Preparation method of low-temperature sintered high-thermal-conductivity aluminum nitride ceramic

Abstract

This invention discloses a method for preparing low-temperature sintered high thermal conductivity aluminum nitride ceramics, belonging to the field of aluminum nitride ceramic technology, comprising: Step S1: Raw material pretreatment. Aluminum nitride powder and samarium oxide powder are selected, wherein the samarium oxide powder accounts for 1-6 wt.% of the total mass of the mixed powder. The powder is dry ball-milled in a ball mill at a speed of 30-60 rpm for 20-36 h to obtain a uniform mixed powder. The mixed powder is then sieved and set aside. Step S2: Spark plasma sintering. The mixed powder after the previous step is placed in a graphite mold of a spark plasma sintering device and sintered under a low vacuum environment. The sintering temperature is 1400-1700℃, the heating rate is 100℃ / min, the holding time is 1-6 min, and after the holding time is completed, the temperature is lowered at a cooling rate of 100℃ / min to complete the first spark plasma sintering. Step S3: Post-treatment. After the spark plasma sintering is completed, the powder is cooled to room temperature in the furnace and demolded to obtain the aluminum nitride ceramic product.

Description

Technical Field

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

[0002] Aluminum nitride (AlN) ceramics are considered ideal materials for high-performance electronic substrates and power device packaging due to their high thermal conductivity, moderate dielectric constant, thermal expansion coefficient matching that of silicon, and excellent high-temperature resistance and thermal shock resistance. However, because aluminum nitride has strong covalent bonds and a small self-diffusion coefficient, traditional sintering methods require holding at temperatures above 1800℃ for several hours or even tens of hours to achieve a certain degree of densification, which presents the following problems:

[0003] 1. High-temperature, long-duration sintering results in high production costs, which is not conducive to large-scale production;

[0004] 2. It can easily lead to abnormal grain growth, reducing the mechanical strength of the material;

[0005] 3. Oxygen readily dissolves in the aluminum nitride lattice or forms defects at grain boundaries, scattering phonons and significantly reducing thermal conductivity.

[0006] In addition, existing technologies often employ methods such as adding sintering aids (e.g., Y2O3, CaO, CaF2) or optimizing the sintering process. Among these, rare earth oxides (e.g., Y2O3, Sm2O3) have been proven to be effective sintering aids. However, in traditional sintering systems, the liquidus temperature of AlN-Al2O3-rare earth oxides remains above 1800℃, making it difficult to fundamentally reduce the sintering temperature. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a method for preparing low-temperature sintered high thermal conductivity aluminum nitride ceramics, which can reduce the sintering temperature of aluminum nitride ceramics and shorten the total sintering time.

[0008] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0009] A method for preparing low-temperature sintered high thermal conductivity aluminum nitride ceramic, the method comprising the following steps:

[0010] Step S1: Raw material pretreatment

[0011] Aluminum nitride powder and samarium oxide powder are selected, wherein the samarium oxide powder accounts for 1 to 6 wt.% of the total mass of the mixed powder. The powder is dry ball-milled in a ball mill at a speed of 30 to 60 rpm for 20 to 36 hours to obtain a uniform mixed powder. The mixed powder is then sieved and set aside for later use.

[0012] Step S2: Spark Plasma Sintering

[0013] The mixed powder after the previous step is placed in the graphite mold of the spark plasma sintering equipment and sintered in a low vacuum environment. The sintering temperature is 1400-1700℃, the sintering heating rate is 100℃ / min, the holding time is 1-6min, and after the holding time is completed, the temperature is reduced at a cooling rate of 100℃ / min to complete the first spark plasma sintering.

[0014] Step S3: Post-processing

[0015] After spark plasma sintering, the product is cooled to room temperature in the furnace and then demolded to obtain aluminum nitride ceramic products.

[0016] Preferably, in step S1, the aluminum nitride powder has a purity of ≥99.8% and an average particle size of 2.4–2.6 μm, and the samarium oxide has a purity of ≥99.9%.

[0017] Preferably, in step S2, after the first discharge plasma sintering is completed, the discharge plasma sintering is repeated 1 to 3 times.

[0018] Preferably, in step S2, the vacuum level of the low vacuum environment is 0.8 to 1.2 Pa.

[0019] Preferably, in step S2, the sintering temperature is 1550–1650°C and the holding time is 4–6 min.

[0020] The above technical solution has the following beneficial effects:

[0021] The sintering temperature is significantly reduced: compared with the traditional sintering temperature of over 1800℃, the sintering temperature of this invention is only 1400-1700℃, which reduces energy consumption and equipment requirements.

[0022] The sintering cycle is significantly shortened: the total sintering time (including heating and cooling) does not exceed 30 minutes, which is significantly more efficient than the several hours to tens of hours of traditional sintering.

[0023] Excellent material properties: The obtained aluminum nitride ceramics have a relative density of over 97.5%. Under the conditions of 4 wt.% Sm2O3 addition, sintering temperature of 1600℃, holding time of 5 min, and single cycle, the thermal conductivity of the prepared aluminum nitride ceramics is as high as 126 W·m. -1 ·K -1 It has a stable dielectric constant and excellent elastic modulus;

[0024] Controllable microstructure: Fine-grained, polyhedral grain structures can be obtained by adjusting process parameters, with smooth contact between grains, reducing defects and further improving the thermal conductivity and mechanical properties of the material;

[0025] High process stability: Raw materials are readily available, process steps are simple, repeatability is high, and it is easy to carry out industrial production. Detailed Implementation

[0026] The specific embodiments of the present invention will be further described below. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0027] A method for preparing low-temperature sintered high thermal conductivity aluminum nitride ceramics specifically includes the following steps:

[0028] Step S1: Raw material pretreatment

[0029] Aluminum nitride powder and samarium oxide (Sm2O3) powder were selected, wherein the samarium oxide (Sm2O3) powder accounted for 1-6 wt.% of the total mass of the mixed powder. The powder was dry ball-milled in a ball mill at a speed of 30-60 rpm for 20-36 h to obtain a uniform mixed powder. The mixed powder was then sieved and sintered for later use.

[0030] Specifically, the mixed powder is a powder obtained by mixing aluminum nitride powder and samarium oxide (Sm2O3) powder. The samarium oxide (Sm2O3) powder accounts for 1 wt.% or 6 wt.% of the total mass of the mixed powder, or it can be 3 wt.% or 4 wt.%. The powder is dry ball-milled in a ball mill at a speed of 30 rpm or 60 rpm for 20 or 36 hours to obtain a uniform mixed powder. Ball milling ensures uniform dispersion of the raw materials, laying the foundation for densification and reaction uniformity in the subsequent sintering process. The mixed powder can be passed through an 80-200 mesh standard sieve for later use. Specifically, it can be passed through an 80 mesh standard sieve or a 200 mesh standard sieve.

[0031] Step S2: Spark Plasma Sintering

[0032] The mixed powder after the previous step is placed in the graphite mold of the spark plasma sintering equipment and sintered in a low vacuum environment. The sintering temperature is 1400-1700℃, the sintering heating rate is 100℃ / min, the holding time is 1-6min, and after the holding time is completed, the temperature is reduced at a cooling rate of 100℃ / min to complete the first spark plasma sintering.

[0033] Specifically, the mixed powder is placed in a graphite mold of a spark plasma sintering (SPCS) equipment and sintered in a low vacuum environment. The sintering temperature is 1400℃, 1700℃, or 1550℃. Compared with the traditional sintering temperature of over 1800℃, the sintering temperature of this invention is only 1400-1700℃, which reduces energy consumption and equipment requirements. The sintering heating rate is 100℃ / min, the holding time is 1min or 6min, and after the holding time, the temperature is cooled to room temperature at a cooling rate of 100℃ / min to complete the first SPCS. The sintering time (including heating and cooling) does not exceed 30min. Compared with the traditional sintering time of several hours to tens of hours, the production efficiency is significantly improved.

[0034] Low vacuum conditions can reduce oxygen partial pressure, decrease the generation of oxidizing impurities, and also contribute to plasma generation and stability;

[0035] The sintering temperature of 1400-1700℃ in this application is 100-400℃ lower than that of the traditional process, and the heating and cooling rate of 100℃ / min can avoid abnormal grain growth and ensure fine grain structure.

[0036] Spark plasma sintering (SPS) is a novel rapid sintering technology that uses plasma generated by pulsed direct current to activate the surface of powder particles, combined with pressure sintering, to achieve rapid densification of materials at low temperatures.

[0037] Sintering mechanism: Sm2O3 reacts with Al2O3 on the surface of aluminum nitride powder to form SmAlO3 liquid phase. In the low-temperature plasma environment of SPS, the formation temperature of this liquid phase is lower than the liquidus temperature of the traditional sintering system. The liquid phase sintering mechanism promotes particle rearrangement and densification. At the same time, the liquid phase can remove oxygen impurities in grain boundaries and lattice, reduce phonon scattering, and improve thermal conductivity.

[0038] Step S3: Post-processing

[0039] After spark plasma sintering, the product is cooled to room temperature in the furnace and then demolded to obtain aluminum nitride ceramic products.

[0040] In some embodiments, in step S1, the aluminum nitride powder has a purity of ≥99.8% and an average particle size of 2.4–2.6 μm, and the samarium oxide (Sm₂O₃) has a purity of ≥99.9%.

[0041] Specifically, the purity of aluminum nitride powder is greater than or equal to 99.8%, and the average particle size is 2.4 μm, 2.6 μm, or 2.5 μm. The purity of samarium oxide (Sm2O3) is greater than or equal to 99.9%, and the average particle size is 99.9%.

[0042] In some embodiments, in step S2, after the first discharge plasma sintering is completed, the discharge plasma sintering is repeated 1 to 3 times.

[0043] Specifically, a short holding time of 1 to 6 minutes combined with 1 to 3 discharge plasma sintering cycles can both achieve particle surface purification and diffusion enhancement through plasma activation, and avoid performance degradation caused by over-sintering. In particular, multiple discharge plasma sintering cycles can further improve the densification degree.

[0044] In some embodiments, in step S2, the vacuum level of the low vacuum environment is 0.8 to 1.2 Pa, specifically 0.8 Pa, 1.2 Pa, or 1 Pa.

[0045] In some embodiments, in step S2, the sintering temperature is 1550-1650°C and the holding time is 4-6 min. Specifically, the sintering temperature is 1550°C or 1650°C and the holding time is 5 min or 6 min.

[0046] Example 1

[0047] A method for preparing low-temperature sintered high thermal conductivity aluminum nitride ceramics specifically includes the following steps:

[0048] Raw material pretreatment: Select AlN powder with a purity of 99.8% (average particle size 2.5μm) and Sm2O3 powder with a purity of 99.9%, mix them at a ratio of 2wt.% of Sm2O3 to the total mass of the mixed powder, put them into a plastic ball mill jar, and dry ball mill at 50rpm for 24h to obtain mixed powder;

[0049] SPS (Spark Plasma Sintering): The mixed powder is loaded into a graphite mold, placed in an SPS device, and sintered under a vacuum of 0.8 to 1.2 Pa. The sintering temperature is 1600℃, the heating rate is 100℃ / min, the holding time is 5min, and the cooling rate is 100℃ / min for a single SPS cycle.

[0050] Post-processing: After cooling to room temperature, the ceramic is demolded to obtain aluminum nitride ceramic.

[0051] The aluminum nitride ceramic was tested and found to have a relative density of 86% and a thermal conductivity of 78 W·m. -1 ·K -1 It has a dielectric constant of 7.9 and an elastic modulus of 291 GPa.

[0052] Example 2

[0053] A method for preparing low-temperature sintered high thermal conductivity aluminum nitride ceramics specifically includes the following steps:

[0054] Raw material pretreatment: Select the same AlN powder and Sm2O3 powder as in Example 1, and mix them according to the ratio of Sm2O3 to 4 wt.% of the total mass of the mixed powder. The ball milling process is the same as in Example 1.

[0055] SPS sintering: sintering temperature 1600℃, heating rate 100℃ / min, holding time 5min, single SPS cycle, other conditions are the same as in Example 1;

[0056] Post-processing: After cooling and demolding, aluminum nitride ceramic is obtained.

[0057] The resulting ceramic has a relative density of 97.5% and a thermal conductivity of 126 W·m. -1 ·K -1 It has a dielectric constant of 9.1 and an elastic modulus of 331 GPa.

[0058] Example 3

[0059] A method for preparing low-temperature sintered high thermal conductivity aluminum nitride ceramics specifically includes the following steps:

[0060] Raw material pretreatment: Select the same AlN powder and Sm2O3 powder as in Example 1, and mix them according to the ratio of Sm2O3 to 3 wt.% of the total mass of the mixed powder. The ball milling process is the same as in Example 1.

[0061] SPS sintering: sintering temperature 1700℃, heating rate 100℃ / min, using double SPS cycles (holding temperature for 2min each time), other conditions are the same as in Example 1;

[0062] Post-processing: After cooling and demolding, aluminum nitride ceramic is obtained.

[0063] The resulting ceramic has a relative density of 98% and a thermal conductivity of 132 W·m. -1 ·K -1 It has a dielectric constant of 9.5 and an elastic modulus of 347 GPa.

[0064] Comparative Example 1 (without Sm2O3 addition)

[0065] A method for preparing aluminum nitride ceramics specifically includes the following steps:

[0066] Raw materials: Only AlN powder from Example 1 was used, without adding Sm2O3, and SPS sintering was carried out directly;

[0067] Sintering process: temperature 1700℃, holding time 5 min, single SPS cycle, other conditions are the same as in Example 1;

[0068] Results: The obtained ceramic had a relative density of 69% and a thermal conductivity of 48 W·m. -1 ·K -1It has a dielectric constant of 7.7, an elastic modulus of 236 GPa, and exhibits significant porosity.

[0069] Comparative Example 2 (Traditional Sintering Process)

[0070] A method for preparing aluminum nitride ceramics specifically includes the following steps:

[0071] Raw materials: The same AlN powder and Sm2O3 powder as in Example 1 were selected, and the Sm2O3 was prepared in a ratio of 3 wt.% of the total mass of the mixed powder. The ball milling process was the same as in Example 1.

[0072] Sintering process: Traditional nitrogen-protected sintering is adopted at a temperature of 1850℃ and a holding time of 5 hours;

[0073] Results: The obtained ceramic had a relative density of 86.5% and a thermal conductivity of 79 W·m. -1 ·K -1 It has a dielectric constant of 8.1 and an elastic modulus of 265 GPa.

[0074] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A method for preparing low-temperature sintered high thermal conductivity aluminum nitride ceramic, characterized in that, The preparation method includes the following steps: Step S1: Raw material pretreatment Aluminum nitride powder and samarium oxide powder are selected, wherein the samarium oxide powder accounts for 1 to 6 wt.% of the total mass of the mixed powder. The powder is dry ball-milled in a ball mill at a speed of 30 to 60 rpm for 20 to 36 hours to obtain a uniform mixed powder. The mixed powder is then sieved and set aside for later use. Step S2: Spark Plasma Sintering The mixed powder after the previous step is placed in the graphite mold of the spark plasma sintering equipment and sintered in a low vacuum environment. The sintering temperature is 1400-1700℃, the sintering heating rate is 100℃ / min, the holding time is 1-6min, and after the holding time is completed, the temperature is reduced at a cooling rate of 100℃ / min to complete the first spark plasma sintering. Step S3: Post-processing After spark plasma sintering, the product is cooled to room temperature in the furnace and then demolded to obtain aluminum nitride ceramic products.

2. The method for preparing a low-temperature sintered high thermal conductivity aluminum nitride ceramic according to claim 1, characterized in that, In step S1, the aluminum nitride powder has a purity of ≥99.8% and an average particle size of 2.4–2.6 μm, and the samarium oxide has a purity of ≥99.9%.

3. The method for preparing a low-temperature sintered high thermal conductivity aluminum nitride ceramic according to claim 1, characterized in that, In step S2, after the first discharge plasma sintering is completed, the discharge plasma sintering is repeated 1 to 3 times.

4. The method for preparing a low-temperature sintered high thermal conductivity aluminum nitride ceramic according to claim 1, characterized in that, In step S2, the vacuum level of the low vacuum environment is 0.8 to 1.2 Pa.

5. The method for preparing a low-temperature sintered high thermal conductivity aluminum nitride ceramic according to claim 1, characterized in that, In step S2, the sintering temperature is 1550–1650℃, and the holding time is 4–6 min.