High-toughness silicon carbide ceramic and process for producing same

Abstract

The application discloses a high-toughness silicon carbide ceramic and a production process thereof, and relates to the technical field of silicon carbide ceramics. The silicon carbide ceramic is prepared from the following raw materials in components: silicon carbide powder, polyacrylic acid modified alumina whisker, composite sintering aid, carbon agent, binder, dispersant and lubricant. The polyacrylic acid modified alumina whisker is prepared from polyacrylic acid and alumina whisker; the composite sintering aid is prepared from carbon powder, boron carbide and carbon black; and the lubricant is zinc stearate. The production process of the high-toughness silicon carbide ceramic comprises the following steps: preparing the polyacrylic acid modified alumina whisker, preparing the composite sintering aid, uniformly mixing the slurry, preparing a ceramic blank, and preparing the silicon carbide ceramic. The silicon carbide ceramic prepared by the application has good toughness, high strength, excellent thermal shock resistance and high-temperature stability.

Description

Technical Field

[0001] This invention relates to the field of silicon carbide ceramics technology, specifically to a high-toughness silicon carbide ceramic and its production process. Background Technology

[0002] Silicon carbide ceramics, with their high hardness, wear resistance, high temperature resistance, and excellent chemical stability, are widely used in hot-end components of aerospace engines, motor housings of new energy vehicles, and structural components of high-temperature kilns. However, traditional silicon carbide ceramics have inherent defects such as high brittleness and low fracture toughness, which makes them prone to sudden fracture under dynamic loads or drastic temperature changes. Examples include the fragmentation of spacecraft nozzles under thermal shock and the spalling of industrial kiln linings due to temperature fluctuations, which seriously restricts their application in high-end equipment.

[0003] As modern industry moves towards extreme operating conditions, stringent requirements are placed on the comprehensive performance of silicon carbide ceramics: in terms of mechanical stress, they must withstand higher bending loads; in terms of thermal environment, they must withstand high-temperature oxidation above 1500℃ and rapid cooling and heating cycles; and at the same time, they must maintain a high elastic modulus to ensure structural stability. Prior art CN119638432B discloses a carbon fiber reinforced silicon carbide ceramic and its preparation method, which improves ceramic performance by preparing modified silicon carbide microspheres, but suffers from insufficient thermal shock resistance and poor high-temperature oxidation resistance. Prior art CN119735443A discloses a high-strength and high-toughness SiC... f -Si3N4-Si composite ceramics, their preparation methods and applications, but Si3N4 in the system is easily oxidized at high temperatures to generate SiO2 and N2, resulting in insufficient oxidation resistance; the improvement in toughness and strength is limited, restricting its application in high-load scenarios.

[0004] In summary, although the existing technical solutions have improved some properties of silicon carbide ceramics to a certain extent, the following technical problems still exist: insufficient toughness and strength, poor thermal shock resistance and high-temperature stability. Summary of the Invention

[0005] In order to solve the above-mentioned problems in the prior art, the present invention provides a high-toughness silicon carbide ceramic and its production process, and achieves the following objectives: to prepare silicon carbide ceramics with high toughness and high strength, which also have excellent thermal shock resistance and high temperature stability.

[0006] To achieve the above objectives, the following technical solution is adopted:

[0007] A high-toughness silicon carbide ceramic, by weight, comprises the following raw materials: 75-85 parts silicon carbide powder, 5-8 parts polyacrylic acid modified alumina whiskers, 3-5 parts composite sintering aid, 2-3 parts carbon agent, 4-6 parts binder, 0.5-1.0 parts dispersant, and 0.3-0.5 parts lubricant.

[0008] The silicon carbide powder is a submicron silicon carbide powder with a purity of ≥99% and a particle size of 0.5-1μm.

[0009] The polyacrylic acid modified alumina whiskers are prepared from polyacrylic acid and alumina whiskers.

[0010] The composite sintering aid is prepared from carbon powder, boron carbide, and carbon black.

[0011] The carbon agent is nano carbon black with a particle size of 50-100 nm.

[0012] The adhesive is polyvinyl alcohol.

[0013] The dispersant is polyethylene glycol, specifically PEG-4000.

[0014] The lubricant is zinc stearate.

[0015] This invention also provides a production process for high-toughness silicon carbide ceramics, comprising the following steps:

[0016] Step 1: Preparation of polyacrylic acid modified alumina whiskers

[0017] (1) Pretreatment of alumina whiskers

[0018] Alumina whiskers were dispersed in hydrochloric acid at a solid-liquid ratio of 0.08-0.12 g / mL. The mixture was ultrasonically stirred for 30-40 min at a power of 200-300 W. After ultrasonication, the whiskers were centrifuged at 4000-5000 rpm for 15-20 min. After centrifugation, the whiskers were washed with deionized water until neutral and then dried at 80-90℃ for 10-12 h. The dried whiskers were then added to a NaOH solution. In the reaction, the solid-liquid ratio of the dried whiskers to NaOH solution is 0.07-0.1 g / mL, the temperature is 60-70℃, and the reaction is stirred for 2-3 hours. After the reaction, the mixture is centrifuged at 4000-5000 rpm for 15-20 minutes. After centrifugation, the mixture is washed with deionized water until neutral, and then vacuum dried at 60-70℃, with a vacuum of 0.08-0.09 MPa for 4-6 hours to obtain hydroxylated alumina whiskers.

[0019] The hydrochloric acid has a mass fraction of 5%.

[0020] The alumina whiskers have an aspect ratio of 10-50 and a purity of ≥99%.

[0021] The concentration of the NaOH solution is 0.1 mol / L.

[0022] (2) Preparation of polyacrylic acid solution

[0023] Polyacrylic acid is dissolved in deionized water to prepare a solution with a mass fraction of 1.5-2.0%. A dispersing agent is added at a mass ratio of 1:(14-16) to polyacrylic acid. The ultrasonic power is 150-200W, and the solution is ultrasonically dispersed for 15-20 minutes. Then, the pH of the solution is adjusted to 8-9 with ammonia water to obtain a polyacrylic acid solution.

[0024] The molecular weight of the polyacrylic acid is 2000-5000 Da;

[0025] The dispersing agent is a 0.5% (w / w) aqueous solution of polyethylene glycol, and the polyethylene glycol used is PEG-4000.

[0026] (3) Synthesis of polyacrylic acid modified alumina whiskers

[0027] Hydroxylated alumina whiskers were added to a polyacrylic acid solution at a solid-liquid ratio of 0.08-0.1 g / mL. The solution was heated to 60-70℃ and stirred at 300-400 rpm for 2-3 hours. Then, a crosslinking agent was added at a mass ratio of 1:(25-30) to the hydroxylated alumina whiskers. The solution was heated to 80-85℃ and reacted for 1-1.5 hours. After the reaction, the solution was centrifuged at 8000-9000 rpm for 10-20 minutes. After centrifugation, the solution was washed 3-5 times with deionized water and then freeze-dried at -40℃ to -50℃ under a vacuum of 10-20 Pa for 18-24 hours to obtain polyacrylic acid-modified alumina whiskers.

[0028] The crosslinking agent is an aqueous solution of epichlorohydrin with a mass fraction of 0.1%.

[0029] Step 2: Preparation of composite sintering aid

[0030] Add carbon powder and boron carbide to a ball mill, with a mass ratio of carbon powder to boron carbide of 1:(3-3.5) and a ball-to-material ratio of (8-10):1. The milling speed is 300-400 rpm, and the milling time is 8-10 hours. After the milling is completed, add carbon black and polyethylene glycol solution, with a mass ratio of carbon black to carbon powder of (1-1.5):1. The amount of polyethylene glycol solution used is 15-20% of the total mass of carbon powder, boron carbide, and carbon black. Adjust the milling speed to 200-250 rpm and continue milling for 2-3 hours. Then, dry the mixture at 80-90℃ for 4-6 hours to obtain the composite sintering aid.

[0031] The polyethylene glycol solution is a 1% (w / w) aqueous solution of polyethylene glycol, and the polyethylene glycol is PEG-4000; the carbon black has a particle size of 50-100 nm; the carbon powder has a particle size of 1-5 μm; and the boron carbide has a particle size of 100-200 nm.

[0032] Step 3: Mix the slurry thoroughly.

[0033] Add silicon carbide powder to a high-shear disperser at 1500-2000 rpm, and add deionized water while stirring. The mass ratio of deionized water to silicon carbide powder is (1.5-2):1. Stir for 10-15 minutes, and adjust the pH to 8-9 with ammonia water to form a preliminary suspension. Add polyacrylic acid modified alumina whiskers and dispersant to the preliminary suspension and perform ultrasonic dispersion while maintaining shear stirring. The ultrasonic power is 300-400W, and the ultrasonic time is 30-40 minutes. Add composite sintering aid and carbon agent, and continue shear stirring for 20-30 minutes. Then reduce the stirring speed to 800-1000 rpm, and add binder and lubricant in sequence. Stir for 30-40 minutes to obtain a mixed slurry.

[0034] Step 4: Prepare the ceramic blank

[0035] The mixed slurry is passed through a 100-mesh sieve and fed into a centrifugal spray dryer for spray granulation. The conveying rate is 10-15 L / h. The centrifugal spray dryer is set with the following parameters: inlet temperature 180-200℃, outlet temperature 80-90℃, and atomizing disc speed 15000 rpm. After granulation, granulated powder is obtained. The granulated powder is passed through an 80-mesh sieve and loaded into a mold. A pressure of 150-200 MPa is applied and held for 3-5 minutes. Then, the pressure is slowly released at a rate ≤50 MPa / min to obtain a raw preform.

[0036] Step 5: Obtaining silicon carbide ceramics

[0037] The green blank is added to a graphite tube sintering furnace, and high-purity argon gas is introduced at a flow rate of 5-10 L / min. First, the temperature is raised to 600-650℃ at a rate of 2-3℃ / min and held for 2-2.5 h. Then, the temperature is raised to 1400-1450℃ at a rate of 8-10℃ / min and held for 30-60 min. The temperature is then raised to 1900-1950℃ at a rate of 4-5℃ / min and held for 2-3 h. Finally, the temperature is slowly lowered to room temperature at a rate of 5-7℃ / min to obtain silicon carbide ceramic.

[0038] The beneficial effects of this invention are as follows:

[0039] (1) The high-toughness silicon carbide ceramic of the present invention has excellent toughness and strength. The fracture toughness reaches 12.3-12.9 MPa·m. 1 / 2 Its flexural strength is 578-585 MPa, and its elastic modulus is 414-421 GPa.

[0040] (2) The high-toughness silicon carbide ceramic of the present invention has excellent thermal shock resistance. The silicon carbide ceramic prepared by the present invention exhibits cracking after 52-56 cycles.

[0041] (3) The silicon carbide ceramic prepared by this invention has excellent high-temperature stability. After holding at 1200±10℃ for 24h, the mass change rate is only 0.012-0.019%. This proves that the addition of polyacrylic acid modified alumina whiskers and composite sintering aids effectively inhibits the oxidation weight loss of silicon carbide ceramics at high temperatures. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0043] Example 1: A high-toughness silicon carbide ceramic and its production process

[0044] A high-toughness silicon carbide ceramic, by weight, comprises the following raw materials: 75 parts silicon carbide powder, 8 parts polyacrylic acid modified alumina whiskers, 5 parts composite sintering aid, 2 parts carbon agent, 4 parts binder, 0.5 parts dispersant, and 0.3 parts lubricant.

[0045] A production process for high-toughness silicon carbide ceramics includes the following steps:

[0046] Step 1: Preparation of polyacrylic acid modified alumina whiskers

[0047] (1) Pretreatment of alumina whiskers

[0048] Alumina whiskers were dispersed in hydrochloric acid at a solid-liquid ratio of 0.12 g / mL, and ultrasonically stirred for 40 min at a power of 200 W. After ultrasonication, the whiskers were centrifuged at 4000 rpm for 20 min. After centrifugation, the whiskers were washed with deionized water until neutral and then dried at 80 °C for 12 h. The dried whiskers were then added to NaOH solution at a solid-liquid ratio of 0.1 g / mL at 60 °C and stirred for 3 h. After the reaction, the whiskers were centrifuged at 4000 rpm for 20 min. After centrifugation, the whiskers were washed with deionized water until neutral and then vacuum dried at 60 °C under a vacuum of 0.08 MPa for 6 h to obtain hydroxylated alumina whiskers.

[0049] The hydrochloric acid has a mass fraction of 5%.

[0050] The alumina whiskers have an aspect ratio of 10-50 and a purity of ≥99%.

[0051] The concentration of the NaOH solution is 0.1 mol / L.

[0052] (2) Preparation of polyacrylic acid solution

[0053] Polyacrylic acid was dissolved in deionized water to prepare a 1.5% solution. A dispersing agent was added at a mass ratio of 1:14 to the polyacrylic acid. The ultrasonic power was 150W, and the solution was ultrasonically dispersed for 20 minutes. The pH of the solution was then adjusted to 8 with ammonia to obtain the polyacrylic acid solution.

[0054] The molecular weight of the polyacrylic acid is 2000-5000 Da;

[0055] The dispersing agent is a 0.5% (w / w) aqueous solution of polyethylene glycol, and the polyethylene glycol used is PEG-4000.

[0056] (3) Synthesis of polyacrylic acid modified alumina whiskers

[0057] Hydroxylated alumina whiskers were added to a polyacrylic acid solution at a solid-liquid ratio of 0.1 g / mL. The mixture was heated to 60°C and stirred at 300 rpm for 3 hours. Then, a crosslinking agent was added at a mass ratio of 1:25 to the hydroxylated alumina whiskers, and the mixture was heated to 80°C and reacted for 1.5 hours. After the reaction, the mixture was centrifuged at 8000 rpm for 20 minutes. After centrifugation, the mixture was washed three times with deionized water and then freeze-dried at -40°C under a vacuum of 10 Pa for 24 hours to obtain polyacrylic acid-modified alumina whiskers.

[0058] The crosslinking agent is an aqueous solution of epichlorohydrin with a mass fraction of 0.1%.

[0059] Step 2: Preparation of composite sintering aid

[0060] Carbon powder and boron carbide were added to a ball mill at a mass ratio of 1:3 and a ball-to-material ratio of 8:1. The milling speed was 300 rpm for 10 hours. After ball milling, carbon black and polyethylene glycol solution were added at a mass ratio of 1:1. The amount of polyethylene glycol solution was 15% of the total mass of carbon powder, boron carbide, and carbon black. The milling speed was adjusted to 200 rpm, and ball milling continued for 3 hours. Then, the mixture was dried at 80℃ for 6 hours to obtain the composite sintering aid.

[0061] The polyethylene glycol solution is a 1% (w / w) aqueous solution of polyethylene glycol, and the polyethylene glycol is PEG-4000; the carbon black has a particle size of 50-100 nm; the carbon powder has a particle size of 1-5 μm; and the boron carbide has a particle size of 100-200 nm.

[0062] Step 3: Mix the slurry thoroughly.

[0063] Silicon carbide powder was added to a high-shear disperser at 1500 rpm while stirring with deionized water at a mass ratio of 1.5:1. The mixture was stirred for 15 minutes, and the pH was adjusted to 8 with ammonia to form a preliminary suspension. Polyacrylic acid-modified alumina whiskers and a dispersant were added to the preliminary suspension and ultrasonically dispersed while maintaining shear stirring. The ultrasonic power was 300 W and the ultrasonic time was 40 minutes. Composite sintering aid and carbon agent were added, and shear stirring was continued for 20 minutes. Then the stirring speed was reduced to 800 rpm, and binder and lubricant were added in sequence. The mixture was stirred for 40 minutes to obtain a mixed slurry.

[0064] Step 4: Prepare the ceramic blank

[0065] The mixed slurry is passed through a 100-mesh sieve and fed into a centrifugal spray dryer for spray granulation. The conveying rate is 10 L / h. The centrifugal spray dryer is set with the following parameters: inlet temperature 180℃, outlet temperature 80℃, and atomizing disc speed 15000 rpm. After granulation, granulated powder is obtained. The granulated powder is passed through an 80-mesh sieve and loaded into a mold. A pressure of 150 MPa is applied and held for 5 minutes. Then, the pressure is slowly released at a rate ≤50 MPa / min to obtain a preform.

[0066] Step 5: Obtaining silicon carbide ceramics

[0067] The raw blank was added to a graphite tube sintering furnace, and high-purity argon gas was introduced at a flow rate of 5 L / min. First, the temperature was raised to 600℃ at a rate of 2℃ / min and held for 2.5 h. Then, the temperature was raised to 1400℃ at a rate of 8℃ / min and held for 60 min. The temperature was then raised to 1900℃ at a rate of 4℃ / min and held for 3 h. Finally, the temperature was slowly lowered to room temperature at a rate of 5℃ / min to obtain silicon carbide ceramic.

[0068] Example 2: A high-toughness silicon carbide ceramic and its production process

[0069] A high-toughness silicon carbide ceramic, by weight, comprises: 80 parts silicon carbide powder, 6 parts polyacrylic acid modified alumina whiskers, 4 parts composite sintering aid, 3 parts carbon agent, 5 parts binder, 0.8 parts dispersant, and 0.4 parts lubricant.

[0070] A production process for high-toughness silicon carbide ceramics includes the following steps:

[0071] Step 1: Preparation of polyacrylic acid modified alumina whiskers

[0072] (1) Pretreatment of alumina whiskers

[0073] Alumina whiskers were dispersed in hydrochloric acid at a solid-liquid ratio of 0.1 g / mL, and ultrasonically stirred for 40 min at a power of 300 W. After ultrasonication, the whiskers were centrifuged at 5000 rpm for 20 min. After centrifugation, the whiskers were washed with deionized water until neutral and then dried at 85℃ for 11 h. The dried whiskers were then added to NaOH solution at a solid-liquid ratio of 0.09 g / mL at 65℃ and stirred for 3 h. After the reaction, the whiskers were centrifuged at 5000 rpm for 20 min. After centrifugation, the whiskers were washed with deionized water until neutral and then vacuum dried at 70℃ and a vacuum of 0.09 MPa for 5 h to obtain hydroxylated alumina whiskers.

[0074] The hydrochloric acid has a mass fraction of 5%.

[0075] The alumina whiskers have an aspect ratio of 10-50 and a purity of ≥99%.

[0076] The concentration of the NaOH solution is 0.1 mol / L.

[0077] (2) Preparation of polyacrylic acid solution

[0078] Polyacrylic acid was dissolved in deionized water to prepare a 2.0% solution. A dispersing agent was added at a mass ratio of 1:15 to the polyacrylic acid. The ultrasonic power was 200W, and the solution was ultrasonically dispersed for 15 minutes. The pH of the solution was then adjusted to 9 with ammonia to obtain the polyacrylic acid solution.

[0079] The molecular weight of the polyacrylic acid is 2000-5000 Da;

[0080] The dispersing agent is a 0.5% (w / w) aqueous solution of polyethylene glycol, and the polyethylene glycol used is PEG-4000.

[0081] (3) Synthesis of polyacrylic acid modified alumina whiskers

[0082] Hydroxylated alumina whiskers were added to a polyacrylic acid solution at a solid-liquid ratio of 0.08 g / mL. The mixture was heated to 65°C and stirred at 400 rpm for 3 hours. Then, a crosslinking agent was added at a mass ratio of 1:30 to the hydroxylated alumina whiskers, and the mixture was heated to 85°C and reacted for 1.5 hours. After the reaction, the mixture was centrifuged at 9000 rpm for 20 minutes. After centrifugation, the mixture was washed five times with deionized water and then freeze-dried at -50°C under a vacuum of 20 Pa for 22 hours to obtain polyacrylic acid-modified alumina whiskers.

[0083] The crosslinking agent is an aqueous solution of epichlorohydrin with a mass fraction of 0.1%.

[0084] Step 2: Preparation of composite sintering aid

[0085] Carbon powder and boron carbide were added to a ball mill at a mass ratio of 1:3 and a ball-to-material ratio of 10:1. The milling speed was 400 rpm for 8 hours. After ball milling, carbon black and polyethylene glycol solution were added at a mass ratio of 1.5:1. The amount of polyethylene glycol solution was 20% of the total mass of carbon powder, boron carbide, and carbon black. The milling speed was adjusted to 250 rpm, and ball milling continued for 2 hours. Then, the mixture was dried at 90℃ for 4 hours to obtain the composite sintering aid.

[0086] The polyethylene glycol solution is a 1% (w / w) aqueous solution of polyethylene glycol, and the polyethylene glycol is PEG-4000; the carbon black has a particle size of 50-100 nm; the carbon powder has a particle size of 1-5 μm; and the boron carbide has a particle size of 100-200 nm.

[0087] Step 3: Mix the slurry thoroughly.

[0088] Silicon carbide powder was added to a high-shear disperser at 1500 rpm while stirring. Deionized water was added at a mass ratio of 2:1 (deionized water to silicon carbide powder). The mixture was stirred for 15 minutes, and the pH was adjusted to 9 with ammonia to form a preliminary suspension. Polyacrylic acid-modified alumina whiskers and a dispersant were added to the preliminary suspension and ultrasonically dispersed while maintaining shear stirring. The ultrasonic power was 400 W, and the ultrasonic time was 40 minutes. Composite sintering aid and carbon agent were added, and shear stirring was continued for 30 minutes. Then, the stirring speed was reduced to 800 rpm, and binder and lubricant were added in sequence. The mixture was stirred for 40 minutes to obtain a mixed slurry.

[0089] Step 4: Prepare the ceramic blank

[0090] The mixed slurry is passed through a 100-mesh sieve and fed into a centrifugal spray dryer for spray granulation. The conveying rate is 15 L / h. The centrifugal spray dryer is set with the following parameters: inlet temperature 190℃, outlet temperature 90℃, and atomizing disc speed 15000 rpm. After granulation, granulated powder is obtained. The granulated powder is passed through an 80-mesh sieve and loaded into a mold. A pressure of 200 MPa is applied and held for 5 minutes. Then, the pressure is slowly released at a rate ≤50 MPa / min to obtain a preform.

[0091] Step 5: Obtaining silicon carbide ceramics

[0092] The green blank was added to a graphite tube sintering furnace, and high-purity argon gas was introduced at a flow rate of 10 L / min. First, the temperature was raised to 650℃ at a rate of 3℃ / min and held for 2.5 h. Then, the temperature was raised to 1450℃ at a rate of 10℃ / min and held for 60 min. The temperature was then raised to 1950℃ at a rate of 5℃ / min and held for 3 h. Finally, the temperature was slowly lowered to room temperature at a rate of 7℃ / min to obtain silicon carbide ceramic.

[0093] Example 3: A high-toughness silicon carbide ceramic and its production process

[0094] A high-toughness silicon carbide ceramic, by weight, comprises: 85 parts silicon carbide powder, 5 parts polyacrylic acid modified alumina whiskers, 3 parts composite sintering aid, 3 parts carbon agent, 6 parts binder, 1.0 part dispersant, and 0.5 parts lubricant.

[0095] A production process for high-toughness silicon carbide ceramics includes the following steps:

[0096] Step 1: Preparation of polyacrylic acid modified alumina whiskers

[0097] (1) Pretreatment of alumina whiskers

[0098] Alumina whiskers were dispersed in hydrochloric acid at a solid-liquid ratio of 0.08 g / mL, and ultrasonically stirred for 30 min at a power of 300 W. After ultrasonication, the whiskers were centrifuged at 5000 rpm for 15 min. After centrifugation, the whiskers were washed with deionized water until neutral and then dried at 90 °C for 10 h. The dried whiskers were then added to NaOH solution at a solid-liquid ratio of 0.07 g / mL at 70 °C and stirred for 2 h. After the reaction, the whiskers were centrifuged at 5000 rpm for 15 min. After centrifugation, the whiskers were washed with deionized water until neutral and then vacuum dried at 70 °C and a vacuum of 0.09 MPa for 4 h to obtain hydroxylated alumina whiskers.

[0099] The hydrochloric acid has a mass fraction of 5%.

[0100] The alumina whiskers have an aspect ratio of 10-50 and a purity of ≥99%.

[0101] The concentration of the NaOH solution is 0.1 mol / L.

[0102] (2) Preparation of polyacrylic acid solution

[0103] Polyacrylic acid was dissolved in deionized water to prepare a 2.0% (w / w) solution. A dispersing agent was added at a mass ratio of 1:16 to polyacrylic acid. The ultrasonic power was 200W, and the solution was ultrasonically dispersed for 15 minutes. The pH of the solution was then adjusted to 9 with ammonia to obtain the polyacrylic acid solution.

[0104] The molecular weight of the polyacrylic acid is 2000-5000 Da;

[0105] The dispersing agent is a 0.5% (w / w) aqueous solution of polyethylene glycol, and the polyethylene glycol used is PEG-4000.

[0106] (3) Synthesis of polyacrylic acid modified alumina whiskers

[0107] Hydroxylated alumina whiskers were added to a polyacrylic acid solution at a solid-liquid ratio of 0.08 g / mL. The mixture was heated to 70°C and stirred at 400 rpm for 2 hours. Then, a crosslinking agent was added at a mass ratio of 1:30 to the hydroxylated alumina whiskers, and the mixture was heated to 85°C and reacted for 1 hour. After the reaction, the mixture was centrifuged at 9000 rpm for 10 minutes. After centrifugation, the mixture was washed five times with deionized water and then freeze-dried at -50°C under a vacuum of 20 Pa for 18 hours to obtain polyacrylic acid-modified alumina whiskers.

[0108] The crosslinking agent is an aqueous solution of epichlorohydrin with a mass fraction of 0.1%.

[0109] Step 2: Preparation of composite sintering aid

[0110] Carbon powder and boron carbide were added to a ball mill at a mass ratio of 1:3.5 and a ball-to-material ratio of 10:1. The milling speed was 400 rpm for 9 hours. After ball milling, carbon black and polyethylene glycol solution were added at a mass ratio of 1.5:1. The amount of polyethylene glycol solution was 20% of the total mass of carbon powder, boron carbide, and carbon black. The milling speed was adjusted to 250 rpm, and ball milling continued for 3 hours. Then, the mixture was dried at 90℃ for 5 hours to obtain the composite sintering aid.

[0111] The polyethylene glycol solution is a 1% (w / w) aqueous solution of polyethylene glycol, and the polyethylene glycol is PEG-4000; the carbon black has a particle size of 50-100 nm; the carbon powder has a particle size of 1-5 μm; and the boron carbide has a particle size of 100-200 nm.

[0112] Step 3: Mix the slurry thoroughly.

[0113] Silicon carbide powder was added to a high-shear disperser at 2000 rpm while stirring. Deionized water was added at a mass ratio of 2:1 (deionized water to silicon carbide powder). The mixture was stirred for 10 minutes, and the pH was adjusted to 9 with ammonia to form a preliminary suspension. Polyacrylic acid-modified alumina whiskers and a dispersant were added to the preliminary suspension and ultrasonically dispersed while maintaining shear stirring. The ultrasonic power was 400 W and the ultrasonic time was 30 minutes. Composite sintering aid and carbon agent were added, and shear stirring was continued for another 30 minutes. Then the stirring speed was reduced to 1000 rpm, and binder and lubricant were added in sequence. The mixture was stirred for another 30 minutes to obtain a mixed slurry.

[0114] Step 4: Prepare the ceramic blank

[0115] The mixed slurry is passed through a 100-mesh sieve and fed into a centrifugal spray dryer for spray granulation. The conveying rate is 15 L / h. The centrifugal spray dryer is set with the following parameters: inlet temperature 200℃, outlet temperature 90℃, and atomizing disc speed 15000 rpm. After granulation, granulated powder is obtained. The granulated powder is passed through an 80-mesh sieve and loaded into a mold. A pressure of 200 MPa is applied and held for 3 minutes. Then, the pressure is slowly released at a rate ≤50 MPa / min to obtain a preform.

[0116] Step 5: Obtaining silicon carbide ceramics

[0117] The raw blank was added to a graphite tube sintering furnace, and high-purity argon gas was introduced at a flow rate of 10 L / min. First, the temperature was raised to 650℃ at a rate of 3℃ / min and held for 2 hours. Then, the temperature was raised to 1450℃ at a rate of 10℃ / min and held for 30 minutes. The temperature was then raised to 1950℃ at a rate of 5℃ / min and held for 2 hours. Finally, the temperature was slowly lowered to room temperature at a rate of 7℃ / min to obtain silicon carbide ceramic.

[0118] Comparative Example 1

[0119] A silicon carbide ceramic, by weight, comprises: 80 parts silicon carbide powder, 4 parts composite sintering aid, 3 parts carbon agent, 5 parts binder, 0.8 parts dispersant, and 0.4 parts lubricant.

[0120] A process for producing silicon carbide ceramics includes the following steps:

[0121] Step 1: Preparation of composite sintering aid

[0122] This step is the same as the "Preparation of Composite Sintering Aid" step in Example 2.

[0123] Step 2: Mix the slurry thoroughly.

[0124] Silicon carbide powder was added to a high-shear disperser at 1500 rpm while stirring. Deionized water was added at a mass ratio of 2:1 to silicon carbide powder. The mixture was stirred for 15 minutes, and the pH was adjusted to 9 with ammonia to form a preliminary suspension. Composite sintering aid, carbon agent, and dispersant were added, and shear stirring was continued for 30 minutes. Then the stirring speed was reduced to 800 rpm, and binder and lubricant were added in sequence. The mixture was stirred for 40 minutes to obtain a mixed slurry.

[0125] Step 3: Prepare the ceramic blank

[0126] This step is the same as the "preparing ceramic blank" step in Example 2.

[0127] Step 4: Obtaining silicon carbide ceramics

[0128] This step is the same as the "Preparation of silicon carbide ceramics" step in Example 2.

[0129] Comparative Example 2

[0130] A silicon carbide ceramic, by weight, comprises the following raw materials: 80 parts silicon carbide powder, 6 parts polyacrylic acid modified alumina whiskers, 3 parts carbon agent, 5 parts binder, 0.8 parts dispersant, and 0.4 parts lubricant.

[0131] A process for producing silicon carbide ceramics includes the following steps:

[0132] Step 1: Preparation of polyacrylic acid modified alumina whiskers

[0133] This step is the same as the "Preparation of polyacrylic acid modified alumina whiskers" step in Example 2.

[0134] Step 2: Mix the slurry thoroughly.

[0135] Silicon carbide powder was added to a high-shear disperser at 1500 rpm while stirring with deionized water at a mass ratio of 2:1. The mixture was stirred for 15 minutes, and the pH was adjusted to 9 with ammonia to form a preliminary suspension. Polyacrylic acid-modified alumina whiskers and a dispersant were added to the preliminary suspension while maintaining shear stirring and ultrasonic dispersion at a power of 400 W for 40 minutes. The stirring speed was then reduced to 800 rpm, and the binder and lubricant were added sequentially. The mixture was stirred for 40 minutes to obtain a slurry.

[0136] Step 3: Prepare the ceramic blank

[0137] This step is the same as the "preparing ceramic blank" step in Example 2.

[0138] Step 4: Obtaining silicon carbide ceramics

[0139] This step is the same as the "Preparation of silicon carbide ceramics" step in Example 2.

[0140] Example 4 Performance Testing

[0141] (a) The silicon carbide ceramics prepared in Examples 1-3 and Comparative Examples 1-2 were subjected to fracture toughness tests according to the test methods provided in GB / T23806-2009. The sample dimensions were: length 18 mm, width 4 mm, thickness 3 mm, and chamfer 0.12 mm. The flexural strength was tested according to the test methods provided in GB / T6569-2006, and the elastic modulus was tested according to the test methods provided in GB / T10700-2006. The specific test results are shown in Table 1.

[0142] Table 1

[0143]

[0144] As shown in Table 1, the fracture toughness of the silicon carbide ceramics prepared in Examples 1-3 reached 12.3-12.9 MPa·m. 1 / 2 The flexural strength was 578-585 MPa, and the elastic modulus was 414-421 GPa, showing a significant improvement compared to comparative examples 1-2. This demonstrates that polyacrylic acid-modified alumina whiskers and composite sintering aids effectively enhance the toughness and strength of silicon carbide ceramics.

[0145] (ii) The silicon carbide ceramics prepared in Examples 1-3 and Comparative Examples 1-2 were subjected to thermal shock resistance tests according to the test methods provided in GB / T30873-2014. The number of cycles in which cracks appeared under a rapid cooling cycle from 1200℃ to room temperature was tested. The specific test results are shown in Table 2.

[0146] Table 2

[0147]

[0148] As shown in Table 2, the silicon carbide ceramics prepared in Examples 1-3 exhibited cracks after 52-56 cycles. This demonstrates that the silicon carbide ceramics prepared in this invention possess excellent thermal shock resistance.

[0149] (III) The oxidation resistance of the silicon carbide ceramics prepared in Examples 1-3 and Comparative Examples 1-2 was tested. The sample size was 10×10×3mm. 3 The temperature is 1200±10℃, and the holding time is 24h; the formula for calculating the rate of mass change is: Δm=(m0-m t ) / m0×100%, where m0 is the sample mass before testing, m t The sample quality is shown in Table 3. Specific test results are shown in Table 3.

[0150] Table 3

[0151]

[0152] As shown in Table 3, the mass change rate of the silicon carbide ceramics prepared in Examples 1-3 after holding at 1200±10℃ for 24 hours was 0.012-0.019%. The addition of polyacrylic acid modified alumina whiskers and composite sintering aids effectively suppressed oxidation weight loss at high temperatures, proving that the silicon carbide ceramics prepared by this invention have excellent high-temperature stability.

[0153] The specific parameters of the raw materials used in this invention are as follows:

[0154] The silicon carbide powder is a submicron silicon carbide powder with a purity of ≥99% and a particle size of 0.5-1μm.

[0155] The carbon agent is nano carbon black with a particle size of 50-100 nm.

[0156] The adhesive is polyvinyl alcohol.

[0157] The dispersant is polyethylene glycol PEG-4000.

[0158] The lubricant is zinc stearate.

[0159] Obviously, there are many other possible implementation methods under the concept of this invention. It should be stated here that any changes made under the inventive concept of this invention will fall within the protection scope of this invention.

Claims

1. A high-toughness silicon carbide ceramic, characterized in that: The silicon carbide ceramic has the following raw material composition: silicon carbide powder, polyacrylic acid modified alumina whiskers, composite sintering aid, carbon agent, binder, dispersant, and lubricant. The polyacrylic acid-modified alumina whiskers are prepared as follows: Alumina whiskers are dispersed in hydrochloric acid at a solid-liquid ratio of 0.08-0.12 g / mL, and ultrasonically stirred for 30-40 min. After ultrasonication, the whiskers are centrifuged and dried. The dried whiskers are then added to NaOH solution at a solid-liquid ratio of 0.07-0.1 g / mL, and the reaction is carried out at 60-70℃ for 2-3 h. After the reaction, the whiskers are centrifuged, washed, and dried to obtain hydroxylated alumina whiskers. Hydroxylated alumina whiskers were added to a polyacrylic acid solution, with a solid-liquid ratio of 0.08-0.1 g / mL. The solution was heated to 60-70°C and stirred for 2-3 hours. Then, a crosslinking agent was added, with a mass ratio of 1:(25-30) between the crosslinking agent and the hydroxylated alumina whiskers. The solution was heated to 80-85°C and reacted for 1-1.5 hours. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain polyacrylic acid-modified alumina whiskers. The crosslinking agent was a 0.1% (w / w) aqueous solution of epichlorohydrin. The composite sintering aid is prepared from carbon powder, boron carbide, and carbon black; The lubricant is zinc stearate; The carbon agent is nano-carbon black with a particle size of 50-100nm.

2. The high-toughness silicon carbide ceramic according to claim 1, characterized in that: The raw materials are formulated in the following weight proportions: 75-85 parts silicon carbide powder, 5-8 parts polyacrylic acid modified alumina whiskers, 3-5 parts composite sintering aid, 2-3 parts carbon agent, 4-6 parts binder, 0.5-1.0 parts dispersant, and 0.3-0.5 parts lubricant.

3. The production process of high-toughness silicon carbide ceramic according to any one of claims 1-2, characterized in that: The process includes the following steps: preparation of polyacrylic acid modified alumina whiskers, preparation of composite sintering aid, slurry mixing, preparation of ceramic blanks, and preparation of silicon carbide ceramics. The preparation of the polyacrylic acid modified alumina whiskers includes the steps of alumina whisker pretreatment, polyacrylic acid solution preparation, and synthesis of polyacrylic acid modified alumina whiskers.

4. The production process of high-toughness silicon carbide ceramic according to claim 3, characterized in that: The polyacrylic acid solution was prepared by dissolving polyacrylic acid in deionized water to prepare a solution with a mass fraction of 1.5-2.0%, adding a dispersing agent at a mass ratio of 1:(14-16) and ultrasonically dispersing for 15-20 minutes; then adjusting the pH of the solution to 8-9 with ammonia to obtain the polyacrylic acid solution; the dispersing agent was a 0.5% polyethylene glycol aqueous solution, and the polyethylene glycol used was PEG-4000.

5. The production process of high-toughness silicon carbide ceramic according to claim 3, characterized in that: The preparation of the composite sintering aid involves adding carbon powder and boron carbide to a ball mill, with a mass ratio of carbon powder to boron carbide of 1:(3-3.5) and a ball-to-material ratio of (8-10):1, and ball milling for 8-10 hours. After ball milling, carbon black and polyethylene glycol solution are added, with a mass ratio of carbon black to carbon powder of (1-1.5):1, and the amount of polyethylene glycol solution is 15-20% of the total mass of carbon powder, boron carbide, and carbon black. Ball milling continues for 2-3 hours. After drying, the composite sintering aid is obtained. The polyethylene glycol solution is a 1% (w / w) aqueous solution of polyethylene glycol, and the polyethylene glycol is PEG-4000.

6. The production process of high-toughness silicon carbide ceramic according to claim 3, characterized in that: The slurry is mixed as follows: Silicon carbide powder is added to a high-shear disperser at a speed of 1500-2000 rpm, and deionized water is added while stirring. The mass ratio of deionized water to silicon carbide powder is (1.5-2):

1. Stir for 10-15 minutes, and adjust the pH value to 8-9 with ammonia water to form a preliminary suspension. Polyacrylic acid modified alumina whiskers and dispersant are added to the preliminary suspension and ultrasonically dispersed while maintaining shear stirring for 30-40 minutes. Composite sintering aid and carbon agent are added, and shear stirring is continued for 20-30 minutes. Then the stirring speed is reduced to 800-1000 rpm, and binder and lubricant are added in sequence. Stir for 30-40 minutes to obtain a mixed slurry.

7. The production process of high-toughness silicon carbide ceramic according to claim 3, characterized in that: The process of preparing ceramic blanks involves: passing the mixed slurry through a 100-mesh sieve and feeding it into a centrifugal spray dryer for spray granulation; after granulation, granulated powder is obtained, which is then passed through an 80-mesh sieve, loaded into a mold, and subjected to a pressure of 150-200 MPa for 3-5 minutes; the pressure is then slowly released to obtain the blank.

8. The production process of high-toughness silicon carbide ceramic according to claim 7, characterized in that: The centrifugal spray dryer is configured with the following parameters: inlet temperature 180-200℃, outlet temperature 80-90℃, and atomizing disc rotation speed 15000rpm.

9. The production process of high-toughness silicon carbide ceramic according to claim 3, characterized in that: The silicon carbide ceramic was prepared by: adding the raw blank into a graphite tube sintering furnace and passing high-purity argon gas; first, heating to 600-650℃ at a heating rate of 2-3℃ / min and holding for 2-2.5h; then heating to 1400-1450℃ at a heating rate of 8-10℃ / min and holding for 30-60min; continuing to heat to 1900-1950℃ at a heating rate of 4-5℃ / min and holding for 2-3h; and then slowly cooling to room temperature to obtain silicon carbide ceramic.

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