A silicon carbide composite ceramic and a preparation method thereof

Abstract

The present invention relates to the field of ceramics, and provides a silicon carbide composite ceramic and a preparation method thereof. By weight, the silicon carbide composite ceramic comprises the following raw materials: 90 - 110 parts of composite silicon carbide, 10 - 20 parts of composite filler, 15 - 25 parts of boron carbide, 5 - 10 parts of auxiliary agent, 1 - 5 parts of modified polyvinyl alcohol, and 150 - 250 parts of dispersion medium. The silicon carbide composite ceramic provided by the present invention has the characteristics of high mechanical strength and high toughness.

Description

Technical Field

[0001] The present invention relates to the field of ceramics, and particularly to a silicon carbide composite ceramic and a preparation method thereof. Background Art

[0002] Silicon carbide ceramics, which are high-temperature structural ceramics, have many excellent properties such as high wear resistance, thermal conductivity, electrical insulation, heat resistance, and corrosion resistance, and are widely used in industrial fields such as machinery, electronics, petrochemical industry, metallurgy, etc. and the national defense industry.

[0003] However, silicon carbide is a strong covalent bond compound, and its low diffusion coefficient under high-temperature sintering conditions makes it difficult to sinter densely. And the fracture toughness of single-phase silicon carbide ceramics is generally low. Currently, the industry tends to introduce a second phase such as boron carbide, short fibers, graphene, etc. during the batching process to obtain silicon carbide composite ceramics, while maintaining the excellent properties of silicon carbide ceramics, further improving its mechanical strength, toughness, thermal properties, electrical conductivity, etc.

[0004] Although silicon carbide composite ceramics already have the above-mentioned many excellent properties compared with single-phase silicon carbide ceramics, there are still some unsolved defects. For example, although adding graphene to silicon carbide ceramics can significantly improve the toughness of the composite ceramics, graphene is still extremely easy to agglomerate due to the strong van der Waals force between the lamellae, which may lead to the toughness of the composite ceramics not reaching the ideal effect. Also, binders such as sodium carboxymethylcellulose and polyvinyl alcohol used in the preparation of silicon carbide composite ceramics have room for improvement in their heat resistance, which may affect the strength and toughness of the prepared ceramics.

[0005] Patent CN 107602131B discloses a silicon carbide composite ceramic, which is a layered silicon carbide / reaction-sintered silicon carbide composite ceramic based on graphene, including the following raw material components: silicon carbide coarse powder I, silicon carbide fine powder II, graphene nanosheets, charcoal black, silicon powder, dispersant, binder. Compared with single reaction silicon carbide ceramics, its mechanical properties are significantly improved. However, the binder selected in this application is sodium carboxymethylcellulose, and sodium carboxymethylcellulose has the defect of instability at high temperatures, which may lead to a decrease in the mechanical strength of the prepared silicon carbide composite ceramic.

[0006] Therefore, there is an urgent need in the market for a silicon carbide composite ceramic with high mechanical strength and high toughness. Summary of the Invention

[0007] Aiming at the problems existing in the prior art, the present invention synthesizes a silicon carbide composite ceramic with high mechanical strength and high toughness by using composite silicon carbide as the main component, and combining with composite fillers, boron carbide, additives, and modified polyvinyl alcohol.

[0008] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0009] On the one hand, the present invention provides a silicon carbide composite ceramic. By weight, the silicon carbide composite ceramic comprises the following raw materials: 90 - 110 parts of composite silicon carbide, 10 - 20 parts of composite filler, 15 - 25 parts of boron carbide, 5 - 10 parts of auxiliary agent, 1 - 5 parts of modified polyvinyl alcohol, and 150 - 250 parts of dispersion medium.

[0010] In some embodiments of the present invention, the composite silicon carbide is composed of silicon carbide coarse powder and silicon carbide fine powder.

[0011] Preferably, the mass ratio of the silicon carbide coarse powder to the silicon carbide fine powder is 1:(2 - 3); the average particle size of the silicon carbide coarse powder is 25 - 35 μm, and the average particle size of the silicon carbide fine powder is 3 - 8 μm.

[0012] The applicant selects silicon carbide coarse powder and silicon carbide fine powder with specific particle sizes and mass ratios to be mixed to form composite silicon carbide as the main component of the silicon carbide ceramic. The fine powder can fill the large pores of the coarse powder, thereby improving the overall density of the composite ceramic and enabling the silicon carbide composite ceramic to have better mechanical strength.

[0013] In some embodiments of the present invention, the preparation method of the composite filler comprises the following steps:

[0014] (1) Add aluminum isopropoxide to isopropanol, heat to 75 - 85 °C, stir, add a mixed solution of isopropanol and deionized water, carry out condensation reflux, centrifuge, take the precipitate, wash, and dry to obtain boehmite powder for standby;

[0015] (2) Under the condition of 0 - 5 °C, add sulfuric acid aqueous solution to graphite powder, stir, add potassium permanganate, stir, stir at 35 - 45 °C for 1 - 2 h, raise the temperature to 65 - 75 °C and stir for 20 - 40 min, cool to room temperature, add deionized water, dropwise add hydrogen peroxide aqueous solution at 75 - 85 °C, stand, centrifuge, wash, and freeze-dry to obtain graphene oxide for standby;

[0016] (3) Mix the graphene oxide obtained in step (2) with thionyl chloride, carry out ultrasonic treatment at 35 - 45 °C for 20 - 40 min, heat to 60 - 70 °C, stir for 1.5 - 2.5 h, cool to room temperature, carry out reduced pressure distillation, add 1,2-dichloroethane, stir, add 1,2-dimethylpiperidin-4-amine, carry out ultrasonic treatment, heat to 85 - 95 °C, stir for 1.5 - 2.5 h, carry out reduced pressure distillation, add absolute ethanol, carry out ultrasonic treatment, centrifuge, wash, and dry to obtain modified graphene for standby;

[0017] (4) Add the boehmite powder from step (1) and the modified graphene from step (3) into deionized water, ultrasonicate, heat to 180 - 190 °C, stir for 10 - 11 h, centrifuge, wash, and dry to obtain the composite filler.

[0018] Among them, in the step (2), the mass ratio of graphite powder, sulfuric acid in the sulfuric acid aqueous solution, and potassium permanganate is 1:(95 - 100):(55 - 60).

[0019] In some embodiments of the present invention, in the step (3), the mass ratio of graphene oxide and 1,2 - dimethylpiperidin - 4 - amine is 1:(0.3 - 0.5).

[0020] Preferably, in the step (3), the mass ratio of graphene oxide and 1,2 - dimethylpiperidin - 4 - amine is 1:0.4.

[0021] In some embodiments of the present invention, in the step (4), the mass ratio of modified graphene and boehmite powder is 1:(0.4 - 0.6).

[0022] Preferably, in the step (4), the mass ratio of modified graphene and boehmite powder is 1:0.5.

[0023] In the preparation process of the silicon carbide composite ceramic, adding graphene as a carbon source can effectively improve the problem of insufficient toughness of the silicon carbide ceramic. However, without surface treatment, graphene still has a high possibility of agglomeration in the water - based system even under the action of a dispersing agent. Agglomerates will cause problems such as uneven structure, reduced strength and toughness of the ceramic material.

[0024] On the one hand, the applicant uses graphite powder as a raw material, synthesizes graphene oxide under the oxidation of concentrated sulfuric acid and potassium permanganate, and then activates graphene oxide with the chlorinating reagent thionyl chloride and introduces 1,2 - dimethylpiperidin - 4 - amine, increasing the amino hydrophilic groups in the structure of the modified graphene, thereby improving the dispersibility of graphene in water. And the amino group of the introduced 1,2 - dimethylpiperidin - 4 - amine undergoes a grafting reaction with the carboxyl group on the surface of graphene oxide, making the structure of the modified graphene oxide contain stable amide bonds, so that the modified graphene has good dispersibility and stability in water. Further, the piperidine heterocyclic structure introduced by 1,2 - dimethylpiperidin - 4 - amine has elasticity and can play a role in reducing friction to a certain extent, making the composite filler have lubricating properties. On the other hand, the applicant uses the hydrothermal method to compound boehmite and modified graphene to obtain the composite filler. Boehmite has a large number of hydroxyl groups on its surface and good corrosion resistance, which synergistically improves the dispersibility and corrosion resistance of the composite filler, and further improves the toughness and strength of the silicon carbide composite ceramic.

[0025] In some embodiments of the present invention, the adjuvant is polyacrylic acid or polyethylene glycol.

[0026] In some embodiments of the present invention, the method for preparing the modified polyvinyl alcohol comprises the following steps:

[0027] 1) Place the jute fiber in an aqueous sulfuric acid solution, soak it at 55 - 65 °C for 1 - 2 h, take out the solid, wash it, dry it, then add it to an aqueous sodium hydroxide solution, soak it at 20 - 30 °C for 1 - 2 h, take out the solid, wash it, dry it, and then add it to a mixed solution of silane coupling agent KH590 and absolute ethanol, soak it at 20 - 30 °C for 4 - 6 h, take out the solid, and dry it to obtain the modified jute fiber for standby;

[0028] 2) Mix the modified jute fiber obtained in step 1) with polyvinyl alcohol powder, melt - blend them at 145 - 155 °C, and hot - press them into shape to obtain the modified polyvinyl alcohol.

[0029] Wherein, in step 1), the mass ratio of the jute fiber to the silane coupling agent in the mixed solution of silane coupling agent KH590 and absolute ethanol is 1:(0.2 - 0.4).

[0030] In some embodiments of the present invention, in step 2), the mass ratio of the polyvinyl alcohol powder to the modified jute fiber is 1:(0.4 - 0.6).

[0031] Preferably, in step 2), the mass ratio of the polyvinyl alcohol powder to the modified jute fiber is 1:0.5.

[0032] When preparing the silicon carbide composite ceramic, using a binder can improve the strength of the green ceramic body, improve the plasticity during the forming process, reduce cracks after sintering, and improve the uniformity. Among them, polyvinyl alcohol is an environmentally friendly binder with good water solubility, but the stability of polyvinyl alcohol at high temperatures is poor, resulting in its inability to function well in the high - temperature environment of ceramic preparation.

[0033] The applicant selects jute fiber as the modified matrix to modify polyvinyl alcohol powder. Jute fiber, one of the cheapest natural fibers, has good heat resistance, mechanical properties, antibacterial properties and solubility. The addition of jute fiber can restrict the movement of polyvinyl alcohol molecular chains, thereby improving the thermal stability of polyvinyl alcohol. Further, the applicant conducts combined modification of jute fiber with acid, alkali and silane coupling agent KH590, increasing the active groups on the surface of jute fiber, and thus effectively improving the compatibility between jute fiber and polyvinyl alcohol. In particular, the mercapto group in silane coupling agent KH590 can react with the hydroxyl groups on the surface of jute fiber, and the mercapto group has high reaction activity, which can effectively improve the binding force between jute fiber and polyvinyl alcohol, making the heat resistance of polyvinyl alcohol more effectively improved, and thus playing a role in enhancing the strength and toughness of the silicon carbide composite ceramic.

[0034] In some embodiments of the present invention, the dispersion medium is an aqueous ethanol solution of 40 - 60 wt%.

[0035] Preferably, the dispersion medium is an aqueous ethanol solution of 50 wt%.

[0036] On the other hand, the present invention also provides a method for preparing the silicon carbide composite ceramic described in the above technical solution, including the following steps:

[0037] S1. Add composite silicon carbide, composite filler, boron carbide and additives to the dispersion medium, ball mill, add modified polyvinyl alcohol, and ball mill to obtain a slurry for standby;

[0038] S2. Spray granulate, press mold, pre-sinter and finally sinter the slurry in step S1 to obtain the silicon carbide composite ceramic.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] (1) The present invention uses composite silicon carbide as the main component, and synthesizes a silicon carbide composite ceramic with composite filler, peroxoboron carbide, additives and modified polyvinyl alcohol. Through the synergistic effect between components, the silicon carbide composite ceramic has the characteristics of high mechanical strength and high toughness.

[0041] (2) The present invention uses graphite powder as the raw material, synthesizes graphene oxide under the oxidation of concentrated sulfuric acid and potassium permanganate, and then uses the chlorinating reagent thionyl chloride to activate graphene oxide and introduce 1,2-dimethylpiperidin-4-amine, improving the dispersion of graphene in water. Further, the applicant uses the hydrothermal method to compound boehmite and modified graphene to obtain a composite filler, synergistically improving the dispersion and corrosion resistance of the composite filler, and thus playing a role in enhancing the strength and toughness of the silicon carbide composite ceramic.

[0042] (3) The present invention selects jute fiber as the modified matrix to modify polyvinyl alcohol powder, improving the thermal stability of polyvinyl alcohol. And the applicant conducts combined modification of jute fiber with acid, alkali and silane coupling agent KH590, increasing the active groups on the surface of jute fiber, effectively improving the bonding force between jute fiber and polyvinyl alcohol, making the heat resistance of polyvinyl alcohol more effectively improved, and thus playing a role in enhancing the strength and toughness of silicon carbide composite ceramics.

[0043] (4) The silicon carbide composite ceramics prepared by the present invention have high mechanical strength and high toughness, and can be widely applied to ceramic materials, having good commercial application value. Specific Embodiments

[0044] The present invention will be described below in conjunction with specific implementation schemes. It should be noted that the following examples are examples of the present invention, only used to illustrate the present invention, and not used to limit the present invention. Without departing from the gist or scope of the present invention, other combinations and various improvements within the concept of the present invention can be made.

[0045] In the following examples and comparative examples, except for the composite filler and modified polyvinyl alcohol, the other compound monomers and related reagents used can be purchased from the market. Among them, the average particle size of the silicon carbide coarse powder is 30μm, and the average particle size of the silicon carbide fine powder is 5μm; polyacrylic acid is purchased from Zaozhuang Changxin Chemical Co., Ltd.; polyethylene glycol is PEG 200, purchased from Shandong Baihua Chemical Co., Ltd.; polyvinyl alcohol powder is PVA 1788, purchased from Shanxi Jinyang Pharmaceutical Excipients Co., Ltd.

[0046] Preparation Example 1

[0047] The synthesis method of composite filler A includes the following steps:

[0048] (1) Add 5g of aluminum isopropoxide to 20ml of isopropanol, heat to 80°C, stir for 30min, add a mixed solution of 10ml of isopropanol and 1.5ml of deionized water (control the addition time to 30min), carry out condensation reflux for 6h, centrifuge, take the precipitate, wash it 3 times with absolute ethanol, and dry it at 100°C for 15h to obtain boehmite powder for standby;

[0049] (2) Under the condition of 0°C, add 100ml of 98wt% sulfuric acid aqueous solution to 10g of graphite powder, stir for 1h, add 57g of potassium permanganate, stir for 1h, stir at 40°C for 1.5h, raise the temperature to 70°C and stir for 30min, cool to room temperature, add 100ml of deionized water, and dropwise add 30wt% hydrogen peroxide aqueous solution at 80°C until the solution turns yellow and no longer fades and no more bubbles are generated, let it stand until natural stratification, centrifuge, wash with deionized water until pH = 7, and freeze-dry at -40°C for 24h to obtain graphene oxide for standby;

[0050] (3) Mix 10 g of the graphene oxide obtained in step (2) with 100 ml of thionyl chloride, ultrasonicate at 40 °C for 30 min, heat to 65 °C, stir for 2 h, cool to room temperature, distill under reduced pressure, add 50 ml of 1,2-dichloroethane, stir for 1 h, add 4 g of 1,2-dimethylpiperidin-4-amine, ultrasonicate for 30 min, heat to 90 °C, stir for 2 h, distill under reduced pressure, add 60 ml of absolute ethanol, ultrasonicate for 5 min, centrifuge, wash with absolute ethanol three times, and dry in vacuo at 60 °C for 10 h to obtain modified graphene for standby;

[0051] (4) Add 5 g of the boehmite powder obtained in step (1) and 10 g of the modified graphene obtained in step (3) to 200 ml of deionized water, ultrasonicate for 30 min, heat to 185 °C, stir for 10.5 h, centrifuge, wash with deionized water three times, and dry at 80 °C for 6 h to obtain composite filler A.

[0052] Preparation Example 2

[0053] Composite filler B, the specific implementation method is the same as that of composite filler A, the difference is that: in step (3), the mass of 1,2-dimethylpiperidin-4-amine is replaced with 2.7 g.

[0054] Preparation Example 3

[0055] Composite filler C, the specific implementation method is the same as that of composite filler A, the difference is that: in step (4), the mass of the boehmite powder is replaced with 3.6 g.

[0056] Preparation Example 4

[0057] The synthesis method of modified polyvinyl alcohol A includes the following steps:

[0058] 1) Place 5 g of jute fibers in 50 ml of 0.1 wt% sulfuric acid aqueous solution, soak at 60 °C for 1.5 h, take out the solid, wash with deionized water three times, dry at 60 °C for 24 h, then add to 50 ml of 0.5 wt% sodium hydroxide aqueous solution, soak at 25 °C for 1.5 h, take out the solid, wash with deionized water until the pH = 7, dry at 60 °C for 24 h, and then add to 100 ml of the mixed solution of silane coupling agent KH590 and absolute ethanol (silane coupling agent KH590: 1.5 wt%, absolute ethanol: 98.5 wt%), soak at 25 °C for 5 h, take out the solid, and dry at 60 °C for 24 h to obtain modified jute fibers for standby;

[0059] 2) Mix 5 g of the modified jute fibers obtained in step 1) with 10 g of polyvinyl alcohol powder, melt-blend at 150 °C, and hot-press at 160 °C to obtain modified polyvinyl alcohol A.

[0060] Preparation Example 5

[0061] Modified polyvinyl alcohol B, the specific implementation method is the same as that of modified polyvinyl alcohol A, the difference is that: in step 2), the mass of the modified jute fiber is replaced by 3 g.

[0062] Example 1

[0063] A silicon carbide composite ceramic, by weight, the silicon carbide composite ceramic comprises the following raw materials: 100 parts of composite silicon carbide, 15 parts of composite filler A, 20 parts of boron carbide, 7.5 parts of polyethylene glycol, 3 parts of modified polyvinyl alcohol A, and 200 parts of dispersion medium.

[0064] The composite silicon carbide is composed of silicon carbide coarse powder and silicon carbide fine powder, and the mass ratio is 1:2.5.

[0065] The dispersion medium is an ethanol aqueous solution of 50 wt%.

[0066] The preparation method of the silicon carbide composite ceramic in this embodiment comprises the following steps:

[0067] S1. Add the composite silicon carbide, composite filler A, boron carbide and polyethylene glycol into the dispersion medium, ball mill for 7 h, add the modified polyvinyl alcohol A, and ball mill for 13 h to obtain a slurry for standby;

[0068] S2. Spray granulate the slurry in step S1 (spraying pressure is 0.2 MPa, inlet air temperature is 140 °C, outlet air temperature is 100 °C), pressure molding (pressure is 160 MPa, pressure holding time is 15 s), pre-sintering (in a vacuum environment, heating to 900 °C at a rate of 10 °C / min, holding for 40 min, then heating to 1800 °C at a rate of 10 °C / min, holding for 1.5 min, and cooling in the furnace to 600 °C), final sintering (heating to 2000 °C at a rate of 20 °C / min, holding for 1.5 h), thus obtaining the silicon carbide composite ceramic.

[0069] Example 2

[0070] A silicon carbide composite ceramic, by weight, the silicon carbide composite ceramic comprises the following raw materials: 90 parts of composite silicon carbide, 15 parts of composite filler A, 15 parts of boron carbide, 5 parts of polyacrylic acid, 1 part of modified polyvinyl alcohol A, and 150 parts of dispersion medium.

[0071] The composite silicon carbide is composed of silicon carbide coarse powder and silicon carbide fine powder, and the mass ratio is 1:2.

[0072] The dispersion medium is an ethanol aqueous solution of 40 wt%.

[0073] The preparation method of the silicon carbide composite ceramic in this embodiment comprises the following steps:

[0074] S1. Add composite silicon carbide, composite filler A, boron carbide, and polyacrylic acid into a dispersion medium, ball mill for 6 h, add modified polyvinyl alcohol A, and ball mill for 10 h to obtain a slurry for standby;

[0075] S2. Spray granulate, press into shape, pre-sinter, and finally sinter the slurry in step S1 to obtain a silicon carbide composite ceramic.

[0076] Among them, the conditions for spray granulation, pressure forming, pre-sintering, and final sintering are the same as those in Example 1.

[0077] Example 3

[0078] A silicon carbide composite ceramic, by weight, the silicon carbide composite ceramic comprises the following raw materials: 110 parts of composite silicon carbide, 15 parts of composite filler A, 25 parts of boron carbide, 10 parts of polyacrylic acid, 5 parts of modified polyvinyl alcohol A, and 250 parts of dispersion medium.

[0079] The composite silicon carbide is composed of silicon carbide coarse powder and silicon carbide fine powder, and the mass ratio is 1:3.

[0080] The dispersion medium is an ethanol aqueous solution of 60 wt%.

[0081] The preparation method of the silicon carbide composite ceramic in this example comprises the following steps:

[0082] S1. Add composite silicon carbide, composite filler A, boron carbide, and polyacrylic acid into a dispersion medium, ball mill for 8 h, add modified polyvinyl alcohol A, and ball mill for 15 h to obtain a slurry for standby;

[0083] S2. Spray granulate, press into shape, pre-sinter, and finally sinter the slurry in step S1 to obtain a silicon carbide composite ceramic.

[0084] Among them, the conditions for spray granulation, pressure forming, pre-sintering, and final sintering are the same as those in Example 1.

[0085] Example 4

[0086] A silicon carbide composite ceramic, by weight, the silicon carbide composite ceramic comprises the following raw materials: 95 parts of composite silicon carbide, 10 parts of composite filler A, 17 parts of boron carbide, 6 parts of polyethylene glycol, 3 parts of modified polyvinyl alcohol A, and 180 parts of dispersion medium.

[0087] Among them, the composite silicon carbide and the dispersion medium are the same as those in Example 1.

[0088] The preparation method of the silicon carbide composite ceramic in this example is the same as that in Example 1.

[0089] Example 5

[0090] A silicon carbide composite ceramic, by weight, the silicon carbide composite ceramic comprises the following raw materials: 105 parts of composite silicon carbide, 20 parts of composite filler A, 22 parts of boron carbide, 9 parts of polyacrylic acid, 3 parts of modified polyvinyl alcohol A, and 230 parts of dispersion medium.

[0091] Among them, both the composite silicon carbide and the dispersion medium are the same as in Example 1.

[0092] In this example, the preparation method of the silicon carbide composite ceramic is the same as that in Example 1.

[0093] Example 6

[0094] This example provides a silicon carbide composite ceramic and its preparation method. The specific implementation method is the same as that in Example 1, except that composite filler B is used to replace composite filler A in equal amounts.

[0095] Example 7

[0096] This example provides a silicon carbide composite ceramic and its preparation method. The specific implementation method is the same as that in Example 1, except that composite filler C is used to replace composite filler A in equal amounts.

[0097] Example 8

[0098] This example provides a silicon carbide composite ceramic and its preparation method. The specific implementation method is the same as that in Example 1, except that modified polyvinyl alcohol B is used to replace modified polyvinyl alcohol A in equal amounts.

[0099] Comparative Example 1

[0100] This comparative example provides a silicon carbide composite ceramic and its preparation method. The specific implementation method is the same as that in Example 1, except that modified graphene is used to replace composite filler A in equal amounts.

[0101] The preparation method of the modified graphene is the same as that in Preparation Example 1.

[0102] Comparative Example 2

[0103] This comparative example provides a silicon carbide composite ceramic and its preparation method. The specific implementation method is the same as that in Example 1, except that boehmite powder is used to replace composite filler A in equal amounts.

[0104] The preparation method of the boehmite powder is the same as that in Preparation Example 1.

[0105] Comparative Example 3

[0106] This comparative example provides a silicon carbide composite ceramic and a preparation method thereof. The specific implementation manner is the same as that of Example 1, except that PVA 1788 is used to equivalently replace modified polyvinyl alcohol A.

[0107] Performance test

[0108] The mechanical strength and toughness of the silicon carbide composite ceramics of the above Examples 1-8 and Comparative Examples 1-3 were tested, and the test results are shown in Table 1.

[0109] The mechanical strength of the silicon carbide composite ceramic was judged by testing the flexural strength, with reference to the standard GB / T 4741-1999; the toughness was judged by testing the fracture toughness, with reference to the standard GB / T 23806-2009.

[0110] Table 1

[0111] Group Flexural Strength (MPa) <![CDATA[Fracture toughness (MPa·m 1 / 2 )]]> Example 1 570 6.5 Example 2 565 6.0 Example 3 560 6.2 Example 4 562 6.1 Example 5 564 6.2 Example 6 545 5.4 Example 7 540 5.5 Example 8 536 5.3 Comparative Example 1 520 5.0 Comparative Example 2 517 4.8 Comparative Example 3 515 4.6

[0112] It can be seen from the data in Table 1 that the silicon carbide composite ceramics in Examples 1-5 of the present invention generally have good mechanical strength and toughness. Among them, in Examples 6-7, the modification ratio of 1,2-dimethylpiperidin-4-amine and the ratio between boehmite powder and modified graphene in the synthesis process of the composite filler were changed, resulting in poor improvement of the dispersibility and stability of the composite filler, and causing a certain degree of decrease in the flexural strength and fracture toughness of the silicon carbide composite ceramic; in Example 8, the ratio between modified jute fiber and polyvinyl alcohol powder in the modified polyvinyl alcohol was changed, resulting in poor improvement of the mechanical strength of polyvinyl alcohol, and further causing a decrease in the flexural strength and fracture toughness of the silicon carbide composite ceramic; in Comparative Examples 1-3, modified graphene and boehmite powder were respectively used to equivalently replace composite filler A and PVA 1788 was used to equivalently replace modified polyvinyl alcohol A. The test found that the mechanical strength and toughness of the silicon carbide composite ceramic both showed poor results.

[0113] The above embodiments are only for explaining the technical concept and characteristics of the present invention, and the purpose is to enable those who are familiar with this technology to understand the content of the present invention and implement it. It cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A silicon carbide composite ceramic, characterized in that, By weight parts, the silicon carbide composite ceramic comprises the following raw materials: 90-110 parts of composite silicon carbide, 10-20 parts of composite filler, 15-25 parts of boron carbide, 5-10 parts of additive, 1-5 parts of modified polyvinyl alcohol, and 150-250 parts of dispersion medium; Wherein, the additive is polyacrylic acid or polyethylene glycol; The preparation method of the composite filler comprises the following steps: (1) Add aluminum isopropoxide into isopropanol, heat to 75-85 °C, stir, add a mixed solution of isopropanol and deionized water, carry out condensation reflux, centrifuge, take the precipitate, wash, and dry to obtain boehmite powder for standby; (2) Under the condition of 0-5 °C, add sulfuric acid aqueous solution to graphite powder, stir, add potassium permanganate, stir, stir at 35-45 °C for 1-2 h, raise the temperature to 65-75 °C and stir for 20-40 min, cool to room temperature, add deionized water, dropwise add hydrogen peroxide aqueous solution at 75-85 °C, stand, centrifuge, wash, and freeze-dry to obtain graphene oxide for standby; (3) Mix the graphene oxide obtained in step (2) with thionyl chloride, carry out ultrasonic treatment at 35-45 °C for 20-40 min, heat to 60-70 °C, stir for 1.5-2.5 h, cool to room temperature, carry out reduced pressure distillation, add 1,2-dichloroethane, stir, add 1,2-dimethylpiperidin-4-amine, carry out ultrasonic treatment, heat to 85-95 °C, stir for 1.5-2.5 h, carry out reduced pressure distillation, add absolute ethanol, carry out ultrasonic treatment, centrifuge, wash, and dry to obtain modified graphene for standby; (4) Add the boehmite powder obtained in step (1) and the modified graphene obtained in step (3) into deionized water, carry out ultrasonic treatment, heat to 180-190 °C, stir for 10-11 h, centrifuge, wash, and dry to obtain the composite filler; In step (3), the mass ratio of graphene oxide to 1,2-dimethylpiperidin-4-amine is 1:(0.3-0.5); In step (4), the mass ratio of modified graphene to boehmite powder is 1:(0.4-0.6); The preparation method of the modified polyvinyl alcohol comprises the following steps: 1) Place jute fiber in sulfuric acid aqueous solution, soak at 55-65 °C for 1-2 h, take out the solid, wash, dry, add it to sodium hydroxide aqueous solution, soak at 20-30 °C for 1-2 h, take out the solid, wash, dry, add it to a mixed solution of silane coupling agent KH590 and absolute ethanol, soak at 20-30 °C for 4-6 h, take out the solid, and dry to obtain modified jute fiber for standby; 2) Mix the modified jute fiber obtained in step 1) with polyvinyl alcohol powder, carry out melt blending at 145-155 °C, and carry out hot pressing to obtain the modified polyvinyl alcohol; In step 2), the mass ratio of polyvinyl alcohol powder to modified jute fiber is 1:(0.4-0.6).

2. The silicon carbide composite ceramic according to claim 1, wherein The composite silicon carbide is composed of silicon carbide coarse powder and silicon carbide fine powder.

3. The silicon carbide composite ceramic according to claim 1, wherein The dispersion medium is an ethanol aqueous solution with a concentration of 40-60 wt%.

4. The preparation method of the silicon carbide composite ceramic according to any one of claims 1-3, characterized in that, Comprises the following steps: S1. Add the composite silicon carbide, composite filler, boron carbide and additive into the dispersion medium, carry out ball milling, add the modified polyvinyl alcohol, and carry out ball milling to obtain a slurry for standby; S2. Spray granulate, press into shape, pre-sinter, and finally sinter the slurry in step S1 to obtain the silicon carbide composite ceramic.