Gelcasting-based method for preparing β"-aluminum oxide ceramic

Abstract

Disclosed is a gelcasting-based method for preparing β"-aluminum oxide ceramic. The method comprises: obtaining β"-aluminum oxide ceramic precursor powder having a set β"-phase content; adding a monomer and a cross-linking agent to a solvent to obtain a first mixture and performing first ball milling on the first mixture to obtain a premix; adding the β"-aluminum oxide ceramic precursor powder and a dispersant to the premix to obtain a second mixture and performing second ball milling on the second mixture to obtain a first slurry; defoaming the first slurry under vacuum to obtain a second slurry; adding an initiator to the second slurry to obtain a third mixture and performing third ball milling on the third mixture to obtain a third slurry; placing the third slurry into a mold for curing and molding to obtain a preform and demolding the preform to obtain a green body; and subjecting the green body to binder removal and sintering to obtain β"-aluminum oxide ceramic.

Description

A method for preparing β"-alumina ceramic based on gel casting

[0001] Cross-reference to Related Applications

[0002] This application claims priority to Chinese Patent Application No. 202411267335.X, filed on September 11, 2024, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0003] The present disclosure relates to the technical field of inorganic non-metallic materials, and in particular to a method for preparing β"-alumina ceramic based on gel casting. BACKGROUND

[0004] β"-alumina ceramic is used as a solid electrolyte material for sodium-sulfur / nickel batteries due to its excellent sodium ion conduction performance, and is the most important core component in the solid-state battery system. β"-alumina ceramic has a crystal structure composed of overlapping aluminum-oxygen block layers and sodium-oxygen layers. Aluminum ions Al 3+ are distributed in the voids of the tetrahedron composed of oxygen ions O 2- The aluminum-oxygen block layer composed of closely packed aluminum ions Al 3+ and oxygen ions O 2- These closely packed aluminum-oxygen block layers are connected by [NaO] - in the sparse sodium-oxygen layer, so that Na ions can shuttle between the closely packed aluminum-oxygen block layers at high temperatures. When the temperature reaches 250°C or above, β"-alumina ceramic has an ionic conductivity close to that of aqueous solution salt, and becomes the preferred solid-state electrolyte for many sodium-based batteries (sodium-sulfur batteries and Zebra batteries, etc.).

[0005] However, the existing β"-alumina ceramic has certain shortcomings in terms of β" phase content, green body processing capability, bulk density after sintering, and mechanical properties. Therefore, how to improve the comprehensive performance of β"-alumina ceramic is a technical problem that needs to be solved at present. SUMMARY

[0006] A method for preparing β"-alumina ceramic based on gel casting is provided by utilizing one or more embodiments of the present disclosure to improve the comprehensive performance of β"-alumina ceramic.

[0007] According to some embodiments of the present disclosure, a method for preparing a gel-casting based β"-alumina ceramic comprises: obtaining a β"-alumina ceramic precursor powder having a set β" phase content; adding monomers and a crosslinking agent into a solvent to obtain a first mixture, and performing first ball milling on the first mixture to obtain a pre-mixture; adding the β"-alumina ceramic precursor powder and a dispersant into the pre-mixture to obtain a second mixture, and performing second ball milling on the second mixture to obtain a first slurry; performing vacuum degassing on the first slurry to obtain a second slurry; adding an initiator into the second slurry to obtain a third mixture, and performing third ball milling on the third mixture to obtain a third slurry; placing the third slurry into a mold for solidification molding to obtain a green body, and performing demolding on the green body to obtain a green compact; and performing degreasing and sintering on the green compact to obtain a β"-alumina ceramic. BRIEF DESCRIPTION OF DRAWINGS

[0008] The accompanying drawings, which are incorporated herein and constitute part of the specification, illustrate embodiments consistent with the present disclosure and serve to explain the principles of the present disclosure together with the specification.

[0009] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure or the related art, the accompanying drawings needed to be used in the embodiments or the related art description will be briefly introduced. Obviously, those skilled in the art can obtain other drawings according to these drawings without any creative effort.

[0010] FIG. 1 shows a flowchart of a method for preparing a gel-casting based β"-alumina ceramic according to some embodiments of the present disclosure. Embodiments of the present disclosure

[0011] In order to make the objects, technical solutions and advantages of the embodiments of the present disclosure clearer, the technical solutions in the embodiments of the present disclosure will be described clearly and completely below with reference to the drawings in the embodiments of the present disclosure. Obviously, the described embodiments are only some of the embodiments of the present disclosure, rather than all the embodiments of the present disclosure. Based on the embodiments in the present disclosure, all other embodiments obtained by those skilled in the art without any creative effort fall within the protection scope of the present disclosure.

[0012] Various embodiments of the present disclosure can exist in a range of forms; it should be understood that the description in a range form is merely for the convenience and brevity, and should not be understood as a hard limitation on the scope of the present disclosure; therefore, it should be considered that the described range has specifically disclosed all possible sub-ranges and single values within the range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the described range, such as 1, 2, 3, 4, 5, and 6, which applies to any range. In addition, whenever a numerical range is indicated in this document, it refers to any cited number (fraction or integer) within the indicated range.

[0013] In addition, in the description of the present disclosure, the terms "include", "contain" and the like mean "include but not limited to". In this document, relational terms such as "first" and "second" and the like are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. In this document, "and / or" describes the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B can represent the cases of A alone, A and B together, and B alone. Where A and B can be singular or plural. In this document, "one or more" means one or more, and "multiple" means two or more. "At least one", "at least one of the following" or the like means any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can mean a, b, c, a-b (i.e. a and b), a-c, b-c, or a-b-c, where a, b, and c can be single or multiple.

[0014] Unless otherwise specifically stated, the various raw materials, reagents, instruments and equipment, etc. used in the present disclosure can be purchased on the market or can be prepared by existing methods.

[0015] The creative idea of the present disclosure is:

[0016] Gelcasting is an advanced ceramic forming process that combines the principles of polymer chemistry. It involves mixing ceramic powders, organic monomers, cross-linking agents, initiators, and catalysts into a slurry, which is then injected into a mold. Through temperature-induced polymerization of the organic monomers, a three-dimensional network structure gel is formed, and the ceramic powders are solidified in situ to form a ceramic green body. Gelcasting has the advantages of good green body uniformity, high strength, direct mechanical processing, no need for expensive equipment, and no special requirements for the mold.

[0017] Developing a low-cost, high-beta" phase content beta"-alumina ceramic preparation technology through gelcasting is an effective means to improve the comprehensive performance of beta"-alumina ceramics. However, applying gelcasting to the preparation of beta"-alumina ceramics requires overcoming the following difficulties:

[0018] I. Slurry preparation and solid content control

[0019] 1) How to balance the solid content and performance of the slurry: The solid content of the slurry is a key factor affecting the performance of the solidified ceramic green body. Higher solid content helps to improve the density and strength of the ceramic green body, but excessive solid content can lead to increased slurry viscosity, making it difficult to flow and inject into the mold, and may cause performance degradation after sintering, such as grain coarsening and strength reduction. Therefore, the solid content of the slurry needs to be precisely controlled to find the best balance between performance and processability.

[0020] 2) How to select and control the amount of dispersant: To reduce the viscosity of the slurry and improve its flowability, a dispersant is usually added. However, the selection and amount of dispersant need to be strictly controlled to avoid adverse effects on the surface properties of the ceramic powder and the performance of the formed ceramic green body.

[0021] II. Gelation process control

[0022] 1) How to control the appropriate polymerization rate: The gelation process is a process of inducing monomer polymerization through temperature to form a three-dimensional network structure. During the gelation process, the polymerization rate needs to be precisely controlled to ensure that the three-dimensional network structure of the gel has sufficient strength and stability, while avoiding problems such as excessive brittleness or insufficient strength of the three-dimensional network structure of the gel due to too fast or too slow polymerization rates.

[0023] 2) How to remove air bubbles: During the gelation process, the presence of air bubbles can seriously affect the quality and performance of the ceramic green body. Therefore, effective measures need to be taken to remove air bubbles from the slurry to ensure the density and uniformity of the solidified ceramic green body.

[0024] III. Sintering process optimization

[0025] How to control sintering temperature and time: The sintering temperature and time of β"-alumina ceramic have important influence on the performance of finished product. Therefore, it is necessary to optimize the sintering process parameters such as sintering temperature and time to ensure that the ceramic material has excellent mechanical properties and thermal stability.

[0026] Figure 1 shows a flowchart of a preparation method of gel-casting based β"-alumina ceramic according to some embodiments of the present disclosure.

[0027] Referring to Figure 1, to solve the above technical problems, according to some embodiments of the present disclosure, a preparation method of gel-casting based β"-alumina ceramic comprises:

[0028] S1, obtaining a β"-alumina ceramic precursor powder with a set β" phase content;

[0029] S2, adding monomers and crosslinking agents to a solvent to obtain a first mixture, and performing first ball milling on the first mixture to obtain a premix;

[0030] S3, adding the β"-alumina ceramic precursor powder and a dispersing agent to the premix to obtain a second mixture, and performing second ball milling on the second mixture to obtain a first slurry;

[0031] S4, vacuum deaerating the first slurry to obtain a second slurry;

[0032] S5, adding an initiator to the second slurry to obtain a third mixture, and performing third ball milling on the third mixture to obtain a third slurry;

[0033] S6, placing the third slurry in a mold for solidification molding to obtain a green compact, and demolding the green compact to obtain a green body; and

[0034] S7, performing degassing and sintering on the green body to obtain a β"-alumina ceramic.

[0035] In some embodiments, the set β" phase content is ≥ 95%.

[0036] A high set β" phase content means that the ceramic material will have more excellent performance, such as higher strength, better thermal stability, and more superior electrical properties. Limiting the set β" phase content of the β"-alumina ceramic precursor powder to be ≥ 95% helps to ensure that the β" phase content of the obtained β"-alumina ceramic is ≥ 95%. For example, the set β" phase content of the β"-alumina ceramic precursor powder can be 95%, 96%, 97%, 98%, 99%, etc.

[0037] In embodiments of the present disclosure, the monomer and the crosslinking agent are key ingredients for forming the gel network, the monomer and the crosslinking agent are dissolved in the solvent to form a first mixture, and the first mixture is subjected to a first ball milling to form a uniform pre-mixture. The first ball milling process helps to promote uniform mixing of the monomer and the crosslinking agent, laying a foundation for subsequent steps.

[0038] In some embodiments, the mass concentration of the pre-mixture can be 10% to 20%, and the mass concentration of the pre-mixture refers to the percentage of the total mass of the monomer and the crosslinking agent in the pre-mixture to the mass of the pre-mixture. The mass ratio of the monomer to the crosslinking agent can be (4-6):1, the monomer can include one or more of methyl acrylamide, acrylamide, and hydroxymethyl acrylamide, and the crosslinking agent can include N,N'-methylene bisacrylamide.

[0039] The mass concentration of the pre-mixture is an important parameter, which directly affects the uniformity, flowability of each slurry and the performance of the final product. Limiting the mass concentration of the pre-mixture to the range of 10% to 20% can make the monomer and the crosslinking agent fully dissolved and uniformly mixed in the solvent. Good solubility ensures that the monomer and the crosslinking agent can be uniformly distributed in the entire pre-mixture, providing a good foundation for subsequent reactions with other ingredients (such as β"-alumina ceramic precursor powder). At the same time, it helps to improve the uniformity of subsequent polymerization and crosslinking, and the flowability and stability of each slurry, avoiding uneven local reaction. For example, the mass concentration of the pre-mixture can be 10%, 12%, 14%, 16%, 18%, 20%, etc.

[0040] In the process of curing and forming of the third slurry into the mold, i.e. in the process of gel casting, the mass ratio of the monomer to the crosslinking agent is a crucial parameter, which directly affects the polymerization reaction rate and the formation of the three-dimensional gel network structure during the gelation process. By setting the mass ratio of the monomer to the crosslinking agent to the range of (4-6):1, the polymerization reaction rate during the curing and forming process can be controlled within a certain range, so that the polymerization reaction rate is neither too fast to cause local agglomeration and stress concentration, nor too slow to cause low production efficiency, thereby helping to form a uniform, dense and stable three-dimensional gel network structure, ensuring the strength of the green body. For example, the mass ratio of the monomer to the crosslinking agent can be 4:1, 4.5:1, 5:1, 5.5:1, 6:1, etc.

[0041] The β"-alumina ceramic precursor powder and the dispersant are added to the pre-mixture to obtain a second mixture, and the second mixture is subjected to a second ball milling. The β"-alumina ceramic precursor powder, the dispersant, the monomer and the crosslinking agent in the second mixture can be fully mixed and uniformly dispersed in the solvent through the second ball milling process. The addition of the dispersant helps to reduce the agglomeration phenomenon between the powder particles, and improve the uniformity and flowability of the first slurry.

[0042] In some embodiments, the dispersant has a mass of 0.1% to 0.3% of the mass of the β"-alumina ceramic precursor powder, and the dispersant comprises one or more of sodium polymethacrylate, sodium hexametaphosphate, and sodium polyacrylate.

[0043] The dispersant mainly functions to adsorb on the surface of the β"-alumina ceramic precursor powder particles, and prevent agglomeration between the β"-alumina ceramic precursor powder particles by electrostatic repulsion or steric hindrance effect, thereby improving the dispersibility of the β"-alumina ceramic precursor powder in the solvent. The amount of the dispersant is crucial to ensure good dispersibility of the β"-alumina ceramic precursor powder in the solvent, and the stability and fluidity of the final slurries. Controlling the mass of the dispersant to be within the range of 0.1% to 0.3% of the mass of the β"-alumina ceramic precursor powder helps to form a stable first slurry system and improve the fluidity of the first slurry. However, an excessive amount of the dispersant can cause the dispersant to agglomerate or form micellar structures, thereby increasing the viscosity of the first slurry system. For example, the mass of the dispersant can be 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, or the like, of the mass of the β"-alumina ceramic precursor powder.

[0044] In some embodiments, the mass ratio of the β"-alumina ceramic precursor powder to the premix solution can be (1 to 2.3): 1, and the solid content of the first slurry can be 50% to 70%; the ball-to-material ratio of the second ball milling can be (3 to 5): 1, and the second ball milling time can be 10 h to 15 h.

[0045] The mass ratio of the β"-alumina ceramic precursor powder to the premix solution is a key process parameter, which directly affects the strength of the green body and the sintering density and microstructure of the β"-alumina ceramic after sintering. Setting the mass ratio of the β"-alumina ceramic precursor powder to the premix solution within the range of (1 to 2.3): 1 helps to improve the strength of the green body, the sintering density and microstructure of the β"-alumina ceramic after sintering, and avoid defects, and in addition, helps to improve the controllability and stability of the process. For example, the mass ratio of the β"-alumina ceramic precursor powder to the premix solution can be 1:1, 1.2:1, 1.5:1, 1.8:1, 2:1, 2.3:1, or the like.

[0046] Defining the solid content of the first slurry to be 50% to 70% can reduce the shrinkage and deformation of the green body after drying, and helps to improve the strength of the green body, and the sintering density and microstructure of the β"-alumina ceramic after sintering. For example, the solid content of the first slurry can be 50%, 55%, 60%, 65%, 70%, or the like.

[0047] The ball-to-material ratio of the second ball milling is limited to (3-5):1, and the time of the second ball milling is limited to 10-15 hours, which can improve the grinding efficiency of the second ball milling and help to improve the uniformity of the first material slurry. For example, the ball-to-material ratio of the second ball milling can be 3:1, 3.5:1, 4:1, 4.5:1, 5:1, etc., and the time of the second ball milling can be 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, etc.

[0048] The first material slurry can contain air bubbles, which can cause defects in the inner part of the green body obtained in the subsequent solidification molding process. Therefore, the air bubbles in the first material slurry need to be removed through a vacuum debubbling process to obtain a second material slurry without air bubbles.

[0049] An initiator is added to the second material slurry to obtain a third mixture; the addition of the initiator is a key step to start the gelation polymerization reaction in the solidification molding process. The third mixture is subjected to a third ball milling, which can uniformly disperse the initiator in the third material slurry, preparing for the subsequent gelation polymerization reaction in the solidification molding process.

[0050] In some embodiments, the mass of the initiator is 10-12% of the mass of the monomer, and the initiator includes one or more of ammonium persulfate and sodium persulfate.

[0051] Limiting the mass of the initiator to 10-12% of the mass of the monomer can effectively initiate the gelation polymerization reaction and control the polymerization rate, so as to leave sufficient time for the subsequent injection molding (placing the third material into a mold).

[0052] The third material slurry containing the initiator is placed into a mold, and the monomer can undergo a gelation polymerization reaction by controlling the temperature and holding time of the solidification molding, so as to form a three-dimensional gel network structure, thereby in-situ solidifying and molding the β"-alumina ceramic precursor powder into a preform. After the solidification molding is completed, a demolding operation is performed to obtain a complete green body.

[0053] In some embodiments, the temperature of the solidification molding is 80-100°C, and the holding time of the solidification molding is 10-15 hours.

[0054] The temperature of the solidification molding and the holding time of the solidification molding are key factors to ensure that the chemical reaction between the monomer and the crosslinking agent is fully carried out and a stable three-dimensional gel network structure is formed. The temperature of the solidification molding is limited to 80-100°C, and the holding time of the solidification molding is limited to 10-15h, so that the polymerization reaction rate between the monomer and the crosslinking agent is moderate. If the temperature of the solidification molding is too low, the polymerization reaction rate will be too slow, and a longer time will be required to complete the solidification molding. If the temperature of the solidification molding is too high, unnecessary side reactions may occur, affecting the structure and performance of the three-dimensional gel network structure. At the same time, it can ensure that the monomer and crosslinking agent in the entire third slurry system can fully react to form a uniform three-dimensional gel network structure. In addition, by controlling the temperature of the solidification molding and the holding time of the solidification molding, the three-dimensional gel network structure can gradually shrink and densify during the formation process, thereby reducing the risk of stress concentration. For example, the temperature of the solidification molding can be 80°C, 85°C, 90°C, 95°C, 100°C, etc., and the holding time of the solidification molding can be 10h, 11h, 12h, 13h, 14h, 15h, etc.

[0055] In some embodiments, by controlling the temperature of the solidification molding to be 80-100°C and the holding time of the solidification molding to be 10-15h, the chemical reaction between the monomer and the crosslinking agent can be ensured to be sufficient, and the uniformity of the solidification molding can be ensured.

[0056] The green body contains a certain amount of organic matter (such as monomer, crosslinking agent, dispersant, etc.), which needs to be removed through the degassing process before sintering. After the degassing is completed, the sintering treatment is carried out to form a dense combination between the β"-alumina ceramic precursor powder particles, and a β"-alumina ceramic with excellent performance is obtained.

[0057] In some embodiments, the temperature of the degassing is 500-600°C, and the holding time of the degassing is 1.5-2.5h.

[0058] The temperature of the degassing is limited to 500-600°C, and the holding time of the degassing is limited to 1.5-2.5h, which can effectively and completely remove the organic matter in the green body, avoiding the removal at high temperature, causing pores on the surface of the β"-alumina ceramic, and affecting the performance of the β"-alumina ceramic. For example, the temperature of the degassing can be 500°C, 520°C, 540°C, 560°C, 580°C, 600°C, etc., and the holding time of the degassing can be 1.5h, 1.7h, 1.9h, 2.0h, 2.2h, 2.4h, 2.5h, etc.

[0059] In some embodiments, the temperature of the sintering is 1600-1650°C, and the holding time of the sintering is 20-40min.

[0060] The sintering temperature is 1600-1650°C, and the holding time is 20-40 min, which helps to achieve a better density of the β"-alumina ceramic and to make the microstructure of the β"-alumina ceramic uniform. If the sintering temperature is too low, the density of the β"-alumina ceramic is low. If the sintering temperature is too high, the grains in the β"-alumina ceramic grow abnormally. For example, the sintering temperature can be 1600°C, 1610°C, 1620°C, 1630°C, 1640°C, 1650°C, etc., and the holding time can be 20 min, 22 min, 25 min, 30 min, 35 min, 40 min, etc.

[0061] In some embodiments, the β"-alumina ceramic satisfies at least one of the following properties: β" content ≥ 95%, volume density ≥ 96% of the theoretical volume density, and four-point bending strength ≥ 250 MPa.

[0062] The present disclosure is further described below in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present disclosure and not to limit the scope of the present disclosure. The experimental methods in the following examples, if not specified, are generally determined according to the industry standards. If there is no corresponding industry standard, the general international standards, conventional conditions, or the conditions recommended by the manufacturer are used.

[0063] Example 1

[0064] The present embodiment provides a preparation method of a β"-alumina ceramic based on gel casting, comprising the following steps:

[0065] S1, preparing a β"-alumina ceramic precursor powder with a β" phase content of 98% by a solid-phase synthesis method;

[0066] S2, adding 4 parts by mass of methacrylamide (C4H7NO) and 1 part by mass of N'-methylenebisacrylamide (linear molecular formula: (CH2=CHCONH)2CH2) to 28.5 parts by mass of water to obtain a first mixture, and then performing first ball milling on the first mixture for 15 min to obtain a uniformly mixed premix;

[0067] S3, adding 30 parts by mass of the β"-alumina ceramic precursor powder and 0.003 parts by mass of a sodium polyacrylate dispersant (CAS No. 9003-04-7) to the premix to obtain a second mixture, and then performing second ball milling on the second mixture at a ball-to-material ratio of 3:1 for 12 h to obtain a first slurry;

[0068] S4, vacuum deaerating the first slurry to obtain a second slurry;

[0069] S1, 0.4 parts by mass of ammonium persulfate ((NH4)2S2O8) was added to the second slurry to obtain a third mixture, and then the third mixture was subjected to third ball milling for 15 min to obtain a third slurry;

[0070] S6, the third slurry was placed in a mold and placed in an oven at a temperature of 90°C for 12h to perform curing molding to obtain a preform, and then the preform was demolded to obtain a green body, and the strength of the green body reached 15MPa; and,

[0071] S7, the green body was subjected to degassing at a temperature of 500°C for 2h, and then sintering was performed at a temperature of 1600°C for 2h to obtain a β"-alumina ceramic. The β"-alumina ceramic had a β" phase content of ≥95%, a bulk density of 3.216g / cm 3 , a theoretical bulk density of 98.95%, and a four-point bending strength of 286MPa.

[0072] Example 2

[0073] The present embodiment provides a preparation method of a β"-alumina ceramic based on gel casting molding, comprising the following steps:

[0074] S1, a β"-alumina ceramic precursor powder with a β" phase content of 98% was prepared by a solid phase synthesis method;

[0075] S2, 10 parts by mass of methacrylamide (C4H7NO) and 2 parts by mass of N'-methylene bisacrylamide (linear molecular formula: (CH2=CHCONH)2CH2) were added to 108 parts by mass of water to obtain a first mixture, and then the first mixture was subjected to first ball milling for 15 min to obtain a uniformly mixed pre-mixture;

[0076] S3, 160 parts by mass of the β"-alumina ceramic precursor powder and 0.32 parts by mass of a sodium polyacrylate dispersant (CAS No. 9003-04-7) were added to the pre-mixture to obtain a second mixture, and then the second mixture was subjected to second ball milling with a ball-to-material ratio of 3:1 for 12h to obtain a first slurry;

[0077] S4, the first slurry was vacuum degassed to obtain a second slurry;

[0078] S5, 1.1 parts by mass of ammonium persulfate ((NH4)2S2O8) was added to the second slurry to obtain a third mixture, and then the third mixture was subjected to third ball milling for 15 min to obtain a third slurry;

[0079] S6, placing the third slurry into a mold, placing in an oven under a temperature condition of 90°C for 12h to perform curing forming to obtain a preform, then demolding the preform to obtain a green body, and the green body strength reaches 15MPa; and

[0080] S7, performing glue removal of the green body under a temperature condition of 500°C for 2h, and then performing sintering under a temperature condition of 1600°C for 2h to obtain a β"-alumina ceramic. The β"-alumina ceramic has a β" phase content of ≥95%, a bulk density of 3.184g / cm 3 , a theoretical bulk density of 97.97%, and a four-point bending strength of 268MPa.

[0081] Example 3

[0082] The embodiment provides a preparation method of a β"-alumina ceramic based on gel casting, comprising the following steps:

[0083] S1, preparing a β"-alumina ceramic precursor powder with a β" phase content of 98% by a solid phase synthesis method;

[0084] S2, adding 12 parts by mass of methacrylamide (C4H7NO) and 2 parts by mass of N'-methylenebisacrylamide (linear molecular formula: (CH2=CHCONH)2CH2) into 80 parts by mass of water to obtain a first mixture, and then performing first ball milling on the first mixture for 15min to obtain a uniformly mixed premix; wherein,

[0085] S3, adding 135 parts by mass of the β"-alumina ceramic precursor powder and 0.4 parts by mass of a sodium polyacrylate dispersant (CAS No. 9003-04-7) into the premix to obtain a second mixture, and then performing second ball milling on the second mixture at a ball-to-material ratio of 5:1 for 12h to obtain a first slurry;

[0086] S4, vacuum deaerating the first slurry to obtain a second slurry;

[0087] S5, adding 1.44 parts by mass of ammonium persulfate ((NH4)2S2O8) into the second slurry to obtain a third mixture, and then performing third ball milling on the third mixture for 15min to obtain a third slurry;

[0088] S6, placing the third slurry into a mold, placing in an oven under a temperature condition of 80°C for 12h to perform curing forming to obtain a preform, then demolding the preform to obtain a green body, and the green body strength reaches 23MPa; and

[0089] S7, the green body is degassed at a temperature of 500°C for 2h, and then sintered at a temperature of 1620°C for 2h to obtain the β"-alumina ceramic. The β"-alumina ceramic has a β" phase content of ≥95%, a bulk density of 3.208g / cm 3 , a theoretical bulk density of 98.71%, and a four-point bending strength of 274MPa.

[0090] Comparative Example 1

[0091] This comparative example provides a preparation method of a β"-alumina ceramic based on gel casting, comprising the following steps:

[0092] S1, a β"-alumina ceramic precursor powder having a β" phase content of 98% is prepared by a solid phase synthesis method;

[0093] S2, 12 parts by mass of methacrylamide (C4H7NO) and 6 parts by mass of N'-methylenebisacrylamide (linear molecular formula: (CH2=CHCONH)2CH2) are added to 60 parts by mass of water to obtain a first mixture, and then the first mixture is subjected to first ball milling for 15min to obtain a uniformly mixed premix;

[0094] S3, 135 parts by mass of the β"-alumina ceramic precursor powder and 0.3 parts by mass of a sodium polyacrylate dispersant (CAS No.: 9003-04-7) are added to the premix to obtain a second mixture, and then the second mixture is subjected to second ball milling at a ball-to-material ratio of 5:1 for 12h to obtain a first slurry;

[0095] S4, the first slurry is vacuum degassed to obtain a second slurry;

[0096] S5, 1.44 parts by mass of ammonium persulfate ((NH4)2S2O8) is added to the second slurry to obtain a third mixture, and then the third mixture is subjected to third ball milling for 15min to obtain a third slurry;

[0097] S6, the third slurry is placed in a mold and placed in an oven at a temperature of 80°C for 12h for solidification molding to obtain a preform, and then the preform is demolded to obtain a green body, and the green body has a strength of less than 5MPa; and

[0098] S7, the green body is degassed at a temperature of 500°C for 2h, and then sintered at a temperature of 1620°C for 2h to obtain the β"-alumina ceramic. The β"-alumina ceramic has a β" phase content of ≥95%, a bulk density of 2.922g / cm 3 , a theoretical bulk density of 89.9%, and a four-point bending strength of 64MPa.

[0099] Comparative Example 2

[0100] The present comparative example provides a preparation method of β"-alumina ceramic based on gel casting, comprising the following steps:

[0101] S1, preparing a β"-alumina ceramic precursor powder with a β" phase content of 98% by a solid phase synthesis method;

[0102] S2, adding 10 parts by mass of methacrylamide (C4H7NO) and 2 parts by mass of N'-methylene bisacrylamide (linear molecular formula: (CH2=CHCONH)2CH2) to 108 parts by mass of water to obtain a first mixture, and then performing first ball milling on the first mixture for 15 min to obtain a uniformly mixed premix;

[0103] S3, adding 160 parts by mass of β"-alumina ceramic precursor powder and 0.48 parts by mass of sodium polyacrylate dispersant (CAS No. 9003-04-7) to the premix to obtain a second mixture, and then performing second ball milling on the second mixture with a ball-to-material ratio of 3:1 and a grinding time of 12 h to obtain a first slurry;

[0104] S4, vacuum degassing the first slurry to obtain a second slurry;

[0105] S5, adding 1.1 parts by mass of ammonium persulfate ((NH4)2S2O8) to the second slurry to obtain a third mixture, and then performing third ball milling on the third mixture for 15 min to obtain a third slurry;

[0106] S6, placing the third slurry in a mold and placing it in an oven at a temperature of 90°C for 12 h for curing and forming to obtain a preform, then demolding the preform to obtain a green body, and the green body strength reaches 16 MPa; and

[0107] S7, performing degassing of the green body at a temperature of 500°C for 2 h, and then performing sintering at a temperature of 1550°C for 2 h to obtain a β"-alumina ceramic. The β" phase content of the β"-alumina ceramic is ≥95%, the bulk density is 3.014 g / cm 3 , only 92.7% of the theoretical bulk density, and the four-point bending strength is 124 MPa.

[0108] Comparative Example 3

[0109] The present comparative example provides a preparation method of β"-alumina ceramic based on gel casting, comprising the following steps:

[0110] S1, a β"-alumina ceramic precursor powder with a β" phase content of 98% is prepared by a solid phase synthesis method;

[0111] S2, 10 parts by mass of methacrylamide (C4H7NO) and 2 parts by mass of N'-methylenebisacrylamide (linear molecular formula: (CH2=CHCONH)2CH2) are added to 108 parts by mass of water to obtain a first mixture, and then the first mixture is subjected to first ball milling for 15 min to obtain a uniformly mixed premix;

[0112] S3, 80 parts by mass of the β"-alumina ceramic precursor powder and 0.1 parts by mass of a sodium polyacrylate dispersant (CAS No. 9003-04-7) are added to the premix to obtain a second mixture, and then the second mixture is subjected to second ball milling with a ball-to-material ratio of 3:1 for 12 h to obtain a first slurry;

[0113] S4, the first slurry is subjected to vacuum degassing to obtain a second slurry;

[0114] S5, 1.1 parts by mass of ammonium persulfate ((NH4)2S2O8) is added to the second slurry to obtain a third mixture, and then the third mixture is subjected to third ball milling for 15 min to obtain a third slurry;

[0115] S6, the third slurry is placed in a mold and placed in an oven at a temperature of 90°C for 12 h for curing and forming to obtain a preform, and then the preform is demolded to obtain a green body, and the green body strength reaches 10 MPa; and

[0116] S7, the green body is subjected to degassing at a temperature of 500°C for 2 h, and then sintering at a temperature of 1550°C for 2 h to obtain a β"-alumina ceramic. The β" phase content of the β"-alumina ceramic is ≥95%, the bulk density is 2.936 g / cm 3 , only 90.3% of the theoretical bulk density, and the four-point bending strength is 92 MPa.

[0117] In addition, according to one or more of the technical solutions in the embodiments of the present disclosure, at least the following technical effects or advantages are achieved:

[0118] In the embodiments of the present disclosure, the process parameters of the preparation method of the β"-alumina ceramic are reasonably designed, which helps to improve the dispersibility and uniformity of each slurry, improve the flowability of each slurry, optimize the curing and forming process, and improve the sintering quality, thereby improving the comprehensive performance of the β"-alumina ceramic.

[0119] In the embodiments of the present disclosure, the prepared β"-alumina ceramic has a high β" phase content, a strong green body processing capability, a high bulk density and excellent mechanical properties after sintering.

[0120] In the embodiments of the present disclosure, the β"-alumina ceramic has a β" phase content of ≥95%, a bulk density of ≥96% of the theoretical bulk density, and a four-point bending strength of ≥250 MP.

[0121] In summary, the preparation method of the β"-alumina ceramic based on gel casting according to some embodiments of the present disclosure has the following advantages compared with the related art:

[0122] The preparation method of the β"-alumina ceramic based on gel casting according to some embodiments of the present disclosure comprises: obtaining a β"-alumina ceramic precursor powder with a set β" phase content; adding monomers and a crosslinking agent into a solvent to obtain a first mixture, and performing first ball milling on the first mixture to obtain a premix; adding the β"-alumina ceramic precursor powder and a dispersing agent into the premix to obtain a second mixture, and performing second ball milling on the second mixture to obtain a first slurry; performing vacuum degassing on the first slurry to obtain a second slurry; adding an initiator into the second slurry to obtain a third mixture, and performing third ball milling on the third mixture to obtain a third slurry; placing the third slurry into a mold for solidification molding to obtain a preform, demolding the preform to obtain a green body; and performing degassing and sintering on the green body to obtain the β"-alumina ceramic. The preparation method of the β"-alumina ceramic based on gel casting according to the present disclosure reasonably designs the process parameters of the preparation method of the β"-alumina ceramic, effectively improves the dispersibility and uniformity of the β"-alumina ceramic precursor powder in the solvent through the multi-stage ball milling process combined with the addition of the dispersing agent; effectively removes the bubbles in the first slurry through vacuum degassing, and further improves the flowability of the first slurry; by adding the initiator into the second slurry and controlling the solidification molding temperature and the holding time of the solidification molding, the chemical reaction between the monomers and the crosslinking agent can be fully carried out, forming a stable three-dimensional gel network structure, which helps to ensure the uniformity of the solidification molding and the strength of the green body. In the degassing and sintering stage, by reasonably controlling the process, the impurities and defects in the β"-alumina ceramic can be further reduced, the sintering quality can be improved, and thus the comprehensive performance of the β"-alumina ceramic is improved.

[0123] The foregoing is merely illustrative of the various implementations of the present disclosure and the general principles thereof. Numerous modifications can be made to these illustrations, and equivalents can be substituted therefor, without departing from the scope of the present disclosure. The specific embodiments commensurate with the specific application are intended to be illustrative only and not limiting of the scope of the application as set forth in the following claims.

Claims

1. A method for preparing a β"-alumina ceramic based on gel casting, comprising: obtaining a β"-alumina ceramic precursor powder with a set β" phase content; adding monomers and a crosslinking agent to a solvent to obtain a first mixture, and performing first ball milling on the first mixture to obtain a premix; adding the β"-alumina ceramic precursor powder and a dispersant to the premix to obtain a second mixture, and performing second ball milling on the second mixture to obtain a first slurry; vacuum degassing the first slurry to obtain a second slurry; adding an initiator to the second slurry to obtain a third mixture, and performing third ball milling on the third mixture to obtain a third slurry; placing the third slurry in a mold for curing and molding to obtain a green body, and demolding the green body to obtain a green compact; and, performing debinding and sintering on the green compact to obtain a β"-alumina ceramic.

2. The method of claim 1, wherein, The set β" phase content is ≥ 95%.

3. The method of claim 1, wherein, The mass concentration of the premix is 10%-20%, wherein the mass ratio of the monomers to the crosslinking agent is (4-6) : 1, the monomers include one or more of methyl acrylamide, acrylamide, and hydroxymethyl acrylamide, and the crosslinking agent includes N, N'-methylene bisacrylamide.

4. The method of claim 1, wherein, The mass of the dispersant is 0.1%-0.3% of the mass of the β"-alumina ceramic precursor powder, and the dispersant includes one or more of sodium polymethacrylate, sodium hexametaphosphate, and sodium polyacrylate.

5. The method of claim 1, wherein, The mass ratio of the β"-alumina ceramic precursor powder to the premix is (1-2.3) : 1, and the solid content of the first slurry is 50%-70%; the ball-to-material ratio of the second ball milling is (3-5) : 1, and the time of the second ball milling is 10-15 hours.

6. The method of claim 1, wherein, The mass of the initiator is 10%-12% of the mass of the monomers, and the initiator includes one or more of ammonium persulfate and sodium persulfate.

7. The method of claim 1, wherein, The temperature of the curing and molding is 80-100℃, and the holding time of the curing and molding is 10-15 hours.

8. The method of claim 1, wherein, The temperature of the debinding is 500-600℃, and the holding time of the debinding is 1.5-2.5 hours.

9. The method of claim 1, wherein, The temperature of the sintering is 1600-1650℃, and the holding time of the sintering is 20-40 minutes.

10. The method according to any one of claims 1 to 9, wherein, The β"-alumina ceramic satisfies at least one of the following properties: the β" phase content is ≥ 95%, the bulk density reaches more than 96% of the theoretical bulk density, and the four-point bending strength is ≥ 250 MPa.

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