A surface sealing method for porous ceramic material

Abstract

The present invention belongs to the technical field of inorganic functional materials, and specifically discloses a surface sealing method for porous ceramic materials. The present invention adopts a dense ceramic material of the same material as the porous ceramic as a sealing medium. In the ceramic forming stage, a dense ceramic slurry is poured onto the surface of the porous ceramic material, and a gel injection molding process is adopted for curing. The cured ceramic body is dried, organic matter is removed, sintered, and the like, and the sealing of the porous ceramic surface is completed. The main body of the material prepared by the method of the present invention is a porous ceramic, and the surface is a dense ceramic sealing layer, wherein the porous ceramic has a pore content higher than 20%, and the dense ceramic has a pore content less than 1%, and the dense ceramic is used to prevent the porous ceramic material from absorbing water. The ceramic material prepared by the method of the present invention has the advantages of lightweight porous ceramic materials, low dielectric constant, high temperature resistance, corrosion resistance, and heat insulation, and can also improve the reliability of porous ceramic materials in liquid media and high humidity environments.

Description

Technical Field

[0001] The invention belongs to the technical field of inorganic functional materials, relates to the preparation of ceramic materials, and specifically to a surface sealing method for porous ceramic materials. Background Art

[0002] Porous ceramics are inorganic non-metallic powder sintered bodies containing a certain amount of voids. The fundamental difference between them and other inorganic non-metallic (dense ceramic) materials is whether they contain voids (pores) and the volume fraction of the voids (pores) they contain [1]. The presence of a certain amount of pores significantly changes the structure, properties, and functions of ceramics. Compared with dense ceramics, porous ceramics have the following characteristics: 1. Low volume density and light weight; 2. Large surface area and good filtration performance; 3. Low thermal conductivity, good thermal and sound insulation performance; 4. Good chemical and physical stability; 5. Simple process and low cost. These excellent characteristics make porous ceramics more widely used than dense ceramics.

[0003] However, porous wave-transmitting ceramic materials have a high specific surface area and are prone to moisture absorption. The dielectric loss of the material is extremely sensitive to moisture, so moisture absorption will seriously affect the material's wave-transmitting performance. Based on this, researchers have begun to study the surface sealing of porous ceramics. At present, the methods of sealing porous ceramics mostly use organic sealing or metal sealing. Both methods can achieve effective sealing of porous ceramic materials, but both have some limitations. When organic materials are used to seal the surface of porous ceramics, the overall temperature resistance of the material will be severely reduced, and it cannot serve in high-temperature scenes, limiting the application field of the material; when metal is used to seal the surface of porous ceramics, the surface corrosion resistance is severely reduced, and it cannot be used in corrosive environments such as strong acids and alkalis. Summary of the invention

[0004] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a surface sealing method for porous ceramic materials. The present invention uses dense ceramic materials as sealing media. In the ceramic forming stage, dense ceramic slurry is poured onto the surface of the porous ceramic material, and solidified by gel injection molding process. The solidified ceramic body is dried, organic matter is removed, sintered, and other processes are performed to complete the sealing of the porous ceramic surface. The ceramic material prepared by the method of the present invention has the advantages of lightweight porous ceramic materials, low dielectric constant, high temperature resistance, corrosion resistance, heat insulation, etc., and can also improve the reliability of porous ceramic materials in liquid media and high humidity environments.

[0005] The present invention is achieved through the following technical solutions:

[0006] A surface sealing method for a porous ceramic material comprises the following steps:

[0007] (1) preparing a porous ceramic slurry: adding a dispersant, a monomer, a cross-linking agent, and a catalyst into deionized water and stirring them thoroughly to form a premixed liquid, adding a ceramic powder and a pore-forming agent into the premixed liquid to form a ceramic slurry, and ball milling the ceramic slurry using a ball mill to form a porous ceramic slurry;

[0008] (2) Porous ceramic preforming: adding an initiator to the porous ceramic slurry and stirring evenly, pouring the slurry into a mold, sealing the mold, placing the sealed mold in a curing box, and controlling the curing degree to reach 75-85%;

[0009] (3) preparing a dense ceramic slurry: adding a dispersant, a monomer, a cross-linking agent, and a catalyst into deionized water and stirring them thoroughly to form a premixed liquid, adding ceramic powder into the premixed liquid to form a ceramic slurry, and using a ball mill to mix the ceramic slurry to form a dense ceramic slurry;

[0010] (4) pouring a dense layer: adding an initiator to the dense ceramic slurry, and using a vacuum degassing machine to stir evenly and remove bubbles in the slurry; taking the mold with the porous ceramic formed body out of the curing box, pouring the dense ceramic slurry onto the surface of the porous ceramic slurry, sealing it, placing the sealed mold in the curing box, and curing it in a two-stage curing method. During the first stage of curing, the curing is controlled so that the curing degree of the dense part reaches 75-85%, and then entering the second stage of curing. During the second stage of curing, the curing is controlled so that the overall curing degree reaches 100%;

[0011] (5) demolding, drying, debinding, and sintering the solidified green body to complete the surface-sealed porous ceramic.

[0012] A further improvement of the present invention is:

[0013] The porous ceramic is an oxide ceramic, a carbide ceramic or a nitride ceramic, and the material of the dense ceramic and the porous ceramic must be the same material.

[0014] Furthermore, the dispersant is polyacrylamide or tetramethylammonium hydroxide or a mixture of the two;

[0015] and / or, the monomer is methacrylamide;

[0016] And / or, the cross-linking agent is polyethylene glycol diacrylate;

[0017] And / or, the catalyst is N,N,N,N-tetramethylethylenediamine;

[0018] And / or, the pore-forming agent is plastic microspheres or high molecular organic polymer powder;

[0019] And / or, the initiator is sodium persulfate.

[0020] Furthermore, in the porous ceramic material, the mass distribution ratio of the dispersant, monomer, initiator, cross-linking agent, catalyst, deionized water, ceramic powder and pore-forming agent is 10-20: 4-8: 4-8: 4-8: 1-4: 180-220: 630-695: 78-122.

[0021] Furthermore, in the dense ceramic material, the mass distribution ratio of the dispersant, the monomer, the initiator, the cross-linking agent, the catalyst, the deionized water and the ceramic powder is 10-20: 4-8: 4-8: 4-8: 1-4: 180-220: 630-695.

[0022] Furthermore, when the porous ceramic is preformed, the temperature of the curing box is adjusted to 30-40° C. and kept warm for 5-10 hours.

[0023] Furthermore, when pouring the dense layer, during the first stage of curing, the temperature of the curing box is adjusted to 30-40°C and kept warm for 5-10 hours; during the second stage of curing, the temperature of the curing box is adjusted to 60-90°C and kept warm for 12-24 hours.

[0024] Furthermore, the drying process is carried out in a constant temperature and humidity drying oven, the drying temperature is 60-90°C, the time is 30-40 hours, and the humidity is 70-90%; the debinding process is carried out in a muffle furnace, the debinding temperature is 500-600°C, and the insulation time is 3-10 hours; the sintering process is carried out in a high-temperature furnace, the sintering temperature is 1500-2080°C, and the time is 4-6 hours.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The sealing medium used in the present invention is a dense ceramic material. In the ceramic forming stage, a dense ceramic slurry is poured onto the surface of the porous ceramic material, and a gel injection molding process is used for curing. The cured ceramic body is dried, organic matter is removed, sintered, and other processes are performed to complete the sealing of the porous ceramic surface. The main body of the material prepared by the method of the present invention is a porous ceramic, and the surface is a dense ceramic sealing layer, wherein the porous ceramic pore content is higher than 20%, and the dense ceramic pore content is less than 1%, and the dense ceramic is used to prevent the porous ceramic material from absorbing water. The ceramic material prepared by the method of the present invention has the advantages of lightweight, low dielectric constant, high temperature resistance, corrosion resistance, and heat insulation of porous ceramic materials, and can improve the reliability of porous ceramic materials in liquid media and high humidity environments. For example, the weight loss of the product prepared by the present invention is less than 0.1% after being soaked in concentrated sulfuric acid for 24 hours; the product prepared by the present invention is heated to 300°C and rapidly cooled to room temperature, and the product appearance is not damaged and no cracks are generated on the surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is an appearance diagram of the end-face sealed alumina porous ceramic prepared by the present invention;

[0028] Figure 2 The alumina porous ceramic ink for end face sealing prepared by the present invention is dyed. DETAILED DESCRIPTION

[0029] The present invention is described in detail below in conjunction with specific embodiments.

[0030] Example 1: Preparation of porous alumina ceramic (porosity 30%) and sealing its surface

[0031] 19 parts of polyacrylamide, 4 parts of methacrylamide, 4 parts of polyethylene glycol diacrylate, and 1 part of N,N,N,N-tetramethylethylenediamine are added to 195 parts of deionized water and stirred to form a premixed solution, 630 parts of alumina ceramic powder and 122 parts of pore-forming agent are added to the premixed solution to form a ceramic slurry, and the ceramic slurry is ball-milled and mixed using a ball mill to form a porous ceramic slurry;

[0032] Add 4 parts of initiator sodium persulfate to the porous ceramic slurry and stir well, pour the slurry into the mold, seal the mold, place the sealed mold in the curing box, control the curing degree (adjust the curing box temperature to 30°C, keep warm for 5 hours), and achieve 80% curing;

[0033] 19 parts of polyacrylamide, 4 parts of methacrylamide, 4 parts of polyethylene glycol diacrylate, and 1 part of N,N,N,N-tetramethylethylenediamine are added to 195 parts of deionized water and stirred to form a premixed liquid, 630 parts of alumina ceramic powder are added to the premixed liquid to form a ceramic slurry, and the ceramic slurry is ball-milled and mixed using a ball mill to form a dense ceramic slurry;

[0034] Add 4 parts of initiator sodium persulfate to the dense ceramic slurry, and use a vacuum defoamer to stir evenly and remove bubbles from the slurry;

[0035] The mold with the porous ceramic formed body is taken out from the curing box, and the dense ceramic slurry is poured onto the surface of the porous ceramic slurry, and the mold is sealed again. The sealed mold is placed in the curing box and cured by a two-stage curing method. First, the curing degree is controlled (the curing box temperature is adjusted to 30°C and kept warm for 5 hours) so that the dense part reaches a curing degree of 80%, and then enters the second stage of curing (the curing box temperature is adjusted to 80°C and kept warm for 12 hours) so that the overall curing degree reaches 100%;

[0036] The solidified green body is demoulded, dried, organic matter is removed, and sintered to complete the preparation of surface-sealed porous ceramics; wherein the drying process is carried out in a constant temperature and humidity drying oven at a temperature of 70°C, a humidity of 80%, and a drying time of 36 hours; the debinding process is carried out in a muffle furnace at a debinding temperature of 600°C and a holding time of 3 hours; the sintering process is carried out in a high-temperature muffle furnace at a sintering temperature of 1600°C and a holding time of 5 hours;

[0037] The surface sealed porous ceramics prepared are as follows Figure 1 As shown, the portion above the dotted line is a dense ceramic sealing layer, and the portion below the dotted line is a porous ceramic.

[0038] The prepared samples were characterized by ink staining method, as shown in the attached Figure 2 As shown, the porous part absorbs ink and appears black, while the dense sealing layer cannot absorb ink and appears white.

[0039] Example 2: Preparation of silicon carbide porous ceramics (porosity 20%) and sealing of its surface

[0040] 13 parts of polyacrylamide, 5 parts of methacrylamide, 5 parts of polyethylene glycol diacrylate, and 2 parts of N,N,N,N-tetramethylethylenediamine are added to 220 parts of deionized water and stirred to form a premixed solution, 662 parts of alumina ceramic powder and 93 parts of pore-forming agent are added to the premixed solution to form a ceramic slurry, and the ceramic slurry is ball-milled and mixed using a ball mill to form a porous ceramic slurry;

[0041] Add 5 parts of initiator sodium persulfate to the porous ceramic slurry and stir well, pour the slurry into the mold, seal the mold, place the sealed mold in the curing box, control the curing degree (adjust the curing box temperature to 40°C, keep warm for 8h), and achieve 80% curing;

[0042] 13 parts of polyacrylamide, 5 parts of methacrylamide, 5 parts of polyethylene glycol diacrylate, and 2 parts of N,N,N,N-tetramethylethylenediamine are added to 220 parts of deionized water and stirred to form a premixed solution, 662 parts of alumina ceramic powder are added to the premixed solution to form a ceramic slurry, and the ceramic slurry is ball-milled and mixed using a ball mill to form a dense ceramic slurry;

[0043] Add 5 parts of initiator sodium persulfate to the dense ceramic slurry, and use a vacuum defoamer to stir evenly and remove bubbles in the slurry;

[0044] The mold with the porous ceramic formed body is taken out from the curing box, and the dense ceramic slurry is poured onto the surface of the porous ceramic slurry, and the mold is sealed again. The sealed mold is placed in the curing box and cured by a two-stage curing method. First, the curing degree is controlled (the curing box temperature is adjusted to 40°C and kept warm for 8 hours) so that the dense part reaches a curing degree of 80%, and then the second stage of curing is performed (the curing box temperature is adjusted to 80°C and kept warm for 24 hours) so that the overall curing degree reaches 100%;

[0045] The solidified green body is demolded, dried, organic matter is removed, and sintered to complete the preparation of surface-sealed porous ceramics; the drying process is carried out in a constant temperature and humidity drying oven at a temperature of 90°C, a humidity of 80%, and a drying time of 24 hours; the debinding process is carried out in a muffle furnace at a debinding temperature of 550°C and a holding time of 10 hours; the sintering process is carried out in a high-temperature muffle furnace at a sintering temperature of 2080°C and a holding time of 5 hours.

[0046] Example 3: Preparation of porous alumina ceramics (porosity 20%) and sealing of its surface

[0047] 20 parts of polyacrylamide, 8 parts of methacrylamide, 8 parts of polyethylene glycol diacrylate, and 4 parts of N,N,N,N-tetramethylethylenediamine are added to 186 parts of deionized water and stirred to form a premixed solution, 695 parts of alumina ceramic powder and 78 parts of pore-forming agent are added to the premixed solution to form a ceramic slurry, and the ceramic slurry is ball-milled and mixed using a ball mill to form a porous ceramic slurry;

[0048] Add 8 parts of initiator sodium persulfate to the porous ceramic slurry and stir well, pour the slurry into the mold, seal the mold, place the sealed mold in the curing box, control the curing degree (adjust the curing box temperature to 30°C, keep warm for 5 hours), and achieve 80% curing;

[0049] 20 parts of polyacrylamide, 8 parts of methacrylamide, 8 parts of polyethylene glycol diacrylate, and 4 parts of N,N,N,N-tetramethylethylenediamine are added to 186 parts of deionized water and stirred to form a premixed solution, 695 parts of alumina ceramic powder are added to the premixed solution to form a ceramic slurry, and the ceramic slurry is ball-milled and mixed using a ball mill to form a dense ceramic slurry;

[0050] Add 8 parts of initiator sodium persulfate to the dense ceramic slurry, and use a vacuum defoamer to stir evenly and remove bubbles in the slurry;

[0051] The mold with the porous ceramic formed body is taken out from the curing box, and the dense ceramic slurry is poured onto the surface of the porous ceramic slurry, and the mold is sealed again. The sealed mold is placed in the curing box and cured by a two-stage curing method. First, the curing degree is controlled (the curing box temperature is adjusted to 30°C and kept warm for 5 hours) so that the dense part reaches a curing degree of 80%, and then enters the second stage of curing (the curing box temperature is adjusted to 80°C and kept warm for 12 hours) so that the overall curing degree reaches 100%;

[0052] The solidified green body is demoulded, dried, organic matter is removed, and sintered to complete the preparation of surface-sealed porous ceramics; the drying process is carried out in a constant temperature and humidity drying oven at a temperature of 70°C, a humidity of 80%, and a drying time of 36 hours; the debinding process is carried out in a muffle furnace at a debinding temperature of 600°C and a holding time of 3 hours; the sintering process is carried out in a high-temperature muffle furnace at a sintering temperature of 1600°C and a holding time of 5 hours.

[0053] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent transformation or modification made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A surface sealing method for porous ceramic materials, characterized in that: The following steps are involved: (1) preparing a porous ceramic slurry: adding a dispersant, a monomer, a cross-linking agent, and a catalyst into deionized water and stirring them thoroughly to form a premixed liquid, adding a ceramic powder and a pore-forming agent into the premixed liquid to form a ceramic slurry, and ball milling the ceramic slurry using a ball mill to form a porous ceramic slurry; (2) Porous ceramic preforming: adding an initiator to the porous ceramic slurry and stirring evenly, pouring the slurry into a mold, sealing the mold, placing the sealed mold in a curing box, and controlling the curing degree to reach 75-85%; (3) preparing a dense ceramic slurry: adding a dispersant, a monomer, a cross-linking agent, and a catalyst into deionized water and stirring them thoroughly to form a premixed liquid, adding ceramic powder into the premixed liquid to form a ceramic slurry, and using a ball mill to mix the ceramic slurry to form a dense ceramic slurry; (4) pouring a dense layer: adding an initiator to the dense ceramic slurry, and using a vacuum degassing machine to stir evenly and remove bubbles in the slurry; taking the mold with the porous ceramic formed body out of the curing box, pouring the dense ceramic slurry onto the surface of the porous ceramic slurry, sealing it, placing the sealed mold in the curing box, and curing it in a two-stage curing method. During the first stage of curing, the curing is controlled so that the curing degree of the dense part reaches 75-85%, and then entering the second stage of curing. During the second stage of curing, the curing is controlled so that the overall curing degree reaches 100%; (5) demolding, drying, debinding, and sintering the solidified green body to complete the surface-sealed porous ceramic.

2. The surface sealing method of a porous ceramic material according to claim 1, characterized in that: The porous ceramic is an oxide ceramic, a carbide ceramic or a nitride ceramic, and the material of the dense ceramic and the porous ceramic must be the same material.

3. The surface sealing method of a porous ceramic material according to claim 1, characterized in that: The dispersant is polyacrylamide or tetramethylammonium hydroxide or a mixture of the two; and / or, the monomer is methacrylamide; And / or, the cross-linking agent is polyethylene glycol diacrylate; And / or, the catalyst is N,N,N,N-tetramethylethylenediamine; And / or, the pore-forming agent is plastic microspheres or high molecular organic polymer powder; And / or, the initiator is sodium persulfate.

4. The surface sealing method of a porous ceramic material according to claim 1, characterized in that: In the porous ceramic material, the mass distribution ratio of the dispersant, the monomer, the initiator, the cross-linking agent, the catalyst, the deionized water, the ceramic powder and the pore-forming agent is 10-20: 4-8: 4-8: 4-8: 1-4: 180-220: 630-695: 78-122.

5. The surface sealing method of a porous ceramic material according to claim 1, characterized in that: In the dense ceramic material, the mass distribution ratio of the dispersant, the monomer, the initiator, the cross-linking agent, the catalyst, the deionized water and the ceramic powder is 10-20: 4-8: 4-8: 4-8: 1-4: 180-220: 630-695.

6. The surface sealing method of a porous ceramic material according to claim 1, characterized in that: When the porous ceramic is preformed, the temperature of the curing box is adjusted to 30-40° C. and kept warm for 5-10 hours.

7. The surface sealing method of a porous ceramic material according to claim 1, characterized in that: When pouring the dense layer, during the first stage of curing, the temperature of the curing box is adjusted to 30-40° C. and kept warm for 5-10 hours; during the second stage of curing, the temperature of the curing box is adjusted to 60-90° C. and kept warm for 12-24 hours.

8. The surface sealing method of a porous ceramic material according to claim 1, characterized in that: The drying process is carried out in a constant temperature and humidity drying oven, the drying temperature is 60-90°C, the time is 30-40h, and the humidity is 70-90%; the debinding process is carried out in a muffle furnace, the debinding temperature is 500-600°C, and the insulation time is 3-10h; The sintering process is carried out in a high-temperature furnace, the sintering temperature is 1500-2080° C., and the time is 4-6 hours.

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