Two-component rare earth monosilicate spraying powder with porous structure as well as preparation method and application of two-component rare earth monosilicate spraying powder

Abstract

The invention relates to two-component rare earth monosilicate spraying powder with a porous structure as well as a preparation method and application of the two-component rare earth monosilicate spraying powder, and belongs to the technical field of ceramic powder materials. The problems that in the prior art, rare earth silicate forming a SiC matrix environment barrier coating easily reacts with water vapor or / and CMAS to generate phase change, the thermal expansion coefficient is not matched with a matrix material, and the purity is low, so that the coating is poor in corrosion resistance and prone to falling off and losing efficacy are solved. The chemical formula of the rare earth silicate powder with the porous structure is (RExYb1-x) 2SiO5, RE is a rare earth element, and x is equal to 0.1-0.9; the average particle size of the powder is 20-45 [mu] m, the porosity is 30-60%, and the pore diameter is 1-5 [mu] m; in a thermal cycle process, the powder has relatively high phase stability and relatively low thermal conductivity and thermal expansion coefficient; the rare earth silicate is prepared by combining a template method with a sol-gel method, and compared with an existing solid phase method, the rare earth silicate is high in product purity, controllable in morphology and structure, low in synthesis temperature, capable of forming porous powder at a time and easy to operate.

Description

Technical Field

[0001] The present invention relates to the technical field of ceramic powder materials, and in particular to a porous dual-component rare earth monosilicate spray powder, a preparation method thereof, and applications thereof. Background Art

[0002] Environmental barrier coatings (EBCs) can create a barrier between SiC ceramic-matrix composites and the corrosive gas environment, preventing or mitigating corrosion and damage to high-temperature structural components caused by water vapor and CMAS, thereby improving the service life and safety and reliability of hot-end components. Rare earth silicates are popular candidates for EBCs due to their excellent thermal expansion coefficient matching with the SiC matrix, chemical compatibility, low water vapor volatility, low oxygen permeability, and resistance to molten salt corrosion.

[0003] Although the thermal expansion coefficient of the double silicate RE2Si2O7 is (4.1-6.0)×10 -6 / ℃, and the thermal expansion coefficient of SiC matrix material (4.7×10 -6 / ℃) is very well matched, but the existence of multiple crystal forms and phases makes the material prone to phase changes during thermal cycling, leading to coating peeling. In a water-oxygen corrosion environment, RE2Si2O7 reacts with water vapor to form volatile substances, resulting in impure components in the coating, forming a mixture of RE2Si2O7 and RE2SiO5, which makes the coating prone to failure. In a CMAS corrosion environment, RE2Si2O7 / RE2SiO5 easily reacts with molten CMAS to form apatite-structured substance, which quickly penetrates into the coating and accelerates its failure. The above factors pose challenges to the engineering application of RE2Si2O7 as a coating material.

[0004] Although the current monosilicate RE2SiO5 has excellent high temperature phase stability and corrosion resistance, its thermal expansion coefficient is relatively high, about (7-9)×10 -6 K -1 , which directly affects the thermal matching between the coating and the substrate material, thereby affecting the adhesion and durability of the coating.

[0005] It can be seen that the physicochemical properties of rare earth silicate materials have a decisive influence on the performance of EBC. The physicochemical properties of rare earth silicate materials depend not only on their composition but also on the preparation process. Currently, the preparation method of rare earth monosilicates is mostly solid-phase method. This process is relatively mature, but it is easy to introduce impurities during the preparation process, resulting in poor powder composition uniformity and large particles. In addition, rare earth oxides generally have high melting points. The solid-phase method of preparing rare earth silicate powder generally requires long-term calcination at high temperature (1500-1700℃), which is energy-intensive and costly. The synthesized powder has low phase purity and is prone to decomposition, which affects the performance of the coating.

[0006] Therefore, there is an urgent need to design a rare earth silicate material with a stable phase structure and a low thermal expansion coefficient and a preparation method thereof to improve the adhesion, corrosion resistance and thermal matching of the rare earth silicate EBC with the substrate. Summary of the Invention

[0007] In view of the above analysis, the embodiments of the present invention aim to provide a porous dual-component rare earth monosilicate spray powder, a preparation method, and an application thereof, to solve at least one of the problems in the prior art of the rare earth silicates constituting the SiC substrate environmental barrier coating being easily susceptible to phase change by reaction with water vapor and / or CMAS, the mismatch between the thermal expansion coefficient and the substrate material, and the low purity resulting in poor corrosion resistance of the coating and easy shedding and failure.

[0008] In a first aspect, an embodiment of the present invention provides a rare earth silicate powder with a porous structure, wherein the chemical formula of the rare earth silicate is (RE x Yb 1-x )2SiO5, wherein RE is a rare earth element selected from any one of Y, Lu, Er, Sc, and Ho, and x=0.1 to 0.9.

[0009] Furthermore, the average particle size of the rare earth silicate powder is 20 to 45 μm.

[0010] Furthermore, the porosity of the rare earth silicate powder is 30-60%, and the diameter of the pores is 1-5 μm.

[0011] Furthermore, the rare earth silicate has a single X2-type phase structure and a purity of 95-99%.

[0012] Furthermore, the thermal conductivity of the rare earth silicate powder material is (1.3-2.2) W·m -1 ·K -1 , the thermal expansion coefficient is (5.5~6.4)×10 -6 / ℃.

[0013] In a second aspect, an embodiment of the present invention provides a method for preparing a porous rare earth silicate powder, the method comprising:

[0014] (1) preparing a polymethyl methacrylate template agent suspension;

[0015] (2) adding the template agent suspension to a mixed solution of a silicon source and a rare earth element source to react and obtain a gel;

[0016] (3) The gel is dried and calcined.

[0017] Furthermore, the rare earth element source includes an RE source and a Yb source in a molar ratio of 9:1 to 1:9, and RE is selected from any one of Y, Lu, Er, Sc, and Ho.

[0018] Furthermore, in step (1), the particle size of the polymethyl methacrylate template is 0.5 to 2.5 μm.

[0019] Furthermore, in step (1), the concentration of the polymethyl methacrylate in the suspension is 1.2 to 1.5 g / L.

[0020] Furthermore, in step (2), the silicon source is at least one of Na2SiO3·9H2O and tetraethyl orthosilicate.

[0021] Furthermore, the RE source is at least one of RE(NO3)3·6H2O and RECl3·6H2O, and RE is selected from any one of Y, Lu, Er, Sc, and Ho.

[0022] Furthermore, the Yb source is at least one of Yb(NO3)3·6H2O and YbCl3·6H2O.

[0023] Furthermore, the molar ratio of the silicon source to the rare earth source is 1:2 to 1.2:2.

[0024] Furthermore, in step (2), the reaction conditions are: reaction at a temperature of 60-80° C. for 3 to 5 hours.

[0025] Furthermore, in step (3), the drying temperature is 80-100° C. and the drying time is 1-3 hours.

[0026] Furthermore, the calcination condition is: maintaining the temperature at 1100-1250° C. for 2-4 hours.

[0027] In a third aspect, an embodiment of the present invention provides a use of the above-mentioned porous rare earth silicate powder in an environmental barrier coating.

[0028] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0029] 1. The rare earth silicate disclosed in the present invention is a two-component rare earth monosilicate. As one of the two components, Yb has a smaller ionic radius and is not easy to react with CMAS to affect the coating effect. Compared with the existing single-component rare earth silicate, the addition of another component causes the lattice distortion of ytterbium monosilicate, reduces the thermal conductivity and thermal expansion coefficient, and can ensure the phase stability of the rare earth monosilicate. In addition, the introduction of RE 3+ It can inhibit the formation of apatite structure of rare earth silicates in water, oxygen or CMAS corrosion environment, while RE 3+ The compositional deviation between grain boundaries and grain surfaces improves the coating's resistance to water-oxygen corrosion and CMAS corrosion. By selecting the cationic rare earth components and limiting their ratios, the thermal conductivity and thermal expansion coefficient of the rare earth monosilicate are reduced while improving its phase stability during thermal cycling, thereby enhancing the adhesion and corrosion resistance of the rare earth monosilicate environmental barrier coating in specific applications.

[0030] 2. The porous rare earth silicate powder of the present invention is nearly spherical, with an average particle size of 20-45 μm, a porosity of 30-60%, and a pore diameter of 1-5 μm. The micron-scale porous structure uniformly present in the powder can effectively reduce the thermal conductivity and thermal expansion coefficient of the powder, making it suitable for the preparation of environmental barrier coatings for high-temperature resistant SiC ceramic-based thermal structural materials. The thermal conductivity of the rare earth silicate powder of the present invention is (1.3-2.2) W·m -1 ·K -1 , the thermal expansion coefficient is (5.5~6.4)×10 -6 / ℃, and the thermal expansion coefficient of SiC ceramic matrix composite material (4.7×10 -6 / ℃) is close; compared with the single main element rare earth monosilicate powder, the thermal expansion coefficient of the dual-component rare earth monosilicate of the present invention is reduced by 21.4 to 28.8%.

[0031] 3. The present invention adopts a template method combined with a sol-gel process to prepare the rare earth silicate. Compared with the existing solid-phase preparation method of rare earth silicate, it can realize molecular-level reaction between raw materials, improve the degree of reaction, and obtain a product with high purity, controllable morphology and structure, low synthesis temperature, and one-time forming of porous powder without the need for complex subsequent processing technology. It is simple to operate and has a fast preparation speed.

[0032] 4. During the gel preparation process, the present invention controls parameters such as the PMMA template particle size and distribution, addition amount, and distribution uniformity, which influence the structural morphology of the resulting two-component rare earth monosilicate, including size, porosity, pore size, and uniformity, thereby affecting the product performance of the two-component rare earth monosilicate of the present invention. Specifically, the PMMA template employed in the present invention has a particle size of 0.5 to 2.5 μm. To improve the uniformity of the template distribution, the template is prepared as a suspension and added to the raw material precursor solution in this form to produce a product with uniform internal pore size distribution and controllable size. The concentration of the PMMA template in the suspension is 1.2-1.5 g / L.

[0033] 5. In order to control the size, porosity, and internal pore structure of the obtained two-component rare earth monosilicate within the required range, the present invention regulates the drying temperature of the gel obtained by the reaction to be 80-100°C. Low-temperature drying is conducive to forming a pore structure with uniform distribution and small pore size, which is conducive to maintaining the integrity and stability of the gel skeleton. However, too low a temperature affects production efficiency; too high a drying temperature causes the solvent to evaporate quickly, and the surface tension of the liquid inside the pores increases, which may cause the pores to merge or collapse, making the pore structure uneven and the pore size distribution widened, ultimately leading to changes in or even destruction of the gel skeleton.

[0034] 6. The present invention controls the temperature of subsequent calcination of the dry gel to 1100-1250°C. When the PMMA template agent is removed, high temperature is beneficial to improving the crystallinity of the powder and reducing the impurity content. However, too high a temperature will affect the pore structure inside the gel, resulting in a wider pore size distribution, uneven pore structure, and even reduced porosity. In addition, compared with the existing solid-phase method, the calcination temperature of the present invention is greatly reduced, reducing energy consumption and cost.

[0035] 7. The coating produced by thermal spraying the powder has a uniform structure and a porosity adjustable within a range of 5-15%. This reduces the thermal conductivity and thermal expansion coefficient of the coating, thereby significantly improving the thermal cycling stability and thermal insulation effect of the environmental barrier coating. After 3,000 thermal cycles at 1,400°C, the coating produced from the powder exhibited no surface defects such as cracks or flaking.

[0036] In the present invention, the above-mentioned technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of the present invention will be described in the following description, and some advantages will become apparent from the description or be learned through practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The accompanying drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like parts throughout the drawings.

[0038] Figure 1 The porous structure of ytterbium yttrium monosilicate (Y 0.2 Yb 0.8 ) SEM scanning image of 2SiO5 nanopowder;

[0039] Figure 2 XRD spectrum of the porous ytterbium yttrium monosilicate nanopowder prepared in Example 1 of the present invention;

[0040] Figure 3 This is an XRD spectrum of the porous ytterbium-scandium monosilicate nanopowder prepared in Example 2 of the present invention;

[0041] Figure 4 This is a graph showing the test results of thermal conductivity of porous ytterbium yttrium monosilicate nanopowder prepared in Example 1 of the present invention from room temperature to 1350°C;

[0042] Figure 5 This is a graph showing the test results of the thermal expansion coefficient of the porous ytterbium-scandium monosilicate nanopowder prepared in Example 2 of the present invention from room temperature to 1350° C.;

[0043] Figure 6 This is a macroscopic image of the surface morphology of the coating of the EBC prepared by spraying the ytterbium yttrium monosilicate nanopowder of Example 1 after 3000 thermal cycles at 1400°C;

[0044] Figure 7 This is the powder morphology obtained in Comparative Example 1. DETAILED DESCRIPTION

[0045] The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein the accompanying drawings constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0046] Environmental barrier coating (EBC) can establish a barrier between SiC ceramic-based composites and the gas corrosive environment, and can prevent or slow down the corrosion and damage of water vapor and CMAS to high-temperature components of composite materials. Rare earth silicates have become a popular candidate material for environmental barrier coatings due to their own characteristics.

[0047] However, during thermal cycling, existing rare earth disilicates are prone to phase change, reaction with water vapor, and reaction with molten CMAS due to their various crystal forms, leading to coating peeling and failure. While existing rare earth monosilicates have excellent high-temperature phase stability, their high thermal expansion coefficient directly affects the thermal compatibility between the coating and the substrate material, thereby affecting the coating's adhesion and durability.

[0048] Therefore, the present invention provides a porous rare earth silicate powder, the chemical formula of the rare earth silicate is (RE x Yb 1-x )2SiO5, wherein RE is a rare earth element selected from any one of Y, Lu, Er, Sc, and Ho, and x=0.1 to 0.9.

[0049] RE 3+ When Yb is introduced into monosilicate, the presence of the two components causes lattice distortion of the monosilicate crystal. This lattice distortion triggers the high entropy effect in the thermodynamics of the material, stimulates the diffusion hysteresis effect in the kinetics of the material and the cocktail effect of performance improvement, thereby inhibiting the formation of apatite structure of rare earth silicate in water-oxygen or CMAS corrosion environment. 3+ The composition deviation between grain boundaries and grain surfaces will improve the coating's resistance to water-oxygen corrosion and CMAS corrosion.

[0050] Specifically, the rare earth element Yb has a smaller ionic radius, and the Yb2SiO5 material with X2-crystal form has the most beneficial comprehensive performance in corrosion resistance, thermal properties and elastic properties among many rare earth silicate materials.

[0051] Specifically, in the chemical formula (RE x Yb 1-x )2SiO5, the value range of x is 0.1-0.9, and the molar ratio of RE to Yb is limited to 1:9 to 9:1, which helps to ensure the structural stability and phase stability of the material.

[0052] According to some preferred embodiments of the present invention, the value of x can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 or 0.9, and accordingly, the molar ratio of RE to Yb can be 1:9, 1:4, 3:7, 2:3, 1:1, 3:2, 7:3, 4:1 or 9:1.

[0053] It should be noted that in order to improve the effect and efficiency of the rare earth silicate powder in the process of preparing the coating through the thermal spraying process, on the basis of ensuring its bonding strength with the substrate, the prepared coating has a certain porosity to reduce the thermal conductivity and thermal expansion coefficient of the coating, thereby improving the thermal cycling stability and thermal insulation effect of the environmental barrier coating. The present invention needs to limit the particle size of the rare earth silicate powder.

[0054] Specifically, the average particle size of the rare earth silicate powder is 20 to 45 μm. If the particle size is too large, the powder will not fully melt during the thermal spraying process, which can easily lead to an increase in unmelted (unmelted) particles in the coating, affecting the coating quality and reducing its bonding stability and corrosion resistance to the substrate. If the particle size is too small, the spray gun barrel will clog and the powder will be easily blown away by the recoil airflow, affecting the spraying efficiency. However, if the particle size is too small, it will also affect the bonding strength between the coating and the substrate.

[0055] Specifically, according to some preferred embodiments of the present invention, the particle size of the rare earth silicate powder can be any value in the range of 20 to 45 μm, such as 20 μm, 23 μm, 25 μm, 27 μm, 30 μm, 32 μm, 35 μm, 38 μm, 40 μm, 43 μm or 45 μm.

[0056] It should be noted that in order to make the dual-component rare earth element monosilicate powder not only have lower thermal conductivity and thermal expansion coefficient, but also ensure the cohesive strength of the coating prepared therefrom, the present invention needs to adjust the porosity and pore size of the powder.

[0057] Specifically, the porosity of the dual-component rare earth element monosilicate powder is 30-60%. Although a higher porosity can reduce the thermal conductivity and thermal expansion coefficient of the powder and coating, an excessively high porosity will affect the hardness and strength of the coating and lead to a reduction in the corrosion resistance of the coating.

[0058] According to some preferred embodiments of the present invention, the porosity of the binary rare earth element monosilicate powder is any value in the range of 30% to 60%, such as 30%, 33%, 35%, 37%, 40%, 42%, 45%, 48%, 50%, 53%, 55%, 57% or 60%.

[0059] Specifically, the pore diameter of the dual-component rare earth element monosilicate powder is 1 to 5 μm. Although a larger pore diameter will reduce the thermal conductivity and thermal expansion coefficient of the powder, a larger pore diameter will affect the hardness and strength of the prepared coating and reduce the corrosion resistance of the coating.

[0060] According to some preferred embodiments of the present invention, the pore diameter of the two-component rare earth element monosilicate powder is any value in the range of 1 to 5 μm, such as 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm or 5 μm, and the pore diameter in the same powder can also be a range value between any two values within the above range.

[0061] It should be noted that the rare earth silicate described herein has a single X2-type crystalline phase structure with a purity of 95-99%. This single X2-type phase structure is relatively stable, is less susceptible to phase transitions during thermal cycling, and is less likely to react with water, oxygen, or CMAS. It also contains fewer impurities and has high purity, ensuring uniformity of powder composition and improving stability.

[0062] Specifically, the thermal conductivity of the rare earth silicate powder of the present invention is (1.3-2.2) W·m -1 ·K -1 , the thermal expansion coefficient is (5.5~6.4)×10 -6 / ℃, which is much lower than the thermal expansion coefficient of existing monosilicates (7-9)×10 -6 K -1 , which is close to the thermal performance parameters of SiC ceramic substrate composite materials (4.7×10-6 / ℃) and has high thermal matching with the substrate.

[0063] The present invention also discloses a method for preparing the above-mentioned porous rare earth silicate powder, the method comprising:

[0064] (1) preparing a polymethyl methacrylate template suspension;

[0065] (2) adding the template agent suspension to a mixed solution of a silicon source and a rare earth source to react and obtain a gel;

[0066] (3) The gel is dried and calcined.

[0067] In the step (1), considering that polymethyl methacrylate (PMMA) has the advantages of low density, high mechanical strength, easy processing, low cost, and low melting point, which is conducive to forging removal, the present invention uses PMMA as the template.

[0068] It should be noted that during the gel preparation process, in order to control the structural morphology of the two-component rare earth monosilicate, including size, porosity, pore size and uniformity, and improve its performance in preparing a coating on the surface of a SiC substrate, the present invention requires the regulation of the added PMMA template particles, including parameters such as particle size and distribution, addition amount, and distribution uniformity.

[0069] Specifically, in step (1), in order to ensure that the pore size of the obtained two-component rare earth monosilicate powder meets the requirements, the PMMA template particles used in the present invention have a particle size of 0.5 to 2.5 μm and a uniform and concentrated particle size distribution, so that product particles with uniform pore size can be obtained. The gel material prepared using the template agent within this particle size range is subsequently dried and calcined to obtain a two-component rare earth monosilicate powder with a pore diameter of 1 to 5 μm.

[0070] According to some preferred embodiments of the present invention, the particle size of the PMMA template agent particles can be 0.5 μm, 1 μm, 1.5 μm, 2 μm, or 2.5 μm.

[0071] It should be noted that the uniformity and stacking mode of the template particles in the reaction solution will also affect the porosity, pore diameter and uniformity of the final product material, so the presence state of the added PMMA template needs to be limited.

[0072] Specifically, in step (1), in order to better control the amount of PMMA template added and the uniformity of its dispersion in the solution after addition, the present invention configures the template into a suspension and adds it to the raw material precursor solution in the form of a suspension.

[0073] More specifically, in order to improve the degree of suspension and dispersion of the PMMA template particles, the present invention adds a dispersant such as PEG (polyethylene glycol) or polyacrylic acid (PAA) to the suspension, and the added mass is 0.5%-1.2% of the mass of the PMMA template. It should be noted that the relative molecular weight of the dispersant needs to reach 10 4 .

[0074] It should be noted that pH will affect the direction and morphology of material crystal growth. The present invention requires controlling the pH of the PMMA template suspension.

[0075] Specifically, the present invention adds citric acid to the suspension to adjust the pH value within the range of 3-9; according to some preferred embodiments of the present invention, the concentration of citric acid is 0.1-0.2 mol / L, which can be 0.12 mol / L, 0.15 mol / L, 0.18 mol / L, or 0.2 mol / L.

[0076] According to some preferred embodiments of the present invention, the PMMA suspension can be prepared by the following method: first, a citric acid solution with a concentration of 0.1 to 0.2 mol / L is prepared, and then 1.2 to 1.5 g of PMMA powder with a particle size of 0.5 to 2.5 μm is added to the solution, stirred evenly, and an appropriate amount of PEG is added as a dispersant, and ultrasonic dispersion is performed to obtain a suspension M.

[0077] It should be noted that the present invention adopts existing technology to prepare PMMA particles, which can be suspension polymerization, emulsion polymerization, dispersion polymerization, seed swelling polymerization, etc., and the present invention preferably adopts emulsion polymerization.

[0078] It should be noted that in the emulsion polymerization method of PMMA particles, the type and amount of the emulsifier are crucial to the stability of the dispersion medium.

[0079] Specifically, the present invention preferably uses sodium dodecyl sulfate (SDS) emulsifier, and the mass ratio of SDS to MMA is in the range of 1:6 to 1:20.

[0080] It should be noted that the type and amount of the initiator affect the polymerization reaction rate and the particle size of the particles.

[0081] Specifically, the present invention preferably uses ammonium persulfate (APS) as an initiator, and the mass ratio of the initiator to MMA is in the range of 1:50 to 1:150.

[0082] According to some preferred embodiments of the present invention, the specific steps of preparing PMMA particles by emulsion polymerization include: adding deionized water and emulsifier sodium dodecyl sulfate (SDS) in a three-necked flask in sequence to obtain an aqueous solution with a concentration of 0.5-1.5wt%, stirring and heating to 65-75°C, adding 0.1-0.2wt% ammonium persulfate (APS), and after complete dissolution, starting to add 15-10wt% MMA dropwise, and the addition is completed within 1.5h to 2h; after the reaction is completed, breaking the emulsion with an appropriate amount of saturated sodium chloride solution; centrifuging, washing with deionized water three times, and drying in a vacuum oven at 60°C.

[0083] According to some preferred embodiments of the present invention, in step (2), the specific steps of preparing the mixed solution N of the silicon source and the rare earth element source are as follows:

[0084] Prepare rare earth element salt solution A: Dissolve Yb(NO3)3·6H2O and RE salt in a stoichiometric mixture of anhydrous ethanol and deionized water, wherein the volume ratio of ethanol to water is 5:1 and the concentration of rare earth salt is 0.1-0.9 mol / L. Add dilute ammonia dropwise to the mixture until the pH reaches 9-10.

[0085] Prepare silicon source solution B: Add Na2SiO3·9H2O to deionized water to prepare a solution with a concentration of 0.6-1.2 mol / L. Add HCl solution to the solution to adjust the pH value to within the range of 1.1-2.

[0086] Solution A and solution B are thoroughly mixed to obtain a mixed solution N of a silicon source and a rare earth element source, wherein the molar ratio of the silicon source to the rare earth element source in the mixed solution is 1:2 to 1.2:2.

[0087] The present invention can replace Yb(NO3)3·6H2O with YbCl3·6H2O; the RE salt can be at least one of RE(NO3)3·6H2O and RECl3·6H2O; and the silicon source can also be tetraethyl orthosilicate.

[0088] It should be noted that in order to ensure the purity, porosity, pore size and uniformity of the obtained binary rare earth element monosilicate, the rate of addition of the PMMA template needs to be controlled to improve the uniformity of the template added to the reaction solution.

[0089] Specifically, in step (2), the present invention adds the PMMA suspension dropwise into the mixed solution of the silicon source and the rare earth element source.

[0090] More specifically, the present invention uses a dropping speed of 4ml / min-6ml / min to add the PMMA template suspension to the solution N. If the dropping speed is too fast, the PMMA is unevenly dispersed in the solution and is prone to agglomeration, resulting in a decrease in the porosity of the material and local densification, affecting the effective reduction of the thermal conductivity and thermal expansion coefficient of the powder material. The unevenness of the PMMA template will lead to uneven internal stress of the gel material, which is prone to shrinkage and deformation during subsequent drying and calcining treatments, thereby affecting dimensional stability. However, the delivery rate cannot be too slow to prevent affecting production efficiency.

[0091] According to some preferred embodiments of the present invention, the dropping rate of the PMMA template suspension can be 4 ml / min, 4.2 ml / min, 4.5 ml / min, 4.8 ml / min, 5 ml / min, 5.3 ml / min, 5.5 ml / min, 5.8 ml / min, or 6 ml / min.

[0092] Specifically, in order to increase the porosity of the two-component rare earth monosilicate powder, the present invention controls the mass ratio of the added polymethyl methacrylate (PMMA) template to the added silicon source to be 0.1:1 to 0.35:1. If too much is added, the porosity of the two-component rare earth monosilicate powder obtained after the reaction is too high, affecting the hardness and strength of the coating in practical applications; if too little is added, the porosity of the two-component rare earth monosilicate powder after the reaction is too low, which has limited effect on reducing the thermal conductivity and thermal expansion coefficient of the powder and coating, thereby affecting its thermal matching performance with the SiC substrate.

[0093] According to some preferred embodiments of the present invention, the ratio of the mass of the PMMA template to the mass of the silicon source can be 0.1:1, 0.15:1, 0.2:1, 0.25:1, 0.3:1, or 0.35:1.

[0094] It should be noted that, in order to further improve the uniformity of the dispersion of the PMMA template in the reaction solution, the present invention preferably performs ultrasonic treatment on the reaction solution for generating the gel.

[0095] It should be noted that, in order to ensure the smooth reaction of the raw materials and prevent the decomposition of the PMMA template, the temperature and time of the gel formation reaction need to be regulated.

[0096] Specifically, the reaction temperature in step (2) of the present invention is 60-80°C and the reaction time is 3-5 hours. A too high reaction temperature will lead to an uneven internal structure of the gel and uneven pore distribution. A too low reaction temperature will lead to an insufficiently tight gel structure, too low strength, and easy deformation. A too short reaction time will result in an incomplete reaction and an imperfect cross-linked network structure, thereby affecting the strength and stability of the gel and making it prone to deformation and cracking. However, a too long reaction time will promote excessive growth and merging of micelles, thereby expanding the pore diameter and widening the pore size distribution.

[0097] According to some preferred embodiments of the present invention, in step (2), the temperature of the gel reaction is any value in the range of 60-80°C, such as 60°C, 63°C, 65°C, 68°C, 70°C, 72°C, 76°C, and 80°C; and the reaction time can be 3h, 3.5h, 4h, 4.5h, or 5h.

[0098] It should be noted that in order to control the size, porosity and internal pore structure of the obtained two-component rare earth monosilicate within the required range, the present invention needs to control the temperature and time of drying the gel.

[0099] Specifically, the present invention regulates the drying temperature of the gel prepared by the reaction to be 80-100°C. Low-temperature drying is conducive to forming a pore structure with uniform distribution and small pore size, which is conducive to maintaining the integrity and stability of the gel skeleton. However, too low a temperature affects production efficiency; too high a drying temperature causes the solvent to evaporate quickly, increasing the surface tension of the liquid inside the pores, which may cause the pores to merge or collapse, making the pore structure uneven and the pore size distribution wider, ultimately leading to changes in or even destruction of the gel skeleton.

[0100] According to some preferred embodiments of the present invention, the temperature for drying the gel is any temperature within the range of 80-100°C, such as 80°C, 85°C, 90°C, 95°C or 100°C.

[0101] More specifically, the drying time of the gel prepared by regulating the reaction in the present invention is 3-5 hours. If the drying time is too short, the water inside the gel will not be fully evaporated, the shrinkage will be incomplete, the gel skeleton strength will be insufficient, and it will be easy to deform. However, if the drying temperature is too long, local shrinkage will be excessive, resulting in structural collapse or pore closure, uneven internal stress, and reduced porosity and structural stability.

[0102] According to some preferred embodiments of the present invention, the drying time for the gel can be 3 h, 3.5 h, 4 h, 4.5 h, or 5 h.

[0103] It should be noted that in order to remove the template in the dried gel and ensure the structural composition of the two-component rare earth element monosilicate, the present invention needs to control the calcination temperature and time.

[0104] Specifically, the present invention calcines the dried gel at a temperature of 1100-1250°C. High temperatures are beneficial for increasing the crystallinity of the powder and reducing the impurity content, but excessively high temperatures can affect the pore structure inside the gel, leading to a wider pore size distribution, an uneven pore structure, and even a reduction in porosity. In addition, compared with the existing solid-phase method that requires increasing the temperature to above the melting point of the raw materials (1500-1700°C), the present invention greatly reduces the template removal calcination temperature, thereby reducing energy consumption and costs.

[0105] According to some preferred embodiments of the present invention, the calcination temperature of the dried gel is any value within the range of 1100-1250°C, such as 1100°C, 1130°C, 1150°C, 1175°C, 1200°C, 1230°C, and 1250°C.

[0106] Specifically, the present invention calcines the dried gel for 2-4 hours. The crystallinity of the material increases with calcination time, thereby improving the purity of the product. However, if the calcination time is too long, pores may merge or collapse, resulting in a localized dense internal structure and reduced porosity. This may also lead to internal cracks or defects, affecting the high-temperature stability of the powder and the coating prepared therefrom.

[0107] According to some preferred embodiments of the present invention, the calcination time of the dried gel can be 2 h, 2.5 h, 3 h, 3.5 h, or 4 h.

[0108] The present invention adopts a template method combined with a sol-gel process to prepare the rare earth silicate. Compared with the existing rare earth silicate solid-phase preparation method, the present invention can realize molecular-level reaction between raw materials, improve the reaction degree, obtain a product with high purity, controllable morphology and structure, and has a low synthesis temperature. Porous powder can be formed in one step without the need for complex subsequent processing processes, and the operation is simple and the preparation speed is fast.

[0109] The physicochemical properties of the rare earth silicate nanopowder prepared by the method of the present invention are the same as those of the rare earth silicate nanopowder described in the first aspect, and will not be described in detail here.

[0110] The present invention also provides an application of porous rare earth silicate powder in an environmental barrier coating (EBC).

[0111] The coating prepared from the powder by thermal spraying has a uniform structure and an adjustable porosity within the range of 5 to 15%, which can reduce the thermal conductivity and thermal expansion coefficient of the coating, thereby significantly improving the thermal cycle stability and thermal insulation effect of the environmental barrier coating.

[0112] According to some preferred embodiments of the present invention, the above-mentioned rare earth silicate powder is coated on the surface of the SiC ceramic-based composite material using thermal spraying technology. When the coating thickness is 0.1 to 0.35 mm, the EBC is cycled 3000 times in an air-cooled environment at a temperature of 1400°C. It is found that the EBC prepared using the rare earth silicates of Examples 1-5 is in good condition, with no apparent peeling, cracking, flaking or other adverse phenomena. By observation under 1400°C conditions, it has good resistance to water vapor and CMAS corrosion.

[0113] The technical solutions of the present invention are further illustrated by using the following examples and comparative examples.

[0114] Examples 1-5

[0115] The porous structure of the dual-component rare earth silicate nanopowder material is prepared by a template method combined with a sol-gel method, which specifically includes the following steps:

[0116] S1: Preparation of polymethyl methacrylate (PMMA) microparticle templates by emulsion polymerization:

[0117] Deionized water and sodium dodecyl sulfate (SDS) were sequentially added to a three-necked flask to obtain an aqueous solution with a concentration of 0.5-1.5 wt.%, and the solution was heated to 65-75°C with stirring. 0.1-0.2 wt.% ammonium persulfate (APS) was added. After complete dissolution, 15-10 wt.% methyl methacrylate (MMA) was added dropwise over a period of 1.5-2 hours. After the reaction was complete, an appropriate amount of saturated sodium chloride solution was used to break the emulsion. The solution was centrifuged, washed three times with deionized water, dried in a vacuum oven at 60°C, and ground to obtain fluffy PMMA particles.

[0118] S2: Prepare PMMA suspension:

[0119] A 0.1-0.2 mol / L citric acid aqueous solution is prepared with deionized water, and then 1.2-1.5 g / L of PMMA particles prepared in step S1 are added to the solution, stirred evenly, and an appropriate amount of PEG dispersant is added, followed by ultrasonic dispersion to obtain a suspension M;

[0120] S3: Preparation of silicon source-rare earth source solution N:

[0121] Prepare rare earth salt solution A: Dissolve Yb(NO3)3·6H2O and RE salt in a stoichiometric mixture of anhydrous ethanol and deionized water (5:1 by volume) and a rare earth salt concentration of 0.1-0.9 mol / L. Add dilute ammonia dropwise to the mixture until the pH reaches 9-10.

[0122] Prepare silicon source solution B by adding Na2SiO3·9H2O to deionized water to prepare a solution with a concentration of 0.6-1.2 mol / L. Add HCl solution to the solution to adjust the pH value to the range of 1.1-2.

[0123] Solution A and solution B are thoroughly mixed to obtain a mixed solution N of a silicon source and a rare earth source, wherein the molar ratio of the silicon source to the rare earth element source in the mixed solution is 1:2 to 1.2:2.

[0124] S4: Suspension M is added dropwise to solution N at a rate of 4 ml / min-6 ml / min, and ultrasonically reacted in water at 60-80°C for 3-5 hours until the solution forms a gel, and the gel is dried and dehydrated at 80-100°C for 3-5 hours to form a xerogel;

[0125] S5: calcining the dry gel in S4 at a temperature of 1100° C. to 1250° C. for 2 to 4 hours to obtain a dual-component rare earth silicate thermal spraying powder material with a porous structure.

[0126] The RE salts used in Examples 1-5, process parameters, obtained products and their characterization data are shown in Table 1:

[0127] Table 1 Process parameters and product performance parameters of Examples 1-5

[0128]

[0129]

[0130] Comparative Example 1 is a single-component rare earth silicate Yb2SiO5 prepared by a solid-phase method and purchased from the market.

[0131] As shown in Table 1, the rare earth silicate powder prepared by the template method combined with the sol-gel process in the present invention is nearly spherical, with an average particle size of 20 to 45 μm, a porosity of 30 to 60%, and a pore diameter of 1 to 5 μm. The micron-scale porous structure uniformly present in the powder can effectively reduce the thermal conductivity and thermal expansion coefficient of the powder, making it suitable for preparing environmental barrier coatings for high-temperature resistant SiC ceramic-based thermal structural materials. The thermal conductivity of the rare earth silicate powder of the present invention is (1.3-2.2) W·m -1 ·K -1 , the thermal expansion coefficient is (5.5~6.4)×10 -6 / ℃, and the thermal expansion coefficient of SiC ceramic matrix composite material (4.7×10 -6 / ℃) is close; compared with the single main element rare earth monosilicate powder, the thermal expansion coefficient of the dual-component rare earth monosilicate of the present invention is reduced by 21.4% to 28.8%.

[0132] In addition, compared with the existing rare earth silicate solid-phase preparation method, it can realize molecular-level reactions between raw materials, improve the degree of reaction, and obtain products with high purity, controllable morphology and structure. The synthesis temperature is low, porous powder can be formed in one step, and no complicated subsequent processing process is required. The operation is simple and the preparation speed is fast.

[0133] Figure 2 This is the XRD spectrum of the porous ytterbium yttrium monosilicate powder prepared by Example 1 of the present invention. As can be seen from the figure, the XRD characteristic peaks of the prepared ytterbium yttrium monosilicate powder are completely consistent with the standard PDF cards of X2-Y2SiO5 and X2-Yb2SiO5, and no other miscellaneous peaks appear.

[0134] Figure 3 This is the XRD spectrum of the porous ytterbium-scandium monosilicate powder prepared by Example 2 of the present invention. As can be seen from the figure, the XRD characteristic peaks of the prepared ytterbium-scandium monosilicate are completely consistent with the standard PDF cards of X2-Y2SiO5 and X2-Sc2SiO5, and no other miscellaneous peaks appear.

[0135] Figure 4 The thermal conductivity coefficient test results of the porous ytterbium yttrium monosilicate powder prepared in Example 1 of the present invention from 0°C to 1350°C are shown in the figure. It can be seen from the figure that within the temperature range of 0-1350°C, (Y 0.2 Yb 0.8 )2SiO5 has a lower thermal conductivity than Y2SiO5.

[0136] Figure 5 The thermal expansion coefficient test results of the porous structure of ytterbium-scandium monosilicate powder prepared in Example 2 of the present invention from 25°C to 1350°C are shown in the figure. It can be seen from the figure that from room temperature to 1350°C, (Y 0.2 Yb 0.8 The thermal expansion coefficient of )2SiO5 powder is significantly smaller than that of Y2SiO5.

[0137] Figure 7 This is the morphology of the Yb2SiO5 powder in Comparative Example 1. It can be seen from the figure that the powder is relatively dense and does not have a loose and uniform porous structure.

[0138] Application Examples

[0139] Using thermal spraying process, respectively using the (Y 0.2 Yb0.8 )2SiO5 and Y2SiO5 of comparative example 1 were used to prepare EBC, with a coating thickness of 0.3mm; and the EBC was circulated 3000 times in an air-cooled environment at a temperature of 1400°C. It was found that the EBC prepared using the rare earth silicate of Example 1 was in good condition, with no undesirable phenomena such as peeling and cracking on the surface, and had good resistance to water vapor and CMAS corrosion. Figure 6 As shown; however, the EBC prepared by using the rare earth silicate in Comparative Example 1 showed surface chipping and flaking, and had poor resistance to water vapor and CMAS corrosion.

[0140] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A porous rare earth silicate powder, characterized in that: The chemical formula of the rare earth silicate is (RE x Yb 1-x )2SiO5, wherein RE is a rare earth element selected from any one of Y, Lu, Er, Sc, and Ho, and x=0.1 to 0.

9.

2. The rare earth silicate powder according to claim 1, characterized in that The average particle size of the rare earth silicate powder is 20 to 45 μm.

3. The rare earth silicate powder according to claim 1, characterized in that The porosity of the rare earth silicate powder is 30-60%, and the diameter of the pores is 1-5 μm.

4. The rare earth silicate powder according to claim 1, characterized in that The rare earth silicate has a single X2-type phase structure and a purity of 95-99%.

5. The rare earth silicate powder according to claim 1, characterized in that The thermal conductivity of the rare earth silicate powder is (1.3-2.2) W·m -1 ·K -1 , the thermal expansion coefficient is (5.5~6.4)×10 -6 / ℃.

6. A method for preparing porous rare earth silicate powder, characterized in that: The method comprises: (1) preparing a polymethyl methacrylate template suspension; (2) adding the template suspension to a mixed solution of a silicon source and a rare earth element source to react and obtain a gel; (3) drying and calcining the gel; The rare earth element source comprises an RE source and a Yb source in a molar ratio of 9:1 to 1:9, and RE is selected from any one of Y, Lu, Er, Sc, and Ho.

7. The method according to claim 6, characterized in that In step (1), the particle size of the polymethyl methacrylate template is 0.5 to 2.5 μm, and the concentration in the suspension is 1.2 to 1.5 g / L.

8. The method according to claim 6, characterized in that In step (2), the silicon source is at least one of Na2SiO3·9H2O and tetraethyl orthosilicate; The RE source is at least one of RE(NO3)3·6H2O and RECl3·6H2O, and the Yb source is at least one of Yb(NO3)3·6H2O and YbCl3·6H2O; The molar ratio of the silicon source to the rare earth source is 1:2 to 1.2:2; In step (2), the reaction conditions are: reaction at a temperature of 60 to 80° C. for 3 to 5 hours.

9. The method according to claim 6, characterized in that In step (3), the drying temperature is 80-100° C.; The calcination conditions are: maintaining the temperature at 1100-1250° C. for 2-4 hours.

10. Use of the porous rare earth silicate powder according to any one of claims 1 to 9 in an environmental barrier coating.

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