Sn-doped Bi-Sb-based thermoelectric material and preparation method thereof

Abstract

The invention discloses a Sn-doped Bi-Sb-based thermoelectric material and a preparation method thereof, the preparation method comprises the following steps: proportioning, smelting and cooling according to the atomic weight ratio of Bi: Sb: Sn = 0.85: (0.15-x): x (x is 0.01-0.03) to obtain a blank, and the smelting process is electromagnetic smelting in a vacuum environment; the blank is mechanically ground to obtain a powdery sample, the powdery sample is pressed into a block material through a hot pressing process, the hot pressing temperature is 200-260 DEG C, the hot pressing pressure is 3-4 T, and the hot pressing time is 20-40 min. According to the preparation method, the P-type Bi-Sb-based material with relatively good thermoelectric performance can be obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of deep cold zone thermoelectric material preparation, and specifically relates to a Sn-doped Bi-Sb-based thermoelectric material and a preparation method thereof. Background Art

[0002] In recent years, with the continuous development and updating of advanced technologies such as bio-intelligence, high-precision detection, and terahertz chips in the civil and military fields, new requirements have been put forward for rapid refrigeration and precise temperature control technologies for deep cold areas. At present, cryogenic cooling usually relies on traditional vapor compression refrigeration technology, or uses cryogenic liquids such as liquid nitrogen / liquid helium. However, these refrigeration methods have certain limitations: the vapor compression system is not only heavy, but also the moving parts are prone to vibration and mechanical failure, which shortens the service life of the equipment. Liquid nitrogen / liquid helium is not suitable for high-density electronic equipment. In the field of deep space exploration, the life of satellites is limited by the amount of refrigeration they carry. For those application scenarios that require extremely high reliability and performance, high-performance thermoelectric coolers are ideal equipment, so it is crucial to study thermoelectric materials and their preparation for deep cold zone applications.

[0003] Thermoelectric materials are a new type of green energy material that can convert heat energy and electrical energy into each other. Through the Seebeck effect, thermoelectric materials can convert temperature differences into electrical energy to achieve temperature difference power generation; while using the Peltier effect, thermoelectric materials can convert electrical energy into temperature differences to achieve solid-state refrigeration functions. It can be seen that the rational development and utilization of thermoelectric materials can achieve huge commercial value. Thermoelectric refrigeration devices have many advantages such as active two-way temperature control, fast response speed, small size, no moving parts, no noise, long service life, high reliability, etc., and can be used in 5G optical communication modules, medical testing, aerospace equipment and other fields.

[0004] The invention patent application with publication number CN110752285A discloses a manufacturing method for improving the performance of N-type Bi-Sb-Te-Se based thermoelectric materials. The manufacturing method for improving the performance of N-type Bi-Sb-Te-Se based thermoelectric materials includes: weighing metal particles as raw materials according to the stoichiometric ratio of each element in the chemical formula Bi2-xSbxTe3-ySey+zwt%Te, mixing and smelting to obtain a master alloy, wherein 0≤x≤2, 0≤y≤3, 0≤z≤30; placing the master alloy in a vacuum ball mill and ball milling it into nano-scale powder, the nano-scale powder is a multi-phase material including Bi2-xSbxTe3-ySey and Te; using spark plasma sintering technology to sinter the nano-scale powder into a block to obtain the N-type Bi-Sb-Te-Se based thermoelectric material, wherein the sintering temperature in the spark plasma sintering technology is higher than the melting point of the Te phase and lower than the melting point of Bi2-xSbxTe3-ySey. The manufacturing method for improving the performance of N-type Bi-Sb-Te-Se based thermoelectric materials provided in the embodiment of the present application improves the thermoelectric performance of N-type Bi-Sb-Te-Se based thermoelectric materials by ball milling a master alloy through a ball milling process and sintering the nano-scale powder obtained after ball milling through a liquid phase sintering technology.

[0005] However, the key functional materials in thermoelectric devices are composed of a combination of P-type and N-type thermoelectric materials. Among the thermoelectric materials for deep cold zone applications, N-type Bi1-xSbx thermoelectric materials are relatively classic, as shown in Comparative Example 1, but there is a lack of matching P-type Bi-Sb-based materials. Although P-type Bi-Sb-based materials can theoretically be prepared by P-type doping methods, there is currently a lack of relevant research. At the same time, impurities may be generated during the doping process, affecting the thermoelectric and mechanical properties of the material.

[0006] The present invention prepares a Sn-doped Bi-Sb-based thermoelectric material for the application scenario of thermoelectric refrigeration in deep cold regions. The process technology involved can realize the rapid preparation of the material, saving a lot of preparation time for subsequent mass production. The P-type Bi-Sb-based material prepared by this method has excellent thermoelectric and mechanical properties, providing a research direction for thermoelectric materials for deep cold region applications. Summary of the invention

[0007] The invention provides a method for preparing a Sn-doped Bi-Sb-based thermoelectric material, and the preparation method can obtain a P-type Bi-Sb-based material with good thermoelectric performance.

[0008] The present invention provides a method for preparing a Sn-doped Bi-Sb-based thermoelectric material, comprising:

[0009] (1) preparing materials, melting and cooling according to the atomic weight ratio of Bi:Sb:Sn=0.85:(0.15-x):x, where x is 0.01-0.03 to obtain a blank, wherein the melting process is electromagnetic melting under a vacuum environment;

[0010] (2) The blank is mechanically ground to obtain a powder sample, and the powder sample is pressed into a block material by a hot pressing process, wherein the hot pressing temperature is 50-260° C., the hot pressing pressure is 1-4T, and the hot pressing time is 20-120 min.

[0011] Preferably, the atomic weight x of Sn is 0.025-0.3, which can ensure effective P-type doping without generating impurity phases.

[0012] Preferably, the hot pressing temperature is 200-260°C, the hot pressing pressure is 3-4T, and the hot pressing time is 20-40min. A dense alloy material with a grain size of 2-6μm can be obtained. Dense materials are conducive to improving the electrical conductivity of the material, and small grains are conducive to reducing the thermal conductivity of the material and enhancing the mechanical properties of the material at the same time.

[0013] Preferably, the power of the electromagnetic melting is 2500W, and the time is 3-5 minutes. More preferably, the time of the electromagnetic melting is 4-5 minutes.

[0014] Preferably, before smelting, the raw materials are placed in a quartz glass tube, the quartz glass tube is evacuated, and then the quartz glass tube is sealed.

[0015] Preferably, the raw material includes Bi particles, Sb particles and Sn particles.

[0016] Preferably, the blank is manually ground before mechanical grinding. The mechanical ball milling process has certain requirements on the particle size of the material. If the particle size is too large, the final ball milling effect is not good, and it will be difficult to refine the large particles. Therefore, the present invention first pre-treats the block after molten alloying, that is, manually grinds the block into fine particles using a mortar.

[0017] Preferably, cyclohexane is added before or during mechanical grinding, and after mechanical grinding, the cyclohexane is dried and evaporated to obtain a powdered sample. By adding cyclohexane, a liquid seal is formed on the one hand, which can largely avoid oxidation problems; on the other hand, wet grinding has a better particle refinement effect than dry grinding.

[0018] The present invention also provides a Sn-doped Bi-Sb-based thermoelectric material, characterized in that it is prepared by the Sn-doped Bi-Sb-based thermoelectric material preparation method.

[0019] The grain size of the Sn-doped Bi-Sb-based thermoelectric material is 2-6 μm, and a smaller grain size is beneficial to improving the strength of the material and reducing the thermal conductivity of the material.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention controls the Sn content to form an appropriate amount of holes to obtain a P-type Bi-Sb-based thermoelectric material. When the Sn content is too high, the alloy will generate impurities that have an adverse effect on the performance. In addition, the present invention adopts an electromagnetic melting method to achieve melting in a very short time under a vacuum environment, thereby avoiding the generation of oxide impurities and SbSn second phases, which is conducive to achieving full alloying.

[0022] The present invention controls the hot pressing temperature to avoid the molten state that makes it difficult to form during the hot pressing process, and also controls the hot pressing pressure to make the material more compact and optimize the electrical properties; and controls the heat preservation and pressure holding time to make the crystal structure of the material more orderly. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A flow chart of a method for preparing a Sn-doped Bi-Sb-based thermoelectric material is provided for Example 1 of the present invention;

[0024] Figure 2 This is a cross-sectional SEM image of the Sn-doped Bi-Sb-based thermoelectric material prepared in Example 1 of the present invention;

[0025] Figure 3 The thermoelectric performance curve of the Sn-doped Bi-Sb-based thermoelectric material prepared in Examples 1-4 of the present invention;

[0026] Figure 4 The mechanical properties diagram of the Sn-doped Bi-Sb-based thermoelectric material prepared in Examples 1-4 of the present invention;

[0027] Figure 5 EBSD grain size data diagram of Sn-doped Bi-Sb-based thermoelectric materials prepared in Examples 1-4 of the present invention;

[0028] Figure 6 The electrical performance curves of the Sn-doped Bi-Sb-based thermoelectric materials prepared in Example 1, Example 2, Example 4 and Comparative Examples 2 to 4 of the present invention under different hot pressing pressure conditions are shown;

[0029] Figure 7 The XRD spectrum of the Bi-Sb thermoelectric material prepared in Comparative Example 5 of the present invention;

[0030] Figure 8 This is the XRD spectrum of the Sn-doped Bi-Sb-based thermoelectric material prepared in Comparative Example 1 of the embodiment of the present invention. DETAILED DESCRIPTION

[0031] The present invention provides a process for rapidly and efficiently preparing Bi-Sb-based thermoelectric materials, and prepares p-type and n-type thermoelectric materials with excellent performance. The raw materials are fully alloyed by electromagnetic smelting in a short time, and the alloy grain size is refined by mechanical ball milling to prepare for the preparation of polycrystalline materials. Polycrystalline materials are beneficial to improving the mechanical properties of the materials, and can enhance phonon scattering and thus reduce the thermal conductivity of the materials, and ultimately improve the thermoelectric conversion efficiency of the materials. Compared with the prior art, the materials and processing technology of this process improve the pretreatment efficiency of the materials while ensuring the same effect, saving time and manpower for subsequent mass production.

[0032] The present invention adopts hot pressing method to prepare P-type and N-type thermoelectric materials with excellent performance, explores process parameters such as hot pressing temperature, hot pressing pressure, and heat preservation and pressing time, and adjusts the temperature parameters in the hot pressing process appropriately with the different proportions of material components. Using the same matrix to prepare P-type and N-type materials can greatly avoid thermal mismatch and mechanical mismatch problems, saving manpower and material resources for subsequent production.

[0033] The preparation method and high-performance material provided by the present invention provide important reference and technical support for the research and development of Bi-Sb-based thermoelectric materials for deep cold zones.

[0034] Example 1

[0035] This embodiment provides a method for preparing Sn-doped Bi-Sb-based thermoelectric material, such as Figure 1 As shown, including:

[0036] (1) The required weight of each element of the P-type material (Bi, Sb, Sn) is calculated according to the atomic weight ratio of each component in Table 1, and the overall mass of the thermoelectric material is controlled to be about 10g.

[0037] (2) Add anhydrous ethanol to the quartz glass tube, use a numerically controlled ultrasonic cleaner to ultrasonicate for 3 minutes, pour out the anhydrous ethanol, and place the tube in a forced air drying oven until the quartz glass tube is completely dried.

[0038] (3) Use a weighing balance to weigh the calculated mass of each element and use aluminum foil to deliver the raw materials to the bottom of the quartz glass tube.

[0039] (4) Install the quartz glass tube on the vacuum tube sealing machine, and evacuate the inside of the tube while monitoring the vacuum degree in real time. When the internal pressure of the quartz glass tube reaches 10Pa, ignite the gas produced by the hydrogen and oxygen machine, and use the burning flame to fuse the quartz glass plug and the quartz glass tube together. After sealing, turn off the hydrogen and oxygen machine, stop evacuating the tube, and remove it after cooling down to room temperature.

[0040] (5) Place the vacuum quartz glass tube into an electromagnetic melting device with a power of 2500W. After smelting for 4 minutes, clamp the quartz glass tube with a metal clamp and shake it continuously to mix the molten metal liquid inside evenly. After shaking for about 1 minute, the smelting is terminated. After cooling, the raw material becomes an ingot sample with a metallic luster.

[0041] (6) After breaking the quartz glass tube, take out the sample and use a mortar to grind the ingot sample into the maximum particle size range that can be accepted by the mechanical ball mill in the next step.

[0042] (7) Pour the coarse powder sample into a cemented carbide ball mill, then add cemented carbide balls of various sizes and pour in cyclohexane, wherein the ball-to-material ratio is controlled at about 15:1. The addition of cyclohexane can achieve the purpose of liquid sealing and can utilize wet grinding to make the ball milling effect better.

[0043] (8) Pour the slurry sample after ball milling into a beaker and place it in a vacuum drying oven to reduce the vacuum degree to below 0 Pa. Heat it to 80 °C to evaporate the cyclohexane and then take out the sample. Pour the powder sample onto weighing paper, wrap it, and place it in a vacuum bag. Vacuum it for subsequent experiments.

[0044] (9) Use a weighing balance to weigh 1.5g of the powder required for preparation and pour it into a hot pressing mold made of mold steel. Turn on the hot press and cooling water tank, place the mold in the hot pressing chamber and insert a thermocouple into the mold to monitor the temperature applied to the sample in real time. After evacuating the chamber, set the hot pressing temperature to 260℃, the hot pressing pressure to 4T, the heat preservation and pressure holding time to 30min and start the hot pressing program. After the hot pressing is completed and cooled to below 80℃, the vacuum is broken, the chamber is opened to remove the mold, and the hot pressed material is demolded using a cold press to finally obtain a cylindrical thermoelectric material with a diameter of 12.72mm.

[0045] Example 2-Example 4

[0046] Compared with Example 1, the atomic weight of each element is different, and the corresponding hot pressing temperature is also different, as shown in Table 1 for details.

[0047] Comparative Example 1

[0048] The difference compared with Example 1 is that the Sn atomic weight is 0.4 and the hot pressing temperature is 200°C.

[0049] Comparative Example 2-Comparative Example 4

[0050] The difference compared with Example 1, Example 2 and Example 4 is that the hot pressing pressure in step (9) is 1T.

[0051] Comparative Example 5

[0052] The difference from Example 1 is that the smelting method in step (5) is mechanical ball milling alloying, and the Sn doping amount is 0.

[0053] Table 1: Atomic weight ratio and hot pressing temperature of each component in Examples 1 to 4 and Comparative Example 1

[0054] serial number Bi Sb Sn Hot pressing temperature Example 1 0.85 0.14 0.01 260℃ Example 2 0.85 0.13 0.02 260℃ Example 3 0.85 0.125 0.025 200℃ Example 4 0.85 0.12 0.03 200℃ Comparative Example 1 0.85 0.11 0.04 200℃

[0055] like Figure 2 As shown, no pores were observed in the Sn-doped Bi-Sb-based thermoelectric material prepared in Example 1, indicating that the density of the sample after hot pressing was very good.

[0056] like Figure 3 As shown in (a)-(d), the Sn-doped Bi-Sb-based thermoelectric materials prepared in Examples 1-4 have good thermoelectric properties. 0.85 Sb 0.125 Sn 0.025 When the sample is at 260K, the maximum Seebeck coefficient reaches 95.5μV K-1; the thermal conductivity is stable at around 2W m-1K-1 in the temperature range of 110K-230K; and the zT value can reach 0.15 at 240K.

[0057] like Figure 4 As shown, the sample cross section was subjected to nanoindentation test, and the Sn-doped Bi-Sb-based thermoelectric materials prepared in Examples 1 to 4 had good mechanical properties, among which the Bi0.85Sb0.125Sn0.025 sample had the highest hardness of 0.78 GPa and an elastic modulus of 39.2 GPa.

[0058] like Figure 5 As shown in (a)-(b), the average grain size of Example 1 is 2-6 μm.

[0059] like Figure 6 As shown in (a)-(c), compared with the lower pressing pressures of Comparative Examples 2 to 4, the thermoelectric materials prepared by the appropriate pressing pressures provided in Examples 1, 2 and 4 of the present invention, that is, when the hot pressing pressure is 4T, have higher Seeebck coefficients and electrical conductivity, and better electrical properties of the materials.

[0060] like Figure 7 As shown in (a)-(b), the thermoelectric material obtained in Comparative Example 5 requires at least 12 hours or more to fully alloy the material by mechanical ball milling. It can be seen from the phase diagram that no impurity peaks appear when ball milling is performed for 12 hours or more, so it takes a long time. The smelting method provided by the present invention can obtain a pure billet in just a few minutes.

[0061] like Figure 8 As shown in (a)-(b), compared with the embodiments provided in the present invention, when the Sn doping amount of the thermoelectric material prepared in Comparative Example 1 is too high, there will be impurity peaks on the XRD spectrum. After comparison with PDF#33-0118, it is found that the second phase is SbSn alloy. The appearance of the second phase will affect the final performance of the material.

Claims

1. A method for preparing Sn-doped Bi-Sb-based thermoelectric material, characterized in that: include: (1) preparing materials, melting and cooling according to the atomic weight ratio of Bi:Sb:Sn=0.85:(0.15-x):x, where x is 0.01-0.03 to obtain a blank, wherein the melting process is electromagnetic melting under a vacuum environment; (2) The blank is mechanically ground to obtain a powder sample, and the powder sample is pressed into a block material by a hot pressing process, wherein the hot pressing temperature is 50-260° C., the hot pressing pressure is 1-4T, and the hot pressing time is 20-120 min.

2. The method for preparing Sn-doped Bi-Sb-based thermoelectric material according to claim 1, characterized in that: The atomic weight x of Sn is 0.025-0.

03.

3. The method for preparing Sn-doped Bi-Sb-based thermoelectric material according to claim 1, characterized in that: The hot pressing temperature is 200-260° C., the hot pressing pressure is 3-4T, and the hot pressing time is 20-40 minutes.

4. The method for preparing Sn-doped Bi-Sb-based thermoelectric material according to claim 1, characterized in that: The power of the electromagnetic melting is 2500W, and the time is 3-5 minutes.

5. The method for preparing Sn-doped Bi-Sb-based thermoelectric material according to claim 1, characterized in that: Before smelting, the raw materials are placed in a quartz glass tube, the quartz glass tube is evacuated, and then the quartz glass tube is sealed.

6. The method for preparing Sn-doped Bi-Sb-based thermoelectric material according to claim 5, characterized in that: The raw materials include Bi particles, Sb particles and Sn particles.

7. The method for preparing Sn-doped Bi-Sb-based thermoelectric material according to claim 1, characterized in that: Before mechanical grinding, the blanks are ground manually.

8. The method for preparing Sn-doped Bi-Sb-based thermoelectric material according to claim 1, characterized in that: Cyclohexane is added before or during mechanical grinding. After mechanical grinding, the cyclohexane is dried and evaporated to obtain a powdered sample.

9. A Sn-doped Bi-Sb-based thermoelectric material, characterized in that: The Sn-doped Bi-Sb-based thermoelectric material is prepared by the preparation method of the Sn-doped Bi-Sb-based thermoelectric material according to any one of claims 1 to 8.

10. The Sn-doped Bi-Sb-based thermoelectric material according to claim 9, characterized in that: The grain size of the Sn-doped Bi-Sb-based thermoelectric material is 2-6 μm.

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