Method for preparing lanthanum zirconate hollow tube based on carbon template

Abstract

The invention relates to a method for preparing a lanthanum zirconate hollow pipe, in particular to a method for preparing a lanthanum zirconate hollow pipe based on a carbon template. The invention aims to solve the technical problem that no preparation method for the lanthanum zirconate hollow tube exists at present. According to the preparation method, the lanthanum zirconate hollow tube is prepared by using the carbon fiber as the template at low cost and adopting a sol impregnation method, so that the morphology of the lanthanum zirconate hollow tube is controllable. The carbon fibers have inherent hydroxyl groups through surface treatment in the production process, and adsorption of the lanthanum zirconate precursor is facilitated. In order to enable the lanthanum zirconate hollow pipe to have certain strength, the lanthanum zirconate hollow pipe needs to be densified. The carbon fiber is used as a carrier in the process so that collapse of the lanthanum zirconate hollow structure can be avoided, and the prepared lanthanum zirconate hollow pipe has high temperature resistance, light weight and easy formability and has important significance for expanding light-weight research of lanthanum zirconate.

Description

Technical Field

[0001] This invention relates to a method for preparing lanthanum zirconate hollow tubes. Background Technology

[0002] Lanthanum zirconate is a rare-earth zirconate with a pyrochlore structure and an extremely high melting point (2300℃). It exhibits high-temperature stability over a wide temperature range because it undergoes no phase transition from room temperature to its melting point. Furthermore, lanthanum zirconate has a room-temperature thermal conductivity of only 1.56 W / m². m -1 K -1 It has even lower thermal conductivity at high temperatures, only 1.15 W / m² at 1450℃. m -1 K -1 This is a remarkably low value for dense crystalline materials. Due to its excellent high-temperature performance, lanthanum zirconate has found important applications in many areas, including thermal barrier coatings. However, lanthanum zirconate has a relatively high density (6.05 g / cm³). 3 Lanthanum zirconium (LZZ) is approximately three times the size of quartz and twice the size of mullite, making it unsuitable as a substrate for thermal insulation materials, hindering their lightweighting. To address this issue, hollowing can be employed. Research on lightweighting lanthanum zirconium three-dimensional materials primarily focuses on the preparation of porous lanthanum zirconium ceramics, mainly utilizing the volatilization of organic matter and foaming to create pore structures; the combination of these two methods can also produce hierarchical pore structures. Pore size adjustment mainly depends on altering the lanthanum zirconium solid content. The main application of lanthanum zirconium two-dimensional materials is as a thermal barrier coating on metal-based engine blades. Due to the limited coating thickness and the need for densification of lanthanum zirconium to reduce oxygen diffusion rates and protect the substrate, there is currently no demand for lightweighting research on lanthanum zirconium two-dimensional materials. Lanthanum zirconium hollow spheres, as the main research target for lightweighting lanthanum zirconium zero-dimensional materials, possess excellent microstructure, but currently, research is mostly limited to hollow sphere powder preparation; the forming of bulk thermal insulation materials is a significant factor limiting their application. Lanthanum zirconium one-dimensional materials are currently mainly lanthanum zirconium fibers, mostly prepared via electrospinning, and have not yet been industrialized. Compared to zero-dimensional powders, one-dimensional materials have advantages in the assembly of thermal insulation materials. However, there is currently no research on lanthanum zirconate hollow fibers or hollow tubes. Summary of the Invention

[0003] The present invention aims to solve the technical problem that there is currently no method for preparing lanthanum zirconate hollow tubes, and provides a method for preparing lanthanum zirconate hollow tubes based on carbon templates.

[0004] The method for preparing lanthanum zirconate hollow tubes based on carbon templates of the present invention is carried out according to the following steps:

[0005] I. Preparation of Lanthanum Zirconate Solution: Lanthanum source and zirconium source are dispersed in a mixed solution of water and anhydrous ethanol to obtain lanthanum zirconate solution;

[0006] 2. Impregnation: The short-cut carbon fibers are immersed in the lanthanum zirconate solution prepared in step 1 and impregnated in a water bath at 40℃~80℃. During this process, heating causes the hydrolysis equilibrium to shift to the right, and the lanthanum zirconate solution is converted into lanthanum zirconate sol. After the water bath, the solution is allowed to stand at room temperature to allow the sol particles to fully combine with the carbon fibers. The carbon fibers are then filtered out using fine gauze and dried in a drying oven to obtain the lanthanum zirconate precursor.

[0007] 3. Sintering: Under a protective atmosphere, the lanthanum zirconate precursor prepared in step 2 is heated to 800℃~1200℃ and held for 2h~5h, then cooled to room temperature; to densify the lanthanum zirconate, it is heat-treated again at high temperature under a protective atmosphere at 1000℃~1500℃ and held for 3h~5h, then cooled to room temperature; finally, under an air atmosphere, it is heated to 400℃~900℃ and held for 1h~4h to remove the carbon fibers, forming a hollow lanthanum zirconate tube.

[0008] This invention is the first to prepare lanthanum zirconate hollow tubes. First, lanthanum zirconate has an extremely high melting point, exhibits no phase change from room temperature to its melting point, and possesses ultra-low thermal conductivity. The advantages of its composition determine that the lanthanum zirconate hollow tubes have good high-temperature stability and thermal insulation capabilities.

[0009] Secondly, hollow lanthanum zirconate tubes facilitate the expansion of lightweight applications for lanthanum zirconate. Hollow structures exhibit superior mechanical properties compared to solid structures of the same mass. Compared to zero-dimensional hollow spheres, one-dimensional hollow tubes are easier to stack to form bulk porous insulation materials. When using hollow lanthanum zirconate tubes to assemble insulation materials, the hollow structure not only avoids the disadvantage of lanthanum zirconate's high density but also provides more pores, making the solid-phase heat conduction pathway more complex and thus helping to reduce the material's thermal conductivity.

[0010] Third, the process of this invention is simple. Without the aid of large equipment such as spinning machines, carbon fibers are used as templates to deposit lanthanum zirconate into a one-dimensional morphology. During the heat treatment process, the carbon fibers play a supporting role, preventing lanthanum zirconate from collapsing and abnormally shrinking during high-temperature densification.

[0011] Fourth, the template method facilitates control over the morphology of lanthanum zirconate hollow tubes. If high-temperature densification is considered a homogeneous shrinkage process, the inner diameter of the lanthanum zirconate hollow tube is entirely determined by the carbon fiber diameter, while the tube thickness is determined by the impregnation process parameters. Therefore, by adjusting the carbon fiber diameter and impregnation process parameters, lanthanum zirconate hollow tubes with different morphologies can be obtained.

[0012] In summary, this invention utilizes carbon fiber as a template and employs a sol-gel impregnation method to prepare lanthanum zirconate hollow tubes at a low cost, achieving controllable morphology. Surface treatment of the carbon fiber during production imparts inherent hydroxyl groups, facilitating the adsorption of the lanthanum zirconate precursor. To ensure sufficient strength, the lanthanum zirconate hollow tubes require densification. The carbon fiber acts as a carrier in this process, preventing the collapse of the lanthanum zirconate hollow structure. The prepared lanthanum zirconate hollow tubes possess high-temperature resistance, lightweight properties, and ease of molding, making them significant for expanding research on lightweight lanthanum zirconate. Attached Figure Description

[0013] Figure 1 SEM image of the short-cut carbon fiber in step two of Experiment 1;

[0014] Figure 2 The carbon element distribution diagram in EDS of the short-cut carbon fibers in step two of Experiment 1;

[0015] Figure 3 The distribution of oxygen in the EDS of the short-cut carbon fibers in step two of Experiment 1;

[0016] Figure 4 SEM image of the lanthanum zirconate hollow tube prepared for Experiment 1;

[0017] Figure 5 The cross-sectional microstructure of the lanthanum zirconate hollow tube prepared for Experiment 1 is shown.

[0018] Figure 6 Photograph of the thermal insulation material prepared for Experiment 2. Detailed Implementation

[0019] Specific Implementation Method 1: This implementation method is a method for preparing lanthanum zirconate hollow tubes based on carbon templates, specifically carried out according to the following steps:

[0020] I. Preparation of Lanthanum Zirconate Solution: Lanthanum source and zirconium source are dispersed in a mixed solution of water and anhydrous ethanol to obtain lanthanum zirconate solution;

[0021] 2. Impregnation: The short-cut carbon fibers are immersed in the lanthanum zirconate solution prepared in step 1 and impregnated in a water bath at 40℃~80℃; after standing at room temperature, the carbon fibers are filtered out using fine gauze and then dried in a drying oven to obtain the lanthanum zirconium oxide precursor.

[0022] 3. Sintering: Under a protective atmosphere, the lanthanum zirconate precursor prepared in step 2 is heated to 800℃~1200℃ and held for 2h~5h, then cooled to room temperature; to densify the lanthanum zirconate, it is heat-treated again at high temperature under a protective atmosphere at 1000℃~1500℃ and held for 3h~5h, then cooled to room temperature; finally, under an air atmosphere, it is heated to 400℃~900℃ and held for 1h~4h to remove the carbon fibers, forming a hollow lanthanum zirconate tube.

[0023] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the lanthanum source mentioned in step one is La(NO3)3. 6H2O, La2O3 or LaCl3 6H2O. Everything else is the same as in Specific Implementation Method 1.

[0024] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the zirconium source mentioned in step one is ZrO2 or Zr(NO3)4. 5H2O or ZrOCl2 8H2O. Everything else is the same as in specific implementation method one or two.

[0025] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the molar ratio of water to anhydrous ethanol in step one is 1:(1~10). Everything else is the same as in Specific Implementation Methods One to Three.

[0026] Specific Implementation Method Five: This implementation method differs from Specific Implementation Method Four in that the concentrations of lanthanum and zirconium in the lanthanum zirconate solution described in step one are both 0.01 mol / L to 0.2 mol / L. Everything else is the same as in Specific Implementation Method Four.

[0027] Specific Implementation Method Six: This implementation method differs from Specific Implementation Method Five in that the preparation method of the short-cut carbon fiber in step two is as follows: Take carbon fiber, cut it initially with scissors to control the length to be less than 1 cm; then add deionized water, wherein the mass ratio of carbon fiber to deionized water is 1:(50~100), and then put it into a soymilk maker to cut it 1 to 3 times; after cutting, filter out the carbon fiber with fine gauze, and then put it into a drying oven at 40℃~60℃ for 24h~48h to obtain short-cut carbon fiber. Everything else is the same as in Specific Implementation Method Five.

[0028] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Method Six in that: in step two, the chopped carbon fibers are immersed in the lanthanum zirconate solution prepared in step one for 10 to 30 minutes, and then immersed in a water bath at 40°C to 80°C; and then left to stand at room temperature for 12 to 48 hours. Everything else is the same as in Specific Implementation Method Six.

[0029] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Method Seven in that: in step two, the precursor is dried in a drying oven at 50℃~80℃ for 24h~48h to obtain the zirconium oxy lanthanum precursor. Everything else is the same as in Specific Implementation Method Seven.

[0030] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Method Eight in that the protective atmosphere described in step three is argon. Everything else is the same as in Specific Implementation Method Eight.

[0031] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Method Nine in that, in step three, the zirconium oxide lanthanum precursor prepared in step two is heated from room temperature to 800℃~1200℃ at a heating rate of 5℃ / min under a protective atmosphere and held at that temperature for 2h~5h. Everything else is the same as in Specific Implementation Method Nine.

[0032] The invention was verified using the following experiments:

[0033] Experiment 1: This experiment demonstrates a method for preparing lanthanum zirconate hollow tubes based on carbon templates, specifically carried out according to the following steps:

[0034] I. Preparation of Lanthanum Zirconate Solution: A lanthanum source and a zirconium source are dispersed in a mixed solution of water and anhydrous ethanol to obtain a lanthanum zirconate solution; the lanthanum source is La(NO3)3. 6H2O; the zirconium source is ZrOCl2 8H2O; the molar ratio of water to anhydrous ethanol is 1:5; the concentrations of lanthanum and zirconium in the lanthanum zirconate solution are both 0.05 mol / L;

[0035] 2. Impregnation: The short-cut carbon fibers are immersed in the lanthanum zirconate solution prepared in step 1 and impregnated in a water bath at 60°C for 20 min; after standing at room temperature for 24 h, the carbon fibers are filtered out using fine gauze and then dried in a drying oven at 80°C for 24 h to obtain the lanthanum zirconium oxide precursor.

[0036] The method for preparing the chopped carbon fiber is as follows: Take carbon fiber and cut it into short sections with scissors to control the length to be less than 1 cm; then add deionized water, wherein the mass ratio of carbon fiber to deionized water is 1:80, and then put it into a soymilk maker to cut it into short sections 1 to 3 times; after the short sectioning is completed, filter out the carbon fiber with fine gauze, and then put it into a drying oven at 40℃ to 60℃ to dry for 24h to 48h to obtain chopped carbon fiber;

[0037] 3. Sintering: Under a nitrogen atmosphere, the zirconium oxide lanthanum precursor prepared in step 2 is heated from room temperature to 1000℃ at a heating rate of 5℃ / min and held for 5h, then cooled to room temperature; to densify the lanthanum zirconate, it is heat-treated again at high temperature under an argon atmosphere at 1200℃ and held for 3h, then cooled to room temperature; finally, under an air atmosphere, it is heated to 600℃ and held for 2h to remove the carbon fibers, forming a hollow lanthanum zirconate tube.

[0038] Figure 1 The image shows a SEM image of the short-cut carbon fiber from step two of Experiment 1. The carbon fiber diameter is approximately 10 μm, and the short-cut fiber maintains a straight morphology.

[0039] Figure 2 This is an EDS (Electrode Spectroscopy) diagram of the carbon element distribution in the short-cut carbon fibers from step two of Experiment 1. Figure 3 The image shows the oxygen distribution in the EDS of the short-cut carbon fibers from step two of Experiment 1. The EDS results show that the carbon content of the carbon fibers is 93.29 wt.%, and the oxygen content is 3.64 wt.%, with both elements evenly distributed. The presence of oxygen indicates that the carbon fiber surface has certain hydroxyl groups, which can adsorb lanthanum zirconate particles.

[0040] Figure 4 The SEM image of the lanthanum zirconate hollow tube prepared for Experiment 1 shows that the lanthanum zirconate hollow tube has a good tubular morphology, and the tube wall is composed of several lanthanum zirconate grains. After sintering heat treatment, the lanthanum zirconate precursor is dehydrated to form lanthanum zirconate, which is then densified at high temperature to form grains.

[0041] Figure 5 The image shows the cross-sectional microstructure of the lanthanum zirconate hollow tube prepared for Experiment 1. It can be seen that the lanthanum zirconate tube wall is approximately 1 μm thick, and the inner wall is smooth and crack-free. The relatively thick wall and good compactness give the lanthanum zirconate hollow tube a certain mechanical strength, thus meeting the conditions for assembling it into a sample.

[0042] Experiment 2: Preparation of thermal insulation materials, the specific process is as follows:

[0043] 1. Preparation of slurry: Disperse the lanthanum zirconate hollow tubes prepared in Experiment 1 into a mixture of deionized water and silica sol, and stir with a mixer at 1000 r / min for 15 min to ensure thorough mixing and uniformity to form a slurry. The amount of lanthanum zirconate hollow tubes and silica sol added is 3% and 10% of the mass of deionized water, respectively.

[0044] The preparation steps of the silica sol are as follows: First, pour tetraethyl orthosilicate into a beaker, then add anhydrous ethanol, then add water to form a mixture, and finally add a few drops of dilute hydrochloric acid and stir evenly. Then, place the beaker in a 60°C water bath for 30 minutes to obtain the silica sol; the molar ratio of TEOS: H2O: anhydrous ethanol: HCl is 1:4:4:7.5×10⁻⁶. -4 The concentration of dilute hydrochloric acid is 0.2 mol / L;

[0045] II. Preparation of Green Body by Pressure Drainage: Pour the slurry prepared in step one into a mold and let it stand for 10 minutes until the lanthanum zirconate hollow tube settles naturally. Place a pressure plate wrapped with fine gauze (300 mesh) on the top of the mold. The pressure plate has multiple through holes for drainage. Apply pressure to a certain depth and continue to hold the pressure for 30 seconds to obtain the green body. Excess water in the slurry is discharged through the through holes on the pressure plate. Then, place the mold in a refrigerator (around -20℃) and freeze for 24 hours to ensure the slurry is completely frozen. Then, place the mold in a freeze dryer (temperature: around -50℃; vacuum degree: 50~100Pa) and freeze dry for 72 hours. Finally, place the dried green body in a muffle furnace and heat treat at 1100℃ for 4 hours to obtain the insulation material, with a size of 2cm×2cm×1cm (e.g., Figure 6 As shown), it has a regular and uniform shape and a density of 0.1 g / cm³. 3 During the pressurized drainage process, the lanthanum zirconate hollow tubes overlap to form a network structure. Zero-dimensional materials often require pressurized sintering to form, and the small pores between the microspheres result in a high density of the formed sample. However, the easy overlap of lanthanum zirconate hollow tubes (a one-dimensional material) determines their ease of forming, and the network structure formed by the overlap allows the formed sample to have a lower density.

Claims

1. A method for preparing lanthanum zirconate hollow tubes based on carbon templates, characterized in that... The method is performed according to the following steps: I. Preparation of Lanthanum Zirconate Solution: Lanthanum source and zirconium source are dispersed in a mixed solution of water and anhydrous ethanol to obtain lanthanum zirconate solution; 2. Impregnation: The short-cut carbon fibers are immersed in the lanthanum zirconate solution prepared in step 1 and impregnated in a water bath at 40℃~80℃; after standing at room temperature, the carbon fibers are filtered out using fine gauze and then dried in a drying oven to obtain the lanthanum zirconium oxide precursor.

3. Sintering: Under a protective atmosphere, the lanthanum zirconate precursor prepared in step 2 is heated to 800℃~1200℃ and held for 2h~5h, then cooled to room temperature; to densify the lanthanum zirconate, it is heat-treated again at high temperature under a protective atmosphere at 1000℃~1500℃ and held for 3h~5h, then cooled to room temperature; finally, under an air atmosphere, it is heated to 400℃~900℃ and held for 1h~4h to remove the carbon fibers, forming a hollow lanthanum zirconate tube.

2. The method for preparing lanthanum zirconate hollow tubes based on carbon templates according to claim 1, characterized in that... The lanthanum source mentioned in step one is La(NO3)3. 6H2O, La2O3 or LaCl3 6H2O.

3. The method for preparing lanthanum zirconate hollow tubes based on carbon templates according to claim 1, characterized in that... The zirconium source mentioned in step one is ZrO2 or Zr(NO3)4. 5H2O or ZrOCl2 8H2O.

4. The method for preparing lanthanum zirconate hollow tubes based on carbon templates according to claim 1, characterized in that... The molar ratio of water to anhydrous ethanol mentioned in step one is 1:(1~10).

5. The method for preparing lanthanum zirconate hollow tubes based on carbon templates according to claim 1, characterized in that... In step one, the concentrations of lanthanum and zirconium in the lanthanum zirconate solution are both 0.01 mol / L to 0.2 mol / L.

6. The method for preparing lanthanum zirconate hollow tubes based on carbon templates according to claim 1, characterized in that... The preparation method of the short-cut carbon fiber described in step two is as follows: Take carbon fiber and cut it into short pieces with scissors to control the length to be less than 1 cm; then add deionized water, wherein the mass ratio of carbon fiber to deionized water is 1:(50~100), and then put it into a soymilk maker to cut it into short pieces 1 to 3 times; after the short cutting is completed, filter out the carbon fiber with fine gauze, and then put it into a drying oven at 40℃~60℃ for 24h~48h to dry it to obtain short-cut carbon fiber.

7. The method for preparing lanthanum zirconate hollow tubes based on carbon templates according to claim 1, characterized in that... In step two, the short-cut carbon fibers are immersed in the lanthanum zirconate solution prepared in step one for 10 to 30 minutes, and then immersed in a water bath at 40 to 80 degrees Celsius; and left to stand at room temperature for 12 to 48 hours.

8. The method for preparing lanthanum zirconate hollow tubes based on carbon templates according to claim 1, characterized in that... In step two, the sample is dried in a drying oven at 50℃~80℃ for 24h~48h to obtain the zirconium oxy lanthanum precursor.

9. The method for preparing lanthanum zirconate hollow tubes based on carbon templates according to claim 1, characterized in that... The protective atmosphere described in step three is argon.

10. A method for preparing lanthanum zirconate hollow tubes based on a carbon template according to claim 9, characterized in that... In step three, the zirconium oxide lanthanum precursor prepared in step two is heated from room temperature to 800℃~1200℃ at a heating rate of 5℃ / min under a protective atmosphere and held at that temperature for 2h~5h.

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