A method for improving the performance of thermoelectric materials prepared by hot-pressing

Abstract

The application relates to the field of bismuth telluride-based materials, and aims to solve the problem that the performance of a material prepared by a hot-pressing method is lower than that of a material prepared by a zone melting method in the prior art, and provides a method for improving the performance of a thermoelectric material prepared by a hot-pressing method, which comprises the following steps: weighing raw materials according to a chemical formula Bi x Sb 2‑x Te 3‑y Se y The value range of x is 0.3-0.6, the value range of y is 0-0.08, P-type alloy ingots are obtained by smelting under vacuum and high temperature; the P-type alloy ingots are crushed and then ball milled to obtain P-type powder, the particle size of the P-type powder is adjusted according to the value of x; and the P-type powder is subjected to vacuum hot-pressing sintering. The method can effectively improve the performance of P-type bismuth telluride materials prepared by a hot-pressing method, has low requirements on devices, and is high in preparation efficiency.

Description

Technical Field

[0001] This invention relates to the field of thermoelectric materials, and more particularly to a method for improving the performance of thermoelectric materials prepared by hot pressing. Background Technology

[0002] Thermoelectric semiconductor materials can directly convert heat energy into electrical energy through the movement of charge carriers within the material. Due to their advantages such as small size, high reliability, and zero noise and pollution, they have wide applications in solid-state refrigeration and waste heat power generation. Currently, the main bottleneck limiting the replacement of thermoelectric materials with compressors and internal combustion engines is their low thermoelectric conversion efficiency. Commercially, the main methods for preparing thermoelectric materials are zone melting and powder metallurgy. Thermoelectric materials prepared by zone melting suffer from uneven electrical properties and poor mechanical properties, resulting in low material utilization, short device lifespan, and severely limiting the material's application range and scenarios. Powder metallurgy mainly uses hot pressing and hot extrusion. Hot extrusion has low efficiency and high cost, but produces materials with high performance and mechanical properties. Hot pressing falls between the two, with efficiency close to that of zone melting, lower cost, high material strength, and good uniformity, but currently, the performance of the prepared materials is not high. Thermoelectric performance is measured by the thermoelectric figure of merit (ZT = α). 2 The ZT (Zen conductivity) of P-type materials prepared by hot pressing (σ / κ*T, where α is the Seebeck coefficient, σ is the electrical conductivity, κ is the thermal conductivity, and T is the temperature) is evaluated. At room temperature (300 K), the ZT of P-type materials prepared by hot pressing is only 0.9-1.0, which is lower than that of materials prepared by zone melting. This limits the commercialization and widespread use of hot-pressed materials. Therefore, an ideal hot pressing solution is urgently needed to improve the properties of the prepared materials and promote their commercial application.

[0003] For example, the invention disclosed in publication number CN113328031A is "a high-strength and high-efficiency bismuth telluride bulk material and its preparation method and application", wherein the bismuth telluride bulk material is in the form of sheets; the bismuth telluride bulk material is Bi 0.5 Sb 1.5 Te 3+x The preparation process of P-type lamellar bismuth telluride bulk material involves melting Bi, Te, Sb, or Se elements in a specific stoichiometric ratio, cooling them to obtain bismuth telluride-based alloy rods, melting the alloy rods, and then dripping them layer by layer to obtain the bismuth telluride bulk material. This material requires melting and dripping equipment, resulting in a long preparation time and high equipment requirements. Summary of the Invention

[0004] To overcome the problem that the performance of materials prepared by hot pressing is lower than that of materials prepared by zone melting in the prior art, this invention provides a method to improve the performance of thermoelectric materials prepared by hot pressing. This method effectively reduces high-frequency short-wavelength phonons, reduces the grain size of the material, increases grain boundary scattering, strengthens the material texture, and further improves the thermoelectric performance of materials prepared by hot pressing.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for improving the performance of thermoelectric materials prepared by hot pressing includes the following steps:

[0007] S1, according to the chemical formula Bi x Sb 2-x Te 3-y Se y Weigh the raw materials, with x ranging from 0.3 to 0.6 and y ranging from 0 to 0.08, and melt them under vacuum and high temperature to obtain P-type alloy ingots;

[0008] S2. After crushing the P-type alloy ingot, ball mill it to obtain P-type powder. The particle size of the P-type powder is adjusted according to the value of x.

[0009] S3. Vacuum hot pressing sintering is performed on the P-type powder.

[0010] This invention optimizes the preparation of high-performance P-type thermoelectric materials by hot pressing: First, it controls the Sb content in the P-type material and introduces Se doping to increase the concentration of antisite defects and carriers, thereby increasing electrical conductivity. At the same time, the introduced point defects can effectively scatter high-frequency short-wavelength phonons to reduce thermal conductivity. Then, by processing the material powder, the grain size is reduced, increasing grain boundary scattering, which scatters low-frequency long-wavelength phonons to reduce lattice thermal conductivity. Finally, the sintering process is improved to strengthen the material texture and further enhance the thermoelectric performance of the material.

[0011] Preferably, the D of the P-type powder in S2 90 Particle size, D 50 The relationship between particle size and x is:

[0012] The D of the P-type powder in S2 90 Particle size, D 50 The relationship between particle size and x is:

[0013] When 0.5 ≤ x ≤ 0.6, D 90 >600μm; when 0.45≤x<0.5, 100μm<D 90 <600μm; when 0.3≤x<0.45, D 50 <50μm, D 90 <100μm.

[0014] As the particle size of small-diameter P-type powder gradually decreases, its thermal conductivity decreases, but its electrical conductivity also decreases, leading to an increase in the material's cutting size and thus affecting material utilization. Therefore, it is necessary to regulate the composition of the P-type material in S1. The two are interrelated; the smaller the particle size, the lower the x-value needs to be. At the same time, the y-value can be adjusted within the range of 0 to 0.08 based on the electrical and thermal conductivity values.

[0015] Preferably, the ball milling in step S2 is carried out in a vacuum environment or an inert atmosphere.

[0016] Ball milling in a vacuum or inert atmosphere can prevent powder oxidation and reduce powder surface defects.

[0017] Preferably, the inert atmosphere is an argon atmosphere or a nitrogen atmosphere.

[0018] Argon and nitrogen are inert gases that do not react with powder materials, and at the same time, they prevent the powder from coming into contact with oxygen or water vapor during the ball milling process.

[0019] Preferably, the sintering temperature in S3 is 450–550°C, the sintering pressure is 30–80 MPa, and the sintering time is 15–60 min.

[0020] After sintering, the density of the material is >97%. Within the range of 450 to 550°C, as the sintering temperature increases, the texture strength of the material will increase, thereby increasing the electrical conductivity.

[0021] Preferably, the vacuum is a vacuum degree of less than 0.1 Pa.

[0022] Preferably, the raw materials in S1 are Bi powder, Sb powder, Te powder and Se powder, and the purity of Bi powder, Sb powder, Te powder and Se powder is not less than 99.99%.

[0023] Preferably, the melting temperature in S1 is 600-800℃ and the melting time is 5-7h.

[0024] Therefore, the present invention has the following beneficial effects: (1) it can effectively improve the performance of P-type bismuth telluride materials prepared by hot pressing; (2) it has low requirements for equipment and high preparation efficiency. Attached Figure Description

[0025] Figure 1 The conductivity is the electrical conductivity of the materials obtained in Examples 1-5 and Comparative Example 1.

[0026] Figure 2 The thermoelectric figure of merit is the value of the materials obtained in Examples 1-5 and Comparative Example 1.

[0027] Figure 3The maximum temperature difference chamber diagram is shown for the thermoelectric coolers prepared from the materials obtained in Examples 1-5 and Comparative Example 1.

[0028] Figure 4 The resistance box diagram shows the thermoelectric cooler prepared from the materials obtained in Examples 1-5 and Comparative Example 1. Detailed Implementation

[0029] The present invention will be further described below with reference to the accompanying drawings and specific implementation methods.

[0030] Example 1

[0031] Hot-pressed bismuth telluride-based materials are prepared by the following steps:

[0032] 1) Batching and smelting / material preparation

[0033] Preparation of Bi x Sb 2-x Te 3-y Se y P-type bismuth telluride, with x = 0.5 and y = 0, high-purity Bi powder, Sb powder and Te powder were weighed according to the chemical ratio and melted at 650℃ for 6 hours under vacuum (keeping the vacuum degree less than 0.1 Pa) to obtain P-type alloy ingots.

[0034] 2) Powder processing

[0035] The P-type alloy ingot was crushed in a jaw crusher, and the crushed material was then ball-milled under argon atmosphere to obtain P-type powder with a particle size D. 50 <350μm, D 90 <800μm;

[0036] 3) Sintering

[0037] Small-diameter P-type powder was loaded into a sintering mold and sintered under vacuum, sintering pressure of 50 MPa, and 500°C for 45 minutes.

[0038] Example 2

[0039] Hot-pressed bismuth telluride-based materials are prepared by the following steps:

[0040] 1) Composition control, element doping

[0041] Preparation of Bi x Sb 2-x Te 3-y Se y P-type bismuth telluride, with x value of 0.45 and y value of 0, high-purity Bi powder, Sb powder, Te powder and Se powder were weighed according to the chemical ratio and melted at 650℃ for 6 hours under vacuum to obtain P-type alloy ingots.

[0042] 2) Powder processing

[0043] P-type alloy ingots are crushed in a jaw crusher, and the crushed material is then ball-milled under argon atmosphere to obtain P-type powder. 50 <200μm, D 90 <500μm;

[0044] 3) Sintering

[0045] The powder was loaded into a sintering mold and sintered under vacuum, sintering pressure of 50 MPa, and 500°C for 45 minutes.

[0046] Comparative Example 1

[0047] Hot-pressed bismuth telluride-based materials are prepared by the following steps:

[0048] 1) Composition control, element doping

[0049] Preparation of Bi x Sb 2-x Te 3-y Se y P-type bismuth telluride, with x = 0.5 and y = 0, high-purity Bi powder, Sb powder and Te powder were weighed according to the chemical ratio and melted at 650℃ for 6 hours under vacuum to obtain P-type alloy ingots.

[0050] 2) Powder processing

[0051] The P-type alloy ingot was crushed in a jaw crusher, and the crushed material was then ball-milled under argon atmosphere to obtain P-type powder with a particle size D. 50 <200μm, D 90 <500μm;

[0052] 3) Sintering

[0053] The powder was loaded into a sintering mold and sintered under vacuum, sintering pressure of 50 MPa, and 500°C for 45 minutes.

[0054] Example 3

[0055] Hot-pressed bismuth telluride-based materials are prepared by the following steps:

[0056] 1) Composition control, element doping

[0057] Preparation of Bi x Sb 2-x Te 3-y Se y P-type bismuth telluride, with x value of 0.45 and y value of 0.03, high-purity Bi powder, Sb powder, Te powder and Se powder were weighed according to the chemical ratio and melted at 650℃ for 6 hours under vacuum to obtain P-type alloy ingot;

[0058] 2) Powder processing

[0059] The P-type alloy ingot was crushed in a jaw crusher, and the crushed material was then ball-milled under argon atmosphere to obtain P-type powder with a particle size D. 50 <200μm, D 90 <500μm;

[0060] 3) Sintering

[0061] The powder was loaded into a sintering mold and sintered under vacuum, sintering pressure of 50 MPa, and 500°C for 45 minutes.

[0062] Example 4

[0063] Hot-pressed bismuth telluride-based materials are prepared by the following steps:

[0064] 1) Composition control, element doping

[0065] Preparation of Bi x Sb 2-x Te 3-y Se y P-type bismuth telluride, with x value of 0.45 and y value of 0.03, high-purity Bi powder, Sb powder, Te powder and Se powder were weighed according to the chemical ratio and melted at 650℃ for 6 hours under vacuum to obtain P-type alloy ingot;

[0066] 2) Powder processing

[0067] The P-type alloy ingot was crushed in a jaw crusher, and the crushed material was then ball-milled under argon atmosphere to obtain P-type powder with a particle size D. 50 <200μm, D 90 <500μm;

[0068] 3) Sintering

[0069] The powder was loaded into a sintering mold and sintered under vacuum, sintering pressure of 50 MPa, and temperature of 550°C for 45 minutes.

[0070] Example 5

[0071] Hot-pressed bismuth telluride-based materials are prepared by the following steps:

[0072] 1) Composition control, element doping

[0073] Preparation of Bi x Sb 2-x Te 3-y Se yP-type bismuth telluride, with x value of 0.43 and y value of 0.03, high-purity Bi powder, Sb powder, Te powder and Se powder were weighed according to the chemical ratio and melted at 650℃ for 6 hours under vacuum to obtain P-type alloy ingot;

[0074] 2) Powder processing

[0075] The P-type alloy ingot was crushed in a jaw crusher, and the crushed material was then ball-milled under argon atmosphere to obtain P-type powder with a particle size D. 50 <50μm, D 90 <100μm;

[0076] 3) Sintering

[0077] The powder was loaded into a sintering mold and sintered under vacuum, sintering pressure of 50 MPa, and temperature of 550°C for 45 minutes.

[0078] The hot-pressed crystal rods obtained in Comparative Example 1 and Examples 1-5 were cut into performance wafers. The Seebeck coefficient and conductivity of the performance wafers were tested by ZEM, and the thermal conductivity was calculated by LFA testing. Finally, the thermoelectric figure of merit zT of the material was calculated by formula. Simultaneously, the obtained crystal rods were used to prepare thermoelectric cooler products. The selected paired N-type materials were all from the same batch and the same crystal rod material. 127 pairs of 6.0A, 40*40mm products were prepared by cutting the thermoelectric arms to the same size. The device performance dTmax and resistance R were tested at 31°C using Harman Threshold. The test results are as follows: Figures 1-4 As shown in the table below.

[0079]

[0080] The test results show that the hot-pressed bismuth telluride-based material prepared by the present invention has good thermoelectric properties, and the thermoelectric cooler made from the material obtained by the present invention has low resistance and can maintain a high maximum temperature difference.

[0081] Comparing Example 1 and Comparative Example 1, it can be seen that for thermoelectric materials prepared by hot pressing, reducing the particle size can improve the material performance. Example 2, compared to Comparative Example 1, further adjusted the Sb content based on the particle size. Example 3, based on Example 2, added Se doping. Example 3 exhibited the best performance, followed by Example 2. This indicates that in the hot pressing process, while refining the powder particle size, it is also necessary to control the powder composition. Adjusting the Sb content and doping with Se can effectively improve the performance of P-type materials.

[0082] The performance of Example 3 is slightly inferior to that of Example 4, which indicates that the performance of the resulting material improves with increasing sintering temperature.

Claims

1. A method for improving the performance of thermoelectric materials prepared by hot pressing, characterized in that, Includes the following steps: S1, according to the chemical formula Bi x Sb 2-x Te 3-y Se y Weigh the raw materials, with x ranging from 0.3 to 0.6 and y ranging from 0 to 0.08, and melt them under vacuum and high temperature to obtain P-type alloy ingots; S2. After crushing the P-type alloy ingot, ball mill it to obtain P-type powder. The particle size of the P-type powder is adjusted according to the value of x. S3. Vacuum hot pressing sintering of P-type powder; The D of the P-type powder in S2 90 Particle size, D 50 The relationship between particle size and x is: When 0.5 ≤ x ≤ 0.6, D 90 >600μm; when 0.45≤x<0.5, 100μm<D 90 <600μm; when 0.3≤x<0.45, D 50 <50μm, D 90 <100μm.

2. The method for improving the performance of thermoelectric materials prepared by hot pressing according to claim 1, characterized in that, The ball milling in S2 is carried out in a vacuum environment or an inert atmosphere.

3. The method for improving the performance of thermoelectric materials prepared by hot pressing according to claim 2, characterized in that, The inert atmosphere is an argon atmosphere or a nitrogen atmosphere.

4. A method for improving the performance of thermoelectric materials prepared by hot pressing according to claim 1, 2, or 3, characterized in that, The sintering temperature in S3 is 450–550℃, the sintering pressure is 30–80MPa, and the sintering time is 15–60min.

5. A method for improving the performance of thermoelectric materials prepared by hot pressing according to claim 1 or 2, characterized in that, The vacuum is defined as a vacuum degree of less than 0.1 Pa.

6. The method for improving the performance of thermoelectric materials prepared by hot pressing according to claim 1, characterized in that, The raw materials in S1 are Bi powder, Sb powder, Te powder and Se powder, and the purity of Bi powder, Sb powder, Te powder and Se powder is not less than 99.99%.

7. The method for improving the performance of thermoelectric materials prepared by hot pressing according to claim 1, characterized in that, The melting temperature in S1 is 600-800℃, and the melting time is 5-7h.

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