A method for preparing large-size zirconium boride / silicon carbide composite ceramics

Abstract

The invention provides a preparation method of large-size zirconium boride / silicon carbide composite ceramics, belonging to the technical field of composite ceramics; the preparation method comprises granulation, sintering and impregnation steps; the granulation step comprises: adding zirconium boride powder to anhydrous ethanol, stirring evenly, adding phenolic resin, boron carbide and polyvinyl alcohol, stirring evenly again, adding modified silicon carbide and an auxiliary agent to obtain slurry, and performing spray granulation to obtain granulated powder; the mass ratio of the anhydrous ethanol, the zirconium boride powder, the phenolic resin, the boron carbide, the polyvinyl alcohol, the modified silicon carbide and the auxiliary agent is 49.2-50.6:61.5-62.4:1.0-1.2:1.8-2.2:1.0-1.4:5.1-5.4:4.0-4.2; the product prepared by the method of the invention has high density, good toughness, high mechanical properties and excellent high temperature resistance.

Description

Technical Field

[0001] The invention belongs to the technical field of composite ceramics, and in particular relates to a method for preparing large-size zirconium boride / silicon carbide composite ceramics. Background Art

[0002] Zirconium boride ZrB2, due to its excellent mechanical properties, low density, melting point above 3000℃, and good thermal conductivity, has become the research subject of high-temperature resistant ceramic materials. It is widely used in aerospace, electric machinery, metallurgy, nuclear power generation and other fields and has broad application and development potential.

[0003] However, in the crystal structure of zirconium boride, B atoms and Zr atoms are combined by covalent bonds to form a stable crystal structure. Its strong covalent bond structure makes the ceramic material easy to break directly when subjected to external force impact, and it is difficult to absorb energy through plastic deformation. It exhibits strong brittleness and poor toughness. It is easy to crack or break during processing, which limits the preparation of large-size ceramics. In addition, zirconium boride has a high melting point. At conventional sintering temperatures, the diffusion effect between zirconium boride particles is not obvious, making it more difficult to densify during the sintering process, affecting the mechanical properties of the ceramic. During the sintering process, zirconium boride is also prone to grain growth. The abnormal growth of grains leads to an uneven internal structure of the ceramic material, thereby affecting the mechanical properties and thermal stability of the ceramic.

[0004] As a refractory raw material, silicon carbide has high thermal conductivity and stable chemical properties, good wear resistance, small thermal expansion coefficient and high elastic modulus. Adding silicon carbide to the zirconium boride matrix to prepare zirconium boride-silicon carbide composite ceramics can significantly improve the brittleness of zirconium boride. When the composite ceramic material is subjected to external force, silicon carbide can absorb energy and prevent further expansion of cracks, thereby enhancing the toughness of the ceramic material. Silicon carbide can also inhibit grain growth, improve sintering performance, promote the densification of zirconium boride during the sintering process, reduce the sintering temperature of zirconium boride, and improve the fracture toughness and thermal stability of the composite ceramic material.

[0005] CN112500171A discloses a method for preparing a densified zirconium boride-silicon carbide composite ceramic. The raw materials of the composite ceramic include ZrB2 powder, titanium carbide powder, sintering aid, zirconium source, boron carbide and C source. The zirconium source, boron source and C source are introduced into the raw materials of the composite ceramic. Ultrafine zirconium boride grains are synthesized in the zirconium boride ceramic matrix through in-situ reaction, thereby improving the sintering activity of the zirconium boride and facilitating densification. The introduction of the sintering aid is conducive to the formation of a liquid phase, promoting the rearrangement between particles and facilitating the formation of a sintering neck, thereby reducing the sintering temperature to 2100-2200°C. The composite ceramic prepared by the pressureless sintering method of the patent has a bending strength of 584-706MPa and a fracture toughness of 5.92-6.69MPa·m 1 / 2 , Vickers hardness is 23.66-25.24Gpa;

[0006] It can be seen that the composite ceramic product produced by this method has high bending strength, but the fracture toughness is still low and the brittleness is high.

[0007] Moreover, zirconium boride and silicon carbide have high hardness, which increases the difficulty of processing and the difficulty of preparing large-size composite ceramic products. During the research and development process, technicians also found that when used in an ambient temperature of over 2000°C, the mass change rate per unit area of ​​zirconium boride-silicon carbide ceramic products is high, the mechanical properties are unstable, which reduces the scope of use of ceramic products. Summary of the invention

[0008] In order to solve the technical problems existing in the prior art, the present invention provides a method for preparing large-sized zirconium boride / silicon carbide composite ceramics, which has a high degree of densification, good toughness, and high mechanical properties. When used at an ambient temperature of more than 2000°C, the mass change rate per unit area is low and the mechanical properties are stable.

[0009] In view of the above technical problems, the present invention adopts the following technical solutions:

[0010] A method for preparing large-size zirconium boride / silicon carbide composite ceramics, comprising granulation, sintering and impregnation steps, as follows:

[0011] 1. Granulation

[0012] Add zirconium boride powder to anhydrous ethanol, stir evenly, then add phenolic resin, boron carbide and polyvinyl alcohol, stir evenly again, add modified silicon carbide and additives to obtain slurry, and obtain granulated powder by spray granulation;

[0013] The particle size of the zirconium boride powder is 150-170 nm;

[0014] The mass ratio of the anhydrous ethanol, zirconium boride powder, phenolic resin, boron carbide, polyvinyl alcohol, modified silicon carbide and additives is 49.2-50.6:61.5-62.4:1.0-1.2:1.8-2.2:1.0-1.4:5.1-5.4:4.0-4.2;

[0015] The preparation method of modified silicon carbide includes primary treatment, secondary treatment and modification steps, which are specifically as follows:

[0016] (1) One-time processing

[0017] The silicon carbide is placed in a reaction container, and after the mixed solution is introduced, it is stirred evenly, the temperature is increased to 105-115°C, and the mixture is stirred for 5.7-6.2 hours. After the stirring is completed, it is washed with deionized water until it is neutral, filtered, and dried at 93-96°C to constant weight to obtain pretreated silicon carbide; trishydroxymethylaminomethane is added to the deionized water, and after stirring, sodium hydroxide solution is added to adjust the pH value to 8.3-8.7, and then dopamine hydrochloride is added for ultrasonic treatment. The ultrasonic time is 1.3-1.7 hours, the ultrasonic frequency is 28-32kHz, and the ultrasonic power is 136-142W. After the ultrasonic treatment, a primary treatment liquid is obtained; the pretreated silicon carbide is placed in the primary treatment liquid, the temperature is increased to 36-40°C, and the reaction is stirred at 492-506rpm for 4.8-5.2 hours. After the stirring reaction is completed, it is filtered out and washed with deionized water, and dried at 98-102°C to constant weight to obtain a primary treatment silicon carbide;

[0018] The particle size of the silicon carbide is 210-230nm;

[0019] The mixed solution is obtained by mixing deionized water, hydrogen peroxide solution and ammonia solution, wherein the mass ratio of the deionized water, hydrogen peroxide solution and ammonia solution is 5.0-5.5:1.0-1.4:0.7-1.2; the mass concentration of the hydrogen peroxide solution is 26-30%, and the mass concentration of the ammonia solution is 20-25%;

[0020] The mass ratio of silicon carbide to the mixed solution is 10.3-10.7:106-113;

[0021] The mass ratio of the deionized water, trimethylolaminosilane and dopamine hydrochloride is 117-124:1.42-1.47:0.24-0.26;

[0022] The mass concentration of the sodium hydroxide solution is 20-25%;

[0023] The mass ratio of the pre-treated silicon carbide to the primary treatment liquid is 8.2-8.4:70-75;

[0024] (2) Secondary processing

[0025] Put hexamethylene diisocyanate in N, N-dimethylformamide, stir evenly to obtain a secondary treatment liquid; put the primary treated silicon carbide in N, N-dimethylformamide, stir evenly, add the secondary treatment liquid, control the addition rate to 2.6-3.2g / min, add tin isooctanoate after the addition is completed, raise the temperature to 80-84°C, stir and react for 5.7-6.2h, wait until it naturally returns to room temperature, filter, wash and dry to obtain secondary treated silicon carbide;

[0026] In the secondary treatment liquid, the mass ratio of hexamethylene diisocyanate to N,N-dimethylformamide is 9.7-10.2:117-125;

[0027] The mass ratio of the primary treated silicon carbide, N,N-dimethylformamide, secondary treated liquid, and tin isooctanoate is 7.3-7.7:95-106:25.6-26.3:0.6-0.9;

[0028] (3) Modification

[0029] Deionized water and polyvinyl pyrrolidone are added to isopropanol, and after stirring evenly, ethyl orthosilicate is added, and then sodium hydroxide solution is added to adjust the pH value to 9.8-10.2, and magnetic stirring reaction is carried out at a rotation speed of 225-235 rpm and a reaction time of 5.7-6.2 hours to obtain silica sol; 3-aminopropyltrimethylsilane and 3-aminopropyltriethoxysilane are added to the ethanol solution, and stirred evenly to obtain an amino reagent; the amino reagent is added to the silica sol, the temperature is increased to 56-60°C, and the heat is kept for reaction for 4.2-4.7 hours, and then secondary treated silicon carbide and glutaraldehyde are added, the temperature is increased to 74-80°C at a rate of 0.8-1.2°C / min, magnetic stirring is carried out for 5.8-6.2 hours, the rotation speed is 302-316 rpm, and after the stirring is completed, after filtering, washing and drying, heat treatment is carried out at 258-263°C for 3.2-3.7 hours to obtain modified silicon carbide;

[0030] The mass ratio of isopropanol, deionized water, polyvinyl pyrrolidone and tetraethyl orthosilicate is 98-104:9.2-9.7:1.3-1.5:10.4-10.8;

[0031] The mass concentration of the sodium hydroxide solution is 18-22%;

[0032] The mass ratio of the ethanol solution, 3-aminopropyltrimethylsilane and 3-aminopropyltriethoxysilane is 96-105:0.6-1.0:0.7-1.2;

[0033] The mass concentration of the ethanol solution is 28-32%;

[0034] The mass ratio of the amino reagent, silica sol, secondary treated silicon carbide, and glutaraldehyde is 53-57:2.3-2.8:9.3-9.7:1.2-1.5;

[0035] The preparation method of the auxiliary agent is as follows: adding zirconium carbide and hafnium boride to anhydrous ethanol, stirring evenly, adding dodecyl hydroxystearic acid, and performing ball milling treatment, wherein the ball milling time is 30-35 minutes, the ball milling speed is 142-155 rpm, the ball milling temperature is 37-42° C., and after the ball milling is completed, drying is performed to obtain the auxiliary agent;

[0036] The mass ratio of the zirconium carbide, hafnium boride, anhydrous ethanol and dodecyl hydroxystearic acid is 4.6-5.0:3.0-3.2:76-82:1.5-1.7.

[0037] 2. Sintering

[0038] The granulated powder is compression molded at a pressure of 136-142 MPa for 28-32 seconds to obtain a green body, which is placed in a pressureless sintering furnace and sintered in an argon atmosphere. The temperature is first increased to 510-530°C at a rate of 5.8-6.2°C / min, and kept warm for 30-40 minutes. The temperature is then increased to 1570-1620°C at a rate of 10-14°C / min, and kept warm for 16-25 minutes. The temperature is then increased to 1975-1988°C at a rate of 7.6-8.3°C / min, and kept warm for 2.8-3.2 hours. The green body is processed into a product with a diameter of 280-320 mm and a length of 190-210 mm to obtain primary ceramics.

[0039] 3. Impregnation

[0040] Add polycarbosilane to xylene, stir evenly to obtain an impregnation solution; place the primary ceramic in the impregnation solution so that the impregnation solution completely covers the primary ceramic, control the vacuum degree to -0.06--0.10MPa, the temperature to 63-67°C, and the impregnation time to 3.8-4.2h. After the impregnation is completed, increase the temperature to 146-153°C, keep warm and solidify for 5.8-6.2h, and sinter after cooling and decompression. First, increase the temperature to 882-895°C at a rate of 2.8-3.2°C / min, keep warm for 0.8-1.2h, and then increase the temperature to 1975-1986°C at a rate of 4.8-5.2°C / min, and keep warm for 2.8-3.2h. The above operation is an impregnation-solidification-sintering step. Repeat the above impregnation-solidification-sintering step 3 times to obtain a large-sized zirconium boride / silicon carbide composite ceramic;

[0041] The mass ratio of xylene to polycarbosilane is 98-104:41-45.

[0042] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0043] 1. The present invention uses zirconium boride as a ceramic matrix and silicon carbide as a reinforcing phase to modify silicon carbide. Specifically, silicon carbide is first hydroxylated to make the surface of silicon carbide contain more hydroxyl groups, and then polydopamine is coated on its surface to make its surface contain amino groups, which also enhances the dispersion performance of silicon carbide. Then, isocyanate groups are used for secondary treatment. The isocyanate groups can combine with the hydroxyl and amino groups on the surface of the silicon carbide treated once to form a stable cross-linked structure, which helps to improve the densification of the ceramic. Then, silica sol is introduced. The silica sol can form a silicon oxide film on the surface of silicon carbide, which effectively blocks the oxidation of the ceramic by oxygen, thereby improving the antioxidant properties of the ceramic and its Amination treatment is performed to improve the binding property with modified silicon carbide and the bonding strength with modified silicon carbide, thereby improving the mechanical properties of the product. Then, aldehyde groups are introduced so that the aldehyde groups can be cross-linked with the amino groups on the surface of the silica sol and the amino groups of the modified silicon carbide, so that the modified silicon carbide particles present a stable three-dimensional cross-linked network structure, which effectively promotes the sintering of zirconium boride and improves the mechanical properties and stability of the product. In the preparation method of the additive, ball milling treatment is performed and a surfactant is added to cause defects in the lattice of zirconium carbide and hafnium boride, improve the surface roughness, and improve the compatibility of the additive with other components, so that the product has a high degree of densification, good mechanical properties, excellent high temperature resistance and good stability.

[0044] 2. The composite ceramics prepared by the method of the present invention have a density of 99.1-99.4% and a fracture toughness of 8.8-9.2 MPa·m 1 / 2 , flexural strength is 453.2-454.8MPa;

[0045] 3. The mass change rate of the composite ceramics prepared by the method of the present invention after being kept in an air atmosphere at a temperature of 2000°C for 120 hours is 32-37 mg / cm 2 ;

[0046] 4. The composite ceramics prepared by the method of the present invention were heated to 2000°C at a rate of 40°C / min, kept at 2000°C for 96 hours, then cooled to room temperature at a rate of 20°C / min, then heated to 2000°C at a rate of 30°C / min, kept at 2000°C for 96 hours, and then naturally cooled to room temperature. The fracture toughness was measured again to be 8.5-9.0 MPa·m 1 / 2 , the flexural strength is 431.9-438.9MPa. DETAILED DESCRIPTION

[0047] In order to more clearly understand the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described.

[0048] Example 1

[0049] 1. Granulation

[0050] 62.0 g of zirconium boride powder was added to 50.0 g of anhydrous ethanol, and after stirring, 1.1 g of phenolic resin, 2.0 g of boron carbide and 1.2 g of polyvinyl alcohol were added, and after stirring again, 5.3 g of modified silicon carbide and 4.1 g of auxiliary agent were added to obtain slurry, and granulated by spraying to obtain granulated powder;

[0051] The particle size of the zirconium boride powder is 160 nm;

[0052] The preparation method of modified silicon carbide includes primary treatment, secondary treatment and modification steps, which are specifically as follows:

[0053] (1) One-time processing

[0054] 10.5 g of silicon carbide was placed in a reaction container, 110 g of the mixed solution was introduced and stirred evenly, the temperature was raised to 110° C., and the mixture was stirred for 6.0 h. After the stirring was completed, the mixture was washed with deionized water until neutral, filtered, and dried at 95° C. to constant weight to obtain pretreated silicon carbide; 1.45 g of trishydroxymethylaminomethane was added to 120 g of deionized water, the mixture was stirred evenly, 23 wt % sodium hydroxide solution was added to adjust the pH value to 8.5, and then 0.25 g of dopamine hydrochloride was added for ultrasonic treatment. The ultrasonic time was 1.5 h, the ultrasonic frequency was 30 kHz, and the ultrasonic power was 140 W. After the ultrasonic treatment, a primary treatment liquid was obtained; 8.3 g of the pretreated silicon carbide was placed in 72 g of the primary treatment liquid, the temperature was raised to 38° C., and the reaction was stirred at 500 rpm for 5.0 h. After the stirring reaction was completed, the mixture was filtered out and washed with deionized water, and dried at 100° C. to constant weight to obtain a primary treatment silicon carbide;

[0055] The particle size of the silicon carbide is 220 nm;

[0056] The mixed solution is obtained by mixing deionized water, hydrogen peroxide solution and ammonia solution, wherein the mass ratio of the deionized water, hydrogen peroxide solution and ammonia solution is 5.3:1.2:1.0; the mass concentration of the hydrogen peroxide solution is 28%, and the mass concentration of the ammonia solution is 22%;

[0057] (2) Secondary processing

[0058] 10.0 g of hexamethylene diisocyanate was placed in 120 g of N, N-dimethylformamide, and the mixture was stirred to obtain a secondary treatment liquid; 7.5 g of the primary treated silicon carbide was placed in 100 g of N, N-dimethylformamide, and the mixture was stirred to obtain a secondary treatment liquid. 26.0 g of the secondary treatment liquid was added, and the addition rate was controlled to be 3.0 g / min. After the addition was completed, 0.8 g of tin isooctanoate was added, the temperature was raised to 82°C, and the mixture was stirred for reaction for 6.0 hours. After the mixture was naturally restored to room temperature, the mixture was filtered, washed, and dried to obtain a secondary treated silicon carbide;

[0059] (3) Modification

[0060] 9.5 g of deionized water and 1.4 g of polyvinyl pyrrolidone were added to 100 g of isopropanol, and after stirring, 10.6 g of tetraethyl orthosilicate was added, and then 20 wt % sodium hydroxide solution was added to adjust the pH value to 10.0, and a magnetic stirring reaction was performed at a speed of 230 rpm for 6.0 h to obtain a silica sol; 0.8 g of 3-aminopropyltrimethylsilane and 1.0 g of ethanol solution were added to 100 g of 30 wt % 3-aminopropyltriethoxysilane, stir evenly to obtain an amino reagent; add 55g of the amino reagent to 2.6g of silica sol, raise the temperature to 58°C, keep warm for 4.5h, then add 9.5g of secondary treated silicon carbide and 1.4g of glutaraldehyde, raise the temperature to 76°C at a rate of 1.0°C / min, magnetically stir for 6.0h, the speed is 310rpm, after the stirring is completed, filter, wash and dry, and heat treat at 260°C for 3.0h to obtain modified silicon carbide;

[0061] The preparation method of the auxiliary agent is as follows: 4.8g of zirconium carbide and 3.1g of hafnium boride are added to 80g of anhydrous ethanol, and after stirring evenly, 1.6g of dodecyl hydroxystearic acid is added, and ball milling is performed. The ball milling time is 32min, the ball milling speed is 150rpm, and the ball milling temperature is 40°C. After the ball milling is completed, drying is performed to obtain the auxiliary agent.

[0062] 2. Sintering

[0063] The granulated powder is compression molded at a pressure of 140 MPa for 30 seconds to obtain a green body, which is placed in a pressureless sintering furnace and sintered in an argon atmosphere. The temperature is first increased to 520°C at a rate of 6.0°C / min and kept for 35 minutes, then increased to 1600°C at a rate of 12°C / min and kept for 20 minutes, and then increased to 1980°C at a rate of 8.0°C / min and kept for 3.0 hours. The product is processed into a product with a diameter of 300 mm and a length of 200 mm to obtain primary ceramics.

[0064] 3. Impregnation

[0065] Add 43g of polycarbosilane to 100g of xylene, stir evenly to obtain an impregnation solution; place the primary ceramic in the impregnation solution so that the impregnation solution completely covers the primary ceramic, control the vacuum degree to -0.08MPa, the temperature to 65°C, and the impregnation time to 4.0h. After the impregnation is completed, increase the temperature to 150°C, keep it warm and cure for 6.0h, and then sinter after cooling and pressure relief, first increase the temperature to 890°C at a rate of 3.0°C / min, keep it warm for 1.0h, then increase the temperature to 1980°C at a rate of 5.0°C / min, and keep it warm for 3.0h. The above operation is the impregnation-curing-sintering step. Repeat the above impregnation-curing-sintering step 3 times to obtain a large-sized zirconium boride / silicon carbide composite ceramic.

[0066] Example 2

[0067] 1. Granulation

[0068] 61.5 g of zirconium boride powder was added to 49.2 g of anhydrous ethanol, and after stirring, 1.0 g of phenolic resin, 1.8 g of boron carbide and 1.0 g of polyvinyl alcohol were added, and after stirring again, 5.1 g of modified silicon carbide and 4.0 g of auxiliary agent were added to obtain slurry, and granulated by spraying to obtain granulated powder;

[0069] The particle size of the zirconium boride powder is 150 nm;

[0070] The preparation method of modified silicon carbide includes primary treatment, secondary treatment and modification steps, which are specifically as follows:

[0071] (1) One-time processing

[0072] 10.3 g of silicon carbide was placed in a reaction container, 106 g of the mixed solution was introduced and stirred evenly, the temperature was raised to 105°C, and the mixture was stirred for 5.7 h. After the stirring was completed, the mixture was washed with deionized water until it was neutral, filtered, and dried at 93°C to constant weight to obtain pretreated silicon carbide; 1.42 g of trishydroxymethylaminomethane was added to 117 g of deionized water, the mixture was stirred evenly, 20 wt % sodium hydroxide solution was added to adjust the pH value to 8.3, and then 0.24 g of dopamine hydrochloride was added for ultrasonic treatment. The ultrasonic time was 1.3 h, the ultrasonic frequency was 28 kHz, and the ultrasonic power was 136 W. After the ultrasonic treatment, a primary treatment liquid was obtained; 8.2 g of the pretreated silicon carbide was placed in 70 g of the primary treatment liquid, the temperature was raised to 36°C, and the reaction was stirred at 492 rpm for 4.8 h. After the stirring reaction was completed, the mixture was filtered out and washed with deionized water, and dried at 98°C to constant weight to obtain a primary treatment silicon carbide;

[0073] The particle size of the silicon carbide is 210 nm;

[0074] The mixed solution is obtained by mixing deionized water, hydrogen peroxide solution and ammonia solution, wherein the mass ratio of the deionized water, hydrogen peroxide solution and ammonia solution is 5.0:1.4:0.7; the mass concentration of the hydrogen peroxide solution is 26%, and the mass concentration of the ammonia solution is 20%;

[0075] (2) Secondary processing

[0076] 9.7 g of hexamethylene diisocyanate was placed in 117 g of N, N-dimethylformamide, and stirred to obtain a secondary treatment liquid; 7.3 g of primary treated silicon carbide was placed in 95 g of N, N-dimethylformamide, and stirred to obtain a secondary treatment liquid. 25.6 g of secondary treatment liquid was added, and the addition rate was controlled to be 2.6 g / min. After the addition was completed, 0.6 g of tin isooctanoate was added, the temperature was raised to 80°C, and the reaction was stirred for 5.7 hours. After the reaction was naturally restored to room temperature, the silicon carbide was filtered, washed, and dried to obtain a secondary treatment liquid.

[0077] (3) Modification

[0078] 9.2 g of deionized water and 1.3 g of polyvinyl pyrrolidone were added to 98 g of isopropanol, and after stirring, 10.4 g of tetraethyl orthosilicate was added, and then 18 wt % sodium hydroxide solution was added to adjust the pH value to 9.8, and a magnetic stirring reaction was performed at a speed of 225 rpm for 5.7 h to obtain a silica sol; 0.6 g of 3-aminopropyltrimethylsilane and 0.7 g of ethyl orthosilicate were added to 96 g of 28 wt % ethanol solution. 3-aminopropyltriethoxysilane, stir evenly to obtain an amino reagent; add 53g of the amino reagent to 2.3g of silica sol, raise the temperature to 56°C, keep warm for 4.2h, then add 9.3g of secondary treated silicon carbide and 1.2g of glutaraldehyde, raise the temperature to 74°C at a rate of 0.8°C / min, magnetically stir for 5.8h, the speed is 302rpm, after the stirring is completed, filter, wash and dry, and heat treat at 258°C for 3.2h to obtain modified silicon carbide;

[0079] The preparation method of the auxiliary agent is as follows: 4.6g of zirconium carbide and 3.0g of hafnium boride are added to 76g of anhydrous ethanol, and after stirring evenly, 1.5g of dodecyl hydroxystearic acid is added, and ball milling is performed. The ball milling time is 30min, the ball milling speed is 142rpm, and the ball milling temperature is 37°C. After the ball milling is completed, the auxiliary agent is dried to obtain the auxiliary agent.

[0080] 2. Sintering

[0081] The granulated powder is compression molded at a pressure of 136 MPa for 32 seconds to obtain a green body, which is placed in a pressureless sintering furnace and sintered in an argon atmosphere. The temperature is first increased to 510°C at a rate of 5.8°C / min and kept warm for 40 minutes, then increased to 1620°C at a rate of 14°C / min and kept warm for 16 minutes, and then increased to 1988°C at a rate of 7.6°C / min and kept warm for 2.8 hours. The product is processed into a product with a diameter of 320 mm and a length of 210 mm to obtain primary ceramics.

[0082] 3. Impregnation

[0083] Add 41g of polycarbosilane to 98g of xylene, stir evenly to obtain an impregnation solution; place the primary ceramic in the impregnation solution so that the impregnation solution completely covers the primary ceramic, control the vacuum degree to -0.10MPa, the temperature to 63°C, and the impregnation time to 3.8h. After the impregnation is completed, increase the temperature to 146°C, keep warm and cure for 5.8h, and sinter after cooling and pressure relief, first increase the temperature to 882°C at a rate of 2.8°C / min, keep warm for 1.2h, then increase the temperature to 1975°C at a rate of 4.8°C / min, and keep warm for 3.2h. The above operation is the impregnation-curing-sintering step. Repeat the above impregnation-curing-sintering step 3 times to obtain a large-sized zirconium boride / silicon carbide composite ceramic.

[0084] Example 3

[0085] 1. Granulation

[0086] 62.4 g of zirconium boride powder was added to 50.6 g of anhydrous ethanol, and after stirring, 1.2 g of phenolic resin, 2.2 g of boron carbide and 1.4 g of polyvinyl alcohol were added, and after stirring again, 5.4 g of modified silicon carbide and 4.2 g of auxiliary agent were added to obtain slurry, and granulated by spraying to obtain granulated powder;

[0087] The particle size of the zirconium boride powder is 170 nm;

[0088] The preparation method of modified silicon carbide includes primary treatment, secondary treatment and modification steps, which are specifically as follows:

[0089] (1) One-time processing

[0090] 10.7 g of silicon carbide was placed in a reaction container, 113 g of the mixed solution was introduced and stirred evenly, the temperature was raised to 115°C, and the mixture was stirred at this temperature for 6.2 h. After the stirring was completed, the mixture was washed with deionized water until it was neutral, filtered, and dried at 96°C to constant weight to obtain pretreated silicon carbide; 1.47 g of tris(hydroxymethyl)aminomethane was added to 124 g of deionized water, the mixture was stirred evenly, 25 wt% of sodium hydroxide solution was added to adjust the pH value to 8.7, and then 0.26 g of dopamine hydrochloride was added for ultrasonic treatment. The ultrasonic time was 1.7 h, the ultrasonic frequency was 32 kHz, and the ultrasonic power was 142 W. After the ultrasonic treatment, a primary treatment liquid was obtained; 8.4 g of the pretreated silicon carbide was placed in 75 g of the primary treatment liquid, the temperature was raised to 40°C, and the reaction was stirred at 506 rpm for 5.2 h. After the stirring reaction was completed, the mixture was filtered out and washed with deionized water, and dried at 102°C to constant weight to obtain a primary treatment silicon carbide;

[0091] The particle size of the silicon carbide is 230 nm;

[0092] The mixed solution is obtained by mixing deionized water, hydrogen peroxide solution and ammonia solution, wherein the mass ratio of the deionized water, hydrogen peroxide solution and ammonia solution is 5.5:1.0:1.2; the mass concentration of the hydrogen peroxide solution is 30%, and the mass concentration of the ammonia solution is 25%;

[0093] (2) Secondary processing

[0094] 10.2 g of hexamethylene diisocyanate was placed in 125 g of N, N-dimethylformamide, and stirred to obtain a secondary treatment liquid; 7.7 g of primary treated silicon carbide was placed in 106 g of N, N-dimethylformamide, and stirred to obtain a secondary treatment liquid. 26.3 g of the secondary treatment liquid was added, and the addition rate was controlled to be 3.2 g / min. After the addition was completed, 0.9 g of tin isooctanoate was added, the temperature was raised to 84°C, and the reaction was stirred for 6.2 hours. After the reaction was naturally restored to room temperature, the silicon carbide was filtered, washed, and dried to obtain a secondary treatment liquid.

[0095] (3) Modification

[0096] 9.7 g of deionized water and 1.5 g of polyvinyl pyrrolidone were added to 104 g of isopropanol, and after stirring evenly, 10.8 g of tetraethyl orthosilicate was added, and then a 22 wt % sodium hydroxide solution was added to adjust the pH value to 10.28, and a magnetic stirring reaction was performed at a speed of 235 rpm for a reaction time of 6.2 h to obtain a silica sol; 1.0 g of 3-aminopropyltrimethylsilane and 1.2 g of 3-aminopropyltriethoxysilane, stir evenly to obtain an amino reagent; add 57g of the amino reagent to 2.8g of silica sol, raise the temperature to 60°C, keep warm for 4.7h, then add 9.7g of secondary treated silicon carbide and 1.5g of glutaraldehyde, raise the temperature to 80°C at a rate of 1.2°C / min, magnetically stir for 6.2h, the speed is 316rpm, after the stirring is completed, filter, wash and dry, and heat treat at 2638°C for 2.7h to obtain modified silicon carbide;

[0097] The preparation method of the auxiliary agent is as follows: 5.0g of zirconium carbide and 3.2g of hafnium boride are added to 82g of anhydrous ethanol, and after stirring evenly, 1.7g of dodecyl hydroxystearic acid is added, and ball milling is performed. The ball milling time is 35min, the ball milling speed is 155rpm, and the ball milling temperature is 42°C. After the ball milling is completed, drying is performed to obtain the auxiliary agent.

[0098] 2. Sintering

[0099] The granulated powder is compression molded at a pressure of 142 MPa for 28 seconds to obtain a green body, which is placed in a pressureless sintering furnace and sintered in an argon atmosphere. The temperature is first increased to 530°C at a rate of 6.2°C / min and kept warm for 30 minutes, then increased to 1570°C at a rate of 10°C / min and kept warm for 25 minutes, and then increased to 1975°C at a rate of 8.3°C / min and kept warm for 3.2 hours. The product is processed into a product with a diameter of 280 mm and a length of 190 mm to obtain primary ceramics.

[0100] 3. Impregnation

[0101] Add 45g of polycarbosilane to 104g of xylene, stir evenly to obtain an impregnation solution; place the primary ceramic in the impregnation solution so that the impregnation solution completely covers the primary ceramic, control the vacuum degree to -0.06MPa, the temperature to 67°C, and the impregnation time to 4.2h. After the impregnation is completed, increase the temperature to 153°C, keep it warm and cure for 6.2h, and then sinter after cooling and pressure relief, first increase the temperature to 895°C at a rate of 3.2°C / min, keep it warm for 0.8h, then increase the temperature to 1986°C at a rate of 5.2°C / min, and keep it warm for 2.8h. The above operation is the impregnation-curing-sintering step. Repeat the above impregnation-curing-sintering step 3 times to obtain a large-sized zirconium boride / silicon carbide composite ceramic.

[0102] Comparative Example 1

[0103] Based on Example 1, the changes are as follows:

[0104] In the preparation method of modified silicon carbide in the granulation step, the primary treatment and secondary treatment steps are omitted;

[0105] In the modification step, the secondary treated silicon carbide is replaced by silicon carbide without any treatment in an equal amount, and the particle size of the silicon carbide is 220 nm;

[0106] The rest of the operations are the same.

[0107] Comparative Example 2

[0108] Based on Example 1, the changes are that in the granulation step,

[0109] (1) In the preparation method of modified silicon carbide, the modification step is omitted, and the modified silicon carbide is replaced by an equal amount of secondary treated silicon carbide during granulation;

[0110] (2) The preparation method of the auxiliary agent is to uniformly mix 4.8 g of zirconium carbide and 3.1 g of hafnium boride to obtain the auxiliary agent;

[0111] The rest of the operations are the same.

[0112] Performance Testing

[0113] The performance of the large-sized zirconium boride / silicon carbide composite ceramic products prepared in Examples 1-3 and Comparative Examples 1-2 was tested as follows:

[0114]

[0115] The mass change rate is the mass change rate per unit area of ​​the large-sized zirconium boride / silicon carbide composite ceramic products obtained in Examples 1-3 and Comparative Examples 1-2 after being placed in an air atmosphere at a temperature of 2000°C for 120 hours;

[0116] The high temperature resistance performance is tested by heating the ceramic product to 2000℃ at a rate of 40℃ / min, keeping it at 2000℃ for 96h, then cooling it to room temperature at a rate of 20℃ / min, and then heating it to 2000℃ at a rate of 30℃ / min, keeping it at 2000℃ for 96h. After it naturally cools to room temperature, the fracture toughness and flexural strength are tested again.

[0117] The present invention uses zirconium boride as a ceramic matrix and silicon carbide as a reinforcing phase to modify silicon carbide. Specifically, silicon carbide is firstly subjected to a hydroxylation treatment so that the surface of silicon carbide contains more hydroxyl groups, and then polydopamine is coated on the surface so that the surface contains amino groups, thereby enhancing the dispersion performance of silicon carbide. Then, an isocyanate group is used for secondary treatment. The isocyanate group can combine with the hydroxyl group and the amino group on the surface of the silicon carbide treated once to form a stable cross-linked structure, which is helpful to improve the densification degree of the ceramic. Then, a silica sol is introduced. The silica sol can form a silicon oxide film on the surface of the silicon carbide, effectively blocking the oxidation of the ceramic by oxygen, thereby improving the antioxidant performance of the ceramic, and the silicon carbide is subjected to secondary treatment. Amination treatment is performed to improve the binding property with modified silicon carbide and the bonding strength with modified silicon carbide, thereby improving the mechanical properties of the product. Then, aldehyde groups are introduced so that the aldehyde groups can be cross-linked with the amino groups on the surface of the silica sol and the amino groups of the modified silicon carbide, so that the modified silicon carbide particles present a stable three-dimensional cross-linked network structure, which effectively promotes the sintering of zirconium boride and improves the mechanical properties and stability of the product. In the preparation method of the additive, ball milling treatment is performed and a surfactant is added to cause defects in the lattice of zirconium carbide and hafnium boride, thereby improving the surface roughness and improving the compatibility of the additive with other ingredients. Ultimately, the product has a high degree of densification, good mechanical properties, excellent high temperature resistance and good stability.

[0118] In the preparation method of modified silicon carbide in Comparative Example 1, the primary treatment and the secondary treatment are omitted, and silica sol is directly used for coating. The agglomeration force between the silicon carbide particles is strong. When the silica sol is modified, the modification effect is uneven, which affects the densification and homogeneity of the ceramic product, thereby making the mechanical properties of the product uneven, the stability performance at high temperature is poor, and the service life of the product is shortened; Comparative Example 2 does not use silica sol for coating, and directly uses secondary treated silicon carbide for granulation, which will weaken the high-temperature oxidation resistance of the product, resulting in lower mechanical properties of the ceramic product after high-temperature treatment. In addition, in the process of preparing the auxiliary agent in Comparative Example 2, zirconium carbide and hafnium boride are directly mixed, which have poor compatibility with other ingredients, affecting the homogeneity of the granulated powder, thereby affecting the sintering performance of the ceramic product, and ultimately reducing the mechanical properties, density and stability of the product.

[0119] Unless otherwise specified, all ratios and percentages described in the present invention are by mass ratios and percentages are by mass percentages.

[0120] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention is described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing large-size zirconium boride / silicon carbide composite ceramics, characterized in that: It includes granulation, sintering and impregnation steps; The granulation step comprises adding zirconium boride powder to anhydrous ethanol, stirring evenly, adding phenolic resin, boron carbide and polyvinyl alcohol, stirring evenly again, adding modified silicon carbide and an auxiliary agent to obtain a slurry, and performing spray granulation to obtain a granulated powder; The method for preparing modified silicon carbide comprises primary treatment, secondary treatment and modification steps; The primary treatment step comprises adding tris(hydroxymethyl)aminomethane to deionized water, stirring evenly, adding sodium hydroxide solution to adjust the pH value to 8.3-8.7, then adding dopamine hydrochloride, and performing ultrasonic treatment to obtain a primary treatment liquid; placing the pretreated silicon carbide in the primary treatment liquid and stirring for reaction to obtain a primary treatment silicon carbide; The secondary treatment step comprises placing hexamethylene diisocyanate in N,N-dimethylformamide, stirring evenly to obtain a secondary treatment liquid; placing the primary treated silicon carbide in N,N-dimethylformamide, stirring evenly, adding the secondary treatment liquid, and then adding tin isooctanoate, reacting at 80-84° C. for 5.7-6.2 hours to obtain the secondary treated silicon carbide; The modification step comprises adding 3-aminopropyltrimethylsilane and 3-aminopropyltriethoxysilane to an ethanol solution, stirring evenly to obtain an amino reagent; adding the amino reagent to a silica sol and reacting at 56-60° C. for 4.2-4.7 hours, then adding secondary treated silicon carbide and glutaraldehyde, stirring at 74-80° C. for 5.8-6.2 hours, and then heat treating at 258-263° C. for 3.2-3.7 hours to obtain modified silicon carbide; The preparation method of the auxiliary agent is as follows: zirconium carbide and hafnium boride are added to anhydrous ethanol, stirred evenly, and then dodecyl hydroxystearic acid is added to perform ball milling treatment. After the ball milling is completed, the auxiliary agent is dried to obtain the auxiliary agent.

2. The method for preparing a large-size zirconium boride / silicon carbide composite ceramic according to claim 1, characterized in that: In the granulation step, the particle size of the zirconium boride powder is 150-170 nm; The mass ratio of the anhydrous ethanol, zirconium boride powder, phenolic resin, boron carbide, polyvinyl alcohol, modified silicon carbide and additives is 49.2-50.6:61.5-62.4:1.0-1.2:1.8-2.2:1.0-1.4:5.1-5.4:4.0-4.

2.

3. The method for preparing a large-size zirconium boride / silicon carbide composite ceramic according to claim 1, characterized in that: In the one-time treatment step, the ultrasonic treatment has an ultrasonic time of 1.3-1.7 h, an ultrasonic frequency of 28-32 kHz, and an ultrasonic power of 136-142 W; The mass ratio of the deionized water, trimethylolaminosilane and dopamine hydrochloride is 117-124:1.42-1.47:0.24-0.26; The mass concentration of the sodium hydroxide solution is 20-25%; The mass ratio of the pre-treated silicon carbide to the primary treatment liquid is 8.2-8.4:70-75.

4. The method for preparing a large-size zirconium boride / silicon carbide composite ceramic according to claim 1, characterized in that: In the one-time treatment step, the preparation method of the pretreated silicon carbide is to place silicon carbide in a reaction container, introduce a mixed solution and stir evenly, raise the temperature to 105-115° C., keep warm and stir for 5.7-6.2 hours, and after the stirring is completed, wash with deionized water until neutral, filter, and dry at 93-96° C. to constant weight to obtain pretreated silicon carbide; The particle size of the silicon carbide is 210-230nm; The mixed solution is obtained by mixing deionized water, hydrogen peroxide solution and ammonia solution, wherein the mass ratio of the deionized water, hydrogen peroxide solution and ammonia solution is 5.0-5.5:1.0-1.4:0.7-1.2; the mass concentration of the hydrogen peroxide solution is 26-30%, and the mass concentration of the ammonia solution is 20-25%; The mass ratio of the silicon carbide to the mixed solution is 10.3-10.7:106-113.

5. The method for preparing a large-size zirconium boride / silicon carbide composite ceramic according to claim 1, characterized in that: In the secondary treatment step, in the secondary treatment liquid, the mass ratio of hexamethylene diisocyanate to N,N-dimethylformamide is 9.7-10.2:117-125; The mass ratio of the primary treated silicon carbide, N,N-dimethylformamide, secondary treated liquid and tin isooctanoate is 7.3-7.7:95-106:25.6-26.3:0.6-0.

9.

6. The method for preparing a large-size zirconium boride / silicon carbide composite ceramic according to claim 1, characterized in that: In the modification step, the preparation method of the silica sol is to add deionized water and polyvinyl pyrrolidone to isopropanol, stir evenly, add tetraethyl orthosilicate, then add sodium hydroxide solution to adjust the pH value to 9.8-10.2, perform magnetic stirring reaction, the rotation speed is 225-235rpm, the reaction time is 5.7-6.2h, and obtain silica sol; The mass ratio of isopropanol, deionized water, polyvinyl pyrrolidone and tetraethyl orthosilicate is 98-104:9.2-9.7:1.3-1.5:10.4-10.8; The mass concentration of the sodium hydroxide solution is 18-22%.

7. The method for preparing a large-size zirconium boride / silicon carbide composite ceramic according to claim 1, characterized in that: In the modification step, the mass ratio of the ethanol solution, 3-aminopropyltrimethylsilane, and 3-aminopropyltriethoxysilane is 96-105:0.6-1.0:0.7-1.2; The mass concentration of the ethanol solution is 28-32%; The mass ratio of the amino reagent, silica sol, secondary treated silicon carbide and glutaraldehyde is 53-57:2.3-2.8:9.3-9.7:1.2-1.

5.

8. The method for preparing a large-size zirconium boride / silicon carbide composite ceramic according to claim 1, characterized in that: In the preparation method of the auxiliary agent, the ball milling treatment has a ball milling time of 30-35 min, a ball milling speed of 142-155 rpm, and a ball milling temperature of 37-42° C. The mass ratio of the zirconium carbide, hafnium boride, anhydrous ethanol and dodecyl hydroxystearic acid is 4.6-5.0:3.0-3.2:76-82:1.5-1.

7.

9. The method for preparing a large-size zirconium boride / silicon carbide composite ceramic according to claim 1, characterized in that: The sintering step comprises: pressing the granulated powder under a pressure of 136-142 MPa for 28-32 seconds to obtain a green body, placing the green body in a pressureless sintering furnace, and sintering the green body in an argon atmosphere, first heating the temperature to 510-530° C. at a rate of 5.8-6.2° C. / min, keeping the temperature for 30-40 minutes, then heating the temperature to 1570-1620° C. at a rate of 10-14° C. / min, keeping the temperature for 16-25 minutes, and then heating the temperature to 1975-1988° C. at a rate of 7.6-8.3° C. / min, keeping the temperature for 2.8-3.2 hours, and processing the green body into a product with a diameter of 280-320 mm and a length of 190-210 mm to obtain a primary ceramic.

10. The method for preparing a large-size zirconium boride / silicon carbide composite ceramic according to claim 1, characterized in that: The impregnation step is to add polycarbosilane to xylene, stir evenly to obtain an impregnation solution; place the primary ceramic in the impregnation solution so that the impregnation solution completely covers the primary ceramic, control the vacuum degree to -0.06--0.10MPa, the temperature to 63-67°C, and the impregnation time to 3.8-4.2h. After the impregnation is completed, the temperature is increased to 146-153°C, and the temperature is kept and cured for 5.8-6.2h. After cooling and depressurizing, sintering is performed, firstly, the temperature is increased to 882-895°C at a rate of 2.8-3.2°C / min, and the temperature is kept for 0.8-1.2h, and then the temperature is increased to 1975-1986°C at a rate of 4.8-5.2°C / min, and the temperature is kept for 2.8-3.2h. The above operation is an impregnation-curing-sintering step, and the above impregnation-curing-sintering step is repeated 3 times to obtain a large-sized zirconium boride / silicon carbide composite ceramic; The mass ratio of xylene to polycarbosilane is 98-104:41-45.

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