High-solid-content aluminum oxide slurry and fine-grain aluminum oxide ceramic material

Abstract

The invention relates to high-solid-content aluminum oxide slurry which comprises 65-80 wt% of aluminum oxide powder, 1-3 wt% of a dispersing agent and 5-30 wt% of a solvent. The particle size D50 of the alumina powder is 200-600 nm, the particle size D90 of the alumina powder is 0.8-2 [mu] m, and the specific surface area BET of the alumina powder is 4-15 m < 2 > / g; the dispersing agent is a combination of dispersing agents containing ester groups, phosphate groups and polyoxyethylene structures; the viscosity of the aluminum oxide slurry with high solid content is 3000 to 10000 cp. The composite dispersing agent is prepared through the synergistic effect of functional groups in the dispersing agent containing an ester group, a phosphate group and a polyoxyethylene structure, good dispersity in slurry with the aluminum oxide powder content as high as 65-80 wt% is achieved, and finally the aluminum oxide ceramic material which is small in grain size, high in density and excellent in Vickers hardness and dielectric property is prepared.

Description

Technical Field

[0001] This invention belongs to the field of special ceramics technology, specifically relating to a high-solids-content alumina slurry and a fine-grained alumina ceramic material. Background Technology

[0002] Alumina ceramics are ceramic materials with excellent comprehensive performance and have been widely used in power devices, 5G communications, and other fields. To meet the requirements of higher operating environments, alumina materials need to achieve higher bulk density, thereby obtaining higher Vickers hardness and breakdown voltage. High purity and fine grain refinement are the main ways to improve the performance of alumina materials, specifically manifested in small and uniform crystal particles and high bulk density.

[0003] Nano-alumina powder is beneficial for preparing high-performance fine-grained alumina materials, and the tape casting process is a key technology for its large-scale preparation. Increasing the thickness of the tape cast film can significantly improve production efficiency. However, achieving good dispersion of nano-alumina powder in the slurry is not easy. When preparing the tape cast slurry, multiple factors must be considered, including the amount of ball milling solvent, dispersant, slurry solid content, and ball milling process. Furthermore, the synergistic effect between various components in the tape cast slurry directly affects the uniformity of the slurry, the uniformity of the film, and the final performance of the ceramic material.

[0004] Because nano-alumina ceramic powder has a smaller particle size and a larger specific surface area, the amounts of solvents and dispersants in the slurry formulation design need to be adjusted accordingly. Increasing the solvent directly reduces the solid content of the slurry. Lower solid content is detrimental to thick-film casting, especially for cast films thicker than 300 μm, which are more prone to cracking and warping defects. Excessive dispersant in the formulation significantly increases intermolecular forces within the slurry, resulting in increased viscosity, poorer flowability, and hindering leveling during casting. This leads to warping, deformation, and significant thickness variations in the resulting films. Conversely, insufficient dispersant results in inadequate dispersion of the nano-alumina powder, excessive large particle agglomerates, and uneven slurry mixing, ultimately leading to a lower bulk density of the sintered material.

[0005] Therefore, preparing a nano-alumina casting slurry with high solid content, uniform particle dispersion, and suitable for thick film casting, and ultimately sintering it to obtain an alumina material with uniform grain size and high bulk density, has become a technical challenge. Summary of the Invention

[0006] The purpose of this invention is to provide an alumina slurry with high solid content, uniform particle dispersion, and suitable for thick film casting. This alumina slurry can produce a cast film with a thickness of more than 300 μm. After sintering, the cast film can produce an alumina ceramic material with fine average grain size, excellent bulk density, Vickers hardness, and breakdown voltage resistance.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0008] In a first aspect, this application provides a high-solids-content alumina slurry, comprising 65-80 wt% alumina powder, 1-3 wt% dispersant, and 5-30 wt% solvent; wherein the alumina powder has a particle size D50 of 200-600 nm, a particle size D90 of 0.8-2 μm, and a specific surface area BET of 4-15 m². 2 / g; the dispersant is a combination of dispersants containing ester groups, phosphate groups and polyethylene oxide structures; the viscosity of the high solids content alumina slurry is 3000~10000 cp.

[0009] In some possible implementations, the ester-containing dispersant includes at least one of polyacrylate, polycaprolactone polyol ester, glyceryl stearate, and hydroxyacrylate.

[0010] In some possible implementations, the phosphate-containing dispersant includes at least one of castor oil phosphate, polyphosphate, diester phosphate, and triethyl phosphate.

[0011] In some possible embodiments, the dispersant containing a polyethylene oxide structure includes at least one of fatty alcohol polyoxyethylene ether phosphate, dodecylamine polyoxyethylene ether, fatty alcohol ether phosphate, and lauryl alcohol polyoxyethylene ether sulfosuccinate.

[0012] In some possible embodiments, the dispersant contains ester groups, phosphate groups and polyethylene oxide structures in a mass ratio of (0.1-0.3):1:(0.1-0.5).

[0013] In some possible implementations, the solvent is a mixture of toluene and ethanol.

[0014] In the above possible implementation, the mass ratio of toluene to ethanol is 1:(0.5 to 1.5).

[0015] Secondly, this application provides a method for preparing a high-solids-content alumina slurry, characterized by comprising the following steps:

[0016] S1. First step of mixing: Add alumina powder to the solvent, and disperse it by grinding to obtain the first mixed slurry;

[0017] S2. Second mixing step: Add dispersant to the first mixed slurry, continue grinding and dispersing to obtain the second mixed slurry;

[0018] S3. Third step of mixing: Add binder and plasticizer to the second mixed slurry and continue grinding and dispersing, then degas under vacuum to obtain the high solids content alumina slurry.

[0019] Thirdly, this application provides a ceramic cast film, which is formed by casting a high-solids-content alumina slurry provided in the first aspect of this application to obtain a ceramic cast film with a thickness of 300-600 μm.

[0020] Fourthly, this application provides a fine-grained alumina ceramic material, which is prepared by stacking, forming, debinding and sintering the ceramic cast film provided in the third aspect of this application, and has an average grain size of 1~2 μm.

[0021] Beneficial effects:

[0022] By leveraging the synergistic effect of functional groups in dispersants containing ester groups, phosphate groups, and polyethylene oxide structures, a composite dispersant was prepared. This achieved good dispersibility in slurries with alumina powder content as high as 65-80 wt%, and produced thick films with a casting thickness exceeding 300 μm. Ultimately, alumina ceramic materials with fine grain size, high density, excellent Vickers hardness, and superior dielectric properties were obtained. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only a part of the embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 Here is a SEM image of the fine-grained alumina ceramic material in Example 4;

[0025] Figure 2 The image shows the SEM image of the fine-grained alumina ceramic material in Comparative Example 4. Detailed Implementation

[0026] The embodiments of the present invention will be described in detail below with reference to the examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present invention and not to limit the scope of the invention. Specific conditions not specified in the examples shall be carried out under conventional conditions or the manufacturer's recommended conditions. If the manufacturers of the reagents or instruments used are not specified, they can be conventional products that are commercially available or purchased.

[0027] It should be noted that the following embodiments are examples of this application and are used only to illustrate this application, and are not intended to limit this application. Other combinations and various modifications within the scope of this application are possible without departing from the spirit or scope of this application.

[0028] The following provides a detailed description of the high-solids-content alumina slurry, the preparation method of the high-solids-content alumina slurry, the ceramic cast film, and the fine-grained alumina ceramic material provided in this application.

[0029] High Solids Alumina Slurry

[0030] This embodiment provides a high-solids-content alumina slurry, wherein the mass proportion of alumina powder can be as high as 65-80 wt%, which can better balance the slurry viscosity, tensile strength of green ceramic sheets, sintering shrinkage rate, and sintering density. Furthermore, an excessively high mass proportion of alumina powder will result in excessively high slurry viscosity, poor flowability, or poor uniformity of cast film thickness; conversely, an excessively low mass proportion of alumina powder will result in an overly thin slurry or an excessively thin cast film.

[0031] The alumina powder used in this embodiment has a particle size D50 of 200~600 nm, a D90 of 0.8~2 μm, and a specific surface area BET of 4~15 m². 2 / g, if the alumina powder has a small particle size and a large specific surface area, it will be more difficult to disperse; if the alumina powder has a large particle size and a small specific surface area, it will be detrimental to the improvement of the mechanical properties of the ceramic material after sintering.

[0032] This embodiment provides a high-solids-content alumina slurry, comprising 1-3 wt% dispersant, thus achieving a slurry with better stability. Too low a dispersant content will result in excessively high slurry viscosity and poor stability, while too high a dispersant content will lead to a sharp increase in slurry viscosity and poor flowability.

[0033] In this embodiment, the dispersant is a combination of dispersants containing ester groups, phosphate groups, and polyethylene oxide structures. The dispersants containing ester groups include at least one of polyacrylate, polycaprolactone polyol ester, glyceryl stearate, and hydroxy acrylate, preferably polyacrylate. Commercially available examples include BYK-LP-C, BYK-307, and BYK-358N from BYK Chemicals (Germany), SNF FLOSPERSE 3000 from Essen (France), and SNDISPERSANT SF8, SNDISPERSANT 9228, and SNDISPERSANT 5023 from Sinopco.

[0034] Dispersants containing phosphate groups include at least one of castor oil phosphate, polyphosphate, diester phosphate, and triethyl phosphate, preferably castor oil phosphate. Commercially available examples include BYK-103, BYK-110, BYK-145, BYK2009 from BYK Chemicals (Germany), TEGO DISPERS 655 from Evonik, and 1403 from Shoucheng Chemicals.

[0035] Dispersants containing a polyethylene oxide structure include at least one of fatty alcohol polyoxyethylene ether phosphate, dodecylamine polyoxyethylene ether, fatty alcohol ether phosphate, and lauryl alcohol polyoxyethylene ether sulfosuccinate, preferably fatty alcohol polyoxyethylene ether phosphate, such as AEO-3 and AEO-9 from Jinyu Chemical Co., Ltd.

[0036] In this embodiment, the synergistic effect of the long-chain steric hindrance of the dispersant and the electrostatic adsorption of polar groups on the long chain can obtain a high-solids-content alumina slurry with alumina powder content of up to 65-80 wt% and good stability. In addition, it can also reduce particle agglomeration and refine the particle size.

[0037] In some alternative embodiments, the dispersant contains ester groups, phosphate groups and polyethylene oxide structures in a mass ratio of (0.1-0.3):1:(0.1-0.5).

[0038] This embodiment provides a high solids content alumina slurry, comprising 5-30 wt% solvent. The solvent may be a mixture of benzene and alcohol, or benzene and ester, preferably a mixture of toluene and ethanol, and more preferably a mixture of toluene and ethanol in a weight ratio of 1:(0.5-1.5).

[0039] As is well known in the art, this embodiment also includes 3-12 wt% binder, which can comprehensively balance the tensile strength of the green ceramic sheet and the sintering density of the material. Too high a mass ratio will lead to poor sintering density; too low a mass ratio will lead to low tensile strength of the green ceramic sheet or even casting cracking.

[0040] The binder can be polyvinyl butyral resin, which has a molecular weight of 50,000 to 150,000 and a hydroxyl content of 15 to 25 wt%. Choosing this type of polyvinyl butyral makes the casting slurry more stable and avoids flocculation of ceramic powder, which would prevent the slurry from being cast. In some embodiments, the polyvinyl butyral binder can be added in the form of a solution with a mass concentration higher than 30%, and the solvent type is the same as or similar to that of the high-solids-content alumina slurry solvent.

[0041] As is well known in the art, this embodiment also includes a plasticizer, the mass ratio of which is 35-65% of the binder. This enables the green ceramic sheet to have suitable tensile strength. If the mass ratio is too high, the tensile strength will be low, and if the mass ratio is too low, the ceramic cast film will be brittle, which is not conducive to subsequent processing.

[0042] The plasticizer can be selected from one or more combinations of dibutyl phthalate, glycerol, polyethylene glycol, diisobutyl phthalate, and dioctyl phthalate.

[0043] In this embodiment, the viscosity of the high-solids alumina slurry is 3000~10000 cp, which is beneficial for subsequent tape casting steps and for increasing the density of the ceramic material after sintering.

[0044] <Preparation Method of High Solids Alumina Slurry>

[0045] S1. First step of mixing: Toluene, ethanol and alumina powder are added to the ball mill jar in sequence, and then mixed at a speed of 30-60 r / min and at room temperature for 0.5-2 hours to obtain the first mixed slurry.

[0046] S2. Second mixing step: Add dispersant to the first mixed slurry, and then continue mixing for 4 to 12 hours at a speed of 30 to 60 r / min and at room temperature to obtain the second mixed slurry;

[0047] S3. Third step mixing: Add binder and plasticizer to the second mixed slurry and continue ball milling for 4 to 12 hours. Then filter the slurry and transfer it to a vacuum degassing tank. Continue mixing at a vacuum degree of less than -0.085 MPa and a stirring speed of 10 to 50 r / min for 0.5 to 2 hours to obtain a high solids content alumina slurry.

[0048] <Ceramic Cast Film>

[0049] The high-solids-content alumina slurry provided in the first aspect of this application is suitable for thick film casting and can easily produce ceramic casting films with a thickness of 300 to 600 μm, which is beneficial to improving the Vickers hardness, breakdown voltage and other properties of the sintered ceramic material.

[0050] <Fine-grained alumina ceramic materials>

[0051] The ceramic casting film provided in the third aspect of this application can be used to prepare fine-grained alumina ceramic materials through steps such as stacking, forming, debinding and sintering. The average grain size of 1~2 μm is beneficial to improving the bulk density of alumina ceramic materials and further enhancing the Vickers hardness and dielectric properties of alumina ceramic materials.

[0052] Example

[0053] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that the embodiments are merely illustrative of the present invention and should not be construed as specific limitations thereof.

[0054] In this embodiment, the raw materials are all commercially available bulk industrial products, and the manufacturers include BASF, Wanhua Chemical, Asahikawa Chemical, Huafeng, etc.

[0055] Preparation Example 1

[0056] S1. First step mixing: Using a 10 L ball mill jar, add 7 wt% toluene, 7 wt% ethanol, and 72 wt% alumina powder (particle size D50: 300 nm; particle size D90: 1.6 μm; specific surface area BET: 12 m²) sequentially. 2 / g), and then mix at 50r / min for 1 hour to obtain the first mixed slurry;

[0057] S2. Second step mixing: Add 2.2 wt% dispersant to the first mixed slurry, and then mix at 50 r / min for 8 hours to obtain a second mixed slurry in which alumina powder is uniformly dispersed;

[0058] S3. Third step mixing: Add 8 wt% polyvinyl butyral (PVB) and 3.8 wt% dibutyl phthalate to the second mixed slurry, and then mix at 50 r / min for 8 hours to obtain the third mixed slurry; after filtering the third mixed slurry, transfer it to a vacuum degassing tank, and then continue mixing and degassing for 2 hours under a vacuum of -0.090 MPa and a stirring speed of 30 r / min to obtain a high solids content alumina slurry.

[0059] Preparation Examples 2-8

[0060] The preparation methods of Preparation Examples 2-8 are the same as those of Preparation Example 1, except that the content of alumina powder, the type and content of dispersant, and the type and content of solvent are different, as detailed in Table 1.

[0061] Preparation of Comparative Examples 1-5

[0062] The preparation methods for Comparative Examples 1 to 5 are the same as those for Preparation Example 1, except that the content of alumina powder, the type and content of dispersant, and the type and content of solvent are different, as detailed in Table 1.

[0063] Comparative Example 6

[0064] The formulation and preparation method of Comparative Example 6 are the same as those of Preparation Example 1, except that the alumina powder has a particle size D50 of 800 nm, a particle size D90 of 3.2 μm, and a specific surface area BET of 3 m². 2 / g.

[0065] Viscosity evaluation

[0066] The viscosity of the high solids content alumina slurry of the prepared example and the comparative prepared example was measured using a Brookfield DV2T viscometer with a 27# rotor at 25℃ / 5rpm / 3min.

[0067] Table 1

[0068]

[0069] Example 1

[0070] The high-solids-content alumina slurry obtained in Preparation Example 1 was used to prepare a ceramic film by casting on a casting machine at a casting speed of 0.3 m / min.

[0071] Fine-grained alumina ceramic material was obtained by sintering the cast film at a maximum temperature of 1450 ℃ for 4 h.

[0072] Examples 2-8

[0073] The preparation methods of Examples 2-8 are the same as those of Example 1.

[0074] Comparative Examples 1-6

[0075] The preparation methods of Comparative Examples 2-8 are the same as those of Example 1.

[0076] Ceramic Cast Film Thickness Testing

[0077] The thickness of the ceramic cast film in the embodiment and comparative examples was tested using a Keyence CL-3000 series color laser coaxial displacement meter.

[0078] Ceramic Cast Film Appearance Evaluation

[0079] Visually inspect the ceramic cast film for defects such as cracks. If there are no cracks, use the symbol ○; if there are a few small cracks, use the symbol ×; if there are a lot of serious cracks, use the symbol ××.

[0080] Grain size evaluation

[0081] A field emission scanning electron microscope (SEM), model JCM-7000, was used to photograph the ceramic section of the product for morphological observation. The particle size of the fine-grained alumina ceramic material was measured at three different locations, and the average value was calculated after measuring 30 grains at each location.

[0082] Bulk density evaluation

[0083] The volume density of the sample was tested using a true density meter, model number 250217P10266, through the gas expansion displacement method based on Archimedes' principle.

[0084] Vickers hardness evaluation

[0085] Referring to the national standard GB / T 16534-1996, the Vickers hardness tester model is GSD-754K.

[0086] Dielectric strength evaluation

[0087] The Bailibo VBT withstand voltage breakdown tester was used, and the sample thickness was measured with vernier calipers. The maximum voltage was set to 30kV and the voltage rise time was 60s. After the test was completed, the breakdown voltage was read and recorded. The dielectric strength was calculated according to the formula: Dielectric strength = Breakdown voltage / Thickness (unit: kV / mm).

[0088] The performance evaluation results of the examples and comparative examples are shown in Table 2.

[0089] Table 2

[0090]

[0091] It should be noted that, based on the explanations and descriptions in the foregoing specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some equivalent modifications and alterations to the present invention should also be within the scope of protection of the claims of the present invention. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the invention.

Claims

1. A high-solids-content alumina slurry, characterized in that, The composition includes 65-80 wt% alumina powder, 1-3 wt% dispersant, and 5-30 wt% solvent; the alumina powder has a particle size D50 of 200-600 nm, a particle size D90 of 0.8-2 μm, and a specific surface area BET of 4-15 m². 2 / g; the dispersant is a combination of dispersants containing ester groups, phosphate groups and polyethylene oxide structures; the viscosity of the high solids content alumina slurry is 3000~10000 cp.

2. The high-solids-content alumina slurry according to claim 1, characterized in that, The ester-containing dispersant includes at least one of polyacrylate, polycaprolactone polyol ester, glyceryl stearate, and hydroxyacrylate.

3. The high-solids-content alumina slurry according to claim 1, characterized in that, The dispersant containing phosphate groups includes at least one of castor oil phosphate, polyphosphate, diester phosphate, and triethyl phosphate.

4. The high-solids-content alumina slurry according to claim 1, characterized in that, The dispersant containing a polyethylene oxide structure includes at least one of fatty alcohol polyoxyethylene ether phosphate, dodecylamine polyoxyethylene ether, fatty alcohol ether phosphate, and lauryl alcohol polyoxyethylene ether sulfosuccinate.

5. The high-solids-content alumina slurry according to claim 1, characterized in that, The dispersant contains ester groups, phosphate groups and polyethylene oxide structures in a mass ratio of (0.1-0.3):1:(0.1-0.5).

6. The high-solids-content alumina slurry according to claim 1, characterized in that, The solvent is a mixture of toluene and ethanol.

7. The high-solids-content alumina slurry according to claim 6, characterized in that, The mass ratio of toluene to ethanol is 1:(0.5 to 1.5).

8. A method for preparing a high-solids-content alumina slurry as described in any one of claims 1 to 7, characterized in that, Includes the following steps: S1. First step of mixing: Add alumina powder to the solvent, and disperse it by grinding to obtain the first mixed slurry; S2. Second mixing step: Add dispersant to the first mixed slurry, continue grinding and dispersing to obtain the second mixed slurry; S3. Third step of mixing: Add binder and plasticizer to the second mixed slurry and continue grinding and dispersing, then degas under vacuum to obtain the high solids content alumina slurry.

9. A ceramic cast film, characterized in that, After the high-solids-content alumina slurry as described in any one of claims 1 to 7 is cast, a ceramic cast film with a thickness of 300 to 600 μm is obtained.

10. A fine-grained alumina ceramic material, characterized in that, The ceramic cast film as described in claim 9 is prepared by stacking, forming, debinding and sintering steps, and its average grain size is 1~2 μm.

Images