Silicon carbide ceramic microspheres, and preparation method and application thereof

Abstract

The application discloses silicon carbide ceramic microspheres, a preparation method and application thereof, and relates to the technical field of ceramic powder preparation. 3 The preparation process of the application mainly comprises four processes of dispersion, granulation, screening and densification. The silicon carbide ceramic microspheres are spherical or near-spherical in shape, and the diameter is 20-200 mu m, and the density is 2.9-3.1 g / cm 3 The application solves the problems of low bulk density and poor density uniformity of the existing ceramic powder.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ceramic powder preparation, in particular to a silicon carbide ceramic microsphere and a preparation method and application thereof. BACKGROUND

[0002] Ceramic material components are widely used in high-temperature industrial fields due to their excellent properties such as high specific strength, high specific modulus, corrosion resistance, high-temperature resistance, low density and multiple functions. The density and density uniformity of a ceramic component are the two simplest and most intuitive indicators for evaluating the performance of the ceramic component when the material composition used is certain. Regarding the improvement of the density indicator, because the final sintering of the ceramic component is the close combination between ceramic powder particles, high density means low porosity between particles, therefore, the industry usually adopts ceramic powder with particle grading or ceramic powder with small particle size for sintering after forming; regarding the improvement of the density uniformity indicator, it is directly related to the forming method of the ceramic component. The forming of the ceramic material can be roughly divided into three categories: one is to use ceramic granulated powder as the raw material and to be formed by dry pressing or isostatic pressing; the other is to use ceramic slurry as the raw material and to be formed by slurry injection, tape casting or sol-gel method; the third is to add a plasticizer to the ceramic powder to form a viscous plastic ceramic material and to be formed by hot-pressing or injection molding; in order to improve the density uniformity of the final ceramic component, it is required that the ceramic powder particles have small internal friction under a specific state in the above three forming processes, so as to achieve good flowability, that is, the ceramic granulated powder can move to reach the closest packing density under the action of external force, the ceramic slurry can flow freely under the assistance of solvent, and the ceramic viscous plastic material can fill every corner of the mold under pressure.

[0003] At present, the silicon carbide (SiC) powder used in industry is generally prepared by mechanical crushing method, that is, large particle silicon carbide is crushed and then the desired mesh size silicon carbide fine powder is prepared by screening method. The shape of this silicon carbide powder is irregular, the particle size is not uniform, and most of them are angular. After the particles are stacked, a large number of irregular overlapping pores are formed between the particles, so that the final density cannot be improved. In addition, the friction between the particles is large, which leads to poor flowability of the powder / slurry and uneven density. Therefore, there is an urgent need for a new ceramic powder. SUMMARY

[0004] In order to solve the above technical problems, the purpose of the present application is to provide a silicon carbide ceramic microsphere and a preparation method and application thereof, so as to solve the problems of low bulk density and poor density uniformity of the existing ceramic powder.

[0005] The technical solution of this invention to solve the above-mentioned technical problems is as follows: A silicon carbide ceramic microsphere is provided, wherein the silicon carbide ceramic microsphere is spherical or nearly spherical in shape, with a diameter of 20-200 μm and a density of 2.9-3.1 g / cm³. 3 .

[0006] The beneficial effects of the present invention are as follows: the silicon carbide ceramic microspheres of the present invention are spherical or near-spherical in shape. Whether they are dry powder, or formulated into ceramic slurry or plastic material, they have better flowability and higher bulk density compared with irregular angular silicon carbide powder.

[0007] The present invention also provides a method for preparing the above-mentioned silicon carbide ceramic microspheres, comprising the following steps:

[0008] (1) Alcohol dispersion: Submicron silicon carbide powder is uniformly dispersed in an alcohol solution to obtain a dispersion;

[0009] (2) Evaporation of alcohol: The dispersion obtained in step (1) is heated and the alcohol evaporates. After cooling to room temperature, dispersible submicron silicon carbide powder is obtained.

[0010] (3) Spray granulation: Liquid polycarbosilane is sprayed in a mist onto the dispersible submicron silicon carbide powder obtained in step (3), mixed, heated for cross-linking, and then heated for curing to obtain silicon carbide particles.

[0011] (4) Sieve splitting: The silicon carbide particles obtained in step (3) are sieved and then split under vacuum and 800-1200℃ conditions to obtain porous silicon carbide microspheres.

[0012] (5) CVI densification: The porous silicon carbide microspheres obtained in step (4) are subjected to a methyltrichlorosilane densification deposition reaction by chemical vapor infiltration to obtain silicon carbide ceramic microspheres.

[0013] The beneficial effects of this invention are as follows: The preparation process of this invention mainly consists of four processes: dispersion, granulation, sieving, and densification. Specifically, using submicron silicon carbide powder as raw material, firstly, an alcohol solution is used as a dispersant to uniformly disperse the agglomerated submicron silicon carbide powder, allowing the alcohol to evaporate and obtaining uniformly dispersed submicron silicon carbide powder; then, liquid polycarbosilane is used as a binder to bind the dispersed and dried submicron silicon carbide powder together, and it is rolled into spheres by a mixing granulator; the cross-linking, curing, and pyrolysis of the binder ensure that the spherical submicron silicon carbide powder is firmly bonded, not easily broken, and the spherical structure is preserved; finally, to improve the density of the microspheres, a chemical vapor infiltration method is used, using the open pores of the porous silicon carbide microspheres as vapor infiltration channels to generate a SiC matrix inside the porous silicon carbide microspheres, thus densifying the microspheres to obtain dense silicon carbide microspheres. These silicon carbide ceramic microspheres solve the problem of uneven density and low bulk density caused by the poor flowability of irregularly shaped silicon carbide powder during the ceramic forming process.

[0014] Based on the above technical solution, the present invention can be further improved as follows:

[0015] Furthermore, in step (1), the particle size of the submicron silicon carbide powder is 0.3-0.5 μm.

[0016] Furthermore, in step (1), the purity of the submicron silicon carbide powder is 99.99%.

[0017] Furthermore, in step (1), the volume fraction of the alcohol solution is 70-90%.

[0018] Furthermore, in step (1), the mass ratio of submicron silicon carbide powder to alcohol solution is 1:0.8-1.2.

[0019] Furthermore, in step (1), the dispersion process is completed by mixing for 20-40 minutes.

[0020] Furthermore, a rotary granulator is used for mixing.

[0021] Furthermore, in step (2), the temperature is increased to 78-90℃ for 110-130 min.

[0022] Furthermore, in step (3), the mass ratio of liquid polycarbosilane to dispersible submicron silicon carbide powder is 0.2:0.8-1.2.

[0023] Furthermore, in step (3), the mixture is stirred for 110-130 minutes.

[0024] Furthermore, in step (3), the crosslinking process is completed by heating at 160-170℃ for 25-35 minutes.

[0025] Furthermore, in step (3), the product is heated at 200-235℃ for 110-130 minutes to complete the curing process.

[0026] Furthermore, in steps (1)-(3), all steps are carried out in the mixing granulator drum, with a drum rotation speed of 30-50 r / min and a drum tilt angle of 10-15°.

[0027] Furthermore, in step (4), the material is passed through a 70-mesh, 80-mesh, 100-mesh, 150-mesh, 200-mesh, or 400-mesh sieve before pyrolysis.

[0028] Furthermore, in step (4), the pyrolysis lasts for 1.5-2.5 hours.

[0029] Furthermore, in step (5), dense deposition is carried out at 900-1100℃ for 30-60 hours.

[0030] Furthermore, in step (5), chemical vapor permeation is carried out in the form of vacuum, argon as diluent gas and hydrogen bubbling.

[0031] The present invention also provides the application of the above-mentioned silicon carbide ceramic microspheres in the preparation of ceramic powders.

[0032] The present invention has the following beneficial effects:

[0033] 1. The silicon carbide ceramic microspheres of the present invention have a particle size of 20-200μm, which is a wide range. In the preparation process, they are sieved into different particle size ranges by sieving, which can meet the different particle size requirements and the particle size distribution requirements of ceramic forming.

[0034] 2. The silicon carbide ceramic microspheres of this invention, under the action of a mixing granulator, undergo cross-linking and solidification with liquid polycarbosilane, causing the original submicron silicon carbide particles to adhere and overlap into spherical shapes. After pyrolysis, due to its ceramic yield being close to 60%, uniform and fine nanoscale pores are formed at the overlapping pores of the original submicron silicon carbide particles. This facilitates the subsequent entry of chemical vapor phase reaction gases into the porous microspheres for densification and silicon carbide formation, ultimately achieving a density of 2.9-3.1 g / cm³. 3 .

[0035] 3. In the preparation process of silicon carbide ceramic microspheres of the present invention, liquid polycarbosilane is cracked into high-purity silicon carbide, and then densified by chemical vapor infiltration to produce silicon carbide. The submicron silicon carbide powder in the first step is purified, which can ensure the high purity of silicon carbide ceramic microspheres throughout the process. Attached Figure Description

[0036] Figure 1 This is a process flow diagram of the present invention;

[0037] Figure 2SEM image of the porous silicon carbide microspheres prepared in Example 1;

[0038] Figure 3 SEM image (100 μm) of the silicon carbide ceramic microspheres prepared in Example 1;

[0039] Figure 4 SEM image (10 μm) of the silicon carbide ceramic microspheres prepared in Example 1;

[0040] Figure 5 The image shows a SEM image of the porous silicon carbide microspheres prepared in Comparative Example 1. Detailed Implementation

[0041] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer should be followed. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0042] In the following examples, the liquid polycarbosilane was purchased from the Institute of Chemistry, Chinese Academy of Sciences, as vinyl-modified perhydropolycarbosilane.

[0043] Example 1:

[0044] A silicon carbide ceramic microsphere is prepared by means of the following steps: (process flow is shown in...) Figure 1 )

[0045] (1) Alcohol dispersion: Submicron silicon carbide powder with a purity of 99.99% (particle size of 0.3-0.5μm) and alcohol solution (volume fraction of 80%) are poured into the barrel of the mixing granulator at a mass ratio of 1:1. The mixing granulator is started to make the barrel rotate at a speed of 40r / min and a barrel tilt angle of 13°. Mix for 30min to make it uniformly dispersed in the alcohol solution to obtain a dispersion.

[0046] (2) Alcohol evaporation: Continue to maintain the rotation and angle of the barrel, turn on the barrel temperature control of the mixing granulator, heat the barrel wall, control the barrel wall temperature to 85℃, bake for 120 minutes, turn off the barrel temperature control, and let the barrel wall drop to room temperature to obtain dispersible submicron silicon carbide powder.

[0047] (3) Spray granulation and cross-linking curing: Continue to maintain the rotation and angle of the barrel, and spray liquid polycarbosilane into the dispersed submicron silicon carbide powder obtained in step (3) in a mist form using an atomizing sprayer at a mass ratio of 0.2:1. Mix for 120 min, turn on the temperature control of the mixing granulator barrel, heat the barrel wall, heat at 165°C for 30 min for cross-linking, and then heat at 220°C for 120 min for curing to obtain silicon carbide granules;

[0048] (4) Sieve splitting: The silicon carbide particles obtained in step (3) are passed through a 70-mesh sieve. The sieved silicon carbide particles are poured into a crucible of a vacuum pyrolysis furnace and pyrolyzed under vacuum and 1000℃ conditions for 2 hours to obtain porous silicon carbide microspheres.

[0049] (5) CVI densification: The porous silicon carbide microspheres obtained in step (4) are placed in a chemical vapor infiltration furnace, a vacuum is drawn, and methyltrichlorosilane precursor is introduced into the furnace in the form of hydrogen bubbling with argon as diluent. Densification is carried out at 1000℃ for 40h to obtain silicon carbide ceramic microspheres.

[0050] Example 2:

[0051] A silicon carbide ceramic microsphere is prepared by the following steps:

[0052] (1) Alcohol dispersion: Submicron silicon carbide powder with a purity of 99.99% (particle size of 0.3-0.5μm) and alcohol solution (volume fraction of 70%) are poured into the barrel of the mixing granulator at a mass ratio of 1:0.8. The mixing granulator is started to make the barrel rotate at a speed of 30r / min and a barrel tilt angle of 10°. The mixture is mixed for 20min to make it uniformly dispersed in the alcohol solution to obtain a dispersion.

[0053] (2) Alcohol evaporation: Continue to maintain the rotation and angle of the barrel, turn on the barrel temperature control of the mixing granulator, heat the barrel wall, control the barrel wall temperature to 78℃, bake for 130 minutes, turn off the barrel temperature control, and let the barrel wall drop to room temperature to obtain dispersible submicron silicon carbide powder.

[0054] (3) Spray granulation and cross-linking curing: Continue to maintain the rotation and angle of the barrel, and spray the liquid polycarbosilane into the dispersed submicron silicon carbide powder obtained in step (3) in a mist form according to a mass ratio of 0.2:0.8. Mix for 110 min, turn on the temperature control of the mixing granulator barrel, heat the barrel wall, heat at 160°C for 35 min for cross-linking, and then heat at 200°C for 110 min for curing to obtain silicon carbide particles;

[0055] (4) Sieve splitting: The silicon carbide particles obtained in step (3) are passed through a 400-mesh sieve. The sieved silicon carbide particles are poured into a crucible of a vacuum pyrolysis furnace and pyrolyzed under vacuum and 800°C conditions for 2.5 hours to obtain porous silicon carbide microspheres.

[0056] (5) CVI densification: The porous silicon carbide microspheres obtained in step (4) are placed in a chemical vapor infiltration furnace, a vacuum is drawn, and methyltrichlorosilane precursor is introduced into the furnace in the form of hydrogen bubbling with argon as diluent. Densification is carried out at 900°C for 60 hours to obtain silicon carbide ceramic microspheres.

[0057] Example 3:

[0058] A silicon carbide ceramic microsphere is prepared by the following steps:

[0059] (1) Alcohol dispersion: Submicron silicon carbide powder with a purity of 99.99% (particle size of 0.3-0.5μm) and alcohol solution (volume fraction of 90%) are poured into the barrel of the mixing granulator at a mass ratio of 1:1.2. The mixing granulator is started to make the barrel rotate at a speed of 50r / min and a tilt angle of 15°. The mixture is mixed for 40min to make it uniformly dispersed in the alcohol solution to obtain a dispersion.

[0060] (2) Alcohol evaporation: Continue to maintain the rotation and angle of the barrel, turn on the barrel temperature control of the mixing granulator, heat the barrel wall, control the barrel wall temperature to 90℃, bake for 110 minutes, turn off the barrel temperature control, and let the barrel wall drop to room temperature to obtain dispersible submicron silicon carbide powder.

[0061] (3) Spray granulation and cross-linking curing: Continue to maintain the rotation and angle of the barrel, and spray liquid polycarbosilane into the dispersed submicron silicon carbide powder obtained in step (3) in a mist form according to a mass ratio of 0.2:1.2. Mix for 130 min, turn on the temperature control of the mixing granulator barrel, heat the barrel wall, heat at 170°C for 25 min for cross-linking, and then heat at 235°C for 110 min for curing to obtain silicon carbide particles;

[0062] (4) Sieve splitting: The silicon carbide particles obtained in step (3) are passed through a 100-mesh sieve. The sieved silicon carbide particles are poured into a crucible of a vacuum pyrolysis furnace and pyrolyzed under vacuum and 1200℃ conditions for 1.5h to obtain porous silicon carbide microspheres.

[0063] (5) CVI densification: The porous silicon carbide microspheres obtained in step (4) were placed in a chemical vapor infiltration furnace, a vacuum was drawn, and methyltrichlorosilane precursor was introduced into the furnace in the form of hydrogen bubbling with argon as the diluent. Densification was carried out at 1100℃ for 30 h to obtain silicon carbide ceramic microspheres. Comparative Example 1:

[0064] A porous silicon carbide microsphere is prepared by the following steps:

[0065] In step (3) spray granulation and cross-linking curing process: continue to maintain the rotation and angle of the barrel, spray liquid polycarbosilane in a mist onto the dispersible submicron silicon carbide powder obtained in step (3) at a mass ratio of 0.05:1, mix for 50 min, turn on the temperature control of the mixing granulator barrel, heat the barrel wall, heat at 165℃ for 30 min for cross-linking, and then heat at 220℃ for 120 min for curing to obtain silicon carbide particles;

[0066] The remaining preparation process and process parameters are the same as in Example 1 (excluding step (5)).

[0067] Test case

[0068] I. The silicon carbide ceramic microspheres prepared in Example 1 were analyzed by GDMS (glow discharge mass spectrometry), and the results are shown in Table 1.

[0069] Table 1 GDMS Data (Unit: ppm wt)

[0070]

[0071]

[0072] As shown in Table 1, the silicon carbide ceramic microspheres prepared by this invention have a purity of 99.999%.

[0073] 2. The porous silicon carbide microspheres prepared in step (4) of Example 1 and Comparative Example 1, as well as the silicon carbide ceramic microspheres prepared in Example 1, were subjected to SEM analysis. The results are shown in [Figure 1]. Figures 2-5 .

[0074] Depend on Figure 2 It can be seen that porous silicon carbide microspheres are obtained by using polycarbosilane as a binder, after cross-linking, curing and pyrolysis.

[0075] Depend on Figures 3-4 It can be seen that after chemical vapor infiltration (CVI), the originally porous silicon carbide microspheres no longer have visible pores and become very dense.

[0076] Depend on Figure 5 It is known that if the amount of liquid polycarbosilane binder sprayed is too small or the mixing and granulation time is too short during the spray granulation process, the granulated spheres will be incomplete and there will be many broken particles.

[0077] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing silicon carbide ceramic microspheres, characterized in that, The silicon carbide ceramic microspheres are spherical or nearly spherical in shape, with a diameter of 20-200 μm and a density of 2.9-3.1 g / cm³. 3 ; The method for preparing the silicon carbide ceramic microspheres includes the following steps: (1) Alcohol dispersion: Submicron silicon carbide powder is uniformly dispersed in an alcohol solution to obtain a dispersion; (2) Evaporation of alcohol: The dispersion obtained in step (1) is heated and the alcohol evaporates. Then it is cooled to room temperature to obtain dispersible submicron silicon carbide powder. (3) Spray granulation: Liquid polycarbosilane is sprayed in a mist onto the dispersible submicron silicon carbide powder obtained in step (2), mixed, heated for cross-linking, and then heated for curing to obtain silicon carbide particles; (4) Sieve splitting: The silicon carbide particles obtained in step (3) are sieved and then split under vacuum and 800-1200℃ conditions to obtain porous silicon carbide microspheres. (5) CVI densification: The porous silicon carbide microspheres obtained in step (4) are subjected to a methyltrichlorosilane densification deposition reaction by chemical vapor infiltration to obtain silicon carbide ceramic microspheres. In step (3), the mass ratio of liquid polycarbosilane to dispersible submicron silicon carbide powder is 0.2:0.8-1.

2.

2. The method for preparing silicon carbide ceramic microspheres according to claim 1, characterized in that, In step (1), the particle size of the submicron silicon carbide powder is 0.3-0.5 μm.

3. The method for preparing silicon carbide ceramic microspheres according to claim 1, characterized in that, In step (2), heat at 78-90℃ for 110-130 min.

4. The method for preparing silicon carbide ceramic microspheres according to claim 1, characterized in that, In step (3), mix for 110-130 minutes.

5. The method for preparing silicon carbide ceramic microspheres according to claim 1, characterized in that, In step (3), the crosslinking process is completed by heating at 160-170℃ for 25-35 minutes.

6. The method for preparing silicon carbide ceramic microspheres according to claim 1, characterized in that, In step (3), the product is heated at 200-235℃ for 110-130 minutes to complete the curing process.

7. The method for preparing silicon carbide ceramic microspheres according to claim 1, characterized in that, In step (5), dense deposition is carried out at 900-1100℃ for 30-60 hours.

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