Tantalate ceramic with low oxygen diffusion and its preparation method and application

Abstract

The present invention belongs to the field of oxygen-barrier coatings, specifically relating to a tantalate ceramic with low oxygen diffusion properties, its preparation method, and its application. The tantalate ceramic with low oxygen diffusion properties provided by the present invention has the chemical formula Re3TaO7, where Re is one or more of La, Ce, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb, and Y. The tantalate ceramic provided by the present invention exhibits high-temperature thermal insulation properties, high-temperature stability, and low oxygen diffusion properties. As a thermal barrier coating, it can effectively inhibit metal oxidation and oxide layer thickening, significantly extending its service life.

Description

Technical Field

[0001] The present invention belongs to the technical field of oxygen barrier coatings, and in particular relates to a tantalate ceramic with low oxygen diffusion, a preparation method and an application thereof. Background Art

[0002] Thermal barrier coatings (TBCs) are complex multilayer systems composed of a high-temperature alloy substrate, a metallic bond layer, and a ceramic layer. Over the past few decades, researchers have devoted significant research to understanding the failure mechanisms of TBCs. A key issue is the diffusion of oxygen through the ceramic layer to the metal bond layer interface, where it reacts with the metal elements (NiCoCrAlY) in the bond layer to form metal oxides. As the metal elements are depleted, the bonding strength of the bond layer decreases, leading to coating delamination and ultimately coating failure. Oxygen can originate from two main sources. First, the presence of lateral pores in ceramic coatings produced by atmospheric plasma spraying allows atmospheric oxygen to diffuse through these pores to the bond layer interface, but this oxygen diffusion is virtually independent of temperature. Second, at high temperatures, oxygen ions diffuse through the ceramic layer's crystal lattice to reach the bond layer interface. Oxygen diffusion through the crystal lattice increases exponentially with temperature, and above 1300°C, diffusion of oxygen within the crystal lattice dominates.

[0003] With the increasing service temperatures of current engines (the turbine inlet temperature of a first-stage aircraft engine with a thrust-to-weight ratio of 12-15 can reach 1700-1800°C), the yttria-stabilized zirconia (YSZ) ceramic currently in service suffers from the following serious drawbacks. First, its high-temperature stability is insufficient. When the service temperature exceeds 1250°C, YSZ undergoes a phase transformation accompanied by a 4-6% volume expansion, leading to cracking and failure of the coating. A more serious problem is the high oxygen diffusion capacity of YSZ. At high temperatures, oxygen ions more readily diffuse into the metal bond layer, promoting oxide growth and causing coating spalling. Current methods for inhibiting metal oxide growth rely primarily on the oxidation resistance of the metal bond layer. However, in next-generation thermal barrier coatings, which face higher temperatures, the oxygen content from lattice diffusion exceeds the oxygen content diffused through the pores formed by atmospheric plasma spraying. Consequently, the oxygen content reaching the metal bond layer increases dramatically, making the metal bond layer alone insufficient for oxygen barrier. Summary of the Invention

[0004] In view of this, the object of the present invention is to provide a tantalate ceramic with low oxygen diffusion, a preparation method and application thereof. The tantalate ceramic provided by the present invention has high-temperature thermal insulation performance, high-temperature stability and low oxygen diffusion performance. As a thermal barrier coating, it can effectively inhibit metal oxidation and oxide layer thickening, and significantly extend the service life.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] The present invention provides a tantalate ceramic with low oxygen diffusion, the chemical formula of which is Re3TaO7, wherein Re is one or more of La, Ce, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb and Y.

[0007] Preferably, the density of the tantalate ceramic is 90-99%, and the grain size is 10 nm-10 μm.

[0008] The present invention also provides a method for preparing the tantalate ceramics described in the above technical solution, comprising the following steps:

[0009] Re nitrate, tantalum oxynitrate and water are mixed to obtain a mixed solution, the pH value of the mixed solution is adjusted to a weak alkaline value, and then the mixed solution is allowed to stand, filtered, washed and dried in sequence to obtain an initial powder;

[0010] The initial powder is subjected to pressureless reaction sintering to obtain tantalate ceramics.

[0011] Preferably, the pH value of the weak alkaline solution is between 7 and 9.

[0012] Preferably, the standing time is 10 to 30 hours.

[0013] Preferably, the temperature of the pressureless reaction sintering is 1400-1700° C., and the holding time is 8-20 hours.

[0014] Preferably, the heating procedure for heating to the pressureless reaction sintering temperature is: heating from room temperature to 1100-1300°C at a heating rate of 5-20°C / min, and then heating from 1100-1300°C to the pressureless reaction sintering temperature at a heating rate of 2-10°C / min.

[0015] Preferably, before the pressureless reaction sintering is performed, the method further comprises: pressing the initial powder to obtain a precursor green body; the pressing pressure is 100 to 280 MPa, and the holding time is 5 to 30 minutes.

[0016] Preferably, the reagent used to adjust the pH value of the mixed solution is ammonia water.

[0017] The present invention also provides the use of the tantalate ceramics described in the above technical solution or the tantalate ceramics prepared by the preparation method described in the above technical solution in thermal barrier coatings.

[0018] The present invention provides a tantalate ceramic with low oxygen diffusion, having the chemical formula Re3TaO7, where Re is one or more of La, Ce, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb, and Y. The tantalate ceramic provided by the present invention inhibits the migration of oxygen atoms by creating a high Re-Re diffusion barrier. Furthermore, the Ta-Ta confinement effect on oxygen atoms is introduced, causing oxygen atoms to become confined interstitial atoms at the Ta-Ta boundary, hindering their diffusion. Furthermore, an "entropy-stabilized" defective fluorite tantalate structure is prepared by doping with multiple rare earth elements, resulting in a tantalate with low oxygen diffusion, high-temperature thermal insulation properties, and high-temperature phase stability. As a thermal barrier coating, this tantalate can effectively inhibit metal oxidation and oxide layer thickening, significantly extending its service life.

[0019] The tantalate powder prepared by the reverse coprecipitation method has good crystallinity, a low sintering temperature, and controllable elements, phases and microstructures. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the XRD pattern of the tantalate ceramic prepared in Example 1 of the present invention;

[0021] Figure 2 This is an SEM image of the tantalate ceramic powder prepared in Example 2 of the present invention;

[0022] Figure 3 This is a diffusion energy barrier test diagram of the tantalate ceramic prepared in Example 1 of the present invention;

[0023] Figure 4 This is a test graph of the ion diffusion rate of the tantalate ceramic and YSZ ceramic prepared in Example 1 of the present invention;

[0024] Figure 5 Arrhenius plots of the ionic conductivity of conventional YSZ ceramics and the tantalate ceramics prepared in Examples 1 to 6 of the present invention. DETAILED DESCRIPTION

[0025] The present invention provides a tantalate ceramic with low oxygen diffusion, the chemical formula of which is Re3TaO7, wherein Re is one or more of La, Ce, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb and Y.

[0026] Unless otherwise specified, the present invention has no special requirements on the sources of the raw materials used, and commercially available products known to those skilled in the art can be used.

[0027] The tantalate ceramic with low oxygen diffusion provided by the present invention has a chemical formula of Re3TaO7, wherein Re is one or more of La, Ce, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb, and Y, preferably La, Sm, Gd, Dy, Ho, Er, Yb, or Y. When Re is any of the above, the present invention does not specifically limit the ratio of different types of Re, and any ratio may be used.

[0028] In the present invention, the density of the tantalate ceramic is preferably 90-99%, more preferably 95-99%, and the grain size is preferably 10 nm-10 μm, more preferably 20 nm-3 μm.

[0029] The present invention also provides a method for preparing the tantalate ceramics described in the above technical solution, comprising the following steps:

[0030] Re nitrate, tantalum oxynitrate and water are mixed to obtain a mixed solution, the pH value of the mixed solution is adjusted to a weak alkaline value, and then allowed to stand, filtered, washed and dried to obtain an initial powder;

[0031] The initial powder is subjected to pressureless reaction sintering to obtain tantalate ceramics.

[0032] In the present invention, after the pH value of the obtained mixed solution of Re nitrate, tantalum oxynitrate and water is adjusted to weak alkalinity, the solution is allowed to stand, filtered, washed and dried in sequence to obtain an initial powder.

[0033] In the present invention, the mixing is preferably carried out under stirring conditions; the stirring rate is preferably 200-500 rpm, more preferably 200-300 rpm; the stirring temperature is preferably 20-60°C, more preferably 25-45°C; the stirring time is preferably 3-8h, more preferably 4-6h.

[0034] In the present invention, the pH value of the weak alkaline solution is preferably between 7 and 9, more preferably between 8 and 9; the reagent used to adjust the pH value of the mixed solution is preferably ammonia water; the mass concentration of the ammonia water is preferably 10 to 50%, more preferably 20 to 35%.

[0035] In the present invention, the standing time is preferably 10 to 30 hours, more preferably 15 to 25 hours. The present invention allows the metal salts to precipitate by standing, so that the desired cations are precipitated to the lower layer for better purification.

[0036] The present invention has no particular limitation on the filtration, and any filtration method well known in the art may be used.

[0037] In the present invention, the washing agent is preferably deionized water or ethanol, more preferably deionized water; the number of washing times is preferably 3 to 8 times, more preferably 4 times.

[0038] In the present invention, the drying temperature is preferably 100-150° C., more preferably 120° C.; the drying time is preferably 5-30 h, more preferably 10-24 h; and the drying is preferably carried out in a drying oven.

[0039] After drying, the dried powder is preferably ground to obtain an initial powder. In the present invention, the grinding is preferably performed using an agate mortar; the grinding is preferably performed until the particle size of the obtained powder is 10 to 100 nm, more preferably 15 to 50 nm.

[0040] After obtaining the initial powder, the present invention performs pressureless reaction sintering on the initial powder to obtain tantalate ceramics.

[0041] In the present invention, the temperature of the pressureless reaction sintering is preferably 1400-1700° C., more preferably 1500-1600° C., and the holding time is preferably 8-20 hours, more preferably 10-15 hours.

[0042] In the present invention, the heating procedure for heating to the pressureless reaction sintering temperature is preferably: heating from room temperature to 1100-1300°C at a heating rate of 5-20°C / min, and then heating from 1100-1300°C to the pressureless reaction sintering temperature at a heating rate of 2-10°C / min. More preferably, the heating procedure is: heating from room temperature to 1200°C at a heating rate of 5-10°C / min, and then heating from 1200°C to the pressureless reaction sintering temperature at a heating rate of 2-5°C / min.

[0043] In the present invention, the cooling procedure from the pressureless reaction sintering temperature to room temperature is preferably: cooling from the pressureless reaction sintering temperature to 1100-1300°C at a rate of 2-10°C / min, and then cooling to room temperature at a rate of 5-20°C / min. More preferably, it is: cooling from the pressureless reaction sintering temperature to 1200°C at a rate of 2-5°C / min, and then cooling to room temperature at a rate of 5-10°C / min.

[0044] In the present invention, the number of times of the pressureless reaction sintering is preferably 1 to 2 times, more preferably 1 time.

[0045] Before performing pressureless reaction sintering, the present invention further comprises: pressing the initial powder to obtain a precursor green body.

[0046] In the present invention, the pressing pressure is preferably 100-280 MPa, more preferably 150-250 MPa, and the holding time is preferably 5-30 min, more preferably 15-25 min; and the pressing is preferably cold isostatic pressing.

[0047] Prior to pressing, the present invention preferably places the initial powder in a mold and compacts it using a uniaxial press. In the present invention, the compaction pressure is preferably 5-15 MPa, more preferably 10 MPa, and the dwell time is preferably 5-10 minutes, more preferably 5 minutes. The present invention does not particularly limit the mold; molds well known in the art can be used. In an embodiment of the present invention, the mold has a diameter of 10 mm.

[0048] The oxygen diffusion rate of the tantalate ceramic prepared by the present invention is 1 / 50 of that of the traditional YSZ material. The tantalate ceramic material prepared by the present invention has the advantages of high-temperature phase stability and low thermal conductivity on the basis of a lower oxygen diffusion rate, meets the service requirements of the next generation of high-temperature thermal barrier coatings, and can greatly improve the working efficiency of gas turbines and aircraft engines.

[0049] The present invention also provides the use of the tantalate ceramics described in the above technical solution or the tantalate ceramics prepared by the preparation method described in the above technical solution in thermal barrier coatings.

[0050] The present invention has no special limitation on the application of the tantalate ceramic in the thermal barrier coating, and any application method well known in the art may be used.

[0051] The technical solutions of the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention, but they should not be understood as limiting the scope of protection of the present invention.

[0052] The equipment and raw materials used in the following examples are as follows:

[0053] The Yb source and Ta source (Yb(NO3)3·6H2O, TaO(NO3)3) used in the following examples were produced by Aladdin Biochemical Technology Co., Ltd. with a purity of ≥99.9%. Anhydrous ethanol was produced by Sinopharm Chemical Reagent Co., Ltd. with a purity of ≥99.9%. Ammonia was produced by Shanghai Lingfeng Chemical Reagent Co., Ltd. with a purity of ≥99%.

[0054] The pH test instrument is a Mettler-Toledo pH meter produced by Mettler-Toledo Instruments Shanghai Co., Ltd., the magnetic stirrer is a B11-3 magnetic stirrer produced by Shanghai Silu Instrument Co., Ltd., the drying oven is an electric blast drying oven, DHG9040HA drying oven produced by Zhejiang Hangzhou Lantian Laboratory Instrument Factory, and the pressureless reaction sintering furnace is a KSL-1700 muffle furnace produced by Hefei Kejing Material Technology Co., Ltd.

[0055] Example 1

[0056] Yb(NO3)3·6H2O and TaO(NO3)3 are used as raw materials and mixed according to the molar ratio of the metal elements in the chemical formula. Deionized water is added to prepare a transparent solution, which is stirred at 300 rpm at 25°C for 6 hours using a magnetic stirrer. Subsequently, an appropriate amount of dilute ammonia water (mass concentration of 25%) is added to the prepared transparent solution under stirring, and the pH value of the solution is adjusted to 9. After standing for 20 hours, the resulting layered solution is filtered, then washed four times with deionized water, and then placed in a drying oven, dried at 120°C for 24 hours, and then ground to obtain an initial powder;

[0057] 2 g of the initial powder was weighed and placed in a mold with a diameter of 10 mm. After compaction with a uniaxial pressure of 10 MPa and holding pressure for 5 minutes, cold isostatic pressing was performed at a pressure of 250 MPa and holding pressure for 15 minutes to obtain a precursor green body.

[0058] The precursor body is placed in a muffle furnace for pressureless reaction sintering, and the temperature is increased from room temperature to 1200°C at a heating rate of 10°C / min, then increased to 1600°C at a heating rate of 5°C / min, kept at this temperature for 10 hours, cooled to 1200°C at a cooling rate of 5°C / min, and then cooled to room temperature at a cooling rate of 10°C / min to obtain dense and uniform tantalate ceramics with a density of up to 99%.

[0059] Example 2

[0060] Yb(NO3)3·6H2O and TaO(NO3)3 are used as raw materials and mixed according to the molar ratio of the metal elements in the chemical formula. Deionized water is added to prepare a transparent solution, which is stirred at 300 rpm at 25°C for 6 hours using a magnetic stirrer. Subsequently, an appropriate amount of dilute ammonia water (mass concentration of 25%) is added to the prepared transparent solution under stirring, and the pH value of the solution is adjusted to 9. After standing for 20 hours, the resulting layered solution is filtered, then washed four times with deionized water, and then placed in a drying oven, dried at 120°C for 24 hours, and then ground to obtain an initial powder;

[0061] The obtained initial powder was subjected to a first pressureless reaction sintering, wherein the temperature was increased from room temperature to 1200°C at a heating rate of 10°C / min, then increased to 1600°C at a heating rate of 5°C / min, held at that temperature for 15 hours, then cooled to 1200°C at a cooling rate of 5°C / min, and then cooled to room temperature at a cooling rate of 10°C / min, to obtain a nano-scale tantalate ceramic powder with a grain size of approximately 20 nm.

[0062] 2 g of nano-scale tantalate ceramic powder was weighed and placed in a mold with a diameter of 10 mm. The powder was compacted using a uniaxial pressure of 15 MPa and maintained at this pressure for 5 minutes to obtain a precursor green body.

[0063] The precursor body is placed in a muffle furnace for a second pressureless reaction sintering, and the temperature is increased from room temperature to 1200°C at a heating rate of 10°C / min, and then increased to 1600°C at a heating rate of 5°C / min, and kept at this temperature for 5 hours. Then, the temperature is cooled to 1200°C at a cooling rate of 5°C / min, and then cooled to room temperature at a cooling rate of 10°C / min to obtain dense and uniform tantalate ceramics with a density of up to 99%.

[0064] Example 3

[0065] The difference from Example 1 is that the rare earth element Yb is replaced by Y, and the corresponding Y source is Y(NO3)3·6H2O. The rest of the content is consistent with Example 1.

[0066] Example 4

[0067] The difference from Example 1 is that the rare earth element Yb is replaced by Dy, and the corresponding Dy source is Dy(NO3)3·6H2O. The rest of the content is consistent with Example 1.

[0068] Example 5

[0069] The difference from Example 1 is that 50% of the molar ratio of the rare earth element Yb is replaced by Y, forming a chemical formula of Y 1.5 Yb 1.5 The tantalate ceramic of TaO7 corresponds to a Y source of Y(NO3)3·6H2O, and the rest of the contents are consistent with those in Example 1.

[0070] Example 6

[0071] The difference from Example 1 is that 50% of the rare earth element Yb is replaced by Gd, forming a compound with the chemical formula Yb 1.5 Gd 1.5 The tantalate ceramic of TaO7 corresponds to a Gd source of Gd(NO3)3·6H2O, and the rest of the contents are consistent with those in Example 1.

[0072] Comparative Example 1

[0073] The difference from Example 1 is that magnetic stirring was not performed after adding deionized water for dissolution, and the pH value was 6. The rest of the contents were the same as Example 1. The tantalate ceramic obtained did not form a single phase.

[0074] Comparative Example 2

[0075] The difference from Example 2 is that the temperature of the second pressureless reaction sintering is changed from 1600° C. to 1350° C., and the rest of the contents are the same as Example 2. The density of the obtained tantalate ceramic block is poor at 78%.

[0076] Performance Testing

[0077] (1) The tantalate ceramics prepared in Example 1 were subjected to X-ray diffraction testing, and the results were as follows: Figure 1 shown.

[0078] Depend on Figure 1 It can be concluded that the tantalate ceramics prepared by the present invention have good crystallinity and are a single fluorite structure.

[0079] (2) The tantalate ceramic powder prepared in Example 2 was scanned by electron microscope. The results are as follows: Figure 2 shown.

[0080] from Figure 2 It can be seen from the figure that the tantalate ceramic powder prepared by the present invention has good crystallinity, and its grain size is about 20 nm.

[0081] (3) The diffusion energy barrier of the tantalate ceramics prepared in Example 1 was tested, and the results were as follows: Figure 3 shown.

[0082] from Figure 3 It can be seen from the figure that the diffusion barrier of Re-Re is high, and Ta-Ta has a confining effect on oxygen atoms, which makes the oxygen atoms become confined interstitial atoms at the Ta-Ta boundary. This is also the main reason for the low diffusion rate of oxygen in tantalate.

[0083] (4) The diffusion rate of ions in the tantalate ceramic prepared in Example 1 at 1200°C was simulated by molecular dynamics. The current thermal barrier coating material YSZ was also measured for comparison. The results are as follows: Figure 4 As shown, (a) is the tantalate ceramic prepared in Example 1, and (b) is 8YSZ.

[0084] from Figure 4 It can be seen that in tantalate ceramics (a) and 8YSZ (b), ion diffusion only comes from oxygen ions, and cations hardly diffuse. Moreover, the oxygen diffusion rate of tantalate is significantly lower than that of 8YSZ, which is about 1 / 50 of that of 8YSZ, indicating that tantalate has good impedance capability.

[0085] (5) The ionic conductivity of the tantalate ceramics prepared in Examples 1 to 6 was tested by electrochemical impedance spectroscopy. The thermal barrier coating material YSZ currently in service was also measured for comparison. The results are shown in Table 1. Figure 5 .

[0086] from Figure 5 It can be seen that the electrical conductivity of YSZ is significantly higher than that of the tantalate ceramics prepared by the present invention, indicating that the tantalate ceramics prepared by the present invention have significant oxygen barrier properties.

[0087] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention rather than all the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A tantalate ceramic with low oxygen diffusion, characterized in that: The chemical formula is Re3TaO7, wherein Re is one or two of La, Ce, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb and Y; The tantalate ceramic has a density of 90-99% and a grain size of 10 nm-10 µm; The preparation method of the tantalate ceramic comprises the following steps: Re nitrate, tantalum oxynitrate and water are mixed to obtain a mixed solution, the pH value of the mixed solution is adjusted to a weak alkaline value, and then the mixed solution is allowed to stand, filtered, washed and dried in sequence to obtain an initial powder; The initial powder is subjected to pressureless reaction sintering to obtain tantalate ceramics; The temperature of the pressureless reaction sintering is 1400-1700°C, and the holding time is 8-20h; The heating program for heating to the pressureless reaction sintering temperature is: heating from room temperature to 1100-1300°C at a heating rate of 5-20°C / min, and then heating from 1100-1300°C to the pressureless reaction sintering temperature at a heating rate of 2-10°C / min.

2. The method for preparing the tantalate ceramic according to claim 1, characterized in that: The following steps are involved: Re nitrate, tantalum oxynitrate and water are mixed to obtain a mixed solution, and after adjusting the pH value of the mixed solution to a weak alkaline state, the mixed solution is allowed to stand, filtered, washed and dried in sequence to obtain an initial powder; the Re is one or two of La, Ce, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb and Y; The initial powder is subjected to pressureless reaction sintering to obtain tantalate ceramics; The temperature of the pressureless reaction sintering is 1400-1700°C, and the holding time is 8-20h; The heating program for heating to the pressureless reaction sintering temperature is: heating from room temperature to 1100-1300°C at a heating rate of 5-20°C / min, and then heating from 1100-1300°C to the pressureless reaction sintering temperature at a heating rate of 2-10°C / min.

3. The preparation method according to claim 2, characterized in that The pH value of the weak alkaline solution is between 7 and 9.

4. The preparation method according to claim 2, characterized in that The standing time is 10 to 30 hours.

5. The preparation method according to claim 2, characterized in that Before the pressureless reaction sintering is performed, the method further includes: pressing the initial powder to obtain a precursor green body; the pressing pressure is 100-280 MPa, and the holding time is 5-30 minutes.

6. The preparation method according to claim 2 or 3, characterized in that The reagent used to adjust the pH value of the mixed solution is ammonia water.

7. Use of the tantalate ceramic according to claim 1 or the tantalate ceramic prepared by the preparation method according to any one of claims 2 to 6 in thermal barrier coatings.

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