Rare earth b-site doped tantalate thermal barrier material and preparation method therefor

Abstract

The present application discloses a rare earth B-site doped tantalate thermal barrier material. The chemical formula of the rare earth B-site doped tantalate thermal barrier material is A2+2x(RexTa1-x)2O7, wherein A is any one of divalent metal elements, Re is any one of rare earth elements, and the numerical range of x is 0.05≤x≤0.3. The preparation method comprises: respectively dissolving a divalent metal oxide AO and a trivalent rare earth oxide Re2O3 in concentrated nitric acid in proportion to implement a reaction, and then mixing the resulting solution with a TaOCl3 solution to obtain a mixed solution; in an ultrasonic vibration environment, reversely titrating the mixed solution into an ammonia aqueous solution to form a colloidal precipitate; centrifuging and washing the colloidal precipitate with deionized water, and carrying out drying to obtain precursor powder; carrying out wet ball milling, drying and sieving to obtain uniform powder; and carrying out cold isostatic pressing molding on the powder, and then carrying out sintering to obtain the product. The thermal barrier material of the present application has low thermal conductivity, a high thermal expansion coefficient and a low rare earth content, and has good popularization prospects in the field of thermal insulation protection of hot-end components such as gas turbines.

Description

A rare earth B-site doped tantalate thermal barrier material and preparation method thereof

[0001] Cross-references

[0002] This application claims priority to Chinese Patent Application No. 2023117683245, filed on December 21, 2023, entitled “A rare earth B-site doped tantalate thermal barrier material and its preparation method,” all disclosures of which are incorporated herein by reference in their entirety. Technical Field

[0003] The present application relates to the field of thermal barrier materials, and in particular to a rare earth B-site doped tantalate thermal barrier material and a preparation method thereof. Background Art

[0004] Thermal barrier materials, due to their high melting point, high-temperature phase stability, and low thermal conductivity, are key surface protection materials for high-temperature hot-end components in gas turbines and aircraft engines. Currently, the most commonly used thermal barrier material is yttria-partially stabilized zirconia (6%-8% YSZ). However, at temperatures above 1200°C, YSZ is prone to phase transitions, leading to volume expansion and coating failure, which significantly limits the temperature range within which yttria-stabilized zirconia can be used.

[0005] Rare earth tantalates (RETaO4) have extremely low thermal conductivity, high thermal expansion coefficient and comprehensive mechanical properties. They are considered to be the new generation of thermal barrier materials with the greatest development potential and have attracted much attention from researchers. Typical rare earth tantalate crystal types include RETaO4, RE3TaO7, etc. This type of tantalate requires a large amount of rare earth elements to participate in the construction of the crystal lattice. However, rare earths are scarce strategic resources, which leads to high costs for rare earth tantalates and limits their scope of application. To this end, patent 202110479426.X proposes to use divalent alkaline elements to replace the A position where the rare earth elements are located to obtain an AB2O6 type tantalate ceramic that does not contain rare earth elements. However, the replacement of trivalent rare earth elements at the A position by divalent alkaline elements results in insufficient oxygen vacancies, resulting in properties such as thermal conductivity and thermal expansion coefficient still not being optimal.

[0006] Therefore, there is an urgent need to research and develop a tantalate thermal barrier ceramic material with low thermal conductivity, high thermal expansion coefficient and low cost to meet the higher temperature service requirements of the hot end components of gas turbines.

[0007] Application Contents

[0008] Based on the above technical problems, the present application provides a rare earth B-site doped tantalate thermal barrier material, which has the characteristics of low thermal conductivity, high thermal expansion coefficient and low rare earth content.

[0009] The specific plan for this application is as follows

[0010] One of the purposes of this application is to provide a rare earth B-doped tantalate thermal barrier material, the chemical formula of which is A 2+2x (Re x Ta 1-x )2O7, wherein A is any divalent metal element, Re is any rare earth element, and the numerical range of x is 0.05≤x≤0.3.

[0011] Among them, A is selected from any one of Mg, Ca, Sr, Ba, Zn, Co, Fe, Cu, and Ni; Re is selected from any one of La, Y, Sc, Yb, Gd, Nd, Pr, Sm, Er, and Dy.

[0012] The present application replaces the original trivalent rare earth element at the A position with a divalent metal element, and partially replaces the Ta element at the B position with a rare earth element, thereby achieving the goal of reducing the rare earth element content while also forming sufficient oxygen vacancies and point defects; the rare earth element partially replaces the Ta at the B position to form a defective fluorite structure, and the randomly distributed trivalent rare earth ions and oxygen vacancies increase the disorder of the crystal, thereby reducing the thermal conductivity and improving the thermal insulation performance of the coating material; at the same time, the thermal expansion coefficient of the material is improved, effectively reducing the difference in thermal expansion coefficient with the nickel-based high-temperature alloy substrate, thereby extending the service life of the material.

[0013] The second object of this application is to provide a method for preparing the above-mentioned rare earth B-site doped tantalate thermal barrier material, comprising the following steps:

[0014] S1, dissolving a divalent metal oxide AO and a trivalent rare earth oxide Re2O3 in concentrated nitric acid in proportion to react, and then mixing with a TaOCl3 solution to obtain a mixed solution;

[0015] S2. Under ultrasonic vibration, reversely titrate the mixed solution into an aqueous ammonia solution to form a colloidal precipitate, and let it stand; during the titration process, control the pH of the reaction system to be ≥10;

[0016] S3, centrifuging and washing the colloidal precipitate with deionized water, and drying to obtain a precursor powder;

[0017] S4, wet ball milling the precursor powder, drying it, and sieving it to obtain a uniform powder;

[0018] S5. The powder is formed by cold isostatic pressing and then sintered to obtain a block-shaped thermal barrier material.

[0019] In S1, Ta2Cl5 is dissolved in deionized water to obtain TaOCl3 solution.

[0020] Among them, in S3, the centrifugal speed is 5000-8000 r / min.

[0021] Among them, in S4, the wet ball milling parameters are: the ball milling medium is anhydrous ethanol, the ball milling speed is 400-600 r / min, and the ball milling time is 20-30 h; among them, the ball milling beads are made of zirconia.

[0022] Among them, in S4, the drying temperature is 80-100° C., and the drying time is 15-20 hours.

[0023] Among them, in S4, during screening, the mesh aperture is 50-90 μm; optionally, the mesh aperture is 74 μm.

[0024] Among them, in S5, the cold isostatic pressing pressure is 300-500 MPa, and the holding time is 5-15 minutes.

[0025] Among them, in S5, the sintering temperature is 1300-1600°C, and the sintering holding time is 5-10h.

[0026] The beneficial effects of this application are:

[0027] The rare earth B-doped tantalate thermal barrier material described in this application has a thermal conductivity of less than 1.5W / (mK) at 1200°C and a thermal expansion coefficient of more than 10.0×10 -6 K -1 The material's preparation process is reliable, its performance is stable, and it is suitable for large-scale batch production. It has a good promotion prospect in the field of thermal insulation protection of hot-end components such as gas turbines and aircraft engines. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIG1 is a diagram of Ba described in Example 1. 2.4 (Sm 0.2 Ta 0.8 )SEM microstructure of 2O7 thermal barrier material;

[0029] Figure 2 is the Ca 2.2 (Yb 0.1 Ta 0.9 )SEM microstructure of 2O7 thermal barrier material;

[0030] FIG3 is a diagram of Zn described in Example 3. 2.4( Y 0.2 Ta 0.8 )SEM microstructure of 2O7 thermal barrier material;

[0031] FIG4 is a thermal conductivity curve of the thermal barrier materials described in Examples 1-3 and Comparative Examples 1-4 at different temperatures;

[0032] FIG5 is a thermal expansion coefficient curve of the thermal barrier materials described in Examples 1-3 and Comparative Examples 1-4 at different temperatures. DETAILED DESCRIPTION

[0033] Below, the technical solution of the present application is described in detail through specific embodiments. However, it should be clearly stated that these embodiments are provided for illustration and are not to be construed as limiting the scope of the present application.

[0034] Example 1

[0035] Ba 2.4 (Sm 0.2 Ta 0.8 )2O7 thermal barrier material, the preparation method thereof comprises the following steps:

[0036] S1, divalent metal oxide BaO, trivalent rare earth oxide Sm2O3 and Ta2Cl5 are mixed by Ba 2.4 (Sm 0.2 Ta 0.8 )2O7 was weighed; BaO and Sm2O3 were dissolved in concentrated nitric acid and reacted sufficiently to obtain clear solutions; Ta2Cl5 was dissolved in deionized water to form a TaOCl3 solution; the TaOCl3 solution was mixed with the two clear solutions and stirred with a glass rod to obtain a clear mixed solution;

[0037] S2. Under ultrasonic vibration, reverse titrate the mixed solution into aqueous ammonia solution to form a colloidal precipitate. During the titration process, the pH value of the reaction system is maintained at ≥10. After the titration is completed, the mixture is allowed to stand for 24 hours.

[0038] S3, centrifuging and washing the colloidal precipitate with deionized water at a centrifugal speed of 7000 r / min until the pH of the supernatant after centrifugation is neutral, then washing with anhydrous ethanol and drying in an oven to obtain a precursor powder;

[0039] S4. Wet-mill the precursor powder using anhydrous ethanol as the milling medium and zirconium oxide as the milling beads. The milling speed is 600 r / min and the milling time is 20 h. The milled slurry is placed in a drying oven for drying at a temperature of 100° C. for 20 h. The slurry is then sieved using a sieve aperture of 74 μm to obtain a uniform powder.

[0040] S5, the powder is subjected to cold isostatic pressing with a molding pressure of 400 MPa and a holding time of 8 min; the prepared block is placed in a sintering furnace for high-temperature solid-phase sintering with a sintering temperature of 1550 ° C and a sintering holding time of 8 h to obtain a dense Ba 2.4 (Sm 0.2 Ta 0.8 )2O7 thermal barrier material.

[0041] The Ba 2.4 (Sm 0.2 Ta0.8 )2O7 thermal barrier material SEM microstructure, as shown in Figure 1.

[0042] Example 2

[0043] Ca 2.2 (Yb 0.1 Ta 0.9 )2O7 thermal barrier material, the preparation method thereof comprises the following steps:

[0044] S1, divalent metal oxide CaO, trivalent rare earth oxide Yb2O3 and Ta2Cl5 are mixed by Ca 2.2 (Yb 0.1 Ta 0.9 )2O7 is weighed; CaO and Yb2O3 are dissolved in concentrated nitric acid and reacted sufficiently to obtain a clear solution, and Ta2Cl5 is dissolved in deionized water to form a TaOCl3 solution; the TaOCl3 solution is mixed with the two clear solutions and stirred with a glass rod to obtain a clear mixed solution;

[0045] S2. Under ultrasonic vibration, reverse titrate the mixed solution into aqueous ammonia solution to form a colloidal precipitate. During the titration process, the pH value of the reaction system is maintained at ≥10. After the titration is completed, the mixture is allowed to stand for 24 hours.

[0046] S3, centrifuging and washing the colloidal precipitate with deionized water at a centrifugal speed of 6000 r / min until the pH of the supernatant after centrifugation is neutral, then washing with anhydrous ethanol and drying in an oven to obtain a precursor powder;

[0047] S4. Wet-grind the precursor powder using anhydrous ethanol as the ball milling medium and zirconium oxide as the ball milling beads at a speed of 500 r / min for 24 h. Dry the slurry obtained by ball milling in a drying oven at a drying temperature of 100° C. for 20 h. Sieve the slurry using a sieve aperture of 74 μm to obtain a uniform powder.

[0048] S5, the powder is subjected to cold isostatic pressing with a molding pressure of 350MPa and a holding time of 10min; the prepared block is placed in a sintering furnace for high-temperature solid-phase sintering with a sintering temperature of 1500℃ and a sintering holding time of 8h to obtain a dense Ca 2.2 (Yb 0.1 Ta 0.9 )2O7 thermal barrier material.

[0049] The Ca 2.2 (Yb 0.1 Ta 0.9 )2O7 thermal barrier material SEM microstructure, as shown in Figure 2.

[0050] Example 3

[0051] Zn 2.4 (Y 0.2 Ta 0.8 )2O7 thermal barrier material, the preparation method thereof comprises the following steps:

[0052] S1, divalent metal oxide ZnO, trivalent rare earth oxide Y2O3 and Ta2Cl5 according to Zn 2.4 (Y 0.2 Ta 0.8 )2O7 is weighed; ZnO and Y2O3 are dissolved in concentrated nitric acid and reacted sufficiently to obtain a clear solution, and Ta2Cl5 is dissolved in deionized water to form a TaOCl3 solution; the TaOCl3 solution is mixed with the two clear solutions and stirred with a glass rod to obtain a clear mixed solution;

[0053] S2. Under ultrasonic vibration, reverse titrate the mixed solution into an ammonia solution to form a colloidal precipitate. During the titration process, the pH value of the ammonia solution is maintained at ≥10. After the titration is completed, let it stand for 24 hours;

[0054] S3, centrifuging and washing the colloidal precipitate with deionized water at a centrifugal speed of 6800 r / min until the pH value of the supernatant after centrifugation is neutral, then washing with anhydrous ethanol and drying in an oven to obtain a precursor powder;

[0055] S4. Wet-grind the precursor powder using anhydrous ethanol as the ball milling medium and zirconium oxide as the ball milling beads at a speed of 600 r / min for 20 h. Dry the slurry obtained by ball milling in a drying oven at a drying temperature of 100° C. for 20 h. Sieve the slurry using a sieve aperture of 74 μm to obtain a uniform powder.

[0056] S5, the powder is subjected to cold isostatic pressing with a molding pressure of 350 MPa and a holding time of 8 min; the prepared block is placed in a sintering furnace for high-temperature solid-phase sintering with a sintering temperature of 1550 ° C and a sintering holding time of 8 h to obtain a dense Zn 2.4 (Y 0.2 Ta 0.8 )2O7 thermal barrier material.

[0057] The Zn 2.4 (Y 0.2 Ta 0.8 )2O7 thermal barrier material SEM microstructure, as shown in Figure 3.

[0058] Comparative Example 1

[0059] The difference from Example 1 is that x=0, and the method of Example 1 is used to prepare Ba2Ta2O7 tantalate thermal barrier ceramic material without rare earth doping Ta site.

[0060] Comparative Example 2

[0061] The difference from Example 1 is that x=0.5, and Ba3(Sm 0.5 Ta 0.5 )2O7 rare earth B-site doped tantalate thermal barrier ceramic material.

[0062] Comparative Example 3

[0063] The difference from Example 2 is that x=0, and the method of Example 2 is used to prepare Ca2Ta2O7 tantalate thermal barrier ceramic material without rare earth doping Ta site.

[0064] Comparative Example 4

[0065] The difference from Example 2 is that x=0.5, and the method of Example 2 is used to prepare Ca3(Yb 0.5 Ta 0.5 )2O7 rare earth B-site doped tantalate thermal barrier ceramic material.

[0066] The thermal conductivity curves and thermal expansion coefficient curves of the thermal barrier materials prepared in the above Examples 1-3 and Comparative Examples 1-4 at different temperatures are shown in Figures 4 and 5, respectively. It can be seen that the thermal conductivity and thermal expansion performance of Examples 1-3 of the present application are better than those of Comparative Examples 1-4. The thermal conductivity of the rare earth B-doped tantalate thermal barrier materials prepared in Examples 1-3 at 1200°C is less than 1.5W / (mK), and the thermal expansion coefficient is greater than 10.0×10 -6 K -1 The main reason is that when the rare earth doping amount x at the B site is less than 0.05, insufficient oxygen vacancies and point defects are formed, which cannot play a role in reducing thermal conductivity. When the rare earth doping amount x at the B site is greater than 0.3, the rare earth doping amount is excessive and cannot be fully dissolved and replaced. The excessive rare earth will form rare earth oxides or rare earth salts, resulting in increased thermal conductivity and reduced fracture toughness of the material, which is not conducive to the performance of the material.

[0067] The above is only a preferred specific implementation method of the present application, but the scope of protection of the present application is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes based on the technical solution and application concept of the present application within the technical scope disclosed in the present application, and they should be covered by the scope of protection of the present application.

Claims

1. A rare earth B-doped tantalate thermal barrier material, the chemical formula of which is A 2+2x (Re x Ta 1-x )2O7, wherein the numerical range of x is 0.05≤x≤0.3; A is selected from any one of Mg, Sr, Ba, Zn, Co, Fe, Cu, and Ni; Re is selected from any one of La, Y, Sc, Yb, Gd, Nd, Pr, Sm, Er, and Dy.

2. The method for preparing the rare earth B-site doped tantalate thermal barrier material according to claim 1, comprising the following steps: S1, dissolving the divalent metal oxide AO and the trivalent rare earth oxide Re2O3 in concentrated nitric acid in proportion to react, and then mixing with the TaOCl3 solution to obtain a mixed solution; S2. Under ultrasonic vibration environment, reversely titrate the mixed solution into aqueous ammonia solution to form a colloidal precipitate, and let it stand; during the titration process, control the pH of the reaction system to be ≥10; S3, centrifuging and washing the colloidal precipitate with deionized water, and drying to obtain a precursor powder; S4, wet ball milling the precursor powder, drying it, and sieving it to obtain a uniform powder; S5. The powder is formed by cold isostatic pressing and then sintered to obtain a block thermal barrier material.

3. The method for preparing the rare earth B-site doped tantalate thermal barrier material according to claim 2, wherein: In S3, the centrifugal speed is 5000-8000 r / min.

4. The method for preparing the rare earth B-site doped tantalate thermal barrier material according to claim 2, wherein: In S4, the wet ball milling parameters are as follows: the ball milling medium is anhydrous ethanol, the ball milling speed is 400-600 r / min, and the ball milling time is 20-30 h.

5. The method for preparing the rare earth B-site doped tantalate thermal barrier material according to claim 2, wherein: In S4, the drying temperature is 80 to 100° C. and the drying time is 15 to 20 hours.

6. The method for preparing the rare earth B-site doped tantalate thermal barrier material according to claim 2, wherein: In S4, during screening, the mesh size is 50-90 μm.

7. The method for preparing the rare earth B-site doped tantalate thermal barrier material according to claim 2, wherein, in S5, the cold isostatic pressing pressure is 300-500 MPa, and the holding time is 5-15 min.

8. The method for preparing the rare earth B-site doped tantalate thermal barrier material according to claim 2, wherein: In S5, the sintering temperature is 1300-1600°C, and the sintering holding time is 5-10 hours.

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