CN107954723B - Preparation method of alpha-phase silicon nitride powder - Google Patents

Preparation method of alpha-phase silicon nitride powder Download PDF

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CN107954723B
CN107954723B CN201711372158.1A CN201711372158A CN107954723B CN 107954723 B CN107954723 B CN 107954723B CN 201711372158 A CN201711372158 A CN 201711372158A CN 107954723 B CN107954723 B CN 107954723B
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silicon nitride
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nitride powder
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CN107954723A (en
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谢志鹏
胡尊兰
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Zhejiang Yingdesai Semiconductor Materials Co ltd
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Tsinghua University
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Abstract

The invention discloses a preparation method of alpha-phase silicon nitride powder. The preparation method comprises the following steps: (1) reacting silicon tetrachloride with liquid ammonia in a two-liquid phase interface of an organic solvent and the liquid ammonia to obtain precursor silicon imine; the organic solvent is toluene or a mixture of toluene and xylene; (2) carrying out thermal decomposition on the silicon imine obtained in the step (1) to obtain amorphous silicon nitride powder; (3) and (3) carrying out crystallization treatment on the amorphous silicon nitride powder in the step (2) to obtain the alpha-phase silicon nitride powder. In the method, silicon tetrachloride reacts with liquid ammonia at the two liquid phase interfaces of the organic solvent and the liquid ammonia, the reaction rate can be slowed down by diluting the silicon tetrachloride at lower temperature and controlling the feeding rate, the synthesis of the precursor is effectively controlled, the precursor is prevented from forming aggregates, the reaction area is enlarged by the interface reaction, and NH is accelerated4Dissolving Cl in liquid ammonia; the alpha-Si prepared by the invention3N4The powder has controllable crystal form and appearance, uniform grain size distribution and simple process, and can meet the production requirement.

Description

Preparation method of alpha-phase silicon nitride powder
Technical Field
The invention relates to a method for preparing silicon nitride powder by a precursor method, in particular to a method for preparing alpha-phase silicon nitride powder, belonging to the field of inorganic nonmetal powder materials.
Background
In the high-temperature engineering material, the silicon nitride ceramic has excellent performance. The mechanical property is good, the hardness is high, and the elastic modulus is high; the thermal property is stable, the thermal expansion coefficient is small, and the high temperature resistance is realized; the chemical stability is good, and the corrosion is not easy to occur; good insulation and the like. The alloy is increasingly applied to chemical corrosion-resistant devices, high-temperature-resistant and wear-resistant parts of engines, automobile bearings, cutting tools and the like.
The silicon nitride ceramic sintering starting powder has both an alpha phase and a beta phase. The starting powder has a significant influence on the structural and mechanical properties of the silicon nitride ceramic. alpha-Si3N4Has high solubility and excellent sintering activity. From alpha-Si3N4Dissolving precipitated beta-Si3N4The crystal grains have long columnar appearance and larger length-diameter ratio, and are composed of beta-Si3N4Powder firingSi of junction3N4The material still keeps equiaxial crystal form and has poor mechanical property. Therefore, the high alpha-phase silicon nitride powder is obtained, and has important significance for preparing silicon nitride ceramics.
At present, the main production methods of silicon nitride powder include a silicon powder direct nitriding method, a carbothermic method, a self-propagating method and the like. The direct silicon powder nitriding method realizes industrial large-scale production, but the alpha phase content is difficult to control in the method; silicon nitride powder prepared by carbothermic method, residual SiO2Is not easy to remove; the self-propagating method has the advantages that the reaction rate is not easy to control, and the obtained powder has high impurity content. Further, there are a sol-gel method, a high-temperature gas phase method, and the like. These methods have high cost, strict requirements on raw materials, low yield and are not suitable for large-scale production.
Disclosure of Invention
The invention aims to provide a preparation method of alpha-phase silicon nitride powder, which can obtain silicon nitride powder with high alpha-phase, long columnar and equiaxed crystal forms, low impurity content and low oxygen content by controlling the feeding mode, the feeding speed, the thermal decomposition and crystallization treatment conditions.
The invention provides a preparation method of alpha-phase silicon nitride powder, which comprises the following steps:
(1) reacting silicon tetrachloride with liquid ammonia in two liquid phase interfaces of an organic solvent and the liquid ammonia to obtain precursor amino silicon or silicon imine; the organic solvent is toluene or a mixture of toluene and xylene;
(2) carrying out thermal decomposition on the silicon imine obtained in the step (1) to obtain amorphous silicon nitride powder;
(3) and (3) carrying out crystallization treatment on the amorphous silicon nitride powder in the step (2) to obtain the alpha-phase silicon nitride powder.
In the preparation method, in the step (1), in the mixture of toluene and xylene, the volume ratio of toluene to xylene may be (1-9): 1, specifically can be (1-3): 1. 1: 1 or 3: 1.
the preparation method comprises the step (1), wherein the method comprises the following steps of feeding materials into a reaction kettle before the reaction: placing the organic solvent and the liquid ammonia in a reaction kettle, and standing for layering; and adding the silicon tetrachloride solution diluted by the organic solvent into the organic solvent, and diffusing the silicon tetrachloride to an interface obtained by standing and layering to finish the feeding.
The volume ratio of the organic solvent to the liquid ammonia may be 4: (1-6), specifically 4: 1.
the volume concentration of silicon tetrachloride in the silicon tetrachloride solution diluted by the organic solvent can be 1-25%, and specifically can be 1-10%, 5% or 10%.
The adding speed of the silicon tetrachloride solution diluted by the organic solvent can be 1-5 mL/min, and specifically can be 3-5 mL/min, 3mL/min or 5 mL/min.
The silicon tetrachloride solution diluted by the organic solvent can be pumped into the reaction kettle in a manner of pressurizing the feeding tank.
The reaction is carried out under stirring conditions; the stirring adopts a straight blade type stirring paddle. The stirring speed can be 50-200 revolutions per minute, and specifically can be 70-100 revolutions per minute, 70 revolutions per minute or 100 revolutions per minute.
The reaction temperature can be-35 to-60 ℃, and specifically can be-45 to-55 ℃, 45 ℃, 50 ℃ or-55 ℃; the time can be 0.5-3 h, specifically 1h and 1.5 h. Specifically, the low-temperature condition of the reaction is realized by low-temperature secondary refrigerant circulation, and heat preservation is carried out through a vacuum heat preservation layer on the outer layer of the cavity of the reaction kettle; the secondary refrigerant in the secondary refrigerant circulating layer is ethanol or glycol water solution with the volume concentration of 50-60%.
The method also comprises the steps of washing, drying and removing impurities of the obtained product in sequence after the reaction is finished. The washing can be carried out in a reaction kettle by adopting liquid ammonia. The drying can be vacuum drying, and the temperature can be 100-120 ℃, and particularly can be 120 ℃; the time can be 2-8 h, specifically 4-6 h, 4h or 6 h; the vacuum degree can be 6.7 multiplied by 10-1～6.7×10-2Specifically, it may be 7 × 10-2Pa. The impurity removal is to remove residual ammonium chloride and organic solvent, and the specific steps can be as follows: heating the dried product in nitrogen atmosphere to warmThe temperature can be 360-800 ℃, and specifically can be 600 ℃; the time can be 2-4 h, specifically 2 h.
The method also comprises a step of recovering liquid ammonia and the organic solvent after the reaction is finished, and the liquid ammonia and the organic solvent can be recovered by distillation by utilizing different boiling points of the organic solvent and the liquid ammonia. And adding the liquid ammonia and the organic solvent into the reaction kettle again to carry out the reaction.
In the preparation method, in the step (2), the thermal decomposition can be performed in a nitrogen atmosphere, and the temperature can be 900-1200 ℃, particularly 1000 ℃; the time can be 2-4 h, specifically 2 h; specifically, the nitrogen atmosphere can be flowing nitrogen or the pressure of the nitrogen is 0.2-4 Mpa.
In the preparation method, in the step (3), the crystallization treatment may be performed in a nitrogen atmosphere, and the temperature may be 1300 to 1600 ℃, specifically 1300 to 1550 ℃, 1350 ℃, 1400 ℃ or 1550 ℃; the time can be 2-12 h, specifically 2-12 h, 2h, 6h or 12 h. Specifically, the nitrogen atmosphere can be flowing nitrogen or the pressure of the nitrogen is 0.2-4 Mpa.
In the above-mentioned preparation method, in the step (3), the crystallization treatment may be performed in the presence of an additive; the additive can be Fe powder, Ni powder, Cu powder or alpha-Si3N4Pulverizing; the mass of the additive can be 0.1-5 percent, such as 5 percent, of the sum of the mass of the amorphous silicon nitride powder and the mass of the additive; the alpha-Si3N4The diameter of the powder may be 200-500 nm, such as 200 nm.
The invention further provides the alpha-phase silicon nitride powder prepared by the preparation method. The crystal form of the alpha-phase silicon nitride powder may be at least one of a long columnar form, a long segment form, and an equiaxed form. The alpha-phase silicon nitride powder is micron-sized.
The invention also provides a reaction kettle used in the preparation method of the alpha-phase silicon nitride powder, which comprises a closed reaction cavity; a silicon tetrachloride feeding pipe is arranged in the reaction cavity; a straight blade type stirring paddle is arranged in the reaction cavity; the reaction cavity is sequentially provided with a secondary refrigerant circulation layer and a vacuum heat-insulating layer from inside to outside.
The secondary refrigerant in the secondary refrigerant circulating layer can be ethanol or glycol aqueous solution with the volume concentration of 50-60%.
The reaction kettle also comprises a silicon tetrachloride feeding tank for storing a silicon tetrachloride solution diluted by an organic solvent, and the silicon tetrachloride solution diluted by the organic solvent is added into an interface obtained by standing and layering in the reaction cavity through the silicon tetrachloride feeding pipe.
The invention has the beneficial effects that:
(1) the low temperature condition of-35 to-60 ℃ is realized by adopting a secondary refrigerant circulating in a jacket of the reaction kettle. By adopting the circulation mode, the internal structure of the equipment can be simplified, the reaction vessel is easy to clean, and the operation outside the equipment is simpler. Stirring in the kettle, and using a straight blade type stirring paddle, enabling liquid to flow radially, and keeping a liquid phase interface stable;
(2) liquid ammonia is used as reaction raw material and detergent, so that the introduction of impurities can be reduced, the filtration and cleaning processes are carried out in a closed reaction kettle, and NH is added4Dissolving Cl in liquid ammonia to form NH4Cl·3NH3The formation of ammonium chloride smoke or aggregates is avoided, and the operation is simple;
(3) the reaction of silicon tetrachloride and liquid ammonia is violent, the reaction rate can be slowed down by diluting the silicon tetrachloride and controlling the feeding rate at lower temperature, the synthesis of the precursor is effectively controlled, the precursor is prevented from forming aggregates, the reaction area is enlarged by the interface reaction, and NH is accelerated4Dissolving Cl in liquid ammonia;
(4) the reaction raw materials are industrial by-product silicon tetrachloride and industrially easily-obtained liquid ammonia, and the liquid ammonia and the organic solvent after reaction can be recycled;
(5) the crystal form, the morphology and the particle size of the silicon nitride can be accurately controlled by adjusting parameters such as atmosphere, temperature, heat preservation time, additives and the like in the thermal decomposition and crystallization processes;
(6) the alpha-Si prepared by the invention3N4And (3) powder. The crystal form and the appearance are controllable, the grain size distribution is uniform, the process is simple, and the production requirement can be met.
Drawings
FIG. 1 is a schematic view of the structure of a reaction vessel used in the method of the present invention.
The respective labels in FIG. 1 are as follows:
the system comprises a reaction cavity 1, a silicon tetrachloride feeding pipe 2, a straight blade type stirring paddle 3, a secondary refrigerant circulating layer 4, a vacuum heat-insulating layer 5, a reaction kettle air release valve 6, a rupture disk 7, a reaction kettle pressure gauge 8, a thermometer 9, a feeding tank 10 (a silicon tetrachloride organic solution storage tank), a nitrogen valve 11, a liquid ammonia feeding valve 12, a secondary refrigerant inlet 13, a reaction kettle liquid outlet 14 and a secondary refrigerant outlet 15.
FIG. 2 is a schematic view of the process for preparing alpha-phase silicon nitride powder according to the present invention.
FIG. 3 is an X-ray diffraction pattern of the amorphous silicon nitride powder prepared in example 1.
FIG. 4 is an X-ray diffraction pattern of the α -phase silicon nitride powder prepared in example 1.
FIG. 5 is an SEM photograph of the alpha-phase silicon nitride powder prepared in example 1.
FIG. 6 is an X-ray diffraction pattern of the α -phase silicon nitride powder prepared in example 2.
FIG. 7 is an SEM photograph of the alpha-phase silicon nitride powder prepared in example 2.
FIG. 8 is an X-ray diffraction pattern of the α -phase silicon nitride powder prepared in example 3.
FIG. 9 is an SEM photograph of the alpha-phase silicon nitride powder prepared in example 3.
Detailed Description
The experimental procedures used in the following examples are all conventional procedures unless otherwise specified.
Materials, reagents and the like used in the following examples are commercially available unless otherwise specified.
The purity of toluene, liquid ammonia and silicon tetrachloride used in the following examples was > 99.5%, 99.99% and 99.5%.
As shown in FIG. 1, the reaction vessel used in the following examples comprises a reaction chamber 1 with an interior made of an anticorrosive material; a silicon tetrachloride feeding tank 10 is arranged above the reaction cavity 1, and a silicon tetrachloride solution diluted by an organic solvent in the feeding tank 10 is added into an interface obtained by standing and layering in the reaction cavity 1 through a silicon tetrachloride feeding pipe 2 arranged in the reaction cavity 1; a straight blade type stirring paddle 3 is arranged in the reaction cavity 1; the reaction cavity 1 is sequentially provided with a secondary refrigerant circulation layer 4 and a vacuum heat-insulating layer 5 from inside to outside; the secondary refrigerant used in the secondary refrigerant circulation layer 4 is ethanol or glycol water solution with the volume concentration of 50-60%; a reaction kettle vent valve 6, a rupture disk 7, a thermometer 9, a nitrogen valve 11 and a liquid ammonia feed valve 12 are respectively arranged above the reaction cavity 1, and a reaction kettle pressure gauge 8 is arranged on a pipeline arranged on the rupture disk; the secondary refrigerant circulating layer is provided with a secondary refrigerant inlet 13 and a secondary refrigerant outlet 15; the bottom of the reaction cavity 1 is provided with a reaction kettle liquid outlet 14.
When the device is used, the secondary refrigerant is added into the secondary refrigerant circulation layer 4 through the secondary refrigerant inlet 13, the temperature in the reaction cavity 1 is kept through the vacuum insulation layer 5, the temperature in the cavity is controlled to be-35 to-60 ℃, and the specific temperature can be read by the thermometer 9; placing an organic solvent and liquid ammonia in a reaction kettle, opening a nitrogen valve 11 after standing and layering, adding a silicon tetrachloride solution diluted by the organic solvent into an interface obtained by standing and layering in a reaction cavity 1 from a feeding pipe 2 in a nitrogen pressurization mode, closing the nitrogen valve 11, and opening a vent valve 6 of the reaction kettle to release nitrogen; starting the straight blade type stirring paddle 3, and reacting silicon tetrachloride with liquid ammonia at the two liquid phase interfaces of the organic solvent and the liquid ammonia; liquid ammonia is used in the reaction, the liquid ammonia is easy to gasify, the pressure in the reaction kettle is increased, when the pressure exceeds a certain pressure value, the rupture disk 6 is ruptured instantly, the pressure is released, and the explosion of the reaction kettle is avoided; the reaction kettle pressure gauge 8 is used for detecting the pressure in the reaction kettle, can timely operate to deflate, avoids overhigh pressure in the kettle and avoids danger; after the reaction, opening a liquid ammonia feed valve 12, adding liquid ammonia into the cavity of the reaction kettle to wash the reaction product, and filtering the reaction product through a filter element at a liquid outlet 14 of the reaction kettle; the coolant and refrigerant are discharged from the coolant outlet 15.
Example 1 preparation of alpha-phase silicon nitride powder
The alpha-phase silicon nitride powder is prepared according to the flow chart shown in fig. 2, and the specific steps are as follows:
(1) controlling the temperature in the reaction kettle to be-45 ℃, and adjusting the volume to be 200 DEG CThe mixed solution of toluene and xylene with the volume of 200 and liquid ammonia with the volume of 100 are placed in a reaction kettle shown in figure 1 and are kept stand for layering; mixing silicon tetrachloride with the volume of 5 and toluene with the volume of 95, putting the opening of a silicon tetrachloride feeding pipe into a toluene layer in a reaction kettle, the mixed solution of silicon tetrachloride and toluene is injected into the toluene layer by pressurizing nitrogen in the feeding tank, controlling the feeding speed to be 3mL/min, enabling silicon tetrachloride to diffuse to a liquid phase interface of toluene and liquid ammonia, continuously stirring by a stirring paddle at the rotating speed of 70 r/min, reacting silicon tetrachloride and liquid ammonia at the interface of toluene and liquid ammonia at the reaction temperature of-45 ℃ for 1h to generate white flocculent powder, filtering the white powder, through a filter element of a liquid outlet at the bottom of the reaction kettle, toluene and liquid ammonia are recovered and returned to the reaction kettle for recycling through distillation and filtration, white solids are left in the kettle, the white solids are washed by the liquid ammonia and are uniformly stirred, and the toluene and reaction by-product ammonium chloride are washed away; transferring the washed white solid into a vacuum drying oven at 120 deg.C for 4 hr under vacuum degree of 7 × 10-2Pa; placing the dried white solid in an alumina crucible, and removing residual ammonium chloride and organic solvent in an atmosphere furnace under the following specific conditions: the temperature is 600 ℃, the time is 2 hours, and nitrogen flows through the nitrogen atmosphere (the nitrogen flow rate is 40mL/min), so that the solid of the silicon imine is obtained;
(2) thermally decomposing the solid silicon imine obtained in the step (1) in an atmosphere furnace at the nitrogen flow rate of 40mL/min and the temperature of 1000 ℃ for 2h to obtain amorphous silicon nitride powder, wherein an XRD spectrogram is shown in figure 3;
(3) in an atmosphere furnace, the amorphous silicon nitride powder obtained in the step (2) is crystallized for 2 hours in a flowing nitrogen atmosphere (nitrogen flow rate 40mL/min) at 1400 ℃, and finally high alpha phase submicron grade Si with uniform appearance is obtained3N4And (3) powder. The XRD pattern is shown in FIG. 4, and the SEM photograph is shown in FIG. 5.
The alpha-phase silicon nitride powder prepared in the embodiment has the mass percentage of 80%, and has a long columnar crystal form, the diameter of the long columnar crystal form is 0.20-0.50 mu m, the length-diameter ratio of the long columnar crystal form is 15-25, and the oxygen content of the long columnar crystal form<3% and a specific surface area of 47m2/g。
Example 2 preparation of alpha-phase silicon nitride powder
The alpha-phase silicon nitride powder is prepared according to the flow chart shown in fig. 2, and the specific steps are as follows:
(1) controlling the temperature in the reaction kettle to be-50 ℃, placing 300 volumes of mixed solution of toluene and 100 volumes of dimethylbenzene and 100 volumes of liquid ammonia in the reaction kettle shown in figure 1, and standing for layering; mixing 10 volumes of silicon tetrachloride and 90 volumes of toluene, placing the opening of a silicon tetrachloride feeding pipe into a toluene layer in a reaction kettle, the mixed solution of silicon tetrachloride and toluene is injected into the toluene layer by pressurizing nitrogen in the feeding tank, controlling the feeding speed to be 5mL/min, enabling silicon tetrachloride to diffuse to a liquid phase interface of toluene and liquid ammonia, continuously stirring by a stirring paddle at the rotating speed of 100 revolutions per minute, reacting silicon tetrachloride and liquid ammonia at the interface of toluene and liquid ammonia at the reaction temperature of-50 ℃ for 1h to generate white flocculent powder, filtering the white powder, through a filter element of a liquid outlet at the bottom of the reaction kettle, toluene and liquid ammonia are recovered and returned to the reaction kettle for recycling through distillation and filtration, white solids are left in the kettle, the white solids are washed by the liquid ammonia and are uniformly stirred, and toluene and reaction by-product ammonium chloride are washed away; transferring the washed white solid into a vacuum drying oven at 120 deg.C for 6h under vacuum degree of 7 × 10-2Pa; placing the dried white solid in an alumina crucible, and removing residual ammonium chloride and organic solvent in an atmosphere furnace, wherein the specific conditions are as follows: the temperature is 600 ℃, the time is 2 hours, and nitrogen flows through the nitrogen atmosphere (the nitrogen flow rate is 40mL/min), so that the solid of the silicon imine is obtained;
(2) in an atmosphere furnace, carrying out thermal decomposition on the solid silicon imine obtained in the step (1) at the nitrogen flow rate of 40mL/min and the temperature of 1000 ℃ for 2h to obtain amorphous silicon nitride powder;
(3) in an atmosphere furnace, the amorphous silicon nitride powder obtained in the step (2) is crystallized for 6 hours at 1350 ℃ in a flowing nitrogen atmosphere (the nitrogen flow rate is 40mL/min), and finally the high alpha phase submicron Si with uniform appearance is obtained3N4And (3) powder. The XRD spectrum is shown in FIG. 6, and the SEM photograph is shown in FIG. 7.
The alpha-phase silicon nitride powder prepared by the embodiment has the mass percentage of 88%, and has a long columnar crystal form, the diameter of the long columnar crystal form is 0.15-0.35 mu m, the length-diameter ratio of the long columnar crystal form is 15-40, and the oxygen content of the long columnar crystal formMeasurement of<6% and a specific surface area of 76m2/g。
Example 3 preparation of alpha-phase silicon nitride powder
The alpha-phase silicon nitride powder is prepared according to the flow chart shown in fig. 2, and the specific steps are as follows:
(1) controlling the temperature in the reaction kettle to be-55 ℃, placing 400 volumes of toluene and 100 volumes of liquid ammonia in the reaction kettle shown in figure 1, and standing for layering; mixing 10 volumes of silicon tetrachloride and 90 volumes of toluene, placing the opening of a silicon tetrachloride feeding pipe into a toluene layer in a reaction kettle, the mixed solution of silicon tetrachloride and toluene is injected into the toluene layer by pressurizing nitrogen in the feeding tank, controlling the feeding speed to be 5mL/min, enabling silicon tetrachloride to diffuse to a liquid phase interface of toluene and liquid ammonia, continuously stirring by a stirring paddle at the rotating speed of 100 r/min, reacting silicon tetrachloride and liquid ammonia at the interface of toluene and liquid ammonia at the reaction temperature of-55 ℃ for 1h to generate white flocculent powder, filtering the white powder, through a filter element of a liquid outlet at the bottom of the reaction kettle, toluene and liquid ammonia are recovered and returned to the reaction kettle for recycling through distillation and filtration, white solids are left in the kettle, the white solids are washed by the liquid ammonia and are uniformly stirred, and toluene and reaction by-product ammonium chloride are washed away; transferring the washed white solid into a vacuum drying oven at 120 deg.C for 6h under vacuum degree of 7 × 10-2Pa; placing the dried white solid in an alumina crucible, and removing residual ammonium chloride and organic solvent in an atmosphere furnace, wherein the specific conditions are as follows: the temperature is 600 ℃, the time is 2 hours, and nitrogen flows through the nitrogen atmosphere (the nitrogen flow rate is 40mL/min), so that the solid of the silicon imine is obtained;
(2) in an atmosphere furnace, carrying out thermal decomposition on the solid silicon imine obtained in the step (1) at the nitrogen flow rate of 40mL/min and the temperature of 1000 ℃ for 2h to obtain amorphous silicon nitride powder;
(3) mixing the amorphous silicon nitride powder obtained in the step (2) with alpha-Si with the diameter of 200nm3N4Grinding and mixing (amorphous silicon nitride powder and alpha-Si)3N4The powder mass ratio is 95: 5) crystallizing at 1550 deg.C for 12h in an atmosphere furnace in flowing nitrogen atmosphere (nitrogen flow rate 40mL/min) to obtain high alpha-phase submicron phase with uniform morphologyGrade Si3N4And (3) powder. The XRD spectrum is shown in FIG. 8, and the SEM photograph is shown in FIG. 9.
The mass percentage content of the alpha-phase silicon nitride powder prepared by the embodiment is 80%, and the powder is in an equiaxed crystal form or a long rod crystal form, the diameter of the powder is 0.10-0.40 mu m, and the specific surface area of the powder is 254.4m2/g。
The above-mentioned 3 embodiments of the present invention have been described in detail, but the above-mentioned contents are only preferred embodiments of the present invention, and should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made within the scope of the present invention shall fall within the scope of the present invention.

Claims (4)

1. A preparation method of alpha-phase silicon nitride powder comprises the following steps:
(1) reacting silicon tetrachloride with liquid ammonia in a two-liquid phase interface of an organic solvent and the liquid ammonia to obtain precursor silicon imine; the organic solvent is toluene or a mixture of toluene and xylene;
in the step (1), in the mixture of toluene and xylene, the volume ratio of toluene to xylene is (1-9): 1;
in the step (1), the method comprises the following steps of feeding materials into a reaction kettle before the reaction: placing the organic solvent and the liquid ammonia in a reaction kettle, and standing for layering; adding a silicon tetrachloride solution diluted by the organic solvent into the organic solvent, and diffusing the silicon tetrachloride to an interface obtained by standing and layering to finish the feeding;
in the step (1), the method further comprises the steps of washing, drying and impurity removal of the obtained product in sequence after the reaction is finished;
the drying is vacuum drying, the temperature is 100-120 ℃, the time is 2-8 h, and the vacuum degree is 6.7 multiplied by 10-1～6.7×10-2；
The volume ratio of the organic solvent to the liquid ammonia is 4: (1-6); the volume concentration of silicon tetrachloride in the silicon tetrachloride solution diluted by the organic solvent is 1-25 percent;
the adding speed of the silicon tetrachloride solution diluted by the organic solvent is 1-5 mL/min;
in the step (1), the reaction is carried out under the condition of stirring; the stirring adopts a straight blade type stirring paddle; the stirring speed is 50-200 r/min;
the reaction temperature is-35 to-60 ℃, and the reaction time is 0.5 to 3 hours;
in the step (1), liquid ammonia is adopted for washing in a reaction kettle;
the impurity removal is to remove residual ammonium chloride and organic solvent, and comprises the following steps: heating the dried product in a nitrogen atmosphere at the temperature of 360-800 ℃ for 2-4 h;
(2) carrying out thermal decomposition on the silicon imine obtained in the step (1) to obtain amorphous silicon nitride powder;
in the step (2), the thermal decomposition is carried out in a nitrogen atmosphere at 900-1200 ℃ for 2-4 h;
(3) crystallizing the amorphous silicon nitride powder in the step (2) to obtain alpha-phase silicon nitride powder;
in the step (3), the crystallization treatment is carried out in a nitrogen atmosphere at 1300-1600 ℃ for 2-12 h;
the reaction kettle used in the preparation method of the alpha-phase silicon nitride powder comprises a closed reaction cavity; a silicon tetrachloride feeding pipe is arranged in the reaction cavity; a straight blade type stirring paddle is arranged in the reaction cavity; the reaction cavity is sequentially provided with a secondary refrigerant circulation layer and a vacuum insulation layer from inside to outside;
a reaction kettle vent valve, a rupture disk, a thermometer, a nitrogen valve and a liquid ammonia feed valve are respectively arranged above the reaction cavity, and a reaction kettle pressure gauge is arranged on a pipeline arranged on the rupture disk; the secondary refrigerant circulating layer is provided with a secondary refrigerant inlet and a secondary refrigerant outlet;
a liquid outlet of the reaction kettle is arranged at the bottom of the reaction cavity;
and a filter element is arranged at the liquid outlet of the reaction kettle.
2. The method of claim 1, wherein: what is needed isThe crystallization treatment is carried out in the presence of an additive; the additive is Fe powder, Ni powder, Cu powder or alpha-Si3N4Pulverizing; and/or the mass of the additive is 0.1-5% of the sum of the mass of the amorphous silicon nitride powder and the mass of the additive; and/or, the alpha-Si3N4The diameter of the powder is 200-500 nm.
3. The alpha-phase silicon nitride powder prepared by the preparation method of claim 1 or 2.
4. The α -phase silicon nitride powder according to claim 3, characterized in that: the crystal form of the alpha-phase silicon nitride powder is at least one of long columnar, long segment and equiaxed; and/or the alpha-phase silicon nitride powder is micron-sized.
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