Preparation method of high-alpha-phase silicon nitride powder

Abstract

According to the preparation method of the high-alpha-phase silicon nitride powder, the silicon powder is used as a raw material to produce the silicon nitride powder, the production time is short, the high-alpha-phase silicon nitride powder is prepared, and the alpha-phase silicon nitride powder can be used for preparing silicon nitride ceramics; in the preparation process, extra silicon nitride powder does not need to serve as a diluent, the production cost is greatly reduced, and the prepared alpha-phase silicon nitride powder has the advantages of being high in phase content, easy to grind, high in sintering activity and the like.

Description

Technical Field

[0001] The invention relates to the technical field of silicon nitride preparation, in particular to a method for preparing high α-phase silicon nitride powder. Background Art

[0002] Silicon nitride ceramics are used as valves, pipes, grading wheels and ceramic cutting tools in the machinery industry. The most widely used is silicon nitride ceramic bearing balls. Compared with steel balls, silicon nitride ceramic bearing balls have outstanding advantages: low density, high temperature resistance, self-lubrication, and corrosion resistance. They are used in high-speed machine tool electric spindle high-speed bearings, aerospace engines, wind turbine bearings, automobile engine bearings and other equipment bearings.

[0003] In the prior art, after silicon powder is prepared into silicon nitride by combustion synthesis, some by-products will be produced, which are characterized by high oxygen content and impurity element levels, and the proportion of by-products is about 5-10%. The by-products need to consume a lot of manpower and material resources as solid waste treatment. In addition, in the process of preparing silicon nitride from silicon powder by combustion synthesis in the prior art, silicon nitride powder must be added as a diluent, and the production cost is relatively high. In addition, the silicon nitride produced not only contains α-phase silicon nitride but also β-phase silicon nitride. α-phase silicon nitride is a low-temperature stable phase, and β-phase silicon nitride is a high-temperature stable phase. During the sintering process of silicon nitride ceramics, α-phase silicon nitride will undergo abnormal grain growth, and the phase will be deformed into columnar β-phase silicon nitride. This structure plays a bridging, bifurcation, and deflection role in crack expansion, which can improve the toughness of the material and greatly improve the strength of the ceramic. Therefore, a high α-phase content is an important guarantee for obtaining high-performance silicon nitride ceramics. α-phase silicon nitride powder has relatively small particles and a relatively uniform particle size distribution. Most importantly, its sintering activity is higher than that of β-phase silicon nitride powder, and it can obtain a greater driving force during the sintering and densification process of silicon nitride ceramics. Therefore, high α-phase silicon nitride powder is usually used as the sintering powder for high-density silicon nitride ceramics. During the sintering process of silicon nitride powder, a transformation from α phase to β phase occurs, and the phase change is accompanied by the densification of the sintered body.

[0004] The reaction time of the existing silicon powder nitridation process is very long, generally up to more than 50 hours;

[0005] The alpha phase of silicon nitride produced by the existing silicon powder nitriding process is not high, generally below 90%, and the free silicon content is relatively large, generally above 0.1%. The quality of silicon nitride silicon powder produced by the existing mature processes on the market is generally not high, and can only be used in ordinary structural parts and other occasions with lower requirements. It cannot meet the requirements of producing Grade I and Grade II materials corresponding to the national standard "Silicon Nitride Balls for Ceramic Ball Bearings" GB / T31703-2015. It can be seen that the existing technology needs further development.

[0006] Therefore, there is an urgent need for a method for preparing high α-phase silicon nitride powder that can solve the above problems. Summary of the invention

[0007] The purpose of the present invention is to provide a method for preparing high α-phase silicon nitride powder to solve the problems existing in the above-mentioned prior art.

[0008] To achieve the above object, the present invention provides the following solutions:

[0009] The present invention provides a method for preparing high α-phase silicon nitride powder, comprising the following steps:

[0010] S1. Put silicon powder into a square crucible;

[0011] S2. The crucibles loaded with silicon powder are stacked and placed in an internal heat dewaxing and sintering furnace;

[0012] S3. Start the internal heat dewaxing and sintering furnace and evacuate it;

[0013] S4. Start the heating program, heat and fill with nitrogen;

[0014] S5. When the temperature reaches the predetermined temperature of 1100-1200°C, start heat preservation;

[0015] S6. After the silicon powder starts to react and absorbs part of the nitrogen, the pressure is controlled;

[0016] S7. After 8 to 10 hours of reaction, the gas flow rate is increased, and the heating program is turned off after 3 hours of reaction, and the furnace is cooled;

[0017] S8. The powder after the reaction is taken out and crushed using a jaw crusher;

[0018] S9. Put the crushed powder into a horizontal ball mill and mill for 6 to 8 hours;

[0019] S10. The ball-milled powder is loaded into a silicon nitride crucible with a diameter of 150 mm and a height of 100 mm and placed in an internal heat dewaxing and sintering furnace;

[0020] S11. Evacuate the chamber and start the heating process;

[0021] S12. When the temperature reaches 1250-1300°C, start heat preservation and fill with nitrogen to control the pressure. After heat preservation for 3-5 hours, turn off the heating program and cool with the furnace to obtain high α-phase silicon nitride powder.

[0022] Preferably, in step S1, the purity of the silicon powder is 99.99%, and D50 is 5-10 μm.

[0023] Preferably, in step S3, the pressure is evacuated to below 50 Pa.

[0024] Preferably, in step S4, the heating temperature is 800-900°C, and nitrogen is charged to a pressure of 500-1000Pa.

[0025] Preferably, in step S6, the pressure is controlled at 1000-2000 Pa, and the inflation flow rate is maintained at 0.8-1.0 m 3 / h.

[0026] Preferably, in step S7, the inflation flow rate is increased to 2.0-2.5 m 3 / h.

[0027] Preferably, in step S11, the pressure is evacuated to below 50 Pa.

[0028] Preferably, in step S12, the pressure is controlled to be 0.1-0.2 MPa.

[0029] Compared with the prior art, the present invention has achieved the following beneficial technical effects:

[0030] The present invention provides a method for preparing high α-phase silicon nitride powder. Silicon powder is produced by using silicon powder as a raw material. The production time is short and high α-phase silicon nitride powder is prepared. The α-phase silicon nitride powder can be used for the preparation of silicon nitride ceramics. No additional silicon nitride powder is required as a diluent during the preparation process, which greatly reduces the production cost. The prepared α-phase silicon nitride powder has the advantages of high phase content, easy grinding, high sintering activity, etc. DETAILED DESCRIPTION

[0031] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0032] The purpose of the present invention is to provide a method for preparing high α-phase silicon nitride powder to solve the problems existing in the prior art.

[0033] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below in conjunction with specific implementation methods.

[0034] Embodiment 1:

[0035] This embodiment provides a method for preparing high α-phase silicon nitride powder, comprising the following steps:

[0036] Step 1: Put silicon powder with a purity of 99.99% and a D50 of 5 microns into a square crucible;

[0037] Step 2: stack the crucibles filled with silicon powder in the first step and put them into an internal heat dewaxing and sintering integrated furnace;

[0038] Step 3: Start the internal heat dewaxing and sintering integrated furnace and evacuate the vacuum to below 50Pa;

[0039] Step 4: Start the heating program, heat to 800°C, and start filling with an appropriate amount of nitrogen to make the pressure reach 500Pa;

[0040] Step 5: When the temperature reaches the preset 1100°C, start heat preservation;

[0041] Step 6: After the silicon powder starts to react and absorbs part of the nitrogen, start to control the pressure below 1000Pa and keep the inflation flow rate at 0.8 cubic meters per hour;

[0042] Step 7: After the sixth step has reacted for 8 hours, the gas flow rate is increased to 2.0 cubic meters per hour. After 3 hours of reaction, the heating program is turned off and the furnace is cooled;

[0043] Step 8: Take out the powder after step 7 and crush it with a jaw crusher;

[0044] Step 9: Put the powder crushed in step 8 into a horizontal ball mill and mill for 6 hours;

[0045] Step 10: Place the powder after ball milling in step 9 into a silicon nitride crucible with a diameter of 150 mm and a height of 100 mm, and place it into an internal heat dewaxing and sintering integrated furnace;

[0046] Step 11: Vacuum the pressure to below 50Pa and start the heating process;

[0047] Step 12: Start keeping the temperature at 1250-1300℃ and fill with nitrogen at a pressure of 0.1MPa. After keeping the temperature for 3 hours, turn off the heating and cool with the furnace.

[0048] Embodiment 2:

[0049] This embodiment provides a method for preparing high α-phase silicon nitride powder, comprising the following steps:

[0050] Step 1: Put silicon powder with a purity of 99.99% and a D50 of 8 microns into a square crucible;

[0051] Step 2: stack the crucibles filled with silicon powder in the first step and put them into an internal heat dewaxing and sintering integrated furnace;

[0052] Step 3: Start the internal heat dewaxing and sintering integrated furnace and evacuate the vacuum to below 50Pa;

[0053] Step 4: Start the heating program, heat to 850°C, and start filling with an appropriate amount of nitrogen to make the pressure reach 800Pa;

[0054] Step 5: When the temperature reaches the preset 1150°C, start heat preservation;

[0055] Step 6: After the silicon powder starts to react and absorbs part of the nitrogen, start to control the pressure below 1500Pa and keep the inflation flow rate at 0.9 cubic meters per hour;

[0056] Step 7: After the sixth step reacts for 9 hours, start to increase the gas flow rate to 2.2 cubic meters per hour. After 3 hours of reaction, turn off the heating program and cool with the furnace;

[0057] Step 8: Take out the powder after step 7 and crush it with a jaw crusher;

[0058] Step 9: Put the powder crushed in step 8 into a horizontal ball mill and mill for 7 hours;

[0059] Step 10: Place the powder after ball milling in step 9 into a silicon nitride crucible with a diameter of 150 mm and a height of 100 mm, and place it into an internal heat dewaxing and sintering integrated furnace;

[0060] Step 11: Vacuum the pressure to below 50Pa and start the heating process;

[0061] Step 12: Start keeping warm at 1280℃ and fill with nitrogen at a pressure of 0.15MPa. After keeping warm for 4 hours, turn off the heating and cool with the furnace.

[0062] Embodiment 3:

[0063] This embodiment provides a method for preparing high α-phase silicon nitride powder, comprising the following steps:

[0064] Step 1: Put silicon powder with a purity of 99.99% and a D50 of 10 microns into a square crucible;

[0065] Step 2: stack the crucibles filled with silicon powder in the first step and put them into an internal heat dewaxing and sintering integrated furnace;

[0066] Step 3: Start the internal heat dewaxing and sintering integrated furnace and evacuate the vacuum to below 50Pa;

[0067] Step 4: Start the heating program, heat to 900°C, and start filling with an appropriate amount of nitrogen to make its pressure reach 1000Pa;

[0068] Step 5: When the temperature reaches the preset 1200°C, start heat preservation;

[0069] Step 6: After the silicon powder starts to react and absorbs part of the nitrogen, start to control the pressure below 2000Pa and keep the inflation flow rate at 1.0 cubic meter per hour;

[0070] Step 7: After the sixth step reacts for 10 hours, start to increase the gas flow rate to 2.5 cubic meters per hour. After 3 hours of reaction, turn off the heating program and cool with the furnace;

[0071] Step 8: Take out the powder after step 7 and crush it with a jaw crusher;

[0072] Step 9: Put the powder crushed in step 8 into a horizontal ball mill and mill for 8 hours;

[0073] Step 10: Place the powder after ball milling in step 9 into a silicon nitride crucible with a diameter of 150 mm and a height of 100 mm, and place it into an internal heat dewaxing and sintering integrated furnace;

[0074] Step 11: Vacuum the pressure to below 50Pa and start the heating process;

[0075] Step 12: Start keeping the temperature at 1300℃ and fill with nitrogen at a pressure of 0.2MPa. After keeping the temperature for 5 hours, turn off the heating and cool with the furnace.

[0076] The applicant conducted 12 batches of tests using the preparation method of high α-phase silicon nitride powder in Example 3 from June to August 2024. The preparation amount of each test was 50 kg, and the prepared silicon nitride powder was tested. The test results are as follows:

[0077] Silicon powder nitriding inspection record

[0078]

[0079]

[0080] It can be seen from the above test results that the method for preparing high α-phase silicon nitride powder provided by the present invention can prepare high α-phase silicon nitride powder.

[0081] The present invention uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the method and core ideas of the present invention. At the same time, for those skilled in the art, according to the ideas of the present invention, there will be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for preparing high α-phase silicon nitride powder, characterized in that: The following steps are involved: S1. Put silicon powder into a square crucible; S2. The crucibles loaded with silicon powder are stacked and placed in an internal heat dewaxing and sintering furnace; S3. Start the internal heat dewaxing and sintering furnace and evacuate it; S4. Start the heating program, heat and fill with nitrogen; S5. When the temperature reaches the predetermined temperature of 1100-1200°C, start heat preservation; S6. After the silicon powder starts to react and absorbs part of the nitrogen, the pressure is controlled; S7. After 8 to 10 hours of reaction, the gas flow rate is increased, and the heating program is turned off after 3 hours of reaction, and the furnace is cooled; S8. The powder after the reaction is taken out and crushed using a jaw crusher; S9. Put the crushed powder into a horizontal ball mill and mill for 6 to 8 hours; S10. The ball-milled powder is loaded into a silicon nitride crucible with a diameter of 150 mm and a height of 100 mm and placed in an internal heat dewaxing and sintering furnace; S11. Evacuate the chamber and start the heating process; S12. When the temperature reaches 1250-1300°C, start heat preservation and fill with nitrogen to control the pressure. After heat preservation for 3-5 hours, turn off the heating program and cool with the furnace to obtain high α-phase silicon nitride powder.

2. The method for preparing high α-phase silicon nitride powder according to claim 1, characterized in that: In step S1, the purity of silicon powder is 99.99% and D50 is 5-10 μm.

3. The method for preparing high α-phase silicon nitride powder according to claim 1, characterized in that: In step S3, the pressure is evacuated to below 50 Pa.

4. The method for preparing high α-phase silicon nitride powder according to claim 1, characterized in that: In step S4, the heating temperature is 800-900°C, and nitrogen is filled to a pressure of 500-1000Pa.

5. The method for preparing high α-phase silicon nitride powder according to claim 1, characterized in that: In step S6, the pressure is controlled at 1000-2000 Pa and the inflation flow rate is maintained at 0.8-1.0 m 3 / h.

6. The method for preparing high α-phase silicon nitride powder according to claim 1, characterized in that: In step S7, the inflation flow rate is increased to 2.0-2.5 m 3 / h.

7. The method for preparing high α-phase silicon nitride powder according to claim 1, characterized in that: In step S11, the pressure is evacuated to below 50 Pa.

8. The method for preparing high α-phase silicon nitride powder according to claim 1, characterized in that: In step S12, the pressure is controlled to be 0.1-0.2 MPa.

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