Preparation method of high-thermal-conductivity aluminum nitride ceramic based on double-atmosphere heat treatment

Abstract

This invention belongs to the field of ceramic technology, specifically relating to a method for in-situ deoxidation and improvement of thermal conductivity of aluminum nitride ceramics through dual-atmosphere heat treatment. The method includes the following steps: ball milling and mixing aluminum nitride, sintering aids, and solvents to obtain a ceramic slurry; spray granulating the ceramic slurry to obtain AlN granulated powder; placing the AlN granulated powder in a CO / N2 atmosphere and holding it at 400-800°C for a first-stage heat treatment; then molding the resulting treated AlN ceramic powder to obtain an AlN ceramic green body; and finally, subjecting the AlN ceramic green body to a second-stage hot isostatic pressing treatment in an H2 / N2 atmosphere. This invention achieves in-situ purification without relying on external additives, thereby improving the thermal conductivity of AlN ceramics.

Description

Technical Field

[0001] This invention belongs to the field of ceramic technology, specifically relating to a method for in-situ deoxidation of aluminum nitride ceramics to improve thermal conductivity through dual-atmosphere heat treatment. Background Technology

[0002] Aluminum nitride (AlN) ceramics are widely used in high-power electronic packaging, electrostatic chucks, and LED heat dissipation substrates due to their excellent thermal conductivity, electrical insulation, and thermal expansion matching. Lattice oxygen impurities in AlN are one of the key intrinsic factors leading to a significant decrease in thermal conductivity. Theoretically, the thermal conductivity of AlN with a perfect lattice can exceed 320 W·m. -1 ·K -1 However, the actual sintered body typically only has 170~200 W·m -1 ·K -1 The fundamental reason lies in the solid solution behavior of oxygen in the AlN lattice. Oxygen atoms readily substitute for nitrogen sites to form an Al-ON solid solution structure, introducing numerous lattice defects and localized stress fields, which strongly scatter phonons, thereby inhibiting heat conduction. Furthermore, the presence of alumina impurities (Al₂O₃) and AlON forms a non-thermally conductive glassy phase or discontinuous interface layer at grain boundaries, further hindering phonon transport between grains. Therefore, effectively removing oxygen without introducing secondary impurities is the core technological bottleneck for improving the thermal conductivity of AlN ceramics.

[0003] Traditional AlN deoxidation methods typically involve using ceramic powders with low oxygen content, altering the degreasing atmosphere, extending sintering time, and applying high-temperature, high-concentration CO strong reduction. While this process can remove some oxygen impurities, it is often accompanied by grain coarsening, nitrogen vacancy generation, and grain boundary structure destruction, leading to decreased thermal conductivity and deteriorated material stability. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for preparing high thermal conductivity aluminum nitride ceramics based on dual-atmosphere heat treatment. The method of the present invention can improve the thermal conductivity of the ceramics.

[0005] To address the aforementioned technical problems, this invention provides a deoxidation method for AlN ceramics based on dual-atmosphere heat treatment (a method for preparing high thermal conductivity aluminum nitride ceramics based on dual-atmosphere heat treatment), comprising the following steps: 1) Aluminum nitride (AlN, powder), sintering aid and solvent are ball-milled and mixed to obtain ceramic slurry (uniformly mixed ceramic slurry); Sintering aid: Aluminum nitride = 1%~5wt% (preferably 3%); 2) Spray granulation of the ceramic slurry obtained in step 1) to obtain AlN granulated powder (spherical AlN granulated powder with an average particle size of about 60~100 μm). 3) Place the AlN granulated powder obtained in step 2) in a CO / N2 atmosphere and keep it at 400~800°C for the first stage of heat treatment for 10~120 minutes to obtain the treated AlN ceramic powder. In a CO / N2 atmosphere, the volume content of CO is 35-45%; Explanation: When AlN granulated powder is heat-treated under a CO / N2 atmosphere, CO reacts with adsorbed oxygen on the AlN surface, the amorphous Al-O layer, and interfacial oxides to generate CO2 gas, thereby achieving the removal of active oxygen and purification of grain boundaries. 4) The processed AlN ceramic powder obtained in step 3) is subjected to molding treatment to obtain AlN ceramic green body; 5) The AlN ceramic green body obtained in step 4) is subjected to the second stage of hot isostatic pressing (hot pressing sintering) in H2 / N2 atmosphere at a temperature of 1600~1850°C and a pressure of (30 ±1) MPa for 0.5~3 hours. In the H2 / N2 atmosphere, the volume content of H2 is 5~80% (preferably 5~25%).

[0006] Note: The purpose of step (5) is to achieve deep deoxygenation and grain boundary purification.

[0007] As an improvement to the AlN ceramic deoxidation method based on dual-atmosphere heat treatment of the present invention: Aluminum nitride, sintering aid, solvent, dispersant, and binder are ball-milled and mixed to obtain a ceramic slurry; Sintering aid: aluminum nitride = 1%~5wt% (preferably 3%); dispersant: aluminum nitride = 0.4~0.6 wt%; binder: aluminum nitride = 1.3~1.7 wt%.

[0008] As a further improvement to the AlN ceramic deoxidation method based on dual-atmosphere heat treatment of the present invention: The sintering aid is any one or two of the following: Y2O3, CaO, Li2O, YF3, CaF2, LiF, MgF2.

[0009] As a further improvement to the AlN ceramic deoxidation method based on dual-atmosphere heat treatment of the present invention, the sintering aid is any one of the following: It is composed of CaO and Y2O3 in a weight ratio of 2:1; It is composed of CaF2 and YF3 in a weight ratio of 2:1; It is composed of CaF2 and Y2O3 in a weight ratio of 2:1.

[0010] As a further improvement to the AlN ceramic deoxidation method based on dual-atmosphere heat treatment of the present invention, the solvent in step 1) is any one of the following: methanol, ethanol, isopropanol (preferably), ethylene glycol; Note: Use 250-350 ml of solvent for every 100g of aluminum nitride (AlN).

[0011] As a further improvement to the AlN ceramic deoxidation method based on dual-atmosphere heat treatment of the present invention: the forming process in step 4) includes dry pressing and cold isostatic pressing in sequence; The pressure for dry pressing is 20~30MPa, and the holding time is 0.5~1.5min; The pressure for cold isostatic pressing is 150~200MPa, and the holding time is 1~2min.

[0012] As a further improvement to the AlN ceramic deoxidation method based on dual-atmosphere heat treatment of the present invention: Step 3): In a CO / N2 atmosphere, the volume content of CO is 40%, the heat treatment temperature is 700 °C, and the heat treatment time is 60 min. Step 5): In the H2 / N2 atmosphere, the volume content of H2 is 25%, the hot isostatic pressing temperature is 1750°C, the holding time is 2 hours, and the pressure is (30 ± 1) MPa.

[0013] As a further improvement to the AlN ceramic deoxidation method based on dual-atmosphere heat treatment of the present invention, step 4): The pressure for dry pressing is 25~30 MPa, and the holding time is 1 minute; The pressure for cold isostatic pressing is 175~200MPa, and the holding time is 1.5 min.

[0014] This invention is based on a "dual-atmosphere heat treatment" deoxidation technology for AlN ceramics. The manufacturing process is as follows: Raw material weighing → batching → ball milling → spray granulation → CO reduction → dry pressing → cold isostatic pressing → H2 hot pressing sintering → finished ceramic product.

[0015] This invention achieves preliminary reduction of Al2O3 through preheating in a CO atmosphere, followed by further removal of residual oxygen in an H2 atmosphere, thus realizing in-situ purification without relying on exogenous additives and improving the thermal conductivity of the ceramic. The thermal conductivity of the AlN ceramic obtained by this invention is 178~225 W / (m×K), and the density can reach as high as 99.7%~99.80%.

[0016] This invention proposes for the first time a CO / N2 atmosphere deoxidation mechanism based on a combination of low-temperature weak reduction and interfacial activation. Traditional AlN deoxidation methods typically involve using low-oxygen-content ceramic powders, altering the degreasing atmosphere, extending sintering time, and applying high-temperature, high-concentration CO strong reduction. While this process can remove some oxygen impurities, it often results in grain coarsening, nitrogen vacancy generation, and grain boundary structure destruction, leading to decreased thermal conductivity and reduced material stability. In contrast, this invention achieves mild and controllable interfacial selective deoxidation at a low temperature of only 400–800 °C, strictly controlling the CO volume fraction to 35–45%, by introducing a CO / N2 mixture. Under these conditions, CO does not undergo a complete reduction reaction with Al2O3, but instead selectively reacts with adsorbed oxygen on the AlN particle surface, the amorphous Al-O layer, and the Al-ON transition interface to generate CO2, thereby removing surface active oxygen and purifying grain boundaries while maintaining the integrity of the AlN main crystal structure. The essence of this process is the synergistic effect of "interfacial activation-oxygen migration-weak reduction," achieving effective removal of oxygen impurities while significantly reducing the reaction temperature. The proposed strategy of "low-temperature weak reduction + interfacial oxygen activation and removal" transforms the CO atmosphere from a traditional strong reducing agent to an "interfacial oxygen cleaning agent." This not only avoids the problem of crystal damage at high temperatures but also creates a purer interfacial environment for subsequent deep deoxygenation of the H2 atmosphere, forming a deoxygenation pathway and mechanism that is completely different from existing technologies.

[0017] This invention proposes a "dual-atmosphere staged deoxidation path" that works synergistically with the first-stage CO atmosphere pre-deoxidation in the second-stage heat treatment, achieving a layered purification process for AlN ceramics from the surface to the grain boundaries and then to the interior of the grains. Unlike traditional single H2 deoxidation processes (typically carried out at 1200~1350 °C with an H2:N2 volume ratio of 2:1~4:1), this invention employs a composite condition of high temperature (1600~1850 °C) + low H2 concentration (5~25%) + high pressure (30 MPa). By controlling the partial pressure of hydrogen and thermodynamic equilibrium, a synergistic reaction of "deep reduction and nitriding regeneration" is achieved. This strategy prevents H2 from acting as a strong reducing agent, instead allowing it to selectively act on the Al-ON composite oxides at the grain boundaries and deep oxygen impurities in a mild and controllable manner, converting them into gaseous H2O for discharge. Simultaneously, the high-temperature nitrogen environment promotes the reformation of Al-N bonds, thereby restoring lattice integrity and preventing excessive nitrogen vacancies. Meanwhile, the high external pressure provided by the hot-pressing environment promotes grain boundary migration and pore closure, enabling simultaneous deoxidation and densification, effectively preventing grain boundary hydrogen embrittlement and thermal cracking defects that occur during traditional H2 deoxidation. Under the optimized dual-atmosphere synergistic deoxidation pathway of this invention, the oxygen content of AlN ceramics is reduced to 0.15 wt%, and the room temperature thermal conductivity is increased to 225 W·m. -1 ·K -1It is significantly superior to conventional H2 deoxygenation processes (oxygen content approximately 0.3~0.5 wt%, thermal conductivity <180 W·m). -1 ·K -1 This fully demonstrates the significant innovation of the present invention in terms of deoxygenation mechanism, thermal balance control and synergistic performance improvement.

[0018] In summary, this invention features a simple process. The "dual-atmosphere heat treatment process" effectively removes oxygen impurities from AlN powder and sintered bodies. Preheating in a CO atmosphere generates CO2 gas through reaction with adsorbed oxygen on the AlN surface, the amorphous Al-O layer, or interfacial oxides, thereby removing active oxygen and purifying grain boundaries. In the second stage, during the H2 / N2 mixed gas hot isostatic pressing process, H2 reacts with oxide impurities to generate volatile H2O gas, achieving deep reduction and removal of oxygen-containing phases such as Al2O3 and AlON. Simultaneously, it promotes the volatilization and recrystallization of the grain boundary liquid phase, resulting in AlN ceramics with clean grain boundaries and dense grain bonding, exhibiting high thermal conductivity. This is primarily based on the fact that at high temperatures, H2 can promote the diffusion of O from the lattice to the grain boundaries (by reducing the interfacial energy of oxides and forming gaseous H2O), accelerating the escape of oxygen from the lattice, thus achieving lattice deoxidation. This method achieves in-situ purification without relying on external additives, thereby improving the thermal conductivity of AlN ceramics. This invention employs a standard dual-atmosphere treatment process to effectively remove oxygen impurities from AlN ceramics and improve the thermal conductivity of the material. Attached Figure Description

[0019] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0020] Figure 1 This is a flowchart of the AlN ceramic preparation process. Detailed Implementation

[0021] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto: In the following cases: Commercial AlN powder (purity ≥98%) with an average particle size of 1~5 μm; Al2O3 impurity content of approximately 1.5wt%; oxygen content (i.e., the total amount of oxygen in Al2O3 and AlON) of 1.2~1.5wt%; CO gas (industrial grade, purity ≥99%); H2 gas (industrial grade, purity ≥99%); nitrogen or argon is used as the protective atmosphere. PVA is polyvinyl alcohol with a degree of alcoholysis of 98%~99% and an average degree of polymerization of 1750±50; PAA is polyacrylic acid with a weight-average molecular weight Mw=4000.

[0022] Example 1: A method for deoxidizing AlN ceramics using a dual atmosphere of CO / N2 and H2 / N2, comprising the following steps: 1) Take 100 g of commercial AlN powder with a purity of 98% and an average particle size of 2 μm (oxygen content of 1.2 wt%), add 3 wt% Y2O3 as a sintering aid, add 300 ml isopropanol (as solvent), and add 0.5 wt% PAA as a dispersant and 1.5 wt% PVA as a binder; after ball milling for 4 hours, a uniform slurry (uniformly mixed ceramic slurry) is obtained.

[0023] Note: That is, the amount of Y2O3 added is 3 g, the amount of PAA added is 0.5 g, and the amount of PVA added is 1.5 g; Ball milling can be performed in a planetary ball mill at a speed of 300 rpm with a ball-to-material ratio of 1:5 (by mass).

[0024] 2) Spray granulation of the slurry obtained in step 1) (the centrifugal speed of the atomizing disc is set to 25000±1000rpm, the inlet temperature is 180℃, and the outlet temperature is 95℃ to obtain spherical AlN granulated powder (average particle size is about 80 μm).

[0025] 3) The spherical AlN granulated powder obtained in step 2) is loaded into a quartz boat (or fluidized bed device) and subjected to the first stage of heat treatment at 700°C for 60 min under a CO / N2 atmosphere (CO volume fraction 40%). CO reacts with the adsorbed oxygen on the surface of AlN particles, the amorphous Al-O layer and the Al-ON transition interface to generate CO2 gas, which is then discharged, thereby achieving the removal of active oxygen and grain boundary purification of the spherical AlN granulated powder; the result is named treated AlN ceramic powder.

[0026] Explanation: CO / N2 (CO volume fraction 40%) means: CO=40%, N2=60%, and % is by volume.

[0027] 4) The processed AlN ceramic powder obtained in step 3) is first dry-pressed (25 MPa, 1 min) and then cold isostatically pressed (175 MPa, 1.5 min) to obtain AlN ceramic green body.

[0028] 5) The AlN ceramic green body obtained in step 4) is hot-pressed and sintered at 1700°C and 30MPa for 2 hours in an H2 / N2 atmosphere (H2 volume fraction 25%) to carry out the second stage of deep deoxidation and grain boundary purification.

[0029] High-density AlN ceramics (density up to 99.8%) were obtained, with thermal conductivity increased to 198 W·m. -1 ·K -1 The oxygen content dropped to 0.7 wt%.

[0030] The oxygen content of the ceramic powder was tested according to GB / T 37252-2018; the density was tested according to the national standard GB / T 5593-2015 "Structural Ceramic Materials for Electronic Components"; and the thermal conductivity of aluminum nitride ceramic (AlN) was tested according to the national standard GB / T39862-2021 "Test of Thermal Conductivity of High Thermal Conductivity Ceramics".

[0031] Example 2: A method for deoxidizing AlN ceramics using a dual atmosphere of CO / N2 and H2 / N2, comprising the following steps: 1) Take 100 g of AlN powder with a purity of 99% and an average particle size of 3 μm (oxygen content of 1.2 wt%), add 2 wt% CaO and 1 wt% Y2O3 as composite sintering aids, add 350 ml of ethanol, and add 0.5 wt% PAA as dispersant and 1.5 wt% PVA as binder. After ball milling for 6 h, a uniform slurry is obtained.

[0032] 2) Spray granulation of the slurry (inlet temperature 190°C, outlet temperature 100°C) to obtain spherical powder (average particle size about 70 μm).

[0033] 3) The spherical AlN granulated powder obtained in step 2) is loaded into a quartz boat (or fluidized bed device) and subjected to the first stage of heat treatment at 600°C for 40 min under a CO / N2 atmosphere (CO volume fraction 35%). The resulting product is named treated AlN ceramic powder.

[0034] 4) The processed AlN ceramic powder obtained in step 3) is first dry-pressed (25 MPa, 1 min) and then cold isostatically pressed (175 MPa, 1.5 min) to obtain AlN ceramic green body.

[0035] 5) The AlN ceramic preform obtained in step 4) was hot-pressed and sintered at 1750°C and 30MPa for 1 hour in an H2 / N2 atmosphere (H2 volume fraction 50%) to obtain a high-density AlN ceramic (density up to 99.2%) with thermal conductivity increased to 165 W·m. -1 ·K -1 The oxygen content dropped to 0.6 wt%.

[0036] Example 3: A method for deoxidizing AlN ceramics using a dual atmosphere of CO / N2 and H2 / N2, comprising the following steps: 1) Take 100g of AlN powder with a purity of 98% and an average particle size of 5μm (oxygen content of 1.2wt%), add 3wt% Li2O as a sintering aid, add 250 ml of methanol, and add 0.5wt% PAA as a dispersant and 1.5wt% PVA as a binder. After ball milling for 3 h, a uniform slurry is obtained.

[0037] 2) Spray granulation of the slurry obtained in step 1) (inlet temperature 150°C, outlet temperature 90°C) to obtain spherical AlN granulated powder (particle size about 90 μm).

[0038] 3) The spherical AlN granulated powder obtained in step 2) is loaded into a quartz boat (or fluidized bed device) and subjected to the first stage of heat treatment at 800°C for 20 min under a CO / N2 atmosphere (CO volume fraction 45%). The resulting product is named treated AlN ceramic powder.

[0039] 4) The processed AlN ceramic powder obtained in step 3) is first dry-pressed (25 MPa, 1 min) and then cold isostatically pressed (200 MPa, 1.5 min) to obtain AlN ceramic green body.

[0040] 5) The AlN ceramic preform obtained in step 4) was hot-pressed and sintered at 1650°C and 20 MPa for 2 hours in an H2 / N2 atmosphere (H2 volume fraction 10%). A dense AlN ceramic (density 98.8%) was finally obtained, with an oxygen content of approximately 0.9 wt% and a thermal conductivity increased to 178 W·m. -1 ·K -1 .

[0041] Note: This case uses a fluorine-free additive system.

[0042] Example 4: A method for deoxidizing AlN ceramics using a dual atmosphere of CO / N2 and H2 / N2, comprising the following steps: 1) Take 100 g of commercial AlN powder with a purity of 98.5% and an average particle size of 1 μm (oxygen content of 1.2 wt%), add 2 wt% CaF2 and 1 wt% YF3 as sintering aids, add 300 ml of ethylene glycol, and add 0.5 wt% PAA as dispersant and 1.5 wt% PVA as binder. After ball milling for 4 hours, a uniform slurry is obtained.

[0043] 2) Spray granulation of the slurry obtained in step 1) (inlet temperature 200°C, outlet temperature 95°C); to obtain spherical AlN granulated powder.

[0044] 3) The spherical AlN granulated powder obtained in step 2) is loaded into a quartz boat (or fluidized bed device) and subjected to the first stage of heat treatment at 500°C for 60 min under a CO / N2 atmosphere (CO volume fraction 40%). The resulting product is named treated AlN ceramic powder.

[0045] 4) The processed AlN ceramic powder obtained in step 3) is first dry-pressed (25 MPa, 1 min) and then cold isostatically pressed (175 MPa, 1.5 min) to obtain AlN ceramic green body.

[0046] 5) The AlN ceramic preform obtained in step 4) was hot-pressed and sintered at 1800°C and 30 MPa for 1 hour in an H2 / N2 atmosphere (H2 volume fraction 80%). This yielded a high-density AlN ceramic (density reaching 99.5%) with an increased thermal conductivity of 193 W·m. -1 ·K -1 The oxygen content dropped to 0.8 wt%.

[0047] Note: This case uses a fluoride additive system.

[0048] Example 5: A method for deoxidizing AlN ceramics using a dual atmosphere of CO / N2 and H2 / N2, comprising the following steps: 1) Take 100 g of AlN powder with a purity of 98% and an average particle size of 2 μm (oxygen content of 1.2 wt%), add 3 wt% MgF2 as a sintering aid, add 300 ml isopropanol solvent, add 0.5 wt% PAA as a dispersant and 1.5 wt% PVA as a binder, and ball mill for 4 h to obtain a uniform slurry.

[0049] 2) Spray granulation of the slurry obtained in step 1) (inlet temperature 180°C, outlet temperature 90°C).

[0050] 3) The spherical AlN granulated powder obtained in step 2) is loaded into a quartz boat (or fluidized bed device) and subjected to the first stage of heat treatment at 450°C for 120 min under a CO / N2 atmosphere (CO volume fraction 40%). The resulting product is named treated AlN ceramic powder.

[0051] 4) The processed AlN ceramic powder obtained in step 3) is subjected to dry pressing (30 MPa, 1 min) and cold isostatic pressing (180 MPa, 1.5 min) to obtain AlN ceramic green body.

[0052] 5) The AlN ceramic preform obtained in step 4) is hot-pressed and sintered at 1850°C and 30 MPa for 3 hours in an H2 / N2 atmosphere (H2 volume fraction 5%).

[0053] The resulting ceramic has a density of 99.5%, an oxygen content of 0.5 wt%, and a thermal conductivity of 181 W·m. -1 ·K -1 .

[0054] Example 6: A method for deoxidizing AlN ceramics using a dual atmosphere of CO / N2 and H2 / N2, comprising the following steps: 1) 100 g of commercial AlN powder with an average particle size of 1 μm, purity ≥98%, and oxygen content of about 0.8 wt% was selected as raw material. 2 wt% CaF2 and 1 wt% Y2O3 were added as composite sintering aids, 300 ml of isopropanol (as solvent) was added, and 0.5 wt% PAA was added as dispersant and 1.5 wt% PVA as binder. After ball milling for 8 hours, a uniform slurry was obtained.

[0055] 2) Spray granulation of the slurry obtained in step 1) (inlet temperature 180 °C, outlet temperature 95 °C) to obtain spherical granulated powder (average particle size 80 μm).

[0056] 3) Place the granulated powder in a quartz tube furnace (or fluidized bed device) and heat-treat it at 700 °C for 60 min in a CO / N2 mixed gas with a CO volume fraction of 40% for the first stage of heat treatment. The resulting powder is named the treated AlN ceramic powder.

[0057] 4) The processed AlN ceramic powder obtained in step 3) is subjected to bidirectional dry pressing at 25 MPa (holding pressure for 1 min), and then subjected to cold isostatic pressing at 175 MPa (holding pressure for 1.5 min) to obtain AlN ceramic green body.

[0058] 5) The AlN ceramic green body obtained in step 4) was hot-pressed and sintered at 1750 °C and 30 MPa for 2 h in an H2 / N2 atmosphere (H2 volume fraction 25%).

[0059] The resulting AlN ceramic had an oxygen content reduced to 0.15 wt%, a relative density of 99.7%, and a room temperature thermal conductivity of 225 W / (m·K).

[0060] Example 7: In Example 6, “2 wt% CaF2 and 1 wt% Y2O3 as composite sintering aids” is replaced with “2 wt% LiF and 1 wt% Y2O3 as sintering aids”, and the rest is the same as in Example 6.

[0061] The results showed that the ceramic had an oxygen content of 0.3 wt%, a relative density of 99.2%, and a room temperature thermal conductivity of approximately 208 W / (m·K).

[0062] Comparative Example 1: Preparation method of AlN ceramics by two-stage hydrogen atmosphere heat treatment: That is, compared to Example 6, the following changes are made: Both steps 3) and 5) are changed to be performed under an H2 / N2 atmosphere (H2 volume fraction 25%): First stage: heat treatment at 700 ℃ for 60 min; Second stage: hot pressing and sintering at 1700 ℃ and 30 MPa for 2 h.

[0063] The results showed that the oxygen content of the obtained ceramic was reduced to 0.25 wt%, the relative density was 98.9%, and the thermal conductivity was only 160 W / (m·K).

[0064] The analysis is as follows: The deoxidation efficiency of H2 atmosphere alone is insufficient. H2 has low activity at 700 °C and has limited ability to remove oxygen from hydroxyl groups or amorphous Al-O layers on the powder surface. It is difficult to completely remove adsorbed oxygen and interface oxides. The residual oxide film at the grain boundary leads to severe phonon scattering and limited improvement in thermal conductivity.

[0065] Comparative Example 2: Preparation method of AlN ceramics by conventional nitrogen atmosphere sintering: That is, compared to Example 6, the following changes are made: Both steps 3) and 5) are changed to be performed under a pure N2 atmosphere: First stage: Hold at 700℃ for 60 min; Second stage: Hot pressing and sintering at 1700℃ and 30 MPa for 2 h.

[0066] The results showed that the obtained ceramic had an oxygen content of 0.62 wt%, a relative density of 97.1%, and a room temperature thermal conductivity of only 140 W / (m·K).

[0067] The analysis is as follows: In the absence of a reducing atmosphere, surface hydroxyl groups and Al-ON phase cannot be effectively removed, grain boundary impurities remain severely, phonon conduction channels are blocked, resulting in a significant decrease in thermal conductivity.

[0068] Comparative Example 3, compared to Example 6, is modified as follows: Change "hot pressing and sintering at 1750 °C and 30 MPa for 2 h in H2 / N2 (H2 volume fraction 25%) atmosphere" in step 5) to "sintering at 1350 °C and atmospheric pressure for 5 hours in H2 / N2 (H2 volume fraction 25%) atmosphere".

[0069] The rest is the same as in Example 6.

[0070] The results showed that the obtained ceramic had an oxygen content of 0.13 wt%, a relative density of 95%, and a room temperature thermal conductivity of only 120 W / (m·K).

[0071] Finally, it should be noted that the above examples are merely some specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments and many variations are possible. All variations that can be directly derived or conceived by those skilled in the art from the disclosure of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A method for preparing high thermal conductivity aluminum nitride ceramics based on dual-atmosphere heat treatment, characterized in that... Includes the following steps: 1) Aluminum nitride, sintering aid and solvent are ball-milled and mixed to obtain ceramic slurry; Sintering aid: Aluminum nitride = 1%~5wt%; 2) Spray granulation of the ceramic slurry obtained in step 1) to obtain AlN granulated powder; 3) Place the AlN granulated powder obtained in step 2) in a CO / N2 atmosphere and keep it at 400~800°C for the first stage of heat treatment for 10~120 minutes to obtain the treated AlN ceramic powder. In a CO / N2 atmosphere, the volume content of CO is 35-45%; 4) The processed AlN ceramic powder obtained in step 3) is subjected to molding treatment to obtain AlN ceramic green body; 5) The AlN ceramic green body obtained in step 4) is subjected to a second stage of hot isostatic pressing in an H2 / N2 atmosphere at a temperature of 1600~1850°C and a pressure of (30 ±1) MPa for 0.5~3 hours. In an H2 / N2 atmosphere, the volume content of H2 is 5-80%.

2. The method for preparing high thermal conductivity aluminum nitride ceramics based on dual-atmosphere heat treatment according to claim 1, characterized in that: Aluminum nitride, sintering aid, solvent, dispersant, and binder are ball-milled and mixed to obtain a ceramic slurry; Sintering aid: Aluminum nitride = 1%~5wt%; Dispersant: Aluminum nitride = 0.4~0.6 wt%, Binder: Aluminum nitride = 1.3~1.7 wt%.

3. The method for preparing high thermal conductivity aluminum nitride ceramics based on dual-atmosphere heat treatment according to claim 1 or 2, characterized in that: The sintering aid is any one or two of the following: Y2O3, CaO, Li2O, YF3, CaF2, LiF, MgF2.

4. The method for preparing high thermal conductivity aluminum nitride ceramic based on dual-atmosphere heat treatment according to claim 3, characterized in that: The sintering aid is any one of the following: It is composed of CaO and Y2O3 in a weight ratio of 2:1; It is composed of CaF2 and YF3 in a weight ratio of 2:1; It is composed of CaF2 and Y2O3 in a weight ratio of 2:

1.

5. The method for preparing high thermal conductivity aluminum nitride ceramics based on dual-atmosphere heat treatment according to any one of claims 1 to 4, characterized in that: The solvent in step 1) is any of the following: methanol, ethanol, isopropanol, or ethylene glycol.

6. The method for preparing high thermal conductivity aluminum nitride ceramics based on dual-atmosphere heat treatment according to claim 5, characterized in that: The molding process in step 4) includes dry pressing and cold isostatic pressing in sequence; The pressure for dry pressing is 20~30MPa, and the holding time is 0.5~1.5min; The pressure for cold isostatic pressing is 150~200MPa, and the holding time is 1~2min.

7. The method for preparing high thermal conductivity aluminum nitride ceramic based on dual-atmosphere heat treatment according to claim 6, characterized in that: Step 3): In a CO / N2 atmosphere, the volume content of CO is 40%, the heat treatment temperature is 700 °C, and the heat treatment time is 60 min; Step 5): In the H2 / N2 atmosphere, the volume content of H2 is 25%, the hot isostatic pressing temperature is 1750°C, the holding time is 2 hours, and the pressure is (30 ± 1) MPa.

8. The method for preparing high thermal conductivity aluminum nitride ceramic based on dual-atmosphere heat treatment according to claim 7, characterized in that: Step 4): Dry pressing pressure is 25~30 MPa, holding time is 1 min; cold isostatic pressing pressure is 175~200 MPa, holding time is 1.5 min.

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