Preparation method of silicon nitride powder

Abstract

The invention relates to the technical field of inorganic non-metallic materials, provides a preparation method of silicon nitride powder, and solves the problems that the content of alpha-Si3N4 in the silicon nitride powder prepared in the prior art is low, the quality is relatively poor and the nitriding time is long. Comprising the following preparation steps: 1) preparing raw materials; 2) ball-milling the raw materials; 3) primary sintering; 4) secondary sintering; and 5) grinding to obtain the silicon nitride powder.

Description

Technical Field

[0001] The present invention relates to the technical field of inorganic non-metallic materials, and in particular to a method for preparing silicon nitride powder. Background Art

[0002] As a key ceramic structural material, Si3N4 has been widely used in semiconductor, metallurgy, aerospace, machinery, photovoltaic, medical and fine grinding industries due to its excellent chemical stability, heat resistance and wear resistance, good insulation performance, high strength, good thermal shock resistance. Si3N4 powder is one of the key raw materials of Si3N4 ceramics, mainly in the form of α-Si3N4 and β-Si3N4. Among them, α-Si3N4 has higher sintering activity and is the preferred material for silicon nitride-based materials.

[0003] Chinese patent application No. 201610972014.9 discloses a method for preparing silicon nitride nanowires, silicon nitride nanowires, silicon nitride powder and silicon nitride submicron powder. Using cheap and easily available silicon powder as raw material, without the use of catalyst, the silicon powder is granulated and then subjected to nitridation reaction to prepare silicon nitride particles, and then through simple operations such as grinding, crushing, washing, sedimentation separation, and drying, high-purity silicon nitride nanowires and silicon nitride powder products can be obtained at the same time. It is a simple, economical and suitable method for industrial mass production of silicon nitride nanowires. However, the content of α-phase-Si3N4 (>95%) in the silicon nitride powder prepared by the invention is relatively low.

[0004] Chinese patent application No. 202010282836.0 discloses a method for preparing high-purity α-silicon nitride powder and high-purity α-silicon nitride powder, the method comprising: adding a catalyst to fine silicon powder with a particle size of less than 100 microns, the catalyst can generate a metal compound by a reversible reaction under the reaction conditions for preparing silicon nitride powder, and allow the presence of metal halides; placing the fine silicon powder with the catalyst in a nitriding furnace, in a mixed atmosphere of nitrogen and argon, and keeping it warm for 50-180 hours at a temperature of 1050℃-1400℃ to obtain silicon nitride powder by a nitriding reaction. The method described in the invention, through the catalyst that forms a volatile metal halide by a reversible reaction, is transported back and forth between the surfaces of the powder particles, repeatedly catalyzes at multiple sites, and fully catalyzes the surface reaction with less metal impurities. The special effect ensures the purity of the product and increases the α-phase content of the product, meeting the requirements of high-purity silicon nitride powder. However, the nitriding time of this invention is relatively long. Summary of the invention

[0005] Therefore, in view of the above problems, the present invention provides a method for preparing silicon nitride powder to solve the problems that the silicon nitride powder prepared by the prior art has a low α-phase-Si3N4 content, relatively poor quality and a long nitriding time.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for preparing silicon nitride powder comprises the following preparation steps:

[0008] S1. Preparation of raw materials: 100-120 parts by weight of silicon powder, 1.0-2.5 parts by weight of cobalt, 50-100 parts by weight of KCl;

[0009] S2, ball milling of raw materials: silicon powder, cobalt and KCl are taken according to weight parts, mixed evenly, and ball milled once, and then anhydrous ethanol is added in a weight ratio of silicon powder to anhydrous ethanol of 1:2-2.5, and ball milled twice to obtain slurry, and the slurry is dried to obtain mixed powder;

[0010] S3, primary sintering: adding the mixed powder obtained in step S2 into a modified Al2O3 corundum crucible, then placing the modified Al2O3 corundum crucible into a vacuum sintering furnace, introducing N2 protective gas, raising the temperature to 900-920°C at a heating rate of 5°C / min, and keeping the temperature for 50-65min;

[0011] S4, secondary sintering: continue to increase the temperature to 1200-1250°C at a heating rate of 5°C / min, keep warm for 4 hours, and cool to room temperature;

[0012] S5. After grinding, silicon nitride powder is obtained.

[0013] Furthermore, the preparation method of the modified Al2O3 corundum crucible is:

[0014] I. Mix acrylamide and N,N′-methylenebisacrylamide in a weight ratio of 20-25:1, and add 0.5-1 parts by weight of a dispersant to obtain a mixed solution;

[0015] II. Add a regulator to the mixed solution obtained in step I to adjust the pH to 9, add 30-35 parts by weight of the first corundum raw material, and ball mill three times to obtain a first mixed slurry, and add 40-45 parts by weight and 20-25 parts by weight of the second corundum raw material and the third corundum raw material to the first mixed slurry, respectively, and ball mill four times to obtain a second mixed slurry;

[0016] III. Vacuum-treat the second mixed slurry obtained in step II, add 3-6 parts by weight of a catalyst and 0.1-1 parts by weight of an initiator, stir evenly and inject into a mold, cure in a water bath, then keep warm in an oven for 24 hours, increase the temperature to 100-120°C, keep warm for 10-12 hours, then sinter in a vacuum sintering furnace, and cool to room temperature to obtain the modified Al2O3 corundum crucible.

[0017] Furthermore, the primary ball milling and secondary ball milling are as follows: in a ball milling jar, 400-500 g of silicon nitride ceramic grinding balls with a diameter of 1-2 mm are added, the weight ratio of the silicon nitride ceramic grinding balls to silicon powder is 3-4:1, the rotation speed is 200-300 r / min, and the time is 10-20 h.

[0018] Furthermore, the purity of the silicon powder is ≧99.9%, and the particle size is ≦5 μm.

[0019] Furthermore, the purity of the cobalt is ≧99.99%, and the particle size is ≦2 μm.

[0020] Furthermore, the purity of the KCl is ≧99.5%.

[0021] Furthermore, the first corundum raw material is α-Al2O3 powder with a particle size of 0.040-0.045nm; the second corundum raw material is α-Al2O3 powder with a particle size of 1-3nm; and the third corundum raw material is α-Al2O3 powder with a particle size of 0.045-1nm.

[0022] Furthermore, the dispersant is ammonium polyacrylate, the regulator is concentrated aqueous ammonia, the catalyst is N,N,Nˊ,Nˊ-tetramethylethylenediamine, and the initiator is ammonium sulfate.

[0023] Furthermore, the three ball millings and the four ball millings are carried out in a ball milling jar at a rotation speed of 45-50 r / min for 6-8 h.

[0024] Furthermore, in step III, the sintering treatment is as follows: introducing N2 protection, raising the temperature to 1500-1600° C., and keeping the temperature for 150-180 minutes.

[0025] By adopting the above technical solution, the beneficial effects of the present invention are:

[0026] 1. High-purity α-Si3N4 powder is prepared by direct nitridation, with Co metal and KCl dual catalyst acting on silicon powder, and a two-stage heating process. First, a sintering is performed, and KCl reaches a completely molten state at 900-920°C; then a secondary sintering is performed, and the temperature is raised to 1200-1250°C for nitridation reaction. Silicon powder and KCl are in contact with each other in three different ways, and three growth mechanisms occur when the corresponding nitridation reaction grows α-Si3N4. The first one: silicon powder is in direct contact with KCl molten salt. At the same time, Co-Si liquid phase is formed. Then silicon powder and Co-Si liquid phase are in contact with N2, and the reaction generates needle-shaped α-Si3N4. Then N2 is in contact with silicon powder to generate Si3N4 particles in situ. The second one: silicon powder is completely wrapped by KCl molten salt. At this time, N2 continuously diffuses into the Co-Si liquid phase through the KCl molten salt layer. N atoms contact Si atoms to generate spherical α-Si3N4. The third one: silicon powder is in partial contact with KCl molten salt. Silicon atoms in gaseous form detach from the surface through the gas-gas-solid (VVS) mechanism and react with nearby nitrogen atoms to form a layer of α-Si3N4.

[0027] 2. Primary sintering: Pre-treat silicon powder particles with molten KCl at a relatively low temperature to provide a liquid phase environment. KCl molten salt can absorb a large amount of heat released by the nitridation reaction. This isolation and endothermic effect is conducive to complete and uniform nitridation, preventing local agglomeration and the formation of β-Si3N4 caused by local overheating. In addition, the catalytic effect of Co metal produces Co-Si liquid phase, which reduces the nitridation temperature of silicon particles and can greatly shorten the nitridation reaction time. Through the synergistic effect of the catalyst and the nitridation process, the silicon powder is completely nitrided in a relatively short time to generate high-purity α-Si3N4 powder.

[0028] 3. A modified Al2O3 corundum crucible is prepared by adding dispersants, initiators and catalysts to corundum raw materials with different particle sizes. Since the dispersants, initiators and catalysts are all organic substances, they can be discharged cleanly during the sintering of the Al2O3 corundum crucible. Therefore, the crucible has good strength, good thermal stability and no residual nitrogen and oxygen impurities, thereby reducing the influence of the crucible material on its quality when preparing high-purity α-Si3N4 powder during the nitridation process. DETAILED DESCRIPTION

[0029] Example 1

[0030] A method for preparing silicon nitride powder comprises the following preparation steps:

[0031] (1) Preparation of raw materials: 100 parts by weight of silicon powder, 1.0 parts by weight of cobalt, and 50 parts by weight of KCl; wherein the purity of silicon powder is 99.9% and the particle size is 5 μm; the purity of cobalt is 99.99% and the particle size is 2 μm; the purity of KCl is 99.5%;

[0032] (2) Ball milling of raw materials: silicon powder, cobalt and KCl are taken according to weight parts, mixed evenly, and ball milled once. 400 g of silicon nitride ceramic grinding balls with a diameter of 1 mm are added to the ball mill, the weight ratio of the silicon nitride ceramic grinding balls to silicon powder is 3:1, the rotation speed is 200 r / min, and the time is 10 h; then anhydrous ethanol is added in a weight ratio of silicon powder to anhydrous ethanol of 1:2, and a second ball milling is performed. 400 g of silicon nitride ceramic grinding balls with a diameter of 1 mm are added to the ball mill, the weight ratio of the silicon nitride ceramic grinding balls to silicon powder is 3:1, the rotation speed is 200 r / min, and the time is 10 h; slurry is obtained, and the slurry is dried to obtain mixed powder;

[0033] (3) Preparation of modified Al2O3 corundum crucible

[0034] I. Mix acrylamide and N,N′-methylenebisacrylamide in a weight ratio of 20:1, and add 0.5 parts by weight of ammonium polyacrylate to obtain a mixed solution;

[0035] II. Add concentrated ammonia to the mixed solution obtained in step I, adjust the pH to 9, add 30 parts by weight of the first corundum raw material, and perform ball milling three times in a ball mill at a speed of 45 r / min for 6 hours to obtain a first mixed slurry, and add 40 parts by weight and 20 parts by weight of the second corundum raw material and the third corundum raw material to the first mixed slurry, respectively, and perform ball milling four times in a ball mill at a speed of 45 r / min for 6 hours to obtain a second mixed slurry; wherein the first corundum raw material is an α-Al2O3 powder with a particle size of 0.040 nm; the second corundum raw material is an α-Al2O3 powder with a particle size of 1 nm; and the third corundum raw material is an α-Al2O3 powder with a particle size of 0.045 nm;

[0036] III. Vacuum-treat the second mixed slurry obtained in step II, add 3 parts by weight of N,N,N',N'-tetramethylethylenediamine and 0.1 parts by weight of ammonium sulfate, stir evenly and inject into the mold, solidify in a water bath, then keep warm in an oven for 24 hours, increase the temperature to 100°C, keep warm for 10 hours, then sinter in a vacuum sintering furnace, pass N2 protection, increase the temperature to 1500°C, keep warm for 150 minutes, and cool to room temperature to obtain the modified Al2O3 corundum crucible;

[0037] (4) primary sintering: adding the mixed powder obtained in step (2) into a modified Al2O3 corundum crucible, then placing the modified Al2O3 corundum crucible into a vacuum sintering furnace, introducing N2 protective gas, raising the temperature to 900°C at a heating rate of 5°C / min, and keeping the temperature for 50 min;

[0038] (5) Secondary sintering: Continue to increase the temperature to 1200°C at a heating rate of 5°C / min, keep at this temperature for 4 h, and cool to room temperature;

[0039] (6) After grinding, the silicon nitride powder is obtained.

[0040] Example 2

[0041] A method for preparing silicon nitride powder comprises the following preparation steps:

[0042] (1) Preparation of raw materials: 110 parts by weight of silicon powder, 1.5 parts by weight of cobalt, and 80 parts by weight of KCl; wherein the purity of the silicon powder is 99.9% and the particle size is 5 μm; the purity of the cobalt is 99.99% and the particle size is 2 μm; and the purity of the KCl is 99.5%;

[0043] (2) Ball milling of raw materials: silicon powder, cobalt and KCl are taken according to weight parts, mixed evenly, and ball milled once. In a ball mill, 450 g of silicon nitride ceramic grinding balls with a diameter of 1.5 mm are added, the weight ratio of the silicon nitride ceramic grinding balls to silicon powder is 3.5:1, the rotation speed is 250 r / min, and the time is 15 h; then, anhydrous ethanol is added in a weight ratio of silicon powder to anhydrous ethanol of 1:2, and a second ball milling is performed. In a ball mill, 450 g of silicon nitride ceramic grinding balls with a diameter of 1.5 mm are added, the weight ratio of the silicon nitride ceramic grinding balls to silicon powder is 3.5:1, the rotation speed is 250 r / min, and the time is 15 h; a slurry is obtained, and the slurry is dried to obtain a mixed powder;

[0044] (3) Preparation of modified Al2O3 corundum crucible

[0045] I. Mix acrylamide and N,N′-methylenebisacrylamide in a weight ratio of 20:1, and add 0.8 parts by weight of ammonium polyacrylate to obtain a mixed solution;

[0046] II. Add concentrated ammonia to the mixed solution obtained in step I, adjust the pH to 9, add 30-35 parts by weight of the first corundum raw material, and ball mill three times in a ball mill at a speed of 45-50r / min for 6-8h to obtain a first mixed slurry, add 40-45 parts by weight and 20-25 parts by weight of the second corundum raw material and the third corundum raw material to the first mixed slurry, respectively, and ball mill four times in a ball mill at a speed of 45-50r / min for 6-8h to obtain a second mixed slurry; wherein the first corundum raw material is; the second corundum raw material is α-Al2O3 powder with a particle size of 1-3nm; the third corundum raw material is α-Al2O3 powder with a particle size of 0.045-1nm;

[0047] III. Vacuum-treat the second mixed slurry obtained in step II, add 3-6 parts by weight of N,N,N',N'-tetramethylethylenediamine and 0.1-1 parts by weight of ammonium sulfate, stir evenly and inject into the mold, solidify in a water bath, then keep warm in an oven for 24 hours, increase the temperature to 100-120°C, keep warm for 10-12 hours, then sinter in a vacuum sintering furnace, pass N2 protection, increase the temperature to 1500-1600°C, keep warm for 150-180 minutes, and cool to room temperature to obtain the modified Al2O3 corundum crucible;

[0048] (4) primary sintering: adding the mixed powder obtained in step S2 into a modified Al2O3 corundum crucible, and then placing the modified Al2O3 corundum crucible into a vacuum sintering furnace, introducing N2 protective gas, raising the temperature to 900-920°C at a heating rate of 5°C / min, and keeping the temperature for 50-65min;

[0049] (5) Secondary sintering: Continue to increase the temperature to 1200-1250°C at a heating rate of 5°C / min, keep at this temperature for 4 hours, and cool to room temperature;

[0050] (6) After grinding, the silicon nitride powder is obtained.

[0051] Example 3

[0052] A method for preparing silicon nitride powder comprises the following preparation steps:

[0053] (1) Preparation of raw materials: 100-120 parts by weight of silicon powder, 1.0-2.5 parts by weight of cobalt, and 50-100 parts by weight of KCl; wherein the purity of silicon powder is ≥99.9% and the particle size is ≤5 μm; the purity of cobalt is ≥99.99% and the particle size is ≤2 μm; the purity of KCl is ≥99.5%;

[0054] (2) ball milling of raw materials: silicon powder, cobalt and KCl are taken according to weight parts, mixed evenly, and ball milled once. In a ball mill, 400-500 g of silicon nitride ceramic grinding balls with a diameter of 1-2 mm are added, the weight ratio of the silicon nitride ceramic grinding balls to silicon powder is 3-4:1, the rotation speed is 200-300 r / min, and the time is 10-20 h; then, anhydrous ethanol is added according to the weight ratio of silicon powder to anhydrous ethanol of 1:2-2.5, and a second ball milling is performed. In a ball mill, 400-500 g of silicon nitride ceramic grinding balls with a diameter of 1-2 mm are added, the weight ratio of the silicon nitride ceramic grinding balls to silicon powder is 3-4:1, the rotation speed is 200-300 r / min, and the time is 10-20 h; slurry is obtained, and the slurry is dried to obtain mixed powder;

[0055] (3) Preparation of modified Al2O3 corundum crucible

[0056] I. Mix acrylamide and N,N′-methylenebisacrylamide in a weight ratio of 20:1, and add 0.5-1 parts by weight of ammonium polyacrylate to obtain a mixed solution;

[0057] II. Add concentrated ammonia to the mixed solution obtained in step I, adjust the pH to 9, add 30-35 parts by weight of the first corundum raw material, and ball mill three times in a ball mill at a speed of 45-50r / min for 6-8h to obtain a first mixed slurry, add 40-45 parts by weight and 20-25 parts by weight of the second corundum raw material and the third corundum raw material to the first mixed slurry, respectively, and ball mill four times in a ball mill at a speed of 45-50r / min for 6-8h to obtain a second mixed slurry; wherein the first corundum raw material is; the second corundum raw material is α-Al2O3 powder with a particle size of 1-3nm; the third corundum raw material is α-Al2O3 powder with a particle size of 0.045-1nm;

[0058] III. Vacuum-treat the second mixed slurry obtained in step II, add 3-6 parts by weight of N,N,N′,N′-tetramethylethylenediamine and 0.1-1 parts by weight of ammonium sulfate, stir evenly and inject into the mold, solidify in a water bath, then keep warm in an oven for 24 hours, increase the temperature to 100-120°C, keep warm for 10-12 hours, then sinter in a vacuum sintering furnace, pass N2 protection, increase the temperature to 1500-1600°C, keep warm for 150-180 minutes, and cool to room temperature to obtain the modified Al2O3 corundum crucible;

[0059] (4) primary sintering: adding the mixed powder obtained in step S2 into a modified Al2O3 corundum crucible, and then placing the modified Al2O3 corundum crucible into a vacuum sintering furnace, introducing N2 protective gas, raising the temperature to 900-920°C at a heating rate of 5°C / min, and keeping the temperature for 50-65min;

[0060] (5) Secondary sintering: Continue to increase the temperature to 1200-1250°C at a heating rate of 5°C / min, keep at this temperature for 4 hours, and cool to room temperature;

[0061] (6) After grinding, the silicon nitride powder is obtained.

[0062] Comparative Example 1

[0063] The difference from Example 1 is that the raw materials do not use cobalt and KCl in the technical solution, but only use silicon powder; the crucible used for vacuum sintering does not use the modified Al2O3 corundum crucible in the technical solution, but uses a commercially available Al2O3 corundum crucible. Other technical solutions are the same as Example 1.

[0064] Table 1 shows the test results of silicon nitride powder data of Example 1, Example 2, Example 3 and Comparative Example 1.

[0065] Table 1

[0066] project Example 1 Example 2 Example 3 Comparative Example 1 <![CDATA[α-Si3N4 phase content (%)]]> 99.2％ 99.1％ 99.1％ 82.3％

[0067] As can be seen from Table 1, the α-Si3N4 phase content in the silicon nitride powder prepared by this technical solution is as high as 99.1%-99.2%, which is a high-purity silicon nitride powder.

[0068] Although the present invention has been specifically shown and described in conjunction with the preferred embodiments, it should be understood by those skilled in the art that various changes may be made to the present invention in form and details without departing from the spirit and scope of the present invention as defined by the appended claims, all of which are within the scope of protection of the present invention.

Claims

1. A method for preparing silicon nitride powder, characterized in that: The method comprises the following preparation steps: S1. Preparation of raw materials: 100-120 parts by weight of silicon powder, 1.0-2.5 parts by weight of cobalt, 50-100 parts by weight of KCl; S2, ball milling of raw materials: silicon powder, cobalt and KCl are taken according to weight parts, mixed evenly, and ball milled once, and then anhydrous ethanol is added in a weight ratio of silicon powder to anhydrous ethanol of 1:2-2.5, and ball milled twice to obtain slurry, and the slurry is dried to obtain mixed powder; S3, primary sintering: adding the mixed powder obtained in step S2 into a modified Al2O3 corundum crucible, then placing the modified Al2O3 corundum crucible into a vacuum sintering furnace, introducing high-purity N2 protective gas, raising the temperature to 900-920°C at a heating rate of 5°C / min, and keeping the temperature for 50-65min; S4, secondary sintering: continue to increase the temperature to 1200-1250°C at a heating rate of 5°C / min, keep warm for 4 hours, and cool to room temperature; S5. After grinding, silicon nitride powder is obtained.

2. The method for preparing silicon nitride powder according to claim 1, characterized in that: The preparation method of the modified Al2O3 corundum crucible is: I. Mix acrylamide and N,N′-methylenebisacrylamide in a weight ratio of 20-25:1, and add 0.5-1 parts by weight of a dispersant to obtain a mixed solution; II. Add a regulator to the mixed solution obtained in step I to adjust the pH to 9, add 30-35 parts by weight of the first corundum raw material, and ball mill three times to obtain a first mixed slurry, and add 40-45 parts by weight and 20-25 parts by weight of the second corundum raw material and the third corundum raw material to the first mixed slurry, respectively, and ball mill four times to obtain a second mixed slurry; III. Vacuum-treat the second mixed slurry obtained in step II, add 3-6 parts by weight of a catalyst and 0.1-1 parts by weight of an initiator, stir evenly and inject into a mold, cure in a water bath, then keep warm in an oven for 24 hours, increase the temperature to 100-120°C, keep warm for 10-12 hours, then sinter in a vacuum sintering furnace, and cool to room temperature to obtain the modified Al2O3 corundum crucible.

3. The method for preparing silicon nitride powder according to claim 1, characterized in that: The first ball milling and the second ball milling are as follows: 400-500g of silicon nitride ceramic grinding balls with a diameter of 1-2mm are added into a ball milling jar, the weight ratio of the silicon nitride ceramic grinding balls to silicon powder is 3-4:1, the rotation speed is 200-300r / min, and the time is 10-20h.

4. The method for preparing silicon nitride powder according to claim 1, characterized in that: The purity of the silicon powder is ≧99.9%, and the particle size is ≦5 μm.

5. The method for preparing silicon nitride powder according to claim 1, characterized in that: The purity of the cobalt is ≧99.99%, and the particle size is ≦2 μm.

6. The method for preparing silicon nitride powder according to claim 1, characterized in that: The purity of the KCl is ≧99.5%.

7. The method for preparing silicon nitride powder according to claim 2, characterized in that: The first corundum raw material is α-Al2O3 powder with a particle size of 0.040-0.045nm; the second corundum raw material is α-Al2O3 powder with a particle size of 1-3nm; the third corundum raw material is α-Al2O3 powder with a particle size of 0.045-1nm.

8. The method for preparing silicon nitride powder according to claim 2, characterized in that: The dispersant is ammonium polyacrylate, the regulator is concentrated ammonia water, the catalyst is N,N,N',N'-tetramethylethylenediamine, and the initiator is ammonium sulfate.

9. The method for preparing silicon nitride powder according to claim 2, characterized in that: The three times ball milling and the four times ball milling are carried out in a ball milling jar at a rotation speed of 45-50 r / min for 6-8 hours.

10. The method for preparing silicon nitride powder according to claim 2, characterized in that: In step III, the sintering treatment is as follows: introducing high-purity N2 for protection, raising the temperature to 1500-1600° C., and keeping the temperature for 150-180 minutes.