A method for preparing aluminum nitride spherical powder

Abstract

This invention provides a spherical aluminum nitride powder with narrow particle size distribution and good flowability, and its preparation method, belonging to the field of spherical powder preparation technology. The preparation method of the spherical aluminum nitride powder includes the following steps: (1) dissolving ammonium polyacrylate and citric acid in an ethanol aqueous solution, then mixing nano-alumina powder and carbon powder at a weight ratio of 72-76:24-28 and adding them to the above solution to prepare a slurry; (2) spray granulating the slurry obtained in step (1) at 100-120℃ to obtain a precursor; (3) sintering the precursor under a nitrogen atmosphere at a pressure of 0.1-0.4 MPa and a sintering temperature of 1650-1700℃ for 2 hours to obtain spherical aluminum nitride powder. The spherical aluminum nitride powder prepared by this invention has the characteristics of narrow particle size distribution, high sphericity, good sphericity, good flowability and resistance to deformation, and has better application prospects in the field of filler materials.

Description

Technical Field

[0001] This invention belongs to the field of spherical powder preparation technology, specifically relating to an aluminum nitride spherical powder with narrow particle size distribution and good flowability, and its preparation method. Background Technology

[0002] Aluminum nitride (AlN) has attracted much attention due to its excellent thermal properties, thermal conductivity, electrical insulation and heat resistance. It is expected to replace alumina and silicon dioxide as a more advantageous filler material in the fields of heat dissipation materials, packaging materials and substrate materials for electronic devices.

[0003] Alumina and silica, when used as fillers, are typically prepared as spherical particles because spherical particles offer advantages over other particle shapes. Firstly, spherical particles exhibit better flowability. Due to their spherical shape and smaller specific surface area, they flow more readily during handling and processing, facilitating molding, injection, and coating operations. Secondly, spherical particles possess good packing density. Their shape and close packing characteristics allow for the achievement of high packing density during preparation. Thirdly, the narrow particle size distribution of spherical particles provides a more uniform material structure and properties, contributing to improved product stability, reliability, and consistency.

[0004] Currently, existing methods for preparing AlN spherical raw material powder mainly include atomization, direct sintering, and two-step heat treatment. Direct sintering involves in-situ growth of AlN under a high-pressure nitrogen atmosphere to produce spherical powder; however, the powder prepared by this method suffers from severe agglomeration, low sphericity, poor sphericity, wide particle size distribution, and limited controllability. Atomization involves ball milling treated AlN powder with a binder and alcohol, followed by granulation into AlN spherical powder using a spray granulator; however, this method suffers from pollution caused by the evaporation of alcohol solvent into the air during granulation and drying, and it also requires sophisticated equipment, is costly, and causes environmental pollution. Two-step heat treatment combines the advantages of the first two methods, first preparing a spherical precursor, and then sintering to produce AlN spherical powder; however, existing methods still suffer from high production costs, environmental pollution, high operational risks, and limited controllability.

[0005] For example, patent document CN103588182B discloses a method for preparing spherical aluminum nitride powder. This method involves mixing spherical aluminum powder, aluminum nitride powder, and ammonium chloride powder, followed by in-situ nitriding. The mixture is then reacted in a porous graphite crucible with an outer graphite carbon felt insulation layer and an inner protective layer. The spherical aluminum nitride powder is prepared by initiating a combustion reaction through electrical current. However, this patented method employs a dry process, which is complex. Furthermore, it requires controlling the particle size of the raw material powders to obtain spherical powder with good uniformity.

[0006] In addition, patent document CN 113292053 B discloses a carbothermal reduction process for preparing highly dispersible aluminum nitride powder. This process uses ultrafine Al2O3 and carbon black as raw materials. A viscous slurry is formed by adding a precisely controlled amount of polymer dispersant aqueous solution, followed by ball milling. A mixture of aluminum nitride and carbon is then prepared through a carbothermal reduction reaction, and finally, aluminum nitride powder is obtained by carbon removal. While this patented method uses a wet process to prepare aluminum nitride powder and solves the problem of complex preparation, the resulting raw material powder has poor sphericity, meaning the powder is not essentially spherical, leading to poor flowability.

[0007] Patent document CN 115196970 A discloses a method for preparing highly fluid alumina oxynitride spherical powder. The method uses nano-alumina and carbon black as raw materials, and forms a viscous slurry by adding precisely controlled amounts of polymer dispersant, binder, and aqueous solution. This slurry is then ball-milled and mixed. After separating the slurry, spherical precursor powder is prepared by spray granulation. Finally, spherical alumina oxynitride powder is obtained through a carbothermal reduction reaction. However, this patented method uses a two-step heat treatment process with water as a solvent to prepare spherical alumina oxynitride powder. While this solves the environmental pollution problem, the method lacks means to control the powder particle size, and the slurry preparation process is cumbersome, making it unsuitable for mass production.

[0008] Therefore, how to prepare AlN spherical powder with narrow particle size distribution, good sphericity, high sphericity, good particle flowability, and is not prone to agglomeration, while having a simple and safe manufacturing process, low environmental pollution, and enhanced controllability of spherical particle size, has become an urgent technical problem to be solved. Summary of the Invention

[0009] The present invention aims to solve the aforementioned technical problems by providing an aluminum nitride spherical powder with a narrow particle size distribution and good flowability, and a method for preparing the same. The technical objective of this invention is twofold: firstly, to address the problems of complex processes, low safety, significant environmental pollution, and poor controllability in existing AlN spherical powder preparation processes; and secondly, to address the problems of wide particle size distribution, low sphericity, and poor particle flowability in existing spherical powder preparation processes.

[0010] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution:

[0011] This invention first provides a method for preparing aluminum nitride spherical powder with narrow particle size distribution and good flowability, comprising the following steps:

[0012] (1) Slurry preparation: Ammonium polyacrylate and citric acid are dissolved in a solvent, and then nano alumina powder and carbon powder are mixed at a weight ratio of 72-76:24-28 and added to the above solution to prepare a slurry. The slurry is ball-milled and then separated. Among them, the ammonium polyacrylate accounts for 3-6 wt% of the total weight of nano alumina powder and carbon powder, and the citric acid accounts for 0.01-0.03 wt% of the solvent. The solvent is an aqueous ethanol solution with an ethanol content of 1-3 wt%.

[0013] (2) Preparation of precursor powder: The slurry obtained in step (1) is spray-granulated at 100-120°C to obtain precursor powder;

[0014] (3) Preparation of AlN spherical powder: The precursor powder obtained in step (2) is sintered in a nitrogen atmosphere at a pressure of 0.1-0.4 MPa and a sintering temperature of 1650-1700℃ for 2-5 hours to obtain aluminum nitride spherical powder.

[0015] The preparation method provided by this invention involves compounding ammonium polyacrylate and citric acid in a certain proportion, and using a small amount of ethanol added to deionized water as a solvent to prepare a slurry and precursor powder. This results in aluminum nitride spherical powders with narrow particle size distribution, high sphericity, good sphericity, good flowability, and resistance to deformation after sintering. However, the inventors have verified that other process conditions adversely affect the particle size distribution, sphericity, sphericity, and flowability of the prepared aluminum nitride spherical powders. Therefore, the process parameters in this invention are extremely important; only by using this invention can aluminum nitride spherical powders with excellent results be prepared.

[0016] Furthermore, the purity of both the alumina powder and the carbon powder in step (1) is greater than 99.9%, the particle size of the alumina powder is 30-50 nm, and the particle size of the carbon powder is 20-30 nm.

[0017] Furthermore, the ball milling and separation operation described in step (1) is as follows: the slurry is ball milled in a nylon ball milling jar for 6 to 10 hours at a speed of 200 to 220 r / min, and the slurry is separated by a filter screen after the ball milling is completed.

[0018] Furthermore, the total weight of the ammonium polyacrylate and citric acid mentioned in step (1) accounts for 2 to 3 wt% of the weight of the ethanol aqueous solution.

[0019] Furthermore, the peristaltic pump frequency for spray granulation in step (2) is 20-30 Hz, the air inlet temperature is 280-310 ℃, and the atomizer frequency is 180-200 Hz.

[0020] Furthermore, in step (3), the heating rate before sintering is controlled to be 12-15℃ / min, and the cooling rate after sintering is 7-8℃ / min.

[0021] Furthermore, in step (3), a vacuum process is performed before introducing nitrogen gas to control the vacuum level to 10. -1 ~10 -2 Pa.

[0022] A second objective of this invention is to provide aluminum nitride spherical powder prepared by any of the methods described above. The aluminum nitride spherical powder obtained by this invention has the characteristics of narrow particle size distribution, high sphericity, good sphericity, good flowability, and resistance to deformation.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] (1) The preparation process of this invention is simple and highly controllable. This controllability allows spherical AlN powder to be customized according to the specific application requirements to meet the requirements of different fields. It has good application prospects in the fields of electronics and thermal management.

[0025] (2) The present invention prepares the precursor by compounding the dispersant and adding a small amount of ethanol to the solvent, which solves the problems of high equipment requirements, high operation risk and high cost in the previous preparation of spherical powder. The powder preparation method has a wide range of applications and good prospects.

[0026] (3) The process of the present invention is highly safe, has little environmental pollution, and the raw materials used are also less harmful to the human body and the environment;

[0027] (4) The spherical powder prepared by the present invention has the characteristics of narrow particle size distribution, high sphericity, good sphericity, good flowability and not easy to deform, and has better application prospects in the field of filler materials. Attached Figure Description

[0028] Figure 1 These are images showing the viscosity of slurries with different solid contents prepared in Example 1.

[0029] Figure 2 This is a scanning electron microscope image of the precursor prepared from the slurry with a solid content of 15 wt% in Example 1.

[0030] Figure 3 This is a scanning electron microscope image of the precursor prepared from the slurry with a solid content of 30 wt% in Example 1.

[0031] Figure 4 These are XRD images of the powder prepared in Example 1 at different temperatures.

[0032] Figure 5 This is an SEM image of sintered AlN spherical powder.

[0033] Figure 6 These are particle size analysis photos of sintered AlN spherical powder.

[0034] Figure 7 This is an SEM image of AlN spherical powder prepared in Comparative Example 2.

[0035] Figure 8 This is an SEM image of AlN spherical powder prepared in Comparative Example 3. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the invention is described in detail below with reference to embodiments. It should be noted that the following embodiments are for explanation and illustration only and are not intended to limit the invention. Non-essential improvements and adjustments made by those skilled in the art based on the above description are still within the scope of protection of this invention.

[0037] Example 1

[0038] This embodiment provides a method for preparing AlN spherical powder, including the following steps:

[0039] (1) Slurry preparation: Nano-alumina powder and carbon powder (carbon black, both with a purity >99.9%, wherein the particle size of nano-alumina powder is 30-50 nm and the particle size of carbon black is 20-30 nm) were weighed as powder raw materials, wherein the carbon powder content was 24 wt% and the alumina powder content was 76 wt%. Ethanol aqueous solution was used as solvent, and 3 wt% of polyammonium acrylate (PAA) and 0.01 wt% of citric acid were weighed as total weight of the powder raw materials and solvent. Depending on the solid content, the solvent content accounted for 85 wt% of the total mass of the raw material powder and solvent, and the solvent contained 98 wt% deionized water and 2 wt% ethanol. Then, the weighed raw materials were mixed and placed in a nylon ball mill jar, and ball milled at 200 rpm for 10 h, wherein the ball-to-material ratio was 10:1. Then, the slurry after ball milling is separated from the grinding balls by passing it through a filter screen. The slurry is then poured into a collection bucket and sealed with plastic wrap for later use.

[0040] (2) Preparation of precursor powder: Turn on the cooling water and vacuum pump, then turn on the power of the spray granulator, set the atomizer frequency to 200Hz and the inlet temperature to 300℃. Turn on the heating, dust removal, and induced draft fan switches. When the inlet temperature reaches 80℃, turn on the atomizer switch. When the inlet temperature rises to 300℃, turn on the peristaltic pump switch and set the peristaltic frequency to 30Hz, then pump in deionized water. Preheat for 40 minutes. When the outlet temperature stabilizes at 110℃, start pumping in the prepared slurry. After all the slurry has been pumped in, turn off the heating. When the temperature drops to room temperature, remove the collection bottle and seal the powder in a bag.

[0041] (3) Preparation of AlN spherical powder: The prepared precursor powder is placed in a carbon crucible and then placed in an atmosphere furnace. The furnace is first evacuated to a vacuum degree of 10. -1 Pa, and then vacuum sintering at 700℃. When the temperature reaches 700℃, nitrogen gas is introduced and the nitrogen gas pressure is stabilized at 0.1 MPa. Then, sintering is carried out at 1700℃ for 2 hours to obtain AlN spherical powder.

[0042] Example 2

[0043] This embodiment provides a method for preparing AlN spherical powder, including the following steps:

[0044] (1) Slurry preparation: Nano-alumina powder and carbon powder (carbon black, both with a purity >99.9%, wherein the particle size of nano-alumina powder is 30-50nm and the particle size of carbon black is 20-30nm) were weighed as powder raw materials, wherein the carbon powder content was 26wt% and the alumina powder content was 74wt%. Ethanol aqueous solution was used as solvent, and 6wt% of ammonium polyacrylate and 0.02wt% of citric acid were weighed as solvent. According to different solid contents, the solvent content accounted for 80wt% of the total mass of raw material powder and solvent, the deionized water content in the solvent was 98wt%, and the ethanol content was 2wt%. Then, the weighed raw materials were mixed and placed in a nylon ball mill jar, and ball milled at a ball mill speed of 220rpm for 10h, wherein the ball-to-material ratio was 8:1. Then, the slurry after ball milling was separated from the grinding balls by filtering the slurry through a filter screen, and the slurry was poured into a collection bucket and sealed with plastic wrap for later use.

[0045] (2) Preparation of precursor powder: Turn on the cooling water and vacuum pump, then turn on the power of the spray granulator, set the atomizer frequency to 180Hz and the inlet temperature to 280℃. Turn on the heating, dust removal, and induced draft fan switches. When the inlet temperature reaches 80℃, turn on the atomizer switch. When the inlet temperature rises to 280℃, turn on the peristaltic pump switch and set the peristaltic frequency to 20Hz, then pump in deionized water. Preheat for 40 minutes. When the outlet temperature stabilizes at 120℃, start pumping in the prepared slurry. After all the slurry has been pumped in, turn off the heating. When the temperature drops to room temperature, remove the collection bottle and seal the powder in a bag.

[0046] (3) Preparation of AlN spherical powder: The prepared precursor powder is placed in a carbon crucible and then placed in an atmosphere furnace. The furnace is first evacuated to a vacuum degree of 10. -2 Pa, and then vacuum sintering at 600℃. When the temperature reaches 600℃, nitrogen gas is introduced and the nitrogen gas pressure is stabilized at 0.1 MPa. Then, sintering is carried out at 1650℃ for 2 hours to obtain AlN spherical powder.

[0047] Example 3

[0048] This embodiment provides a method for preparing AlN spherical powder, including the following steps:

[0049] (1) Slurry preparation: Weigh nano-alumina powder and carbon powder (carbon black, both with a purity >99.9%, wherein the particle size of nano-alumina powder is 30-50nm and the particle size of carbon black is 20-30nm) as powder raw materials, wherein the carbon powder content is 25wt% and the alumina powder content is 75wt%. Use ethanol aqueous solution as solvent, and weigh 5wt% of the total weight of the powder raw materials and 0.02wt% of the solvent mass of ammonium polyacrylate and citric acid. According to different solid contents, the solvent mass is 70wt% of the total mass of powder raw materials and solvent, wherein the deionized water content in the solvent is 98wt% and the ethanol content is 2wt%. Then, mix the weighed raw materials and put them into a nylon ball mill jar, place it on a ball mill and ball mill at a speed of 210rpm for 6h, wherein the ball-to-material ratio is 10:1. Then, the slurry after ball milling is separated from the grinding balls by filtering the slurry through a filter screen, pour the slurry into a collection bucket and seal it with plastic wrap for later use.

[0050] (2) Preparation of precursor powder: Turn on the cooling water and vacuum pump, then turn on the power of the spray granulator, set the atomizer frequency to 190Hz and the inlet temperature to 310℃. Turn on the heating, dust removal, and induced draft fan switches. When the inlet temperature reaches 80℃, turn on the atomizer switch. When the inlet temperature rises to 310℃, turn on the peristaltic pump switch and set the peristaltic frequency to 30Hz, then pump in deionized water. Preheat for 40 minutes. When the outlet temperature stabilizes at 100℃, start pumping in the prepared slurry. After all the slurry has been pumped in, turn off the heating. When the temperature drops to room temperature, remove the collection bottle and seal the powder in a bag.

[0051] (3) Preparation of AlN spherical powder: The prepared precursor powder is placed in a carbon crucible and then placed in an atmosphere furnace. The furnace is first evacuated to a vacuum degree of 10. -1 Pa, and then vacuum sintering at 700℃. When the temperature reaches 700℃, nitrogen gas is introduced and the nitrogen gas pressure is stabilized at 0.1 MPa. Then, sintering is carried out at 1680℃ for 2 hours to obtain AlN spherical powder.

[0052] Test Example 1

[0053] The aluminum nitride spherical powders prepared in the above examples were characterized, and the results are as follows (taking Example 1 as an example, the characterization results of Examples 2 and 3 are not significantly different):

[0054] Figure 1 This is a viscosity profile of the slurry prepared by the method described in this embodiment. Figure 1 The viscosity of the slurry is directly proportional to its solid content. The higher the viscosity, the easier it is to cause clogging during spray granulation. Therefore, the highest solid content prepared in this example is 30 wt% (Example 3).

[0055] Figure 2 The image shows an electron microscope (EM) image of the precursor prepared from the 15 wt% solids content slurry in the method described in this embodiment. The image shows that the prepared precursor has high sphericity and uniform particle size. The final average particle size was calculated to be 40.26 μm.

[0056] Figure 3 The image shows an electron microscope (EM) image of the precursor prepared from the slurry with a solid content of 30 wt% in the method described in this embodiment. The image shows that the prepared precursor has high sphericity and uniform particle size. The final average particle size was calculated to be 51.38 μm.

[0057] Figure 4 The XRD patterns at different temperatures prepared by the method described in this embodiment show that sintering temperatures of 1650–1700 °C can produce pure-phase AlN spherical powder.

[0058] Figure 5The image shows an electron microscope image of the AlN spherical powder prepared by the method described in this embodiment. As can be seen from the image, the prepared AlN spherical powder has good sphericity, a porous surface structure, and very little powder fragmentation.

[0059] Figure 6 The figure shows the particle size distribution of the AlN spherical powder prepared by the method described in this embodiment. It can be seen from the figure that the sintered powder has a uniform particle size distribution and a narrow distribution range. The average particle size of the sintered powder is 33.53 μm, which is smaller than that of the precursor powder.

[0060] Comparative Example 1

[0061] The method of Example 1 is different except that the ethanol aqueous solution in step (1) is replaced with deionized water. The slurry prepared in this way contains more air bubbles. The presence of air bubbles reduces the uniformity of the slurry, which will affect the granulation product of subsequent spray granulation, resulting in low sphericity, poor uniformity of particle size distribution, and poor sphericity of particles.

[0062] Comparative Example 2

[0063] The method in Example 1 differs from that citric acid is not added in step (1). Under the same ball milling time, the homogeneity of the slurry deteriorates. The pH value of the solution can affect the ionization degree and charge properties of PAA, thereby affecting its dispersion performance. A neutral to slightly acidic environment is beneficial to the dispersion effect of PAA. The dispersion effect of PAA in the slurry without pH adjustment by citric acid is relatively poor, resulting in poor slurry homogeneity and affecting the granulation product, leading to low sphericity and poor uniformity of particle size distribution (e.g., ...). Figure 7 ).

[0064] Comparative Example 3

[0065] The method of Example 1 is followed, except that citric acid is replaced with hydroxyethyl cellulose in step (1). Under the same ball milling time conditions, the uniformity of the slurry is poor. The granulation product has a low spheroidization rate, and there is adhesion between spherical particles (such as...). Figure 8 Achieving good uniformity in the slurry requires a longer ball milling time.

[0066] Comparative Example 4

[0067] The method of Example 1 is followed, except that steps (1) and (2) are replaced by directly mixing nano-carbon powder and alumina powder by ball milling. Without pre-forming treatment, the product grown in situ during sintering exhibits poor sphericity and severe agglomeration between particles.

Claims

1. A method for preparing aluminum nitride spherical powder with narrow particle size distribution and good flowability, characterized in that, Includes the following steps: (1) Slurry preparation: Ammonium polyacrylate and citric acid are dissolved in a solvent, and then nano alumina powder and carbon powder are mixed at a weight ratio of 72-76:24-28 and added to the above solvent to prepare a slurry. The slurry is ball-milled and then separated. The ammonium polyacrylate accounts for 3-6 wt% of the total weight of nano alumina powder and carbon powder, citric acid accounts for 0.01-0.03 wt% of the solvent weight, and the solvent weight accounts for 85 wt% of the total weight of raw material powder and solvent. The solvent is an aqueous ethanol solution with an ethanol content of 1-3 wt%. (2) Preparation of precursor powder: The slurry obtained in step (1) is spray-granulated at 100-120°C to obtain precursor powder; (3) Preparation of aluminum nitride spherical powder: The precursor powder obtained in step (2) is sintered in a nitrogen atmosphere at a pressure of 0.1-0.4 MPa and a sintering temperature of 1650-1700°C for 2-5 hours to obtain aluminum nitride spherical powder.

2. The preparation method according to claim 1, characterized in that, The alumina powder and carbon powder mentioned in step (1) have a purity greater than 99.9%, the particle size of the alumina powder is 30-50 nm, and the particle size of the carbon powder is 20-30 nm.

3. The preparation method according to claim 1, characterized in that, The ball milling operation in step (1) is as follows: the slurry is ball milled in a nylon ball milling jar for 6 to 10 hours, and the ball milling speed is 200 to 220 r / min.

4. The preparation method according to claim 1, characterized in that, The separation operation described in step (1) involves separating the slurry through a filter screen after ball milling.

5. The preparation method according to claim 1, characterized in that, The total weight of the ammonium polyacrylate and citric acid mentioned in step (1) accounts for 2 to 3 wt% of the solvent weight.

6. The preparation method according to claim 1, characterized in that, The peristaltic pump frequency for spray granulation in step (2) is 20-30 Hz, the air inlet temperature is 280-310°C, and the atomizer frequency is 180-200 Hz.

7. The preparation method according to claim 1, characterized in that, In step (3), the heating rate before sintering is controlled to be 12-15°C / min, and the cooling rate after sintering is 7-8°C / min.

8. The preparation method according to claim 1, characterized in that, The vacuum degree is controlled to be 10 Pa before nitrogen is introduced in step (3) -1 ~10 -2 Pa.

9. Spherical aluminum nitride powder prepared by the method according to any one of claims 1-8.

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