Method for rapidly synthesizing nano pure-phase AlN powder

Abstract

The invention relates to a method for rapidly synthesizing nano pure-phase AlN powder, and belongs to the field of ceramic powder preparation. The invention relates to a method for rapidly synthesizing nano pure-phase AlN powder, which comprises the following steps of: polymerizing methyl methacrylate on the surface of gamma-Al2O3 powder through a polymerization reaction to form gamma-Al2O3 powder coated with polymethyl methacrylate on the surface, namely gamma-Al2O3 coated PMMA (polymethyl methacrylate); carrying out pyrolysis carbonization on PMMA (polymethyl methacrylate) in the obtained gamma-Al2O3 coated PMMA powder in a nitrogen environment to obtain C-coated gamma-Al2O3 powder which is marked as gamma-Al2O3 coated C; and in a nitrogen environment, directly and quickly heating the obtained gamma-Al2O3 (at) C to an AlN synthesis temperature, and carrying out heat preservation for a period of time, so as to synthesize the nano pure-phase AlN powder. According to the technology, commercialized gamma-Al2O3 and MMA which are environmentally friendly and low in price are used as main raw materials, the controllability of the technological process is high, the heating rate in the carbon thermal reduction process is high, the AlN synthesis temperature is low, the heat preservation time is short, the efficiency is high, and the prepared pure-phase AlN powder is small in particle size. The method is simple and feasible in process, energy-saving, environment-friendly and suitable for industrial production.

Description

Technical Field

[0001] The invention relates to a method for rapidly synthesizing nano pure phase AlN powder, and belongs to the field of ceramic powder preparation. Background Art

[0002] In recent years, with the advancement of science and technology, ultra-large-scale integrated circuits and electronic devices have been moving towards high density, high frequency, high power, high reliability, miniaturization, and multifunctionality. As one of the third-generation semiconductor materials, AlN ceramics not only have excellent thermal conductivity and mechanical properties, but also possess a linear expansion coefficient close to that of silicon. Furthermore, they possess high volume resistivity, low dielectric constant and dielectric loss, high temperature resistance, corrosion resistance, and are non-toxic. These advantages hold broad application prospects in high-end electronic devices such as 5G communications, microwave TR components, and IGBT modules.

[0003] AlN powder is a key raw material for sintering AlN ceramics. Currently, among the three main methods for preparing AlN powder—direct nitridation of aluminum powder, wet chemical methods, and carbothermal reduction nitridation—carbothermal reduction nitridation has become an important method for preparing high-quality AlN powder due to its advantages such as high product purity, good sintering activity, and strong resistance to hydration. Typically, a mixed powder of Al2O3 and activated carbon or carbon black is the main raw material for preparing AlN powder by carbothermal reduction nitridation. However, when synthesizing AlN powder using this raw material, it often requires prolonged incubation at relatively high temperatures to completely convert Al2O3 to AlN. This results in large primary particle size, difficulty in powder refinement, and difficulty controlling the purity of the AlN fine powder.

[0004] To prepare fine AlN powder, some studies have used aluminum nitrate (Al(NO3)3·9H2O) as an Al source and sucrose, glucose, or starch as a C source, in the presence of urea, to generate an Al2O3 / C precursor through combustion synthesis or pyrolysis, which is then followed by carbothermal reduction and nitridation to synthesize AlN. Other studies have used γ-Al2O3 as an Al source and sucrose as a C source, first preparing a sucrose / alumina foam precursor, then pyrolyzing it and then carbothermal reduction and nitridation to synthesize fine AlN powder (MAO Xi-Xi, et al., Journal of Inorganic Materials, 34(2019)1123-1127). Our group previously used γ-Al2O3 as an Al source and glucose as a C source, first hydrothermally preparing γ-Al2O3@C, and then carbothermal reduction and nitridation to synthesize nano-AlN powder in a relatively short holding time. However, this method faces the challenge of requiring high pressure for the hydrothermal process and the difficulty in controlling the pressure. It can be seen that improving the contact state between Al2O3 and C and increasing the distribution uniformity of C are the keys to promoting the carbon thermal reduction nitridation of Al2O3 to generate AlN and realizing the preparation of AlN fine powder. Summary of the Invention

[0005] The present invention aims to provide a method for rapidly synthesizing pure nano-AlN powder. Specifically, using γ-Al2O3 powder as the Al source and methyl methacrylate (MMA), N,N-methylenebisacrylamide (MBA), and methacrylic acid (MA) as the C sources, γ-Al2O3@PMMA is first prepared through polymerization, followed by pyrolysis to prepare γ-Al2O3@C. Finally, a carbothermal reduction nitridation method is used, with the temperature rapidly raised to the AlN synthesis temperature and a short holding time to produce pure nano-AlN powder. This method coats the surface of the γ-Al2O3 powder with MMA through polymerization, followed by pyrolysis to achieve uniform distribution of C on the γ-Al2O3 surface. During the carbothermal reduction nitridation process, the C coating, combined with the rapid heating, suppresses the γ→α phase transition and particle growth of the Al2O3, thereby promoting the rapid carbothermal reduction nitridation of the γ-Al2O3 to form AlN. This technology uses commercially available, environmentally friendly, and inexpensive γ-Al2O3 and MMA as its primary raw materials. The process is highly controllable, with a fast heating rate during the carbothermal reduction process, low AlN synthesis temperature, and short holding time, resulting in high efficiency. Furthermore, the resulting pure AlN powder has a small particle size. This method is simple, energy-efficient, and environmentally friendly, making it suitable for industrial production.

[0006] A method for rapidly synthesizing nano-pure phase AlN powder,

[0007] S1, methyl methacrylate is polymerized on the surface of γ-Al2O3 powder through polymerization reaction to form γ-Al2O3 powder coated with polymethyl methacrylate (PMMA), which is recorded as γ-Al2O3@PMMA;

[0008] S2, in a nitrogen environment, pyrolyzing and carbonizing the PMMA in the γ-Al2O3@PMMA powder obtained in step S1 to obtain C-coated γ-Al2O3 powder, denoted as γ-Al2O3@C;

[0009] S3, in a nitrogen environment, directly and rapidly heating the obtained γ-Al2O3@C to the AlN synthesis temperature, keeping the temperature for a period of time, and synthesizing nano-pure phase AlN powder.

[0010] In the above technical solution, in step S3, the heating rate is 40-9000°C / min.

[0011] Furthermore, the temperature is raised to 1550-1680°C at a heating rate of 40-9000°C / min, and the holding time is 0-60 minutes. In the present invention, the holding time can be 0, that is, the AlN powder is already formed after the temperature is raised to the target temperature.

[0012] Preferably, in step S3, the heating rate is 500-9000°C / min. The γ-Al2O3@C prepared by the method of the present invention can produce nano-pure AlN powder at extremely fast heating rates and short holding times. Generally speaking, the faster the heating rate, the shorter the holding time, preferably 0-10 minutes.

[0013] Furthermore, in a nitrogen environment, the obtained γ-Al2O3@C is heated to 1550-1680°C at a heating rate of 3500-9000°C / min and kept at this temperature for 0-3 minutes to synthesize nano-pure phase AlN powder.

[0014] Preferably, in step S3, the heating rate is 40-500°C / min. The γ-Al2O3@C prepared by the method of the present invention can also yield nano-pure AlN powder at a conventional heating rate and a relatively long holding time. Generally speaking, the faster the heating rate, the shorter the holding time, preferably 10-60 minutes.

[0015] Furthermore, in a nitrogen environment, the obtained γ-Al2O3@C is heated to 1550-1650°C at a heating rate of 40-500°C / min and kept at this temperature for 10-60 minutes to synthesize nano-pure phase AlN powder.

[0016] In the above technical solution, the γ-Al2O3 powder is nano γ-Al2O3 powder with an average particle size of less than 100nm and a specific surface area of more than 80m 2 / g.

[0017] In the above technical solution, the step S1 is specifically as follows: adding γ-Al2O3 powder and methacrylic acid to anhydrous ethanol 8-24 times the mass of γ-Al2O3 powder in a mass ratio of 100:1 to obtain a uniform slurry; adding methyl methacrylate, polyvinyl pyrrolidone (PVP), azobisisobutyronitrile (AIBN), and N,N methylenebisacrylamide to the obtained slurry, and further adding anhydrous ethanol 56-72 times the mass of γ-Al2O3 powder to make the total mass of anhydrous ethanol in the slurry 64-96 times the mass of γ-Al2O3 powder, stirring to uniformly disperse the slurry; finally, keeping the prepared slurry at 60-80°C for 4-6h, separating, drying, and sieving the product to obtain γ-Al2O3@PMMA.

[0018] Among them, the mass ratio of methyl methacrylate to γ-Al2O3 powder is 7-10:1, the mass ratio of PVP to γ-Al2O3 powder is 0.05-0.08:1, the mass ratio of azobisisobutyronitrile to methyl methacrylate is 0.015-0.030:1, and the mass ratio of N,N-methylenebisacrylamide to methyl methacrylate is 0.1-0.3:1.

[0019] In the above technical solution, step S2 is specifically as follows: heating the γ-Al2O3@PMMA obtained in step S1 to 600-700°C at a rate of 5-20°C / min in a nitrogen environment, and keeping the temperature for 2.5-4h to obtain γ-Al2O3@C.

[0020] In the above technical solution, the method includes a carbon removal step, wherein the obtained nano pure phase AlN powder is kept at 500-700° C. in air or oxygen for 2-5 hours to remove residual carbon.

[0021] Another object of the present invention is to provide nano pure phase AlN powder prepared by the above method, wherein the average particle size of the AlN powder is 70 to 110 nm.

[0022] The present invention has the following beneficial effects: the raw materials used in the synthesis method of the present invention are nano-γ-Al2O3 powder with a flocculent porous structure and MMA, which are easily available and low in cost; the polymerization reaction for preparing γ-Al2O3@PMMA is carried out under relatively low temperature conditions, is easy to implement, and the process is easy to control; the temperature for preparing γ-Al2O3@C is not high, and the equipment requirements are not high; the C layer coated on the surface of γ-Al2O3 is combined with a rapid heating process to effectively inhibit the phase transformation of γ-Al2O3 to α-Al2O3 during the carbon thermal reduction nitridation process to synthesize AlN, thereby maintaining the nano-powder characteristics of γ-Al2O3 to the temperature for forming AlN, effectively shortening the diffusion distance of the substance forming AlN by inhibiting the growth of Al2O3 powder, and at the same time, combined with the advantage of side chain groups breaking and releasing gas during the pyrolysis process of PMMA, the C layer has good air permeability and is conducive to gas exchange, thereby promoting the rapid synthesis of pure phase AlN, effectively shortening the reaction time, and improving the synthesis efficiency of AlN powder. The raw materials of the present invention are commercial powders, which are cheap, have low raw material costs, are environmentally friendly, simple and easy to control, and are easy to industrialize. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 XRD patterns (a) and SEM images (b) of γ-Al2O3 used in Examples 1, 2, 3, 4, 5 and 6, and Comparative Examples 1, 2, 3, 4 and 5;

[0024] Figure 2 XRD patterns (a), SEM images (b) and TEM images (c) of γ-Al2O3@C used in Examples 1, 2, 3, 4, 5 and 6;

[0025] Figure 3 XRD patterns of AlN powders obtained in Examples 1, 2 and 3;

[0026] Figure 4 SEM images of AlN powders obtained in Examples 1, 2 and 3;

[0027] Figure 5 The XRD spectrum of the powder obtained by ultra-fast heating of γ-Al2O3@C to 1450℃ and keeping it at 1500℃ for 3 minutes in Example 1 (a), the SEM image of the powder kept at 1450℃ for 3 minutes (b), and the SEM image of the powder kept at 1500℃ for 3 minutes (c).

[0028] Figure 6 The XRD patterns of AlN powders obtained in Examples 4 and 5 are shown below:

[0029] Figure 7 The SEM images of AlN powders obtained in Examples 4 and 5 are shown;

[0030] Figure 8 This is the XRD pattern of the AlN powder obtained in Example 6;

[0031] Figure 9 This is the SEM image of the AlN powder obtained in Example 6;

[0032] Figure 10 XRD patterns of AlN powders obtained in Comparative Examples 1, 2 and 3;

[0033] Figure 11 The SEM images of AlN powders obtained in Comparative Examples 1 and 2 are shown;

[0034] Figure 12 The XRD patterns of the AlN powders obtained in Comparative Examples 4 and 5 are shown. DETAILED DESCRIPTION

[0035] The following non-limiting examples may enable those skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0036] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; the reagents and materials described are all commercially available unless otherwise specified.

[0037] One of the specific implementation methods:

[0038] A method for rapidly synthesizing nano-pure phase AlN powder comprises the following steps:

[0039] S1, preparation of γ-Al2O3@PMMA by MMA polymerization: First, weigh γ-Al2O3 powder and MA at a mass ratio of 100:1, add anhydrous ethanol 8-24 times the mass of γ-Al2O3, and stir magnetically in a three-necked flask for 30 minutes to obtain a slurry; then weigh MMA, PVP, AIBN, and MBA, and add them to the prepared slurry, wherein the mass ratio of MMA to γ-Al2O3 powder is 7-10:1, the mass ratio of PVP to γ-Al2O3 powder is 0.05-0.08:1, and the mass ratio of AIBN to MMA is 0. The ratio is 0.015-0.030:1, and the mass ratio of MBA to MMA is 0.1-0.3:1. In addition, anhydrous ethanol is added in an amount of 56-72 times the mass of the γ-Al2O3 powder to make the total mass of anhydrous ethanol in the slurry 64-96 times the mass of the γ-Al2O3 powder, and the slurry is stirred to uniformly disperse. Finally, the prepared slurry is kept warm in an oil bath at 60-80°C for 4-6 hours, and the product is centrifuged at 500-1000 rpm for 3-5 times to obtain powder. The obtained powder is dried and passed through a 40-70 mesh sieve to obtain γ-Al2O3@PMMA.

[0040] S2, pyrolysis of γ-Al2O3@PMMA to prepare γ-Al2O3@C: the γ-Al2O3@PMMA prepared in step S1 is heated to 600-700°C at a rate of 5-20°C / min in a nitrogen atmosphere and kept at this temperature for 2.5-4h to obtain γ-Al2O3@C.

[0041] S3, synthesis of AlN powder by carbon thermal reduction and nitridation of γ-Al2O3@C: heating the γ-Al2O3@C prepared in step S2 to 1550-1680°C at a heating rate of 500-9000°C / min in a nitrogen atmosphere and keeping the temperature for 0-10 minutes, or heating the temperature to 1550-1650°C at a heating rate of 40-500°C / min and keeping the temperature for 10-60 minutes to obtain nano pure phase AlN powder.

[0042] In step S1 of the present invention, the alumina powder used has a specific surface area greater than 80m 2 / g, γ-Al2O3 with an average particle size of less than 100nm.

[0043] Preferably, first, γ-Al2O3 powder and MA are weighed in a mass ratio of 100:1, anhydrous ethanol 12.8 times the mass of γ-Al2O3 is added, and the mixture is magnetically stirred in a three-necked flask for 30 minutes to obtain a slurry; then, MMA, PVP, AIBN, and MBA are weighed and added to the prepared slurry, wherein the mass ratio of MMA to γ-Al2O3 powder is 8:1, the mass ratio of PVP to γ-Al2O3 powder is 0.06:1, the mass ratio of AIBN to MMA is 0.025:1, and the mass ratio of MBA to MMA is 0.2:1, and then anhydrous ethanol 67.2 times the mass of γ-Al2O3 powder is added, and the slurry is stirred to uniformly disperse; finally, the prepared slurry is kept at 70°C in an oil bath for 5 hours, the product is centrifuged at 800 rpm 3 times, the obtained powder is dried, and passed through a 50-mesh sieve to obtain γ-Al2O3@PMMA.

[0044] In step S2 of the present invention, the temperature is preferably increased to 650° C. at a rate of 10° C. / min and kept at this temperature for 3 h.

[0045] In step S3 of the present invention, the preferred ultrafast heating rate is 4000-9000°C / min, the AlN powder synthesis temperature is 1600°C, and the holding time is 3 minutes; the rapid heating rate is 50°C / min, the AlN powder synthesis temperature is 1600-1620°C, and the holding time is 30-60 minutes.

[0046] The powder obtained after step S3 of the present invention may further include a carbon removal step, wherein the AlN powder synthesized by carbothermal reduction nitridation is kept at 500-700° C. in air or oxygen for 2-5 hours to remove residual carbon, thereby obtaining pure phase nano-AlN powder.

[0047] Example 1

[0048] S1, first, the specific surface area of 115m 2 / g, 10g of γ-Al2O3 powder with an average particle size of 13nm was placed in a three-necked flask with 0.1g of MA and 128g of anhydrous ethanol and magnetically stirred for 30 minutes to obtain a slurry. Then, 80g of MMA, 0.6g of PVP, 2g of AIBN, 16g of MBA, and 672g of anhydrous ethanol were added to the slurry and stirred to uniformly disperse the slurry. The prepared slurry was incubated at 70°C in an oil bath for 5 hours and centrifuged three times at 800rpm to obtain a powder. The resulting powder was dried and passed through a 50-mesh sieve to obtain γ-Al2O3@PMMA. Figure 1 XRD pattern (a), SEM image (b) and TEM image (c) of γ-Al2O3 powder.

[0049] S2, the prepared γ-Al2O3@PMMA was heated to 650℃ at 10℃ / min and kept warm for 3h to obtain γ-Al2O3@C. The XRD pattern (a), SEM image (b) and TEM image (c) of γ-Al2O3@C are shown in Figure 2 .from Figure 2 It can be seen that the obtained powder is composed of γ-Al2O3 and C, and still presents the nano-flocculated morphology of γ-Al2O3. In addition, C is coated on the surface of γ-Al2O3, indicating that a C-coated γ-Al2O3 structure is obtained, namely γ-Al2O3@C, in which the B region is the C coating layer with a high C content, as shown in Table 1.

[0050] S3, the γ-Al2O3@C was heated to 1600℃ in nitrogen at a heating rate of 6000℃ / min and kept at this temperature for 3min to obtain nano pure phase AlN powder with an average particle size of 81.8nm. The XRD pattern of the obtained AlN powder is shown in Figure 3 , SEM images are shown in Figure 4 .

[0051] In order to reveal the phase composition characteristics of AlN powder before formation, Figure 5 (a) XRD patterns of the powders obtained by heating γ-Al2O3@C at 1450℃ and 1500℃ for 3 min are also shown. It can be seen that the γ→α phase transition of Al2O3 does not occur during the AlN formation process, indicating that the γ-Al2O3@C of the present invention combined with the ultra-fast heating CRN process can suppress the high-temperature phase transition of γ-Al2O3 and maintain the nanostructure of γ-Al2O3 until the AlN formation temperature ( Figure 5 (b) and 5(c)).

[0052] Table 1 Figure 2 The element contents (at.%) of the marked A and B regions.

[0053]

[0054] Example 2

[0055] Example 2 The method of Example 1 is followed, except that the carbon thermal reduction nitriding temperature in step S3 is 1650°C. The XRD pattern of the obtained AlN powder is shown in FIG. Figure 3 Only the diffraction peak of AlN was detected, indicating that pure AlN powder was synthesized. Figure 4 , the average particle size is 102.4nm.

[0056] Example 3

[0057] Example 3 The method of Example 1 is followed, except that the carbon thermal reduction nitridation temperature in step S3 is 1650°C and the temperature is kept for 2 minutes. The XRD pattern of the obtained AlN powder is shown in FIG. Figure 3, the diffraction peak of AlN indicates that pure phase AlN powder is synthesized, and its morphology is shown in Figure 4 , the average particle size is 97.4nm.

[0058] Example 4

[0059] Example 4 The method of Example 1 was followed, except that the heating rate of the carbon thermal reduction nitridation in step S3 was 50°C / min, and the temperature was kept at 1600°C for 60 min to prepare pure AlN powder. The XRD pattern of the powder was shown in FIG. Figure 6 , SEM images are shown in Figure 7 , the average particle size is 89.9nm.

[0060] Example 5

[0061] Example 5 The method of Example 1 was followed, except that the heating rate of the carbon thermal reduction nitridation in step S3 was 50°C / min, and the pure phase AlN powder was prepared at 1620°C for 30 min. The XRD pattern of the powder was shown in FIG. Figure 6 , SEM images are shown in Figure 7 , the average particle size is 76.3nm.

[0062] Example 6

[0063] Example 6 The method of Example 1 was followed, except that the heating rate of the carbon thermal reduction nitridation in step S3 was 4000°C / min, and the pure phase AlN powder was prepared at 1600°C for 3 minutes. The XRD pattern is shown in FIG. Figure 8 , appearance see Figure 9 , the average particle size is 107.0nm.

[0064] Comparative Example 1

[0065] Comparative Example 1: Using the mixed powder of γ-Al2O3 powder and activated carbon powder described in Example 1 as raw materials, AlN powder was prepared according to the carbon thermal reduction nitridation method in step S3 of Example 1. The obtained powder contained α-Al2O3 ( Figure 10 ), the primary particle size of the obtained powder is relatively large, reaching submicron ( Figure 11 ).

[0066] Comparative Example 2

[0067] Comparative Example 2 The method of Example 1 was followed, except that the heating rate of the carbon thermal reduction nitridation in step S3 was 50°C / min. The obtained powder was mainly composed of γ-Al2O3 and contained a small amount of α-Al2O3 ( Figure 10 ), no AlN was formed, and the powder still showed the morphology characteristics of nano-γ-Al2O3 ( Figure 11This indicates that the γ-Al2O3@C of the present invention can inhibit the γ→α phase transformation of Al2O3, maintaining the phase and morphology of γ-Al2O3 up to the AlN formation temperature of 1600°C. However, at a rapid heating rate of 50°C / min, rather than the ultra-fast 6000°C / min heating rate described in Example 1, AlN formation was not rapid, and a longer holding time (e.g., 60 minutes in Example 4) was required to synthesize pure AlN powder.

[0068] Comparative Example 3

[0069] Comparative Example 3 The method of Example 1 was followed, except that the heating rate of the carbon thermal reduction nitridation in step S3 was 50°C / min, and the temperature was kept at 1650°C. The obtained powder was mainly composed of γ-Al2O3 and contained a small amount of α-Al2O3 ( Figure 10 ). This indicates that the γ-Al2O3@C of the present invention can inhibit the γ→α phase transformation of Al2O3 and maintain the phase and morphology of γ-Al2O3 to the AlN formation temperature of 1650℃.

[0070] Comparative Example 4

[0071] The difference between Comparative Example 4 and Example 1 is that the γ-Al2O3@C is prepared by the glucose hydrothermal method described in the Chinese invention patent application number 202310061503.9. Figure 12 The phase composition analysis results show that the obtained powder contains γ-Al2O3 in addition to AlN powder, indicating that the γ-Al2O3@C is not suitable for the ultrafast heating CRN process described in the present invention.

[0072] Comparative Example 5

[0073] The difference between Comparative Example 5 and Example 1 is that the γ-Al2O3@C is prepared by the glucose hydrothermal method described in the Chinese invention patent application number 202310061503.9, and the AlN synthesis temperature is 1650°C. Figure 12 As shown, the obtained powder contains γ-Al2O3 in addition to AlN powder, indicating that the γ-Al2O3@C is not suitable for the ultrafast heating CRN process described in the present invention.

Claims

1. A method for rapidly synthesizing nano-pure phase AlN powder, characterized by: S1, methyl methacrylate is polymerized on the surface of γ-Al2O3 powder through polymerization reaction to form γ-Al2O3 powder coated with polymethyl methacrylate, which is recorded as γ-Al2O3@PMMA; S2, in a nitrogen environment, pyrolyzing and carbonizing the polymethyl methacrylate in the γ-Al2O3@PMMA powder obtained in step S1 to obtain C-coated γ-Al2O3 powder, denoted as γ-Al2O3@C; S3, in a nitrogen environment, directly and rapidly heating the obtained γ-Al2O3@C to the AlN synthesis temperature, keeping the temperature for a period of time, and synthesizing nano-pure phase AlN powder.

2. The method according to claim 1, wherein: In step S3, the heating rate is 500-9000°C / min.

3. The method according to claim 2, wherein: In a nitrogen environment, the obtained γ-Al2O3@C is heated to 1550-1680°C at a heating rate of 3500-9000°C / min and kept at this temperature for 0-10 minutes to synthesize nano-pure phase AlN powder.

4. The method according to claim 1, wherein: In step S3, the heating rate is 40-500°C / min.

5. The method according to claim 4, characterized in that: In a nitrogen environment, the obtained γ-Al2O3@C is heated to 1550-1650°C at a heating rate of 40-500°C / min and kept at this temperature for 10-60 minutes to synthesize nano-pure phase AlN powder.

6. The method according to claim 1, wherein: The γ-Al2O3 powder is nano γ-Al2O3 powder with an average particle size of less than 100nm and a specific surface area of more than 80m 2 / g.

7. The method according to claim 1, wherein: The step S1 specifically comprises: adding γ-Al2O3 powder and methacrylic acid to anhydrous ethanol 8-24 times the mass of the γ-Al2O3 powder in a mass ratio of 100:1 to obtain a uniform slurry; adding methyl methacrylate, polyvinyl pyrrolidone, azobisisobutyronitrile, and N,N-methylenebisacrylamide to the obtained slurry; further adding anhydrous ethanol 56-72 times the mass of the γ-Al2O3 powder to make the total mass of anhydrous ethanol in the slurry 64-96 times the mass of the γ-Al2O3 powder; stirring to uniformly disperse the slurry; finally, keeping the prepared slurry at 60-80°C for 4-6 hours, separating, drying, and sieving the product to obtain γ-Al2O3@PMMA. Among them, the mass ratio of methyl methacrylate to γ-Al2O3 powder is 7-10:1, the mass ratio of polyvinyl pyrrolidone to γ-Al2O3 powder is 0.05-0.08:1, the mass ratio of azobisisobutyronitrile to methyl methacrylate is 0.015-0.030:1, and the mass ratio of N,N-methylenebisacrylamide to methyl methacrylate is 0.1-0.3:

1.

8. The method according to claim 1, wherein: The step S2 specifically comprises: heating the γ-Al2O3@PMMA obtained in step S1 to 600-700°C at a rate of 5-20°C / min in a nitrogen environment, and keeping the temperature for 2.5-4 hours to obtain γ-Al2O3@C.

9. The method according to claim 1, wherein: The method comprises a carbon removal step, wherein the obtained nano pure phase AlN powder is kept at 500-700° C. in air or oxygen for 2-5 hours to remove residual carbon.

10. AlN powder obtained by the method according to any one of claims 1 to 9, characterized in that: The average particle size of the AlN powder is 70-110 nm.

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