A tantalate ceramic with a fluorite structure having low thermal conductivity, a preparation method thereof, and applications thereof

Abstract

The present invention belongs to the technical field of thermal barrier coatings, and particularly relates to a tantalate ceramic with a low thermal conductivity fluorite structure, a preparation method thereof, and an application thereof. The tantalate ceramic with a low thermal conductivity fluorite structure provided by the present invention has a defective fluorite structure, and its chemical formula is Re1 x Re2 y Dy z TaO7, wherein x + y + z = 3, and x, y, and z are independently 0.5 to 1.5, and Re1 and Re2 are independently yttrium, holmium, erbium, thulium, or ytterbium. Dy with the smallest Re-O bond energy is introduced into the tantalate to form a large bond energy difference with Ta-O. By introducing two other rare earth ions, mass difference and bond energy disorder are constructed. On the basis of ensuring the stability of the crystal structure at high temperature, a ceramic system with a lower thermal conductivity is obtained by constructing uneven chemical bonds in the system. The co-doping of multiple rare earths increases the entropy value of the ceramic system, improves the high-temperature stability of the tantalate ceramic, and enables long-term service at high temperature.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermal barrier coatings, and particularly relates to a tantalate ceramic with a low thermal conductivity fluorite structure, a preparation method thereof, and an application thereof. Background Art

[0002] Thermal barrier coatings are heat-insulating functional coatings widely applied to the surfaces of hot-end components such as the combustion chambers and blades of aero-turbine engines, which can reduce the surface temperature of the protected metal, thereby improving the working efficiency and service life.

[0003] Currently, the widely used thermal barrier coating material is 6-8 wt.% yttria-stabilized zirconia (6-8YSZ). With the increase of the current engine service temperature (the inlet temperature in front of the turbine of a first-class aero-engine with a thrust-to-weight ratio of 12-15 can reach 1700-1800 °C), this ceramic material currently has two serious defects. First, the high-temperature stability of this ceramic material is insufficient. When the service temperature exceeds 1250 °C, YSZ undergoes a phase change and is accompanied by a volume expansion of 4-6%, resulting in the coating cracking and failing. Second, the thermal conductivity of this ceramic material is also relatively high (about 2.5 W·m -1 ·K -1 -1, 900 °C), which causes the temperature of the alloy matrix to be too high and reduces the engine efficiency. Therefore, with the requirements of high thrust-to-weight ratio and higher temperature economy of the engine, it is urgent to seek new thermal barrier coating materials. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a tantalate ceramic with a low thermal conductivity fluorite structure, a preparation method thereof, and an application thereof. The tantalate ceramic with a low thermal conductivity fluorite structure provided by the present invention has a low thermal conductivity and excellent high-temperature stability, and the thermal barrier coating prepared therefrom can serve for a long time at high temperatures.

[0005] To achieve the above purpose, the present invention provides the following technical solutions:

[0006] The present invention provides a tantalate ceramic with a low thermal conductivity fluorite structure, which has a defective fluorite structure and a chemical formula of Re1 x Re2 y Dy z TaO7, wherein x + y + z = 3, and x, y, and z are independently 0.5-1.5, and Re1 and Re2 are independently yttrium, holmium, erbium, thulium, or ytterbium.

[0007] Preferably, when 0.88 < z < 1.32, the 2θ angle of the (111) plane of the X-ray diffraction peak of the tantalate ceramic with a low thermal conductivity fluorite structure is 29.08-29.7°; the radius difference between Re1 ions and Re2 ions in the tantalate ceramic with a low thermal conductivity fluorite structure

[0008] The present invention also provides a method for preparing the tantalate ceramic with low thermal conductivity and fluorite structure described in the above technical solution, comprising the following steps:

[0009] Mix the oxides of Re1, the oxides of Re2, the oxides of Dy and the oxides of Ta, and successively carry out wet grinding, washing and drying to obtain a mixed metal oxide powder;

[0010] Press the mixed metal oxide powder, and sinter the obtained ceramic green body to obtain the tantalate ceramic with low thermal conductivity and fluorite structure.

[0011] Preferably, the rotation speed of the wet grinding is 1500-2000 r / min; the time of the wet grinding is 5-8 h; the grinding solvent used for the wet grinding is one or more of isopropanol, absolute ethanol and deionized water; the diameter of the grinding balls used for the wet grinding is 0.3-0.5 mm, and the material is zirconia.

[0012] Preferably, the mass ratio of the total amount of the oxides of Re1, the oxides of Re2, the oxides of Dy and the oxides of Ta, the grinding solvent to the grinding balls is 1-2:8-10:2-3.

[0013] Preferably, the pressure of the pressing is 200-280 MPa, and the pressure holding time is 10-20 min.

[0014] Preferably, the sintering temperature is 1500-1750 °C, and the heat preservation time is 10-30 h.

[0015] The present invention also provides the application of the tantalate ceramic with low thermal conductivity and fluorite structure described in the above technical solution or the tantalate ceramic with low thermal conductivity and fluorite structure prepared by the preparation method described in the above technical solution in a thermal barrier coating.

[0016] The present invention also provides a tantalate ceramic thermal barrier coating, the components of which include the tantalate ceramic with low thermal conductivity and fluorite structure described in the above technical solution or the tantalate ceramic with low thermal conductivity and fluorite structure prepared by the preparation method described in the above technical solution.

[0017] The present invention also provides a method for preparing the tantalate ceramic thermal barrier coating described in the above technical solution, comprising the following steps:

[0018] Spray the powder obtained by crushing the tantalate ceramic with low thermal conductivity and fluorite structure described in the above technical solution or the tantalate ceramic with low thermal conductivity and fluorite structure prepared by the preparation method described in the above technical solution onto a substrate to form a tantalate ceramic thermal barrier coating.

[0019] The present invention provides a tantalate ceramic with low thermal conductivity and fluorite structure, which has a defective fluorite structure and the chemical formula is Re1 x Re2 y Dyz TaO7, where x + y + z = 3, and x, y, and z are independently 0.5 to 1.5, and Re1 and Re2 are independently yttrium, holmium, erbium, thulium, or ytterbium. In the present invention, Dy with the smallest Re-O bond energy is introduced into the tantalate, forming a large bond energy difference with Ta-O. Two other rare earth ions are introduced to construct mass differences and bond energy disorder. The Dy-O bond energy is only 1 / 4 of the Ta-O bond energy, and the bond energies (Re-O) of the two other doped rare earth ions are all higher than the Dy-O bond energy and lower than the Ta-O bond energy. By constructing non-uniform chemical bonds in the system, it is more conducive to scattering low-frequency phonons with longer wavelengths. Moreover, factors such as the intrinsic oxygen vacancies in the system and the ionic radius differences formed after doping rare earth ions scatter medium and high-frequency phonons, regulating phonon scattering in a larger wavelength range, and obtaining a ceramic system with a lower thermal conductivity. On the other hand, co-doping with multiple rare earths increases the entropy value of the ceramic system, improves the high-temperature stability of the tantalate ceramic. The high-temperature phase and the low-temperature phase are both tetragonal and remain consistent, and no phase change occurs at high temperatures. The thermal barrier coating prepared using it can achieve long-term service at high temperatures. The results of the examples show that the thermal conductivity of the low-thermal-conductivity tantalate ceramic material provided by the present invention is low (the thermal conductivity of the tantalate ceramic material at 100 °C is 1.02 W / (m·K), and the thermal conductivity of the thermal barrier coating prepared using it is 0.46 W / (m·K)), only 0.29 times that of the currently used 8YSZ (at room temperature), and the prepared tantalate ceramic thermal expansion coating has an extremely low thermal conductivity of only 0.71 W·m -1 K -1 (1500 °C), with stable high-temperature physical and chemical properties, meeting the requirements for the next-generation thermal barrier coating.

[0020] The present invention also provides a preparation method for the above-mentioned low-thermal-conductivity fluorite-structured tantalate ceramic. The preparation process is simple, easy to operate, low in cost, with small powder loss, and the element, phase composition, and microstructure are controllable. Description of the Drawings

[0021] Figure 1 XRD pattern of the low-thermal-conductivity fluorite-structured tantalate ceramic prepared in Example 1 of the present invention;

[0022] Figure 2 SEM image of the low-thermal-conductivity fluorite-structured tantalate ceramic prepared in Example 1 of the present invention;

[0023] Figure 3 Bond energy evaluation test result diagram between cations and anions in the low-thermal-conductivity fluorite-structured tantalate ceramic prepared in Example 1 of the present invention;

[0024] Figure 4 BSE image of the tantalate ceramic thermal barrier coating prepared in Application Example 1 of the present invention. Detailed Embodiments

[0025] The present invention provides a tantalate ceramic with a low-thermal-conductivity fluorite structure, which has a defective fluorite structure and a chemical formula of Re1 x Re2 y Dy z TaO7, where x + y + z = 3, and x, y, and z are independently 0.5 to 1.5, and Re1 and Re2 are independently yttrium, holmium, erbium, thulium, or ytterbium.

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

[0027] The low-thermal-conductivity tantalate ceramic provided by the present invention has a defective fluorite structure and a chemical formula of Re1 x Re2 y Dy z TaO7, where x + y + z = 3, and x, y, and z are independently 0.5 to 1.5, and Re1 and Re2 are independently yttrium, holmium, erbium, thulium, or ytterbium.

[0028] In the present invention, x is preferably 0.68 to 1.44, more preferably 1; y is preferably 0.68 to 1.44, more preferably 1; 0.88 < z < 1.32, preferably 0.9 to 1.3, and most preferably 1.

[0029] In the present invention, Re1 is preferably yttrium (Y), holmium (Ho), erbium (Er), thulium (Tm), or ytterbium (Yb), more preferably yttrium or holmium; Re2 is preferably yttrium (Y), holmium (Ho), erbium (Er), thulium (Tm), or ytterbium (Yb), more preferably ytterbium.

[0030] In the present invention, Dy with the smallest Re-O bond energy is introduced into the tantalate to form a large bond energy difference with Ta-O, and two other rare earth ions are introduced to construct mass differences and bond energy disorder. The Dy-O bond energy is only 1 / 4 of the Ta-O bond energy, and the bond energies (Re-O) of the two other rare earth ions incorporated are higher than the Dy-O bond energy and lower than the Ta-O bond energy. By constructing non-uniform chemical bonds in the system, it is more conducive to scattering low-frequency phonons with longer wavelengths. Moreover, factors such as the intrinsic oxygen vacancies in the system and the ionic radius differences formed after incorporating rare earth ions scatter medium- and high-frequency phonons, regulating phonon scattering in a larger wavelength range, and obtaining a ceramic system with a lower thermal conductivity. On the other hand, co-doping with multiple rare earths increases the entropy value of the ceramic system, improves the high-temperature phase stability of the tantalate ceramic, and enables the thermal barrier coating prepared therefrom to serve for a long time at high temperatures.

[0031] In the present invention, the grain size of the low-thermal-conductivity fluorite structure tantalate ceramic is preferably 0.3 to 10 μm, more preferably 1 to 6 μm, and the density is preferably 96 to 99%, more preferably 98 to 99%.

[0032] When 0.88 < z < 1.32, the 2θ angle of the (111) plane of the X-ray diffraction peak of the low-thermal-conductivity fluorite-structured tantalate ceramic is preferably 29.08° to 29.7°, more preferably 29.46° to 29.63°. The radius difference Δr between Re1 ions and Re2 ions in the low-thermal-conductivity fluorite-structured tantalate ceramic is preferably The grain size of the low-thermal-conductivity fluorite-structured tantalate ceramic is preferably 2 to 8 μm, more preferably 3 to 7 μm.

[0033] Technical principle of the present invention: Heat conduction in solids is mainly achieved by lattice vibration and the movement of free electrons. For tantalate ceramics, they have a large band gap and can be considered electron insulators. Therefore, heat conduction in tantalate materials relies on lattice vibration, that is, phonon heat transfer. In the tantalate ceramic provided by the present invention, there are intrinsic oxygen vacancies, which can significantly scatter high-frequency phonons with shorter wavelengths. By introducing different rare earth ions and constructing different ion radius differences, medium-high-frequency phonons with longer wavelengths can be scattered. For low-frequency phonons with long wavelengths, due to their long wavelengths, the above-mentioned point defects cannot reach their scattering sources. Therefore, the present invention introduces different binding energies to scatter low-frequency long-wavelength phonons by softening the crystal dispersion relationship and changing the vibration frequency.

[0034] In the present invention, the ion radius difference is first controlled Because increasing the ion radius is not conducive to lattice stability on the one hand, and a larger ion radius is likely to form phonon standing waves, triggering phonon resonance phenomena. Secondly, the 2θ angle of the (111) plane of the X-ray diffraction (XRD) peak is controlled to be 29.08° to 29.7°. When the main peak position of the (111) plane is lower than 29.08°, the obtained ceramic block is unstable at high temperatures and will undergo a phase change at 950 to 1000 °C, not meeting the use requirements of thermal barrier coatings; when the main peak position of the (111) plane is higher than 29.7°, the grains of the obtained ceramic block will grow abnormally at high temperatures, resulting in a reduction in material performance.

[0035] Considering the crystal structure and ion size difference problems, the present invention first fixes dysprosium (Dy) in the system because the Dy-O bond energy is only 1 / 4 of the Ta-O bond energy, and the bond energies (Re-O) of the other two rare earth ions incorporated are higher than the Dy-O bond energy and lower than the Ta-O bond energy (the binding energy between cations and anions in tantalate calculated according to density functional theory Figure 3), thus forming a large inhomogeneity of chemical bonds in the system, which is more conducive to scattering low-frequency phonons with longer wavelengths. Moreover, factors such as the intrinsic oxygen vacancies in the system and the ionic radius differences formed after doping rare earth ions scatter medium and high-frequency phonons. Therefore, the tantalate ceramics prepared by the present invention can scatter phonons with different wavelengths in the whole range, regulate the thermal conductivity, and better meet the purpose of using thermal barrier coatings at high temperatures.

[0036] The present invention also provides a method for preparing the low-thermal-conductivity fluorite-structured tantalate ceramics described in the above technical solution, comprising the following steps:

[0037] Mix the oxides of Re1, the oxides of Re2, the oxides of Dy, and the oxides of Ta, and successively carry out wet grinding, washing, and drying to obtain a mixed metal oxide powder;

[0038] Press the mixed metal oxide powder, and sinter the obtained ceramic green body to obtain low-thermal-conductivity fluorite-structured tantalate ceramics.

[0039] In the present invention, the oxides of Re1, the oxides of Re2, the oxides of Dy, and the oxides of Ta are mixed and wet-ground to obtain a wet-ground mixed suspension.

[0040] In the present invention, the oxides of Re1 and the oxides of Re2 are independently preferably Re2O3; the oxide of Dy is preferably Dy2O3; the oxide of Ta is preferably Ta2O5; the particle sizes of the oxides of Re1, the oxides of Re2, the oxides of Dy, and the oxides of Ta are independently preferably 3-8 μm, and the purity is independently preferably ≥99.9%.

[0041] In the present invention, the rotation speed of the wet grinding is preferably 1500-2000 r / min, more preferably 2000 r / min; the time of the wet grinding is preferably 5-8 h, more preferably 6 h; the grinding solvent used for the wet grinding is preferably one or more of isopropanol, absolute ethanol, and deionized water, more preferably isopropanol; the diameter of the grinding balls used for the wet grinding is preferably 0.3-0.5 mm, more preferably 0.3-0.4 mm, and the material is preferably zirconia. When the grinding solvent is the above several kinds, the present invention has no special limitation on the ratio of different kinds of grinding solvents, and any ratio can be used.

[0042] In the present invention, the total amount of the oxides of Re1, the oxides of Re2, the oxides of Dy, and the oxides of Ta, the mass ratio of the grinding solvent to the grinding balls is preferably 1-2:8-10:2-3, more preferably 1-1.5:9-10:2-2.5.

[0043] Before washing, the present invention preferably screens the mixed material liquid obtained by wet grinding; the screening is preferably carried out with a 300-mesh sieve. The present invention separates the ball materials in the wet grinding mixed suspension through screening.

[0044] After obtaining the wet grinding mixed suspension, the present invention washes the wet grinding mixed suspension to obtain wet grinding powder. In the present invention, the reagent used for washing is preferably ethanol or isopropanol, more preferably ethanol; the number of washing times is preferably 4 to 6 times, more preferably 5 times; after each washing ends, the present invention preferably carries out solid-liquid separation on the obtained washing mixed liquid; the solid-liquid separation is preferably screening; the screening is preferably carried out with a 300-mesh sieve. The present invention has no special limitation on the dosage of the reagent used for washing, as long as the wet grinding powder is washed clean.

[0045] After obtaining the wet grinding powder, the present invention dries the wet grinding powder to obtain a mixed metal oxide powder. In the present invention, the drying is preferably blast drying; the equipment for blast drying is preferably a blast drying oven; the drying temperature is preferably 100 to 120 °C, more preferably 110 to 120 °C; the drying time is preferably 10 to 15 h, more preferably 11 to 13 h.

[0046] After the drying, the present invention preferably grinds the dried wet grinding powder; the grinding is preferably carried out with an agate mortar.

[0047] After obtaining the mixed metal oxide powder, the present invention presses the mixed metal oxide powder to obtain a ceramic green body.

[0048] Before the pressing, the present invention preferably further includes: compacting the mixed metal oxide powder; the equipment used for compacting is preferably a uniaxial press; the compacting is preferably carried out by placing the mixed metal oxide powder in a mold; the pressure used for compacting is preferably 3 to 15 MPa, more preferably 10 MPa; the pressure holding time used for compacting is preferably 2 to 10 min, more preferably 5 min. The present invention has no special limitation on the mold, and a mold well-known in the art can be used. In the embodiments of the present invention, the diameter of the mold is 10 mm.

[0049] In the present invention, the pressing is preferably unidirectional die pressing, bidirectional die pressing or cold isostatic pressing, more preferably cold isostatic pressing; the pressure of the pressing is preferably 200 to 280 MPa, more preferably 220 to 250 MPa, and the pressure holding time is preferably 10 to 20 min, more preferably 10 to 15 min.

[0050] After obtaining the ceramic green body, the present invention sinters the ceramic green body to obtain a low-thermal-conductivity fluorite-structured tantalate ceramic. In the present invention, the sintering temperature is preferably 1500 - 1750 °C, more preferably 1600 - 1700 °C, and the heat preservation time is preferably 10 - 30 h, more preferably 20 - 30 h; the sintering is preferably pressureless reactive sintering.

[0051] In the present invention, the heating program for heating to the sintering temperature is preferably: heating from room temperature to 1200 °C at a heating rate of 5 - 10 °C / min, and then heating from 1200 °C to the sintering temperature at a heating rate of 2 - 5 °C / min. More preferably: heating from room temperature to 1200 °C at a heating rate of 5 - 8 °C / min, and then heating from 1200 °C to the sintering temperature at a heating rate of 2 - 3 °C / min.

[0052] In the present invention, the cooling program for cooling from the sintering temperature to room temperature is preferably: cooling from the sintering temperature to 1200 °C at a cooling rate of 2 - 5 °C / min, and then cooling to room temperature at a cooling rate of 5 - 10 °C / min. More preferably: cooling from the sintering temperature to 1200 °C at a cooling rate of 2 - 3 °C / min, and then cooling to room temperature at a cooling rate of 5 - 8 °C / min.

[0053] The present invention uses a solid-phase method to perform pressureless reactive sintering to prepare a low-thermal-conductivity fluorite-structured tantalate ceramic. The process is simple, the operation is convenient, the cost is low, the powder loss is small, and the elements, phase composition and microstructure are controllable.

[0054] The present invention also provides the application of the low-thermal-conductivity fluorite-structured tantalate ceramic described in the above technical solution or the low-thermal-conductivity fluorite-structured tantalate ceramic prepared by the preparation method described in the above technical solution in a thermal barrier coating.

[0055] The present invention also provides a tantalate ceramic thermal barrier coating, the components of which include the low-thermal-conductivity fluorite-structured tantalate ceramic described in the above technical solution or the low-thermal-conductivity fluorite-structured tantalate ceramic prepared by the preparation method described in the above technical solution.

[0056] The present invention also provides a preparation method for the tantalate ceramic thermal barrier coating described in the above technical solution, including the following steps:

[0057] Spray the powder obtained by crushing the low-thermal-conductivity fluorite-structured tantalate ceramic described in the above technical solution or the low-thermal-conductivity fluorite-structured tantalate ceramic prepared by the preparation method described in the above technical solution onto the substrate to form a tantalate ceramic thermal barrier coating.

[0058] In the present invention, the particle size of the powder obtained by crushing the low-thermal-conductivity fluorite-structured tantalate ceramic is preferably 30 - 100 μm, more preferably 30 - 60 μm.

[0059] In the present invention, the spraying is preferably atmospheric plasma spraying; the parameters of the atmospheric plasma spraying are as follows: after preheating the substrate twice with a spray gun, powder deposition is carried out on the preheated substrate. The spraying voltage is preferably 100 - 160V, more preferably 120 - 160V, the spraying current is preferably 360 - 430A, more preferably 380 - 420A, the main gas argon flow rate is preferably 85 - 95L / min, more preferably 85 - 90L / min, the hydrogen flow rate is 12 - 18L / min, more preferably 13 - 16L / min, the distance between the spray gun and the substrate is preferably 85 - 100mm, more preferably 90 - 95mm, the spray gun moving speed is preferably 400 - 500mm / s, more preferably 420 - 480mm / s, and the powder feeding rate control is preferably 8.6 - 11.5g / min, more preferably 9 - 11g / min; the number of spraying times is preferably 30 - 65 times, more preferably 40 - 50 times, and most preferably 45 times.

[0060] In the embodiment of the present invention, the substrate is a superalloy substrate sprayed with a NiCoCrAlY bonding layer.

[0061] In the present invention, the thickness of the tantalate ceramic thermal barrier coating is preferably 300 - 500μm, more preferably 350 - 450μm, and most preferably 425μm.

[0062] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the embodiments in the present invention, but they cannot be understood as limiting the protection scope of the present invention.

[0063] The equipment and raw materials used in the following embodiments are as follows:

[0064] The metal oxide nanopowders (Ho2O3, Y2O3, Dy2O3, Yb2O3, and Ta2O5) are produced by Shanghai Macklin Biochemical Technology Co., Ltd., with a purity ≥ 99.9%;

[0065] Isopropyl alcohol is produced by Shanghai Lingfeng Chemical Reagent Co., Ltd., with a purity ≥ 99.9%;

[0066] Absolute ethanol is produced by Sinopharm Chemical Reagent Co., Ltd., with a purity ≥ 99.9%;

[0067] The high-energy wet mill used in the wet grinding process is the 01 - HDDM high-energy wet mill produced by Union Process Company of the United States;

[0068] The electrothermal forced-air drying oven used for the drying oven is the DHG9040HA drying oven produced by Zhejiang Hangzhou Lantian Laboratory Instrument Factory;

[0069] The pressureless reaction sintering furnace uses the KSL-1700 muffle furnace produced by Hefei Kejing Materials Technology Co., Ltd.

[0070] Example 1

[0071] Commercially available metal oxide powders (Y2O3, Yb2O3, Dy2O3, and Ta2O5 with particle sizes of 3 - 8 μm and purity ≥ 99.9%) were weighed according to the molar ratio of metal atoms nY∶nYb∶nDy∶nTa = 1∶1∶1∶1 and mixed using a high-energy wet mill. Isopropyl alcohol and ZrO2 grinding balls with a diameter of 0.3 mm were used as the wet grinding medium. The mass ratio of grinding balls, powder, and isopropyl alcohol was controlled to be 10∶1∶2, and the wet mill was rotated at 2000 r / min. After wet grinding for 6 h, the mixed slurry was washed 5 times through a 300-mesh sieve with ethanol to separate the grinding balls. The separated mixed solution was dried in a blast drying oven at 120 °C for 12 h, and then the powder was ground using an agate mortar for later use.

[0072] 3 g of the mixed and dried powder was weighed and placed into a mold with a diameter of 10 mm, and compacted under a uniaxial pressure of 10 MPa for 5 min. The formed green body was subjected to cold isostatic pressing at a pressure of 250 MPa for 15 min to obtain a ceramic green body.

[0073] The ceramic green body was placed in a muffle furnace for pressureless reaction sintering. It was heated from room temperature to 1200 °C at a heating rate of 5 °C / min, then heated to 1650 °C at a heating rate of 2 °C / min, held for 30 h, cooled to 1200 °C at a cooling rate of 2 °C / min, and then cooled to room temperature at a cooling rate of 5 °C / min to obtain a dense and uniform low-thermal-conductivity fluorite-structured tantalate ceramic with a density of up to 99%.

[0074] Example 2

[0075] Commercially available metal oxide powders (Ho2O3, Yb2O3, Dy2O3, and Ta2O5 with particle sizes of 3 - 8 μm and purity ≥ 99.9%) were weighed according to the molar ratio of metal atoms nHo∶nYb∶nDy∶nTa = 1∶1∶1∶1 and mixed using a high-energy wet mill. Absolute ethanol and ZrO2 grinding balls with a diameter of 0.3 mm were used as the wet grinding medium. The mass ratio of grinding balls, powder, and isopropyl alcohol was controlled to be 10∶1∶3, and the wet mill was rotated at 2000 r / min. After wet grinding for 6 h, the mixed slurry was washed 5 times through a 300-mesh sieve with ethanol to separate the grinding balls. The separated mixed solution was dried in a blast drying oven at 120 °C for 12 h, and then the powder was ground using an agate mortar for later use.

[0076] Weigh 3 g of the mixed and dried powder and put it into a mold with a diameter of 10 mm. Compact it under a uniaxial pressure of 10 MPa for 5 min; subject the formed green body to cold isostatic pressing at a pressure of 250 MPa for 15 min to obtain a ceramic green body.

[0077] Put the ceramic green body into a muffle furnace for pressureless reactive sintering. Heat it from room temperature to 1200 °C at a heating rate of 5 °C / min, then heat it to 1650 °C at a heating rate of 2 °C / min, hold for 30 h, cool it to 1200 °C at a cooling rate of 2 °C / min, and then cool it to room temperature at a cooling rate of 5 °C / min to obtain a dense and uniform tantalate ceramic with a low thermal conductivity fluorite structure, and the relative density can reach 98%.

[0078] Example 3

[0079] The difference from Example 1 is that the molar ratio of metal atoms is nY∶nYb∶nDy∶nTa = 0.7∶1.3∶1∶1, and the rest is the same as in Example 1.

[0080] Example 4

[0081] The difference from Example 2 is that the metal element Yb is replaced by an equimolar amount of Y, and the rest is the same as in Example 2.

[0082] Example 5

[0083] The difference from Example 2 is that the molar ratio of metal atoms is nHo∶nYb∶nDy∶nTa = 0.75∶1.0∶1.25∶1, and the rest is the same as in Example 2.

[0084] Example 6

[0085] The difference from Example 1 is that the molar ratio of metal atoms is nHo∶nYb∶nDy∶nTa = 1.28∶0.8∶0.92∶1, and the rest is the same as in Example 1.

[0086] Comparative Example 1

[0087] The difference from Example 1 is that the molar ratio of metal atoms is nY∶nYb∶nDy∶nTa = 1.7∶1∶0.3∶1, and the rest is the same as in Example 1.

[0088] Comparative Example 2

[0089] The difference from Example 1 is that the sintering temperature is 1400 °C and the holding time is 10 h. The rest is the same as in Example 1. Compared with Example 1, the sample is not a single fluorite phase and has a lower relative density.

[0090] Application Example 1

[0091] The low-thermal-conductivity fluorite-structured tantalate ceramic obtained in Example 1 was crushed and granulated into a spray powder with a particle size of 30 - 50 μm and high fluidity;

[0092] The superalloy substrate with the NiCoCrAlY bonding layer already sprayed was installed on the spraying rack. The distance between the spray gun and the substrate was adjusted to 90 mm. The substrate was preheated twice with the spraying parameters of a spraying voltage of 160 V, a current of 380 A, a main gas argon flow rate of 90 L / min, a hydrogen flow rate of 16 L / min, and a spray gun moving speed of 460 mm / s. After preheating, powder deposition was carried out on the substrate at a powder feeding rate of 9.0 g / min for 45 times, and the final coating thickness was 425 μm, obtaining a tantalate ceramic thermal barrier coating.

[0093] Application Example 2

[0094] The difference from Application Example 1 is that the low-thermal-conductivity fluorite-structured tantalate ceramic obtained in Example 1 was replaced with the low-thermal-conductivity fluorite-structured tantalate ceramic obtained in Example 2, and the rest was the same as Application Example 1.

[0095] Application Example 3

[0096] The difference from Application Example 1 is that the low-thermal-conductivity fluorite-structured tantalate ceramic obtained in Example 1 was replaced with the low-thermal-conductivity fluorite-structured tantalate ceramic obtained in Example 3, and the rest was the same as Application Example 1.

[0097] Application Example 4

[0098] The difference from Application Example 1 is that the voltage was adjusted to 400 V and the hydrogen flow rate was 18 L / min, and the rest was the same as Application Example 1.

[0099] Comparative Application Example 1

[0100] The difference from Application Example 1 is that the distance between the spray gun and the substrate was 105 mm, and the rest was the same as Application Example 1. As a result, the sprayed powder could not be well deposited on the substrate.

[0101] Comparative Application Example 2

[0102] The difference from Application Example 1 is that the distance between the spray gun and the substrate was 75 mm, and the rest was the same as Application Example 1. As a result, a molten area appeared in the sprayed coating.

[0103] Comparative Application Example 3

[0104] The difference from Application Example 4 is that the spray gun moving speed was adjusted to 380 mm / s, and the rest was the same as Application Example 4. As a result, a molten area appeared in the sprayed coating.

[0105] Performance Test

[0106] (1) The thermal conductivities of the low-thermal-conductivity fluorite-structured tantalate ceramics obtained in Examples 1-6, the tantalate ceramics obtained in Comparative Examples 1-2, and the thermal barrier coatings of the tantalate ceramics obtained in Application Examples 1-4 were tested and verified, and the results are shown in Table 1.

[0107] Table 1 Thermal conductivities of the low-thermal-conductivity fluorite-structured tantalate ceramics obtained in Examples 1-6, the tantalate ceramics obtained in Comparative Examples 1-2, and the thermal barrier coatings of the tantalate ceramics obtained in Application Examples 1-4

[0108]

[0109]

[0110] As can be seen from Table 1, the tantalate bulk materials prepared in the present invention have an ultra-low thermal conductivity, which is only 0.29 times that of the currently used YSZ material. The thermal conductivity of the prepared coating material is even lower, only 0.7 W / (m·k) at 1500 °C.

[0111] (2) The low-thermal-conductivity fluorite-structured tantalate ceramic prepared in Example 1 was subjected to X-ray diffraction testing, and the results are as Figure 1 shown.

[0112] From Figure 1 it can be concluded that the low-thermal-conductivity fluorite-structured tantalate ceramic prepared in the present invention has good crystallinity and is a single fluorite structure.

[0113] (3) The low-thermal-conductivity fluorite-structured tantalate ceramic prepared in Example 1 was subjected to scanning electron microscopy, and the results are as Figure 2 shown.

[0114] From Figure 2 it can be seen that the low-thermal-conductivity fluorite-structured tantalate ceramic prepared in the present invention has a very high density (99%), the average grain size is 2-3 μm, and the grain size distribution is uniform.

[0115] (4) The bond energy between cations and anions in the low-thermal-conductivity fluorite-structured tantalate ceramic prepared in Example 1 was tested, and the results are as Figure 3 shown.

[0116] From Figure 3 it can be concluded that the bond energy of Ta-O is the strongest and the bond energy of Dy-O is the weakest, which forms highly disordered chemical bonds in the system and scatters phonons with a wide range of wavelengths, thus significantly reducing the thermal conductivity of the ceramic.

[0117] (5) The tantalate ceramic thermal barrier coating prepared in Application Example 1 of the present invention was subjected to backscattered electron imaging testing, and the results are as Figure 4 shown.

[0118] FromFigure 4 It can be seen that the thickness of the tantalate ceramic thermal barrier coating is about 425 μm, the powder melting state is good, the porosity is less, and the ceramic layer and the bonding layer are closely combined.

[0119] (6) The tantalate ceramic prepared in Comparative Example 1 was subjected to X-ray diffraction test, and as a result, a peak appeared at 28.3° in the XRD pattern.

[0120] Although the above embodiments have made a detailed description of the present invention, they are only a part of the embodiments of the present invention rather than all embodiments. People can also obtain other embodiments based on these embodiments without creative efforts, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A tantalate ceramic with a low thermal conductivity fluorite structure, characterized in that, It has a defective fluorite structure with the chemical formula Re1 x Re2 y Dy z TaO7, where x + y + z = 3, and x and y are independently 0.5 to 1.5, 0.88 < z < 1.32, and Re1 and Re2 are independently yttrium, holmium, erbium, thulium or ytterbium; The 2θ angle of the (111) plane of the X-ray diffraction peak of the low-thermal-conductivity fluorite-structured tantalate ceramic is 29.08 to 29.7°; the radius difference between Re1 ions and Re2 ions in the low-thermal-conductivity fluorite-structured tantalate ceramic 2. A method for preparing the tantalate ceramic with a low thermal conductivity fluorite structure according to claim 1, characterized in that, It includes the following steps: Mix the oxides of Re1, Re2, Dy and Ta, and successively carry out wet grinding, washing and drying to obtain a mixed metal oxide powder; Press the mixed metal oxide powder, and sinter the obtained ceramic green body to obtain a low-thermal-conductivity fluorite-structured tantalate ceramic.

3. According to the preparation method described in claim 2, characterized in that, The rotation speed of the wet grinding is 1500-2000 r / min; the time of the wet grinding is 5-8 h; the grinding solvent used for the wet grinding is one or more of isopropyl alcohol, absolute ethanol and deionized water; the diameter of the grinding balls used for the wet grinding is 0.3-0.5 mm, and the material is zirconia.

4. According to the preparation method described in claim 2 or 3, characterized in that, The total amount of the oxides of Re1, Re2, Dy and Ta, the mass ratio of the grinding solvent to the grinding balls is 1-2:8-10:2-3.

5. According to the preparation method described in claim 2, characterized in that, The pressure of the pressing is 200-280 MPa, and the pressure holding time is 10-20 min.

6. According to the preparation method described in claim 2, characterized in that, The temperature of the sintering is 1500-1750 °C, and the heat preservation time is 10-30 h.

7. The application of the tantalate ceramic with a low thermal conductivity fluorite structure according to claim 1 or the tantalate ceramic with a low thermal conductivity fluorite structure prepared by the preparation method described in any one of claims 2 to 6 in a thermal barrier coating.

8. A tantalate ceramic thermal barrier coating, characterized in that, Its components include the low-thermal-conductivity fluorite-structured tantalate ceramic described in claim 1 or the low-thermal-conductivity fluorite-structured tantalate ceramic prepared by the preparation method described in any one of claims 2-6.

9. A method for preparing the tantalate ceramic thermal barrier coating according to claim 8, characterized in that, It includes the following steps: Spray the powder obtained by crushing the low-thermal-conductivity fluorite-structured tantalate ceramic described in claim 1 or the low-thermal-conductivity fluorite-structured tantalate ceramic prepared by the preparation method described in any one of claims 2-6 onto the substrate to form a tantalate ceramic thermal barrier coating.

Images