Ingot production method, ingot, thermoelectric conversion material, thermoelectric conversion element, thermoelectric conversion module, thermoelectric conversion system, and temperature control system

Abstract

According to the present invention, a Mg-containing raw material is melted to obtain a molten metal. The molten metal is transferred to a mold, and a Mg-containing ingot is cast under predetermined conditions. The predetermined conditions are set so that the vaporization of Mg is suppressed compared to when the predetermined conditions are not satisfied in the casting of the ingot.

Description

Method for producing ingot, ingot, thermoelectric conversion material, thermoelectric conversion element, thermoelectric conversion module, thermoelectric conversion system, and temperature control system

[0001] The present disclosure relates to a method for producing an ingot, an ingot, a thermoelectric conversion material, a thermoelectric conversion element, a thermoelectric conversion module, a thermoelectric conversion system, and a temperature control system.

[0002] Conventionally, methods for producing Mg-containing materials such as Mg₃(Sb,Bi)₂-based thermoelectric conversion materials by melting or sintering are known. The notation (Sb,Bi) means that at least one selected from the group consisting of Sb and Bi is contained.

[0003] For example, Non-Patent Document 1 discloses Mg 3.05 Sb 2-x-y Bi y-x Te x (x≦0.04, y≦1.5) describes a method for producing a sample having the composition. This sample is produced by melting high-purity elemental Mg, Bi, Te, and Sb in stoichiometric amounts in a tantalum tube sealed inside a quartz ampoule.

[0004] Non-Patent Document 2 discloses that 1 kg or more of Mg 3.1 Sb 1.5 Bi 0.49 Te 0.01 powder can be obtained by a predetermined ball milling process. The obtained powder is hot-pressed using a graphite die to produce a sample for evaluation.

[0005] Non-Patent Document 3 discloses coarse-grained Mg₃Bi 2-x Sb x describes a method for easily growing crystals of . Mg 3.15 Bi 1.4975 Sb 0.5 Te 0.0025 and Mg 3.15 Bi 1.2475 Sb 0.75 Te 0.0025The raw materials, weighed according to their composition, are placed in a crucible of ZrO2. The crucible of ZrO2 is placed inside a tantalum tube, which is sealed by arc welding. Then they are placed inside a quartz tube and sealed. Next, crystal growth is promoted by a predetermined heat treatment inside a rocking furnace, resulting in coarse-grained Mg3Bi 2-x Sb x The bulk crystals are synthesized.

[0006] X. Shi, C. Sun, Z. Bu, X. Zhang, Y. Wu, S. Lin, W. Li, A. Faghaninia, A. Jain, and Y. Pei, Advanced Science 6, 1802286 (2019).C. Xu, Z. Liang, H. Shang, D. Wang, H. Wang, F. Ding, J. Mao, and Z. Ren, Materials Today Physics 17, 100336 (2021).N. Chen, H. Zhu, G. Li, Z. Fan, X. Zhang, J. Yang, T. Lu, Q. Liu, X. Wu, Y. Yao, Y. Shi, and H. Zhao, Nature Communications 14, 4932 (2023).

[0007] This disclosure provides a method for manufacturing ingots that is advantageous in terms of ease of scaling up the production of Mg-containing ingots.

[0008] The method for manufacturing an ingot according to this disclosure includes: melting a raw material containing Mg to obtain a molten metal; and transferring the molten metal to a mold to cast an ingot containing Mg under predetermined conditions, wherein the predetermined conditions are set such that the vaporization of Mg is suppressed compared to when the predetermined conditions are not met during the casting of the ingot.

[0009] According to this disclosure, the production of Mg-containing ingots is easily scaled up.

[0010] Figure 1 is a flowchart showing an example of a method for manufacturing an ingot according to the present disclosure. Figure 2 is a diagram showing an example of an apparatus for manufacturing an ingot according to the present disclosure. Figure 3 is a schematic diagram showing the casting of an ingot in the apparatus shown in Figure 2. Figure 4 is a diagram showing another example of an apparatus for manufacturing an ingot according to the present disclosure. Figure 5 is a schematic diagram showing the casting of an ingot in the apparatus shown in Figure 4. Figure 6 is a diagram showing another example of a mold. Figure 7 is a diagram showing another example of ingot casting. Figure 8 is a diagram showing yet another example of a mold. Figure 9 is a diagram showing yet another example of a mold. Figure 10 is a cross-sectional view showing an example of an ingot according to the present disclosure. Figure 11 is a cross-sectional view showing an example of a thermoelectric material according to the present disclosure. Figure 12 is a cross-sectional view showing an example of a thermoelectric element according to the present disclosure. Figure 13 is a perspective view showing an example of a thermoelectric module. Figure 14 is a side view showing an example of a thermoelectric system. Figure 15A is a side view showing an example of a temperature control system. Figure 15B is a side view showing an example of a temperature control system. Figure 16 is a graph showing the X-ray diffraction (XRD) pattern of the sample according to Example 3. Figure 17 is a graph showing the XRD pattern of the sample according to Comparative Example 1. Figure 18 is an elemental mapping image of the sample according to Example 3 obtained by scanning electron microscopy energy-dispersive X-ray spectroscopy (SEM-EDX). Figure 19 is an elemental mapping image of the sample according to Comparative Example 1 obtained by SEM-EDX. Figure 20 is a photograph showing a cross-section of the ingot according to Example 4. Figure 21 is a photograph showing a cross-section of the ingot according to Example 5.

[0011] (Knowledge forming the basis of this disclosure) From the viewpoint of reducing the manufacturing cost of Mg-containing materials such as Mg3(Sb,Bi)2-based thermoelectric conversion materials, scaling up the production of such materials is important. According to the methods described in Non-Patent Documents 1 and 3, a complex structure is used for sealing. Such sealing is considered important to prevent the composition of the material produced by the vaporization of Mg at high temperatures from deviating from the desired range. On the other hand, when such a complex structure is required for sealing, it is considered difficult to scale up the production of Mg-containing materials. According to the method described in Non-Patent Document 2, special measures are considered necessary to prevent the risk of the powder igniting in the air. For this reason, it is difficult to say that scaling up the production of Mg-containing materials is easy according to the method described in Non-Patent Document 2.

[0012] In light of these circumstances, the inventors diligently investigated whether they could develop a technology that would allow for easy scaling up of the production of Mg-containing ingots. After much trial and error, the inventors newly discovered that the production of Mg-containing ingots can be easily scaled up by performing casting in a manner that suppresses the vaporization of Mg. Based on this new finding, the inventors completed the method for producing the ingots described herein.

[0013] (Embodiments of the Disclosure) Embodiments of the Disclosure will be described below with reference to the drawings.

[0014] (Embodiment 1) Figure 1 is a flowchart showing an example of an ingot manufacturing method. As shown in Figure 1, in step S1, a raw material 15a containing Mg is melted to obtain molten metal 15b. Next, in step S2, the molten metal 15b is transferred to a mold 14, and an ingot 2a containing Mg is cast under predetermined conditions. The predetermined conditions in step S2 are set so that the vaporization of Mg is suppressed compared to when these predetermined conditions are not met during ingot casting. Whether or not the vaporization of Mg is suppressed can be determined, for example, based on the relative magnitudes of specific X-ray diffraction intensity ratios that are considered to be related to the vaporization of Mg, as described in the examples. For example, when this X-ray diffraction intensity ratio is relatively small, it can be said that the vaporization of Mg is suppressed compared to when this X-ray diffraction intensity ratio is relatively large.

[0015] Figure 2 shows an example of an ingot manufacturing apparatus. As shown in Figure 2, the manufacturing apparatus 1a comprises, for example, a chamber 11, a first container 12, a heater 13a, and a mold 14. The first container 12, the heater 13a, and the mold 14 are arranged inside the chamber 11. The heater 13a heats the first container 12. The heater 13a is arranged, for example, around the first container 12. The mold 14 is arranged, for example, below the first container 12.

[0016] The material and shape of the chamber 11 are not limited to any particular material and shape, as long as steps S1 and S2 can be performed. In steps S1 and S2, the inside of the chamber 11 is maintained in an atmosphere such as a vacuum or an inert gas atmosphere. Preferably, the inside of the chamber 11 is maintained in an inert gas atmosphere mainly composed of argon. In this case, argon is the most abundant component by volume in the inert gas.

[0017] The pressure inside the chamber 11 in steps S1 and S2 is not limited to a specific value as long as steps S1 and S2 can be performed. This pressure is, for example, 0.1 atm or more, and preferably 1 atm or more.

[0018] For example, in step S1, the first container 12 is heated by a heater 13a while the raw material 15a is placed inside the first container 12. In this way, the first container 12 is used as a crucible. As a result, the raw material 15a melts inside the first container 12, and molten metal 15b is obtained. The raw material 15a may be placed inside the first container 12 before it is heated, or it may be placed inside the first container 12 after it has been heated. After a portion of the raw material 15a has melted inside the first container 12, the remaining raw material 15a may be placed inside the first container 12.

[0019] The material and shape of the first container 12 are not limited to any particular material and shape, as long as they can dissolve the raw material 15a. Examples of materials for the first container 12 are carbon, zirconia, alumina, and calcia.

[0020] The heater 13a is not limited to any particular heater, as long as it can melt the raw material 15a inside the first container 12. Examples of heaters 13a include resistance heaters and high-frequency induction heaters. If the heater 13a is a resistance heater, it is equipped with a resistance heating element. If the heater 13a is a high-frequency induction heater, it is equipped with a metal heating coil. A power supply (not shown) that supplies electricity to the heater 13a is located, for example, outside the chamber 11. This power supply is connected to the heater 13a by electrical wiring so that it can supply electricity to the heater 13a.

[0021] Figure 3 is a schematic diagram showing the casting of an ingot in the manufacturing apparatus shown in Figure 2. The molten metal 15b inside the first container 12 is poured towards the mold 14, for example, while the first container 12 is tilted, and transferred to the mold 14. The molten metal 15b transferred to the mold 14 is cooled and solidified in the mold 14, and the ingot 2a is cast. An opening may be provided at the bottom of the first container 12, and the molten metal 15b may be supplied towards the mold 14 from this opening. The ingot 2a is removed from the mold 14. The mold 14 is used as a mold in the casting of the ingot 2a.

[0022] The predetermined conditions are not limited to specific conditions, as long as they are defined in such a way that the vaporization of Mg is suppressed compared to when these predetermined conditions are not met during ingot casting. The predetermined conditions include, for example, that the mold 14 has a predetermined shape. As shown in Figure 2, the mold 14 has an opening 16 through which the molten metal 15b passes when the molten metal 15b is transferred to the mold 14. The predetermined conditions include, for example, A O <V 2 / 3 This may also include satisfying the first condition. In this first condition, A O V is the minimum opening area of ​​the opening 16, and V is the internal volume of the mold 14. In this case, since vaporization of Mg is suppressed by using a mold 14 that satisfies the first condition, scaling up the production of Mg-containing ingots may become easier. 2 / 3 and A O The dimensions of both are L 2 Since these have the same dimensions, they can be compared.

[0023] The specified conditions are, A O ≤0.95V 2 / 3 This may also be the case. In the mold 14, for example, 0.1V 2 / 3 ≤ A O <V 2 / 3 , 0.2V 2 / 3 ≤ A O <V 2 / 3 , 0.3V 2 / 3 ≤ A O <V 2 / 3 , 0.4V 2 / 3 ≤ A O <V 2 / 3 , or 0.5V 2 / 3 ≤ A O <V 2 / 3 It may be satisfied if the condition is met.

[0024] As shown in Figure 2, the opening 16 is formed, for example, in a straight shape. The opening 16 may also be formed to be tapered.

[0025] The inner circumferential surface of the mold 14 has a bottom surface 14b and a side surface 14l that intersects with the bottom surface 14b. The predetermined conditions are, for example, D L / D B>1 may also include satisfying the second condition. In the second condition, D L D is the length of the side surface 14l in the direction perpendicular to the bottom surface 14b, B This is the representative diameter of the base surface 14b. In this case, since vaporization of Mg is suppressed by using a mold 14 that satisfies the second condition, scaling up the production of Mg-containing ingots may become easier. The side surface 14l is, for example, perpendicular to the base surface 14b. For example, if the base surface 14b is a circle in plan view, D B is the diameter of the circle. For example, if the base 14b is a rectangle in plan view, D B is the length of the longer side.

[0026] In the mold 14, D L / D B ≥ 1.1, D L / D B ≥ 1.2, D L / D B ≥ 1.3, D L / D B ≥ 1.4, or D L / D B The condition ≥ 1.5 may also be satisfied. In the mold 14, for example, 5.0 ≥ D L / D B The conditions are met.

[0027] Figure 4 shows another example of an ingot manufacturing apparatus. Figure 5 is a schematic diagram showing the casting of ingots in the manufacturing apparatus shown in Figure 4. Manufacturing apparatus 1b shown in Figure 4 is configured similarly to manufacturing apparatus 1a, except for parts that are not specifically explained. Components that are the same as or correspond to components of manufacturing apparatus 1a are given the same reference numerals, and detailed explanations are omitted. The explanation of manufacturing apparatus 1a also applies to manufacturing apparatus 1b, unless there is a technical contradiction.

[0028] As shown in Figure 4, the manufacturing apparatus 1b includes a heater 13b. The heater 13b heats the mold 14. The heater 13b is arranged, for example, around the mold 14. Examples of heaters 13b include resistance heaters and high-frequency induction heaters. If the heater 13b is a resistance heater, it includes a resistance heating element. If the heater 13b is a high-frequency induction heater, it includes a metal heating coil. A power supply (not shown) that supplies electricity to the heater 13b is located, for example, outside the chamber 11. This power supply is connected to the heater 13b by electrical wiring so that it can supply electricity to the heater 13b.

[0029] With the inside of the chamber 11 maintained in a predetermined atmosphere such as a vacuum or an inert gas atmosphere, the mold 14 is preheated by the heater 13b before the molten metal 15b is transferred to the mold 14. This makes it difficult for voids to form inside the ingot 2a. The preheating temperature of the mold 14 is not limited to a specific temperature. For example, the preheating temperature of the mold 14 may be the phase transition temperature between the α phase and the β phase in the material of the ingot 2a, or a temperature close to the phase transition temperature. For example, the preheating temperature of the mold 14 may be 750°C or higher and 850°C or lower. The preheating of the mold 14 may be performed before or after step S1, or simultaneously with step S1.

[0030] As shown in Figure 5, after the mold 14 has been preheated, the molten metal 15b is transferred to the mold 14. After transferring the molten metal 15b to the mold 14, the mold 14 may be kept at a predetermined temperature for a predetermined period of time. This makes it less likely for voids to form inside the ingot 2a. The predetermined temperature may be, for example, the preheating temperature, and the predetermined period may be, for example, 10 minutes or more and 5 hours or less.

[0031] After a predetermined period has elapsed since transferring the molten metal 15b to the mold 14, the mold 14 may be slowly cooled. This makes it less likely for voids to form inside the ingot 2a. The slow cooling rate of the mold 14 is, for example, 10°C / hour or more and 200°C / hour or less.

[0032] In step S2 of the manufacturing of the ingot 2a using manufacturing apparatus 1a and 1b, the mold 14 may be rapidly cooled followed by slow cooling. In this case, even if the mold 14 is not preheated, it is less likely that voids will form inside the ingot 2a. Also, the thickness of the mold 14 may be less than or equal to a predetermined value (for example, 10 mm). In this case, even if the mold 14 is not preheated, it is less likely that voids will form inside the ingot 2a.

[0033] Figure 6 shows another example of the mold 14. As shown in Figure 6, the predetermined conditions are, for example, A O <A B This may also include satisfying the third condition. A B This is the area of ​​the bottom surface 14b of the inner circumferential surface of the mold 14. By using such a mold 14, the vaporization of Mg is suppressed, which can make it easier to scale up the production of Mg-containing ingots.

[0034] In the mold 14, 0.1A B ≤ A O ≤0.95A B , 0.2A B ≤ A O ≤0.95A B , 0.3A B ≤ A O ≤0.95A B , 0.4A B ≤ A O ≤0.95A B , or 0.5A B ≤ A O ≤0.95A B The conditions may be met.

[0035] The shape of the mold 14 is preferably simple. In this case, the ingot 2a is easy to remove from the mold 14. For example, the mold 14 may be substantially cylindrical or substantially rectangular, including an inner circumferential surface with a tapered shape. The mold 14 may be configured as a split mold. In this case, the mold 14 may have a complex shape.

[0036] The material of the mold 14 is not limited to any particular material, as long as it allows for the casting of the ingot 2a. Examples of materials for the mold 14 include carbon, copper, iron, alumina, calcia, and zirconia. If the material of the mold 14 is a metal such as copper or iron, a release agent may be applied to the inner surface of the mold 14 to prevent adhesion between the inner surface of the mold 14 and the ingot 2a.

[0037] The specified conditions may include, for example, water cooling of the mold 14. Water cooling of the mold 14 suppresses the vaporization of Mg, which may make it easier to scale up the production of Mg-containing ingots. Water cooling of the mold 14 is achieved, for example, by circulating cooling water between a jacket provided around the mold 14 and the outside of the chamber 11.

[0038] Figure 7 shows another example of ingot casting. As shown in Figure 7, in ingot casting, the mold 17b may be positioned in contact with the opening 16 of the mold 14, and a riser 17a may be formed. The riser 17a is formed when the molten metal 15b solidifies inside the mold 17b. This makes it less likely for defects such as shrinkage cavities to occur in the ingot 2a.

[0039] Figure 8 shows yet another example of the mold 14. As shown in Figure 8, the mold 14 comprises, for example, one opening 16, a plurality of spaces 14a for casting, and a connecting passage 18. The one opening 16 and the plurality of spaces 14a are connected by the connecting passage 18. With this configuration, the molten metal 15b is guided through the one opening 16 and the connecting passage 18 into the plurality of spaces 14a, making it easy to manufacture a plurality of ingots 2a of the desired size at once.

[0040] Figure 9 shows yet another example of the mold 14. As shown in Figure 9, the inside of the mold 14 is divided into multiple spaces 14c, and adjacent spaces 14c are connected by connecting passages 19. An opening 16 is formed in one of the multiple spaces 14c. In this case, it is easy to manufacture multiple ingots 2a of the desired size at once.

[0041] The raw material 15a is not limited to any particular material as long as it contains Mg. In addition to Mg, the raw material 15a may further contain at least one selected from the group consisting of Sb and Bi, or it may further contain both Sb and Bi. The raw material 15a may also be a raw material for Mg3(Sb,Bi)2-based thermoelectric materials. In the raw material 15a, Mg may exist as elemental or as an alloy. The same applies to Sb and Bi.

[0042] The shape of the raw material 15a is not limited to a specific shape. The raw material 15a may be in the form of a lump, a plate, or a powder.

[0043] Figure 10 is a cross-sectional view showing an example of an ingot. The composition of the ingot 2a is not limited to a specific composition as long as it contains Mg. As shown in Figure 10, the ingot 2a comprises, for example, a plurality of crystal grains 21, a Bi-rich portion 22a, and a Mg-rich portion 22b. The crystal grains 21 contain Mg and Bi. The Bi-rich portion 22a is a region where the concentration of Bi is higher than the surrounding area. The Mg-rich portion 22b is a region where the concentration of Mg is higher than the surrounding area. With such a configuration, the thermoelectric conversion material produced from the ingot 2a is likely to exhibit the desired thermoelectric conversion characteristics. The presence of the Bi-rich portion 22a and the Mg-rich portion 22b can be confirmed, for example, based on an elemental mapping image obtained by SEM-EDX using a sample produced from the ingot 2a. Note that it is sufficient that the Bi concentration in the Bi-rich portion 22a is higher than the surrounding area, and the concentration of elements other than Bi, such as Mg, in the Bi-rich portion 22a may be higher than the concentration of Bi. The number of Bi-rich portions 22a and Mg-rich portions 22b in the ingot 2a may be 1 or 2 or more.

[0044] The maximum diameter of the Mg-rich portion 22b is not limited to a specific size. For example, the maximum diameter of the Mg-rich portion 22b is 10 μm or more. With this configuration, the thermoelectric conversion material made from the ingot 2a is more likely to exhibit the desired thermoelectric conversion characteristics.

[0045] The maximum diameter of the Mg-rich portion 22b is, for example, 100 μm or less.

[0046] In ingot 2a, the diffraction intensity ratio r1 is, for example, 0.1 or less, and preferably 0.01 or less. In this case, the thermoelectric conversion material produced from ingot 2a is more likely to exhibit the desired thermoelectric conversion characteristics. The diffraction intensity ratio r1 is the ratio P1 / P0 of the diffraction intensity P1 to the diffraction intensity P0. The diffraction intensity P0 is the intensity of the diffraction peak that appears in the diffraction angle range 2θ from 25° to 26° in the X-ray diffraction pattern obtained by X-ray diffraction measurement of a sample produced from ingot 2a. This diffraction peak originates from the alloy containing Mg and Bi. The diffraction intensity P1 is the intensity of the diffraction peak that appears in the diffraction angle range 2θ from 26° to 27° in the above X-ray diffraction pattern. Cu-Kα rays are used for this X-ray diffraction measurement. This diffraction peak originates from Bi. When predetermined conditions are met and the vaporization of Mg is suppressed during the casting of the ingot by the above manufacturing method, elemental Bi is less likely to precipitate in ingot 2a. Therefore, it is thought that the thermoelectric conversion material produced from ingot 2a will be more likely to exhibit the desired thermoelectric conversion characteristics.

[0047] Ingot 2a may contain Sb, Te, or other metallic elements, as needed.

[0048] Figure 11 is a cross-sectional view showing an example of the thermoelectric conversion material of this disclosure. As shown in Figure 11, the thermoelectric conversion material 3a comprises a plurality of crystal grains 31, a Bi-rich portion 32a, and a Mg-rich portion 32b. The crystal grains 31 contain Mg and Bi. The Bi-rich portion 32a is a region where the Bi concentration is higher than the surrounding area. The Mg-rich portion 32b is a region where the Mg concentration is higher than the surrounding area and is adjacent to the Bi-rich portion. With such a configuration, the thermoelectric conversion material 3a is likely to exhibit the desired thermoelectric conversion characteristics. The presence of the Bi-rich portion 32a and the Mg-rich portion 32b can be confirmed, for example, based on an elemental mapping image obtained by SEM-EDX using a sample prepared from the thermoelectric conversion material 3a. Note that it is sufficient for the Bi concentration in the Bi-rich portion 32a to be higher than the surrounding area, and the concentration of elements other than Bi, such as Mg, in the Bi-rich portion 32a may be higher than the concentration of Bi. The number of Bi-rich portions 32a and Mg-rich portions 32b in the thermoelectric conversion material 3a may be 1 or 2 or more.

[0049] The thermoelectric conversion material 3a can be manufactured by processing an ingot 2a to have a predetermined shape, for example, by slicing, dicing, and polishing. When manufacturing the thermoelectric conversion material 3a from the ingot 2a, heat treatment may be performed as needed. Alternatively, the thermoelectric conversion material 3a may be manufactured by processing the ingot 2a to have a predetermined shape without performing any heat treatment.

[0050] As shown in Figure 11, the thermoelectric conversion material 3a has, for example, a first surface 30a and a second surface 30b which are a pair of end faces in a specific direction (z-axis direction), and a third surface 30c which extends in a direction intersecting the first surface 30a and the second surface 30b.

[0051] A thermoelectric conversion element can be provided using the thermoelectric conversion material 3a. Figure 12 is a cross-sectional view showing an example of a thermoelectric conversion element. As shown in Figure 12, the thermoelectric conversion element 4a comprises the thermoelectric conversion material 3a, a first electrode 40a, and a second electrode 40b. The first electrode 40a is electrically connected to the first surface 30a. The second electrode 40b is electrically connected to the second surface 30b.

[0052] The first electrode 40a is arranged, for example, along the first surface 30a. The first electrode 40a may be in contact with the first surface 30a. The second electrode 40b is arranged, for example, along the second surface 30b. The second electrode 40b may be in contact with the second surface 30b. Each of the first electrode 40a and the second electrode 40b is formed, for example, by sputtering, thermal spraying, or plating. Each of the first electrode 40a and the second electrode 40b contains, for example, a metal. The metal contained in each of the first electrode 40a and the second electrode 40b is not limited to a specific metal. Each of the first electrode 40a and the second electrode 40b contains, for example, at least one selected from the group consisting of copper, copper alloys, nickel, nickel alloys, iron, and iron alloys. Each of the first electrode 40a and the second electrode 40b may have a single-layer structure or a multi-layer structure. To improve wettability to solder paste or silver paste used for connecting to other components, the outermost surfaces of the first electrode 40a and the second electrode 40b may each contain at least one selected from the group consisting of gold, silver, and tin.

[0053] The thicknesses of the first electrode 40a and the second electrode 40b are not limited to any specific value. Their thicknesses are, for example, between 0.1 μm and 10 μm.

[0054] A thermoelectric conversion module equipped with a thermoelectric conversion element 4a can be provided. Figure 13 is a perspective view showing an example of a thermoelectric conversion module. As shown in Figure 13, the thermoelectric conversion module 100 comprises a thermoelectric conversion element 4a and a conductor 5. The conductor 5 is electrically connected to the thermoelectric conversion element 4a.

[0055] The thermoelectric conversion module 100 is, for example, a thermoelectric conversion module having a π-type structure. The thermoelectric conversion module 100 further comprises a thermoelectric conversion element 4k. In the thermoelectric conversion module 100, a plurality of thermoelectric conversion elements 4a and a plurality of thermoelectric conversion elements 4k are arranged alternately, and adjacent thermoelectric conversion elements 4a and thermoelectric conversion elements 4k are electrically connected by a conductor 5. As a result, a plurality of thermoelectric conversion elements 4a and a plurality of thermoelectric conversion elements 4k are electrically connected in series. One of the thermoelectric conversion elements 4a and 4k is an N-type thermoelectric conversion element, and the other of the thermoelectric conversion elements 4a and 4k is a P-type thermoelectric conversion element. The thermoelectric conversion element 4k is a known N-type thermoelectric conversion element or a known P-type thermoelectric conversion element.

[0056] As shown in Figure 13, the thermoelectric conversion module 100 further comprises, for example, a pair of substrates 6. The substrates 6 are, for example, an electrical insulator, such as a ceramic plate, and the thermoelectric conversion elements 4a, 4k, and conductor 5 are arranged between the pair of substrates 6. For example, the conductor 5 is patterned on one surface of each substrate 6.

[0057] The thermoelectric conversion module 100 can transport heat by passing an electric current through it. When an electric current is generated in the thermoelectric conversion module 100, the Peltier effect generated by the thermoelectric conversion elements 4a and 4k transports heat between the pair of substrates 6, creating a temperature difference between these substrates. This allows, for example, an object to be cooled.

[0058] In the thermoelectric conversion module 100, electricity can also be generated by creating a temperature difference using heat from a heat source. In this case, the Seebeck effect occurs in the thermoelectric conversion elements 4a and 4k due to the temperature difference, generating an electromotive force.

[0059] A thermoelectric conversion system equipped with a thermoelectric conversion material 3a can be provided. Figure 14 is a side view showing an example of a thermoelectric conversion system. As shown in Figure 14, the thermoelectric conversion system 300 comprises a thermoelectric conversion module 100 and a heat source 8. The heat source 8 is arranged, for example, in contact with one of the substrates 6.

[0060] According to the thermoelectric conversion system 300, for example, heat from the heat source 8 can be used to create a temperature difference in the thermoelectric conversion module 100, thereby generating electricity.

[0061] The thermoelectric conversion system 300 can also be applied to applications that generate electricity by utilizing the temperature difference that arises between an object and its surroundings due to heat generation. For example, temperature differences may occur on equipment casings, pipes, building walls, or the surfaces of structures in contact with the outside air, depending on operating conditions, solar radiation, or the surrounding environment. When the thermoelectric conversion module 100 is thermally connected to these surfaces, an electromotive force is generated by the Seebeck effect according to the temperature difference. Furthermore, if a larger voltage or current is required, multiple thermoelectric conversion modules 100 may be electrically connected in series or parallel. By combining multiple modules, the amount of power obtained can be increased.

[0062] A temperature control system equipped with a thermoelectric conversion material 3a can be provided. Figures 15A and 15B are side views showing an example of a temperature control system. As shown in Figures 15A and 15B, the temperature control system 500 comprises a thermoelectric conversion module 100 and a temperature-controlled object 9. The temperature-controlled object 9 is, for example, positioned in contact with one of the substrates 6. The temperature-controlled object 9 may be, for example, a structure that is the target of temperature control, a member for temperature control of the structure that is the target of temperature control, or a laminate of the structure and the member. In Figures 15A and 15B, arrows pointing inward from the thermoelectric conversion module 100 indicate heat absorption, and arrows pointing outward from the thermoelectric conversion module 100 indicate heat dissipation. In Figure 15A, the current flow when the temperature-controlled object 9 is cooled in the temperature control system 500 is shown by a dashed line. Current flows from the N-type thermoelectric conversion element through the N-type thermoelectric conversion element and the P-type thermoelectric conversion element. By generating such a current, the Peltier effect occurs, and by adjusting the magnitude of the current, the object to be temperature controlled 9 can be precisely cooled. For example, in the thermoelectric conversion module 100, the thermoelectric conversion elements 4a and 4k are an N-type thermoelectric conversion element and a P-type thermoelectric conversion element, respectively.

[0063] In FIG. 15B, the flow of current when heating the temperature-controlled object 9 in the temperature control system 500 is indicated by a broken line. Current flows from the P-type thermoelectric conversion element through the N-type thermoelectric conversion element and the P-type thermoelectric conversion element. By adjusting the magnitude of such current, the temperature-controlled object 9 can be precisely heated.

[0064] (Supplementary Note) From the above description, the following technique is disclosed. (Technical 1) Melving a raw material containing Mg to obtain a molten metal, and transferring the molten metal into a mold and casting an Mg-containing ingot under predetermined conditions, wherein the predetermined conditions are defined such that vaporization of Mg is suppressed compared to a case where the predetermined conditions are not satisfied in casting of the ingot. A method for producing an ingot. (Technical 2) The mold has an opening through which the molten metal passes when the molten metal is transferred into the mold, and the predetermined condition is A O <V 2 / 3 that satisfies the first condition, wherein in the first condition, A O is the minimum opening area of the opening, and V is the internal volume of the mold. The method for producing an ingot according to Technical 1. (Technical 3) An inner peripheral surface of the mold has a bottom surface and a side surface intersecting the bottom surface, and the predetermined condition is D L / D B that satisfies the second condition of >1, wherein in the second condition, D L is the length of the side surface in a direction orthogonal to the bottom surface, and D B is the representative diameter of the bottom surface. The method for producing an ingot according to Technical 1 or 2. (Technical 4) The mold has an opening through which the molten metal passes when the molten metal is transferred into the mold, and the predetermined condition is A O <A B that satisfies the third condition, wherein in the third condition, A O is the minimum opening area of the opening, and A B(Technology 5) The method for manufacturing an ingot according to any one of Technology 1 to 3, wherein the area is the bottom surface area of ​​the inner circumferential surface of the mold. (Technology 6) The method for manufacturing an ingot according to any one of Technology 1 to 4, wherein the predetermined condition includes water cooling the mold. (Technology 7) The method for manufacturing an ingot according to Technology 6, further comprising preheating the mold before transferring the molten metal to the mold. (Technology 8) The method for manufacturing an ingot according to Technology 6, further comprising keeping the mold at a predetermined temperature for a predetermined period of time after transferring the molten metal to the mold. (Technology 9) The method for manufacturing an ingot according to Technology 8, wherein the Mg-rich portion has a maximum diameter of 10 μm or more. (Technology 10) An ingot according to Technology 8 or 9, having a diffraction intensity ratio of 0.1 or less, wherein the diffraction intensity ratio is the ratio of the intensity of the diffraction peak appearing in the diffraction angle 2θ range of 26° to 27° in the X-ray diffraction pattern obtained by X-ray diffraction measurement of a sample made from the ingot to the intensity of the diffraction peak appearing in the diffraction angle 2θ range of 25° to 26° in the X-ray diffraction pattern, and Cu-Kα rays are used for the X-ray diffraction measurement. (Technology 11) A thermoelectric conversion material comprising a plurality of crystal grains containing Mg and Bi, a Bi-rich portion having a higher Bi concentration than the surrounding area, and a Mg-rich portion having a higher Mg concentration than the surrounding area and adjacent to the Bi-rich portion. (Technology 12) A thermoelectric conversion element comprising the thermoelectric conversion material according to Technology 11. (Technology 13) A thermoelectric conversion module comprising the thermoelectric conversion material according to Technology 11. (Technology 14) A thermoelectric conversion system comprising the thermoelectric conversion material described in Technology 11. (Technology 15) A temperature control system comprising the thermoelectric conversion material described in Technology 11. (Technology 16) A heat transport method comprising transporting heat from a heat source by passing an electric current through the thermoelectric conversion material described in Technology 11. (Technology 17) A power generation method comprising generating electricity by creating a temperature difference in the thermoelectric conversion material described in Technology 11 using heat from a heat source.

[0065] Hereinafter, the present disclosure will be described in detail with reference to examples. However, the present disclosure is not limited to the examples shown below.

[0066] (Example 1) Mg 3.15 Sb 0.9 Bi 1.095 Te 0.005 An ingot according to Example 1 having the above composition was produced as follows. A production apparatus similar to the production apparatus shown in Figure 2 was prepared. A heater including a high-frequency induction heating coil was placed in a metal chamber. Granular or crushed flaky Mg, Sb, Bi, and Te were used as raw materials. The amounts of Mg, Sb, Bi, and Te in the raw materials were adjusted such that the ingot had the above composition. These raw materials were placed in a graphite crucible, and this crucible was arranged inside the heater so as to be surrounded by the high-frequency induction heating coil. In addition, a substantially cylindrical graphite mold was placed inside the chamber below the crucible. The mold had an opening with an inner diameter of 45 mm, and the minimum opening area A0 of this opening was about 16 cm 2 . The inner diameter of the bottom of the mold was 35 mm, and the depth of the mold, which is the length of the side surface of the inner peripheral surface of the mold in the direction orthogonal to the bottom surface of the inner peripheral surface of the mold, was 100 mm. The internal volume V of the mold was about 126 cm 3 , and V 2 / 3 was about 25 cm 2 . Therefore, in this mold, the condition of A0 < V 2 / 3 was satisfied.

[0067] Next, after evacuating the inside of the chamber, argon gas was introduced into the chamber, and the pressure inside the chamber was adjusted to 2 atm. Thereafter, the high-frequency induction heating coil was energized to heat the crucible and melt the raw materials. By tilting the crucible, the molten metal obtained by melting the raw materials was poured into the mold. The molten metal was poured into the mold such that the crucible was almost full of molten metal. Next, the mold was left to naturally cool to room temperature over about 12 hours, after which the mold was taken out from the chamber, and the ingot according to Example 1 obtained by solidification of the molten metal was taken out from the mold. No water cooling was performed during cooling of the mold.

[0068] (Example 2) An ingot according to Example 2 was obtained in the same manner as in Example 1, except for the points described below. The composition of the ingot according to Example 2 was Mg 3.15 Sb 0.9 Bi 1.095 Te 0.005 Instead of graphite molds, copper molds were used. The molds had an opening with an inner diameter of 52 mm, and the minimum opening area A0 of this opening was approximately 21 cm². 2 The inner diameter of the bottom of the mold was 45 mm, and the depth of the mold, which is the length of the side surface of the inner circumference of the mold in a direction perpendicular to the bottom surface of the inner circumference of the mold, was 60 mm. The internal volume V of the mold was approximately 111 cm³. 3 V 2 / 3 Approximately 23 cm 2 Therefore, in this mold, A0 < V 2 / 3 The conditions were met. With a mold for the riser, as shown in Figure 7, placed on top of the mold, molten metal was poured into the mold. To prevent the mold from sticking to the ingot, the mold was water-cooled during the ingot casting process.

[0069] (Example 3) An ingot according to Example 3 was obtained in the same manner as in Example 1, except for the following points. The composition of the ingot was Mg 3.15 Sb 1.5 Bi 0.49 Te 0.005 The amounts of Mg, Sb, Bi, and Te in the raw materials were adjusted to achieve the desired result.

[0070] (Example 4) An ingot according to Example 4 was obtained in the same manner as in Example 1, except for the following points. The composition of the ingot was Mg 3.15 Sb 1.0 Bi 0.997 Te 0.003The amounts of Mg, Sb, Bi, and Te in the raw materials were adjusted to achieve the following. The mold was preheated to 800°C in an argon atmosphere. The molten metal obtained from the melting of the raw materials was poured into the graphite mold preheated to 800°C, and the mold temperature was maintained at 800°C for 1 hour. After that, the mold was slowly cooled at a rate of 100°C / hour. The molten metal was poured into the mold with a mold for the riser placed on top of the mold. The bottom surface of the mold was approximately square with sides of 60 mm, and the depth of the mold body was 80 mm. Therefore, the ingot according to Example 4 had a square cross-section with sides of 60 mm and a main body with a height of 80 mm, and a riser section that widened upward from the main body. In the mold used in Example 4, A0 < V 2 / 3 The conditions were met.

[0071] (Example 5) An ingot according to Example 5 was obtained in the same manner as in Example 4, except that the molten metal was poured into the mold without preheating and then allowed to cool naturally to room temperature.

[0072] (Comparative Example 1) An ingot according to Comparative Example 1 was obtained in the same manner as in Example 1, except for the following points. The composition of the ingot was Mg 3.15 Sb 1.0 Bi 0.997 Te 0.003 The amounts of Mg, Sb, Bi, and Te in the raw materials were adjusted to achieve the desired result. An iron mold was used instead of a graphite mold. This mold had an opening with an inner diameter of 112 mm, and the minimum opening area A0 of this opening was approximately 99 cm². 2 The inner diameter of the bottom of the mold was 110 mm, and the depth of the mold, which is the length of the side surface of the inner circumference of the mold in a direction perpendicular to the bottom surface of the inner circumference of the mold, was 20 mm. The internal volume V of the mold was approximately 194 cm³. 3 V 2 / 3 Approximately 33 cm 2 Therefore, in this mold, A0 < V 2 / 3 The conditions were not met. Molten metal was poured into the mold to a depth of 20 mm. A release agent containing boron nitride was pre-applied to the inner surface of the mold to prevent the ingot from sticking to the mold. The pressure inside the chamber was adjusted to 0.5 atm.

[0073] (Comparative Example 2) An ingot according to Comparative Example 2 was obtained in the same manner as in Comparative Example 1, except that the pressure inside the chamber was adjusted to 2 atm.

[0074] (X-ray diffraction) Using a wire saw, sections cut from the ingots for each example and comparative example were ground in a mortar to prepare powder samples. Powder X-ray diffraction (XRD) measurements were performed on these samples using an Aeris X-ray diffractometer manufactured by Malvern Panalytical. Cu-Kα rays were used as the X-ray source for this measurement. Figure 16 is a graph showing the XRD pattern of the sample for Example 3. Figure 17 is a graph showing the XRD pattern of the sample for Comparative Example 1. As shown in Figure 16, in the XRD pattern of the sample for Example 3, only diffraction peaks originating from Mg3(Sb,Bi)2-based material belonging to space group P-3m1 were observed. Similarly, in the XRD patterns of the samples for Examples 1 and 2, only diffraction peaks originating from Mg3(Sb,Bi)2-based material were observed. On the other hand, as shown in Figure 17, in the XRD pattern for Comparative Example 1, in addition to diffraction peaks originating from Mg3(Sb,Bi)2-based material, diffraction peaks originating from elemental Bi were also observed. This suggests that elemental Bi precipitated due to the vaporization of Mg during ingot casting. A comparison of each example with Comparative Example 1 shows, for example, A0 < V 2 / 3 It is understood that when this condition is met, the vaporization of Mg during ingot casting is suppressed compared to when this condition is not met.

[0075] In the XRD pattern according to Comparative Example 1, the diffraction intensity ratio r1 was 1.02. The diffraction intensity ratio r1 is the ratio of the intensity of the diffraction peak appearing in the diffraction angle 2θ range of 26° to 27° to the intensity of the diffraction peak appearing in the diffraction angle 2θ range of 25° to 26°. The diffraction peak appearing in the diffraction angle 2θ range of 25° to 26° originates from Mg3(Sb,Bi)2-based material, and the intensity of the diffraction peak appearing in the diffraction angle 2θ range of 26° to 27° originates from elemental Bi. In the XRD patterns according to each example, the diffraction intensity ratio r1 was 0.01 or less.

[0076] (Evaluation of Thermoelectric Properties) Using a wire saw, samples for measuring the Seebeck coefficient S and electrical resistivity ρ, and samples for measuring thermal conductivity κ were prepared from the ingots of each example and comparative example. The length of the sample for measuring the Seebeck coefficient S and electrical resistivity ρ was 10 mm, and the cross section perpendicular to the length of the sample had a side length of 2 mm. The sample for measuring thermal conductivity κ was a flat plate with a square shape in plan view, with a side length of 10 mm and a thickness of 1 mm. The Seebeck coefficient S and electrical resistivity ρ of the samples of each example and comparative example were measured using the ZEM-3 thermoelectric property measuring device manufactured by Advance Engineering Co., Ltd. The thermal conductivity κ of the samples of each example and comparative example was measured using the LF457 thermal conductivity measuring device manufactured by Netsch Corporation. The dimensionless figure of merit zT of the samples of each example and comparative example was set to zT = S 2 The zT was calculated using the relationship T / (ρκ). The results are shown in Table 1. As shown in Table 1, the zT values ​​of the samples in each example were high. On the other hand, the zT values ​​of the samples in each comparative example were remarkably low.

[0077] (SEM-EDX) After polishing the cross-sections of the ingots prepared for each example and Comparative Example 1 with abrasive paper, samples were prepared by processing them using a Leica EM TIC 3X ion milling system. SEM-EDX was performed on these samples using a Hitachi High-Technologies Corporation scanning electron microscope SU8220 and a Bruker energy-dispersive X-ray fluorescence (EDX) analyzer. Figure 18 is an elemental mapping image of the sample according to Example 3 obtained by SEM-EDX. Figure 19 is an elemental mapping image of the sample according to Comparative Example 1 obtained by SEM-EDX. As shown in Figure 18, in the sample according to Example 3, a Bi-rich area with a higher Bi concentration than the surrounding area and a Mg-rich area with a higher Mg concentration than the surrounding area were observed. The Mg-rich area was adjacent to the Bi-rich area. In the elemental mapping images obtained by SEM-EDX of the samples according to the other examples, Mg-rich areas adjacent to Bi-rich areas were also observed. On the other hand, as shown in Figure 19, no Mg-rich region adjacent to the Bi-rich region was observed in the sample according to Comparative Example 1. The maximum diameter of the Mg-rich region indicated by the arrow in Figure 18 was 28 μm. In the ingots according to each example, it is thought that the vaporization of Mg was suppressed during the casting of the ingot, resulting in the formation of such Mg-rich regions. In the XRD patterns of the samples according to each example, no diffraction peaks originating from elemental Mg were detected. Since Mg is an extremely light element compared to Sb and Bi, it does not scatter X-rays easily, so it is thought that no diffraction peaks originating from elemental Mg were detected.

[0078] (Observation of the cross-section of the ingot) The ingot according to Example 4 was cut at six points separated from each other in the height direction to expose the cross-section. Figure 20 is a photograph showing the cross-section of the ingot according to Example 4. In Figure 20, the fragment (a1) corresponds to the riser, and the fragment (a7) is the fragment furthest from the riser in the height direction of the ingot. The fragments (a2), (a3), (a4), (a5), and (a6) are in this order that they are closer to the fragment (a1) in the height direction of the ingot. The ingot according to Example 5 was cut at five points separated from each other in the height direction to expose the cross-section. Figure 21 is a photograph showing the cross-section of the ingot according to Example 5. In Figure 21, the fragment (b1) corresponds to the riser, and the fragment (b6) is the fragment furthest from the riser in the height direction of the ingot. Fragments (b2), (b3), (b4), and (b5) are positioned in this order, with the ingot being taller, and are therefore closer to fragment (b1).

[0079] As shown in Figure 21, a cavity was observed in the cross-section of a fragment near the center of the main body in the height direction of the ingot in Example 5. On the other hand, no such cavity was observed in the ingot in Example 4. This suggests that cavities are less likely to occur in ingots obtained by preheating the mold, etc.

[0080]

[0081] While this disclosure is described in detail with reference to specific examples, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of this disclosure.

[0082] The ingot manufacturing method of this disclosure can be used, for example, in applications where ease of scaling up is important.

Claims

1. A method for producing an ingot, comprising: melting a raw material containing Mg to obtain a molten metal; and transferring the molten metal to a mold to cast an ingot containing Mg under predetermined conditions, wherein the predetermined conditions are set such that the vaporization of Mg is suppressed during the casting of the ingot compared to when the predetermined conditions are not met.

2. The mold has an opening through which the molten metal passes when the molten metal is transferred to the mold, and the predetermined conditions are A O <V 2 / 3 This includes satisfying the first condition, and in the first condition, A O The method for manufacturing an ingot according to claim 1, wherein V is the minimum opening area of ​​the opening, and V is the internal volume of the mold.

3. The inner circumferential surface of the mold has a bottom surface and a side surface that intersects with the bottom surface, and the predetermined conditions are D L / D B > Including the fulfillment of the second condition of 1, in the said second condition, D L D is the length of the side surface in a direction perpendicular to the bottom surface. B The method for manufacturing an ingot according to claim 1, wherein is the representative diameter of the bottom surface.

4. The mold has an opening through which the molten metal passes when transferring the molten metal into the mold, and the predetermined condition is that A O <A B satisfies the third condition, and in the third condition, A O is the minimum opening area of the opening, and A B is the area of the bottom surface of the inner peripheral surface of the mold, the method for producing an ingot according to claim 1.

5. The method for manufacturing an ingot according to claim 1, wherein the predetermined conditions include water cooling of the mold.

6. The method for manufacturing an ingot according to claim 1, further comprising preheating the mold before transferring the molten metal to the mold.

7. The method for manufacturing an ingot according to claim 6, further comprising transferring the molten metal to the mold and then maintaining the mold at a predetermined temperature for a predetermined period of time.

8. An ingot comprising a plurality of crystal grains containing Mg and Bi, a Bi-rich region having a higher Bi concentration than the surrounding area, and a Mg-rich region having a higher Mg concentration than the surrounding area and adjacent to the Bi-rich region.

9. The ingot according to claim 8, wherein the Mg-rich portion has a maximum diameter of 10 μm or more.

10. Having a diffraction intensity ratio of 0.1 or less, wherein the diffraction intensity ratio is the ratio of the intensity of the diffraction peak appearing in the diffraction angle 2θ range of 26° to 27° in the X-ray diffraction pattern obtained by X-ray diffraction measurement of a sample made from the ingot to the intensity of the diffraction peak appearing in the diffraction angle 2θ range of 25° to 26° in the X-ray diffraction pattern, and Cu-Kα rays are used for the X-ray diffraction measurement, the ingot according to claim 8.

11. A thermoelectric conversion material comprising: a plurality of crystal grains containing Mg and Bi; a Bi-rich region having a higher Bi concentration than the surrounding area; and an Mg-rich region having a higher Mg concentration than the surrounding area and adjacent to the Bi-rich region.

12. A thermoelectric element comprising the thermoelectric material described in claim 11.

13. A thermoelectric conversion module comprising the thermoelectric conversion material described in claim 11.

14. A thermoelectric conversion system comprising the thermoelectric conversion material described in claim 11.

15. A temperature control system comprising the thermoelectric conversion material described in claim 11.

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