A method for preparing porous indium oxide ceramic thermoelectric material

Abstract

The present invention discloses a method for preparing a porous indium oxide ceramic thermoelectric material, which belongs to the technical field of thermoelectric materials. The preparation method is as follows: various raw materials of In2O3, WO3 and Ta2O5 are weighed in proportion, poured into a ball mill, and evenly milled in a planetary ball mill using anhydrous ethanol as a medium, and then dried and sieved. The sieved powder is placed in a stainless steel mold and pressure-maintained under a certain pressure to obtain a ceramic body, which is then placed in a high-temperature furnace for sintering to complete a high-temperature solid-phase reaction to obtain a dense ceramic body. After calcination, the furnace is cooled, and the block is taken out when the temperature drops to room temperature to obtain a WO3 and Ta2O5-doped indium oxide porous ceramic thermoelectric material. The conductivity of the sample after doping is greatly improved, while the WO3 pore formation optimizes the lattice thermal conductivity. At the same time, the density of the sample after secondary sintering is increased by 10% compared to the pure sample. The method has the advantages of simple required equipment, easy operation, low cost and significant effect.

Description

Technical Field

[0001] The invention relates to a method for preparing a porous indium oxide ceramic thermoelectric material, belonging to the technical field of energy materials. Background Art

[0002] With the continuous development of social economy, environmental and energy issues are increasingly valued by mankind. Thermoelectric materials can directly realize the mutual conversion of thermal energy and electrical energy. Thermoelectric devices are pollution-free, lightweight, small in size, and have a long lifespan, and are increasingly attracting people's attention. Thermoelectric modules with thermoelectric devices as core components have broad application prospects in semiconductor refrigeration, thermoelectric batteries, etc. Thermoelectric figure of merit ZT is an important indicator to characterize the thermoelectric conversion efficiency of materials. This value can be obtained by the following formula: zT=σS 2 T / κ, where S, σ, T, and κ represent the Seebeck coefficient, electrical conductivity, absolute temperature, and thermal conductivity, respectively. Since the three important parameters S, σ, and κ that determine the thermoelectric properties of a material exhibit distinct changes with changes in the material's carrier concentration, how to independently regulate (or synergistically regulate) these parameters is key to maintaining the material's high thermoelectric performance. Currently, high-performance thermoelectric materials include Bi2Te3, PbTe, PbS, and GeTe alloys, but these materials involve rare metals or toxic and hazardous elements, which are not conducive to the concept of green and sustainable development. Therefore, finding and studying compounds composed of non-toxic, inexpensive, abundant, and industrially applicable elements as suitable thermoelectric materials is also an important foundational task.

[0003] It's well known that for polycrystalline materials, larger grain sizes increase electrical and thermal conductivity, while smaller grain sizes decrease them. Therefore, for high-quality polycrystalline thermoelectric materials, both high electrical conductivity and low thermal conductivity are required. This creates a conflict in optimizing grain size; adjusting grain size alone cannot resolve the dilemma of achieving both high electrical conductivity and low thermal conductivity. Indium oxide is an intrinsic n-type semiconductor material, with electrons as the primary charge carrier. As an oxide, it is inexpensive and non-toxic. However, pure indium oxide has low electrical conductivity and high intrinsic thermal conductivity.

[0004] Therefore, it is now necessary to prepare a thermoelectric material with high electrical conductivity and low thermal conductivity. Summary of the Invention

[0005] Existing thermoelectric materials cannot resolve the contradiction of obtaining both high electrical conductivity and low thermal conductivity by adjusting the grain size. The present invention provides a method for preparing a porous indium oxide ceramic thermoelectric material. The present invention uses In2O3 as a ceramic matrix and obtains the porous indium oxide ceramic thermoelectric material by doping Ta2O5 and WO3 and performing secondary sintering. The mass ratio of In2O3, Ta2O5 and WO3 is 131:1:2 to 131:1:4.

[0006] The method for preparing the porous indium oxide ceramic thermoelectric material of the present invention specifically comprises the following steps:

[0007] (1) Weigh In2O3 powder, Ta2O5 powder and WO3 powder in proportion.

[0008] (2) In2O3 powder and Ta2O5 powder are first mixed and then ball-milled, dried, and sieved. The obtained Ta2O5-doped In2O3 powder is pressed into a green body and then sintered. When the temperature drops to room temperature, the block is taken out to obtain Ta2O5-doped indium oxide ceramic thermoelectric material.

[0009] (3) The indium oxide ceramic thermoelectric material obtained in step (1) is crushed and WO3 is added for ball milling, drying, and sieving. The obtained WO3 and Ta2O5 co-doped powder is pressed into a green body and then sintered for a second time. After the temperature drops to room temperature, the block is taken out to finally obtain a porous indium oxide ceramic thermoelectric material.

[0010] Preferably, the method is characterized in that the medium used for ball milling in step (1) and step (2) is anhydrous ethanol, the mass ratio of balls, materials and anhydrous ethanol is 2:1:0.6, the ball milling time is 12 to 24 hours, the ball mill speed is 300 to 400 r / min, and the particle size of the particles in the liquid after ball milling is 0.1 to 10 μm.

[0011] Preferably, in step (1) and step (2), the drying temperature is 60-80° C., the drying time is 12-24 h, and the size of the sieve used for sieving is 200-325 mesh.

[0012] Preferably, the specific method for pressing the powder into a green body in step (1) and step (2) is: loading the powder into a stainless steel mold with a diameter of 15 mm, maintaining the pressure at a pressure of 5 to 10 MPa for 5 to 10 minutes, and obtaining a ceramic green body with a diameter of 15 mm and a thickness of 1 to 3 mm.

[0013] Preferably, the sintering temperature in step (1) is 1200-1400° C. and the holding time is 5-8 hours.

[0014] Preferably, the secondary sintering temperature in step (2) is 1300-1400° C. and the holding time is 6-10 h.

[0015] The principle of the present invention: For In2O3, high valence ions Ta 5+ 、W 6+Doping is an effective means of improving electrical conductivity, as high-valent ion doping can introduce additional electrons, increasing the material's carrier concentration and thus optimizing the matrix's electrical conductivity. WO3 sublimates significantly at 850°C. Leveraging its readily sublimable nature, high-valent ion doping with In2O3 can be used to create pores in the matrix, reducing its thermal conductivity and thereby improving the thermoelectric performance of indium oxide ceramic thermoelectric materials.

[0016] Beneficial effects of the present invention

[0017] (1) The electrical conductivity of the porous indium oxide ceramic thermoelectric material prepared by this method is significantly improved compared with that of the pure indium oxide sample. The high-priced Ta and W enter the matrix, providing a large number of electrons and increasing the carrier concentration. At the same time, WO3 acts as a pore-forming agent, which reduces the thermal conductivity of the sample, introduces defects inside the sample and provides a large number of holes.

[0018] (2) Secondary sintering significantly improved the density of the sample from 74% to 85%, while also causing the grains to grow and improving the electrical conductivity of the sample.

[0019] (3) The porous indium oxide ceramic thermoelectric material synthesized by this method has a simple process and high powder purity. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is the SEM image of the indium oxide material prepared in Comparative Example 4.

[0021] Figure 2 This is the SEM image of the porous indium oxide ceramic thermoelectric material prepared in Example 1.

[0022] Figure 3 These are XRD patterns of the ceramic thermoelectric materials prepared in Example 1, Comparative Example 1, and Comparative Example 4.

[0023] Figure 4 This is a comparison of the thermoelectric properties of ceramic thermoelectric materials prepared in Example 1, Comparative Example 1, and Comparative Example 4. (a) Electrical conductivity (b) Thermal conductivity (c) Thermoelectric figure of merit ZT. DETAILED DESCRIPTION

[0024] The technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific embodiments. However, the following embodiments are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0025] The purity of the In2O3 powder, Ta2O5 powder and WO3 powder in the present invention is greater than 99.99%.

[0026] Example 1

[0027] A method for preparing a porous indium oxide ceramic thermoelectric material, comprising the following steps:

[0028] (1) Weigh 98.5 g of In2O3 powder, 0.75 g of Ta2O5 powder, and 1.5 g of WO3 powder.

[0029] (2) In2O3 powder and Ta2O5 powder were ball-milled, wherein the mass ratio of balls, materials and anhydrous ethanol was 2:1:0.6, the ball-milling time was 24 h, the ball mill speed was 400 r / min, and the particle size of the particles in the liquid after ball milling was 0.1-10 μm. After the ball milling, the powder was dried at 60 ° C for 24 h and then sieved through 325 mesh to obtain Ta2O5-doped powder. The Ta2O5-doped powder was loaded into a stainless steel mold with a diameter of 15 mm and maintained at a pressure of 10 MPa for 10 min to obtain a ceramic embryo with a diameter of 15 mm and a thickness of 3 mm. The ceramic embryo was sintered in a high-temperature furnace at a sintering temperature of 1400 ° C for 6 h, and then cooled in the furnace to obtain Ta2O5-doped indium oxide ceramics.

[0030] (3) Adding WO3 powder to the Ta2O5-doped indium oxide ceramic obtained in step (1) and ball milling under the same ball milling conditions as in step (1) to obtain WO3-doped powder, and loading the WO3-doped powder into a stainless steel mold with a diameter of 15 mm, maintaining the pressure at a pressure of 10 MPa for 10 min to obtain a ceramic body with a diameter of 15 mm and a thickness of 3 mm, and sintering the body in a high-temperature furnace at a sintering temperature of 1400°C and a sintering time of 6 h, and then cooling the body in the furnace to obtain a porous indium oxide ceramic thermoelectric material.

[0031] The porous indium oxide ceramic thermoelectric material obtained in this example was cut into 12×3×3 mm strips for electrical performance testing, and the remaining part was polished into 6×6×1 mm slices for thermal performance testing. Figure 3 It can be seen that after doping with Ta2O5 and WO3, the sample matches the indium oxide pdf standard card very well, indicating successful doping and no second phase. Due to the increase in carrier concentration caused by Ta2O5 doping, the conductivity is significantly improved to 43Scm -1 The substitution of Ta and W for In generates more free electrons. At the same time, WO3 is easy to sublimate. During the sintering process, pores, holes and abundant dislocation defects are formed. These defects will provide abundant phonon scattering centers, and the lattice thermal conductivity is thus reduced to 0.533Wm -1 K -1 The SEM morphology of the sample is shown in Figure 2. Figure 2 As shown in the figure, the grains of the sample are obviously larger than those of the pure sample, and the density of the sample is also significantly improved. Figure 4We can see that the electrical conductivity of the sample is improved compared with the pure sample, while the thermal conductivity is greatly reduced. The final thermoelectric figure of merit ZT reaches 0.23 at 973K, which is 3.2 times the maximum ZT value (0.07) of the pure In2O3 bulk sample.

[0032] In summary, by introducing tantalum oxide and tungsten oxide, the carrier concentration of indium oxide polycrystalline material is greatly improved, the lattice thermal conductivity of the matrix is ​​reduced, and the thermoelectric performance is improved. This method has the advantages of convenience, simplicity and easy operation.

[0033] Example 2

[0034] A method for preparing a porous indium oxide ceramic thermoelectric material, comprising the following steps:

[0035] (1) Weigh 98.5 g of In2O3 powder, 0.75 g of Ta2O5 powder, and 3 g of WO3 powder.

[0036] (2) In2O3 powder and Ta2O5 powder were ball-milled, wherein the mass ratio of balls, materials and anhydrous ethanol was 2:1:0.6, the ball-milling time was 12 h, the ball mill speed was 300 r / min, and the particle size of the particles in the liquid after ball milling was 0.1-10 μm. After the ball milling, the powder was dried at 80 °C for 12 h and then sieved through 200 mesh to obtain Ta2O5-doped powder. The Ta2O5-doped powder was loaded into a stainless steel mold with a diameter of 15 mm and maintained at a pressure of 5 MPa for 10 min to obtain a ceramic embryo with a diameter of 15 mm and a thickness of 1 mm. The ceramic embryo was sintered in a high-temperature furnace at a sintering temperature of 1200 °C and a sintering time of 8 h. It was then cooled in the furnace to obtain Ta2O5-doped indium oxide ceramics.

[0037] (3) adding WO3 powder to the Ta2O5-doped indium oxide ceramic obtained in step (1) and ball milling the same as in step (1) to obtain WO3-doped powder; loading the WO3-doped powder into a stainless steel mold with a diameter of 15 mm; maintaining the pressure at a pressure of 10 MPa for 10 min to obtain a ceramic body with a diameter of 15 mm and a thickness of 1 mm; and sintering the body in a high-temperature furnace at a sintering temperature of 1300° C. and a sintering time of 10 h; and then cooling the body in the furnace to obtain a porous indium oxide ceramic thermoelectric material.

[0038] The porous indium oxide ceramic thermoelectric material prepared in this embodiment was cut into 12×3×3mm strips for electrical performance testing, and the remaining part was polished into 6×6×1mm slices for thermal performance testing. Due to the increase in carrier concentration caused by Ta2O5 doping, the conductivity was significantly improved to 38Scm -1The substitution of Ta and W for In generates more free electrons. At the same time, WO3 is easy to sublime. During the sintering process, it sublimates to form pores, holes and abundant dislocation defects. These defects will provide abundant phonon scattering centers, thus reducing the lattice thermal conductivity to 0.524Wm -1 K -1 The final thermoelectric figure of merit ZT reaches 0.20 at 973K, which is 2.8 times the maximum ZT value (0.07) of pure In2O3 bulk sample.

[0039] In summary, by introducing tantalum oxide and tungsten oxide, the carrier concentration of indium oxide polycrystalline material is greatly improved, the lattice thermal conductivity of the matrix is ​​reduced, and the thermoelectric performance is improved. This method has the advantages of convenience, simplicity and easy operation.

[0040] Example 3

[0041] A method for preparing a porous indium oxide ceramic thermoelectric material, comprising the following steps:

[0042] (1) Weigh 98.5 g of In2O3 powder, 0.75 g of Ta2O5 powder, and 1.5 g of WO3 powder.

[0043] (2) In2O3 powder and Ta2O5 powder were ball-milled, wherein the mass ratio of balls, materials and anhydrous ethanol was 2:1:0.6, the ball-milling time was 24 h, the ball mill speed was 400 r / min, and the particle size of the particles in the liquid after ball milling was 0.1-10 μm. After the ball milling, the powder was dried at 60 ° C for 24 h and then sieved through 325 mesh to obtain Ta2O5-doped powder. The Ta2O5-doped powder was loaded into a stainless steel mold with a diameter of 15 mm and maintained at a pressure of 10 MPa for 5 min to obtain a ceramic embryo with a diameter of 15 mm and a thickness of 3 mm. The ceramic embryo was sintered in a high-temperature furnace at a sintering temperature of 1300 ° C and a sintering time of 6 h. It was then cooled in the furnace to obtain Ta2O5-doped indium oxide ceramics.

[0044] (3) adding WO3 powder to the Ta2O5-doped indium oxide ceramic obtained in step (1) and ball milling the same as in step (1) to obtain WO3-doped powder; loading the WO3-doped powder into a stainless steel mold with a diameter of 15 mm; maintaining the pressure at a pressure of 10 MPa for 10 min to obtain a ceramic body with a diameter of 15 mm and a thickness of 3 mm; and sintering the body in a high-temperature furnace at a sintering temperature of 1300° C. and a sintering time of 6 h; and then cooling the body in the furnace to obtain a porous indium oxide ceramic thermoelectric material.

[0045] The porous indium oxide ceramic thermoelectric material prepared in this embodiment was cut into 12×3×3mm strips for electrical performance testing, and the remaining part was polished into 6×6×1mm slices for thermal performance testing. Due to the increase in carrier concentration caused by Ta2O5 doping, the conductivity was significantly improved to 40Scm -1 The substitution of Ta and W for In generates more free electrons. At the same time, WO3 is easy to sublime. During the sintering process, it sublimates to form pores, holes and abundant dislocation defects. These defects will provide abundant phonon scattering centers, thus reducing the lattice thermal conductivity to 0.581Wm -1 K -1 The final thermoelectric figure of merit ZT reaches 0.20 at 973K, which is 2.7 times the maximum ZT value (0.07) of pure In2O3 bulk sample.

[0046] In summary, by introducing tantalum oxide and tungsten oxide, the carrier concentration of indium oxide polycrystalline material is greatly improved, the lattice thermal conductivity of the matrix is ​​reduced, and the thermoelectric performance is improved. This method has the advantages of convenience, simplicity and easy operation.

[0047] Example 4

[0048] A method for preparing a porous indium oxide ceramic thermoelectric material, comprising the following steps:

[0049] (1) Weigh 98.5 g of In2O3 powder, 0.75 g of Ta2O5 powder, and 1.5 g of WO3 powder.

[0050] (2) In2O3 powder and Ta2O5 powder were ball-milled, wherein the mass ratio of balls, materials and anhydrous ethanol was 2:1:0.6, the ball-milling time was 24 h, the ball mill speed was 400 r / min, and the particle size of the particles in the liquid after ball milling was 0.1-10 μm. After the ball milling, the powder was dried at 60 ° C for 24 h and then sieved through 325 mesh to obtain Ta2O5-doped powder. The Ta2O5-doped powder was loaded into a stainless steel mold with a diameter of 15 mm and maintained at a pressure of 10 MPa for 10 min to obtain a ceramic embryo with a diameter of 15 mm and a thickness of 3 mm. The ceramic embryo was sintered in a high-temperature furnace at a sintering temperature of 1400 ° C and a sintering time of 7 h. It was then cooled in the furnace to obtain Ta2O5-doped indium oxide ceramics.

[0051] (3) adding WO3 powder to the Ta2O5-doped indium oxide ceramic obtained in step (1) and ball milling the same as in step (1) to obtain WO3-doped powder; loading the WO3-doped powder into a stainless steel mold with a diameter of 15 mm; maintaining the pressure at a pressure of 10 MPa for 10 min to obtain a ceramic body with a diameter of 15 mm and a thickness of 3 mm; and sintering the body in a high-temperature furnace at a sintering temperature of 1400° C. and a sintering time of 7 h; and then cooling the body in the furnace to obtain a porous indium oxide ceramic thermoelectric material.

[0052] The porous indium oxide ceramic thermoelectric material prepared in this embodiment was cut into 12×3×3mm strips for electrical performance testing, and the remaining part was polished into 6×6×1mm slices for thermal performance testing. Due to the increase in carrier concentration caused by Ta2O5 doping, the conductivity was significantly improved to 35Scm -1 The substitution of Ta and W for In generates more free electrons. At the same time, WO3 is easy to sublime. During the sintering process, it sublimates to form pores, holes and abundant dislocation defects. These defects will provide abundant phonon scattering centers, thus reducing the lattice thermal conductivity to 0.581Wm -1 K -1 The final thermoelectric figure of merit ZT reaches 0.18 at 973K, which is 2.5 times the maximum ZT value (0.07) of pure In2O3 bulk sample.

[0053] In summary, by introducing tantalum oxide and tungsten oxide, the carrier concentration of indium oxide polycrystalline material is greatly improved, the lattice thermal conductivity of the matrix is ​​reduced, and the thermoelectric performance is improved. This method has the advantages of convenience, simplicity and easy operation.

[0054] Example 5

[0055] A method for preparing a porous indium oxide ceramic thermoelectric material, comprising the following steps:

[0056] (1) Weigh 98.5 g of In2O3 powder, 0.75 g of Ta2O5 powder, and 1.5 g of WO3 powder.

[0057] (2) In2O3 powder and Ta2O5 powder were ball-milled, wherein the mass ratio of balls, materials and anhydrous ethanol was 2:1:0.6, the ball-milling time was 24 h, the ball mill speed was 400 r / min, and the particle size of the particles in the liquid after ball milling was 0.1-10 μm. After the ball milling, the powder was dried at 60 ° C for 24 h and then sieved through 325 mesh to obtain Ta2O5-doped powder. The Ta2O5-doped powder was loaded into a stainless steel mold with a diameter of 15 mm and maintained at a pressure of 10 MPa for 10 min to obtain a ceramic embryo with a diameter of 15 mm and a thickness of 3 mm. The ceramic embryo was sintered in a high-temperature furnace at a sintering temperature of 1400 ° C for 6 h, and then cooled in the furnace to obtain Ta2O5-doped indium oxide ceramics.

[0058] (3) Adding WO3 powder to the Ta2O5-doped indium oxide ceramic obtained in step (1) and ball milling under the same ball milling conditions as in step (1) to obtain WO3-doped powder, and loading the WO3-doped powder into a stainless steel mold with a diameter of 15 mm, maintaining the pressure at a pressure of 10 MPa for 10 min to obtain a ceramic body with a diameter of 15 mm and a thickness of 3 mm, and sintering the body in a high-temperature furnace at a sintering temperature of 1400°C and a sintering time of 6 h, and then cooling the body in the furnace to obtain a porous indium oxide ceramic thermoelectric material.

[0059] The porous indium oxide ceramic thermoelectric material prepared in this embodiment was cut into 12×3×3mm strips for electrical performance testing, and the remaining part was polished into 6×6×1mm slices for thermal performance testing. Due to the increase in carrier concentration caused by Ta2O5 doping, the conductivity was significantly improved to 30Scm -1 The substitution of Ta and W for In generates more free electrons. At the same time, WO3 is easy to sublimate. During the sintering process, pores, holes and abundant dislocation defects are formed. These defects will provide abundant phonon scattering centers, and the lattice thermal conductivity is thus reduced to 0.528Wm -1 K -1 The final thermoelectric figure of merit ZT reaches 0.17 at 973K, which is 2.5 times the maximum ZT value (0.07) of pure In2O3 bulk sample.

[0060] In summary, by introducing tantalum oxide and tungsten oxide, the carrier concentration of indium oxide polycrystalline material is greatly improved, the lattice thermal conductivity of the matrix is ​​reduced, and the thermoelectric performance is improved. This method has the advantages of convenience, simplicity and easy operation.

[0061] Comparative Example 1

[0062] For comparison, the difference between this embodiment and embodiment 1 is that tungsten oxide is not doped. The specific preparation steps are as follows:

[0063] (1) Weigh 98.5 g of In2O3 powder and 0.75 g of Ta2O5 powder.

[0064] (2) In2O3 powder and Ta2O5 powder were ball-milled, wherein the mass ratio of balls, materials and anhydrous ethanol was 2:1:0.6, the ball-milling time was 24 h, the ball mill speed was 400 r / min, and the particle size of the particles in the liquid after ball milling was 0.1-10 μm. After the ball milling, the powder was dried at 60 ° C for 24 h and then sieved through 325 mesh to obtain Ta2O5-doped powder. The Ta2O5-doped powder was loaded into a stainless steel mold with a diameter of 15 mm and maintained at a pressure of 10 MPa for 10 min to obtain a ceramic embryo with a diameter of 15 mm and a thickness of 3 mm. The ceramic embryo was sintered in a high-temperature furnace at a sintering temperature of 1400 ° C for 6 h, and then cooled in the furnace to obtain Ta2O5-doped indium oxide ceramics.

[0065] The Ta2O5-doped indium oxide ceramic prepared in this comparative example was cut into 12×3×3 mm strips for electrical performance testing, and the remaining portion was polished into 6×6×1 mm slices for thermal performance testing. Figure 3 It can be seen that after doping with Ta2O, the indium oxide polycrystalline sample matches the standard pdf card very well, indicating successful doping and no second phase. Due to the increase in carrier concentration caused by Ta2O5 doping, the conductivity is increased to 28Scm -1 The substitution of Ta for In produces more free electrons, but due to the absence of WO3, the final conductivity is still relatively low compared with Example 1. Figure 4 It can be seen that the final thermal conductivity of the sample doped with Ta2O5 is 0.822Wm -1 K -1 The final thermoelectric figure of merit ZT reaches 0.1 at 973K, which is lower than that of Example 1.

[0066] In summary, the introduction of tantalum oxide increases the carrier concentration of indium oxide polycrystalline materials. However, without WO3 as a pore-forming agent, the lattice thermal conductivity is high, and the performance is not as good as the co-doping effect of Ta2O5 and WO3.

[0067] Comparative Example 2

[0068] For comparison, the difference between this comparative example and Example 1 is that Ta2O5 is not doped. The specific preparation method is as follows:

[0069] (1) Weigh 98.5 g of In2O3 powder and 1.5 g of WO3 powder.

[0070] (2) In2O3 powder and WO3 powder were ball-milled, wherein the mass ratio of balls, materials and anhydrous ethanol was 2:1:0.6, the ball-milling time was 24 h, the ball mill speed was 400 r / min, and the particle size of the particles in the liquid after ball milling was 0.1-10 μm. After the ball milling, the powder was dried at 60 ° C for 24 h and then sieved through 325 mesh to obtain Ta2O5-doped powder. The Ta2O5-doped powder was loaded into a stainless steel mold with a diameter of 15 mm and maintained at a pressure of 10 MPa for 10 min to obtain a ceramic embryo with a diameter of 15 mm and a thickness of 3 mm. The ceramic embryo was sintered in a high-temperature furnace at a sintering temperature of 1400 ° C and a sintering time of 6 h. It was then cooled in the furnace to obtain WO3-doped indium oxide ceramics.

[0071] The WO3-doped indium oxide ceramic prepared in this comparative example was cut into 12×3×3 mm strips for electrical performance testing, and the remaining part was polished into 6×6×1 mm slices for thermal performance testing. Due to the increase in carrier concentration caused by WO3 doping, the conductivity increased to 20 Scm -1 The substitution of W for In generates more free electrons. At the same time, WO3 is easy to sublime, and pores are formed during the sintering process. Therefore, the lattice thermal conductivity is reduced to 0.633Wm -1 K -1 The final thermoelectric figure of merit ZT reaches 0.11 at 973K, which is relatively average compared with the performance of Example 1.

[0072] In summary, the introduction of tungsten oxide alone has limited effect on optimizing electrical properties, which proves that the co-doping of Ta2O5 and WO3 has better effect.

[0073] Comparative Example 3

[0074] As a comparison, this embodiment differs from embodiment 1 in that no secondary sintering is performed, and specifically includes the following steps:

[0075] (1) Weigh 98.5 g of In2O3 powder, 0.75 g of Ta2O5 powder, and 1.5 g of WO3 powder.

[0076] (2) In2O3 powder, Ta2O5 powder and WO3 powder were ball-milled, wherein the mass ratio of ball, material and anhydrous ethanol was 2:1:0.6, the ball-milling time was 24 h, the ball mill speed was 400 r / min, and the particle size of the liquid after ball milling was 0.1-10 μm. After ball milling, the powder was dried at 60 ° C for 24 h and then sieved through 325 mesh to obtain Ta2O5-doped powder. The Ta2O5-doped powder was loaded into a stainless steel mold with a diameter of 15 mm and maintained at a pressure of 10 MPa for 10 min to obtain a ceramic embryo with a diameter of 15 mm and a thickness of 3 mm. The ceramic embryo was sintered in a high-temperature furnace at a sintering temperature of 1400 ° C for 6 h, and then cooled in the furnace to obtain Ta2O5 and WO3 co-doped indium oxide ceramics.

[0077] The Ta2O5 and WO3 co-doped indium oxide ceramic obtained in this comparative example was cut into 12×3×3mm strips for electrical performance testing, and the remaining part was polished into 6×6×1mm slices for thermal performance testing. The test showed that the conductivity of the sample doped with Ta2O5 and WO3 was only increased to 24Scm without secondary sintering. -1 Without secondary sintering, the grain size of the sample is relatively smaller, and the electrical conductivity is not significantly improved. The final thermoelectric figure of merit ZT is 0.14 at 973K.

[0078] In summary, secondary sintering has a great influence on the electrical properties of indium oxide polycrystalline materials.

[0079] Comparative Example 4

[0080] As a comparison, this comparative example differs from Example 1 in that Ta2O5 and WO3 are not doped. The specific preparation steps are as follows:

[0081] (1) Weigh 98.5 g of In2O3 powder.

[0082] (2) In2O3 powder was ball-milled, wherein the mass ratio of balls, materials and anhydrous ethanol was 2:1:0.6, the ball-milling time was 24 h, the ball mill speed was 400 r / min, and the particle size of the particles in the liquid after ball-milling was 0.1-10 μm. After the ball-milling, the powder was dried at 60 °C for 24 h and then sieved through 325 mesh to obtain Ta2O5-doped powder. The Ta2O5-doped powder was loaded into a stainless steel mold with a diameter of 15 mm and maintained at a pressure of 10 MPa for 10 min to obtain a ceramic embryo with a diameter of 15 mm and a thickness of 3 mm. The ceramic embryo was sintered in a high-temperature furnace at a sintering temperature of 1400 °C and a sintering time of 6 h. The indium oxide ceramic was then cooled in the furnace to obtain the indium oxide ceramic.

[0083] The indium oxide ceramic obtained in this example was cut into 12×3×3 mm strips for electrical performance testing, and the remaining part was polished into 6×6×1 mm slices for thermal performance testing. Figure 3 It can be seen that the indium oxide polycrystalline sample matches the standard PDF card very well, indicating that the indium oxide phase composition is of high purity and has no impurities. Figure 4 It can be seen that the conductivity of the undoped indium oxide polycrystalline sample is only 13Scm -1 ,like Figure 1 As shown, the sample has smaller grains and lower density. The thermal conductivity is 1.3Wm -1 K -1 , the thermoelectric figure of merit is only 0.07.

[0084] Comparative Example 5

[0085] As a comparison, this comparative example differs from Example 1 in that the sintering temperature is 1500° C., and the specific preparation steps are as follows:

[0086] (1) Weigh 98.5g of In2O3 powder, 0.75g of Ta2O5 powder, and 3g of WO3 powder

[0087] (2) In2O3 powder and Ta2O5 powder were ball-milled, wherein the ratio of balls, materials and anhydrous ethanol was 2:1:0.6, the ball-milling time was 24 h, the ball mill speed was 400 r / min, and the particle size of the particles in the liquid after ball milling was 0.1-10 μm. After the ball milling, the powder was dried at 60 ° C for 24 h and then sieved through 325 mesh to obtain Ta2O5-doped powder. The Ta2O5-doped powder was loaded into a stainless steel mold with a diameter of 15 mm and maintained at a pressure of 10 MPa for 10 min to obtain a ceramic embryo with a diameter of 15 mm and a thickness of 3 mm. The ceramic embryo was sintered in a high-temperature furnace at a sintering temperature of 1500 ° C and a sintering time of 6 h. It was then cooled in the furnace to obtain Ta2O5-doped indium oxide ceramics.

[0088] (3) adding WO3 powder to the Ta2O5-doped indium oxide ceramic obtained in step (1) and ball milling the same as in step (1) to obtain WO3-doped powder; loading the WO3-doped powder into a stainless steel mold with a diameter of 15 mm; maintaining the pressure at a pressure of 10 MPa for 10 min to obtain a ceramic body with a diameter of 15 mm and a thickness of 3 mm; and sintering the body in a high-temperature furnace at a sintering temperature of 1500° C. and a sintering time of 6 h; and then cooling the body in the furnace to obtain a porous indium oxide ceramic thermoelectric material.

[0089] The porous indium oxide ceramic thermoelectric material obtained in this example was cut into 12 × 3 × 3 mm strips for electrical performance testing, and the remaining material was polished into 6 × 6 × 1 mm slices for thermal performance testing. After increasing the reaction temperature to 1500°C, the electrical conductivity of the sample did not significantly improve compared to the pure indium oxide polycrystalline sample, resulting in a final thermoelectric figure of merit of only 0.13.

[0090] In summary, the experiments show that Figure 4 It can be seen that the indium oxide porous ceramic thermoelectric material provided by the present invention has excellent thermoelectric performance and good electrical properties. The best-performing sample has a three-fold improvement in performance compared to the pure indium oxide sample. After adding tungsten oxide, secondary sintering can cause the tungsten oxide to sublime and form pores, while creating good conditions for grain growth, ultimately achieving improved electrical conductivity while reducing lattice thermal conductivity. When the tungsten oxide content is reduced or the reaction temperature is lowered too much, the performance of indium oxide decreases. This is because too low a tungsten oxide content will result in too few pores. Although the electrical conductivity is improved, the thermal conductivity remains very high. Lowering the reaction temperature will cause the grains to not fully grow during the sintering process of the sample, greatly deteriorating the electrical conductivity. Increasing the reaction temperature will cause a large amount of doped WO3 to sublime, which in turn deteriorates the electrical conductivity of the sample. Ultimately, we determined that the mass ratio of indium oxide In2O3, tantalum oxide Ta2O5, and tungsten oxide WO3 is 65:2:1 as the optimal ratio. The best-performing doped sample can be obtained by sintering at the optimal temperature of 1400°C for 6 hours. All performance characteristics are good during actual use.

Claims

1. A method for preparing a porous indium oxide ceramic thermoelectric material, characterized in that: In2O3 powder is used as a ceramic matrix, and a porous indium oxide ceramic thermoelectric material is obtained by doping Ta2O5 powder and WO3 powder and then sintering. The mass ratio of In2O3 powder, Ta2O5 powder and WO3 powder is 131:1:2 to 131:1:

4. The method specifically includes the following steps: mixing In2O3 powder and Ta2O5 powder, ball milling, drying and sieving the mixture; pressing the obtained Ta2O5-doped In2O3 powder into a green body and sintering the green body at a sintering temperature of 1200-1400°C and a holding time of 5-8 hours; taking out the block after the temperature drops to room temperature to obtain a Ta2O5-doped indium oxide ceramic thermoelectric material; adding WO3 powder, ball milling, drying and sieving the mixture; pressing the obtained WO3 and Ta2O5 co-doped powder into a green body and performing a secondary sintering at a holding time of 1300-1400°C for 6-10 hours; taking out the block after the temperature drops to room temperature to finally obtain a porous indium oxide ceramic thermoelectric material.

2. The method for preparing the porous indium oxide ceramic thermoelectric material according to claim 1, wherein: The medium used for ball milling is anhydrous ethanol, the mass ratio of balls, materials and anhydrous ethanol is 2:1:0.6, the ball milling time is 12~24h, the ball mill speed is 300~400r / min, and the particle size of the powder after ball milling is 0.1~10μm.

3. The method for preparing the porous indium oxide ceramic thermoelectric material according to claim 1, wherein: The drying temperature is 60~80℃, the drying time is 12~24h, and the sieve size is 200~325 mesh.

4. The method for preparing the porous indium oxide ceramic thermoelectric material according to claim 1, wherein: The specific method of pressing the powder into a green body is as follows: the powder is loaded into a stainless steel mold with a diameter of 15 mm, and the pressure is maintained at a pressure of 5-10 MPa for 5-10 minutes to obtain a ceramic green body with a diameter of 15 mm and a thickness of 1-3 mm.

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