Preparation method of silicon nitride powder and silicon nitride powder

Abstract

The embodiment of the present disclosure provides a method for preparing silicon nitride powder and silicon nitride powder, which relates to the technical field of silicon nitride. The method comprises: mixing silicon powder, diluent and catalyst according to a preset ratio, using ethanol as a solvent, mixing the mixed silicon powder, diluent, catalyst and solvent in a ball mill by silicon nitride grinding balls to obtain a slurry, drying, cooling and sieving the slurry to obtain a silicon-based precursor powder; placing the silicon-based precursor powder in a constant temperature section of a tubular heating furnace, placing a mixture of melamine and polyvinyl chloride as an activator in a non-constant temperature section of the tubular heating furnace close to the air inlet, continuously introducing nitrogen into the tubular heating furnace, reacting at a target temperature, and obtaining the silicon nitride powder. The present disclosure can improve the quality of silicon nitride powder.

Description

Technical Field

[0001] The embodiments of the present disclosure relate to the technical field of ceramic powders, and in particular to a method for preparing silicon nitride powder and silicon nitride powder. Background Art

[0002] High-quality Si3N4 powder is the foundation for producing high-performance Si3N4 ceramics. To produce high-performance Si3N4 ceramics with high flexural strength and thermal conductivity, the powder must not only be highly pure but also meet the following requirements: low oxygen, low carbon, ultrafine, and high α-phase content. These characteristics directly determine the defects (lattice oxygen, pores, etc.), impurities, and grain boundary size in the Si3N4 ceramic, thereby affecting thermal conductivity and flexural strength. Summary of the Invention

[0003] The purpose of the present disclosure is to provide a method for preparing silicon nitride powder and silicon nitride powder, thereby overcoming, at least to a certain extent, the problem of poor quality of silicon nitride powder caused by limitations and defects in related technologies.

[0004] According to one aspect of the present disclosure, a method for preparing silicon nitride powder is provided, comprising: mixing silicon powder, a diluent, and a catalyst in a predetermined ratio; using ethanol as a solvent; ball milling the mixed silicon powder, diluent, catalyst, and solvent in a ball mill using silicon nitride grinding balls to obtain a slurry; and drying, cooling, and sieving the slurry to obtain a silicon-based precursor powder.

[0005] The silicon-based precursor powder is placed in the constant temperature section of a tubular heating furnace, and a mixture of melamine and polyvinyl chloride is placed as an activator in the non-constant temperature section of the tubular heating furnace close to the air inlet. Nitrogen is continuously introduced into the tubular heating furnace, and the reaction is carried out at the target temperature to obtain the silicon nitride powder.

[0006] In an exemplary embodiment of the present disclosure, the target temperature is 1250-1300° C., and the reaction time at the target temperature is 10-24 hours.

[0007] In an exemplary embodiment of the present disclosure, the particle size of the silicon powder is 1-2 μm, and the purity of the silicon powder is ≥99.995%.

[0008] In an exemplary embodiment of the present disclosure, the diluent is silicon nitride powder, the purity of the diluent is greater than 99.9%, and the α-phase content is greater than 95 wt %.

[0009] In an exemplary embodiment of the present disclosure, the catalyst is one or both of Co and Ni, and the particle size of the catalyst is 50 nm to 1 μm.

[0010] In an exemplary embodiment of the present disclosure, the mass ratio of the silicon powder, diluent, catalyst, solvent and silicon nitride grinding balls is 1:(0.25~0.43):(0.00625~0.025):(2.5~5):(5~7.5).

[0011] In an exemplary embodiment of the present disclosure, the ball milling mixing is a ball milling mechanical wet mixing, the rotation speed of the ball milling mixing is 200-400 rpm, and the ball milling mixing time is 3-6 hours.

[0012] In an exemplary embodiment of the present disclosure, the mass ratio of the melamine to the polyvinyl chloride in the mixture is 1: (0.33~3).

[0013] In an exemplary embodiment of the present disclosure, the mass ratio of the silicon-based precursor to the activator is 1:(0.8~1.6).

[0014] According to one aspect of the present disclosure, there is provided a silicon nitride powder, which is prepared according to any one of the above-mentioned methods for preparing silicon nitride powder.

[0015] In the technical solution provided in the embodiments of the present disclosure, a mixture of melamine and polyvinyl chloride is placed as an activator in a non-constant temperature zone on the side of the tube furnace close to the air inlet, and the characteristic of the temperature curve in the non-constant temperature zone gradually increasing is utilized to enable the activator to be continuously decomposed. The intermediate of the high-temperature decomposition of the activator enters the constant temperature zone along with the nitrogen gas introduced into the air inlet, so that it can fully activate the silicon powder during the whole process of synthesizing the silicon nitride powder. On the one hand, the intermediate of the high-temperature decomposition of melamine provides a highly active gas-phase supplementary nitrogen source, reducing the number of high-energy chemical bonds that need to be broken, thereby lowering the reaction temperature and shortening the reaction time. On the other hand, the hydrogen chloride obtained by the high-temperature decomposition of polyvinyl chloride etches the elemental silicon and the oxide film on its surface to form Si-Cl and Si-O-Cl bonds, which have lower bond energy and higher reaction activity, thereby lowering the reaction temperature and shortening the reaction time. Hydrogen chloride etches the oxide film on the surface of the silicon powder, and then nitriding to form silicon nitride powder, thereby reducing the oxygen content in the silicon nitride product. Hydrogen chloride etches elemental silicon and the oxide film on its surface, forming a gas-phase silicon-containing product. This gas-phase silicon-containing product reacts with N2 and a highly reactive gas-phase supplemental nitrogen source to form α-Si3N4 whiskers via the VS growth mechanism, thereby increasing the α-phase content in the silicon nitride product and improving the quality of the silicon nitride powder. The method provided by the disclosed embodiments has a simple operation process, shortens reaction time, reduces energy consumption, and is conducive to 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 disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings are incorporated into 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 drawings described below are only some embodiments of the present disclosure, and those skilled in the art can derive other drawings based on these drawings without inventive effort.

[0018] Figure 1 A flow chart schematically illustrates a method for preparing silicon nitride powder in an embodiment of the present disclosure.

[0019] Figure 2 A schematic diagram of a tubular heating furnace in an embodiment of the present disclosure is schematically shown.

[0020] Figure 3 1 is an XRD pattern of silicon nitride powder prepared according to Example 1 without using an activator of the mixture composition.

[0021] Figure 4 Schematic diagram of an SEM image of the silicon nitride powder prepared according to Example 1 in the disclosed embodiment when magnified 10,000 times.

[0022] Figure 5 Schematic diagram of an SEM image of the silicon nitride powder prepared according to Example 1 in the disclosed embodiment when magnified 20,000 times.

[0023] Figure 6 Schematic diagram of an SEM image of the silicon nitride powder prepared according to Example 1 in the disclosed embodiment when magnified 50,000 times.

[0024] Figure 7 This is a schematic diagram of another SEM image of the silicon nitride powder prepared according to Example 1 in the embodiment of the present disclosure when magnified 50,000 times. DETAILED DESCRIPTION

[0025] 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 limited to the examples set forth herein; rather, these embodiments are provided so that the present disclosure will be more comprehensive and complete and will fully convey the concepts of the example embodiments 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 that other methods, components, devices, steps, etc. may be employed. In other cases, well-known technical solutions are not shown or described in detail to avoid obscuring various aspects of the present disclosure.

[0026] The terms "a", "an", "the" and "said" are used in this specification to indicate the presence of one or more elements / components, etc.; the terms "including" and "having" are used to express open-ended inclusion and mean that additional elements / components, etc. may exist in addition to the listed elements / components, etc.; the terms "first" and "second" are used only as labels and are not intended to limit the quantity of their objects.

[0027] In order to solve the above technical problems, the present disclosure provides a method for preparing silicon nitride powder in an embodiment for preparing silicon nitride nanopowder. Figure 1 As shown in , it mainly includes the following steps:

[0028] In step S110, silicon powder, a diluent, and a catalyst are mixed in a predetermined ratio, and ethanol is used as a solvent. The mixed silicon powder, diluent, catalyst, and solvent are ball-milled in a ball mill using silicon nitride grinding balls to obtain a slurry, which is then dried, cooled, and sieved to obtain a silicon-based precursor powder.

[0029] In step S120, the silicon-based precursor powder is placed in the constant temperature section of a tubular heating furnace, the activator is placed in the non-constant temperature section of the tubular heating furnace close to the air inlet, nitrogen is continuously introduced into the tubular heating furnace, and the reaction is carried out at the target temperature to obtain the silicon nitride powder.

[0030] Next, the preparation method of the silicon nitride powder in the embodiment of the present disclosure is described in detail.

[0031] In step S110, silicon powder, diluent and catalyst are mixed in a preset ratio, ethanol is used as a solvent, and the mixed silicon powder, diluent, catalyst and solvent are ball-milled in a ball mill using silicon nitride grinding balls. After obtaining the slurry, it is dried, cooled and sieved to obtain a silicon-based precursor powder.

[0032] In the embodiments of the present disclosure, the particle size of the silicon powder can be 1 μm, 2 μm, 1.5 μm, etc. The purity of the silicon powder is greater than or equal to 99.995%. In some embodiments, the diluent can be silicon nitride powder, the purity of the diluent can be greater than 99.9%, and the α-phase content of the diluent is greater than 95wt%. The catalyst can be one or both of Co and Ni, and the particle size of the catalyst can be 50nm~1μm. The solvent can be anhydrous ethanol. In some embodiments, silicon nitride grinding balls are a grinding medium, and the mass ratio of silicon powder, diluent, catalyst, solvent and silicon nitride grinding balls can be 1:(0.25~0.43):(0.00625~0.025):(2.5~5):(5~7.5). The ball milling mixing method can be a ball milling mechanical wet mixing, the ball milling mixing speed is 200~400 rpm, and the ball milling mixing time is 3~6 hours.

[0033] After the silicon powder, diluent, catalyst and solvent are mechanically wet-mixed in a ball mill using silicon nitride grinding balls, a slurry can be obtained. The slurry can be further dried, cooled and sieved to obtain a silicon-based precursor powder.

[0034] In step S120, the silicon-based precursor powder is placed in the constant temperature section of a tubular heating furnace, and a mixture of melamine and polyvinyl chloride is placed as an activator in the non-constant temperature section of the tubular heating furnace near the air inlet. Nitrogen is continuously introduced into the tubular heating furnace, and the reaction is carried out at the target temperature to obtain the silicon nitride powder.

[0035] In the embodiment of the present disclosure, the silicon-based precursor powder obtained in step S110 can be placed in the constant temperature section of the tubular heating furnace, and the temperature of the constant temperature section can be the target temperature. In addition, the activator can be placed in the non-constant temperature section of the tubular heating furnace close to the air inlet. That is, the non-constant temperature section is set on the side close to the air inlet, and the constant temperature section is set on the side away from the air inlet. The temperature of the non-constant temperature section can be different from the target temperature, as long as the activator can be completely decomposed. Moreover, the greater the distance from the constant temperature, the lower the temperature of the non-constant temperature section. The structure of the tubular heating furnace can be as follows Figure 2 As shown in .

[0036] The activator may be a mixture of melamine and polyvinyl chloride, wherein the mass ratio of melamine to polyvinyl chloride in the mixture is 1:(0.33-3), and the mass ratio of the silicon-based precursor to the activator is 1:(0.8-1.6).

[0037] After placing the silicon-based precursor powder and activator in corresponding positions in a tubular heating furnace, nitrogen can be continuously introduced into the tubular heating furnace to react at the target temperature to obtain silicon nitride powder. The target temperature can be 1250-1300°C, and the reaction time at the target temperature after introducing nitrogen is 10-24 hours.

[0038] In the embodiment of the present disclosure, a mixture of melamine and polyvinyl chloride is placed as an activator in a non-constant temperature zone on the side of a tubular furnace close to the air inlet, and the characteristic of the temperature curve in the non-constant temperature zone gradually increasing is utilized to enable the activator to continuously decompose. Furthermore, the pyrolysis intermediate of the activator enters the constant temperature zone along with the nitrogen introduced from the air inlet, so that the activator fully activates the silicon powder during the entire synthesis process of the silicon nitride powder. The high-temperature decomposition intermediate of melamine provides a highly active gas-phase supplementary nitrogen source, reducing the number of high-energy chemical bonds that need to be broken, thereby lowering the reaction temperature and shortening the reaction time. In addition, the hydrogen chloride decomposed by the high-temperature decomposition of polyvinyl chloride etches the elemental silicon and the oxide film on its surface to form Si-Cl and Si-O-Cl bonds, which have lower bond energy and higher reaction activity, thereby lowering the reaction temperature and shortening the reaction time, and then nitriding to form silicon nitride powder, thereby reducing the oxygen content in the silicon nitride product. Hydrogen chloride etches elemental silicon and the oxide film on its surface, forming a gas-phase silicon-containing product. This gas-phase silicon-containing product reacts with nitrogen and a highly reactive gas-phase supplemental nitrogen source to form α-Si3N4 whiskers via the VS growth mechanism, thereby increasing the α-phase content in the silicon nitride product and improving the quality of the silicon nitride powder. Furthermore, the method provided in the disclosed embodiments features a simple operation, shortened reaction time, and reduced energy consumption, facilitating industrial production.

[0039] On this basis, the preparation method of the silicon nitride powder disclosed in the present invention can be specifically described in combination with the examples.

[0040] In some embodiments, silicon nitride powder may be prepared by placing silicon-based precursor powder in a constant temperature section without using an activator, including the following steps:

[0041] Step 1: 24 g of silicon powder, 6 g of Si3N4 diluent and 0.3 g of 50 nm Co catalyst were mixed, and 60 g of ethanol was used as a solvent. The mixed silicon powder, diluent, catalyst and solvent were mechanically wet-milled in a planetary ball mill using 120 g of silicon nitride grinding balls at a speed of 300 rpm for 6 hours. After obtaining the slurry, it was dried at 70 ° C, cooled and sieved to obtain a silicon-based precursor powder.

[0042] Step 2: Place 5g of silicon-based precursor powder in a crucible and place the crucible in the constant temperature section of a tubular furnace. Continuously introduce nitrogen gas into the furnace at a flow rate of 0.2 L / min. React at 1250°C for 12 hours. The resulting product is a brown powder, a mixture of Si, α-Si3N4, and β-Si3N4. The Si, α-Si3N4, and β-Si3N4 contents are 21.8%, 68.8%, and 9.4%, respectively. Extending the reaction time to 18 hours yields an off-white powder, still a mixture of Si, α-Si3N4, and β-Si3N4, with Si, α-Si3N4, and β-Si3N4 contents of 1.4%, 87.3%, and 11.3%, respectively. The oxygen content in the product is 5.15%. Extending the reaction time to 30 hours maintains essentially unchanged product phase.

[0043] In some embodiments, melamine can also be used as an activator to prepare silicon nitride powder. The preparation method of the silicon nitride powder mainly includes the following steps:

[0044] Step 1: 24 g of silicon powder, 6 g of Si3N4 diluent and 0.3 g of 50 nm Co catalyst are mixed, and 60 g of ethanol is used as a solvent. The mixed silicon powder, diluent, catalyst and solvent are mechanically wet-milled in a planetary ball mill using 120 g of silicon nitride grinding balls at a speed of 300 rpm for 6 hours. After obtaining a slurry, the slurry is dried at 70°C, cooled and sieved to obtain a silicon-based precursor powder.

[0045] Step 2: Place 5g of silicon-based precursor powder in a first crucible, which is then placed in the constant temperature section of a tubular furnace. Place 8g of melamine as an activator in a second crucible, which is then placed in the non-constant temperature section of the tubular furnace, near the air inlet. Nitrogen is continuously introduced into the tubular furnace at a flow rate of 0.2 L / min. The reaction is carried out at 1250°C for 10 hours to obtain an off-white powder composed of Si, α-Si3N4, β-Si3N4, and SiC.

[0046] In some embodiments, polyvinyl chloride can also be used as an activator to prepare silicon nitride powder. The preparation method of the silicon nitride powder mainly includes the following steps:

[0047] Step 1: 24 g of silicon powder, 6 g of Si3N4 diluent and 0.3 g of 50 nm Co catalyst are mixed, and 60 g of ethanol is used as a solvent. The mixed silicon powder, diluent, catalyst and solvent are mechanically wet-milled in a planetary ball mill using 120 g of silicon nitride grinding balls at a speed of 300 rpm for 6 hours. After obtaining a slurry, the slurry is dried at 70 ° C, cooled and sieved to obtain a silicon-based precursor powder.

[0048] Step 2: Take 5g of silicon-based precursor powder and place it in the first crucible, and place the first crucible in the constant temperature section of the tubular heating furnace; place 8g of polyvinyl chloride as an activator in the second crucible, and place the second crucible in the non-constant temperature section of the tubular heating furnace close to the air inlet; continuously introduce nitrogen into the tubular heating furnace with a nitrogen flow rate of 0.2 L / min, and react at 1250°C for 10 hours to obtain a gray-white powder product, which is composed of Si, α-Si3N4, β-Si3N4, SiC and Si2N2O.

[0049] To solve the technical problems existing in the related art, the present disclosure provides a method for preparing silicon nitride powder in an embodiment, which is mainly used to prepare silicon nitride nanopowder. The preparation method of silicon nitride powder is described in detail below with reference to the embodiments.

[0050] It should be noted that, during the entire process of preparing silicon nitride powder, one or more of the mass ratio of melamine to polyvinyl chloride, the type of catalyst, the mass ratio of the silicon-based precursor to the activator, the target temperature, the reaction time at the target temperature, and the mass ratio of silicon powder, diluent, catalyst, solvent and silicon nitride grinding balls can be adjusted.

[0051] Example 1

[0052] Step 1: 24 g of silicon powder, 6 g of Si3N4 diluent and 0.3 g of 50 nm Co catalyst are mixed, and 60 g of ethanol is used as a solvent. The mixed silicon powder, diluent, catalyst and solvent are mechanically wet-milled in a planetary ball mill using 120 g of silicon nitride grinding balls at a speed of 300 rpm for 6 hours. After obtaining the slurry, it is dried at 70°C, cooled and sieved to obtain a silicon-based precursor powder.

[0053] Step 2: Take 5g of silicon-based precursor powder and place it in the first crucible, and place the first crucible in the constant temperature section of the tubular heating furnace; place a mixture of 4g of melamine and 4g of polyvinyl chloride as an activator in the second crucible, and place the second crucible in the non-constant temperature section of the tubular heating furnace close to the air inlet; continuously introduce nitrogen into the tubular heating furnace at a nitrogen flow rate of 0.2 L / min, and react at 1250°C for 10 hours to obtain gray-white silicon nitride nanopowder. The nitridation rate of the gray-white silicon nitride nanopowder is 100%, the α-phase content is 92.1%, and the oxygen content is 1.49%.

[0054] Example 2

[0055] Step 1: 24 g of silicon powder, 6 g of Si3N4 diluent and 0.3 g of 50 nm Co catalyst are mixed, and 60 g of ethanol is used as a solvent. The mixed silicon powder, diluent, catalyst and solvent are mechanically wet-milled in a planetary ball mill using 120 g of silicon nitride grinding balls at a speed of 300 rpm for 6 hours. After obtaining a slurry, the slurry is dried at 70°C, cooled and sieved to obtain a silicon-based precursor powder.

[0056] Step 2: Take 5g of silicon-based precursor powder and place it in the first crucible, and place the first crucible in the constant temperature section of the tubular heating furnace; mix 6g of melamine and 2g of polyvinyl chloride and place them in the second crucible as an activator, and place the second crucible in the non-constant temperature section of the tubular heating furnace close to the air inlet; continuously introduce nitrogen into the tubular heating furnace with a nitrogen flow rate of 0.2L / min, and react at 1250°C for 10 hours to obtain gray-white silicon nitride nanopowder. The nitridation rate of the gray-white silicon nitride nanopowder is 100%, and the α-phase content is 89.1%.

[0057] Example 3

[0058] Step 1: 24 g of silicon powder, 6 g of Si3N4 diluent and 0.3 g of 50 nm Co catalyst are mixed, and 60 g of ethanol is used as a solvent. The mixed silicon powder, diluent, catalyst and solvent are mechanically wet-milled in a planetary ball mill using 120 g of silicon nitride grinding balls at a speed of 300 rpm for 6 hours. After obtaining a slurry, the slurry is dried at 70°C, cooled and sieved to obtain a silicon-based precursor powder.

[0059] Step 2: Take 5g of silicon-based precursor powder and place it in the first crucible, and place the first crucible in the constant temperature section of the tubular heating furnace; mix 2g of melamine and 6g of polyvinyl chloride and place them in the second crucible as an activator, and place the second crucible in the non-constant temperature section of the tubular heating furnace close to the air inlet; continuously introduce nitrogen into the tubular heating furnace with a nitrogen flow rate of 0.2L / min, and react at 1250°C for 12 hours to obtain gray-white silicon nitride nanopowder. The nitridation rate of the gray-white silicon nitride nanopowder is 100%, and the α-phase content is 86.2%.

[0060] Example 4

[0061] Step 1: 24 g of silicon powder, 6 g of Si3N4 diluent and 0.3 g of 50 nm Co catalyst are mixed, and 60 g of ethanol is used as a solvent. The mixed silicon powder, diluent, catalyst and solvent are mechanically wet-milled in a planetary ball mill using 120 g of silicon nitride grinding balls at a speed of 300 rpm for 6 hours. After obtaining a slurry, the slurry is dried at 70°C, cooled and sieved to obtain a silicon-based precursor powder.

[0062] Step 2: Take 5g of silicon-based precursor powder and place it in the first crucible, and place the first crucible in the constant temperature section of the tubular heating furnace; mix 3g of melamine and 3g of polyvinyl chloride and place them in the second crucible as an activator, and place the second crucible in the non-constant temperature section of the tubular heating furnace close to the air inlet; continuously introduce nitrogen into the tubular heating furnace at a nitrogen flow rate of 0.2L / min, and react at 1250°C for 15 hours to obtain gray-white silicon nitride nanopowder. The nitridation rate of the gray-white silicon nitride nanopowder is 100%, and the α-phase content is 93.7%.

[0063] Example 5

[0064] Step 1: 24 g of silicon powder, 6 g of Si3N4 diluent, 0.21 g of 50 nm Co catalyst, and 0.09 g of 1 μm Ni catalyst were mixed, and 60 g of ethanol was used as a solvent. The mixed silicon powder, diluent, catalyst, and solvent were mechanically wet-milled in a planetary ball mill using 120 g of silicon nitride grinding balls at a speed of 300 rpm for 6 hours. After obtaining the slurry, the slurry was dried at 70°C, cooled, and sieved to obtain a silicon-based precursor powder.

[0065] Step 2: Take 5g of silicon-based precursor powder and place it in the first crucible, and place the first crucible in the constant temperature section of the tubular heating furnace; mix 2g of melamine and 2g of polyvinyl chloride and place them in the second crucible as an activator, and place the second crucible in the non-constant temperature section of the tubular heating furnace close to the air inlet; continuously introduce nitrogen into the tubular heating furnace with a nitrogen flow rate of 0.2L / min, and react at 1250°C for 18 hours to obtain gray-white silicon nitride nanopowder. The nitridation rate of the gray-white silicon nitride nanopowder is 100%, and the α-phase content is 91.8%.

[0066] Example 6

[0067] Step 1: 21 g of silicon powder, 9 g of Si3N4 diluent and 0.15 g of 1 μm Co catalyst were mixed, and 60 g of ethanol was used as a solvent. The mixed silicon powder, diluent, catalyst and solvent were mechanically wet-milled in a planetary ball mill using 120 g of silicon nitride grinding balls at a speed of 300 rpm for 6 hours. After obtaining the slurry, it was dried at 70°C, cooled and sieved to obtain a silicon-based precursor powder.

[0068] Step 2: Take 5g of silicon-based precursor powder and place it in the first crucible, and place the first crucible in the constant temperature section of the tubular heating furnace; mix 4g of melamine and 4g of polyvinyl chloride and place them in the second crucible as an activator, and place the second crucible in the non-constant temperature section of the tubular heating furnace close to the air inlet; continuously introduce nitrogen into the tubular heating furnace with a nitrogen flow rate of 0.2L / min, and react at 1300℃ for 18 hours to obtain gray-white silicon nitride nanopowder. The nitridation rate of the gray-white silicon nitride nanopowder is 100%, and the α-phase content is 87.3%.

[0069] Example 7

[0070] Step 1: 21 g of silicon powder, 9 g of Si3N4 diluent, and 0.45 g of 1 μm Co catalyst are mixed, and 90 g of ethanol is used as a solvent. The mixed silicon powder, diluent, catalyst, and solvent are mechanically wet-milled in a planetary ball mill using 180 g of silicon nitride grinding balls at a speed of 400 rpm for 3 hours. After obtaining the slurry, it is dried at 70°C, cooled, and sieved to obtain a silicon-based precursor powder.

[0071] Step 2: Take 5g of silicon-based precursor powder and place it in the first crucible, and place the first crucible in the constant temperature section of the tubular heating furnace; mix 4g of melamine and 4g of polyvinyl chloride and place them in the second crucible as an activator, and place the second crucible in the non-constant temperature section of the tubular heating furnace close to the air inlet; continuously introduce nitrogen into the tubular heating furnace with a nitrogen flow rate of 0.2L / min, and react at 1250°C for 15 hours to obtain gray-white silicon nitride nanopowder. The nitridation rate of the gray-white silicon nitride nanopowder is 100%, and the α-phase content is 92.9%.

[0072] Example 8

[0073] Step 1: 21 g of silicon powder, 9 g of Si3N4 diluent and 0.6 g of 1 μm Co catalyst were mixed, and 60 g of ethanol was used as a solvent. The mixed silicon powder, diluent, catalyst and solvent were mechanically wet-milled in a planetary ball mill using 120 g of silicon nitride grinding balls at a speed of 200 rpm for 6 hours. After obtaining the slurry, it was dried at 70°C, cooled and sieved to obtain a silicon-based precursor powder.

[0074] Step 2: Take 5 g of silicon-based precursor powder and place it in the first crucible, and place the first crucible in the constant temperature section of the tubular heating furnace; mix 4 g of melamine and 4 g of polyvinyl chloride and place them in the second crucible as an activator, and place the second crucible in the non-constant temperature section of the tubular heating furnace close to the air inlet; continuously introduce nitrogen into the tubular heating furnace at a nitrogen flow rate of 0.2 L / min, and react at 1250°C for 15 hours to obtain gray-white silicon nitride nanopowder. The nitridation rate of the gray-white silicon nitride nanopowder is 100%, and the α-phase content is 91.9%.

[0075] Example 9

[0076] Step 1: 21g of silicon powder, 9g of Si3N4 diluent and 0.6g of 1 μm Ni catalyst are mixed, and 60g of ethanol is used as a solvent. The silicon powder, diluent, catalyst and solvent are mechanically wet-milled in a planetary ball mill with 120g of silicon nitride grinding balls at a speed of 300 rpm for 6 hours. After obtaining the slurry, it is dried at 70°C, cooled and sieved to obtain a silicon-based precursor powder.

[0077] Step 2: Take 5g of silicon-based precursor powder and place it in the first crucible, and place the first crucible in the constant temperature section of the tubular heating furnace; mix 4g of melamine and 4g of polyvinyl chloride and place them in the second crucible as an activator, and place the second crucible in the non-constant temperature section of the tubular heating furnace close to the air inlet; continuously introduce nitrogen into the tubular heating furnace at a nitrogen flow rate of 0.2L / min, and react at 1250°C for 24 hours to obtain gray-white silicon nitride nanopowder. The nitridation rate of the gray-white silicon nitride nanopowder is 100%, and the α-phase content is 91.4%.

[0078] By comparing the processes of preparing silicon nitride powder without using an activator, using melamine as an activator, and using polyvinyl chloride as an activator, it can be seen that under reaction conditions of 1250°C, when no melamine or polyvinyl chloride is added as an activator, although extending the reaction time can increase the nitridation rate to a certain extent, the nitridation reaction is still incomplete, and the β-Si3N4 content in the prepared aluminum nitride powder is relatively high. When melamine or polyvinyl chloride is used alone as an activator, the nitridation rate can be increased to a certain extent, but the silicon powder is still not completely nitrided, and the product contains a large amount of silicon carbide and silicon oxynitride impurities, which affects the quality of the silicon nitride powder.

[0079] When a mixture of melamine and polyvinyl chloride is added as an activator to the reaction process, the nitridation reaction time is significantly shortened at the same reaction temperature, the α-Si3N4 content in the resulting aluminum nitride powder increases, and the oxygen impurity content is significantly reduced. Therefore, by adding a mixture of melamine and polyvinyl chloride as an activator to prepare silicon nitride powder, the nitridation efficiency can be effectively improved, the reaction time can be shortened, and a silicon nitride powder with better performance can be obtained, thereby enhancing the quality and performance of the silicon nitride powder.

[0080] Figure 3 The XRD characteristic diagram of the product obtained by preparing silicon nitride powder in Example 1 and without using the activator represented by the mixture of melamine and polyvinyl chloride. Figure 3 As shown in the figure, when no activator is used, the product is a mixture of Si, α-Si3N4, and β-Si3N4; when melamine is used alone as the activator, the product consists of Si, α-Si3N4, β-Si3N4, and SiC; when polyvinyl chloride is used alone as the activator, the product consists of Si, α-Si3N4, β-Si3N4, SiC, and Si2N2O. When a mixture of melamine and polyvinyl chloride is used as the activator, the silicon powder is completely nitrided, and the product consists only of α-Si3N4 and β-Si3N4, with content of 92.1% and 7.9%, respectively.

[0081] Figure 4 The SEM image of the silicon nitride powder prepared according to Example 1 at a magnification of 10,000 times is shown in FIG. Figure 4 As can be seen from the SEM images in the figure, the silicon nitride product is composed of nanoparticles and nanowires.

[0082] Figure 5 The SEM image of the silicon nitride powder prepared according to Example 1 at a magnification of 20,000 times is shown in FIG. Figure 5 It can be seen that the silicon nitride product is composed of nanoparticles and nanowires.

[0083] Figure 6 and Figure 7 This is a SEM image of the silicon nitride powder prepared according to Example 1 at a magnification of 50,000 times, wherein Figure 6 and Figure 7 The following are SEM images of silicon nitride powder at different locations. Figure 6 and Figure 7 It can be seen that the silicon nitride product is composed of nanoparticles and nanowires.

[0084] It can be seen from this that according to the preparation method of silicon nitride powder based on continuous gas phase activation technology provided by the embodiment of the present disclosure, the intermediates such as hydrogen chloride obtained by the high-temperature decomposition of the activator enter the constant temperature zone along with the nitrogen introduced into the air inlet, which can completely activate the silicon powder during the synthesis process of the silicon nitride powder, thereby reducing the oxygen content in the silicon nitride powder and improving the quality of the silicon nitride powder.

[0085] In an embodiment of the present disclosure, a silicon nitride powder is further provided. The silicon nitride powder can be prepared according to the method of steps S110 to S120.

[0086] In the embodiment of the present disclosure, a mixture of melamine and polyvinyl chloride is placed as an activator in a non-constant temperature zone on the side of a tubular furnace close to the air inlet, and the activator can be continuously decomposed by utilizing the characteristic that the temperature curve of the non-constant temperature zone gradually increases. The intermediate of the high-temperature decomposition of the activator enters the constant temperature zone along with the nitrogen gas introduced into the air inlet, so that the silicon powder is fully activated during the entire synthesis process of the silicon nitride powder. A highly active gas phase is provided to supplement the nitrogen source, thereby reducing the number of high-energy chemical bonds that need to be broken, thereby lowering the reaction temperature and shortening the reaction time. Hydrogen chloride etches the elemental silicon and the oxide film on its surface to form Si-Cl and Si-O-Cl bonds, which have lower bond energy and higher reactivity, thereby lowering the reaction temperature and shortening the reaction time. Hydrogen chloride etches the oxide film on the surface of the silicon powder to form Si-O-Cl bonds, which are then nitrided to form silicon nitride powder, thereby reducing the oxygen content in the silicon nitride product. Hydrogen chloride etches elemental silicon and the oxide film on its surface, forming a gas-phase silicon-containing product. The gas-phase silicon-containing product reacts with N2 and a highly reactive gas-phase supplemental nitrogen source to generate α-Si3N4 whiskers via the VS growth mechanism, thereby increasing the α-phase content in the silicon nitride product. In summary, the method for preparing silicon nitride powder provided by the embodiments of the present disclosure features a simple operation process, shortened reaction time, reduced energy consumption, and improved product quality, facilitating industrial production.

[0087] Furthermore, the figures above are merely illustrative of the processes included in the methods according to exemplary embodiments of the present disclosure and are not intended to be limiting. It is readily understood that the processes illustrated in the figures above do not indicate or limit the temporal order of these processes. Furthermore, it is readily understood that these processes may be executed synchronously or asynchronously, for example, in multiple modules.

[0088] Those skilled in the art will readily appreciate other embodiments of the present disclosure after considering the specification and practicing the invention 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 techniques in the art not disclosed herein. The description and examples are to be considered as exemplary only, with the true scope and spirit of the present disclosure being indicated by the appended claims.

[0089] 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 can 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: Silicon powder, diluent and catalyst are mixed in a preset ratio, ethanol is used as a solvent, the mixed silicon powder, diluent, catalyst and solvent are ball-milled in a ball mill with silicon nitride grinding balls to obtain a slurry, and the slurry is dried, cooled and sieved to obtain a silicon-based precursor powder; the particle size of the silicon powder is 1-2 μm; The silicon-based precursor powder is placed in a constant temperature section of a tubular heating furnace, and a mixture of melamine and polyvinyl chloride is placed as an activator in a non-constant temperature section of the tubular heating furnace close to an air inlet. Nitrogen is continuously introduced into the tubular heating furnace to react at a target temperature to obtain the silicon nitride powder; the mass ratio of the melamine to the polyvinyl chloride in the mixture is 1:(0.33-3); the mass ratio of the silicon-based precursor powder to the activator is 1:(0.8-1.6); wherein the target temperature is 1250-1300°C, and the reaction time for the reaction at the target temperature is 10-24 hours.

2. The method for preparing silicon nitride powder according to claim 1, characterized in that: The purity of the silicon powder is ≥99.995%.

3. The method for preparing silicon nitride powder according to claim 1, characterized in that: The diluent is silicon nitride powder, the purity of the diluent is greater than 99.9%, and the α-phase content is greater than 95wt%.

4. The method for preparing silicon nitride powder according to claim 1, characterized in that: The catalyst is one or both of Co and Ni, and the particle size of the catalyst is 50 nm to 1 μm.

5. The method for preparing silicon nitride powder according to claim 1, characterized in that: The mass ratio of the silicon powder, diluent, catalyst, solvent and silicon nitride grinding ball is 1:(0.25-0.43):(0.00625-0.025):(2.5-5):(5-7.5).

6. The method for preparing silicon nitride powder according to claim 1, characterized in that: The ball milling mixing is a ball milling mechanical wet mixing, the rotation speed of the ball milling mixing is 200-400 rpm, and the ball milling mixing time is 3-6 hours.

7. A silicon nitride powder, characterized in that: The silicon nitride powder is prepared according to the method for preparing silicon nitride powder according to any one of claims 1 to 6.

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