Aluminum nitride powder and method for producing the same

Abstract

The application discloses an aluminum nitride powder and a preparation method thereof, relates to the technical field of ceramics, and solves the technical problem of poor dispersibility, low purity and low activity of AlN powder prepared by an existing method; the application comprises the following steps: adding Al(OH)3, biochar, a monoalkyl phosphate and a phosphate compound into a solvent according to a mass ratio of (70-90):(5-20):(0.1-3):(0.1-5) and uniformly dispersing the mixture by ultrasonic dispersion to form a mixed slurry; the mixed slurry is dried by spray drying to prepare a precursor powder; the precursor powder is pre-burned at 600-900 DEG C under a nitrogen atmosphere, and then high-temperature reaction is carried out by increasing the temperature to 1400-1700 DEG C to obtain the aluminum nitride powder; the aluminum nitride powder prepared by the method has the characteristics of high dispersibility, low oxygen content, low carbon residue and high reaction activity.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ceramics, and particularly relates to an aluminum nitride powder and a preparation method thereof. BACKGROUND

[0002] Aluminum nitride (AlN) ceramic has outstanding advantages in electronic packaging materials. It has extremely high resistivity, can block abnormal current conduction; has super thermal conductivity, can quickly dissipate heat; has significant dielectric constant, unique electrical properties; has high thermal expansion coefficient matching with silicon, can avoid thermal stress damage by cooperative expansion and contraction. With these properties, it becomes an ideal substrate material in the field of electronic packaging. In IGBT, 5G communication radio frequency components, high-power LED and other high-end device packaging, AlN ceramic has great potential, provides guarantee for stable operation and performance improvement of devices, and builds the material foundation for the development of modern electronic technology.

[0003] The raw material of aluminum nitride ceramic is aluminum nitride powder, and the preparation methods of aluminum nitride powder mainly include two kinds, namely direct nitriding method and carbothermal reduction method. Among them, the direct nitriding method is to react aluminum powder with nitrogen, which is violent, poor in safety and difficult to control; and the carbothermal reduction method has high purity, high stability, good forming and sintering properties, so the carbothermal reduction method has become the main production method of AlN powder.

[0004] However, the traditional carbothermal reduction process using carbon black as carbon source has the problem that the aluminum source and the carbon source are difficult to mix uniformly due to the difference in density and polarity, and local component segregation is easy to form. Uneven mixing will lead to inconsistent reaction rates, incomplete reaction in some areas, and residual aluminum oxide or carbon impurities affecting the purity of the powder, resulting in poor dispersibility of the prepared AlN powder, reduced purity and activity. Some researchers choose to add excess carbon or special additives (such as CaF2, Y2O3) to improve the mixing effect, but excess additives may cause side reactions (such as excessive yttrium leading to hard agglomeration of aluminum nitride particles) or increase the difficulty of subsequent impurity removal. In addition, the existing modification and synthesis of aluminum nitride powder are carried out separately, which has the problems of long process flow, high energy consumption, and easy introduction of defects in the intermediate link.

[0005] Therefore, the present application provides a preparation method of AlN powder with good dispersibility, purity and activity. SUMMARY

[0006] The present application is to solve the technical problem of poor dispersibility, low purity and low activity of the AlN powder prepared by the existing method, and aims to provide an aluminum nitride powder and a preparation method thereof, wherein a slurry is prepared by using biochar as a micro-carbon source, adding a monoalkyl phosphate and a phosphate compound, and then performing spray drying, and then a sintering process of "low-temperature modification pretreatment + high-temperature carbon thermal reduction nitriding" is adopted, so that the surface modification of aluminum hydroxide and aluminum oxide and the efficient coupling of reduction nitriding are realized, and finally the aluminum nitride powder with high dispersibility, low oxygen content and high reaction activity is prepared.

[0007] The present application is realized by the following technical solutions.

[0008] The present application provides a preparation method of an aluminum nitride powder, comprising the following steps:

[0009] Al(OH)3, biochar, a monoalkyl phosphate and a phosphate compound are added to a solvent in a mass ratio of (70-90):(5-20):(0.1-3):(0.1-5), and a uniform mixed slurry is formed by ultrasonic dispersion;

[0010] The mixed slurry is prepared into a precursor powder by spray drying;

[0011] The precursor powder is pre-burned at 600-900 DEG C under a nitrogen atmosphere, and then high-temperature reaction is performed at 1400-1700 DEG C to obtain the aluminum nitride powder.

[0012] The present application uses biochar as a green and low-cost carbon source to participate in the carbon thermal reduction nitriding reaction under subsequent high-temperature conditions, and also uses biochar as a physical dispersion carrier in the precursor mixing stage, so that the uniform mixing and dispersion stability of the components in the slurry are enhanced through the porous structure and large specific surface area of the biochar, particle segregation and sedimentation are avoided, and a uniform carbon distribution and reaction environment are provided for the subsequent reaction.

[0013] The phosphate group in the molecular structure of the monoalkyl phosphate can be chemically adsorbed with the hydroxyl group (-OH) on the surface of the nano-sized Al(OH)3, and the hydrophobic alkyl chain is directed outward to form a steric hindrance protective layer on the surface of the Al(OH)3 particles, which effectively inhibits the van der Waals force agglomeration between the nanoparticles and significantly improves the dispersion uniformity and fluidity of the slurry system; at the same time, the modified layer changes the surface energy of the Al(OH)3 and enhances the interfacial compatibility of the Al(OH)3 with the biochar and other substances, which is beneficial to the uniform contact and efficient reaction between the reactants in the subsequent carbon thermal reduction process, thereby improving the overall reaction activity.

[0014] The polyphosphate group in the molecule of the phosphate compound can be chemically bonded with the surface hydroxyl group of Al(OH)3 and its dehydrated product Al2O3 to form an aluminum phosphate coating layer, which can significantly inhibit the agglomeration between particles under high-temperature sintering, improve the anti-agglomeration ability of the powder, and effectively block the diffusion and residual of oxygen atoms in the high-temperature reaction process, thereby reducing the oxygen residual amount.

[0015] Therefore, the present application can improve the mixing uniformity of the slurry, and further improve the reaction activity and dispersibility by mixing the nanoscale aluminum hydroxide, biochar, monoalkyl phosphate and phosphate compound in a specific ratio to prepare a uniform precursor slurry, since the monoalkyl phosphate can be effectively adsorbed on the surface of Al(OH)3 to prevent the agglomeration of nanomaterials. Then, the precursor powder is formed by spray drying, and the "low-temperature modification pretreatment + high-temperature carbon thermal reduction nitriding" is used for staged heating in the subsequent sintering process. In the low-temperature modification pretreatment stage, the aluminum hydroxide is dehydrated, and the phosphate compound is chemically bonded on the surface of Al(OH)3 and Al2O3 to form a protective layer, realizing surface modification and structural stability, avoiding high-temperature agglomeration between particles, and then rapidly heating to perform carbon thermal reduction nitriding under nitrogen protection, so that the modified Al2O3 reacts with biochar in situ to form AlN, and finally the aluminum nitride powder with high dispersibility, low oxygen content and high reaction activity is prepared.

[0016] Further, the mass ratio of Al(OH)3, biochar, monoalkyl phosphate and phosphate compound is (75-85):(10-15):(0.8-2):(1-3). Preferably, the mass ratio of Al(OH)3, biochar, monoalkyl phosphate and phosphate compound is 85:10:0.8:1. It should be noted that the mass ratio of Al(OH)3, biochar, monoalkyl phosphate and phosphate compound in the present application can achieve the technical effects described in the present application within the above range, for example, the mass ratio can also be selected as 75:15:1.5:2, 85:15:2:3, 90:20:3:5, 70:5:0.1:0.1.

[0017] Further, the biochar is prepared by high-temperature pyrolysis of straw. The straw can be selected from agricultural waste such as rice straw, wheat straw, corn straw and rape straw.

[0018] Further, the preparation method of the biochar is as follows: after the straw is washed, it is sequentially dried, crushed, sieved, and pyrolyzed at 550-850℃ under the protection of nitrogen. After pyrolysis is completed, it is naturally cooled to room temperature, ground and sieved to obtain biochar with uniform particle size and high specific surface area.

[0019] Further, the monoalkyl phosphate is selected from at least one of sodium dodecyl phosphate and monooleic acid phosphate. Preferably, it is monooleic acid phosphate.

[0020] Further, the phosphate compound is selected from at least one of aluminum phosphate (AlPO4) and aluminum dihydrogen phosphate (Al(H2PO4)3) ; preferably aluminum dihydrogen phosphate.

[0021] Further, the spray drying is performed by using a pressure type spray dryer, the inlet air temperature is 150-200 DEG C, and the outlet air temperature is 80-120 DEG C.

[0022] Further, the pre-sintering heat preservation time is 2-3 hours, and the nitrogen flow rate is 4-6 L / min.

[0023] Further, the high-temperature reaction heat preservation time is 3-4 h, and the nitrogen flow rate is set in stages, being 9-11 L / min in the early stage of the reaction and being reduced to 5-7 L / min in the later stage of the reaction.

[0024] The second aspect of the application provides an aluminum nitride powder prepared by the method described above.

[0025] Compared with the prior art, the application has the following advantages and beneficial effects:

[0026] The application mixes nanoscale aluminum hydroxide, biochar, monoalkyl phosphate and phosphate compound in a specific ratio to prepare a uniform precursor slurry, since the monoalkyl phosphate can be effectively adsorbed on the surface of Al(OH)3, the nano material can be prevented from agglomeration, the mixing uniformity of the slurry can be improved, and then the reaction activity and dispersity can be improved; then the precursor powder is formed by spray drying, and in the subsequent sintering process, the temperature is raised in stages by using "low-medium temperature modification pretreatment + high-temperature carbon thermal reduction and nitriding", in the low-medium temperature modification pretreatment stage, the aluminum hydroxide is dehydrated, at the same time, the phosphate compound is chemically bonded on the surface of Al(OH)3 and Al2O3 to form a protective layer, surface modification and structure stability are realized, high-temperature agglomeration between particles is avoided, then the temperature is quickly raised, carbon thermal reduction and nitriding are performed under the protection of nitrogen, the modified Al2O3 reacts with biochar in situ to generate AlN, and finally the aluminum nitride powder with high dispersity, low oxygen content and high reaction activity is prepared. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the example embodiments of the application, the following will briefly introduce the drawings needed to be used in the examples, and it should be understood that the following drawings only show some of the embodiments of the application, and therefore should not be regarded as a limitation on the scope, and for those skilled in the art, other related drawings can also be obtained without creative labor. In the drawings:

[0028] Figure 1 The microstructure diagram of the aluminum nitride powder prepared for Example 1;

[0029] Figure 2 Microstructure of the aluminum nitride powder prepared for Comparative Example 1. DETAILED DESCRIPTION

[0030] In order to make the objects, technical solutions, and advantages of the present application clearer, the technical solutions in the embodiments of the present application will be described below in connection with embodiments. Obviously, the illustrative embodiments of the present application and their descriptions are only used to explain the present application and not to limit the present application.

[0031] The following detailed description of the embodiments of the present application of an aluminum nitride powder and a preparation method thereof. However, there will be omitted unnecessary detailed description. For example, there are omitted detailed description of well-known matters and repeated description. This is to avoid the following description unnecessarily long, facilitating the understanding of those skilled in the art.

[0032] The "range" disclosed in the present application is limited in the form of lower limit and upper limit, a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The range defined in this way can include or not include the end value, and can be arbitrarily combined, i.e. any lower limit can be combined with any upper limit to form a range.

[0033] If not specifically stated, all embodiments and optional embodiments of the present application can be combined to form new technical solutions.

[0034] If not specifically stated, all technical features and optional technical features of the present application can be combined to form new technical solutions.

[0035] If not specifically stated, the "includes" and "contains" mentioned in the present application means open, and can also be closed. For example, the "includes" and "contains" can mean that other substances not listed can also be included or contained, or only the listed substances can be included or contained.

[0036] If not specifically stated, all steps of the present application can be performed in sequence or randomly, preferably in sequence. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method can also include step (c), which means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0037] The technical solutions of the application are further described in detail below in combination with examples.

[0038] It should be noted that the experimental methods used in the examples are conventional methods unless otherwise specified. The materials, reagents, methods and instruments used, unless otherwise specified, are conventional materials, reagents, methods and instruments in the art, which can be obtained by commercial channels by those skilled in the art.

[0039] Example 1

[0040] A preparation method of aluminum nitride powder comprises the following steps:

[0041] (1) Raw material pretreatment: corn straw is washed to remove soil and impurities, dried at 60℃, then crushed and sieved; under nitrogen protection, pyrolysis is performed using a vacuum tube furnace, the temperature is raised to 700℃ at a rate of 10℃ / min, and the temperature is kept for 2 h; after pyrolysis is completed, the temperature is naturally cooled to room temperature under nitrogen protection, and then ground and sieved through a 200 mesh sieve to obtain high specific surface area biochar;

[0042] (2) Preparation of precursor slurry: nano-sized Al(OH)3, biochar, monooleic acid phosphate, and aluminum dihydrogen phosphate are mixed in a mass ratio of 85:10:0.8:1, and anhydrous ethanol is used as the solvent; the above-mentioned raw materials are added to anhydrous ethanol, the solid-liquid ratio is 1:1.2, and ultrasonic dispersion is performed for 1 h to form a uniform, hard-agglomerated precursor slurry;

[0043] (3) Spray drying to prepare precursor powder: the above-mentioned precursor slurry is input into a pressure type spray dryer; the inlet air temperature is set to 180℃, the outlet air temperature is set to 100℃, the precursor slurry is atomized into small droplets in hot air and quickly dried, and a porous, uniformly sized, and well-dispersed precursor powder is formed;

[0044] (4) Modification and carbothermal reduction: the precursor powder is placed in a porous graphite tray, and then placed in a high-temperature tube furnace and heated under the action of nitrogen atmosphere; the pre-burning stage is set as follows: the temperature is raised to 800℃, and the temperature is kept for 2 h, and the nitrogen flow rate is 5 L / min; the high-temperature reduction stage is set as follows: the temperature is raised to 1600℃, and the temperature is kept for 3 h; the nitrogen flow rate is set to 10 L / min for the first 2 h to quickly remove CO, and then reduced to 6 L / min for the last 1 h to ensure that the reaction proceeds fully; after cooling, the modified aluminum nitride powder is obtained, and the prepared aluminum nitride powder is as shown in Figure 1 It can be clearly seen that the powder is uniformly distributed and has no agglomeration. Figure 1

[0045] Example 2

[0046] The difference between this example and Example 1 is that the source of biochar is selected to be rice straw, and the other conditions remain unchanged.

[0047] ​Example 3

[0048] The difference between this example and Example 1 is that aluminum dihydrogen phosphate is replaced by aluminum phosphate, and the rest of the conditions remain unchanged.

[0049] Example 4

[0050] The difference between this example and Example 1 is that the mass ratio of Al(OH)3, biochar, monoalkyl phosphate, and phosphate compound is 75:15:1.5:2, and the rest of the conditions remain unchanged.

[0051] Comparative Example 1

[0052] The difference between this comparative example and Example 1 is that monooleic acid phosphate and aluminum dihydrogen phosphate are not added, and the rest of the conditions remain unchanged. The prepared aluminum nitride powder is shown in Figure 2 , and Figure 2 It can be clearly seen that the powder shows agglomeration phenomenon.

[0053] Comparative Example 2

[0054] The difference between this comparative example and Example 1 is that aluminum dihydrogen phosphate is not added, and the rest of the conditions remain unchanged.

[0055] Comparative Example 3

[0056] The difference between this comparative example and Example 1 is that biochar is changed to carbon black, and the rest of the conditions remain unchanged.

[0057] Comparative Example 4

[0058] The difference between this comparative example and Example 1 is that 800°C pre-burning is not performed, and direct heating from room temperature to 1600°C is performed, with constant nitrogen flow of 10 L / min, and the rest of the conditions remain unchanged.

[0059] Comparative Example 5

[0060] The difference between this comparative example and Example 1 is that the pre-burning is set to 500°C, and the rest of the conditions remain unchanged.

[0061] Performance analysis of the aluminum nitride powder prepared in the above examples and comparative examples, wherein laser particle size analysis D 50 (mean particle size) is selected; D 90 / D 10 ratio (characterizing particle size distribution range); oxygen and nitrogen content analysis is performed using an oxygen-nitrogen-hydrogen analyzer, and the results are shown in Table 1.

[0062] Table 1, performance analysis results of aluminum nitride powder

[0063] .

[0064] As can be seen from the data in Table 1, Examples 1-3 used biochar as the carbon source and added monoalkyl phosphates and phosphate compounds for modification. The resulting AlN had a low carbon content, high carbon source utilization efficiency, and more complete reaction. The low oxygen content indicates that after modification with monoalkyl phosphates and phosphate compounds, the antioxidant capacity of AlN was improved, oxygen residue was reduced, and the purity of AlN was improved. In addition, the average particle size of the powder was small, the D90 / D10 ratio was about 4, the particle size distribution was narrow, and the particle size was more uniform, which helped to improve the powder dispersibility.

[0065] Comparative Example 1, without the addition of monoalkyl phosphates and phosphate compounds, showed a significant increase in carbon and oxygen content, a deteriorated particle size distribution, and severe agglomeration.

[0066] Comparative Example 2, without the addition of phosphate compounds, showed increased oxygen content and D 50 and D 90 / D 10 All of these factors significantly increase the oxidation resistance of AlN, decrease the oxygen content, and reduce the purity. At the same time, due to the lack of a protective layer, the powder is prone to agglomeration under high-temperature sintering, resulting in a poor particle size distribution of the obtained aluminum nitride powder.

[0067] In Comparative Example 3, when carbon black was used as the carbon source, the residual carbon was 0.0872%, which was more than 1.7 times higher than that of biochar. This indicates that carbon black has low reactivity as a carbon source, and the carbon did not fully participate in the reduction nitridation reaction, resulting in significant carbon waste or residue. Furthermore, the oxygen content increased to 0.7071%, indicating a decrease in its antioxidant capacity and purity. Simultaneously, the D of the aluminum nitride powder... 50 There has been a certain increase, D 90 / D 10 The increase in particle size also indicates severe agglomeration, uneven particle size distribution, and poor particle development, which affects fluidity and sintering performance.

[0068] Comparative Example 4 was not pre-calcined, and the results showed that its carbon content, oxygen content, and D... 50 and D 90 / D 10 The significant increase indicates that, without pre-calcination modification, monoalkyl phosphates and phosphate compounds failed to fully function, Al(OH)3 was easily oxidized, particle agglomeration intensified, and ultimately the purity, dispersibility and reactivity of AlN powder were significantly reduced.

[0069] Although Comparative Example 5 underwent pre-firing, the results were essentially the same as those without pre-firing. This is because choosing a pre-firing temperature of 500℃ only removes physically adsorbed water and some hydroxyl groups, causing the structural water in Al(OH)3 present in the subsequent high-temperature nitriding stage to evaporate rapidly, resulting in uneven nitriding reaction and abnormal growth of some AlN crystals.

[0070] Finally, it should be noted that the above specific examples are only used to explain the purposes, technical solutions and beneficial effects of the present application in detail, and it should be understood that the above description is only a specific embodiment of the present application and does not limit the protection scope of the present application; although the present application has been described in detail with reference to the foregoing specific embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement, improvement, etc. to part or all of the technical features; and these modifications, equivalent replacement, improvement do not make the essence of the corresponding technical solution deviate from the scope of the technical solutions of the embodiments of the present application, and they should be covered in the scope of the claims and description of the present application.

Claims

1. A method for producing an aluminum nitride powder, characterized by comprising the steps of: The method comprises the following steps: ​ Al(OH)3, biochar, monoalkyl phosphate and phosphate compounds are added into a solvent in a mass ratio of (70-90):(5-20):(0.1-3):(0.1-5), and a uniform mixed slurry is formed by ultrasonic dispersion; The mixed slurry is prepared into a precursor powder by spray drying; The precursor powder is pre-fired at 600-900 DEG C under a nitrogen atmosphere, and then high-temperature reaction is performed at 1400-1700 DEG C, the high-temperature reaction is kept for 3-4 hours, the nitrogen flow is set in stages, the nitrogen flow is 9-11 L / min in the early stage of the reaction, and the nitrogen flow is reduced to 5-7 L / min in the later stage of the reaction, and an aluminum nitride powder is obtained.

2. The method of claim 1, wherein the aluminum nitride powder has a purity of 99.9% or more. The mass ratio of Al(OH)3, biochar, monoalkyl phosphate and phosphate compounds is (75-85):(10-15):(0.8-2):(1-3).

3. The method of claim 1, wherein the aluminum nitride powder has a purity of 99.9% or more. The biochar is prepared by high-temperature pyrolysis of straw.

4. The method of producing an aluminum nitride powder according to claim 1, wherein The biochar is prepared by the following method: the straw is washed, then dried, crushed, sieved, pyrolyzed at 550-850 DEG C under the protection of nitrogen, naturally cooled to room temperature after pyrolysis, ground and sieved, and a biochar with uniform particle size and high specific surface area is obtained.

5. The method of claim 1, wherein the aluminum nitride powder has a purity of 99.9% or more. The monoalkyl phosphate is at least one selected from sodium dodecyl phosphate and monooleic acid phosphate.

6. The method of producing an aluminum nitride powder according to claim 1, wherein The phosphate compound is at least one selected from aluminum phosphate and aluminum dihydrogen phosphate.

7. The method of producing an aluminum nitride powder according to claim 1, wherein The spray drying is performed by using a pressure type spray dryer, the inlet air temperature is 150-200 DEG C, and the outlet air temperature is 80-120 DEG C.

8. The method of producing an aluminum nitride powder according to claim 1, wherein The pre-firing is kept for 2-3 hours, and the nitrogen flow is 4-6 L / min. 9.An aluminum nitride powder prepared by the method of any one of claims 1-8.

Images