Preparation method of sheet-like aluminum nitride ceramic powder and product thereof

Abstract

The application discloses a preparation method of sheet-shaped aluminum nitride ceramic powder and a product thereof. In the application, deionized water is used as a dispersion medium, Al2O3 powder, carbon black and Na3AlF6 are uniformly mixed through ball milling, and a precursor is obtained through drying; and the precursor is subjected to a carbon thermal reduction reaction and a nitriding reaction in a flowing nitrogen atmosphere to obtain micron-grade sheet-shaped aluminum nitride ceramic powder. The application can directly generate sheet-shaped AlN without pre-preparing a sheet-shaped template, and solves the technical defects of existing processes which depend on the morphology of a precursor.

Description

Technical Field

[0001] This invention belongs to the field of functional ceramic powder preparation technology, specifically relating to a method for preparing sheet-like aluminum nitride ceramic powder and its product. Background Technology

[0002] As electronic devices continue to develop towards higher performance, power consumption, and integration, thermal management has become a key factor limiting their reliability and performance. Heat dissipation of integrated circuit components has always been a bottleneck restricting the further development of integrated circuits and electronic devices. In order to effectively dissipate heat, efficient thermally conductive fillers are needed. Among various thermally conductive fillers, aluminum nitride (AlN) ceramic is widely regarded as an ideal material for solving the heat dissipation problem of devices and is becoming increasingly important in high-performance ceramic fillers. This is attributed to the following advantages of AlN: (1) high thermal conductivity (theoretical value 320 W / m × K, commercial aluminum nitride products are greater than 170 W / m × K); (2) high resistivity (10 Ω·cm). 14 (3) Coefficient of thermal expansion (4.2 × 10 Ω·cm), making it particularly suitable for applications requiring high thermal conductivity and electrical insulation; -6 K -1 It is compatible with Si.

[0003] In the preparation of composite materials, adding lamellar fillers to polymers and then pressing them into shape allows the lamellar fillers to oriented within the matrix, significantly improving the composite material's strength, thermal conductivity, and electrical conductivity in specific directions. When lamellar aluminum nitride is used as a filler, its oriented arrangement enhances the in-plane thermal conductivity area of ​​the material, making it suitable for heat dissipation design in electronic devices. Therefore, the preparation of lamellar aluminum nitride ceramic powder is of great significance for the application of high thermal conductivity composite materials.

[0004] Conventional methods for preparing aluminum nitride powder include direct nitriding and carbothermic reduction. However, using near-spherical aluminum powder or alumina powder as raw materials makes it difficult to synthesize flake-shaped aluminum nitride products. To obtain flake-shaped aluminum nitride powder, flake-shaped raw materials are typically used as the basis for in-situ synthesis. Dang et al. used flake-shaped Al₂O₃ powder as a template, mixed it with carbon black, and then prepared flake-shaped aluminum nitride ceramics at 1500℃ under a nitrogen atmosphere via carbothermic reduction nitriding (Science of Advanced Materials, 10, 89–94). Dong Xiaolin et al. used a mixed solution of aluminum salt and nitrogen-containing organic matter as raw materials, employing a precursor method under a nitrogen atmosphere and holding at 900–1200℃ for 2–4 hours to prepare flake-shaped aluminum nitride ceramics (a method for preparing flake-shaped aluminum nitride powder, CN108516835A). Pang Haoran et al. used spherical Al powder as raw material and wet ball milled it to obtain flake Al powder. They successfully prepared flake aluminum nitride ceramics composed of equiaxed micron-sized particles by in-situ direct nitriding in a nitrogen atmosphere (Foundry Technology, 2023, 44(05): 405-410). Although the above method can obtain flake aluminum nitride ceramics, it requires the preparation of flake precursors in advance, which is cumbersome, costly, and the product morphology is difficult to control and the conversion rate is limited. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a method for preparing flake-shaped aluminum nitride ceramic powder and the resulting product. This invention employs a carbothermal reduction method, introducing cryolite to form a liquid phase as the reaction medium to obtain flake-shaped AlN ceramic powder. The aluminum nitride flakes prepared by this invention exhibit clear morphology, uniform dispersion, and a simple process.

[0006] In a first aspect, the present invention provides a method for preparing sheet-like aluminum nitride ceramic powder, the method comprising:

[0007] Using deionized water as the dispersion medium, Al2O3 powder, carbon black and cryolite (Na3AlF6) were ball-milled and mixed evenly, and then dried to obtain the precursor.

[0008] In a flowing nitrogen atmosphere, the precursor slurry is synthesized into aluminum nitride ceramics through carbothermic reduction and nitriding reactions. Excess carbon is then removed in dry air to obtain micron-sized sheet-like aluminum nitride ceramic powder.

[0009] Preferably, the median diameter of the Al2O3 powder is 20 nm to 1 mm.

[0010] Preferably, the median diameter of the carbon black is 10–100 nm.

[0011] Preferably, the mass ratio of Al2O3 powder, carbon black and cryolite is 100:(40-80):(4-15).

[0012] Preferably, the ball milling speed is 100-250 rpm and the ball milling time is 2-8 hours.

[0013] Preferably, the drying temperature of the ball-milled slurry is 60-80°C, and the drying time is 15-24 hours.

[0014] Preferably, the synthesis temperature of the carbothermic reduction reaction is 1500–1600°C, and the reaction time is 6–8 h, wherein the heating rate from 1000°C to the synthesis temperature is controlled at 2–10°C / min.

[0015] Preferably, the temperature for removing excess carbon is controlled at 600–700°C, and the time is 4–10 hours.

[0016] Secondly, the present invention provides a sheet-like aluminum nitride ceramic powder with a radial dimension of 3 to 22 μm, a thickness of 1.0 to 2.5 μm, and an aspect ratio of 3 to 15.

[0017] The beneficial effects of this invention are as follows:

[0018] (1) The present invention uses a carbothermal reduction nitridation process to synthesize near-spherical aluminum nitride powder particles in a conventional manner to synthesize flake aluminum nitride. The raw material cost is low, the process is stable, and it is easy to achieve large-scale production. The AlN flakes prepared are clear in morphology, relatively uniform in distribution, and free of other impurity phases, resulting in relatively pure aluminum nitride ceramics.

[0019] (2) In this invention, cryolite is used to form a liquid phase at 1000–1200°C, which dissolves the alumina raw material to form a molten alumina mixed liquid phase. This molten mixed liquid phase flows and spreads in the gaps between undissolved alumina particles and carbon powder particles, forming a mixed micro-liquid phase layer containing alumina. Then, when the synthesis reaction temperature is raised to between 1500–1600°C, the mixed micro-liquid phase layer undergoes carbothermic reduction nitridation to generate plate-like aluminum nitride products. This process no longer requires the pre-preparation of plate-like precursors, can be accurately controlled by the synthesis process (such as temperature, time, and heating rate), and can generate plate-like products with micron-sized dimensions.

[0020] (3) The radial dimension of the product obtained by the present invention is 3 to 22 μm, the thickness is 1.0 to 2.5 μm, and the aspect ratio is 3 to 15, all of which are within the micrometer size range. This is advantageous for use as a filler in composite materials and can also be used as a thermally conductive filler. It can be a thermally conductive functional ceramic. Attached Figure Description

[0021] Figure 1 The image shows the XRD pattern of aluminum nitride ceramics obtained by sintering aluminum nitride ceramics with different mass fractions of cryolite at 1600°C in Example 1.

[0022] Figure 2The images show SEM images of aluminum nitride ceramics obtained by sintering at 1600°C with different mass fractions of cryolite in Example 1, where (a) 4%; (b) 7%; (c) 10%; and (d) 15%.

[0023] Figure 3 The image shows the EDS diagram of the aluminum nitride ceramic obtained by sintering at 1600°C with 7 parts cryolite added in Example 1, wherein the content of Al is 59.4 wt.%; N is 36.7 wt.%; C is 2.3 wt.%; O is 0.7 wt.%; and Si is 0.9 wt.%.

[0024] Figure 4 The image shows the XRD pattern of aluminum nitride ceramics obtained by sintering aluminum nitride ceramics with different mass fractions of cryolite at 1550°C in Example 2.

[0025] Figure 5 The images show SEM images of aluminum nitride ceramics obtained by sintering at 1550°C with different mass fractions of cryolite in Example 2, where (a) 4%; (b) 7%; (c) 10%; and (d) 15%.

[0026] Figure 6 The image shows an SEM image of the aluminum nitride ceramic obtained by adding 7% cryolite to Example 3 and sintering it at 1500°C.

[0027] Figure 7 This is a SEM image of aluminum nitride ceramic at 1600℃ without cryolite in Comparative Example 1.

[0028] Figure 8 The images show SEM images of aluminum nitride ceramics obtained when 50 parts by mass of cryolite were added in Comparative Example 2. (a) Synthesis temperature 1600℃, (b) Synthesis temperature 1550℃, (c) Synthesis temperature 1500℃. Detailed Implementation

[0029] The embodiments of this application will now be described in detail. However, the embodiments shown below are merely examples used to embody the technical concept of this application, and this application is not limited thereto. It should be noted that the term "process" in this specification is not limited to an independent process; it is included in this term as long as the intended purpose of the process can be achieved, even if it cannot be clearly distinguished from other processes. In addition, the numerical range indicated by "~" represents the range in which the values ​​recorded before and after "~" are respectively the minimum and maximum values.

[0030] At least one embodiment provides a sheet-like aluminum nitride ceramic powder with a radial dimension of 3 to 22 μm, a thickness of 1.0 to 2.5 μm, and a diameter-to-thickness ratio of 3 to 15, all of which are in the micrometer size range, which is advantageous for use as a filler in composite materials.

[0031] Meanwhile, this embodiment also provides a method for preparing the above-mentioned sheet-like aluminum nitride ceramic powder, which is a new method for preparing sheet-like AlN ceramic powder by introducing cryolite combined with carbothermal reduction nitridation, specifically including:

[0032] Step S1: Using deionized water as the dispersion medium, Al2O3 powder, carbon black and cryolite (Na3AlF6) are ball-milled and mixed evenly, and then dried to obtain Al2O3 / C / cryolite precursor, denoted as ACC precursor;

[0033] Step S2: In a flowing nitrogen atmosphere, the ACC precursor slurry is placed in a graphite crucible and then placed in a vacuum sintering furnace. Aluminum nitride ceramics containing residual C are synthesized through carbothermic reduction and nitriding reactions. Excess carbon is then removed in dry air to obtain micron-sized sheet-like aluminum nitride ceramic powder with a certain aspect ratio.

[0034] In one embodiment, the median diameter of the Al2O3 powder is 20 nm to 1 mm, preferably 20 to 100 nm.

[0035] In one embodiment, the median diameter of the carbon black is 10–100 nm.

[0036] In one embodiment, the mass ratio of Al2O3 powder, carbon black and cryolite is 100:(40-80):(4-15).

[0037] In one embodiment, the ball milling speed is 100–250 rpm, and the milling time is 2–8 hours. For example, the mass ratio of grinding balls to powder can be 5:2. The amount of deionized water used is 4–5 times that of alumina.

[0038] In one embodiment, the drying temperature of the ball-milled slurry is 60-80°C, and the drying time is 15-24 hours.

[0039] In one embodiment, the synthesis temperature of the carbothermic reduction reaction is 1500–1600°C, and the reaction time is 6–8 h, wherein the heating rate from 1000°C to the synthesis temperature is controlled at 2–10°C / min.

[0040] This invention introduces cryolite to form a liquid phase at 1000-1200℃, dissolving Al2O3 to form a molten microlayer. This liquid phase spreads directionally in the gaps between unreacted Al2O3 / C particles. Subsequent carbothermic reduction causes the microlayer to undergo directional nitridation, directly generating sheet-like AlN. This eliminates the need for pre-prepared sheet-like templates, overcoming the technical deficiency of existing processes that rely on the morphology of precursors.

[0041] In one embodiment, the temperature for removing excess carbon is controlled at 600–700°C, and the time is 4–10 hours. Preferably, the carbon removal temperature is 600°C, and the holding time is 6 hours.

[0042] This invention uses conventional Al2O3 powder and carbon black, eliminating the pre-morphology control step, and employs a single carbothermal reduction step for direct in-situ synthesis in the liquid phase, reducing equipment complexity and energy consumption, and meeting the needs of large-scale production.

[0043] In addition, the aluminum nitride ceramic powder in this embodiment has a plate-like structure that is oriented in the polymer matrix, which significantly improves the in-plane thermal conductivity of the composite material and is expected to serve as a thermally conductive filler.

[0044] The embodiments of the present invention will be described in detail below with reference to specific examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. Unless otherwise specified, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0045] It should be noted that:

[0046] Unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0047] Unless otherwise specified, all the technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0048] In this invention, unless otherwise specified, percentage (%) or parts refer to weight percentage or parts relative to the composition.

[0049] Unless otherwise specified, the components or preferred components involved in this invention can be combined with each other to form new technical solutions.

[0050] In this invention, unless otherwise stated, the "scope" disclosed herein may take the form of a lower limit and an upper limit, and may be one or more lower limits and one or more upper limits, respectively.

[0051] In this invention, unless otherwise stated, the various reactions or operation steps may be performed sequentially or in a particular order. Preferably, the reaction methods described herein are performed sequentially.

[0052] Unless otherwise stated, the technical and scientific terms used herein have the same meanings as those familiar to those skilled in the art. Furthermore, any methods or materials similar to or equivalent to those described herein may also be used in this invention. Example 1

[0053] 25g of Al2O3 powder with a median particle size of 20nm to 1mm was weighed by mass, 10 to 20g of carbon black powder with a median particle size of 10 to 100nm was weighed by mass, and 1g, 1.75g, 2.5g, and 3.75g of cryolite were weighed by mass in proportions of 4, 7, 10, and 15, respectively. These were added to a ball mill jar and 180mL of deionized water were added. The mixture was ball-milled in a horizontal ball mill at a speed of 100 to 250rpm for 2 to 8 hours at a ball-to-particle ratio of 5:2. The slurry was dried at 60 to 80℃ for 15 to 24 hours after ball milling. Four groups of ACC precursor slurries with different cryolite mass contents were obtained after drying.

[0054] Four appropriate amounts of ACC precursor slurry were weighed and placed in graphite crucibles in a vacuum furnace. The furnace was heated to 1600℃ at a rate of 2–10°C / min and held for 4 hours in a flowing nitrogen atmosphere to obtain four groups of aluminum nitride ceramics.

[0055] The above four groups of aluminum nitride ceramics were kept at 600-700°C in dry air for 4-10 hours to remove residual C, thus obtaining four groups of AlN powders.

[0056] Appendix Figure 1 The images show the XRD patterns of sheet-like aluminum nitride ceramics obtained by holding cryolite at 1600℃ for 4 hours with different mass fractions, indicating that the prepared powder is pure phase AlN; (Attached) Figure 2 (a) Figure 2 Image (d) shows SEM images of aluminum nitride ceramics obtained by holding cryolite at 1600℃ for 4 hours with different mass parts. The images show that most of the aluminum nitride ceramics are plate-like, with radial dimensions of 3–22 μm and thicknesses of 1.0–2.5 μm. EDS analysis was performed on aluminum nitride ceramics with a cryolite mass of 7 parts, as shown in the attached image. Figure 3 ,Depend on Figure 3 (a) Figure 3 As can be seen from (f), Al and N are the main elements, so the sheet-like structure is AlN. Example 2

[0057] Example 2 follows the method of Example 1, except that the temperature is increased to 1550°C at a rate of 2–10°C / min and held for 4 hours in a flowing nitrogen atmosphere to obtain aluminum nitride ceramic. (See attached image) Figure 4 The images show the XRD patterns of sheet-like aluminum nitride ceramics obtained by holding cryolite at 1550℃ for 4 hours with different mass fractions, indicating that the prepared sheet-like powder is pure phase AlN; (Attached) Figure 5 (a) Figure 5 Image (d) shows SEM images of aluminum nitride ceramics obtained by holding cryolite at 1550℃ for 4 hours with different mass fractions. It can be seen from the image that most of the aluminum nitride ceramics are in the form of flakes with a radial dimension of 3~22um and a thickness of 1.0~2.5um. Example 3

[0058] Example 3 follows the method of Example 1, except that 7 parts by weight of cryolite are added and heated to 1500°C for 4 hours in a flowing nitrogen atmosphere at a rate of 2–10°C / min, yielding aluminum nitride ceramics (as shown in Table 1). Figure 6 The image shows an SEM image of aluminum nitride ceramic obtained by sintering aluminum nitride ceramic with 7% cryolite added in Example 3 at 1500°C. The image shows that most of the aluminum nitride ceramic is in the form of flakes with a radial dimension of 3~22 μm and a thickness of 1.0~2.5 μm.

[0059] Comparative Example 1

[0060] The difference between Comparative Example 1 and Example 1 is that cryolite is not added. 25g of Al2O3 powder with a median particle size of 20nm to 1mm and 10 to 20g of carbon black powder with a median particle size of 10 to 100nm were weighed by mass and added to a ball mill jar along with 180mL of deionized water. The mixture was ball-milled for 2 to 8 hours at a speed of 100 to 250 rpm in a horizontal ball mill at a ball-to-particle ratio of 5:2. The dried slurry was then dried at 60 to 80°C for 15 to 24 hours to obtain the ACC precursor slurry.

[0061] Weigh an appropriate amount of ACC precursor slurry into a graphite crucible and place it in a vacuum furnace. In a flowing nitrogen atmosphere, heat the crucible to 1600°C at a rate of 2–10°C / min and hold for 4 hours to obtain aluminum nitride ceramic. Hold the aluminum nitride ceramic in dry air at 600–700°C for 4–10 hours to remove residual C and obtain AlN powder.

[0062] Appendix Figure 7 This is a SEM image of aluminum nitride ceramic powder at 1600℃ without the addition of cryolite. Although XRD shows a pure AlN phase (as shown in Table 1), the SEM image shows that the aluminum nitride ceramic morphology is not plate-like. Therefore, when cryolite is not added to the raw material, a plate-like structure will not be formed.

[0063] Comparative Example 2

[0064] Comparative Example 2 followed the method of Comparative Example 1, except that an excess of cryolite was added: 50 parts by mass were weighed. The ACC precursor slurry was heated to 1600℃, 1550℃, and 1500℃ respectively in a flowing nitrogen environment at a rate of 2–10°C / min and held for 4 hours, followed by decarburization to obtain aluminum nitride ceramics. (See attached image) Figure 8The images show SEM images of aluminum nitride ceramic powder at 1600℃, 1550℃, and 1500℃ when 50 parts by weight of cryolite were added. Although the SEM images show that the powder is in a flaky form, the XRD pattern shows that the powder is not pure AlN and contains a large amount of unreacted Al2O3 phase (as shown in Table 1). Therefore, when cryolite is in excess, the resulting flaky structure is not pure AlN.

[0065] Table 1. Comparison of phase composition of products from Example 3 and Comparative Examples 1-2

[0066]

Claims

1. A method for preparing sheet-like aluminum nitride ceramic powder, characterized in that, The method includes: Using deionized water as the dispersion medium, Al2O3 powder, carbon black and Na3AlF6 were ball-milled and mixed evenly, and then dried to obtain a precursor; the mass ratio of Al2O3 powder, carbon black and Na3AlF6 was 100:(40-80):(4-15). In a flowing nitrogen atmosphere, aluminum nitride is synthesized from the precursor through a carbothermic reduction reaction and a nitriding reaction. Excess carbon is then removed in dry air to obtain micron-sized sheet-like aluminum nitride ceramic powder.

2. The method according to claim 1, characterized in that: The median diameter of the carbon black is 10–100 nm.

3. The method according to claim 1, characterized in that: The ball milling speed is 100-250 rpm, and the ball milling time is 2-8 hours.

4. The method according to claim 1, characterized in that: The drying temperature of the ball-milled slurry is 60-80℃, and the drying time is 15-24h.

5. The method according to claim 1, characterized in that: The synthesis temperature of the carbothermic reduction reaction is 1500–1600°C, and the reaction time is 6–8 h, wherein the heating rate from 1000°C to the synthesis temperature is controlled at 2–10°C / min.

6. The method according to claim 1, characterized in that: The temperature for removing excess carbon is controlled at 600–700°C, and the time is 4–10 hours.

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