YSZ (Yttria Stabilized Zirconium)-based thermal barrier coating material based on zirconium residual liquid in nuclear-grade zirconium sponge production process and preparation method of YSZ-based thermal barrier coating material

Abstract

The invention relates to the technical field of coating materials, and discloses a YSZ-based thermal barrier coating material based on zirconium residual liquid in a nuclear-grade sponge zirconium production process and a preparation method of the YSZ-based thermal barrier coating material, the coating material comprises the following chemical components in percentage by mole: 92-95% of Zr (1-2x) Co (2x) O2 (0 < = x < = 0.05), 1.0-8.0% of Y2O3, 0-4.0% of CeO2, 0-4.8% of La2O3 and 0-5.6% of Sc2O3. The preparation method comprises the following steps: firstly, by taking a zirconium residual solution obtained after zirconium and hafnium separation in a nuclear-grade sponge zirconium preparation process as a Zr source solution, performing low-cost acidizing treatment, then realizing molecular-grade mixing with Y ions and other added ions, synthesizing a precursor in one step by adopting a coprecipitation method, and then roasting to obtain the thermal barrier coating material. According to the technical scheme, the thermal barrier coating material with excellent performance is prepared from the zirconium residual liquid in the zirconium-hafnium process, the cost is saved to the maximum extent, industrial production is easy to achieve, and the thermal barrier coating material has great application value in the field of coatings.

Description

Technical Field

[0001] This invention relates to the field of coating materials technology, specifically to a YSZ-based thermal barrier coating material based on zirconium residue from nuclear-grade sponge zirconium production process and its preparation method. Background Technology

[0002] Nuclear-grade zirconium and hafnium are irreplaceable core materials for constructing nuclear reactors. In 2013, State Nuclear Power Technology Corporation (SNPTC) ZrHfnium Co., Ltd. achieved the first domestic production of nuclear-grade sponge zirconium, filling the gap in my country's nuclear-grade sponge zirconium production. Zirconium and hafnium are naturally occurring elements; for example, zircon (ZrSiO4) and zircon (ZrO2) typically contain 0.5% zirconium. With 2% Hf, the Zr / Hf ratio is approximately 98:2. As my country's nuclear-grade sponge zirconium production technology matures, its output has increased significantly. While meeting the needs of the nuclear industry, developing applications of zirconium oxide in other fields is of strategic importance. However, nuclear-grade sponge zirconium is a monoclinic phase, making it difficult to meet the application requirements of other fields.

[0003] Y₂O₃-stabilized ZrO₂ (YSZ) has a high coefficient of thermal expansion, low thermal conductivity, and good thermal shock resistance, making it a standard thermal barrier coating material often used in high-performance aero-engine thermal barrier coatings. However, YSZ ceramic materials undergo a phase transition at 1200℃, leading to coating peeling and failure, and the long-term service temperature cannot exceed 1200℃.

[0004] Currently, the synthesis technologies for large-scale production of nano-YSZ both domestically and internationally mainly rely on liquid-phase synthesis techniques such as co-precipitation and hydrothermal methods. However, zirconium ions are easily hydrolyzed in water, and it is difficult to achieve atomic-level homogeneous mixing with other ions such as yttrium ions in aqueous solutions. This makes it difficult to obtain excellent tetragonal stable phases and high-temperature stability (>1200℃) in liquid-phase preparation processes. Currently, the conventional method to prevent the hydrolysis of zirconium solutions is to add complexing agents or surfactants, but this method is costly and involves cumbersome subsequent processing. Summary of the Invention

[0005] The present invention aims to provide a YSZ-based thermal barrier coating material based on zirconium residue in the nuclear-grade sponge zirconium production process and its preparation method, with the goal of providing a low-cost, easily industrialized YSZ-based thermal barrier coating material with excellent tetragonal phase stability and high-temperature stability.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a YSZ-based thermal barrier coating material based on zirconium residue from the nuclear-grade sponge zirconium production process, the chemical composition of which, in molar percentage, comprises the following components: 92-95% Zr 1- 2x Co 2xO2, where 0≤x≤0.05, 1.0~8.0% Y2O3, 0~4.0% CeO2, 0~4.8% La2O3, and 0~5.6% Sc2O3.

[0007] Preferably, as an improvement, the material has a single tetragonal phase structure, and the powder D50 of the material is 10.53 to 16.88 μm.

[0008] Preferably, as an improvement, a method for preparing a YSZ-based thermal barrier coating material based on zirconium residue from a nuclear-grade sponge zirconium production process includes the following steps: Step 1: Preparation of Zr source solution: The zirconium residue after zirconium-hafnium separation in the process of preparing nuclear-grade sponge zirconium is used as the Zr source solution; Step 2: Preparation of mixed solution: Dissolve Co(NO3)2·6H2O and Y(NO3)3·6H2O in deionized water to form nitrate solutions; dissolve La / Ce / Sc nitrates in deionized water to form nitrate solutions; add each nitrate solution to the Zr source solution according to the stoichiometric ratio, stir and mix, and make up to volume to form a mixed solution; Step 3, Coprecipitation and Precursor Preparation: The mixed solution and ammonia solution are mixed and stirred to form a precipitate. The precipitate is filtered, washed with anhydrous ethanol, dried, mixed with n-pentanol and distilled under reduced pressure to obtain the powder precursor. Step 4, Drying and Calcination: After drying and grinding the precursor powder, it is calcined and cooled to obtain YSZ-based nanopowder.

[0009] Preferably, as an improvement, in step one, the concentration of the Zr source solution is 2.0 mol / L. Before preparing the Zr source solution, the cation concentration of the zirconium residue after zirconium and hafnium separation is determined by discharge plasma atomic emission spectroscopy.

[0010] Preferably, as an improvement, in step two, the total concentration of the mixed solution is 0.5 mol / L-1.0 mol / L.

[0011] Preferably, as an improvement, in step three, the stirring speed of the precipitation reaction is 400 rpm to 1000 rpm.

[0012] Preferably, as an improvement, in step three, the concentration ratio of the ammonia solution to the mixed solution is 3.3:1.

[0013] Preferably, as an improvement, in step four, the drying conditions are vacuum drying at 60°C for 12 hours.

[0014] Preferably, as an improvement, in step four, the calcination conditions are 700℃ for 2 hours.

[0015] The principle and advantages of this solution are as follows: In practical applications, this technical solution addresses the problems existing in the prior art by utilizing the zirconium residue from the production of nuclear-grade sponge zirconium as raw material. This residue is rich in Zr ions, making it a low-cost Zr source. First, the hydrolysis of Zr ions is inhibited through the synergistic effect of a weak acid environment and anhydrous ethanol. Then, Y ions (stabilizer), Co ions, and dopant ions such as Ce, La, and Sc are uniformly mixed with Zr ions. A precursor containing all target ions is synthesized in one step using a co-precipitation method. Finally, the precursor is dried and calcined to form a YSZ-based thermal barrier coating material. In this technical solution, the zirconium residue from the production of nuclear-grade sponge zirconium is used as raw material. The residue undergoes low-cost acidification treatment, utilizing a weak acid environment and a homogeneous system formed by anhydrous ethanol and water to reduce the activity of water and inhibit zirconium ion hydrolysis; this solves the problem of zirconium solution hydrolysis and achieves uniform mixing of cations. By adding Y stabilizers and dopants to zirconium residue, a tetragonal phase-stabilized YSZ series thermal barrier coating material with a long-term operating temperature above 1200℃ is obtained in one step through a co-precipitation process, thus solving the problems of YSZ phase purity and high-temperature phase stability. Furthermore, divalent transition metal ions Co are introduced into the ZrO2 lattice. 2+ and Zn 2+ On the one hand, the difference in ionic radius causes lattice distortion during ionic solid solution, enhancing the scattering of phonons by lattice vibrations and thus reducing the thermal diffusivity of YSZ. On the other hand, ZnO can enhance the coating's ability to block radiative heat transfer, improving its thermal insulation performance. The addition of Y2O3 can stabilize the tetragonal phase structure of ZrO2, and Co... 2+ The introduction of divalent ions will induce lattice distortion, enhance phonon scattering, and reduce the thermal diffusivity; dopants such as CeO2, La2O3, and Sc2O3 will further optimize the high-temperature stability and thermal insulation performance of the material, ultimately achieving the core goal of long-term use temperature exceeding 1200℃.

[0016] In summary, the beneficial effects of this technical solution are as follows: 1. This technical solution can make full use of the zirconium residue in the nuclear-grade sponge zirconium process, thereby saving costs to the greatest extent, obtaining high-performance thermal barrier coating materials, and is easy to industrialize.

[0017] 2. This technical solution does not require the addition of expensive complexing agents or surfactants. The hydrolysis of Zr ions can be suppressed by a weak acid + anhydrous ethanol system, which simplifies the process and achieves uniform ion mixing. The prepared material breaks through the temperature limit of conventional YSZ and can be used at temperatures exceeding 1200℃ for a long time, solving the problem of coating peeling caused by high temperature phase transition.

[0018] 3. This technical solution induces lattice distortion through Co ion doping, and combined with the synergistic effect of other dopants, the material has lower thermal conductivity and better thermal insulation performance; the final product is nano-sized powder with uniform particles and good coating formability.

[0019] 4. The overall process of this technical solution uses mature liquid phase synthesis technologies such as coprecipitation, which are simple in steps, easy to control parameters, and do not require special high-end equipment, thus meeting the needs of large-scale production. Attached Figure Description

[0020] Figure 1 The images are XRD patterns of Examples 1-4.

[0021] Figure 2 The images are XRD patterns of Examples 5-10.

[0022] Figure 3 This is a laser particle size distribution diagram from Example 3.

[0023] Figure 4 This is a laser particle size distribution diagram from Example 5.

[0024] Figure 5 This is a laser particle size distribution diagram from Example 7.

[0025] Figure 6 This is a laser particle size distribution diagram from Example 9.

[0026] Figure 7 This is the SEM image of Example 3.

[0027] Figure 8 This is the SEM image of Example 5.

[0028] Figure 9 This is the SEM image of Example 7.

[0029] Figure 10 This is the SEM image of Example 9. Detailed Implementation

[0030] The following detailed description provides further details on specific embodiments, but the embodiments of the present invention are not limited thereto. Unless otherwise specified, the technical means used in the following embodiments are conventional means well known to those skilled in the art; the experimental methods used are all conventional methods; and the materials and reagents used are all commercially available.

[0031] Overview of the plan: A YSZ-based thermal barrier coating material based on zirconium residue from nuclear-grade sponge zirconium production process, with a chemical composition of 92-95% Zr (by molar percentage) comprising the following components: 1-2x Co 2x O2, where 0≤x≤0.05, 1.0~8.0%Y2O3, 0~4.0%CeO2, 0~4.8%La2O3, and 0~5.6%Sc2O3.

[0032] A method for preparing a YSZ-based thermal barrier coating material based on zirconium residue from a nuclear-grade sponge zirconium production process includes the following steps: Step 1: Preparation of Zr source solution: The cation concentration in the zirconium residue (Zr(OCl)2 solution, pH=2.5-3.0) after zirconium and hafnium separation was accurately determined by inductively coupled plasma atomic emission spectrometry (ICP); Nitric acid was added to the zirconium residue to adjust the pH of the solution to 2.0; Anhydrous ethanol was added to the solution at 20% by volume, and deionized water was added to make up the volume to prepare a 2.0 mol / L Zr source solution; Step 2, Preparation of Mixed Solution: The chemical composition of the YSZ-based thermal barrier coating material, in molar percentage, includes the following components: 92-95% Zr 1-2x Co 2x O2, wherein 0≤x≤0.05, 1.0~8.0%Y2O3, 0~4.0%CeO2, 0~4.8%La2O3, 0~5.6%Sc2O3. Accurately weigh Co(NO3)2·6H2O and Y(NO3)3·6H2O, and dissolve them separately in deionized water to form nitrate solutions; accurately weigh the La / Ce / Sc nitrates, and dissolve them in deionized water to form nitrate solutions; add each nitrate solution to the Zr source solution according to the stoichiometric ratio, stir and mix, and make up to volume to form a mixed solution with a total concentration of 0.5mol / L-1.0mol / L. Step 3: Co-precipitation and precursor preparation: Add deionized water to ammonia solution, stir, and dilute to volume to form an ammonia solution; simultaneously inject the mixed solution and the ammonia solution into the reactor, and stir rapidly to form a precipitate. The stirring speed for the precipitation reaction is 400 rpm-1000 rpm; filter the precipitate, wash with anhydrous ethanol, and dry to obtain a solid precipitate; mix the solid precipitate with n-pentanol and perform vacuum distillation to obtain the powder precursor; the concentration ratio of the ammonia solution to the mixed solution is 3.3:1. Step 4, Drying and Calcination: The precursor powder was vacuum dried at 60℃ for 12h, ground and passed through a 200-mesh sieve; then calcined at 700℃ for 2h and cooled to obtain YSZ-based nanopowder.

[0033] Example 1 A method for preparing a YSZ-based thermal barrier coating material based on zirconium residue from a nuclear-grade sponge zirconium production process includes the following steps: Step 1: Preparation of Zr source solution: The cation concentration in the zirconium residue (Zr(OCl)2 solution, pH=2.5-3.0) after zirconium and hafnium separation was accurately determined by inductively coupled plasma atomic emission spectrometry (ICP); Nitric acid was added to the zirconium residue to adjust the pH of the solution to 2.0; Anhydrous ethanol was added to the solution at 20% by volume, and deionized water was added to make up the volume to prepare a 2.0 mol / L Zr source solution; Step 2: Preparation of mixed solution: Based on the molar percentage of 93% ZrO2 and 5.0% Y2O3, measure the original Zr solution, accurately weigh Y(NO3)3·6H2O, dissolve it in deionized water to form a Y(NO3)3 solution; mix it with the original Zr solution, stir, and make up to volume to form a 0.8 mol / L mixed solution; Step 3: Co-precipitation and precursor preparation: Deionized water was added to the ammonia solution at a concentration ratio of 3.3:1 to the mixed solution, stirred, and brought to a final volume to form an ammonia solution. The mixed solution and the ammonia solution were simultaneously injected into the reactor, and the mixture was rapidly stirred at 800 rpm to form a precipitate. The precipitate was filtered, washed with anhydrous ethanol, and dried to obtain a solid precipitate. The solid precipitate was mixed with n-pentanol and subjected to vacuum distillation to obtain the powder precursor. Step 4, Drying and Calcination: The precursor powder was vacuum dried at 60℃ for 12 hours, ground and passed through a 200-mesh sieve; after calcination at 700℃ for 2 hours, it was cooled to obtain YSZ nanopowder.

[0034] Example 2 The difference between this embodiment and Embodiment 1 is that in this embodiment, the Zr original solution is measured based on a molar percentage of 93% ZrO2 and 7.0% Y2O3.

[0035] Example 3 The difference between this embodiment and Embodiment 1 is that in this embodiment, 93% Zr is used. 0.99 Co 0.02 O2, 7.0% Y2O3 molar percentage, measure the original Zr solution. Accurately weigh Y(NO3)3·6H2O and Co(NO3)3·6H2O, dissolve them separately in deionized water to form nitrate solutions, mix them with the original Zr solution, stir, and make up to volume to form a 0.8 mol / L mixed solution.

[0036] Example 4 The difference between this embodiment and Embodiment 1 is that in this embodiment, 93% Zr is used. 0.98 Co 0.05O2, 7.0% Y2O3 molar percentage, measure the original Zr solution. Accurately weigh Y(NO3)3·6H2O and Co(NO3)3·6H2O, dissolve them separately in deionized water to form nitrate solutions; mix with the original Zr solution, stir, and dilute to volume to form a 0.8 mol / L mixed solution.

[0037] Example 5 The difference between this embodiment and Embodiment 1 is that in this embodiment, 93% Zr is used. 0.99 Co 0.02 The Zr stock solution was measured based on the molar percentages of O2, 6.0% Y2O3, and 1.0% CeO2. Y(NO3)3·6H2O, Co(NO3)3·6H2O, and Ce(NO3)3·6H2O were accurately weighed and dissolved in deionized water to form nitrate solutions. These solutions were then mixed with the Zr stock solution, stirred, and diluted to a final volume to form a 0.8 mol / L mixed solution.

[0038] Example 6 The difference between this embodiment and Embodiment 1 is that in this embodiment, 93% Zr is used. 0.99 Co 0.02 The Zr stock solution was measured based on the molar percentages of O2, 3.0% Y2O3, and 4.0% CeO2. Y(NO3)3·6H2O, Co(NO3)3·6H2O, and Ce(NO3)3·6H2O were accurately weighed and dissolved in deionized water to form nitrate solutions. These solutions were then mixed with the Zr stock solution, stirred, and diluted to a final volume to form a 0.8 mol / L mixed solution.

[0039] Example 7 The difference between this embodiment and Embodiment 1 is that in this embodiment, 93% Zr is used. 0.99 Co 0.02 Based on the molar percentages of O2, 5.8% Y2O3, and 1.2% La2O3, measure the original Zr solution, accurately weigh Y(NO3)3·6H2O, Co(NO3)3·6H2O, and La(NO3)3·6H2O, and dissolve them separately in deionized water to form nitrate solutions; mix with the original Zr solution, stir, and dilute to a final volume to form a 0.8 mol / L mixed solution.

[0040] Example 8 The difference between this embodiment and Embodiment 1 is that in this embodiment, 93% Zr is used. 0.99 Co 0.02Based on the molar percentages of O2, 2.2% Y2O3, and 4.8% La2O3, measure the original Zr solution, accurately weigh Y(NO3)3·6H2O, Co(NO3)3·6H2O, and La(NO3)3·6H2O, and dissolve them separately in deionized water to form nitrate solutions; mix with the original Zr solution, stir, and dilute to a final volume to form a 0.8 mol / L mixed solution.

[0041] Example 9 The difference between this embodiment and Embodiment 1 is that in this embodiment, 93% Zr is used. 0.99 Co 0.02 Based on the molar percentages of O2, 5.6% Y2O3, and 1.4% Sc2O3, measure the original Zr solution, accurately weigh Y(NO3)3·6H2O, Co(NO3)3·6H2O, and Sc(NO3)3·6H2O, and dissolve them separately in deionized water to form nitrate solutions; mix with the original Zr solution, stir, and dilute to a final volume to form a 0.8 mol / L mixed solution.

[0042] Example 10 The difference between this embodiment and Embodiment 1 is that in this embodiment, 93% Zr is used. 0.99 Co 0.02 Based on the molar percentages of O2, 1.4% Y2O3, and 5.6% Sc2O3, measure the original Zr solution, accurately weigh Y(NO3)3·6H2O, Co(NO3)3·6H2O, and Sc(NO3)3·6H2O, and dissolve them separately in deionized water to form nitrate solutions; mix with the original Zr solution, stir, and dilute to a final volume to form a 0.8 mol / L mixed solution.

[0043] The nanoparticles prepared in the above embodiments and comparative examples were subjected to X-ray diffraction, laser particle size analysis, and scanning electron microscopy tests. The results are as follows: Figure 1-10 As shown: Combination Figure 1 , Figure 2 The XRD patterns of Examples 1-4 (containing only Zr, Y, and Co elements) show that all samples exhibit characteristic YSZ tetragonal phase diffraction peaks, with no impurity phase peaks, indicating that Y2O3 successfully stabilized the tetragonal phase structure of ZrO2. Among them, the Co-doped Examples 3 and 4 show higher diffraction peak intensities, indicating that Co... 2+The introduction of these dopants promoted lattice regularity and improved phase stability. The XRD patterns of Examples 5-10 (with CeO2, La2O3, and Sc2O3 dopants) still maintained a single tetragonal phase structure, with no impurity phase diffraction peaks corresponding to the dopants, proving that Ce, La, and Sc ions were successfully dissolved into the YSZ lattice without disrupting the matrix structure. Comparing the diffraction peak positions of samples with different doping amounts, the diffraction peaks shifted slightly with increasing CeO2, La2O3, and Sc2O3 doping amounts, consistent with the lattice distortion caused by ion solid solution, verifying the compatibility of the dopants with the YSZ matrix.

[0044] Combination Figure 3-6 All powders prepared in the examples exhibited typical nanoscale particle size distribution characteristics, with D10 less than 3.5 μm, D50 between 10.53 μm and 16.88 μm, and D90 not exceeding 50.1 μm. The overall particle distribution was concentrated, with no obvious large particle agglomeration. Example 3, doped with Co (D50 = 16.88 μm), had a slightly larger particle size than Example 1 without Co doping, but it was still within a reasonable range, indicating that Co ion doping had a relatively small impact on particle growth. Examples 5 (D50 = 10.53 μm), 7, and 9, with Ce, La, and Sc dopants, showed a more concentrated particle size distribution, with D50 smaller than the samples without dopants, indicating that the introduction of Ce, La, and Sc elements could inhibit excessive particle growth and optimize powder dispersibility.

[0045] Combination Figure 7-10 SEM images of Examples 3, 5, 7, and 9 show that the powder particles are all irregular nanoparticles with clear outlines, no severe agglomeration, and good dispersibility, consistent with the results of laser particle size analysis. The particles in Example 3 (Co-doped) are relatively uniform in size and have a relatively dense surface, indicating that the introduction of Co ions helps improve particle formation quality. The particles in Examples 5 (Ce-doped), 7 (La-doped), and 9 (Sc-doped) have smoother surfaces and smaller interparticle gaps, indicating that multi-component doping can further improve the particle microstructure. The particle size of all samples is around 100 nm (except for some agglomerates), consistent with the characteristics of nanoparticles, providing a good foundation for subsequent coating preparation.

[0046] In summary, all samples in this embodiment formed a single tetragonal YSZ structure without impurity phases, exhibiting excellent high-temperature stability and exceeding the conventional 1200℃ operating temperature limit of YSZ. Furthermore, the prepared powder is nanoscale with a concentrated particle size distribution, good dispersibility, and regular microstructure, meeting the requirements for powder particles in thermal barrier coating materials. Co ion doping improves phase regularity, while Ce, La, and Sc dopants optimize particle dispersion and microstructure; the synergistic effect of multiple dopants results in superior overall material performance.

[0047] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A YSZ-based thermal barrier coating material based on zirconium raffinate from a nuclear grade zirconium sponge production process, characterized in that: by mole percent, comprising: 92-95% Zr 1-2x Co 2x O2, wherein 0≤x≤0.05, 1.0-8.0% Y2O3, 0-4.0% CeO2, 0-4.8% La2O3, 0-5.6% Sc2O3.

2. The YSZ-based thermal barrier coating material based on the zirconium raffinate in the production process of nuclear-grade zirconium sponge according to claim 1, characterized in that: The material is single tetragonal phase structure, and the powder D50 of the material is 10.53-16.88 μm.

3. A method for producing a YSZ-based thermal barrier coating material from the zirconium raffinate in the production process of nuclear-grade zirconium sponge according to claim 1 or 2, characterized in that, The method comprises the following steps: Step one, preparation of Zr source solution: using the Zr residue after Zr-Hf separation in the process of preparing nuclear grade zirconium sponge as the Zr source solution; Step two, preparation of mixed solution: dissolving Co(NO3)2·6H2O and Y(NO3)3·6H2O in deionized water respectively to form nitrate solutions; dissolving La / Ce / Sc nitrate in deionized water to form a nitrate solution; adding the nitrate solutions according to the stoichiometric ratio into the Zr source solution, stirring and mixing, and constant volume to form a mixed solution; Step three, coprecipitation and preparation of precursor: mixing the mixed solution and ammonia solution and stirring to form a precipitate, filtering, washing with anhydrous ethanol, and then mixing with n-pentanol and distilling under reduced pressure to obtain a powder precursor; Step four, drying and calcination: drying and grinding the precursor powder, and then calcining and cooling to obtain YSZ-based nano powder.

4. The method according to claim 3, wherein the method is characterized in that: In step one, the concentration of the Zr source solution is 2.0 mol / L, and before preparing the Zr source solution, the cation concentration of the Zr residue after Zr-Hf separation is determined by discharge plasma atomic emission spectrometry.

5. The method according to claim 3, wherein the method is characterized by: In step two, the total concentration of the mixed solution is 0.5 mol / L-1.0 mol / L.

6. The method according to claim 3, wherein the method is characterized by: In step three, the stirring speed of the precipitation reaction is 400 rpm-1000 rpm.

7. The method according to claim 6, wherein the method is characterized in that: In step three, the concentration ratio of the ammonia solution to the mixed solution is 3.3:

1.

8. The method according to claim 3, wherein the method is characterized by: In step four, the drying condition is vacuum drying at 60℃ for 12 h.

9. The method according to claim 8, wherein the method is characterized by: In step four, the calcination condition is calcination at 700℃ for 2 h.

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