Nb-doped N-type bismuth-antimony alloy ultralow-temperature thermoelectric material and preparation method thereof

Abstract

The invention discloses an Nb-doped N-type bismuth-antimony alloy ultralow-temperature thermoelectric material and a preparation method, and belongs to the technical field of thermoelectric materials, and the preparation method comprises the following steps: taking Bi block, Sb block and Nb block materials as initial raw materials, weighing the raw materials according to the element stoichiometry of Bi85Sb15-xNbx, and putting the raw materials into a graphite crucible, x = 0.5-1.5; putting the graphite crucible into a high-frequency smelting furnace, vacuumizing, and starting smelting under the protection of inert gas; carrying out ball milling on the smelted alloy in an argon atmosphere; filling the ground powder into a hot pressing mold, and carrying out hot pressing in a vacuum environment; and annealing the hot-pressed material ingot in a tubular furnace to obtain the Nb-doped N-type bismuth-antimony alloy ultralow-temperature thermoelectric material. The maximum ZT value of the Bi85Sb15-xNbx alloy prepared through the method reaches 0.477 at the temperature of-123 DEG C, meanwhile, composition segregation can be effectively restrained through the method, and the uniformity of material compositions is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of thermoelectric materials, and particularly relates to a Nb-doped N-type bismuth-antimony alloy ultralow-temperature thermoelectric material and a preparation method thereof. BACKGROUND

[0002] Thermoelectric materials are functional materials that can convert thermal energy and electrical energy into each other, have advantages such as no moving parts, no noise, and no pollution, and are widely used in thermoelectric power generation and refrigeration technology fields. With the rapid development of deep space exploration and space technology, establishing a lunar base has become the focus of attention of various countries in recent years. In order to solve the problem of energy supply during the lunar night and reduce the launch mass, it is necessary to consider the utilization of lunar in-situ resources. Therefore, developing a power generation system that utilizes the temperature difference between the lunar soil surface and the lunar soil deep layer to generate electricity during the lunar night can effectively solve the problem of energy supply during the lunar night. Thermoelectric materials are the core of the power generation system, and their thermoelectric performance directly affects the conversion efficiency of the power generation system. Under the lunar night environment, the temperature is lower than -150℃, and the performance of traditional thermoelectric materials will be severely degraded at this temperature. Therefore, it is of great significance to prepare a material with high thermoelectric performance at an ultralow-temperature environment below -120℃. The ultralow-temperature thermoelectric material component can be used for the development of the power generation system, and can also be used for the development of a thermoelectric cooling assembly serving in a cryogenic environment. High-spectral cameras, mid-wave infrared detectors, photon detectors, and other series of high-end precision instruments usually need to work in a cryogenic environment to maximize their performance. If a cooling assembly developed using an ultralow-temperature thermoelectric material is used, it is expected to expand the working temperature to the deep cryogenic region, and to cool the next generation of high-integration and high-performance mid-wave infrared detectors and other high-end precision instruments, thereby promoting the transformation and upgrading of the next generation of high-end detector equipment.

[0003] The ultralow-temperature thermoelectric material includes Bi 1-x Sb x alloy, CsBi4Te6 alloy, FeSb2 alloy, etc., wherein the Bi 1-x Sb x alloy is one of the best thermoelectric materials in the low-temperature region below room temperature in terms of thermoelectric performance. The Bi 1-x Sb x alloy is usually prepared by methods such as zone melting, moving heater method, pulling method, high-temperature melting method, powder metallurgy method, and mechanical alloying method, but it is difficult to obtain a material with uniform composition by using conventional preparation methods, and the prepared material has poor thermoelectric performance. Therefore, it is urgent to explore a preparation process method to obtain a Bi 1-x Sb x alloy material with excellent thermoelectric performance, so as to promote the development of lunar soil temperature difference power generation systems and cryogenic environment temperature difference cooling assemblies. SUMMARY

[0004] In view of the problems in the prior art, the application provides an Nb-doped N-type bismuth-antimony alloy ultralow-temperature thermoelectric material and a preparation method thereof to solve the problems in the prior art.

[0005] To achieve the above object, the application provides the following technical scheme: an Nb-doped N-type bismuth-antimony alloy ultralow-temperature thermoelectric material, which has a chemical composition of Bi 85 Sb 15-x Nb x , wherein x = 0.5-1.5.

[0006] A preparation method of the Nb-doped N-type bismuth-antimony alloy ultralow-temperature thermoelectric material, comprising the following steps: (1) using Bi blocks, Sb blocks and Nb blocks as starting raw materials, taking the raw materials according to the element stoichiometry of Bi 85 Sb 15-x Nb x , wherein x = 0.5-1.5; (2) placing the graphite crucible into a high-frequency melting furnace to extract vacuum, and starting melting under the protection of inert gas; (3) performing ball milling on the alloy after melting under an argon atmosphere; (4) placing the ground powder into a hot-pressing mold and performing hot pressing under vacuum; (5) annealing the ingot of the material after hot pressing in a tube furnace to obtain the Nb-doped N-type bismuth-antimony alloy ultralow-temperature thermoelectric material.

[0007] Further, the purity of the Bi blocks is 99.999%.

[0008] Further, in step (2), the graphite crucible is placed into the high-frequency melting furnace to extract vacuum to below 10 Pa, and then 0.04 MPa of protective inert gas is filled to start melting, the melting temperature is 800℃-900℃, and the melting time is 0.5h-1h.

[0009] Further, in step (3), the alloy after melting and stainless steel balls are placed into a stainless steel tank, the weight ratio of the stainless steel balls to the powder is 20:1, and the stainless steel tank is placed into a planetary ball mill to perform ball milling.

[0010] Further, the rotation speed of the planetary ball mill is fixed at 350 rpm, the grinding time is 100h, and argon is filled into the sealed container during the grinding process to prevent oxidation.

[0011] Further, in step (4), the vacuum degree is below 0.1 Pa.

[0012] Further, the hot-pressing pressure is 50MPa-70MPa, the hot-pressing temperature is 250℃±10℃, and the pressure maintaining time is 20min-30min.

[0013] Further, in step (5), the annealing temperature is 180-220 DEG C.

[0014] Further, the annealing time is not less than 7 days. The present application has the beneficial effects that: based on the Nb element multi-component ratio optimization regulation and control of bismuth antimony alloy thermoelectric transport performance, the influence of process parameters such as hot-pressing temperature, hot-pressing pressure and holding time on the performance of bismuth antimony alloy is explored, and the process parameters are dynamically optimized and adjusted to improve the thermoelectric performance of the material. The ZT value of the ultra-low temperature thermoelectric material prepared by the traditional preparation method is low, and the ZT value is usually less than 0.4 in the temperature range of-200 DEG C to room temperature, and component segregation is easily produced, and the material composition is not uniform. The Bi 85 Sb 15-x Nb x The maximum ZT value of the alloy at-123 DEG C reaches 0.477, and the method can effectively suppress the component segregation, and the uniformity of the material composition is improved. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 The Nb-doped N-type bismuth antimony alloy is prepared. 85 Sb 15-x Nb x The thermoelectric material preparation method flow chart.

[0016] Figure 2 The Bi 85 Sb 15-x Nb x X-ray diffraction (XRD) pattern of the alloy (x=0, 0.5, 1, 1.5, wherein x=0 is a reference material).

[0017] Figure 3 The Bi 85 Sb 15-x Nb x Density test results of the alloy ingot sample (x=0, 0.5, 1, 1.5, wherein x=0 is a reference material). DETAILED DESCRIPTION

[0018] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application is further described in detail below with reference to the drawings. It should be understood that the specific embodiments described herein are only used to explain the present application and not to limit the present application.

[0019] The present application provides a preparation method of a Nb-doped N-type bismuth antimony alloy ultra-low temperature thermoelectric material, Figure 1 The material preparation method provided by the embodiment of the present application is realized according to the following steps: (1) According to the atomic weight of each component in the Bi85Sb15-xNbx(x=0, 0.5, 1, 1.5, wherein x=0 is a reference) chemical formula described in Table 1, the weight of each component of the required elemental substance (Bi single substance, Sb single substance, Nb single substance) is calculated, and the total weight of the material is controlled at about 100 g or so.

[0020] Table 1 Bi 85 Sb 15-x Nb x (x=0, 0.5, 1, 1.5) weight of each component of the required elemental substance

[0021] (2) The graphite crucible is cleaned with an ultrasonic cleaner for more than 20 min, and after being taken out, the graphite crucible is wiped with anhydrous ethanol inside and outside, and then placed in a blast drying oven until completely dried.

[0022] (3) The calculated mass of each elemental substance is weighed with a balance, and after weighing, the raw materials are placed in the graphite crucible.

[0023] (4) The graphite crucible is placed in a high-frequency melting device, the melting temperature is set to 800°C, the melting time is 0.5 h, the heating time is 10 min, and the cooling time is natural furnace cooling. After completely cooling to room temperature, the molten ingot sample is taken out from the device.

[0024] (5) The material ingot sample is crushed with a crusher, and the crushing time is 10 s.

[0025] (6) The crushed sample powder and stainless steel balls are poured into a stainless steel sealed ball mill tank, the weight ratio of stainless steel balls to powder is 20:1, the stainless steel sealed tank is placed in a planetary ball mill, the rotation speed is set to 350 rpm, the grinding time is 100 h, and the sealed container is filled with argon during the grinding process to prevent oxidation.

[0026] (7) The surface of the hot-pressed graphite mold is wiped with alcohol cotton.

[0027] (8) The boron nitride powder is diluted with anhydrous ethanol into a solid-liquid mixture, and the solid-liquid mixture is painted to the position where the material powder contacts the surface of the hot-pressed graphite mold.

[0028] (9) Assemble the hot-pressed graphite mold, and place a piece of graphite paper at the position where the material powder contacts the lower surface.

[0029] (10) Weigh 65 g of material powder and pour it into the hot-pressed graphite mold. After placing a piece of graphite paper at the position where the material powder contacts the lower surface, the upper pressing head is placed and pressed tightly, completing the assembly of the hot-pressed mold and the material powder.

[0030] (11) Put the hot-pressing graphite mold filled with material powder into the hot-pressing furnace cavity, vacuumize the hot-pressing furnace cavity to below 0.1 Pa, open the hot-pressing furnace pressurizing device, apply a pressure of 2.8 t to the hot-pressing graphite mold, close the pressurizing device after pressure maintaining for 1 min, open the hot-pressing furnace heating and water cooling device, wait until the hot-pressing graphite mold is heated to 240℃, start the pressurizing device, apply a pressure of 3.8 t to the hot-pressing graphite mold, close the pressurizing and heating device after pressure maintaining for 20 min, naturally cool the furnace to below 70℃, open the hot-pressing furnace to take out the hot-pressed material ingot, the size of the hot-pressed material ingot is φ25 mm x 19 mm, the ingot has no cracks on the surface, and the density is ≥9.2 g / cm 3 to be qualified.

[0031] (12) Put the hot-pressed material ingot into the annealing furnace, set the annealing temperature to 200℃, the heating time to 50 min, and the holding time to 98 h, after the holding time ends, naturally cool the furnace to below 50℃, open the annealing furnace to take out the material ingot.

[0032] (13) Figure 2 The Bi 85 Sb 15-x Nb x alloy X-ray diffraction (XRD) patterns prepared by the method of the examples are shown, and the results show that the Bi 85 Sb 15-x Nb x alloy (x=0, 0.5, 1, 2, 3) has a dominant phase of Bi-Sb structure (space group R3m). The positions of the peaks correspond well to the positions of Bi 85 Sb 15 . No diffraction peaks of pure Nb or other second phases can be seen in the XRD patterns. This means that during the synthesis process, the Nb element is fully alloyed into the Bi-Sb alloy, and no composition segregation is generated.

[0033] (14) Figure 3 The density test results of the Bi 85 Sb 15-x Nb x alloy ingot samples prepared by the method of the examples are shown, and all the samples meet the qualified standard of density ≥9.2 g / cm 3 .

[0034] (15) Test the Bi 85 Sb 15-x Nb xThe thermoelectric performance parameters of the alloy ingot samples (x=0, 0.5, 1, 1.5, wherein x=0 is the reference) at the temperature range of -193℃ to room temperature, including Seebeck coefficient α, electrical conductivity σ and thermal conductivity κ, ZT value at different temperatures is calculated by the above parameters, wherein The ZT value of several alloys reaches the maximum at -123℃, and Table 2 shows the Bi 85 Sb 15-x Nb x The tested thermoelectric performance parameters of the alloy ingot samples (x=0, 0.5, 1, 1.5, wherein x=0 is the reference) at -123℃. After doping Nb element, the Bi 85 Sb 15-x Nb x The ZT value of the alloy (x=0.5, 1, 1.5) is higher than that of the Bi 85 Sb 15 alloy, wherein the Bi 85 Sb 14 Nb1 (x=1) alloy, and the ZT value thereof reaches 0.477 at -123℃.

[0035] Table 2 Bi 85 Sb 15-x Nb x The alloy ingot samples according to the tested thermoelectric performance parameters

[0036] The above merely describes the preferred embodiments of the present application, and is not used to limit the present application, and any modification, equivalent replacement and improvement within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. An Nb-doped N-type bismuth antimony alloy ultra-low temperature thermoelectric material, characterized in that, Bi 85 Sb 15- x Nb x wherein x = 0.5-1.

5.

2. A method of producing an Nb-doped N-type bismuth antimony alloy ultra-low temperature thermoelectric material, characterized by, The method comprises the following steps: (1) Using Bi block, Sb block, Nb bulk material as starting raw material, taking the raw material according to the element stoichiometry of Bi 85 Sb 15-x Nb x , the raw material is put into a graphite crucible, wherein x = 0.5-1.5; (2) Put the graphite crucible into the high-frequency melting furnace to extract vacuum, and start melting under the protection of inert gas; (3) Perform ball milling on the melted alloy under the argon atmosphere; (4) Put the milled powder into a hot-pressing mold to perform hot pressing under vacuum; (5) Anneal the hot-pressed material ingot in a tube furnace to obtain Nb-doped N-type bismuth-antimony alloy ultra-low temperature thermoelectric material.

3. The method of claim 2, wherein the Nb-doped N-type bismuth-antimony alloy ultra-low temperature thermoelectric material is prepared by the steps of: preparing a raw material mixture by mixing a bismuth source, an antimony source, a niobium source, and a fluxing agent; melting the raw material mixture; and solidifying the molten raw material mixture. The purity of the Bi block is 99.999%.

4. The method of claim 2, wherein the Nb-doped N-type bismuth-antimony alloy ultra-low temperature thermoelectric material is prepared by the steps of: preparing a raw material mixture by mixing a bismuth source, an antimony source, a niobium source, and a fluxing agent; melting the raw material mixture; and solidifying the molten raw material mixture. In step (2), the graphite crucible is put into the high-frequency melting furnace to extract vacuum to below 10 Pa, and then 0.04 MPa of protective inert gas is filled to start melting, the melting temperature is 800-900 DEG C, and the melting time is 0.5-1 h.

5. The method of claim 2, wherein the Nb-doped N-type bismuth-antimony alloy ultra-low temperature thermoelectric material is prepared by the steps of: preparing a raw material mixture by mixing a bismuth source, an antimony source, a niobium source, and a fluxing agent; melting the raw material mixture; and solidifying the molten raw material mixture. In step (3), the melted alloy and stainless steel balls are put into a stainless steel tank, the weight ratio of stainless steel balls to powder is 20:1, and the stainless steel tank is put into a planetary ball mill for ball milling.

6. The method of claim 5, wherein the Nb-doped N-type bismuth-antimony alloy ultra-low temperature thermoelectric material is prepared by the steps of: The rotation speed of the planetary ball mill is fixed at 350 rpm, the grinding time is 100 h, and argon is filled in the sealed container during the grinding process to prevent oxidation.

7. The method of claim 2, wherein the Nb-doped N-type bismuth-antimony alloy ultra-low temperature thermoelectric material is prepared by the steps of: preparing a raw material mixture of bismuth, antimony, and niobium; melting the raw material mixture; and casting the molten raw material mixture into a predetermined shape. In step (4), the vacuum degree is below 0.1 Pa.

8. The method of claim 7, wherein the Nb-doped N-type bismuth-antimony alloy ultra-low temperature thermoelectric material is prepared by the steps of: preparing a raw material mixture by mixing a bismuth source, an antimony source, a niobium source, and a fluxing agent; melting the raw material mixture; and solidifying the molten raw material mixture. The hot-pressing pressure is 50-70 MPa, the hot-pressing temperature is 250 DEG C ± 10 DEG C, and the pressure maintaining time is 20-30 min.

9. The method of claim 2, wherein the Nb-doped N-type bismuth-antimony alloy ultra-low temperature thermoelectric material is prepared by the steps of: preparing a raw material mixture of bismuth, antimony, and niobium; melting the raw material mixture; and casting the molten raw material mixture into a predetermined shape. In step (5), the annealing temperature is 180-220 DEG C.

10. The method of claim 9, wherein the Nb-doped N-type bismuth-antimony alloy ultra-low temperature thermoelectric material is prepared by the steps of: preparing a raw material mixture of bismuth, antimony, and niobium; melting the raw material mixture; and casting the molten raw material mixture into a predetermined shape. The annealing time is not less than 7 d.

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