CN117209274A - Tantalate ceramic with low thermal conductivity fluorite structure and preparation method and application thereof - Google Patents
Tantalate ceramic with low thermal conductivity fluorite structure and preparation method and application thereof Download PDFInfo
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Abstract
The invention belongs to the technical field of thermal barrier coatings, and particularly relates to tantalate ceramic with a low-thermal-conductivity fluorite structure, and a preparation method and application thereof. The tantalate ceramic with the low-thermal-conductivity fluorite structure provided by the invention has a defective fluorite structure, and the chemical formula is Re1 x Re2 y Dy z TaO 7 Wherein x+y+z=3, x, y and z are independently 0.5-1.5, R <1 > and Re < 2 > are independently yttrium, holmium, erbium, thulium or ytterbium, dy with minimum Re-O bond energy is introduced into tantalate, huge bond energy difference is formed between the Dy and Ta-O, other two rare earth ions are introduced, the quality difference and the bond energy disorder are constructed, the stable crystal structure at high temperature is ensured, a lower thermal conductivity ceramic system is obtained by constructing uneven chemical bonds in the system, the entropy value of the ceramic system is increased by multi-element rare earth co-doping, the high temperature stability of tantalate ceramic is improved, and long-time service at high temperature is realized.
Description
Technical Field
The invention belongs to the technical field of thermal barrier coatings, and particularly relates to tantalate ceramic with a low-thermal-conductivity fluorite structure, and a preparation method and application thereof.
Background
The thermal barrier coating is a heat-insulating functional coating widely applied to the surfaces of hot end components such as combustion chambers and blades of an aviation turbine engine, and can reduce the surface temperature of protected metal, thereby improving the working efficiency and prolonging the service life.
The thermal barrier coating material widely used at present is 6-8 wt.% yttria stabilized zirconia (6-8 YSZ), and along with the increase of the service temperature of the existing engine (the thrust weight ratio of the front inlet temperature of the turbine of the 12-15-stage aeroengine can reach 1700-1800 ℃), the ceramic material has two serious defects at present. Firstly, the ceramic material has insufficient high-temperature stability, when the service temperature exceeds 1250 ℃, YSZ undergoes phase change and expands with 4-6% of volume, so that the coating cracks and fails. Next, the thermal conductivity of the ceramic material is also high (about 2.5 W.m -1 ·K -1 900 deg.c) results in excessive alloy matrix temperature and reduced engine efficiency. It is therefore imperative to find new thermal barrier coating materials with the need for high thrust to weight ratios and higher temperature economies of the engine.
Disclosure of Invention
In view of the above, the invention aims to provide a low thermal conductivity fluorite structure tantalate ceramic, a preparation method and application thereof.
In order to achieve the above object, the present invention provides the following technical solutions:
the 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 TaO 7 Wherein x+y+z=3, and x, y, z are independently 0.5 to 1.5, R1 and Re2 are independentlyAnd is yttrium, holmium, erbium, thulium or ytterbium.
Preferably, when 0.88<z<1.32, wherein the 2 theta angle of the (111) plane of the X-ray diffraction peak of the tantalate ceramic with the low thermal conductivity fluorite structure is 29.08-29.7 degrees; radius difference of Re1 ion and Re2 ion in tantalate ceramic with low thermal conductivity fluorite structure
The invention also provides a preparation method of the tantalate ceramic with the low-thermal-conductivity fluorite structure, which comprises the following steps:
mixing Re1 oxide, re2 oxide, dy oxide and Ta oxide, and sequentially carrying out wet grinding, washing and drying to obtain mixed metal oxide powder;
and pressing the mixed metal oxide powder, and sintering the obtained ceramic blank to obtain the tantalate ceramic with the low-thermal-conductivity fluorite structure.
Preferably, the rotating speed of the wet grinding is 1500-2000 r/min; the wet milling time is 5-8 hours; the grinding solvent used in the wet grinding is one or more of isopropanol, absolute ethyl alcohol and deionized water; the diameter of the grinding ball used for wet grinding is 0.3-0.5 mm, and the grinding ball is made of zirconia.
Preferably, the mass ratio of the grinding solvent to the grinding balls is 1-2:8-10:2-3, and the total amount of the oxide of Re1, the oxide of Re2, the oxide of Dy and the oxide of Ta.
Preferably, the pressing pressure is 200-280 MPa, and the pressure maintaining time is 10-20 min.
Preferably, the sintering temperature is 1500-1750 ℃, and the heat preservation time is 10-30 h.
The invention also provides application of the low-thermal-conductivity fluorite-structure tantalate ceramic in the technical scheme or the low-thermal-conductivity fluorite-structure tantalate ceramic prepared by the preparation method in the technical scheme in thermal barrier coating.
The invention also provides a tantalate ceramic thermal barrier coating, which comprises the tantalate ceramic with the low thermal conductivity fluorite structure prepared by the technical scheme or the tantalate ceramic with the low thermal conductivity fluorite structure prepared by the preparation method.
The invention also provides a preparation method of the tantalate ceramic thermal barrier coating, which comprises the following steps:
the tantalate ceramic with the low thermal conductivity fluorite structure prepared by the technical scheme or the tantalate ceramic with the low thermal conductivity fluorite structure prepared by the preparation method of the technical scheme is sprayed on a substrate through crushed powder to form the tantalate ceramic thermal barrier coating.
The 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 TaO 7 Wherein x+y+z=3, and x, y, z are independently 0.5 to 1.5, and Re1 and Re2 are independently yttrium, holmium, erbium, thulium or ytterbium. Dy with the minimum Re-O bond energy is introduced into tantalate, huge bond energy difference is formed between the Dy and Ta-O, other two rare earth ions are introduced, the structural quality difference and the bond energy are disordered, the bond energy of Dy-O is only 1/4 of the bond energy of Ta-O, the bond energy (Re-O) of the other two doped rare earth ions is higher than that of Dy-O, the bond energy is lower than that of Ta-O, and by constructing a non-uniform chemical bond in a system, the low-frequency phonon with longer scattering wavelength is more favorable, and the intrinsic oxygen vacancy in the system, the ion radius difference formed after the rare earth ions are doped and other factors are adopted, the phonon scattering in a middle-high frequency phonon with a larger wavelength range is regulated and controlled, so that a lower thermal conductivity ceramic system is obtained; on the other hand, the multi-element rare earth co-doping increases the entropy value of the ceramic system, improves the high-temperature stability of tantalate ceramic, keeps the high-temperature phase and the low-temperature phase to be uniform and tetragonal, does not generate phase change in the high-temperature phase, and realizes long-time service at high temperature by using the thermal barrier coating prepared by the method. The results of the examples show that the low thermal conductivity tantalate ceramic material provided by the invention has low thermal conductivity (the thermal conductivity of the tantalate ceramic material at 100 ℃ is 1.02W/(m.K), the thermal conductivity of the thermal barrier coating prepared by the tantalate ceramic material is 0.46W/(m.K)), which is only 0.29 times that of 8YSZ currently in service (at room temperature), and the prepared tantalate ceramic thermal expansion coating has extremely low thermal conductivity of only 0.71 W.m -1 K -1 (1500 ℃) and stable physical and chemical properties at high temperature, and satisfies the next conditionThe coating is used as a substitute for thermal barrier coating.
The invention also provides a preparation method of the tantalate ceramic with the low thermal conductivity fluorite structure, which has the advantages of simple preparation process, convenient operation, low cost, small powder loss and controllable element, phase composition and microstructure.
Drawings
FIG. 1 is an XRD pattern of tantalate ceramic having a low thermal conductivity fluorite structure prepared in example 1 of the present invention;
FIG. 2 is an SEM image of tantalate ceramic of low thermal conductivity fluorite structure prepared in example 1 of the present invention;
FIG. 3 is a graph showing the results of evaluation test of bond energy between anions and cations in tantalate ceramic of low thermal conductivity fluorite structure prepared in example 1 of the present invention;
FIG. 4 is a BSE chart of the tantalate ceramic thermal barrier coating prepared in application example 1 of the present invention.
Detailed Description
The 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 TaO 7 Wherein x+y+z=3, and x, y, z are independently 0.5 to 1.5, and Re1 and Re2 are independently yttrium, holmium, erbium, thulium or ytterbium.
The present invention is not limited to the specific source of the raw materials, and may be commercially available products known to those skilled in the art, unless otherwise specified.
The tantalate ceramic with the low-thermal-conductivity fluorite structure provided by the invention has a defective fluorite structure, and the chemical formula is Re1 x Re2 y Dy z TaO 7 Wherein x+y+z=3, and x, y, z are independently 0.5 to 1.5, and Re1 and Re2 are independently yttrium, holmium, erbium, thulium or ytterbium.
In the present invention, x is preferably 0.68 to 1.44, more preferably 1; preferably, y is 0.68 to 1.44, more preferably 1;0.88< z <1.32, preferably 0.9 to 1.3, most preferably 1.
In the present invention, the Re1 is preferably yttrium (Y), holmium (Ho), erbium (Er), thulium (Tm) or ytterbium (Yb), more preferably yttrium or holmium; the Re2 is preferably yttrium (Y), holmium (Ho), erbium (Er), thulium (Tm) or ytterbium (Yb), more preferably ytterbium.
Dy with the minimum Re-O bond energy is introduced into tantalate, huge bond energy difference is formed between the Dy and Ta-O, other two rare earth ions are introduced, the structural quality difference and the bond energy are disordered, the bond energy of Dy-O is only 1/4 of the bond energy of Ta-O, the bond energy (Re-O) of the other two doped rare earth ions is higher than that of Dy-O, the bond energy is lower than that of Ta-O, and by constructing a non-uniform chemical bond in a system, the low-frequency phonon with longer scattering wavelength is more favorable, and the intrinsic oxygen vacancy in the system, the ion radius difference formed after the rare earth ions are doped and other factors are adopted, the phonon scattering in a middle-high frequency phonon with a larger wavelength range is regulated and controlled, so that a lower thermal conductivity ceramic system is obtained; on the other hand, the multi-element rare earth co-doping increases the entropy value of the ceramic system, improves the high-temperature phase stability of tantalate ceramic, and realizes long-time service at high temperature by using the thermal barrier coating prepared by the method.
In the present invention, the low thermal conductivity fluorite structured tantalate ceramic preferably has a grain size of 0.3 to 10 μm, more preferably 1 to 6 μm, and a density of 96 to 99%, more preferably 98 to 99%.
When 0.88<z<1.32, the 2 [ theta ] angle of the (111) plane of the X-ray diffraction peak of the low thermal conductivity fluorite structure tantalate ceramic is preferably 29.08 to 29.7 DEG, more preferably 29.46 to 29.63 DEG, and the difference Deltar of the radii of Re1 ion and Re2 ion in the low thermal conductivity fluorite structure tantalate ceramic is preferablyThe crystal grain size of the low thermal conductivity fluorite structure tantalate ceramic is preferably 2-8 μm, more preferably 3-7 μm.
The technical principle of the invention is as follows: the conduction of heat in solids is mainly achieved by lattice vibrations and the movement of free electrons, whereas for tantalate ceramics, having a larger band gap, it is considered as an electronic insulator, so that the conduction of heat in tantalate materials relies on lattice vibrations, i.e. phonon heat transfer. The tantalate ceramic provided by the invention has intrinsic oxygen vacancies, which can obviously scatter high-frequency phonons with shorter wavelength, introduce different rare earth ions, construct different ion radius differences to scatter medium-high frequency phonons with longer wavelength, and for low-frequency phonons with longer wavelength, the scattering source of the dot defect cannot be reached, so that the tantalate ceramic provided by the invention introduces different binding energy, and changes the vibration frequency to achieve the effect of scattering low-frequency long-wavelength phonons by softening the crystal dispersion relation.
In the present invention, the difference in ionic radius is first controlledBecause increasing the ionic radius is unfavorable for lattice stabilization on the one hand, and the larger ionic radius is easy to form phonon standing waves, phonon resonance phenomenon is induced. Secondly, controlling the 2 theta angle of the (111) plane of an X-ray diffraction (XRD) peak to be 29.08-29.7 degrees, and when the main peak position of the (111) plane is lower than 29.08 degrees, the obtained ceramic block is unstable at high temperature and can generate phase change at 950-1000 ℃, so that the use requirement of the thermal barrier coating is not met; when the (111) plane main peak position is higher than 29.7 °, the obtained ceramic block will grow abnormally at high temperature, resulting in a decrease in material energy.
In the invention, the problem of crystal structure and ion size difference is considered, dysprosium (Dy) is firstly contained in a fixed system, because Dy-O bond energy is only 1/4 of Ta-O bond energy, bond energy (Re-O) of other two doped rare earth ions is higher than Dy-O bond energy and lower than Ta-O bond energy (bonding between anions and cations in tantalate obtained by calculation according to density functional theory is shown in figure 3), thus larger chemical bond non-uniformity is formed in the system, the low-frequency phonon with longer scattering wavelength is more facilitated, and intrinsic oxygen vacancies in the system, ion radius difference formed after rare earth ions are doped and other factors are scattered. Therefore, the tantalate ceramic prepared by the invention can scatter phonons with different wavelengths in a full range, regulate and control the heat conductivity, and better meet the purpose of using the thermal barrier coating at high temperature.
The invention also provides a preparation method of the tantalate ceramic with the low-thermal-conductivity fluorite structure, which comprises the following steps:
mixing Re1 oxide, re2 oxide, dy oxide and Ta oxide, and sequentially carrying out wet grinding, washing and drying to obtain mixed metal oxide powder;
and pressing the mixed metal oxide powder, and sintering the obtained ceramic blank to obtain the tantalate ceramic with the low-thermal-conductivity fluorite structure.
The invention mixes Re1 oxide, re2 oxide, dy oxide and Ta oxide, and carries out wet grinding to obtain wet grinding mixed suspension.
In the present invention, the oxide of Re1 and the oxide of Re2 are independently preferably Re 2 O 3 The method comprises the steps of carrying out a first treatment on the surface of the The oxide of Dy is preferably Dy 2 O 3 The method comprises the steps of carrying out a first treatment on the surface of the The oxide of Ta is preferably Ta 2 O 5 The method comprises the steps of carrying out a first treatment on the surface of the The particle size of the oxide of Re1, the oxide of Re2, the oxide of Dy and the oxide of Ta are independently preferably 3-8 mu m, and the purity is independently preferably more than or equal to 99.9%.
In the present invention, the rotational speed of the wet milling is preferably 1500 to 2000r/min, more preferably 2000r/min; the wet milling time is preferably 5 to 8 hours, more preferably 6 hours; the grinding solvent used in the wet grinding is preferably one or more of isopropanol, anhydrous ethanol and deionized water, and more preferably isopropanol; the diameter of the grinding ball used for wet grinding is preferably 0.3-0.5 mm, more preferably 0.3-0.4 mm, and the material is preferably zirconia. When the number of the grinding solvents is several, the mixing ratio of the different types of the grinding solvents is not particularly limited, and the grinding solvents can be mixed at random.
In the present invention, the mass ratio of the polishing solvent to the polishing balls, in total, of the oxide of Re1, the oxide of Re2, the oxide of Dy, and the oxide of Ta is preferably 1 to 2:8 to 10:2 to 3, more preferably 1 to 1.5:9 to 10:2 to 2.5.
The mixed feed liquid obtained by wet grinding is preferably screened before washing; the sieving is preferably performed with a 300 mesh screen. The invention separates the balls in the wet-milling mixed suspension by sieving.
After the wet-grinding mixed suspension is obtained, the wet-grinding mixed suspension is washed to obtain wet-grinding powder. In the present invention, the reagent used for the washing is preferably ethanol or isopropanol, more preferably ethanol; the number of times of the washing is preferably 4 to 6 times, more preferably 5 times; after each washing, the invention preferably carries out solid-liquid separation on the mixed liquid obtained by the washing; the solid-liquid separation is preferably sieving; the sieving is preferably performed with a 300 mesh screen. The invention does not limit the dosage of the reagent used for washing, and the wet-grinding powder is washed completely.
After the wet-grinding powder is obtained, the wet-grinding powder is dried to obtain the mixed metal oxide powder. In the present invention, the drying is preferably forced air drying; the air drying equipment is preferably an air drying oven; the drying temperature is preferably 100-120 ℃, more preferably 110-120 ℃; the drying time is preferably 10 to 15 hours, more preferably 11 to 13 hours.
After the drying, the invention preferably grinds the dried wet grinding powder; the grinding is preferably grinding with an agate mortar.
After the mixed metal oxide powder is obtained, the mixed metal oxide powder is pressed to obtain a ceramic blank.
The present invention preferably further comprises, before the pressing: compacting the mixed metal oxide powder; the equipment used for compaction is preferably a single-shaft press; the compacting is preferably performed by placing the mixed metal oxide powder in a mold; the pressure used for the compaction is preferably 3 to 15MPa, more preferably 10MPa; the dwell time for the compaction is preferably 2 to 10min, more preferably 5min. The present invention is not particularly limited, and a mold known in the art may be used. In an embodiment of the present invention, the diameter of the mold is 10mm.
In the present invention, the pressing is preferably unidirectional pressing, bidirectional pressing or cold isostatic pressing, more preferably cold isostatic pressing; the pressure of the pressing is preferably 200 to 280MPa, more preferably 220 to 250MPa, and the dwell time is preferably 10 to 20min, more preferably 10 to 15min.
After the ceramic blank is obtained, the invention sinters the ceramic blank to obtain tantalate ceramic with low thermal conductivity fluorite structure. In the invention, the sintering temperature is preferably 1500-1750 ℃, more preferably 1600-1700 ℃, and the heat preservation time is preferably 10-30 h, more preferably 20-30 h; the sintering is preferably pressureless reaction sintering.
In the present invention, the temperature-increasing program for increasing the temperature to the sintering temperature is preferably: after the temperature is raised from room temperature to 1200 ℃ at a temperature raising rate of 5-10 ℃/min, the temperature is raised from 1200 ℃ to a sintering temperature at a temperature raising rate of 2-5 ℃/min, more preferably: after the temperature is raised from room temperature to 1200 ℃ at a heating rate of 5-8 ℃/min, the temperature is raised from 1200 ℃ to sintering temperature at a heating rate of 2-3 ℃/min.
In the present invention, the cooling procedure from the sintering temperature to the room temperature is preferably: cooling to 1200 ℃ at a cooling rate of 2-5 ℃/min from the sintering temperature, and cooling to room temperature at a cooling rate of 5-10 ℃/min, more preferably: cooling to 1200 deg.c at the cooling rate of 2-3 deg.c/min and cooling to room temperature at the cooling rate of 5-8 deg.c/min.
The tantalate ceramic with the low thermal conductivity fluorite structure is prepared by adopting a solid-phase method for pressureless reaction sintering, and has the advantages of simple process, convenient operation, low cost, small powder loss, and controllable element, phase composition and microstructure.
The invention also provides application of the low-thermal-conductivity fluorite-structure tantalate ceramic in the technical scheme or the low-thermal-conductivity fluorite-structure tantalate ceramic prepared by the preparation method in the technical scheme in thermal barrier coating.
The invention also provides a tantalate ceramic thermal barrier coating, which comprises the tantalate ceramic with the low thermal conductivity fluorite structure prepared by the technical scheme or the tantalate ceramic with the low thermal conductivity fluorite structure prepared by the preparation method.
The invention also provides a preparation method of the tantalate ceramic thermal barrier coating, which comprises the following steps:
the tantalate ceramic with the low thermal conductivity fluorite structure prepared by the technical scheme or the tantalate ceramic with the low thermal conductivity fluorite structure prepared by the preparation method of the technical scheme is sprayed on a substrate through crushed powder to form the tantalate ceramic thermal barrier coating.
In the present invention, the particle size of the powder obtained by crushing the low thermal conductivity fluorite structured tantalate ceramic is preferably 30 to 100 μm, more preferably 30 to 60 μm.
In the present invention, the spraying is preferably atmospheric plasma spraying; the parameters of the atmospheric plasma spraying are as follows: after preheating a matrix twice by using a spray gun, carrying out powder deposition on the preheated matrix, controlling the spraying voltage to be preferably 100-160V, more preferably 120-160V, the spraying current to be preferably 360-430A, more preferably 380-420A, the main gas argon flow to be preferably 85-95L/min, more preferably 85-90L/min, the hydrogen flow to be 12-18L/min, more preferably 13-16L/min, the distance between the spray gun and a substrate to be preferably 85-100 mm, more preferably 90-95 mm, the moving speed of the spray gun to be preferably 400-500 mm/s, more preferably 420-480 mm/s, and the powder feeding rate to be preferably 8.6-11.5 g/min, more preferably 9-11 g/min; the number of spraying is preferably 30 to 65, more preferably 40 to 50, and most preferably 45.
In the embodiment of the invention, the substrate is a high-temperature alloy substrate sprayed with a NiCoCrAlY bonding layer.
In the present invention, the thickness of the tantalate ceramic thermal barrier coating is preferably 300 to 500. Mu.m, more preferably 350 to 450. Mu.m, and most preferably 425. Mu.m.
The technical solutions of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention, but they should not be construed as limiting the scope of the present invention.
The equipment and materials used in the following examples are as follows:
metal oxide nanopowder (Ho) 2 O 3 、Y 2 O 3 、Dy 2 O 3 、Yb 2 O 3 Ta and the like 2 O 5 ) Is produced by Shanghai Michelia Biochemical technology Co., ltd, and the purity is more than or equal to 99.9%;
the isopropyl alcohol is produced by Shanghai Lingfeng chemical reagent Co., ltd, and the purity is more than or equal to 99.9%;
the absolute ethyl alcohol is produced by the chemical reagent company of the national medicine group, and the purity is more than or equal to 99.9 percent;
the high-energy wet mill used in the wet milling Process is a 01-HDDM high-energy wet mill manufactured by Union Process, inc. of America;
the electrothermal blowing drying oven is a DHG9040HA drying oven produced by Zhejiang Hangzhou blue sky laboratory instrument factory;
the pressureless reaction sintering furnace is a KSL-1700 muffle furnace manufactured by the Synechock materials technology Co.
Example 1
The commercially available metal oxide powder (Y) was weighed in a molar ratio of metal atoms nY: nYb: nDy: nTa =1:1:1 2 O 3 、Yb 2 O 3 、Dy 2 O 3 Ta and the like 2 O 5 The grain size is 3-8 mu m, the purity is more than or equal to 99.9 percent, and the mixture is mixed by a high-energy wet mill and is prepared by isopropanol and ZrO with the diameter of 0.3mm 2 The grinding balls are wet grinding media, and the mass ratio of the grinding balls to the powder to the isopropanol is controlled to be 10:1: 2, wet grinding for 6 hours at the rotating speed of 2000r/min, washing the mixed slurry with ethanol for 5 times by using a 300-mesh screen to separate grinding balls, drying the separated mixed solution in a blast drying box at 120 ℃ for 12 hours, and then grinding the powder with an agate mortar for later use;
weighing 3g of mixed and dried powder, putting the powder into a die with the diameter of 10mm, adopting uniaxial pressure of 10MPa, and maintaining the pressure for 5min for compaction; cold isostatic pressing is carried out on the formed blank body, the pressure is 250MPa, and the pressure is maintained for 15min, so that a ceramic blank body is obtained;
and (3) placing the ceramic blank into a muffle furnace for pressureless reaction sintering, heating to 1200 ℃ from room temperature at a heating rate of 5 ℃/min, heating to 1650 ℃ at a heating rate of 2 ℃/min, preserving heat for 30h, cooling to 1200 ℃ at a cooling rate of 2 ℃/min, and cooling to room temperature at a cooling rate of 5 ℃/min to obtain compact and uniform tantalate ceramic with a low thermal conductivity fluorite structure, wherein the compactness can reach 99%.
Example 2
The commercially available metal oxide powder (Ho) was weighed in a molar ratio of metal atoms nHo: nYb: nDy: nTa =1:1:1 2 O 3 、Yb 2 O 3 、Dy 2 O 3 Ta and the like 2 O 5 The grain size is 3-8 mu m, the purity is more than or equal to 99.9 percent, and the mixture is mixed by a high-energy wet mill, absolute ethyl alcohol and ZrO with the diameter of 0.3mm 2 The grinding balls are wet grinding media, and the mass ratio of the grinding balls to the powder to the isopropanol is controlled to be 10:1: 3, after wet grinding for 6 hours, washing the mixed slurry with ethanol for 5 times by using a 300-mesh screen to separate grinding balls, drying the separated mixed solution in a blast drying box at 120 ℃ for 12 hours, and then grinding the powder with an agate mortar for later use;
weighing 3g of mixed and dried powder, putting the powder into a die with the diameter of 10mm, adopting uniaxial pressure of 10MPa, and maintaining the pressure for 5min for compaction; cold isostatic pressing is carried out on the formed blank body, the pressure is 250MPa, and the pressure is maintained for 15min, so that a ceramic blank body is obtained;
and (3) placing the ceramic blank into a muffle furnace for pressureless reaction sintering, heating to 1200 ℃ from room temperature at a heating rate of 5 ℃/min, heating to 1650 ℃ at a heating rate of 2 ℃/min, preserving heat for 30h, cooling to 1200 ℃ at a cooling rate of 2 ℃/min, and cooling to room temperature at a cooling rate of 5 ℃/min to obtain compact and uniform tantalate ceramic with a low thermal conductivity fluorite structure, wherein the compactness can reach 98%.
Example 3
The difference from example 1 is that the molar ratio of metal atoms is nY: nYb: nDy: nTa =0.7:1.3:1:1, the remainder being identical to example 1.
Example 4
The difference from example 2 is that the metallic element Yb is replaced with an equimolar amount of Y, and the remainder is identical to example 2.
Example 5
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, the remainder being identical to example 2.
Example 6
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, the remainder being identical to example 1.
Comparative example 1
The difference from example 1 is that the molar ratio of metal atoms is nY: nYb: nDy: nTa =1.7:1:0.3:1, the remainder being identical to example 1.
Comparative example 2
The difference from example 1 is that the sintering temperature is 1400 ℃, the holding time is 10h, the rest is identical to example 1, and compared with example 1, the sample is not a single fluorite phase and has lower compactness.
Application example 1
Crushing the tantalate ceramic with the low thermal conductivity fluorite structure obtained in the example 1, and granulating to obtain spraying powder with high fluidity, wherein the particle size of the spraying powder is 30-50 mu m;
and (3) mounting the high-temperature alloy matrix sprayed with the NiCoCrAlY bonding layer on a spraying frame, adjusting the distance between a spray gun and a substrate to be 90mm, preheating the substrate twice by adopting spraying parameters of 160V spraying voltage, 380A current, 90L/min main gas argon flow, 16L/min hydrogen flow and 460mm/s spray gun moving speed, carrying out powder deposition on the preheated substrate at a powder feeding rate of 9.0g/min, and spraying for 45 times, wherein the thickness of the final coating is 425 mu m, thus obtaining the tantalate ceramic thermal barrier coating.
Application example 2
The difference from application example 1 is that the low thermal conductivity fluorite structure tantalate ceramic obtained in example 1 was replaced with the low thermal conductivity fluorite structure tantalate ceramic obtained in example 2, and the rest is the same as application example 1.
Application example 3
The difference from application example 1 is that the low thermal conductivity fluorite structure tantalate ceramic obtained in example 1 was replaced with the low thermal conductivity fluorite structure tantalate ceramic obtained in example 3, and the rest is the same as application example 1.
Application example 4
The difference from application example 1 was that the voltage was adjusted to 400V, the hydrogen flow rate was 18L/min, and the rest was the same as application example 1.
Comparative application example 1
The difference from application example 1 is that the distance between the spray gun and the substrate is 105mm, and the rest corresponds to application example 1, with the result that the spray powder does not deposit well on the substrate.
Comparative application example 2
The difference from application example 1 was that the distance between the spray gun and the substrate was 75mm, and the rest was identical to application example 1, with the result that the coating formed by spraying showed a molten zone.
Comparative application example 3
The difference from application example 4 was that the movement speed of the spray gun was adjusted to 380mm/s, and the rest was the same as application example 4, with the result that the coating formed by spraying showed a molten zone.
Performance testing
(1) Thermal conductivity tests were performed on the tantalate ceramics with low thermal conductivity fluorite structure obtained in examples 1 to 6, the tantalate ceramics obtained in comparative examples 1 to 2, and the tantalate ceramic thermal barrier coatings obtained in application examples 1 to 4, and the results are shown in table 1.
Table 1 thermal conductivity of tantalate ceramics with low thermal conductivity fluorite structure obtained in examples 1 to 6, tantalate ceramics obtained in comparative examples 1 to 2, and tantalate ceramic thermal barrier coatings obtained in application examples 1 to 4
As can be seen from Table 1, the tantalate bulk material prepared in the present invention has ultra-low thermal conductivity, which is only 0.29 times that of the YSZ material currently in service. The thermal conductivity of the prepared coating material is lower, and the thermal conductivity is only 0.7W/(m.k) at 1500 ℃.
(2) The low thermal conductivity fluorite structured tantalate ceramic prepared in example 1 was subjected to an X-ray diffraction test, and the result is shown in fig. 1.
From fig. 1, it can be derived that: the tantalate ceramic with the low-thermal-conductivity fluorite structure prepared by the method has good crystallinity and is of a single fluorite structure.
(3) Electron microscopy was performed on the low thermal conductivity fluorite structured tantalate ceramic prepared in example 1, and the results are shown in fig. 2.
As can be seen from FIG. 2, the tantalate ceramic with the low thermal conductivity fluorite structure prepared by the invention has high density (99%), the average grain size is 2-3 μm, and the grain size distribution is uniform.
(4) The bond energy between the cations and anions in the tantalate ceramic of low thermal conductivity fluorite structure prepared in example 1 was tested and the results are shown in fig. 3.
From fig. 3, it can be derived that: the bond energy of Ta-O is strongest, and the bond energy of Dy-O is weakest, so that highly disordered chemical bonds are formed in the system, and the phonons with a larger range of wavelengths are scattered, so that the thermal conductivity of the ceramic is obviously reduced.
(5) The tantalate ceramic thermal barrier coating prepared in application example 1 of the invention is subjected to back scattering electron imaging test, and the result is shown in fig. 4.
As can be seen from FIG. 4, the thickness of the tantalate ceramic thermal barrier coating is about 425 μm, the powder is in a better molten state, the porosity is less, and the ceramic layer is tightly combined with the bonding layer.
(6) The tantalate ceramic prepared in comparative example 1 was subjected to an X-ray diffraction test, and as a result, a peak appears at 28.3 ° in the XRD pattern.
Although the foregoing embodiments have been described in some, but not all, embodiments of the invention, according to which one can obtain other embodiments without inventiveness, these embodiments are all within the scope of the invention.
Claims (10)
1. A tantalate ceramic with a low thermal conductivity fluorite structure is characterized by having a defective fluorite structure with a chemical formula of Re1 x Re2 y Dy z TaO 7 Wherein x+y+z=3, and x, y, z are independently 0.5 to 1.5, and Re1 and Re2 are independently yttrium, holmium, erbium, thulium or ytterbium.
2. The low thermal conductivity fluorite structured tantalate ceramic of claim 1, characterized in that when 0.88<z<1.32, X-ray of the tantalate ceramic of low thermal conductivity fluorite structureThe 2 theta angle of the (111) plane of the line diffraction peak is 29.08-29.7 degrees; radius difference of Re1 ion and Re2 ion in tantalate ceramic with low thermal conductivity fluorite structure
3. The method for preparing the tantalate ceramic with the low thermal conductivity fluorite structure according to any one of claims 1 to 2, which is characterized by comprising the following steps:
mixing Re1 oxide, re2 oxide, dy oxide and Ta oxide, and sequentially carrying out wet grinding, washing and drying to obtain mixed metal oxide powder;
and pressing the mixed metal oxide powder, and sintering the obtained ceramic blank to obtain the tantalate ceramic with the low-thermal-conductivity fluorite structure.
4. The method according to claim 3, wherein the rotational speed of the wet milling is 1500 to 2000r/min; the wet milling time is 5-8 hours; the grinding solvent used in the wet grinding is one or more of isopropanol, absolute ethyl alcohol and deionized water; the diameter of the grinding ball used for wet grinding is 0.3-0.5 mm, and the grinding ball is made of zirconia.
5. The production method according to claim 3 or 4, wherein the mass ratio of the total amount of the oxide of Re1, the oxide of Re2, the oxide of Dy and the oxide of Ta, the grinding solvent to the grinding balls is 1 to 2:8 to 10:2 to 3.
6. A method of manufacture according to claim 3, wherein the pressing pressure is 200-280 MPa and dwell time is 10-20 min.
7. The method according to claim 3, wherein the sintering temperature is 1500-1750 ℃ and the holding time is 10-30 h.
8. Use of a low thermal conductivity fluorite structured tantalate ceramic according to any one of claims 1 to 2 or prepared by a method according to any one of claims 3 to 7 in a thermal barrier coating.
9. The tantalate ceramic thermal barrier coating is characterized by comprising the tantalate ceramic with the low thermal conductivity fluorite structure according to any one of claims 1 to 2 or the tantalate ceramic with the low thermal conductivity fluorite structure prepared by the preparation method according to any one of claims 3 to 7.
10. The method for preparing the tantalate ceramic thermal barrier coating of claim 9, comprising the steps of:
the tantalate ceramic with low thermal conductivity fluorite structure prepared by any one of claims 1-2 or the tantalate ceramic with low thermal conductivity fluorite structure prepared by any one of claims 3-7 is sprayed on a substrate by crushing the obtained powder to form the tantalate ceramic thermal barrier coating.
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