Method for preparing CoSb3-based thermoelectric material by melt immersion float method

Abstract

The invention discloses a method for preparing a CoSb3-based thermoelectric material through a melt immersion float method, and belongs to the technical field of thermoelectric material preparation. According to the method, a liquid alloy is wrapped by molten glass, and the CoSb3-based thermoelectric material is prepared by combining molten glass purification and isothermal solidification technologies. According to the method, the volatilization of the element Sb is inhibited by wrapping the liquid alloy with the molten glass, two peritectic reactions are fully promoted by combining the molten glass purification and isothermal solidification technology on the premise of not losing components, and the high-volume-fraction CoSb3 thermoelectric material can be rapidly and efficiently obtained. Meanwhile, the process is simple, the solidification process is easy to control, the preparation speed is high, and good application prospects are achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of thermoelectric material preparation, and relates to a CoSb3-based thermoelectric material, in particular to a method for preparing a CoSb3-based thermoelectric material by a melt immersion floating method. BACKGROUND

[0002] As a typical energy conversion material, a thermoelectric material can directly convert heat energy into electric energy through the Seebeck effect, has the advantages of small size, no noise, environmental protection, etc., and is widely used in the fields of aerospace, wearable devices and chip refrigeration.

[0003] As a typical medium-temperature thermoelectric material, the CoSb3-based thermoelectric material has a large carrier mobility, a high electrical conductivity and a high Seebeck coefficient, but its thermal conductivity limits its thermoelectric performance. According to the Co-Sb alloy phase diagram, it is difficult to synthesize a single-phase CoSb3 alloy. When the Co:Sb molar ratio is 1:3, peritectic reactions occur at 1204 K and 1149 K during solidification to generate CoSb2 and CoSb3 phases, respectively. Since the two peritectic reactions cannot be completely carried out, the final sample contains a large amount of impurities, and obtaining a high volume fraction of CoSb3 phase is the basic guarantee for improving the thermoelectric performance of the skutterudite-based thermoelectric material.

[0004] At present, the preparation techniques of the CoSb3-based thermoelectric material mainly include mechanical alloying method, SPS sintering method, high-pressure synthesis method, hydrothermal / solvothermal method, solid-phase reaction method or a combination of the above methods. However, these processes have the disadvantages of long and complicated preparation cycle. Therefore, it is of great significance for the CoSb3-based thermoelectric material to inhibit the volatilization of Sb element and efficiently and quickly prepare pure single-phase CoSb3 compound under the premise of saving time cost. SUMMARY

[0005] In view of the defects and deficiencies of the prior art, the purpose of the present application is to provide a method for preparing a CoSb3-based thermoelectric material by a melt immersion floating method, which solves the technical problems of easy volatilization of element Sb, difficult process control and complex process route in the preparation of the CoSb3-based thermoelectric material in the prior art.

[0006] In order to solve the above technical problems, the present application adopts the following technical solutions: A method for preparing a CoSb3-based thermoelectric material by a melt immersion floating method, characterized by: wrapping a liquid alloy with a molten glass, combining the molten glass purification and isothermal solidification technology to prepare the CoSb3-based thermoelectric material.

[0007] Specifically, the method comprises the following steps: Step one, raw material configuration: the alloy raw material includes Co and Sb.

[0008] Step two, melt glass purification: the configured raw material and glass purifying agent are layered in the reaction container, the glass purifying agent is located at the top and bottom layers, and the raw material is arranged between the two layers of glass purifying agent; after the layered feeding is completed, the alloy is heated until the glass purifying agent melts and covers the surface of the alloy.

[0009] Step three, isothermal solidification: Step 3.1, temperature rising solidification: heat the alloy to 1573 K, rely on electromagnetic stirring to fully mix the alloy liquid, cut off the high-frequency power supply to cool and solidify; when the temperature drops to 873 K, turn on the high-frequency power supply to continue heating, slowly heat to 1023 K-1173 K, and keep warm for 15-20 min after turning off the high-frequency power supply, and the sample is cooled with the furnace; the total time of the temperature rising solidification and the remelting and keeping warm is not more than 30 min.

[0010] Specifically and optionally, step 3.1 can be replaced by: heating the alloy to 1573 K, relying on electromagnetic stirring to fully mix the alloy liquid, and turning off the high-frequency power supply to cool and solidify; repeating the above "temperature rising-solidification" process 4-5 times to ensure uniform distribution of each metal element.

[0011] The application also has the following technical features: Specifically and optionally, the alloy raw material also includes a rare earth element; the rare earth element is selected from one or more of lanthanum, cerium, neodymium, gadolinium, ytterbium, scandium and yttrium, and is preferably lanthanum.

[0012] Specifically, in step two, the heating temperature is 773-873 K.

[0013] Specifically and optionally, the atomic mass percentage of Co and Sb is 1:3.

[0014] Specifically and optionally, the atomic mass percentage of the rare earth element, Co and Sb is 0.2:4:12.

[0015] Specifically, the mass ratio of the raw material to the glass purifying agent is 20:8-15, and is preferably 20:10.

[0016] Specifically, the main component of the glass purifying agent is B2O3.

[0017] Specifically and optionally, the layered material is laid in the following order from top to bottom: glass purifying agent, Sb, Co, Sb, and glass purifying agent.

[0018] Specifically and optionally, the layered paving is in the order from top to bottom: glass purifier, Sb, Co, rare earth element, Sb, glass purifier.

[0019] Compared with the prior art, the present application has the following beneficial technical effects: The present application can obtain high volume fraction CoSb3 thermoelectric material quickly and efficiently by inhibiting the volatilization of element Sb by using molten glass to wrap liquid alloy, combining molten glass purification and isothermal solidification technology, and fully promoting twice peritectic reaction without loss of components. Meanwhile, the process of the present application is simple, the solidification process is easy to control, and the preparation speed is fast, so the present application has good application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The solidification structure of the sample obtained in Examples 1 to 4 is shown. Figure 1 In the middle: (a) is the scanning electron microscope image of the sample prepared in Example 1; (b) is the scanning electron microscope image of the sample prepared in Example 2; (c) is the scanning electron microscope image of the sample prepared in Example 3; (d) is the scanning electron microscope image of the sample prepared in Example 4.

[0021] Figure 2 The X-ray diffraction pattern of the sample obtained in Examples 1 to 4 is shown.

[0022] Figure 3 The thermoelectric properties of the CoSb3 sample obtained in Examples 1 to 4 are shown.

[0023] Figure 4 The La 0.2 Co4Sb 12 sample obtained in Example 5 is shown. Figure 4 In the middle: (a) is the scanning electron microscope image of the La 0.2 Co4Sb 12 sample prepared in Example 3. (b) is the EDS scanning and element distribution result corresponding to figure (a).

[0024] The technical solutions of the present application are further described below in combination with examples. DETAILED DESCRIPTION

[0025] It should be noted that the raw materials used in the present application are conventional raw materials known in the prior art unless otherwise specified.

[0026] In accordance with the above technical solutions, the following specific examples of the present application are given. It should be noted that the present application is not limited to the following specific examples, and any equivalent variations made on the basis of the technical solutions of the present application fall within the scope of protection of the present application.

[0027] Example 1: The embodiment provides a method for preparing CoSb3-based thermoelectric materials by a melt floating method, and the method comprises the following steps. Step one, raw material configuration: taking element single substances as raw materials, Co and Sb metal single substances are weighed according to the atomic mass percentage Co:Sb = 1:3, and the total amount is 20 g.

[0028] Step two, glass purification: the prepared raw materials are sequentially placed in a quartz crucible from top to bottom in the order of glass purification agent, Sb, Co, Sb and glass purification agent, and the amount of the glass purification agent is about 10 g; after the layered feeding is completed, the alloy is heated to 773-873 K through a high-frequency induction coil until the glass purification agent is melted and wrapped on the surface of the alloy; the main component of the glass purification agent is B2O3, and the metal raw materials can be wrapped after the glass purification agent is completely melted.

[0029] Step three, isothermal solidification: Step 3.1, temperature rising solidification: the alloy is heated to 1573 K, the alloy liquid is fully mixed by electromagnetic stirring, the high-frequency power is cut off for cooling and solidification; when the temperature drops to 873 K, the high-frequency power is turned on for continuous heating, the temperature is quickly raised to 1573 K, and then the high-frequency power is turned off for cooling and solidification.

[0030] Step 3.2, remelting and holding: when the temperature drops to 873 K, the high-frequency power is turned on for continuous heating, the temperature is slowly raised to 1123 K, the high-frequency power is turned off after holding for 20 min, and the sample is cooled in the furnace, and the whole process of “temperature rising-solidification-remelting-holding” is not more than 30 min.

[0031] Embodiment 2: The embodiment provides a method for preparing CoSb3-based thermoelectric materials by a melt floating method, and the method is basically the same as that in embodiment 1, and the difference lies in that the holding temperature is set to 1173 K in the remelting and holding stage, and the holding time is 20 min.

[0032] Embodiment 3: The embodiment provides a method for preparing CoSb3-based thermoelectric materials by a melt floating method, and the method is basically the same as that in embodiment 1, and the difference lies in that the holding temperature is set to 1023 K in the remelting and holding stage, and the holding time is 20 min.

[0033] Embodiment 4: The embodiment provides a method for preparing CoSb3-based thermoelectric materials by a melt floating method, and the method is basically the same as that in embodiment 1, and the difference lies in that the “temperature rising-solidification” is repeated 4-5 times in the temperature rising solidification stage, so that the metal single substances are uniformly distributed, and then the remelting and holding treatment is not performed, and the sample is cooled in the furnace.

[0034] Embodiment 5: This embodiment provides a method for preparing CoSb3-based thermoelectric materials using a melt flotation method. This method is essentially the same as in Example 1, except that element La is added. Based on the atomic mass percentage La:Co:Sb = 0.2:4:12, a total of 20 g of elemental La, Co, and Sb is weighed. During the remelting and holding stage, the holding temperature is set to 1123 K, and the holding time is 20 min.

[0035] Effect verification: The samples obtained in Examples 1 to 5 above were examined using a scanning electron microscope. Figure 1 As shown in (a), the CoSb3 sample obtained in Example 1 had only a small amount of (Sb) phase distributed in the CoSb3 tissue, as... Figure 1 As shown in (b-d), the alloy microstructures of the samples obtained in Examples 2 to 4 include not only the CoSb3 phase, but also impurity phases such as (Sb) phase, CoSb phase, and CoSb2 phase. Figure 4 As shown in (a), the La prepared in Example 5 0.2 Co4Sb 12 Only a small amount of (Sb) phase was distributed in the CoSb3 tissue of the sample, from Figure 4 As can be seen from (b), the sample obtained in Example 3 is indeed La-filled cobaltite.

[0036] The samples prepared in Examples 1 to 4 were analyzed using X-ray diffraction. Figure 2 As shown, the XRD pattern of the CoSb3 sample obtained by isothermal solidification in Example 1 did not show obvious impurity peaks, and the peaks were relatively large and sharp, indicating that the sample was well crystallized. The XRD patterns of the samples in Examples 2 to 4 showed obvious impurity phase peaks (CoSb2 phase, CoSb phase, (Sb) phase).

[0037] Thermoelectric figure of merit of the samples in Examples 1 to 4 are as follows: Figure 3 As shown, the peak thermoelectric figure of merit of the sample prepared in Example 2 was 0.04; the peak thermoelectric figure of merit of the sample prepared in Example 3 was 0.013; the peak thermoelectric figure of merit of the sample prepared in Example 4 was 0.017; and the peak thermoelectric figure of merit of the CoSb3 sample prepared in Example 1 was 0.12, which is 3 times that of the sample in Example 2, 9 times that of the sample in Example 3, and 7 times that of the sample in Example 4.

Claims

1. A method for preparing CoSb3-based thermoelectric materials by melt flotation, characterized in that, CoSb3-based thermoelectric materials were prepared by encapsulating a liquid alloy in molten glass, combined with molten glass purification and isothermal solidification techniques. The method includes the following steps: Step 1: Prepare raw materials: The alloy raw materials include Co and Sb; Step 2, molten glass purification: The prepared raw materials and glass purification agent are placed in the reaction vessel in layers, with the glass purification agent at the top and bottom layers and the raw materials placed between the two layers of glass purification agent; after the layered addition is completed, the alloy is heated until the glass purification agent melts and coats the surface of the alloy. Step 3: Perform isothermal solidification. Step 3.1, Heating and solidification: Turn on the high-frequency power supply to heat to 1573 K, then turn off the high-frequency power supply and wait for the temperature to drop to 873 K; repeat the above heating and solidification process multiple times. Step 3.2, remelting and holding: When the temperature drops to 873 K for the last time, turn on the high-frequency power supply to continue heating, slowly raise the temperature to 1023 K to 1173 K, hold for 15 to 20 minutes, then turn off the high-frequency power supply and let the sample cool with the furnace.

2. The method for preparing CoSb3-based thermoelectric materials by melt flotation as described in claim 1, characterized in that, The total time for heating, solidification, and remelting should not exceed 30 minutes.

3. The method for preparing CoSb3-based thermoelectric materials by melt flotation as described in claim 1, characterized in that, The alloy raw materials also include rare earth elements; the rare earth elements are selected from one or more of lanthanum, cerium, neodymium, gadolinium, ytterbium, scandium and yttrium.

4. The method for preparing CoSb3-based thermoelectric materials by melt flotation as described in claim 1, characterized in that, In step two, the heating temperature is 773–873 K.

5. The method for preparing CoSb3-based thermoelectric materials by melt flotation as described in claim 1, characterized in that, The atomic mass percentages of Co and Sb are 1:

3.

6. The method for preparing CoSb3-based thermoelectric materials by melt flotation as described in claim 3, characterized in that, The atomic mass percentages of rare earth elements, Co, and Sb are 0.2:4:

12.

7. The method for preparing CoSb3-based thermoelectric materials by melt flotation as described in claim 1, characterized in that, The mass ratio of raw materials to glass cleaner is 20:8-15.

8. The method for preparing CoSb3-based thermoelectric materials by melt flotation as described in claim 1, characterized in that, The main component of the glass cleaner is B2O3.

9. The method for preparing CoSb3-based thermoelectric materials by melt flotation as described in claim 1, characterized in that, The order of the layered materials from top to bottom is: glass cleaner, Sb, Co, Sb, glass cleaner.

10. The method for preparing CoSb3-based thermoelectric materials by melt flotation as described in claim 3, characterized in that, The layered materials, from top to bottom, are: glass cleaner, Sb, Co, rare earth elements, Sb, glass cleaner.

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