Synthesis method and application of rare earth silicate nano composite powder for environmental barrier coating

Abstract

The invention discloses a synthesis method and application of rare earth silicate nano composite powder for an environmental barrier coating, and aims to solve the problems of silicon volatilization and poor thermal stability in the thermal spraying process of the rare earth silicate environmental barrier coating. The synthesis method comprises the following steps: 1, preparing asymmetric mesoporous silica based on a nano silicon source; 2, co-precipitating the asymmetric mesoporous nano silicon dioxide serving as a nucleation center and rare earth ions, and calcining to prepare high-activity nano precursor powder; and 3, uniformly mixing the nano precursor with potassium sulfate and sodium sulfate, and calcining to obtain the rare earth silicate nano powder. The asymmetric mesoporous silica is selected as a silicon source, a silicon-rich end is supplemented from the nanoscale, silicon loss caused in the spraying process is made up, meanwhile, the rare earth silicate nano-powder is prepared by combining a chemical coprecipitation method with a molten salt method, the effect of optimizing the purity of the nano-powder is achieved, preparation of a high-quality environmental barrier coating material is achieved, and the application prospect is wide. And the thermal stability of the environmental barrier coating is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of thermal protection coating materials, and in particular relates to a multi-step synthesis method of rare earth silicate nanocomposite powder for environmental barrier coating and application thereof. Background Art

[0002] As an important power source, aircraft engines are directly related to national security and economic development, and their value accounts for 20% to 30% of the total value of aircraft. Therefore, developing advanced aircraft engines and increasing the engine's inlet temperature are of great significance for achieving a higher thrust-to-weight ratio and fuel efficiency and reducing nitrogen oxide emissions. Ceramic matrix composites (CMC) have the characteristics of light weight, high specific strength and specific modulus. At the same time, CMC has excellent high-temperature creep resistance, and has a certain ability to resist damage oxidation and crack propagation. It is the main candidate material for the high-thrust-to-weight ratio high-temperature components of the new generation of aircraft engines. Silicon carbide fiber reinforced silicon carbide ceramic matrix composites (SiC f / SiC) has the characteristics of low thermal conductivity, excellent high temperature mechanical properties, and excellent oxidation resistance, corrosion resistance and wear resistance. However, SiC f / SiC faces problems such as external damage, high-temperature water-oxygen corrosion, and low-melting-point oxide corrosion during its service. Therefore, in order to maintain long-term stable operation of hot-end components in extreme environments, an environmental barrier coating must be applied to slow down material failure. Currently, the widely used environmental barrier coating materials are mainly rare earth silicates, but after some thermal cycling experiments, the coating will still have longitudinal cracks and lose local protection. Researchers have found that the life of rare earth silicates can be effectively improved by doping with rare earth ions. Furthermore, high-entropy rare earth silicates have attracted widespread attention as ideal environmental barrier coating materials due to their low thermal conductivity, good phase stability, low thermal expansion coefficient, and excellent corrosion resistance. Due to the high entropy effect, the thermal expansion coefficient can be reduced, which can effectively reduce the stress of the coating system during thermal cycling and avoid cracking and failure of the coating.

[0003] Due to the polymorphic characteristics of rare earth silicates and the dispersion problems of various rare earth ions, the synthesis process and process parameters need to be carefully controlled. At present, solid-phase reaction is widely used in the synthesis of rare earth silicate ceramic materials, but there are problems such as low efficiency, high energy consumption, uneven particle size, and low purity of synthetic powders. There is an urgent need to adopt more advanced synthesis methods. Chemical synthesis methods such as chemical coprecipitation methods mix raw materials in atomic or molecular form, so that ceramic powders with uniform composition, high quality, and high activity can be obtained. At the same time, the purity and proportion of raw materials can be effectively controlled during the liquid phase reaction process, reducing the introduction of impurities and the generation of no environmental dust. Therefore, chemical coprecipitation is a method that is conducive to large-scale automated generation. In addition, the molten salt method is a simple and easy-to-control powder synthesis method. During the high-temperature reaction process, the salt will melt to form a melt, provide a liquid environment, and the fluidity of the reaction components will be enhanced, which will lead to an increase in the diffusion rate. Therefore, the reaction temperature can be reduced, the reaction time can be shortened, and the product purity can be improved. The comprehensive use of multiple synthesis methods is of guiding significance for the synthesis / preparation of high-quality nanoscale powders. Summary of the invention

[0004] The purpose of the present invention is to solve the problems of silicon volatilization and poor thermal stability during the thermal spraying process of rare earth silicate environmental barrier coatings, and to provide a synthesis method for preparing nanocomposite powders using asymmetric mesoporous silica as a silicon source. The synthesis method not only uses nanoscale silicon-rich ends to supplement the silicon loss of the system and ensure the uniformity of the macroscopic components of the powder / coating; it also further introduces nanopores into the powder / coating, reduces the thermal conductivity of the coating and the thermal stress during service, and ultimately achieves the synthesis of high-performance environmental barrier coating nanocomposite materials.

[0005] The method for synthesizing the rare earth silicate nanocomposite powder for the environmental barrier coating of the present invention is achieved by the following steps:

[0006] Step 1: Mix water, hexadecyltrimethylammonium bromide and (a small amount of) aqueous ammonia to obtain a mixed solution, add a nano-silica silicon source to the mixed solution, stir for 8 to 12 hours at room temperature, then add 1,2-bis(triethoxysilyl)ethane and continue stirring to react, and obtain a matchstick-shaped asymmetric mesoporous nano-silica after washing and drying, and ultrasonically disperse the matchstick-shaped asymmetric mesoporous nano-silica with deionized water to obtain an asymmetric mesoporous nano-silica dispersion;

[0007] Step 2: uniformly mix the asymmetric mesoporous nano-silica dispersion and the rare earth ion solution to obtain a rare earth mixed solution, then drop the rare earth mixed solution into ammonia water to react and obtain a precipitate product, and the precipitate product is sequentially aged, dried, and calcined to obtain a precursor nano-powder;

[0008] Step 3: wet-milling the precursor nanopowder and the mixed salt, and drying and calcining the mixture to obtain rare earth silicate nanocomposite powder;

[0009] The mixed salt in step three is a mixture of potassium sulfate and sodium sulfate.

[0010] The application of the rare earth silicate nanocomposite powder for environmental barrier coating of the present invention is to granulate the rare earth silicate nanocomposite powder into spherical powder, and form the environmental barrier coating on the surface of the substrate by using the spherical powder through plasma spraying process.

[0011] The present invention utilizes chemical coprecipitation method and molten salt method to synthesize rare earth silicate nanocomposite powder. On the one hand, asymmetric mesoporous silica is used as a silicon source and nucleation center, and a high-purity nano precursor is prepared in combination with a chemical coprecipitation method. On the other hand, during the high-temperature reaction process, the molten salt will form a melt to provide a liquid environment, and the fluidity of the reaction components will be enhanced, thereby leading to an increase in the diffusion rate. Therefore, the reaction temperature can be reduced, the reaction time can be shortened, and the product purity can be improved. Through the chemical synthesis of the high-purity nano precursor and the high-purity synthesis of the reaction components by the molten salt method, the purity and high quality of the nanocomposite powder are further improved.

[0012] The method for synthesizing rare earth silicate nanocomposite powder for environmental barrier coating of the present invention has the following beneficial effects:

[0013] (1) The present invention utilizes asymmetric mesoporous silica as a silicon source and nucleation center, and simultaneously adopts chemical coprecipitation to prepare a nano precursor, thereby achieving the synthesis of high-quality nano powders.

[0014] (2) The present invention adopts the molten salt method to synthesize rare earth silicate ceramic nanopowders, which not only reduces the reaction temperature and shortens the reaction time, but also improves the purity of the powder, thereby realizing the preparation of high-quality environmental barrier coatings, which has good scientific significance and engineering application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a scanning electron microscope image of the rare earth silicate nanocomposite powder prepared in Example 1;

[0016] Figure 2 This is the XRD pattern of the rare earth silicate nanocomposite powder prepared in Example 1;

[0017] Figure 3 This is a schematic diagram of the preparation principle of the rare earth silicate nanocomposite powder of the present invention;

[0018] Figure 4 This is a microscopic morphology of the powder after agglomeration and granulation in the application example;

[0019] Figure 5This is an environmental barrier coating prepared from the agglomerated powder in the application example. DETAILED DESCRIPTION

[0020] Specific implementation method 1: The synthesis method of rare earth silicate nanocomposite powder for environmental barrier coating in this implementation method is implemented according to the following steps:

[0021] Step 1: Mix water, hexadecyltrimethylammonium bromide and (a small amount of) aqueous ammonia to obtain a mixed solution, add a nano-silica silicon source to the mixed solution, stir for 8 to 12 hours at room temperature, then add 1,2-bis(triethoxysilyl)ethane and continue stirring to react, and obtain a matchstick-shaped asymmetric mesoporous nano-silica after washing and drying, and ultrasonically disperse the matchstick-shaped asymmetric mesoporous nano-silica with deionized water to obtain an asymmetric mesoporous nano-silica dispersion;

[0022] Step 2: uniformly mix the asymmetric mesoporous nano-silica dispersion and the rare earth ion solution to obtain a rare earth mixed solution, then drop the rare earth mixed solution into ammonia water to react and obtain a precipitate product, and the precipitate product is sequentially aged, dried, and calcined to obtain a precursor nano-powder;

[0023] Step 3: wet-milling the precursor nanopowder and the mixed salt, and drying and calcining the mixture to obtain rare earth silicate nanocomposite powder;

[0024] The mixed salt in step three is a mixture of potassium sulfate and sodium sulfate.

[0025] This embodiment adopts an anisotropic growth strategy to grow nano-silica short rods on one side of the mesoporous silica to form a matchstick-shaped asymmetric mesoporous silica, which provides two nucleation regions for the subsequent co-precipitation of rare earth ions. Different nucleation regions have different responses to the volatilization degree of silicon element during the spraying process, but they are uniform in the macroscopic state, which helps to improve the service performance of the environmental barrier coating under complex conditions.

[0026] This embodiment adjusts the morphology and particle size of the powder by controlling the concentration, pH, calcination parameters, etc. of the solution during the coprecipitation process, thereby achieving the purpose of optimizing the preparation of nano precursors. At the same time, the structure and morphology of the rare earth silicate powder are optimized by controlling parameters such as the ratio of the reaction product to the salt, the temperature and time of the molten salt synthesis, etc. The quality of the rare earth silicate nanopowder is further improved by optimizing the preparation process.

[0027] Specific implementation method 2: This implementation method is different from specific implementation method 1 in that the nano-silica silicon source in step 1 is nano-silica, core-shell structured mesoporous silica or nano-silica coated whiskers.

[0028] Specific implementation method three: This implementation method is different from specific implementation methods one or two in that the mass volume ratio of the nano-silica silicon source to 1,2-bis(triethoxysilyl)ethane in step one is (180-220) mg:1 mL.

[0029] Specific implementation method 4: The difference between this implementation method and any one of specific implementation methods 1 to 3 is that in step 1, the matchstick-shaped asymmetric mesoporous nano-silica is ultrasonically dispersed with deionized water, and the mass volume ratio of the matchstick-shaped asymmetric mesoporous nano-silica to deionized water is controlled to be 1 mg: (2-3) mL.

[0030] Specific implementation mode 5: This implementation mode is different from specific implementation modes 1 to 4 in that the rare earth ion solution in step 2 is nitric acid used to dissolve rare earth oxides, or deionized water used to dissolve rare earth nitrates or rare earth acetates.

[0031] Specific implementation method 6: The difference between this implementation method and specific implementation methods 1 to 5 is that the concentration of ammonia water in step 2 is 50wt%.

[0032] In this embodiment, the rare earth mixed solution is added dropwise into ammonia water to react and obtain a precipitate product, and the pH range of the ammonia water system is controlled to be 9-10.

[0033] Specific embodiment 7: This embodiment is different from any one of specific embodiments 1 to 6 in that the calcination temperature of the precipitated product in step 2 is 1000-1400° C. and the calcination time is 6-10 h.

[0034] Specific implementation eight: This implementation is different from specific implementations one to seven in that the rare earth ion solution in step two contains 2 to 5 kinds of rare earth ions.

[0035] Specific embodiment 9: The difference between this embodiment and any one of specific embodiments 1 to 8 is that in step 3, the mass ratio of the precursor nano powder to the mixed salt is 1:(1-2).

[0036] Specific embodiment ten: This embodiment is different from specific embodiment nine in that the mass ratio of potassium sulfate to sodium sulfate in the mixed salt in step three is 1:1.

[0037] Specific embodiment eleven: The difference between this embodiment and specific embodiments one to ten is that the temperature of the calcination treatment in step three is 1000-1400° C., and the calcination treatment time is 2-6 hours.

[0038] Example 1: The synthesis method of rare earth silicate nanocomposite powder for environmental barrier coating in this example is implemented according to the following steps:

[0039] Step 1: 450 mL of water, 900 mg of hexadecyltrimethylammonium bromide and 10.8 mL of aqueous ammonia (concentration of 28 wt%) are mixed to obtain a mixed solution, 120 mg of a nano-silica silicon source is added to the mixed solution, and the mixture is stirred at room temperature for 10 h, followed by adding 0.6 mL of 1,2-bis(triethoxysilyl)ethane and continuing magnetic stirring for 3 h, and after washing and drying, a matchstick-shaped asymmetric mesoporous nano-silica is obtained, and the matchstick-shaped asymmetric mesoporous nano-silica is ultrasonically dispersed with deionized water to obtain an asymmetric mesoporous nano-silica dispersion;

[0040] Step 2: Mix the asymmetric mesoporous nano-silica dispersion with the Y 3+ 、Ho 3+ , Er 3 + , Yb 3+ The rare earth ion solution is mixed into a uniform solution, the concentration of each rare earth ion in the rare earth ion solution is 1 mol / L, the rare earth mixed solution is slowly dripped into 50wt% ammonia water (system pH=9) to obtain a precipitated product, the precipitated product is aged for 24 hours and then dried, and calcined at 1200°C for 6 hours to obtain a precursor nano powder;

[0041] Step 3: 1 kg of precursor nanopowder is mixed with 0.6 kg of potassium sulfate and 0.6 kg of sodium sulfate by ball milling. The mixing medium is anhydrous ethanol. After mixing evenly, it is dried at 80 ° C for 24 hours and calcined at 1400 ° C for 4 hours to obtain (YHoErYb) 2 SiO 5 Nanocomposite powder.

[0042] This embodiment uses asymmetric mesoporous silica as the silicon source, supplements the silicon-rich end of the system from the nanoscale, and compensates for the silicon loss caused by the spraying process. At the same time, the chemical co-precipitation method is combined with the molten salt method to prepare rare earth silicate nanopowders, thereby optimizing the purity of the nanopowders and realizing the preparation of high-quality environmental barrier coating materials.

[0043] Application Example: The process of preparing an environmental barrier coating using rare earth silicate nanocomposite powder is as follows:

[0044] Weigh 600g (YHoErYb) 2 SiO 5 The nanocomposite powder, 20g PVA binder and 1000ml deionized water solvent were used to prepare granulation slurry, and then a spray granulator was used to prepare spherical raw material powder. The air inlet temperature was 300℃, the outlet temperature was 110℃, and the atomization pressure was 0.12MPa. (YHoErYb) was prepared on the substrate by plasma spraying process. 2 SiO 5Environmental barrier coatings.

[0045] The morphology of the powder after agglomeration and granulation in this embodiment is as follows Figure 4 As shown in the figure, the powder has high sphericity and a smooth surface. The fluidity of the powder was tested and it took 96 seconds for 50g of powder to flow through the funnel, which exceeded the fluidity of commercial ceramic powder. Figure 5 As shown in the figure, the coating is tightly stacked, with few internal pores, and the energy spectrum element results are consistent with the expected composition design. Under the cyclic simulation conditions of heating at 1300℃ for 5 minutes and air cooling for 5 minutes, the number of cycles can reach 2000 times, which has good engineering application value.

[0046] This embodiment applies rare earth silicate nanocomposite powder to prepare an environmental barrier coating, thereby achieving the preparation of a high-quality, low-defect environmental barrier coating.

Claims

1. A method for synthesizing rare earth silicate nanocomposite powder for environmental barrier coating, characterized in that The synthesis method is achieved by the following steps: Step 1: Mix water, hexadecyltrimethylammonium bromide and ammonia water to obtain a mixed solution, add a nano-silica silicon source to the mixed solution, stir for 8 to 12 hours at room temperature, then add 1,2-bis(triethoxysilyl)ethane and continue stirring to react, and obtain a matchstick-shaped asymmetric mesoporous nano-silica after washing and drying, and ultrasonically disperse the matchstick-shaped asymmetric mesoporous nano-silica with deionized water to obtain an asymmetric mesoporous nano-silica dispersion; Step 2: uniformly mix the asymmetric mesoporous nano-silica dispersion and the rare earth ion solution to obtain a rare earth mixed solution, then drop the rare earth mixed solution into ammonia water to react and obtain a precipitate product, and the precipitate product is sequentially aged, dried, and calcined to obtain a precursor nano-powder; Step 3: wet-milling the precursor nanopowder and the mixed salt, and drying and calcining the mixture to obtain rare earth silicate nanocomposite powder; The mixed salt in step three is a mixture of potassium sulfate and sodium sulfate.

2. The method for synthesizing rare earth silicate nanocomposite powder for environmental barrier coating according to claim 1, characterized in that In step 1, the nano-silica silicon source is nano-silica, core-shell structured mesoporous silica or nano-silica coated whiskers.

3. The method for synthesizing rare earth silicate nanocomposite powder for environmental barrier coating according to claim 1, characterized in that In step 1, the mass volume ratio of the nano-silica silicon source to 1,2-bis(triethoxysilyl)ethane is (180-220) mg:1 mL.

4. The method for synthesizing rare earth silicate nanocomposite powder for environmental barrier coating according to claim 1, characterized in that In step 2, the rare earth ion solution is prepared by dissolving rare earth oxides with nitric acid, or by dissolving rare earth nitrates or rare earth acetates with deionized water.

5. The method for synthesizing rare earth silicate nanocomposite powder for environmental barrier coating according to claim 1, characterized in that The calcination temperature of the precipitated product in step 2 is 1000-1400° C., and the calcination time is 6-10 hours.

6. The method for synthesizing rare earth silicate nanocomposite powder for environmental barrier coating according to claim 1, characterized in that In step 2, the rare earth ion solution contains 2 to 5 kinds of rare earth ions.

7. The method for synthesizing rare earth silicate nanocomposite powder for environmental barrier coating according to claim 1, characterized in that In step three, the mass ratio of the precursor nanopowder to the mixed salt is 1:(1-2).

8. The method for synthesizing rare earth silicate nanocomposite powder for environmental barrier coating according to claim 7, characterized in that The mass ratio of potassium sulfate to sodium sulfate in the mixed salt in step 3 is 1:

1.

9. The method for synthesizing rare earth silicate nanocomposite powder for environmental barrier coating according to claim 1, characterized in that In step 3, the calcination temperature is 1000-1400° C., and the calcination time is 2-6 hours.

10. The use of the rare earth silicate nanocomposite powder for environmental barrier coating prepared as claimed in claim 1, characterized in that The rare earth silicate nanocomposite powder is granulated into spherical powder, and the spherical powder is used to form an environmental barrier coating on the surface of a substrate by a plasma spraying process.

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