Method for preparing superfine aluminum nitride by low-temperature vacuum carbon thermal nitriding

Abstract

The application discloses a method for preparing superfine aluminum nitride by low-temperature vacuum carbon thermal nitriding, and belongs to the technical field of nitride ceramic preparation. The method comprises the following steps: (1) mixing and grinding alumina and carbon powder raw materials to obtain mixed raw materials, and then mixing and grinding the mixed raw materials with a composite catalyst to obtain mixed materials; (2) dispersing the mixed materials in the step (1) in a cellulose dispersion liquid to obtain a paste; (3) pressing and shaping the paste in the step (2); and (4) performing vacuum carbon thermal nitriding treatment on the shaped body after shaping in the step (3) to obtain superfine aluminum nitride. The composite catalyst is added in the preparation process, so that the reaction required temperature is effectively reduced, the quality of the product under the low-temperature preparation condition is improved, and the raw material utilization rate and conversion rate are maintained to be relatively high.

Description

Technical Field

[0001] This invention belongs to the field of nitride ceramic preparation technology, and relates to a method for preparing ultrafine aluminum nitride by low-temperature vacuum carbothermal nitriding. Background Technology

[0002] Aluminum nitride is an inorganic non-metallic material with a variety of excellent physicochemical properties. It has a wide range of applications and plays an important role in fields such as electronics, ceramics, and composite materials.

[0003] Currently, the main methods for industrial production of aluminum nitride include carbothermal reduction nitridation, low-temperature synthesis, chemical vapor deposition, solution treatment, and high-temperature self-propagating methods. Among these, carbothermal reduction nitridation is the most mature method, offering significant advantages in cost, efficiency, and scalability, and its raw materials are widely available, making it the mainstream method for aluminum nitride production. However, carbothermal reduction nitridation requires high reaction temperatures and stringent reaction conditions, placing high demands on equipment performance and resulting in high energy consumption. For example, patent application number 201810622438.1 discloses a method for preparing aluminum nitride by carbothermal reduction of alumina under vacuum, requiring a reaction temperature of 1550-1650℃. Furthermore, at these higher temperatures, the volatilization of low-valent alumina is severe, hindering efficient alumina conversion and easily leading to raw material waste. While low-temperature synthesis can prepare aluminum nitride at lower temperatures, its products... The quality is poor, the defect rate is high, and most products cannot meet the requirements of industrial products, which is not conducive to industrial mass production. Therefore, it is more suitable for small-scale laboratory research. Chemical vapor deposition can prepare aluminum nitride films with high purity and relatively uniform structure, but its production efficiency is relatively limited, it requires extremely high energy input, and the cost is high. Solution processing requires relatively mild reaction conditions and is simple to operate, but its yield is low, the crystallinity of aluminum nitride is low, the product quality is poor, and it requires a more complex post-processing. High-temperature self-propagating method maintains the reaction through its own exothermic reaction, which can reduce energy consumption and improve reaction efficiency, but its reaction process is difficult to control and has low controllability, which leads to the agglomeration of aluminum nitride and poor uniformity, affecting subsequent use.

[0004] Therefore, it is necessary to provide a method for preparing ultrafine aluminum nitride by low-temperature vacuum carbothermal nitridation, which can effectively reduce the required reaction temperature, improve the utilization rate of alumina and the quality of aluminum nitride products, and achieve the preparation of high-quality aluminum nitride products under mild reaction conditions. Summary of the Invention

[0005] To overcome the problems in the prior art, this invention adds a composite catalyst during the preparation process, causing the composite catalyst to form a molten liquid phase. This lowers the reaction temperature, promotes the main reaction (Al₂O₃ + 3C + N₂ = 2AlN + 3CO) while preventing the volatilization of low-valent alumina, thereby improving the utilization rate of alumina. Furthermore, the aluminum nitride powder prepared by this invention has uniform particle size, excellent dispersibility, no agglomeration, high crystallinity, and high quality.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution: This invention proposes a method for preparing ultrafine aluminum nitride by low-temperature vacuum carbothermic carbide nitriding, the method comprising the following steps: (1) Mix and grind alumina and carbon powder raw materials to obtain mixed raw materials, and then mix and grind the mixed raw materials with composite catalyst to obtain mixed materials.

[0007] The preferred carbon powder is graphite powder.

[0008] Alumina and carbon powder raw materials are mixed and mechanically ground until the particle size of the mixed raw materials reaches about 100 mesh and is relatively uniform.

[0009] The mixed raw materials and composite catalyst are placed in an agate mortar and ground until there are no streaks or spots, the texture is fine and the powder is a uniform dark gray powder, which means that the mixture is relatively uniform.

[0010] (2) The mixture from step (1) is dispersed in a cellulose dispersion to obtain a paste. The cellulose dispersion is a liquid cellulose substance, such as hydroxypropyl methylcellulose (HPMC) or methylcellulose (MC).

[0011] (3) Press and shape the paste from step (2).

[0012] (4) Vacuum carbothermal nitriding treatment is performed on the shaped body after step (3) to obtain ultrafine aluminum nitride.

[0013] Preferably, the composite catalyst is a mixture of chloride and oxide, wherein the chloride includes at least one selected from NaCl, CaCl2, and MgCl2, and the oxide includes at least three selected from CaO, Fe2O3, TiO2, SiO2, and V2O5. When the chloride is a mixture of multiple substances, the substances can be mixed in any proportion, and the oxides can also be mixed in any proportion.

[0014] Preferably, the chloride is added at a mass of 1%-1.5% of the total mass of alumina and toner, and the oxide is added at a mass of 2.5%-3.5% of the total mass of alumina and toner.

[0015] Preferably, the chloride is a mixture of NaCl, CaCl2, and MgCl2, and the oxide is a mixture of CaO, Fe2O3, TiO2, SiO2, and V2O5. In the chloride, the mass of NaCl is 0.5%-1% of the total mass of alumina and carbon powder, the mass of CaCl2 is 0.3%-0.6% of the total mass of alumina and carbon powder, and the mass of MgCl2 is 0.2%-0.4% of the total mass of alumina and carbon powder. In the oxide, the mass of CaO is 0.3%-0.6% of the total mass of alumina and carbon powder, the mass of Fe2O3 is 1%-1.3% of the total mass of alumina and carbon powder, the mass of TiO2 is 0.3%-0.6% of the total mass of alumina and carbon powder, the mass of SiO2 is 0.6%-1% of the total mass of alumina and carbon powder, and the mass of V2O5 is 0.3%-0.5% of the total mass of alumina and carbon powder.

[0016] Preferably, in step (1), the molar ratio of alumina to carbon powder is alumina:carbon powder = 1:3-4.

[0017] Preferably, in step (2), the mass ratio of the mixture to the cellulose dispersion is mixture:cellulose dispersion = 1-2:1.

[0018] Preferably, in step (2), the pressing pressure is 1-3 MPa and the pressing time is 2 min.

[0019] Preferably, in step (3), before the vacuum carbothermal nitriding treatment, the reaction space is evacuated to 1-50 Pa.

[0020] Preferably, in step (3), before the vacuum carbothermal nitriding treatment, nitrogen gas is introduced to make the vacuum degree of the reaction space 400-1000 Pa.

[0021] Preferably, in step (3), the heating temperature of the vacuum carbothermic nitriding treatment is 1300-1450℃, and the holding time is 1.5-3.5h.

[0022] The beneficial effects of this invention are: 1. This invention significantly reduces the reaction temperature required for vacuum carbothermal nitriding by adding a composite catalyst during the preparation of aluminum nitride. This reduces energy consumption and lowers the performance requirements of industrial production equipment. Furthermore, it helps to mitigate the volatilization of low-priced alumina and improves the utilization rate of raw materials.

[0023] 2. This invention, by adding a composite catalyst during the preparation of aluminum nitride, can effectively suppress the volatilization of low-valent alumina, thereby further improving the utilization rate of raw materials, alleviating raw material waste, and increasing the conversion rate of raw materials.

[0024] 3. The aluminum nitride powder prepared by this invention has uniform particle size, excellent dispersibility, no agglomeration, high crystallinity, good product quality, and a high pass rate.

[0025] 4. The preparation method of this invention has good controllability, is easy to operate, and has a high product qualification rate, making it suitable for industrial promotion and application. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the process flow of the present invention; Figure 2 The image shows the XRD pattern of the ultrafine aluminum nitride prepared according to this invention. Figure 3 This is a microstructure diagram of the ultrafine aluminum nitride prepared according to the present invention. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0028] Example 1 This embodiment prepares ultrafine aluminum nitride using the following method: (1) Weigh aluminum oxide and graphite powder raw materials according to the molar ratio of aluminum oxide: carbon powder = 1:3.25, and mechanically grind them to obtain mixed raw materials. Then weigh 1.5% of the total mass of the mixed raw materials, a mixed chloride of MgCl2, NaCl, and CaCl2 (MgCl2: 0.3%, NaCl: 0.7%, CaCl2: 0.5%) and 3.5% of the total mass of the mixed raw materials, a mixed oxide of CaO, Fe2O3, TiO2, SiO2, and V2O5 (CaO: 0.6%, Fe2O3: 1.2%, TiO2: 0.55%, SiO2: 0.7%, V2O5: 0.45%). Add the mixed raw materials, mixed chloride, and mixed oxide to an agate bowl and grind them until they are evenly mixed to obtain a mixed material.

[0029] (2) Weigh the cellulose dispersion according to the mass ratio of the mixture to the cellulose dispersion: 1.5:1, and disperse the mixture in the cellulose dispersion to obtain a mixed liquid.

[0030] (3) Pour the mixed liquid into the mold and apply a pressure of 1 MPa to solidify the mixed liquid.

[0031] (4) Place the shaped body into a graphite crucible, place the graphite crucible in the vacuum induction furnace chamber, close the vacuum induction furnace chamber, evacuate the furnace chamber to 10 Pa, then introduce nitrogen gas until the vacuum degree in the furnace chamber is 700 Pa, start the vacuum induction furnace, raise the temperature to 1400℃ and hold for 2.5 hours. Obtain ultrafine aluminum nitride.

[0032] The ultrafine aluminum nitride prepared in this embodiment has a purity of 97.5% and a particle size of 50-70 nm.

[0033] In this embodiment, the conversion rate of alumina reached 97%.

[0034] The product prepared in this embodiment was subjected to XRD experiments, and the results are as follows: Figure 2 As shown.

[0035] pass Figure 2 It can be seen that the product prepared by this invention is indeed aluminum nitride.

[0036] The microstructure of the product prepared in this embodiment was observed, and the results are as follows: Figure 3 As shown.

[0037] pass Figure 3 It can be seen that the ultrafine aluminum nitride prepared in this embodiment has a particle size of about 50-70 μm. At the same time, the ultrafine aluminum nitride prepared by this invention has a high level of dispersibility and crystallinity.

[0038] Example 2 This embodiment prepares ultrafine aluminum nitride using the following method: (1) Weigh aluminum oxide and graphite powder raw materials according to the molar ratio of aluminum oxide: carbon powder = 1:3, and mechanically grind them to obtain mixed raw materials. Then weigh 1% of the total mass of the mixed raw materials, a mixed chloride of MgCl2, NaCl, and CaCl2 (MgCl2: 0.2%, NaCl: 0.5%, CaCl2: 0.3%) and 2.5% of the total mass of the mixed raw materials, a mixed oxide of CaO, Fe2O3, TiO2, SiO2, and V2O5 (CaO: 0.3%, Fe2O3: 1%, TiO2: 0.3%, SiO2: 0.6%, V2O5: 0.3%). Add the mixed raw materials, mixed chloride, and mixed oxide to an agate bowl and grind them until they are evenly mixed to obtain a mixed material.

[0039] (2) Weigh the cellulose dispersion according to the mass ratio of the mixture to the cellulose dispersion: 1:1, and disperse the mixture in the cellulose dispersion to obtain a mixed liquid.

[0040] (3) Pour the mixed liquid into the mold and apply a pressure of 2MPa to solidify the mixed liquid.

[0041] (4) Place the shaped body into a graphite crucible, place the graphite crucible in the vacuum induction furnace chamber, close the vacuum induction furnace chamber, evacuate the furnace chamber to 50 Pa, then introduce nitrogen gas until the vacuum degree in the furnace chamber is 1000 Pa, start the vacuum induction furnace, raise the temperature to 1450℃ and hold for 3.5 hours. Obtain ultrafine aluminum nitride.

[0042] The ultrafine aluminum nitride prepared in this embodiment has a purity of 98% and a particle size of 90-110 nm.

[0043] In this embodiment, the conversion rate of alumina reached 98%.

[0044] Example 3 This embodiment prepares ultrafine aluminum nitride using the following method: (1) Weigh aluminum oxide and graphite powder raw materials according to the molar ratio of aluminum oxide: carbon powder = 1:4, and mechanically grind them to obtain mixed raw materials. Then weigh 1.2% of the total mass of the mixed raw materials, a mixed chloride of MgCl2, NaCl, and CaCl2 (MgCl2: 0.25%, NaCl: 0.6%, CaCl2: 0.35%) and 3% of the total mass of the mixed raw materials, a mixed oxide of CaO, Fe2O3, TiO2, SiO2, and V2O5 (CaO: 0.45%, Fe2O3: 1.15%, TiO2: 0.4%, SiO2: 0.65%, V2O5: 0.35%). Add the mixed raw materials, mixed chloride, and mixed oxide to an agate bowl and grind them until they are evenly mixed to obtain a mixed material.

[0045] (2) Weigh the cellulose dispersion according to the mass ratio of the mixture to the cellulose dispersion = 2:1, and disperse the mixture in the cellulose dispersion to obtain a mixed liquid.

[0046] (3) Pour the mixed liquid into the mold and apply a pressure of 3 MPa to solidify the mixed liquid.

[0047] (4) Place the shaped body into a graphite crucible, place the graphite crucible in the vacuum induction furnace chamber, close the vacuum induction furnace chamber, evacuate the furnace chamber to 1 Pa, then introduce nitrogen gas until the vacuum degree in the furnace chamber is 400 Pa, start the vacuum induction furnace, raise the temperature to 1300℃ and hold for 1.5 hours. Obtain ultrafine aluminum nitride.

[0048] The ultrafine aluminum nitride prepared in this embodiment has a purity of 96.5% and a particle size of 70-90 nm.

[0049] In this embodiment, the conversion rate of alumina reached 96%.

[0050] Example 4 This embodiment uses the same method as Example 1 to prepare ultrafine aluminum nitride, the difference being that: in this embodiment, the chloride in the composite catalyst is MgCl2, and the oxide is a mixture of CaO, Fe2O3 and TiO2 (CaO: 1%, Fe2O3: 1.5%, TiO2: 1%).

[0051] The ultrafine aluminum nitride prepared in this embodiment has similar properties to that in Example 1, and the raw material conversion rate is also similar to that in Example 1.

[0052] Example 5 This embodiment uses the same method as Example 1 to prepare ultrafine aluminum nitride, the difference being that: in this embodiment, the chloride in the composite catalyst is a mixture of NaCl and CaCl2 (NaCl: 0.5%, CaCl2: 1%), and the oxide is a mixture of Fe2O3, TiO2, SiO2, and V2O5 (Fe2O3: 1%, TiO2: 0.6%, SiO2: 0.6%, V2O5: 0.6%).

[0053] The ultrafine aluminum nitride prepared in this embodiment has similar properties to that in Example 1, and the raw material conversion rate is also similar to that in Example 1.

[0054] Comparative Example 1 This comparative example uses the same method as Example 1 to prepare ultrafine aluminum nitride, the difference being that no composite catalyst is added during the preparation process of this comparative example, and the reaction temperature is 1450℃.

[0055] In this comparative example, when no more aluminum nitride was produced, the purity of aluminum nitride was only 52.5%. A significant amount of unreacted alumina remained in this comparative example. Because no composite catalyst was added, the alumina could not complete the reaction at a relatively low temperature, ultimately leading to a significant reduction in product purity, which failed to meet the requirements for qualified applications.

[0056] Comparative Example 2 This comparative example uses the same method as Example 1 to prepare ultrafine aluminum nitride, the difference being that no composite catalyst is added during the preparation process of this comparative example.

[0057] By testing the material in the middle and upper parts of the graphite crucible, the volatilization results of aluminum-containing materials were obtained. The test results showed that the volatilization rate of alumina in Example 1 was about 1%-2%, while the volatilization rate of alumina in this comparative example was significantly increased to 8%-10%. This proves that the addition of the composite catalyst in this invention effectively inhibits the volatilization rate of alumina raw materials, thereby effectively improving the utilization rate of raw materials, reducing raw material waste, and helping to reduce the overall preparation cost.

[0058] Comparative Example 3 This comparative example uses the same method as Example 2 to prepare ultrafine aluminum nitride, the difference being that no chloride is added during the preparation process of this comparative example.

[0059] The aluminum nitride product in this comparative example contains a significant amount of unreacted aluminum oxide, and the purity of the aluminum nitride is 56%.

[0060] A comparison of this comparative example with Example 2 shows that the absence of chloride prevents the raw materials from achieving a high conversion rate in a short time and at a low temperature, resulting in poor product quality.

[0061] Comparative Example 4 This comparative example uses the same method as Example 2 to prepare ultrafine aluminum nitride, the difference being that no oxides are added during the preparation process of this comparative example.

[0062] The aluminum nitride product in this comparative example contains a significant amount of unreacted aluminum oxide, and the purity of the aluminum nitride is 54.5%.

[0063] A comparison of this comparative example with Example 2 shows that the absence of oxides prevents the raw materials from achieving a high conversion rate in a short time and at a low temperature, resulting in poor product quality.

[0064] In summary, this invention effectively promotes the vacuum carbothermal nitriding process by adding a composite catalyst during the preparation process. Under relatively mild reaction conditions such as a relatively short time and a relatively low temperature, it successfully prepares aluminum nitride products with good quality, including uniform particle size, high crystallinity, and high purity, while maintaining high raw material utilization and conversion rates.

[0065] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made to it in form and detail without departing from the scope defined by the claims of the present invention.

Claims

1. A method for preparing ultrafine aluminum nitride by low-temperature vacuum carbothermal nitridation, characterized in that: The method includes the following steps: ​ (1) Alumina and carbon powder raw materials are mixed and ground to obtain mixed raw materials, and then the mixed raw materials are mixed and ground with composite catalyst to obtain mixed materials; (2) Disperse the mixture from step (1) in a cellulose dispersion to obtain a paste; (3) Press and shape the paste from step (2); (4) The shaped body after step (3) is subjected to vacuum carbothermal nitriding treatment to obtain ultrafine aluminum nitride; The composite catalyst is a mixture of chloride and oxide; the chloride is added at a mass of 1%-1.5% of the total mass of alumina and carbon powder, and the oxide is added at a mass of 2.5%-3.5% of the total mass of alumina and carbon powder. The chloride is a mixture of NaCl, CaCl2, and MgCl2, and the oxide is a mixture of CaO, Fe2O3, TiO2, SiO2, and V2O5. In the chloride mixture, the mass of NaCl is 0.5%-1% of the total mass of alumina and carbon powder, the mass of CaCl2 is 0.3%-0.6% of the total mass of alumina and carbon powder, and the mass of MgCl2 is 0.2%-0.4% of the total mass of alumina and carbon powder. In the oxide mixture, the mass of CaO is 0.3%-0.6% of the total mass of alumina and carbon powder, the mass of Fe2O3 is 1%-1.3% of the total mass of alumina and carbon powder, the mass of TiO2 is 0.3%-0.6% of the total mass of alumina and carbon powder, the mass of SiO2 is 0.6%-1% of the total mass of alumina and carbon powder, and the mass of V2O5 is 0.3%-0.5% of the total mass of alumina and carbon powder.

2. The method according to claim 1, characterized in that: In step (1), the molar ratio of alumina to carbon powder is alumina:carbon powder = 1:3-4.

3. The method according to claim 1, characterized in that: In step (2), the mass ratio of the mixture to the cellulose dispersion is mixture:cellulose dispersion = 1-2:

1.

4. The method according to claim 1, characterized in that: In step (2), the pressing pressure is 1-3 MPa and the pressing time is 2 min.

5. The method according to claim 1, characterized in that: In step (3), before the vacuum carbothermal nitriding treatment, the reaction space is evacuated to 1-50 Pa.

6. The method according to claim 1, characterized in that: In step (3), before the vacuum carbothermal nitriding treatment, nitrogen gas is introduced until the vacuum degree of the reaction space is 400-1000 Pa.

7. The method according to claim 1, characterized in that: In step (3), the heating temperature of the vacuum carbothermic nitriding treatment is 1300-1450℃, and the holding time is 1.5-3.5h.

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