preheating and Reduction: The slurry obtained in step S2 is placed in a drying furnace to evaporate ethanol, resulting in a second mixed powder. The second mixed powder is sieved and then added to a BN crucible. The BN crucible is placed in a sintering furnace equipped with a graphite generator at a pressure of 45-50 MPa. Nitrogen gas is introduced for protection, and the temperature is increased to 1500-1550℃ at a heating rate of 100℃ / min. The temperature is held for 1-4 hours, and then cooled to room temperature at a cooling rate of 10℃ / min to obtain a third mixed powder.

[0011] S4. Hot pressing sintering: The third mixed powder after preheating and reduction in step S3 is transferred to a hot pressing mold. The hot pressing mold is placed in a vacuum hot pressing sintering furnace for hot pressing sintering at a pressure of 30-35 MPa. The temperature is increased to 1750-1800°C at a heating rate of 10°C / min, held for 5-6 hours, and then cooled to room temperature at a cooling rate of 5°C / min to obtain the high thermal conductivity aluminum nitride ceramic.

[0012] The hot pressing mold is made of graphite and has a BN powder coating inside; the BN crucible includes a crucible body and a crucible lid, and the crucible lid has an array of holes.

[0013] Furthermore, the preparation process of the BN powder is as follows:

[0014] a. Mix boric acid and melamine in a molar ratio of 2-3:1 to obtain a mixture. Disperse the mixture in deionized water in a solid-liquid ratio of 1:20-25. Heat the mixture in a water bath at 95-100°C and stir until completely dissolved. Then lower the temperature to 80-85°C and keep it at that temperature for 6-8 hours. Cool to room temperature to obtain a mixed solution.

[0015] b. Filter the mixture obtained in step a, dry the filter cake to obtain the boron nitride precursor;

[0016] c. Transfer the boron nitride precursor obtained in step b to a tube furnace, introduce nitrogen for protection, raise the temperature to 1000-1050℃, hold for 4-6 hours, and cool to room temperature to obtain the BN powder.

[0017] Furthermore, the particle size of the BN powder is 50-500 nm.

[0018] Furthermore, the particle size of the Al2O3 spheres is 20-100 nm.

[0019] Furthermore, the oxygen content of the AlN powder is 0.85 wt%.

[0020] Furthermore, the purity of the Y2O3 is ≥99.99%.

[0021] Furthermore, the nitrogen protection is achieved by introducing nitrogen gas at a flow rate of 2 L / min, wherein the purity of the nitrogen gas is ≥99.999%.

[0022] By adopting the aforementioned technical solution, the beneficial effects of the present invention are as follows:

[0023] 1. The key to obtaining high thermal conductivity AlN ceramics is to avoid the influence of oxygen impurities and prevent excessive oxygen from entering the AlN lattice. Pre-reduction can effectively reduce the oxygen content of the powder and reduce the introduction of oxygen elements; in addition, during sintering, Al2O3 reacts with Y2O3 to co-generate Al5Y3O 12 The three edge phases of AlN grains are YAlO, Y4Al2O9, and Y4Al2O9. After the powder oxide layer is weakened, the edge phase of AlN grains changes from YAlO to Y4Al2O9. Y4Al2O9 is more conducive to purifying oxygen impurities in AlN lattice, achieving high thermal conductivity of AlN ceramics, and making the prepared AlN ceramics have both high thermal conductivity and high bending strength.

[0024] 2. Higher density of AlN ceramics enables them to withstand greater external forces, improving their bending strength and hardness. Sintering at lower temperatures increases the density of AlN ceramics, making the pores between AlN grains smaller and reducing porosity. This results in a smaller area for edge phase flow and convergence, leading to more uniform and finer grain edge phases.

[0025] 3. In the preheating and reduction step, the sieved second mixed powder is added to the BN crucible, and then the BN crucible is placed in a sintering furnace equipped with a graphite generator for preheating and reduction. Ordinary graphite crucibles are not used because BN crucibles are chemically inert to most molten metals, glass, and slag, which can effectively prevent the crucible from reacting with the molten metal Al2O3 and affecting the thermal conductivity of AlN ceramics. Secondly, the thermal conductivity of BN crucibles does not change with temperature, which is especially important for the production process of AlN ceramics where precise temperature control is required, to avoid the heating process affecting the preheating and reduction temperature. Similarly, a BN powder coating is provided inside the hot pressing mold to prevent the crucible from reacting with the molten metal Al2O3 and to accurately control the sintering reaction temperature. Detailed Implementation Example 1

[0026] A method for preparing high thermal conductivity aluminum nitride ceramics includes the following preparation steps:

[0027] (1) Preparation of raw materials: including AlN powder with an oxygen content of 0.85wt%, Y2O3 powder with a purity of ≥99.99%, BN powder with a particle size of 180nm and anhydrous ethanol;

[0028] (2) Preparation of BN powder

[0029] (2-1) Boric acid and melamine are mixed in a molar ratio of 2:1 to obtain a mixture. The mixture is dispersed in deionized water in a solid-liquid ratio of 1:20. The mixture is heated in a water bath at 95°C and stirred until completely dissolved. Then the temperature is lowered to 80°C and kept at that temperature for 6 hours. The mixture is then cooled to room temperature to obtain a mixed solution.

[0030] (2-2) Filter the mixture obtained in step a, dry the filter cake to obtain the boron nitride precursor;

[0031] (2-3) The boron nitride precursor obtained in step b is transferred to a tube furnace, nitrogen gas is introduced for protection, the temperature is raised to 1050°C, held for 4 hours, and cooled to room temperature to obtain the BN powder.

[0032] (3) Ball milling and mixing: Weigh 98 parts by weight of the AlN powder and 2 parts by weight of Y2O3 powder, add them to a ball mill jar, mix them to obtain a first mixed powder, add Al2O3 particles according to the mass ratio of the first mixed powder to Al2O3 particles of 1:6, the particle size of the Al2O3 particles is 20nm, and add anhydrous ethanol to the ball mill jar according to the solid-liquid ratio of the first mixed powder to anhydrous ethanol of 1:1, pass nitrogen gas with a purity of ≥99.999% at a flow rate of 2 L / min for protection, seal, and ball mill for 6h to obtain a slurry;

[0033] (4) Preheating and reduction: The slurry obtained in step (3) is placed in a drying furnace to evaporate ethanol to obtain a second mixed powder. The second mixed powder is sieved and then added to a BN crucible. The BN crucible includes a crucible body and a crucible lid. The crucible lid is provided with an array of holes. The BN crucible is placed in a sintering furnace with a graphite generator at a pressure of 45 MPa. Nitrogen gas with a purity of ≥99.999% is introduced at a flow rate of 2 L / min for protection. The temperature is increased to 1550℃ at a heating rate of 100℃ / min and held for 2 hours. Then, the temperature is cooled to room temperature at a cooling rate of 10℃ / min to obtain a third mixed powder.

[0034] (5) Hot pressing sintering: The third mixed powder after preheating and reduction in step (4) is transferred to a hot pressing mold made of graphite. The hot pressing mold is coated with BN powder. The hot pressing mold is placed in a vacuum hot pressing sintering furnace for hot pressing sintering at a pressure of 35 MPa. The temperature is increased to 1750°C at a heating rate of 10°C / min, held for 5 hours, and then cooled to room temperature at a cooling rate of 5°C / min to obtain the high thermal conductivity aluminum nitride ceramic. Example 2

[0035] A method for preparing high thermal conductivity aluminum nitride ceramics includes the following preparation steps:

[0036] (1) Preparation of raw materials: including AlN powder with an oxygen content of 0.85wt%, Y2O3 powder with a purity of ≥99.99%, BN powder with a particle size of 200nm and anhydrous ethanol;

[0037] (2) Preparation of BN powder

[0038] (2-1) Boric acid and melamine are mixed in a molar ratio of 2:1 to obtain a mixture. The mixture is dispersed in deionized water in a solid-liquid ratio of 1:20. The mixture is heated in a water bath at 100°C and stirred until completely dissolved. Then the temperature is lowered to 80°C and kept at that temperature for 8 hours. The mixture is then cooled to room temperature to obtain a mixed solution.

[0039] (2-2) Filter the mixture obtained in step a, dry the filter cake to obtain the boron nitride precursor;

[0040] (2-3) The boron nitride precursor obtained in step b is transferred to a tube furnace, nitrogen gas is introduced for protection, the temperature is raised to 1050°C, held for 4 hours, and cooled to room temperature to obtain the BN powder.

[0041] (3) Ball milling and mixing: Weigh 96 parts by weight of the AlN powder and 4 parts by weight of Y2O3 powder, add them to a ball mill jar, mix them to obtain a first mixed powder, add Al2O3 particles according to the mass ratio of the first mixed powder to Al2O3 particles of 1:6.5, the particle size of the Al2O3 particles is 50nm, and add anhydrous ethanol to the ball mill jar according to the solid-liquid ratio of the first mixed powder to anhydrous ethanol of 1:1.5. Produce nitrogen gas with a purity of ≥99.999% at a flow rate of 2 L / min, seal, and ball mill for 8 hours to obtain a slurry;

[0042] (4) Preheating and reduction: The slurry obtained in step (3) is placed in a drying furnace to evaporate ethanol to obtain a second mixed powder. The second mixed powder is sieved and then added to a BN crucible. The BN crucible includes a crucible body and a crucible lid. The crucible lid is provided with an array of holes. The BN crucible is placed in a sintering furnace with a graphite generator at a pressure of 45 MPa. Nitrogen gas with a purity of ≥99.999% is introduced at a flow rate of 2 L / min for protection. The temperature is increased to 1550℃ at a heating rate of 100℃ / min and held for 3 hours. Then, the temperature is cooled to room temperature at a cooling rate of 10℃ / min to obtain a third mixed powder.

[0043] (5) Hot pressing sintering: The third mixed powder after preheating and reduction in step (4) is transferred to a hot pressing mold made of graphite. The hot pressing mold is coated with BN powder. The hot pressing mold is placed in a vacuum hot pressing sintering furnace for hot pressing sintering at a pressure of 30 MPa. The temperature is increased to 1780°C at a heating rate of 10°C / min, held for 5 hours, and then cooled to room temperature at a cooling rate of 5°C / min to obtain the high thermal conductivity aluminum nitride ceramic. Example 3

[0044] A method for preparing high thermal conductivity aluminum nitride ceramics includes the following preparation steps:

[0045] (1) Preparation of raw materials: including AlN powder with an oxygen content of 0.85wt%, Y2O3 powder with a purity of ≥99.99%, BN powder with a particle size of 200nm and anhydrous ethanol;

[0046] (2) Preparation of BN powder

[0047] (2-1) Boric acid and melamine are mixed in a molar ratio of 2:1 to obtain a mixture. The mixture is dispersed in deionized water in a solid-liquid ratio of 1:25. The mixture is heated in a water bath at 100°C and stirred until completely dissolved. Then the temperature is lowered to 85°C and kept at that temperature for 7 hours. The mixture is then cooled to room temperature to obtain a mixed solution.

[0048] (2-2) Filter the mixture obtained in step a, dry the filter cake to obtain the boron nitride precursor;

[0049] (2-3) The boron nitride precursor obtained in step b is transferred to a tube furnace, nitrogen gas is introduced for protection, the temperature is raised to 1050°C, held for 5 hours, and cooled to room temperature to obtain the BN powder.

[0050] (3) Ball milling and mixing: Weigh 97 parts by weight of the AlN powder and 3 parts by weight of Y2O3 powder, add them to a ball mill jar, mix them to obtain a first mixed powder, add Al2O3 particles according to the mass ratio of the first mixed powder to Al2O3 particles of 1:7, the particle size of the Al2O3 particles is 100nm, and add anhydrous ethanol to the ball mill jar according to the solid-liquid ratio of the first mixed powder to anhydrous ethanol of 1:1, pass nitrogen gas with a purity of ≥99.999% at a flow rate of 2L / min for protection, seal, and ball mill for 7h to obtain a slurry;

[0051] (4) Preheating and reduction: The slurry obtained in step (3) is placed in a drying furnace to evaporate ethanol to obtain a second mixed powder. The second mixed powder is sieved and then added to a BN crucible. The BN crucible includes a crucible body and a crucible lid. The crucible lid is provided with an array of holes. The BN crucible is placed in a sintering furnace with a graphite generator at a pressure of 50 MPa. Nitrogen gas with a purity of ≥99.999% is introduced at a flow rate of 2 L / min for protection. The temperature is increased to 1550℃ at a heating rate of 100℃ / min and held for 4 hours. Then, the temperature is cooled to room temperature at a cooling rate of 10℃ / min to obtain a third mixed powder.

[0052] (5) Hot pressing sintering: The third mixed powder after preheating and reduction in step (4) is transferred to a hot pressing mold made of graphite. The hot pressing mold is coated with BN powder. The hot pressing mold is placed in a vacuum hot pressing sintering furnace for hot pressing sintering at a pressure of 35 MPa. The temperature is increased to 1800°C at a heating rate of 10°C / min, held for 5 hours, and then cooled to room temperature at a cooling rate of 5°C / min to obtain the high thermal conductivity aluminum nitride ceramic.

[0053] Comparative Example 1

[0054] The difference from Example 1 is that the raw materials used are not AlN powder, Y2O3 powder, BN powder, and anhydrous ethanol as described in this invention. Instead, the raw materials used include: 100 parts aluminum nitride powder, 3 parts sintering aid, 1 part dispersant, 50 parts organic solvent, 10 parts binder, 1 part plasticizer, and 0.5 parts defoamer. The sintering aid includes Y2O3 and niobium pentoxide in a 1:2 ratio. The dispersant is trioleic acid glyceride, the organic solvent is isopropanol, the binder is polyvinyl butyral, the plasticizer is dibutyl phthalate, and the defoamer is octanol. The preparation steps do not include the preparation of BN powder and preheating reduction. The preparation steps include: ball milling and mixing the raw materials, casting and slicing to obtain cast sheets, punching and debinding, and sintering to obtain aluminum nitride ceramic products. Other technical solutions are the same as in Example 1.

[0055] Comparative Example 2

[0056] The difference from Example 1 is that the raw materials used are not AlN powder, Y2O3 powder, BN powder, and anhydrous ethanol as described in this invention. Instead, the raw materials used include: 100 parts aluminum nitride powder, 5 parts sintering aid, 3 parts dispersant, 80 parts organic solvent, 30 parts binder, 10 parts plasticizer, and 1 part defoamer. The sintering aid includes Y2O3 and niobium pentoxide in a 1:2 ratio. The dispersant is trioleic acid glyceride, the organic solvent is isopropanol, the binder is polyvinyl butyral, the plasticizer is dibutyl phthalate, and the defoamer is octanol. The preparation steps do not include the preparation of BN powder and preheating reduction. The preparation steps include: ball milling and mixing the raw materials, casting and slicing to obtain a cast sheet, punching and debinding, and sintering to obtain the aluminum nitride ceramic product. Other technical solutions are the same as in Example 1.

[0057] Comparative Example 3

[0058] The difference from Example 1 is that the raw materials used are not AlN powder, Y2O3 powder, BN powder, and anhydrous ethanol as described in this invention. Instead, the raw materials used include: 100 parts aluminum nitride powder, 10 parts sintering aid, 6 parts dispersant, 100 parts organic solvent, 50 parts binder, 15 parts plasticizer, and 2 parts defoamer. The sintering aid includes Y2O3 and niobium pentoxide in a 1:2 ratio. The dispersant is trioleic acid glyceride, the organic solvent is isopropanol, the binder is polyvinyl butyral, the plasticizer is dibutyl phthalate, and the defoamer is octanol. The preparation steps do not include the preparation of BN powder and preheating reduction. The preparation steps include: ball milling and mixing the raw materials, casting and slicing to obtain cast sheets, punching and debinding, and sintering to obtain aluminum nitride ceramic products. Other technical solutions are the same as in Example 1.

[0059] The performance test results of the products of Examples 1, 2, and 3 and Comparative Examples 1, 2, and 3 are shown in the table below.

[0060] Table 1

[0061]

[0062] Examples 1, 2, and 3 all exhibited good results in terms of thermal conductivity, flexural strength, and density. This demonstrates that the aluminum nitride ceramics prepared using this invention are of high quality.

[0063] 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 high thermal conductivity aluminum nitride ceramics, characterized in that, The preparation steps include the following: S1. Preparation of raw materials: including AlN powder, Y2O3 powder, BN powder and anhydrous ethanol; S2. Ball milling and mixing: Weigh 96-98 parts by weight of the AlN powder and 2-4 parts by weight of Y2O3 powder, add them to a ball mill jar, mix them to obtain a first mixed powder, add Al2O3 particles according to the mass ratio of the first mixed powder to Al2O3 particles of 1:6-7, and add anhydrous ethanol according to the solid-liquid ratio of the first mixed powder to anhydrous ethanol of 1:1-1.5, purge with nitrogen for protection, seal, and ball mill for 6-8 hours to obtain a slurry; S3. Preheating and Reduction: The slurry obtained in step S2 is placed in a drying furnace to evaporate ethanol, resulting in a second mixed powder. The second mixed powder is sieved and then added to a BN crucible. The BN crucible is placed in a sintering furnace equipped with a graphite generator at a pressure of 45-50 MPa. Nitrogen gas is introduced for protection, and the temperature is increased to 1500-1550℃ at a heating rate of 100℃ / min. The temperature is held for 1-4 hours, and then cooled to room temperature at a cooling rate of 10℃ / min to obtain a third mixed powder. S4. Hot pressing sintering: The third mixed powder after preheating and reduction in step S3 is transferred to a hot pressing mold. The hot pressing mold is placed in a vacuum hot pressing sintering furnace for hot pressing sintering at a pressure of 30-35 MPa. The temperature is increased to 1750-1800°C at a heating rate of 10°C / min, held for 5-6 hours, and then cooled to room temperature at a cooling rate of 5°C / min to obtain the high thermal conductivity aluminum nitride ceramic. The hot pressing mold is made of graphite and has a BN powder coating inside; the BN crucible includes a crucible body and a crucible lid, and the crucible lid has an array of holes.

2. The method for preparing high thermal conductivity aluminum nitride ceramic according to claim 1, characterized in that, The preparation process of the BN powder is as follows: a. Mix boric acid and melamine in a molar ratio of 2-3:1 to obtain a mixture. Disperse the mixture in deionized water in a solid-liquid ratio of 1:20-25. Heat the mixture in a water bath at 95-100°C and stir until completely dissolved. Then lower the temperature to 80-85°C and keep it at that temperature for 6-8 hours. Cool to room temperature to obtain a mixed solution. b. Filter the mixture obtained in step a, dry the filter cake to obtain the boron nitride precursor; c. Transfer the boron nitride precursor obtained in step b to a tube furnace, introduce nitrogen for protection, raise the temperature to 1000-1050℃, hold for 4-6 hours, and cool to room temperature to obtain the BN powder.

3. The method for preparing a high thermal conductivity aluminum nitride ceramic according to claim 1, characterized in that: The particle size of the BN powder is 50-500 nm.

4. The method for preparing a high thermal conductivity aluminum nitride ceramic according to claim 1, characterized in that: The oxygen content of the AlN powder is 0.85 wt%.

5. The method for preparing a high thermal conductivity aluminum nitride ceramic according to claim 1, characterized in that: The purity of the Y2O3 is ≥99.99%.

6. A method for preparing a high thermal conductivity aluminum nitride ceramic according to any one of claims 1-2, characterized in that, The nitrogen protection is achieved by introducing nitrogen gas at a flow rate of 2 L / min, wherein the purity of the nitrogen gas is ≥99.999%.

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