Method for preparing ceramic film by sol-gel method

Abstract

The invention discloses a method for preparing a ceramic film by a sol-gel method, and relates to the field of chemical materials. A method for preparing a ceramic film by a sol-gel method comprises the following steps: step 1, preparing a precursor: dissolving pseudo-boehmite in hot water, stirring and dispersing, dropwise adding a nitric acid solution in proportion, continuously stirring, and continuously stirring at the same temperature for a period of time after dropwise adding to obtain boehmite sol; in the preparation process of a target product, after hydrothermal treatment at a certain temperature and for a certain time, pseudo-boehmite is converted into boehmite with high crystallinity, and the conversion process is a regular change process in which crystal grains grow gradually, the crystallinity is higher and higher, and the crystal form tends to be more and more complete; in addition, the method has the advantages of being low in cost, simple in preparation process, environmentally friendly and the like, and compared with other preparation methods, the quality of the prepared aluminum oxide film is more uniform.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical materials, and in particular relates to a method for preparing a ceramic film using a sol-gel method. Background Art

[0002] With the continuous development of new inorganic materials, the preparation and application research of inorganic ceramic membranes have received increasing attention. Ceramic films have high mechanical strength and good thermal stability, so they are widely used in catalytic reactors, electronic technology, biomedicine, food hygiene, energy and chemical industries, etc. Among them, Al2O3 ceramic membranes are the most widely used. There are many methods for preparing Al2O3 ceramic membranes, but few are suitable for industrial production. The sol-gel method is considered to be an ideal method for industrial production of ceramic membranes because of its advantages such as low cost, simple process, easy adjustment of composition, no need for external energy in the coating process, and large coating area.

[0003] The precursor of Al2O3 ceramic membranes is boehmite. Boehmite comes in two forms: highly crystalline boehmite and poorly crystalline pseudo-boehmite. These two forms differ significantly in particle morphology, porosity, and specific surface area. The quality and cost of boehmite sol, a raw material for the sol-gel method, significantly impact the preparation of defect-free ceramic membranes and their performance. Pseudo-boehmite contains a high amount of water, which resides between the flaky particles, resulting in reduced crystallinity. Numerous factors influence the preparation of boehmite sol, and changes in experimental parameters can result in different crystalline forms. Boehmite is the primary precursor for obtaining activated alumina. Therefore, controlling experimental parameters to produce a stably dispersed boehmite sol is a key issue in preparing Al2O3 ceramic membranes. The present invention is therefore proposed in light of this. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a method for preparing ceramic thin films using a sol-gel method that can overcome the above problems or at least partially solve the above problems.

[0005] To solve the above technical problems, the basic concept of the technical solution adopted by the present invention is: a method for preparing a ceramic film by a sol-gel method, mainly comprising the following steps: Step 1: Prepare the precursor: Dissolve pseudo-boehmite in hot water, stir and disperse, then dropwise add nitric acid solution in proportion, continue stirring, and continue stirring at the same temperature for a period of time after the addition is complete to obtain boehmite sol; The mass ratio of the pseudo-boehmite powder to the nitric acid is controlled between 3 and 4, the mass ratio of the pseudo-boehmite powder to water is controlled between 0.2 and 0.5, and the hydrolysis temperature is higher than 80°C. Step 2: Gel preparation: The boehmite sol obtained in step 1 is subjected to a hydrolysis-condensation reaction to generate a gelation reaction to form an alumina gel; Step 3: Coating the substrate: Evenly coating the alumina gel prepared in step 2 on the substrate; Step 4: Heat treatment: The substrate coated with the alumina gel is placed in a sintering furnace for high-temperature sintering and thermal annealing treatment, so that the alumina gel forms a compact and uniform alumina ceramic film.

[0006] Furthermore, in step 1, during the process of adding the nitric acid solution, it is necessary to observe the changes in the liquid and record the moment when the liquid state changes and the amount of nitric acid used.

[0007] Furthermore, in step 1, after the dropwise addition of the nitric acid solution is completed, the stirring time is preferably continued to ensure that the reaction proceeds fully.

[0008] Furthermore, in step four, the process parameters of high-temperature sintering and thermal annealing are adjusted accordingly according to the required performance of the ceramic film.

[0009] Furthermore, the sintering furnace includes a furnace body, a furnace cover, a sintering bin and a support. The sintering furnace is fixedly mounted on the support. The furnace cover is rotatably connected to the furnace mouth of the furnace body. The sintering bin is arranged inside the furnace body.

[0010] In order to ensure that all parts of the film are heated uniformly during high-temperature sintering and thermal annealing, further, two brackets are symmetrically placed in the sintering bin, and a rotating shaft is rotatably connected between the two brackets. A plurality of mounting brackets are fixedly connected to the rotating shaft at equal distances, and a plurality of shaft rods are rotatably connected to the plurality of mounting brackets at equal distances in a circle. A plurality of placement plates are fixedly connected to the shaft rods at equal distances through triangular support rods, and the plurality of placement plates are horizontally distributed under the action of their own gravity. A drive motor is fixedly connected to the end of the furnace body away from the furnace cover, and the output shaft of the drive motor extends into the furnace body. A slot for cooperating with the output shaft is opened at the end of the rotating shaft close to the drive motor, and a plurality of grooves are opened at equal distances in a circle on the output shaft, and protrusions for cooperating with the grooves are circumferentially equidistantly arranged in the slot.

[0011] In order to further ensure the balance of the placement plate, further, friction blocks are symmetrically fixedly connected to the two ends of the shaft, and the friction blocks slide against the adjacent mounting frames. A counterweight block is fixedly connected to the center position of the bottom of the placement plate.

[0012] In order to facilitate accurate positioning of the base, a positioning groove for positioning the base is further provided on the placement plate.

[0013] In order to ensure the stability of the substrate and the film, and at the same time make it easier to take the bracket and the substrate supported on it out of or put into the sintering bin, further, the lower ends of the two brackets are symmetrically fixedly connected with positioning rods, and the positioning rods are located at the corners on both sides of the bottom of the sintering bin. The positioning rods are adjacent to the corners on both sides of the bottom of the sintering bin and are equidistantly provided with multiple arc grooves on the side, and balls are movably connected in the arc grooves.

[0014] To further ensure that the substrate coated with the alumina gel always maintains a stable state during the heat treatment process, further, the length of the positioning rod is the same as the length of the sintering chamber.

[0015] After adopting the above technical scheme, the present invention has the following beneficial effects compared with the prior art: the present invention uses nitric acid as a peptizing agent, and forms a double electric layer on the surface of the particles. The double electric layer causes the particles to repel each other. When the repulsive force is greater than the attractive force between the particles, the aggregated particles are dispersed into small particles to form a sol. In the preparation process of the target product, after hydrothermal treatment at a certain temperature and time, the pseudo-boehmite is converted into high-crystallinity boehmite, and this conversion process is a regular change process in which the grains gradually grow, the crystallinity becomes higher and higher, and the crystal form becomes more and more complete. At the same time, the physically adsorbed water contained in the product gradually decreases, and the structural water contained is consistent with the theoretical value. In addition, the sol-gel method for preparing alumina film has the advantages of low cost, simple preparation process, and environmental friendliness. Compared with other preparation methods, the quality of the alumina film prepared by it is more uniform, and it is particularly suitable for preparing large-area alumina film.

[0016] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In the attached figure: Figure 1 The structure of the present invention is schematically shown Figure 1 ; Figure 2 The structure of the present invention is schematically shown Figure 2 ; Figure 3 Schematic diagram of the structure inside the sintering furnace of the present invention; Figure 4 Schematic diagram of part of the structure of the present invention Figure 1 ; Figure 5 Schematic diagram of part of the structure of the present invention Figure 2 ; Figure 6 For the present invention Figure 3 Schematic diagram of the structure of part A; Figure 7 For the present invention Figure 5 Schematic diagram of the structure of part B.

[0018] In the figure: 1. Sintering furnace; 101. Furnace body; 102. Furnace cover; 103. Sintering chamber; 104. Support; 105. Driving motor; 106. Output shaft; 1061. Groove; 2. Bracket; 201. Rotating shaft; 2011. Slot; 2012. Protrusion; 202. Mounting frame; 203. Shaft; 204. Triangular support rod; 205. Placement plate; 2051. Limiting groove; 206. Friction block; 207. Counterweight; 3. Positioning rod; 301. Ball. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The following embodiments are used to illustrate the present invention but are not used to limit the scope of the present invention.

[0020] Example: Reference Figure 1-Figure 2 A method for preparing a ceramic thin film by a sol-gel method comprises the following steps: Step 1: Prepare the precursor: Dissolve pseudo-boehmite in hot water at a temperature above 80°C, stir and disperse to uniformly mix, then dropwise add the prepared nitric acid solution in proportion, continue stirring during the addition process, and closely observe the changes in the liquid. Record the moment when the liquid state changes and the amount of nitric acid used at this time. After the addition is completed, continue stirring at the same temperature for a period of time to ensure that the reaction is fully carried out, and finally obtain boehmite sol; Among them, the mass ratio of pseudo-boehmite powder to nitric acid is controlled between 3 and 4, the mass ratio of pseudo-boehmite powder to water is controlled between 0.2 and 0.5, and the hydrolysis temperature is higher than 80°C. If the amount of nitric acid is insufficient, the repulsive force between the particles cannot overcome the attractive force, forming a white precipitate and failing to completely peptize. If the amount of nitric acid is too large, the sol will be unstable and prone to agglomeration. Too much water will easily form a particle sol, and too little water will limit the completeness of the hydrolysis. Therefore, the ratio of each material must be strictly controlled within a reasonable range. Step 2: Gel preparation: The boehmite sol obtained in step 1 is allowed to stand for a period of time to allow it to undergo a hydrolysis-condensation reaction and then a gelation reaction to generate an alumina gel; Step 3: Coating the substrate: Evenly coat the alumina gel prepared in step 2 on the clean substrate surface to ensure uniform coating thickness, laying the foundation for the subsequent formation of high-quality ceramic films; Step 4: Heat treatment: The substrate coated with alumina gel is placed in a sintering furnace 1 and sintered at a high temperature of 800°C for 2 hours, followed by thermal annealing and cooling to room temperature to obtain a compact and uniform alumina ceramic film. The sintering furnace 1 includes a furnace body 101, a furnace cover 102, a sintering chamber 103, and a support 104. The sintering furnace 1 is fixedly mounted on the support 104. The furnace cover 102 is rotatably connected to the furnace mouth of the furnace body 101. The sintering chamber 103 is arranged inside the furnace body 101. The sintering furnace 1 is a common sintering furnace 1 on the market. The process parameters of high-temperature sintering and thermal annealing can be adjusted accordingly according to the properties of the required ceramic film. Through this process, the alumina gel can be formed into a compact and uniform alumina ceramic film.

[0021] This method uses pseudo-boehmite as a precursor and nitric acid as a peptizing agent. Under appropriate process conditions, a double electric layer is formed on the surface of the particles. The double electric layer causes the particles to repel each other. When the repulsive force is greater than the attractive force between the particles, the aggregated particles are dispersed into small particles, forming a boehmite sol with good performance. By controlling the experimental parameters, the pseudo-boehmite is transformed into high-crystallinity boehmite after being treated at a certain temperature and time. During the transformation process, the grains gradually grow, the crystallinity becomes higher and higher, and the crystal form becomes more and more complete. At the same time, the physically adsorbed water contained in the product gradually decreases, and the structural water contained is consistent with the theoretical value.

[0022] The sol-gel method for preparing aluminum oxide thin films is low-cost and simple in process, does not require complex equipment and high cost investment, and is conducive to industrial production. At the same time, the method is environmentally friendly and does not generate a large amount of hazardous waste during the preparation process, which meets the requirements of green production.

[0023] Compared with other preparation methods, the aluminum oxide film prepared by this method has more uniform quality and can meet the scenarios with higher requirements on film performance. It is especially suitable for the preparation of large-area aluminum oxide films and can be widely used in catalytic reactors, electronic technology, biomedicine, food hygiene, energy and chemical industry and other fields.

[0024] During the entire preparation process, the process parameters of each step can be adjusted according to actual needs. For example, in step one, the quality of the boehmite sol can be guaranteed by controlling the ratio of pseudo-boehmite, nitric acid and water, as well as the hydrolysis temperature. In step four, the process parameters of high-temperature sintering and thermal annealing are adjusted according to the performance of the required ceramic film, so that ceramic films that meet different performance requirements can be prepared, thereby improving the flexibility and applicability of the process.

[0025] Reference Figure 3 、 Figure 4 、 Figure 5 、 Figure 6 、 Figure 7As shown: two brackets 2 are symmetrically placed in the sintering bin 103, and a rotating shaft 201 is rotatably connected between the two brackets 2. A plurality of mounting brackets 202 are equidistantly fixedly connected to the rotating shaft 201, and a plurality of shafts 203 are rotatably connected to the plurality of mounting brackets 202 at circumferential intervals. A plurality of placement plates 205 are equidistantly fixedly connected to the shaft 203 through triangular support rods 204, and the plurality of placement plates 205 are all horizontally distributed under the action of their own gravity. A drive motor 105 is fixedly connected to one end of the furnace body 101 away from the furnace cover 102, and an output shaft 106 of the drive motor 105 extends into the furnace body 101, and a slot 2011 for cooperating with the output shaft 106 is provided at one end of the rotating shaft 201 close to the drive motor 105, and a plurality of grooves 1061 are opened at circumferential intervals on the output shaft 106, and protrusions 2012 for cooperating with the grooves 1061 are circumferentially equidistantly provided in the slot 2011.

[0026] When it is necessary to place the substrate coated with alumina gel into the furnace body 101, the substrate coated with alumina gel is first placed steadily on the placement plate 205. Since the multiple placement plates 205 are horizontally distributed under the action of their own gravity, the substrate can be placed firmly, avoiding damage to the film coating layer or uneven heating due to tilted placement, which is beneficial to the uniform formation of the film during the subsequent heat treatment process.

[0027] After the base is placed, the furnace cover 102 can be opened, and the placement plate 205 can be lifted into the sintering chamber 103 through the bracket 2. Then, the slot 2011 at one end of the rotating shaft 201 close to the drive motor 105 is docked with the output shaft 106, so that the protrusion 2012 in the slot 2011 is embedded in the groove 1061 of the output shaft 106. This matching structure can ensure stable power transmission, avoid slipping during rotation, and ensure that the rotating shaft 201 can rotate synchronously and stably with the output shaft 106.

[0028] Next, close the furnace cover 102, start the sintering furnace 1 and the drive motor 105, and the drive motor 105 drives the output shaft 106 to rotate, and then drives the rotating shaft 201 to rotate through the cooperation between the slot 2011 and the output shaft 106. When the rotating shaft 201 rotates, it drives multiple mounting frames 202 to rotate synchronously, and the shaft rod 203, triangular support rod 204 and placement plate 205 on the mounting frame 202 rotate together, and the placement plate 205 always remains in a horizontal state, which allows the substrate on the placement plate 205 to receive heat evenly in the sintering chamber 103, avoiding local temperature differences caused by fixed positions, ensuring that all parts of the film are heated evenly during high-temperature sintering and thermal annealing, and is conducive to forming a tight and uniform alumina ceramic film.

[0029] After the heat treatment is completed, the drive motor 105 and the sintering furnace 1 are turned off. After the equipment is cooled to a suitable temperature, the furnace cover 102 is opened. When the plate 205 is placed and the sintering furnace 1 is taken out, the prepared ceramic membrane film can be taken out.

[0030] Reference Figure 6 、 Figure 7 As shown, friction blocks 206 are symmetrically fixedly connected to both ends of the shaft 203 , and the friction blocks 206 slide against the adjacent mounting brackets 202 . A counterweight block 207 is fixedly connected to the center of the bottom of the placement plate 205 .

[0031] The friction blocks 206 at both ends of the shaft 203 slide against the adjacent mounting frame 202, which can effectively reduce the shaking of the shaft 203 through friction damping, and provide stable support for the placement plate 205. The counterweight block 207 at the bottom center of the placement plate 205 further enhances its own balancing ability, so that the placement plate 205 can maintain a stable horizontal state when rotating around the rotating shaft 201 even if it is affected by external force, avoiding the displacement or slipping of the substrate coated with alumina gel due to shaking, thereby further improving the stability of the placement plate 205 and the substrate, and ensuring the uniform forming of the film during the subsequent heat treatment process.

[0032] Reference Figure 4 、 Figure 6 As shown, a limiting groove 2051 for limiting the base is opened on the placement plate 205.

[0033] The limiting groove 2051 opened on the placement plate 205 can play a precise limiting role on the substrate, and can effectively prevent the substrate from being displaced or slipping when the placement plate 205 rotates or is affected by a slight external force, ensuring that the substrate always maintains a stable position during the heat treatment process. This helps to ensure that the alumina gel coated on the substrate is heated evenly, avoiding uneven film thickness or defects due to substrate movement, thereby further improving the quality stability of the final alumina ceramic film, which is consistent with the process requirements of preparing high-quality ceramic films by the sol-gel method.

[0034] Reference Figure 3 、 Figure 4 、 Figure 5 、 Figure 6 As shown: the lower ends of the two brackets 2 are symmetrically fixedly connected with positioning rods 3, which are located at the corners on both sides of the bottom of the sintering bin 103. The positioning rods 3 are equidistantly provided with multiple arc grooves on the side adjacent to the corners on both sides of the bottom of the sintering bin 103, and balls 301 are movably connected in the arc grooves.

[0035] The positioning rods 3 at the lower ends of the two brackets 2 are located at the two side corners of the bottom of the sintering bin 103, which can provide solid support for the entire support structure, enhance its installation stability in the sintering bin 103, and prevent the bracket 2 and the upper rotating shaft 201, placement plate 205 and other components from shaking during operation, thereby ensuring the stability of the substrate and film. At the same time, the ball 301 in the arc groove on the positioning rod 3 contacts the bottom of the sintering bin 103, which can convert the sliding friction between the bracket 2 and the sintering bin 103 into rolling friction, greatly reducing the resistance when taking and placing the bracket 2, so that the bracket 2 and the substrate carried above can be more easily taken out or put in from the sintering bin 103, which not only ensures structural stability but also improves operational convenience.

[0036] Reference Figure 2 、 Figure 3 As shown, the length of the positioning rod 3 is the same as the length of the sintering chamber 103.

[0037] The length of the positioning rod 3 is the same as that of the sintering chamber 103, so that the positioning rod 3 can extend from one end of the sintering chamber 103 to the other end, forming a comprehensive and uniform support contact with the bottom of the sintering chamber 103. This full-length support structure can greatly enhance the overall stability of the bracket 2 in the sintering chamber 103, especially after closing the furnace cover 102, it can effectively resist the impact of changes in the air pressure in the furnace or slight external vibrations on the bracket 2, and avoid displacement or shaking of the bracket 2 and the upper rotating shaft 201, placement plate 205 and other components, thereby ensuring that the substrate coated with alumina gel always remains stable during the heat treatment process, providing reliable guarantee for the preparation of tight and uniform alumina ceramic film.

[0038] It is worth noting that: all components in the present invention are made of high-temperature resistant steel, which can adapt to the high-temperature environment during the high-temperature sintering process, avoid deformation, damage or performance degradation of components due to high temperature, and ensure the stability and durability of the relevant structures of the sintering furnace during the heat treatment process, thereby providing reliable equipment support for the heat treatment steps of preparing ceramic films by the sol-gel method, ensuring the smooth progress of high-temperature sintering, thermal annealing and other processes, which is conducive to the preparation of high-quality alumina ceramic films.

[0039] The contents not described in detail in this specification belong to the prior art known to those skilled in the art.

[0040] The above description is merely a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as above with the preferred embodiment, it is not intended to limit the present invention.

Claims

1. A method for preparing a ceramic thin film by a sol-gel method, characterized in that: The main steps include: Step 1: Prepare the precursor: Dissolve pseudo-boehmite in hot water, stir and disperse, then dropwise add nitric acid solution in proportion, continue stirring, and continue stirring at the same temperature for a period of time after the addition is complete to obtain boehmite sol; The mass ratio of the pseudo-boehmite powder to the nitric acid is controlled between 3 and 4, the mass ratio of the pseudo-boehmite powder to water is controlled between 0.2 and 0.5, and the hydrolysis temperature is higher than 80°C. Step 2: Gel preparation: The boehmite sol obtained in step 1 is subjected to a hydrolysis-condensation reaction to generate a gelation reaction to form an alumina gel; Step 3: Coating the substrate: Evenly coating the alumina gel prepared in step 2 on the substrate; Step 4: Heat treatment: The substrate coated with the alumina gel is placed in a sintering furnace (1) for high-temperature sintering and thermal annealing treatment, so that the alumina gel forms a compact and uniform alumina ceramic film.

2. The method for preparing a ceramic thin film by a sol-gel method according to claim 1, characterized in that: In step 1, during the process of adding nitric acid solution, it is necessary to observe the changes in the liquid and record the moment when the liquid state changes and the amount of nitric acid used.

3. The method for preparing a ceramic thin film by a sol-gel method according to claim 1, characterized in that: In step 1, after the dropwise addition of the nitric acid solution is completed, the stirring time is preferably continued to ensure that the reaction proceeds fully.

4. The method for preparing a ceramic thin film by a sol-gel method according to claim 1, characterized in that: In step 4, the process parameters of high temperature sintering and thermal annealing are adjusted accordingly according to the required performance of the ceramic film.

5. The method for preparing a ceramic thin film by a sol-gel method according to claim 1, characterized in that: The sintering furnace (1) comprises a furnace body (101), a furnace cover (102), a sintering bin (103) and a support (104); the sintering furnace (1) is fixedly mounted on the support (104); the furnace cover (102) is rotatably connected to the furnace mouth of the furnace body (101); and the sintering bin (103) is arranged inside the furnace body (101).

6. The method for preparing a ceramic thin film by a sol-gel method according to claim 5, characterized in that: Two brackets (2) are symmetrically placed in the sintering bin (103), a rotating shaft (201) is rotatably connected between the two brackets (2), a plurality of mounting brackets (202) are equidistantly fixedly connected to the rotating shaft (201), a plurality of shafts (203) are rotatably connected to the plurality of mounting brackets (202) in a circular manner, a plurality of placement plates (205) are equidistantly fixedly connected to the shafts (203) via triangular support rods (204), and the plurality of placement plates (205) are horizontally distributed under the action of their own gravity. The end of the rotating shaft (201) away from the furnace cover (102) is fixedly connected to a driving motor (105), the output shaft (106) of the driving motor (105) extends into the furnace body (101), and the end of the rotating shaft (201) close to the driving motor (105) is provided with a slot (2011) for use with the output shaft (106), a plurality of grooves (1061) are opened on the output shaft (106) at equal intervals around the circumference, and protrusions (2012) for use with the grooves (1061) are provided at equal intervals around the circumference in the slot (2011).

7. The method for preparing a ceramic thin film by a sol-gel method according to claim 6, characterized in that: The two ends of the shaft (203) are symmetrically fixedly connected with friction blocks (206), and the friction blocks (206) are slidably attached to the adjacent mounting frames (202). The center position of the bottom of the placement plate (205) is fixedly connected with a counterweight block (207).

8. The method for preparing a ceramic thin film by a sol-gel method according to claim 6, characterized in that: The placement plate (205) is provided with a limiting groove (2051) for limiting the base.

9. The method for preparing a ceramic thin film by a sol-gel method according to claim 6, characterized in that: The lower ends of the two brackets (2) are symmetrically fixedly connected with positioning rods (3), and the positioning rods (3) are located at the corners on both sides of the bottom of the sintering bin (103). A plurality of arc grooves are equidistantly provided on the side of the positioning rods (3) adjacent to the corners on both sides of the bottom of the sintering bin (103), and balls (301) are movably connected in the arc grooves.

10. The method for preparing a ceramic thin film by a sol-gel method according to claim 9, characterized in that: The length of the positioning rod (3) is the same as the length of the sintering chamber (103).

Images