Method for regulating polymerization induction period of large-size complex-shaped max phase gel injection molding slurry

Abstract

This invention provides a method for controlling the polymerization induction period of large-size, complex-shaped MAX phase gel casting slurry, belonging to the field of ceramic colloidal molding technology. The method first involves calcining the MAX phase powder in air to stabilize its surface oxidation state. Then, monomers, crosslinking agents, polymerization inhibitors, dispersants, defoamers, pH adjusters, and catalysts are added to deionized water and mechanically stirred for 10 seconds to prepare a premix. Next, the MAX phase powder is added to the premix, and the casting slurry is evacuated to boiling within 30 seconds. Finally, an initiator is added to the bubble-free casting slurry, and the casting operation is completed within the polymerization induction period. This method effectively solves the problem of controlling the polymerization induction period of MAX phase gel casting slurry, resulting in large-size, complex-shaped MAX phase ceramic green bodies and sintered bodies with uniform and defect-free microstructures.

Description

Technical Field

[0001] This invention belongs to the field of ceramic colloidal molding technology, and specifically relates to a method for controlling the polymerization induction period of MAX phase gel injection molding slurry with large size and complex shape. Background Technology

[0002] MAX phase ceramics are a class of ternary layered compounds, typically expressed in the general formula M n+1 AX n This is represented by the formula, where n ranges from 1 to 3. Its structural characteristics lie in M ​​being a transition metal, A being a main group element, and X being carbon or nitrogen. This material combines the electrical and thermal conductivity and thermal shock resistance of metals with the hardness, wear resistance, oxidation resistance, and radiation resistance of ceramics. Even in high-temperature environments, its mechanical properties remain superior. These unique physical and chemical properties make it valuable in extreme condition applications, particularly demonstrating great application potential in the field of lead-bismuth fast reactor core structure materials.

[0003] Gel casting is a highly efficient and low-cost ceramic component molding technology, suitable for producing large-sized, complex-shaped ceramic parts, and can also be used to mold large-sized, complex-shaped MAX phase ceramic parts. However, in water-based slurries, the surface of MAX phase ceramic powders carries various hydrated groups, such as =Al–OH and =Al–O. − , −CH2, C=O, ≡Ti–OH, −OTi–(OH)2, ≡Ti–OH2 + 、≡Ti–O − =Ti + =Ti–O − -TiO + -TiO–OH, -TiO–O − and =Al–OH2 + These functional groups endow MAX phase gel molding slurry with high chemical activity, making it difficult to control its polymerization induction period, resulting in a narrow molding window and reducing the uniformity of the microstructure of the molding slurry and the demolded green body. Ultimately, this leads to macroscopic or microstructural defects and reduced mechanical properties in sintered MAX phase ceramic parts. Summary of the Invention

[0004] The technical problem addressed by this invention is to provide a method for controlling the polymerization induction period of large-size, complex-shaped MAX phase gel casting slurry. This method effectively solves the problem of difficulty in controlling the polymerization induction period of MAX phase gel casting slurry in the prior art. By employing the polymerization induction period control method described in this invention, large-size, complex-shaped MAX phase ceramic parts can be prepared, meeting the reliability and safety requirements of such MAX phase ceramic parts under extreme working conditions.

[0005] This invention provides a method for controlling the polymerization induction period of MAX phase gel casting slurry with large size and complex shape, comprising the following steps:

[0006] Step 1: Calcine the MAX phase powder in air atmosphere to stabilize its surface oxidation state, and then ball mill the calcined MAX phase powder to D50≤100 μm to obtain MAX phase ceramic powder suitable for gel casting.

[0007] Step 2: Add monomers, crosslinking agents, polymerization inhibitors, dispersants, defoamers, pH adjusters, and catalysts to deionized water and mechanically stir for 10 seconds to prepare a premix. After the mechanical stirring of the premix stops, add the MAX phase powder from Step 1 to the premix within 30 seconds, and start mechanical stirring or ball milling for 10 seconds to mix the mixture evenly, obtaining a MAX phase gel casting slurry.

[0008] Step 3: After the mechanical stirring or ball milling of the injection slurry described in Step 2 is completed, the injection slurry is evacuated to boiling within 30 seconds to remove internal air bubbles and then restored to normal pressure to obtain a MAX phase ceramic gel injection slurry without internal air bubbles.

[0009] Step 4: Add the initiator to the injection slurry without internal air bubbles described in Step 3, and stir evenly within 30 seconds. Then complete the injection molding operation during the polymerization induction period. After polymerization is completed, demold to obtain a large-sized, complex-shaped MAX phase gel injection molded ceramic green body.

[0010] Wherein, the purity of the MAX phase powder in step 1 is >90 wt.%, the calcination temperature range is 50-500℃, preferably 100℃; the calcination time is 0.5-50 hours, preferably 5 hours; and the calcination heating rate is 2-10℃ / min, preferably 8℃ / min.

[0011] In the MAX phase powder slurry described in step 2:

[0012] Powder content: 70-90 wt.%; Deionized water content: 1-15 wt.%; Polymerization inhibitor content: 5-25 wt.%;

[0013] Based on the weight of MAX phase ceramic powder, the following additives are added: monomer 2-20 wt.%; crosslinking agent 0.2-2 wt.%; dispersant 0.5-5 wt.%; defoamer 0.1-5 wt.%; pH adjuster 0.01-1 wt.%; catalyst 0-0.5 wt.%.

[0014] The monomer is one of acrylamide AM, NN-dimethylacrylamide DMAA, hydroxyethyl methacrylate HEMA, and methyl methacrylate MMA, all of which are analytical grade, with acrylamide AM being preferred.

[0015] The crosslinking agent was N,N-methylenebisacrylamide (MBAM), analytical grade.

[0016] The dispersant is ammonium polyacrylate PAA-NH4, diammonium hydrogen citrate DAC, polyethyleneimine PEI, citrate CA, or tetramethylammonium hydroxide TMAH, preferably ammonium polyacrylate PAA-NH4, a 40% aqueous solution of analytical grade.

[0017] The polymerization inhibitor is at least one of an aqueous solution of phenothiazine and an aqueous solution of catechol, wherein the proportion of phenothiazine is 0-5 wt.% and the proportion of catechol is 0-5 wt.%.

[0018] The defoamer is a polyether defoamer, preferably PLT;

[0019] The pH adjuster is an aqueous solution of sodium hydroxide or ammonia, preferably ammonia with a concentration of 10%;

[0020] The catalyst was tetramethylethylenediamine (TMEDA), analytical grade.

[0021] The mechanical stirring of the premixed liquid is carried out at a stirring speed of 50-2000 rpm and a stirring time of 0.5-15 min. The stirring paddle is made of an inert material, preferably polytetrafluoroethylene. The stirring paddle blade is an integrated blade with no opening angle, and the distance between the stirring paddle blade and the bottom of the slurry container is 0-2 cm, but not 0 cm.

[0022] The mechanical stirring of the injection slurry is performed at a speed of 50-2000 rpm and a duration of 0.5-15 min. The stirring paddle is made of an inert material, preferably polytetrafluoroethylene. The stirring paddle blades are integral blades with no opening angle. The distance between the stirring paddle blades and the bottom of the slurry container is 0-2 cm, but not 0 cm.

[0023] The ball milling mixing of the injection molding slurry is carried out in a ball mill jar made of polytetrafluoroethylene; the ball-to-material weight ratio is 0.5-10; the ball milling time is 3-60 min; the diameter of the grinding balls ranges from 20-150 mm, and the average diameter is 30-80 mm.

[0024] The pH range of the injection slurry is 2-12.

[0025] The time required from the start of vacuuming to boiling in step S3 is 0.1-5 min, and the boiling time is 0.1-5 min.

[0026] The process of removing air bubbles must be completed within the boiling period; the process of restoring to normal pressure refers to restoring from the boiling state to standard atmospheric pressure, which takes 0-30 seconds.

[0027] The solid content of the injection slurry is 30-60 vol.%, and the shear rate is 50 s. -1 At that time, its viscosity range was 50-1000 mPa·s.

[0028] The initiator mentioned in step S4 is preferably an aqueous solution of ammonium persulfate (APS) with a concentration of 2-50%, and the aqueous solution of the initiator accounts for 1-20 wt.% of the MAX phase ceramic powder.

[0029] To ensure uniform mixing, a rod-shaped stirrer, preferably a glass rod or a polytetrafluoroethylene (PTFE) stirrer, must be used. Vigorous stirring should be avoided to prevent the introduction of air into the slurry. The stirring time should be 0.1-15 min.

[0030] The polymerization induction period is 30-900 s.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] (1) The polymerization induction period control method of the present invention can achieve precise control of the polymerization induction period of MAX phase gel molding slurry, effectively solving the problem of difficulty in controlling the polymerization induction period of MAX phase gel molding slurry due to its high reactivity.

[0033] (2) During the polymerization induction period, the MAX phase gel casting ceramic slurry will not polymerize. The casting slurry has high fluidity and good stability. After demolding, it can obtain large-sized complex-shaped MAX phase ceramic parts with uniform microstructure and no defects.

[0034] (3) After adopting the polymerization induction period control method of the present invention, the sintered body of the large-size complex-shaped MAX phase ceramic parts obtained has a more uniform microstructure and higher mechanical properties, which meets the requirements of safety and reliability under extremely harsh service conditions. Detailed Implementation

[0035] To make the technical problems, solutions, and advantages of this invention clearer, a detailed description will be provided below with reference to specific embodiments. Obviously, the described embodiments are only a portion of the embodiments of this invention and do not encompass all implementable cases. Based on the embodiments of this invention, all other implementable cases obtained by those skilled in the art without inventive effort are within the protection scope of this invention.

[0036] This invention provides a method for controlling the polymerization induction period of MAX phase gel casting slurry with large size and complex shape. The application of this method includes the following steps:

[0037] S1: The MAX phase powder is calcined in air to stabilize its surface oxidation state, and then the calcined MAX phase powder is ball-milled to D50≤100 μm to obtain MAX phase ceramic powder suitable for gel casting.

[0038] S2: Add monomers, crosslinking agents, polymerization inhibitors, dispersants, defoamers, pH adjusters, and catalysts to deionized water and mechanically stir for 10 seconds to prepare a premix. After the mechanical stirring of the premix stops, add the MAX phase powder from step S1 to the premix within 30 seconds, and start mechanical stirring or ball milling for 10 seconds to mix the mixture evenly, obtaining a MAX phase gel casting slurry.

[0039] S3: After the mechanical stirring or ball milling of the injection slurry described in step S2 is completed, the injection slurry is evacuated to boiling within 30 seconds to remove internal air bubbles and then restored to normal pressure to obtain a MAX phase ceramic gel injection slurry without internal air bubbles.

[0040] S4: Add the initiator to the injection slurry without internal air bubbles described in S3, stir evenly within 30 seconds, and then complete the injection molding operation during the polymerization induction period. After polymerization is completed, demold to obtain a large-sized complex-shaped MAX phase gel injection molded ceramic green body.

[0041] The following description, in conjunction with specific embodiments, illustrates this point.

[0042] Example 1

[0043] (1) The Ti3SiC2 powder was calcined in air to stabilize its surface oxidation state, and then the calcined Ti3SiC2 powder was ball-milled to D. 50 With a thickness of 30 μm, Ti3SiC2 ceramic powder suitable for gel casting was obtained.

[0044] (2) Add monomers, crosslinking agents, polymerization inhibitors, dispersants, defoamers, pH adjusters and catalysts to deionized water and mechanically stir for 10 seconds to prepare a premixed solution. After the mechanical stirring of the premixed solution stops, add the Ti3SiC2 powder from step (1) to the premixed solution within 30 seconds, and start mechanical stirring or ball milling for 10 seconds to mix the molding slurry evenly, so as to obtain Ti3SiC2 gel molding slurry.

[0045] (3) After the mechanical stirring or ball milling of the injection slurry in step (2) is completed, the injection slurry is vacuumed to boiling within 30 seconds to remove the internal air bubbles and return to normal pressure to obtain Ti3SiC2 ceramic gel injection slurry without internal air bubbles.

[0046] (4) Add the initiator to the molding slurry without internal air bubbles described in (3) and stir it evenly within 30 seconds. Then complete the molding operation during the polymerization induction period. After the polymerization is completed, demold to obtain a large-sized complex-shaped Ti3SiC2 gel molded ceramic green body.

[0047] In step (1), the purity of the Ti3SiC2 powder is 98 wt.%, the calcination temperature range is 50℃, the calcination time is 20 hours, and the calcination heating rate is 8℃ / min.

[0048] In the Ti3SiC2 powder slurry described in step (2):

[0049] The powder content was 82 wt.%; the deionized water content was 6 wt.%; and the polymerization inhibitor content was 12 wt.%.

[0050] Based on the weight of Ti3SiC2 ceramic powder, the following additives are added: monomer 4 wt.%; crosslinking agent 0.4 wt.%; dispersant 2 wt.%; defoamer 1.6 wt.%; pH adjuster 0.3 wt.%.

[0051] The monomer is acrylamide AM, analytical grade;

[0052] The crosslinking agent was N,N-methylenebisacrylamide (MBAM), analytical grade.

[0053] The dispersant is ammonium polyacrylate PAA-NH4, a 40% aqueous solution, analytical grade;

[0054] The polymerization inhibitor is an aqueous solution of phenothiazine and catechol, wherein the concentration of phenothiazine in the aqueous solution is 0 wt.% and the concentration of catechol in the aqueous solution is 0.02 wt.%.

[0055] The defoamer is a polyether defoamer, preferably PLT, which is of analytical grade.

[0056] The pH adjuster is ammonia solution with a concentration of 10%.

[0057] The mechanical stirring of the premixed liquid is carried out at a stirring speed of 150 rpm for 3 min. The stirring paddle is made of polytetrafluoroethylene and the paddle blade is an integrated blade with no opening angle.

[0058] The mechanical stirring of the injection slurry is carried out at a stirring rate of 1200 rpm and a stirring time of 3 min. The stirring paddle is made of polytetrafluoroethylene and the stirring paddle blades are integral blades with no opening angle. The stirring paddle blades are 0.5 cm away from the bottom of the slurry container.

[0059] The ball milling mixing of the injection molding slurry was carried out in a ball mill jar made of polytetrafluoroethylene; the ball-to-material weight ratio was 2; the ball milling time was 12 min; and the average diameter of the grinding balls was 5 mm.

[0060] The pH range of the injection slurry is 10.

[0061] The time required from the start of vacuuming to boiling in step (3) is 0.5 min, and the boiling time is 0.5 min.

[0062] The process of removing air bubbles must be completed within the boiling period; the process of restoring to normal pressure refers to restoring from the boiling state to standard atmospheric pressure, which takes 5 seconds.

[0063] The injection slurry has a solid content of 52 vol.% and a shear rate of 50 s. -1 At that time, its viscosity range was 150 mPa·s.

[0064] The initiator mentioned in step (4) is an aqueous solution of ammonium persulfate (APS) with a concentration of 10%, and the aqueous solution of the initiator accounts for 4 wt.% of the Ti3SiC2 ceramic powder.

[0065] The mixing process is carried out by mechanical stirring with a glass rod to avoid introducing air into the slurry. The stirring time is 0.5 minutes.

[0066] The polymerization induction period is 180 s.

[0067] During the induction period, the Ti3SiC2 casting slurry does not polymerize, exhibiting high fluidity and good stability. After polymerization, the Ti3SiC2 green body shows no macroscopic defects such as cracks or fissures on its surface or interior, and its microstructure is dense and uniform. After sintering, the relative density is 98.2%, the flexural strength is 360 MPa, and the fracture toughness is higher than 5.2 MPa·m. 0.5 The diameter of the components (centrifugal pump impeller) is 230mm, and they have good corrosion resistance, which meets the requirements of nuclear reactor core structural materials for the service performance of Ti3SiC2 ceramic impellers.

[0068] Example 2

[0069] (1) The Ti3AlC2 powder was calcined in air to stabilize its surface oxidation state, and then the calcined Ti3AlC2 powder was ball-milled to D. 50 With a thickness of 20 μm, Ti3AlC2 ceramic powder suitable for gel casting was obtained.

[0070] (2) Add monomers, crosslinking agents, polymerization inhibitors, dispersants, defoamers, pH adjusters and catalysts to deionized water and mechanically stir for 10 seconds to prepare a premixed solution. After the mechanical stirring of the premixed solution stops, add the Ti3AlC2 powder from step (1) to the premixed solution within 30 seconds, and start mechanical stirring or ball milling for 10 seconds to mix the molding slurry evenly, so as to obtain Ti3AlC2 gel molding slurry.

[0071] (3) After the mechanical stirring or ball milling of the injection slurry in step (2) is completed, the injection slurry is vacuumed to boiling within 30 seconds to remove the internal air bubbles and return to normal pressure to obtain Ti3AlC2 ceramic gel injection slurry without internal air bubbles.

[0072] (4) Add the initiator to the molding slurry without internal air bubbles described in (3) and stir it evenly within 30 seconds. Then complete the molding operation during the polymerization induction period. After the polymerization is completed, demold to obtain a large-sized complex-shaped Ti3AlC2 gel molded ceramic green body.

[0073] In step (1), the Ti3AlC2 powder has a purity of 97.5 wt.%, a calcination temperature range of 60℃, a calcination time of 24 hours, and a calcination heating rate of 10℃ / min.

[0074] In the Ti3AlC2 powder slurry described in step (2):

[0075] The powder content was 83 wt.%; the deionized water content was 9 wt.%; and the polymerization inhibitor content was 8 wt.%.

[0076] Based on the weight of Ti3AlC2 ceramic powder, the following additives were added: monomer 5 wt.%; crosslinking agent 0.5 wt.%; dispersant 2.2 wt.%; defoamer 1.7 wt.%; pH adjuster 0.4 wt.%.

[0077] The monomer is acrylamide AM, analytical grade;

[0078] The crosslinking agent was N,N-methylenebisacrylamide (MBAM), analytical grade.

[0079] The dispersant is ammonium polyacrylate PAA-NH4, a 40% aqueous solution, analytical grade;

[0080] The polymerization inhibitor is an aqueous solution of phenothiazine and catechol, wherein the concentration of phenothiazine in the aqueous solution is 0 wt.% and the concentration of catechol in the aqueous solution is 0.05 wt.%.

[0081] The defoamer is a polyether defoamer, preferably PLT, which is of analytical grade.

[0082] The pH adjuster is ammonia solution with a concentration of 10%.

[0083] The mechanical stirring of the premixed liquid is carried out at a stirring rate of 130 rpm for 3.5 min. The stirring paddle is made of polytetrafluoroethylene and the blade shape is an integrated blade with no opening angle.

[0084] The mechanical stirring of the injection slurry is carried out at a stirring rate of 1100 rpm and a stirring time of 3 min. The stirring paddle is made of polytetrafluoroethylene and the stirring paddle blades are integral blades with no opening angle. The stirring paddle blades are 0.5 cm away from the bottom of the slurry container.

[0085] The ball milling mixing of the injection molding slurry was carried out in a ball mill jar made of polytetrafluoroethylene; the ball-to-material weight ratio was 3; the ball milling time was 10 min; and the average diameter of the grinding balls was 6 mm.

[0086] The pH range of the injection slurry is 10.5.

[0087] The time required from the start of vacuuming to boiling in step (3) is 0.6 min, and the boiling time is 0.6 min.

[0088] The process of removing air bubbles must be completed within the boiling period; the process of restoring to normal pressure refers to restoring from the boiling state to standard atmospheric pressure, which takes 4 seconds.

[0089] The initiator mentioned in step (4) is an aqueous solution of ammonium persulfate (APS) with a concentration of 10%, and the aqueous solution of the initiator accounts for 4.1 wt.% of the Ti3AlC2 ceramic powder.

[0090] The solid content of the injection slurry is 50 vol.%, and it is subjected to a shear rate of 50 s⁻¹. -1 At that time, its viscosity range was 120 mPa·s.

[0091] The mixing process is carried out by mechanical stirring with a glass rod to avoid introducing air into the slurry, and the stirring time is 0.4 minutes.

[0092] The polymerization induction period is 200 s.

[0093] During the induction period, the Ti3AlC2 casting slurry does not polymerize, exhibiting high fluidity and good stability. After polymerization, the Ti3AlC2 green body shows no macroscopic defects such as cracks or fissures on its surface or interior, and its microstructure is dense and uniform. After sintering, the relative density is 97.5%, the flexural strength is 330 MPa, and the fracture toughness is higher than 5.3 MPa·m. 0.5The components (centrifugal pump impellers) are all 200mm in diameter, have good corrosion resistance, and meet the requirements of nuclear reactor core structural materials for the service performance of Ti3AlC2 ceramic impellers.

[0094] Example 3

[0095] (1) The Ti2AlC powder was calcined in air to stabilize its surface oxidation state, and then the calcined Ti2AlC powder was ball-milled to D. 50 With a thickness of 15 μm, Ti2AlC ceramic powder suitable for gel casting was obtained.

[0096] (2) Add monomers, crosslinking agents, polymerization inhibitors, dispersants, defoamers, pH adjusters and catalysts to deionized water and mechanically stir for 10 seconds to prepare a premixed solution. After the mechanical stirring of the premixed solution stops, add the Ti2AlC powder from step (1) to the premixed solution within 30 seconds, and start mechanical stirring or ball milling for 10 seconds to mix the molding slurry evenly, to obtain Ti2AlC gel molding slurry.

[0097] (3) After the mechanical stirring or ball milling of the injection slurry in step (2) is completed, the injection slurry is vacuumed to boiling within 30 seconds to remove the internal air bubbles and return to normal pressure to obtain Ti2AlC ceramic gel injection slurry without internal air bubbles.

[0098] (4) Add the initiator to the molding slurry without internal air bubbles described in (3) and stir it evenly within 30 seconds. Then complete the molding operation during the polymerization induction period. After the polymerization is completed, demold to obtain a large-sized complex-shaped Ti2AlC gel molded ceramic green body.

[0099] In step (1), the Ti2AlC powder has a purity of 96.5 wt.%, a calcination temperature range of 40℃, a calcination time of 48 hours, and a calcination heating rate of 10℃ / min.

[0100] In the Ti2AlC powder slurry described in step (2):

[0101] Powder content: 80 wt.%; Deionized water content: 16 wt.%; Polymerization inhibitor content: 4 wt.%;

[0102] Based on the weight of Ti2AlC ceramic powder, the following additives are added: monomer 7 wt.%; crosslinking agent 0.7 wt.%; dispersant 1.5 wt.%; defoamer 3.0 wt.%; pH adjuster 0.5 wt.%.

[0103] The monomer is acrylamide AM, analytical grade;

[0104] The crosslinking agent is N,N-methylenebisacrylamide (MBAM), analytical grade.

[0105] The dispersant is ammonium polyacrylate PAA-NH4, a 40% aqueous solution, analytical grade;

[0106] The polymerization inhibitor is an aqueous solution of phenothiazine and catechol, wherein the concentration of phenothiazine in the aqueous solution is 0 wt.% and the concentration of catechol in the aqueous solution is 0.1 wt.%.

[0107] The defoamer is a polyether defoamer, preferably PLT, which is of analytical grade.

[0108] The pH adjuster is ammonia solution with a concentration of 10%.

[0109] The mechanical stirring of the premixed liquid is carried out at a stirring rate of 200 rpm for 4 min. The stirring paddle is made of polytetrafluoroethylene and the paddle blade is an integrated blade with no opening angle.

[0110] The mechanical stirring of the injection slurry is carried out at a stirring rate of 1500 rpm and a stirring time of 4 min. The stirring paddle is made of polytetrafluoroethylene and the stirring paddle blades are integral blades with no opening angle. The stirring paddle blades are 0.4 cm away from the bottom of the slurry container.

[0111] The ball milling mixing of the injection molding slurry was carried out in a ball mill jar made of polytetrafluoroethylene; the ball-to-material weight ratio was 5; the ball milling time was 20 min; and the average diameter of the grinding balls was 8 mm.

[0112] The pH range of the injection slurry is 9.5.

[0113] The time required from the start of vacuuming to boiling in step (3) is 0.7 min, and the boiling time is 0.7 min.

[0114] The process of removing air bubbles must be completed within the boiling period; the process of restoring to normal pressure refers to restoring from the boiling state to standard atmospheric pressure, which takes 6 seconds.

[0115] The initiator mentioned in step (4) is an aqueous solution of ammonium persulfate (APS) with a concentration of 10%, and the aqueous solution of the initiator accounts for 4.5 wt.% of the Ti2AlC ceramic powder.

[0116] The solid content of the injection slurry is 48 vol.%, and it is applied at a shear rate of 50 s⁻¹. -1 At that time, its viscosity range was 500 mPa·s.

[0117] The mixing process is carried out by mechanical stirring with a glass rod to avoid introducing air into the slurry. The stirring time is 0.7 minutes.

[0118] The polymerization induction period is 300 s.

[0119] During the induction period, the Ti2AlC casting slurry does not polymerize, exhibiting high fluidity and good stability. After polymerization, the Ti2AlC green body shows no macroscopic defects such as cracks or fissures on its surface or interior, and its microstructure is dense and uniform. After sintering, the relative density is 97.7%, the flexural strength is 305 MPa, and the fracture toughness is higher than 5.8 MPa·m. 0.5 The diameter of the components (centrifugal pump impeller) is 220 mm, and they have good corrosion resistance, which meets the requirements of nuclear reactor core structural materials for the service performance of Ti2AlC ceramic impellers.

[0120] This invention discloses a method for controlling the polymerization induction period of large-size, complex-shaped MAX phase gel casting slurry, covering all known MAX phase ceramics. The basic principles, main features, and advantages of this invention have been shown and described above. Those skilled in the art should understand that this invention is not limited to the above embodiments. The embodiments and descriptions in the specification illustrate the principles of this invention. Various changes and modifications can be made to this invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for controlling the polymerization induction period of a large-size, complex-shaped MAX phase gel casting slurry, characterized in that: This control method includes the following steps: Step 1: Calcine the MAX phase powder in air atmosphere to stabilize its surface oxidation state, and then ball mill the calcined MAX phase powder to D50≤100 μm to obtain MAX phase ceramic powder that can be used for gel casting. Step 2: Add monomers, crosslinking agents, polymerization inhibitors, dispersants, defoamers, pH adjusters, and catalysts to deionized water and mechanically stir for 10 seconds to prepare a premix. After the mechanical stirring of the premix stops, add the MAX phase ceramic powder from Step 1 to the premix within 30 seconds, and start mechanical stirring or ball milling for 10 seconds to mix the molding slurry evenly, thus obtaining the MAX phase gel molding slurry. Step 3: After the mechanical stirring or ball milling of the injection slurry described in Step 2 is completed, the injection slurry is vacuumed to boiling within 30 seconds to remove internal air bubbles and then restored to normal pressure to obtain a MAX phase ceramic gel injection slurry without internal air bubbles. Step 4: Add the initiator to the MAX phase ceramic gel casting slurry without internal air bubbles described in Step 3, stir evenly within 30 seconds, and then complete the casting operation during the polymerization induction period. After polymerization is completed, demold to obtain a large-sized complex-shaped MAX phase gel casting ceramic green body. The control is then complete. In step 2, the MAX phase powder in the MAX phase gel casting slurry accounts for 70-90 wt.%; the deionized water accounts for 1-15 wt.%; and the polymerization inhibitor accounts for 5-25 wt.%. Based on the weight of the MAX phase powder, the following additives are added: monomer 2-20 wt.%; crosslinking agent 0.2-2 wt.%; dispersant 0.5-5 wt.%; defoamer 0.1-5 wt.%; pH adjuster 0.01-1 wt.%; catalyst 0-0.5 wt.%. The monomer is one of acrylamide AM, NN-dimethylacrylamide DMAA, hydroxyethyl methacrylate HEMA, and methyl methacrylate MMA; The crosslinking agent is N,N-methylenebisacrylamide (MBAM). The dispersant is ammonium polyacrylate PAA-NH4, diammonium hydrogen citrate DAC, polyethyleneimine PEI, citrate CA, or tetramethylammonium hydroxide TMAH; The polymerization inhibitor is at least one of phenothiazine aqueous solution and catechol aqueous solution; The defoamer is a polyether-based defoamer; The pH adjuster is an aqueous solution of sodium hydroxide or ammonia. The catalyst is tetramethylethylenediamine (TMEDA); The mechanical stirring of the prepared premixed liquid is carried out at a stirring speed of 50-2000 rpm and a stirring time of 0.5-15 min. The stirring paddle is made of inert material. The stirring paddle blade is an integrated blade with no opening angle. The distance between the stirring paddle blade and the bottom of the slurry container is 0-2 cm, and not 0 cm. The mechanical stirring that makes the injection slurry uniformly mixes has a stirring speed of 50-2000 rpm and a stirring time of 0.5-15 min. The stirring paddle is made of an inert material. The stirring paddle blade is an integrated blade with no opening angle. The distance between the stirring paddle blade and the bottom of the slurry container is 0-2 cm, and not 0 cm. The ball milling process used to uniformly mix the injection slurry involves a ball mill jar made of polytetrafluoroethylene (PTFE); a ball-to-material weight ratio of 0.5-10; a ball milling time of 3-60 min; and a grinding ball diameter range of 20-150 mm with an average diameter of 30-80 mm. The pH range of the MAX phase gel injection molding slurry is 2-12; In step 4, the initiator is an aqueous solution of ammonium persulfate (APS); the stirring is done with a rod to avoid introducing air into the slurry due to vigorous stirring, and the stirring time is 0.1-15 min; the polymerization induction period is 30-900 s.

2. The method for controlling the polymerization induction period of large-size complex-shaped MAX phase gel casting slurry according to claim 1, characterized in that: In step 1, the purity of the MAX phase powder is >90 wt.%, the calcination temperature range is 50-500℃, the calcination time is 0.5-50 hours, and the calcination heating rate is 2-10℃ / min.

3. The method for controlling the polymerization induction period of large-size complex-shaped MAX phase gel casting slurry according to claim 2, characterized in that: The MAX phase powder is calcined at 100℃ for 5 hours and at a heating rate of 8℃ / min.

4. The method for controlling the polymerization induction period of large-size complex-shaped MAX phase gel casting slurry according to claim 1, characterized in that: The phenothiazine content is 0-5 wt.%, and the catechol content is 0-5 wt.%; The concentration of the pH adjuster is 10%.

5. The method for controlling the polymerization induction period of a large-size complex-shaped MAX phase gel casting slurry according to claim 4, characterized in that, The monomer is acrylamide AM; the dispersant is ammonium polyacrylate PAA-NH4, 40% aqueous solution, analytical grade; the defoamer is defoamer PLT; the pH adjuster is ammonia water, 10% concentration; the stirring paddle material for mechanically stirring to prepare the premixed liquid is polytetrafluoroethylene; the stirring paddle material for mechanically stirring to uniformly mix the injection slurry is polytetrafluoroethylene.

6. The method for controlling the polymerization induction period of a large-size complex-shaped MAX phase gel casting slurry according to claim 1, characterized in that, In step 3, the process of evacuating to boiling takes 0.1-5 minutes from the start of evacuation to the boiling of the slurry, and the boiling time is also 0.1-5 minutes. The removal of air bubbles must be completed within the boiling time period. The process of restoring to atmospheric pressure (from the boiling state to standard atmospheric pressure) takes 0-30 seconds. The MAX phase ceramic gel casting slurry without internal air bubbles has a solid content of 30-60 vol.% and a shear rate of 50 s⁻¹. -1 At that time, its viscosity range was 50-1000 mPa·s.

7. The method for controlling the polymerization induction period of a large-size complex-shaped MAX phase gel casting slurry according to claim 1, characterized in that, The concentration of the ammonium persulfate APS aqueous solution is 2-50%, and the initiator accounts for 1-20 wt.% of the MAX phase ceramic powder.

8. The method for controlling the polymerization induction period of a large-size complex-shaped MAX phase gel casting slurry according to claim 7, characterized in that, The rod-shaped stirrer is a glass rod or a polytetrafluoroethylene stirring rod.