Method for preparing strong-texture bismuth telluride-based thermoelectric material through construction forming

Abstract

The invention discloses a method for preparing a strong-texture bismuth telluride-based thermoelectric material through construction molding, and the method specifically comprises the steps: respectively weighing Bi, Te and Sb elementary substances according to a design ratio, crushing the Bi, Te and Sb elementary substances into fine powder, sieving the fine powder, and carrying out ball-milling mixing to obtain a mixed material; dividing the obtained mixed material into two equal parts, and carrying out sintering molding by adopting spark plasma sintering equipment, so as to obtain a No.1 sintering blank and a No.2 sintering blank which are the same in size; carrying out mechanical grinding and polishing on one surface of the obtained blank to form a mirror surface; and putting the treated mirror surfaces into a mold in a contact manner, and sintering and molding by using spark plasma to obtain the constructed and molded strong-texture thermoelectric material. The method has the beneficial effects that through two times of spark plasma sintering, sufficient diffusion of alloy elements is facilitated, so that the traditional melting alloying step is omitted, the production efficiency is improved, and the cost is saved. Meanwhile, the orientation consistency of the thermoelectric material can be greatly improved through the secondary sintering forming technology, and the strong-texture thermoelectric material is obtained.

Description

Technical Field

[0001] The invention relates to the field of thermoelectric materials, and in particular to a method for constructing and molding a strongly textured bismuth telluride-based thermoelectric material. Background Art

[0002] Thermoelectric materials realize the conversion of temperature difference into electrical energy based on the Seebeck effect and the Peltier effect. This unique functionality makes them irreplaceable in many applications. For example, in remote areas or deep space exploration, thermoelectric materials can effectively convert ambient temperature differences into electrical energy to provide electrical energy for information transmission. In terms of local cooling of chips and temperature control of medical instruments, thermoelectric materials have become an irreplaceable solution due to their precise temperature control, miniaturization and high reliability. Bismuth telluride-based alloys and their solid solutions have become the only commercially available thermoelectric materials due to their excellent thermoelectric properties near room temperature, and are widely used in the fields of thermoelectric power generation and semiconductor refrigeration. Texturing is of great significance in optimizing the thermoelectric properties of bismuth telluride. By controlling the grain orientation, the electrical conductivity can be significantly improved, the thermal conductivity can be reduced, and the thermoelectric figure of merit (ZT) can be improved.

[0003] The main methods for preparing bismuth telluride-based thermoelectric materials include zone melting, hot pressing, spark plasma sintering (SPS), hot extrusion, etc. The zone melting method is currently the main method for preparing commercial bismuth telluride-based thermoelectric materials, which can prepare bulk materials with consistent crystal orientation. However, the grain size of zone melting bismuth telluride materials is large and the composition is easily segregated, which makes it very easy to cleave and fracture during cutting and slicing, limiting the promotion and application of zone melting bismuth telluride materials in high-end fields such as microelectronic refrigeration.

[0004] It should be pointed out that in recent years, the preparation of thermoelectric materials based on powder metallurgy methods (including hot pressing, SPS, hot extrusion, etc.) requires the preparation of alloy blocks through a smelting-swinging process in advance, and then the preparation of alloy powders. Not only is the process cumbersome, but defects are easily introduced during the powder making process, thereby weakening product performance. Therefore, it is of great significance to develop a short-process method for preparing bismuth telluride-based thermoelectric materials with strong texture, high uniformity and high mechanical strength. Summary of the invention

[0005] The present invention discloses a method for constructing and molding a strongly textured bismuth telluride-based thermoelectric material to solve any of the above and other potential problems in the prior art.

[0006] To achieve the above object, the technical solution of the present invention is: a method for constructing and molding a strongly textured bismuth telluride-based thermoelectric material, the method specifically comprising the following steps:

[0007] S1) weighing Bi, Te, and Sb elements respectively according to the designed ratio, crushing them into fine powders, sieving them, and then ball milling them to obtain a mixed material;

[0008] S2) dividing the mixed material obtained in S1) into two equal parts and sintering them using a spark plasma sintering device to obtain two sintered blanks No. 1 and No. 2 of the same size;

[0009] S3) mechanically grinding and polishing one side of the No. 1 and No. 2 sintered blanks obtained in S2) to form a mirror surface;

[0010] S4) The mirror surfaces of the first and second blanks obtained after the treatment in S3) are placed in contact with each other in a mold, and are formed by spark plasma sintering to obtain a constructed strong texture thermoelectric material.

[0011] Furthermore, the stoichiometric ratio of Bi, Te and Sb in S1) is Bi x Sb 2-x Te 3-y , wherein, 0.35≤x≤0.55, -0.03≤y≤0.03; the rotation speed of the ball milling process is 400-800rpm, and the ball-to-material ratio is 5:1-10:1.

[0012] Furthermore, the single substance in said S1) is sieved through a mesh number of 200 to 400 meshes; and the purity is not less than 99.99%.

[0013] Furthermore, the temperature of the spark plasma sintering in S2) is 400-500° C., the pressure is 35-50 MPa, and the sintering duration is 5-20 min.

[0014] Furthermore, the root mean square roughness of the ground and polished surfaces of the No. 1 and No. 2 sintered blanks in said S3) after grinding and polishing is less than 20 μm.

[0015] Furthermore, the temperature of the spark plasma sintering in S4) is 400-500°C, the pressure is 35-50 MPa, and the sintering duration is 5-20 min.

[0016] Furthermore, the mold material for spark plasma sintering in S2) and S4) is graphite.

[0017] Furthermore, the grain size of the constructed strong texture thermoelectric material is not less than 15.6 μm, and the outer grain orientation is <0001> The main texture accounts for no less than 57.3%, the room temperature compressive strength is no less than 67MP, and the room temperature ZT value is no less than 0.78.

[0018] A bismuth telluride-based thermoelectric material is prepared by the above method.

[0019] Compared with the prior art, the present invention has at least the following beneficial technical effects:

[0020] (1) The use of two spark plasma sintering processes helps to fully diffuse the alloy elements, so the traditional melt alloying step is not required, which improves production efficiency and reduces costs.

[0021] (2) The construction and molding technology not only greatly improves the texturing degree of thermoelectric materials, but also ensures high mechanical strength.

[0022] (3) This method can be used to prepare large-sized thermoelectric materials and improve production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0024] Figure 1 The present invention is a flowchart of a method for constructing and molding a strongly textured bismuth telluride thermoelectric material.

[0025] Figure 2 This is the EBSD pole figure of the thermoelectric material prepared according to Example 1 of the present invention.

[0026] Figure 3 This is the EBSD pole figure of the thermoelectric material prepared according to Example 4 of the present invention. DETAILED DESCRIPTION

[0027] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiment of the present invention. Obviously, the described embodiment is only an embodiment of a part of the present invention, not all embodiments, and is not intended to limit the scope of the present invention. In addition, in the following description, the description of known structures and technologies is omitted to avoid unnecessary confusion of the concepts disclosed in the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work should belong to the scope of protection of the present invention. The present invention is further elaborated below in conjunction with the drawings and embodiments.

[0028] Flowcharts are used in the present application to illustrate the operations performed by the system according to the embodiments of the present application. It should be understood that the preceding or following operations are not necessarily performed accurately in order. On the contrary, various steps may be processed in reverse order or simultaneously. At the same time, other operations may be added to these processes, or one or more operations may be removed from these processes.

[0029] Electron backscatter diffraction (EBSD) is a technique for analyzing the microstructure of materials using a scanning electron microscope (SEM). It obtains information such as crystal texture, crystal defects, grain boundaries, and stress by measuring the backscattered electrons generated when the electron beam interacts with the sample. When the crystal orientation of most grains in a material is concentrated in a certain crystallographic orientation, it is called a preferred orientation or texture; the ratio of the number of grains with a preferred orientation to the total number of grains is called the main texture ratio.

[0030] like Figure 1 As shown, the present invention provides a method for constructing and molding a strong textured bismuth telluride-based thermoelectric material, and the specific technical scheme is as follows:

[0031] A method for forming and preparing a strongly textured bismuth telluride thermoelectric material comprises the following steps:

[0032] Raw material weighing: weigh Bi, Te, and Sb in a certain stoichiometric ratio;

[0033] Preparation of powder: crush the weighed single substance coarse block into fine powder with a crusher, then sieve it and mix it with a ball mill;

[0034] Primary sintering: the mixed powder obtained in step (1) is divided into two parts of equal weight, one of which is spread flat in a mold and loaded into a spark plasma sintering device for sintering, and the other part is subjected to the same operation to obtain two sintered blanks of the same size, No. 1 and No. 2;

[0035] Interface grinding and polishing: mechanically grinding and polishing one side of the No. 1 and No. 2 sintered blanks obtained in step (2) to form a mirror surface;

[0036] Secondary sintering: The mirror surfaces of the first and second blanks obtained in step (3) are placed in contact with each other in a mold, and are formed by spark plasma sintering to obtain a constructed strong texture thermoelectric material.

[0037] Preferably, in step 1), the purity of Bi, Te and Sb is not less than 99.99%.

[0038] Preferably, in step 1), the stoichiometric ratio is Bi x Sb 2-x Te 3-y , where 0.35≤x≤0.55, -0.03≤y≤0.03.

[0039] Preferably, in step 2), the single substance is sieved through a mesh size of 200 to 400.

[0040] Preferably, in step 2), the rotation speed of the ball milling process is 400-800 rpm, and the ball-to-material ratio is 5:1-10:1.

[0041] Preferably, in step 3), the mold material is graphite, the temperature of spark plasma sintering is 400-500° C., the pressure is 35-50 MPa, and the sintering duration is 5-20 min.

[0042] Preferably, in step 4), the root mean square roughness (RMS) of the polished surfaces of the No. 1 and No. 2 sintered blanks after grinding and polishing is less than 20 μm.

[0043] Preferably, in step 5), the conditions adopted for spark plasma sintering are consistent with those in step 3).

[0044] Example 1

[0045] A method for forming and preparing a strongly textured bismuth telluride-based thermoelectric material comprises the following steps:

[0046] (1) According to the stoichiometric ratio Bi 0.45 Sb 1.55 Te3 Accurately weigh Bi, Te, Sb bulk single substances with a purity of not less than 99.99%;

[0047] (2) placing the block obtained in step (1) into a crusher, crushing it at a speed of not less than 1000 rpm, and passing it through a 200-mesh sieve after crushing;

[0048] (3) The fine powder sieved in step (2) was ball-milled. High-purity argon gas was filled into the ball mill. Alumina grinding balls were selected. The ball-to-material ratio was 7:1. The ball milling speed was 600 rpm and the ball milling time was 5 h.

[0049] (4) dividing the powder obtained in step (3) into two portions of equal mass;

[0050] (5) Take one of the portions and lay it flat in a SPS special mold, and sinter it at 450°C and 45 MPa for 10 min to obtain a No. 1 sintered blank with a size of 40 mm × 40 mm × 20 mm;

[0051] (6) Take another portion of the powder obtained in step (3) and repeat step (5) to obtain a second sintered blank with a size of 40 mm × 40 mm × 20 mm;

[0052] (7) mechanically grinding and polishing one side of the No. 1 and No. 2 sintered blanks obtained in steps (5) and (6) to form a mirror surface;

[0053] (8) The mirror surfaces of the first and second blanks obtained in step (7) are placed in contact with each other in the graphite mold of step (5), and sintered at 450° C. and 45 MPa for 15 min to obtain a strongly textured thermoelectric material. The EBSD pole figure of the prepared thermoelectric material is as follows: Figure 2 shown.

[0054] Example 2

[0055] A method for preparing a strongly textured bismuth telluride-based thermoelectric material by forming a structure, the difference from Example 1 is that the stoichiometric ratio in step (1) is Bi 0.4 Sb 1.6 Te3.

[0056] Example 3

[0057] A method for constructing and molding a strongly textured bismuth telluride-based thermoelectric material, which differs from Example 1 in that the dimensions in step (6) and step (8) are 60 mm×60 mm×30 mm.

[0058] Example 4

[0059] A method for forming and preparing a strongly textured bismuth telluride-based thermoelectric material, which differs from Example 1 in that the pressure in step (5), step (6) and step (8) is 35 MPa, and the EBSD pole figure of the prepared thermoelectric material is as follows: Figure 3 shown.

[0060] Example 5

[0061] A method for constructing and molding a strongly textured bismuth telluride-based thermoelectric material, which differs from Example 1 in that the mesh size of the sieve in step (2) is 400 meshes.

[0062] The strongly textured bismuth telluride thermoelectric materials prepared in the above Examples 1 to 5 were tested. The inverse pole figure was tested by EBSD, and the grain size and the main texture ratio were calculated using Aztec software. The test results are shown in Table 1.

[0063]

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for constructing and molding a strongly textured bismuth telluride-based thermoelectric material, characterized in that: The method specifically comprises the following steps: S1) weighing Bi, Te, and Sb elements respectively according to the designed ratio, crushing them into fine powders, sieving them, and then ball milling them to obtain a mixed material; S2) dividing the mixed material obtained in S1) into two equal parts and sintering them using a spark plasma sintering device to obtain two sintered blanks No. 1 and No. 2 of the same size; S3) mechanically grinding and polishing one side of the No. 1 and No. 2 sintered blanks obtained in S2) to form a mirror surface; S4) The mirror surfaces of the first and second blanks obtained after the treatment in S3) are placed in contact with each other in a mold, and are formed by spark plasma sintering to obtain a constructed strong texture thermoelectric material.

2. The method according to claim 1, characterized in that The stoichiometric ratio of Bi, Te and Sb in S1) is Bi x Sb 2-x Te 3-y , wherein, 0.35≤x≤0.55, -0.03≤y≤0.03; the rotation speed of the ball milling process is 400-800rpm, and the ball-to-material ratio is 5:1-10:

1.

3. The method according to claim 1, characterized in that The single substance in said S1) is sieved through a mesh number of 200 to 400 meshes, and the purity is not less than 99.99%.

4. The method according to claim 1, characterized in that: The temperature of the spark plasma sintering in S2) is 400-500°C, the pressure is 35-50MPa, and the sintering duration is 5-20min.

5. The method according to claim 1, characterized in that The root mean square roughness of the polished surfaces of the No. 1 and No. 2 sintered blanks in S3) after grinding and polishing is less than 20 μm.

6. The method according to claim 1, characterized in that The temperature of the spark plasma sintering in S4) is 400-500°C, the pressure is 35-50MPa, and the sintering duration is 5-20min.

7. The method according to claim 1, characterized in that The mold material for spark plasma sintering in S2) and S4) is graphite.

8. The method according to claim 1, characterized in that: The grain size of the constructed strong texture thermoelectric material is not less than 15.6 μm, and the outer grain orientation is <0001> The main texture accounts for no less than 57.3%, the room temperature compressive strength is no less than 67MPa, and the room temperature ZT value is no less than 0.

78.

9. A bismuth telluride-based thermoelectric material, characterized in that: The bismuth telluride-based thermoelectric material is prepared by the method according to any one of claims 1 to 8.

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