Preparation method of flaky ceramic

Abstract

The invention discloses a preparation method of flaky ceramic capable of rapidly absorbing water based on an emulsion binder and a permeable mold. According to the method, ceramic powder, water, a dispersing agent and polymer emulsion are prepared into slurry, and the slurry is poured into a porous mold with high water permeability. By utilizing capillary force of the mold or assisted by vacuum suction, water in the slurry is rapidly and directionally sucked out, meanwhile, emulsion particles are subjected to water loss, fusion and film forming, and the ceramic particles are solidified into a high-strength green body in situ. The forming speed is extremely high, a green body is uniform and compact, the green body strength is high, drying shrinkage is small, defects are few, water serves as a medium, and environment friendliness is achieved. And the method is particularly suitable for high-efficiency and low-cost preparation of large-size and thin-type flaky ceramics.

Description

Technical Field

[0001] This invention belongs to the field of ceramic preparation technology, and specifically relates to a method for preparing sheet-like ceramics. Background Technology

[0002] Sheet ceramics (such as ceramic substrates, film electrode supports, etc.) have wide applications in electronics, energy, chemical industry and other fields; the traditional preparation methods of sheet ceramics mainly include dry pressing, tape casting and slip casting.

[0003] Dry pressing is suitable for products with simple shapes, but for large-sized thin sheet products, problems such as uneven density, delamination, and edge effects are likely to occur. Casting can produce high-quality thin sheets, but the process is complex and requires a large amount of organic solvents and plasticizers, resulting in disadvantages such as high cost, environmental pollution, long drying cycle, and easy warping of the green body. Slip casting uses plaster molds, relies on capillary force to absorb water, has a slow molding speed, low dewatering efficiency for fine-particle slurry, and the green body strength is usually not high.

[0004] In recent years, some improved methods have been proposed, such as pressure-assisted filtration and gel casting. However, these methods either require complex equipment or the introduced reactive monomers may have an impact on operator health and the environment, and still suffer from problems such as large drying shrinkage and numerous defects in the green body. Therefore, developing a simple, fast-forming, high-strength, and environmentally friendly method for preparing sheet ceramics has significant industrial application value. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing sheet ceramics based on emulsion binder and water-permeable mold for rapid water absorption. This method uses emulsion as binder and combines it with a porous mold with high air and water permeability to achieve rapid dehydration of slurry and in-situ solidification of green body, significantly shortening the molding cycle and obtaining sheet ceramic green body with uniform structure, high strength and few defects.

[0006] The technical solution adopted by the present invention to achieve the above objectives is as follows: A method for preparing sheet-like ceramics, the specific steps of which are as follows: Step 1: Slurry preparation Ceramic powder, deionized water, and dispersant are ball-milled and mixed to prepare a uniform and stable ceramic suspension. A polymer emulsion is added to the ceramic suspension as a binder, and a defoamer is added. The mixture is stirred at low speed to obtain a ceramic slurry with a viscosity in the range of 500-3000 mPa·s. The ceramic powder includes, but is not limited to, alumina, zirconium oxide, silicon nitride, and silicon carbide, with a powder D50 of 0.1-5.0 μm; based on the weight of the ceramic powder, the content of each component is as follows: Deionized water: 10-40 wt% Dispersant: 0.3-2.0 wt% Polymer emulsion (solid content meter): 3-10 wt% Defoamer: 0.1-0.5 wt%.

[0007] The polymer emulsion is an aqueous polymer emulsion, preferably one or a mixture of several of the following: acrylate emulsion, styrene-acrylic emulsion, vinyl acetate-ethylene copolymer emulsion (VAE), and styrene-butadiene emulsion; the average particle size of the emulsion is 50-300 nm, and the glass transition temperature (Tg) is -10°C to 25°C. Step 2: Vacuum degassing and casting The ceramic slurry prepared in step 1 is subjected to vacuum degassing to eliminate air bubbles introduced during the stirring process; then, the degassed ceramic slurry is poured into the cavity of the permeable mold; for sheet ceramic products, the permeable mold can be set at the bottom and around the sides or only at the bottom. Furthermore, the permeable mold is a porous mold with micron-level through pores, and its material is one of porous gypsum, porous ceramic, porous resin or a rigid mold with a porous filter membrane on its surface. Step 3: Curing and molding After casting, the porous characteristics of the permeable mold are utilized to quickly draw out the water in the slurry through vacuum suction on the back of the mold or natural capillary force, which rapidly increases the viscosity of the slurry and makes it difficult for the ceramic powder to settle.

[0008] Meanwhile, the polymer emulsion particles in the slurry gradually approach and accumulate as water migrates, forming bridges between the ceramic particles. As more water is absorbed, the emulsion particles fuse and form a film, thus firmly bonding the ceramic particles together and achieving a rapid transformation of the slurry into a solid green body. This water absorption and curing process can be completed within 1-30 minutes, depending on the slurry thickness, mold permeability, and water absorption drive method.

[0009] Furthermore, to accelerate the water absorption process, a vacuum negative pressure of -0.05 to -0.1 MPa is applied to the back of the permeable mold.

[0010] Step 4: Drying and sintering After the green body has fully solidified and gained a certain strength, it is demolded. The demolded green body contains only a small amount of residual moisture, and is then dried in a flat manner for a short time (1-12 hours) at room temperature or low temperature (<60℃) to obtain the final sheet-like ceramic green body. The green body is then debonded and sintered to obtain a dense sheet-like ceramic finished product.

[0011] The beneficial effects of this invention are as follows: Utilizing the powerful capillary suction of the permeable mold (which can be supplemented by vacuum), dehydration and curing can be completed within minutes to tens of minutes, which is much more efficient than traditional casting (drying for hours to days) and grouting (hours).

[0012] The rapid, directional dehydration process inhibits the re-agglomeration and sedimentation of ceramic particles caused by Brownian motion, resulting in an extremely uniform density distribution in the green body. The three-dimensional polymer network formed by the emulsion film has strong adhesion, giving the green body high green strength (up to 3-10 MPa), facilitating handling and processing, and reducing breakage rate.

[0013] Since most of the moisture is removed during the molding stage, subsequent drying shrinkage is minimal, effectively preventing drying cracks and warping. Air bubbles in the slurry are also more easily eliminated during vacuum degassing and rapid dehydration, resulting in fewer defects in the green body.

[0014] Using water as the primary solvent, the emulsion binder is non-toxic or low-toxic, eliminating the need for large amounts of organic solvents and complex plasticizer systems, resulting in a safer production environment, less environmental pressure, and lower raw material costs. By adjusting the type and content of the emulsion and the permeability of the mold, it can flexibly adapt to the preparation needs of sheet ceramics of different materials and thicknesses. Attached Figure Description

[0015] Figure 1 The silicon nitride preform is formed by a waterproof mold as described in Example 1.

[0016] Figure 2 This is a schematic diagram of the silicon nitride preform forming process in Example 1.

[0017] Figure 3 The silicon nitride preform is formed with the aid of plaster mold in Example 1. Detailed Implementation

[0018] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited thereto. Example 1:

[0019] Preparation of sheet-like silicon nitride ceramics: Slurry preparation: Take 1000g of silicon nitride powder (D50≈0.8μm), add 350g of deionized water and 6g of tetramethylammonium hydroxide dispersant, and ball mill at 300rpm for 6 hours. Then add 60g of acrylate emulsion with a solid content of 50% (based on solid content, i.e., 3% of the weight of silicon nitride powder), add 3g of defoamer, and stir at low speed for 1 hour to obtain a silicon nitride slurry with a viscosity of approximately 1500 mPa·s.

[0020] Vacuum degassing and casting: Place the slurry in a vacuum container and degas it for 10 minutes at -0.095 MPa. Cast the degassed slurry into the cavity of a plaster mold (the mass ratio of plaster powder to water is 1.5:1), and set the slurry layer thickness to 4 mm.

[0021] Curing and molding: After standing for 10 minutes, the slurry has no fluidity. The green body is cured after drying at 40℃ for 20 minutes.

[0022] Drying and sintering: After demolding, a complete wet green body is obtained. The wet green body is placed on a flat plate and dried in an oven at 40℃ for 6 hours to obtain a silicon nitride green body. Under nitrogen protection, the green body is heated to 600℃ at 2℃ / min and held for 2 hours to remove the binder. Then, it is heated to 1700℃ at 5℃ / min and held for 5 hours to sinter, resulting in a dense silicon nitride ceramic sheet with a relative density >98% and a smooth surface without cracks.

[0023] Using the same silicon nitride powder and formulation as in Example 1, and employing the same drying process, the material was poured and cured in a conventional mold, resulting in noticeable warping deformation around the edges. The blank formed using a plaster mold exhibited extremely high flatness. Example 2:

[0024] Preparation of sheet-like alumina ceramics: Slurry preparation: Take 1000g of alumina powder (D50≈2μm), add 200g of deionized water and 8g of ammonium polyacrylate dispersant, and ball mill at 300rpm for 4 hours. Then add 40g of acrylate emulsion with a solid content of 50% (based on solid content, i.e., 2% of the weight of ceramic powder), add 3g of defoamer, and stir at low speed for 1 hour to obtain an alumina slurry with a viscosity of approximately 2000 mPa·s.

[0025] Vacuum degassing and casting: Place the slurry in a vacuum container and degas it for 10 minutes at -0.095 MPa. Cast the degassed slurry into the cavity of a porous resin mold (pore size approximately 15-20 μm), with the slurry layer thickness set to 3 mm.

[0026] Curing and molding: Connect a vacuum pump to the back of the mold and apply a vacuum of -0.08 MPa. The water absorption process lasts for about 5 minutes, during which the surface of the slurry loses its gloss and solidifies into a green body.

[0027] Drying and sintering: After demolding, a complete wet green body is obtained. The wet green body is placed on a flat plate and dried in an oven at 60℃ for 6 hours to obtain an alumina ceramic green body. The green body is heated to 600℃ at 2℃ / min and held for 2 hours to remove the binder. Then, it is heated to 1650℃ at 5℃ / min and held for 2 hours to sinter, resulting in a dense alumina ceramic sheet with a relative density >99% and a smooth surface without cracks.

[0028] Traditional plaster mold injection molding Using the same alumina powder and formulation as in Example 2 (but replacing the emulsion with an equal amount of methylcellulose aqueous solution for bonding effect), slurry was poured using a standard plaster mold. The molding time required more than 60 minutes, and the wet strength of the blank after demolding was low (approximately 1.5 MPa). The shrinkage rate after drying was significantly greater than that in Example 1, and there was slight warping at the edges.

Claims

1. A method for preparing sheet-like ceramics, characterized in that: Includes the following steps: S1. Ceramic powder, deionized water, and dispersant are ball-milled and mixed to prepare a uniform and stable ceramic suspension; polymer emulsion is added to the ceramic suspension as a binder, and defoamer is added, and the mixture is stirred at low speed to obtain a ceramic slurry with a viscosity in the range of 500-3000 mPa·s. S2. The ceramic slurry prepared in S1 is subjected to vacuum degassing to eliminate air bubbles introduced during the stirring process; then, the degassed ceramic slurry is poured into the cavity of the permeable mold; for sheet ceramic products, the permeable mold may be set at the bottom and around the sides or only at the bottom; S3. After casting, the permeability of the permeable mold is utilized to quickly remove water from the slurry through vacuum suction on the back of the mold or natural capillary force. At the same time, the polymer emulsion particles in the slurry gradually approach and accumulate as the water migrates, forming bridges between the ceramic particles. As the water is further removed, the emulsion particles fuse and form a film, thereby firmly bonding the ceramic particles together, realizing the rapid transformation of the slurry into a solid green body, forming a sheet-like green body. S4. After demolding the sheet-like green body, it is dried and sintered at high temperature to obtain the final sheet-like ceramic green body; the green body is debonded and sintered to obtain a dense sheet-like ceramic finished product.

2. The method for preparing sheet-like ceramics according to claim 1, characterized in that: In step S1, based on the weight of the ceramic powder, the content of each component is as follows: Deionized water: 10-40 wt% Dispersant: 0.3-2.0 wt% Polymer emulsion (solid content meter): 3-10 wt% Defoamer: 0.1-0.5 wt%.

3. The method for preparing sheet-like ceramics according to claim 1, characterized in that: The polymer emulsion mentioned in step S1 is an aqueous emulsion selected from at least one of acrylate emulsion, styrene-acrylic emulsion, vinyl acetate-ethylene copolymer emulsion, and styrene-butadiene emulsion.

4. The method for preparing sheet-like ceramics according to claim 3, characterized in that, The polymer emulsion has an average particle size of 50-300 nm and a glass transition temperature of -10°C to 25°C.

5. The method for preparing sheet-like ceramics according to claim 3, characterized in that, The permeable mold mentioned in step S2 is a porous mold with micron-level through pores, and its material is one of porous gypsum, porous ceramic, porous resin or a rigid mold with a porous filter membrane on its surface.

6. The method for preparing sheet-like ceramics according to claim 1, characterized in that, In step S3, the water absorption process is accelerated by applying a vacuum negative pressure to the back of the permeable mold, with the vacuum negative pressure being -0.05 to -0.1 MPa.

7. The method for preparing sheet-like ceramics according to claim 1, characterized in that, The ceramic powder is selected from at least one of alumina, zirconium oxide, silicon carbide, and silicon nitride, and the powder D50 is 0.1-5.0 μm.

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