Preparation method of nano-aluminum nitride powder

Abstract

This invention discloses a method for preparing nano-aluminum nitride powder. In a DC electric arc furnace, a sintered block of graphite alumina is used as the anode and a graphite electrode as the cathode. Nitrogen gas is then introduced, and an arc is ignited, causing the nitrogen gas to react with the sintered block of graphite alumina to form aluminum nitride powder A. This invention avoids powder sintering into lumps and the generation of large amounts of high-temperature molten metal during the preparation of nano-aluminum nitride powder. Furthermore, the powder exhibits uniform particle size, high purity, and high conversion rate.

Description

Technical Field

[0001] This invention relates to a method for preparing nano-aluminum nitride powder, belonging to the field of aluminum nitride powder preparation technology. Background Technology

[0002] Aluminum nitride (AlN) has high thermal conductivity (theoretically up to 320 W·m). -1 ·K -1 Good insulation (>10) 14 Ωcm), low dielectric constant (8.0 under 1MHz testing conditions) and dielectric loss (dielectric loss angle tanδ=10 Ωcm). -4 ), and its coefficient of thermal expansion matches that of silicon (3.2 × 10⁻⁶). -6 K -1 With its excellent chemical stability and non-toxicity, it has been widely used in semiconductors, vacuum electronics and other fields, and is also a key material for electronic components used in automotive electronics, aerospace and military defense.

[0003] High-quality powder raw materials are a prerequisite for obtaining high-performance AlN ceramics. To prepare AlN ceramics with high thermal conductivity, it is first necessary to prepare AlN powder with high purity, fine particle size, good dispersibility, and excellent sinterability. These factors all depend on the purity of the initial raw materials, the synthesis method, and the reaction conditions. Improving AlN conversion rate, reducing powder impurity content and reaction energy consumption, shortening the process flow, and saving costs are the most important issues in powder preparation. Furthermore, for AlN, a material with a low self-diffusion coefficient and high sintering temperature requirements (above 1900℃), nano-sized AlN powder exhibits unique advantages in low-temperature sintering densification due to its high surface energy. Meanwhile, grain size affects the final properties of the material. Using nano-AlN powder holds promise for preparing AlN ceramics with nano-grain size, high relative density, high thermal conductivity, and high strength; therefore, the preparation of nano-AlN powder has also attracted close attention from researchers.

[0004] Several articles have reported methods for preparing nano-AlN powder. Both the direct nitriding method and the carbothermic reduction method can be used industrially to prepare nano-AlN powder, but each has its drawbacks. AlN powder prepared by the direct nitriding method is prone to agglomeration and has a low conversion rate. Studies by Dehkordi et al. showed that the conversion rate of AlN powder prepared by the direct nitriding method was only 80%. The carbothermic reduction method requires nanoscale precursors, but nanoparticles are prone to agglomeration; therefore, how to uniformly mix Al2O3 and carbon is a key issue. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a method for preparing nano-aluminum nitride powder.

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

[0007] The present invention discloses a method for preparing nano-aluminum nitride powder. In a DC electric arc furnace, a graphite alumina sintered block is used as the anode and a graphite electrode is used as the cathode. Nitrogen gas is then introduced and an electric arc is ignited, so that the nitrogen gas reacts with the graphite alumina sintered block to form aluminum nitride powder A.

[0008] The method of this invention involves fabricating graphite alumina blocks into the bottom electrode (anode) and graphite electrode (cathode) of a DC electric arc furnace. Then, in a nitrogen-filled environment, the high-temperature electric arc generated between the bottom electrode (anode) and graphite electrode (cathode) of the electric arc furnace promotes the carbothermic reaction in the high-temperature part of the electrode, forming nano-aluminum nitride powder with nitrogen at high temperature. Because the high temperature is generated when the graphite alumina block discharges with the cathode graphite, the alumina melts and vaporizes, and the products generated by carbon and nitrogen nitridation are dispersed under the action of the electric arc and gas. Moreover, the carbon is in excess, so no agglomeration occurs, and nano-sized aluminum nitride powder can be obtained.

[0009] In a preferred embodiment, the method for preparing the graphite alumina sintered block is as follows: mixing graphite and alumina powder, ball milling to obtain a mixed powder, and sintering the mixed powder to obtain a graphite alumina block.

[0010] Further preferably, the alumina is α-alumina. In this invention, either α-alumina or other metastable alumina can be used, but the same high temperature is required for the alumina to undergo a carbothermic nitridation reaction with carbon and nitrogen, and the metastable alumina will transform into α-alumina during the heating process.

[0011] Further preferably, the purity of the graphite powder is ≥99.99%.

[0012] In a further preferred embodiment, the particle size D50 of the graphite powder is 10–20 μm, and the particle size D50 of the alumina powder is 2–5 μm. The inventors have discovered that controlling the particle size of the graphite powder and alumina powder within the above-mentioned range ensures sufficient contact between the graphite and alumina, promoting a complete reaction.

[0013] In a further preferred embodiment, the mass ratio of graphite powder to alumina powder is 0.5 to 1.5:1.

[0014] By controlling the mass ratio of graphite powder to alumina powder within the above range, the final performance is optimal. If the carbon content is too low, some alumina cannot undergo carbothermic nitridation with carbon.

[0015] In a further preferred embodiment, alumina balls are used as grinding balls during ball milling, the ball-to-material ratio is 3-5:1, and the ball milling time is 100-200 hours.

[0016] In actual operation, the ball mill is lined with polyurethane to prevent impurities from entering the raw materials from the metal ball mill drum.

[0017] In a further preferred embodiment, the sintering is carried out under vacuum conditions, with a sintering temperature of 1500–1600°C, a sintering pressure of 35–45 MPa, and a sintering time of 60–120 min.

[0018] In actual operation, the sintering strength is higher when the sintering temperature is 1550℃.

[0019] The inventors discovered that by controlling the sintering temperature and pressure within the aforementioned range during the preparation of graphite alumina sintered blocks, the resulting graphite alumina blocks have high strength, which can prevent anode breakage and ensure the reaction proceeds. In this invention, since the graphite alumina blocks are used as anodes, and the anodes are gradually consumed during the reaction and need to be continuously moved into the furnace, if the strength is insufficient, the anodes are prone to breakage.

[0020] The preferred method is to introduce nitrogen at a flow rate of 4–8 L / min.

[0021] The preferred method involves energizing and igniting the arc, with a controlled current density of 4–6 × 10⁻⁶. 6 A / m². Controlling the current density within the above range ensures a complete reaction. If the current density is too low, the arc temperature will be too low, failing to meet the reaction requirements.

[0022] In actual operation, a dust collector is used to collect nano-aluminum nitride powder A formed by the reaction of nitrogen gas with graphite alumina sintered blocks. However, during the collection process, although the collected dust mainly consists of aluminum nitride, a small amount of aluminum carbide is also generated during the high-temperature reaction. At the same time, a small amount of unreacted alumina and excess carbon powder will enter the dust collector. Therefore, the collected dust is finally heated at high temperature in a nitrogen atmosphere to promote the nitridation of aluminum nitride and alumina into aluminum nitride powder. Then, the aluminum nitride powder is heated in an air stream to decarburize, obtaining high-purity nano-aluminum nitride powder B.

[0023] In a preferred embodiment, a dust collector is used to collect nano-aluminum nitride powder A. The powder collected by the dust collector is placed in a nitrogen atmosphere for nitriding reaction, and then decarburized in an air atmosphere to obtain aluminum nitride powder B.

[0024] In a further preferred embodiment, the nitriding reaction is carried out at a temperature of 1600–1650°C, for a time of 8–10 h, and with a nitrogen flow rate of 2–8 L / min.

[0025] In a further preferred embodiment, the decarburization is carried out in an air atmosphere, the decarburization temperature is 600-700℃, the decarburization time is 7-10h, and the air flow rate is 6-10L / min.

[0026] Principles and advantages

[0027] This invention first involves ball milling a mixture of high-purity graphite and alumina in a certain proportion to obtain a homogeneous graphite and alumina powder. The homogeneous graphite and alumina powder is then sintered under high temperature and high pressure to form graphite alumina blocks. The high-temperature and high-pressure sintered graphite alumina blocks are then used to make the bottom electrode (anode) and graphite electrode (cathode) of a DC electric arc furnace. In a nitrogen-filled environment, the high-temperature electric arc generated between the bottom electrode (anode) and graphite electrode (cathode) of the electric arc furnace promotes the carbothermic reaction in the high-temperature part of the electrode, forming aluminum nitride powder with nitrogen at high temperature.

[0028] This invention does not cause powder sintering into lumps during the preparation of nano-aluminum nitride powder, and does not generate a large amount of high-temperature molten metal, thus meeting the requirements for production safety. Attached Figure Description

[0029] Figure 1 XRD pattern of nano-aluminum nitride powder B obtained in Example 1.

[0030] Figure 2 XRD pattern of nano-aluminum nitride powder B obtained in Example 2.

[0031] Figure 3 XRD pattern of nano-aluminum nitride powder B obtained in Example 3.

[0032] Figure 4 XRD pattern of the nano-aluminum nitride powder obtained in Comparative Example 1.

[0033] Figure 5 XRD pattern of the product without final decarbonization in Comparative Example 2.

[0034] Figure 6 XRD pattern of the product without final decarbonization in Comparative Example 3. Detailed Implementation

[0035] The present invention and its specific implementation methods will be further described in detail below with reference to the embodiments.

[0036] The present invention is characterized by the following steps:

[0037] A. The initial high-purity graphite powder particle size D50 is 10-20 μm, and the α-alumina powder particle size D50 is 2-5 μm. The high-purity graphite powder and α-alumina powder are mixed at a mass ratio of 0.5-1.5:1 and then dry-milled in a ball mill. The ball milling time is 100-200 hours, the ball-to-material ratio is 3-5:1, and the rotation speed is 40-55 rpm.

[0038] B. The ball-milled and mixed graphite alumina powder obtained in step A is sintered into blocks under vacuum, high temperature and high pressure. The sintering temperature is 1500-1600℃, the sintering pressure is 40MPa, and the sintering holding time is 60-120 minutes. The graphite alumina blocks sintered under high temperature and high pressure are then used to make the furnace bottom electrode (anode) and graphite electrode (cathode) of a DC electric arc furnace.

[0039] C. Install the electrodes obtained in step B in a DC electric arc furnace. The high-temperature electric arc generated between the electrodes in the furnace promotes the carbothermic reaction in the high-temperature portion of the electrodes, forming nano-aluminum nitride powder with nitrogen gas at high temperature. The nitrogen gas flow rate is 4–8 L / min, and the current density is 4–6 × 10⁻⁶. 6 A / ㎡;

[0040] D. The dust collected in step C is heated at high temperature in a nitrogen atmosphere to nitride aluminum carbide and aluminum oxide into aluminum nitride. The heating temperature is 1600–1650℃, the holding time is 8–10 hours, and the nitrogen flow rate is 2–8 L / min.

[0041] E. When the aluminum nitride powder obtained in step D is heated and decarburized in an air stream, the temperature is 600-700℃ and the holding time is 7-10 hours. Finally, the aluminum nitride particle size D50 is 300-800nm ​​and the purity is not less than 99%.

[0042] The initial high-purity graphite powder has a particle size D50 of 10-20 μm, the α-alumina powder has a particle size D50 of 2-5 μm, and the mass ratio of high-purity graphite powder to α-alumina powder is 0.5-1.5:1; the ball milling time is 100-200 hours, the ball-to-material ratio is 3-5:1, and the rotation speed is 40-55 rpm.

[0043] The graphite alumina powder is sintered under vacuum at a temperature of 1500–1600°C, a sintering pressure of 40 MPa, and a sintering holding time of 60–120 minutes.

[0044] The DC electric arc furnace is supplied with nitrogen at a flow rate of 4–8 L / min and a current density of 4–6 × 10⁻⁶ L / min. 6 A / ㎡.

[0045] The dust is heated at high temperature in a nitrogen atmosphere to induce the nitridation of aluminum carbide and aluminum oxide into aluminum nitride. The heating temperature is 1600–1650℃, the holding time is 8–10 hours, and the nitrogen flow rate is 2–8 L / min.

[0046] The aluminum nitride powder obtained is heated and decarburized in an air flow with a flow rate of 6-10 L / min at a temperature of 600-700℃ for a holding time of 7-10 hours.

[0047] The following are embodiments of the present invention:

[0048] Example 1

[0049] The initial high-purity graphite powder had a particle size D50 of 20 μm, and the α-alumina powder had a particle size D50 of 2 μm. 500 g of high-purity graphite powder and 1000 g of α-alumina powder were mixed at a mass ratio of 0.5:1 and then dry-milled in a ball mill. The milling time was 150 hours, the ball-to-powder ratio was 3:1, and the milling speed was 40 rpm. The milled graphite alumina powder was then sintered into blocks at 1500℃ and a vacuum pressure of 40 MPa for 60 minutes. These high-temperature, high-pressure sintered graphite alumina blocks were then used to fabricate the furnace bottom electrode (anode) and graphite electrode (cathode) of a DC electric arc furnace. The electrodes were installed in the DC electric arc furnace, and nitrogen gas was introduced at a flow rate of 4 L / min and a current density of 4 × 10⁻⁶. 6 A / ㎡, using the high-temperature electric arc generated between the electrodes of the electric arc furnace to promote the carbothermic reaction in the high-temperature part of the electrode, and forming nano-aluminum nitride powder A with nitrogen at high temperature. The obtained nano-aluminum nitride powder A has a particle size D50 of 420nm and a purity of 92%.

[0050] Nano-aluminum nitride powder was collected from a DC electric arc furnace using a dust collector. The collected dust was heated to 1600℃ in a nitrogen atmosphere with a flow rate of 2L / min and held for 8 hours to nitride aluminum carbide and aluminum oxide into aluminum nitride. Finally, the temperature was lowered to 650℃, and air was introduced and held for 8 hours to decarburize the powder. The resulting nano-aluminum nitride powder had a particle size (D50) of 470nm and a purity of not less than 99%. The XRD pattern is shown below. Figure 1 As shown.

[0051] Example 2

[0052] The initial high-purity graphite powder had a particle size D50 of 10 μm, and the α-alumina powder had a particle size D50 of 2 μm. 1000 g of high-purity graphite powder and 1000 g of α-alumina powder were mixed at a mass ratio of 1:1 and then dry-milled in a ball mill. The milling time was 120 hours, the ball-to-powder ratio was 3:1, and the rotation speed was 55 rpm. The milled graphite alumina powder was then sintered into blocks at 1550℃ and a vacuum pressure of 40 MPa for 80 minutes. These high-temperature, high-pressure sintered graphite alumina blocks were then used to fabricate the furnace bottom electrode (anode) and graphite electrode (cathode) for a DC electric arc furnace. The electrodes were installed in the DC electric arc furnace, and nitrogen gas was introduced at a flow rate of 6 L / min and a current density of 5 × 10⁻⁶. -6A / m², utilizing the high-temperature electric arc generated between the electrodes of an electric arc furnace to promote the carbothermic reaction in the high-temperature part of the electrodes, forms nano-aluminum nitride powder A with a particle size D50 of 460 nm and a purity of 88% under high temperature with nitrogen. The collected dust is heated to 1640℃ in a nitrogen atmosphere with a flow rate of 4 L / min and held for 8 hours to nitride aluminum carbide and aluminum oxide into aluminum nitride. Finally, it is cooled to 700℃ and held with air for 7 hours to decarburize, yielding aluminum nitride B with a particle size D50 of 550 nm and a purity of not less than 99%. XRD pattern as shown. Figure 2 As shown.

[0053] Example 3

[0054] The initial high-purity graphite powder had a particle size D50 of 10 μm, and the α-alumina powder had a particle size D50 of 2 μm. 1500 g of high-purity graphite powder and 1000 g of α-alumina powder were mixed at a mass ratio of 1.5:1 and then dry-milled in a ball mill. The milling time was 180 hours, the ball-to-powder ratio was 5:1, and the milling speed was 55 rpm. The milled graphite alumina powder was then sintered into blocks at 1550℃ and a vacuum pressure of 40 MPa for 100 minutes. These high-temperature, high-pressure sintered graphite alumina blocks were then used to fabricate the furnace bottom electrode (anode) and graphite electrode (cathode) of a DC electric arc furnace. The electrodes were installed in the DC electric arc furnace, and nitrogen gas was introduced at a flow rate of 8 L / min and a current density of 5.5 × 10⁻⁶. 6 A / m², utilizing the high-temperature electric arc generated between the electrodes of an electric arc furnace to promote the carbothermic reaction in the high-temperature part of the electrodes, forms nano-aluminum nitride powder with a particle size D50 of 550 nm and a purity of 85% under high temperature with nitrogen. The collected dust is heated to 1640℃ in a nitrogen atmosphere with a flow rate of 6 L / min and held for 10 hours to nitride aluminum carbide and aluminum oxide into aluminum nitride. Finally, it is cooled to 700℃ and held with air for 7 hours to decarburize, yielding aluminum nitride with a particle size D50 of 630 nm and a purity of not less than 99%. XRD pattern as shown. Figure 3 As shown.

[0055] Comparative Example 1

[0056] Other conditions were the same as in Example 1, except that the collected dust was not heated to 1600°C in a nitrogen atmosphere and held for more than 8 hours to promote complete nitridation of alumina into aluminum nitride. The final product still showed strong α-alumina diffraction peaks after XRD analysis. The XRD pattern is shown below. Figure 4 As shown.

[0057] Comparative Example 2

[0058] Other conditions were the same as in Example 1. Graphite alumina powder was directly reacted with nitrogen in a conventional furnace. Without final decarburization, XRD analysis of the product showed aluminum nitride and carbon diffraction peaks, but the product particle size D50 was 2.2 μm. The XRD pattern is shown below. Figure 5 As shown.

[0059] Comparative Example 3

[0060] All other conditions are the same as in Example 1, except that the current density will be 4 × 10⁻⁶. 5 A / m², without decarbonization products, XRD analysis showed aluminum nitride, aluminum oxide, and carbon diffraction peaks. The XRD pattern is shown below. Figure 6 As shown.

Claims

1. A method for preparing nano-aluminum nitride powder, characterized in that: In a DC electric arc furnace, a graphite alumina sintered block is used as the anode and a graphite electrode as the cathode. Nitrogen gas is then introduced and an arc is ignited, causing the nitrogen gas to react with the graphite alumina sintered block to form aluminum nitride powder A. A dust collector is used to collect nano-aluminum nitride powder A. The powder collected by the dust collector is placed in a nitrogen atmosphere for nitriding reaction, and then decarburized in an air atmosphere to obtain aluminum nitride powder B. The preparation method of the graphite alumina sintered block is as follows: graphite powder and alumina powder are mixed, ball-milled to obtain mixed powder, and the mixed powder is sintered to obtain graphite alumina block; The particle size D50 of the graphite powder is 10~20μm, and the particle size D50 of the alumina powder is 2~5μm; The mass ratio of graphite powder to alumina powder is 0.5~1.5:

1.

2. The method for preparing nano-aluminum nitride powder according to claim 1, characterized in that: The purity of the graphite powder is ≥99.99%.

3. The method for preparing nano-aluminum nitride powder according to claim 1, characterized in that: During the ball milling process, alumina balls are used as grinding balls, the ball-to-material ratio is 3~5:1, and the milling time is 100~200h.

4. The method for preparing nano-aluminum nitride powder according to claim 1, characterized in that: The sintering is carried out under vacuum conditions, with a sintering temperature of 1500~1600℃, a sintering pressure of 35~45MPa, and a sintering time of 60~120min.

5. The method for preparing nano-aluminum nitride powder according to claim 1, characterized in that: The flow rate of nitrogen gas introduced is 4~8 L / min.

6. The method for preparing nano-aluminum nitride powder according to claim 1, characterized in that: Arc ignition is initiated by energizing, with a controlled current density of 4~6×10⁻⁶. 6 A / ㎡.

7. The method for preparing nano-aluminum nitride powder according to claim 1, characterized in that: The nitriding reaction is carried out at a temperature of 1600~1650℃, for a time of 8~10h, and with a nitrogen flow rate of 2~8L / min.

8. The method for preparing nano-aluminum nitride powder according to claim 1, characterized in that: The decarburization is carried out in an air atmosphere at a temperature of 600-700℃ for 7-10 hours, with an air flow rate of 6-10 L / min.

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