Method for preparing porous tantalum carbide ceramic by molten salt assisted template method

Abstract

The invention belongs to the technical field of tantalum carbide ceramics, and particularly relates to a method for preparing porous tantalum carbide ceramics by a molten salt assisted template method, which specifically comprises the following steps: S1, soaking a porous polyurethane foam template in a sodium hydroxide aqueous solution, then cleaning the polyurethane foam template to be neutral by using pure water, and then drying; s2, preparing tantalum carbide slurry, dipping the polyurethane foam template in the tantalum carbide slurry, extruding redundant slurry by using a double-roller press, repeatedly dipping and extruding for 2-3 times, and slowly drying in a drying oven after dipping is completed; s3, preparing mixed salt, drying the polyurethane foam template impregnated with the slurry, putting the dried polyurethane foam template into a graphite crucible, and embedding the polyurethane foam template with the mixed salt; s4, heating, preserving heat and cooling according to a heating procedure to obtain the porous tantalum carbide ceramic with high porosity and relatively high strength; the porous tantalum carbide ceramic provided by the invention can still keep relatively high strength under the condition of high porosity.

Description

Technical Field

[0001] This invention relates to the field of tantalum carbide ceramics technology, and in particular to a method for preparing porous tantalum carbide ceramics using a molten salt-assisted template method. Background Technology

[0002] Currently, the growth of silicon carbide single crystals in PVT faces the challenges of "growing bulk, thickening, and increasing size". During the growth of silicon carbide single crystals, gases such as Si, Si2C, and SiC2 generated by the sublimation of silicon carbide powder will corrode the graphite components in the crucible. The fine carbon particles etched out can easily float into the silicon carbide ingot, thus affecting the yield of the crystal.

[0003] Using porous graphite to filter the atmosphere during silicon carbide growth is an effective solution. However, porous graphite is easily corroded by the sublimated powder atmosphere, has low strength, and is prone to pulverization. Its lifespan is generally limited to no more than one furnace cycle. Tantalum carbide ceramics, on the other hand, are resistant to high temperatures and exhibit high corrosion resistance at high temperatures. Currently, tantalum carbide-coated graphite components are used in silicon carbide crystal growth, significantly improving the quality of silicon carbide crystals without introducing tantalum impurities. Compared to porous graphite, using tantalum carbide ceramics to prepare porous ceramics offers a significant lifespan advantage. Although it is more expensive, the increased number of furnace cycles makes the overall cost per furnace cycle much lower.

[0004] There are many methods for preparing porous ceramics, such as template method, extrusion molding method, foaming method, pore-forming agent, sol-gel method, etc. Among them, the template method is one of the mainstream methods. Currently, there are patent reports on the use of the template method to prepare porous tantalum carbide ceramics. However, in the template method, the impregnation slurry content cannot be completely uniform during sintering. Furthermore, the volatilization of the polymer template forming pores and the sintering shrinkage of the tantalum carbide particles both lead to significant macroscopic and microscopic residual stresses within the ceramic. These stresses easily cause macroscopic and microscopic cracks in the ceramic, resulting in low strength and easy breakage of the porous tantalum carbide ceramic. Summary of the Invention

[0005] This invention provides a method for preparing porous tantalum carbide ceramics using a molten salt-assisted template method. This method is simple to operate and can solve the cracking problem caused by uneven shrinkage during the preparation of porous tantalum carbide ceramics using the template method. The porous tantalum carbide ceramics prepared using this method have adjustable pore sizes and can maintain high strength even with high porosity.

[0006] This invention provides the following technical solution: A method for preparing porous tantalum carbide ceramics using a molten salt-assisted template method specifically includes the following steps: S1. First, immerse the porous polyurethane foam template in a sodium hydroxide aqueous solution, then wash the polyurethane foam template with pure water until it is neutral, and then dry it; S2. Prepare tantalum carbide slurry, then impregnate the polyurethane foam template in the tantalum carbide slurry, use a two-roll press to squeeze out the excess slurry, repeat the impregnation and extrusion 2 to 3 times, and after impregnation, put it in an oven to dry slowly. S3. Prepare a mixed salt. After drying the polyurethane foam template impregnated with the slurry, place it in a graphite crucible and embed the polyurethane foam template with the mixed salt. S4. Heat and hold the temperature according to the heating program and then cool to obtain porous tantalum carbide ceramic with high porosity and high strength. S5. Soak the porous tantalum carbide ceramic in sodium hydroxide solution to remove residual salt, rinse thoroughly with water, and then dry.

[0007] Furthermore, in step S1, the sodium hydroxide aqueous solution contains 5-25 wt% sodium hydroxide, the polyurethane foam template is soaked at 40-60°C, and the soaking time is 0.5-2 hours.

[0008] Soaking in an aqueous sodium hydroxide solution can remove the interlayer membrane between polyurethane template skeletons and increase the surface roughness of the skeletons, thereby improving the uniform coating of the slurry.

[0009] Furthermore, the tantalum carbide slurry is an organic solvent slurry, specifically composed of 50%–75% tantalum carbide, 5%–15% carbon source, 1%–5% binder, 0.1%–5% dispersant, 0.1%–5% rheology modifier, and 15%–35% solvent. The materials are weighed according to the proportion and placed in a zirconia ball mill jar for ball milling at a speed of 200–600 rpm for 2–6 hours.

[0010] Polyurethane templates are highly hydrophobic. If general aqueous tantalum carbide slurry is used, the polyurethane template needs to be modified to improve slurry adhesion. However, modified polyurethane templates cannot guarantee uniform hydrophilicity across all locations, easily leading to uneven slurry adhesion on the template skeleton and ultimately causing cracking of the porous tantalum carbide ceramic. Polyurethane exhibits good wetting properties with organic solvents such as ethanol, xylene, and ethyl acetate. Slurries prepared using organic solvents wet the polyurethane template well, improving the uniformity of slurry adhesion.

[0011] Furthermore, the carbon source is at least one of phenolic resin, furan resin, carbon powder, and graphite powder.

[0012] Furthermore, the adhesive is at least one of ethyl cellulose, polyvinyl butyral, and resin.

[0013] Furthermore, the dispersant is at least one of polyethylene glycol, acrylate copolymer, and polyimide.

[0014] Furthermore, the rheology modifier is at least one of hydrogenated castor oil, fumed silica, and polyamide wax.

[0015] Furthermore, the solvent is at least one of the organic solvents selected from anhydrous ethanol, benzyl alcohol, xylene, toluene, acetylacetone, and ethyl acetate.

[0016] Furthermore, in step S3, the mixed salt is composed of borax, tantalum pentoxide, boron carbide, and potassium fluoride, with a composition ratio of 60-80: 5-10: 0.5-5: 7-25. After weighing each raw material according to the ratio, they are put into a grinding mill for crushing and mixing to obtain the mixed salt.

[0017] In the mixed salt, molten borax at high temperatures has high solubility, capable of dissolving tantalum pentoxide. While providing a molten environment to enhance element diffusion, it can also penetrate into the smaller pores of the porous template, continuously transporting the tantalum source. This tantalum reacts with residual carbon in the template and tantalum carbide slurry to form nano-tantalum carbide, which promotes densification during higher-temperature sintering, thus improving the strength of the porous ceramic. Boron carbide, as a reducing agent, reduces tantalum ions in tantalum pentoxide to active [Ta]. Compared to tantalum metal powder, active [Ta] has a smaller particle size, higher reactivity, and a higher diffusion rate in molten borax. Potassium fluoride can reduce the viscosity of the molten salt and improve the fluidity of the melt.

[0018] Further, in step S4, the specific process is as follows: Evacuate to below 5 Pa, then introduce argon gas to a slightly positive pressure. The temperature needs to be gradually increased step by step. First, increase the temperature to 600-800℃ at a rate of 5-10℃ / min and hold for 0.5 hours; then increase the temperature to 1000-1300℃ at a rate of 3-5℃ / min and hold for 1-2 hours. The substance gradually melts; slow heating is beneficial for uniform temperature distribution and more uniform melting of the mixed salt. Holding at 1300℃ for 2 hours is beneficial for the full reaction of active [Ta] and residual carbon. At this temperature, the molten salt will not volatilize significantly, and its viscosity is low, its fluidity is high, and the reaction can be completed relatively quickly. Then, increase the temperature to 1800-2000℃ at a rate of 2-5℃ / min and hold for 1-2 hours, and then at 170℃... After reaching 0℃, the vacuum is gradually reduced to below 5 Pa. Finally, the temperature is increased to 2000-2200℃ at a rate of 2-5℃ / min and held for 1-2 hours. During the heating process, the molten salt gradually volatilizes, while the porous tantalum carbide ceramic gradually sintersulates and densifies. The slow heating rate and controlled furnace pressure can gradually remove the molten salt and alleviate shrinkage stress during the sintering process of the porous tantalum carbide ceramic, preventing cracking. After the temperature reaches above 2000℃, the molten salt volatilization is complete, the grains in the porous tantalum carbide ceramic sinter and grow, the porosity is further reduced, and there is no significant volume change, thus further improving the strength of the porous tantalum carbide. Subsequently, the temperature is reduced to 600℃ at a rate of 3-5℃ / min, and then cooled to room temperature with the furnace.

[0019] The heating equipment is equipped with an exhaust gas treatment device that can adsorb volatile salts and other harmful byproducts from the reaction process.

[0020] Compared with traditional technologies, this application has the following advantages: In this invention, the preparation process is simple, the raw material utilization rate is high, and the overall cost is low. The borax, boron carbide, potassium fluoride, etc. used in this invention have been widely used in industrial production, with high output and low price. The tantalum pentoxide used is almost completely converted into tantalum carbide after the reaction process, with no residue.

[0021] In this invention, the shape is controllable and the porosity is adjustable.

[0022] The porous tantalum carbide ceramics prepared by the method of this invention have high yield and high compressive strength, making them suitable for use in silicon carbide crystal growth environments.

[0023] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and in order to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below. Attached Figure Description

[0024] Figure 1SEM microstructure of the TaC framework in the porous ceramic prepared in Example 1. Figure 2 This is a SEM microstructure image of the porous TaC ceramic material prepared in Example 1. Figure 3 The image shows the SEM microstructure of the porous TaC ceramic material prepared in Comparative Example 1.

[0025] Figure 4 The image shows the SEM microstructure of the porous TaC ceramic material prepared in Comparative Example 2.

[0026] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. Detailed Implementation

[0027] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, a detailed description of specific embodiments of this application is provided. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. Unless otherwise specifically stated, all raw materials, reagents, instruments, and equipment used in this application are commercially available or can be prepared by existing methods.

[0029] In this application, terms such as "further," "even further," and "particularly" are used to describe purposes and indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0030] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0031] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0032] In this application, numerical intervals (i.e., numerical ranges) are involved. Unless otherwise specified, the selected numerical distributions within the aforementioned numerical intervals are considered continuous and include the two endpoints (i.e., the minimum and maximum values) of the numerical range, as well as every value between these two endpoints. Unless otherwise specified, when a numerical interval refers only to integers within that interval, it includes the two endpoint integers of the numerical range, as well as every integer between the two endpoints. In this document, this is equivalent to directly listing every integer. For example, if t is an integer selected from 1 to 10, it means that t is any integer selected from the group of integers consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10. Furthermore, when multiple ranges are provided to describe features or characteristics, these ranges can be merged. In other words, unless otherwise specified, the ranges disclosed herein should be understood to include any and all subranges to which they are included.

[0033] Unless otherwise specified, the temperature parameters in this application are permitted to be either constant-temperature treatment or variations within a certain temperature range. It should be understood that the constant-temperature treatment allows temperature fluctuations within the precision range of the instrument control, such as ±5℃, ±4℃, ±3℃, ±2℃, or ±1℃.

[0034] This application provides a method for preparing porous tantalum carbide ceramics using a molten salt-assisted template method, specifically including the following steps: S1. First, immerse the porous polyurethane foam template in a sodium hydroxide aqueous solution, then wash the polyurethane foam template with pure water until it is neutral, and then dry it; S2. Prepare tantalum carbide slurry, then impregnate the polyurethane foam template in the tantalum carbide slurry, use a two-roll press to squeeze out the excess slurry, repeat the impregnation and extrusion 2 to 3 times, and after impregnation, put it in an oven to dry slowly. S3. Prepare a mixed salt. After drying the polyurethane foam template impregnated with the slurry, place it in a graphite crucible and embed the polyurethane foam template with the mixed salt. S4. Heat and hold the temperature according to the heating program and then cool to obtain porous tantalum carbide ceramic with high porosity and high strength. S5. Soak the porous tantalum carbide ceramic in sodium hydroxide solution to remove residual salt, rinse thoroughly with water, and then dry.

[0035] In some embodiments, in step S1, the sodium hydroxide aqueous solution contains 5-25 wt% sodium hydroxide, the polyurethane foam template is immersed at a temperature of 40-60°C, and the immersion time is 0.5-2 hours.

[0036] For example, the sodium hydroxide content in the sodium hydroxide aqueous solution can be 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, 20wt%, 21wt%, 22wt%, 23wt%, 24wt%, 25wt%, or any value within the range formed by any two of the above points.

[0037] For example, the immersion temperature of the polyurethane foam template can be 40℃, 45℃, 50℃, 55℃, 60℃, or any value within the range of any two of the above points, and the immersion time can be 0.5h, 1h, 1.5h, 2h, or any value within the range of any two of the above points.

[0038] Soaking in an aqueous sodium hydroxide solution can remove the interlayer membrane between polyurethane template skeletons and increase the surface roughness of the skeletons, thereby improving the uniform coating of the slurry.

[0039] In some embodiments, the tantalum carbide slurry is an organic solvent slurry, specifically composed of 50%–75% tantalum carbide, 5%–15% carbon source, 1%–5% binder, 0.1%–5% dispersant, 0.1%–5% rheology modifier, and 15%–35% solvent. The materials are weighed according to the proportion and placed in a zirconia ball mill jar for ball milling at a speed of 200–600 rpm for 2–6 hours.

[0040] Specifically, based on the total mass of the tantalum carbide slurry, the mass content of tantalum carbide can be 50%, 55%, 60%, 65%, 70%, 75%, or any value within the range formed by any two of the above points.

[0041] During the preparation of the tantalum carbide slurry, the ball milling speed can be 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm, or any value within the range formed by any two of the above points.

[0042] During the preparation of the tantalum carbide slurry, the ball milling time can be 2h, 3h, 4h, 5h, 6h, or any value within the range formed by any two of the above points.

[0043] Polyurethane templates are highly hydrophobic. If general aqueous tantalum carbide slurry is used, the polyurethane template needs to be modified to improve slurry adhesion. However, modified polyurethane templates cannot guarantee uniform hydrophilicity across all locations, easily leading to uneven slurry adhesion on the template skeleton and ultimately causing cracking of the porous tantalum carbide ceramic. Polyurethane exhibits good wetting properties with organic solvents such as ethanol, xylene, and ethyl acetate. Slurries prepared using organic solvents wet the polyurethane template well, improving the uniformity of slurry adhesion.

[0044] In some embodiments, the carbon source is at least one selected from phenolic resin, furan resin, carbon powder, and graphite powder.

[0045] For example, based on the total mass of the tantalum carbide slurry, the mass content of the carbon source can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or any value within the range formed by any two of the above points.

[0046] In some embodiments, the adhesive is at least one of ethyl cellulose, polyvinyl butyral, and resin.

[0047] For example, based on the total mass of tantalum carbide slurry, the mass content of the binder can be 1%, 2%, 3%, 4%, 5%, or any value within the range formed by any two of the above points.

[0048] In some embodiments, the dispersant is at least one of polyethylene glycol, acrylate copolymer, and polyimide.

[0049] For example, based on the total mass of tantalum carbide slurry, the mass content of the dispersant can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any value within the range formed by any two of the above points.

[0050] In some embodiments, the rheology modifier is at least one of hydrogenated castor oil, fumed silica, and polyamide wax.

[0051] For example, based on the total mass of tantalum carbide slurry, the mass content of rheology modifier can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any value within the range formed by any two of the above points.

[0052] In some embodiments, the solvent is at least one of the organic solvents anhydrous ethanol, benzyl alcohol, xylene, toluene, acetylacetone, and ethyl acetate.

[0053] For example, based on the total mass of tantalum carbide slurry, the mass content of the solvent can be 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, or any value within the range formed by any two of the above points.

[0054] In some embodiments, in step S3, the mixed salt is composed of borax, tantalum pentoxide, boron carbide and potassium fluoride, with a composition ratio of 60-80: 5-10: 0.5-5: 7-25. After weighing each raw material according to the ratio, they are put into a grinding mill for crushing and mixing to obtain the mixed salt.

[0055] In the mixed salt, molten borax at high temperatures has high solubility, capable of dissolving tantalum pentoxide. While providing a molten environment to enhance element diffusion, it can also penetrate into the smaller pores of the porous template, continuously transporting the tantalum source. This tantalum reacts with residual carbon in the template and tantalum carbide slurry to form nano-tantalum carbide, which promotes densification during higher-temperature sintering, thus improving the strength of the porous ceramic. Boron carbide, as a reducing agent, reduces tantalum ions in tantalum pentoxide to active Ta. Compared to tantalum metal powder, active Ta has a smaller particle size, higher reactivity, and a higher diffusion rate in molten borax. Potassium fluoride can reduce the viscosity of the molten salt and improve the fluidity of the melt.

[0056] In some embodiments, in step S4, the specific process is as follows: Evacuate to below 5 Pa, then introduce argon gas to a slightly positive pressure. The temperature needs to be gradually increased step by step: first, increase the temperature to 600-800℃ at a rate of 5-10℃ / min and hold for 0.5h; then increase the temperature to 1000-1300℃ at a rate of 3-5℃ / min and hold for 1-2h; the substance gradually melts, and slow heating is beneficial for uniform temperature distribution and more uniform melting of the mixed salt. Holding at 1300℃ for 2h is beneficial for the full reaction of active [Ta] and residual carbon. At this temperature, the molten salt will not volatilize in large quantities, and its viscosity is low, its fluidity is high, and the reaction can be completed relatively quickly; then increase the temperature to 1800-2000℃ at a rate of 2-5℃ / min and hold for 1-2h, and at 1... After reaching 700℃, the vacuum was gradually reduced to below 5 Pa. Finally, the temperature was increased to 2000-2200℃ at a rate of 2-5℃ / min and held for 1-2 hours. During the heating process, the molten salt gradually volatilized, while the porous tantalum carbide ceramic gradually sintered and densified. The slow heating rate and controlled furnace pressure gradually removed the molten salt and alleviated shrinkage stress during the sintering process of the porous tantalum carbide ceramic, preventing cracking. After the temperature reached above 2000℃, the molten salt volatilized completely, and the grains in the porous tantalum carbide ceramic sintered and grew, further reducing the porosity without significant volume change, thus further improving the strength of the porous tantalum carbide. Subsequently, the temperature was reduced to 600℃ at a rate of 3-5℃ / min, and then cooled to room temperature with the furnace.

[0057] The present application will be further described below with reference to specific embodiments and comparative examples, but these should not be construed as limiting the scope of protection of the present application. Unless otherwise specified, the raw materials involved in the following specific embodiments are all commercially available, the instruments used are all commercially available, and the processes involved are conventionally selected by those skilled in the art unless otherwise specified.

[0058] Example 1: Immerse the 80ppi polyurethane template in a 30% NaOH solution and keep it at 60℃ for 1 hour. Then, rinse it repeatedly with clean water to remove any residual NaOH solution from the surface.

[0059] Tantalum carbide, phenolic resin, ethyl cellulose, polyethylene glycol, polyamide wax, anhydrous ethanol, and toluene were weighed in a mass ratio of 70:5:1:0.5:1.5:15:7. The weighed raw materials were placed in a zirconia ball mill jar and mixed at a ball-to-material ratio of 5:1 for 2 hours. After ball milling, tantalum carbide impregnation slurry was obtained.

[0060] Immerse the treated 80ppi polyurethane template in the mixed tantalum carbide slurry, repeatedly pressing until the pores in the template are filled with slurry. Then, use a roller press to squeeze out the excess slurry. After the slurry dries in the air for 10 minutes, repeat the above operation 3 times to ensure that the surface of the polyurethane template skeleton is evenly coated with tantalum carbide slurry. Then, place the template coated with slurry into an oven for drying.

[0061] Borax, tantalum pentoxide, boron carbide, and potassium fluoride were weighed in a mass ratio of 75:5:0.5:19.5, and then put into a grinding mill for crushing and mixing to obtain a mixed salt.

[0062] The dried polyurethane sample was placed in a crucible and then embedded with a mixed salt. It was then placed in a high-temperature carbon tube furnace for high-temperature heat treatment. The specific process was as follows: vacuum was applied to below 5 Pa, then argon gas was introduced to a slightly positive pressure, followed by heating to 700 °C at a rate of 8 °C / min and holding for 0.5 h; then heating to 1200 °C at a rate of 5 °C / min and holding for 1 h; then heating to 2000 °C at a rate of 3 °C / min and holding for 1 h, and gradually evacuating to below 5 Pa after reaching 1700 °C; finally, heating to 2200 °C at a rate of 3 °C / min and holding for 2 h; subsequently cooling to 600 °C at a rate of 5 °C / min, and then cooling to room temperature with the furnace. The porous tantalum carbide ceramic sample was then removed.

[0063] According to the furnace loading, the residual salts decomposed in the exhaust gas device's filter screen and furnace wall surface should be cleaned regularly.

[0064] SEM microstructure images of the prepared samples are shown below. Figure 1 As shown, the tantalum carbide skeletal particles are highly dense with no pores between the grains and have a clean surface free of residual carbon. The porous tantalum carbide ceramics prepared by the method of this invention have a high yield.

[0065] Example 2: 1. Immerse a 60ppi polyurethane template in a 30% NaOH solution and keep it at 60℃ for 1 hour. Then rinse it repeatedly with clean water to remove any residual NaOH solution from the surface.

[0066] 2. Weigh tantalum carbide, phenolic resin, carbon powder, polyvinyl butyral, polyimide, polyamide wax, anhydrous ethanol, and toluene in a mass ratio of 65:3:2:1:0.5:1.5:18:9. Place the weighed raw materials into a zirconia ball mill jar and mix them at a ball-to-material ratio of 5:1 at a ball mill speed of 600 rpm for 2 hours. After ball milling, tantalum carbide impregnation slurry is obtained.

[0067] 3. Immerse the treated 60ppi polyurethane template in the mixed tantalum carbide slurry, repeatedly pressing until the pores in the template are filled with slurry. Then, use a roller press to squeeze out the excess slurry. After the slurry dries in the air for 10 minutes, repeat the above operation 3 times to ensure that the surface of the polyurethane template skeleton is evenly coated with tantalum carbide slurry. Then, place the template coated with slurry into an oven for drying.

[0068] 4. Weigh borax, tantalum pentoxide, boron carbide, and potassium fluoride in a mass ratio of 80:8:0.5:11.5, then put them into a grinding mill for crushing and mixing to obtain a mixed salt.

[0069] 5. Place the dried polyurethane sample in a crucible and embed it using a mixed salt. Place it in a high-temperature carbon tube furnace for high-temperature heat treatment. The specific process is as follows: evacuate to below 5 Pa, then introduce argon gas to a slightly positive pressure, then heat to 700 °C at a heating rate of 8 °C / min and hold for 0.5 h; then heat to 1200 °C at a heating rate of 5 °C / min and hold for 1 h; then heat to 2000 °C at a heating rate of 3 °C / min and hold for 1 h, and gradually evacuate to below 5 Pa after reaching 1700 °C; finally, heat to 2200 °C at a heating rate of 3 °C / min and hold for 2 h; then cool to 600 °C at a cooling rate of 5 °C / min, and then cool to room temperature with the furnace. Remove the porous tantalum carbide ceramic sample.

[0070] 6. Clean the filter screen and furnace wall surface of the exhaust gas device regularly according to the furnace loading capacity to remove residual salts.

[0071] Example 3: Immerse a 50ppi polyurethane template in a 30% NaOH solution and keep it at 60℃ for 1 hour. Then, rinse it repeatedly with clean water to remove any residual NaOH solution from the surface.

[0072] Tantalum carbide, phenolic resin, ethyl cellulose, polyethylene glycol, polyamide wax, anhydrous ethanol, and toluene were weighed in a mass ratio of 70:5:1:0.5:1.5:15:7. The weighed raw materials were placed in a zirconia ball mill jar and mixed at 600 rpm for 2 hours at a ball-to-material ratio of 5:1. After ball milling, tantalum carbide impregnation slurry was obtained.

[0073] The treated 50ppi polyurethane template is immersed in the mixed tantalum carbide slurry and repeatedly squeezed until the pores in the template are filled with slurry. Then, excess slurry is squeezed out using a roller press. After the slurry is air-dried for 10 minutes, the above operation is repeated 5 times to ensure that the surface of the polyurethane template skeleton is evenly coated with tantalum carbide slurry. The template coated with slurry is then placed in an oven for drying.

[0074] Borax, tantalum pentoxide, boron carbide, and potassium fluoride were weighed in a mass ratio of 75:5:0.5:19.5, and then put into a grinding mill for crushing and mixing to obtain a mixed salt.

[0075] The dried polyurethane sample was placed in a crucible and then embedded with a mixed salt. It was then placed in a high-temperature carbon tube furnace for high-temperature heat treatment. The specific process was as follows: vacuum was applied to below 5 Pa, then argon gas was introduced to a slightly positive pressure, followed by heating to 800 °C at a rate of 5 °C / min and holding for 0.5 h; then heating to 1300 °C at a rate of 3 °C / min and holding for 1 h; then heating to 1800 °C at a rate of 2 °C / min and holding for 1 h, and gradually evacuating to below 5 Pa after reaching 1700 °C; finally, heating to 2000 °C at a rate of 2 °C / min and holding for 2 h; subsequently cooling to 600 °C at a rate of 5 °C / min, and then cooling to room temperature with the furnace, before removing the porous tantalum carbide ceramic sample.

[0076] According to the furnace loading, the residual salts decomposed in the exhaust gas device's filter screen and furnace wall surface should be cleaned regularly.

[0077] Comparative Example 1: The comparative example was performed in accordance with Example 1 of the patent "CN202411155032.9; A method for preparing porous TaC ceramics using an organic foam template method".

[0078] NaCl, KCl, K₂TaF₆, and Ta powder were weighed in a mass ratio of 4:5:0.3:0.7 and ball-milled to obtain the required molten salt powder. Then, reaction sintering raw materials were prepared with a molar ratio of tantalum oxide powder to carbon powder of 1:7. A portion of the molten salt powder was mixed with the reaction sintering raw material powder in a mass ratio of 3:1 and ball-milled. Air was used as the ball milling medium, the ball milling speed was 40 r / min, and the ball milling time was 24 h. In actual operation, after ball milling, the mixture was dried in a forced-air drying oven for 10 h to obtain the mixed powder. The mixed powder was pressed into a preform at 20 MPa, with a preform weight of 5.693 g. The preform was then placed in a graphite jar lined with graphite paper on both sides, and the preform was then embedded with the molten salt powder. The process involves using 6g of molten salt powder. First, 30% of the powder is placed at the bottom of a graphite container. Then, a preform made from the mixed powder is placed on top of the molten salt powder, and finally, the remaining molten salt powder is used to wrap the preform. This is then placed in an alumina boat, followed by a tube furnace. A vacuum process is performed to reduce the furnace pressure to below 50 Pa. Argon gas is then introduced into the tube furnace for protection, balancing the furnace pressure with the external atmospheric pressure. The temperature is then increased to 1200℃ at a rate of 5℃ / min and held for 60 minutes. Next, the temperature is increased to 1500℃ at a rate of 3℃ / min and held for 3 hours. After the holding period, the temperature is cooled to 500℃ at a rate of 5℃ / min, and then cooled to room temperature with the furnace. The boat is then removed, the sample is washed with deionized water, and dried to obtain the porous TaC ceramic material.

[0079] SEM microstructure images of the prepared samples are shown below. Figure 2 As shown, the skeletal tantalum carbide particles are small and not dense, with residual carbon on the surface.

[0080] Comparative Example 2: Immerse the 80ppi polyurethane template in a 30% NaOH solution and keep it at 60℃ for 1 hour. Then, rinse it repeatedly with clean water to remove any residual NaOH solution from the surface.

[0081] Tantalum carbide, phenolic resin, ethyl cellulose, polyethylene glycol, polyamide wax, anhydrous ethanol, and toluene were weighed in a mass ratio of 70:5:1:0.5:1.5:15:7. The weighed raw materials were placed in a zirconia ball mill jar and mixed at a ball-to-material ratio of 5:1 for 2 hours. After ball milling, tantalum carbide impregnation slurry was obtained.

[0082] Immerse the treated 80ppi polyurethane template in the mixed tantalum carbide slurry, repeatedly pressing until the pores in the template are filled with slurry. Then, use a roller press to squeeze out the excess slurry. After the slurry dries in the air for 10 minutes, repeat the above operation 3 times to ensure that the surface of the polyurethane template skeleton is evenly coated with tantalum carbide slurry. Then, place the template coated with slurry into an oven for drying.

[0083] The dried polyurethane sample was placed in a crucible and then placed in a high-temperature carbon tube furnace for high-temperature heat treatment. The specific process was as follows: the vacuum was evacuated to below 5 Pa, then argon gas was introduced to a slightly positive pressure, and then the temperature was increased to 700 °C at a heating rate of 8 °C / min and held for 0.5 h; then the temperature was increased to 1200 °C at a heating rate of 5 °C / min and held for 1 h; then the temperature was increased to 2000 °C at a heating rate of 3 °C / min and held for 1 h, and after reaching 1700 °C, the vacuum was gradually reduced to below 5 Pa; finally, the temperature was increased to 2200 °C at a heating rate of 3 °C / min and held for 2 h; then the temperature was decreased to 600 °C at a cooling rate of 5 °C / min, and then cooled to room temperature in the furnace before the porous tantalum carbide ceramic sample was removed.

[0084] SEM microstructure images of the prepared samples are shown below. Figure 3 As shown, the skeletal tantalum carbide grains have many pores, are not dense, and have residual carbon on the surface.

[0085] Performance testing, stress testing, testing methods: Strength tests were conducted on Example 1 and Comparative Example 1. First, test samples with dimensions of 20mm × 20mm × 20mm were prepared using different methods. The compressive strength was measured using an Instron 3369 material testing machine (USA) at a pressure rate of 1 mm / min. The formula for calculating compressive strength is shown in Figure 2-4.

[0086] Where: σ c P is the compressive strength (MPa); P is the pressure applied to the effective area (N); A is the area under pressure (mm). 2 .

[0087] The test results are shown in the table below:

[0088] As shown in the table above, the porous tantalum carbide ceramics prepared by the method of the present invention have high compressive strength.

[0089] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0090] The above are merely specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. In the absence of conflict, the embodiments and features of the embodiments of the present invention can be combined with each other. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing porous tantalum carbide ceramics by a molten salt-assisted templating method, characterized by, Specifically comprising the following steps: S1. First, immerse the porous polyurethane foam template in a sodium hydroxide aqueous solution, then wash the polyurethane foam template to neutral with pure water, and then dry; S2. Prepare a tantalum carbide slurry, then immerse the polyurethane foam template in the tantalum carbide slurry, use a double-roller press to extrude the excess slurry, repeat the immersion and extrusion 2-5 times, and then slowly dry the immersed template in an oven; S3. Prepare a mixed salt, and after drying the polyurethane foam template immersed in the slurry, place it in a graphite crucible and embed the polyurethane foam template with the mixed salt; S4. Heat and cool according to the temperature rising program to obtain a porous tantalum carbide ceramic with high porosity and high strength; S5. Soak the porous tantalum carbide ceramic in a sodium hydroxide solution to remove residual salt, rinse with clean water, and then dry.

2. The method of claim 1, wherein the method is characterized by, In step S1, the sodium hydroxide aqueous solution contains 5-30wt% sodium hydroxide, the polyurethane foam template is immersed at a temperature of 40-60℃ for 0.5-2h.

3. The method of claim 1, wherein the method is characterized by: The tantalum carbide slurry is an organic solvent slurry, which is composed of 50%-75% tantalum carbide, 5%-15% carbon source, 1%-5% binder, 0.1%-5% dispersant, 0.1%-5% rheological agent, and 15%-35% solvent. The materials are weighed according to the proportion, placed in a zirconia ball mill jar, and ball milled at a speed of 200-600rpm for 2-6h.

4. The method of claim 3, wherein the method is characterized by, The carbon source is at least one of phenolic resin, furan resin, carbon powder, and graphite powder.

5. The method of claim 3, wherein the method is characterized by, The binder is at least one of ethyl cellulose, polyvinyl butyral, and resin.

6. The method of claim 3, wherein the porous carbonized polymeric precursor is a polymerized polyacrylonitrile (PAN) precursor. The dispersant is at least one of polyethylene glycol, acrylic ester copolymer, and polyimide.

7. The method of claim 3, wherein the porous carbonized polymeric precursor is a polymerized polyacrylonitrile (PAN) precursor. The rheological agent is at least one of hydrogenated castor oil, fumed silica, and polyamide wax.

8. The method of claim 3, wherein the porous carbonized polymeric precursor is a polymerized polyacrylonitrile (PAN) precursor. The solvent is at least one of organic solvents such as anhydrous ethanol, benzyl alcohol, dimethylbenzene, toluene, acetylacetone, and ethyl acetate.

9. The method of claim 1, wherein the porous carbonized polymeric precursor is a polymerized polyacrylonitrile (PAN) precursor. In step S3, the mixed salt is composed of borax, tantalum pentoxide, boron carbide, and potassium fluoride, with a composition ratio of 60-80:5-10:0.5-5:7-25, respectively. The raw materials are weighed according to the proportion, placed in a pulverizer, and crushed and mixed to obtain the mixed salt.

10. The method of claim 1, wherein the porous carbonized polymeric precursor is a polymerized polyacrylonitrile (PAN) precursor. In step S4, the specific process is as follows: vacuum to below 5pa, then introduce argon to a slight positive pressure, first heat to 600-800℃ at a rate of 5-10℃ / min, and keep for 0.5h; then heat to 1000-1300℃ at a rate of 3-5℃ / min, and keep for 1-2h; then heat to 1800-2000℃ at a rate of 2-5℃ / min, and keep for 1-2h, and gradually vacuum to below 5pa after 1700℃; finally, heat to 2000-2200℃ at a rate of 2-5℃ / min, and keep for 1-2h; then cool to 600℃ at a rate of 3-5℃ / min, and then cool to room temperature with the furnace.

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