Batch preparation method of high-quality aluminum nitride powder

Abstract

The invention provides a batch preparation method of high-quality aluminum nitride powder. In order to solve the problems that industrially prepared aluminum nitride powder is low in quality and cannot meet the quality requirement, and batch amplification of related technologies faces technical bottlenecks and the like, the preparation method adopts high-purity aluminum oxide and carbon black as raw materials, a solid-phase interface strengthening technology and a circulating pulse ventilation technology, so that the nitridation speed is increased, and the nitridation efficiency is improved. The particle size distribution D50 of the high-quality aluminum nitride prepared by the method is less than 1.0 mu m, the oxygen content is 0.8-0.9%, the purity is greater than or equal to 99.9%, and the method has a good industrial production application prospect.

Description

Technical Field

[0001] This invention relates to a method for the mass production of high-quality aluminum nitride powder. The high-quality aluminum nitride powder prepared by this method is mainly used in fields such as heat dissipation substrates and electronic device packaging. Background Technology

[0002] Aluminum nitride (AlN) possesses excellent properties such as high thermal conductivity, high insulation resistance, and a thermal expansion coefficient that matches that of silicon, making it an ideal material for electronic packaging, heat dissipation substrates for high-power devices, and other fields. High-quality aluminum nitride powder requires high purity, low oxygen content, and uniform particle size distribution, and its preparation technology is a key factor restricting the development of related industries.

[0003] AlN powder is synthesized via carbothermal reduction. This method uses alumina (Al₂O₃) powder and high-purity carbon black as starting materials. After ball milling and mixing, the mixture is heated to above 1500°C in a flowing N₂ atmosphere. After a reaction period, AlN is produced. The reaction formula is as follows:

[0004] Al2O3(s) + 3C(s) + N2(g)→2AlN(s) + 3CO(g)

[0005] However, in the process of scaling up the existing carbothermic reduction method, due to the large thickness of the raw material stack, the inner layer of raw material is difficult to contact with nitrogen, resulting in a slow reaction rate. Furthermore, the CO gas generated in the inner layer is even more difficult to expel, further inhibiting the reaction. This leads to poor uniformity of nitriding between the inner and outer layers. The outer layer product is all aluminum nitride, while the inner layer still contains unreacted alumina, which is difficult to meet the demand for high-quality aluminum nitride powder in large-scale production. Summary of the Invention

[0006] The purpose of this invention is to overcome the aforementioned defects in the batch production stage of aluminum nitride powder preparation by carbothermal reduction method in the prior art, and to provide a method for batch production of high-quality aluminum nitride powder, which can obtain high-quality aluminum nitride powder by controlling key technologies even when the deposition thickness is large.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention provides a method for the mass production of high-quality aluminum nitride powder, comprising the following steps:

[0009] S1: Alumina powder, carbon black and deionized water are prepared into a mixture with a solid content of 30-50 wt%. The mixture is wet-milled in a planetary ball mill for 12-24 hours to make it uniform. It is then freeze-dried to constant weight and solid-phase interface strengthening is used to obtain a tightly packed precursor powder.

[0010] S2: The precursor powder of the preparation method is placed into a high-purity graphite crucible and transferred into a graphite sintering furnace. The pressure change in the furnace is controlled by circulating pulse gas exchange. The nitriding reduction reaction is carried out under high-purity nitrogen gas at a certain pressure and flow rate to obtain aluminum nitride semi-finished product.

[0011] S3: Place the aluminum nitride semi-finished product prepared by the method into a muffle furnace, heat it to 600-650℃ at a heating rate of 80-100℃ / h, hold it at that temperature for 3-5h, and then cool it down to room temperature at a cooling rate of 5℃ / min to obtain high-quality aluminum nitride powder.

[0012] Furthermore, the preparation method uses high-purity γ-phase alumina as the raw material, with a particle size D. 50 <1μm, purity >99.99%. Preparation method: Raw material carbon black: particle size D 50 <0.2μm, purity >99%.

[0013] Furthermore, the mass ratio of Al2O3 to C in the preparation method should be controlled at (2.5~2.85):1.

[0014] Furthermore, the freeze-drying conditions are -80℃ followed by drying for 24 hours.

[0015] Furthermore, the solid-phase interface strengthening technology used in the batch synthesis specifically involves regulating the solid-phase interface interaction between raw material powder particles by applying mechanical pressure, promoting the particles to contact and fill in a better spatial arrangement, and ultimately achieving high-density packing of the raw materials. The mechanical pressure ranges from 1 to 10 MPa, and the pressure application time is from 1 to 10 min.

[0016] Furthermore, the heating rate for batch synthesis is 20–40 °C / min, the reaction temperature is 1500–1800 °C, and the holding time is 2–4 h.

[0017] Furthermore, the reaction atmosphere uses high-purity nitrogen gas with a purity of 99.999%. The nitrogen gas flow rate is 0.5–1 L / min, and the nitrogen gas pressure is 0.1–1 MPa.

[0018] Furthermore, the batch synthesis employs a cyclic pulse gas exchange technology, with a gas exchange pressure range of 0–1 atm. The cyclic gas exchange method is as follows: first, nitrogen is introduced at atmospheric pressure for 15 minutes, then a vacuum is drawn to the target low pressure within 5 minutes, followed by nitrogen introduction for 5 minutes to restore atmospheric pressure, and this process is repeated until the heat preservation is completed.

[0019] Furthermore, the carbon removal process takes place in the air atmosphere of the muffle furnace.

[0020] Furthermore, high-quality aluminum nitride powder D 50 <1.0μm, oxygen content is 0.8-0.9%, purity ≥99.9%.

[0021] The present invention has the following beneficial effects:

[0022] The high-quality aluminum nitride batch preparation method provided by this invention uses highly active, ultrafine Al2O3 and C raw materials in the raw material preparation process and improves the uniformity of raw material mixing, which is conducive to increasing the nitriding rate and thus promoting the complete conversion of Al2O3. In the reaction process, increasing the reaction temperature and holding time, and adopting solid-phase interface strengthening technology and circulating pulse gas exchange technology are also conducive to promoting the complete conversion of Al2O3 into AlN, thereby reducing the presence of impurity oxygen content.

[0023] This invention employs solid-phase interface strengthening technology, which increases the nitriding rate and reduces the particle size of the powder by increasing the bulk density of the raw material powder, thereby making the contact between alumina and carbon black more compact and promoting the solid-phase reaction to a certain extent.

[0024] This invention employs circulating pulse ventilation technology, which, by adjusting the charging and venting rates, creates a periodically changing pressure difference within the synthesis furnace. This not only allows the CO gas generated during the reaction to be discharged from the furnace in a timely manner, ensuring the nitrogen concentration within the furnace, but also enables the CO generated during the reaction to detach from the powder in a timely manner, and allows the nitrogen gas from the reaction raw materials to reach the reaction zone deep within the material layer and on the surface of the powder in a timely manner, ensuring sufficient contact between the nitrogen gas and the powder, thereby promoting the degree and progress of the nitriding reaction and improving the synthesis efficiency. Attached Figure Description

[0025] Figure 1 This is a SEM micrograph of the high-quality aluminum nitride powder prepared in Example 1 of the present invention.

[0026] Figure 2 The XRD diffraction pattern of the high-quality aluminum nitride powder prepared in Example 1 of this invention.

[0027] Figure 3 SEM images of the high-quality aluminum nitride powder prepared in Comparative Example 1 of this invention: (a) 1 μm; (b) 400 nm. Detailed Implementation

[0028] This invention provides a method for the mass production of high-quality aluminum nitride powder, comprising the following steps:

[0029] S1: Alumina powder, carbon black and deionized water are prepared into a mixture with a solid content of 30-50 wt%. The mixture is wet-milled in a planetary ball mill for 12-24 hours to ensure uniform mixing. The mixture is then freeze-dried to constant weight. A tightly packed precursor powder is obtained by using solid-phase interface strengthening technology.

[0030] S2: The precursor powder prepared by the method is placed into a high-purity graphite crucible and transferred into a graphite sintering furnace. The pressure change inside the furnace is controlled by circulating pulse gas exchange technology. The nitriding reduction reaction is carried out under high-purity nitrogen gas at a certain pressure and flow rate to obtain aluminum nitride semi-finished product.

[0031] S3: Place the aluminum nitride semi-finished product prepared by the method into a muffle furnace, heat it to 600-650℃ at a heating rate of 80-100℃ / h, hold it at that temperature for 3-5h, and then cool it down to room temperature at a cooling rate of 5℃ / min to obtain high-quality aluminum nitride powder.

[0032] The technical solutions of the present invention will be described below with reference to specific embodiments. These embodiments are only for illustrating the present invention and do not limit the scope of the present invention.

[0033] Example 1

[0034] A method for mass production of high-quality aluminum nitride powder includes the following steps:

[0035] S1: Prepare a slurry with a solid content of 45% by mixing 1000g of alumina, 370g of carbon black and 1.67L of deionized water. Wet mill the slurry in a ball mill for 24 hours. Freeze-dry the alumina / carbon black slurry to obtain a mixture.

[0036] S2: Place the mixture obtained in S1 into a graphite sintering furnace, heat it to 1800℃ at a rate of 40℃ / min, and hold it at a high-purity nitrogen flow rate of 0.5~1L / min for 2 hours. During the holding process, perform cyclic pulse gas exchange. Specifically, first purge nitrogen at atmospheric pressure for 15 minutes, then evacuate to 0 atm within 5 minutes, and then purge nitrogen for 5 minutes to restore atmospheric pressure. Repeat this process until the holding is completed.

[0037] S3: The aluminum nitride semi-finished product obtained in S2 is placed in a muffle furnace and heated to 650°C at a heating rate of 100°C / h in an air atmosphere. It is held at this temperature for 4 hours and then cooled to room temperature at a cooling rate of 5°C / min to obtain high-quality aluminum nitride powder.

[0038] According to the above scheme, only the circulating pulse ventilation technology is used, such as Figure 1 As shown, in this embodiment, the high-quality aluminum nitride powder obtained in S3 has a small particle size, with an average particle size of about 1 μm, and the grains are irregular granules without agglomeration. Figure 2It was found that the aluminum nitride product was a pure phase, with no impurity peaks in the XRD pattern and an oxygen content of 0.87%. The circulating pulse ventilation technology, through a periodic cycle of "normal pressure nitrogen purging - vacuuming - repressurization," creates a dynamic pressure difference within the furnace, allowing CO gas inside the material layer to be expelled, thus preventing its inhibition of the reaction. Simultaneously, fresh, high-purity nitrogen gas can quickly penetrate deep into the material layer, ensuring sufficient contact between the nitrogen and the powder, thereby promoting the nitriding reaction. However, its use alone has limitations: under natural material stacking conditions, the contact between particles is not tight, resulting in low contact efficiency for the solid-phase reaction.

[0039] Example 2

[0040] S1: Prepare a slurry with a solid content of 45% by mixing 1000g of alumina, 370g of carbon black and 1.67L of deionized water. Wet mill the slurry in a ball mill for 24 hours. Freeze-dry the alumina / carbon black slurry to obtain a mixture.

[0041] S2: Place the mixture obtained in S1 into a graphite sintering furnace, heat it to 1800℃ at a rate of 40℃ / min, and hold it at a high-purity nitrogen flow rate of 0.5~1L / min for 2 hours. During the holding process, perform cyclic pulse gas exchange. Specifically, first purge nitrogen at atmospheric pressure for 15 minutes, then evacuate to 0.25atm within 5 minutes, then purge nitrogen again for 5 minutes to restore atmospheric pressure. Repeat this process until the holding is completed.

[0042] S3: The aluminum nitride semi-finished product obtained in S2 is placed in a muffle furnace and heated to 650°C at a heating rate of 100°C / h in an air atmosphere. It is held at this temperature for 4 hours and then cooled to room temperature at a cooling rate of 5°C / min to obtain high-quality aluminum nitride powder.

[0043] According to the above scheme, the high-quality aluminum nitride powder obtained in S3 in this embodiment was detected as a pure phase with an oxygen content of 0.83%.

[0044] Example 3

[0045] S1: Prepare a slurry with a solid content of 45% by mixing 1000g of alumina, 370g of carbon black and 1.67L of deionized water. Wet mill the slurry in a ball mill for 24 hours. Freeze dry the alumina / carbon black slurry to obtain precursor powder.

[0046] S2: Place the precursor powder obtained in S1 into a graphite sintering furnace, heat it to 1800℃ at a rate of 40℃ / min, and hold it at a high-purity nitrogen flow rate of 0.5~1L / min for 2 hours. During the holding process, perform cyclic pulse gas exchange. Specifically, first purge nitrogen at atmospheric pressure for 15 minutes, then evacuate to 0.5atm within 5 minutes, then purge nitrogen for 5 minutes to restore atmospheric pressure. Repeat this process until the holding is completed.

[0047] S3: The aluminum nitride semi-finished product obtained in S2 is placed in a muffle furnace and heated to 650°C at a heating rate of 100°C / h in an air atmosphere. It is held at this temperature for 4 hours and then cooled to room temperature at a cooling rate of 5°C / min to obtain high-quality aluminum nitride powder.

[0048] According to the above scheme, the high-quality aluminum nitride powder obtained in S3 in this embodiment was detected as a pure phase with an oxygen content of 0.80%.

[0049] Example 4

[0050] S1: Prepare a slurry with a solid content of 45% by mixing 1000g of alumina, 370g of carbon black and 1.67L of deionized water. Wet mill the slurry in a ball mill for 24 hours. Freeze dry the alumina / carbon black slurry to obtain precursor powder.

[0051] S2: Place the precursor powder obtained in S1 into a graphite sintering furnace, heat it to 1800℃ at a rate of 40℃ / min, and hold it at a high-purity nitrogen flow rate of 0.5~1L / min for 2 hours. During the holding process, perform cyclic pulse gas exchange. Specifically, first purge nitrogen at atmospheric pressure for 15 minutes, then evacuate to 0.75atm within 5 minutes, then purge nitrogen for 5 minutes to restore atmospheric pressure. Repeat this process until the holding is completed.

[0052] S3: The aluminum nitride semi-finished product obtained in S2 is placed in a muffle furnace and heated to 650°C at a heating rate of 100°C / h in an air atmosphere. It is held at this temperature for 4 hours and then cooled to room temperature at a cooling rate of 5°C / min to obtain high-quality aluminum nitride powder.

[0053] According to the above scheme, the high-quality aluminum nitride powder obtained in S3 in this embodiment was detected as a pure phase with an oxygen content of 0.85%.

[0054] Example 5:

[0055] A method for mass production of high-quality aluminum nitride powder includes the following steps:

[0056] S1: Prepare a slurry with a solid content of 45% by mixing 1000g alumina, 370g carbon black and 1.67L deionized water. Wet mill the slurry in a ball mill for 24 hours. Freeze dry the alumina / carbon black slurry to obtain precursor powder. Using solid-phase interface strengthening technology, apply pressure to the dried mixture at 1MPa mechanical pressure for 5 minutes to obtain a closely packed precursor.

[0057] S2: Place the precursor obtained in S1 into a graphite sintering furnace, heat it to 1800℃ at a heating rate of 40℃ / min, with a high-purity nitrogen flow rate of 0.5~1L / min, hold it at that temperature for 2 hours, and then cool it to room temperature before taking it out.

[0058] S3: The aluminum nitride semi-finished product obtained in S2 is placed in a muffle furnace and heated to 650°C at a heating rate of 100°C / h in an air atmosphere. It is held at this temperature for 4 hours and then cooled to room temperature at a cooling rate of 5°C / min to obtain high-quality aluminum nitride powder.

[0059] According to the above scheme, using only solid-phase interface strengthening technology, the high-quality aluminum nitride powder obtained in S3 of this embodiment was detected as a pure phase with an oxygen content of 1.07%. Solid-phase interface strengthening technology regulates the spatial arrangement of raw material particles by applying mechanical pressure, causing alumina and carbon black to form a highly dense packing, enhancing the interfacial interaction between raw material particles, expanding the contact area of ​​the solid-phase reaction, and increasing the nitriding reaction rate. However, it has significant limitations when used alone: ​​the tightly packed material layer makes it difficult for the CO gas generated in the reaction to quickly escape from the particle surface, easily accumulating inside; nitrogen gas also has difficulty entering the interior of the material layer, ultimately resulting in an oxygen content >1.0%.

[0060] Comparative Example 1

[0061] A method for mass production of high-quality aluminum nitride powder includes the following steps:

[0062] S1: Prepare a slurry with a solid content of 45% by mixing 1000g alumina, 370g carbon black and 1.67L deionized water. Wet mill the slurry in a ball mill for 24 hours. Freeze dry the alumina / carbon black slurry. Using solid-phase interface strengthening technology, apply pressure to the dried mixture at 1MPa mechanical pressure for 5 minutes to obtain a closely packed precursor.

[0063] S2: Place the precursor obtained in S1 into a graphite sintering furnace, heat it to 1800℃ at a rate of 40℃ / min, and hold it at a high-purity nitrogen flow rate of 0.5~1L / min for 2 hours. During the holding process, perform cyclic pulse gas exchange. Specifically, first purge nitrogen at atmospheric pressure for 15 minutes, then evacuate to 0 atm within 5 minutes, and then purge nitrogen for 5 minutes to restore atmospheric pressure. Repeat this process until the holding is completed.

[0064] S3: The aluminum nitride semi-finished product obtained in S2 is placed in a muffle furnace and heated to 650°C at a heating rate of 100°C / h in an air atmosphere. It is held at this temperature for 4 hours and then cooled to room temperature at a cooling rate of 5°C / min to obtain high-quality aluminum nitride powder.

[0065] According to the above plan, such as Figure 3As shown, the aluminum nitride product obtained in S3 of this comparative example has a very small particle size, only about 400 nm, and the particles are mostly monodisperse with little agglomeration. Compared with Example 1 (average particle size about 1 μm), it can be seen that the particle size of aluminum nitride can be effectively reduced by solid-phase interface strengthening technology. The aluminum nitride product was detected as a pure phase with an oxygen content of 0.85%. Its oxygen content is lower than that of products using only circulating pulse ventilation technology (Example 1, oxygen content of 0.87%) or only using solid-phase interface strengthening technology (Example 5, oxygen content of 1.07%).

[0066] Simultaneously employing solid-phase interface strengthening technology and circulating pulse gas exchange technology, the compact packing of solid-phase strengthening ensures sufficient contact between raw material particles, increasing the contact area of ​​the reaction interface; the dynamic pressure difference of circulating pulse gas exchange rapidly removes the CO generated in the reaction, preventing CO from accumulating at the particle interface, while continuously replenishing high-purity nitrogen, ensuring that the closely contacting raw materials are always in a sufficient reaction atmosphere—the combination of these two technologies creates a cycle between "reaction occurrence" and "reaction continuation," jointly promoting the forward progress of the carbothermic reduction reaction.

[0067] Comparative Example 2

[0068] A method for mass production of high-quality aluminum nitride powder includes the following steps:

[0069] S1: Prepare a slurry with a solid content of 45% by mixing 1000g of alumina, 370g of carbon black and 1.67L of deionized water. Wet mill the slurry in a ball mill for 24 hours. Freeze dry the alumina / carbon black slurry to obtain precursor powder.

[0070] S2: Place the precursor powder obtained in S1 into a graphite sintering furnace, heat it to 1800℃ at a rate of 40℃ / min, and hold it at a high-purity nitrogen flow rate of 0.5-1L / min for 2 hours. During the holding process, perform cyclic pulse gas exchange. Specifically, first purge nitrogen at atmospheric pressure for 15 minutes, then evacuate to 0.25 atm within 5 minutes, maintain the low pressure for 15 minutes, and then purge nitrogen to restore atmospheric pressure within 5 minutes. Repeat this process until the holding is completed.

[0071] S3: The aluminum nitride semi-finished product obtained in S2 is placed in a muffle furnace and heated to 650°C at a heating rate of 100°C / h in an air atmosphere. It is held at this temperature for 4 hours and then cooled to room temperature at a cooling rate of 5°C / min to obtain high-quality aluminum nitride powder.

[0072] According to the above scheme, the high-quality aluminum nitride powder obtained in S3 of this comparative example was found to be a pure phase with an oxygen content of 1.78%. Compared with Example 2, the oxygen content of the aluminum nitride powder is significantly increased. A short pulse (0 minutes) can quickly remove oxygen-containing gases (such as Al2O and CO) without disrupting the reaction process. However, maintaining low pressure for 15 minutes leads to two problems: first, AlN begins to decompose under low pressure, producing active Al that adsorbs oxygen; second, prolonged low pressure keeps the reaction in a nitrogen-deficient state, increasing nitrogen vacancies and making it easier for oxygen to enter the crystal lattice. Therefore, although reducing pressure helps deoxygenation, maintaining a prolonged low-pressure state significantly increases the oxygen content.

[0073] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0074] Furthermore, various embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for mass production of high-quality aluminum nitride powder, characterized in that, Includes the following steps: S1: Alumina powder, carbon black and deionized water are prepared into a mixture with a solid content of 30-50 wt%. The mixture is wet-milled in a planetary ball mill for 12-24 hours to make it uniform. It is then freeze-dried to constant weight. The precursor powder with a tight packing is obtained by using solid phase interface strengthening technology. S2: The precursor powder is placed into a high-purity graphite crucible and transferred into a graphite sintering furnace. The pressure change inside the furnace is controlled by circulating pulse gas exchange. The nitriding reduction reaction is carried out under high-purity nitrogen gas at a certain pressure and flow rate to obtain aluminum nitride semi-finished product. S3: Place the aluminum nitride semi-finished product in a muffle furnace, heat it to 600-650℃ at a heating rate of 80-100℃ / h, hold it at that temperature for 3-5h, and then cool it down to room temperature at a cooling rate of 5℃ / min to obtain high-quality aluminum nitride powder.

2. The method for mass production of high-quality aluminum nitride powder as described in claim 1, characterized in that: The alumina powder is high-purity γ-phase alumina with a particle size D. 50 <1μm, purity >99.99%; the carbon black: particle size D 50 <0.2μm, purity >99%.

3. The preparation method according to claim 1, characterized in that, The mass ratio of alumina to carbon black should be controlled at (2.5~2.85):

1.

4. The preparation method according to claim 1, characterized in that, The freeze-drying conditions are -80℃ followed by drying for 24 hours.

5. The preparation method according to claim 1, characterized in that, The aforementioned solid-phase interface strengthening specifically involves regulating the solid-phase interface interaction between raw material powder particles by applying mechanical pressure, promoting the particles to achieve contact and filling in a more optimal spatial arrangement, and ultimately achieving high-density packing of the raw materials. The mechanical pressure ranges from 1 to 10 MPa, and the pressure application time is 1 to 10 minutes.

6. The preparation method according to claim 1, characterized in that, The heating rate is 20-40℃ / min, the reaction temperature is 1500-1800℃, and the holding time is 2-4h.

7. The preparation method according to claim 1, characterized in that, The reaction atmosphere uses high-purity nitrogen gas with a purity of 99.999%. The nitrogen gas flow rate is 0.5–1 L / min. The nitrogen gas pressure is 0.1–1 MPa.

8. The preparation method according to claim 1, characterized in that, The aforementioned cyclic pulse ventilation has a ventilation pressure range of 0–1 atm. The cyclic ventilation method is as follows: first, nitrogen is introduced at normal pressure for 15 minutes, then a vacuum is drawn to the target low pressure within 5 minutes, followed by nitrogen introduction to restore normal pressure within 5 minutes. This process is repeated until the heat preservation is completed.

9. The preparation method according to claim 1, characterized in that, The carbon removal process takes place in the air atmosphere of the muffle furnace.

10. The high-quality aluminum nitride powder prepared by the preparation method according to any one of claims 1-9, characterized in that, The aluminum powder D 50 <1.0μm, oxygen content is 0.8-0.9%, purity ≥99.9%.

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