Method for preparing ceramic membrane by using surface tension

Abstract

The invention discloses a method for preparing a ceramic membrane by using surface tension. Relates to the technical field of ceramic membrane preparation. A method for preparing a ceramic membrane comprises the following steps: S1, immersing a grid frame made of a hydrophilic material into a ceramic membrane precursor colloidal solution, lifting the grid frame from the ceramic membrane precursor colloidal solution, and enabling the ceramic membrane precursor colloidal solution to suspend in gaps of grids to form a liquid bridge, so as to obtain a sample; and S2, drying the sample, and when the liquid bridge is converted into a gel state or an amorphous solid film, sintering the sample to obtain the ceramic film. According to the method disclosed by the invention, the ceramic membrane with any required thickness, no crack and excellent piezoelectric coefficient can be manufactured.

Description

Technical Field

[0001] The present invention relates to the technical field of ceramic membrane preparation, and more particularly to a method for preparing ceramic membranes using surface tension. Background Art

[0002] In the preparation of ceramic membranes, the colloidal membrane plays a crucial role. The colloidal membrane is mainly composed of sub-micron-sized dispersed particles, and its thickness directly affects the physical, chemical properties and final application performance of the membrane. The characteristic of the colloidal membrane lies in its high tunability, and the properties of the material can be optimized by precisely controlling the thickness, particle distribution and structure of the membrane. For example, the colloidal membrane can adjust the photonic crystal path by changing the thickness, which is crucial for improving the performance of optical devices; by changing the structure or thickness of the membrane, the efficiency of the ceramic membrane in energy storage devices can also be improved, or its mechanical and electrical properties can be optimized in piezoelectric ceramic membranes. Especially in piezoelectric ceramic membranes, thick colloidal membranes can effectively improve the mechanical strength and electrical properties of the membrane, thereby enhancing its performance in applications such as sensors and actuators.

[0003] However, traditional deposition and sintering methods have certain limitations in controlling the film quality, thickness and their consistency. In particular, when the thickness of the colloidal membrane reaches the critical cracking thickness (CCT), according to Griffith's crack propagation criterion, further solvent evaporation and concentration increase will cause the stored elastic energy therein to exceed the critical threshold, and the stress accumulated in the membrane may lead to the formation of cracks and the rupture of the membrane, which is a challenge for many application scenarios. For example, in piezoelectric ceramic membranes, this threshold rarely exceeds 5 μm, which poses a challenge to applications such as wearable medical imaging and micro-robots that require piezoelectric materials with a thickness greater than dozens of microns.

[0004] In the prior art, the methods for increasing the CCT (critical conversion temperature) mainly rely on increasing the particle size (such as incorporating solid particles into a pure liquid-phase colloid) or adding adhesives to enhance the mechanical strength of the film. By this method, the thickness of the piezoelectric ceramic thin film can be increased to more than 10 μm. However, the introduction of heterogeneous phases will inevitably affect the material properties, resulting in the piezoelectric coefficient d33 of the thick film being one order of magnitude lower than that of the pure-phase thin film or bulk ceramic. Another type of research explores improving the CCT by adjusting the properties of the substrate, but due to the mismatch in lattice constant, thermal expansion coefficient and hardness between the colloidal thin film and the substrate, it will affect the forming quality of the thin film and make the CCT control more complicated.

[0005] Based on this, there is an urgent need to develop a new method for preparing ceramic membranes to exceed the limitation of the critical crack thickness and achieve the manufacture of thin films with any desired thickness and excellent piezoelectric coefficients. Summary of the Invention

[0006] The object of the present invention is to provide a method for preparing a ceramic film by using surface tension, so as to manufacture a ceramic film with any required thickness, without cracks and excellent piezoelectric coefficient.

[0007] The first aspect of the present invention lies in:

[0008] Providing a method for preparing a ceramic film. In the method of the present invention, by using the capillary bridge phenomenon, the ceramic film precursor colloidal solution is confined within the grid in the frame to utilize the inherent surface tension of the solution, forming a suspension bridge, so as to suspend a pure-phase liquid colloidal film above the substrate, enabling it to undergo phase change processes such as evaporation, drying, and sintering without being affected by tensile stress, thereby obtaining a crack-free ceramic film.

[0009] The second aspect of the present invention lies in:

[0010] The present invention proposes a piezoelectric sensor and an ultrasonic transmitter.

[0011] Specifically, the technical solution adopted according to the first aspect of the present invention is as follows:

[0012] A method for preparing a ceramic film, comprising the following steps:

[0013] S1 Immerse a grid frame made of a hydrophilic material in the ceramic film precursor colloidal solution, lift the grid frame from the ceramic film precursor colloidal solution, and allow the ceramic film precursor colloidal solution to be suspended between the gaps of the grid to form a liquid bridge, obtaining a sample;

[0014] S2 Dry the sample, and when the liquid bridge turns into a gel state or an amorphous solid film, sinter the sample to obtain a ceramic film;

[0015] The temperature of the drying < the thermal decomposition temperature of the grid frame ≤ the temperature of the sintering;

[0016] The shape of each grid of the grid frame includes one of a square, a circle, a triangle, and a hexagon, and the side length or diameter of the grid is less than or equal to 3.5 mm;

[0017] The contact angle of the ceramic film precursor colloidal solution is 0 - 35°.

[0018] According to the embodiments of the present invention, at least one of the following advantages or beneficial effects exists in one of the technical solutions in the technical solution:

[0019] The present invention uses a grid frame made of a hydrophilic material, enabling the ceramic film precursor colloidal solution to penetrate into the grid frame. The grid confines the colloidal solution and forms a complete capillary liquid bridge, similar to the water film formed on a window screen on a rainy day.

[0020] During the drying stage of the liquid bridge, as water and organic solvents evaporate, the liquid bridge gradually shrinks and solidifies, forming a self-supporting gel or an amorphous solid film. As the sintering stage progresses, the temperature rises, and the material constituting the grid framework undergoes thermal decomposition, separating from the capillary bridge film and completely releasing the stress applied to the capillary bridge. The separation at the film edge indicates that the external tensile stress is much smaller than the minimum crack stress. Therefore, the requirements for crack nucleation and propagation are no longer met, preventing further growth of microcracks within the material. At the same time, due to capillary action, the film does not contact the substrate, and there will be no tensile stress on the film. In the absence of external tensile stress in both the longitudinal and transverse directions of the film, the film can spontaneously shrink, solidify, and crystallize during drying and sintering without being affected by external forces, and the microcracks within the material cannot obtain sufficient energy to grow and expand, thus obtaining a crack-free ceramic membrane.

[0021] In addition, for the preparation of the crack-free ceramic membrane of the present invention, it is necessary to enable the ceramic membrane precursor colloidal solution to be suspended between the gaps of the grid to form a liquid bridge. In addition to the grid framework being composed of hydrophilic materials, it is also necessary to control the side length or diameter of the grid to be less than or equal to 3 mm and the contact angle of the ceramic membrane precursor colloidal solution to be 0 - 35°. Among them, under the influence of gravity, when the area of a single grid is too large, the adhesion force between the capillary membrane and the grid wall may not be sufficient to offset the gravity. Therefore, the method of the present invention controls the side length or diameter of the grid to be less than or equal to 3 mm, thereby distributing the weight and gravity over multiple smaller and manageable parts; among them, the contact angle of the ceramic membrane precursor colloidal solution is 0 - 35°, which can enable the ceramic membrane precursor colloidal solution to completely wet the corners of the grid to minimize the surface energy.

[0022] According to an embodiment of the present invention, in step S1, a grid framework made of hydrophilic materials is immersed in the ceramic membrane precursor colloidal solution. After ensuring that the grids in the grid framework are completely wetted, the grid framework is lifted from the ceramic membrane precursor colloidal solution.

[0023] According to an embodiment of the present invention, the concentration of the ceramic membrane precursor colloidal solution is 3.0 - 5.0 mM. Too low a concentration means that the solute is not sufficient to maintain the stability of the capillary membrane during drying, resulting in its rupture, and too high a concentration leads to excessive gravity, such that the adhesion force between the capillary membrane and the grid wall is not sufficient to offset the gravity.

[0024] According to an embodiment of the present invention, the concentration of the ceramic membrane precursor colloidal solution is one of 3.11 mM, 3.36 mM, 3.64 mM, 3.98 mM, 4.39 mM, and 4.89 mM.

[0025] According to an embodiment of the present invention, after the sample is dried, the filling rate of the capillary film at a lower concentration (the proportion of the liquid capillary film formed on the grid) decreases significantly, and the filling rate of the capillary film at a slightly higher concentration performs better.

[0026] According to an embodiment of the present invention, the shape of each grid of the grid frame can be any customized shape, and the shape of the grid includes one of a square, a circle, a triangle, and a hexagon. The customizable grid not only provides design freedom for the film topology but also facilitates the preparation of various film arrays without a destructive cutting process. Moreover, the independent nature of these films enhances their adaptability to microelectromechanical system (MEMS) processing, and the "capillary bridge" topology enables the ceramic film prepared by the present invention to be used in an ultrasonic focusing emitter, providing the possibility for medical imaging.

[0027] According to an embodiment of the present invention, the shape of each grid of the grid frame includes one of a square, a circle, a triangle, and a hexagon, and the side length or diameter of the grid is less than or equal to 3.0 mm.

[0028] According to an embodiment of the present invention, the shape of each grid of the grid frame includes one of a square, a circle, a triangle, and a hexagon, and the side length or diameter of each grid of the grid frame is 0.5 - 3 mm.

[0029] According to an embodiment of the present invention, the grid of the grid frame is a square, and the side length of the square grid is 1 mm, 1.5 mm, 2 mm, 2.5 mm, or 3 mm.

[0030] According to an embodiment of the present invention, the grid of the grid frame is a square. Preferably, when the side length of the square grid is 1.5 mm, almost all concentrations of the ceramic film precursor colloidal solution exhibit a capillary film filling rate (the proportion of the liquid capillary film formed on the grid) exceeding 80%.

[0031] According to an embodiment of the present invention, the grid frame is prepared by commercial methods, including 3D printing and spinning.

[0032] According to an embodiment of the present invention, the contact angle of the ceramic film precursor colloidal solution is 10 - 35°.

[0033] According to an embodiment of the present invention, the contact angle of the ceramic film precursor colloidal solution is 14°, 17°, 22°, 25°, 28°, or 30°.

[0034] According to an embodiment of the present invention, there is a corresponding relationship between the contact angle of the ceramic membrane precursor colloidal solution and the concentration of the ceramic membrane precursor colloidal solution. For example, when the concentration is 4.89 mM, the corresponding CA = 30°.

[0035] According to an embodiment of the present invention, when the concentration of the ceramic membrane precursor colloidal solution is 3.11 mM, the contact angle is about 14°; when the concentration is 3.36 mM, the contact angle is about 17°; when the concentration is 3.64 mM, the contact angle is about 22°; when the concentration is 3.98 mM, the contact angle is about 25°; when the concentration is 4.39 mM, the contact angle is about 28°; when the concentration is 4.89 mM, the contact angle is about 30°.

[0036] According to an embodiment of the present invention, the concentration of the ceramic membrane precursor colloidal solution and the contact angle determine the probability of liquid bridge formation, that is, the capillary membrane filling rate (the proportion of the liquid capillary membrane formed on the grid). Since there is a corresponding relationship between the concentration and the critical angle, it is particularly important to have a suitable concentration of the ceramic membrane precursor colloidal solution. Too low a concentration means that the solute is not sufficient to maintain the stability of the capillary membrane during drying, resulting in its rupture. Too high a concentration means that the gravity is too large, and the adhesion force between the capillary membrane and the grid wall is not sufficient to counteract the gravity.

[0037] According to an embodiment of the present invention, the drying temperature is less than 100 °C, thereby ensuring that only water and organic solvents evaporate.

[0038] According to an embodiment of the present invention, the thickness of the ceramic membrane is 1 - 100 μm. Due to factors such as gravity and air turbulence, the liquid capillary bridge does not always remain stable during the preparation of the ceramic membrane. When the liquid bridge film is too thin, it is easily damaged by air impurities and turbulence. When the liquid bridge film is thicker, external factors are less likely to cause the liquid bridge to break, making it easier to dry and form a complete solid. Therefore, by the method of the present invention, crack-free ceramic thin films with a thickness range from 1 to 100 μm can be prepared.

[0039] According to an embodiment of the present invention, the thickness of the ceramic membrane is mainly determined by the thickness of the grid border.

[0040] According to an embodiment of the present invention, it is challenging to achieve a uniform thickness in the capillary membrane, but the present invention can adjust the thickness distribution by optimizing the solution concentration and drying conditions. Using a high-concentration ceramic membrane precursor colloidal solution can reduce the difference between the thickest and thinnest points to less than 10%. On the contrary, using a low-concentration solution may result in a thickness variation of more than 90%.

[0041] According to an embodiment of the present invention, for the ceramic membrane, due to the influence of surface tension and gravity during the preparation process, the film spontaneously formed by the liquid has a "liquid bridge" structure with "thin in the middle and thick at the edges".

[0042] According to an embodiment of the present invention, the hydrophilic material includes one of hydrophilic resin, silk, and cotton thread.

[0043] According to an embodiment of the present invention, the hydrophilic resin includes at least one of polyurethane acrylate, cyclic trimethylolpropane formal acrylate, and 3,5-trimethylcyclohexyl acrylate.

[0044] According to an embodiment of the present invention, the ceramic membrane precursor colloidal solution includes PbZr 0.52 Ti 0.48 O3, BiFeO3, and Ba 0.85 Ca 0.15 Zr 0.2 Ti 0.3 O3.

[0045] According to an embodiment of the present invention, when the ceramic membrane precursor colloidal solution is PbZr 0.52 Ti 0.48 O3 (PZT), the prepared PZT thin film exhibits a piezoelectric coefficient as high as 221 pC / N.

[0046] According to an embodiment of the present invention, when the ceramic membrane precursor colloidal solution is PbZr 0.52 Ti 0.48 O3 (PZT), the sintering temperature is less than or equal to 900 °C. After testing, the separation of the PZT colloidal film from the grid starts at 350 °C. When the temperature is higher than 400 °C, the weight of the grid framework rapidly decreases until all the grids decompose, while the weight of the PZT will remain at 42%. Therefore, below 400 °C, the shrinkage of the PZT precursor plays a more important role in generating cracks along the interface between the film and the grid. When the temperature is higher than 400 °C, the decomposition of the resin will cause the cracks to expand until the materials are completely separated. At 500 °C, the initial perovskite phase appears, accompanied by some secondary phases, indicating partial sintering. Between 600 and 800 °C, the perovskite phase is basically formed, but there are still a small number of miscellaneous peaks, which are harmful to the performance of the piezoelectric material. When the sintering temperature exceeds 800 °C, the crystals gradually crystallize, and when the sintering temperature is greater than 1000 °C, the grain size is too large and the porosity increases. On the contrary, when the temperature is lower than 800 °C, the ceramics do not crystallize completely. Therefore, preferably, the sintering temperature is greater than 800 °C and less than or equal to 900 °C.

[0047] Specifically, the technical solution adopted in the second aspect of the present invention is as follows:

[0048] A piezoelectric sensor includes a ceramic film, and the ceramic film is prepared by the method for preparing a ceramic film described above.

[0049] An ultrasonic transmitter includes a ceramic film, and the ceramic film is prepared by the method for preparing a ceramic film described above.

[0050] According to an embodiment of the present invention, the ceramic film is a polished ceramic film. Due to the influence of surface tension and gravity, the film spontaneously formed by the liquid in the ceramic film prepared by the present invention has a "liquid bridge" structure with "thin in the middle and thick at the edges". If a flatter ceramic film is required, it can be polished.

[0051] According to an embodiment of the present invention, the ceramic film prepared by the method of the present invention has extremely high density, does not have bendable characteristics, does not have porous characteristics, and the ceramic film of the present invention is very suitable for high-precision sensors and acoustic applications.

[0052] Some of the additional aspects and advantages of the present invention will be given in the following description, some will become obvious from the following description, or be understood through the practice of the present discovery. Description of the Drawings

[0053] The above and / or additional aspects and advantages of the present invention will become obvious and easy to understand from the description of the embodiments in conjunction with the following drawings, where:

[0054] Figure 1 is a flowchart of the method for preparing a ceramic film in Example 1.

[0055] Figure 2 is a schematic diagram of the ceramic film precursor colloidal solution suspended on a grid frame in Example 1.

[0056] Figure 3 is a SEM micrograph of the ceramic film prepared in Example 1.

[0057] Figure 4 is a SEM micrograph of the side 500 μm of the ceramic film prepared in Example 1.

[0058] Figure 5 is a physical picture of the ceramic film prepared in Examples 1-3.

[0059] Figure 6 is a physical picture of the polished ceramic film prepared in Examples 1 and 4-8.

[0060] Figure 7 is a graph showing the relationship between the grid size and the filling rate α of the ceramic film precursor colloidal solution in Examples 1 and 9-12.

[0061] Figure 8 Photographs of the ceramic membranes prepared in Example 1 and Examples 13 - 15.

[0062] Figure 9 SEM images of the ceramic membranes prepared in Example 1, Example 16 and Comparative Example 3.

[0063] Figure 10 Schematic diagram of the spherical three - dimensional piezoelectric sensor prepared in Example 17.

[0064] Figure 11 Schematic diagram of the ultrasonic focusing transmitter prepared in Example 18.

[0065] Figure 12 SEM image of the ceramic membrane prepared in Comparative Example 1.

[0066] Figure 13 Piezoelectricity test chart of the ceramic membrane prepared in Example 1.

[0067] Figure 14 Relationship diagram between the concentration of the ceramic membrane precursor colloidal solution and the contact angle in Examples 1, 19 - 23. Detailed implementation manners

[0068] Words such as "preferably" and "more preferably" in the present invention refer to embodiments of the present invention that can provide certain beneficial effects in certain cases. However, in the same or other cases, other embodiments may also be preferred. In addition, the description of one or more preferred embodiments does not imply that other embodiments are not available, nor is it intended to exclude other embodiments from the scope of the present invention.

[0069] When a numerical range is disclosed herein, the above range is considered continuous and includes the minimum and maximum values of the range, as well as every value between such minimum and maximum values. Further, when the range refers to integers, every integer between the minimum and maximum values of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub - ranges subsumed therein.

[0070] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of the present invention.

[0071] Unless otherwise specified, the reagents, methods, and equipment used in the present invention are all conventional reagents, methods, and equipment in this technical field.

[0072] In the examples and comparative examples, the grids were prepared using commercial stereolithography 3D printing technology (JC-M10, JANSUM). The grid raw material used was a hydrophilic commercial resin JC-H-00, which mainly included polyurethane acrylate (PUA), cyclic trimethylolpropane formal acrylate (CTFA), and 3,5-trimethylcyclohexyl acrylate (TMCHA). The grids were printed with a layer thickness of 25 μm. Before use, the grids need to be rinsed twice with isopropyl alcohol and post-cured by irradiation with 405 nm light. The grids will detach from the gel or amorphous solid film obtained after drying the ceramic membrane precursor colloidal solution of the present invention at a temperature of about 350 °C.

[0073] In the examples and comparative examples, the thickness of the ceramic membrane was 1 - 100 μm, specifically determined by the thickness of the grid frame obtained by printing. In the examples and comparative examples, the thinnest grid frame thickness used was 25 μm.

[0074] Example 1

[0075] A method for preparing a ceramic membrane, the flow chart is as Figure 1 shown, including the following steps:

[0076] S1 Immerse the grid frame made of hydrophilic resin in the ceramic membrane precursor colloidal solution. After ensuring that the grids in the grid frame are completely wetted, lift the grid frame from the ceramic membrane precursor colloidal solution, and let the ceramic membrane precursor colloidal solution suspend between the gaps of the grids to form a liquid bridge, obtaining a sample; in the sample, the schematic diagram of the ceramic membrane precursor colloidal solution hanging on the grid frame is as Figure 2 shown;

[0077] S2 Dry the sample at 60 °C. When the liquid bridge turns into a gel state or an amorphous solid film, sinter the sample at 900 °C to obtain the ceramic membrane.

[0078] The shape of each grid of the above grid frame is square, and the side length is 1.5 mm;

[0079] The concentration of the ceramic membrane precursor colloidal solution is 4.89 mM, and the contact angle CA of the ceramic membrane precursor colloidal solution is 30°.

[0080] The above ceramic membrane precursor colloidal solution is a Pb(Zr 0.52 Ti0. 48 )O3 (PZT) solution, Pb(Zr 0.52 Ti0. 48)The O3 solution contains 10% Pb to compensate for the volatilization of PbO at high temperatures during the annealing process. The preparation method is as follows: First, dissolve 6.8 g of lead(II) acetate trihydrate (Pb(CH3COOH2)·3H2O) in 3 mL of acetic acid (99%) and heat it at 90 °C for 1 hour, and mix it by magnetic stirring. When it is completely dissolved, cool the solution to room temperature. Mix 3.45 g of zirconium(IV) n-propoxide (C 12 H 28 O4Zr, 70 wt.%, in 1-propanol) with 2.45 g of titanium(IV) butoxide (C 16 H 36 O4Ti, 99%) in another container. Then add zirconium(IV) n-propoxide and titanium(IV) butoxide to the lead(II) acetate trihydrate solution and heat it to 90 °C with stirring, and keep it in the air for 6 hours. Store the prepared solution in the air for at least three days for aging to obtain a transparent pale yellow PZT sol.

[0081] The SEM micrograph of the ceramic membrane prepared in Example 1 is as shown in Figure 3 wherein, as can be seen from Figure 3 a-b, the ceramic membrane prepared by the present invention is a dense, pore-free and non-bendable membrane;

[0082] The SEM micrograph of the side of the ceramic membrane prepared in Example 1 at 500 μm is as shown in Figure 4 wherein, as can be known from Figure 4 the ceramic membrane prepared by the present invention is a membrane in the shape of a liquid bridge, thin in the middle and thick at the edges.

[0083] Example 2

[0084] The difference between Example 2 and Example 1 is that in Example 2, the ceramic membrane precursor colloidal solution is BiFeO3 (BFO).

[0085] Example 3

[0086] The difference between Example 3 and Example 1 is that in Example 3, the ceramic membrane precursor colloidal solution is Ba 0.85 Ca 0.15 Zr 0.2 Ti 0.3 O3 (BCZT), with a concentration of 4.89 mM.

[0087] Example 4

[0088] The difference between Example 4 and Example 1 is that in Example 4, the thickness of the ceramic membrane is 80 μm.

[0089] Example 5

[0090] Example 5 is different from Example 1 in that in Example 5, the thickness of the ceramic membrane is 60 μm.

[0091] Example 6

[0092] Example 6 is different from Example 1 in that in Example 6, the thickness of the ceramic membrane is 50 μm.

[0093] Example 7

[0094] Example 7 is different from Example 1 in that in Example 7, the thickness of the ceramic membrane is 40 μm.

[0095] Example 8

[0096] Example 8 is different from Example 1 in that in Example 8, the thickness of the ceramic membrane is 25 μm.

[0097] Example 9

[0098] Example 9 is different from Example 1 in that in Example 9, the side length of each grid of the grid framework is 1.0 mm.

[0099] Example 10

[0100] Example 10 is different from Example 1 in that in Example 9, the side length of each grid of the grid framework is 2.0 mm.

[0101] Example 11

[0102] Example 11 is different from Example 1 in that in Example 11, the side length of each grid of the grid framework is 2.5 mm.

[0103] Example 12

[0104] Example 12 is different from Example 1 in that in Example 12, the side length of each grid of the grid framework is 3.0 mm.

[0105] Example 13

[0106] Example 13 is different from Example 1 in that in Example 13, the shape of each grid of the grid framework is an equilateral triangle with a side length of 1.0 mm.

[0107] Example 14

[0108] Example 14 is different from Example 1 in that in Example 14, the shape of each grid of the grid framework is a rectangle with a side length of 1.0 mm.

[0109] Example 15

[0110] Example 15 is different from Example 1 in that: in Example 15, the shape of each grid of the grid frame is an equilateral hexagon with a side length of 1.0 mm.

[0111] Example 16

[0112] Example 16 is different from Example 1 in that: in Example 16, the sintering temperature is 800 °C.

[0113] Example 17

[0114] Example 17 is a spherical three-dimensional piezoelectric sensor assembled from a hexagonal ceramic membrane array, and the ceramic membrane used is the ceramic membrane prepared in Example 15.

[0115] Example 18

[0116] Example 18 is an ultrasonic focusing transmitter made of a ceramic membrane, and the ceramic membrane used is the ceramic membrane prepared in Example 1.

[0117] Example 19

[0118] Example 19 is different from Example 1 in that: in Example 19, the concentration of the ceramic membrane precursor colloidal solution is 3.11 mM, and the corresponding contact angle is about 14°.

[0119] Example 20

[0120] Example 20 is different from Example 1 in that: in Example 20, the concentration of the ceramic membrane precursor colloidal solution is 3.36 mM, and the corresponding contact angle is about 17°.

[0121] Example 21

[0122] Example 21 is different from Example 1 in that: in Example 21, the concentration of the ceramic membrane precursor colloidal solution is 3.64 mM, and the corresponding contact angle is about 22°.

[0123] Example 22

[0124] Example 22 is different from Example 1 in that: in Example 22, the concentration of the ceramic membrane precursor colloidal solution is 3.98 mM, and the corresponding contact angle is about 25°.

[0125] Example 23

[0126] Example 23 is different from Example 1 in that: in Example 23, the concentration of the ceramic membrane precursor colloidal solution is 4.39 mM, and the corresponding contact angle is about 28°.

[0127] Example 24

[0128] Example 24 is different from Example 1 in that: in Example 24, the shape of each grid of the grid framework is an equilateral triangle with a side length of 1.5 mm.

[0129] Example 25

[0130] Example 25 is different from Example 1 in that: in Example 25, the shape of each grid of the grid framework is a rectangle with a side length of 1.5 mm.

[0131] Comparative Example 1

[0132] Comparative Example 1 is different from Example 1 in that: in Comparative Example 1, a ceramic membrane is prepared by a conventional method, and in this conventional method, a silicon wafer substrate is included, and during the sintering process, the ceramic membrane precursor solution will contact the silicon wafer substrate.

[0133] Comparative Example 2

[0134] Comparative Example 2 is different from Example 1 in that: in Comparative Example 2, a ceramic membrane is prepared by a conventional method, and in this conventional method, electrospinning technology is used to prepare a ceramic electrospun membrane. This membrane has a porous structure, is similar to a textile membrane, and has a certain flexibility.

[0135] Comparative Example 3

[0136] Comparative Example 3 is different from Example 1 in that: in Comparative Example 1, the sintering temperature is 1000 °C.

[0137] Performance test:

[0138] Examples 1 - 3 use different ceramic membrane precursor colloidal solutions to prepare ceramic membranes, and the physical pictures of the obtained ceramic membranes are as Figure 5 shown. Among them, PZT is a lead zirconate titanate ceramic membrane, BFO is a bismuth ferrite ceramic membrane, and BCZT is a barium calcium zirconate titanate ceramic membrane. By using different liquid components in the grid framework, different ceramic membranes can be prepared, which indicates that the method of the present invention has broad application prospects and can provide a platform for extensive research on various biological and chemical processes, and has important application potential in disciplines such as biology, materials science, and chemistry.

[0139] The difference between Example 1 and Examples 4 - 8 lies in the different thicknesses of the ceramic membranes. Figure 6 For the ceramic membranes prepared in Example 1 and Examples 4 - 8, the physical pictures of the polished sides are shown. It can be seen from the figure that the method of the present invention can prepare ceramic membranes with different thicknesses.

[0140] The difference between Example 1 and Examples 9 - 12 lies in the different side lengths of the grids. Figure 7It is a graph showing the relationship between the grid size and the filling rate α (the proportion of the liquid capillary film formed on the grid) of the ceramic membrane precursor colloidal solution in Example 1 and Examples 9 - 12. From the graph, it can be known that, firstly, for different grid sizes, the filling rate α is different; secondly, after the drying treatment, the filling rate α will decrease.

[0141] The difference between Example 1 and Examples 13 - 15 lies in the different shapes of the grids. Figure 8 It is a physical diagram of the ceramic membranes prepared in Example 1 and Examples 13 - 15. From the figure, it can be known that the shape of each grid of the grid framework of the present invention can be any customized shape. The customizable grids not only provide design freedom for the film topology but also facilitate the preparation of various film arrays without the need for a destructive cutting process. Moreover, the independent properties of these films enhance their adaptability to microelectromechanical system (MEMS) processing, and the "capillary bridge" topology enables the ceramic membranes prepared by the present invention to be used in ultrasonic focusing emitters, providing the possibility for medical imaging.

[0142] The difference between Example 1, Example 16 and Comparative Example 3 is the different sintering temperatures. Figure 9 It is the SEM electron micrograph of the ceramic membranes prepared in Example 1, Example 16 and Comparative Example 3. Among them, Figure 9 a corresponds to Example 1. Figure 9 b corresponds to Example 16. Figure 9 c corresponds to Comparative Example 3. From the figure, it can be known that when the sintering temperature reaches 1000 °C, the crystal grains are too large and the pores are too large; when the sintering temperature is 900 °C, the crystal grain size is the most suitable and the ceramic membrane is the densest.

[0143] Figure 10 It is a schematic diagram of the spherical three - dimensional piezoelectric sensor prepared in Example 17. From the figure, it can be seen that the ceramic membrane of the present invention is suitable for being assembled in a piezoelectric sensor. Since the ceramic membrane material of the present invention is formed in separate grids without the interference of a substrate, this enables the ceramic membrane of the present invention to be easily integrated with other materials and systems, paving the way for the construction of electronic components and 3D devices.

[0144] Figure 11 It is a schematic diagram of the ultrasonic focusing transmitter prepared in Example 18. From the figure, it can be seen that the ceramic membrane of the present invention is also suitable for being assembled in an ultrasonic focusing transmitter.

[0145] Figure 12 It is the SEM image of the ceramic membrane prepared in Comparative Example 1. Among them, Figure 12 a of it is the electron micrograph with a scale of 1 mm. Figure 12 b of it is the electron micrograph with a scale of 200 μm. From Figure 12 it can be known that the ceramic membrane prepared in Comparative Example 1 has cracks.

[0146] Figure 13 Piezoelectricity test chart of the ceramic membrane prepared in Example 1. It can be seen from the chart that the piezoelectric coefficient of the ceramic membrane prepared by the present invention can reach 221 pC / N.

[0147] Figure 14 Relationship diagram between the concentration of the ceramic membrane precursor colloidal solution and the contact angle in the preparation methods of Example 1 and Examples 19 - 23. Among them, the error bars are the standard deviation, Concentration is the concentration, and Contact angle is the contact angle. It can be seen from Figure 14 that when the concentration of the ceramic membrane precursor colloidal solution is 3.0 - 5.0 mM and the contact angle is 0 - 35°, it can form a capillary membrane in the grid framework, and finally a crack-free ceramic membrane can be prepared.

[0148] The above are only the embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent transformation made by using the content of the specification of the present invention, directly or indirectly applied in the relevant technical fields, shall be included in the patent protection scope of the present invention by the same token.

Claims

1. A method for preparing a ceramic membrane, characterized in that: The following steps are involved: S1: immersing a grid frame made of a hydrophilic material into a ceramic membrane precursor colloidal solution, lifting the grid frame from the ceramic membrane precursor colloidal solution, allowing the ceramic membrane precursor colloidal solution to be suspended between the gaps of the grid to form a liquid bridge, thereby obtaining a sample; S2 dries the sample, and when the liquid bridge is transformed into a gel state or an amorphous solid film, the sample is sintered to obtain a ceramic membrane; The drying temperature is less than the thermal decomposition temperature of the grid frame and less than the sintering temperature; The side length or diameter of each grid of the grid frame is less than or equal to 3.5 mm; The contact angle of the ceramic membrane precursor colloidal solution is 0-35°.

2. The method according to claim 1, characterized in that: The concentration of the ceramic membrane precursor colloidal solution is 3.0-5.0 mM.

3. The method according to claim 1, characterized in that: The shape of each grid of the grid frame includes one of square, circle, triangle and hexagon, and the side length or diameter of each grid of the grid frame is 0.5-3 mm.

4. The method according to claim 1, characterized in that: The drying temperature is less than 100°C.

5. The method according to claim 1, characterized in that: The thickness of the ceramic film is 1-100 μm.

6. The method according to claim 5, characterized in that: The hydrophilic resin includes at least one of polyurethane acrylate, cyclic trimethylolpropane formal acrylate, and 3,5-trimethylcyclohexyl acrylate.

7. The method according to claim 1, characterized in that: The ceramic film precursor colloidal solution includes PbZr 0.52 Ti 0.48 O3, BiFeO3 and Ba 0.85 Ca 0.15 Zr 0.2 Ti 0.3 At least one of O3.

8. The method according to claim 7, characterized in that: The ceramic membrane precursor colloidal solution is PbZr 0.52 Ti 0.48 When O3, the sintering temperature is less than or equal to 900℃.

9. A piezoelectric sensor, characterized in that: It comprises a ceramic membrane, and the ceramic membrane is prepared by the method for preparing a ceramic membrane according to any one of claims 1 to 8.

10. An ultrasonic transmitter, characterized in that: It comprises a ceramic membrane, and the ceramic membrane is prepared by the method for preparing a ceramic membrane according to any one of claims 1 to 8.

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