A method for producing silicon carbide ceramics

Abstract

The application provides a silicon carbide ceramic preparation method. The method comprises the following steps: 1) configuration of main raw materials: the main raw materials comprise the following components: micron-sized alpha-silicon carbide spherical powder, and polycarbosilane powder with a mass ratio of 2.5%-10% of silicon carbide; 2) preparation of slurry: the polycarbosilane powder is added into a butyl ether solvent to prepare a polycarbosilane solution under magnetic stirring, and then the silicon carbide powder is added into the polycarbosilane solution to continue magnetic stirring, so as to obtain a mixed slurry; 3) rotary evaporation drying: the mixed slurry obtained in the step (2) is subjected to rotary evaporation drying to obtain ceramic powder; 4) discharge plasma sintering: the ceramic powder obtained in the step (3) is subjected to discharge plasma sintering to obtain silicon carbide ceramic. The application can obtain dense silicon carbide ceramic with good performance by directly sintering to generate nanometer silicon carbide grains in situ. The process is simple, short in process flow and convenient to operate, and can effectively reduce the cost and is suitable for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of silicon carbide ceramic preparation, specifically relating to a method for achieving fine-grained strengthened silicon carbide ceramics by directly sintering in-situ self-generated nanocrystals. Background Technology

[0002] Silicon carbide (SiC), due to its crystal structure and the highly covalent nature of the Si-C bonds, exhibits few lattice defects and possesses excellent high-temperature strength, high wear resistance, corrosion resistance, and good electrical and thermal conductivity. Therefore, silicon carbide is widely used in aerospace, defense armor, semiconductors, and the nuclear industry. However, the strong covalent bonding and low diffusion coefficient of silicon carbide make it difficult to sinter. Currently, the preparation of silicon carbide ceramics mainly employs hot pressing and pressureless sintering, while spark plasma sintering has attracted considerable attention due to its ability to significantly reduce sintering temperatures.

[0003] Faced with increasingly stringent performance requirements, silicon carbide ceramics urgently need further performance enhancement. Currently, the main strengthening methods include second-phase strengthening and grain refinement strengthening. Second-phase strengthening improves material properties by introducing dispersed, uniformly fine particles into the silicon carbide ceramic matrix to hinder dislocation movement, but this affects the purity of the silicon carbide ceramic. Grain refinement strengthens improves material properties by increasing the number of grain boundaries through grain refinement. For example, patent CN101182211 uses nano-silicon carbide as the matrix material and employs a two-step forming and sintering technique to prepare nano-silicon carbide ceramics with a grain size of 200 nm.

[0004] Polycarbosilanes are often introduced into materials as precursors for silicon carbide ceramics. After thermal crosslinking and pyrolysis, they can be used to prepare nanoscale silicon carbide. During the pyrolysis of polycarbosilanes, when the temperature is above 200℃, the organic macromolecules undergo a condensation reaction, releasing gas; when the temperature is above 800℃, all the organic macromolecules are transformed into amorphous inorganic matter; and when the temperature is above 1400℃, the amorphous inorganic matter crystallizes into silicon carbide nanocrystals. For example, patent CN101774810 mixes polycarbosilane and α-SiC micropowder, and prepares a surface-modified silicon carbide powder by coating non-spherical α-SiC micropowder with β-SiC nanocrystals through high-temperature pyrolysis. However, in the above-mentioned fine-grained strengthening method, the nanoscale raw material powder is prone to agglomeration, affecting the uniformity of the structure. The method of first preparing the modified powder by pyrolyzing the precursor and then sintering the powder to prepare bulk silicon carbide ceramics increases the complexity of the process and easily introduces impurities.

[0005] In composite material manufacturing, the method of directly generating and growing reinforcing materials within the matrix is ​​called in-situ self-generation. This method effectively avoids the introduction of impurities. Directly sintering a mixture of the ceramic precursor polycarbosilane and raw material powder achieves fine-grained reinforcement through the nanocrystals generated by the in-situ self-generation method. Furthermore, it reduces impurity contamination from the two-step process of first pyrolyzing the precursor to prepare modified powder and then sintering the modified powder. However, the pyrolysis of polycarbosilane at high temperatures releases a large amount of gas, severely affecting the density of the sintered material. This is why high-temperature pyrolysis is currently necessary to prepare powder for silicon carbide ceramics using ceramic precursors. Therefore, ensuring both in-situ self-generation of nanocrystals and maintaining the density of the bulk material is a pressing problem that needs to be solved. Summary of the Invention

[0006] This invention provides a method for preparing silicon carbide ceramics. First, powder is magnetically stirred and mixed, then rotary evaporated to directly obtain a dry mixed powder. Finally, the mixed powder is directly sintered. Through an in-situ self-generation method, dense bulk ceramics are obtained simultaneously by forming nano-silicon carbide in a micron-sized spherical silicon carbide matrix. Nanocrystals can further improve the strength and toughness of silicon carbide, and direct sintering ensures the high purity of the prepared silicon carbide ceramic. The aforementioned preparation method provides a silicon carbide ceramic whose properties meet general process requirements.

[0007] On the one hand, the present invention provides a method for preparing silicon carbide ceramics, which mainly includes the following process steps:

[0008] Step (1) Preparation of main raw materials: The main raw materials include the following components: micron-sized α-silicon carbide spherical powder, and polycarbosilane powder accounting for 2.5%-10% of the silicon carbide powder by mass. The particle size range of the silicon carbide spherical powder is 40-70μm, and the purity is greater than 99%. The molecular weight of the polycarbosilane is 1100-1400. At room temperature, it is a mixture of colorless lumps and powder. The reason for using spherical silicon carbide powder is that spherical powder has better fluidity during sintering, and the gaps between the spherical powder particles facilitate gas discharge, which helps to promote densification and sintering.

[0009] Step (2) Slurry preparation: Weigh the polycarbosilane and put it into a flat-bottomed flask. Then, put the magnetic stir bar into the flat-bottomed flask. The magnetic stir bar is made of polytetrafluoroethylene / magnetic steel and is a cylinder with a size of Ф8mm×40mm.

[0010] Pour butyl ether organic solvent into a flat-bottomed flask, then place the flask containing polycarbosilane, a magnetic stir bar, and butyl ether on a magnetic stirring device. Stir at a speed of 450-800 r / min for 30-60 min until the polycarbosilane is completely dissolved, the solution is transparent, and there is no suspension or precipitation.

[0011] The weighed silicon carbide spherical powder is added to the mixed polycarbosilane solution, and the stirring speed is increased to 800-1500 r / min. The stirring time is 3-6 h to obtain a mixed slurry.

[0012] Step (3) Rotary evaporation drying: Place the flask containing the mixed slurry obtained in step (2) in a rotary evaporator and perform rotary evaporation drying by heating with an oil bath.

[0013] The rotary evaporation drying environment is under negative pressure, the rotary evaporation drying temperature is 130-150℃, the flask rotation speed is 50-100 r / min, and the drying time is 1-2 h, to obtain ceramic powder. The rotary evaporation directly yields dry ceramic powder, not a bulk material. The rotary evaporation drying temperature is the boiling point of butyl ether (141℃) and does not reach the softening point of polycarbosilane (180-230℃). The rotary evaporation directly yields dry ceramic powder.

[0014] Step (4) Spark plasma sintering: The ceramic powder obtained in step (3) is loaded into a graphite mold, and then the graphite mold is placed in a spark plasma sintering equipment. The temperature is first raised to 800℃ at a heating rate of 100-150℃ / min, and the holding time is 2-5min. This helps the powder particles to flow and rearrange, and promotes the gas discharge.

[0015] Continue heating at a rate of 100-150℃ / min to 1200℃.

[0016] While increasing the sintering pressure to 50 MPa, continue heating to 1600 °C at a rate of 50-100 °C / min, ensuring that pressure loading is completed before reaching 1600 °C. During this stage, the simultaneous pressurization and heating facilitates initial densification and sintering.

[0017] When the temperature reaches 1600℃, continue applying pressure and increasing the temperature. While increasing the sintering pressure to 70-80 MPa, continue heating at a rate of 50-100℃ / min to 1750-1800℃, ensuring that pressure loading is completed before reaching the set temperature. The holding time is 1-10 minutes. During this stage, the simultaneous application of pressure and temperature helps to achieve final densification and complete sintering. After sintering, cool with the furnace to obtain the silicon carbide sample.

[0018] On the other hand, the present invention also provides silicon carbide ceramics prepared by the aforementioned preparation method.

[0019] The beneficial effects of this invention include:

[0020] The silicon carbide ceramic preparation method provided by this invention does not require the addition of additional sintering aids, nor does it require thermal crosslinking and curing. After rotary evaporation, it becomes powder that can be directly used for sintering. Furthermore, the main product after the ceramic precursor is pyrolyzed is silicon carbide, which ensures purity and improves the high-temperature performance of silicon carbide ceramics.

[0021] The present invention provides a method for preparing silicon carbide ceramics by employing an in-situ self-generation method, which simultaneously forms nano-silicon carbide grains in-situ within a micron-sized spherical silicon carbide matrix and directly sinters to prepare dense bulk ceramics.

[0022] This invention provides a method for preparing silicon carbide ceramics. By utilizing the high pressure and rapid heating of spark plasma sintering to suppress grain growth, silicon carbide ceramics with multi-level grain size distribution are obtained, solving the problem of poor ceramic density caused by the gas generated from the cracking of polycarbosilane. This method for preparing silicon carbide ceramics has the advantages of short process and simple operation, and can effectively reduce the production cost of silicon carbide ceramics. Attached Figure Description

[0023] Figure 1 This is a process engineering diagram of a silicon carbide ceramic preparation method in the embodiment.

[0024] Figure 2 The image shows the microstructure of spherical silicon carbide as part of a silicon carbide ceramic preparation method described in this embodiment.

[0025] Figure 3 The image shows a spherical silicon carbide XRD pattern from a method for preparing silicon carbide ceramics in this embodiment.

[0026] Figure 4 The image shows the polycarbosilane FTIR spectrum of a silicon carbide ceramic preparation method described in this embodiment.

[0027] Figure 5 The image shown is a fracture morphology diagram of a silicon carbide ceramic sample obtained by adding 2.5 wt% polycarbosilane according to a method for preparing silicon carbide ceramics in this embodiment.

[0028] Figure 6 The image shown is a fracture morphology diagram of a silicon carbide ceramic sample obtained by adding 5 wt% polycarbosilane in one of the silicon carbide ceramic preparation methods described in this embodiment. Detailed implementation method:

[0029] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that the following embodiments are only for further illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below.

[0030] Example 1

[0031] Step (1) Preparation of main raw materials: The main raw materials include the following components: weigh 10 grams of micron-sized α-silicon carbide spherical powder and 0.25 grams of polycarbosilane powder. The particle size range of the silicon carbide spherical powder is 40 μm and the purity is greater than 99%. The molecular weight of the polycarbosilane is 1200.

[0032] Step (2) Slurry preparation: Place polycarbosilane into a flat-bottomed flask, add a magnetic stir bar, the magnetic stir bar is made of polytetrafluoroethylene / magnetic steel, and the magnetic stir bar is a cylinder with a size of Ф8mm×40mm.

[0033] Pour 50 ml of butyl ether organic solvent into a flat-bottomed flask, then place the flask containing polycarbosilane, a magnetic stir bar, and butyl ether on a magnetic stirring device. Stir at 450 r / min for 30 min until the polycarbosilane is completely dissolved and the solution is transparent with no suspension or precipitation.

[0034] The weighed silicon carbide spherical powder was added to the mixed polycarbosilane solution, and the stirring speed was increased to 800 r / min for 3 h to obtain a mixed slurry.

[0035] Step (3) Rotary evaporation drying: Place the flask containing the mixed slurry obtained in step (2) in a rotary evaporator and perform rotary evaporation drying by heating with an oil bath.

[0036] Under negative pressure, the rotary evaporation drying temperature was 140℃, the flask rotation speed was 50 r / min, and the drying time was 2 h to obtain ceramic powder. The rotary evaporation directly yields dry ceramic powder, not bulk material.

[0037] Step (4) Spark Plasma Sintering: The ceramic powder obtained in step (3) is loaded into a graphite mold, and then the graphite mold is placed in a spark plasma sintering apparatus. The temperature is first raised to 800°C at a rate of 100°C / min, and held for 3 minutes to facilitate powder flow and promote gas discharge.

[0038] Continue heating at a rate of 100℃ / min to 1200℃.

[0039] While increasing the sintering pressure to 50 MPa, continue heating to 1600 °C at a rate of 50 °C / min, ensuring that pressure loading is completed before reaching 1600 °C. During this stage, the simultaneous pressurization and heating facilitates initial densification and sintering.

[0040] When the temperature reaches 1600℃, continue applying pressure and increasing the temperature. While increasing the sintering pressure to 80MPa, continue heating at a rate of 50℃ / min to 1750℃. Ensure that pressure loading is completed before reaching 1750℃, and hold at that temperature for 5 minutes. During this stage, the simultaneous application of pressure and temperature helps to achieve final densification and complete sintering. After sintering, cool with the furnace to obtain the silicon carbide sample.

[0041] The fracture morphology of the silicon carbide sample obtained by sintering in this embodiment is shown in the figure below. Figure 5 As shown in the figure, nanocrystals can be observed, indicating that in-situ self-generation of silicon carbide was achieved, specifically the nanocrystals generated by the in-situ pyrolysis of the precursor polycarbosilane. The sample's bending strength was 443 MPa according to the three-point bending strength test. These data demonstrate that high-performance dense silicon carbide ceramics were successfully prepared by direct sintering.

[0042] Example 2

[0043] Preparation of main raw materials: The main raw materials include the following components: 10 grams of micron-sized α-silicon carbide spherical powder and 0.5 grams of polycarbosilane powder. The particle size range of the silicon carbide spherical powder is 40 μm and the purity is greater than 99%. The molecular weight of the polycarbosilane is 1200.

[0044] Step (2) is the same as in Example 1.

[0045] Step (3) is the same as in Example 1.

[0046] Step (4) is the same as in Example 1.

[0047] The fracture morphology of the silicon carbide sample obtained by sintering in this embodiment is shown in the figure below. Figure 6 As shown in the figure, nanocrystals can be observed, indicating that in-situ self-generation of silicon carbide was achieved, specifically the nanocrystals generated by the in-situ pyrolysis of the precursor polycarbosilane. The sample exhibited a bending strength of 475 MPa after a three-point bending strength test. These data demonstrate the successful preparation of high-performance, dense silicon carbide ceramics via direct sintering.

Claims

1. A method for preparing silicon carbide ceramics, characterized in that, Includes the following steps: 1) Preparation of main raw materials: The main raw materials include the following components: micron-sized α-silicon carbide spherical powder, and polycarbosilane powder accounting for 2.5%-10% of the silicon carbide powder by mass; 2) Slurry preparation: Polycarbosilane powder is added to butyl ether solvent and a polycarbosilane solution is prepared under magnetic stirring. Then, silicon carbide powder is added to the polycarbosilane solution and magnetic stirring is continued to obtain a mixed slurry. 3) Rotary evaporation drying: The mixed slurry obtained in step (2) is subjected to rotary evaporation drying to prepare ceramic powder. The dried ceramic powder is obtained directly after rotary evaporation. 4) Spark plasma sintering: The ceramic powder obtained in step (3) is subjected to spark plasma sintering to obtain silicon carbide ceramics in which nano-silicon carbide grains are formed in situ in a micron-sized spherical silicon carbide matrix.

2. The method for preparing silicon carbide ceramics according to claim 1, characterized in that, The particle size range of the micron-sized α-silicon carbide spherical powder is 40-70 μm, and the purity is greater than 99%.

3. The method for preparing silicon carbide ceramics according to claim 1, characterized in that, The molecular weight of polycarbosilane powder is 1100-1400, and it is a mixture of colorless lumps and powders at room temperature.

4. The method for preparing silicon carbide ceramics according to claim 1, characterized in that, The magnetic stirring speed for mixing polycarbosilane and butyl ether solvent is 450-800 r / min, and the stirring time is 30-60 min. The magnetic stir bar is made of polytetrafluoroethylene / magnetic steel and is a cylinder with dimensions of Ф8mm×40mm.

5. The method for preparing silicon carbide ceramics according to claim 1, characterized in that, The magnetic stirring speed for mixing silicon carbide powder and polycarbosilane solution is 800-1500 r / min, and the stirring time is 3-6 h.

6. The method for preparing silicon carbide ceramics according to claim 1, characterized in that, The temperature for rotary drying is 130-150℃, the rotation speed is 50-100 r / min, and the drying time is 1-2 h.

7. The method for preparing silicon carbide ceramics according to claim 1, characterized in that, In step (4), during the heating process of the discharge plasma sintering, the sintering temperature is less than 1200℃ and the heating rate is 100-150℃ / min, and the sintering temperature is greater than 1200℃ and the heating rate is 50-100℃ / min.

8. The method for preparing silicon carbide ceramics according to claim 1, characterized in that, In step (4), the discharge plasma sintering is carried out at 800°C for 2-5 minutes.

9. The method for preparing silicon carbide ceramics according to claim 1, characterized in that, In step (4), when the discharge plasma sintering temperature is raised to 1200°C, the sintering pressure is increased to 50 MPa, and the temperature is further raised to 1600°C.

10. A method for preparing silicon carbide ceramics according to claim 1, characterized in that, In step (4), the discharge plasma sintering is carried out by increasing the sintering pressure to 70-80 MPa when the temperature is raised to 1600℃, while continuing to raise the temperature to 1750-1800℃ and holding for 1-10 minutes.

11. The silicon carbide ceramic material prepared by any one of claims 1-10.

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