Diaphragm and preparation method thereof

Abstract

The present invention belongs to the field of ceramic diaphragm preparation technology and specifically discloses a diaphragm and its preparation method. By alternately stacking two ceramic membranes with different particle sizes and controlling the debinding and sintering processes, the present invention improves the diaphragm strength while minimizing the reduction in product conductivity.

Description

Technical Field

[0001] The invention belongs to the field of ceramic diaphragm preparation technology, and particularly relates to a diaphragm and a preparation method thereof. Background Art

[0002] The solid oxide fuel cell diaphragm is a very important component in solid oxide fuel cells, mainly playing the role of high-temperature ion conductivity. The existing diaphragm production process generally includes ceramic powder grinding, pulping, casting, punching and shearing, and high-temperature sintering. The particle size of existing ceramic powder is generally 150-500nm. A single-layer diaphragm is obtained by casting with a film thickness of 0.15-0.5mm. The sintering temperature is generally above 1300℃. The strength of the diaphragm affects the stability and life of the solid oxide fuel cell and is an important performance that needs to be considered for the diaphragm. The thicker the diaphragm, the greater the strength. However, increasing the thickness of the diaphragm will reduce the power generation efficiency and increase the cost, which is not conducive to the large-scale commercial development of solid oxide fuel cells. Therefore, it is particularly important to improve the strength of the diaphragm without increasing or reducing the thickness of the diaphragm.

[0003] The grain size of the diaphragm significantly affects its strength. Therefore, to better control the grain size and improve its strength, existing processes primarily use small-particle zirconium dioxide powder as the raw material. However, smaller zirconium dioxide powder particles increase the specific surface area, making degassing viscosity difficult to control and making cast film prone to cracking and other quality issues. Furthermore, smaller particle sizes lead to denser powder packing, resulting in lower conductivity after forming the ceramic. Summary of the Invention

[0004] In response to the above-mentioned problems of easy cracking of cast iron and low conductivity of products when reducing the particle size of ceramic powder in order to improve product strength, the present invention provides a diaphragm sheet and a preparation method thereof. The present invention achieves the goal of improving the strength of the diaphragm sheet while minimizing the reduction of product conductivity by alternately stacking two ceramic membranes with different particle sizes and controlling the debinding and sintering processes.

[0005] To achieve the above objectives, the following technical solutions are specifically included:

[0006] A method for preparing a diaphragm sheet comprises the following steps:

[0007] (1) mixing a first ceramic powder, a solvent, and a binder to obtain a first ceramic slurry; and mixing a second ceramic powder, a solvent, and a binder to obtain a second ceramic slurry; the first ceramic powder has an average particle size of 30-150 nm, the second ceramic powder has an average particle size of 150-500 nm, and the second ceramic powder has an average particle size larger than that of the first ceramic powder;

[0008] (2) tape-casting the first ceramic slurry and the second ceramic slurry respectively to obtain a first ceramic film and a second ceramic film;

[0009] (3) alternately stacking the first ceramic thin film and the second ceramic thin film to obtain a stacked body;

[0010] (4) punching and shearing the laminate to obtain a green body;

[0011] (5) The green body is subjected to debinding and sintering in sequence. The heating process of the debinding process is as follows: starting from 130-170°C, heating to 470-630°C at a heating rate of 0.3-0.7°C / min; the heating process of the sintering process is as follows: starting from 470-630°C, heating to 1100-1200°C at a heating rate of 3-5°C / min, then keeping warm for 2.5-4h, then heating to 1250-1420°C at a heating rate of 1-3°C / min, and then keeping warm for 3.8-6.1h.

[0012] The existing technology uses a mixing method of different particle sizes in the preparation of diaphragm sheets to improve the strength of the diaphragm sheets, but the mixing of large and small particle sizes easily leads to uneven particle size distribution, resulting in uneven particle size on the single-layer ceramic film, which is not conducive to the stability of the diaphragm sheet performance. In the scheme of the present invention, two ceramic films with different particle sizes are obtained by respectively casting two ceramic powders with different particle sizes. The two ceramic films with different particle sizes are alternately stacked, which can reduce the particle size to improve the strength of the diaphragm while the presence of relatively large particles can reduce the adverse effects on conductivity. Because two films with different particle sizes are stacked, inconsistent shrinkage between layers will cause cracking. Therefore, compared with conventional sintering processes, the sintering rates of membrane strips with large and small particle sizes at different sintering temperatures are analyzed and fitted to determine the temperature curve of the specific debinding and sintering process of the present invention. By slowly heating up the debinding stage, the product is fully debinded to prevent the diaphragm from becoming uneven due to too fast a discharge rate of organic matter. At the same time, by increasing the rapid heating of the middle section, the shrinkage rates of the two films with different particle sizes are almost the same, and sufficient shrinkage is completed. In the subsequent sintering process, the grains will only continue to grow without any large shrinkage, thereby avoiding cracking of the diaphragm.

[0013] Preferably, in step (1), the first ceramic powder includes zirconia-based ceramic powder; the second ceramic powder includes zirconia-based ceramic powder; the zirconia-based ceramic powder includes at least one of zirconia, zirconia composite ceramic powder, and modified zirconia.

[0014] Preferably, in step (1), the solvents are each selected from at least one of toluene, ethanol, isopropanol, n-butanol, and ethyl acetate.

[0015] Preferably, in step (1), the adhesives are each selected from at least one of polyvinyl butyral (PVB), dioctyl phthalate (DOP), dibutyl phthalate (DBO), butyl benzyl phthalate (BBP), and dioctyl adipate (DOA).

[0016] Preferably, in step (1), the mass ratio of the first ceramic powder, the solvent and the adhesive is first ceramic powder:solvent:adhesive=(80-120):(60-70):(7-15).

[0017] Preferably, in step (1), the mass ratio of the second ceramic powder, the solvent and the adhesive is second ceramic powder:solvent:adhesive=(80-120):(60-70):(7-15).

[0018] Preferably, the average particle size of the first ceramic powder is 80-140 nm, and the average particle size of the second ceramic powder is 150-300 nm.

[0019] Preferably, in step (1), the ratio of the average particle size of the second ceramic powder to the average particle size of the first ceramic powder is 1.2-6.

[0020] Further preferably, in step (1), the ratio of the average particle size of the second ceramic powder to the average particle size of the first ceramic powder is 1.25-5.

[0021] More preferably, in step (1), the ratio of the average particle size of the second ceramic powder to the average particle size of the first ceramic powder is 1.25-1.75.

[0022] Preferably, the first ceramic powder and the second ceramic powder are obtained by grinding; the grinding includes at least one of sand milling and ball milling.

[0023] The average particle size of the first ceramic powder and the second ceramic powder is measured using conventional methods in the art. Specifically, the average particle size of the powder particles can be measured by laser diffraction method, grid screening method, etc. Commonly used equipment include Malvern dry / wet laser particle size analyzer, nanoparticle size analyzer, etc.

[0024] When the particle size difference is too large, the shrinkage rate will be very different at the same sintering temperature, which will easily increase the risk of cracking. Therefore, the average particle size ratio of the two ceramic powders during stacking is preferably between 1.2-6, further preferably between 1.25-5, and further preferably between 1.5-3. This can balance the problems of easy cracking during sintering and electrical conductivity, so that the diaphragm can maintain good sintering and conductivity at the same time, and can further improve the flatness of the diaphragm, so that the overall performance of the diaphragm is better.

[0025] Preferably, in step (2), the thickness of the first ceramic film is 0.005-0.035 mm; the thickness of the second ceramic film is 0.005-0.035 mm.

[0026] Preferably, in step (2), the thickness of the first ceramic film is 0.01-0.03 mm; the thickness of the second ceramic film is 0.01-0.03 mm.

[0027] Preferably, the first ceramic film and the second ceramic film have the same thickness.

[0028] Diaphragms of the same specification have a fixed thickness. Thinner cast film requires more layers, reducing production efficiency and increasing the difficulty of lamination and subsequent processes. Excessively thick cast film can easily crack small particles and make casting difficult. Therefore, a cast film thickness within the range of 0.005-0.035mm can ensure production efficiency, increase the pass rate of cast film, and further improve the flatness of the diaphragm, resulting in better overall performance and enhanced product quality.

[0029] Preferably, in step (3), the total number of layers of the stack is 4-70.

[0030] Further preferably, in step (3), the total number of layers of the stack is 5-31 layers.

[0031] Further preferably, in step (3), the total number of layers of the stack is calculated based on the total number of layers of the first ceramic film and the second ceramic film. When the total number of layers of the stack is an odd number, the first ceramic film and the second ceramic film are symmetrically distributed above and below the middle layer in the stack, and the middle layer is the first ceramic film or the second ceramic film.

[0032] Maintaining symmetry in the lamination process can further avoid warping of the diaphragm due to different shrinkage rates of different particle sizes during sintering (the diaphragm will warp toward the side with greater shrinkage, while if the diaphragm is symmetrical along the middle, the shrinkage on both sides is the same and the warping is small).

[0033] Preferably, in step (3), the laminate is further pressed, the pressing pressure is 400-500 kg, the pressing temperature is 40-60° C., and the pressing is hydrostatic pressing.

[0034] Preferably, in step (5), the heating process of the debinding is: starting from 140-160°C, rising to 490-550°C at a heating rate of 0.4-0.6°C / min; the heating process of the sintering is: starting from 470-630°C, rising to 1120-1150°C at a heating rate of 3.5-4.5°C / min, then keeping warm for 3-3.5h, and then rising to 1300-1400°C at a heating rate of 1.5-2.5°C / min, and then keeping warm for 4-6h.

[0035] The temperature is slowly raised during the debinding stage to allow the product to fully debind and prevent the diaphragm from becoming uneven due to the rapid discharge of organic matter. The temperature is quickly raised to 1100-1200℃ during the sintering stage to make the shrinkage rates of large and small particles consistent, and the temperature is kept warm to allow the grains to fully shrink. Continuous heating and heat preservation are carried out to achieve complete growth of the grains, and then the temperature is naturally cooled to room temperature.

[0036] Preferably, in step (5), the heating rate of the green body from room temperature to the debinding temperature is 0.1-1°C / min.

[0037] Compared with the prior art, the present invention has the following beneficial effects: by alternately stacking two ceramic membranes with different particle sizes and controlling the debinding and sintering processes, the present invention can improve the strength of the diaphragm while minimizing the reduction in the conductivity of the product. In particular, the diaphragm produced by the present invention has a bending strength of up to 0.7-1.1 kgF and a conductivity of up to 180-220 mS / cm. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Schematic diagram of a single-layer diaphragm sheet produced by existing technology.

[0039] Figure 2 Schematic diagram of the diaphragm sheet designed according to the alternating stacking in Example 1.

[0040] Figure 3 This is a schematic diagram of a diaphragm sheet with the same laminate design as in Comparative Example 1. DETAILED DESCRIPTION

[0041] To better illustrate the objectives, technical solutions, and advantages of the present invention, the present invention will be further described below with reference to specific examples. The experimental methods used in the examples and / or comparative examples are conventional methods unless otherwise specified; the materials and reagents used are commercially available unless otherwise specified.

[0042] Examples 1-12 and Comparative Examples 1-11

[0043] S1. Powder grinding: Grind zirconium oxide (1 μm) by sand milling until powders of two particle size ranges are obtained, namely a first ceramic powder (small particle size) and a second ceramic powder (large particle size). The average particle size of the first ceramic powder is 100 nm, and the average particle size of the second ceramic powder is 200 nm. The average particle size of the second ceramic powder is: the average particle size of the first ceramic powder = 2;

[0044] S2. Prepare a tape casting slurry: Take the first ceramic powder and the second ceramic powder of two particle sizes obtained by grinding in S1, mix them with ethanol and PVB in a certain ratio, respectively, to obtain a first ceramic slurry and a second ceramic slurry, respectively; the mass ratio of the first ceramic powder: ethanol: PVB is 80:60:7; the mass ratio of the second ceramic powder: ethanol: PVB is 80:60:7;

[0045] S3, tape casting: the first ceramic slurry and the second ceramic slurry obtained in S2 are tape cast respectively to obtain a first ceramic film and a second ceramic film with a thickness of 0.03 mm;

[0046] S4, lamination: The first ceramic film and the second ceramic film obtained in S3 are alternately laminated, with a total of 5 layers, to obtain a laminate having a certain thickness, and the laminate is then hydrostatically pressed at a pressure of 450 kg and a temperature of 50° C.

[0047] S5, punching and shearing: punching the laminate obtained in S4 into a target size and shape using a die on a punch press to obtain a green body;

[0048] S6, high temperature sintering: The green body obtained in S5 is subjected to debinding and high temperature sintering in sequence, specifically:

[0049] The temperature is raised from room temperature to the debinding stage at a heating rate of 0.5°C / min. The debinding stage starts at about 150°C (temperature 1) and is raised to 500°C (temperature 2) at a rate of 0.5°C / min (heating rate 1). The temperature is raised slowly to allow the product to fully debind and prevent the diaphragm from becoming uneven due to the rapid discharge of organic matter. Complete debinding can be achieved before 500°C.

[0050] The sintering section starts from 500°C, and the heating rate between 500°C and 1150°C is set to 3°C / min (heating rate 2). It is quickly raised to 1150°C (temperature 3) and then kept warm for 3 hours (holding time 1). It is quickly raised to 1150°C to make the shrinkage rates of large and small particles consistent, and kept warm for 3 hours to allow the grains to fully shrink; then the temperature is raised from 1150°C to 1350°C (temperature 4) at a heating rate of 2°C / min (heating rate 3), and kept warm for 5 hours (holding time 2) to achieve complete growth of the grains, and then naturally cooled to room temperature to obtain the diaphragm sheet.

[0051] The difference between Examples 2-10 and Comparative Examples 1-6 and Example 1 lies in step S1 or step S2, as shown in Table 1 for the parameters. The remaining process steps and the corresponding raw materials are the same as those in Example 1.

[0052] The difference between Examples 11-12 and Comparative Examples 7-11 and Example 1 lies in step S6, as detailed in Table 2. The difference between Comparative Example 11 and Example 1 lies in that the sintering curve only includes a heating period followed by a heat preservation step, without a rapid heating period.

[0053] The debinding stage starts at around 150°C (temperature 1) and is heated at a rate of 0.5°C / min (heating rate 1) to 500°C (temperature 2). The temperature is slowly increased to allow the product to fully debind and prevent the diaphragm from becoming uneven due to the rapid discharge of organic matter. Complete debinding can be achieved before 500°C. The sintering stage starts at 500°C and is heated at a rate of 2°C / min (heating rate 2) from 500°C to 1350°C (temperature 3). The temperature is maintained for 5 hours (heating time 2), and then naturally cooled to room temperature.

[0054] The remaining process steps and corresponding raw materials are the same as those in Example 1.

[0055] Table 1

[0056]

[0057]

[0058] Table 2

[0059]

[0060] The performance test methods and requirements are shown in Table 3, and the test results are shown in Table 4:

[0061] Table 3

[0062]

[0063]

[0064] Table 4

[0065]

[0066]

[0067] As can be seen from the above embodiments, the diaphragm prepared by the present invention has a bending strength of up to 0.7-1.1 kgF, is a high-strength ceramic diaphragm, has a conductivity of up to 180-220 mS / cm, and a warpage of up to 400-800 μm.

[0068] Comparative Examples 1 and 2 use only a single small particle size and a single large particle size zirconium oxide powder, respectively. When a single particle size zirconium oxide powder is used, the flatness of the diaphragm is relatively good, and the flatness value is relatively low. However, when a small particle size zirconium oxide powder is used, the conductivity of the diaphragm is low, and the strength of the diaphragm made of large particle size zirconium oxide powder is low. At the same time, the addition of the zirconia powder to the diaphragm is not as good as that of the zirconia powder. Figure 2-3 It can be seen that maintaining upper and lower symmetry during the lamination process can further avoid warping of the diaphragm due to different shrinkage rates of different particle sizes during sintering, and further improve the flatness of the diaphragm.

[0069] The overall zirconia particle size of Comparative Examples 3 and 6 is relatively small, and the electrical conductivity of the diaphragm is relatively low; while the overall zirconia particle size of Comparative Examples 4-5 is relatively large, so the strength of the diaphragm is relatively low. Too large or too small a particle size of zirconia will result in the inability to take both strength and conductivity into account.

[0070] From the results of Comparative Examples 4 and 6, it can be seen that the average particle size ratio of large and small particle size zirconium oxide powders has an impact on the performance of the diaphragm. As the average particle size ratio of large and small particle size zirconium oxide powders increases, the flatness value of the diaphragm tends to increase.

[0071] In Comparative Example 7, the debinding rate was too fast, resulting in insufficient debinding, unstable atmosphere during the green body sintering process, and poor flatness of the sintered diaphragm sheet.

[0072] In Comparative Example 8, the sintering temperature ramp rate was too slow, resulting in delamination and cracking between the diaphragm layers due to inconsistent shrinkage of large and small particles. This cracking significantly reduced the diaphragm's strength and conductivity. The inconsistent shrinkage also led to dimensional differences between the diaphragm layers, resulting in poor flatness.

[0073] In Comparative Example 9, the sintering temperature was low and the holding time was short, so the grains did not grow completely, resulting in low strength and low conductivity of the diaphragm.

[0074] In comparative example 10, the sintering temperature is too high and the holding time is too long, resulting in excessive grain growth and excessive grain size, which causes the diaphragm strength to be lower than the required value.

[0075] In the sintering process of Comparative Example 11, there is no intermediate rapid temperature rise stage, which results in inconsistent shrinkage rates of large and small particles and cracking. The strength and conductivity of the diaphragm are both low, and the flatness of the diaphragm is poor.

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a diaphragm sheet, characterized in that: The steps include: (1) mixing a first ceramic powder, a solvent, and a binder to obtain a first ceramic slurry; and mixing a second ceramic powder, a solvent, and a binder to obtain a second ceramic slurry; the first ceramic powder has an average particle size of 30-150 nm, the second ceramic powder has an average particle size of 150-500 nm, and the second ceramic powder has an average particle size larger than that of the first ceramic powder; (2) tape-casting the first ceramic slurry and the second ceramic slurry respectively to obtain a first ceramic film and a second ceramic film; (3) alternately stacking the first ceramic thin film and the second ceramic thin film to obtain a stacked body; (4) punching and shearing the laminate to obtain a green body; (5) The green body is subjected to debinding and sintering in sequence. The heating process of the debinding process is as follows: starting from 130-170°C, heating to 470-630°C at a heating rate of 0.3-0.7°C / min; the heating process of the sintering process is as follows: starting from 470-630°C, heating to 1100-1200°C at a heating rate of 3-5°C / min, then keeping warm for 2.5-4h, then heating to 1250-1420°C at a heating rate of 1-3°C / min, and then keeping warm for 3.8-6.1h.

2. The method for preparing a diaphragm sheet according to claim 1, wherein: In step (1), the ratio of the average particle size of the second ceramic powder to the average particle size of the first ceramic powder is 1.2-6.

3. The method for preparing a diaphragm sheet according to claim 2, wherein: In step (1), the ratio of the average particle size of the second ceramic powder to the average particle size of the first ceramic powder is 1.25-5.

4. The method for preparing a diaphragm sheet according to claim 1, wherein: In step (2), the thickness of the first ceramic film is 0.005-0.035 mm; the thickness of the second ceramic film is 0.005-0.035 mm.

5. The method for preparing a diaphragm sheet according to claim 4, wherein: In step (2), the thickness of the first ceramic film is 0.01-0.03 mm; the thickness of the second ceramic film is 0.01-0.03 mm.

6. The method for preparing a diaphragm sheet according to claim 1, wherein: In step (3), the total number of layers of the stack is 4-70.

7. The method for preparing a diaphragm sheet according to claim 6, wherein: In step (3), the total number of layers of the stack is an odd number, and in the stack, the first ceramic film and the second ceramic film are symmetrically distributed with an intermediate layer, and the intermediate layer is the first ceramic film or the second ceramic film.

8. The method for preparing a diaphragm sheet according to claim 1, wherein: In step (5), the heating process of the debinding is as follows: starting from 140-160°C, rising to 490-550°C at a heating rate of 0.4-0.6°C / min; the heating process of the sintering is as follows: starting from 470-630°C, rising to 1120-1150°C at a heating rate of 3.5-4.5°C / min, then keeping warm for 3-3.5h, and then rising to 1300-1400°C at a heating rate of 1.5-2.5°C / min, and then keeping warm for 4-6h.

9. The method for preparing a diaphragm sheet according to claim 1, wherein: Include at least one of the following: In step (1), the first ceramic powder includes zirconia-based ceramic powder; the second ceramic powder includes zirconia-based ceramic powder; the zirconia-based ceramic powder includes at least one of zirconia, zirconia composite ceramic powder, and modified zirconia; In step (1), the solvents are each selected from at least one of toluene, ethanol, isopropanol, n-butanol, and ethyl acetate; In step (1), each of the adhesives is selected from at least one of polyvinyl butyral, dioctyl phthalate, dibutyl phthalate, butyl benzyl phthalate, and dioctyl adipate; In step (1), the mass ratio of the first ceramic powder, the solvent and the binder is first ceramic powder: solvent: binder = (80-120): (60-70): (7-15); In step (1), the mass ratio of the second ceramic powder, the solvent and the binder is second ceramic powder: solvent: binder = (80-120): (60-70): (7-15); In step (3), the laminate is further pressed at a pressure of 400-500 kg and a temperature of 40-60°C.

10. A diaphragm sheet produced by the method for producing a diaphragm sheet according to any one of claims 1 to 9.

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