Boron carbide ceramic filter plate and preparation method thereof

Abstract

The invention relates to the technical field of ceramic filter plates, in particular to a boron carbide ceramic filter plate and a preparation method thereof.The preparation method of the boron carbide ceramic filter plate comprises the steps that S1, raw materials are pretreated; s2, mixing, ball-milling and granulating; boron carbide powder and aluminum powder are mixed, ball-milled and granulated, and a mixture is obtained; wherein the aluminum powder accounts for 21%-35% of the total mass of the mixture; s3, forming and sintering are carried out; s2, placing the mixture obtained in the step S2 in a mold for forming, heating to 1200 DEG C in an inert atmosphere for sintering, connecting boron carbide particles through an aluminum-boron intermetallic compound to form an integrated filter plate, carrying out staged heat preservation in the sintering process, and cooling along with a furnace after heat preservation is finished, so as to obtain the boron carbide ceramic filter plate. According to the method, an existing preparation method of the boron carbide ceramic filter plate is changed, the sintering temperature of the boron carbide ceramic filter plate is reduced to 1200 DEG C, sintering energy consumption is greatly reduced, the interface reaction of aluminum and boron carbide is mainly utilized, three-stage sintering is carried out, large deformation is not prone to occurring, and the rejection rate is smaller.

Description

Technical Field

[0001] The invention relates to the technical field of ceramic filter plates, and in particular to a boron carbide ceramic filter plate and a preparation method thereof. Background Art

[0002] Ceramic filter plates, also known as ceramic filter membranes, ceramic plates, ceramic plates, filter plates, etc., are new filter media made of corundum, silicon carbide, etc. through special processes. At present, as the core component of ceramic filters, ceramic filter plates have been widely used in the filtration and dehydration of mine concentrates such as iron concentrate, zinc concentrate, sulfur concentrate, copper concentrate, nickel concentrate, molybdenum concentrate, lead concentrate, tungsten concentrate, manganese concentrate, vanadium ore, aluminum concentrate, gold concentrate, non-metallic concentrate, and solid-liquid separation in industries such as coal, fine chemicals, papermaking, pharmaceuticals, chemical fiber, food, and environmental protection.

[0003] Boron carbide ceramics have good acid and alkali resistance and a small thermal expansion coefficient, so they have good thermal stability and a very large neutron absorption cross-section. They are the best choice for nuclear-grade filter plates and for treating nuclear contaminated wastewater. For example, the invention patent with application number 202210494239.3 discloses a method for preparing a high-purity boron carbide tubular ceramic filter membrane, which has a good filtration effect, but requires a high temperature of 2100°C for sintering for 50 hours. Not only is the energy consumption high, but the dimensional changes caused by high-temperature sintering are uncontrollable, and the scrap rate is high.

[0004] The inventors conducted research on this in the process of using boron carbide, and sought a method for preparing a boron carbide ceramic filter plate that reduces sintering temperature, energy consumption and scrap rate, so as to achieve low-cost and high-efficiency production of the filter plate. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a boron carbide ceramic filter plate and a preparation method thereof, which can reduce the production energy consumption of the boron carbide ceramic filter plate and reduce the scrap rate.

[0006] The technical solution adopted in this application to solve this technical problem is:

[0007] A method for preparing a boron carbide ceramic filter plate comprises the following steps:

[0008] Step S1: pretreatment of boron carbide raw materials;

[0009] Step S2: mixing, ball milling and granulation;

[0010] The boron carbide powder pretreated in step S1 is mixed with aluminum powder for ball milling and granulation to obtain a mixture, wherein the aluminum powder accounts for 21% to 35% of the total mass of the mixture;

[0011] Step S3: forming and sintering;

[0012] The mixed material in step S2 is placed in a mold for forming, and the temperature is raised to 1200° C. for sintering in an inert atmosphere. The boron carbide particles are connected via the aluminum-boron intermetallic compound to form an integrated filter plate. The sintering process is heat-insulated in stages, and after the heat-insulation is completed, the mixture is cooled with the furnace to obtain a boron carbide ceramic filter plate.

[0013] During powder preparation and pretreatment, oxides or impurities on the surface of boron carbide are removed to prevent this component from affecting product quality. During ball milling, boron carbide is fully in contact with aluminum, and aluminum and boron carbide are in contact to form mutual filling. Staged heat preservation allows better contact between boron carbide and aluminum, more complete interface reaction, and a prepared filter plate with stronger performance. When the temperature is high, an intermetallic compound with a higher melting point is produced. Although the intermetallic compound is usually brittle compared to boron carbide, the inventor has tested that its strength exceeds the strength standard required for the filter plate, and can be used for the preparation of boron carbide ceramic filter plates.

[0014] Furthermore, the stage insulation includes at least the following processes:

[0015] The first stage: the temperature is kept at 650-700℃ and the holding time is 1-2h;

[0016] The second stage: the temperature is kept at 850-900℃ and the holding time is 3-5h;

[0017] The third stage: the insulation node is 1175-1200℃, and the insulation time is 3-5h.

[0018] In the above three-stage heat preservation process, the first stage is to enable the mixture to quickly reach the liquidus point of aluminum, so that aluminum and boron carbide are in contact. In the second stage, aluminum and boron carbide strengthen the interface reaction between aluminum and boron carbide to form a connection and promote the rapid consumption of aluminum to generate more aluminum-boron intermetallic compounds and reduce the retention of single substances, because at a relatively low temperature, aluminum and boron mainly form AlB 2 、Al 3 BC is a high-aluminum, low-boron intermetallic compound, which connects the boron carbide particles to form an integrated structure; the third stage is mainly to transform the intermetallic compounds into AlB 2 、Al 3 BC to AlB 12 , forming a hard and stable high-boron sintered component.

[0019] Furthermore, in step S3, the forming process includes two molding processes. The first molding process is before the temperature rise sintering, and the molding pressure is 100-150MPa; the second molding process is after the first stage of heat preservation is completed, and the molding pressure is 20MPa. The molding time is 1-2min.

[0020] At the end of the first stage of insulation, because the temperature is still relatively low, although the aluminum powder has already appeared in liquid phase, the wetting effect of aluminum and boron carbide is not good at this temperature, so it is necessary to perform molding again. On the one hand, a larger contact area is formed between aluminum and boron carbide, and on the other hand, the filter plate can be further compressed during the second molding to reduce its filter aperture.

[0021] Furthermore, the raw material pretreatment steps are as follows: first, the boron carbide powder is stirred and immersed in 1 mol / L hydrochloric acid for 20 minutes, then rinsed with anhydrous ethanol for 3-5 times, and vacuum dried at 90°C-100°C for 2 hours.

[0022] Furthermore, the boron carbide powder is composed of two particle size ranges, wherein the particle size of the small particle size is 6-10 microns, and the particle size of the large particle size is 25-38 microns, wherein the mass ratio of the small particle size to the large particle size is 2:8, and the materials of different particle sizes are filled to form a more compact filtering structure and reduce the filtering pore size.

[0023] Furthermore, the method further comprises step S4: alkaline leaching; placing the boron carbide ceramic filter plate of step S2 in an aqueous solution containing 20%wt sodium hydroxide and 3%wt potassium nitrate and immersing and rinsing for 2-4 hours, and then cleaning with distilled water.

[0024] After alkali leaching, the unreacted aluminum powder or aluminum powder precipitated after high temperature in the filter plate can be removed, so that the filter holes can be unblocked to avoid blockage, and the filter plate can be prevented from being contaminated by the presence of aluminum during use.

[0025] A boron carbide ceramic filter plate is prepared using the method for preparing the boron carbide ceramic filter plate.

[0026] Furthermore, the boron carbide ceramic filter plate has a bending strength of 16-27 MPa and a porosity of 43%-50%.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. The present invention changes the current preparation method of boron carbide ceramic filter plates, lowering the sintering temperature to 1200°C, greatly reducing the sintering energy consumption, because the present invention utilizes the interface reaction between aluminum and boron carbide instead of causing boron carbide to produce liquid phase sintering. Therefore, the present invention has a low sintering temperature, a lower scrap rate, and is less likely to have large dimensional changes.

[0029] 2. The present invention adopts three-stage sintering, which can make the filter plate stable in shape in the early stage of sintering and not easy to deform. After the three-stage sintering, a high-temperature sintered component is formed between the boron carbides, which has high hardness and strength and is suitable for use in the filter plate.

[0030] 3. The present invention also performs alkaline leaching after sintering to remove unreacted or reacted aluminum, thereby preventing this part of aluminum from contaminating the filtering components, and is more suitable for filtering high-temperature substances. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments.

[0032] Boron carbide ceramics have good acid and alkali resistance and a small thermal expansion coefficient, so they have good thermal stability and a very large neutron absorption cross-section. They are the only choice for nuclear-grade filter plates and for treating nuclear contaminated wastewater. At the same time, it is precisely because of this that boron carbide ceramics have poor sintering properties and need to be heated to at least 2000°C for a sintering liquid phase to appear. The sintering cost is too high. At the same time, such a high temperature is not easy to control, which leads to deformation during the sintering process and a high scrap rate, which also limits the production of boron carbide ceramic filter plates. When conducting research in this field, the inventors found that the interface reaction between aluminum and boron carbide ceramics can form intermetallic compounds. Although the aluminum-boron intermetallic compound is slightly weaker than sintered boron carbide in bending strength, it is fully capable of meeting the use requirements of the filter plate. Therefore, a method for preparing the boron carbide ceramic filter plate was invented.

[0033] The preparation method of the boron carbide ceramic filter plate mainly comprises mixing boron carbide ceramic and aluminum by ball milling.

[0034] A method for preparing a boron carbide ceramic filter plate comprises the following steps:

[0035] Step S1: pretreatment of boron carbide raw materials;

[0036] First, stir and soak the boron carbide powder in 1 mol / L hydrochloric acid for 20 minutes, then rinse with anhydrous ethanol for 3-5 times, and dry in a vacuum oven at 90℃-100℃ for 2 hours.

[0037] Step S2: mixing, ball milling and granulation;

[0038] Boron carbide powder and aluminum powder are mixed and ball-milled and granulated to obtain a mixture; the aluminum powder accounts for 21%-35% of the total mass of the mixture; too much aluminum powder will cause the filter holes to be blocked and reduce the filtration efficiency of the filter holes, while too little aluminum powder will deteriorate the sintering performance and the strength of the filter plate after sintering will be poor;

[0039] Step S3: forming and sintering;

[0040] The mixed material in step S2 is placed in a mold for forming, and the temperature is raised to 1200° C. for sintering in an inert atmosphere. The boron carbide particles are connected via the aluminum-boron intermetallic compound to form an integrated filter plate. The sintering process is heat-insulated in stages, and after the heat-insulation is completed, the mixture is cooled with the furnace to obtain a boron carbide ceramic filter plate.

[0041] During the powder preparation and pretreatment process, oxides or impurities on the surface of boron carbide are removed to prevent this component from affecting product quality. During the ball milling process, the oxide layer on the surface of the aluminum powder is also destroyed, so that boron carbide is fully in contact with aluminum to form an intermetallic compound of aluminum and boron carbide. The staged insulation makes the contact between boron carbide and aluminum better, the interface reaction is more complete, and the prepared filter plate has stronger performance. When the temperature is high, aluminum and boron carbide contact to form mutual filling, and then produce an intermetallic compound with a higher melting point in the mutually filled part. Although the intermetallic compound is usually brittle compared to boron carbide, the inventor has tested that its strength exceeds the strength standard required for the filter plate and can be suitable for the preparation of boron carbide ceramic filter plates.

[0042] The stage insulation includes at least the following processes:

[0043] The first stage: heating up to 650-700℃ at a rate of 10-20℃ / min, and keeping warm for 1-2h; quickly reaching the liquidus point of aluminum, so that aluminum contacts boron carbide;

[0044] The second stage: the temperature is raised to 850-900℃ at a rate of 5-10℃ / min and kept at this temperature for 3-5h to strengthen the reaction connection between aluminum and boron carbide and promote the rapid consumption of aluminum to generate more aluminum-boron intermetallic compounds and reduce the retention of single substances, so as to produce a better phase conversion effect in the third stage sintering process and realize the network connection between boron carbide particles;

[0045] The third stage: the temperature is raised to 1175-1200℃ at a rate of 5-10℃ / min, and kept at this temperature for 3-5h. The intermetallic compounds are transformed into each other, and AlB 2 、Al 3 BC to AlB 12 , forming a hard and stable high-temperature sintered component;

[0046] The three-stage sintering temperature is no higher than 1200°C, which can reduce the sintering energy consumption. In addition, due to the three-stage sintering, the generation of intermetallic compounds is completed in the first and second stages, and the connection between the boron carbide particles is achieved. Therefore, when the temperature is increased in the third stage, the deformation is small, the filter plate size is stable, and the scrap rate is low.

[0047] In order to make the size of the filter plate more stable and the filter aperture smaller, in step S2, after the first stage is completed, although the aluminum powder has already appeared in liquid phase, it is molded again. The molding pressure is 20MPa and the duration is 1-2min. Both moldings are carried out in a graphite mold to further compress the filter plate and reduce its filter aperture, so that a larger area of ​​contact is formed between aluminum and boron carbide.

[0048] The boron carbide powder is compounded by particles of two particle size ranges, wherein the particle size of the small particle size is 6-10 microns, and the particle size of the large particle size is 25-38 microns, wherein the small particle size particles account for 20%, and the large particle size particles account for 80%. The materials of different particle sizes are filled to form a more compact filtering structure and reduce the filtering pore size.

[0049] In another embodiment of the present invention, step S3 is also included: alkaline leaching, wherein the boron carbide ceramic filter plate of step S2 is placed in an aqueous solution containing 20%wt sodium hydroxide and 3%wt potassium nitrate and soaked for 2-4 hours, and then cleaned with distilled water.

[0050] The above scheme removes the residual aluminum in the filter plate and dredges the filter pores, and is particularly suitable for filtering strong alkali or high-temperature corrosive fluids.

[0051] Embodiment 1:

[0052] Boron carbide particles with particle sizes of 6 microns and 25 microns are selected and mixed into boron carbide powder in a mass ratio of 2:8. The boron carbide powder is first stirred and immersed in 1 mol / L hydrochloric acid for 20 minutes, then rinsed with anhydrous ethanol for 3-5 times, vacuum dried at 90℃-100℃ for 2 hours, and then added with flaky aluminum powder with a mass percentage of 54% of the boron carbide material after cooling, and then added into a ball mill, and water and a binder are added for ball milling. The ratio of large balls, medium balls and small balls in the ball mill is 3:3:4, and the material-to-ball ratio is 3:1. After ball milling, spray granulation is performed.

[0053] The spray granulated particles are placed in a graphite mold for molding at a pressure of 130MPa for 1.5 minutes. The graphite mold and the material are then placed in an inert atmosphere protected sintering furnace for sintering. The temperature is raised to 650±10°C at a heating rate of 10-20°C / min and kept warm for 2 hours to cause the aluminum powder to melt to form a liquid phase and fully infiltrate with boron carbide. The temperature is then raised to 880±10°C at a heating rate of 5-10°C / min and kept warm for 3 hours to accelerate the interface reaction between aluminum and boron carbide, so that the aluminum powder is consumed completely to produce an aluminum-boron metal intermediate compound, so that the boron carbide particles are combined into the matrix of the filter plate. Finally, the temperature is raised to 1175-1200°C at a heating rate of 5-10°C / min and kept warm for 3 hours to transform the aluminum-boron metal intermediate compound into a high-boron phase and improve the binding force.

[0054] After the graphite mold and the filter plate substrate are cooled to room temperature in the furnace, the filter plate substrate is taken out and immersed in an aqueous solution containing 20% ​​wt sodium hydroxide and 3% wt potassium nitrate for 2 hours to remove aluminum precipitated by high temperature reaction, and the performance thereof is tested.

[0055] After testing, the flexural strength of the obtained filter plate was 25.81 MPa and the porosity was 46.2%.

[0056] Embodiment 2:

[0057] Boron carbide particles with particle sizes of 8 microns and 30 microns are selected and mixed into boron carbide powder in a mass ratio of 2:8. The boron carbide powder is first stirred and immersed in 1 mol / L hydrochloric acid for 20 minutes, then rinsed with anhydrous ethanol for 3-5 times, vacuum dried at 90℃-100℃ for 2 hours, and then added with flaky aluminum powder with a mass percentage of 36% of the boron carbide material after cooling, and then added into a ball mill, and water and a binder are added for ball milling. The ratio of large balls, medium balls and small balls in the ball mill is 3:3:4, and the material-to-ball ratio is 3:1. After ball milling, spray granulation is performed.

[0058] The spray granulated particles are placed in a graphite mold for molding at a pressure of 100MPa for 2 minutes. The graphite mold and the material are then placed in an inert atmosphere protected sintering furnace for sintering. The temperature is raised to 680±10℃ at a heating rate of 10-20℃ / min and kept warm for 2 hours to cause the aluminum powder to melt to form a liquid phase and fully infiltrate with boron carbide. The graphite mold is then taken out while hot and molded again at a pressure of 20MPa for 1 minute. The graphite mold is placed back in the sintering furnace and heated to 900±10℃ at a heating rate of 5-10℃ / min and kept warm for 3 hours to accelerate the interface reaction between aluminum and boron carbide, so that the aluminum powder is consumed completely, an aluminum-boron metal intermediate compound is generated, and the boron carbide particles are combined into the matrix of the filter plate. Finally, the temperature is raised to 1175-1200℃ at a heating rate of 5-10℃ / min and kept warm for 4 hours to transform the aluminum-boron metal intermediate compound into a high boron phase and improve the binding force.

[0059] After the graphite mold and the filter plate substrate are cooled to room temperature in the furnace, the filter plate substrate is taken out and soaked for 2 hours. The filter plate substrate is placed in an aqueous solution containing 20% ​​wt sodium hydroxide and 3% wt potassium nitrate and soaked for 3 hours to remove aluminum precipitated by high temperature reaction, and its performance is tested.

[0060] After testing, the flexural strength of the obtained filter plate was 26.87 MPa and the porosity was 44.4%.

[0061] Embodiment three:

[0062] Boron carbide particles with particle sizes of 10 microns and 38 microns are selected and mixed into boron carbide powder in a mass ratio of 2:8. The boron carbide powder is first stirred and immersed in 1 mol / L hydrochloric acid for 20 minutes, then rinsed with anhydrous ethanol for 3-5 times, vacuum dried at 90℃-100℃ for 2 hours, and then added with flaky aluminum powder with a mass percentage of 27% of the boron carbide material after cooling, and then added into a ball mill, and water and a binder are added for ball milling. The ratio of large balls, medium balls and small balls in the ball mill is 3:3:4, and the material-to-ball ratio is 3:1. After ball milling, spray granulation is performed.

[0063] The spray granulated particles are placed in a graphite mold for molding at a pressure of 150MPa for 1 minute. The graphite mold and the material are then placed in an inert atmosphere protected sintering furnace for sintering. The temperature is raised to 700±10°C at a heating rate of 10-20°C / min and kept warm for 1 hour to cause the aluminum powder to melt to form a liquid phase and fully infiltrate with boron carbide. The temperature is then raised to 850±10°C at a heating rate of 5-10°C / min and kept warm for 3 hours to accelerate the interface reaction between aluminum and boron carbide, so that the aluminum powder is consumed completely to produce an aluminum-boron metal intermediate compound, so that the boron carbide particles are combined into the matrix of the filter plate. Finally, the temperature is raised to 1175-1200°C at a heating rate of 5-10°C / min and kept warm for 5 hours to transform the aluminum-boron metal intermediate compound into a high-boron phase and improve the binding force.

[0064] After the graphite mold and the filter plate substrate were cooled to room temperature in the furnace, the filter plate substrate was taken out and its performance was tested. The test showed that the bending strength of the obtained filter plate was 21.98 MPa and the porosity was 47.1%.

[0065] Embodiment 4:

[0066] Boron carbide particles with particle sizes of 6 microns and 38 microns are selected and mixed into boron carbide powder in a mass ratio of 2:8. The boron carbide powder is first stirred and immersed in 1 mol / L hydrochloric acid for 20 minutes, then rinsed with anhydrous ethanol for 3-5 times, vacuum dried at 90℃-100℃ for 2 hours, and then added with flaky aluminum powder with a mass percentage of 54% of the boron carbide material after cooling, and then added into a ball mill, and water and a binder are added for ball milling. The ratio of large balls, medium balls and small balls in the ball mill is 3:3:4, and the material-to-ball ratio is 3:1. After ball milling, spray granulation is performed.

[0067] The spray granulated particles are placed in a graphite mold for molding at a pressure of 100MPa for 2 minutes. Then the graphite mold and the material are placed in a sintering furnace protected by an inert atmosphere for sintering. The temperature is raised to 650±10℃ at a heating rate of 10-20℃ / min and kept warm for 2 hours to cause the aluminum powder to melt to form a liquid phase and fully infiltrate with boron carbide. Then the graphite mold is taken out while hot and molded again at a pressure of 20MPa for 1 minute. The graphite mold is placed in the sintering furnace again and heated to 900±10℃ at a heating rate of 5-10℃ / min. The temperature is kept warm for 3 hours to accelerate the interface reaction between aluminum and boron carbide, so that the aluminum powder is consumed completely, and an aluminum-boron metal intermediate compound is produced, so that the boron carbide particles are combined into the matrix of the filter plate. Finally, the temperature is raised to 1175-1200℃ at a heating rate of 5-10℃ / min and kept warm for 3 hours to transform the aluminum-boron metal intermediate compound into a high-boron phase and improve the binding force.

[0068] After the graphite mold and the filter plate substrate were cooled to room temperature in the furnace, the filter plate substrate was taken out and its performance was tested. The test showed that the bending strength of the obtained filter plate was 25.95 MPa and the porosity was 43.7%.

[0069] Embodiment five:

[0070] Boron carbide particles with particle sizes of 8 microns and 25 microns are selected and mixed into boron carbide powder in a mass ratio of 2:8. The boron carbide powder is first stirred and immersed in 1 mol / L hydrochloric acid for 20 minutes, then rinsed with anhydrous ethanol for 3-5 times, vacuum dried at 90℃-100℃ for 2 hours, and then added with flaky aluminum powder with a mass percentage of 36% of the boron carbide material after cooling, and then added into a ball mill, and water and a binder are added for ball milling. The ratio of large balls, medium balls and small balls in the ball mill is 3:3:4, and the material-to-ball ratio is 3:1. After ball milling, spray granulation is performed.

[0071] The spray granulated particles are placed in a graphite mold for molding at a pressure of 130MPa for 1.5 minutes. The graphite mold and the material are then placed in an inert atmosphere protected sintering furnace for sintering. The temperature is raised to 700±10℃ at a heating rate of 10-20℃ / min and kept warm for 1 hour to cause the aluminum powder to melt to form a liquid phase and fully infiltrate with boron carbide. The temperature is then raised to 880±10℃ at a heating rate of 5-10℃ / min and kept warm for 3 hours to accelerate the interface reaction between aluminum and boron carbide, so that the aluminum powder is consumed completely to produce aluminum-boron metal intermediate compounds, so that the boron carbide particles are combined into the matrix of the filter plate. Finally, the temperature is raised to 1175-1200℃ at a heating rate of 5-10℃ / min and kept warm for 4 hours to transform the aluminum-boron metal intermediate compounds into high-boron phases and improve the binding force.

[0072] After the graphite mold and the filter plate substrate are cooled to room temperature in the furnace, the filter plate substrate is taken out and immersed in an aqueous solution containing 20% ​​wt sodium hydroxide and 3% wt potassium nitrate for 4 hours to remove aluminum precipitated by high temperature reaction, and the performance thereof is tested.

[0073] After testing, the flexural strength of the obtained filter plate was 25.03 MPa and the porosity was 48.9%.

[0074] Embodiment six:

[0075] Boron carbide particles with particle sizes of 10 microns and 30 microns are selected and mixed into boron carbide powder in a mass ratio of 2:8. The boron carbide powder is first stirred and immersed in 1 mol / L hydrochloric acid for 20 minutes, then rinsed with anhydrous ethanol for 3-5 times, vacuum dried at 90℃-100℃ for 2 hours, and then added with flaky aluminum powder with a mass percentage of 27% of the boron carbide material after cooling, and then added into a ball mill, and water and a binder are added for ball milling. The ratio of large balls, medium balls and small balls in the ball mill is 3:3:4, and the material-to-ball ratio is 3:1. After ball milling, spray granulation is performed.

[0076] The spray granulated particles are placed in a graphite mold for molding at a pressure of 100MPa for 2 minutes. The graphite mold and the material are then placed in an inert atmosphere protected sintering furnace for sintering. The temperature is raised to 680±10℃ at a heating rate of 10-20℃ / min and kept warm for 2 hours to cause the aluminum powder to melt to form a liquid phase and fully infiltrate with boron carbide. The graphite mold is then taken out while hot and molded again at a pressure of 20MPa for 1 minute. The graphite mold is then placed in the sintering furnace again and heated to 880±10℃ at a heating rate of 5-10℃ / min and kept warm for 5 hours to accelerate the interface reaction between aluminum and boron carbide, so that the aluminum powder is consumed completely, an aluminum-boron metal intermediate compound is generated, and the boron carbide particles are combined into the matrix of the filter plate. Finally, the temperature is raised to 1175-1200℃ at a heating rate of 5-10℃ / min and kept warm for 5 hours to transform the aluminum-boron metal intermediate compound into a high boron phase and improve the binding force.

[0077] After the graphite mold and the filter plate substrate are cooled to room temperature in the furnace, the filter plate substrate is taken out and immersed in an aqueous solution containing 20% ​​wt sodium hydroxide and 3% wt potassium nitrate for 3 hours to remove aluminum precipitated by high temperature reaction, and the performance thereof is tested.

[0078] After testing, the flexural strength of the obtained filter plate was 21.52 MPa and the porosity was 46.5%.

[0079] Embodiment seven:

[0080] Boron carbide particles with particle sizes of 8 microns and 30 microns are selected and mixed into boron carbide powder in a mass ratio of 2:8. The boron carbide powder is first stirred and immersed in 1 mol / L hydrochloric acid for 20 minutes, then rinsed with anhydrous ethanol for 3-5 times, vacuum dried at 90℃-100℃ for 2 hours, and then added with flaky aluminum powder with a mass percentage of 36% of the boron carbide material after cooling, and then added into a ball mill, and water and a binder are added for ball milling. The ratio of large balls, medium balls and small balls in the ball mill is 3:3:4, and the material-to-ball ratio is 3:1. After ball milling, spray granulation is performed.

[0081] The spray granulated particles are placed in a graphite mold for molding at a pressure of 100MPa for 2 minutes. The graphite mold and the material are then placed in an inert atmosphere protected sintering furnace for sintering. The temperature is raised to 680±10℃ at a heating rate of 10-20℃ / min and kept warm for 2 hours to cause the aluminum powder to melt to form a liquid phase and fully infiltrate with boron carbide. The graphite mold is then taken out while hot and molded again at a pressure of 20MPa for 2 minutes. The graphite mold is placed back in the sintering furnace and heated to 900±10℃ at a heating rate of 5-10℃ / min for 3 hours to accelerate the interface reaction between aluminum and boron carbide, so that the aluminum powder is consumed completely, an aluminum-boron metal intermediate compound is generated, and the boron carbide particles are combined into the matrix of the filter plate. Finally, the temperature is raised to 1175-1200℃ at a heating rate of 5-10℃ / min and kept warm for 1.5 hours to transform the aluminum-boron metal intermediate compound into a high boron phase and improve the binding force.

[0082] After the graphite mold and the filter plate substrate were cooled to room temperature in the furnace, the filter plate substrate was taken out and its performance was tested. The test showed that the bending strength of the obtained filter plate was 16.82 MPa and the porosity was 45.1%.

[0083] Embodiment eight:

[0084] Boron carbide particles with particle sizes of 8 microns and 30 microns are selected and mixed into boron carbide powder in a mass ratio of 2:8. The boron carbide powder is first stirred and immersed in 1 mol / L hydrochloric acid for 20 minutes, then rinsed with anhydrous ethanol for 3-5 times, vacuum dried at 90℃-100℃ for 2 hours, and then added with flaky aluminum powder with a mass percentage of 36% of the boron carbide material after cooling, and then added into a ball mill, and water and a binder are added for ball milling. The ratio of large balls, medium balls and small balls in the ball mill is 3:3:4, and the material-to-ball ratio is 3:1. After ball milling, spray granulation is performed.

[0085] The spray granulated particles are placed in a graphite mold for molding at a pressure of 100MPa for 2 minutes. The graphite mold and the material are then placed in an inert atmosphere protected sintering furnace for sintering. The temperature is raised to 680±10℃ at a heating rate of 10-20℃ / min and kept warm for 2 hours to cause the aluminum powder to melt to form a liquid phase and fully infiltrate with boron carbide. The graphite mold is then taken out while hot and molded again at a pressure of 20MPa for 2 minutes. The graphite mold is placed back in the sintering furnace and heated to 900±10℃ at a heating rate of 5-10℃ / min and kept warm for 3 hours to accelerate the interface reaction between aluminum and boron carbide, so that the aluminum powder is consumed completely, an aluminum-boron metal intermediate compound is generated, and the boron carbide particles are combined into the matrix of the filter plate. Finally, the temperature is raised to 1175-1200℃ at a heating rate of 5-10℃ / min and kept warm for 7 hours to transform the aluminum-boron metal intermediate compound into a high boron phase and improve the binding force.

[0086] After the graphite mold and the filter plate substrate are cooled to room temperature in the furnace, the filter plate substrate is taken out and immersed in an aqueous solution containing 20% ​​wt sodium hydroxide and 3% wt potassium nitrate for 3 hours to remove aluminum precipitated by high temperature reaction, and the performance thereof is tested.

[0087] After testing, the flexural strength of the obtained filter plate was 26.64 MPa and the porosity was 46.5%.

[0088] In the above tests, the flexural strength was tested using the RH-T300 flexural strength tester, and the porosity was tested using the T / CSTM00553-2022 lightweight porous material porosity determination method.

[0089] It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention.

Claims

1. A method for preparing a boron carbide ceramic filter plate, characterized in that: The following steps are involved: Step S1: pretreatment of boron carbide raw materials; Step S2: mixing, ball milling and granulation; The boron carbide powder pretreated in step S1 is mixed with aluminum powder for ball milling and granulation to obtain a mixture, wherein the aluminum powder accounts for 21% to 35% of the total mass of the mixture; Step S3: forming and sintering; The mixed material in step S2 is placed in a mold for forming, and the temperature is raised to 1200° C. for sintering in an inert atmosphere. The boron carbide particles are connected via the aluminum-boron intermetallic compound to form an integrated filter plate. The sintering process is heat-insulated in stages, and after the heat-insulation is completed, the mixture is cooled with the furnace to obtain a boron carbide ceramic filter plate.

2. The method for preparing a boron carbide ceramic filter plate according to claim 1, characterized in that: The stage insulation includes at least the following processes: The first stage: the temperature is kept at 650-700℃ and the holding time is 1-2h; The second stage: the temperature is kept at 850-900℃ and the holding time is 3-5h; The third stage: the insulation node is 1175-1200℃, and the insulation time is 3-5h.

3. The method for preparing a boron carbide ceramic filter plate according to claim 2, characterized in that: In step S3, the forming process includes two molding processes, the first molding process is before the temperature rise sintering, the molding pressure is 100-150MPa, and the second molding process is after the first stage of heat preservation is completed, the molding pressure is 20MPa.

4. The method for preparing a boron carbide ceramic filter plate according to claim 1, characterized in that: The raw material pretreatment steps are as follows: first, the boron carbide powder is stirred and immersed in 1 mol / L hydrochloric acid for 20 minutes, then rinsed with anhydrous ethanol for 3-5 times, and vacuum dried at 90° C.-100° C. for 2 hours.

5. The method for preparing a boron carbide ceramic filter plate according to claim 1, characterized in that: The boron carbide powder is composed of particles of two particle size ranges, wherein the particle size of the small particle size particles is 6-10 microns, and the particle size of the large particle size particles is 25-38 microns, wherein the mass ratio of the small particle size particles to the large particle size particles is 2:

8.

6. The method for preparing a boron carbide ceramic filter plate according to claim 1, characterized in that: The method also includes step S4: alkaline leaching; placing the boron carbide ceramic filter plate of step S2 in an aqueous solution containing 20%wt sodium hydroxide and 3%wt potassium nitrate for immersion and rinsing for 2-4 hours, and then cleaning with distilled water.

7. A boron carbide ceramic filter plate, characterized in that: It is prepared using the preparation method of a boron carbide ceramic filter plate as claimed in any one of claims 1 to 6.

8. The boron carbide ceramic filter plate according to claim 7, characterized in that: The boron carbide ceramic filter plate has a bending strength of 16-27 MPa and a porosity of 43%-50%.