Preparation method of flaky aluminum nitride ceramic powder and product thereof

Abstract

The invention discloses a preparation method of flaky aluminum nitride ceramic powder and a product thereof. The preparation method comprises the following steps: by taking deionized water as a dispersion medium, uniformly mixing Al2O3 powder, carbon black and Na3AlF6 through ball milling, and drying to obtain a precursor; and in a flowing nitrogen atmosphere, the precursor is subjected to a carbon thermal reduction reaction and a nitridation reaction to obtain the micron-sized flaky aluminum nitride ceramic powder. According to the method, a flaky template does not need to be prepared in advance, flaky AlN can be directly generated, and the technical defect that an existing process depends on precursor morphology is overcome.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of functional ceramic powder preparation, and particularly relates to a preparation method of flaky aluminum nitride ceramic powder and a product thereof. BACKGROUND

[0002] With the development of electronic devices towards higher performance, power consumption and integration, thermal management has become a key factor limiting its reliability and performance. The heat dissipation of integrated circuit components has always been a bottleneck limiting factor restricting the further development of integrated circuits and electronic devices. In order to effectively dissipate heat, high-efficiency heat-conducting fillers are needed. Among various heat-conducting fillers, aluminum nitride (AlN) ceramic is widely considered as an ideal material to solve the problem of device heat dissipation and becomes 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 product greater than 170 W / m×K); (2) high resistivity (10 14 Ω·cm), making it particularly suitable for applications requiring high thermal conductivity and electrical insulation; (3) thermal expansion coefficient (4.2×10 -6 K -1 ) matching Si.

[0003] In the preparation of composite materials, flaky fillers are added to polymers, and then molded by pressing. The flaky fillers are oriented in the matrix, which can significantly improve the strength, thermal conductivity, electrical conductivity and other properties of the composite material in a specific direction. If flaky aluminum nitride is used as a filler, its directional arrangement can enhance the in-plane thermal conductivity area of the material, which is suitable for the heat dissipation design of electronic devices. Therefore, the preparation of flaky aluminum nitride ceramic powder is of great significance for the application of high-thermal-conductivity composite materials.

[0004] The conventional preparation methods of aluminum nitride powder include direct nitridation method and carbothermal reduction method. It is difficult to synthesize flaky aluminum nitride product by using near-spherical aluminum powder or alumina powder as raw material. In order to obtain flaky aluminum nitride powder, flaky raw material is usually used as the basis for in-situ synthesis. Dang et al. prepared flaky aluminum nitride ceramic by mixing flaky Al2O3 powder with carbon black as a template and then by carbothermal reduction nitridation method at 1500℃ in nitrogen atmosphere (Science of Advanced Materials, 10, 89-94.); Dong Xiaolin et al. prepared flaky aluminum nitride ceramic by using a mixed solution of aluminum salt and nitrogen-containing organic matter as raw material, adopting precursor method in nitrogen atmosphere and keeping at 900-1200℃ for 2-4h (A method for preparing flaky aluminum nitride powder, CN108516835A); Pang Haoran et al. prepared flaky aluminum nitride ceramic composed of equiaxed microparticles by in-situ direct nitridation method in nitrogen atmosphere by wet ball milling spherical Al powder to obtain flaky Al powder (Foundry Technology, 2023, 44(05): 405-410.). Although the above methods can obtain flaky aluminum nitride ceramic, they need to prepare flaky precursor in advance, which is complicated, high in cost, difficult to control the morphology of the product and limited in conversion rate. SUMMARY

[0005] The purpose of the present application is to overcome the shortcomings of the prior art and provide a preparation method of flaky aluminum nitride ceramic powder and the product thereof. The present application adopts carbothermal reduction method to obtain flaky AlN ceramic powder by introducing cryolite to form a liquid phase as a reaction medium. The flaky aluminum nitride prepared by the present application has clear morphology, uniform dispersion and simple process.

[0006] In a first aspect, the present application provides a preparation method of flaky aluminum nitride ceramic powder, which comprises: mixing Al2O3 powder, carbon black and cryolite (Na3AlF6) uniformly by ball milling with deionized water as dispersion medium, and drying to obtain a precursor; synthesizing aluminum nitride ceramic by carbon thermal reduction reaction and nitridation reaction of the precursor slurry in flowing nitrogen atmosphere, and removing excess carbon in dry air to obtain micron-sized flaky aluminum nitride ceramic powder.

[0007] Preferably, the median diameter of the Al2O3 powder is 20nm-1mm.

[0008] Preferably, the median diameter of the carbon black is 10-100nm.

[0009] Preferably, the mass ratio of the Al2O3 powder, carbon black and cryolite is 100:(40-80):(4-15). Preferably, the ball milling rotation speed is 100-250 rpm, and the ball milling time is 2-8 h.

[0010] Preferably, the drying temperature of the mixed slurry after ball milling is 60-80 °C, and the drying time is 15-24 h.

[0011] Preferably, the synthesis temperature of the carbothermal reduction reaction is 1500-1600 °C, and the reaction time is 6-8 h, wherein the temperature rising rate from 1000 °C to the synthesis temperature is controlled at 2-10 °C / min.

[0012] Preferably, the temperature for removing excess carbon is controlled at 600-700 °C, and the time is 4-10 h.

[0013] In a second aspect, the present application provides a flaky aluminum nitride ceramic powder, which has a radial dimension of 3-22 mm, a thickness of 1.0-2.5 mm, and an aspect ratio of 3-15.

[0014] The present application has the following advantages: (1) The present application uses a conventional carbothermal reduction nitridation process for synthesizing near-spherical aluminum nitride powder particles to synthesize flaky aluminum nitride, which has low raw material cost, stable process, and is easy to realize large-scale production. The prepared aluminum nitride has clear flaky morphology, relatively uniform distribution, and no other impurity phase, and the aluminum nitride ceramic is relatively pure.

[0015] (2) The present application uses ice to form a liquid phase at 1000-1200 °C, and dissolves the aluminum oxide raw material to form a molten aluminum oxide mixed liquid phase. The molten mixed liquid phase flows and lays in the gap between the undissolved aluminum oxide particles and the carbon powder particles to form a mixed micro-liquid phase layer containing aluminum oxide. Then, when the synthesis reaction temperature is increased to 1500-1600 °C, the mixed micro-liquid phase layer undergoes carbothermal reduction nitridation to generate flaky aluminum nitride products. This process does not need to prepare flaky precursors in advance, can be accurately controlled by synthesis process (such as temperature, time, and temperature rising rate), and can generate micron-sized flaky products.

[0016] (3) The product obtained by the present application has a radial dimension of 3-22 mm, a thickness of 1.0-2.5 mm, and an aspect ratio of 3-15, all of which are in the micron size range, which is beneficial for use as a filler for composite materials, and can be used as a thermal conductive filler, which can be a thermal conductive functional ceramic. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 FIG. 4 is an XRD pattern of the aluminum nitride ceramic sintered at 1600 °C by adding different mass fractions of ice in Example 1.

[0018] Figure 2SEM images of the aluminum nitride ceramic sintered at 1600℃ with different mass fractions of ice in Example 1, wherein (a) 4%; (b) 7%; (c) 10%; (d) 15%.

[0019] Figure 3 EDS image of the aluminum nitride ceramic sintered at 1600℃ with 7 mass fractions of ice in Example 1, wherein the content of Al element is 59.4wt.%; the content of N element is 36.7wt.%; the content of C element is 2.3wt.%; the content of O element is 0.7wt.%; and the content of Si element is 0.9wt.%.

[0020] Figure 4 XRD image of the aluminum nitride ceramic sintered at 1550℃ with different mass fractions of ice in Example 2.

[0021] Figure 5 SEM images of the aluminum nitride ceramic sintered at 1550℃ with different mass fractions of ice in Example 2, wherein (a) 4%; (b) 7%; (c) 10%; (d) 15%.

[0022] Figure 6 SEM image of the aluminum nitride ceramic sintered at 1500℃ with 7 mass fractions of ice in Example 3.

[0023] Figure 7 SEM image of the aluminum nitride ceramic sintered at 1600℃ without adding ice in Comparative Example 1.

[0024] Figure 8 SEM image of the aluminum nitride ceramic sintered with 50 mass fractions of ice in Comparative Example 2, (a) synthesis temperature 1600℃, (b) synthesis temperature 1550℃, (c) synthesis temperature 1500℃. DETAILED DESCRIPTION

[0025] Hereinafter, the embodiments of the present application will be described in detail. However, the embodiments shown below are examples for embodying the technical idea of the present application, and the present application is not limited thereto. It should be noted that the term "process" in the present specification includes not only a separate process, but also a range in which the intended purpose of the process can be achieved without being clearly distinguished from other processes. In addition, the numerical range indicated using "~" indicates a range in which the values indicated before and after "~" are respectively included as the minimum value and the maximum value.

[0026] At least one embodiment provides a flaky aluminum nitride ceramic powder having a radial dimension of 3-22 mm, a thickness of 1.0-2.5 mm, and a radial thickness ratio of 3-15, all in the micron size range, which is advantageous for use as a filler for a composite material.

[0027] Meanwhile, the embodiment also provides a preparation method of the flaky aluminum nitride ceramic powder, which is a new method for preparing the flaky AlN ceramic powder by introducing cryolite in combination with the carbothermal reduction nitridation method, and specifically comprises the following steps: Step S1, uniformly mixing Al2O3 powder, carbon black and cryolite (Na3AlF6) by ball milling in deionized water as a dispersion medium, and drying to obtain an Al2O3 / C / cryolite precursor, which is denoted as an ACC precursor; Step S2, placing the ACC precursor slurry in a graphite crucible in a flowing nitrogen atmosphere, and placing the graphite crucible into a vacuum sintering furnace to synthesize aluminum nitride ceramic containing residual C through a carbothermal reduction reaction and a nitridation reaction, and then removing the excess carbon in dry air to obtain micron-scale flaky aluminum nitride ceramic powder with a certain aspect ratio.

[0028] In one embodiment, the median diameter of the Al2O3 powder is 20 nm to 1 mm, and is preferably 20 to 100 nm.

[0029] In one embodiment, the median diameter of the carbon black is 10 to 100 nm.

[0030] In one embodiment, the mass ratio of the Al2O3 powder, the carbon black and the cryolite is 100: (40 to 80): (4 to 15).

[0031] In one embodiment, the ball milling speed is 100 to 250 rpm, and the ball milling time is 2 to 8 h. For example, the mass ratio of the grinding ball to the powder can be 5:2. The amount of deionized water is 4 to 5 times that of the aluminum oxide.

[0032] In one embodiment, the drying temperature of the mixed slurry after ball milling is 60 to 80°C, and the time is 15 to 24 h.

[0033] In one embodiment, the synthesis temperature of the carbothermal reduction reaction is 1500 to 1600°C, and the reaction time is 6 to 8 h, wherein the temperature rising rate from 1000°C to the synthesis temperature is controlled to be 2 to 10°C / min.

[0034] The present application introduces cryolite to form a liquid phase at 1000 to 1200°C, dissolves Al2O3 to form a molten micro-layer, the liquid phase is directionally spread in the gap between the unreacted Al2O3 / C particles, and the subsequent carbothermal reduction makes the micro-layer directionally nitridate, directly generating flaky AlN, without the need to prepare a flaky template in advance, and solving the technical defects of the existing process which depends on the morphology of the precursor.

[0035] In one embodiment, the temperature for removing the excess carbon is controlled to be 600 to 700°C, and the time is 4 to 10 h. Preferably, the carbon removal temperature is 600°C, and the holding time is 6 h.

[0036] The application adopts conventional Al2O3 powder and carbon black to remove the pre-morphology regulation step, and directly synthesizes in-situ by liquid phase through a single carbon thermal reduction step, thereby reducing equipment complexity and energy consumption, and meeting the demand of large-scale production.

[0037] In addition, the sheet structure of the aluminum nitride ceramic powder in the embodiment is arranged in the polymer matrix, and the in-plane thermal conductivity of the composite material is significantly improved, and the aluminum nitride ceramic powder is expected to be used as a thermal conductive filler.

[0038] The embodiments of the application will be described in detail below with specific examples, but those skilled in the art will understand that the following examples are only used to illustrate the application, and should not be regarded as limiting the scope of the application. Based on the examples in the application, all other examples obtained by those skilled in the art without creative labor are within the scope of protection of the application. If the specific conditions are not specified, the conventional conditions or the conditions recommended by the manufacturer are used. If the manufacturer of the reagent or instrument is not specified, it is a conventional product that can be purchased on the market.

[0039] It should be noted that: In the application, all the embodiments and preferred implementation methods mentioned in the text can be combined to form new technical solutions, unless otherwise specified.

[0040] In the application, all the technical features and preferred features mentioned in the text can be combined to form new technical solutions, unless otherwise specified.

[0041] In the application, unless otherwise specified, the percentage (%) or part refers to the percentage by weight or weight of the composition.

[0042] In the application, unless otherwise specified, each component or its preferred component involved can be combined to form a new technical solution.

[0043] In the application, unless otherwise specified, the "range" disclosed in the application can be one or more lower limits and one or more upper limits in the form of lower limit and upper limit.

[0044] In the application, unless otherwise specified, each reaction or operation step can be sequentially performed or performed according to the sequence. Preferably, the reaction method in the text is sequentially performed.

[0045] Unless otherwise specified, the professional and scientific terms used in the text have the same meaning as those familiar to those skilled in the art. In addition, any method or material similar or equivalent to the described content can also be applied to the application. Example 1

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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 mm and thicknesses of 1.0–2.5 mm. 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

[0050] 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 3~22mm and a thickness of 1.0~2.5mm. Example 3

[0051] Example 3 was carried out according to the method of Example 1, except that 7 parts by mass of ice crystals were added and the temperature was raised to 1500°C at a rate of 2-10°C / min in a flowing nitrogen atmosphere and held for 4h to obtain aluminum nitride ceramic (as shown in Table 1). The SEM image of the aluminum nitride ceramic obtained by sintering 7% by mass of ice crystals at 1500°C is shown in Figure 2. Figure 6 Figure 2 is an SEM image of the aluminum nitride ceramic obtained by sintering 7% by mass of ice crystals at 1500°C. As can be seen from the figure, the aluminum nitride ceramic is mostly in the form of a sheet, with a radial dimension of 3-22mm and a thickness of 1.0-2.5mm.

[0052] Comparative Example 1 Comparative Example 1 differs from Example 1 in that no ice crystals were added. 25g of Al2O3 powder with a median particle size of 20nm-1mm was weighed out by mass parts, and 10-20g of carbon black powder with a median particle size of 10-100nm was weighed out by mass parts, which was added to a ball mill tank and 180mL of deionized water was added, and the ball-to-material ratio was 5:2, and the slurry was ball milled on a horizontal ball mill at a speed of 100-250rpm for 2-8h. The dry temperature of the mixed slurry after ball milling was 60-80°C, and the drying time was 15-24h, and the ACC precursor slurry was obtained after drying.

[0053] An appropriate amount of ACC precursor slurry was weighed out in a graphite crucible and placed in a vacuum furnace, and the temperature was raised to 1600°C at a rate of 2-10°C / min in a flowing nitrogen atmosphere and held for 4h to obtain aluminum nitride ceramic. The above-mentioned aluminum nitride ceramic was held at 600-700°C in dry air for 4-10h to remove residual C, and AlN powder was obtained.

[0054] Figure 1 is an SEM image of the aluminum nitride ceramic powder obtained by sintering 50% by mass of ice crystals at 1600°C. Figure 7 Figure 1 is an SEM image of the aluminum nitride ceramic powder obtained by sintering 50% by mass of ice crystals at 1600°C.

[0055] Comparative Example 2 Comparative Example 2 was carried out according to the method of Comparative Example 1, except that an excess of ice crystals was added: 50 parts by mass. The ACC precursor slurry was raised to 1600°C, 1550°C, and 1500°C at a rate of 2-10°C / min in a flowing nitrogen atmosphere and held for 4h, and then the carbon was removed to obtain aluminum nitride ceramic. Figure 8 Figures 3, 4, and 5 are SEM images of the aluminum nitride ceramic powder obtained by sintering 50% by mass of ice crystals at 1600°C, 1550°C, and 1500°C, respectively. Although the SEM images show that the powder is in the form of a sheet, the XRD patterns show that the powder is not pure AlN, but also contains a large amount of unreacted Al2O3 phase (as shown in Table 1), so when the amount of ice crystals is excessive, the sheet structure formed is not pure AlN.

[0056] Table 1. Results of product phase composition comparison of Example 3 and Comparative Examples 1-2

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 the precursor; 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. A novel method for preparing sheet-like aluminum nitride ceramic powder according to claim 1, characterized in that: The median diameter of the Al2O3 powder is 20 nm to 1 mm.

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

4. The method according to claim 1, characterized in that: The mass ratio of Al2O3 powder, carbon black and cryolite is 100:(40-80):(4-15).

5. 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.

6. 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.

7. 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.

8. 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.

9. A sheet-like aluminum nitride ceramic powder, prepared by the method according to any one of claims 1-8, characterized in that: The radial dimension of the sheet aluminum nitride is 3-22 mm, the thickness is 1.0-2.5 mm, and the aspect ratio is 3-15.

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