A method for preparing pressureless sintered silicon carbide gel injection molding

Abstract

The application relates to a preparation method of pressureless sintering silicon carbide gel injection molding, which comprises the following steps: mixing and dispersing modified silicon carbide superfine powder, monomers and a crosslinking agent into water, adding initiators, carbon black and dispersants after stirring, uniformly mixing, vacuum defoaming to obtain a mixed slurry; adding the mixed slurry into a mold, immersing the bottom of the mold containing the mixed slurry into a freezing bath, demolding to obtain a wet blank after the reaction is completed, drying the wet blank to obtain a dry blank, and sintering the dry blank to obtain silicon carbide ceramics. The application has the effect of improving the drying performance of pressureless sintering gel injection molding silicon carbide.

Description

Technical Field

[0001] This application relates to the field of silicon carbide ceramic technology, and in particular to a method for preparing pressureless sintered silicon carbide gel casting. Background Technology

[0002] Silicon carbide ceramics possess excellent physical and chemical properties, including high hardness, low coefficient of thermal expansion, high thermal conductivity, and good semiconductor performance. Therefore, silicon carbide ceramics are widely used in the manufacture of high-temperature resistant materials, wear-resistant materials, and semiconductors.

[0003] In recent years, new colloidal molding techniques such as pressure filtration molding, gel casting, and direct solidification casting have become effective methods for preparing highly reliable ceramic parts with complex shapes. Gel casting is a suitable method for preparing complex, irregularly shaped silicon carbide parts. It utilizes ultrafine silicon carbide powder, boron carbide, and carbon black as sintering aids to obtain ceramic products with high density.

[0004] Currently, gel casting using cross-linking curing can produce high-density green bodies. However, moisture and dispersants are also locked within the cross-linked network along with the ceramic powder, making them difficult to remove during drying and requiring significant energy. Because the green body has low strength in the initial drying stage, it generates substantial internal stress under heating or pressure, leading to defects such as cracking and delamination. Increasing the proportion of colloid can improve cracking, but simultaneously, the cross-linked network structure becomes denser, making it even harder to remove moisture and other liquids. This makes drying difficult for pressureless sintered silicon carbide gel casting green bodies, thus requiring further improvement. Summary of the Invention

[0005] To improve the drying performance of wet silicon carbide ceramic blanks, this application provides a method for preparing pressureless sintered silicon carbide gel casting.

[0006] The preparation method of pressureless sintering silicon carbide gel casting provided in this application adopts the following technical solution:

[0007] A method for preparing pressureless sintered silicon carbide gel by injection molding, characterized by comprising the following steps:

[0008] Modified silicon carbide ultrafine powder, monomer and crosslinking agent are mixed and dispersed in water, and then initiator, carbon black and dispersant are added after stirring. After mixing evenly, vacuum defoaming is performed to obtain a mixed slurry.

[0009] The mixed slurry is added to the mold, and the bottom of the mold containing the mixed slurry is immersed in a freezing bath. After the reaction is completed, the mold is demolded to obtain a wet blank. The wet blank is dried to obtain a dry blank, and the dry blank is sintered without pressure to obtain silicon carbide ceramic.

[0010] Using directionally grown ice crystals as templates, a gel with oriented microchannel pores was synthesized. When the mold was slowly immersed in a freezing bath at the bottom, the ice crystals grew unidirectionally from the immersion end, forming a microchannel pore structure. The monomers that were originally dispersed in the slurry were concentrated in the amorphous region and polymerized efficiently through the action of an initiator. This resulted in the final hydrogel sample having micron-sized channels arranged parallel to the ice crystal growth direction, which is beneficial for the removal of moisture during the drying process, solves the problem of difficult drying, and improves the stability of silicon carbide ceramics.

[0011] Preferably, the monomer is N-isopropylacrylamide.

[0012] N-Isopropylacrylamide is an acrylamide derivative monomer with hydrophilic amide groups and hydrophobic isopropyl groups in its molecule. Its homopolymer has a low critical dissolution temperature and can rapidly form a polymer gel under ice bath conditions.

[0013] Preferably, the mass fraction of the N-isopropylacrylamide is 1-2% of the mixed slurry.

[0014] The wet blank prepared according to the above mass fraction content has a rich orientation microchannel pore structure and is easy to dry.

[0015] Preferably, the crosslinking agent is N,N'-methylenebisacrylamide.

[0016] N,N'-methylenebisacrylamide contains two allyl double bonds, which can undergo an addition reaction with N-isopropylacrylamide to form a cross-linked structure and rapidly generate a polymer gel.

[0017] Preferably, the mass ratio of N-isopropylacrylamide to N,N'-methylenebisacrylamide is 1:(0.1-0.15).

[0018] The wet blank obtained according to the above mass ratio has a well-formed pore structure.

[0019] Preferably, the mass fraction of the carbon black is 0.8-1.2% of the mixed slurry.

[0020] Carbon black is a nanomaterial with high surface area and porosity, which can improve the density and hardness of silicon carbide ceramics. Silicon carbide ceramics prepared according to the above mass fraction content have high density and hardness.

[0021] Preferably, the silicon carbide ceramic further includes boron carbide.

[0022] Boron carbide can significantly improve the hardness of silicon carbide ceramics, making them more wear-resistant and corrosion-resistant; boron carbide can also improve the thermal conductivity of silicon carbide ceramics, reduce heat loss at high temperatures, and improve the quality and service life of silicon carbide ceramics.

[0023] Preferably, the boron carbide has a mass fraction of 0.5-0.7% in the mixed slurry.

[0024] Silicon carbide ceramics prepared according to the above mass fraction content have high density and hardness.

[0025] Preferably, the initiator includes an oxidant, a reducing agent, and a catalyst.

[0026] By constructing an initiation system, monomers and crosslinking agents can be rapidly crosslinked and polymerized under freeze bath conditions to form a polymer gel with a good pore structure, which is beneficial for the subsequent drying process.

[0027] Preferably, the mass ratio of the oxidant, reducing agent and catalyst is 1:0.1:(0.2-0.3).

[0028] The wet blank prepared according to the above mass ratio has a good pore structure.

[0029] In summary, this application includes at least one of the following beneficial technical effects:

[0030] 1. Using directionally grown ice crystals as templates, a gel with oriented microchannel pores is synthesized. When the bottom of the mold is slowly immersed in a freezing bath, the ice crystals grow unidirectionally from the immersion end, forming a microchannel pore structure. The monomers originally dispersed in the slurry are concentrated in the amorphous region and undergo efficient polymerization through the action of an initiator. This results in the final hydrogel sample having micron-sized channels arranged parallel to the ice crystal growth direction, which is beneficial for the removal of moisture during the drying process, solves the problem of difficult drying, and improves the stability of silicon carbide ceramics.

[0031] 2. By controlling the proportions of monomers, crosslinking agents, and initiators, polymer gels with good morphology and structure can be obtained, which facilitates the removal of moisture and improves the drying performance and stability of silicon carbide ceramics. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the dried blank prepared in Example 3 of the preparation method of pressureless sintering silicon carbide gel injection molding in this application.

[0033] Figure 2 This is a schematic diagram of the dried blank prepared in Example 3 of the preparation method of pressureless sintering silicon carbide gel injection molding in this application.

[0034] Figure 3 This is a schematic diagram of the dried blank prepared in Example 12 of the preparation method of pressureless sintering silicon carbide gel injection molding in this application.

[0035] Figure 4This is a schematic diagram of the dried blank prepared in Example 15 of the preparation method of pressureless sintering silicon carbide gel injection molding in this application.

[0036] Figure 5 This is a schematic diagram of the interior of the preform prepared in Example 15 of the preparation method of pressureless sintering silicon carbide gel injection molding in this application after drying.

[0037] Figure 6 This is a schematic diagram of the dried blank prepared in Comparative Example 1 in the preparation method of pressureless sintering silicon carbide gel injection molding of this application. Detailed Implementation

[0038] This application discloses a method for preparing pressureless sintered silicon carbide gel by injection molding. The following embodiments further illustrate this application in detail:

[0039] Example

[0040] Example 1

[0041] Modified silicon carbide ultrafine powder, N-isopropylacrylamide, and N,N'-methylenebisacrylamide were mixed and dispersed in deionized water. After stirring at 200 rpm for 30 min, an initiator, carbon black, boron carbide, and a dispersant were added. After mixing evenly, the mixture was vacuum defoamed for 15 min to obtain a mixed slurry. The modified silicon carbide ultrafine powder accounted for 50% of the mass of the mixed slurry, N-isopropylacrylamide accounted for 1%, N,N'-methylenebisacrylamide accounted for 0.1%, the initiator accounted for 0.65%, including 0.5% potassium persulfate as an oxidant, 0.05% ammonium bisulfite as a reducing agent, 0.1% palladium chloride as a catalyst, 0.8% carbon black, 1.2% CE64 dispersant, and 0.5% boron carbide. The mixed slurry was added to the mold, and the bottom of the mold containing the mixed slurry was immersed in a liquid nitrogen freezing bath for 15 minutes. After the reaction was completed, the mold was demolded to obtain a wet blank. The wet blank was dried in a drying oven at 25°C for 10 hours, then the temperature was raised to 35°C and dried for another 10 hours. Finally, the temperature was raised to 45°C and held for 3 days to obtain a dry blank. The dry blank was placed in a pressureless sintering furnace and sintered at 1700°C for 3 days to obtain silicon carbide ceramic.

[0042] Example 2

[0043] Modified silicon carbide ultrafine powder, N-isopropylacrylamide, and N,N'-methylenebisacrylamide were mixed and dispersed in deionized water. After stirring at 200 rpm for 30 min, an initiator, carbon black, boron carbide, and a dispersant were added. After mixing evenly, the mixture was defoamed under vacuum for 15 min to obtain a mixed slurry. The modified silicon carbide ultrafine powder accounted for 50% of the mass of the mixed slurry, N-isopropylacrylamide accounted for 2%, N,N'-methylenebisacrylamide accounted for 0.3%, the initiator accounted for 0.7%, including 0.5% potassium persulfate as an oxidant, 0.05% ammonium bisulfite as a reducing agent, 0.15% palladium chloride as a catalyst, 1.2% carbon black, 1.2% CE64 dispersant, and 0.7% boron carbide. The mixed slurry was added to the mold, and the bottom of the mold containing the mixed slurry was immersed in a liquid nitrogen freezing bath for 15 minutes. After the reaction was completed, the mold was demolded to obtain a wet blank. The wet blank was dried in a drying oven at 25°C for 10 hours, then the temperature was raised to 35°C and dried for another 10 hours. Finally, the temperature was raised to 45°C and held for 3 days to obtain a dry blank. The dry blank was placed in a pressureless sintering furnace and sintered at 1700°C for 3 days to obtain silicon carbide ceramic.

[0044] Example 3

[0045] Modified silicon carbide ultrafine powder, N-isopropylacrylamide, and N,N'-methylenebisacrylamide were mixed and dispersed in deionized water. After stirring at 200 rpm for 30 min, an initiator, carbon black, boron carbide, and dispersant were added. After mixing evenly, the mixture was defoamed under vacuum for 15 min to obtain a mixed slurry. The modified silicon carbide ultrafine powder accounted for 50% of the mass of the mixed slurry, N-isopropylacrylamide accounted for 1.5%, N,N'-methylenebisacrylamide accounted for 0.1875%, the initiator accounted for 0.675%, including 0.5% potassium persulfate as an oxidant, 0.05% ammonium bisulfite as a reducing agent, 0.125% palladium chloride as a catalyst, 1% carbon black, 1.2% CE64 dispersant, and 0.6% boron carbide. The mixed slurry was added to the mold, and the bottom of the mold containing the mixed slurry was immersed in a liquid nitrogen freezing bath for 15 minutes. After the reaction was completed, the mold was demolded to obtain a wet blank. The wet blank was dried in a drying oven at 25°C for 10 hours, then the temperature was raised to 35°C and dried for another 10 hours. Finally, the temperature was raised to 45°C and held for 3 days to obtain a dry blank. The dry blank was placed in a pressureless sintering furnace and sintered at 1700°C for 3 days to obtain silicon carbide ceramic.

[0046] Example 4

[0047] Example 4 is based on Example 3. The only difference between Example 4 and Example 3 is that in Example 4, the mass percentage of N-isopropylacrylamide is 0.5% and the mass percentage of N,N'-methylenebisacrylamide is 0.0625%.

[0048] Example 5

[0049] Example 5 is based on Example 3. The only difference between Example 5 and Example 3 is that in Example 5, the mass percentage of N-isopropylacrylamide is 2.5% and the mass percentage of N,N'-methylenebisacrylamide is 0.3125%.

[0050] Example 6

[0051] Example 6 is based on Example 3. The only difference between Example 6 and Example 3 is that in Example 6, the mass percentage of N-isopropylacrylamide is 1.5% and the mass percentage of N,N'-methylenebisacrylamide is 0.075%.

[0052] Example 7

[0053] Example 7 is based on Example 3. The only difference between Example 7 and Example 3 is that in Example 7, the mass percentage of N-isopropylacrylamide is 1.5% and the mass percentage of N,N'-methylenebisacrylamide is 0.3%.

[0054] Example 8

[0055] Example 8 is based on Example 3. The only difference between Example 8 and Example 3 is that the mass percentage of carbon black in Example 8 is 0.6%.

[0056] Example 9

[0057] Example 9 is based on Example 3. The only difference between Example 9 and Example 3 is that the mass percentage of carbon black in Example 9 is 1.4%.

[0058] Example 10

[0059] Example 10 is based on Example 3. The only difference between Example 10 and Example 3 is that the mass percentage of boron carbide in Example 10 is 0.4%.

[0060] Example 11

[0061] Example 11 is based on Example 3. The only difference between Example 11 and Example 3 is that the mass percentage of boron carbide in Example 11 is 0.8%.

[0062] Example 12

[0063] Example 12 is based on Example 3. The only difference between Example 12 and Example 3 is that in Example 12, the mass percentage of oxidant is 0.54%, the mass percentage of reductant is 0.054%, and the mass percentage of catalyst is 0.081%.

[0064] Example 13

[0065] Example 13 is based on Example 3. The only difference between Example 13 and Example 3 is that in Example 13, the mass ratio of oxidant is 0.465%, the mass ratio of reducing agent is 0.047%, and the mass ratio of catalyst is 0.163%.

[0066] Example 14

[0067] Example 14 is based on Example 3. The only difference between Example 14 and Example 3 is that carbon black is not added in Example 14.

[0068] Example 15

[0069] Example 15 is based on Example 3. The only difference between Example 15 and Example 3 is that boron carbide is not added in Example 15.

[0070] Comparative Example 1

[0071] Comparative Example 1 is based on Example 3. The only difference between Comparative Example 1 and Example 3 is that the liquid nitrogen freezing bath in Comparative Example 1 is replaced with a 40°C water bath.

[0072] Performance testing

[0073] (1) Density test: The sample was prepared into a cubic silicon carbide ceramic specimen of 100mm*200mm*20mm. The density was calculated based on the volume and mass. Each sample was tested three times, and the average value was taken after measurement. The results are recorded in Table 1.

[0074] (2) The standard GB 16534-2009 "Test Method for Room Temperature Hardness of Fine Ceramics" was selected. Vickers hardness tester was used to test 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.

[0075] (3) Drying performance test: The wet blank is dried and the condition of the dried blank is observed and recorded. The results are recorded in Table 1.

[0076] Table 1. Test results of density and hardness of silicon carbide ceramics

[0077] Test results <![CDATA[Density (g / cm 3 )]]> Hardness (GPa) Will it crack after drying? Example 1 3.15 25 No cracks Example 2 3.15 26 No cracks Example 3 3.16 28 No cracks Example 4 3.11 24 No cracks Example 5 3.12 22 No cracks Example 6 3.12 24 No cracks Example 7 3.13 23 No cracks Example 8 3.12 21 No cracks Example 9 3.13 22 No cracks Example 10 3.12 20 No cracks Example 11 3.14 22 No cracks Example 12 3.13 18 Deformation Example 13 3.11 17 Deformation Example 14 3.13 16 Deformation Example 15 3.12 15 Deformation Comparative Example 1 3.01 11 Severe deformation

[0078] As shown in Table 1, the densities of Examples 1-3 are greater than 3.15 g / cm³. 3 The hardness is greater than 25 GPa, and the green body does not crack after drying, which shows that the silicon carbide ceramic prepared in this application has high density and hardness, and good drying and performance.

[0079] As shown in Table 1, the only difference between Examples 4-7 and Example 3 is that the amounts of N-isopropylacrylamide and N,N'-methylenebisacrylamide were changed in Examples 4-7, and the density in Examples 4-7 was less than 3.13 g / cm³. 3 The hardness is less than 25 GPa, and the green body does not crack after drying. The density in Example 3 is 3.23 g / cm³. 3 The hardness is 25 GPa. Compared with Example 3, the drying performance, density and hardness of Examples 4-7 have decreased. This is because the amount of monomer and crosslinking agent has changed. The change in the amount of monomer and crosslinking agent will affect the micro-crosslinking structure of the polymer gel, the size and number of pores will change, the pore structure will deteriorate, affecting the discharge of water during drying, and thus affecting the density and hardness of the ceramic. The performance of silicon carbide ceramics has deteriorated.

[0080] As shown in Table 1, the only differences between Examples 8 and 9 and Example 3 are: the carbon black mass percentage in Example 8 is 0.6%, the carbon black mass percentage in Example 9 is 1.4%, and the density in Examples 8 and 9 is less than 3.13 g / cm³. 3 The hardness is less than 22 GPa, and the green body does not crack after drying. Compared with Example 3, the density and hardness of Examples 8 and 9 have decreased. This is because the amount of carbon black has changed. Too little or too little carbon black will affect the thermal stability and sintering performance of silicon carbide ceramics, and the density and hardness of silicon carbide ceramics have decreased.

[0081] As shown in Table 1, the only differences between Examples 10 and 11 and Example 3 are: the mass percentage of boron carbide in Example 10 is 0.4%, the mass percentage of boron carbide in Example 11 is 0.8%, and the density in Examples 10 and 11 is less than 3.14 g / cm³. 3 The hardness is less than 22 GPa, and the green body does not crack after drying. Compared with Example 3, the density and hardness of Examples 10 and 11 have decreased. This is because the amount of boron carbide used has changed. Too much or too little boron carbide will affect the thermal conductivity of silicon carbide ceramics. The heat loss of silicon carbide ceramics at high temperatures has increased, and the density and hardness of silicon carbide ceramics have decreased, thus reducing the quality and service life of the products.

[0082] As shown in Table 1, the differences between Examples 12 and 13 and Example 3 are only as follows: in Example 12, the mass ratio of oxidant, reducing agent, and catalyst is 1:0.1:0.15; in Example 13, the mass ratio of oxidant, reducing agent, and catalyst is 1:0.1:0.35; and the density in Examples 12 and 13 is less than 3.13 g / cm³. 3The hardness is less than 18 GPa, and the green body deforms after drying. Compared with Example 3, the drying performance, density and hardness are all reduced. This is because the proportion of each component in the initiator has changed. The change in the initiator system will affect the polymerization rate of monomers and crosslinking agents, and thus affect the pore structure of polymer gel, thereby affecting the drying performance and reducing the density and hardness of silicon carbide ceramics.

[0083] As shown in Table 1, the only differences between Examples 14 and 15 and Example 3 are: no carbon black was added in Example 14, no boron carbide was added in Example 15, and the density in Examples 14 and 15 was less than 3.13 g / cm³. 3 The hardness is less than 16 GPa, and the green body deforms after drying. Compared with Example 3, the drying performance, density and hardness of Examples 14 and 15 are all reduced. This is because carbon black or boron carbide is not added. The lack of carbon black or boron carbide will affect the sintering performance of silicon carbide ceramics. The heat loss of silicon carbide ceramics at high temperature will increase, and the density and hardness of silicon carbide ceramics will decrease, thus reducing the quality and service life of the ceramics.

[0084] As shown in Table 1, the only difference between Comparative Example 1 and Example 3 is that the liquid nitrogen freezing bath in Comparative Example 1 was replaced with a 40°C water bath, and the density in Comparative Example 1 was 3.01 g / cm³. 3 The hardness was 11 GPa. After drying, the green body was severely deformed. Compared with Comparative Example 1 and Example 3, the drying performance, density and hardness were significantly reduced. This is because replacing the liquid nitrogen freezing bath with a 40°C water bath caused the polymerization rate of monomers and crosslinking agents to be too fast under high temperature water bath conditions. Without the guiding effect of ice crystal templates, the pore structure of the polymer gel became more disordered, which affected the drying performance of the wet green body. The density and hardness of the silicon carbide ceramic were significantly reduced.

[0085] This specific embodiment is merely an explanation of this application and is not intended to limit it. Based on the above description, those skilled in the art can make various changes and modifications without departing from the technical concept of this application. The technical scope of this application is not limited to the contents of the specification but must be determined according to the scope of the claims.

Claims

1. A method for preparing pressureless sintered silicon carbide gel by injection molding, characterized in that: Includes the following steps: Modified silicon carbide ultrafine powder, monomer and crosslinking agent are mixed and dispersed in water, and after stirring, initiator, carbon black and dispersant are added. After mixing evenly, vacuum defoaming is performed to obtain a mixed slurry. The mixed slurry is added to the mold, and the bottom of the mold containing the mixed slurry is immersed in a freeze bath. After the reaction is completed, the mold is demolded to obtain a wet blank. The wet blank is dried to obtain a dry blank, and the dry blank is sintered without pressure to obtain silicon carbide ceramic. The silicon carbide ceramic also includes boron carbide; The initiator includes an oxidant, a reducing agent, and a catalyst; The mass ratio of the oxidant, reducing agent and catalyst is 1:0.1:(0.2-0.3).

2. The preparation method of pressureless sintering silicon carbide gel casting according to claim 1, characterized in that: The monomer is N-isopropylacrylamide.

3. The preparation method of pressureless sintering silicon carbide gel casting according to claim 2, characterized in that: The mass fraction of N-isopropylacrylamide is 1-2% of the mixed slurry.

4. The preparation method of pressureless sintering silicon carbide gel casting according to claim 3, characterized in that: The crosslinking agent is N,N'-methylenebisacrylamide.

5. The preparation method of pressureless sintering silicon carbide gel casting according to claim 4, characterized in that: The mass ratio of N-isopropylacrylamide to N,N'-methylenebisacrylamide is 1:(0.1-0.15).

6. The preparation method of pressureless sintered silicon carbide gel casting according to claim 1, characterized in that: The mass fraction of carbon black is 0.8-1.2% of the mixed slurry.

7. The preparation method of pressureless sintering silicon carbide gel casting according to claim 1, characterized in that: The boron carbide mass fraction is 0.5-0.7% of the mixed slurry.

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