CN114988880A - Preparation method for preparing silicon carbide ceramic through gel injection molding and pressureless sintering - Google Patents
Preparation method for preparing silicon carbide ceramic through gel injection molding and pressureless sintering Download PDFInfo
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Abstract
The application relates to a preparation method for preparing silicon carbide ceramic through gel casting and pressureless sintering, which relates to the technical field of silicon carbide ceramic; which comprises the following steps: s1, chemically modifying the surface of the silicon carbide fine powder by sodium polyacrylate and a silane coupling agent to obtain modified silicon carbide powder for later use; s2, preparing acrylamide, N-methylene bisacrylamide, a pour inhibitor, deionized water and a dispersing agent, uniformly stirring, adding boron carbide powder, carbon powder and the modified silicon carbide powder obtained in the step S1, continuously stirring uniformly, performing ball mixing, and performing vacuum defoaming to obtain a prefabricated mixed slurry; and S3, stirring the prefabricated mixed slurry obtained in the step S2, adding a retarder, continuously stirring, adding a redox initiator, stirring, performing injection molding, and curing to form a blank. According to the application, after the silicon carbide powder is modified, the anti-gelling agent is added into the system, so that the curing content and curing uniformity of the system are improved.
Description
Technical Field
The application relates to the field of silicon carbide ceramics, in particular to a preparation method for preparing silicon carbide ceramics by gel casting and pressureless sintering.
Background
The silicon carbide ceramic belongs to one of ceramic materials, has excellent normal-temperature mechanical properties and high bending strength, and can be prepared in a complex manner through pressureless sintering.
The Chinese patent application with publication number CN102875150A discloses a method for preparing a silicon carbide ceramic impeller by gel casting and pressureless sintering, which adopts a boron-containing sintering aid-containing silicon carbide solid-phase sintering formula system, gel casting and pressureless sintering processes, and comprises eight steps of ceramic slurry preparation, injection molding, demolding, drying, machining, degumming, pressureless sintering and machining.
However, the process flow is complex, the induction period is short, the monomer polymerization conversion rate is low, the system has a phenomenon of non-uniform curing, the powder is too fine and is easy to agglomerate, and the solid content of the slurry is too low and can only reach 55 vol% at most, so that the inventor thinks that a silicon carbide ceramic for improving the solid content and the curing uniformity of the ceramic system is necessary to develop.
Disclosure of Invention
In order to solve the problems, the application provides a preparation method for preparing silicon carbide ceramics by gel casting pressureless sintering.
The preparation method for preparing the silicon carbide ceramic through gel casting pressureless sintering adopts the following technical scheme:
a preparation method for preparing silicon carbide ceramic through gel casting pressureless sintering comprises the following steps:
the method comprises the following steps:
s1, chemically modifying the surface of the silicon carbide fine powder by sodium polyacrylate and a silane coupling agent to obtain modified silicon carbide powder for later use;
s2, preparing acrylamide, N-methylene bisacrylamide, a pour inhibitor, deionized water and a dispersing agent, uniformly stirring, adding boron carbide powder, carbon powder and the modified silicon carbide powder obtained in the step S1, continuously stirring uniformly, performing ball mixing, and performing vacuum defoaming to obtain a prefabricated mixed slurry;
and S3, stirring the prefabricated mixed slurry obtained in the step S2, adding a retarder, continuously stirring, adding a redox initiator, stirring, performing injection molding, and curing to form a blank.
After the silicon carbide powder is chemically modified by the sodium polyacrylate and the silane coupling agent, sodium ions on the surface are attached to the surface of the silicon carbide powder, the steric hindrance effect is enhanced, the dispersion effect among the silicon carbide powder is enhanced, the stability of the system is improved, the solid content of the whole system is further improved, the silicon carbide fine powder containing the sodium ions is more hydrophilic to deionized water by the silane coupling agent on the surface, the uniformity of the prepared silicon carbide ceramic is improved, and meanwhile, the modified silicon carbide is simple to operate and does not need particle grading; the retarder can prolong the polymerization time of the system, thereby improving the feasibility of operation, and the retarder can solve the problem of low monomer polymerization conversion rate.
Preferably, the redox initiator comprises ammonium bisulfite and ammonium persulfate.
Acrylamide is used as a monomer, N, N-methylene bisacrylamide is used as a cross-linking agent, ammonium bisulfite and ammonium persulfate are used as redox initiators, cross-linking and curing are carried out, a stable net structure is obtained, and at the moment, the modified silicon carbide powder is cured in the net structure, so that the stability of the silicon carbide powder can be improved, and further the stability of the whole system can be improved.
Preferably, the mass ratio of the ammonium bisulfite to the ammonium persulfate is 1 (0.9-1.1).
Controlling the mass ratio of ammonium bisulfite to ammonium persulfate in the above range can improve the performance of redox initiator.
Preferably, the anti-coagulant comprises tert-butyl catechol, phenothiazine, hydroquinone and diphenylamine.
The phenol group is matched with the amino group to react with the free radical, so that the polymerization time can be prolonged, and the feasibility of operation can be ensured.
Preferably, the anti-coagulant is prepared by the following method:
(1) mixing tert-butyl catechol with phenothiazine to obtain a phenol-based mixture;
(2) mixing hydroquinone with diphenylamine to obtain an amino mixture;
(3) and (3) mixing the phenol-based mixture obtained in the step (1) with the amino mixture obtained in the step (2), and uniformly stirring to obtain the anticoagulant.
Preferably, the retarder is acetylacetone.
The acetylacetone is selected as the retarder, so that the capture capability of the carbon black to free radicals can be reduced, and the conversion rate of monomer polymerization is improved.
Preferably, the step S1 is specifically: respectively dissolving sodium polyacrylate and a silane coupling agent in deionized water to obtain a sodium polyacrylate solution and a silane coupling agent solution, mixing the sodium polyacrylate solution and the silane coupling agent solution to obtain a modifier solution, adding silicon carbide fine powder into the modifier solution, stirring and heating at the heating temperature of 60-100 ℃, the heating time of 2-6h and the stirring speed of 50-80r/min, then carrying out centrifugal separation at the rotation speed of 6500 and 7500r/min to remove the upper-layer liquid, setting the drying temperature at 30-50 ℃ and the drying time of 10-20h to obtain the modified silicon carbide powder.
Preferably, the mass ratio of the sodium polyacrylate to the silicon carbide powder is 0.005-0.015:1, and the concentration of the sodium polyacrylate in the modifier solution is 20-50%.
Preferably, the stirring temperature in the step S3 is 16-18 ℃, and the stirring time is 2-4 min.
In summary, the present application includes at least one of the following beneficial technical effects:
1. the sodium polyacrylate is used for modifying the silicon carbide fine powder, so that the strength of the silicon carbide fine powder is improved, the dispersibility of the silicon carbide fine powder is improved, and the silane coupling agent is synchronously added, so that the curing uniformity of the silicon carbide fine powder is improved, and the curing uniformity effect of a system is improved; the modified silicon carbide powder is solidified in a network structure formed by cross-linking reaction by adopting a redox initiator, so that the solidification uniformity of the system can be improved;
2. the anticoagulant is added into the system to react with free radicals, so that the polymerization time can be prolonged, and the feasibility of operation is ensured;
3. the adoption of acetylacetone as retarder can reduce the capture capability of carbon black to free radicals, thereby improving the polymerization conversion rate of monomers.
Detailed Description
The present application will now be described in further detail with reference to examples.
Example 1
Preparing a pour inhibitor: weighing 80mg of tert-butyl catechol and phenothiazine according to the mass ratio of 1:1, mixing to obtain a phenol-based mixture, weighing 80mg of hydroquinone and diphenylamine according to the mass ratio of 1:1, mixing to obtain an amino mixture, and uniformly mixing the phenol-based mixture and the amino mixture to obtain the anticoagulant.
Preparation of a redox initiator: 8.9mg of ammonium bisulfite and 11.1mg of ammonium persulfate are weighed and mixed to obtain the redox initiation system.
Preparing silicon carbide ceramic:
s1, respectively dissolving 0.2g of sodium polyacrylate and 0.2g of silane coupling agent in deionized water to prepare a sodium polyacrylate solution with the concentration of 50% and a silane coupling agent solution with the concentration of 50%, then passing silicon carbide through a screen with the thickness of 1.2 microns, mixing the sodium polyacrylate solution and the silane coupling agent solution to obtain a modifier solution, weighing 100g of sieved silicon carbide fine powder, adding the silicon carbide fine powder into the modifier solution, controlling the heating temperature to be 60 ℃, stirring at the speed of 50r/min for 6h, controlling the speed of a centrifugal machine to be 7500r/min, carrying out centrifugal separation on the mixture, removing upper-layer liquid, and adjusting the temperature of a dryer to be 30 ℃ and drying at constant temperature for 20h to obtain modified silicon carbide powder;
s2, weighing 22mg of acrylamide, 2mg of N, N-methylene bisacrylamide and 160mg of the anti-gelling agent, adding all the acrylamide, 2mg of N, N-methylene bisacrylamide and 160mg of the anti-gelling agent into deionized water, uniformly stirring to obtain a mixed solvent, adding 3g of boron carbide powder, 5g of carbon powder and the modified silicon carbide powder prepared in the step S1 into the mixed solvent to obtain a solid content of 62 vol%, stirring for 2 hours at a speed of 70r/min, then mixing in a ball mill, and defoaming under a vacuum condition to obtain mixed slurry;
s3, pouring the mixed slurry obtained in the step S2 into a slurry tank, adding 0.3g of retarder while stirring until the temperature of the system reaches 16 ℃, adding 20mg of the prepared redox initiation system, stirring for 4min, injection molding, and curing.
Wherein, the silane coupling agent is KH560, and the retarder is acetylacetone.
Example 2
Preparing a pour inhibitor: weighing 100mg of tert-butyl catechol and phenothiazine according to the mass ratio of 1:1, mixing to obtain a phenol-based mixture, weighing 100mg of hydroquinone and diphenylamine according to the mass ratio of 1:1, mixing to obtain an amino mixture, and uniformly mixing the phenol-based mixture and the amino mixture to obtain the anticoagulant.
Preparation of a redox initiation system: and weighing 19mg of ammonium bisulfite and 21mg of ammonium persulfate, and mixing to obtain the redox initiation system.
Preparing silicon carbide ceramic:
s1, respectively dissolving 1.8g of sodium polyacrylate and 1.5g of silane coupling agent in deionized water to prepare a sodium polyacrylate solution with the concentration of 20% and a silane coupling agent solution with the concentration of 20%, passing silicon carbide through a 1-micron screen, mixing the sodium polyacrylate solution and the silane coupling agent solution to obtain a modifier solution, weighing 120g of sieved silicon carbide fine powder, adding the silicon carbide fine powder into the modifier solution, controlling the heating temperature to be 100 ℃, stirring at the speed of 80r/min for 2h, controlling the speed of a centrifugal machine to be 6500r/min, carrying out centrifugal separation on the mixture, removing upper-layer liquid, and adjusting the temperature of a dryer to be 50 ℃ and drying at constant temperature for 10h to obtain modified silicon carbide powder;
s2, weighing 40mg of acrylamide, 4mg of N, N-methylene bisacrylamide and 200mg of the anti-coagulant, adding all the acrylamide, 4mg of N, N-methylene bisacrylamide and 200mg of the anti-coagulant into deionized water, uniformly stirring to obtain a mixed solvent, adding 6g of boron carbide powder, 8.4g of carbon powder and the modified silicon carbide powder prepared in the step S1 into the mixed solvent to obtain a solid content of 65 vol%, stirring for 1h at a speed of 90r/min, then mixing in a ball mill, and defoaming under a vacuum condition to obtain mixed slurry;
s3, pouring the mixed slurry obtained in the step S2 into a slurry tank, adding 0.5g of retarder while stirring until the temperature of the system reaches 18 ℃, adding 40mg of the prepared redox initiation system, stirring for 3min, injecting into a mold, and curing.
Wherein, the silane coupling agent is KH560, and the retarder is acetylacetone.
Example 3
Preparing a pour inhibitor: weighing 90mg of tert-butyl catechol and phenothiazine according to the mass ratio of 1:1, mixing to obtain a phenol-based mixture, weighing 90mg of hydroquinone and diphenylamine according to the mass ratio of 1:1, mixing to obtain an amino mixture, and uniformly mixing the phenol-based mixture and the amino mixture to obtain the anticoagulant.
Preparation of a redox initiation system: weighing 15mg of ammonium bisulfite and 15mg of ammonium persulfate, and mixing to obtain the redox initiation system.
Preparing silicon carbide ceramic:
s1, respectively dissolving 1.1g of sodium polyacrylate and 1g of silane coupling agent in deionized water to prepare a sodium polyacrylate solution with the concentration of 35% and a silane coupling agent solution with the concentration of 35%, mixing the sodium polyacrylate solution with the silane coupling agent solution to obtain a modifier solution, sieving silicon carbide through a 0.8-micron screen, weighing 110g of sieved silicon carbide fine powder, adding the silicon carbide fine powder into the modifier solution, controlling the heating temperature to be 80 ℃, stirring at the speed of 65r/min for 4h, controlling the speed of a centrifugal machine to be 7000r/min to centrifugally separate the mixture, removing upper-layer liquid, and adjusting the temperature of a dryer to be 40 ℃ to dry at constant temperature for 15h to obtain modified silicon carbide powder;
s2, weighing 30mg of acrylamide, 3mg of N, N-methylene bisacrylamide and 180mg of the anti-gelling agent, adding all the acrylamide, 3mg of N, N-methylene bisacrylamide and 180mg of the anti-gelling agent into deionized water, uniformly stirring to obtain a mixed solvent, adding 4.4g of boron carbide powder, 6.6g of carbon powder and the modified silicon carbide powder prepared in the step S1 into the mixed solvent to obtain a solid content of 63 vol%, stirring for 1.5h at a stirring speed of 80r/min, then mixing in a ball mill, and defoaming under a vacuum condition to obtain mixed slurry;
s3, pouring the mixed slurry obtained in the step S2 into a slurry tank, adding 0.4g of retarder while stirring until the temperature of the system reaches 17 ℃, adding 30mg of the prepared redox initiation system, stirring for 3min, injecting into a mold, and curing.
Wherein, the silane coupling agent is KH560, and the retarder is acetylacetone.
Example 4
Example 4 based on example 3, example 4 differs from example 3 only in that: the mass of ammonium bisulfite weighed in example 4 was 17.7mg, and the mass of ammonium persulfate was 12.3 mg.
Example 5
Example 5 based on example 3, example 5 differs from example 3 only in that: the mass of ammonium bisulfite weighed in example 5 was 13mg, and the mass of ammonium persulfate was 17 mg.
Example 6
Example 6 based on example 3, example 6 differs from example 3 only in that: the amount of sodium polyacrylate weighed in example 6 was 3 g.
Example 7
Example 7 based on example 3, example 7 differs from example 3 only in that: the amount of sodium polyacrylate weighed in example 7 was 0.1 g.
Comparative example 1
Comparative example 1 is based on example 3, the only difference between comparative example 1 and example 3 being: in comparative example 1 no sodium polyacrylate was added.
Comparative example 2
Comparative example 2 is based on example 3, and the only difference between comparative example 2 and example 3 is that: in the redox initiation system prepared in comparative example 2, 0mg of ammonium bisulfite was weighed and 30mg of ammonium persulfate was weighed.
Comparative example 3
Comparative example 3 based on example 3, comparative example 3 differs from example 3 only in that: in the redox initiation system prepared in comparative example 3, ammonium bisulfite was replaced with tetramethylethylenediamine.
Comparative example 4
Comparative example 4 based on example 3, comparative example 4 differs from example 4 only in that: in the redox initiation system prepared in comparative example 4, 30mg of ammonium bisulfite was weighed and 0mg of ammonium persulfate was weighed.
Comparative example 5
Comparative example 5 is based on example 3, the only difference between comparative example 5 and example 3 being: in comparative example 5 no retarder was added.
Performance test
Performance tests were carried out on the green bodies prepared in examples 1 to 7 and comparative examples 1 to 5
(1) And performing density multipoint testing on the prepared silicon carbide ceramic, respectively detecting the bottom wall and the two opposite side walls of the blank body, testing each sample for three times, averaging after testing, filling the result in a table 1, then calculating the standard deviation of three sampling points, and filling the calculated value in the table 1.
TABLE 1
Performance data analysis
As can be seen from Table 1, the samples of examples 1-3 all had densities of 2.40g/cm 3 Above, the standard deviation of the density is below 0.030, and the surface is smooth and uniform, so that the silicon carbide ceramic prepared by the method has high solid content and good curing uniformity.
As can be seen from table 1, example 4 differs from example 3 only in that: the mass of the ammonium bisulfite weighed in the embodiment 3 is 15mg, the mass of the ammonium persulfate weighed in the embodiment 4 is 17.7mg, and the mass of the ammonium bisulfite weighed in the embodiment 4 is 12.3 mg; EXAMPLE 3 average of Density measurements at various points on the sampleThe value was 2.46g/cm 3 Standard deviation of 0.008, and average value of density detection of each point of the sample of example 4 of 2.36g/cm 3 The standard deviation is 0.053, the average density of example 4 is reduced compared with that of example 3, the standard deviation value is larger, the surface of example 3 is flat and uniform, the surface of example 4 has slight black spots, the crosslinking reaction is exothermic, the excessive ammonium bisulfite causes the system to generate heat obviously, the embryo body in the system is heated and expanded, so that the stability of the whole system is reduced, and the agglomeration and the black spots occur.
As can be seen from table 1, the only difference between example 5 and example 3 is that: the mass of ammonium bisulfite weighed in example 3 was 15mg, the mass of ammonium persulfate weighed in example 5 was 15mg, the mass of ammonium bisulfite weighed in example 5 was 13mg, the mass of ammonium persulfate weighed in example 3 was 17mg, and the average value of density measurement at each point of the sample in example 3 was 2.46g/cm 3 The standard deviation is 0.008, and the average value of density detection of each point of the samples of example and 5 is 2.33g/cm 3 The standard deviation is 0.050, the average density of the sample in example 5 is reduced compared with that in example 3, the standard deviation value is increased, and the surface of the sample in example 3 is flat and uniform; the surface of example 5 showed slight black spots, because the content of ammonium bisulfite was too low, the redox initiation system was not sufficient for cross-linking reaction, the silicon carbide powder was difficult to solidify in the net structure, the stability of the silicon carbide powder was reduced, agglomeration occurred, the solid content of the whole system was reduced, the uniformity was reduced, and partial agglomeration and black spots appeared on the surface.
As can be seen from table 1, the only difference between example 6 and example 3 is that: the amount of the sodium polyacrylate weighed in example 3 was 0.6g, the amount of the sodium polyacrylate weighed in example 6 was 3g, and the average value of the density detection at each point of the sample in example 3 was 2.46g/cm 3 Standard deviation of 0.008, and average value of density detection of each point of the sample of example 6 of 2.32g/cm 3 The standard deviation is 0.062, the average density of example 6 is reduced compared with that of example 3, the standard deviation value is larger, the surface of example 3 is flat and uniform, and the surface of the sample of example 6 is obviously blackened and generates caking because of the sodium acrylate in the systemIf the amount is too large, a film can be formed on the surface of the silicon carbide powder, so that the silicon carbide powder is aggregated, the dispersing effect of the silicon carbide powder is reduced, the solid content is reduced, and the phenomenon of uniform curing of the whole system is difficult to promote, so that the average density value of the system in example 6 is reduced, the standard deviation is increased, and partial agglomeration and black spots appear on the interface.
As can be seen from table 1, the only difference between example 7 and example 3 is that: the amount of the sodium polyacrylate weighed in example 3 was 0.6g, the amount of the sodium polyacrylate weighed in example 7 was 0.1g, and the average value of the density detection at each point of the sample in example 3 was 2.46g/cm 3 The standard deviation was 0.008 and the average of the density measurements of the individual spots of the sample of example 7 was 2.29g/cm 3 The standard deviation is 0.067, and compared with example 3, in example 7, the average density is reduced, the standard deviation value is increased, the surface of example 3 is flat and uniform, and after the content of sodium polyacrylate is reduced, the amount of polypropylene is not enough to modify all silicon carbide powder, so that the modification effect of the silicon carbide powder is difficult to improve, the silicon carbide powder in the system has poor modification effect, the dispersion effect of the silicon carbide powder is reduced, the solid content is reduced, and the curing uniformity of the system is difficult to improve, so that the average density of the system in example 7 is reduced, the standard deviation is increased, the surface of example 7 has obvious black spots, and caking is generated.
As can be seen from table 1, comparative example 1 differs from example 3 only in that: in comparative example 1, no sodium polyacrylate was added, and the average value of density measurement of each point of the sample of comparative example 1 was 2.24g/cm 3 The standard deviation is 0.109, and the number of black spots and agglomerates appearing on the surface is large and the area is large, because the silicon carbide powder in the comparative example 1 is not improved, so that the dispersion performance of the silicon carbide powder is difficult to improve, the dispersion uniformity of the silicon carbide powder in the system is reduced, the stability of the system is reduced, the solid content is reduced, the density standard deviation value of the comparative example 1 is large, the average value is reduced, and the number of black spots and agglomerates on the surface is large and the area is large.
From Table 1It can be seen that comparative example 2 differs from example 3 only in that: in comparative example 2, the amount of ammonium bisulfate added was 0mg, the amount of sodium persulfate was 30mg, and the average value of density measurement of each point of the sample of comparative example 2 was 2.23g/cm 3 The standard deviation is 0.084, and the surface black spots of the comparative example 2 are massive and large in area, because ammonium bisulfite is not added in the system, the initiation effect on crosslinking curing is reduced, the curing reaction effect is reduced, so that the network structure formed by the system is reduced, the fixing effect on the silicon carbide powder is difficult to improve, the stability of the system is reduced, the solid content is reduced, the density standard deviation value in the comparative example 2 is large, the average value is reduced, and the surface black spots are massive and large in area.
As can be seen from table 1, comparative example 3 differs from example 3 only in that: comparative example 3 ammonium bisulfite was replaced with tetramethylethylenediamine, and the average value of density measurements at each point of the sample of comparative example 3 was 2.25g/cm 3 The standard deviation is 0.086, and the surface black spots of the comparative example 3 are large in agglomeration and large in area, because when tetramethylethylenediamine and sodium persulfate are used as a catalyst and an initiator, the induction period is short, and silicon carbide powder solidified in the crosslinking reaction is less, so that the stability of the system is difficult to improve, the solid content is reduced, and the curing uniformity of the system is difficult to improve, so that the density standard deviation value of the comparative example 3 is large, the average value is reduced, and the surface black spots and agglomeration are large and large in area.
As can be seen from table 1, comparative example 4 differs from example 3 only in that: in the redox initiation system prepared in comparative example 4, 30mg of ammonium bisulfite was weighed, 0mg of ammonium persulfate was weighed, and the average value of density measurements at each point of the sample of comparative example 4 was 2.24g/cm 3 The standard deviation is 0.090, the black spots on the surface of the comparative example 4 are huge in agglomeration and large in area, because the shortage of sodium persulfate in the application is not enough to initiate the crosslinking curing reaction between acrylamide and N, N-methylene-bisacrylamide in the system, the solid content of the system is reduced, the uniformity of the silicon carbide powder is difficult to improve, and therefore the uniformity of the system is difficult to improve,thus, the average density value of comparative example 4 was decreased, the standard deviation became large, and the surface black spots and the lumps were large and the area was large.
As can be seen from table 1, comparative example 5 differs from example 3 only in that: comparative example 5 No retarder was added, and the average value of density measurement of each point of the sample of comparative example 5 was 2.24g/cm 3 The standard deviation is 0.078, and the black spots on the surface of the comparative example 5 are large in agglomeration and large in area, because the carbon black has strong capture capability on free radicals after the retarder is not added, the polymerization conversion rate of the monomer is difficult to improve, the solid content of the system is reduced, the uniformity of the system is difficult to improve, the average density value of the comparative example 5 is reduced, the standard deviation is large, and the black spots and the agglomeration on the surface are large in amount and large in area.
The present embodiment is merely illustrative and not restrictive, and various changes and modifications may be made by persons skilled in the art without departing from the scope of the present invention as defined in the appended claims. The technical scope of the present application is not limited to the contents of the specification, and must be determined according to the scope of the claims.
Claims (9)
1. A preparation method for preparing silicon carbide ceramic through gel casting and pressureless sintering is characterized by comprising the following steps: the method comprises the following steps:
s1, chemically modifying the surface of the silicon carbide fine powder by sodium polyacrylate and a silane coupling agent to obtain modified silicon carbide powder for later use;
s2, preparing acrylamide, N-methylene bisacrylamide, a pour inhibitor, deionized water and a dispersing agent, uniformly stirring, adding boron carbide powder, carbon powder and the modified silicon carbide powder obtained in the step S1, continuously stirring uniformly, performing ball mixing, and performing vacuum defoaming to obtain a prefabricated mixed slurry;
and S3, stirring the prefabricated mixed slurry obtained in the step S2, adding a retarder, continuously stirring, adding a redox initiator, stirring, performing injection molding, and curing to form a blank.
2. The method for preparing silicon carbide ceramic by gel-casting pressureless sintering according to claim 1, wherein the method comprises the following steps: the redox initiator includes ammonium bisulfite and ammonium persulfate.
3. The method for preparing silicon carbide ceramic through gel casting pressureless sintering according to claim 2, wherein the method comprises the following steps: the mass ratio of the ammonium bisulfite to the ammonium persulfate is 1 (0.9-1.1).
4. The method for preparing silicon carbide ceramic by gel-casting pressureless sintering according to claim 1, wherein the method comprises the following steps: the anti-coagulant comprises tert-butyl catechol, phenothiazine, hydroquinone and diphenylamine.
5. The method for preparing silicon carbide ceramic through gel casting pressureless sintering according to claim 4, wherein the method comprises the following steps: the anti-coagulant is prepared by the following method:
(1) mixing tert-butyl catechol with phenothiazine to obtain a phenol-based mixture;
(2) mixing hydroquinone with diphenylamine to obtain an amino mixture;
(3) and (3) mixing the phenol-based mixture obtained in the step (1) with the amino mixture obtained in the step (2), and uniformly stirring to obtain the anticoagulant.
6. The method for preparing silicon carbide ceramic by gel-casting pressureless sintering according to claim 1, wherein the method comprises the following steps: the retarder is acetylacetone.
7. The method for preparing silicon carbide ceramic by gel casting pressureless sintering according to claim 1, wherein the method comprises the following steps: the step S1 specifically includes: respectively dissolving sodium polyacrylate and a silane coupling agent in deionized water to obtain a sodium polyacrylate solution and a silane coupling agent solution, mixing the sodium polyacrylate solution and the silane coupling agent solution to obtain a modifier solution, adding silicon carbide fine powder into the modifier solution, stirring and heating at the heating temperature of 60-100 ℃, the heating time of 2-6h and the stirring speed of 50-80r/min, then carrying out centrifugal separation at the rotation speed of 6500 and 7500r/min to remove the upper-layer liquid, setting the drying temperature at 30-50 ℃ and the drying time of 10-20h to obtain the modified silicon carbide powder.
8. The method for preparing silicon carbide ceramic through gel casting pressureless sintering according to claim 7, wherein the method comprises the following steps: the mass ratio of the sodium polyacrylate to the silicon carbide powder is 0.005-0.015:1, and the concentration of the sodium polyacrylate in the modifier solution is 20-50%.
9. The method for preparing silicon carbide ceramic by gel casting pressureless sintering according to claim 1, wherein the method comprises the following steps: in the step S3, the stirring temperature is 16-18 ℃, and the stirring time is 2-4 min.
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