Silicon carbide ceramic and preparation method thereof
During the preparation process of silicon carbide ceramics, the cross-linking reaction and thermal cracking are used to perform cross-linking reactions and thermal cracking, and the problem of poor yield and quality of silicon carbide ceramics is solved, and materials with high density, low porosity and high flexural strength are achieved.
Patent Information
- Application Number
- CN202510405823.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-02
- Publication Date
- 2025-07-01
AI Technical Summary
At this stage, the ceramic yield of silicon carbide ceramics is relatively low, and the actual utilization rate of silicone polymer precursors is relatively low, resulting in poor product quality.
By adding specific crosslinking agents and initiators to the vinyl hydrogen-based polycarbsilane solution, crosslinking reactions and thermal cracking are performed to prepare silicon carbide ceramics with high density, low porosity and high flexural strength.
The yield and product quality of silicon carbide ceramics are improved, and a more uniform microstructure is formed, which reduces the generation of cracks and improves the fracture toughness of the material.
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Figure CN120229960A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of ceramic materials, and more particularly, to a silicon carbide ceramic and a method for preparing the same. Background Art
[0002] Silicon carbide ceramic is a kind of silicon carbide product, which has the characteristics of good corrosion resistance, high strength, high hardness, etc. A relatively common synthesis method of silicon carbide products is to prepare by sintering an organosilicon polymer precursor.
[0003] Current types of organosilicon polymers include polysiloxane, polycarbosilane, polysilazane, etc. Among them, the main elements of polycarbosilane polymers are elements such as Si, C, H, etc., and relatively few impurities are generated during the high-temperature pyrolysis to form silicon carbide. At present, the preparation process of silicon carbide ceramics usually directly uses polycarbosilane for pyrolysis. However, small molecule gases are easily generated during the direct pyrolysis of the organosilicon polymer precursor, resulting in a low ceramic yield of the current silicon carbide ceramics and a low actual utilization rate of the organosilicon polymer precursor. Summary of the Invention
[0004] The present invention aims to simultaneously improve the yield and product quality of silicon carbide ceramics.
[0005] To solve the above problems, the present invention provides a silicon carbide ceramic and a method for preparing the same.
[0006] In a first aspect, the present invention provides a method for preparing a silicon carbide ceramic, the method for preparing the silicon carbide ceramic comprising:
[0007] Adding a crosslinking agent to a vinylhydrocarbyl polycarbosilane solution, mixing evenly to obtain a vinylhydrocarbyl polycarbosilane crosslinked solution, wherein the crosslinking agent comprises any one or more of 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane, 1,4-bis(ethenyldimethylsilyl)benzene, vinyl-POSS and tris(isopropenyloxy)vinylsilane, and the structural formula of the vinylhydrocarbyl polycarbosilane is as shown in formula (Ⅰ):
[0008]
[0009] In formula (Ⅰ), x is from 1 to 1000, and y is from 1 to 1000;
[0010] Adding an initiator to the vinylhydrocarbyl polycarbosilane crosslinked solution, mixing evenly to obtain an organosilicon precursor mixed solution;
[0011] Thermally curing and then thermally pyrolyzing the organosilicon precursor mixed solution to obtain a silicon carbide ceramic.
[0012] Optionally, based on the mass of the vinyl hydrogen polycarbosilane crosslinking solution being 100%, the addition amount of the crosslinking agent is 0.1% to 50%.
[0013] Optionally, based on the mass of the vinyl hydrogen polycarbosilane crosslinking solution being 100%, the addition amount of the initiator is 0.1% to 10%.
[0014] Optionally, based on the mass of the vinyl hydrogen polycarbosilane crosslinking solution being 100%, the addition amount of the crosslinking agent is 6% to 12%, and the addition amount of the initiator is 1% to 3%.
[0015] Optionally, the initiator includes any one or several of benzoyl peroxide, azobisisobutyronitrile, azobisisoheptonitrile, tert-butyl peroxybenzoate, methyl ethyl ketone peroxide, diisopropyl peroxydicarbonate.
[0016] Optionally, the crosslinking agent is vinyl-POSS, and the initiator is benzoyl peroxide.
[0017] Optionally, the temperature of the thermal curing is 40°C to 300°C, and the curing time is 10 min to 24 h.
[0018] Optionally, the temperature of the thermal pyrolysis is 600°C to 2000°C, and the pyrolysis time is 10 min to 5 h.
[0019] Optionally, the heating rate of the thermal pyrolysis is 1°C / min to 50°C / min.
[0020] In a second aspect, the present invention provides a silicon carbide ceramic, and the silicon carbide ceramic is prepared by the preparation method of the silicon carbide ceramic described above.
[0021] The beneficial effects of the preparation method of the silicon carbide ceramic of the present invention are as follows:
[0022] By selecting a specific crosslinking agent to carry out a crosslinking reaction with vinyl hydrogen polycarbosilane, the present invention promotes the connection between polymer chains and forms a crosslinked network of high-density organosilicon polymers. Thereby reducing the escape of volatiles and the mass loss during the decomposition process, and increasing the ceramic yield. Moreover, the polycarbosilane used in the present invention has active groups such as vinyl (C═C) and silicon-hydrogen bond (Si-H) at the same time, which endows it with good reaction activity and crosslinking performance. In addition, the initiator can control the progress of the crosslinking reaction, making the crosslinking more uniform, avoiding local over-crosslinking or under-crosslinking, so that the pyrolyzed silicon carbide ceramic has a more uniform microstructure, reducing the generation of cracks, and improving the fracture toughness of the material. Thus, while increasing the yield of the silicon carbide ceramic, a high-density, low-porosity, and high flexural strength silicon carbide ceramic can be prepared. Description of the Drawings
[0023] Figure 1 Schematic diagram of the preparation process of silicon carbide ceramics in the embodiments of the present invention. Specific embodiments
[0024] To make the above objects, features and advantages of the present invention more obvious and understandable, the specific embodiments of the present invention will be described in detail below.
[0025] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by those skilled in the technical field to which this application belongs; the terms used in the specification of this application are only for the purpose of describing specific embodiments, and are not intended to limit this application;
[0026] The term "including" and its variants used herein are open-ended, that is, "including but not limited to"; the term "based on" means "at least partially based on"; the term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments"; the term "optionally" means "optional embodiment". The relevant definitions of other terms will be given in the following description. It should be noted that the concepts of "first", "second", etc. mentioned in the present invention are used to distinguish different objects, rather than to describe a specific order or primary-secondary relationship. In addition, the terms "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of this application, unless otherwise specified, the meaning of "a plurality" is two or more.
[0027] In the process of preparing silicon carbide ceramics by pyrolysis of polycarbosilane, cross-linking the polycarbosilane with a cross-linking agent before pyrolysis can improve the ceramic yield. However, the degree of cross-linking reaction is affected by various factors, such as the type, dosage, reaction time, reaction temperature, etc. of the cross-linking agent. It is difficult to precisely control the degree of cross-linking, which may lead to insufficient cross-linking or over-cross-linking. Therefore, the selection and use method of the cross-linking agent have an important impact on the quality and yield improvement of silicon carbide ceramics.
[0028] In order to expand the variety selection of cross-linking agents for polycarbosilane and achieve the effect of simultaneously improving the yield and product quality of silicon carbide ceramics, the present invention provides a silicon carbide ceramic and a preparation method thereof. Referring to Figure 1 As shown, as a first aspect, the preparation method of the silicon carbide ceramic according to the embodiment of the present invention includes:
[0029] A crosslinking agent is added to the vinyl amino polycarbosilane solution and mixed evenly to obtain a vinyl amino polycarbosilane crosslinking solution. Among them, the crosslinking agent includes any one or several of 2,4,6,8-tetramethyl-2,4,6,8-tetravinyl cyclotetrasiloxane, 1,4-bis(vinyl dimethylsilyl) benzene, vinyl-POSS, and tris(isopropenyloxy)vinyl silane. The structural formula of the vinyl amino polycarbosilane is shown in Formula (Ⅰ):
[0030]
[0031] In Formula (Ⅰ), x is from 1 to 1000, and y is from 1 to 1000;
[0032] An initiator is added to the vinyl amino polycarbosilane crosslinking solution and mixed evenly to obtain an organosilicon precursor mixed solution;
[0033] The organosilicon precursor mixed solution is subjected to thermal curing and thermal cracking in sequence to obtain a silicon carbide ceramic.
[0034] In the embodiments of the present invention, by selecting a specific crosslinking agent to carry out a crosslinking reaction with the vinyl amino polycarbosilane, the connection between polymer chains is promoted, and a crosslinking network of high-density organosilicon polymers is formed. Thereby reducing the escape of volatiles and the mass loss during the decomposition process, and increasing the ceramic yield. Moreover, the polycarbosilane adopted in the present invention simultaneously has active groups such as vinyl (C=C) and silicon-hydrogen bond (Si-H), which endows it with good reaction activity and crosslinking performance. In addition, the initiator can control the progress of the crosslinking reaction, making the crosslinking more uniform, avoiding the situation of local over-crosslinking or under-crosslinking, enabling the silicon carbide ceramic after pyrolysis to have a more uniform microstructure, reducing the generation of cracks, and improving the fracture toughness of the material. Therefore, through a large number of experiments, based on the determined crosslinking agent and initiator, by finely regulating the addition amounts of the crosslinking agent and the initiator, a silicon carbide ceramic with high density, low porosity, and high flexural strength can be prepared while increasing the yield of the silicon carbide ceramic.
[0035] In some optional embodiments, based on the mass of the vinyl amino polycarbosilane crosslinking solution being 100%, the addition amount of the crosslinking agent is 0.1% to 50%, and the addition amount of the initiator is 0.1% to 10%.
[0036] The crosslinking agent and initiator adopted in the present invention have a relatively large addition range, so as to more conveniently control the degree of the crosslinking reaction according to the requirements of the yield and product quality.
[0037] In some optional embodiments, the initiator includes any one or several of benzoyl peroxide, azobisisobutyronitrile, azobisisoheptonitrile, tert-butyl peroxybenzoate, methyl ethyl ketone peroxide, and diisopropyl peroxydicarbonate.
[0038] Further, preferably, based on the mass of the vinyl hydrogen polycarbosilane crosslinking solution being 100%, the addition amount of the crosslinking agent is 6% to 12%, the addition amount of the initiator is 1% to 3%, the crosslinking agent is vinyl-POSS, and the initiator is benzoyl peroxide.
[0039] Since the dosage ratio and addition amount of both the crosslinking agent and the initiator will affect the degree and speed of crosslinking, and thus affect the structure and properties of the silicon carbide ceramic after pyrolysis. In the present invention, within a relatively large initially determined range, the addition amounts of the crosslinking agent and the initiator are further finely adjusted, so that while increasing the yield of the silicon carbide ceramic, a silicon carbide ceramic with high density, low porosity, and high flexural strength can be prepared.
[0040] In some alternative embodiments, the temperature of thermal curing is 40°C to 300°C, and the curing time is 10 min to 24 h.
[0041] The crosslinking reaction is promoted through the thermal curing operation. The cured organosilicon polymer has higher thermal stability, can withstand higher temperatures without deformation or decomposition, thereby forming a more stable network structure and improving the mechanical strength and heat resistance of the material.
[0042] In some alternative embodiments, the temperature of thermal pyrolysis is 600°C to 2000°C, the pyrolysis time is 10 min to 5 h, and the heating rate of thermal pyrolysis is 1°C / min to 50°C / min.
[0043] Specifically, in an air, vacuum, argon, or nitrogen atmosphere, the thermally cured product can be directly heated from the thermal curing temperature to 600°C to 2000°C at a heating rate of 1°C / min to 50°C / min, and then held for 10 min to 5 h, thereby realizing the thermal pyrolysis of the polycarbosilane crosslinking network to obtain the desired silicon carbide ceramic.
[0044] As a second aspect, a silicon carbide ceramic according to an embodiment of the present invention is prepared by the preparation method of the silicon carbide ceramic described above.
[0045] The present invention is described in detail below through specific examples and comparative examples:
[0046] Example 1
[0047] S1: 2,4,6,8 - Tetramethyl - 2,4,6,8 - tetravinylcyclotetrasiloxane was added to the vinyl hydrogen polycarbosilane solution and stirred and mixed evenly to obtain a vinyl hydrogen polycarbosilane crosslinking solution. Among them, based on the mass of the vinyl hydrogen polycarbosilane crosslinking solution being 100%, the addition amount of 2,4,6,8 - tetramethyl - 2,4,6,8 - tetravinylcyclotetrasiloxane was 0.1%. The structural formula of 2,4,6,8 - tetramethyl - 2,4,6,8 - tetravinylcyclotetrasiloxane is as shown in formula (Ⅱ):
[0048]
[0049] S2: Add 0.5% of benzoyl peroxide to the vinyl amino polycarbosilane crosslinking solution, stir and mix evenly to obtain an organosilicon precursor mixed solution.
[0050] S3: Thermally cure the organosilicon precursor mixed solution at 50 °C for 20 h to obtain a polycarbosilane crosslinked product.
[0051] S4: Under vacuum conditions, heat the polycarbosilane crosslinked product to 600 °C at a heating rate of 1 °C / min and carry out pyrolysis at 600 °C for 5 h to prepare silicon carbide ceramics.
[0052] Example 2
[0053] S1: Add 1,4-bis(vinyl dimethylsilyl)benzene to the vinyl amino polycarbosilane solution, stir and mix evenly to obtain a vinyl amino polycarbosilane crosslinking solution. Among them, based on the mass of the vinyl amino polycarbosilane crosslinking solution being 100%, the addition amount of 1,4-bis(vinyl dimethylsilyl)benzene is 8%.
[0054] S2: Add 10% of azobisisobutyronitrile to the vinyl amino polycarbosilane crosslinking solution, stir and mix evenly to obtain an organosilicon precursor mixed solution.
[0055] S3: Thermally cure the organosilicon precursor mixed solution at 80 °C for 15 h to obtain a polycarbosilane crosslinked product.
[0056] S4: Under an argon atmosphere, heat the polycarbosilane crosslinked product to 800 °C at a heating rate of 5 °C / min and carry out pyrolysis at 800 °C for 4.5 h to prepare silicon carbide ceramics.
[0057] Example 3
[0058] S1: Add vinyl-POSS to the vinyl amino polycarbosilane solution, stir and mix evenly to obtain a vinyl amino polycarbosilane crosslinking solution. Among them, based on the mass of the vinyl amino polycarbosilane crosslinking solution being 100%, the addition amount of vinyl-POSS is 25%. The structural formula of vinyl-POSS is shown in Formula (Ⅲ):
[0059]
[0060] In Formula (Ⅲ), R is a vinyl group.
[0061] S2: Add 6% of 2,2'-azobis(2-methylbutyronitrile) to the vinyl hydrogen polycarbosilane crosslinking solution, stir and mix evenly to obtain an organosilicon precursor mixed solution.
[0062] S3: Thermally cure the organosilicon precursor mixed solution at 150 °C for 8 h to obtain a polycarbosilane crosslinked product.
[0063] S4: Under an air atmosphere, heat the polycarbosilane crosslinked product to 1000 °C at a heating rate of 20 °C / min and carry out pyrolysis at 1000 °C for 3 h to prepare silicon carbide ceramics.
[0064] Example 4
[0065] S1: Add tris(isopropenyloxy)vinylsilane to the vinyl hydrogen polycarbosilane solution, stir and mix evenly to obtain a vinyl hydrogen polycarbosilane crosslinking solution. Among them, based on the mass of the vinyl hydrogen polycarbosilane crosslinking solution being 100%, the addition amount of tris(isopropenyloxy)vinylsilane is 50%. The structural formula of tris(isopropenyloxy)vinylsilane is as shown in formula (IV):
[0066]
[0067] S2: Add 3% of tert-butyl peroxybenzoate to the vinyl hydrogen polycarbosilane crosslinking solution, stir and mix evenly to obtain an organosilicon precursor mixed solution.
[0068] S3: Thermally cure the organosilicon precursor mixed solution at 300 °C for 10 min to obtain a polycarbosilane crosslinked product.
[0069] S4: Under a nitrogen atmosphere, heat the polycarbosilane crosslinked product to 2000 °C at a heating rate of 50 °C / min and carry out pyrolysis at 2000 °C for 10 min to prepare silicon carbide ceramics.
[0070] Example 5
[0071] The difference between this example and Example 1 is that 1,4-bis(ethenyldimethylsilyl)benzene is used as the crosslinking agent, the addition amount of 1,4-bis(ethenyldimethylsilyl)benzene is 0.5%, and methyl ethyl ketone peroxide is used as the initiator, and the addition amount of the initiator is 0.1%.
[0072] Example 6
[0073] The difference between this example and Example 1 is that 1,4-bis(ethenyldimethylsilyl)benzene is used as the crosslinking agent, the addition amount of 1,4-bis(ethenyldimethylsilyl)benzene is 3%, and diisopropyl peroxydicarbonate is used as the initiator, and the addition amount of the initiator is 0.4%.
[0074] Example 7
[0075] The difference between this example and Example 1 is that 1,4-bis(vinyldimethylsilyl)benzene is used as the crosslinking agent, the addition amount of 1,4-bis(vinyldimethylsilyl)benzene is 5%, and the addition amount of benzoyl peroxide is 0.8%.
[0076] Example 8
[0077] The difference between this example and Example 1 is that vinyl-POSS is used as the crosslinking agent, the addition amount of vinyl-POSS is 6%, and the addition amount of benzoyl peroxide is 1%.
[0078] Example 9
[0079] The difference between this example and Example 1 is that vinyl-POSS is used as the crosslinking agent, the addition amount of vinyl-POSS is 8%, and the addition amount of benzoyl peroxide is 1.8%.
[0080] Example 10
[0081] The difference between this example and Example 1 is that vinyl-POSS is used as the crosslinking agent, the addition amount of vinyl-POSS is 10%, and the addition amount of benzoyl peroxide is 2.5%.
[0082] Example 11
[0083] The difference between this example and Example 1 is that vinyl-POSS is used as the crosslinking agent, the addition amount of vinyl-POSS is 12%, and the addition amount of benzoyl peroxide is 3%.
[0084] Example 12
[0085] The difference between this example and Example 1 is that tris(isopropenyloxy)vinylsilane is used as the crosslinking agent, the addition amount of tris(isopropenyloxy)vinylsilane is 15%, and the addition amount of benzoyl peroxide is 5%.
[0086] Example 13
[0087] The difference between this example and Example 1 is that tris(isopropenyloxy)vinylsilane is used as the crosslinking agent, the addition amount of tris(isopropenyloxy)vinylsilane is 20%, and the addition amount of benzoyl peroxide is 6%.
[0088] Example 14
[0089] The difference between this example and Example 1 is that the addition amount of 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane is 30%, and the addition amount of benzoyl peroxide is 8.5%.
[0090] Example 15
[0091] The difference between this example and Example 1 is that the addition amount of 2,4,6,8 - tetramethyl - 2,4,6,8 - tetravinylcyclotetrasiloxane is 50%, and the addition amount of benzoyl peroxide is 10%.
[0092] Comparative Example
[0093] In this comparative example, xylene was used as a solvent to dissolve vinylhydrogen polycarbosilane, and then the mixed solution was pyrolyzed at 600 °C for 5 h.
[0094] Silicon carbide ceramics were prepared by using the preparation methods in Examples 1 - 15 and the comparative example of the present invention. The relevant yield data and product performance data are compared as follows, where ① represents 2,4,6,8 - tetramethyl - 2,4,6,8 - tetravinylcyclotetrasiloxane, ② represents 1,4 - bis(ethenyldimethylsilyl)benzene, ③ represents vinyl - POSS, and ④ represents tris(isopropenyloxy)vinylsilane. a represents benzoyl peroxide, b represents azobisisobutyronitrile, c represents azobis(2,4 - dimethylvaleronitrile), d represents tert - butyl peroxybenzoate, e represents methyl ethyl ketone peroxide, and f represents diisopropyl peroxydicarbonate.
[0095] Table 1 Yield data and product performance data of silicon carbide ceramics in Examples 1 - 15 and the comparative example
[0096]
[0097]
[0098] As can be seen from Table 1, compared with directly pyrolyzing polycarbosilane, when using vinyl - POSS as a cross - linker and benzoyl peroxide as an initiator, the yield and flexural strength of silicon carbide ceramics are both significantly improved, the porosity decreases, and the densification degree increases. Among them, when the addition amount of vinyl - POSS is 6% - 12% and the addition amount of benzoyl peroxide is 1% - 3%, the yield of silicon carbide ceramics is significantly improved, reaching more than 80%. At the same time, the densification of the prepared silicon carbide ceramics is enhanced, the porosity is all below 30%, and the mechanical properties of the silicon carbide ceramics are optimized, and the flexural strength reaches more than 300 MPa.
[0099] Although the present invention is disclosed as above, the protection scope of the present invention is not limited thereto. Without departing from the spirit and scope of the present invention, those skilled in the art can make various changes and modifications, and these changes and modifications will all fall within the protection scope of the present invention.
Claims
1. A method for preparing silicon carbide ceramics, characterized in that: include: A crosslinking agent is added to the vinyl hydrogen polycarbosilane solution and mixed evenly to obtain a vinyl hydrogen polycarbosilane crosslinking liquid, wherein the crosslinking agent includes any one or more of 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane, 1,4-bis(vinyldimethylsilyl)benzene, vinyl-POSS and tri(isoallyloxy)vinylsilane, and the structural formula of the vinyl hydrogen polycarbosilane is shown in formula (I): In formula (I), x is 1 to 1000, and y is 1 to 1000; Adding an initiator to the vinyl hydrogen polycarbosilane crosslinking liquid and mixing them evenly to obtain an organosilicon precursor mixed solution; The organic silicon precursor mixed solution is thermally cured and thermally cracked in sequence to obtain silicon carbide ceramics.
2. The method for preparing silicon carbide ceramics according to claim 1, characterized in that: Based on the mass of the vinyl hydrogen polycarbosilane cross-linking liquid being 100%, the added amount of the cross-linking agent is 0.1% to 50%.
3. The method for preparing silicon carbide ceramics according to claim 2, characterized in that: Based on the mass of the vinyl hydrogen polycarbosilane cross-linking liquid being 100%, the added amount of the initiator is 0.1% to 10%.
4. The method for preparing silicon carbide ceramics according to claim 3, characterized in that: Based on 100% of the mass of the vinyl hydrogen polycarbosilane crosslinking liquid, the added amount of the crosslinking agent is 6% to 12%, and the added amount of the initiator is 1% to 3%.
5. The method for preparing silicon carbide ceramics according to claim 1, characterized in that: The initiator includes any one or more of benzoyl peroxide, azobisisobutyronitrile, azobisisoheptanenitrile, tert-butyl perbenzoate, methyl ethyl ketone peroxide and diisopropyl peroxydicarbonate.
6. The method for preparing silicon carbide ceramics according to claim 5, characterized in that: The cross-linking agent is vinyl-POSS, and the initiator is benzoyl peroxide.
7. The method for preparing silicon carbide ceramics according to claim 1, characterized in that: The thermal curing temperature is 40° C. to 300° C., and the curing time is 10 min to 24 h.
8. The method for preparing silicon carbide ceramics according to claim 1, characterized in that: The temperature of the thermal cracking is 600° C. to 2000° C., and the thermal cracking time is 10 min to 5 h.
9. The method for preparing silicon carbide ceramics according to claim 8, characterized in that: The heating rate of the thermal cracking is 1°C / min to 50°C / min.
10. A silicon carbide ceramic, characterized in that: The silicon carbide ceramic is prepared by the method for preparing the silicon carbide ceramic according to any one of claims 1 to 9.