Silicon nitride powder and preparation method thereof

Abstract

The invention provides silicon nitride powder and a preparation method thereof, and relates to the technical field of ceramic materials. The preparation method of the silicon nitride powder comprises the following steps: mixing silicon dioxide powder, carbon source powder and initial silicon nitride powder to obtain precursor powder; placing the precursor powder in a tubular heating furnace, continuously introducing nitrogen into the tubular heating furnace, and sequentially executing a first heating and heat preservation process and a second heating and heat preservation process to obtain silicon nitride coarse powder; wherein the temperature of the first heating and heat preservation process is lower than that of the second heating and heat preservation process, and the heat preservation time of the first heating and heat preservation process is longer than that of the second heating and heat preservation process; and carrying out decarburization treatment on the silicon nitride coarse powder to obtain target silicon nitride powder. The quality of the silicon nitride powder can be improved.

Description

Technical Field

[0001] The present disclosure relates to the technical field of ceramic materials, and in particular to a silicon nitride powder and a preparation method thereof. Background Art

[0002] High-quality silicon nitride (Si3N4) powder is the basis for the preparation of high-performance silicon nitride ceramic products. For the preparation of high-performance silicon nitride ceramic products with high flexural strength and high thermal conductivity, silicon nitride powder not only needs to be of high purity, but also needs to meet the indicators of low oxygen, low carbon, ultrafine, and high α phase. These indicators will directly determine the defects (lattice oxygen, pores, etc.), impurities, and grain boundary size in silicon nitride ceramics, thereby affecting thermal conductivity and flexural strength. At present, there is a problem of poor product quality in the preparation of silicon nitride powder.

[0003] It should be noted that the information disclosed in the above background technology section is only used to enhance the understanding of the background of the present disclosure, and therefore may include information that does not constitute the prior art known to ordinary technicians in the field. Summary of the invention

[0004] The purpose of the present disclosure is to provide a silicon nitride powder and a preparation method thereof, thereby overcoming the problem of poor quality of silicon nitride powder at least to a certain extent.

[0005] According to a first aspect of the present disclosure, a method for preparing silicon nitride powder is provided, comprising: mixing silicon dioxide powder, carbon source powder and initial silicon nitride powder to obtain a precursor powder; placing the precursor powder in a tubular heating furnace, continuously introducing nitrogen into the tubular heating furnace, and sequentially performing a first heating and insulation process and a second heating and insulation process to obtain a coarse silicon nitride powder; wherein the temperature of the first heating and insulation process is lower than the temperature of the second heating and insulation process, and the insulation time of the first heating and insulation process is longer than the insulation time of the second heating and insulation process; and decarburizing the coarse silicon nitride powder to obtain the target silicon nitride powder.

[0006] Optionally, the particle size of the silicon dioxide powder is 300 nm to 500 nm, and the purity is greater than or equal to 99.99%.

[0007] Optionally, the carbon source powder is carbon black, and the particle size is 10 nm to 30 nm. Specifically, the particle size may be 20 nm.

[0008] Optionally, the particle size of the initial silicon nitride powder is 400 nm to 600 nm, the purity is greater than or equal to 99.9%, and the α-phase content is greater than 95 wt%.

[0009] Optionally, the molar ratio of silicon dioxide powder, carbon source powder and initial silicon nitride powder is 1:(3-5):(0.25-0.43).

[0010] Optionally, executing the first heating and insulation process and the second heating and insulation process in sequence includes: controlling the temperature of the tubular heating furnace to rise to the temperature of the first heating and insulation process, and insulating the temperature for the insulation time of the first heating and insulation process; after insulating the temperature of the first heating and insulation process for the insulation time, controlling the temperature of the tubular heating furnace to rise to the temperature of the second heating and insulation process, and insulating the temperature for the insulation time of the second heating and insulation process.

[0011] Optionally, the temperature of the first heating and heat preservation process is 1450° C. to 1500° C., and the heat preservation time of the first heating and heat preservation process is 3 h to 6 h.

[0012] Optionally, the temperature of the second heating and heat preservation process is 1600° C. to 1650° C., and the heat preservation time of the second heating and heat preservation process is 0.5 h to 2 h.

[0013] Optionally, the decarburization treatment is performed at a temperature of 600° C. to 700° C. and for a time of 1 h to 4 h.

[0014] According to a second aspect of the present disclosure, a silicon nitride powder is provided. The silicon nitride powder is prepared by any of the above-mentioned methods for preparing silicon nitride powder.

[0015] In the scheme of the embodiment of the present disclosure, a two-step temperature-raising carbon thermal reduction synthesis process is adopted. In the first heating and heat preservation process, the temperature is relatively low, and a silicon nitride layer can be formed on the surface of the silicon dioxide particles, so that the silicon nitride layer can be used to hinder the sintering and agglomeration of the silicon dioxide particles; in the second heating and heat preservation process, the temperature is relatively high, and continuous nitridation is carried out, thereby promoting the further occurrence of the reaction and helping to reduce the oxygen content. In summary, the preparation process of the disclosed scheme is simple, highly controllable, easy to implement, and effectively reduces the synthesis temperature and energy consumption. By hindering the sintering and agglomeration of silicon dioxide particles, it is beneficial to reduce the agglomeration degree of silicon nitride powder and improve the sintering activity of silicon nitride powder. The carbon and oxygen impurity contents in the silicon nitride powder prepared by the disclosed process are low, wherein the carbon impurity content can reach less than 0.8%, and the oxygen impurity content can reach less than 1.0%. In addition, the α-phase content in the silicon nitride powder prepared by the present disclosure can reach more than 98%. The disclosed preparation scheme is suitable for industrial production.

[0016] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings herein are incorporated into the specification and constitute a part of the specification, illustrate embodiments consistent with the present disclosure, and together with the specification are used to explain the principles of the present disclosure. Obviously, the accompanying drawings described below are only some embodiments of the present disclosure, and for ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without creative work.

[0018] Figure 1 The flowchart of the method for preparing silicon nitride powder according to an exemplary embodiment of the present disclosure is schematically shown.

[0019] Figure 2 The SEM (Scanning Electron Microscope) image of the silicon nitride powder prepared in Example 1 of the present disclosure is shown, wherein a, b, c, and d are SEM images of the silicon nitride powder when magnified 50,000 times, 20,000 times, 10,000 times, and 5,000 times, respectively.

[0020] Figure 3 The SEM image of the silicon nitride powder prepared in Example 2 of the present disclosure is shown. Among them, a, b, c, and d are SEM images of the silicon nitride powder when magnified 50,000 times, 20,000 times, 10,000 times, and 5,000 times, respectively.

[0021] Figure 4 The SEM image of the silicon nitride powder prepared in Comparative Example 1 of the present disclosure is shown, wherein a, b, c, and d are SEM images of the silicon nitride powder when magnified 50,000 times, 20,000 times, 10,000 times, and 2,000 times, respectively.

[0022] Figure 5 Schematic diagram of XRD (X-Ray Diffraction) of silicon nitride products obtained in several embodiments of the present disclosure and Comparative Example 1. DETAILED DESCRIPTION

[0023] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in a variety of forms and should not be construed as being limited to the examples set forth herein; on the contrary, these embodiments are provided so that the present disclosure will be more comprehensive and complete, and the concepts of the example embodiments are fully conveyed to those skilled in the art. The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, many specific details are provided to provide a full understanding of the embodiments of the present disclosure. However, those skilled in the art will appreciate that the technical solutions of the present disclosure may be practiced while omitting one or more of the specific details, or other methods, processes, steps, etc. may be adopted. In other cases, known technical solutions are not shown or described in detail to avoid obscuring various aspects of the present disclosure.

[0024] In addition, the accompanying drawings are only schematic illustrations of the present disclosure and are not necessarily drawn to scale. The same reference numerals in the figures represent the same or similar parts, and thus their repeated descriptions will be omitted. The flowcharts shown in the accompanying drawings are only exemplary illustrations and do not necessarily include all the steps. For example, some steps can also be decomposed, while some steps can be combined or partially combined, so the actual execution order may change according to actual conditions. In addition, all the terms "first", "second", etc. below are only for the purpose of distinction and should not be used as limitations of the present disclosure.

[0025] At present, the scheme for preparing silicon nitride powder has disadvantages such as high reaction temperature, poor powder dispersibility, and high carbon / oxygen impurity content, which results in poor silicon nitride powder preparation process and the quality of the prepared silicon nitride powder may be poor.

[0026] In order to solve or at least alleviate the above problems, the embodiments of the present disclosure provide a new method for preparing silicon nitride powder.

[0027] Figure 1 The flowchart of the method for preparing silicon nitride powder according to an exemplary embodiment of the present disclosure is schematically shown. Figure 1 The method for preparing silicon nitride powder according to the embodiment of the present disclosure comprises the following steps:

[0028] S12. Mixing silicon dioxide powder, carbon source powder and initial silicon nitride powder to obtain precursor powder.

[0029] In an exemplary embodiment of the present disclosure, the particle size of the silica powder is 300nm to 500nm, and the purity is greater than or equal to 99.99%. The carbon source powder can be carbon black, and the particle size is 10nm to 30nm. Specifically, the particle size can be 20nm. The particle size of the initial silicon nitride powder is 400nm to 600nm, the purity is greater than or equal to 99.9%, and the α phase content is greater than 95wt%.

[0030] Specifically, the above substances can be mixed uniformly by mechanical stirring to obtain a precursor powder, wherein the molar ratio of the silicon dioxide powder, the carbon source powder and the initial silicon nitride powder can be 1: (3-5): (0.25-0.43).

[0031] S14. Place the precursor powder in a tubular heating furnace, continuously introduce nitrogen into the tubular heating furnace, and sequentially perform a first heating and heat preservation process and a second heating and heat preservation process to obtain coarse silicon nitride powder.

[0032] In an exemplary embodiment of the present disclosure, the temperature of the first heating and keeping process is lower than that of the second heating and keeping process, and the keeping time of the first heating and keeping process is longer than that of the second heating and keeping process.

[0033] First, the temperature of the tubular heating furnace can be controlled to rise to the temperature of the first heating and heat preservation process, and the heat preservation time of the first heating and heat preservation process can be maintained. After the heat preservation time of the first heating and heat preservation process, the temperature of the tubular heating furnace can be controlled to rise to the temperature of the second heating and heat preservation process, and the heat preservation time of the second heating and heat preservation process can be maintained.

[0034] Specifically, the temperature of the first heating and heat preservation process is 1450° C. to 1500° C., and the heat preservation time of the first heating and heat preservation process is 3 hours to 6 hours. The temperature of the second heating and heat preservation process is 1600° C. to 1650° C., and the heat preservation time of the second heating and heat preservation process is 0.5 hours to 2 hours.

[0035] S16. Decarburizing the coarse silicon nitride powder to obtain target silicon nitride powder.

[0036] Specifically, the decarburization treatment temperature is 600° C. to 700° C., and the time is 1 h to 4 h.

[0037] In the preparation scheme of silicon nitride powder of the embodiment of the present disclosure, on the basis of the carbon thermal reduction method, the initial silicon nitride powder is used as a seed, and the silicon nitride powder is prepared by a two-step heating method. The specific process is: first, the reactant is heated to 1450°C to 1500°C and kept warm for 3h to 6h, and then the product is further heated to 1600°C to 1650°C and kept warm for 0.5h to 2h. Since carbon thermal reduction synthesis requires high temperature, and high temperature easily causes the silicon dioxide raw material to sinter and agglomerate before synthesizing silicon nitride, the disclosed scheme adopts a two-step heating carbon thermal reduction synthesis process, first reacting at a lower temperature of 1450°C to 1500°C, forming a silicon nitride layer on the surface of the silicon dioxide particles, thereby using the silicon nitride layer to hinder the sintering and agglomeration of the silicon dioxide particles, and then heating to a higher temperature of 1600°C to 1650°C to continue nitridation, thereby promoting further reaction and reducing oxygen content. The advantages of the scheme disclosed in the present invention include at least: on the one hand, the preparation process is simple, highly controllable, and easy to implement. The synthesis temperature is lowered, and energy consumption is reduced. On the other hand, the sintering and agglomeration of silicon dioxide particles are hindered, which is beneficial to reducing the degree of agglomeration of silicon nitride powder and improving the sintering activity of silicon nitride powder. On the other hand, the carbon and oxygen impurity contents in silicon nitride powder are low, among which the carbon impurity content can reach less than 0.8%, the oxygen impurity content can reach less than 1.0%, and the α-phase content in silicon nitride powder can reach more than 98%. In general, the method provided by the present invention has a simple operation process, low energy consumption, and high quality of silicon nitride powder, which is conducive to industrial production.

[0038] The scheme of the embodiment of the present disclosure is described below through examples and comparative examples.

[0039] Example 1

[0040] First, 17.99 g of silicon dioxide powder with a particle size of 300 nm, 10.79 g of carbon black and 6 g of initial silicon nitride powder were mixed and uniformly stirred by mechanical stirring to obtain a precursor powder.

[0041] Next, 3 g of the precursor powder was placed in a crucible, and the crucible was placed in a tubular heating furnace. Nitrogen was continuously introduced into the tubular heating furnace at a nitrogen flow rate of 1.5 L / min, and after reacting at 1500° C. for 3 h, the temperature was further raised to 1600° C. and reacted for 2 h to obtain coarse silicon nitride powder.

[0042] Then, the silicon nitride coarse powder was kept at 700° C. for 1 hour to obtain silicon nitride powder.

[0043] refer to Figure 2 The silicon nitride powder prepared in Example 1 of the present disclosure has a spherical morphology composed of a small amount of primary particles, a low degree of agglomeration, and a narrow particle size distribution.

[0044] Example 2

[0045] First, 17.99 g of silicon dioxide powder with a particle size of 300 nm, 10.79 g of carbon black and 6 g of initial silicon nitride powder were mixed and uniformly stirred by mechanical stirring to obtain a precursor powder.

[0046] Next, 3 g of the precursor powder was placed in a crucible, and the crucible was placed in a tubular heating furnace. Nitrogen was continuously introduced into the tubular heating furnace at a nitrogen flow rate of 1.5 L / min, and after reacting at 1500° C. for 4 h, the temperature was further raised to 1600° C. and reacted for 1 h to obtain coarse silicon nitride powder.

[0047] Then, the silicon nitride coarse powder was kept at 700° C. for 1 hour to obtain silicon nitride powder.

[0048] refer to Figure 3 The silicon nitride powder prepared in Example 2 of the present disclosure has a spherical morphology composed of a small amount of primary particles, a low degree of agglomeration, and a narrow particle size distribution.

[0049] Example 3

[0050] First, 17.99 g of silicon dioxide powder with a particle size of 300 nm, 10.79 g of carbon black and 6 g of initial silicon nitride powder were mixed and uniformly stirred by mechanical stirring to obtain a precursor powder.

[0051] Next, 3 g of the precursor powder was placed in a crucible, and the crucible was placed in a tubular heating furnace. Nitrogen was continuously introduced into the tubular heating furnace at a nitrogen flow rate of 1.5 L / min, and after reacting at 1500° C. for 4.5 h, the temperature was further raised to 1600° C. and reacted for 0.5 h to obtain coarse silicon nitride powder.

[0052] Then, the silicon nitride coarse powder was kept at 700° C. for 1 hour to obtain silicon nitride powder.

[0053] Example 4

[0054] First, 20.56 g of silicon dioxide powder with a particle size of 300 nm, 12.33 g of carbon black and 4 g of initial silicon nitride powder were mixed and uniformly stirred by mechanical stirring to obtain a precursor powder.

[0055] Next, 3 g of the precursor powder was placed in a crucible, and the crucible was placed in a tubular heating furnace. Nitrogen was continuously introduced into the tubular heating furnace at a nitrogen flow rate of 1.5 L / min, and after reacting at 1500° C. for 3 h, the temperature was further raised to 1600° C. and reacted for 2 h to obtain coarse silicon nitride powder.

[0056] Then, the silicon nitride coarse powder was kept at 700° C. for 1 hour to obtain silicon nitride powder.

[0057] Example 5

[0058] First, 20.56 g of silicon dioxide powder with a particle size of 300 nm, 12.33 g of carbon black and 4 g of initial silicon nitride powder were mixed and uniformly stirred by mechanical stirring to obtain a precursor powder.

[0059] Next, 3 g of the precursor powder was placed in a crucible, and the crucible was placed in a tubular heating furnace. Nitrogen was continuously introduced into the tubular heating furnace at a nitrogen flow rate of 1.5 L / min, and after reacting at 1500° C. for 4 h, the temperature was further raised to 1600° C. and reacted for 1 h to obtain coarse silicon nitride powder.

[0060] Then, the silicon nitride coarse powder was kept at 700° C. for 1 hour to obtain silicon nitride powder.

[0061] Example 6

[0062] First, 20.56 g of silicon dioxide powder with a particle size of 300 nm, 12.33 g of carbon black and 4 g of initial silicon nitride powder were mixed and uniformly stirred by mechanical stirring to obtain a precursor powder.

[0063] Next, 3 g of the precursor powder was placed in a crucible, and the crucible was placed in a tubular heating furnace. Nitrogen was continuously introduced into the tubular heating furnace at a nitrogen flow rate of 1.5 L / min, and after reacting at 1500° C. for 4 h, the temperature was further raised to 1600° C. and reacted for 2 h to obtain coarse silicon nitride powder.

[0064] Then, the silicon nitride coarse powder was kept at 700° C. for 1 hour to obtain silicon nitride powder.

[0065] Example 7

[0066] First, 17.99 g of silicon dioxide powder with a particle size of 300 nm, 14.38 g of carbon black and 6 g of initial silicon nitride powder were mixed and uniformly stirred by mechanical stirring to obtain a precursor powder.

[0067] Next, 3 g of the precursor powder was placed in a crucible, and the crucible was placed in a tubular heating furnace. Nitrogen was continuously introduced into the tubular heating furnace at a nitrogen flow rate of 1.5 L / min, and after reacting at 1500° C. for 4 h, the temperature was further raised to 1600° C. and reacted for 1 h to obtain coarse silicon nitride powder.

[0068] Then, the silicon nitride coarse powder was kept at 680° C. for 1.5 hours to obtain silicon nitride powder.

[0069] Example 8

[0070] First, 17.99 g of silicon dioxide powder with a particle size of 300 nm, 17.98 g of carbon black and 6 g of initial silicon nitride powder were mixed and uniformly stirred by mechanical stirring to obtain a precursor powder.

[0071] Next, 3 g of the precursor powder was placed in a crucible, and the crucible was placed in a tubular heating furnace. Nitrogen was continuously introduced into the tubular heating furnace at a nitrogen flow rate of 1.5 L / min, and after reacting at 1500° C. for 4 h, the temperature was further raised to 1600° C. and reacted for 1 h to obtain coarse silicon nitride powder.

[0072] Then, the silicon nitride coarse powder is kept at 600° C. for 4 hours to obtain silicon nitride powder.

[0073] Example 9

[0074] First, 17.99 g of silicon dioxide powder with a particle size of 300 nm, 10.79 g of carbon black and 6 g of initial silicon nitride powder were mixed and uniformly stirred by mechanical stirring to obtain a precursor powder.

[0075] Next, 3 g of the precursor powder was placed in a crucible, and the crucible was placed in a tubular heating furnace. Nitrogen was continuously introduced into the tubular heating furnace at a nitrogen flow rate of 1.5 L / min, and after reacting at 1500° C. for 6 h, the temperature was further raised to 1650° C. and reacted for 1 h to obtain coarse silicon nitride powder.

[0076] Then, the silicon nitride coarse powder was kept at 700° C. for 1 hour to obtain silicon nitride powder.

[0077] Example 10

[0078] First, 17.99 g of silicon dioxide powder with a particle size of 300 nm, 10.79 g of carbon black and 6 g of initial silicon nitride powder were mixed and uniformly stirred by mechanical stirring to obtain a precursor powder.

[0079] Next, 3 g of the precursor powder was placed in a crucible, and the crucible was placed in a tubular heating furnace. Nitrogen was continuously introduced into the tubular heating furnace at a nitrogen flow rate of 1.5 L / min, and after reacting at 1450° C. for 6 h, the temperature was further raised to 1600° C. and reacted for 1 h to obtain coarse silicon nitride powder.

[0080] Then, the silicon nitride coarse powder was kept at 700° C. for 1 hour to obtain silicon nitride powder.

[0081] Comparative Example 1

[0082] First, 17.99 g of silicon dioxide powder with a particle size of 300 nm, 10.79 g of carbon black and 6 g of initial silicon nitride powder were mixed and uniformly stirred by mechanical stirring to obtain a precursor powder.

[0083] Next, 3 g of the precursor powder was placed in a crucible, and the crucible was placed in a tubular heating furnace. Nitrogen was continuously introduced into the tubular heating furnace at a nitrogen flow rate of 1.5 L / min, and the reaction was carried out at 1600° C. for 5 h to obtain coarse silicon nitride powder.

[0084] Then, the silicon nitride coarse powder was kept at 700° C. for 1 hour to obtain silicon nitride powder.

[0085] refer to Figure 4 The silicon nitride powder prepared in Comparative Example 1 did not use the two-step heating method disclosed in the present invention. The silicon nitride powder finally prepared had an irregular morphology composed of a large number of primary particles, a high degree of agglomeration, and a wide particle size distribution.

[0086] refer to Figure 5 Based on the results of XRD, all products are composed of α-Si3N4 and β-Si3N4. Among them, the α-phase content in the silicon nitride powder prepared by the embodiments of the present disclosure reaches more than 98%, while the α-phase content in the silicon nitride powder prepared without the two-step heating method is only 94.0%.

[0087] In addition, the silicon nitride powders prepared in the above-mentioned Example 1, Example 2 and Comparative Example 1 were tested, and the test results are shown in Table 1:

[0088] Table 1

[0089]

[0090]

[0091] Through Example 1, Example 2 and Comparative Example 1, and combined with Table 1, the α-phase content in the silicon nitride powder prepared in the embodiment of the present disclosure is greater than 98%, and the α-phase content is significantly increased compared with the silicon nitride prepared without the two-step heating method. At the same time, the carbon and oxygen impurity contents of the silicon nitride powder prepared in the embodiment of the present disclosure are slightly higher than the carbon and oxygen impurity contents of the silicon nitride powder prepared in Comparative Example 1, but are still at a relatively low level overall.

[0092] Furthermore, the present disclosure also provides a silicon nitride powder, which is prepared by the above-mentioned method for preparing silicon nitride powder.

[0093] It should be noted that although the steps of the method in the present disclosure are described in a specific order in the drawings, this does not require or imply that the steps must be performed in this specific order, or that all the steps shown must be performed to achieve the desired results. Additionally or alternatively, some steps may be omitted, multiple steps may be combined into one step, and / or one step may be decomposed into multiple steps, etc.

[0094] In addition, the above-mentioned figures are only schematic illustrations of the processes included in the method according to the exemplary embodiments of the present disclosure, and are not intended to be limiting. It is easy to understand that the processes shown in the above-mentioned figures do not indicate or limit the time sequence of these processes. In addition, it is also easy to understand that these processes can be performed synchronously or asynchronously, for example, in multiple modules.

[0095] Those skilled in the art will readily appreciate other embodiments of the present disclosure after considering the specification and practicing what is disclosed herein. This application is intended to cover any variations, uses, or adaptations of the present disclosure that follow the general principles of the present disclosure and include common knowledge or customary technical means in the art that are not disclosed in the present disclosure. The specification and embodiments are to be considered merely as exemplary, and the true scope and spirit of the present disclosure are indicated by the claims.

[0096] It should be understood that the present disclosure is not limited to the exact structures that have been described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof. The scope of the present disclosure is limited only by the appended claims.

Claims

1. A method for preparing silicon nitride powder, characterized in that: include: Mixing silicon dioxide powder, carbon source powder and initial silicon nitride powder to obtain precursor powder; Placing the precursor powder in a tubular heating furnace, continuously introducing nitrogen into the tubular heating furnace, and sequentially performing a first heating and heat preservation process and a second heating and heat preservation process to obtain silicon nitride coarse powder; wherein the temperature of the first heating and heat preservation process is lower than the temperature of the second heating and heat preservation process, and the heat preservation time of the first heating and heat preservation process is longer than the heat preservation time of the second heating and heat preservation process; The silicon nitride coarse powder is decarburized to obtain target silicon nitride powder.

2. The preparation method according to claim 1, characterized in that: The particle size of the silicon dioxide powder is 300nm to 500nm, and the purity is greater than or equal to 99.99%.

3. The preparation method according to claim 1, characterized in that: The carbon source powder is carbon black, and the particle size is 10nm to 30nm.

4. The preparation method according to claim 1, characterized in that: The initial silicon nitride powder has a particle size of 400 nm to 600 nm, a purity greater than or equal to 99.9%, and an α-phase content greater than 95 wt %.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The molar ratio of the silicon dioxide powder, the carbon source powder and the initial silicon nitride powder is 1:(3-5):(0.25-0.43).

6. The preparation method according to claim 1, characterized in that: Sequentially performing the first heating and heat preservation process and the second heating and heat preservation process includes: Controlling the temperature of the tubular heating furnace to rise to the temperature of the first heating and heat preservation process, and heat preservation for the heat preservation time of the first heating and heat preservation process; After the first heating and heat preservation process is maintained for a heat preservation time, the temperature of the tubular heating furnace is controlled to rise to a temperature of the second heating and heat preservation process, and the temperature is maintained for a heat preservation time of the second heating and heat preservation process.

7. The preparation method according to claim 1 or 6, characterized in that: The temperature of the first heating and heat preservation process is 1450° C. to 1500° C., and the heat preservation time of the first heating and heat preservation process is 3 hours to 6 hours.

8. The preparation method according to claim 1 or 6, characterized in that: The temperature of the second heating and heat preservation process is 1600° C. to 1650° C., and the heat preservation time of the second heating and heat preservation process is 0.5 h to 2 h.

9. The preparation method according to claim 1, characterized in that: The temperature of the decarburization treatment is 600°C to 700°C, and the time is 1h to 4h.

10. A silicon nitride powder, characterized in that: The silicon nitride powder is prepared by the method for preparing the silicon nitride powder according to any one of claims 1 to 9.

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