Preparation method of high-porosity aluminum nitride powder precursor

Abstract

The invention discloses a preparation method of a high-porosity aluminum nitride powder precursor, and belongs to the technical field of electronic ceramics, and the preparation method comprises the following steps: S1, raw material mixing: uniformly stirring and mixing water, an aluminum source, a carbon source, aluminum sol and a thickening agent in proportion to form slurry; s2, stirring and foaming: adding a foaming agent into the uniformly mixed slurry in the step S1, and stirring and foaming until the volume of the slurry is increased to 2.5 times or more; s3, injection molding and solidification: adding a curing agent into the foamed slurry in the step S2, continuously stirring, then performing injection molding and solidification on the slurry to obtain an aluminum nitride precursor, and drying to obtain a high-porosity aluminum nitride powder precursor; s4, the dried high-porosity aluminum nitride powder precursor in the step S3 is put into a vacuum sintering furnace to be subjected to a carbon thermal reduction nitridation reaction, and the aluminum nitride powder is obtained.According to the method, the gas replacement circulation effect in the nitridation process can be optimized, the situation that a gas path is blocked due to collapse of precursor blocks is effectively prevented, and then the nitridation reaction stability and the powder quality are guaranteed.

Description

Technical Field

[0001] This invention belongs to the field of electronic ceramics technology, specifically relating to a method for preparing a high-porosity aluminum nitride powder precursor. Background Technology

[0002] Carbothermal reduction is a typical method for industrial production of aluminum nitride powder. This method has significant advantages such as low cost, stable process, and the ability to achieve large-scale mass production. Aluminum nitride powder prepared by this method also has advantages such as high purity, uniform and controllable particle size distribution, and ease of subsequent molding and sintering processing, and has broad prospects in industrial applications.

[0003] Currently, to improve the quality of aluminum nitride powder, the industry typically employs methods such as increasing the replacement and flow efficiency of nitrogen in the reaction atmosphere, reducing the partial pressure of carbon monoxide in the system, and increasing the partial pressure of nitrogen to promote the forward progress of the carbothermic reduction synthesis reaction. However, simply increasing the partial pressure of nitrogen can lead to two problems: firstly, the dramatic increase in nitrogen consumption results in a significant rise in production costs; secondly, the introduction of a large amount of gas can easily cause significant gradient changes in the temperature field inside the furnace, which in turn can lead to uneven nitriding reactions and affect powder quality.

[0004] In addition, the precursor blocks prepared by conventional mixing methods in the existing technology have low strength and are prone to collapse during the nitriding reaction, which in turn blocks the nitrogen flow channel. This not only reduces the nitrogen replacement and flow efficiency and affects the nitriding reaction effect, but also leads to an increase in the oxygen content of the final aluminum nitride powder, further deteriorating the powder quality.

[0005] Therefore, there is an urgent need for a method to prepare a high-porosity aluminum nitride powder precursor that can optimize the gas displacement and flow effect during the nitriding process and effectively prevent the precursor block from collapsing and blocking the gas path. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a high-porosity aluminum nitride powder precursor, which can optimize the gas displacement and flow effect during the nitriding process, effectively prevent the precursor block from collapsing and blocking the gas path, and thus ensure the stability of the nitriding reaction and the quality of the powder.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing a high-porosity aluminum nitride powder precursor includes the following steps:

[0009] Step S1: Raw material mixing: Mix water, aluminum source, carbon source, aluminum sol and thickener in proportion to form a slurry;

[0010] Step S2: Stirring and foaming: Add the foaming agent to the well-mixed slurry from step S1 and stir and foam until the slurry volume increases to more than 2.5 times.

[0011] Step S3: Casting and solidification: Add the curing agent to the foamed slurry from step S2 and stir continuously. Then cast the slurry into a mold and solidify it into an aluminum nitride precursor. After drying, a high-porosity aluminum nitride powder precursor is obtained.

[0012] Step S4: The dried high-porosity aluminum nitride powder precursor from step S3 is placed in a vacuum sintering furnace for carbothermic reduction nitriding reaction to obtain aluminum nitride powder.

[0013] A further improvement of the technical solution of the present invention is that, in step S1, the mass fraction of each raw material is as follows: water 10%, aluminum source 35%-40%, carbon source 20%-25%, aluminum sol 20%-30%, and thickener 0.8%-1%.

[0014] A further improvement to the technical solution of the present invention is that: 10% water, 35%-40% aluminum source, 20%-25% carbon source and 20%-30% aluminum sol are mixed in a disperser and then 0.8%-1% thickener is added and the mixture is stirred until the slurry forms a suspension.

[0015] A further improvement to the technical solution of this invention is that: the water used is deionized water, and the aluminum source is... Böhmstone or The carbon source is high-purity carbon black, the aluminum sol is alumina sol with a solid content of 30%, and the thickener is xanthan gum or carrageenan.

[0016] A further improvement to the technical solution of this invention lies in that: the aluminum source uses a particle size of... of This is to improve the efficiency of the carbothermic reduction reaction and the purity of aluminum nitride powder.

[0017] A further improvement of the technical solution of the present invention is that: in step S2, the foaming agent is a plant-based foaming agent, and the addition amount is 1%-2%. During the foaming process, the volume of the slurry increases so that the interior of the slurry is filled with fine pores.

[0018] A further improvement to the technical solution of the present invention is that the plant-based foaming agent is tea saponin or rosin soap.

[0019] A further improvement of the technical solution of the present invention is that: in step S3, the curing agent is high-purity gelatinized starch, and the addition amount is 2%-4%, so as to synergistically improve the strength of the aluminum nitride precursor block with aluminum sol and thickener.

[0020] A further improvement of the technical solution of the present invention is that the drying adopts a segmented drying method. First, the solidified aluminum nitride precursor is placed in an oven and dried at 40°C for 12 hours to remove most of the free water in the slurry. Then, the temperature is raised to 105°C and dried until completely dry.

[0021] A further improvement to the technical solution of the present invention is that: in step S4, flowing nitrogen gas is introduced into the vacuum sintering furnace, the nitriding temperature is 1600℃, the holding time is 3h, and the nitrogen gas flow rate is 4m³ / h. 3 The mixture after nitriding is decarbonized in an oxygen atmosphere to obtain aluminum nitride powder. The decarbonization temperature is 600℃ and the holding time is 3h. After decarbonization, the mixture is cooled to room temperature to obtain aluminum nitride powder.

[0022] The technological advancements achieved by this invention due to the adoption of the above technical solutions are as follows:

[0023] The method for preparing high-porosity aluminum nitride powder precursor provided by this invention employs a closed-loop process of "raw material mixing - stirring and foaming - molding and solidification - carbothermic reduction". By adding a foaming agent to the aluminum nitride powder precursor slurry and stirring and foaming, a large number of micro-interconnected pores are introduced inside the aluminum nitride powder precursor, which is conducive to gas displacement and circulation. The addition of aluminum sol and curing agent provides strength support for the precursor after drying, preventing the precursor block from collapsing and blocking the gas passage, thereby improving the quality of aluminum nitride powder and reducing the oxygen content of the powder.

[0024] The high-porosity aluminum nitride powder precursor structure prepared by this invention has two advantages. First, the precursor has high strength, which can provide support for the pore channels through which nitrogen enters the precursor. Second, during the nitriding process, the high-porosity aluminum nitride powder precursor structure allows nitrogen to directly enter the precursor and participate in the carbothermic reduction nitriding reaction, thereby improving the quality of aluminum nitride powder. At the same time, this invention uses water as a solvent, which is safer and more environmentally friendly than the traditional method that uses organic solvents such as alcohol, and has less harm to the environment.

[0025] The present invention uses deionized water, which can eliminate the interference of impurity ions in the water on the reaction and improve the purity of the powder; Böhmstone or As an aluminum source, all of them possess high activity and high purity, making them suitable for carbothermal reduction reactions; high-purity carbon black sources can reduce the introduction of impurities and have high reactivity, accelerating the carbothermal reduction nitriding process; alumina sol with a solid content of 30% can enhance the adhesion and stability of the slurry and improve the structural strength of the precursor; xanthan gum or carrageenan thickeners can effectively adjust the viscosity of the slurry, prevent raw material sedimentation and stratification, and at the same time improve the stability of pores during foaming, avoiding excessive pore coalescence.

[0026] This invention uses a particle size of of This increases the contact area with carbon sources and nitrogen, significantly improving the rate of carbothermic reduction nitridation reaction, shortening the reaction cycle, and reducing production energy consumption. With a stable crystal structure and strong chemical inertness, aluminum nitride powder is not prone to phase transformation or the introduction of impurities during the reaction process. When combined with an appropriate particle size, the formation of intermediate products can be reduced, further improving the purity and crystallinity of the aluminum nitride powder and ensuring the mechanical and thermal properties of the powder.

[0027] The plant-based foaming agent used in this invention is environmentally friendly and non-toxic, leaving no harmful residues after combustion. This avoids secondary pollution to aluminum nitride powder and aligns with green production principles. The addition of 1%-2% allows for precise control of the foaming degree, ensuring the slurry volume reaches the target multiple while preventing over-foaming that could lead to slurry rupture or excessively large pores. This ensures the slurry is filled with fine, uniform, and stable pores. Compared to chemical foaming agents, the plant-based foaming agent has a gentler foaming process and a more concentrated pore size distribution, improving the consistency of the precursor's pore structure and guaranteeing the uniformity of the final powder's performance.

[0028] The tea saponin and rosin soap used in this invention have excellent surface activity and strong foaming ability. They can quickly form a stable foam system in the slurry, and the foam has a long half-life, which can be maintained until the molding is completed and the pore structure is effectively preserved.

[0029] The high-purity gelatinized starch curing agent used in this invention introduces no impurities, ensuring the purity of the precursor. An addition of 2%-4% can form a synergistic effect with aluminum sol and thickener, significantly improving the strength and toughness of the precursor block. This effectively prevents the precursor from being damaged or cracked due to stress during drying, handling, and the initial stage of sintering. At the same time, it enhances the precursor's ability to support the pore structure and prevents pore collapse during the drying process.

[0030] The segmented drying method used in this invention avoids excessive differences in the evaporation rates of moisture inside and outside the slurry caused by rapid high-temperature drying, preventing stress from being generated inside the precursor and thus avoiding defects such as cracking, deformation, and pore collapse. Low-temperature drying at 40℃ for 12 hours can slowly remove most of the free water, laying the foundation for subsequent high-temperature drying, while also gradually densifying the precursor structure and improving its strength. High-temperature drying at 105℃ can completely remove residual moisture, ensuring that the precursor is completely dry and preventing the residual moisture from rapidly vaporizing during sintering, which would damage the powder structure and pore morphology, thus ensuring the structural integrity and performance stability of the final aluminum nitride powder.

[0031] The vacuum sintering furnace used in this invention introduces flowing nitrogen gas, which participates in the carbothermic reduction reaction and forms an inert protective atmosphere to isolate oxygen. Simultaneously, it continuously removes impurities generated during the reaction, promoting the forward carbothermic reduction nitriding reaction and increasing the reaction conversion rate. The nitriding temperature of 1600℃ and the holding time of 3 hours are well-matched, ensuring sufficient reaction between the aluminum and carbon sources to generate highly crystalline aluminum nitride, avoiding incomplete reaction that could lead to a decrease in powder purity. The oxygen atmosphere at 600℃ for 3 hours effectively removes residual carbon impurities after sintering, further improving the purity of the aluminum nitride powder. Furthermore, this temperature does not damage the aluminum nitride crystal structure, ensuring powder performance. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to embodiments:

[0033] This invention provides a method for preparing a high-porosity aluminum nitride powder precursor, comprising the following steps:

[0034] Step S1: Raw material mixing: Mix water, aluminum source, carbon source, aluminum sol and thickener in proportion to form a slurry;

[0035] Furthermore, the mass fractions of each raw material are as follows: water 10%, aluminum source 35%-40%, carbon source 20%-25%, aluminum sol 20%-30%, and thickener 0.8%-1%. Specifically, 10% water, 35%-40% aluminum source, 20%-25% carbon source, and 20%-30% aluminum sol by mass are mixed in a disperser. After the mixture is evenly mixed, 0.8%-1% thickener is added and the mixture is stirred until the slurry forms a suspension.

[0036] The water used is deionized water, and the aluminum source is... Böhmstone or The carbon source is high-purity carbon black, the aluminum sol is alumina sol with a solid content of 30%, and the thickener is xanthan gum or carrageenan. Preferably, xanthan gum is used as the thickener, and the aluminum source has a particle size of [missing information]. of To improve the efficiency of carbothermic reduction reaction and the purity of aluminum nitride powder;

[0037] Step S2: Stirring and foaming: Add the foaming agent to the well-mixed slurry from step S1 and stir and foam until the slurry volume increases to more than 2.5 times.

[0038] Furthermore, the foaming agent is a plant-based foaming agent, with an addition amount of 1%-2%. During the foaming process, the volume of the slurry increases so that the interior of the slurry is filled with fine pores. The plant-based foaming agent can be tea saponin or rosin soap. Preferably, the plant-based foaming agent is tea saponin.

[0039] Step S3: Casting and solidification: Add the curing agent to the foamed slurry from step S2 and stir continuously. Then cast the slurry into a mold and solidify it into an aluminum nitride precursor. After drying, a high-porosity aluminum nitride powder precursor is obtained.

[0040] Furthermore, the curing agent uses high-purity gelatinized starch, with an addition amount of 2%-4%, to synergistically enhance the strength of the aluminum nitride precursor block with aluminum sol and thickener; the drying adopts a segmented drying method, first placing the solidified aluminum nitride precursor into an oven and drying it at 40℃ for 12 hours to remove most of the free water in the slurry, and then raising the temperature to 105℃ to dry it completely.

[0041] Step S4: The dried high-porosity aluminum nitride powder precursor from step S3 is placed in a vacuum sintering furnace for carbothermic reduction nitriding reaction to obtain aluminum nitride powder.

[0042] Furthermore, flowing nitrogen gas was introduced into the vacuum sintering furnace, the nitriding temperature was 1600℃, and the holding time was 3 hours, with a nitrogen flow rate of 4 m³ / h. 3 The mixture after nitriding is decarbonized in an oxygen atmosphere to obtain aluminum nitride powder. The decarbonization temperature is 600℃ and the holding time is 3h. After decarbonization, the mixture is cooled to room temperature to obtain aluminum nitride powder.

[0043] Example

[0044] The method for preparing the high-porosity aluminum nitride powder precursor in this embodiment includes the following steps:

[0045] Step S1: Disperse 1625g of alumina, 1000g of high-purity carbon black and 1250g of alumina sol evenly in 500g of deionized water, stir and mix in a disperser, add 40g of xanthan gum and continue stirring until the slurry forms a suspension.

[0046] Step S2: Add 75g of tea saponin foaming agent to the well-mixed slurry from step S1, and stir to foam until the slurry volume increases to more than 2.5 times.

[0047] Step S3: Add 150g of high-purity gelatinized starch to the foamed slurry from step S2 and stir continuously. Then, pour the slurry into a mold and solidify it into an aluminum nitride precursor. After that, put the solidified aluminum nitride precursor into an oven and dry it at 40°C for 12 hours to remove most of the free water in the slurry. Then, raise the temperature to 105°C and dry it until completely dry to obtain a high-porosity aluminum nitride powder precursor.

[0048] Step S4: Place the dried high-porosity aluminum nitride powder precursor from Step S3 into a vacuum sintering furnace. Introduce flowing nitrogen gas into the furnace. The nitriding temperature is 1600℃, and the holding time is 3 hours. The nitrogen flow rate is... The mixture after nitriding is decarbonized in an oxygen atmosphere to obtain aluminum nitride powder. The decarbonization temperature is 600℃ and the holding time is 3h. After decarbonization, the mixture is cooled to room temperature to obtain aluminum nitride powder.

[0049] Comparative Example

[0050] 2000g of alumina and 1000g of high-purity carbon black were uniformly dispersed in alcohol. 10g of dispersant oleic acid and 30g of PVB were added and mechanically mixed evenly. After drying and granulating the mixture, the precursor block was placed in a graphite crucible, and flowing nitrogen gas was introduced. Nitrification was carried out at 1600℃ for 3 hours. After cooling, air was introduced into a decarbonization furnace and the temperature was maintained at 600℃ for 3 hours to obtain aluminum nitride powder.

[0051] The comparative and example examples used the same nitriding and decarbonization processes, and the material loading mass and nitrogen gas flow rate were the same.

[0052] The specific details are shown in Table 1:

[0053] Table 1. Performance test results of aluminum nitride powders prepared in the examples and comparative examples.

[0054] Test Name Nitriding process Oxygen content Example 1600℃ / 3h 0.52% Comparative Example 1600℃ / 3h 0.75%

[0055] A comparison of the examples and comparative examples reveals that the aluminum nitride prepared in the comparative example has a higher oxygen content. This is mainly because the precursor block has fewer gas flow channels, resulting in less nitrogen entering the precursor. In contrast, this example, by introducing aluminum sol and high-purity gelatinized starch, significantly improves the strength of the precursor after drying. The introduced macroscopic pores enhance gas flow and displacement efficiency, allowing nitrogen to directly enter the precursor block and participate in the carbothermic reduction nitriding reaction. Therefore, it improves the quality of aluminum nitride and reduces the oxygen content after nitriding.

[0056] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.

Claims

1. A method for preparing a high-porosity aluminum nitride powder precursor, characterized in that... Includes the following steps: Step S1: Raw material mixing: Mix water, aluminum source, carbon source, aluminum sol and thickener in proportion to form a slurry; Step S2: Stirring and foaming: Add the foaming agent to the well-mixed slurry from step S1 and stir and foam until the slurry volume increases to more than 2.5 times. Step S3: Casting and solidification: Add the curing agent to the foamed slurry from step S2 and stir continuously. Then cast the slurry into a mold and solidify it into an aluminum nitride precursor. After drying, a high-porosity aluminum nitride powder precursor is obtained. Step S4: The dried high-porosity aluminum nitride powder precursor from step S3 is placed in a vacuum sintering furnace for carbothermic reduction nitriding reaction to obtain aluminum nitride powder.

2. The method for preparing a high-porosity aluminum nitride powder precursor according to claim 1, characterized in that: In step S1, the mass fractions of each raw material are as follows: water 10%, aluminum source 35%-40%, carbon source 20%-25%, aluminum sol 20%-30%, and thickener 0.8%-1%.

3. The method for preparing a high-porosity aluminum nitride powder precursor according to claim 2, characterized in that: Mix 10% water, 35%-40% aluminum source, 20%-25% carbon source, and 20%-30% aluminum sol in a disperser. After mixing evenly, add 0.8%-1% thickener and continue stirring until the slurry forms a suspension.

4. The method for preparing a high-porosity aluminum nitride powder precursor according to claim 3, characterized in that: The water used is deionized water, and the aluminum source is... Böhmstone or The carbon source is high-purity carbon black, the aluminum sol is alumina sol with a solid content of 30%, and the thickener is xanthan gum or carrageenan.

5. The method for preparing a high-porosity aluminum nitride powder precursor according to claim 4, characterized in that: The aluminum source uses a particle size of of This is to improve the efficiency of the carbothermic reduction reaction and the purity of aluminum nitride powder.

6. The method for preparing a high-porosity aluminum nitride powder precursor according to claim 5, characterized in that: In step S2, the foaming agent is a plant-based foaming agent, and the addition amount is 1%-2%. During the foaming process, the volume of the slurry increases so that the interior of the slurry is filled with fine pores.

7. The method for preparing a high-porosity aluminum nitride powder precursor according to claim 6, characterized in that: The plant-based foaming agent is tea saponin or rosin soap.

8. The method for preparing a high-porosity aluminum nitride powder precursor according to claim 7, characterized in that: In step S3, the curing agent is high-purity gelatinized starch, with an addition amount of 2%-4%, to synergistically enhance the strength of the aluminum nitride precursor block with aluminum sol and thickener.

9. The method for preparing a high-porosity aluminum nitride powder precursor according to claim 8, characterized in that: The drying process employs a segmented drying method. First, the solidified aluminum nitride precursor is placed in an oven and dried at 40°C for 12 hours to remove most of the free water in the slurry. Then, the temperature is raised to 105°C and dried until completely dry.

10. The method for preparing a high-porosity aluminum nitride powder precursor according to claim 9, characterized in that: In step S4, flowing nitrogen gas is introduced into the vacuum sintering furnace, the nitriding temperature is 1600℃, the holding time is 3 hours, and the nitrogen flow rate is 4 m³ / h. 3 The mixture after nitriding is decarbonized in an oxygen atmosphere to obtain aluminum nitride powder. The decarbonization temperature is 600℃ and the holding time is 3h. After decarbonization, the mixture is cooled to room temperature to obtain aluminum nitride powder.