Thermoelectric conversion element, joining member, thermoelectric conversion module, thermoelectric conversion system, power generation method, and production method for thermoelectric conversion element

Abstract

The present disclosure provides a thermoelectric conversion element that is advantageous in terms of suppressing increase in an electric resistance in hot air. A thermoelectric conversion element 10 according to the present disclosure is provided with a first metal layer 15 and a thermoelectric conversion unit 11a. The thermoelectric conversion unit 11a includes Mg and at least one selected from the group consisting of Sb and Bi. The thermoelectric conversion unit 11a is provided with a thermoelectric conversion layer 11 and first joining layers 14. The first joining layers 14 each include at least one selected from the group consisting of Fe and Ni. The first joining layers 14 each satisfy the condition 2.5≤α / β≤6.5. On this condition, α is a content ratio of Mg based on the number of atoms in the first joining layer 14, and β is the sum of content ratios of Sb and Bi based on the numbers of atoms in the first joining layer 14.

Description

Thermoelectric conversion element, bonding material, thermoelectric conversion module, thermoelectric conversion system, power generation method, and method for manufacturing thermoelectric conversion element

[0001] The present disclosure relates to a thermoelectric conversion element, a bonding material, a thermoelectric conversion module, a thermoelectric conversion system, a power generation method, and a method for manufacturing a thermoelectric conversion element.

[0002] Conventionally, thermoelectric conversion materials containing Mg and at least one element selected from the group consisting of Sb and Bi have been known.

[0003] For example, Patent Document 1 discloses Mg 3+m A a B b D 2-e E e In this thermoelectric conversion material, D is at least one element selected from the group consisting of Sb and Bi.

[0004] In Non-Patent Document 1, a specific n-type Mg 3+δ The thermoelectric conversion performance of (Sb, Bi) is described. For example, Mg 3.2 Sb 1.5 Bi 0.49 Te 0.01 It is described that a polycrystalline sintered body having the composition exhibits a ZT of 1.51±0.06 at 716K.

[0005] Non-patent document 2 describes n-type Mg 3.1 Co 0.1 Sb 1.5 Bi 0.49 Te 0.01 This sample is produced by placing powder of a thermoelectric conversion material between iron powders on a graphite die, and then hot pressing the powders.

[0006] Non-Patent Document 3 describes n-type Mg 3.2 Sb 1.5 Bi 0.49 Te 0.01 and stainless steel (SUS304).

[0007] Patent Document 2 describes a thermoelectric conversion element in which a pair of electrode layers made of a metal material are formed on both sides of a thermoelectric conversion layer made of magnesium silicide. In this thermoelectric conversion element, a buffer layer made of a mixture of magnesium silicide and a metal material is formed between the thermoelectric conversion layer and the electrode layer. The metal material is a nickel-based material.

[0008] Japanese Patent No. 6127281 Japanese Patent Application Laid-Open No. 2009-260173

[0009] Tamaki et al., Advanced Materials 28, 10182-10187 (2016)Zhu et al., Journal of Power Sources 414, 393-400 (2019)Yin et al., Acta Materialia 198, 25-34 (2020)

[0010] The present disclosure provides a thermoelectric conversion element that is advantageous from the viewpoint of suppressing an increase in electrical resistance in high-temperature air.

[0011] The thermoelectric conversion element of the present disclosure comprises: a first metal layer; and a thermoelectric conversion section containing Mg and at least one selected from the group consisting of Sb and Bi; the thermoelectric conversion section comprises: a thermoelectric conversion layer; and a first bonding layer disposed between the first metal layer and the thermoelectric conversion layer in the thickness direction of the thermoelectric conversion layer; the first bonding layer contains at least one selected from the group consisting of Fe and Ni; and the first bonding layer satisfies a first condition expressed as 2.5≦α / β≦6.5, in which α is the Mg content in the first bonding layer on an atomic number basis, and β is the sum of the Sb and Bi contents in the first bonding layer on an atomic number basis.

[0012] According to the present disclosure, it is possible to provide a thermoelectric conversion element that is advantageous from the viewpoint of suppressing an increase in electrical resistance in high-temperature air.

[0013] FIG. 1 is a cross-sectional view schematically showing a thermoelectric conversion element according to a first embodiment. FIG. 2 is a flowchart showing a method for manufacturing a thermoelectric conversion element according to the first embodiment. FIG. 3 is a cross-sectional view schematically showing an example of a thermoelectric conversion element according to a second embodiment. FIG. 4 is a cross-sectional view schematically showing another example of a thermoelectric conversion element according to the second embodiment. FIG. 5 is a perspective view showing a thermoelectric conversion module according to a third embodiment. FIG. 6 is a side view showing a thermoelectric conversion system according to a fourth embodiment. FIG. 7 is a scanning electron microscope image of a cross section of a junction of a thermoelectric conversion element according to a first example. FIG. 8 is a scanning electron microscope image of a cross section of a junction of a thermoelectric conversion element according to a sixth example.

[0014] (Findings underlying the present disclosure) Thermoelectric conversion technology, in which solid-state elements convert thermal energy into electrical energy to generate electricity, is widely known. A planar thermoelectric conversion module can be constructed by electrically connecting n-type and p-type thermoelectric conversion elements in series and thermally in parallel on a substrate. Power generation is achieved by applying a temperature difference to such a thermoelectric conversion module. To achieve good electrical connection in a thermoelectric conversion module, it is conceivable to use thermoelectric conversion elements in which a thermoelectric conversion material is metal-plated, or in which metal powder or a metal plate is bonded to a thermoelectric conversion material by a method such as sintering. When generating power using a thermoelectric conversion element, the thermoelectric conversion element may be placed in a high-temperature air environment (e.g., air at 400°C) for a long period of time. Even in such cases, it is important to suppress an increase in electrical resistance in the thermoelectric conversion element.

[0015] Patent Document 1 describes Mg 3+m A a B b D 2-e E e However, the structure of a thermoelectric conversion element including the thermoelectric conversion material is not described.

[0016] In Non-Patent Document 1, n-type Mg 3+δIt has been disclosed that in order to enhance the thermoelectric conversion performance of a (Sb, Bi) thermoelectric conversion material, the presence of excess Mg relative to the stoichiometric ratio is necessary. However, according to the inventors' investigations, Mg is easily oxidized and has a high vapor pressure. Therefore, in a high-temperature air environment, Mg is easily lost in a thermoelectric conversion material containing Mg and at least one element selected from the group consisting of Sb and Bi due to oxidation or sublimation of Mg. As a result, when such a thermoelectric conversion material is placed in a high-temperature air environment for a long period of time, the electrical resistance of the thermoelectric conversion element increases, and the thermoelectric conversion performance is likely to decrease. The inventors have focused on this problem.

[0017] Therefore, the present inventors have conducted extensive research into a configuration in which the electrical resistance of a thermoelectric conversion element containing a thermoelectric conversion material containing Mg and at least one element selected from the group consisting of Sb and Bi is less likely to increase in high-temperature air.

[0018] Non-Patent Document 2 describes a sample prepared by sandwiching powder of a thermoelectric conversion material between iron powders and placing them on a graphite die, and then hot-pressing the powders. 3.2 Sb 1.5 Bi 0.49 Te 0.01 and stainless steel (SUS304). According to experiments by the present inventors to reproduce the samples described in Non-Patent Documents 2 and 3, it was revealed that the initial properties of the reproduced samples varied and that the electrical resistance of the samples increased in high-temperature air.

[0019] In the thermoelectric conversion element described in Patent Document 2, a buffer layer made of a mixture of magnesium silicide and a metal material is formed between a thermoelectric conversion layer made of magnesium silicide and an electrode layer. However, in this thermoelectric conversion element, there is no excess Mg relative to the stoichiometric ratio, and Patent Document 2 does not provide any knowledge to solve the above-mentioned problems related to thermoelectric conversion elements.

[0020] Therefore, the present inventors, after extensive trial and error, have newly discovered that the electrical resistance of a thermoelectric conversion element is less likely to increase in high-temperature air by providing a predetermined bonding layer between a metal layer and a layer containing a thermoelectric conversion material. Based on this new finding, the present inventors have completed the thermoelectric conversion element according to the present disclosure.

[0021] (Embodiments of the Present Disclosure) Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0022] (First Embodiment) FIG. 1 is a cross-sectional view schematically illustrating a thermoelectric conversion element according to a first embodiment. As shown in FIG. 1, a thermoelectric conversion element 10 includes a first metal layer 15 and a thermoelectric conversion unit 11a. The thermoelectric conversion unit 11a contains Mg and at least one element selected from the group consisting of Sb and Bi. The thermoelectric conversion unit 11a includes a thermoelectric conversion layer 11 and a first bonding layer 14. The first bonding layer 14 contains at least one element selected from the group consisting of Fe and Ni. The first bonding layer 14 satisfies the condition 2.5≦α / β≦6.5. In this condition, α is the Mg content in the first bonding layer 14 based on the atomic number, and β is the sum of the Sb and Bi contents in the first bonding layer 14 based on the atomic number. Because the first bonding layer 14 is configured in this manner, even if the thermoelectric conversion element 10 is placed in a high-temperature air environment (e.g., air at 400°C), an increase in the electrical resistance of the thermoelectric conversion element 10 is likely to be suppressed. It is thought that even if the thermoelectric conversion element 10 is placed in a high-temperature air environment, the first bonding layer 14 makes it difficult for Mg to be lost from the thermoelectric conversion material contained in the thermoelectric conversion layer 11.

[0023] First bonding layer 14 may satisfy the condition α / β≧2.6, may satisfy the condition α / β≧2.8, or may satisfy the condition α / β≧3.0.

[0024] 1 , the first bonding layer 14 is disposed, for example, between the thermoelectric conversion layer 11 and the first metal layer 15 in the thickness direction of the first bonding layer 14. One main surface (first main surface) of the first bonding layer 14 is in contact with the thermoelectric conversion layer 11, and the other main surface (second main surface) of the first bonding layer 14 is in contact with the first metal layer 15.

[0025] As long as the condition 2.5≦α / β≦6.5 is satisfied, α is not limited to a specific value. For example, the condition 18%≦α≦32%, 18%≦α≦30%, or 19%≦α≦30% may be satisfied.

[0026] As long as the condition 2.5≦α / β≦6.5 is satisfied, β is not limited to a specific value. For example, the condition 3%≦β≦15%, the condition 4%≦β≦12%, or the condition 4%≦β≦10% may be satisfied.

[0027] The structure of first bonding layer 14 is not limited to a specific structure as long as it contains at least one element selected from the group consisting of Fe and Ni and satisfies the condition 2.5≦α / β≦6.5. As shown in FIG. 1 , first bonding layer 14 has, for example, particles 14a and phase 14b, which is a solid phase different from particles 14a. Particles 14a contain at least one element selected from the group consisting of Fe and Ni. Phase 14b is present between particles 14a. In addition, phase 14b contains Mg. With this configuration, an increase in the electrical resistance of thermoelectric conversion element 10 is more likely to be suppressed even when thermoelectric conversion element 10 is placed in a high-temperature air environment.

[0028] The phase 14b may be a continuous phase or a dispersed phase, and may have a melting point lower than that of the particles 14a, for example.

[0029] The sum γ of the atomic content of Fe and Ni in the first bonding layer 14 is not limited to a specific value. The first bonding layer 14 satisfies, for example, the condition γ≧65%. With this configuration, the electrical resistance of the thermoelectric conversion element 10 is unlikely to increase. In addition, the bonding strength between the thermoelectric conversion layer 11 and the first metal layer 15 is likely to be high.

[0030] First bonding layer 14 may satisfy the condition γ≧66%, may satisfy the condition γ≧67%, may satisfy the condition γ≧68%. First bonding layer 14 satisfies the condition γ≦80%, for example.

[0031] In the first bonding layer 14, the ratio α / γ is not limited to a specific value. The first bonding layer 14 satisfies the condition 0.002<α / γ<0.6, for example. With this configuration, even if the thermoelectric conversion element 10 is placed in a high-temperature air environment, an increase in the electrical resistance of the thermoelectric conversion element 10 is more likely to be suppressed. In addition, the bonding strength between the thermoelectric conversion layer 11 and the first metal layer 15 is likely to be high.

[0032] In first bonding layer 14, α / γ may be included in a range defined by a pair of numerical values ​​selected from the group consisting of 0.005, 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, and 0.5.

[0033] 1 , for example, the thermoelectric conversion layer 11 is disposed in its thickness direction between the first composite metal layer 12 and the second composite metal layer 13. Each of the first composite metal layer 12 and the second composite metal layer 13 includes a first bonding layer 14 and a first metal layer 15.

[0034] The three-dimensional shape of the thermoelectric conversion element 10 is not limited to a specific shape. The thermoelectric conversion element 10 may be a rectangular parallelepiped. In this case, the cross section of the thermoelectric conversion element 10 perpendicular to the paper surface of FIG. 1 is rectangular or square. The thermoelectric conversion element 10 may be a cylindrical column. In this case, the cross section of the thermoelectric conversion element 10 perpendicular to the paper surface of FIG. 1 is circular. The thermoelectric conversion element 10 may be a shape in which the cross section of the thermoelectric conversion element 10 perpendicular to the paper surface of FIG. 1 is irregular.

[0035] The thickness of each layer in the thermoelectric conversion element 10 is not limited to a specific value. The thickness of the thermoelectric conversion layer 11 is, for example, 0.5 mm or more and 10 mm or less. The thickness of the first bonding layer 14 is, for example, 0.01 mm or more and 0.2 mm or less. The thickness of the first metal layer 15 is, for example, 0.05 mm or more and 1 mm or less. Having the thickness of each layer within such a range is advantageous from the viewpoint of the manufacturing cost of the thermoelectric conversion element 10 and the workability in manufacturing the thermoelectric conversion element 10.

[0036] The cross-sectional view shown in FIG. 1 is a schematic view. The multiple interfaces formed by the portions of the layered structure may be parallel to each other or may not be parallel to each other. The interfaces may have irregularities. The cross-sectional shape may be rectangular, and the sides of the cross-sectional shape may have irregularities or curves. A pair of adjacent sides in the cross-sectional shape may intersect at a right angle, or may intersect at an angle less than 90°, or at an angle greater than 90° and less than 180°.

[0037] The thermoelectric conversion material contained in the thermoelectric conversion layer 11 is not limited to a specific material as long as it contains Mg and at least one element selected from the group consisting of Sb and Bi. The thermoelectric conversion layer 11 has, for example, a La2O3 type crystal structure and contains Mg 3+m A a D 2-e E e The n-type thermoelectric conversion material has a composition represented by the formula: In this composition, element A is at least one element selected from the group consisting of La, Y, Yb, Mn, and Zn. Element D is at least one element selected from the group consisting of Sb and Bi. Element E is at least one element selected from the group consisting of Te and Se. The value of m is -0.1 or more and 0.4 or less. The value of a is 0 or more and 0.1 or less. The value of e is 0.001 or more and 0.06 or less.

[0038] Thermoelectric conversion layer 11 may contain the same type of element as the element contained in first bonding layer 14. For example, thermoelectric conversion layer 11 may contain the same type of element as the element contained in first bonding layer 14, derived from the raw material of first bonding layer 14.

[0039] The particles 14a may contain only one of Fe and Ni, or may contain both Fe and Ni. The particles 14a may contain elemental Fe or elemental Ni. The particles 14a may contain an alloy containing at least one selected from the group consisting of Fe and Ni. For example, the particles 14a may contain an iron-based alloy such as stainless steel, or a nickel-based alloy such as Inconel or Hastelloy. Inconel and Hastelloy are registered trademarks. The particles 14a may contain a metal other than Fe and Ni. The particles 14a may contain metals such as Cr and Mo, for example.

[0040] The particles 14a may contain the same type of element as the element contained in the thermoelectric conversion layer 11 or the phase 14b. For example, the particles 14a may contain the same type of element as the element contained in the thermoelectric conversion layer 11 or the phase 14b, derived from the raw material of the thermoelectric conversion layer 11 or the raw material of the phase 14b.

[0041] The average particle size q of the particles 14a is not limited to a specific value. For example, the average particle size q satisfies the condition 0.5 μm≦q≦100 μm. In this case, the bonding strength between the thermoelectric conversion layer 11 and the first metal layer 15 tends to be high. The average particle size q is, for example, the median diameter d50 in a volume-based particle size distribution obtained by laser diffraction particle size distribution measurement.

[0042] Phase 14b may contain the same type of element as that contained in thermoelectric conversion layer 11 or particles 14a. For example, phase 14b may contain the same type of element as that contained in thermoelectric conversion layer 11 or particles 14a, derived from the raw material of thermoelectric conversion layer 11 or the raw material of particles 14a.

[0043] The metal contained in the first metal layer 15 is not limited to a specific metal. For example, the first metal layer 15 contains at least one selected from the group consisting of Fe, Ni, Cu, and Ag. In this case, the electrical resistance of the thermoelectric conversion element 10 tends to be low.

[0044] The first metal layer 15 may contain elemental Fe, elemental Ni, elemental Cu, or elemental Ag. The first metal layer 15 may contain an alloy. Examples of alloys are stainless steel, Inconel, and Hastelloy. The first metal layer 15 may contain oxygen-free copper.

[0045] An example of a manufacturing method for the thermoelectric conversion element 10 will be described. FIG. 2 is a flowchart showing a manufacturing method for the thermoelectric conversion element of the first embodiment. This manufacturing method includes, for example, heating a metal plate, powder, and bonding material in a predetermined state to sinter the powder and bond the metal plate and the sintered powder body. The predetermined state is a state in which the bonding material is disposed between the metal plate and the powder in the thickness direction of the metal plate. The bonding material contains Mg and at least one element selected from the group consisting of Fe and Ni. The powder contains Mg and at least one element selected from the group consisting of Sb and Bi.

[0046] As shown in Fig. 2, powder is prepared in step S1. The powder is prepared, for example, by weighing predetermined amounts of raw materials according to a known powder production method using an arc melting method and a ball mill. The powder may be prepared with reference to the methods described in Non-Patent Documents 1 to 3. The powder is, for example, a powder of the thermoelectric conversion material described above.

[0047] In step S2, a bonding material is prepared. As described above, the bonding material contains Mg and at least one selected from the group consisting of Fe and Ni, and is capable of bonding the thermoelectric conversion material and the metal member.

[0048] The bonding material is, for example, a paste-like composition. The bonding material is prepared, for example, by mixing a high-melting-point metal-containing powder, which is the raw material for the particles 14a, a low-melting-point Mg-containing powder, which is the raw material for the phase 14b, an organic binder, and an organic solvent. The high-melting-point metal-containing powder contains, for example, at least one selected from the group consisting of Fe and Ni. This metal powder may be a powder of elemental Fe, a powder of elemental Ni, or a powder of an alloy containing at least one selected from the group consisting of Fe and Ni. Examples of alloys include stainless steel, Inconel, and Hastelloy. The low-melting-point Mg-containing powder may be a powder of elemental Mg or a powder of an alloy containing Mg. An example of an alloy is an alloy of Mg and Cu.

[0049] The average particle size p of the particles contained in the metal-containing powder is not limited to a specific value. The average particle size p satisfies, for example, the condition 0.5 μm≦p≦100 μm. This tends to increase the bonding strength between the thermoelectric conversion material and the metal member. The average particle size p is, for example, the median diameter d50 in a volume-based particle size distribution obtained by laser diffraction particle size distribution measurement.

[0050] The average particle size p may satisfy the condition 1 μm≦p≦50 μm, or 2 μm≦p≦50 μm, or 5 μm≦p≦30 μm.

[0051] The ratio of the content of the high-melting-point metal-containing powder in the bonding material to the content of the Mg-containing powder in the bonding material is, for example, 97 / 3 or more and 99.5 / 0.5 or less by mass. This makes it easier to suppress an increase in the electrical resistance of the thermoelectric conversion element 10 even when the manufactured thermoelectric conversion element 10 is placed in a high-temperature air environment. In addition, during the manufacture of the thermoelectric conversion element 10, leakage of molten Mg from the Mg-containing powder to the outside and significant diffusion of Mg toward the thermoelectric conversion material are prevented. As a result, the thermoelectric conversion element 10 can be manufactured stably.

[0052] The organic binder contained in the bonding material is not limited to a specific organic binder. For example, the organic binder has the property of evaporating or decomposing during the production of the thermoelectric conversion element 10 and not easily remaining in the thermoelectric conversion element 10. The organic binder is, for example, a butyl rubber-based resin or an acrylic-based resin. The organic solvent dissolves or disperses the organic binder. For example, the organic solvent is a naphthenic hydrocarbon solvent or toluene.

[0053] In preparing the bonding material, a binder solution may be prepared by dissolving or dispersing an organic binder in an organic solvent before adding the metal-containing powder. The concentration of the organic binder in the binder solution is, for example, 1 mass % or more and 15 mass % or less. In this case, the bonding material is likely to have a viscosity suitable for application. The ratio of the mass of the metal-containing powder to the mass of the binder solution in the bonding material is, for example, 3 / 2 to 9. In this case, the bonding material is likely to have a viscosity suitable for application.

[0054] In step S3, the bonding material is applied to the metal plate and dried. The method for applying the bonding material to the metal plate is not limited to a specific method. For example, the method is a doctor blade method. When drying the bonding material, the organic solvent is evaporated to obtain a dried coating film. The bonding material can be dried using a hot plate or an oven. In this way, precursors of the first composite metal layer 12 and the second composite metal layer 13 are obtained. The metal plate is, for example, a disk.

[0055] In step S4, the powder prepared in step S1 and the precursors of the first composite metal layer 12 and the second composite metal layer 13 prepared in step S3 are filled into a cylindrical carbon sintering mold according to the arrangement shown in Fig. 1. In other words, the powder and the precursors of the first composite metal layer 12 and the second composite metal layer 13 are arranged so that the bonding material is disposed between the metal plate and the powder in the thickness direction of the metal plate. The metal plate has a diameter equal to or smaller than the inner diameter of the sintering mold, for example. The sintering mold is then sandwiched between a punch in the thickness direction of the metal plate.

[0056] In step S5, pressure is applied to the punch to pressurize the inside of the sintering mold, and the powder sintered body and the metal plate are bonded together. This results in a laminate in which the powder sintered body and the metal plate are bonded together. The powder sintering may be performed using an electric heating method such as spark plasma sintering, or may be performed using a hot press method involving heating with an electric heater or high-frequency heating. The powder sintering is performed, for example, in an argon atmosphere with a low oxygen partial pressure or in a vacuum. This makes it difficult for the thermoelectric conversion material contained in the powder to oxidize. The powder sintering is preferably performed in an argon atmosphere. In this case, Mg is less likely to evaporate.

[0057] The sintering temperature of the powder is, for example, equal to or higher than the melting point of Mg, i.e., 650°C or higher. When the first metal layer 15 contains at least one selected from the group consisting of Fe and Ni, the sintering temperature of the powder may be adjusted to about 900°C. On the other hand, when the first metal layer 15 contains Cu or Ag, the sintering temperature of the powder can be adjusted to 720°C or lower. This prevents the metal components contained in the first metal layer 15 from fusing with Mg and melting.

[0058] In step S6, the laminate obtained in step S5 is removed from the sintering mold, and the laminate is cut to obtain rectangular parallelepiped thermoelectric conversion elements 10. The method for cutting the laminate is not limited to a specific method. For example, the laminate can be cut using a diamond cutter or a wire saw.

[0059] (Embodiment 2) Fig. 3 is a cross-sectional view schematically showing an example of a thermoelectric conversion element according to embodiment 2. The thermoelectric conversion element according to embodiment 2 is configured in the same manner as the thermoelectric conversion element according to embodiment 1, except for portions that will be particularly described. Components of the thermoelectric conversion element according to embodiment 2 that are the same as or correspond to components of the thermoelectric conversion element according to embodiment 1 are given the same reference numerals, and detailed description thereof will be omitted. The description of the thermoelectric conversion element according to embodiment 1 also applies to embodiment 2, unless technically inconsistent.

[0060] As shown in FIG. 3 , the thermoelectric conversion element 30 further includes a second metal layer 35 in addition to the first metal layer 15 and the thermoelectric conversion unit 11a. The second metal layer 35 contains at least one element selected from the group consisting of Cu and Ag. The first metal layer 15 is disposed between the second metal layer 35 and the thermoelectric conversion unit 11a in the thickness direction of the first metal layer 15. Additionally, the first metal layer 15 contains at least one element selected from the group consisting of Fe and Ni. This configuration facilitates electrical connection between a thermoelectric conversion element 30 and another thermoelectric conversion element adjacent to the thermoelectric conversion element 30 when fabricating a thermoelectric conversion module using multiple thermoelectric conversion elements 30. Furthermore, even if the second metal layer 35 is disposed at the end of the thermoelectric conversion element 30 in the thickness direction of the first metal layer 15, the temperature for joining the first metal layer 15 and the second metal layer 35 to the thermoelectric conversion unit 11a can be increased to approximately 900°C.

[0061] In the thermoelectric conversion element 30, the first metal layer 15 may contain elemental Fe, elemental Ni, or an alloy containing at least one element selected from the group consisting of Fe and Ni. Examples of the alloy include stainless steel, Inconel, and Hastelloy.

[0062] In the thermoelectric conversion element 30, the second metal layer 35 contains, for example, Cu or Ag.

[0063] 3 , the thermoelectric conversion element 30 further includes, for example, a second bonding layer 34. The second bonding layer 34 is disposed between the first metal layer 15 and the second metal layer 35 in the thickness direction of the second bonding layer 34. The second bonding layer 34 contains, for example, at least one selected from the group consisting of Cu and Ag. The second bonding layer 34 may contain elements such as Mg, Sn, Ti, and Al. For example, the content of each of the elements Mg, Sn, Ti, and Al in the second bonding layer 34 is 1 mass % or less.

[0064] 3 , for example, the thermoelectric conversion layer 11 is disposed in its thickness direction between a first composite metal layer 32 and a second composite metal layer 33. Each of the first composite metal layer 32 and the second composite metal layer 33 includes a first bonding layer 14, a first metal layer 15, a second bonding layer 34, and a second metal layer 35.

[0065] The thermoelectric conversion element 30 can be manufactured, for example, in the same manner as the thermoelectric conversion element 10. The raw material of the second bonding layer 34 is, for example, a paste-like composition containing a metal component. The raw material of the second metal layer 35 is, for example, a metal plate.

[0066] 4 is a cross-sectional view schematically illustrating another example of a thermoelectric conversion element according to the second embodiment. For example, when the second bonding layer 34 and the second metal layer 35 contain the same type of metal, the boundary between the second bonding layer 34 and the second metal layer 35 may not be clear in the cross section of the thermoelectric conversion element 30. For example, when both the second bonding layer 34 and the second metal layer 35 contain Cu or Ag, the boundary between them is not clear, and the second bonding layer 34 and the second metal layer 35 appear to be a single layer. In this case, as shown in FIG. 4 , the portion that appears to be a single layer may be considered to be the second metal layer 35.

[0067] Third Embodiment FIG. 5 is a perspective view showing an example of a thermoelectric conversion module according to the present disclosure. As shown in FIG. 5 , the thermoelectric conversion module 100 includes a p-type thermoelectric converter 20, an n-type thermoelectric converter 10a, and a first electrode 51. The n-type thermoelectric converter 10a includes a thermoelectric conversion element 10 or a thermoelectric conversion element 30. The thermoelectric conversion material included in the p-type thermoelectric converter 20 is not limited to a specific material and may include, for example, a known p-type thermoelectric conversion material. The first electrode 51 electrically connects one end of the p-type thermoelectric converter 20 to one end of the n-type thermoelectric converter 10a. With this configuration, even when the thermoelectric conversion module 100 is placed in a high-temperature air environment, an increase in the electrical resistance of the thermoelectric conversion element 10 or the thermoelectric conversion element 30 included in the n-type thermoelectric converter 10a is likely to be suppressed.

[0068] 5, the thermoelectric conversion module 100 further includes, for example, a second electrode 52 and a third electrode 53. The second electrode 52 is electrically connected to the other end of the p-type thermoelectric converter 20. The third electrode 53 is electrically connected to the other end of the n-type thermoelectric converter 10a.

[0069] The thermoelectric conversion module 100 further includes, for example, a pair of substrates 60. One of the pair of substrates 60 is disposed in contact with the first electrode 51, and the other of the pair of substrates 60 is disposed in contact with the second electrode 52 and the third electrode 53. With this configuration, temperature variations are unlikely to occur in the thermoelectric conversion module 100 in a direction parallel to the main surfaces of the substrates 60. The material of the substrates 60 is not limited to a specific material. The substrates 60 include, for example, alumina or aluminum nitride.

[0070] (Embodiment 4) Fig. 6 is a side view showing a thermoelectric conversion system according to embodiment 4. As shown in Fig. 6, a thermoelectric conversion system 300 includes a thermoelectric conversion module 100 and a heat source 70. The heat source 70 is disposed on the first electrode 51 side of the thermoelectric conversion module 100.

[0071] According to the thermoelectric conversion system 300, a temperature difference is generated in the thermoelectric conversion module 100 by heat from the heat source 70, and electric power can be generated.

[0072] In the thermoelectric conversion system 300, the heat source 70 may include a heat transfer tube through which a predetermined heat medium is introduced. The heat medium may be a gas such as exhaust gas or a liquid such as water or oil. The heat source 70 may include a plate material for collecting radiant heat.

[0073] As shown in FIG. 6 , for example, in a thermoelectric conversion system 300 , one of a pair of substrates 60 of a thermoelectric conversion module 100 is disposed between a heat source 70 and the thermoelectric conversion module 100 .

[0074] (Additional Note) From the above description, the following techniques are disclosed.

[0075] (Technology 1) A thermoelectric conversion element comprising: a first metal layer; and a thermoelectric conversion unit containing Mg and at least one selected from the group consisting of Sb and Bi, wherein the thermoelectric conversion unit comprises: a thermoelectric conversion layer; and a first bonding layer disposed between the first metal layer and the thermoelectric conversion layer in a thickness direction of the thermoelectric conversion layer, wherein the first bonding layer contains at least one selected from the group consisting of Fe and Ni, and wherein the first bonding layer satisfies a first condition expressed as 2.5≦α / β≦6.5, wherein in the first condition, α is the content of Mg in the first bonding layer on an atomic number basis, and β is the sum of the contents of Sb and Bi in the first bonding layer on an atomic number basis.

[0076] (Technology 2) The thermoelectric conversion element according to Technology 1, wherein the first bonding layer has particles containing at least one selected from the group consisting of Fe and Ni, and a phase that is present between the particles and forms a solid phase different from the particles, and the phase contains Mg.

[0077] (Technology 3) The thermoelectric conversion element according to Technology 1 or 2, wherein the first bonding layer satisfies a second condition expressed as 0.002<α / γ<0.6, and in the second condition, γ is a sum of the contents of Fe and Ni in the first bonding layer on an atomic number basis.

[0078] (Technology 4) The thermoelectric conversion element according to any one of Technologies 1 to 3, wherein a sum γ of the contents of Fe and Ni in the first bonding layer based on the number of atoms satisfies a third condition of γ≧65%.

[0079] (Technology 5) The thermoelectric conversion element according to any one of Technologies 1 to 4, wherein the first metal layer contains at least one selected from the group consisting of Fe, Ni, Cu, and Ag.

[0080] (Technology 6) The thermoelectric conversion element according to any one of Technologies 1 to 5, further comprising a second metal layer containing at least one selected from the group consisting of Cu and Ag, wherein the first metal layer is disposed between the second metal layer and the thermoelectric conversion part in a thickness direction of the first metal layer, and contains at least one selected from the group consisting of Fe and Ni.

[0081] (Technology 7) A bonding material containing Mg and at least one selected from the group consisting of Fe and Ni, capable of bonding a thermoelectric conversion material and a metal member.

[0082] (Technology 8) A thermoelectric conversion module comprising: a p-type thermoelectric converter; an n-type thermoelectric converter; and an electrode electrically connecting one end of the p-type thermoelectric converter and one end of the n-type thermoelectric converter, wherein the n-type thermoelectric converter includes the thermoelectric conversion element according to any one of technologies 1 to 7.

[0083] (Technology 9) A thermoelectric conversion system comprising: the thermoelectric conversion module according to Technology 8; and a heat source disposed on the electrode side.

[0084] (Technology 10) A power generation method, comprising generating electric power by generating a temperature difference using heat from a heat source in the thermoelectric conversion module according to Technology 8.

[0085] (Technology 11) A method for manufacturing a thermoelectric conversion element, comprising: heating a metal plate, a powder, and a bonding material in a state where the bonding material is disposed between the metal plate and the powder in a thickness direction of the metal plate, to sinter the powder and bond the metal plate and a sintered body of the powder, wherein the bonding material contains Mg and at least one selected from the group consisting of Fe and Ni, and the powder contains Mg and at least one selected from the group consisting of Sb and Bi.

[0086] (Technology 12) The manufacturing method according to Technology 11, wherein the bonding material contains particles containing at least one selected from the group consisting of Fe and Ni, and an average particle size p of the particles satisfies a fourth condition expressed as 0.5 μm≦p≦100 μm.

[0087] The present disclosure will be described in detail below with reference to examples, although the thermoelectric conversion material of the present disclosure is not limited to the specific embodiments shown below.

[0088] Example 1 Raw material powders were weighed in a glove box under an argon atmosphere, and 2.00 g of Mg powder, 4.70 g of Sb powder, 2.63 g of Bi powder, and 0.03 g of Te were weighed out. The weighed raw material powders were sealed in a super-hard steel container (Model No. 8001) manufactured by SPEX Sample Prep, together with a super-hard steel ball. Thereafter, the raw material powders sealed in the container were mixed for two hours using a shake mill device (Model No. 8000D) manufactured by SPEX Sample Prep, to produce a powder of a thermoelectric conversion material by a mechanochemical reaction. As a result, Mg 3.2 Sb 1.5 Bi 0.49 Te 0.01 A powder of a thermoelectric conversion material having the composition and a La2O3 type crystal structure was obtained.

[0089] 90 g of naphthenic hydrocarbon solvent was weighed into a beaker, and a total of 10 g of butyl rubber binder was added in small amounts while stirring with a stirrer to prepare a 10 wt % binder solution. 6.93 g of stainless steel powder (SUS304 powder), 0.07 g of Mg powder, and 3.0 g of binder solution were placed in a polyethylene container. The ratio of the amount of stainless steel powder added to the amount of Mg powder added was 99.0 by mass. According to the volume-based particle size distribution of the stainless steel powder obtained by laser diffraction particle size distribution measurement, the particle size of the stainless steel powder was in the range of 1 micrometer to 50 micrometers. In addition, the average particle size (median diameter d50) of the stainless steel powder was approximately 10 micrometers. The contents of the container were mixed by shaking with a shake mill for 6 minutes to obtain a paste-like bonding material according to Example 1.

[0090] The bonding material according to Example 1 was applied to one main surface of a stainless steel disk having a diameter of 19.9 mm and a thickness of 0.2 mm, to form a coating film of the bonding material having a thickness of 0.1 mm.

[0091] The stainless steel disk on which the coating film of the bonding material was formed was placed on a hot plate heated to 120° C. to dry the bonding material for 15 minutes, thereby obtaining two stainless steel plates with the bonding material.

[0092] In a glove box under an argon atmosphere, each component was packed in a carbon sintering mold having an inner diameter of 20 mm in the following order: Two stainless steel plates with bonding material were placed so that the coating of the bonding material was in contact with the powder of the thermoelectric conversion material.

[0093] Carbon punch having an outer diameter of 20 mm Carbon sheet having a diameter of 20 mm First stainless steel plate with bonding material 5.0 g of thermoelectric conversion material powder Second stainless steel plate with bonding material Carbon sheet having a diameter of 20 mm Carbon punch having an outer diameter of 20 mm The sintering mold filled with the raw material was placed inside the chamber of an SPS Syntex SPS-515S spark plasma sintering apparatus, and the environment of the sintering mold was adjusted to an argon atmosphere. The sintering mold was heated to 850 °C while applying a pressure of 50 MPa inside the sintering mold, to sinter the thermoelectric conversion material powder and bond the thermoelectric conversion material powder to the stainless steel plate.

[0094] Next, the sintering mold was cooled to room temperature by furnace cooling, and then the contents inside the sintering mold were removed. The contents were then polished with abrasive paper to remove the carbon sheet from the contents, thereby obtaining a laminate according to Example 1.

[0095] The laminate according to Example 1 was cut with a diamond cutter to obtain rectangular parallelepiped thermoelectric conversion elements according to Example 1 measuring 3.4 mm x 3.4 mm x 3.5 mm. The number of thermoelectric conversion elements obtained was 12.

[0096] (Measurement of Electrical Resistance) Using a Keithley current source, Model No. 6221, and a Keithley voltmeter, Model No. 2182A, the electrical resistance between the pair of stainless steel plates in the thermoelectric conversion element according to Example 1 was measured according to the four-terminal method. As shown in Table 1, the average electrical resistance of the three thermoelectric conversion elements was 6 mΩ. The thermoelectric conversion elements of Example 1 were placed in a box-shaped electric furnace, Model No. F-1404-P, manufactured by Tokyo Glass Machinery, set at 400°C, and heat-treated in an air environment at 400°C for four days. Next, the electric furnace was returned to room temperature, and the thermoelectric conversion elements were removed. The surfaces of the stainless steel plates were polished with abrasive paper to remove the oxide film on the surface. Thereafter, the electrical resistance between the pair of stainless steel plates in the thermoelectric conversion element was measured according to the four-terminal method. As a result, the average electrical resistance of the three thermoelectric conversion elements after heat treatment was 6.2 mΩ.

[0097] (Cross-Section Observation of Thermoelectric Conversion Element) The side surface of the thermoelectric conversion element of Example 1 was polished with abrasive paper. Next, a cross-section of the thermoelectric conversion element was exposed by ion milling using a Leica argon ion milling machine, model EM TIC 3X, to obtain a sample for cross-section observation. This sample was observed using a Hitachi High-Technologies scanning electron microscope (SEM), model SU8220. Figure 7 is an SEM image of the cross-section of the joint of the thermoelectric conversion element of Example 1. In Figure 7, the layer indicated by reference numeral "51" is a layer containing a thermoelectric conversion material. The layer indicated by reference numeral "52" is a bonding layer derived from the bonding material. The layer indicated by reference numeral "53" is a stainless steel plate. As shown in Figure 7, a layer structure was confirmed at the joint of the thermoelectric conversion element of Example 1. As shown in Figure 7, the bonding layer indicated by reference numeral "52" was confirmed to have a first region, which was a dark, particulate region, and a second region, which was a bright region between the particles. The thickness of this layer was approximately 30 μm. Composition analysis was performed by energy dispersive X-ray spectroscopy (EDX) in the same field of view as in Figure 7. As a result, in the second portion of the bonding layer, Sb and Bi contained in the thermoelectric conversion material were detected in addition to Mg. In the layer containing the thermoelectric conversion material, Cr, which is thought to be derived from stainless steel, was detected in addition to Mg, Sb, and Bi. In the first portion of the bonding layer, Fe, Ni, and Cr were detected.

[0098] (Quantitative analysis) Based on the above SEM-EDX results, the atomic number-based content of each element in the bonding layer was determined. The results are shown in Table 1. The size of the SEM-EDX measurement field was adjusted to take into account the influence of the measurement location on the measurement results so that the measurement results would be average results for the bonding layer.

[0099] Examples 2 to 4 and Comparative Examples 1 to 3 Thermoelectric conversion elements according to Examples 2 to 4 and Comparative Examples 1 to 3 were produced in the same manner as in Example 1, except that the mass ratio of the amount of stainless steel powder added to the amount of Mg powder added was changed as shown in Table 1. In Comparative Example 1, no Mg powder was added. For each of these thermoelectric conversion elements, electrical resistance measurements, cross-sectional observations, and quantitative analyses were performed in the same manner as in Example 1. The results are shown in Table 1.

[0100] Example 5 A thermoelectric conversion element according to Example 5 was produced in the same manner as Example 1, except for the following points. An oxygen-free copper plate was used instead of the stainless steel plate. In addition, the heating temperature of the sintering mold was adjusted to 680°C. For the thermoelectric conversion element according to Example 5, electrical resistance measurement, cross-sectional observation, and quantitative analysis were performed in the same manner as Example 1. The results are shown in Table 1.

[0101] Example 6 A thermoelectric conversion element according to Example 6 was fabricated in the same manner as in Example 1, except for the following points. Instead of the stainless steel powder used in preparing the bonding material of Example 1, a different stainless steel powder having a particle size of 100 micrometers or less was used. The average particle size of this stainless steel powder was in the range of 60 to 80 micrometers. For the thermoelectric conversion element according to Example 6, electrical resistance measurements, cross-sectional observations, and quantitative analyses were performed in the same manner as in Example 1. The results are shown in Table 1. FIG. 8 is an SEM image of the cross section of the bonding portion of the thermoelectric conversion element according to Example 6. The thickness of the bonding layer, which is the layer designated by the reference numeral "52" in FIG. 8, was in the range of approximately 100 to 150 micrometers.

[0102] Example 7 A thermoelectric conversion element according to Example 7, having a structure as shown in FIG. 3, was fabricated in the same manner as Example 1, except for the following points. A paste-like bonding material containing Mg and Cu was applied to an oxygen-free copper disk, and the bonding material was dried to obtain two copper plates with a bonding material. The components were filled into a sintering mold in the following order. The two copper plates with a bonding material were arranged so that the bonding material of the copper plates with a bonding material was in contact with the stainless steel plate.

[0103] Carbon punch having an outer diameter of 20 mm Carbon sheet having a diameter of 20 mm First copper plate with bonding material First stainless steel plate with bonding material 5.0 g of thermoelectric conversion material powder Second stainless steel plate with bonding material Second copper plate with bonding material Carbon sheet having a diameter of 20 mm Carbon punch having an outer diameter of 20 mm For the thermoelectric conversion element of Example 7, electrical resistance measurement, cross-sectional observation, and quantitative analysis were performed in the same manner as in Example 1. The results are shown in Table 1.

[0104] As shown in Table 1, a comparison between the examples and the comparative examples suggests that when the condition 2.5≦α / β≦6.5 is satisfied in the junction layer of the thermoelectric conversion element, an increase in the electrical resistance of the thermoelectric conversion element in high-temperature air is likely to be suppressed.

[0105]

[0106] The thermoelectric conversion element of the present disclosure can be used for purposes such as power generation or temperature control.

[0107] REFERENCE SIGNS LIST 10, 30 Thermoelectric conversion element 10a n-type thermoelectric converter 11 Thermoelectric conversion layer 11a Thermoelectric conversion section 14 First bonding layer 14a Particle 14b Phase 15 First metal layer 20 P-type thermoelectric converter 35 Second metal layer 51 First electrode 70 Heat source 100 Thermoelectric conversion module 300 Thermoelectric conversion system

Claims

1. a first metal layer; A thermoelectric conversion unit containing Mg and at least one selected from the group consisting of Sb and Bi, The thermoelectric conversion unit is A thermoelectric conversion layer; a first bonding layer disposed between the first metal layer and the thermoelectric conversion layer in a thickness direction of the thermoelectric conversion layer, The first bonding layer contains at least one selected from the group consisting of Fe and Ni, the first bonding layer satisfies a first condition expressed by 2.5≦α / β≦6.5, In the first condition, α is a content rate of Mg in the first bonding layer based on the atomic number, and β is a sum of a content rate of Sb and a content rate of Bi in the first bonding layer based on the atomic number, The thickness of the first bonding layer is 0.01 mm or more and 0.2 mm or less. Thermoelectric conversion element.

2. The first bonding layer has particles containing at least one selected from the group consisting of Fe and Ni. The thermoelectric conversion element according to claim 1 .

3. the first bonding layer satisfies a second condition expressed by 0.002<α / γ<0.6, In the second condition, γ is the sum of the contents of Fe and Ni in the first bonding layer on an atomic number basis; The thermoelectric conversion element according to claim 1 .

4. The sum γ of the contents of Fe and Ni in the first bonding layer based on the atomic number satisfies a third condition of γ≧65%; The thermoelectric conversion element according to claim 1 .

5. The first metal layer contains at least one selected from the group consisting of Fe, Ni, Cu, and Ag. The thermoelectric conversion element according to claim 1 .

6. Further comprising a second metal layer containing at least one selected from the group consisting of Cu and Ag; the first metal layer is disposed between the second metal layer and the thermoelectric conversion part in a thickness direction of the first metal layer, and contains at least one selected from the group consisting of Fe and Ni; The thermoelectric conversion element according to claim 1 .

7. Contains Mg and at least one selected from the group consisting of Fe and Ni; The thermoelectric conversion material and the metal member can be joined. Bonding material.

8. A p-type thermoelectric converter; An n-type thermoelectric converter; an electrode electrically connecting one end of the p-type thermoelectric converter and one end of the n-type thermoelectric converter; The n-type thermoelectric converter includes the thermoelectric conversion element according to claim 1. Thermoelectric conversion module.

9. The thermoelectric conversion module according to claim 8 ; A heat source disposed on the electrode side. Thermoelectric conversion system.

10. The thermoelectric conversion module according to claim 8, further comprising: generating electric power by generating a temperature difference using heat from a heat source. Power generation method.

11. The method includes heating a metal plate, a powder, and a bonding material in a state in which the bonding material is disposed between the metal plate and the powder in a thickness direction of the metal plate, to sinter the powder and bond the metal plate and a sintered body of the powder, The bonding material contains Mg and at least one selected from the group consisting of Fe and Ni, The powder contains Mg and at least one selected from the group consisting of Sb and Bi. A method for manufacturing a thermoelectric conversion element.

12. The bonding material contains particles including at least one selected from the group consisting of Fe and Ni, The average particle size p of the particles satisfies a fourth condition expressed by 0.5 μm≦p≦100 μm; The method of claim 11.

13. The first bonding layer has a phase that exists between the particles and forms a solid phase different from the particles, The phase contains Mg. The thermoelectric conversion element according to claim 2 .

14. In the first condition, α satisfies the condition 19%≦α≦30%. The thermoelectric conversion element according to claim 1 .