Loose spherical zirconium oxide-based powder with hierarchical pore structure and preparation method and coating of loose spherical zirconium oxide-based powder

Abstract

The invention provides loose spherical zirconium oxide-based powder with a hierarchical pore structure, a preparation method of the loose spherical zirconium oxide-based powder and a coating, and relates to the field of zirconium oxide preparation. Mixing the multi-lanthanide doped zirconium oxide-based fine powder, metal zirconium powder, ZrB2 nanoparticles, carbon nanotubes, PMMA microspheres and water to obtain first slurry; mixing the multi-lanthanide doped zirconium oxide-based fine powder, hollow SiO2 microspheres and water to obtain second slurry; arranging the second slurry on the surface of the first slurry by adopting spray freeze drying to obtain spherical composite precursor powder; performing heat treatment on the spherical composite precursor powder to obtain heat-treated powder; in a nitrogen atmosphere, performing pulse plasma in-situ strengthening treatment on the powder subjected to heat treatment to obtain loose spherical zirconium oxide-based powder; according to the method, through material design and process collaborative optimization, the sphericity, pore controllability and high-temperature comprehensive performance of the powder are effectively improved, and the method is suitable for the fields of high-end thermal barrier coatings, catalytic carriers and the like.

Description

Technical Field

[0001] This application relates to the field of zirconia preparation, and more particularly to a loose spherical zirconia-based powder with a hierarchical porous structure, its preparation method, and coating. Background Technology

[0002] Zirconia possesses low thermal conductivity and excellent thermal stability, making it suitable for coating high-temperature components in aerospace and energy fields, such as gas turbine blades and engine combustion chambers. This coating effectively reduces the substrate temperature, improves thermal efficiency, and extends component lifespan. Existing preparation methods for zirconia powder include chemical co-precipitation, hydrolytic hydrothermal synthesis, and organic gel mesh synthesis, as well as electrofusion and spray drying. Chemical co-precipitation involves adding a precipitant to form a precipitate of zirconium salts and dopants, followed by calcination and other subsequent treatments to obtain the powder. Hydrolytic hydrothermal synthesis involves a chemical reaction in a high-temperature, high-pressure aqueous solution or steam environment to prepare the powder. The organic gel mesh synthesis utilizes the network structure of an organic gel to control powder formation.

[0003] However, the zirconia prepared by the above method still has the following problems: 1. Uncontrollable pore structure: Traditional processes make it difficult to precisely control the pore structure inside the powder. The pores are randomly distributed, which cannot meet the specific requirements of porosity and pore structure in applications such as high-end thermal barrier coatings and catalyst supports, thus affecting the performance of the material. 2. Low sphericity: Zirconia powder prepared by conventional methods has poor sphericity. In subsequent processing and application, the powder has poor flowability and is prone to agglomeration, resulting in unstable product quality. For example, when preparing coatings by thermal spraying, it will affect the uniformity and density of the coating. 3. Insufficient overall high-temperature performance: The single doping mode and simple process design result in defects in high-temperature stability, thermal shock resistance, and high-temperature wear resistance of the prepared zirconia powder, which limits its application in high-temperature fields, such as poor performance in high-temperature components such as gas turbines.

[0004] Therefore, there is an urgent need to provide a method for preparing zirconia-based powder to solve the above problems. Summary of the Invention

[0005] The purpose of this application is to provide a loose spherical zirconia-based powder with a hierarchical porous structure, its preparation method, and coating, in order to solve the above-mentioned problems.

[0006] To achieve the above objectives, the first aspect of this application provides a method for preparing loosely porous spherical zirconia-based powder with a hierarchical porous structure, comprising: A first slurry was obtained by mixing multi-lanthanide-doped zirconium oxide fine powder, metallic zirconium powder, ZrB2 nanoparticles, carbon nanotubes, PMMA microspheres and water. A second slurry was obtained by mixing multi-lanthanide-doped zirconium oxide fine powder, hollow SiO2 microspheres, and water. The second slurry was applied to the surface of the first slurry by spray freeze-drying to obtain spherical composite precursor powder; The spherical composite precursor powder is heat-treated to obtain heat-treated powder. Under a nitrogen atmosphere, the heat-treated powder is subjected to pulsed plasma in-situ strengthening treatment to obtain loose spherical zirconia-based powder with a hierarchical porous structure. The raw materials for the multi-component lanthanide-doped zirconium oxide-based fine powder, based on a total mass of 100%, include: 3-5% Y2O3, 5-8% CeO2, 1-3% La2O3, balance ZrO2.

[0007] Optionally, the method for preparing the loose spherical zirconia-based powder with a hierarchical porous structure satisfies at least one of the following conditions: (1) In the first slurry, the mass of water is 30-60% of the mass of the solid powder; (2) In the first slurry, the total mass of solid powder, calculated on a 100% basis, includes: 5-15% of the zirconium metal powder, 5-10% of the ZrB2 nanoparticles, 1-3% of the carbon nanotubes, 5-15% of the PMMA microspheres, and the remainder is the multi-component lanthanide-doped zirconium oxide-based fine powder; (3) In the second slurry, the mass of water is 30-60% of the mass of the solid powder; (4) In the second slurry, the total mass of solid powder, calculated on a 100% basis, includes: 10-20% of the hollow SiO2 microspheres, the remainder being the multi-component lanthanide-doped zirconium oxide-based fine powder.

[0008] Optionally, the method for preparing the loose spherical zirconia-based powder with a hierarchical porous structure satisfies at least one of the following conditions: (1) The particle size of the multi-component lanthanide-doped zirconium oxide-based fine powder is 1-3 μm; (2) The particle size of the zirconium metal powder is 1-2 μm; (3) The particle size of the ZrB2 nanoparticles is 50-100 nm; (4) The carbon nanotubes include nano-carbon nanotubes; (5) The particle size of the PMMA microspheres is 1-5 μm; (6) The diameter of the hollow SiO2 microspheres is 5-20 μm.

[0009] Optionally, during the spray freeze-drying process, the ratio of the spraying speed of the first slurry to the spraying speed of the second slurry is 1:1.2-1.5.

[0010] Optionally, the spray freeze-drying includes a rapid freezing stage and a vacuum drying stage performed sequentially; The temperature during the rapid freezing stage is -70°C to -90°C; The temperature of the vacuum drying stage is -40℃ to -60℃, the time is 12h to 24h, and the vacuum degree is ≤10Pa.

[0011] Optionally, the method for preparing the loose spherical zirconia-based powder with a hierarchical porous structure satisfies at least one of the following conditions: (1) The heat treatment includes a first heat treatment, a second heat treatment and a third heat treatment performed sequentially; The first heat treatment is carried out under an inert atmosphere, with a holding temperature of 400-600℃ and a time of 0.5-1.5h; The second heat treatment is carried out in air, with a holding temperature of 800-1000℃ and a time of 1-3 hours; The third heat treatment is carried out in air, with a holding temperature of 1100-1300℃ and a time of 0.5-1.5h; (2) The power of the pulsed plasma in-situ strengthening treatment is 20-40kW, the powder feeding rate is 50-150g / min, and the pulse frequency is 5-10Hz.

[0012] The second aspect of this application provides a porous spherical zirconia-based powder with a hierarchical porous structure, which is prepared by the method for preparing the porous spherical zirconia-based powder with a hierarchical porous structure.

[0013] Optionally, it includes a kernel and a first and a second overlay layer disposed on the kernel; The raw materials for the core include a first slurry; The raw material for the first coating layer includes the second slurry; The second coating layer includes ZrN.

[0014] Optionally, the loose spherical zirconia-based powder with a hierarchical porous structure satisfies at least one of the following conditions: (1) The particle size of the loose spherical zirconia-based powder is 20-100 μm; (2) The sphericity of the loose spherical zirconia-based powder is ≥95%; (3) The porosity of the loose spherical zirconia-based powder is 30-60%; (4) The thickness of the first coating layer is 5-10 μm; (5) The thickness of the second coating layer is 1-5 μm.

[0015] A third aspect of this application provides a coating comprising the aforementioned loosely spherical zirconia-based powder having a hierarchical porous structure.

[0016] Compared with the prior art, the beneficial effects of this application include: The method for preparing loose spherical zirconia-based powder with a hierarchical porous structure provided in this application first prepares spherical composite precursor powder through a spray freeze-drying process, then heat-treats the precursor powder using an atmosphere sintering process to remove the template agent and fix the structure, and finally performs pulsed plasma in-situ strengthening treatment on the heat-treated powder to obtain loose spherical zirconia-based composite powder with a controllable hierarchical porous structure. This method effectively improves the sphericity, porosity controllability, and high-temperature comprehensive performance of the powder through synergistic optimization of material design and process, and is suitable for high-end thermal barrier coatings, catalyst supports, and other fields.

[0017] The loose spherical zirconia-based powder with a multi-level porous structure provided in this application has a multi-level porous structure of "micron-sized through-pores and nano-sized mesopores" in its core, which enables the material to have a large specific surface area, which is beneficial for its role in application scenarios. It has good thermal stability, thermal shock resistance, and high-temperature wear resistance. Under high-temperature environment, it can maintain structural stability and does not undergo significant phase transformation or cracking, so as to meet the needs of high-temperature application scenarios such as high-end thermal barrier coatings.

[0018] The coating provided in this application utilizes the low thermal conductivity and good thermal stability of loose spherical zirconia-based powder with a multi-level porous structure to form a coating on the surface of high-temperature components in aerospace, energy and other fields, such as gas turbine blades and engine combustion chambers, effectively reducing the substrate temperature of the component, improving thermal efficiency, and extending the service life of the component. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation on the scope of this application.

[0020] Figure 1 SEM image of the loose spherical zirconia-based powder with a hierarchical porous structure provided in Example 1. Detailed Implementation

[0021] First, the solution provided in this application will be explained in more detail as follows: The first aspect of this application provides a method for preparing loosely porous spherical zirconia-based powder with a hierarchical porous structure, comprising: A first slurry was obtained by mixing multi-lanthanide-doped zirconium oxide fine powder, metallic zirconium powder, ZrB2 nanoparticles, carbon nanotubes, PMMA microspheres and water. It is worth noting that zirconium metal powder has properties such as high melting point and good corrosion resistance. Adding zirconium metal powder to the first slurry can enhance the strength and stability of the core layer by taking advantage of these properties. In high-temperature applications, such as high-end thermal barrier coatings, the core formed by the first slurry serves as the basic support structure. Zirconium metal powder helps to improve the overall material's ability to resist thermal and mechanical stress at high temperatures, ensuring that the material maintains its structural integrity in extreme environments. In addition, ZrB2 nanoparticles are used to improve the high-temperature wear resistance of loose spherical zirconia-based powder. ZrB2 nanoparticles are added to the first slurry. They have high hardness, excellent high-temperature wear resistance and thermal stability. They can directly fill the gaps in the multi-level porous structure of the core, thereby improving the high-temperature wear resistance of the entire powder from the perspective of "internal structure strengthening". A second slurry was obtained by mixing multi-lanthanide-doped zirconium oxide fine powder, hollow SiO2 microspheres, and water. It should be noted that the main function of the first coating layer formed by the second slurry is to enhance the thermal insulation performance, and hollow SiO2 microspheres are added to achieve this purpose. If zirconium powder is added to the second slurry, the high thermal conductivity of the zirconium powder may destroy the thermal insulation effect of the shell, resulting in a decrease in the thermal insulation performance of the entire material, which cannot meet the thermal insulation requirements of high-end thermal barrier coatings and other application scenarios. It should also be noted that hollow SiO2 microspheres are used to improve the thermal insulation performance of loose spherical zirconia-based powder and enable the loose spherical zirconia-based powder to be used stably without phase change at 1300℃ for 100h, which is suitable for high-end thermal barrier coatings and other fields with high thermal insulation requirements. The second slurry was applied to the surface of the first slurry by spray freeze-drying to obtain spherical composite precursor powder; The spherical composite precursor powder is heat-treated to obtain heat-treated powder. It should be noted that heat treatment can carbonize the carbon nanotubes and PMMA microspheres in the spherical composite precursor powder to form a hierarchical porous structure, thereby controlling the porosity and specific surface area. Under a nitrogen atmosphere, the heat-treated powder is subjected to pulsed plasma in-situ strengthening treatment to obtain loose spherical zirconia-based powder with a hierarchical porous structure. It should be noted that under a nitrogen atmosphere, through the synergistic effect of nitrogen and pulse energy, a 1-5 μm thick ZrN reinforcing phase is generated in situ on the powder surface after heat treatment, which improves the surface hardness and structural stability of the loose spherical zirconia-based powder. The raw materials for the multi-component lanthanide-doped zirconium oxide-based fine powder, based on a total mass of 100%, include: 3-5% Y2O3, 5-8% CeO2, 1-3% La2O3, balance ZrO2.

[0022] Optionally, the raw materials for the multi-lanthanide-doped zirconium oxide-based fine powder, based on a total mass of 100%, may contain Y2O3 at any value between 3%, 4%, 5%, or 3-5%, CeO2 at any value between 5%, 6%, 7%, 8%, or 5-8%, La2O3 at any value between 1%, 2%, 3%, or 1-3%, with the balance being ZrO2.

[0023] It is important to note that the design of the proportion range of each dopant component in the multi-component lanthanide-doped zirconium oxide fine powder is to synergistically improve the high-temperature stability and thermal shock resistance of the material. The specific reasons are as follows: The reasons for using 3-5% Y2O3 by mass are as follows: 1. Stabilizing the crystal structure: Y2O3 can effectively stabilize the tetragonal phase structure of zirconia. Under high temperature conditions, zirconia undergoes a phase transition, and an appropriate amount of Y2O3 doping can suppress this phase transition and ensure the stability of the material structure. When the mass percentage of Y2O3 is less than 3%, the stabilizing effect is insufficient, and the material is prone to phase transition at high temperatures, leading to volume changes and reducing the stability and thermal shock resistance of the material. When the mass percentage of Y2O3 is higher than 5%, excessive Y2O3 may cause excessive lattice distortion, which also has an adverse effect on the material's performance, such as reducing the material's strength. 2. Optimizing overall performance: A Y2O3 mass percentage range of 3-5% helps to improve the overall performance of the material. Within this range, while ensuring a stable crystal phase, it can balance the material's hardness, toughness, and other properties. For example, in high-end thermal barrier coating applications, it can ensure that the coating maintains good thermal insulation performance at high temperatures while also providing a certain mechanical strength to resist thermal and mechanical stress. The reasons for using 5-8% CeO2 by mass are: 1. Improved thermal shock resistance: CeO2 has excellent oxygen storage and release capabilities. Doping an appropriate amount of CeO2 into zirconia-based materials can effectively improve the material's thermal shock resistance. When the mass percentage of CeO2 is less than 5%, its oxygen storage and release capabilities have little effect on improving thermal shock resistance; when the mass percentage of CeO2 exceeds 8%, it may lead to a loose internal structure, reducing the material's density and strength, and affecting the material's performance in practical applications. 2. Enhanced oxygen ion conductivity: A CeO2 mass percentage of 5-8% can enhance the material's oxygen ion conductivity. In some applications, such as solid oxide fuel cells, good oxygen ion conductivity is crucial. CeO2 doping enables the material to meet other performance requirements while possessing good oxygen ion conductivity, thus improving the material's functionality.

[0024] The reasons for setting the La2O3 mass percentage to 1-3% are as follows: 1. Grain refinement: La2O3 doping can refine the grains of zirconia, making the microstructure of the material more uniform. When the La2O3 mass percentage is less than 1%, the grain refinement effect is not significant, and its optimization effect on material performance cannot be fully utilized; when the La2O3 mass percentage is greater than 3%, it may cause La2O3 to agglomerate in the material, destroying the uniformity of the material structure and reducing the material performance; 2. Improved high-temperature stability: An appropriate amount of La2O3 can further improve the high-temperature stability of the material. Under high-temperature conditions, it can inhibit the growth of zirconia grains, maintain the structural stability of the material, and thus improve the service life of the material in high-temperature environments. When the La2O3 mass percentage is within the range of 1-3%, this function can be achieved well, without significantly interfering with the effects of other dopants.

[0025] It is also worth noting that this application breaks through the traditional single-doping mode by using multi-component synergistic doping and gradient functional design. It employs a ternary composite doped zirconium oxide matrix of "Y2O3-CeO2-La2O3" to synergistically improve high-temperature stability and thermal shock resistance. Through core-shell gradient structure design, ZrB2 nanoparticles are introduced into the core to enhance wear resistance, and hollow SiO2 microspheres are introduced into the first coating layer to strengthen thermal insulation, achieving functional synergy. Furthermore, a dual-template control agent is used to form a multi-level porous structure, introducing a dual-template system of "carbon nanotubes and PMMA microspheres" to precisely control the multi-level porous structure of the powder core, from "micron-sized through-pores to nano-sized mesopores," achieving a porosity of 30-60%. Within a controllable range, the specific surface area is increased, solving the problem of random and uncontrollable porosity in traditional processes. Furthermore, through process synergistic optimization and in-situ strengthening mechanisms, the traditional spray drying process is upgraded to a combined "spray-freeze drying" process, improving sphericity to ≥95%. A three-step atmosphere-based heat treatment of "inert shaping-oxidation and air densification" is adopted to achieve complete removal of dual template agents and uniform structural shaping. Through nitrogen atmosphere pulsed plasma treatment, a ZrN reinforcing phase is generated in situ, increasing the surface hardness to 1200-1500 HV, balancing density and performance. Finally, through precise control of raw materials and parameters, the proportion of multi-component doping, the amount of dual template agents, the gradient slurry ratio, and key process parameters (such as freezing temperature, sintering stage temperature, plasma pulse frequency, etc.) are clearly defined, forming a quantifiable and repeatable preparation system to ensure the stability and controllability of powder performance.

[0026] In some embodiments, the method for preparing the loose spherical zirconia-based powder with a hierarchical porous structure satisfies at least one of the following conditions: (1) In the first slurry, the mass of water is 30-60% of the mass of the solid powder; Optionally, in the first slurry, the mass of water can be any value between 30%, 40%, 50%, 60% or 30-60% of the mass of the solid powder; (2) In the first slurry, the total mass of solid powder, calculated on a 100% basis, includes: 5-15% of the zirconium metal powder, 5-10% of the ZrB2 nanoparticles, 1-3% of the carbon nanotubes, 5-15% of the PMMA microspheres, and the remainder is the multi-component lanthanide-doped zirconium oxide-based fine powder; Optionally, in the first slurry, the total mass of solid powder is 100%, and the zirconium metal powder can be any value between 5%, 10%, 15% or 5-15%, the ZrB2 nanoparticles can be any value between 5%, 6%, 7%, 8%, 9%, 10% or 5-10%, the carbon nanotubes can be any value between 1%, 2%, 3% or 1-3%, the PMMA microspheres can be any value between 5%, 10%, 15% or 5-15%, and the remainder is multi-component lanthanide-doped zirconium oxide-based fine powder; (3) In the second slurry, the mass of water is 30-60% of the mass of the solid powder; Optionally, in the second slurry, the mass of water can be any value between 30%, 40%, 50%, 60% or 30-60% of the mass of the solid powder; (4) In the second slurry, the total mass of solid powder, calculated on a 100% basis, includes: 10-20% of the hollow SiO2 microspheres, the remainder being the multi-component lanthanide-doped zirconium oxide-based fine powder.

[0027] Optionally, in the second slurry, the total mass of solid powder is 100%, and the hollow SiO2 microspheres can be any value between 10%, 15%, 20% or 10-20%, with the remainder being multi-component lanthanide-doped zirconium oxide-based fine powder.

[0028] It should be noted that when the mass percentage of hollow SiO2 microspheres is less than 10%, they cannot effectively perform their thermal insulation function and cannot meet the thermal insulation performance requirements of high-end thermal barrier coatings. When the mass percentage is higher than 20%, too many hollow SiO2 microspheres may reduce the structural strength of the shell, leading to a decrease in the overall mechanical properties of the material. Under external force or high temperature environment, structural damage is likely to occur, affecting the service life and reliability of the material.

[0029] In some embodiments, the method for preparing the loose spherical zirconia-based powder with a hierarchical porous structure satisfies at least one of the following conditions: (1) The particle size of the multi-component lanthanide-doped zirconium oxide-based fine powder is 1-3 μm; Optionally, the particle size of the multi-component lanthanide-doped zirconium oxide-based fine powder can be any value between 1 μm, 2 μm, 3 μm, or 1-3 μm; (2) The particle size of the zirconium metal powder is 1-2 μm; Optionally, the particle size of the zirconium metal powder can be any value between 1 μm, 1.5 μm, 2 μm, or 1-2 μm; (3) The particle size of the ZrB2 nanoparticles is 50-100 nm; Optionally, the particle size of ZrB2 nanoparticles can be any value between 50nm, 60nm, 70nm, 80nm, 90nm, 100nm or 50-100nm. (4) The carbon nanotubes include nano-carbon nanotubes; In some embodiments, the particle size of the carbon nanotubes is 10-50 nm; (5) The particle size of the PMMA microspheres is 1-5 μm; Optionally, the particle size of PMMA microspheres can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm or any value between 1 and 5 μm; (6) The diameter of the hollow SiO2 microspheres is 5-20 μm.

[0030] Optionally, the diameter of the hollow SiO2 microspheres can be any value between 5μm, 10μm, 15μm, 20μm, or 5-20μm.

[0031] In some embodiments, during the spray freeze-drying process, the ratio of the spraying speed of the first slurry to the spraying speed of the second slurry is 1:1.2-1.5.

[0032] Optionally, the ratio of the spraying speed of the first slurry to the spraying speed of the second slurry can be 1:1.2, 1:1.3, 1:1.4, 1:1.5 or any value between 1:1.2 and 1.5.

[0033] It is important to note that the spraying speed of the second slurry should be slightly higher than that of the first slurry. This is because, during the formation of the core-shell structure, it is crucial to ensure that the first coating layer can uniformly and completely encapsulate the core. If the spraying speed of the second slurry is too slow, it may result in uneven thickness of the first coating layer, failing to completely cover the core. Conversely, if the spraying speed of the second slurry is too fast, it may lead to an excessively thick first coating layer, affecting the uniformity of material properties. Maintaining the ratio of the spraying speed of the first slurry to that of the second slurry between 1:1.2 and 1.5 ensures that the first coating layer effectively encapsulates the core while guaranteeing the stability of the core-shell structure and the consistency of material properties.

[0034] In some embodiments, the spray freeze-drying includes a rapid freezing stage and a vacuum drying stage performed sequentially; The temperature during the rapid freezing stage is -70°C to -90°C; Optionally, the temperature of the rapid freezing stage can be -70°C, -80°C, -90°C, or any value between -70°C and -90°C; The temperature of the vacuum drying stage is -40℃ to -60℃, the time is 12h to 24h, and the vacuum degree is ≤10Pa.

[0035] Optionally, the temperature of the vacuum drying stage can be any value of -40℃, -50℃, -60℃ or -40--60℃, and the vacuum degree can be any value of 10Pa, 5Pa, 1Pa or ≤10Pa.

[0036] It is important to note that the rapid freezing stage is used to quickly freeze the slurry into a solid state, so that the droplets of the core and the first coating layer can be rapidly solidified to fix their shape and avoid deformation or uneven mixing in subsequent processing; the vacuum drying stage, on the other hand, ensures that the ice crystals in the material sublimate while preventing the material structure from being damaged or the components from being lost due to excessive temperature, and ensures that the stability of the core-shell structure is maintained during the removal of moisture.

[0037] When the temperature during the rapid freezing stage is below -90°C, the freezing rate is too fast, which may cause the water in the slurry to freeze instantly, forming large ice crystals and destroying the uniformity of the core-shell structure. When the temperature is above -70°C, the freezing rate is too slow, and the droplets may flow or mix before solidification, affecting the formation of the core-shell structure. When the temperature during the vacuum drying stage is above -40°C, some components in the material may volatilize or the structure may change. When the temperature is below -60°C, the ice crystal sublimation rate is too slow, which will prolong the freeze-drying time and reduce production efficiency.

[0038] In some embodiments, the method for preparing the loose spherical zirconia-based powder with a hierarchical porous structure satisfies at least one of the following conditions: (1) The heat treatment includes a first heat treatment, a second heat treatment and a third heat treatment performed sequentially; The first heat treatment is carried out under an inert atmosphere, with a holding temperature of 400-600℃ and a time of 0.5-1.5h; Optionally, the first heat treatment is carried out in an inert atmosphere, and the holding temperature can be any value between 400℃, 500℃, 600℃ or 400-600℃, and the time can be any value between 0.5h, 1h, 1.5h or 0.5-1.5h. The second heat treatment is carried out in air, with a holding temperature of 800-1000℃ and a time of 1-3 hours; Optionally, the holding temperature of the second heat treatment can be any value between 800℃, 900℃, 1000℃ or 800-1000℃, and the time can be any value between 1h, 2h, 3h or 1-3h. The third heat treatment is carried out in air, with a holding temperature of 1100-1300℃ and a time of 0.5-1.5h; Optionally, the holding temperature for the third heat treatment can be any value between 1100℃, 1200℃, 1300℃ or 1100-1300℃, and the holding time can be any value between 0.5h, 1h, 1.5h or 0.5-1.5h. It is important to note that the first heat treatment is carried out under an inert atmosphere. Its core function is to protect the zirconium powder and carbon nanotubes in the first slurry from reacting with oxygen prematurely, and to achieve temporary bonding and shaping of inorganic particles by softening the organic matter (PMMA microspheres) in the slurry. In addition, the inert atmosphere can also prevent the decomposition of PMMA microspheres (organic matter) at this stage (PMMA microspheres need to be burned off in the air atmosphere of the second heat treatment to form pores). Only by softening (PMMA softening temperature is about 100-150℃) are inorganic particles such as multi-component lanthanide-doped zirconium oxide fine powder, zirconium powder, and ZrB2 nanoparticles temporarily bonded together, fixing the core layer structure of the precursor. The second heat treatment is carried out in air, which contains oxygen. In this stage, oxygen is needed to burn off the dual template agents (carbon nanotubes and PMMA microspheres) and oxidize the metallic zirconium. The template agents are organic matter, which can be fully burned and decomposed when heated in an air atmosphere, thereby removing the template agents and leaving a porous structure. At the same time, the metallic zirconium is oxidized in the presence of oxygen, and the resulting oxides help to enhance certain properties of the material, such as improving the high-temperature stability of the material. When the temperature of the second heat treatment is below 800℃, the dual template agent burns off slowly, which may result in incomplete burn-off and residues inside the material, affecting the pore structure and material properties. Furthermore, the oxidation of zirconium oxide is incomplete, failing to fully leverage its enhancing effect on material properties. Conversely, when the temperature exceeds 1000℃, the dual template agent may burn rapidly, leading to uncontrolled pore structure formation and affecting the uniformity of the material's pores. Excessively high temperatures may also cause excessive volatilization of some components within the material or other adverse phase transformation reactions. The holding time of the second heat treatment is designed to ensure complete burn-off of the dual template agent and sufficient oxidation of the zirconium. Too short a time results in insufficient reaction between the dual template agent and zirconium; too long a time, while ensuring a more complete reaction, increases energy consumption and production time, and may also lead to excessive grain growth, affecting the material's microstructure and properties. The third heat treatment is carried out in air. During the densification and shaping stage, oxygen in the air can continue to react with some impurities or unreacted components on the material surface, further purifying the surface and helping to improve the material's density and performance. When the temperature of the third heat treatment is below 1100℃, the atomic diffusion rate is slow, making it difficult for the material to achieve the ideal densification effect and effectively eliminate internal porosity, resulting in insufficient strength and stability. When the temperature of the third heat treatment is above 1300℃, the material may undergo over-sintering, leading to abnormal grain growth and deterioration of the material's mechanical properties and microstructure, such as brittleness, affecting its performance in practical applications. The holding time of the third heat treatment is designed to allow sufficient time for the atoms inside the material to diffuse and rearrange, achieving the purpose of densification and shaping. If the time is too short, the densification process will be insufficient, resulting in structural instability; if the time is too long, it may lead to the aforementioned over-sintering problems, reducing material quality. (2) The power of the pulsed plasma in-situ strengthening treatment is 20-40kW, the powder feeding rate is 50-150g / min, and the pulse frequency is 5-10Hz.

[0039] Optionally, the power of the pulsed plasma in-situ enhancement treatment can be any value between 20kW, 30kW, 40kW or 20-40kW, the powder feeding rate can be any value between 50 g / min, 100 g / min, 150 g / min or 50-150 g / min, and the pulse frequency can be any value between 5 Hz, 6 Hz, 7 Hz, 8 Hz, 9 Hz, 10 Hz or 5-10 Hz.

[0040] It is important to note that the power of pulsed plasma in-situ strengthening treatment needs to reach a certain level to provide sufficient energy for the in-situ generation of ZrN reinforcing phases on the powder surface and pore edges. A lower limit of 20kW ensures that the plasma has enough energy to decompose nitrogen gas and generate nitrogen-active particles. These particles react with zirconium in the powder to generate ZrN. If the power is below 20kW, the energy is insufficient, the reaction cannot proceed fully, the amount of ZrN generated is small, and the surface hardness and structural stability of the powder cannot be effectively improved. To avoid excessive reaction and adverse effects, the upper limit of the power is set at 40kW. This is because excessively high power will cause the reaction to be too violent, which may lead to local overheating of the powder, causing powder particles to agglomerate, deform, or even melt, destroying the original hierarchical porous structure and sphericity of the powder, and affecting powder performance. In addition, excessively high power will also increase energy consumption and production costs, making it uneconomical.

[0041] When the powder feeding rate is greater than or equal to 50 g / min, the uniformity and efficiency of the reaction are guaranteed. This ensures that the powder enters the plasma region evenly, guaranteeing that each powder particle has the opportunity to fully contact and react with the nitrogen-active particles. This ensures that the ZrN reinforcing phase is uniformly generated on the powder surface and at the edges of the pores, improving the consistency of the overall powder performance. If the powder feeding rate is too slow, the amount of powder participating in the reaction per unit time is small, resulting in low production efficiency. To prevent incomplete reaction and blockage, the upper limit of the powder feeding rate is set at 150 g / min. If the powder feeding is too fast, too much powder enters the plasma region, and some powder may not be able to fully react with the nitrogen-active particles in time before leaving the reaction region, resulting in incomplete ZrN formation and affecting the strengthening effect. At the same time, excessively fast powder feeding may also cause powder accumulation, blockage of the powder feeding pipe, or agglomeration in the reaction region, affecting the normal progress of the reaction.

[0042] By controlling the pulse frequency to 5-10Hz, the generation of ZrN can be optimized. When the pulse frequency is greater than or equal to 5Hz, the rhythm of plasma discharge generating nitrogen active particles can be ensured to be moderate, allowing the powder sufficient time to react with the active particles to generate ZrN. At the same time, the reaction system is given a certain recovery time to avoid problems such as local overheating caused by excessive reaction concentration. At this frequency, the reaction between nitrogen active particles and powder is relatively sufficient, which is conducive to the uniform and stable growth of ZrN on the powder surface and pore edges. When the pulse frequency is increased to 10Hz, the reaction efficiency can be improved to a certain extent, increasing the amount of ZrN generated per unit time. However, if the frequency is too high, the requirements for the discharge system and control precision of the equipment will be higher, increasing the equipment cost and maintenance difficulty. At the same time, the excessively high frequency may cause the reaction to be too frequent, resulting in instability of the reaction system and affecting the quality of the ZrN reinforcing phase and powder performance.

[0043] The second aspect of this application provides a porous spherical zirconia-based powder with a hierarchical porous structure, which is prepared by the method for preparing the porous spherical zirconia-based powder with a hierarchical porous structure.

[0044] In some embodiments, a kernel and a first overlay layer and a second overlay layer disposed on the kernel are included; It should be noted that the kernel includes a multi-level porous structure; The raw materials for the core include a first slurry; The raw material for the first coating layer includes the second slurry; The second coating layer includes ZrN.

[0045] In some embodiments, the loosely spherical zirconia-based powder with a hierarchical porous structure satisfies at least one of the following conditions: (1) The particle size of the loose spherical zirconia-based powder is 20-100 μm; Optionally, the particle size of the loose spherical zirconia-based powder can be any value between 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm or 20-100 μm; It should be noted that when the particle size of the loose spherical zirconia-based powder is 20-100μm, the appropriate particle size range can ensure the uniformity and stability of the powder in application. In thermal barrier coatings, the appropriate particle size can make the coating more uniformly applied to the surface of the component. (2) The sphericity of the loose spherical zirconia-based powder is ≥95%; Optionally, the sphericity of the loose spherical zirconia-based powder can be any value of 95%, 96%, 97%, 98%, 99% or ≥95%; It is important to note that powders with high sphericity have good flowability, which allows them to be distributed more evenly during processes such as spraying and 3D printing, ensuring consistent product quality and reducing agglomeration. (3) The porosity of the loose spherical zirconia-based powder is 30-60%; It should be noted that when the porosity of the loose spherical zirconia-based powder is 30-60%, it can ensure the lightweight properties of the material while meeting the requirements of the thermal barrier coating's thermal insulation performance. Optionally, the porosity of the loose spherical zirconia-based powder can be any value between 30%, 40%, 50%, 60%, or 30-60%. (4) The thickness of the first coating layer is 5-10 μm; Optionally, the thickness of the first coating layer can be any value between 5μm, 6μm, 7μm, 8μm, 9μm, 10μm or 5-10μm; (5) The thickness of the second coating layer is 1-5 μm.

[0046] Optionally, the thickness of the second coating layer can be any value between 1μm, 2μm, 3μm, 4μm, 5μm or 1-5μm.

[0047] A third aspect of this application provides a coating comprising the aforementioned loosely spherical zirconia-based powder having a hierarchical porous structure.

[0048] The implementation schemes of this application will be described in detail below with reference to specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating this application and should not be regarded as limiting the scope of this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used without specified manufacturers are all conventional products that can be purchased commercially.

[0049] Example 1 This embodiment provides a loosely porous spherical zirconia-based powder with a hierarchical porous structure and its preparation method. The specific preparation steps are as follows: S1: The first solid powder and water are mixed and the mixture is wet-milled to obtain a first slurry. The total mass of the first solid powder, based on 100%, includes: 10% zirconium metal powder (particle size 1.5 μm), 7% ZrB2 nanoparticles (particle size 80 nm), 2% carbon nanotubes (particle size 30 nm), 11% PMMA microspheres (particle size 3 μm), and the remainder is multi-component lanthanide-doped zirconium oxide-based fine powder (particle size 2 μm). The mass of water in the first slurry is 45% of the mass of the solid powder. S2: The second solid powder is mixed with water and then wet-milled to obtain a second slurry. The total mass of the second solid powder is 100%, including: 15% hollow SiO2 microspheres (diameter 12μm) and the remainder is multi-component lanthanide-doped zirconium oxide fine powder (particle size 2μm). The mass of water in the second slurry is 45% of the mass of the solid powder. S3: A double-layer nozzle device is used, with the inner layer spraying the first slurry and the outer layer spraying the second slurry. The second slurry is placed on the surface of the first slurry using a spray-freeze-drying process. The ratio of the spraying speed of the first slurry to that of the second slurry is 1:1.3. The spray-freeze-drying process includes a rapid freezing stage and a vacuum drying stage performed sequentially. The temperature of the rapid freezing stage is -80℃; the temperature of the vacuum drying stage is -50℃, the time is 18h, and the vacuum degree is 5Pa, to obtain the composite precursor powder. S4: The spherical composite precursor powder is heat-treated to obtain heat-treated powder; the heat treatment includes a first heat treatment, a second heat treatment and a third heat treatment performed sequentially; the first heat treatment is performed in an inert atmosphere, with a holding temperature of 500℃ and a time of 1 hour; the second heat treatment is performed in air, with a holding temperature of 900℃ and a time of 2 hours; the third heat treatment is performed in air, with a holding temperature of 1200℃ and a time of 1 hour. S5: Under a nitrogen atmosphere, the heat-treated powder is subjected to pulsed plasma in-situ strengthening treatment. The power of the pulsed plasma in-situ strengthening treatment is 30kW, the powder feeding rate is 100g / min, and the pulse frequency is 7Hz, to obtain loose spherical zirconia-based powder with a multi-level porous structure. The particle size of the multi-component lanthanide-doped zirconium oxide fine powder is 2 μm. The raw materials, based on a total mass of 100%, include: 4% Y2O3, 6.5% CeO2, 2% La2O3, and the balance is ZrO2.

[0050] The porous spherical zirconia-based powder with a hierarchical porous structure includes a core and a first coating layer and a second coating layer disposed on the core; the raw material of the core includes a first slurry; the raw material of the first coating layer includes a second slurry; the second coating layer includes ZrN; the particle size of the porous spherical zirconia-based powder is 50 μm; the sphericity is 97%; the porosity is 45%; the thickness of the first coating layer is 7 μm; and the thickness of the second coating layer is 3 μm.

[0051] SEM images of the loosely spherical zirconia-based powder with a hierarchical porous structure are shown below. Figure 1 As shown.

[0052] Example 2 The difference from Example 1 is that the total mass of the first solid powder, calculated as 100%, includes: 8% metallic zirconium powder, 6% ZrB2 nanoparticles, 1.5% carbon nanotubes, 9% PMMA microspheres, and the remainder is multi-component lanthanide-doped zirconium oxide-based fine powder.

[0053] Example 3 The difference from Example 1 is that the total mass of the second solid powder, calculated as 100%, includes: 12% hollow SiO2 microspheres, and the remainder is multi-component lanthanide-doped zirconium oxide-based fine powder.

[0054] Comparative Example 1 The difference from Example 1 is that the first solid powder in step S1 does not contain zirconium powder.

[0055] Comparative Example 2 The difference from Example 1 is that the first solid powder in step S1 does not contain ZrB2 nanoparticles.

[0056] Comparative Example 3 The difference from Example 1 is that the first solid powder in step S1 does not contain carbon nanotubes and PMMA microspheres.

[0057] Comparative Example 4 The difference from Example 1 is that the multi-component lanthanide-doped zirconium oxide fine powder in steps S1 and S2 is replaced with ZrO2, that is, the zirconium oxide fine powder is not doped.

[0058] Comparative Example 5 The difference from Example 1 is that step S2 is not performed. Instead, the first slurry prepared in S1 is directly spray-dried to obtain composite precursor powder, which is then subjected to heat treatment and pulsed plasma in-situ strengthening treatment in sequence.

[0059] Comparative Example 6 The difference from Example 1 is that in step S4, the first heat treatment is carried out in air.

[0060] Comparative Example 7 The difference from Example 1 is that in step S4, the third heat treatment is performed directly.

[0061] Comparative Example 8 The difference from Example 1 is that the pulsed plasma in-situ strengthening treatment in step S5 is not performed.

[0062] Comparative Example 9 The difference from Example 1 is that in step S3, the spraying speed of the first slurry and the spraying speed of the second slurry are set to be the same.

[0063] The loose spherical zirconia-based powders prepared in the above examples and comparative examples were subjected to performance tests, and the specific test results are shown in Table 1.

[0064] Table 1 Performance Tests

[0065] analyze: As can be seen from the above experiments, based on the performance test results, Example 1 (the first solid powder contains 10% zirconium metal powder, 7% ZrB2 nanoparticles, 2% carbon nanotubes, and 11% PMMA microspheres, and the second solid powder contains 15% hollow SiO2 microspheres, and is subjected to complete three-step heat treatment and pulsed plasma strengthening) has the best performance, with a compressive strength of 75 MPa, a surface hardness of 1350 HV, no phase transformation rate at 1300℃×100h, and no cracking after 35 thermal shock cycles; Example 2 (with a slightly reduced ratio of first solid powder zirconium metal powder and PMMA microspheres) and Example 3 (with a slightly adjusted ratio of second solid powder hollow SiO2 microspheres) showed slightly inferior performance compared to Example 1, but were still superior to all comparative examples. The comparative examples, due to the lack of key raw materials (e.g., comparative example 1 lacked zirconium metal powder, comparative example 2 lacked ZrB2 nanoparticles, comparative example 3 lacked dual template agent, and comparative example 4 lacked multi-component doping) or key processes (e.g., comparative example 5 lacked the S2 step, comparative example 6 changed the first heat treatment to an air atmosphere, comparative example 7 lacked the first two heat treatment steps, comparative example 8 lacked plasma strengthening, and comparative example 9 had an inappropriate spraying speed ratio), all exhibited problems such as a sharp drop in compressive strength (minimum 35 MPa), no decrease in high-temperature phase transformation rate (minimum 60%), and a reduction in the number of thermal shock cycles (minimum 12 cycles).

[0066] Therefore, the synergistic effect of raw materials such as multi-component lanthanide doping, zirconium metal powder, ZrB2 nanoparticles, and dual template agents, as well as the progressive process of double-layer spray freeze-drying, three-step heat treatment, and pulsed plasma strengthening, are key to ensuring the "high strength and high stability" of the porous spherical zirconium oxide-based powder. The parameters in Example 1 are adapted to the requirements of high-temperature scenarios such as advanced thermal barrier coatings. Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

[0067] Furthermore, those skilled in the art will understand that although some embodiments herein include certain features included in other embodiments but not others, combinations of features from different embodiments are intended to be within the scope of this application and form different embodiments. For example, any of the claimed embodiments can be used in any combination. The information disclosed in this background section is intended only to enhance the understanding of the general background of this application and should not be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

Claims

1. A method for preparing a porous spherical zirconia-based powder with a hierarchical porous structure, characterized in that, include: A first slurry was obtained by mixing multi-lanthanide-doped zirconium oxide fine powder, metallic zirconium powder, ZrB2 nanoparticles, carbon nanotubes, PMMA microspheres and water. A second slurry was obtained by mixing multi-lanthanide-doped zirconium oxide fine powder, hollow SiO2 microspheres, and water. The second slurry was applied to the surface of the first slurry by spray freeze-drying to obtain spherical composite precursor powder; The spherical composite precursor powder is heat-treated to obtain heat-treated powder. Under a nitrogen atmosphere, the heat-treated powder is subjected to pulsed plasma in-situ strengthening treatment to obtain loose spherical zirconia-based powder with a hierarchical porous structure. The raw materials for the multi-component lanthanide-doped zirconium oxide-based fine powder, based on a total mass of 100%, include: 3-5% Y2O3, 5-8% CeO2, 1-3% La2O3, balance ZrO2.

2. The method for preparing loose spherical zirconia-based powder with a hierarchical porous structure according to claim 1, characterized in that, At least one of the following conditions must be met: (1) In the first slurry, the mass of water is 30-60% of the mass of the solid powder; (2) In the first slurry, the total mass of solid powder, calculated on a 100% basis, includes: 5-15% of the zirconium metal powder, 5-10% of the ZrB2 nanoparticles, 1-3% of the carbon nanotubes, 5-15% of the PMMA microspheres, and the remainder is the multi-component lanthanide-doped zirconium oxide-based fine powder; (3) In the second slurry, the mass of water is 30-60% of the mass of the solid powder; (4) In the second slurry, the total mass of solid powder, calculated on a 100% basis, includes: 10-20% of the hollow SiO2 microspheres, the remainder being the multi-component lanthanide-doped zirconium oxide-based fine powder.

3. The method for preparing loose spherical zirconia-based powder with a hierarchical porous structure according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The particle size of the multi-component lanthanide-doped zirconium oxide-based fine powder is 1-3 μm; (2) The particle size of the zirconium metal powder is 1-2 μm; (3) The particle size of the ZrB2 nanoparticles is 50-100 nm; (4) The carbon nanotubes include nano-carbon nanotubes; (5) The particle size of the PMMA microspheres is 1-5 μm; (6) The diameter of the hollow SiO2 microspheres is 5-20 μm.

4. The method for preparing loose spherical zirconia-based powder with a hierarchical porous structure according to claim 1, characterized in that, During the spray freeze-drying process, the ratio of the spraying speed of the first slurry to the spraying speed of the second slurry is 1:1.2-1.

5.

5. The method for preparing loose spherical zirconia-based powder with a hierarchical porous structure according to claim 1, characterized in that, The spray freeze-drying includes a rapid freezing stage and a vacuum drying stage performed sequentially. The temperature during the rapid freezing stage is -70°C to -90°C; The temperature of the vacuum drying stage is -40℃ to -60℃, the time is 12h to 24h, and the vacuum degree is ≤10Pa.

6. The method for preparing loose spherical zirconia-based powder with a hierarchical porous structure according to claim 1, characterized in that, At least one of the following conditions must be met: (1) The heat treatment includes a first heat treatment, a second heat treatment and a third heat treatment performed sequentially; The first heat treatment is carried out under an inert atmosphere, with a holding temperature of 400-600℃ and a time of 0.5-1.5h; The second heat treatment is carried out in air, with a holding temperature of 800-1000℃ and a time of 1-3 hours; The third heat treatment is carried out in air, with a holding temperature of 1100-1300℃ and a time of 0.5-1.5h; (2) The power of the pulsed plasma in-situ strengthening treatment is 20-40kW, the powder feeding rate is 50-150g / min, and the pulse frequency is 5-10Hz.

7. A loosely shaped zirconia-based powder with a hierarchical porous structure, characterized in that, It is prepared by the method for preparing loose spherical zirconia-based powder with a hierarchical porous structure as described in any one of claims 1-6.

8. The porous spherical zirconia-based powder with a hierarchical porous structure according to claim 7, characterized in that, Includes a kernel and a first and a second overlay layer disposed on the kernel; The raw materials for the core include a first slurry; The raw material for the first coating layer includes the second slurry; The second coating layer includes ZrN.

9. The porous spherical zirconia-based powder with a hierarchical porous structure according to claim 7 or 8, characterized in that, At least one of the following conditions must be met: (1) The particle size of the loose spherical zirconia-based powder is 20-100 μm; (2) The sphericity of the loose spherical zirconia-based powder is ≥95%; (3) The porosity of the loose spherical zirconia-based powder is 30-60%; (4) The thickness of the first coating layer is 5-10 μm; (5) The thickness of the second coating layer is 1-5 μm.

10. A coating, characterized in that, Includes the loose spherical zirconia-based powder with a hierarchical porous structure as described in any one of claims 7-9.

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