CN118495958A - A method for preparing ceramics by enhanced gel casting - Google Patents

Abstract

The present application relates to a method for preparing ceramics by enhanced gel injection molding, which includes the following steps: centrifuging a modified nanocellulose composite component, mixing the treated modified nanocellulose composite component with deionized water, adding acrylamide and stirring after ultrasound to obtain a suspension, adding N,N'-methylenebisacrylamide, a dispersant, a defoamer and a suspending agent to the suspension, stirring to obtain a premixed liquid; adding ceramic powder and a sintering aid to the premixed liquid, stirring to obtain a prefabricated slurry, ball milling the prefabricated slurry and vacuum degassing, vibrating at a frequency of 5-10Hz during vacuum degassing, and obtaining a slurry after vacuum degassing; adding a catalyst and an initiator to the slurry, stirring and pouring it into a mold, and drying at a constant temperature and humidity after the slurry is formed to obtain a green body; sintering the green body, and obtaining a silicon carbide ceramic product after heat preservation. The present application has the effect of reducing green body cracking and improving product strength.

Description

A method for preparing ceramics by enhanced gel casting

Technical Field

The present application relates to the field of ceramic preparation, and in particular to a method for preparing ceramics by enhanced gel casting.

Background Art

In recent years, new colloidal molding such as filter press molding, direct solidification molding by gel casting molding machine, etc., in-situ curing is an effective method for preparing ceramic parts with high reliability and complex shapes. Gel casting molding has been widely studied in the fields of porous materials, composite materials, and functional materials. Silicon carbide ceramics have excellent room temperature mechanical properties, such as high bending strength, excellent oxidation resistance, good corrosion resistance, high wear resistance, and low friction coefficient, and high temperature mechanical properties (strength, creep resistance, etc.) are the best among known ceramic materials. The high temperature strength of materials sintered by hot pressing, pressureless sintering, and hot isostatic pressing can be maintained up to 1600℃, which is the best high temperature strength among ceramic materials. Therefore, its products are widely used in the heating and heat exchange industry.

However, microcracks and deformations often occur during gel injection molding. The biggest reason is that the gel drying conditions are harsh. In order to sinter ceramics to dense density, ultrafine powders are often used as the main raw material. It is difficult to obtain slurries with high solid content of ultrafine powders. For example, pressureless sintered silicon carbide is basically ultrafine powder. Even after powder modification, the solid content can only be about 55% (VOL). The strength of the wet blank is very low and it is easy to crack. Therefore, for the preparation of ceramics by gel injection molding, obtaining enhanced gel and then solving the problem of gel injection cracking are important core issues.

Summary of the invention

In order to reduce the cracking phenomenon of gel-casting ceramics, the present application provides a method for preparing ceramics by enhanced gel-casting.

The present application provides a method for preparing ceramics by enhanced gel casting, which adopts the following technical scheme:

A method for preparing ceramics by enhanced gel casting, comprising the following steps:

Preparing a premixed liquid: subjecting the modified nanocellulose composite component to high-speed centrifugation to obtain a treated modified nanocellulose composite component, mixing the treated modified nanocellulose composite component with deionized water, adding acrylamide to the suspension after ultrasonication to obtain a suspension, adding N,N'-methylenebisacrylamide, a dispersant, a defoaming agent and a suspending agent to the suspension, and stirring to obtain a premixed liquid;

Prepare slurry: add ceramic powder and sintering aid to the premixed liquid obtained above, stir to obtain prefabricated slurry, ball-mill the prefabricated slurry and vacuum degassing, vibrate at a frequency of 5-10 Hz during vacuum degassing, and obtain slurry after vacuum degassing;

Preparation of green body: adding catalyst and initiator to slurry, stirring and pouring into mold, drying at constant temperature and humidity after the slurry is formed to obtain green body;

Preparation of silicon carbide ceramics: The green body is sintered and kept warm to obtain a silicon carbide ceramic product.

By adopting the above technical scheme, the strength of the wet green body prepared by this method is improved, the modified nanocellulose composite component has good mechanical properties, and a stable gel network structure is formed between the pores of the gel network structure. Fine fiber filaments exist between the pores, so that the slurries can have better contact, the connection tightness between the green bodies formed by the gel columns is effectively improved, and the cracking phenomenon of the green body formed by the prepared gel injection molding is improved, thereby improving the quality and strength of the prepared silicon carbide ceramic product.

Preferably, the sintering aid comprises one of carbon black and boron carbide or a mixture of the two, and the silicon carbide ceramic powder comprises one of primary silicon carbide powder particles and secondary silicon carbide powder particles or a mixture of the two.

Preferably, in the step of preparing silicon carbide ceramics, the green body is sintered by pressureless sintering; the mass ratio of the silicon carbide ceramic powder, carbon black and boron carbide is (48-49):1:0.3.

Preferably, in the step of preparing silicon carbide ceramics, the green body is sintered by reaction sintering; the mass ratio of the primary carbide powder particles, the secondary silicon carbide powder particles and the sintering aid is 1.5:1:(0.25-0.3).

By adopting the above technical scheme, the present method can be used to prepare pressureless sintered silicon carbide ceramics, and can also be used to prepare reaction sintered structural ceramics of various materials such as silicon carbide, silicon nitride, and alumina; under different sintering methods, different sintering aids are preferably mixed with silicon carbide ceramic powder, the stability of the prepared slurry is improved, and the quality and strength of the ceramic silicon carbide product obtained in the subsequent sintering process can also be further improved.

Preferably, the content of acrylamide accounts for 0.03-0.05% of the total weight of the slurry, the content of the catalyst accounts for 0.005-0.007% of the total weight of the green body, and the content of the initiator accounts for 0.03-0.05% of the total weight of the green body.

By adopting the above technical solution, each component in the preferred system is within the above mass range, which can effectively improve the stability of the prepared green body, thereby improving the quality of the prepared ceramic product.

Preferably, the modified nanocellulose composite component accounts for 12-14% of the total mass of the pulp.

By adopting the above technical solution, the proportion of the modified nanocellulose component is preferably within the above range, which can further improve the stability and product strength of the prepared slurry.

Preferably, the modified nanocellulose composite component comprises hydroxylated boron nitride, nanocellulose and polyethyleneimine.

By adopting the above technical scheme, hydroxylated boron carbide has a layered structure with high thermal conductivity, thermal stability and antioxidant properties; nanocellulose has the advantages of biodegradability, renewability and excellent mechanical properties, which can make the connection between the various components in the slurry more tightly; polyethyleneimine is a branched polymer with a large number of amino groups on the molecular chain, which has the advantages of functional filler and improved interface performance of composite materials. The combination of the three can synergistically improve the overall strength of the modified nanocellulose composite component, and improve the stability of the prepared nanocellulose composite component, thereby making the combination between the various components in the green body tighter, thereby improving the product quality and strength of the prepared green body material.

Preferably, the modified nanocellulose is prepared by the following method:

The nanocellulose is mixed with deionized water to obtain a nanocellulose suspension, hydroxylated boron nitride is added, a composite dispersion is obtained after ultrasonic treatment, and a nanocellulose-boron nitride composite material is obtained after filtration and drying;

After the pH value of polyethyleneimine is adjusted to alkaline, a nanocellulose-boron nitride composite material is added, the temperature is raised, the reaction is stirred, and centrifugation is performed to obtain a prefabricated composite material. The prefabricated composite material is mixed with deionized water, filtered, suction filtered, and freeze-dried to obtain modified nanocellulose.

By adopting the above technical scheme, nanocellulose and hydroxylated boron nitride are compounded to prepare a nanocellulose-boron nitride composite material, so that the compatibility between nanocellulose and hydroxylated boron nitride is improved, and the overall stability of the system can be further improved; the nanocellulose-boron nitride composite material is modified to polyethyleneimine, so that a large number of amino groups are attached to the surface of the nanocellulose-boron nitride composite feed, the hydrogen bond density is reduced, the overall stability of the modified nanocellulose is improved, and the strength of the composite material is enhanced, thereby improving the quality of the prepared ceramic product.

Preferably, the mass ratio of hydroxyboron nitride, nanocellulose and polyethyleneimine is (0.42-0.48):1:0.67.

By adopting the above technical solution, preferably the mass ratio of hydroxylated boron nitride, nanocellulose and polyethyleneimine is within the above range, which can further improve the stability of the prepared nanocellulose composite material.

Preferably, the hydroxylated boron nitride is prepared by the following method:

The boron nitride is mixed with a sodium hydroxide solution for hydrolysis, and then mixed with deionized water after centrifugal washing, and then centrifuged after ultrasonication. The supernatant is filtered and dried to obtain hydroxylated boron nitride.

By adopting the above technical scheme, boron nitride is subjected to alkali treatment and combined with liquid-assisted ultrasound to prepare hydroxylated boron nitride, and the hydroxyl functional groups are modified on the surface, which improves the dispersibility of boron nitride in the system and improves the compatibility between boron nitride, nanocellulose and polyethyleneimine, so as to further improve the compactness of the prepared slurry, thereby improving the quality and strength of ceramic products.

In summary, the present application includes at least one of the following beneficial technical effects:

Adding modified nanocellulose composite components to the slurry, a stable gel network structure is constructed between the slurries. There are fine fiber filaments between the gaps in the gel network structure, so that the connection tightness between the various components of the slurry system is improved, so as to improve the cracking phenomenon of the green body formed by gel injection molding, and further improve the strength and quality of ceramic products;

The present application can prepare pressureless sintered silicon carbide ceramics, and can also prepare reaction sintered structural ceramics of various materials such as silicon carbide, silicon nitride, and alumina. By adjusting the components and proportions of the sintering aid and the silicon carbide ceramic powder to adapt to different sintering conditions, the prepared wet green body has high strength and strong stability.

The modified nanocellulose component prepared by compounding hydroxylated boron nitride, nanocellulose and polyethyleneimine can synergistically improve the strength of the green body. The components in the green body are more tightly bound and can be dispersed more evenly in the system, thereby improving the stability of the green body and further improving the quality of the prepared ceramic products.

DETAILED DESCRIPTION

The present application is further described in detail below with reference to the embodiments:

Material description: The dispersant is a mixture of DolaPIX CE 64 and MQ-5088 in a mass ratio of 1:1; the defoamer is n-octanol (CAS No.: 111-87-5); the suspending agent is MQ-818; the catalyst is tetramethylethylenediamine; the initiator is a 5% ammonium persulfate aqueous solution; the length of the nanocellulose is 400-500nm, the width is 4-5nm, and the aspect ratio is 80-125.

Example

Preparation of Nanocomposite Cellulose Components:

The boron nitride powder was dispersed in a 5 mol/L sodium hydroxide solution, hydrolyzed at 120°C for 24 hours, centrifuged after hydrolysis, and repeatedly washed three times with deionized water to remove residual sodium hydroxide. The washed boron nitride powder was dispersed in 800 ml of deionized water and ultrasonically treated in an ultrasonic disperser for 16 hours. After the ultrasonic treatment, the obtained suspension was centrifuged at 2000 rpm for 5 minutes to remove the unpeeled boron nitride. The obtained supernatant was vacuum filtered and dried at 60°C for 12 hours to obtain hydroxylated boron nitride.

239.23 g of nanocellulose was dispersed in deionized water, stirred at a speed of 500 rpm for 30 min and ultrasonically treated for 5 min to obtain a nanocellulose dispersion, 100.48 g of the prepared hydroxylated boron nitride was added to the nanocellulose dispersion, stirred at a speed of 500 rpm for 60 min, and then ultrasonically treated for 30 min to obtain a mixed solution, the mixed solution was filtered through a cellulose acetate microporous filter membrane with a pore size of 0.22 μm, and vacuum-assisted filtration was performed, and the obtained solid was dried at 60° C. for 12 h to obtain a boron nitride-nanocellulose composite component.

The pH value of 160.29 g of polyethyleneimine was adjusted to 10, the boron nitride-nanocellulose composite component prepared above was mixed with 1000 ml of deionized water, and polyethyleneimine was added, the temperature was raised to 100°C and stirred at 200 rpm for 10 hours, the reaction solution was centrifuged for 10 minutes, the supernatant was drained, and the reaction was repeated 3 times. 1000 ml of deionized water was added again to disperse, and the mixture was filtered through a 100 nm filter membrane, and then transferred to a -20°C environment for freeze-drying for 24 hours to obtain a nano-composite cellulose component.

Enhanced gel casting ceramics are prepared by the following method:

Preparation of a premix: high-speed centrifugation of 240 g of the composite nanocellulose component at a speed of 12500 r/min for 10 min to obtain a treated composite nanocellulose component, mix the treated composite nanocellulose component with 300 g of deionized water, ultrasonically oscillate for 20 min, add 56 g of acrylamide, continue stirring for 2 h to obtain a suspension, add 8 g of N,N'-methylenebisacrylamide, 40 g of a dispersant, 10 g of a defoaming agent and 10 g of a suspending agent to the suspension in sequence, stir for 2 h to obtain a premix.

Preparation of slurry: Add 768g of F240 silicon carbide powder, 512g of F1200 silicon carbide powder and 153.6g of carbon black to the premixed liquid in sequence, stir at a speed of 2000rpm for 15min to obtain a pre-made slurry, ball mill the pre-made slurry for 12h at a ball milling speed of 50r/min, then vacuum degasse for 10min, and vibrate at a frequency of 5Hz while degassing to obtain a slurry.

Preparation of green body: Add 0.1g catalyst and 0.8g initiator to the slurry, stir at 6000rpm for 3min at 15℃, pour into the mold to form, keep the formed green body at 40℃ and 40% humidity to dry, the drying system is from low temperature and high humidity to low humidity and high temperature to obtain green body.

Preparation of silicon carbide ceramics: The dried green body is sintered at 1700°C and kept warm for 5 hours to obtain a silicon carbide ceramic product.

Example

Preparation of Nanocomposite Cellulose Components:

The boron nitride powder was dispersed in a 5 mol/L sodium hydroxide solution, hydrolyzed at 120°C for 24 hours, centrifuged after hydrolysis, and repeatedly washed three times with deionized water to remove residual sodium hydroxide. The washed boron nitride powder was dispersed in 800 ml of deionized water and ultrasonically treated in an ultrasonic disperser for 16 hours. After the ultrasonic treatment, the obtained suspension was centrifuged at 2000 rpm for 5 minutes to remove the unpeeled boron nitride. The obtained supernatant was vacuum filtered and dried at 60°C for 12 hours to obtain hydroxylated boron nitride.

232.56 g of nanocellulose was dispersed in deionized water, stirred at a speed of 500 rpm for 30 min and ultrasonically treated for 5 min to obtain a nanocellulose dispersion, 111.63 g of hydroxylated boron nitride was added to the nanocellulose dispersion, stirred at a speed of 500 rpm for 60 min, and then ultrasonically treated for 30 min to obtain a mixed solution, the mixed solution was filtered through a cellulose acetate microporous filter membrane with a pore size of 0.22 μm, and vacuum-assisted filtration was performed, and the obtained solid was dried at 60° C. for 12 h to obtain a boron nitride-nanocellulose composite component.

The pH value of 155.81 g of polyethyleneimine was adjusted to 10, the boron nitride-nanocellulose composite component prepared above was mixed with 1000 ml of deionized water, and polyethyleneimine was added, the temperature was raised to 100°C and stirred at 200 rpm for 10 hours, the reaction solution was centrifuged for 10 minutes, the supernatant was drained, and the reaction was repeated 3 times. 1000 ml of deionized water was added again to disperse, and the mixture was filtered through a 100 nm filter membrane, and then transferred to a -20°C environment for freeze-drying for 24 hours to obtain a nano-composite cellulose component.

Enhanced gel casting ceramics are prepared by the following method:

Preparation of a premix: high-speed centrifugation of 350 g of the composite nanocellulose component at a speed of 12500 r/min for 10 min to obtain a treated composite nanocellulose component, mix the treated composite nanocellulose component with 350 g of deionized water, ultrasonically oscillate for 20 min, add 100 g of acrylamide, continue stirring for 2 h to obtain a suspension, add 10 g of N,N'-methylenebisacrylamide, 125 g of a dispersant, 17.5 g of a defoaming agent and 12.5 g of a suspending agent to the suspension in sequence, stir for 2 h to obtain a premix.

Preparation of slurry: 882.6 g of F240 silicon carbide powder, 588.4 g of F1200 silicon carbide powder and 176.52 g of carbon black were added to the premixed liquid in sequence, stirred at a speed of 2000 rpm for 30 min to obtain a pre-made slurry, and the pre-made slurry was ball-milled for 16 h at a ball-milling speed of 30 r/min, followed by vacuum degassing for 10 min, and vibrated at a frequency of 10 Hz while degassing to obtain a slurry.

Preparation of green body: Add 0.125g catalyst and 1g initiator to the slurry, stir at 6000rpm for 3min at 15℃, pour into the mold to form, keep the formed green body at 40℃ and 40% humidity to dry, the drying system is from low temperature and high humidity to low humidity and high temperature to obtain green body.

Preparation of silicon carbide ceramics: The dried green body is sintered at 1710°C and kept warm for 2 hours to obtain a silicon carbide ceramic product.

Example

Preparation of Nanocomposite Cellulose Components:

The boron nitride powder was dispersed in a 5 mol/L sodium hydroxide solution, hydrolyzed at 120°C for 24 hours, centrifuged after hydrolysis, and repeatedly washed three times with deionized water to remove residual sodium hydroxide. The washed boron nitride powder was dispersed in 800 ml of deionized water and ultrasonically treated in an ultrasonic disperser for 16 hours. After the ultrasonic treatment, the obtained suspension was centrifuged at 2000 rpm for 5 minutes to remove the unpeeled boron nitride. The obtained supernatant was vacuum filtered and dried at 60°C for 12 hours to obtain hydroxylated boron nitride.

235.85 g of nanocellulose was dispersed in deionized water, stirred at a speed of 500 rpm for 30 min and ultrasonically treated for 5 min to obtain a nanocellulose dispersion, 106.13 g of hydroxylated boron nitride was added to the nanocellulose dispersion, stirred at a speed of 500 rpm for 60 min, and then ultrasonically treated for 30 min to obtain a mixed solution, the mixed solution was filtered through a cellulose acetate microporous filter membrane with a pore size of 0.22 μm, and vacuum-assisted filtration was performed, and the obtained solid was dried at 60° C. for 12 h to obtain a boron nitride-nanocellulose composite component.

The pH value of 158.02 g of polyethyleneimine was adjusted to 10, the boron nitride-nanocellulose composite component prepared above was mixed with 1000 ml of deionized water, and polyethyleneimine was added, the temperature was raised to 100°C and stirred at 200 rpm for 10 hours, the reaction solution was centrifuged for 10 minutes, the supernatant was drained, and the reaction was repeated 3 times. 1000 ml of deionized water was added again to disperse, and the mixture was filtered through a 100 nm filter membrane, and then transferred to a -20°C environment for freeze-drying for 24 hours to obtain a nano-composite cellulose component.

Enhanced gel casting ceramics are prepared by the following method:

Preparation of a premix: high-speed centrifugation of 322 g of the composite nanocellulose component at a speed of 12500 r/min for 10 min to obtain a treated composite nanocellulose component, mix the treated composite nanocellulose component with 320 g of deionized water, ultrasonically oscillate for 20 min, add 78 g of acrylamide, continue stirring for 2 h to obtain a suspension, add 9.2 g of N,N'-methylenebisacrylamide, 80.5 g of dispersant, 13.8 g of defoaming agent and 11.5 g of suspending agent to the suspension in sequence, stir for 2 h to obtain a premix.

Preparation of slurry: 1368.92 g of silicon carbide ultrafine powder, 28.52 g of carbon black and 8.56 g of boron carbide were added to the premixed liquid in sequence, stirred at a speed of 2000 rpm for 30 min to obtain a pre-made slurry, and the pre-made slurry was ball-milled for 14 h at a ball-milling speed of 40 r/min, followed by vacuum degassing for 10 min, and vibrated at a frequency of 10 Hz during degassing to obtain a slurry.

Preparation of the green body: Add 0.115g of catalyst and 0.92g of initiator to the slurry, stir at 6000rpm for 3min at 15℃, pour into the mold to form, and keep the formed green body at 40℃ and 40% humidity to dry. The drying system is from low temperature and high humidity to low humidity and high temperature to obtain the green body.

Preparation of silicon carbide ceramics: The dried green body is pressurelessly sintered at 2100° C. and kept warm for 3.5 hours to obtain a silicon carbide ceramic product.

Example

Example 4 is based on Example 3. In Example 4, during the preparation of the slurry, 1369.66 g of ultrafine silicon carbide powder, 27.95 g of carbon black, and 8.39 g of boron carbide were added. During the preparation of the silicon carbide ceramic powder, the pressureless sintering temperature was 2200°C.

Example

Example 5 is based on Example 3. The difference between Example 5 and Example 3 is that 7 g of N,N'-methylenebisacrylamide is added in Example 5.

Example

Example 6 is based on Example 3. The difference between Example 6 and Example 3 is that 11 g of N,N'-methylenebisacrylamide is added in Example 6.

Example

Example 7 is based on Example 3. The difference between Example 7 and Example 3 is that 0.05 g of catalyst is added in Example 7.

Example

Example 8 is based on Example 3. The difference between Example 8 and Example 3 is that 0.2 g of catalyst is added in Example 8.

Example

Example 9 is based on Example 3. The difference between Example 9 and Example 3 is that 0.6 g of initiator is added in Example 9.

Example

Example 10 is based on Example 3. The difference between Example 10 and Example 3 is that 1.2 g of initiator is added in Example 10.

Example

Example 11 is based on Example 3. The difference between Example 11 and Example 3 is that when preparing the nano-composite cellulose component in Example 11, 88.67 g of hydroxylated boron carbide, 246.31 g of nanocellulose and 165.02 g of polyethyleneimine are used.

Example

Example 12 is based on Example 3. The difference between Example 12 and Example 3 is that when preparing the nano-composite cellulose component, Example 12 uses 122.18 g of hydroxylated boron carbide, 226.24 g of nanocellulose, and 151.58 g of polyethyleneimine.

Example

Example 13 is based on Example 3. The difference between Example 13 and Example 3 is that in Example 13, polyethyleneimine is not added when preparing the nanocomposite cellulose component.

Example

Example 14 is based on Example 3. The difference between Example 14 and Example 3 is that in Example 14, no hydroxylated boron nitride is added when preparing the nanocomposite cellulose component.

Example

Example 15 is based on Example 3. The difference between Example 15 and Example 3 is that in Example 15, when preparing the nanocomposite cellulose component, hydroxylated boron nitride is replaced by ordinary boron nitride.

Comparative Example 1

Comparative Example 1 is based on Example 3, and in Comparative Example 1, the nanocomposite cellulose component is replaced with ordinary nanocellulose.

Comparative Example 2

Comparative Example 2 is based on Example 3, and in Comparative Example 2, the nanocomposite cellulose component is replaced with an equal amount of deionized water.

Performance testing

The following performance tests were performed on the samples of Examples 1-15 and Comparative Examples 1-2:

(1) Drying performance test: Dry the wet blank and observe and record the condition of the dry blank after drying. The results are recorded in Table 1.

(2) Using GB/T 6569-2006 Fine Ceramics Bending Strength Test Method as the test standard, the samples were tested for bending strength. Each sample was tested three times at room temperature, and the average value was taken. The test results were filled in Table 1.

(3) According to GB 16534-2009 Test method for room temperature hardness of fine ceramics, a Vickers hardness tester was used to test and calculate the Vickers hardness of the sample. Each sample was tested three times and the average value was taken after measurement. The results are recorded in Table 1.

Table 1 Test results of samples of Examples 1-15 and Comparative Examples 1-2

Test items Surface condition after drying Bending strength/MPa Hardness(GPa) Example 1 No cracking 432 twenty four Example 2 No cracking 434 25 Example 3 No cracking 456 28 Example 4 No cracking 458 28 Example 5 No cracking 437 twenty one Example 6 No cracking 433 twenty two Example 7 No cracking 428 twenty one Example 8 No cracking 423 twenty two Example 9 No cracking 424 20 Example 10 No cracking 422 twenty one Embodiment 11 No cracking 425 twenty two Example 12 No cracking 426 20 Example 13 No cracking 422 20 Embodiment 14 No cracking 428 twenty two Embodiment 15 No cracking 425 twenty three Comparative Example 1 Slight cracking 399 18 Comparative Example 2 Cracks and deformation 387 15

Data analysis

As can be seen from Table 1, the green bodies of Examples 1-4 have no cracking after drying, the flexural strength is 430 MPa or above, and the hardness is 24 Gpa or above, indicating that the silicon carbide ceramics prepared in this application have good stability and strength.

It can be seen from Table 1 that when the content of N,N'-methylenebisacrylamide is too high or too low, when the content of the catalyst is too much or too little, when the content of the initiator is too much or too little, the overall stability of the system is affected, thereby reducing the stability of the prepared green body. Therefore, the flexural strength and hardness of Examples 5-10 are slightly reduced.

In Example 11 and Example 12, when preparing the nano-composite cellulose component, the mass ratios of hydroxylated boron carbide, nanocellulose and polyethylene imine are not within the range specified in the present application. When the content of hydroxylated boron nitride is too little, the hydroxyl content in the system decreases, which reduces the dispersion effect of the nano-composite cellulose in the green body and affects the overall uniformity of the system. When the content of hydroxylated boron carbide is too much, it is difficult to further improve the connection tightness between the nano-composite cellulose component and the various components in the system. Therefore, the performance of Example 11 and Example 12 is reduced.

In Example 13, polyethyleneimine was not added, which made it difficult to improve the relationship between hydroxylated boron carbide and nanocellulose, resulting in a decrease in the strength of the nanocomposite cellulose component and reduced stability of the green body. Therefore, various properties of Example 13 were reduced.

In Example 14, hydroxylated boron carbide was not added, and the dispersion effect of nanocellulose was reduced. Agglomeration occurred in the system and affected the solid content of the system. The stability and strength of the system were also affected. Therefore, the performance of Example 14 was reduced.

In Example 15, hydroxylated boron carbide was replaced with ordinary boron carbide, the dispersibility of the nanocellulose composite material decreased, and sedimentation occurred in the system, which affected the uniformity of the prepared ceramic system, so the various performances of Example 15 decreased.

In Comparative Example 1, the composite nanofiber component is replaced with ordinary nanocellulose. The dispersion performance of ordinary nanocellulose in the system is difficult to improve. At the same time, the thermal stability and strength are difficult to be further improved. Therefore, the various performances of Comparative Example 1 are reduced.

In Comparative Example 2, no composite nanocellulose component is added, which makes it difficult for the components in the green body to be tightly combined and form a stable network cross-linked structure, thus affecting the stability of the green body.

This specific embodiment is only an explanation of the present application, and it is not a limitation of the present application. Through the above description, relevant staff can make various changes and modifications without deviating from the technical idea of the present application. The technical scope of the present application is not limited to the content in the specification, and its technical scope must be determined according to the scope of the claims.

Claims (10)

1. A method for preparing ceramics by enhanced gel casting, characterized in that it comprises the following steps: Preparing a premixed liquid: subjecting the modified nanocellulose composite component to high-speed centrifugation to obtain a treated modified nanocellulose composite component, mixing the treated modified nanocellulose composite component with deionized water, adding acrylamide to the suspension after ultrasonication to obtain a suspension, adding N,N'-methylenebisacrylamide, a dispersant, a defoaming agent and a suspending agent to the suspension, and stirring to obtain a premixed liquid; Prepare slurry: add ceramic powder and sintering aid to the premixed liquid obtained above, stir to obtain prefabricated slurry, ball-mill the prefabricated slurry and vacuum degassing, vibrate at a frequency of 5-10 Hz during vacuum degassing, and obtain slurry after vacuum degassing; Preparation of green body: adding catalyst and initiator to slurry, stirring and pouring into mold, drying at constant temperature and humidity after the slurry is formed to obtain green body; Preparation of silicon carbide ceramics: The green body is sintered and kept warm to obtain a silicon carbide ceramic product. 2. The method for preparing ceramics by enhanced gel casting according to claim 1 is characterized in that: the sintering aid includes one or a mixture of carbon black and boron carbide, and the ceramic powder includes one or a mixture of primary silicon carbide powder particles and secondary silicon carbide powder particles. 3. The method for preparing ceramics by enhanced gel casting according to claim 2 is characterized in that: in the step of preparing silicon carbide ceramics, the green body is sintered by pressureless sintering; the mass ratio of the silicon carbide ceramic powder, carbon black and boron carbide is (48-49):1:0.3. 4. The method for preparing ceramics by enhanced gel casting according to claim 2 is characterized in that: in the step of preparing silicon carbide ceramics, the green body sintering adopts reaction sintering; the mass ratio between the primary carbide powder particles, the secondary silicon carbide powder particles and the sintering aid is 1.5:1:(0.25-0.3). 5. The method for preparing ceramics by enhanced gel casting according to claim 1, characterized in that the content of acrylamide accounts for 0.03-0.05% of the total weight of the slurry, the content of the catalyst accounts for 0.005-0.007% of the total weight of the green body, and the content of the initiator accounts for 0.03-0.05% of the total weight of the green body. 6. The method for preparing ceramics by enhanced gel casting according to claim 1, characterized in that the modified nanocellulose composite component accounts for 12-14% of the total mass of the slurry. 7. The method for preparing ceramics by enhanced gel casting according to claim 1, characterized in that the modified nanocellulose composite component comprises hydroxylated boron nitride, nanocellulose and polyethyleneimine. 8. The method for preparing ceramics by enhanced gel casting according to claim 7, characterized in that the modified nanocellulose is prepared by the following method: The nanocellulose is mixed with deionized water to obtain a nanocellulose suspension, hydroxylated boron nitride is added, a composite dispersion is obtained after ultrasonic treatment, and a nanocellulose-boron nitride composite material is obtained after filtration and drying; After the pH value of polyethyleneimine is adjusted to alkaline, a nanocellulose-boron nitride composite material is added, the temperature is raised, the reaction is stirred, and centrifugation is performed to obtain a prefabricated composite material. The prefabricated composite material is mixed with deionized water, filtered, suction filtered, and freeze-dried to obtain modified nanocellulose. 9. The method for preparing ceramics by enhanced gel casting according to claim 7, characterized in that the mass ratio of the hydroxylated boron nitride, nanocellulose and polyethyleneimine is (0.42-0.48):1:0.67. 10. The method for preparing ceramics by enhanced gel casting according to claim 7, characterized in that: the hydroxylated boron nitride is prepared by the following method: The boron nitride is mixed with a sodium hydroxide solution for hydrolysis, and then mixed with deionized water after centrifugal washing, and then centrifuged after ultrasonication. The supernatant is filtered and dried to obtain hydroxylated boron nitride.