Alumina ceramic slurry as well as preparation method and application thereof

Abstract

The invention relates to the technical field of ceramics, in particular to aluminum oxide ceramic slurry as well as a preparation method and application thereof. The aluminum oxide ceramic slurry is prepared from alpha-aluminum oxide coarse powder, alpha-aluminum oxide fine powder, modified aluminum oxide powder, acrylamide, N, N '-methylene bisacrylamide and deionized water, multiple active functional groups are introduced into the surface of the modified aluminum oxide powder, interface bonding of particles with a dispersion medium and a polymer monomer is enhanced, and the surface of the particles is improved. According to the present invention, with the preparation method, the particle agglomeration tendency is reduced, such that the slurry can maintain the low viscosity under the high solid content condition so as to meet the gel injection molding process requirements, and the sintering body obtained through the gel injection molding has characteristics of high bending strength and high hardness, and can be widely used in the fields of electronic devices, mechanical sealing members, biomedical apparatuses and instruments, and the like.

Description

Technical Field

[0001] The present invention relates to the field of ceramic technology, and in particular to an alumina ceramic slurry and a preparation method and application thereof. Background Art

[0002] As an advanced ceramic molding process, gel casting technology realizes slurry solidification molding through in-situ polymerization reaction, and has the advantages of being able to prepare complex shapes and high green body strength. Alumina ceramics are widely used in electronic devices, mechanical seals, biomedicine and other fields due to their excellent mechanical properties, high temperature resistance and chemical stability. However, traditional alumina ceramic slurry faces multiple technical bottlenecks in the gel casting process.

[0003] First, there is an inherent contradiction between the high solid content requirement and the rheological properties of the slurry. Although increasing the solid content can reduce sintering shrinkage, it will cause the slurry viscosity to rise sharply, affecting the casting performance. Conventional dispersants are difficult to effectively maintain system stability when the solid content exceeds 60%, which can easily cause particle sedimentation or agglomeration, resulting in uneven green body density.

[0004] Secondly, the surface characteristics of the powder restrict the interfacial bonding strength. The strong polarity of the hydroxyl groups on the surface of alumina particles easily leads to the formation of a hydrogen bond network in the slurry, which increases the viscosity. Existing surface modification technologies mostly use a single coupling agent for treatment. Although it can improve the dispersibility, the modified layer is easy to decompose and fail during the high-temperature sintering stage, and it is impossible to effectively regulate the powder-matrix interface characteristics.

[0005] Furthermore, the decomposition residues of organic components and the accumulation of shrinkage stress during sintering can easily lead to defects such as micro cracks. The lack of compatibility between the polymer network and ceramic particles in conventional slurries leads to significant volume shrinkage (usually >15%) of the green body during the degreasing and sintering stage, which seriously affects the dimensional accuracy of the product and reduces the mechanical reliability of the final product.

[0006] Therefore, developing an alumina ceramic slurry system with high solid content, excellent rheological properties and sintering stability remains a technical challenge that needs to be overcome in this field. Summary of the invention

[0007] In view of this, the purpose of the present invention is to propose an alumina ceramic slurry and its preparation method and application, so as to solve the problems of traditional alumina ceramic slurry having prominent contradiction between solid content and rheological properties, insufficient powder dispersion stability, high sintering shrinkage rate and the mechanical properties of the final product being difficult to meet high-end application requirements.

[0008] Based on the above purpose, the present invention provides a method for preparing an alumina ceramic slurry, comprising the following steps:

[0009] (1) Add α-aluminum oxide nanopowder into the deionized water / ethanol mixed solution, ultrasonicate for 8 - 12 min, then add γ-methacryloxypropyltrimethoxysilane, heat up to 55 - 65 °C, stir and react for 5 - 7 h, centrifuge, wash, and dry under vacuum to obtain vinylated aluminum oxide powder;

[0010] (2) Under nitrogen protection, add vinylated aluminum oxide nanopowder into anhydrous toluene, ultrasonicate for 8 - 12 min, then add acrylic acid, γ-methacryloxypropyltrimethoxysilane, and 2-hydroxyethyl acrylate, heat up to 75 - 85 °C, add benzoyl peroxide, stir and react for 6 - 10 h, centrifuge, wash, and dry under vacuum to obtain core-shell aluminum oxide powder;

[0011] (3) Add the core-shell aluminum oxide powder into the deionized water / ethanol mixed solution, ultrasonicate for 8 - 12 min, then add γ-methacryloxypropyltrimethoxysilane, heat up to 55 - 65 °C, adjust the pH to 8.5 - 8.8 with ammonia water, stir and react for 6 - 10 h, centrifuge, wash, and dry under vacuum to obtain modified aluminum oxide powder;

[0012] (4) Add α-aluminum oxide coarse powder, α-aluminum oxide fine powder, modified aluminum oxide powder, and deionized water into a ball milling tank, ball mill at a rotation speed of 350 - 550 rpm for 1.5 - 2.5 h to obtain a premixed slurry;

[0013] (5) Add acrylamide and N,N'-methylenebisacrylamide into the premixed slurry, stir for 10 - 20 min, then transfer to a vacuum degassing machine, perform vacuum degassing treatment for 20 - 40 min, adjust the pH to 8.5 - 8.9 with ammonia water, and finally add deionized water to obtain an alumina ceramic slurry with a solid content of 66.4% - 69.8%.

[0014] Preferably, in step (1), the weight ratio of α-aluminum oxide nanopowder, deionized water / ethanol mixed solution, and γ-methacryloxypropyltrimethoxysilane is 10 - 30:300 - 800:0.5 - 2.

[0015] Preferably, in step (1), the particle size D50 of α-aluminum oxide nanopowder is 20 - 100 nm.

[0016] Preferably, the volume ratio of the deionized water / ethanol mixed solution is 1:3.

[0017] Preferably, in step (2), the weight ratio of vinylated aluminum oxide nanopowder, anhydrous toluene, acrylic acid, γ-methacryloxypropyltrimethoxysilane, 2-hydroxyethyl acrylate, and benzoyl peroxide is 10 - 30:300 - 800:12 - 35:0.5 - 2:5 - 15:0.1 - 0.2.

[0018] Preferably, in the step (3), the weight ratio of the core-shell alumina powder, deionized water / ethanol mixed solution and γ-methacryloxypropyltrimethoxysilane is 10-30:300-800:3-10.

[0019] Preferably, in the step (4), the weight ratio of the α-alumina coarse powder, α-alumina fine powder, modified alumina powder and deionized water is 200-240:60-100:10-30:100-200.

[0020] Preferably, in the step (4), the particle size D50 of the α-alumina coarse powder is 0.8-1.2 μm, and the particle size D50 of the α-alumina fine powder is 0.2-0.4 μm.

[0021] Preferably, in the step (4), the grinding medium for ball milling is silicon nitride balls, and the ball-to-material ratio for ball milling is 1:1.

[0022] Preferably, in the step (5), the weight ratio of acrylamide, N,N'-methylenebisacrylamide and the premixed slurry is 20-30:1-2:400-550.

[0023] Preferably, in the step (5), the vacuum degree for vacuum degassing treatment is -0.095 ± 0.001 MPa.

[0024] Furthermore, the present invention also provides an alumina ceramic slurry obtained by the above preparation method of the alumina ceramic slurry.

[0025] Furthermore, the present invention also provides an application of the alumina ceramic slurry, and alumina ceramics can be prepared by gel-casting molding.

[0026] Advantages of the present invention:

[0027] The present invention treats alumina powder by a multi-stage surface modification technology, significantly improving the dispersion stability and interfacial bonding performance of the ceramic slurry, achieving high solid content, low viscosity, excellent sedimentation stability and high mechanical properties of the sintered body. Multiple active functional groups (such as carboxyl, hydroxyl, alkenyl) are introduced on the surface of the modified alumina powder, enhancing the interfacial bonding between the particles and the dispersion medium and polymer monomers, reducing the tendency of particle agglomeration, and enabling the slurry to maintain a low viscosity under high solid content conditions, meeting the requirements of the forming process. At the same time, the introduction of polar groups enhances the electrostatic repulsion and steric hindrance effects between particles, significantly improving the sedimentation stability of the slurry and avoiding the problem of particle stratification during storage.

[0028] During the sintering process of the alumina ceramic slurry provided by the present invention, the surface active groups of the modified powder form chemical bonds with the matrix material, promoting uniform grain growth and densification, reducing structural defects and dimensional changes caused by sintering shrinkage, and significantly improving the dimensional accuracy and mechanical properties of the sintered body. The final product exhibits high flexural strength and high hardness and can be widely applied in fields such as electronic devices, mechanical seals, and biomedical devices. Detailed Embodiments

[0029] To make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the following further elaborates on the present invention in detail with reference to specific embodiments.

[0030] Example 1:

[0031] (1) Add 10 g of α-alumina nanopowder (particle size D50 = 50 nm) to 300 g of a deionized water / ethanol mixed solution (volume ratio 1:3), ultrasonically treat for 8 min, then add 0.5 g of γ-methacryloxypropyltrimethoxysilane, raise the temperature to 55 °C, stir and react for 5 h, centrifuge, wash, and vacuum dry to obtain vinylated alumina powder;

[0032] (2) Under nitrogen protection, add 10 g of vinylated alumina nanopowder to 300 g of anhydrous toluene, ultrasonically treat for 8 min, then add 12 g of acrylic acid, 0.5 g of γ-methacryloxypropyltrimethoxysilane, and 5 g of 2-hydroxyethyl acrylate, raise the temperature to 75 °C, add 0.1 g of benzoyl peroxide, stir and react for 6 h, centrifuge, wash, and vacuum dry to obtain core-shell alumina powder;

[0033] (3) Add 10 g of core-shell alumina powder to 300 g of a deionized water / ethanol mixed solution (volume ratio 1:3), ultrasonically treat for 10 min, then add 3 g of γ-methacryloxypropyltrimethoxysilane, raise the temperature to 55 °C, adjust the pH to 8.5 with ammonia water, stir and react for 6 h, centrifuge, wash, and vacuum dry to obtain modified alumina powder;

[0034] (4) Add 200 g of α-alumina coarse powder (particle size D50 = 1.0 μm), 60 g of α-alumina fine powder (particle size D50 = 0.3 μm), 10 g of modified alumina powder, and 100 g of deionized water to a ball milling tank, use silicon nitride balls as the grinding medium (ball-to-material ratio 1:1), and ball mill at 350 rpm for 1.5 h to obtain a premixed slurry;

[0035] (5) Add 20 g of acrylamide and 1 g of N,N'-methylenebisacrylamide to 400 g of the premixed slurry, mix at a rotation speed of 150 rpm for 10 min, then transfer to a vacuum degassing machine, degas at a vacuum degree of -0.094 MPa for 20 min, adjust the pH to 8.5 with ammonia water, and finally supplement deionized water to obtain an alumina ceramic slurry with a solid content of 66.4%.

[0036] Example 2:

[0037] (1) Add 20 g of α-alumina nanopowder (particle size D50 = 50 nm) to 500 g of a deionized water / ethanol mixed solution (volume ratio 1:3), ultrasonicate for 10 min, then add 1 g of γ-methacryloxypropyltrimethoxysilane, heat up to 60 °C, stir and react for 6 h, centrifuge, wash, and vacuum dry to obtain vinylated alumina powder;

[0038] (2) Under nitrogen protection, add 20 g of vinylated alumina nanopowder to 500 g of anhydrous toluene, ultrasonicate for 10 min, then add 20 g of acrylic acid, 1 g of γ-methacryloxypropyltrimethoxysilane, and 10 g of 2-hydroxyethyl acrylate, heat up to 80 °C, add 0.15 g of benzoyl peroxide, stir and react for 8 h, centrifuge, wash, and vacuum dry to obtain core-shell alumina powder;

[0039] (3) Add 20 g of core-shell alumina powder to 500 g of a deionized water / ethanol mixed solution (volume ratio 1:3), ultrasonicate for 10 min, then add 5 g of γ-methacryloxypropyltrimethoxysilane, heat up to 60 °C, adjust the pH to 8.7 with ammonia water, stir and react for 8 h, centrifuge, wash, and vacuum dry to obtain modified alumina powder;

[0040] (4) Add 220 g of α-alumina coarse powder (particle size D50 = 1.0 μm), 80 g of α-alumina fine powder (particle size D50 = 0.3 μm), 20 g of modified alumina powder, and 150 g of deionized water to a ball mill tank, use silicon nitride balls as the grinding medium (ball-to-material ratio 1:1), ball mill at a rotation speed of 400 rpm for 2 h to obtain a premixed slurry;

[0041] (5) Add 25 g of acrylamide and 1.5 g of N,N'-methylenebisacrylamide to 450 g of the premixed slurry, mix at a rotation speed of 200 rpm for 15 min, then transfer to a vacuum degassing machine, degas at a vacuum degree of -0.095 MPa for 30 min, adjust the pH to 8.8 with ammonia water, and finally supplement deionized water to obtain an alumina ceramic slurry with a solid content of 68.5%.

[0042] Example 3:

[0043] (1) Add 30 g of α-aluminum oxide nanopowder (particle size D50 = 50 nm) to 800 g of a deionized water / ethanol mixed solution (volume ratio 1:3), ultrasonicate for 12 min, then add 2 g of γ-methacryloxypropyltrimethoxysilane, heat up to 65 °C, stir and react for 7 h, centrifuge, wash, and dry under vacuum to obtain vinylated aluminum oxide powder;

[0044] (2) Under nitrogen protection, add 30 g of vinylated aluminum oxide nanopowder to 800 g of anhydrous toluene, ultrasonicate for 12 min, then add 35 g of acrylic acid, 2 g of γ-methacryloxypropyltrimethoxysilane, and 15 g of 2-hydroxyethyl acrylate, heat up to 85 °C, add 0.2 g of benzoyl peroxide, stir and react for 10 h, centrifuge, wash, and dry under vacuum to obtain core-shell aluminum oxide powder;

[0045] (3) Add 30 g of core-shell aluminum oxide powder to 800 g of a deionized water / ethanol mixed solution (volume ratio 1:3), ultrasonicate for 10 min, then add 10 g of γ-methacryloxypropyltrimethoxysilane, heat up to 65 °C, adjust the pH to 8.8 with ammonia water, stir and react for 8 h, centrifuge, wash, and dry under vacuum to obtain modified aluminum oxide powder;

[0046] (4) Add 240 g of α-aluminum oxide coarse powder (particle size D50 = 1.0 μm), 100 g of α-aluminum oxide fine powder (particle size D50 = 0.3 μm), 30 g of modified aluminum oxide powder, and 200 g of deionized water to a ball mill tank, use silicon nitride balls as the grinding medium (ball-to-material ratio 1:1), and ball mill at 550 rpm for 2.5 h to obtain a premixed slurry;

[0047] (5) Add 30 g of acrylamide and 2 g of N,N'-methylenebisacrylamide to 550 g of the premixed slurry, mix at 250 rpm for 20 min, then transfer to a vacuum degassing machine, degas at a vacuum degree of -0.096 MPa for 40 min, adjust the pH to 8.9 with ammonia water, and finally add deionized water to obtain an alumina ceramic slurry with a solid content of 69.8%.

[0048] Comparative Example 1:

[0049] The difference between Comparative Example 1 and Example 2 is that the modified aluminum oxide powder in step (4) is replaced with vinylated aluminum oxide powder;

[0050] The specific steps are as follows:

[0051] (1) Add 20 g of α-aluminum oxide nanopowder (particle size D50 = 50 nm) to 500 g of a deionized water / ethanol mixed solution (volume ratio 1:3), ultrasonicate for 10 min, then add 1 g of γ-methacryloxypropyltrimethoxysilane, heat up to 60 °C, stir and react for 6 h, centrifuge, wash, and vacuum dry to obtain vinylated aluminum oxide powder;

[0052] (2) Add 220 g of α-aluminum oxide coarse powder (particle size D50 = 1.0 μm), 80 g of α-aluminum oxide fine powder (particle size D50 = 0.3 μm), 20 g of vinylated aluminum oxide powder, and 150 g of deionized water to a ball milling tank. Using silicon nitride balls as the grinding medium (ball-to-material ratio 1:1), ball mill at 400 rpm for 2 h to obtain a premixed slurry;

[0053] (3) Add 25 g of acrylamide and 1.5 g of N,N'-methylenebisacrylamide to 450 g of the premixed slurry, mix at 200 rpm for 15 min, then transfer to a vacuum degassing machine, degas at a vacuum degree of -0.095 MPa for 30 min, adjust the pH to 8.8 with ammonia water, and finally supplement deionized water to obtain an alumina ceramic slurry with a solid content of 68.5%.

[0054] Comparative Example 2:

[0055] The difference between Comparative Example 2 and Example 2 is that the modified alumina powder in step (4) is replaced with core-shell alumina powder;

[0056] The specific steps are as follows:

[0057] (1) Add 20 g of α-aluminum oxide nanopowder (particle size D50 = 50 nm) to 500 g of a deionized water / ethanol mixed solution (volume ratio 1:3), ultrasonicate for 10 min, then add 1 g of γ-methacryloxypropyltrimethoxysilane, heat up to 60 °C, stir and react for 6 h, centrifuge, wash, and vacuum dry to obtain vinylated aluminum oxide powder;

[0058] (2) Under nitrogen protection, add 20 g of vinylated aluminum oxide nanopowder to 500 g of anhydrous toluene, ultrasonicate for 10 min, then add 20 g of acrylic acid, 1 g of γ-methacryloxypropyltrimethoxysilane, and 10 g of 2-hydroxyethyl acrylate, heat up to 80 °C, add 0.15 g of benzoyl peroxide, stir and react for 8 h, centrifuge, wash, and vacuum dry to obtain core-shell alumina powder;

[0059] (3) Add 220 g of coarse α-aluminum oxide powder (particle size D50 = 1.0 μm), 80 g of fine α-aluminum oxide powder (particle size D50 = 0.3 μm), 20 g of core-shell aluminum oxide powder (particle size D50 = 50 nm), and 150 g of deionized water into a ball mill tank. Using silicon nitride balls as the grinding medium (ball-to-material ratio 1:1), perform ball milling at a rotational speed of 400 rpm for 2 h to obtain a premixed slurry;

[0060] (4) Add 25 g of acrylamide and 1.5 g of N,N'-methylenebisacrylamide into 450 g of the premixed slurry, mix at a rotational speed of 200 rpm for 15 min, then transfer it to a vacuum degassing machine, perform degassing at a vacuum degree of -0.095 MPa for 30 min, adjust the pH to 8.8 with ammonia water, and finally supplement deionized water to obtain an alumina ceramic slurry with a solid content of 68.5%.

[0061] Comparative Example 3:

[0062] The difference between Comparative Example 3 and Example 2 is that acrylic acid was not added in step (2);

[0063] The specific steps are as follows:

[0064] (1) Add 20 g of α-aluminum oxide nanopowder (particle size D50 = 50 nm) into 500 g of a deionized water / ethanol mixed solution (volume ratio 1:3), ultrasonicate for 10 min, then add 1 g of γ-methacryloxypropyltrimethoxysilane, heat up to 60 °C, stir and react for 6 h, centrifuge, wash, and vacuum dry to obtain vinylated aluminum oxide powder;

[0065] (2) Under nitrogen protection, add 20 g of vinylated aluminum oxide nanopowder into 500 g of anhydrous toluene, ultrasonicate for 10 min, then add 1 g of γ-methacryloxypropyltrimethoxysilane and 10 g of 2-hydroxyethyl acrylate, heat up to 80 °C, add 0.15 g of benzoyl peroxide, stir and react for 8 h, centrifuge, wash, and vacuum dry to obtain core-shell aluminum oxide powder;

[0066] (3) Add 20 g of core-shell aluminum oxide powder into 500 g of a deionized water / ethanol mixed solution (volume ratio 1:3), ultrasonicate for 10 min, then add 5 g of γ-methacryloxypropyltrimethoxysilane, heat up to 60 °C, adjust the pH to 8.7 with ammonia water, stir and react for 8 h, centrifuge, wash, and vacuum dry to obtain modified aluminum oxide powder;

[0067] (4) Add 220 g of coarse α-aluminum oxide powder (particle size D50 = 1.0 μm), 80 g of fine α-aluminum oxide powder (particle size D50 = 0.3 μm), 20 g of modified alumina powder (particle size D50 = 50 nm), and 150 g of deionized water to a ball mill jar. Using silicon nitride balls as the grinding medium (ball-to-material ratio 1:1), perform ball milling at a rotation speed of 400 rpm for 2 h to obtain a premixed slurry;

[0068] (5) Add 25 g of acrylamide and 1.5 g of N,N'-methylenebisacrylamide to 450 g of the premixed slurry, mix at a rotation speed of 200 rpm for 15 min, then transfer to a vacuum degassing machine, perform degassing treatment at a vacuum degree of -0.095 MPa for 30 min, adjust the pH to 8.8 with ammonia water, and finally supplement deionized water to obtain an alumina ceramic slurry with a solid content of 68.5%.

[0069] Comparative Example 4:

[0070] The difference between Comparative Example 4 and Example 2 is that: in step (2), γ-methacryloxypropyltrimethoxysilane was not added;

[0071] The specific steps are as follows:

[0072] (1) Add 20 g of α-aluminum oxide nanopowder (particle size D50 = 50 nm) to 500 g of a deionized water / ethanol mixed solution (volume ratio 1:3), ultrasonicate for 10 min, then add 1 g of γ-methacryloxypropyltrimethoxysilane, heat up to 60 °C, stir and react for 6 h, centrifuge, wash, and vacuum dry to obtain vinylated alumina powder;

[0073] (2) Under nitrogen protection, add 20 g of vinylated alumina nanopowder to 500 g of anhydrous toluene, ultrasonicate for 10 min, then add 20 g of acrylic acid and 10 g of hydroxyethyl acrylate, heat up to 80 °C, add 0.15 g of benzoyl peroxide, stir and react for 8 h, centrifuge, wash, and vacuum dry to obtain core-shell alumina powder;

[0074] (3) Add 20 g of core-shell alumina powder to 500 g of a deionized water / ethanol mixed solution (volume ratio 1:3), ultrasonicate for 10 min, then add 5 g of γ-methacryloxypropyltrimethoxysilane, heat up to 60 °C, adjust the pH to 8.7 with ammonia water, stir and react for 8 h, centrifuge, wash, and vacuum dry to obtain modified alumina powder;

[0075] (4) Add 220 g of α-aluminum oxide coarse powder (particle size D50 = 1.0 μm), 80 g of α-aluminum oxide fine powder (particle size D50 = 0.3 μm), 20 g of modified alumina powder (particle size D50 = 50 nm) and 150 g of deionized water into a ball milling tank. Using silicon nitride balls as the grinding medium (ball-to-material ratio 1:1), ball mill at a rotation speed of 400 rpm for 2 h to obtain a premixed slurry;

[0076] (5) Add 25 g of acrylamide and 1.5 g of N,N'-methylenebisacrylamide into 450 g of the premixed slurry, mix at a rotation speed of 200 rpm for 15 min, then transfer to a vacuum degassing machine, degas at a vacuum degree of -0.095 MPa for 30 min, adjust the pH to 8.8 with ammonia water, and finally supplement deionized water to obtain an alumina ceramic slurry with a solid content of 68.5%.

[0077] Comparative Example 5:

[0078] The difference between Comparative Example 5 and Example 2 is that: hydroxyethyl acrylate was not added in step (2);

[0079] The specific steps are as follows:

[0080] (1) Add 20 g of α-aluminum oxide nanopowder (particle size D50 = 50 nm) into 500 g of a deionized water / ethanol mixed solution (volume ratio 1:3), ultrasonicate for 10 min, then add 1 g of γ-methacryloxypropyltrimethoxysilane, heat up to 60 °C, stir and react for 6 h, centrifuge, wash, and vacuum dry to obtain vinylated alumina powder;

[0081] (2) Under nitrogen protection, add 20 g of vinylated alumina nanopowder into 500 g of anhydrous toluene, ultrasonicate for 10 min, then add 20 g of acrylic acid and 1 g of γ-methacryloxypropyltrimethoxysilane, heat up to 80 °C, add 0.15 g of dibenzoyl peroxide, stir and react for 8 h, centrifuge, wash, and vacuum dry to obtain core-shell alumina powder;

[0082] (3) Add 20 g of core-shell alumina powder into 500 g of a deionized water / ethanol mixed solution (volume ratio 1:3), ultrasonicate for 10 min, then add 5 g of γ-methacryloxypropyltrimethoxysilane, heat up to 60 °C, adjust the pH to 8.7 with ammonia water, stir and react for 8 h, centrifuge, wash, and vacuum dry to obtain modified alumina powder;

[0083] (4) Add 220 g of coarse α-aluminum oxide powder (particle size D50 = 1.0 μm), 80 g of fine α-aluminum oxide powder (particle size D50 = 0.3 μm), 20 g of modified alumina powder (particle size D50 = 50 nm), and 150 g of deionized water to a ball mill jar. Using silicon nitride balls as the grinding medium (ball-to-material ratio 1:1), perform ball milling at a rotational speed of 400 rpm for 2 h to obtain a premixed slurry;

[0084] (5) Add 25 g of acrylamide and 1.5 g of N,N'-methylenebisacrylamide to 450 g of the premixed slurry. Mix at a rotational speed of 200 rpm for 15 min, then transfer to a vacuum degassing machine and degas at a vacuum degree of -0.095 MPa for 30 min. Adjust the pH to 8.8 with ammonia water, and finally supplement deionized water to obtain an alumina ceramic slurry with a solid content of 68.5%.

[0085] Performance testing:

[0086] Viscosity: Using an NDJ-8S type rotational viscometer, under the constant temperature condition of 25 °C, select a No. 4 rotor and measure the apparent viscosity of the slurry at a rotational speed of 30 rpm. Each sample is tested in parallel 3 times, and the arithmetic mean is taken. The results are shown in Table 1.

[0087] Sedimentation stability: Inject 50 ml of the slurry into a standard colorimetric tube and place it statically in a constant temperature environment of 25 °C. Record the sedimentation interface height every 24 hours and continuously observe for 7 days. When the height of the sedimentation layer exceeds 5% of the total height, it is judged as unstable.

[0088] Preparation of sintered body: Add 0.15 g of ammonium persulfate initiator (pre-dissolved in 5 ml of deionized water) to the slurry, stir for 5 min, then add 1 g of tetramethylethylenediamine, immediately inject it into a polytetrafluoroethylene mold, and gel-cure in a constant temperature oven at 40 °C for 2 h. Take out the gel blank from the mold and place it in an environment with a humidity of 90% for 24 h, then dry it in an oven at 80 °C for 48 h to obtain a dried blank. Heat it to 600 °C at a rate of 2 °C / min and hold for 1 h to remove organic matter, then heat it to 1650 °C at a rate of 5 °C / min and hold for 2 h, and take it out after cooling to 200 °C with the furnace to obtain a sintered body.

[0089] Linear shrinkage rate: Measure the dimensions of the sample before and after sintering and calculate the linear shrinkage rate. The results are shown in Table 1.

[0090] Flexural strength: Refer to GB / T 6569-2006, use a WDW-3100 electronic universal testing machine, with a span of 20 mm and a loading rate of 0.5 mm / min. The results are shown in Table 1.

[0091] Hardness: According to GB / T 16534-2009, use an HVS-1000 microhardness tester, with a load of 4.9 N and a holding time of 15 s. The results are shown in Table 1.

[0092] Table 1 Performance Test Results

[0093]

[0094]

[0095] Data Analysis:

[0096] From the data of Examples 1 - 3 in Table 1, it can be seen that the alumina ceramic slurry prepared by the present invention has excellent comprehensive properties. It has a high solid content, a small viscosity, good sedimentation stability, which can ensure the uniformity and stability of the slurry during storage and use. The sintered body shows a low linear shrinkage rate, indicating that the material has a small size change during sintering, which helps to improve the dimensional accuracy of the ceramic product. At the same time, the sintered body has high flexural strength and hardness, indicating that its internal microstructure is dense, the bonding force between grains is strong, and the porosity is low, which can meet the requirements of high-performance ceramic materials. The realization of these excellent properties may be due to the introduction of modified alumina powder. Through surface modification, the dispersibility and interfacial bonding properties of the powder are improved, so that the ceramic slurry can form a more uniform microstructure during subsequent forming and sintering processes, thus significantly improving the mechanical properties of the final material.

[0097] From the data of Example 2 and Comparative Example 1 in Table 1, it can be seen that the use of modified alumina powder in the present invention can significantly improve the viscosity and sedimentation stability of the ceramic slurry and have a positive impact on the mechanical properties of the sintered body. The vinylated alumina without final surface modification has a single surface functional group, which is prone to particle agglomeration in the slurry, resulting in an increase in viscosity and a sudden drop in sedimentation stability. The active groups introduced by the modification treatment effectively improve the dispersion stability of polymer monomers and alumina particles in the slurry, and also construct a continuous phase reinforcement structure during sintering, which can more effectively transfer stress loads, improve the flexural strength, and at the same time reduce the structural defects caused by sintering shrinkage.

[0098] From the data of Example 2 and Comparative Example 2 in Table 1, it can be seen that the use of modified alumina powder further optimizes the viscosity of the ceramic slurry and the mechanical properties of the sintered body compared with core-shell alumina powder. Although the core-shell structure initially improves the particle dispersibility, it lacks vinyl functional groups, resulting in difficulty in effectively constructing connections between polymer monomers and alumina particles, and it cannot better combine with the matrix material during the sintering process to promote the uniform densification of the ceramic material and reduce the pores and defects in the microstructure.

[0099] From the data of Example 2 and Comparative Example 3 in Table 1, it can be seen that adding acrylic acid during the surface modification of alumina powder plays an important role in controlling the viscosity of the slurry and improving the properties of the sintered body. As an acidic monomer, its carboxyl group can form a coordination bond with the hydroxyl groups on the alumina surface, generating an electrostatic stabilization effect in the slurry. During the polymerization stage, the acrylic acid unit can increase the polarity of the polymer chain and enhance the compatibility with the inorganic phase. Experimental data show that the lack of acrylic acid leads to an increase in the viscosity of the slurry, which is due to the aggregation effect caused by insufficient surface charge density of the particles. During the sintering process, the carboxylic acid groups derived from acrylic acid participate in the formation of metal-organic coordination cross-linking points, and this dual mechanism significantly enhances the flexural properties of the material.

[0100] From the data of Example 2 and Comparative Example 4 in Table 1, it can be seen that adding γ-methacryloxypropyltrimethoxysilane during the modification of alumina powder is of great significance for improving the properties of the slurry and the sintered body. γ-Methacryloxypropyltrimethoxysilane functions as both a coupling agent and a comonomer, effectively constructing an organic-inorganic hybrid interface layer and enabling the stress to be buffered in a gradient manner at the interface.

[0101] From the data of Example 2 and Comparative Example 5 in Table 1, it can be seen that adding 2-hydroxyethyl acrylate during the surface modification of alumina powder has a significant effect on improving the comprehensive properties of the slurry and the sintered body. This may be because the hydroxyl functional group of 2-hydroxyethyl acrylate can participate in the construction of the hydrogen bond network to improve the rheology of the slurry, enhance its dispersibility and stability in the slurry, thereby reducing the viscosity of the slurry and prolonging its sedimentation stability. During the sintering process, the introduction of 2-hydroxyethyl acrylate may promote the uniform growth and densification of grains, reduce the defects and pores inside the sintered body, and further improve the flexural strength and hardness. This indicates that 2-hydroxyethyl acrylate not only plays the role of a dispersion stabilizer during the powder modification process, but may also enhance the interfacial bonding performance between the powder and the matrix material through chemical reactions, thus significantly improving the final properties of the ceramic material.

[0102] Those of ordinary skill in the art should understand that: the discussion of any of the above embodiments is only exemplary and is not intended to imply that the scope of the present invention is limited to these examples; under the concept of the present invention, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations in different aspects of the present invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A method for preparing an alumina ceramic slurry, characterized in that: The following steps are involved: (1) adding α-alumina nanopowder to a deionized water / ethanol mixed solution, ultrasonicating for 8-12 minutes, then adding γ-methacryloxypropyltrimethoxysilane, heating to 55-65° C., stirring for reaction for 5-7 hours, centrifuging, washing, and vacuum drying to obtain olefinic alumina powder; (2) under nitrogen protection, adding olefinic alumina nanopowder into anhydrous toluene, ultrasonicating for 8-12 min, adding acrylic acid, γ-methacryloxypropyltrimethoxysilane and hydroxyethyl acrylate, heating to 75-85° C., adding dibenzoyl peroxide, stirring for 6-10 h, centrifuging, washing, and vacuum drying to obtain core-shell alumina powder; (3) adding the core-shell alumina powder to a deionized water / ethanol mixed solution, ultrasonicating for 8-12 minutes, then adding γ-methacryloxypropyltrimethoxysilane, heating to 55-65° C., adjusting the pH to 8.5-8.8 with ammonia water, stirring the reaction for 6-10 hours, centrifuging, washing, and vacuum drying to obtain a modified alumina powder; (4) Add α-alumina coarse powder, α-alumina fine powder, modified alumina powder and deionized water into a ball mill, and mill at a speed of 350-550 rpm for 1.5-2.5 h to obtain a premixed slurry; (5) adding acrylamide and N,N'-methylenebisacrylamide to the premixed slurry for 10-20 minutes, then transferring to a vacuum degassing machine, vacuum degassing for 20-40 minutes, adjusting the pH to 8.5-8.9 with ammonia water, and finally adding deionized water to obtain an alumina ceramic slurry with a solid content of 66.4%-69.8%; In the step (2), the weight ratio of olefinated aluminum oxide nanopowder, anhydrous toluene, acrylic acid, γ-methacryloxypropyltrimethoxysilane, hydroxyethyl acrylate and dibenzoyl peroxide is 10-30:300-800:12-35:0.5-2:5-15:0.1-0.2; In the step (3), the weight ratio of the core-shell alumina powder, the deionized water / ethanol mixed solution and γ-methacryloxypropyltrimethoxysilane is 10-30:300-800:3-10; In the step (4), the weight ratio of the α-alumina coarse powder, the α-alumina fine powder, the modified alumina powder and the deionized water is 200-240:60-100:10-30:100-200.

2. The method for preparing alumina ceramic slurry according to claim 1, characterized in that: In the step (1), the weight ratio of α-alumina nanopowder, deionized water / ethanol mixed solution and γ-methacryloxypropyltrimethoxysilane is 10-30:300-800:0.5-2.

3. The method for preparing alumina ceramic slurry according to claim 1, characterized in that: The particle size D50 of the α-alumina nanopowder in step (1) is 20-100 nm.

4. The method for preparing alumina ceramic slurry according to claim 1, characterized in that: The volume of the deionized water / ethanol mixed solution is 1:

3.

5. The method for preparing alumina ceramic slurry according to claim 1, characterized in that: In the step (4), the particle size D50 of the α-alumina coarse powder is 0.8-1.2 μm, and the particle size D50 of the α-alumina fine powder is 0.2-0.4 μm.

6. The method for preparing alumina ceramic slurry according to claim 1, characterized in that: The grinding medium of the ball milling in the step (4) is silicon nitride balls, and the ball-to-material ratio of the ball milling is 1:

1.

7. The method for preparing alumina ceramic slurry according to claim 1, characterized in that: In the step (5), the weight ratio of acrylamide, N,N'-methylenebisacrylamide and premixed slurry is 20-30:1-2:400-550.

8. The method for preparing alumina ceramic slurry according to claim 1, characterized in that: The vacuum degree of the vacuum degassing treatment in step (5) is -0.095±0.001MPa.

9. An alumina ceramic slurry, characterized in that: The alumina ceramic slurry is obtained by the preparation method of any one of claims 1 to 8.

10. An application of the alumina ceramic slurry according to claim 9, characterized in that: Alumina ceramics were prepared by gel casting.

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