Preparation method of silicon nitride powder and silicon nitride powder

Abstract

The embodiment of the invention provides a preparation method of silicon nitride powder and the silicon nitride powder, and relates to the technical field of silicon nitride.The method comprises the steps that silicon powder, a diluent and a catalyst are mixed according to a preset proportion, ethyl alcohol is used as a solvent, and a mixture is obtained; the preparation method comprises the following steps: carrying out ball-milling mixing on proportioned silicon powder, a diluent, a catalyst and a solvent in a ball mill through silicon nitride grinding balls to obtain slurry, and drying, cooling and sieving the slurry to obtain silicon-based precursor powder; the preparation method comprises the following steps: putting silicon-based precursor powder into a constant-temperature section of a tubular heating furnace, putting a mixture of melamine and polyvinyl chloride as an activating agent into a non-constant-temperature section, close to one side of an air inlet, of the tubular heating furnace, continuously introducing nitrogen into the tubular heating furnace, and reacting at a target temperature to obtain the silicon nitride powder. The quality of the silicon nitride powder can be improved.

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 basis for the preparation of high-performance Si3N4 ceramic products. For the preparation of high-performance Si3N4 ceramic products with high bending strength and high thermal conductivity, Si3N4 powder not only needs to be of high purity, but also needs to meet the indicators of low oxygen, low carbon, ultrafine, high α phase, etc. These indicators will directly determine the defects (lattice oxygen, pores, etc.), impurities and grain boundary size in Si3N4 ceramics, thereby affecting thermal conductivity and bending 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 the problem of poor quality of silicon nitride powder caused by limitations and defects of related technologies to at least a certain extent.

[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 according to a preset ratio, using ethanol as a solvent, ball milling the mixed silicon powder, the diluent, the catalyst and the solvent in a ball mill with silicon nitride grinding balls to obtain a slurry, and drying, cooling and sieving the slurry to obtain a silicon-based precursor powder; 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 to react at a target temperature to obtain the silicon nitride powder.

[0005] In an exemplary embodiment of the present disclosure, the target temperature is 1250-1300° C., and the reaction time for the reaction at the target temperature is 10-24 hours.

[0006] 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%.

[0007] 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 95wt%.

[0008] 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.

[0009] 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):(0.625%~2.5%):(2.5~5):(5~7.5).

[0010] 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 time of the ball milling mixing is 3-6 hours.

[0011] 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).

[0012] 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).

[0013] According to one aspect of the present disclosure, there is provided a silicon nitride powder, wherein the silicon nitride powder is prepared according to any one of the above-mentioned methods for preparing silicon nitride powder.

[0014] In the technical solution provided 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 near the air inlet side of a tube furnace, and the activator can be continuously decomposed by utilizing the characteristic that the temperature curve in 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 introduced into the air inlet, so that the silicon powder is fully activated during the whole process of the synthesis of the silicon nitride powder. On the one hand, 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 reducing 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 reducing the reaction temperature and shortening the reaction time. Hydrogen chloride etches the oxide film on the surface of the silicon powder, and then nitridation forms 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 to form a gas phase silicon-containing product, which reacts with N2 and a highly active gas phase supplementary nitrogen source to generate α-Si3N4 whiskers through 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 embodiment of the present disclosure has a simple operation process, shortens the reaction time, reduces energy consumption, and is conducive to industrial production.

[0015] 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

[0016] 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.

[0017] Figure 1 A flow chart schematically shows a method for preparing silicon nitride powder in an embodiment of the present disclosure.

[0018] Figure 2 A schematic diagram of a tubular heating furnace in an embodiment of the present disclosure is schematically shown.

[0019] Figure 3 1 is an XRD diagram of silicon nitride powder prepared according to Example 1 without using an activator of the mixture composition.

[0020] Figure 4 This is a schematic diagram of a SEM image of the silicon nitride powder prepared according to Example 1 in the disclosed embodiment when magnified 10,000 times.

[0021] Figure 5 This is a schematic diagram of a SEM image of the silicon nitride powder prepared according to Example 1 in the disclosed embodiment when magnified 20,000 times.

[0022] Figure 6 This is a schematic diagram of a SEM image of the silicon nitride powder prepared according to Example 1 in the disclosed embodiment when magnified 50,000 times.

[0023] Figure 7 This is a schematic diagram of another SEM image of the silicon nitride powder prepared according to Example 1 in the disclosed embodiment when magnified 50,000 times. DETAILED DESCRIPTION

[0024] 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 one or more embodiments in any suitable manner. 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, components, devices, 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.

[0025] The terms "a", "an", "the" and "said" used in this specification are used to indicate the presence of one or more elements / components, etc.; the terms "including" and "having" are used to express an open-ended inclusion and mean that there may be additional elements / components, etc. in addition to the listed elements / components, etc.; the terms "first" and "second" etc. are used only as labels and are not intended to limit the quantity of their objects.

[0026] 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: 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 and mixed in a ball mill using silicon nitride grinding balls, and the slurry is dried, cooled and sieved to obtain a silicon-based precursor powder; In step S120, the silicon-based precursor powder is placed in the constant temperature section of the 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.

[0027] Next, the method for preparing the silicon nitride powder in the embodiment of the present disclosure is described in detail.

[0028] 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 and mixed 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.

[0029] In the disclosed embodiments, the particle size of silicon powder can be 1 μm, 2 μm, 1.5 μm, etc. The purity of 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): (0.625%~2.5%): (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.

[0030] After the silicon powder, diluent, catalyst and solvent are wet-mixed by ball milling in a ball mill using silicon nitride grinding balls, a slurry can be obtained, and the slurry can be further dried, cooled and sieved to obtain a silicon-based precursor powder.

[0031] 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 close to the air inlet. Nitrogen is continuously introduced into the tubular heating furnace to react at the target temperature to obtain the silicon nitride powder.

[0032] In the disclosed embodiment, 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 arranged on the side close to the air inlet, and the constant temperature section is arranged 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 .

[0033] 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).

[0034] After placing the silicon-based precursor powder and the activator at the corresponding positions of the 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℃, and the reaction time at the target temperature after introducing nitrogen is 10~24 hours.

[0035] In the disclosed embodiment, a mixture of melamine and polyvinyl chloride is placed as an activator in a non-constant temperature zone near the air inlet of a tubular furnace, and the activator can be continuously decomposed by utilizing the characteristic that the temperature curve in the non-constant temperature zone gradually increases. 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 reducing 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 reducing 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 to form a gas phase silicon-containing product, which reacts with N2 and a highly active gas phase supplementary nitrogen source to generate α-Si3N4 whiskers through the VS growth mechanism, thereby increasing the α phase content in the silicon nitride product and improving the quality of the silicon nitride powder. In addition, the method provided in the embodiment of the present disclosure has a simple operation process, shortens the reaction time, reduces energy consumption, and is conducive to industrial production.

[0036] On this basis, the method for preparing the silicon nitride powder disclosed in the present invention can be specifically described in combination with the embodiments.

[0037] 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: Step 1: 24 g of silicon powder, 6 g of Si3N4 diluent and 0.3 g of 50 nm Co catalyst are mixed, 60 g of ethanol is used as solvent, and the silicon powder, diluent, catalyst and solvent are mechanically wet mixed by ball milling in a planetary ball mill with 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.

[0038] Step 2: Take 5g of silicon-based precursor powder and place it in a crucible, and place the crucible in the constant temperature section of a tubular heating furnace; continue to introduce nitrogen into the tubular heating furnace, with a nitrogen flow rate of 0.2 L / min, and react at 1250°C for 12 hours. The obtained product is a brown powder, which is a mixture of Si, α-Si3N4 and β-Si3N4. The contents of Si, α-Si3N4 and β-Si3N4 are 21.8%, 68.8% and 9.4%, respectively. Extend the reaction time to 18 hours, and the obtained product is an off-white powder, which is still a mixture of Si, α-Si3N4 and β-Si3N4, with the contents of Si, α-Si3N4 and β-Si3N4 being 1.4%, 87.3% and 11.3%, respectively; the oxygen content in the product is 5.15%. Continue to extend the reaction time to 30 hours, and the physical phase of the product remains basically unchanged.

[0039] 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: Step 1: 24 g of silicon powder, 6 g of Si3N4 diluent and 0.3 g of 50 nm Co catalyst are mixed, 60 g of ethanol is used as solvent, and the silicon powder, diluent, catalyst and solvent are mechanically wet mixed by ball milling in a planetary ball mill with 120 g of silicon nitride grinding balls at a speed of 300 rpm for 6 hours. After obtaining the slurry, the slurry is dried at 70°C, cooled and sieved to obtain a silicon-based precursor powder.

[0040] 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; put 8g of melamine as an activator in the second crucible, and place the second crucible in the non-constant temperature section of the tubular heating furnace near the air inlet. Continuously introduce nitrogen into the tubular heating furnace at a nitrogen flow rate of 0.2 L / min, react at 1250°C for 10 hours, and obtain a gray-white powder product, which is composed of Si, α-Si3N4, β-Si3N4 and SiC.

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

[0042] 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, react at 1250°C for 10 hours, and obtain a gray-white powder product, which is composed of Si, α-Si3N4, β-Si3N4, SiC and Si2N2O.

[0043] In order 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 method for preparing silicon nitride powder is described in detail below in conjunction with an embodiment.

[0044] 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 silicon-based precursor to activator, target temperature, reaction time at target temperature, and the mass ratio of silicon powder, diluent, catalyst, solvent and silicon nitride grinding balls can be adjusted.

[0045] Example 1 Step 1: 24 g of silicon powder, 6 g of Si3N4 diluent and 0.3 g of 50 nm Co catalyst are mixed, 60 g of ethanol is used as solvent, and the mixed silicon powder, diluent, catalyst and solvent are mechanically wet mixed by ball milling in a planetary ball mill with 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.

[0046] 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 with a nitrogen flow rate of 0.2 L / min, 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%.

[0047] Example 2 Step 1: 24 g of silicon powder, 6 g of Si3N4 diluent and 0.3 g of 50 nm Co catalyst are mixed, 60 g of ethanol is used as solvent, and the silicon powder, diluent, catalyst and solvent are mechanically wet mixed by ball milling in a planetary ball mill with 120 g of silicon nitride grinding balls at a speed of 300 rpm for 6 hours. After obtaining the 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; 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, 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%.

[0049] Example 3 Step 1: 24 g of silicon powder, 6 g of Si3N4 diluent and 0.3 g of 50 nm Co catalyst are mixed, 60 g of ethanol is used as solvent, and the silicon powder, diluent, catalyst and solvent are mechanically wet mixed by ball milling in a planetary ball mill with 120 g of silicon nitride grinding balls at a speed of 300 rpm for 6 hours. After obtaining the slurry, the slurry is dried at 70°C, cooled and sieved to obtain a silicon-based precursor powder.

[0050] 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, 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%.

[0051] Example 4 Step 1: 24 g of silicon powder, 6 g of Si3N4 diluent and 0.3 g of 50 nm Co catalyst are mixed, 60 g of ethanol is used as solvent, and the silicon powder, diluent, catalyst and solvent are mechanically wet mixed by ball milling in a planetary ball mill with 120 g of silicon nitride grinding balls at a speed of 300 rpm for 6 hours. After obtaining the slurry, the slurry is dried at 70°C, cooled and sieved to obtain a silicon-based precursor powder.

[0052] 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 3 g of melamine and 3 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 with a nitrogen flow rate of 0.2 L / min, 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%.

[0053] Example 5 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 are prepared, and 60 g of ethanol is used as a solvent. The prepared silicon powder, diluent, catalyst, and solvent are mechanically wet-mixed by ball milling 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 is dried at 70°C, cooled, and sieved to obtain a silicon-based precursor powder.

[0054] 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 2 g of melamine and 2 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 with a nitrogen flow rate of 0.2 L / 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%.

[0055] Example 6 Step 1: 21 g of silicon powder, 9 g of Si3N4 diluent and 0.15 g of 1 μm Co catalyst are mixed, 60 g of ethanol is used as solvent, and the silicon powder, diluent, catalyst and solvent are mechanically wet mixed by ball milling in a planetary ball mill with 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.

[0056] 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 with a nitrogen flow rate of 0.2 L / min, react at 1300°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 87.3%.

[0057] Example 7 Step 1: 21 g of silicon powder, 9 g of Si3N4 diluent, and 0.45 g of 1 μm Co catalyst are prepared, and 90 g of ethanol is used as a solvent. The prepared silicon powder, diluent, catalyst, and solvent are mechanically wet-mixed by ball milling 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.

[0058] 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 with a nitrogen flow rate of 0.2 L / min, 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%.

[0059] Example 8 Step 1: 21 g of silicon powder, 9 g of Si3N4 diluent and 0.6 g of 1 μm Co catalyst are mixed, 60 g of ethanol is used as solvent, and the silicon powder, diluent, catalyst and solvent are mechanically wet mixed by ball milling in a planetary ball mill with 120 g of silicon nitride grinding balls at a speed of 200 rpm for 6 hours. After obtaining the slurry, it is dried at 70°C, cooled and sieved to obtain a silicon-based precursor powder.

[0060] 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 with a nitrogen flow rate of 0.2 L / min, 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%.

[0061] Example 9 Step 1: 21 g of silicon powder, 9 g of Si3N4 diluent and 0.6 g of 1 μm Ni catalyst are mixed, 60 g of ethanol is used as solvent, and the mixed silicon powder, diluent, catalyst and solvent are mechanically wet mixed by ball milling in a planetary ball mill with 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.

[0062] 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 with a nitrogen flow rate of 0.2 L / min, 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%.

[0063] By comparing the process of preparing silicon nitride powder without using an activator, using melamine as an activator, and using polyvinyl chloride as an activator, it can be learned that under the reaction conditions of 1250°C, when melamine or polyvinyl chloride is not added as an activator, although the nitridation rate can be increased to a certain extent by extending the reaction time, the nitridation reaction is still incomplete, and the content of β-Si3N4 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 more silicon carbide and silicon oxynitride impurities, which affects the quality of the silicon nitride powder.

[0064] After adding the mixture of melamine and polyvinyl chloride as an activator to the reaction process, at the same reaction temperature, the nitridation reaction time is significantly shortened, the α-Si3N4 content in the generated aluminum nitride powder is increased, and the oxygen impurity content is significantly reduced. Therefore, by adding the 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 silicon nitride powder with better performance can be obtained, thereby improving the quality and performance of silicon nitride powder.

[0065] 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 an activator, the product consists of Si, α-Si3N4, β-Si3N4 and SiC; when polyvinyl chloride is used alone as an activator, the product consists of Si, α-Si3N4, β-Si3N4, SiC and Si2N2O. When a mixture of melamine and polyvinyl chloride is used as an activator, the silicon powder is completely nitrided and the product consists only of α-Si3N4 and β-Si3N4, with contents of 92.1% and 7.9% respectively.

[0066] 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 From the SEM images in the figure, it can be seen that the silicon nitride product is composed of nanoparticles and nanowires.

[0067] 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.

[0068] Figure 6 and Figure 7 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 SEM images of silicon nitride powder at different locations are shown. Figure 6 and Figure 7 It can be seen that the silicon nitride product is composed of nanoparticles and nanowires.

[0069] 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.

[0070] In the embodiment of the present disclosure, a silicon nitride powder is also provided. The silicon nitride powder can be prepared according to the method of step S110 to step S120.

[0071] In the disclosed embodiment, a mixture of melamine and polyvinyl chloride is placed as an activator in a non-constant temperature zone near the air inlet of a tube furnace, and the activator can be continuously decomposed by utilizing the characteristic that the temperature curve in 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 introduced from the air inlet, so that the silicon powder is fully activated during the whole process of synthesizing 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 reducing 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 reducing 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 to form a gas phase silicon-containing product, which reacts with N2 and a highly active gas phase supplemental nitrogen source to generate α-Si3N4 whiskers through 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 in the embodiments of the present disclosure has a simple operation process, shortened reaction time, reduced energy consumption, and improved product quality, which is conducive to industrial production.

[0072] 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.

[0073] 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 modification, use or adaptation of the present disclosure, which follows the general principles of the present disclosure and includes common knowledge or customary techniques in the art that are not disclosed in the present disclosure. The specification and examples are intended to be exemplary only, and the true scope and spirit of the present disclosure are indicated by the appended claims.

[0074] 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: 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 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 to react at a target temperature to obtain the silicon nitride powder.

2. The method for preparing silicon nitride powder according to claim 1, characterized in that: The target temperature is 1250-1300° C., and the reaction time for the reaction at the target temperature is 10-24 hours.

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

4. 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%.

5. 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.

6. 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):(0.625%-2.5%):(2.5-5):(5-7.5).

7. 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.

8. The method for preparing silicon nitride powder according to claim 1, characterized in that: The mass ratio of the melamine to the polyvinyl chloride in the mixture is 1: (0.33-3).

9. The method for preparing silicon nitride powder according to claim 1, characterized in that: The mass ratio of the silicon-based precursor to the activator is 1:(0.8~1.6).

10. 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 9.

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