A method for preparing low-cost boron carbide powder and ceramics

Abstract

The application provides a preparation method of low-cost boron carbide powder and ceramics, and belongs to the technical field of boron carbide powder and ceramics. The preparation method of the boron carbide powder is as follows: a carbon source is added into a boron source solution, polyvinyl alcohol is added, stirring is carried out for 30-35 min, ultrasonic dispersion is carried out by adding sodium carbonate and silicon dioxide, primary powder is obtained through spray granulation, and the primary powder is crushed after calcination to obtain boron carbide powder. The boron carbide powder obtained by the above method has the advantages of low cost, uniform particle size, good dispersity and good quality stability. The boron carbide powder is mixed with a ceramic reinforcing body to prepare ceramic blanks. The boron carbide ceramics prepared through a densification treatment step and a sintering step have high strength and toughness and excellent high-temperature oxidation performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of boron carbide powder and ceramics, and particularly relates to a preparation method of low-cost boron carbide powder and ceramics. BACKGROUND

[0002] Boron carbide is an ultra-hard ceramic material with excellent comprehensive performance. It has extremely high hardness, with a Mohs hardness of 9.3, and extremely low density, only 2.52 g / cm 3 It is one of the lightest ultra-hard materials known at present; at the same time, boron carbide has a high melting point of 2450 DEG C, excellent high-temperature resistance, and good chemical stability, neutron absorption capacity, and thermal and electrical conductivity, so that it is widely used in the fields of nuclear industry, armor protection, wear-resistant parts, cutting tools, etc.

[0003] Boron carbide ceramics are prepared by taking boron carbide powder as the main raw material, and the particle size, purity and dispersity of the boron carbide powder directly determine the densification degree, mechanical properties and stability of the boron carbide ceramics.

[0004] The existing technology usually adopts carbothermal reduction method to prepare boron carbide powder, which is to take boric acid, boron oxide or borax as the boron source and graphite as the carbon source, mix the boron source and the carbon source, and then perform high-temperature reaction to generate boron carbide. The boron carbide obtained by this method has high purity, but the high-temperature reaction has high energy consumption, and the particle size of the powder is uneven, a large number of agglomerates are generated, and the product quality is unstable.

[0005] In the process of preparing boron carbide ceramics by using boron carbide powder, due to the strong covalent bond characteristics of boron carbide, the sintering activity is low, and the boron carbide ceramics prepared thereby are difficult to realize densification.

[0006] The existing technology usually adopts the method of adding sintering aids or optimizing sintering process to improve the densification of boron carbide ceramics, and the main methods include pressureless sintering method and hot-pressing sintering method.

[0007] The hot-pressing sintering method applies pressure at high temperature to improve the density of the ceramics, but the equipment is complex and the energy consumption is high. Although the pressure can improve the density, it can easily lead to uneven stress distribution in the ceramics, thereby reducing the toughness of the ceramics. The pressureless sintering method usually adds sintering aids such as aluminum oxide and magnesium oxide to reduce the sintering temperature, but the addition of the sintering aids can form low-melting-point phases at the grain boundaries of the ceramics, thereby significantly reducing the high-temperature strength and chemical stability of the ceramics, and the components such as aluminum oxide can also form brittle glass phases at the grain boundaries, thereby reducing the toughness, especially the toughness at high temperature.

[0008] In order to improve the toughness of boron carbide ceramics, the prior art usually adopts the method of introducing a second phase to increase the toughness, which is the most widely used toughening technology at present, such as adding silicon carbide, titanium boride, carbon fiber and other components as the second phase, which can improve the toughness of the ceramic to a certain extent through multiple toughening mechanisms, but the second phase component is added in a large amount, and the particle agglomeration increases the internal defects, which makes the mechanical properties of the ceramic decrease; moreover, the introduction of the second phase easily leads to stress concentration, and the toughening mechanism itself consumes the carrying capacity of the ceramic, thereby causing the strength performance to decrease; and the compatibility of the introduced toughening phase with the boron carbide matrix is poor, and the interfacial bonding force is weak, thereby causing the performance of the product to be unstable, and in a high-temperature oxidation environment, the toughness and strength are greatly reduced, which ultimately limits the use range of boron carbide ceramics.

[0009] Therefore, a preparation method of boron carbide powder and ceramics is provided, which can reduce the cost, improve the particle size uniformity and quality stability of the boron carbide powder, and the boron carbide ceramics prepared by using the boron carbide powder can improve the toughness, enhance the strength performance, and ensure the high-temperature oxidation performance, which is a technical problem to be solved in the prior art. SUMMARY

[0010] In order to solve the technical problems existing in the prior art, the present application provides a preparation method of low-cost boron carbide powder and ceramics, which has good particle size uniformity and quality stability, and the boron carbide ceramics prepared by using the boron carbide powder can improve the toughness, enhance the strength performance, and have excellent high-temperature oxidation performance.

[0011] In view of the above technical problems, the present application adopts the following technical solutions:

[0012] A preparation method of boron carbide ceramics, comprising the steps of preparing boron carbide powder, preparing ceramic reinforcement, preparing ceramic green body, densification treatment and sintering, and the specific operation is as follows:

[0013] 1. Preparation of boron carbide powder

[0014] (1) Preparation of carbon source

[0015] The rice husk is put into anhydrous ethanol for ball milling treatment, the ball milling time is 1.8-2.3h, the ball milling speed is 260-300rpm, after ball milling, vacuum drying at 60-62℃ for 10-12h, the vacuum degree is-0.08~-0.085MPa, then in a nitrogen atmosphere, 400-410℃ for 1.0-1.5h, natural cooling to room temperature, to obtain the carbon source;

[0016] The mass ratio of the rice husk and anhydrous ethanol is 40-45:120;

[0017] (2) Preparation of boron source solution

[0018] The boric acid is added to anhydrous ethanol for ball milling, the ball milling time is 1.0-1.5h, the ball milling rotation speed is 700-800rpm, after the ball milling, the boron source solution is obtained;

[0019] The mass ratio of the boric acid and the anhydrous ethanol is 120-124:250;

[0020] (3) Preparation of the primary powder

[0021] The carbon source, polyvinyl alcohol, sodium carbonate and silicon dioxide are added to the boron source solution, the stirring is carried out at 1000-1200rpm for 30-35min, the ultrasonic dispersion is carried out, the ultrasonic power is 130-160W, the ultrasonic frequency is 50-55kHz, the ultrasonic time is 30-40min, the spray granulation is carried out, the inlet temperature is controlled at 180-183℃, the primary powder is obtained;

[0022] The mass ratio of the boron source solution, the carbon source, the polyvinyl alcohol, the sodium carbonate and the silicon dioxide is 370-374:40-45:1.0-1.3:1.4-1.7:0.8-1.0;

[0023] (4) Post-treatment

[0024] The primary powder is put into the calcination furnace, the temperature is increased to 300-320℃ at the rate of 6.0-8.0℃ / min, the temperature is kept for 40-50min, then the temperature is increased to 1360-1400℃ at the rate of 3.0-4.0℃ / min under the argon atmosphere, the temperature is kept for 3.5-4.0h, after the natural decrease of the room temperature, the crushing is carried out, the boron carbide powder is obtained.

[0025] 2. Preparation of the ceramic reinforcement

[0026] The Y(NO3)3·6H2O is added to the deionized water, after the uniform stirring, the hexamethylenetetramine is added, the stirring is carried out at 40-42℃, 230-250rpm for 30-35min, the mixed solution is obtained;

[0027] The mass ratio of the deionized water, the Y(NO3)3·6H2O and the hexamethylenetetramine is 40:3.0-3.2:4.5-4.8;

[0028] The silicon carbide powder and zirconium diboride powder are put into anhydrous ethanol and ultrasonic dispersed for 35-40 min, the ultrasonic power is 180-200 W, the ultrasonic frequency is 36-45 kHz, after the ultrasonic dispersion, the mixed liquid is added, the adding rate is controlled to be 0.8-1.2 g / min, the stirring speed is controlled to be 120-130 rpm during the adding, after the adding is completed, the temperature is increased to 85-88 ℃, and the reaction is preserved for 3.0-4.0 h, after the reaction is completed, the centrifugal washing is carried out, the vacuum drying is carried out at 80-83 ℃ for 10-12 h, then the ceramic reinforcing body is obtained by transferring into a muffle furnace, increasing the temperature to 280-300 ℃ at a rate of 2.0-2.5 ℃ / min, preserving for 45-50 min, then increasing the temperature to 600-610 ℃ at a rate of 3.5-4.0 ℃ / min, preserving for 2.0-2.3 h, and cooling to room temperature along with the furnace.

[0029] The mass ratio of the silicon carbide powder, the zirconium diboride powder, the anhydrous ethanol and the mixed liquid is 10.0-10.4:2.0-2.5:110:47.5-48.0.

[0030] 3. Preparing a ceramic green body

[0031] The boron carbide powder, the ceramic reinforcing body, the boron nitride and the yttrium borate are added into the anhydrous ethanol, mixed uniformly, the polyvinyl alcohol is added, and stirring is carried out at 800-1000 rpm for 45-55 min, after the stirring is completed, drying is carried out, and the ceramic powder is obtained, the ceramic powder is put into a mold for molding treatment to obtain a molded body, the molding pressure is controlled to be 150-200 MPa, the molded body is placed in an argon atmosphere, the temperature is increased to 800-820 ℃ at a rate of 2.0-2.5 ℃ / min, and the temperature is preserved for 1.8-2.2 h, and the ceramic green body is obtained by cooling to room temperature along with the furnace.

[0032] The mass ratio of the anhydrous ethanol, the boron carbide powder, the ceramic reinforcing body, the boron nitride, the yttrium borate and the polyvinyl alcohol is 200:30-32:6-7:2-3:1.2-1.5:1.0-1.3.

[0033] 4. Densification treatment

[0034] (1) Preparing a composite sol

[0035] adding aluminum isopropylate into anhydrous ethanol, stirring at 60-62℃ for 20-25min, adding lactic acid solution under the condition of 60-62℃ water bath, controlling the adding rate at 0.6-1.0g / min, after the adding is completed, stirring at 140-160rpm for 1.4-1.7h, after the stirring is completed, adding zirconium source solution, stirring at room temperature for 28-33min, increasing the temperature to 45-50℃, adding polyvinylpyrrolidone solution, after the stirring is uniform, adding 10-12wt% ammonia water solution to adjust the pH value to 3.5-4.0, stirring for 1.5-2.0h, aging at room temperature for 4.0-5.0h in the dark, obtaining the composite sol;

[0036] The mass ratio of the anhydrous ethanol, aluminum isopropylate, lactic acid solution, zirconium source solution, polyvinylpyrrolidone solution is 110:20-23:13.0-13.5:155-160:35.0-35.3;

[0037] The mass concentration of the lactic acid solution is 80-85%;

[0038] The preparation method of the zirconium source solution is adding zirconium oxychloride into anhydrous ethanol, stirring at 58-60℃ for 18-25min, adding concentrated nitric acid solution, after the stirring is uniform, stirring at 40-42℃ for 1.2-1.5h, obtaining the zirconium source solution;

[0039] The mass volume ratio of the anhydrous ethanol, zirconium oxychloride, concentrated nitric acid solution in the zirconium source solution is 120g:32-34g:6.8-7.0mL;

[0040] The mass concentration of the concentrated nitric acid solution is 62-66%;

[0041] The polyvinylpyrrolidone solution is a mixture of deionized water and polyvinylpyrrolidone, and the mass ratio of the deionized water and polyvinylpyrrolidone is 34:1.0-1.3;

[0042] (2) Immersion

[0043] Placing the ceramic green body into the vacuum immersion device, controlling the vacuum degree at -0.090--0.095MPa, vacuum pressure maintaining for 25-35min, then injecting the composite sol, the composite sol completely immersing the ceramic green body, increasing the pressure to 0.52-0.55MPa, pressure maintaining for 1.8-2.0h, taking out the ceramic green body, drying at 60-65℃ for 3.8-4.0h, vacuum drying at 115-120℃ for 1.8-2.3h, obtaining the dense ceramic body.

[0044] 5. Sintering

[0045] Put the dense ceramic body into the sintering furnace, raise the temperature to 1100-1200 DEG C at a rate of 2.5-3.0 DEG C / min, sinter for 60-70 min, then raise the temperature to 1850-1880 DEG C at a rate of 4.5-5.0 DEG C / min, sinter for 2.3-2.5 h, and naturally cool to room temperature to obtain boron carbide ceramics.

[0046] Compared with the prior art, the present application has the following beneficial effects:

[0047] 1. The boron carbide powder is prepared by using boron carbide powder, first, rice husk is used as a carbon source, which replaces traditional graphite and other components, greatly reducing the cost of raw materials, and the rice husk has the characteristics of porosity and high activity, which is beneficial to the full contact and reaction with the boron source; polyvinyl alcohol is used as a dispersant and binder, sodium carbonate is used as a mineralizer, and silicon dioxide is used as an inducer, which prevents the agglomeration of the boron source and the carbon source, reduces the reaction activation energy in the synthesis reaction process, and thus obtains uniform, good dispersion and good quality stability of the boron carbide powder;

[0048] Then, silicon carbide and zirconium diboride are used as the core of the reinforcing body, and yttrium nitrate is hydrolyzed in the presence of hexamethylenetetramine, so that yttria is uniformly coated on the surface of silicon carbide and zirconium diboride, yttria as an interfacial compatibilizer can improve the interfacial bonding force between the reinforcing body and the boron carbide matrix, avoid the agglomeration of particles, and also provide sintering sites for the subsequent sintering step, thereby effectively playing the role of toughening and reinforcing, and improving the strength and toughness of the ceramic and high-temperature oxidation resistance; In the densification treatment step, the green body is impregnated with a composite sol, aluminum isopropoxide and zirconium oxychloride form an alumina-zirconia composite sol, which can effectively fill the pores of the green body, reduce the porosity of the green body, thereby improving the mechanical properties of the ceramic, and zirconia and alumina can form a protective layer on the surface of boron carbide, greatly improving the high-temperature oxidation resistance of the product, and finally improving the comprehensive performance of the boron carbide ceramic;

[0049] 2. The boron carbide powder prepared by the method of the present application has low cost, uniform particle size, good dispersion and good quality stability;

[0050] 3. The boron carbide ceramic prepared by the method of the present application has a room temperature fracture toughness of 9.64-9.87 MPa·m 1 / 2 , and a room temperature bending strength of 631.2-635.3 MPa;

[0051] 4. The boron carbide ceramic prepared by the method of the present application has a size change rate of 0.08-0.11% at 1800 DEG C for 168 h, and a linear ablation rate of 0.49-0.52 μm / s under 2500 DEG C oxyacetylene ablation for 300 s;

[0052] 5. The boron carbide ceramic prepared by the method of the present application is measured again for fracture toughness of 9.19-9.49 MPa·m and bending strength of 604.1-615.0 MPa after being heated to 1700℃ at a rate of 30℃ / min in air atmosphere and oxidized for 360h. 1 / 2 DETAILED DESCRIPTION

[0053] In order to more clearly understand the technical features, objectives and effects of the present application, the specific embodiments of the present application are described below.

[0054] Example 1

[0055] 1. Preparation of boron carbide powder

[0056] (1) Preparation of carbon source

[0057] 45g of rice husk is put into 120g of anhydrous ethanol for ball milling treatment, the ball milling time is 2.3h, the ball milling rotation speed is 300rpm, after the ball milling, vacuum drying is performed at 62℃ for 12h, the vacuum degree is -0.085MPa, then in a nitrogen atmosphere, heat preservation is performed at 410℃ for 1.5h, and after natural cooling to room temperature, the carbon source is obtained;

[0058] (2) Preparation of boron source solution

[0059] 124g of boric acid is put into 250g of anhydrous ethanol for ball milling treatment, the ball milling time is 1.5h, the ball milling rotation speed is 800rpm, and after the ball milling, the boron source solution is obtained;

[0060] (3) Preparation of primary powder

[0061] 45g of the carbon source is added into 374g of the boron source solution, 1.3g of polyvinyl alcohol is added, stirring is performed at 1200rpm for 35min, 1.7g of sodium carbonate and 1.0g of silicon dioxide are added, ultrasonic dispersion is performed, the ultrasonic power is 160W, the ultrasonic frequency is 55kHz, the ultrasonic time is 40min, spray granulation is performed, the inlet temperature is controlled to be 183℃, and the primary powder is obtained;

[0062] (4) Post-treatment

[0063] The primary powder is put into a calcining furnace, the temperature is increased to 320℃ at a rate of 8.0℃ / min, heat preservation is performed for 50min, then in an argon atmosphere, the temperature is increased to 1400℃ at a rate of 4.0℃ / min, heat preservation is performed for 4.0h, and after natural reduction to room temperature, the boron carbide powder is obtained after crushing.

[0064] 2. Preparation of ceramic reinforcement

[0065] ​Into 40 g of deionized water, 3.2 g of Y(NO3)3·6H2O was added, after stirring uniformly, 4.8 g of hexamethylenetetramine was added, stirring at 42℃, 250 rpm for 35 min, to obtain a mixed solution;

[0066] Into 110 g of anhydrous ethanol, 10.4 g of silicon carbide powder and 2.5 g of zirconium diboride powder were placed and ultrasonic dispersed for 40 min, the ultrasonic power was 200 W and the ultrasonic frequency was 45 kHz; after the ultrasonic dispersion was completed, 48.0 g of the mixed solution was added at a rate of 1.2 g / min, while the stirring speed was controlled at 130 rpm; after the addition was completed, the temperature was increased to 88℃, and the reaction was maintained for 4.0 h; after the reaction was completed, the product was washed by centrifugation, and then vacuum dried at 83℃ for 12 h; then it was transferred into a muffle furnace, the temperature was increased to 300℃ at a rate of 2.5℃ / min, and maintained for 50 min; then the temperature was increased to 610℃ at a rate of 4.0℃ / min, and maintained for 2.3 h; and then the furnace was cooled to room temperature to obtain a ceramic reinforcing body.

[0067] 3. Preparation of ceramic green body

[0068] Into 200 g of anhydrous ethanol, 32 g of boron carbide powder, 7 g of ceramic reinforcing body, 3 g of boron nitride, and 1.5 g of yttrium borate were added, and after being mixed uniformly, 1.3 g of polyvinyl alcohol was added, and stirred at 1000 rpm for 55 min; after the stirring was completed, the product was dried to obtain a ceramic powder; the ceramic powder was placed into a mold for molding treatment to obtain a molded body, the molding pressure was controlled at 200 MPa, and the molded body was placed in an argon atmosphere, the temperature was increased to 820℃ at a rate of 2.5℃ / min, and maintained for 2.2 h; and then the furnace was cooled to room temperature to obtain a ceramic green body.

[0069] 4. Densification treatment

[0070] (1) Preparation of composite sol

[0071] Into 110 g of anhydrous ethanol, 23 g of aluminum isopropoxide was added, and stirred at 62℃ for 25 min; under the condition of a 62℃ water bath, 13.5 g of lactic acid solution was added at a rate of 1.0 g / min; after the addition was completed, the product was maintained and stirred at 160 rpm for 1.7 h; after the stirring was completed, 160 g of zirconium source solution was added, and stirred at room temperature for 33 min; the temperature was increased to 50℃, 35.3 g of polyvinylpyrrolidone solution was added, and stirred uniformly; then 12 wt% ammonia water solution was added to adjust the pH value to 4.0; the product was maintained and stirred for 2.0 h; and then it was aged for 5.0 h at room temperature in the dark to obtain a composite sol.

[0072] The preparation method of the zirconium source solution is that 34 g of zirconium oxychloride is added into 120 g of anhydrous ethanol, and stirred at 60 ℃ for 25 min, 7.0 mL of concentrated nitric acid solution is added, and after stirring uniformly, it is stirred at 42 ℃ for 1.5 h to obtain the zirconium source solution;

[0073] The mass concentration of the lactic acid solution is 85%;

[0074] The mass concentration of the concentrated nitric acid solution is 66%;

[0075] The polyvinylpyrrolidone solution is a mixture of deionized water and polyvinylpyrrolidone, and the mass ratio of the deionized water and polyvinylpyrrolidone is 34:1.3;

[0076] (2) Immersion

[0077] The ceramic green body is placed into a vacuum immersion device, the vacuum degree is controlled to be -0.095 MPa, vacuum pressure is maintained for 35 min, then the composite sol is injected, the composite sol completely immerses the ceramic green body, the pressure is increased to 0.55 MPa, pressure maintaining is performed for 2.0 h, the ceramic green body is taken out, drying is performed at 65 ℃ for 4.0 h, and vacuum drying is performed at 120 ℃ for 2.3 h to obtain a dense ceramic body.

[0078] 5. Sintering

[0079] The dense ceramic body is placed into a sintering furnace, the temperature is increased to 1200 ℃ at a rate of 3.0 ℃ / min, and sintering is performed for 70 min, then the temperature is increased to 1880 ℃ at a rate of 5.0 ℃ / min, and sintering is performed for 2.5 h, and natural cooling is performed to room temperature to obtain a boron carbide ceramic.

[0080] Example 2

[0081] 1. Preparation of boron carbide powder

[0082] (1) Preparation of carbon source

[0083] 40 g of rice husk is placed into 120 g of anhydrous ethanol for ball milling treatment, the ball milling time is 1.8 h, the ball milling rotation speed is 260 rpm, after the ball milling is completed, vacuum drying is performed at 60 ℃ for 10 h, the vacuum degree is -0.08 MPa, then in a nitrogen atmosphere, 400 ℃ is maintained for 1.0 h, and after natural cooling to room temperature, the carbon source is obtained;

[0084] (2) Preparation of boron source solution

[0085] 120 g of boric acid is added into 250 g of anhydrous ethanol for ball milling treatment, the ball milling time is 1.0 h, the ball milling rotation speed is 700 rpm, and after the ball milling is completed, the boron source solution is obtained;

[0086] (3) Preparation of primary powder

[0087] To 370 g of boron source solution, 40 g of carbon source, 1.0 g of polyvinyl alcohol, 1000 rpm stirring for 30 min, 1.4 g of sodium carbonate and 0.8 g of silicon dioxide were added, ultrasonic dispersion was carried out, the ultrasonic power was 130 W, the ultrasonic frequency was 50 kHz, the ultrasonic time was 30 min, spray granulation was carried out, the inlet temperature was controlled to be 180 ℃, and primary powder was obtained;

[0088] (4) Post-treatment

[0089] The primary powder was placed into a calcining furnace, the temperature was increased to 300 ℃ at a rate of 6.0 ℃ / min, and the temperature was kept for 40 min, then the temperature was increased to 1360 ℃ at a rate of 3.0 ℃ / min under an argon atmosphere, and the temperature was kept for 3.5 h, and after natural reduction to room temperature, the boron carbide powder was obtained by crushing.

[0090] 2. Preparation of ceramic reinforcement

[0091] To 40 g of deionized water, 3.0 g of Y(NO3)3·6H2O was added, after stirring uniformly, 4.5 g of hexamethylenetetramine was added, and stirring was carried out at 40 ℃ and 230 rpm for 30 min, and a mixed solution was obtained;

[0092] 10.0 g of silicon carbide powder and 2.0 g of zirconium diboride powder were placed into 110 g of anhydrous ethanol, ultrasonic dispersion was carried out, the ultrasonic time was 35 min, the ultrasonic power was 180 W, the ultrasonic frequency was 36 kHz, after the ultrasonic dispersion was completed, 47.5 g of the mixed solution was added, the addition rate was controlled to be 0.8 g / min, the stirring speed was controlled to be 120 rpm during the addition, after the addition was completed, the temperature was increased to 85 ℃, and the reaction was kept for 3.0 h, after the reaction was completed, the ceramic reinforcement was obtained by centrifugal washing and vacuum drying at 80 ℃ for 10 h, and then the ceramic reinforcement was placed into a muffle furnace, the temperature was increased to 280 ℃ at a rate of 2.0 ℃ / min, the temperature was kept for 45 min, then the temperature was increased to 600 ℃ at a rate of 3.5 ℃ / min, the temperature was kept for 2.0 h, and the furnace was cooled to room temperature.

[0093] 3. Preparation of ceramic green body

[0094] To 200 g of anhydrous ethanol, 30 g of boron carbide powder, 6 g of ceramic reinforcement, 2 g of boron nitride and 1.2 g of yttrium borate were added, after mixing uniformly, 1.0 g of polyvinyl alcohol was added, stirring was carried out at 800 rpm for 45 min, after the stirring was completed, the ceramic powder was obtained by drying; the ceramic powder was placed into a mold for molding treatment to obtain a molded body, the molding pressure was controlled to be 150 MPa, the molded body was placed in an argon atmosphere, the temperature was increased to 800 ℃ at a rate of 2.0 ℃ / min, the temperature was kept for 1.8 h, and the furnace was cooled to room temperature, and the ceramic green body was obtained.

[0095] 4. Densification treatment

[0096] (1) Preparation of composite sol

[0097] Into 110 g of anhydrous ethanol, 20 g of aluminum isopropoxide was added, stirred at 60 ℃ for 20 min, and then 13.0 g of a lactic acid solution was added at a rate of 0.6 g / min under the condition of a 60 ℃ water bath. After the addition was completed, the mixture was stirred at 140 rpm for 1.4 h. After the stirring was completed, 155 g of a zirconium source solution was added, and the mixture was stirred at room temperature for 28 min. The temperature was increased to 45 ℃, and 35.0 g of a polyvinylpyrrolidone solution was added. After the mixture was stirred uniformly, 10 wt% of an ammonia water solution was added to adjust the pH value to 3.5. The mixture was stirred for 1.5 h, and then was aged for 4.0 h at room temperature in the dark to obtain a composite sol.

[0098] The zirconium source solution was prepared by adding 32 g of zirconium oxychloride into 120 g of anhydrous ethanol, stirring at 58 ℃ for 18 min, and then adding 6.8 mL of a concentrated nitric acid solution. After the mixture was stirred uniformly, the mixture was stirred at 40 ℃ for 1.2 h to obtain the zirconium source solution.

[0099] The mass concentration of the lactic acid solution was 80%.

[0100] The mass concentration of the concentrated nitric acid solution was 62%.

[0101] The polyvinylpyrrolidone solution was a mixture of deionized water and polyvinylpyrrolidone, and the mass ratio of the deionized water to the polyvinylpyrrolidone was 34:1.0.

[0102] (2) Impregnation

[0103] The ceramic green body was placed into a vacuum impregnation device, and the vacuum degree was controlled to be -0.090 MPa. The ceramic green body was vacuumed for 25 min, and then the composite sol was injected. The composite sol completely immersed the ceramic green body, and the pressure was increased to 0.52 MPa. The pressure was maintained for 1.8 h, and then the ceramic green body was taken out. The ceramic green body was dried at 60 ℃ for 3.8 h and then was vacuum dried at 115 ℃ for 1.8 h to obtain a dense ceramic body.

[0104] 5. Sintering

[0105] The dense ceramic body was placed into a sintering furnace, and the temperature was increased to 1100 ℃ at a rate of 2.5 ℃ / min. The temperature was maintained for 60 min, and then the temperature was increased to 1850 ℃ at a rate of 4.5 ℃ / min. The temperature was maintained for 2.3 h, and then the temperature was naturally cooled to room temperature to obtain a boron carbide ceramic.

[0106] Example 3

[0107] 1. Preparation of boron carbide powder

[0108] (1) Preparation of carbon source

[0109] The 43 g of rice husk was put into 120 g of anhydrous ethanol for ball milling, the ball milling time was 2.0 h, the ball milling rotation speed was 280 rpm, after the ball milling, the 62℃ vacuum drying was carried out for 12 h, the vacuum degree was-0.083 MPa, then the 406℃ heat preservation was carried out for 1.3 h under the nitrogen atmosphere, and the natural cooling was carried out to the room temperature, and the carbon source was obtained;

[0110] (2) Preparation of boron source solution

[0111] The 122 g of boric acid was put into 250 g of anhydrous ethanol for ball milling, the ball milling time was 1.3 h, the ball milling rotation speed was 750 rpm, and the boron source solution was obtained after the ball milling;

[0112] (3) Preparation of primary powder

[0113] The 43 g of carbon source was added into the 372 g of boron source solution, 1.2 g of polyvinyl alcohol was added, 1100 rpm stirring was carried out for 33 min, 1.6 g of sodium carbonate and 1.0 g of silicon dioxide were added, ultrasonic dispersion was carried out, the ultrasonic power was 150 W, the ultrasonic frequency was 53 kHz, the ultrasonic time was 35 min, spray granulation was carried out, the inlet temperature was controlled to be 182℃, and the primary powder was obtained;

[0114] (4) Post-treatment

[0115] The primary powder was put into a calcining furnace, the temperature was increased to 310℃ at a rate of 7.0℃ / min, the heat preservation was carried out for 45 min, then the temperature was increased to 1380℃ at a rate of 3.5℃ / min under the argon atmosphere, the heat preservation was carried out for 3.7 h, the natural reduction was carried out to the room temperature, and the boron carbide powder was obtained after the crushing.

[0116] 2. Preparation of ceramic reinforcement

[0117] The 3.2 g of Y(NO3)3·6H2O was added into 40 g of deionized water, after the uniform stirring, the 4.7 g of hexamethylenetetramine was added, the stirring was carried out at 42℃ and 240 rpm for 32 min, and the mixed solution was obtained;

[0118] Put 10.2 g of silicon carbide powder, 2.3 g of zirconium diboride powder into 110 g of anhydrous ethanol, ultrasonic dispersion, ultrasonic time is 37 min, ultrasonic power is 190 W, ultrasonic frequency is 40 kHz, after ultrasonic dispersion, add 47.9 g of mixed solution, control the adding rate to be 1.0 g / min, control the stirring speed to be 125 rpm at the same time, after adding, increase the temperature to 87℃, and keep the reaction for 3.5 h, after the reaction, centrifugal washing, vacuum drying at 82℃ for 12 h, then put into the muffle furnace, increase the temperature to 290℃ at the rate of 2.3℃ / min, keep the temperature for 47 min, then increase the temperature to 606℃ at the rate of 3.8℃ / min, keep the temperature for 2.2 h, and cool down to room temperature in the furnace, to obtain the ceramic reinforcement.

[0119] 3. Preparation of ceramic green body

[0120] Add 32 g of boron carbide powder, 6.5 g of ceramic reinforcement, 2.6 g of boron nitride, and 1.3 g of yttrium borate into 200 g of anhydrous ethanol, mix uniformly, then add 1.2 g of polyvinyl alcohol, stir at 900 rpm for 50 min, dry after stirring to obtain ceramic powder; Put the ceramic powder into a mold for molding treatment to obtain a shaped body, control the molding pressure to be 180 MPa, place the shaped body in an argon atmosphere, increase the temperature to 810℃ at the rate of 2.3℃ / min, keep the temperature for 2.0 h, and cool down to room temperature in the furnace to obtain a ceramic green body.

[0121] 4. Densification treatment

[0122] (1) Preparation of composite sol

[0123] Add 21 g of aluminum isopropyl alcohol into 110 g of anhydrous ethanol, stir at 62℃ for 23 min, add 13.3 g of lactic acid solution under the condition of 62℃ water bath, control the adding rate to be 0.8 g / min, after adding, keep stirring at 150 rpm for 1.6 h, after stirring, add 158 g of zirconium source solution, stir at room temperature for 30 min, increase the temperature to 48℃, add 35.2 g of polyvinylpyrrolidone solution, stir uniformly, then add 12 wt% ammonia water solution to adjust the pH value to be 3.8, keep stirring for 1.8 h, and age for 4.5 h at room temperature in the dark to obtain a composite sol;

[0124] The preparation method of the zirconium source solution is as follows: add 33 g of zirconium oxychloride into 120 g of anhydrous ethanol, keep stirring at 60℃ for 20 min, add 7.0 mL of concentrated nitric acid solution, stir uniformly, then keep stirring at 42℃ for 1.3 h to obtain a zirconium source solution;

[0125] The mass concentration of the lactic acid solution is 82%;

[0126] The mass concentration of the concentrated nitric acid solution is 64%;

[0127] The polyvinylpyrrolidone solution is a mixture of deionized water and polyvinylpyrrolidone, and the mass ratio of the deionized water and polyvinylpyrrolidone is 34:1.2;

[0128] (2) Immersion

[0129] The ceramic green body is placed into a vacuum immersion device, the vacuum degree is controlled to be -0.0935 MPa, vacuum pressure is maintained for 30 min, then the composite sol is injected, the ceramic green body is completely immersed in the composite sol, the pressure is increased to 0.53 MPa, pressure maintaining is performed for 2.0 h, the ceramic green body is taken out, drying is performed at 63℃ for 4.0 h, vacuum drying is performed at 118℃ for 2.0 h, and a dense ceramic body is obtained.

[0130] 5. Sintering

[0131] The dense ceramic body is placed into a sintering furnace, the temperature is increased to 1150℃ at a rate of 2.8℃ / min, sintering is performed for 65 min, then the temperature is increased to 1870℃ at a rate of 4.8℃ / min, sintering is performed for 2.4 h, and natural cooling is performed to room temperature, and a boron carbide ceramic is obtained.

[0132] Comparative Example 3-1

[0133] On the basis of Example 3, the following changes are made:

[0134] 1. In the step of preparing the boron carbide powder, in the step of preparing the primary powder, the step of "adding 1.2 g of polyvinyl alcohol, stirring at 1100 rpm for 33 min, and adding 1.6 g of sodium carbonate and 1.0 g of silicon dioxide" is omitted;

[0135] 2. In the densification treatment step, the composite sol is prepared by uniformly mixing aluminum oxide and zirconium oxide, and the mass ratio of the aluminum oxide and the zirconium oxide is 1:2; the particle size of the aluminum oxide is 120 nm, and the particle size of the zirconium oxide is 150 nm;

[0136] The remaining operations are exactly the same.

[0137] Comparative Example 3-2

[0138] On the basis of Example 3, the following changes are made:

[0139] The ceramic reinforcing body is a mixture of silicon carbide powder, zirconium diboride powder, and yttrium oxide, and the mass ratio of the silicon carbide powder, the zirconium diboride powder, and the yttrium oxide is 10.2:2.3:1.0;

[0140] The remaining operations are exactly the same.

[0141] Performance test

[0142] The boron carbide ceramics prepared from Example 1-3, Comparative Example 3-1 and Comparative Example 3-2 were respectively tested for mechanical properties, fracture toughness and high-temperature oxidation performance, and the test results are as follows:

[0143]

[0144] The fracture toughness after high-temperature oxidation and the bending strength after high-temperature oxidation, specifically, the boron carbide ceramics prepared from Example 1-3, Comparative Example 3-1 and Comparative Example 3-2 were respectively subjected to temperature rising at a rate of 30℃ / min to 1700℃ in an air atmosphere, and were kept for oxidation for 360h, and then the fracture toughness and the bending strength were measured again.

[0145] In the preparation of boron carbide powder step of Comparative Example 3-1, the polyvinyl alcohol, sodium carbonate and silicon dioxide components were omitted from the primary powder, resulting in uneven dispersion of the slurry for spray granulation, poor dispersion of the obtained boron carbide powder, and serious agglomeration and uneven particle size, which can cause an increase in internal defects of the ceramic, a decrease in strength and toughness, and poor filling capacity of the composite sol of Comparative Example 3-1 for the mixture of aluminum oxide and zirconium oxide powder, poor reactivity of the powder with the matrix, and thus affecting the product density, greatly reducing the strength and toughness of the product, and affecting the high-temperature oxidation performance; the ceramic reinforcement of Comparative Example 3-2 is a mixture of silicon carbide powder, zirconium diboride powder and yttrium oxide, and the yttrium oxide particles exist alone and are prone to agglomeration, uneven dispersion, and uneven distribution on the surface of the silicon carbide and zirconium dioxide, affecting the sintering performance of yttrium oxide, resulting in poor interfacial bonding between the ceramic reinforcement and the boron carbide matrix, and reduced toughness and strength improvement effect, ultimately affecting the comprehensive performance of the boron carbide ceramic.

[0146] Unless otherwise specified, the percentages used in the present application are mass percentages.

[0147] Finally, it should be noted that the above only describes the preferred embodiments of the present application and is not intended to limit the present application. Although the present application 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 replacements to some technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing boron carbide ceramics, characterized in that, The preparation method involves mixing boron carbide powder with ceramic reinforcement to prepare a ceramic blank, and then obtaining boron carbide ceramic through densification and sintering steps. The method for preparing the boron carbide powder is as follows: add a carbon source to a boron source solution, add polyvinyl alcohol, stir for 30-35 minutes, add sodium carbonate and silicon dioxide for ultrasonic dispersion, spray granulation to obtain primary powder, calcination and pulverization to obtain boron carbide powder; The carbon source is prepared by ball milling rice husks in anhydrous ethanol, drying them, and then keeping them at 400-410℃ for 1.0-1.5h under a nitrogen atmosphere. The boron source solution is prepared by ball milling boric acid in anhydrous ethanol; the ceramic reinforcement is prepared by placing silicon carbide powder and zirconium diboride powder in anhydrous ethanol, ultrasonically dispersing them, adding the mixture, keeping it at 85-88℃ for 3.0-4.0h, centrifuging, washing and drying it, and then calcining it in a muffle furnace to obtain the ceramic reinforcement. The preparation method of the mixture is as follows: Y(NO3)3·6H2O is added to deionized water, stirred evenly, and then hexamethylenetetramine is added. The mixture is stirred at 40-42℃ and 230-250rpm for 30-35min to obtain the mixture. The densification process includes the preparation of a composite sol and an impregnation process. The steps for preparing the composite sol are as follows: aluminum isopropoxide is added to anhydrous ethanol and stirred until homogeneous; lactic acid solution is added in a water bath at 60-62°C and stirred for 1.4-1.7 h; zirconium source solution is added and stirred at room temperature for 28-33 min; the temperature is raised to 45-50°C; polyvinylpyrrolidone solution is added and stirred until homogeneous; the pH value is adjusted to 3.5-4.0; the mixture is kept at this temperature and stirred for 1.5-2.0 h; and then aged at room temperature in the dark for 4.0-5.0 h to obtain the composite sol.

2. The method for preparing boron carbide ceramics according to claim 1, characterized in that, In the preparation step of the primary powder, the mass ratio of the boron source solution, carbon source, polyvinyl alcohol, sodium carbonate and silicon dioxide is 370-374:40-45:1.0-1.3:1.4-1.7:0.8-1.0; In the preparation step of the carbon source, the mass ratio of rice husk to anhydrous ethanol is 40-45:

120. In the preparation step of the boron source solution, the mass ratio of boric acid to anhydrous ethanol is 120-124:

250.

3. The method for preparing boron carbide ceramics according to claim 1, characterized in that, The calcination process involves placing the primary powder into a calcination furnace, raising the temperature to 300-320°C at a rate of 6.0-8.0°C / min, holding it at that temperature for 40-50 min, and then raising the temperature to 1360-1400°C at a rate of 3.0-4.0°C / min under an argon atmosphere, holding it at that temperature for 3.5-4.0 h.

4. The method for preparing boron carbide ceramics according to claim 1, characterized in that, In the method for preparing the ceramic reinforcement, the mass ratio of silicon carbide powder, zirconium diboride powder, anhydrous ethanol, and the mixed liquid is 10.0-10.4:2.0-2.5:110:47.5-48.

0. In the mixture, the mass ratio of deionized water, Y(NO3)3·6H2O, and hexamethylenetetramine is 40:3.0-3.2:4.5-4.

8.

5. The method for preparing boron carbide ceramics according to claim 1, characterized in that, The steps for preparing the ceramic green body are as follows: add boron carbide powder, ceramic reinforcement, boron nitride, and yttrium borate to anhydrous ethanol, mix evenly, add polyvinyl alcohol, stir at 800-1000 rpm for 45-55 min, dry after stirring to obtain ceramic powder; place the ceramic powder into a mold for molding to obtain a molded body, control the molding pressure at 150-200 MPa, place the molded body in an argon atmosphere, raise the temperature to 800-820℃ at a rate of 2.0-2.5℃ / min, hold at the temperature for 1.8-2.2 h, and cool to room temperature in the furnace to obtain the ceramic green body; The mass ratio of anhydrous ethanol, boron carbide powder, ceramic reinforcement, boron nitride, yttrium borate, and polyvinyl alcohol is 200:30-32:6-7:2-3:1.2-1.5:1.0-1.

3.

6. The method for preparing boron carbide ceramics according to claim 1, characterized in that, In the step of preparing the composite sol, the mass ratio of anhydrous ethanol, aluminum isopropoxide, lactic acid solution, zirconium source solution, and polyvinylpyrrolidone solution is 110:20-23:13.0-13.5:155-160:35.0-35.

3. The mass concentration of the lactic acid solution is 80-85%; The polyvinylpyrrolidone solution is a mixture of deionized water and polyvinylpyrrolidone, wherein the mass ratio of deionized water to polyvinylpyrrolidone is 34:1.0-1.

3.

7. The method for preparing boron carbide ceramic according to claim 1, characterized in that, In the step of preparing the composite sol, the method for preparing the zirconium source solution is as follows: add zirconium oxychloride to anhydrous ethanol, keep warm and stir at 58-60℃ for 18-25 min, add concentrated nitric acid solution, stir evenly, and keep warm and stir at 40-42℃ for 1.2-1.5 h to obtain the zirconium source solution. The mass-to-volume ratio of the anhydrous ethanol, zirconium oxychloride, and concentrated nitric acid solution is 120g:32-34g:6.8-7.0mL; The concentrated nitric acid solution has a mass concentration of 62-66%.

8. The method for preparing boron carbide ceramic according to claim 5, characterized in that, The impregnation step is as follows: the ceramic blank is placed in a vacuum impregnation device, the vacuum degree is controlled at -0.090 to -0.095 MPa, the vacuum pressure is maintained for 25-35 minutes, then the composite sol is injected, the composite sol completely impregnates the ceramic blank, the pressure is increased to 0.52-0.55 MPa, the pressure is maintained for 1.8-2.0 hours, the ceramic blank is taken out, dried at 60-65℃ for 3.8-4.0 hours, and vacuum dried at 115-120℃ for 1.8-2.3 hours to obtain a dense ceramic blank.

9. The method for preparing boron carbide ceramic according to claim 8, characterized in that, The sintering step is as follows: a dense ceramic blank is placed into a sintering furnace, the temperature is increased to 1100-1200℃ at a rate of 2.5-3.0℃ / min, and sintered at that temperature for 60-70 min. Then, the temperature is increased to 1850-1880℃ at a rate of 4.5-5.0℃ / min, and sintered at that temperature for 2.3-2.5 h. The blank is then naturally cooled to room temperature to obtain boron carbide ceramic.

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