A one-step, efficient method for synthesizing CoSb3-based high-performance thermoelectric materials

Abstract

The present invention relates to a one-step, efficient method for synthesizing CoSb3-based high-performance thermoelectric materials, and belongs to the field of thermoelectric materials and applications. By regulating the added content of the rare earth element Yb to regulate the peritectic solidification process of the Co-Sb alloy directly at a Co:Sb ratio of 1:3, the reaction can be complete, and a single-phase CoSb3 thermoelectric material can be obtained efficiently and simply. In addition to regulating the phase transformation process of the peritectic solidification process, the rare earth element Yb can also improve the thermoelectric performance in the later thermoelectric performance test, so that the rare earth Yb process plays a role. The method is simple and easy to implement, has high repeatability, can be carried out in batches, and significantly improves performance. It has an important impact on the application and production of thermoelectric devices.

Description

Technical Field

[0001] The present invention belongs to the field of thermoelectric materials and their applications, and in particular relates to a one-step and efficient method for synthesizing CoSb3-based thermoelectric materials. Background Art

[0002] Thermoelectric materials can achieve direct conversion of heat and electricity through the Seebeck effect and the Peltier effect, which can not only improve energy efficiency but also meet special power supply or cooling needs. Thermoelectric materials play an irreplaceable role in the utilization of waste heat from automobile exhaust, industrial waste heat power generation, interstellar exploration power supply, chip heat exchange, etc. Thermoelectric conversion efficiency is usually characterized by the dimensionless ZT value, ZT = (α 2 σT) / k, where α is the Seebeck coefficient, σ is the electrical conductivity, k is the thermal conductivity, T is the absolute temperature, and PF = α 2 σ is the power factor.

[0003] Thermoelectric materials can be categorized by their application temperature range into room-temperature, medium-temperature, and high-temperature thermoelectric materials. Room-temperature thermoelectric materials primarily utilize the difference between body temperature and ambient temperature for thermoelectric conversion, enabling applications such as health monitoring and driving electronic components, such as electronic watches. Medium-temperature thermoelectric materials, on the other hand, primarily target secondary utilization of industrial waste heat and waste heat from automobile exhaust, significantly improving energy efficiency. Therefore, medium-temperature thermoelectric materials have broad application demands.

[0004] Skutterudite-based CoSb3, a thermoelectric material with great potential for application in the medium-temperature range, has attracted considerable attention due to its non-toxicity, stability, and easily tunable properties. However, the synthesis of pure single-phase CoSb3 alloys is challenging due to the Co-Sb alloy phase. This is because, when melted with a Co:Sb molar ratio of 1:3, the peritectic reactions (CoSb+L→CoSb2) and (CoSb2+L→CoSb3) occur at 936°C and 874°C, respectively, during solidification. These two peritectic reactions are incomplete during solidification, resulting in a significant amount of residual impurities in the final sample: CoSb, CoSb2, and Sb. The presence of these impurities significantly degrades the thermoelectric performance of CoSb3 materials. Obtaining a high volume fraction of the CoSb3 phase is essential for improving thermoelectric performance. To achieve this high volume fraction of the CoSb3 phase, currently commonly used preparation techniques avoid peritectic reactions. The publicly published patent "A method for rapidly preparing CoSb3 by a solid-phase reaction method" (CN109604605A[P].2019) obtains a single-phase skutterudite sample through a solid-phase reaction process involving mixing Co powder and Sb powder in a 1:3 ratio, high-energy ball milling, compression molding, and vacuum sintering. However, this process is relatively cumbersome, and the powder is prone to oxidation during the high-energy ball milling process. Furthermore, to avoid incomplete peritectic reactions and oxidation during the powder ball milling process, the publicly published patent "A method for efficiently preparing pure CoSb3-based intermediate-temperature thermoelectric materials" (CN108754230B[P].2020) selects components in the Co-Sb hypoeutectic range to obtain high-purity CoSb3 materials under the TGZM effect. This process produces high-purity samples, but the number of samples obtained each time is small, and a stable temperature gradient must be controlled. To ensure complete liquid phase migration, a long static isothermal treatment time is required. Therefore, obtaining pure single-phase CoSb3 material under an efficient and short process is of great significance for the practical application of CoSb3 thermoelectric materials. Summary of the Invention

[0005] Technical problems to be solved

[0006] To overcome the shortcomings of existing technologies, the present invention provides a method for efficiently synthesizing high-performance CoSb3-based thermoelectric materials. By controlling the solidification process and adding the rare earth element Yb, a Co:Sb ratio of 1:3 is achieved to promote the complete occurrence of two peritectic reactions. This allows for the efficient production of large quantities of single-phase thermoelectric CoSb3 structures, providing reliable material support for the construction of thermoelectric devices.

[0007] Technical Solution

[0008] A one-step, efficient method for synthesizing CoSb3-based high-performance thermoelectric materials is characterized by the following steps:

[0009] Step 1: Ingredient design and weighing

[0010] According to the Co-Sb alloy phase diagram, a composition with a Co:Sb atomic ratio of 1:3 was selected for rare earth Yb addition, and the Yb addition amount x = 0.1;

[0011] Step 2: Loading the sample and vacuuming

[0012] The weighed sample was placed in a corundum crucible and a cover was placed on the corundum crucible; the corundum crucible was then placed in a graphite crucible; the graphite crucible was placed in the induction coil of the induction heating furnace, and a heat insulation board made of refractory bricks was placed under the graphite crucible; an insulation cover made of refractory bricks was placed between the graphite crucible and the coil, and a W-Ra thermocouple was inserted into the upper edge of the graphite crucible to monitor the temperature; the furnace chamber was cleaned, the furnace door was closed, and the vacuum operation was carried out; the vacuum in the furnace was evacuated to 2.0×10 -3 Below Pa, high-purity argon gas is filled in for atmosphere protection;

[0013] Step 3: Alloy Melting

[0014] The temperature was raised from room temperature to 1050℃ at a rate of 20℃ / min, and the heating system was turned off after holding for 30min. The sample was cooled and solidified in the furnace. After cooling to room temperature, the alloy ingot was taken out and the above steps were repeated for secondary melting. The above steps were repeated to melt the alloy Yb 0.1 Co4Sb 12 ;

[0015] Step 4: Cutting and tissue characterization

[0016] The test samples were cut by electric spark cutting, and the cut samples were finely polished to make the surface smooth.

[0017] A one-step, efficient method for synthesizing CoSb3-based high-performance thermoelectric materials is characterized by the following steps:

[0018] Step 1: Ingredient design and weighing

[0019] According to the Co-Sb alloy phase diagram, a composition with a Co:Sb atomic ratio of 1:3 was selected for rare earth Yb addition, and the Yb addition amount x = 0.2;

[0020] Step 2: Loading the sample and vacuuming

[0021] The weighed sample was placed in a corundum crucible and a cover was placed on the corundum crucible; the corundum crucible was then placed in a graphite crucible; the graphite crucible was placed in the induction coil of the induction heating furnace, and a heat insulation board made of refractory bricks was placed under the graphite crucible; an insulation cover made of refractory bricks was placed between the graphite crucible and the coil, and a W-Ra thermocouple was inserted into the upper edge of the graphite crucible to monitor the temperature; the furnace chamber was cleaned, the furnace door was closed, and the vacuum operation was carried out; the vacuum in the furnace was evacuated to 2.0×10 -3Below Pa, high-purity argon gas is filled in for atmosphere protection;

[0022] Step 3: Alloy Melting

[0023] The temperature was raised from room temperature to 1050℃ at a rate of 20℃ / min, and the heating system was turned off after holding for 30min. The sample was cooled and solidified in the furnace. After cooling to room temperature, the alloy ingot was taken out and the above steps were repeated for secondary melting. The above steps were repeated to melt the alloy Yb 0.2 Co4Sb 12 ;

[0024] Step 4: Cutting and tissue characterization

[0025] The test samples were cut by electric spark cutting, and the cut samples were finely polished to make the surface smooth.

[0026] Beneficial effects

[0027] The present invention provides a one-step, efficient method for synthesizing CoSb3-based high-performance thermoelectric materials. By regulating the added content of the rare earth element Yb, the peritectic solidification process of the Co-Sb alloy directly carried out at a Co:Sb ratio of 1:3 can be completely reacted. This method is an efficient and simple method for obtaining single-phase CoSb3 thermoelectric materials. In addition, in addition to regulating the phase transformation process during the peritectic solidification process, the rare earth element Yb can also improve thermoelectric performance in subsequent thermoelectric performance testing, allowing the rare earth Yb to play a role throughout the entire process. This method is simple and easy to implement, has high reproducibility, can be carried out in batches, and significantly improves performance. It has a significant impact on the application and production of thermoelectric devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like parts throughout the drawings.

[0029] Figure 1 This is the Co-Sb alloy phase diagram.

[0030] Figure 2 (a), (b) and (c) are the metallographic structure evolution diagrams of alloys 1, 2 and 3 respectively. Figure 2 (a) It can be seen that when Yb is not doped, there are CoSb phase, CoSb2 phase, Sb phase and CoSb3 phase; Figure 2 When the Yb doping content in (b) is 0.1, only part of the CoSb phase remains, and the content of the CoSb3 phase is greatly increased; Figure 2 When the Yb doping content in (c) is 0.2, it can be seen that it is a CoSb3 single-phase structure, indicating that the effect is best under this doping content.

[0031] Figure 3(a) and (b) are EBSD grain morphologies of alloys 1 and 3, respectively. Figure 3 (a) and (b) are the phase composition and grain orientation without Yb doping, respectively. It can be seen that the CoSb phase and CoSb2 phase are obviously distributed. Figure 3 (c) and (d) are the phase composition and grain distribution when Yb doping is 0.2, respectively. It can be seen that CoSb3 is distributed in a single phase, and the grain size refinement effect is very obvious, which is the microstructure expected to improve thermoelectric performance.

[0032] Figure 4 The thermoelectric performance curves for alloys 1, 2, and 3 show that when Yb is not doped, the thermoelectric figure of merit (ZT) changes slowly with increasing temperature, reaching a maximum value of less than 0.2. When the Yb doping content is 0.1, the thermoelectric figure of merit (ZT) increases significantly with increasing temperature, reaching a maximum value of 0.58 at 795K. When the doping content is 0.2, the thermoelectric figure of merit (ZT) increases significantly, reaching 1.04 at 736K. DETAILED DESCRIPTION

[0033] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only intended to illustrate the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0034] The role of the rare earth element Yb is to promote the phase transformation of the peritectic reaction process, so that the phase transformation process (CoSb+L—CoSb2 and CoSb2+L—CoSb3) that was originally difficult to complete can be completed quickly. It provides a reliable method for the efficient synthesis of single-phase CoSb3. Usually, in order to avoid the complex peritectic reaction to produce too many impurities Sb, CoSb and CoSb2, researchers often use powder metallurgy technology to carry out solid-state reaction to prepare single-phase CoSb3 materials. The solid-state reaction usually takes about a week to prepare, and the efficiency is low. This invention directly controls the solidification process and uses the Yb element to change the thermodynamic process of the reaction. It completes a more thorough phase transformation in the liquid phase with a total time of less than 5 hours, which greatly improves the synthesis efficiency. And it can make the thermoelectric figure of merit ZT>1.

[0035] The present invention provides a one-step method for efficiently synthesizing CoSb3-based high-performance thermoelectric materials, comprising the following steps:

[0036] The first step is ingredient design and weighing

[0037] Based on the Co-Sb alloy phase diagram, rare earth Yb was added at locations with a Co:Sb atomic ratio of 1:3. Three compositions were set, with Yb addition amounts x = 0, 0.1, and 0.2 (atomic ratio). The specific composition ratios are shown in Table 1. 200g of each component was weighed.

[0038] Table 1 Alloy composition design

[0039]

[0040]

[0041] Step 2: Load samples and vacuum

[0042] Place the weighed sample into a corundum crucible with an inner diameter of 45 mm, an outer diameter of 50 mm, and a height of 80 mm. Place a corundum lid with a diameter of 50 mm on top of the crucible. Place the crucible into a graphite crucible. Place the graphite crucible into the induction coil of an induction heating furnace, with a 6 mm thick insulation board made of refractory bricks underneath. Place an insulation jacket made of refractory bricks between the graphite crucible and the coil, and insert a W-Ra thermocouple into the upper edge of the graphite crucible. Clean the furnace chamber, close the furnace door, and evacuate. Evacuate the furnace to a vacuum of 2.0 × 10 -3 Pa, some high-purity (99.99%) argon gas is filled in for atmosphere protection, and the furnace still maintains negative pressure.

[0043] The third step is alloy melting

[0044] The temperature was raised from room temperature to 1050℃ at a rate of 20℃ / min. After holding for 30min, the heating system was turned off and the sample was cooled and solidified in the furnace. After cooling to room temperature, the alloy ingot was taken out and the above steps were repeated for secondary melting. The above steps were repeated to melt alloys No. 1, 2 and 3 Co4Sb 12 , Yb 0.1 Co4Sb 12 and Yb 0.2 Co4Sb 12 .

[0045] The fourth step is cutting and tissue performance characterization.

[0046] The test samples were cut using spark cutting. The cutting size for the electrical test sample was 5mm×5mm×15mm; the thermal performance test sample was 10mm in diameter and 2mm thick. The cut samples were finely polished to achieve a smooth surface.

[0047] In order to enable those skilled in the art to better understand the present invention, the present invention is described in detail below with reference to specific embodiments.

[0048] Example 1:

[0049] The raw materials Co (99.95%), Sb (99.95%), and Yb (99.95%) are mixed according to the atomic ratio (Yb: Co: Sb is 1.23%: 24.69%: 74.07%) and loaded into a corundum crucible with the dimensions of an inner diameter of 45 mm, an outer diameter of 50 mm, and a height of 80 mm. The corundum crucible is placed in a graphite crucible, which is then placed in the induction coil of an induction heating furnace. A 10 mm thick refractory brick is laid under the graphite crucible, and the graphite crucible is insulated with an insulation sleeve made of refractory bricks. A W-Ra thermocouple is inserted above the graphite crucible to measure the temperature. The furnace door is then closed and vacuumed until the vacuum reaches 2.0×10 -3 Pa, high-purity (99.99%) argon gas was filled in for atmosphere protection, and the furnace was still under negative pressure, at which point the barometer reading was -0.05 Pa. Induction heating was then performed, with the temperature rising from room temperature to 1050°C at a rate of 20°C / min. After holding for 30 minutes, the heating system was turned off, and the sample solidified as the furnace cooled.

[0050] After solidification strictly according to the above preparation parameters, it can be seen that the sample prepared by this method is almost a single-phase CoSb3 structure, and the grains are obviously refined, such as Figure 3 (c) and (d); it can also be seen Figure 4 The sample Yb 0.2 Co4Sb 12 The thermoelectric figure of merit (ZT) is significantly improved, reaching 1.04 at 736 K. The preparation process can produce single-phase CoSb3 thermoelectric materials with ZT>1 in less than 5 hours, with high preparation efficiency and significant results.

[0051] Example 2:

[0052] The preparation process is the same as that of Example 1. However, element Yb is not added, and 200g of Co and Sb are added at a molar ratio of 1:3. After the preparation is completed, analysis shows that there are a large number of impurities in the phase, namely CoSb phase, CoSb2 phase, and Sb phase. Among them, the target phase CoSb3 content is relatively low, such as Figure 3 In addition, the thermoelectric figure of merit of this sample is not higher than 0.2, which is a poor effect.

[0053] Example 3:

[0054] The preparation process is the same as that of Example 1. However, the atomic ratio of Yb doping is 0.62%. (The atomic ratio of the raw materials is: Yb: Co: Sb is 0.62%: 24.84%: 74.54%). After the preparation, the analysis found that the impurities in the sample were greatly reduced, but a small amount of impurities still existed, such as Figure 1In addition, thermoelectric performance tests found that ZT reached a maximum of 0.58 at 795K. Compared to the undoped sample, this improvement was not significant, and there is still considerable room for improvement to reach 1.

[0055] The above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with this technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed in the present invention, and these modifications or replacements should all be included in the scope of protection of the present invention.

Claims

1. A one-step, efficient method for synthesizing CoSb3-based high-performance thermoelectric materials, characterized in that Here are the steps: Step 1: Ingredient design and weighing According to the Co-Sb alloy phase diagram, the composition with Co:Sb atomic ratio of 1:3 is selected for rare earth Yb addition, and the amount of element Yb added is x = 0.2; Step 2: Loading the sample and vacuuming Raw materials Co, Sb, and Yb, all with a purity of 99.95%, were mixed in an atomic ratio of Yb:Co:Sb of 1.23%:24.69%:74.07% and placed in a corundum crucible. The weighed sample was placed in the corundum crucible and a cover was placed on the corundum crucible. The corundum crucible was then placed in a graphite crucible. The graphite crucible was placed in the induction coil of an induction heating furnace, and a heat insulation board made of refractory bricks was placed under the graphite crucible. A heat insulation jacket made of refractory bricks was placed between the graphite crucible and the coil, and a W-Ra thermocouple was inserted into the upper edge of the graphite crucible to monitor the temperature. The furnace chamber was cleaned, the furnace door was closed, and the vacuum operation was performed. The vacuum in the furnace was evacuated to 2.0 × 10 -3 Below Pa, high-purity argon gas is filled in for atmosphere protection; Step 3: Alloy Melting The temperature was raised from room temperature to 1050 °C at a rate of 20 °C / min, and the heating system was turned off after holding for 30 min. The sample was cooled and solidified in the furnace. After cooling to room temperature, the alloy ingot was taken out and the above steps were repeated for secondary melting. The above steps were repeated to melt the alloy Yb 0.2 Co4Sb 12 ; Step 4: Cutting and tissue characterization The test samples were cut by electric spark cutting, and the cut samples were finely polished to make the surface smooth; The preparation process can be completed in less than 5 hours. ZT > 1 single-phase CoSb3 thermoelectric material.

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