A method for preparing bismuth telluride-based textured bulk thermoelectric material

Abstract

The present invention discloses a method for preparing a bismuth telluride-based bulk thermoelectric material. The method combines a magnetic field-assisted zone melting process, a layer-by-layer covering and pressurizing and vibration-assisted orientation process, a cold isostatic pressing process, a vacuum sintering process, and a hot isostatic pressing process. High-purity tellurium, bismuth, antimony, selenium, etc. are used as raw materials. A zone melting method is first used to prepare a bismuth telluride ingot. The ingot is then crushed, ground, and sieved. The sieved powder is then pressed into a bulk material using a layer-by-layer covering and pressurizing and vibration-assisted orientation process. Finally, a cold isostatic pressing process, a vacuum sintering process, and a hot isostatic pressing process are combined to prepare a textured bulk thermoelectric material with good orientation and nearly complete density. The present invention can significantly improve the orientation of bismuth telluride grains. The obtained bismuth telluride-based bulk material has both good thermoelectric properties and mechanical processing properties. The method is a preparation method with high material utilization, simplicity, high preparation efficiency, and good application prospects.

Description

Technical Field

[0001] The present invention relates to the field of thermoelectric functional materials, and in particular to a method for preparing a bismuth telluride-based bulk thermoelectric material with high strength, high performance and layered structure characteristics. Background Art

[0002] Thermoelectric conversion materials are a class of functional materials that utilize the Seebeck and Peltier effects of semiconductor materials to directly convert heat and electricity. They are primarily used for thermoelectric power generation and thermoelectric cooling. With energy and environmental challenges becoming increasingly prominent, thermoelectric conversion technology, with its advantages of being pollution-free, noise-free, compact, long-lasting, precisely controllable, safe, and environmentally friendly, is of great significance in alleviating energy crises and environmental pollution.

[0003] The performance of thermoelectric materials is usually characterized by the dimensionless thermoelectric figure of merit ZT: ZT = (S 2 σ / κ)T, where S is the Seebeck coefficient, σ is the electrical conductivity, κ is the thermal conductivity, and T is the absolute temperature. Bismuth telluride-based thermoelectric materials are among the best performing thermoelectric materials near room temperature, with ZT values reaching around 1.0.

[0004] The crystal structure of Bi2Te3-based materials belongs to the R3m trigonal system. Along the c-axis, the crystal structure can be viewed as a hexahedral layered structure. The bond between Te and Bi is a strong chemical bond, while adjacent Te layers are connected by van der Waals bonds. This weak bond between Te layers results in Bi2Te3 being susceptible to cleavage along the c-axis, resulting in poor mechanical properties and hindering material processing and device fabrication.

[0005] Bi2Te3-based materials can be prepared using the zone melting method and the Bridgman method. By controlling the preparation process parameters, well-oriented crystal materials can be obtained. These methods are commonly used in current industrial production. However, simultaneously improving the mechanical and thermoelectric properties of the materials is of great significance for increasing material utilization and expanding their application areas.

[0006] Previously, many people have tried to prepare bismuth telluride-based thermoelectric materials by refining the particle size and combining sintering processes such as hot pressing, spark plasma sintering, and hot extrusion. Although the mechanical properties have been improved, the preferred orientation of the grains has been severely damaged, resulting in a low thermoelectric figure of merit of the material. In addition, the ball milling process will introduce other impurities, affecting the thermoelectric performance of the material.

[0007] Hot isostatic pressing (HIP) involves applying uniform pressure in all directions to powders or sintered materials (or parts) to be compacted in a sealed container at high temperature and pressure, using high-pressure gas as the medium. This creates a high-density material (or part). This technique achieves high density at relatively low temperatures, effectively suppressing grain growth. The resulting sintered samples exhibit uniform grains, high density, and excellent mechanical properties. Compared to traditional sintering methods, HIP sintering technology can sinter a large number of samples at once, conserving resources, improving preparation efficiency, and reducing production costs. Summary of the Invention

[0008] The technical purpose of the present invention is to provide a method for preparing bismuth telluride-based bulk thermoelectric materials with simple process, excellent thermoelectric performance, good machining performance and high preparation efficiency, in response to existing bulk thermoelectric material preparation methods.

[0009] In order to achieve the above technical objectives, the technical solution of the present invention is: using high-purity bismuth, antimony, tellurium, selenium, etc. as raw materials, a zone melting method is adopted to prepare bismuth telluride-based bulk thermoelectric materials, and after crushing and grinding, a roller-type layer-by-layer covering and pressurization is used in combination with vibration-assisted orientation to prepare bismuth telluride-based bulk materials with good orientation, and a cold isostatic pressing process, a vacuum sintering process and a hot isostatic pressing process are combined to sinter the above-mentioned bismuth telluride-based bulk materials with good grain orientation into nearly completely dense bulk thermoelectric materials under appropriate process conditions.

[0010] The specific preparation process of the bismuth telluride-based bulk thermoelectric material is as follows:

[0011] (1) Preparation of bismuth telluride-based thermoelectric material ingots by zone melting method;

[0012] (2) polishing the surface of the bismuth telluride-based thermoelectric material ingot obtained in step (1) with sandpaper, ultrasonically cleaning the polished ingot in alcohol, repeatedly cleaning the ingot with deionized water, and drying it in a vacuum, and then crushing, grinding, and sieving the ingot in a glove box to obtain a powder with a desired particle size distribution range;

[0013] (3) Using a roller-type layer-by-layer covering and pressurizing method combined with a vibration-assisted tending device to cover and pressurize the powder obtained in step (2) layer by layer to obtain a layered block material of the desired thickness;

[0014] (4) The layered block material obtained in step (3) is plastic-sealed and placed in a cold isostatic pressing device for pressurization to obtain a green blank with a certain strength.

[0015] (5) placing the green blank material obtained in step (4) into a vacuum sintering furnace for low-temperature pre-sintering to obtain a pre-sintered bulk material;

[0016] (6) The bulk material obtained in step (5) is placed in a hot isostatic pressing furnace for sintering to obtain a bismuth telluride bulk thermoelectric material having a density close to the theoretical density, good orientation and excellent machinability.

[0017] In the step (1), bismuth with a purity of 99.999%, antimony with a purity of 99.999%, tellurium with a purity of 99.999%, and selenium with a purity of 99.999% are used as raw materials, and the process parameters include a magnetic field strength of 0.1 Tesla to 5 Tesla, a melting temperature of 700 to 950°C, a melting zone width of 30 to 40 mm, a temperature gradient of 25 to 50°C / cm, and a growth rate of 25 to 30 mm / h are adopted to obtain a bismuth telluride-based thermoelectric material ingot.

[0018] In the step (2), sandpaper with a mesh size of 500 to 3000 is selected, ultrasonic cleaning is performed for 10 to 20 minutes, and deionized water is used for 5 to 10 times. The product is crushed, ground, and sieved in a glove box filled with an inert gas. An agate or steel container is used to crush the ingot or grind the powder, and the powder is sieved using a standard nylon sieve. The inert gas is preferably argon.

[0019] In the step (3), the surface of the carrier is polished and coated with a layer of polymer adhesive with a thickness of 1 to 1000 μm, preferably epoxy glue, and the roller-type layer-by-layer covering is pressurized and combined with a vibration-assisted trending device to evacuate a vacuum degree of <10 Pa. The reciprocating frequency of the roller in the device is 1 to 10 times / second, the pressure applied by the roller is 50 to 300 MPa, and the connecting rods at both ends of the roller continuously rise as the thickness of the layered block increases, and the rising speed is 5 to 500 mm / h. The mesh aperture of the screen at the top of the device is the maximum particle size of the added powder, the vibration direction is horizontal, the frequency is 5 to 40 Hz, and the amplitude is 1 to 5 mm. The vibration direction of the carrier in the device is horizontal, the frequency is 20 to 80 Hz, and the amplitude is 1 to 5 mm. The thickness of the layered block is not limited.

[0020] In the step (4), the pressure in the cold isostatic pressing process is 50-300 MPa.

[0021] In the step (5), the vacuum degree of vacuum sintering is <10 Pa, the sintering temperature is 350~450℃, the heating rate is 2~20℃ / min, and the holding time is 30~300 minutes.

[0022] In the step (6), the hot isostatic pressing sintering temperature is 300-480°C, the pressure is 80-200 MPa, the heating rate is 1-3°C / min, and the holding time is 60-180 minutes.

[0023] In summary, the preparation method of bismuth telluride-based bulk thermoelectric material provided by the present invention combines zone melting process, layer-by-layer covering and pressurizing and vibration-assisted orientation process, cold isostatic pressing process, vacuum sintering process and hot isostatic pressing process. Using high-purity tellurium, bismuth, antimony, selenium and the like as raw materials, the zone melting method is first used to prepare bismuth telluride ingots, and then the ingots are crushed, ground and sieved, and then the sieved powder is pressed into a layered block with good grain orientation using layer-by-layer covering and pressurizing and vibration-assisted process, and then the cold isostatic pressing process, vacuum sintering process and hot isostatic pressing process are successively combined to prepare a layered bulk thermoelectric material with an ideal grain orientation and close to complete densification. Compared with the existing preparation process, it has the following beneficial effects:

[0024] After grinding the bismuth telluride ingots produced by the zone melting method into powder, the sieved powder is pressed into a layered block with well-defined grain orientation using a layer-by-layer covering and pressure-assisted vibration device, significantly improving the grain orientation of the bismuth telluride powder. The material is then sintered into a bulk thermoelectric material with a density of 98% to 100% by combining cold isostatic pressing, vacuum sintering, and hot isostatic pressing (HIPP) processes, controlling temperature, pressure, and time. This combined process allows for the simultaneous sintering of large batches of samples, significantly improving preparation efficiency and reducing production costs.

[0025] The bismuth telluride-based bulk material prepared using this process has thermoelectric properties that surpass those of bismuth telluride-based zone-melting crystals, and has good mechanical processing performance, showing good application and industrialization prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a flowchart of the preparation process of the bismuth telluride-based bulk thermoelectric material of the present invention;

[0027] Figure 2 Schematic diagram of the roller-type layer-by-layer covering and pressurizing combined with vibration-assisted orientation device used in the present invention;

[0028] Figure 3 1 is the X-ray diffraction pattern of the bismuth telluride-based bulk thermoelectric material prepared in the comparative example and Examples 1 to 4 of the present invention;

[0029] Figure 4 is a graph showing the relationship between the electrical conductivity of the bismuth telluride-based bulk thermoelectric materials prepared in the comparative example and Examples 1 to 4 of the present invention and the temperature;

[0030] Figure 5 is a graph showing the relationship between the Seebeck coefficient of the bismuth telluride-based bulk thermoelectric materials prepared in the comparative example and Examples 1 to 4 of the present invention and the temperature;

[0031] Figure 6is a graph showing the relationship between the thermal conductivity of the bismuth telluride-based bulk thermoelectric materials prepared in the comparative example and Examples 1 to 4 of the present invention and the temperature;

[0032] Figure 7 1 is a graph showing the relationship between the thermoelectric figure of merit ZT of the bismuth telluride-based bulk thermoelectric materials prepared in the control example and examples 1 to 4 of the present invention and the change with temperature. DETAILED DESCRIPTION

[0033] In order to better understand the present invention, the content of the present invention is further illustrated below in conjunction with the examples, but the content of the present invention is not limited to the following examples.

[0034] Comparative Example:

[0035] This example is a comparative example for the following examples 1 to 4. This example uses a zone melting process to prepare a bismuth telluride-based bulk thermoelectric material. The details are as follows:

[0036] Bismuth telluride alloy was prepared by zone melting method. Appropriate amounts of high-purity bismuth, tellurium and selenium were weighed as matrix materials and loaded into a quartz tube. The tube was evacuated to a vacuum degree of 10 Pa and sealed with a flame gun. The sealed quartz tube was melted in a rocking furnace at 750°C for 4 hours. After cooling, the tube was placed in a zone melting furnace for zone melting to obtain bismuth telluride alloy: the zone melting temperature was 750°C, the growth rate was 25 mm / h, the melting zone width was 30 mm, and the temperature gradient was 25°C / cm.

[0037] The bismuth telluride alloy obtained by zone melting was cut into 2×2×9 mm strips and φ10×1.5 mm discs, which were used to measure the electrical transport properties and thermal transport properties, respectively.

[0038] Example 1

[0039] In this embodiment, a bismuth telluride-based bulk thermoelectric material is prepared by combining a zone melting process, a layer-by-layer covering and pressurizing process with a vibration-assisted process, a cold isostatic pressing process, a vacuum sintering process, and a hot isostatic pressing process, as follows:

[0040] (1) preparing a bismuth telluride alloy by a zone melting method, which is exactly the same as the process of preparing a bismuth telluride alloy by the zone melting method in the comparative example;

[0041] (2) Using the bismuth telluride alloy prepared in step (1) as the starting material, crushing, grinding, and sieving to obtain a powder material with a particle size in the range of 180 to 380 μm, and weighing an appropriate amount of the powder;

[0042] (3) polishing the surface of the carrier in the layer-by-layer pressurized and vibration-assisted orientation device, and attaching a layer of epoxy glue with a thickness of 20 μm as an adhesive;

[0043] (4) The powder prepared in step (2) is loaded into a layer-by-layer pressurized and vibration-assisted orientation device, and the device is vacuumed to a vacuum degree of <10Pa. Then, the vibration frequency of the carrier in the device is adjusted to 50Hz, the amplitude is 1mm, and the pressure of the cylinder on the carrier is adjusted to 120MPa. The powder is continuously and evenly spread on the carrier through the vibration of the screen on the top of the device. The screen aperture is the maximum particle size of the powder 380um, the vibration frequency is 10Hz, the amplitude is 5mm, and the carrier surface is bonded. When the agent is basically completely covered, the reciprocating frequency of the cylinder is adjusted to 5 times / second, and the rising speed of the connecting rods at both ends of the cylinder is 10mm / h. The rising speed of the connecting rod is the same as the increasing rate of the thickness of the block material. At this time, the cylinder begins to cover and pressurize the powder layer by layer. Since the surface of the carrier is polished and a thin layer of epoxy glue is attached as a binder, the powder has a good orientation on the carrier and will not stick to the drum. When the thickness of the layered block material reaches 10mm, the device is stopped and the layered block material is peeled off from the carrier.

[0044] (5) The layered block material prepared in step (4) is plastic-sealed and placed in a cold isostatic pressing device to be pressurized to achieve initial densification at a pressure of 300 MPa. After the cold isostatic pressing is completed, the outer plastic bag of the block material is removed to obtain a initially dense green blank material;

[0045] (6) The preliminarily dense green material prepared in step (5) is placed in a vacuum sintering furnace for pre-sintering at a temperature of 400°C, a heating rate of 3°C / min, a holding time of 120 min, and naturally cooled to obtain a pre-sintered block material;

[0046] (7) The pre-sintered bulk material prepared in step (6) was placed in a hot isostatic pressing device at a temperature of 450°C, a heating rate of 2°C / min, and a holding time of 120 min to obtain a nearly fully dense bulk thermoelectric material with good grain orientation.

[0047] The nearly fully dense, well-oriented bulk thermoelectric material after hot isostatic pressing was cut into 2×2×9 mm strips and φ10×1.5 mm discs, which were used to measure the electrical and thermal transport properties, respectively.

[0048] Example 2

[0049] In this embodiment, a zone melting process, a layer-by-layer covering pressurization and vibration-assisted process, a cold isostatic pressing process, a vacuum sintering process and a hot isostatic pressing process are combined to prepare a bismuth telluride-based bulk thermoelectric material. Compared with the process of preparing a nearly completely dense, well-oriented bulk thermoelectric material in Example 1, this process is different only in that the particle size of the powder material obtained by sieving in step (2) is in the range of 120 to 180 μm. The other processes are exactly the same as those in Example 1.

[0050] The nearly fully dense, well-oriented bulk thermoelectric material after hot isostatic pressing was cut into 2×2×9 mm strips and φ10×1.5 mm discs, which were used to measure the electrical and thermal transport properties, respectively.

[0051] Example 3

[0052] In this embodiment, a zone melting process, a layer-by-layer covering pressurization and vibration-assisted process, a cold isostatic pressing process, a vacuum sintering process, and a hot isostatic pressing process are combined to prepare a bismuth telluride-based bulk thermoelectric material. Compared with the process of preparing a nearly fully dense, well-oriented bulk thermoelectric material in Example 1, this process differs only in that the particle size of the powder material obtained by sieving in step (2) is in the range of 96 to 120 μm. The other processes are exactly the same as those in Example 1.

[0053] The nearly fully dense, well-oriented bulk thermoelectric material after hot isostatic pressing was cut into 2×2×9 mm strips and φ10×1.5 mm discs, which were used to measure the electrical and thermal transport properties, respectively.

[0054] Example 4

[0055] In this embodiment, a zone melting process, layer-by-layer covering and pressurizing with vibration-assisted process, cold isostatic pressing process, vacuum sintering process and hot isostatic pressing process are combined to prepare bismuth telluride-based bulk thermoelectric material. Compared with the process of preparing a nearly fully dense, well-oriented bulk thermoelectric material in Example 1, this process is different only in that the particle size of the powder material obtained by sieving in step (2) is less than 96 μm. The other processes are exactly the same as those in Example 1.

[0056] The nearly fully dense, well-oriented bulk thermoelectric material after hot isostatic pressing was cut into 2×2×9 mm strips and φ10×1.5 mm discs, which were used to measure the electrical and thermal transport properties, respectively.

[0057] like Figure 3 As shown, the X-ray diffraction patterns of the bismuth telluride-based bulk thermoelectric materials prepared in Examples 1 to 4 above show that the main phase composition of the bismuth telluride-based bulk thermoelectric materials prepared by combining the zone melting process, layer-by-layer covering pressurization and vibration-assisted orientation process, cold isostatic pressing process, vacuum sintering process and hot isostatic pressing process remains unchanged; its thermoelectric characteristic curve is shown in FIG. Figures 4 to 7 As shown, it can be seen that the bismuth telluride-based bulk thermoelectric materials of Examples 1 to 4 prepared by layer-by-layer covering, pressurizing and vibration-assisted orientation process have electrical conductivities and Seebeck coefficients that are not much different from those of the control examples, and their thermal conductivities are significantly lower than those of the control examples. The preparation method used in the present invention can effectively improve the thermoelectric figure of merit of the thermoelectric materials.

[0058] After grinding the bismuth telluride ingots produced by the zone melting method into powder, the sieved powder is pressed into a well-oriented layered block using a layer-by-layer covering and pressure-assisted vibration device, significantly improving the orientation of the bismuth telluride grains. The material is then sintered into a high-density bulk thermoelectric material with a high thermoelectric figure of merit of 98% to 100% by combining cold isostatic pressing, vacuum sintering, and hot isostatic pressing (HIPP) processes. These processes, combined with controlled temperature, pressure, and time, allow for the simultaneous sintering of large batches of samples, significantly improving preparation efficiency and reducing production costs.

[0059] The embodiments described above provide a detailed description of the technical solutions of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements or equivalent substitutions made within the scope of the principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a bismuth telluride-based bulk thermoelectric material, characterized in that: The following process steps are combined: (1) Preparation of bismuth telluride-based thermoelectric material ingots by zone melting method; (2) polishing the surface of the bismuth telluride-based thermoelectric material ingot obtained in step (1) with sandpaper, ultrasonically cleaning the polished ingot in alcohol, repeatedly cleaning the ingot with deionized water, and drying it in a vacuum; then crushing, grinding, and sieving the ingot in a glove box to obtain a powder with a desired particle size distribution range; (3) Using a roller-type layer-by-layer covering and pressurizing method combined with a vibration-assisted orientation device to cover and pressurize the powder obtained in step (2) layer by layer to obtain a layered block material of the desired thickness; (4) Plastic-sealing the layered block material obtained in step (3), placing it in a cold isostatic pressing device for pressurization, and obtaining a green blank with a certain strength; (5) placing the green blank material obtained in step (4) into a vacuum sintering furnace for low-temperature pre-sintering to obtain a pre-sintered bulk material; (6) placing the bulk material obtained in step (5) into a hot isostatic pressing furnace for sintering to obtain a bismuth telluride bulk thermoelectric material having good orientation and excellent machinability; In the step (3), a layer-by-layer covering and pressurizing and vibration-assisted orientation device is used to cover and pressurize the sieved powder layer by layer and vibrate to assist in orientation, so as to improve the degree of grain orientation of the material; In the step (5), the green blank material obtained in the step (4) is placed in a vacuum sintering furnace with a vacuum degree of <10 Pa, a sintering temperature of 350-450°C, a heating rate of 2-20°C / min, and a holding time of 30-300 minutes; In the step (6), the pre-fired block material is placed in a hot isostatic pressing device at a sintering temperature of 300-480°C, a pressure of 80-200 MPa, a heating rate of 1-3°C / min, and a holding time of 60-180 minutes.

2. The method for preparing a bismuth telluride-based bulk thermoelectric material according to claim 1, wherein: In the step (1), bismuth with a purity of 99.999%, antimony with a purity of 99.999%, tellurium with a purity of 99.999%, and selenium with a purity of 99.999% are used as raw materials, and the process parameters include a magnetic field strength of 0.1 Tesla to 5 Tesla, a melting temperature of 700 to 950°C, a melting zone width of 30 to 40 mm, a temperature gradient of 25 to 50°C / cm, and a growth rate of 25 to 30 mm / h are adopted to obtain a bismuth telluride-based thermoelectric material ingot.

3. The method for preparing a bismuth telluride-based bulk thermoelectric material according to claim 1, wherein: In the step (2), the surface of the zone melting ingot is polished and cleaned with sandpaper of 500-3000 mesh, ultrasonically cleaned for 10-20 minutes, and washed with deionized water 5-10 times. The crushing, grinding and sieving processes are all carried out in a glove box filled with an inert gas protective atmosphere, using an agate or steel container for crushing and grinding, and the powder is sieved using a standard nylon sieve.

4. The method for preparing a bismuth telluride-based bulk thermoelectric material according to claim 1, wherein: In the step (3), the surface of the carrier in the vibration-assisted orientation device is polished and coated with a layer of polymer adhesive with a thickness of 1 to 1000 μm.

5. The method for preparing the bismuth telluride-based bulk thermoelectric material according to claim 4, wherein: The polymer adhesive is epoxy glue.

6. The method for preparing a bismuth telluride-based bulk thermoelectric material according to claim 1, wherein: In the step (3), the roller pressure in the vibration-assisted orientation device is 50-300 MPa, the roller reciprocating motion frequency is 1-10 times / second, and the rising speed of the connecting rods at both ends of the roller is 5-500 mm / h.

7. The method for preparing a bismuth telluride-based bulk thermoelectric material according to claim 1, wherein: In the step (4), the layered block material is placed in a cold isostatic pressing device at a pressure of 50 to 300 MPa.

Images