A method for pressureless sintering of zirconium boride ceramic material

Abstract

This invention provides a method for preparing zirconium boride ceramic materials by pressureless sintering, belonging to the field of zirconium boride ceramic technology. The method includes the steps of preparing zirconium boride composite powder, modifying silicon carbide nanowires, and mixing and sintering. The modified silicon carbide nanowires include acid treatment and modification steps. The modification step involves adding aluminum isopropoxide to anhydrous ethanol, adding nitric acid solution, stirring at 60-63°C for 1.5-2.0 h, adding acid-treated silicon carbide nanowires, ultrasonically dispersing, evaporating in a water bath and drying, placing in a muffle furnace, and holding at 490-500°C for 2.0-2.2 h to obtain modified silicon carbide nanowires. The ceramic material prepared by the method of this invention has high density, good mechanical properties, excellent high-temperature oxidation resistance, and excellent stability in complex environments.

Description

Technical Field

[0001] This invention belongs to the field of zirconium boride ceramic technology, specifically relating to a method for preparing zirconium boride ceramic materials by pressureless sintering. Background Technology

[0002] Zirconium boride is a compound of metalloid boron and metallic zirconium, belonging to the hexagonal crystal system. In its crystal structure, zirconium and boron atoms are bonded by strong covalent bonds, forming a two-dimensional network structure. Zirconium boride has a high melting point of 3245℃, a Vickers hardness of 23 GPa, excellent wear resistance, and good electrical and thermal conductivity. It is also resistant to strong acid and alkali corrosion, and can serve as a structural support in extreme environments (high temperature, high pressure, corrosion, etc.). It is widely used in aerospace, metallurgy, electronics, and nuclear industries.

[0003] Zirconium boride ceramics are dense composite materials formed by the synthesis, molding and sintering of zirconium boride. They can be used as structural-functional integrated materials, simultaneously undertaking structural support and heat resistance properties in ultra-high temperature environments.

[0004] Existing technologies for preparing zirconium boride ceramics generally include hot pressing sintering, hot isostatic pressing sintering, spark plasma sintering, and pressureless sintering. Compared with pressureless sintering, hot pressing sintering, hot isostatic pressing sintering, and spark plasma sintering have drawbacks such as complex equipment and processes, high cost, low production efficiency, and difficulty in large-scale production.

[0005] Pressureless sintering can be achieved under normal pressure, without the need for complex equipment and processes, resulting in low production costs and enabling large-scale industrial production. However, when pure zirconium boride powder is directly sintered at high temperatures without pressure, the self-diffusion coefficient of zirconium boride is relatively low, usually requiring a high sintering temperature. Furthermore, abnormal grain growth occurs during sintering, leading to poor product density and high porosity, which in turn results in poor mechanical properties of zirconium boride ceramics that cannot meet application requirements.

[0006] Existing technologies typically involve adding metal sintering aids (Fe, Ni, etc.) or ceramic sintering aids (B4C, etc.), which can lower the sintering temperature. However, their effect on improving the density of ceramic products is limited, and the addition of sintering aids will further affect the high-temperature oxidation resistance of ceramic products.

[0007] Others use zirconium oxide, boron oxide and carbon powder as raw materials to generate zirconium boride in situ, but its powder dispersion performance is still poor, which affects the overall stability of the product.

[0008] Other methods involve adding reinforcing phases such as silicon carbide and pre-treating these phases with acid leaching to enhance their bonding with zirconium boride. This, in turn, improves the fracture toughness of ceramic products through mechanisms such as crack bridging and whisker pull-out. However, simple pre-treatment steps cannot establish chemical bonds between the reinforcing phase and zirconium boride, resulting in low interfacial bonding strength and limited improvement in the toughness of ceramic products. Furthermore, the thermal expansion coefficients of the reinforcing phase and the zirconium boride matrix do not match, making it easy for cracks to form during sintering as the temperature rises, thus shortening the service life of ceramic products.

[0009] Researchers also discovered that zirconium boride ceramics prepared by the pressureless sintering method in existing technologies have poor performance in complex environments. In environments with rapid temperature changes, the mechanical properties of ceramic products drop sharply, seriously affecting the service life of the products in complex environments.

[0010] Therefore, providing a method for preparing zirconium boride ceramic materials, employing a pressureless sintering method to improve the density of the ceramic, enhance its mechanical properties, improve its resistance to high-temperature oxidation, and extend its service life in complex environments, is a technical problem that urgently needs to be solved in the existing technology. Summary of the Invention

[0011] To address the technical problems existing in the prior art, this invention provides a method for preparing zirconium boride ceramic materials by pressureless sintering, which improves the density of the ceramic materials, enhances the mechanical properties of zirconium boride ceramic materials, and ensures stability in high-temperature and complex environments.

[0012] To address the aforementioned technical problems, the present invention adopts the following technical solution:

[0013] A method for preparing zirconium boride ceramic materials by pressureless sintering includes the steps of preparing zirconium boride composite powder, modifying silicon carbide nanowires, and mixing and sintering. The specific operation steps are as follows:

[0014] 1. Preparation of zirconium boride composite powder

[0015] (1) Preparation of initial mixture

[0016] Add Zr(NO3)4·5H2O to deionized water and stir until completely dissolved. Then add boric acid and stir at 150-170 rpm for 30-35 min. Add citric acid and stir until homogeneous. Add 15-20 wt% ammonia solution to adjust the pH to 4.0-4.5. Increase the temperature to 60-63℃ at a rate of 1.2-1.6℃ / min and keep stirring at this temperature for 60-70 min to obtain the initial mixture.

[0017] The mass ratio of Zr(NO3)4·5H2O, deionized water, boric acid, and citric acid is 3.2-3.5:30:1.2-1.3:3.5-3.8.

[0018] (2) kH570 modified titanium carbide

[0019] Titanium carbide was added to a 10-13 wt% hydrogen peroxide solution, the temperature was raised to 60-64℃, and the mixture was stirred at 250-280 rpm for 1.8-2.3 h. After filtration and washing, the mixture was added to a 65-68 wt% ethanol solution and stirred evenly. Then, KH570 silane coupling agent was added, and glacial acetic acid was added to adjust the pH to 4.2-4.8. The temperature was raised to 62-66℃ and the mixture was stirred for 2.5-3.0 h. After centrifugation at 8000-8300 rpm for 10-15 min, the mixture was washed and dried to obtain KH570 modified titanium carbide.

[0020] The titanium carbide has a particle size of 200-250 nm;

[0021] The mass ratio of titanium carbide, hydrogen peroxide solution, ethanol solution, and KH570 silane coupling agent is 10-15:65:100:1.2-1.5.

[0022] (3) Composite

[0023] Zirconia and neodymium oxide were added to the initial mixture and ultrasonically dispersed at a power of 200-220W, a frequency of 50-54kHz, and a dispersion time of 25-30min. Then, KH570 modified titanium carbide was added, and ultrasonic dispersion was continued for 15-20min. After ultrasonic dispersion, the mixture was heated in a water bath at 78-80℃ for 5-6h, and then vacuum dried at 60-65℃ and -0.09 to -0.08MPa for 10-12h. After drying, the temperature was increased to 560-580℃ at a rate of 2.0-3.0℃ / min under a mixed atmosphere and held for 1.0-1.5h. Then, the temperature was increased to 1300-1350℃ at a rate of 3.5-4.0℃ / min and held for 2.5-3.0h. The mixture was then naturally cooled to room temperature to obtain zirconium boride composite powder.

[0024] The mass ratio of the initial mixture, zirconium oxide, neodymium oxide, and KH570 modified titanium carbide is 100:0.4-0.7:0.3-0.5:3.0-3.5;

[0025] The mixed atmosphere is a mixture of argon and hydrogen, with a volume ratio of argon to hydrogen of 8.8-9:1-1.2.

[0026] 2. Modified silicon carbide nanowires

[0027] (1) Acid treatment

[0028] A mixture of hydrofluoric acid solution and 2.5-3.0 times the volume of nitric acid solution was mixed and cooled to 1-4°C in an ice bath to obtain a mixed acid solution. Silicon carbide nanowires were placed in anhydrous ethanol, stirred evenly, and then the mixed acid solution was added. The mixture was stirred at 160-180 rpm for 25-30 min under ice bath conditions. After washing and drying, acid-treated silicon carbide nanowires were obtained.

[0029] The hydrofluoric acid solution has a mass concentration of 32-38%.

[0030] The mass concentration of the nitric acid solution is 60-64%;

[0031] The silicon carbide nanowires have a diameter of 50-80 nm and a length of 1-5 μm;

[0032] The mass ratio of silicon carbide nanowires, anhydrous ethanol, and mixed acid solution is 10-13:200:80-85.

[0033] (2) Modification

[0034] Aluminum isopropoxide was added to anhydrous ethanol and stirred until homogeneous. Then, nitric acid solution was added, and the temperature was raised to 60-63℃. The mixture was stirred at 280-320 rpm for 1.5-2.0 h. After stirring, acid-treated silicon carbide nanowires were added and ultrasonically dispersed at a power of 210-230 W, a frequency of 35-40 kHz, and a duration of 15-25 min. The mixture was then evaporated in a water bath at 78-82℃ for 4-5 h and dried at 60-64℃ for 8-10 h. After drying, the mixture was placed in a muffle furnace and the temperature was raised to 490-500℃ at a rate of 4.0-5.0℃ / min. The temperature was held for 2.0-2.2 h, and the mixture was cooled to room temperature in the furnace to obtain modified silicon carbide nanowires.

[0035] The mass-to-volume ratio of aluminum isopropoxide, anhydrous ethanol, nitric acid solution, and acid-treated silicon carbide nanowires is 10-12 g: 300 mL: 2.5-2.8 mL: 4.6-5.3 g.

[0036] The mass concentration of the nitric acid solution is 6-7%;

[0037] 3. Mixing and sintering

[0038] Zirconium boride composite powder, modified silicon carbide nanowires, polyethylene glycol 4000, and yttrium oxide are placed in a high-speed mixer and mixed at 800-900 rpm for 8-12 min to obtain a mixture. The mixture is then formed into a rough blank under a pressure of 110-120 MPa. The rough blank is sintered in an argon atmosphere, with the temperature increased to 760-780℃ at a rate of 3.5-4.5℃ / min and held for 35-45 min. Then, the temperature is increased to 1500-1550℃ at a rate of 2.5-3.0℃ / min and held for 35-45 min. Finally, the temperature is increased to 1750-1780℃ at a rate of 1.5-2.0℃ / min and held for 1.0-1.3 h. The mixture is then cooled to room temperature in the furnace to obtain the zirconium boride ceramic material.

[0039] The mass ratio of the zirconium boride composite powder, modified silicon carbide nanowires, polyethylene glycol 4000, and yttrium oxide is 100:8.0-8.5:1.8-2.3:1.2-1.6.

[0040] This invention employs a pressureless sintering method to prepare zirconium boride ceramics. First, a sol-gel method is used to prepare zirconium boride composite powder. Specifically, zirconium nitrate is used to dissociate Zr⁴⁺, boric acid to dissociate B³⁺, and citric acid is used as a complexing agent. The temperature is increased to initiate a complexation reaction, forming stable complexes with metal ions. Furthermore, titanium carbide is introduced. KH₅₇₀ is used to modify the titanium carbide. The silanol groups at one end of the KH₅₇₀ ... As a phase transformation toughening phase, it effectively absorbs crack propagation energy, thereby improving the fracture toughness of the product. Neodymium oxide, as a sintering aid, reduces the sintering activation energy of zirconium boride, improves the density of the product, and thus enhances the stability of the product in complex environments with high and low temperature variations. This invention also introduces modified silicon carbide nanowires. Specifically, the silicon carbide nanowires are first etched with hydrofluoric acid and nitric acid to provide surface active sites. Then, under the action of aluminum isopropoxide, alumina is coated on the surface of the silicon carbide nanowires. Alumina can act as a transition layer to alleviate the mismatch in thermal expansion coefficients between silicon carbide and zirconium boride, thereby effectively relieving stress, enhancing the fracture toughness of the product, and forming a composite oxide layer to improve the mechanical properties and high-temperature oxidation resistance of the ceramic product.

[0041] Compared with the prior art, the present invention achieves the following beneficial effects:

[0042] 1. The zirconium boride ceramic material prepared by the method of the present invention has a density of 99.4-99.7%;

[0043] 2. The zirconium boride ceramic material prepared by the method of the present invention has a flexural strength of 518.5-524.6 MPa, a compressive strength of 680.7-688.3 MPa, and a fracture toughness of 11.96-12.74 MPa·m. 1 / 2 ;

[0044] 3. The zirconium boride ceramic material prepared by the method of this invention was heated to 1600°C at a rate of 15°C / min in air, held at that temperature for 168 hours, and allowed to naturally return to room temperature. The measured mass change rate was 6.13-6.35 mg / cm³. 2 The flexural strength is 495.7-507.8 MPa, and the fracture toughness is 11.37-12.27 MPa·m. 1 / 2 ;

[0045] 4. The zirconium boride ceramic material prepared by the method of this invention is heated to 1500℃ in air at a rate of 30℃ / min and held at that temperature for 6 hours. It is then immediately immersed in deionized water at 20℃ for 6 hours. This process constitutes one treatment cycle. After 10 consecutive treatment cycles, the flexural strength is measured again to be 489.5-501.5 MPa, and the fracture toughness is 11.24-12.12 MPa·m. 1 / 2 . Detailed Implementation

[0046] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention are now described.

[0047] Example 1

[0048] 1. Preparation of zirconium boride composite powder

[0049] (1) Preparation of initial mixture

[0050] Add 3.2g Zr(NO3)4·5H2O to 30g deionized water and stir until completely dissolved. Then add 1.3g boric acid and stir at 150rpm for 30min. Add 3.5g citric acid and stir until homogeneous. Add 15wt% ammonia solution to adjust the pH to 4.0. Increase the temperature to 60℃ at a rate of 1.2℃ / min and keep stirring for 60min to obtain the initial mixture.

[0051] (2) kH570 modified titanium carbide

[0052] 10g of titanium carbide was added to 65g of 10wt% hydrogen peroxide solution, the temperature was raised to 60℃, and the mixture was stirred at 250rpm for 1.8h. After filtration and washing, the mixture was added to 100g of 65wt% ethanol solution, stirred evenly, 1.2g of kH570 silane coupling agent was added, and glacial acetic acid was added to adjust the pH to 4.2. The temperature was raised to 62℃, and the mixture was stirred for 2.5h. After centrifugation at 8000rpm for 10min, the mixture was washed and dried to obtain kH570 modified titanium carbide.

[0053] The titanium carbide has a particle size of 200 nm;

[0054] (3) Composite

[0055] Add 0.4g of zirconium oxide and 0.3g of neodymium oxide to 100g of initial mixed solution, and perform ultrasonic dispersion. The ultrasonic power is 200W, the ultrasonic frequency is 50kHz, and the dispersion time is 25min. Then add 3.0g of kH570 modified titanium carbide and continue ultrasonic dispersion for 15min. After ultrasonic dispersion, heat in a water bath at 78℃ for 5h, and then vacuum dry at 60℃ and -0.08MPa for 10h. After drying, under a mixed atmosphere, increase the temperature to 560℃ at a rate of 2.0℃ / min and hold for 1.0h. Increase the temperature to 1300℃ at a rate of 3.5℃ / min and hold for 2.5h. Allow to cool naturally to room temperature to obtain zirconium boride composite powder.

[0056] The mixed atmosphere is a mixture of argon and hydrogen, with a volume ratio of argon to hydrogen of 8.8:1.2.

[0057] 2. Modified silicon carbide nanowires

[0058] (1) Acid treatment

[0059] Hydrofluoric acid solution and 2.5 times the volume of nitric acid solution were mixed and cooled to 1°C in an ice bath to obtain a mixed acid solution. 10g of silicon carbide nanowires were placed in 200g of anhydrous ethanol, stirred evenly, and then 80g of the mixed acid solution was added. The mixture was stirred at 160rpm for 25min under ice bath conditions. After washing and drying, acid-treated silicon carbide nanowires were obtained.

[0060] The hydrofluoric acid solution has a mass concentration of 32%.

[0061] The mass concentration of the nitric acid solution is 60%.

[0062] The silicon carbide nanowires have a diameter of 50 nm and a length of 1 μm.

[0063] (2) Modification

[0064] 10g of aluminum isopropoxide was added to 300mL of anhydrous ethanol and stirred until homogeneous. Then, 2.5mL of 7wt% nitric acid solution was added, and the temperature was raised to 60℃. The mixture was stirred at 280rpm for 1.5h. After stirring, 4.6g of acid-treated silicon carbide nanowires were added and ultrasonically dispersed at a power of 210W, a frequency of 35kHz, and a duration of 15min. The mixture was then evaporated in a water bath at 78℃ for 4h and dried at 60℃ for 8h. After drying, the mixture was placed in a muffle furnace and the temperature was raised to 490℃ at a rate of 4.0℃ / min and held for 2.0h. After cooling to room temperature in the furnace, modified silicon carbide nanowires were obtained.

[0065] 3. Mixing and sintering

[0066] 100g of zirconium boride composite powder, 8.0g of modified silicon carbide nanowires, 1.8g of polyethylene glycol 4000, and 1.2g of yttrium oxide were placed in a high-speed mixer and mixed at 800 rpm for 8 minutes to obtain a mixture. The mixture was then formed into a rough blank under a pressure of 110 MPa. The rough blank was sintered in an argon atmosphere, with the temperature increased to 760℃ at a rate of 3.5℃ / min and held for 35 minutes. Then, the temperature was increased to 1500℃ at a rate of 2.5℃ / min and held for 35 minutes. Finally, the temperature was increased to 1750℃ at a rate of 1.5℃ / min and held for 1.0 h. The mixture was then cooled to room temperature in the furnace to obtain zirconium boride ceramic material.

[0067] Example 2

[0068] 1. Preparation of zirconium boride composite powder

[0069] (1) Preparation of initial mixture

[0070] Add 3.5g Zr(NO3)4·5H2O to 30g deionized water and stir until completely dissolved. Then add 1.2g boric acid and stir at 170rpm for 35min. Add 3.8g citric acid and stir until homogeneous. Add 20wt% ammonia solution to adjust the pH to 4.5. Increase the temperature to 63℃ at a rate of 1.6℃ / min and keep stirring for 70min to obtain the initial mixture.

[0071] (2) kH570 modified titanium carbide

[0072] 15g of titanium carbide was added to 65g of 13wt% hydrogen peroxide solution, the temperature was raised to 64℃, and the mixture was stirred at 280rpm for 2.3h. After filtration and washing, the mixture was added to 100g of 68wt% ethanol solution, stirred evenly, 1.5g of kH570 silane coupling agent was added, and glacial acetic acid was added to adjust the pH to 4.8. The temperature was raised to 66℃, and the mixture was stirred for 3.0h. After centrifugation at 8300rpm for 15min, the mixture was washed and dried to obtain kH570 modified titanium carbide.

[0073] The titanium carbide has a particle size of 250 nm;

[0074] (3) Composite

[0075] Add 0.7g of zirconium oxide and 0.5g of neodymium oxide to 100g of initial mixed solution, and perform ultrasonic dispersion. The ultrasonic power is 220W, the ultrasonic frequency is 54kHz, and the dispersion time is 30min. Then add 3.5g of kH570 modified titanium carbide and continue ultrasonic dispersion for 20min. After ultrasonic dispersion, heat in an 80℃ water bath for 6h, and then vacuum dry at 65℃ and -0.09MPa for 12h. After drying, under a mixed atmosphere, increase the temperature to 580℃ at a rate of 3.0℃ / min and hold for 1.5h. Then increase the temperature to 1350℃ at a rate of 4.0℃ / min and hold for 3.0h. Allow to cool naturally to room temperature to obtain zirconium boride composite powder.

[0076] The mixed atmosphere is a mixture of argon and hydrogen, with a volume ratio of argon to hydrogen of 9:1.

[0077] 2. Modified silicon carbide nanowires

[0078] (1) Acid treatment

[0079] Hydrofluoric acid solution and 3.0 times the volume of nitric acid solution were mixed and cooled to 4°C in an ice bath to obtain a mixed acid solution. 13g of silicon carbide nanowires were placed in 200g of anhydrous ethanol, stirred evenly, and then 85g of the mixed acid solution was added. The mixture was stirred at 180rpm for 30min under ice bath conditions. After washing and drying, acid-treated silicon carbide nanowires were obtained.

[0080] The hydrofluoric acid solution has a mass concentration of 38%.

[0081] The mass concentration of the nitric acid solution is 64%.

[0082] The silicon carbide nanowires have a diameter of 80 nm and a length of 5 μm.

[0083] (2) Modification

[0084] 12g of aluminum isopropoxide was added to 300mL of anhydrous ethanol and stirred until homogeneous. Then, 2.8mL of 6wt% nitric acid solution was added, and the temperature was raised to 63℃. The mixture was stirred at 320rpm for 2.0h. After stirring, 5.3g of acid-treated silicon carbide nanowires were added and ultrasonically dispersed at a power of 230W, a frequency of 40kHz, and a duration of 25min. The mixture was then evaporated in a water bath at 82℃ for 4h and dried at 64℃ for 10h. After drying, the mixture was placed in a muffle furnace and the temperature was raised to 500℃ at a rate of 5.0℃ / min and held for 2.2h. After cooling to room temperature in the furnace, modified silicon carbide nanowires were obtained.

[0085] 3. Mixing and sintering

[0086] 100g of zirconium boride composite powder, 8.5g of modified silicon carbide nanowires, 2.3g of polyethylene glycol 4000, and 1.6g of yttrium oxide were placed in a high-speed mixer and mixed at 900 rpm for 12 min to obtain a mixture. The mixture was then formed into a rough blank under a pressure of 120 MPa. The rough blank was sintered in an argon atmosphere, with the temperature increased to 780℃ at a rate of 4.5℃ / min and held for 45 min. Then, the temperature was increased to 1550℃ at a rate of 3.0℃ / min and held for 45 min. Finally, the temperature was increased to 1780℃ at a rate of 2.0℃ / min and held for 1.3 h. The mixture was then cooled to room temperature in the furnace to obtain zirconium boride ceramic material.

[0087] Example 3

[0088] 1. Preparation of zirconium boride composite powder

[0089] (1) Preparation of initial mixture

[0090] Add 3.4g Zr(NO3)4·5H2O to 30g deionized water and stir until completely dissolved. Then add 1.2g boric acid and stir at 160rpm for 33min. Add 3.6g citric acid and stir until homogeneous. Add 18wt% ammonia solution to adjust the pH to 4.2. Increase the temperature to 62℃ at a rate of 1.4℃ / min and keep stirring for 65min to obtain the initial mixture.

[0091] (2) kH570 modified titanium carbide

[0092] 12g of titanium carbide was added to 65g of 11wt% hydrogen peroxide solution, the temperature was raised to 62℃, and the mixture was stirred at 270rpm for 2.0h. After filtration and washing, the mixture was added to 100g of 66wt% ethanol solution, stirred evenly, 1.4g of kH570 silane coupling agent was added, glacial acetic acid was added to adjust the pH to 4.5, the temperature was raised to 64℃, and the mixture was stirred for 2.8h. After centrifugation at 8200rpm for 12min, the mixture was washed and dried to obtain kH570 modified titanium carbide.

[0093] The titanium carbide has a particle size of 230 nm;

[0094] (3) Composite

[0095] Add 0.6g of zirconium oxide and 0.4g of neodymium oxide to 100g of initial mixed solution, and perform ultrasonic dispersion. The ultrasonic power is 210W, the ultrasonic frequency is 52kHz, and the dispersion time is 27min. Then add 3.2g of kH570 modified titanium carbide and continue ultrasonic dispersion for 17min. After ultrasonic dispersion, heat in an 80℃ water bath for 5h, and then vacuum dry at 62℃ and -0.09MPa for 12h. After drying, under a mixed atmosphere, increase the temperature to 570℃ at a rate of 2.5℃ / min and hold for 1.3h, then increase the temperature to 1330℃ at a rate of 3.7℃ / min and hold for 2.7h. Allow to cool naturally to room temperature to obtain zirconium boride composite powder.

[0096] The mixed atmosphere is a mixture of argon and hydrogen, with a volume ratio of argon to hydrogen of 9:1.

[0097] 2. Modified silicon carbide nanowires

[0098] (1) Acid treatment

[0099] Hydrofluoric acid solution and 2.7 times the volume of nitric acid solution were mixed and cooled to 2°C in an ice bath to obtain a mixed acid solution. 12g of silicon carbide nanowires were placed in 200g of anhydrous ethanol, stirred evenly, and then 83g of the mixed acid solution was added. The mixture was stirred at 170rpm for 27min under ice bath conditions. After washing and drying, acid-treated silicon carbide nanowires were obtained.

[0100] The hydrofluoric acid solution has a mass concentration of 36%.

[0101] The mass concentration of the nitric acid solution is 62%.

[0102] The silicon carbide nanowires have a diameter of 65 nm and a length of 3 μm.

[0103] (2) Modification

[0104] 12g of aluminum isopropoxide was added to 300mL of anhydrous ethanol and stirred until homogeneous. Then, 2.7mL of 6wt% nitric acid solution was added, and the temperature was raised to 62℃. The mixture was stirred at 300rpm for 1.8h. After stirring, 5.0g of acid-treated silicon carbide nanowires were added and ultrasonically dispersed at a power of 220W, a frequency of 37kHz, and a duration of 20min. The mixture was then evaporated in an 80℃ water bath for 5h and dried at 62℃ for 10h. After drying, the mixture was placed in a muffle furnace and the temperature was raised to 495℃ at a rate of 4.5℃ / min and held for 2.2h. After cooling to room temperature with the furnace, modified silicon carbide nanowires were obtained.

[0105] 3. Mixing and sintering

[0106] 100g of zirconium boride composite powder, 8.3g of modified silicon carbide nanowires, 2.0g of polyethylene glycol 4000, and 1.4g of yttrium oxide were placed in a high-speed mixer and mixed at 850 rpm for 10 min to obtain a mixture. The mixture was then formed into a rough blank under a pressure of 115 MPa. The rough blank was sintered in an argon atmosphere, with the temperature increased to 770℃ at a rate of 4.0℃ / min and held for 40 min. Then, the temperature was increased to 1530℃ at a rate of 2.8℃ / min and held for 40 min. Finally, the temperature was increased to 1770℃ at a rate of 1.8℃ / min and held for 1.2 h. The mixture was then cooled to room temperature in the furnace to obtain zirconium boride ceramic material.

[0107] Comparative Example 3-1

[0108] The changes made in Example 3 are as follows:

[0109] (1) In the step of preparing zirconium boride composite powder, the step of preparing the initial mixture is omitted; in the composite step, "100g of initial mixture components" is replaced with "15g of zirconium boride"; the particle size of the zirconium boride is 120nm;

[0110] (2) In the process of modifying silicon carbide nanowires, the modification step is omitted; in the mixing and sintering step, the modified silicon carbide nanowires are replaced with acid-treated silicon carbide nanowires in equal amounts.

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

[0112] Comparative Example 3-2

[0113] The changes made in Example 3 are as follows:

[0114] In the preparation of zirconium boride composite powder, the step of modifying titanium carbide with kH570 is omitted; in the composite step, the kH570 modified titanium carbide is replaced in equal amounts with untreated titanium carbide; the particle size of the titanium carbide is 230 nm.

[0115] In the compounding step, zirconium oxide and neodymium oxide components are omitted;

[0116] The rest of the operations are exactly the same.

[0117] Performance testing

[0118] 1. Mechanical properties

[0119] The zirconium boride ceramic materials prepared in Examples 1-3, Comparative Example 3-1, and Comparative Example 3-2 were subjected to performance tests, and the results are as follows:

[0120]

[0121] 2. High-temperature oxidation resistance

[0122] The zirconium boride ceramic materials prepared in Examples 1-3, Comparative Example 3-1, and Comparative Example 3-2 were placed in air and heated to 1600°C at a rate of 15°C / min. After being held at this temperature for 168 hours and allowed to naturally return to room temperature, the mass change rate, flexural strength, and fracture toughness were tested. The results are as follows:

[0123]

[0124] 3. Stability in complex environments

[0125] The zirconium boride ceramic materials prepared in Examples 1-3, Comparative Examples 3-1, and 3-2 were placed in air and heated to 1500°C at a rate of 30°C / min, held at that temperature for 6 hours, and then immediately immersed in deionized water at 20°C for 6 hours. This process constituted one treatment cycle. After 10 consecutive treatment cycles, the flexural strength and fracture toughness were tested again, and the results are as follows:

[0126]

[0127] Comparative Example 3-1 directly uses zirconium oxide powder, which exhibits severe particle agglomeration and poor dispersibility. The interfacial strength between zirconium oxide and titanium carbide is low, and when mixed with acid-treated silicon carbide nanowires, the interaction between the silicon carbide nanowires and the matrix is ​​weak. This results in low density of the ceramic product, insignificant toughening effect, low strength, poor overall oxidation performance, and poor stability. Comparative Example 3-2 uses unmodified titanium carbide and zirconium boride composite, which has poor interfacial compatibility, easily agglomerates to form pores, reduces density, and easily leads to stress concentration, reducing toughness. By omitting zirconium oxide and neodymium oxide components in the composite step and retaining the alumina-coated silicon carbide nanowire component, it possesses certain high-temperature oxidation resistance, exceeding that of Comparative Example 1-1, but still not reaching the level of Example 3.

[0128] Unless otherwise stated, all percentages used in this invention are mass percentages.

[0129] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing zirconium boride ceramic materials by pressureless sintering, characterized in that, The process includes steps such as preparing zirconium boride composite powder, modifying silicon carbide nanowires, and mixing and sintering. The preparation of zirconium boride composite powder includes the steps of preparing a preliminary mixture, kH570 modified titanium carbide, and composite preparation. The steps for preparing the initial mixed solution are as follows: add Zr(NO3)4·5H2O to deionized water, stir until completely dissolved, add boric acid, stir at 150-170 rpm for 30-35 min, add citric acid and stir evenly, add 15-20 wt% ammonia solution to adjust the pH to 4.0-4.5, increase the temperature to 60-63℃ at a rate of 1.2-1.6℃ / min, keep warm and stir for 60-70 min to obtain the initial mixed solution; The composite step is as follows: zirconium oxide and neodymium oxide are added to the initial mixture and ultrasonically dispersed. Then, KH570 modified titanium carbide is added and ultrasonically dispersed again. After heating in a water bath, the mixture is dried and kept at 560-580℃ for 1.0-1.5h and 1300-1350℃ for 2.5-3.0h in a mixed atmosphere to obtain zirconium boride composite powder. The modified silicon carbide nanowires include acid treatment and modification steps; The modification step is as follows: aluminum isopropoxide is added to anhydrous ethanol, nitric acid solution is added, and the mixture is stirred at 60-63°C for 1.5-2.0 h. Acid-treated silicon carbide nanowires are added, and the mixture is ultrasonically dispersed. After evaporation in a water bath, the mixture is dried and placed in a muffle furnace at 490-500°C for 2.0-2.2 h to obtain modified silicon carbide nanowires.

2. The method for preparing zirconium boride ceramic materials by pressureless sintering according to claim 1, characterized in that, In the step of preparing the initial mixed solution, the mass ratio of Zr(NO3)4·5H2O, deionized water, boric acid, and citric acid is 3.2-3.5:30:1.2-1.3:3.5-3.

8.

3. The method for preparing zirconium boride ceramic materials by pressureless sintering according to claim 1, characterized in that, The steps for modifying titanium carbide with kH570 are as follows: titanium carbide is added to a 10-13 wt% hydrogen peroxide aqueous solution, the temperature is raised to 60-64℃, and the mixture is stirred at 250-280 rpm for 1.8-2.3 h. After filtration and washing, the mixture is added to a 65-68 wt% ethanol solution, stirred evenly, and then kH570 silane coupling agent is added. Glacial acetic acid is added to adjust the pH to 4.2-4.8, the temperature is raised to 62-66℃, and the mixture is stirred for 2.5-3.0 h. After centrifugation at 8000-8300 rpm for 10-15 min, the mixture is washed and dried to obtain kH570 modified titanium carbide. The titanium carbide has a particle size of 200-250 nm; The mass ratio of titanium carbide, hydrogen peroxide solution, ethanol solution, and kH570 silane coupling agent is 10-15:65:100:1.2-1.

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4. The method for preparing zirconium boride ceramic materials by pressureless sintering according to claim 1, characterized in that, In the composite step, the mass ratio of the initial mixture, zirconium oxide, neodymium oxide, and kH570 modified titanium carbide is 100:0.4-0.7:0.3-0.5:3.0-3.5; The mixed atmosphere is a mixture of argon and hydrogen, with a volume ratio of argon to hydrogen of 8.8-9:1-1.

2.

5. The method for preparing zirconium boride ceramic materials by pressureless sintering according to claim 1, characterized in that, The acid treatment step is as follows: a hydrofluoric acid solution and 2.5-3.0 times the volume of nitric acid solution are mixed and cooled to 1-4°C in an ice bath to obtain a mixed acid solution; silicon carbide nanowires are placed in anhydrous ethanol, stirred evenly, and then the mixed acid solution is added. Under ice bath conditions, the mixture is stirred at 160-180 rpm for 25-30 min, washed and dried to obtain acid-treated silicon carbide nanowires. The mass concentration of the hydrofluoric acid solution is 32-38%; The mass concentration of the nitric acid solution is 60-64%; The silicon carbide nanowires have a diameter of 50-80 nm and a length of 1-5 μm; The mass ratio of silicon carbide nanowires, anhydrous ethanol, and mixed acid solution is 10-13:200:80-85.

6. The method for preparing zirconium boride ceramic materials by pressureless sintering according to claim 1, characterized in that, In the modification step, the mass-to-volume ratio of aluminum isopropoxide, anhydrous ethanol, nitric acid solution, and acid-treated silicon carbide nanowires is 10-12 g: 300 mL: 2.5-2.8 mL: 4.6-5.3 g. The mass concentration of the nitric acid solution is 6-7%.

7. The method for preparing zirconium boride ceramic materials by pressureless sintering according to claim 1, characterized in that, The mixing and sintering step is as follows: zirconium boride composite powder, modified silicon carbide nanowires, polyethylene glycol 4000, and yttrium oxide are placed in a high-speed mixer and mixed at 800-900 rpm for 8-12 minutes to obtain a mixture. The mixture is then formed into a rough blank under a pressure of 110-120 MPa. The rough blank is sintered in an argon atmosphere, with the temperature increased to 760-780℃ at a rate of 3.5-4.5℃ / min and held for 35-45 minutes. Then, the temperature is increased to 1500-1550℃ at a rate of 2.5-3.0℃ / min and held for 35-45 minutes. Finally, the temperature is increased to 1750-1780℃ at a rate of 1.5-2.0℃ / min and held for 1.0-1.3 hours. The mixture is then cooled to room temperature in the furnace to obtain zirconium boride ceramic material.

8. The method for preparing zirconium boride ceramic materials by pressureless sintering according to claim 7, characterized in that, The mass ratio of the zirconium boride composite powder, modified silicon carbide nanowires, polyethylene glycol 4000, and yttrium oxide is 100:8.0-8.5:1.8-2.3:1.2-1.6.

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