Device and method for preparing silicon nitride powder with high sintering activity by self-propagating method

Abstract

The invention discloses a device and a method for preparing silicon nitride powder with high sintering activity by a self-propagating method. The method comprises the following steps: mixing silicon powder and silicon nitride powder to obtain a mixed raw material; putting a porous plate into a crucible, scattering magnesium powder on the porous plate, and stacking the mixed raw material on the magnesium powder; sealing and vacuumizing the crucible, then filling nitrogen, repeating the operation for a plurality of times, and keeping the nitrogen atmosphere and pressure in the crucible; igniting the magnesium powder in the crucible, and starting a self-propagating combustion reaction; and cooling the crucible to obtain the silicon nitride powder with high sintering activity. The device comprises an ignition system, a self-propagating autoclave and a temperature detection module, one end of the ignition system and one end of the temperature detection module extend into the self-propagating high-pressure kettle. According to the method and the device, a continuous ventilation low-pressure self-propagating method is adopted, sufficient nitrogen is ensured to participate in the reaction, the raw materials are completely reacted, the yield and the purity of the product are ensured, the alpha-phase content of the product is relatively high, and the self-propagating device is simple in structure and convenient to operate.

Description

Technical Field

[0001] The invention relates to the technical field of powder material preparation, and in particular to a device and method for preparing high-sintering active silicon nitride powder by a self-propagating method. Background Art

[0002] At present, the methods for preparing high α-phase silicon nitride micro-nano powders mainly include self-propagating synthesis, direct nitridation, carbon thermal reduction and silicimide decomposition. The self-propagating synthesis method is widely used because of its low raw material cost and relatively simple process flow, but the control of reaction temperature and time of this method is relatively difficult, which easily leads to uneven product particle size distribution, and the required gas pressure is large or the atmosphere is complex, and the equipment requirements are high. Patent "A method for preparing silicon nitride nanomaterials" (application number: CN202410907277.6). The direct nitridation method can prepare high-purity silicon nitride powder, but it requires a high temperature and long reaction process, high energy consumption and high cost; patent "A method for preparing α-phase and β-phase silicon nitride powder by improved direct nitridation method" (application number: CN201310290727.3). Although the carbon thermal reduction method is simple in technology and has low raw material costs, it is easy to introduce impurities and the product particle size and purity are difficult to control. Patent "A method for preparing doped silicon nitride powder" (patent number: CN202110282426.0). Although the silanimide decomposition method can obtain high-purity and high-uniformity powders, the equipment investment is large, the production cost is high, and the technical difficulty is relatively high. Patent "Silicon nitride powder and method for producing silicon nitride sintered body" (application number: JP2023010125).

[0003] In general, the self-propagating method has important application value in the preparation of powder materials due to its high energy efficiency, simple process, fast reaction speed and strong controllability. The efficient preparation of various powder materials, including silicon nitride, benefits from the unique advantages of the self-propagating method, showing its broad development prospects and potential. However, the production process of high-purity, high-α-phase silicon nitride micro-nano powders still faces problems such as difficult impurity control and poor batch production stability. Summary of the invention

[0004] It is urgently necessary to improve the purity and α-phase content of silicon nitride powder by optimizing process parameters, improving raw material ratios and introducing high-efficiency purification technology on the basis of self-propagating synthesis method, while reducing production costs and achieving stable mass production with high quality and high yield, so as to provide a solid raw material guarantee for the research and development of high-performance silicon nitride ceramics and related application materials.

[0005] In view of the above problems, the present invention proposes a device and method for preparing high sintering active silicon nitride powder by self-propagating method through research on the self-propagating synthesis reaction process of silicon nitride and thermodynamic and kinetic calculations of the system, especially systematic analysis of the reaction pressure of silicon nitride. The present invention is a preparation technology of high α-phase silicon nitride powder. The invention prepares α-silicon nitride powder through thermodynamic calculations of silicon nitride self-propagating reaction and sintering process design and generates silicon magnesium nitride in situ. The preparation process is simple, the powder particle size is controllable, and the powder yield and purity are high.

[0006] The technical solution adopted by the present invention is:

[0007] 1. A method for preparing highly sintered active silicon nitride powder by self-propagating method:

[0008] S1, mixing silicon powder and silicon nitride powder to obtain a mixed raw material;

[0009] S2, placing a porous plate into a crucible, and sprinkling magnesium powder onto the upper end surface of the porous plate, and then piling the mixed raw material obtained in step S1 onto the magnesium powder, and then sealing the crucible;

[0010] S3, evacuating the crucible described in step S2 to a vacuum state and then filling it with nitrogen, as one operation, repeating the operation several times, and maintaining the nitrogen atmosphere and pressure in the crucible;

[0011] S4, igniting the magnesium powder in the crucible described in step S2 to start a self-propagating combustion reaction;

[0012] S5, cooling the crucible described in step S4 to room temperature, and then obtaining highly sintered active silicon nitride powder.

[0013] Preferably, in step S1, the mass ratio of silicon powder to silicon nitride is 1:0.1-2;

[0014] Preferably, in step S2, magnesium powder accounts for 1-5% of the mass of the mixed raw material, and a plurality of through holes with a pore size of 0.001-0.1 cm are opened on the porous plate, so that nitrogen can penetrate the carbon fiber plate, but powder cannot pass through the through holes.

[0015] Preferably, in step S3, the nitrogen is high-purity nitrogen with a purity of 99.999%, and the speed of nitrogen filling is 1-10 ml / min; when performing the last operation, the nitrogen pressure in the graphite crucible is 0.1-0.5 MPa by opening the vent valve.

[0016] In step S4, the ignition is to energize and ignite the molybdenum wire connected to the frequency converter through the frequency converter, thereby igniting the magnesium powder in the crucible; during the reaction, the maximum temperature in the crucible is 1300-1700° C., and when the temperature does not rise any more, the operation in step S5 is performed;

[0017] Preferably, in step S5, the cooling rate is 100-200°C / min.

[0018] Preferably, the output current of the inverter is 5-10A, the voltage is 5-20V, and the power-on time is 30-300S.

[0019] 2. A device for preparing highly sintered active silicon nitride powder by self-propagating method:

[0020] The device comprises an ignition system, a self-propagating autoclave and a temperature detection module; one end of the ignition system and one end of the temperature detection module extend into the self-propagating autoclave.

[0021] The self-propagating autoclave comprises an ignition molybdenum wire, a stainless steel furnace body, a mullite insulation felt, a graphite crucible, a porous carbon fiber plate, a furnace cover and a pressure reducing valve;

[0022] The upper end of the stainless steel furnace body is open and a furnace cover is installed at the opening. A graphite crucible is installed at the bottom of the stainless steel furnace body. Mullite insulation felt is arranged between the stainless steel furnace body and the graphite crucible. A porous carbon fiber plate is placed at the bottom of the graphite crucible. A pressure reducing valve for communicating with the cavity in the stainless steel furnace body is installed on the furnace cover.

[0023] The ignition system includes a frequency converter, positive and negative wires, copper electrodes, an insulating shell and an ignition molybdenum wire; the ignition molybdenum wire is U-shaped, the upper end of the U-shape is fixedly installed on the furnace cover of the self-propagating autoclave through the insulating shell, the lower end of the U-shape extends into the graphite crucible and is located on the porous carbon fiber plate, the output end of the frequency converter is electrically connected to the two copper electrodes through the positive and negative wires, and the two copper electrodes are respectively electrically connected to the two branch ends of the upper end of the ignition molybdenum wire.

[0024] The temperature detection module includes a corundum-coated tube, a thermocouple thermometer and a temperature display;

[0025] The outer peripheral surface of the platinum-rhodium wire in the thermocouple thermometer is coated with a corundum-coated tube. The thermocouple thermometer passes through the furnace cover of the self-propagating autoclave and extends into the self-propagating autoclave and is arranged between the mullite insulation felt and the graphite crucible. The thermocouple thermometer is electrically connected to the temperature display.

[0026] The furnace cover is also equipped with a pressure gauge for communicating with the cavity in the stainless steel furnace body; the stainless steel furnace body and the graphite crucible are both provided with a through hole in the same distribution on the bottom side, as a group of through holes, and the through holes in the group are connected through a graphite nitrogen pipeline; a flow meter is installed at the gas outlet of the high-pressure gas cylinder, one end of the gas conduit is connected to the flow meter, and the other end of the gas conduit is connected to the graphite nitrogen pipeline, so that the high-pressure gas cylinder is connected to the cavity in the graphite crucible through the graphite nitrogen pipeline.

[0027] Compared with the prior art, the present invention has the following outstanding advantages and beneficial effects:

[0028] 1. Based on the influence of nitrogen pressure on the combustion reaction and its thermodynamic and kinetic calculations, the present invention proposes to prepare silicon nitride powder by a low-pressure self-propagating method with continuous ventilation in a self-propagating reactor, which not only ensures sufficient nitrogen to participate in the nitridation reaction of silicon powder, but also enables the raw materials to react completely, thereby ensuring the yield and purity of the product.

[0029] 2. The ignition agent in the present invention is magnesium powder. Compared with the traditional titanium powder ignition agent, magnesium powder has the characteristics of large heat release and rapid reaction, which can improve the combustion efficiency under low pressure. Titanium and magnesium can both be used as ceramic sintering aids, but titanium has a greater negative impact on thermal conductivity while improving the mechanical properties of silicon nitride ceramics. The corresponding magnesium combustion product is beneficial to the improvement of ceramic thermal conductivity as a sintering aid. The use of low-pressure magnesium powder to ignite the synthetic silicon nitride powder not only ensures the full reaction of the raw materials, but also can be used as a sintering aid for sintering silicon nitride ceramics. Therefore, the yield and purity of the product are guaranteed, and it also has good sintering performance.

[0030] 3. The porous carbon fiber plate in the present invention provides sufficient nitrogen for the growth of silicon nitride powder without affecting the placement of raw material powder, avoiding incomplete reaction, which is beneficial to improving the reaction yield, inhibiting the formation of β silicon nitride, and the product α phase content is high. Highly sintered active silicon nitride powder with a particle size of several microns can be prepared through simple steps such as ball milling and mixing.

[0031] 4. The preparation process of the present invention is simple, the equipment requirements are lower, less nitrogen is used, and the synthesized silicon nitride powder has high purity, high yield and low cost. It has broad application prospects in the fields of special silicon nitride ceramics, high-performance grinding tools and abrasives, high thermal conductivity ceramic substrates, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of the structure of the device in Example 1.

[0033] In the figure: 1.1, inverter, 1.2, positive and negative wires, 1.3, copper electrodes, 1.4, insulating shell, 1.5, ignition molybdenum wire, 2.1, stainless steel furnace body, 2.2, mullite insulation felt, 2.3, graphite crucible, 2.4, porous carbon fiber plate, 2.5, furnace cover, 2.6, pressure reducing valve, 3.1, corundum coated tube, 3.2, platinum rhodium wire, 3.3, thermocouple, 3.4, temperature display, 4.1, high-pressure gas cylinder, 4.2, flow meter, 4.3, gas duct, 4.4, graphite nitrogen pipeline, 4.5 barometer.

[0034] Figure 2 This is the XRD test diagram in Example 2-5.

[0035] Figure 3 This is the XPS peak diagram of the product in Example 4.

[0036] Figure 4 This is the SEM test picture in Example 2-5.

[0037] In the figure: a is embodiment 2, b is embodiment 3, c is embodiment 4, and d is embodiment 5.

[0038] Figure 5 This is the particle size distribution diagram in Example 2-5.

[0039] In the figure: a is embodiment 2, b is embodiment 3, c is embodiment 4, and d is embodiment 5. DETAILED DESCRIPTION

[0040] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. These implementation cases are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0041] Embodiments of the present invention are as follows:

[0042] Example 1

[0043] This embodiment assembles a device suitable for the preparation method of the present invention. The structural schematic diagram of the device is shown in FIG. Figure 1 As shown, the device includes an ignition system 1, a self-propagating autoclave 2 and a temperature detection module 3; one end of the ignition system 1 and one end of the temperature detection module 3 extend into the self-propagating autoclave 2.

[0044] The self-propagating autoclave 2 comprises an ignition molybdenum wire 1.5, a stainless steel furnace body 2.1, a mullite insulation felt 2.2, a graphite crucible 2.3, a porous carbon fiber plate 2.4, a furnace cover 2.5 and a pressure reducing valve 2.6; the upper end of the stainless steel furnace body 2.1 is open and the furnace cover 2.5 is installed at the opening, the bottom of the stainless steel furnace body 2.1 is equipped with a graphite crucible 2.3, a mullite insulation felt 2.2 is arranged between the stainless steel furnace body 2.1 and the graphite crucible 2.3, the mullite insulation felt 2.2 is close to the stainless steel furnace body 2.1, a porous carbon fiber plate 2.4 is placed at the bottom of the graphite crucible 2.3, and a pressure reducing valve 2.6 for communicating with the cavity in the stainless steel furnace body 2.1 is installed on the furnace cover 2.5.

[0045] The ignition system 1 includes a frequency converter 1.1, positive and negative wires 1.2, copper electrodes 1.3, an insulating shell 1.4 and an ignition molybdenum wire 1.5; the ignition molybdenum wire 1.5 is U-shaped, the upper end of the U-shape is fixedly installed on the furnace cover 2.5 of the self-propagating autoclave 2 through the insulating shell 1.4, the lower end of the U-shape extends into the graphite crucible 2.3 and is located on the porous carbon fiber plate 2.4, the output end of the frequency converter 1.1 is electrically connected to the two copper electrodes 1.3 through the positive and negative wires 1.2, and the two copper electrodes 1.3 are electrically connected to the two branch ends of the upper end of the ignition molybdenum wire 1.5 respectively.

[0046] The temperature detection module 3 includes a corundum-coated tube 3.1, a thermocouple thermometer 3.3 and a temperature display 3.4; the outer peripheral surface of the platinum-rhodium wire 3.2 in the thermocouple thermometer 3.3 is coated with the corundum-coated tube 3.1 and is arranged between the mullite insulation felt 2.2 and the graphite crucible 2.3, and the thermocouple thermometer 3.3 is electrically connected to the temperature display 3.4.

[0047] A barometer 4.5 for communicating with the cavity in the stainless steel furnace body 2.1 is also installed on the furnace cover 2.5; a through hole is formed on the bottom side of the stainless steel furnace body 2.1 and the graphite crucible 2.3 in the same distribution, as a group of through holes, and the through holes in the group are connected through a graphite nitrogen pipeline 4.4; a flow meter 4.2 is installed at the gas outlet of the high-pressure gas cylinder 4.1, one end of the gas conduit 4.3 is connected to the flow meter 4.2, and the other end of the gas conduit 4.3 is connected to the graphite nitrogen pipeline 4.4, so that the high-pressure gas cylinder 4.1 is connected to the cavity in the graphite crucible 2.3 through the graphite nitrogen pipeline 4.4.

[0048] The method for preparing high sintering active silicon nitride powder using the device comprises the following steps:

[0049] S1. Silicon powder (Si) and silicon nitride powder (Si 3 N 4 ) to obtain a mixed raw material;

[0050] S2, placing the porous carbon fiber circular plate 2.4 as a powder carrier into the graphite crucible 2.3, and spreading magnesium powder on the upper end surface of the porous carbon fiber circular plate 2.4, and then loosely piling the mixed raw material obtained in step S1 on the magnesium powder, and then sealing the graphite crucible 2.3;

[0051] S3, evacuating the graphite crucible 2.3 in step S2 to a vacuum state and then filling it with high-purity nitrogen, as a single operation, repeating the operation several times, and maintaining the nitrogen atmosphere and pressure in the graphite crucible 2.3;

[0052] S4, igniting the magnesium powder in the graphite crucible 2.3 in step S2 to start a self-propagating combustion reaction;

[0053] S5, rapidly cooling the graphite crucible 2.3 in step S4, and then obtaining highly sintered active silicon nitride powder.

[0054] Example 2

[0055] a. Place the porous carbon fiber plate 2-3 cm above the air outlet to facilitate the flow of nitrogen, then take out 10g of magnesium powder as an ignition agent and sprinkle it evenly on the porous plate.

[0056] b. Using silicon powder and silicon nitride powder as raw materials, according to Si:Si 3 N 4 =15:5 ratio, take 225g silicon powder and 75g silicon nitride and mix them evenly using a mechanical mixer.

[0057] c. Put the raw materials in step b into a graphite crucible and put it into a self-propagating reactor after assembly.

[0058] d. After completing step c, seal the furnace, evacuate the self-propagating reactor to -0.1 MPa, and then fill it with nitrogen to normal pressure. Repeat the filling and degassing operation three times. The pressure is controlled at 0.2 MPa when nitrogen is filled for the third time.

[0059] e. Maintain the pressure of step d and continue to introduce nitrogen while energizing the connected molybdenum wire through the inverter to start ignition. The inverter current is 10A and the voltage is between 10-16V. Ignition is completed after 1 minute of power-on, and the maximum temperature rises to 1496℃.

[0060] f. After the reaction in step e burned for 31 minutes, the temperature no longer increased, the reaction vessel began to cool down, and finally 353.6 g of high α-phase silicon nitride was taken out.

[0061] Example 3

[0062] a. Place the porous carbon fiber plate 2-3 cm above the air outlet to facilitate the flow of nitrogen, then take out 10g of magnesium powder as an ignition agent and sprinkle it evenly on the porous plate.

[0063] b. Using silicon powder and silicon nitride powder as raw materials, according to Si:Si 3 N 4 =7:3 ratio, take 210g silicon powder and 90g silicon nitride and mix them evenly using a mechanical mixer.

[0064] c. Put the raw materials in step b into a graphite crucible and put it into a self-propagating reactor after assembly.

[0065] d. After completing step c, seal the furnace, evacuate the self-propagating reactor to -0.1 MPa, and then fill it with nitrogen to normal pressure. Repeat the filling and degassing operation three times. The pressure is controlled at 0.2 MPa when nitrogen is filled for the third time.

[0066] e. Maintain the pressure of step d and continue to introduce nitrogen while energizing the connected molybdenum wire through the inverter to start ignition. The inverter current is 10A and the voltage is between 10-16V. Ignition is completed after 1 minute of power-on, and the maximum temperature rises to 1442℃.

[0067] f. After the reaction in step e was burned for 25 minutes, the temperature no longer increased, the reaction vessel began to be cooled, and finally 369.7 g of high α-phase silicon nitride was taken out.

[0068] Example 4

[0069] a. Place the porous carbon fiber plate 2-3 cm above the air outlet to facilitate the circulation of nitrogen, then take out 10g of magnesium powder as an ignition agent and sprinkle it evenly on the porous plate.

[0070] b. Using silicon powder and silicon nitride powder as raw materials, according to Si:Si 3 N 4 =13:7 ratio, take 195g silicon powder and 105g silicon nitride and mix them evenly using a mechanical mixer.

[0071] c. Put the raw materials in step b into a graphite crucible and put it into a self-propagating reactor after assembly.

[0072] d. After completing step c, seal the furnace, evacuate the self-propagating reactor to -0.1 MPa, and then fill it with nitrogen to normal pressure. Repeat the filling and degassing operation three times. The pressure is controlled at 0.2 MPa when nitrogen is filled for the third time.

[0073] e. Maintain the pressure of step d and continue to introduce nitrogen while energizing the connected molybdenum wire through the inverter to start ignition. The inverter current is 10A and the voltage is between 10-16V. Ignition is completed after 1 minute of power-on, and the maximum temperature rises to 1514℃.

[0074] f. After the reaction in step e burned for 30 minutes, the temperature no longer increased, the reaction vessel began to cool down, and finally 395.9 g of high α-phase silicon nitride was taken out.

[0075] Example 5

[0076] a. Place the porous carbon fiber plate 2-3cm above the gas outlet to facilitate the flow of nitrogen. Then take out 10g of magnesium powder as an ignition agent and sprinkle it evenly on the porous plate.

[0077] b. Using silicon powder and silicon nitride powder as raw materials, according to Si:Si 3 N 4 =6:4 ratio, take 180g silicon powder and 120g silicon nitride and mix them evenly using a mechanical mixer.

[0078] c. Put the raw materials in step b into a graphite crucible and put it into a self-propagating reactor after assembly.

[0079] d. After completing step c, seal the furnace, evacuate the self-propagating reactor to -0.1 MPa, and then fill it with nitrogen to normal pressure. Repeat the filling and degassing operation three times. The pressure is controlled at 0.2 MPa when nitrogen is filled for the third time.

[0080] e. Maintain the pressure of step d and continue to introduce nitrogen while energizing the connected molybdenum wire through the inverter to start ignition. The inverter current is 10A and the voltage is between 10-16V. Ignition is completed after 1 minute of power-on, and the maximum temperature rises to 1480℃.

[0081] f. After the reaction in step e was burned for 25 minutes, the temperature no longer increased, the reaction vessel began to cool down, and finally 354.3 g of high α-phase silicon nitride was taken out.

[0082] The Mg1s peak of the product obtained in Example 4 is shown in the XPS test. Figure 3 As shown, it is shown that the material formed in situ is MgSiN 2 ,MgSiN 2 It is considered to be one of the best non-oxide sintering aids for sintering high thermal conductivity silicon nitride ceramics.

[0083] The XRD patterns of the products obtained in Examples 2-5 are as follows: Figure 2 As shown, it can be clearly seen that the products of Example 4 and Example 5 have higher α phase and higher α-Si 3 N 4 The content is helpful for the sintering densification of silicon nitride ceramics.

[0084] The scanning electron microscope (SEM) photos of the microscopic morphology of each product obtained in Examples 2-5 are as follows: Figure 4As shown in the photos, no hexagonal prismatic β-Si 3 N 4 phase, and with the decrease of Si powder content in the raw material fraction, the particle size of the product decreases significantly.

[0085] The particle size test diagrams of the products obtained in Examples 2-5 are as follows: Figure 5 As shown in the figure, the particle size distribution of the product powder can be clearly seen, and there is a large difference in the particle size distribution between different embodiments.

[0086] It can be seen from Examples 2-5 that the highly sintered active silicon nitride powder prepared by the high temperature and ultra-low pressure self-propagating method of the present invention is micron-sized and has a yield of 85% to 90%.

[0087] Comparative Example 1

[0088] a. Place the porous carbon fiber plate 2-3 cm above the gas outlet to facilitate the flow of nitrogen. Then take out 10g of titanium powder as an ignition agent and sprinkle it evenly on the porous plate.

[0089] b. Using silicon powder and silicon nitride powder as raw materials, according to Si:Si 3 N 4 =6:4 ratio, take 180g silicon powder and 120g silicon nitride and mix them evenly using a mechanical mixer.

[0090] c. Put the raw materials in step b into a graphite crucible and put it into a self-propagating reactor after assembly.

[0091] d. After completing step c, seal the furnace, evacuate the self-propagating reactor to -0.1 MPa, and then fill it with nitrogen to normal pressure. Repeat the filling and degassing operation three times. The pressure is controlled at 0.2 MPa when nitrogen is filled for the third time.

[0092] e. Maintain the pressure of step d and continue to introduce nitrogen while energizing the connected molybdenum wire through the inverter to start ignition. The inverter current is 10A and the voltage is between 10-16V. Ignition is completed after 1 minute of power-on, and the maximum temperature rises to 1398℃.

[0093] f. After the reaction in step e burned for 31 minutes, the temperature no longer increased, the reaction vessel began to cool down, and finally 332.1 g of high α-phase silicon nitride was taken out.

[0094] Comparative Example 2

[0095] a. Place the porous carbon fiber plate 2-3 cm above the air outlet to facilitate the flow of nitrogen, then take out 10g of titanium powder as an ignition agent and sprinkle it evenly on the porous plate.

[0096] b. Using silicon powder and silicon nitride powder as raw materials, according to Si:Si3 N 4 =7:3 ratio, take 210g silicon powder and 90g silicon nitride and mix them evenly using a mechanical mixer.

[0097] c. Put the raw materials in step b into a graphite crucible and put it into a self-propagating reactor after assembly.

[0098] d. After completing step c, seal the furnace, evacuate the self-propagating reactor to -0.1 MPa, and then fill it with nitrogen to normal pressure. Repeat the filling and degassing operation three times. The pressure is controlled at 0.2 MPa when nitrogen is filled for the third time.

[0099] e. Maintain the pressure of step d and continue to introduce nitrogen while energizing the connected molybdenum wire through the inverter to start ignition. The inverter current is 10A and the voltage is between 10-16V. Ignition is completed after 1 minute of power-on, and the maximum temperature rises to 1431℃.

[0100] f. After the reaction in step e was burned for 28 minutes, the temperature no longer increased, the reaction vessel began to be cooled, and finally 353.6 g of high α-phase silicon nitride was taken out.

[0101] The above is only a preferred embodiment of the present invention. It should be pointed out that ordinary technicians in this technical field can make several improvements and modifications without departing from the method of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing highly sintered active silicon nitride powder by a self-propagating method, characterized in that: S1, mixing silicon powder and silicon nitride powder to obtain a mixed raw material; S2, placing a porous plate into a crucible, and sprinkling magnesium powder onto the upper end surface of the porous plate, and then piling the mixed raw material obtained in step S1 onto the magnesium powder, and then sealing the crucible; S3, evacuating the crucible described in step S2 to a vacuum state and then filling it with nitrogen, as one operation, repeating the operation several times, and maintaining the nitrogen atmosphere and pressure in the crucible; S4, igniting the magnesium powder in the crucible described in step S2 to start a self-propagating combustion reaction; S5, cooling the crucible described in step S4 to room temperature, and then obtaining highly sintered active silicon nitride powder.

2. The method for preparing highly sintered active silicon nitride powder by a self-propagating method according to claim 1, characterized in that: In the step S1, the mass ratio of silicon powder to silicon nitride is 1:0.1-2; In the step S2, the magnesium powder accounts for 1-5% of the mass of the mixed raw material, and a plurality of through holes with a pore size of 0.001-0.1 cm are opened on the porous plate.

3. The method for preparing highly sintered active silicon nitride powder by a self-propagating method according to claim 1, characterized in that: In the step S3, the purity of nitrogen is 99.999%, and the speed of nitrogen filling is 1-10 ml / min; when the last operation is performed, the nitrogen pressure in the crucible is 0.1-0.5 MPa.

4. The method for preparing highly sintered active silicon nitride powder by a self-propagating method according to claim 1, characterized in that: In step S4, the ignition is to energize and ignite the molybdenum wire connected to the frequency converter through the frequency converter, thereby igniting the magnesium powder in the crucible; during the reaction, the maximum temperature in the crucible is 1300-1700° C., and when the temperature does not rise any more, the operation in step S5 is performed; In the step S5, the cooling rate is 100-200°C / min.

5. The method for preparing highly sintered active silicon nitride powder by a self-propagating method according to claim 4, characterized in that: The output current of the frequency converter is 5-10A, the voltage is 5-20V, and the power-on time is 30-300S.

6. A device for preparing highly sintered active silicon nitride powder by a self-propagating method according to any one of claims 1 to 5, characterized in that: It comprises an ignition system (1), a self-propagating autoclave (2) and a temperature detection module (3); one end of the ignition system (1) and one end of the temperature detection module (3) extend into the self-propagating autoclave (2).

7. The device for preparing highly sintered active silicon nitride powder by self-propagating method according to claim 6, characterized in that: The self-propagating autoclave (2) comprises an ignition molybdenum wire (1.5), a stainless steel furnace body (2.1), a mullite insulation felt (2.2), a graphite crucible (2.3), a porous carbon fiber plate (2.4), a furnace cover (2.5) and a pressure reducing valve (2.6); The upper end of the stainless steel furnace body (2.1) is open and a furnace cover (2.5) is installed at the opening; a graphite crucible (2.3) is installed at the bottom of the stainless steel furnace body (2.1); a mullite insulation felt (2.2) is arranged between the stainless steel furnace body (2.1) and the graphite crucible (2.3); a porous carbon fiber plate (2.4) is placed at the bottom of the graphite crucible (2.3); and a pressure reducing valve (2.6) for communicating with the cavity inside the stainless steel furnace body (2.1) is installed on the furnace cover (2.5).

8. The device for preparing highly sintered active silicon nitride powder by self-propagating method according to claim 7, characterized in that: The ignition system (1) comprises a frequency converter (1.1), positive and negative wires (1.2), copper electrodes (1.3), an insulating shell (1.4) and an ignition molybdenum wire (1.5); the ignition molybdenum wire (1.5) is U-shaped, the upper end of the U-shape is fixedly mounted on the furnace cover (2.5) of the self-propagating autoclave (2) through the insulating shell (1.4), the lower end of the U-shape extends into the graphite crucible (2.3) and is located on the porous carbon fiber plate (2.4), the output end of the frequency converter (1.1) is electrically connected to the two copper electrodes (1.3) through the positive and negative wires (1.2), and the two copper electrodes (1.3) are respectively electrically connected to the two branch ends of the upper end of the ignition molybdenum wire (1.5).

9. The device for preparing highly sintered active silicon nitride powder by self-propagating method according to claim 8, characterized in that: The temperature detection module (3) comprises a corundum-coated tube (3.1), a thermocouple thermometer (3.3) and a temperature display (3.4); The outer peripheral surface of the platinum-rhodium wire (3.2) in the thermocouple thermometer (3.3) is coated with a corundum-coated tube (3.1); the thermocouple thermometer (3.3) passes through the furnace cover (2.5) of the self-propagating autoclave (2) and extends into the self-propagating autoclave (2) and is arranged between the mullite insulation felt (2.2) and the graphite crucible (2.3); the thermocouple thermometer (3.3) is electrically connected to a temperature display (3.4).

10. The device for preparing highly sintered active silicon nitride powder by self-propagating method according to claim 7, characterized in that: The furnace cover (2.5) is also provided with a pressure gauge (4.5) for communicating with the cavity in the stainless steel furnace body (2.1); the stainless steel furnace body (2.1) and the graphite crucible (2.3) are both provided with a through hole in the same distribution on the bottom side, as a group of through holes, and the through holes in the group are communicated with each other through a graphite nitrogen pipeline (4.4); a flow meter (4.2) is installed at the gas outlet of the high-pressure gas cylinder (4.1), one end of the gas conduit (4.3) is communicated with the flow meter (4.2), and the other end of the gas conduit (4.3) is communicated with the graphite nitrogen pipeline (4.4), so that the high-pressure gas cylinder (4.1) is communicated with the cavity in the graphite crucible (2.3) through the graphite nitrogen pipeline (4.4).

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