WO2019177147A1 - Thermoelectric conversion element - Google Patents

Thermoelectric conversion element Download PDF

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Publication number
WO2019177147A1
WO2019177147A1 PCT/JP2019/010818 JP2019010818W WO2019177147A1 WO 2019177147 A1 WO2019177147 A1 WO 2019177147A1 JP 2019010818 W JP2019010818 W JP 2019010818W WO 2019177147 A1 WO2019177147 A1 WO 2019177147A1
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WO
WIPO (PCT)
Prior art keywords
electrode
thermoelectric conversion
silicide
conversion element
element body
Prior art date
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PCT/JP2019/010818
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French (fr)
Japanese (ja)
Inventor
中田　嘉信
Original Assignee
三菱マテリアル株式会社
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Publication date
Priority claimed from JP2019040845A external-priority patent/JP7242999B2/en
Application filed by 三菱マテリアル株式会社 filed Critical 三菱マテリアル株式会社
Priority to US16/957,968 priority Critical patent/US11152554B2/en
Priority to EP19768346.9A priority patent/EP3767689A4/en
Priority to CN201980007644.4A priority patent/CN111630672A/en
Priority to KR1020207019226A priority patent/KR20200130806A/en
Publication of WO2019177147A1 publication Critical patent/WO2019177147A1/en

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    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
    • C04B35/58—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C1/00—Making non-ferrous alloys
    • C22C1/04—Making non-ferrous alloys by powder metallurgy
    • C22C1/05—Mixtures of metal powder with non-metallic powder
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C9/00—Alloys based on copper
    • C22C9/10—Alloys based on copper with silicon as the next major constituent
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N10/00—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects
    • H10N10/01—Manufacture or treatment
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N10/00—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects
    • H10N10/80—Constructional details
    • H10N10/81—Structural details of the junction
    • H10N10/817—Structural details of the junction the junction being non-separable, e.g. being cemented, sintered or soldered
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N10/00—Thermoelectric devices comprising a junction of dissimilar materials, i.e. devices exhibiting Seebeck or Peltier effects
    • H10N10/80—Constructional details
    • H10N10/85—Thermoelectric active materials
    • H10N10/851—Thermoelectric active materials comprising inorganic compositions

Definitions

  • thermoelectric conversion element including an element main body made of a thermoelectric conversion material of a silicide compound and electrodes formed on one surface of the element main body and the other surface facing each other.
  • thermoelectric conversion elements made of thermoelectric conversion materials are electronic elements that can convert heat and electricity to each other using phenomena such as the Seebeck effect and Peltier effect.
  • the Seebeck effect is an effect of converting thermal energy into electric energy, and is a phenomenon in which an electromotive force is generated when a temperature difference is generated between both ends of the thermoelectric conversion material. Such electromotive force is determined by the characteristics of the thermoelectric conversion material. In recent years, thermoelectric power generation utilizing this effect has been actively developed.
  • thermoelectric conversion material As an index representing the characteristics of such a thermoelectric conversion element (thermoelectric conversion material), for example, the power factor (PF) expressed by the following formula (1) or the dimensionless figure of merit expressed by the following formula (2) (ZT) is used.
  • PF S 2 ⁇ (1)
  • ZT S 2 ⁇ T / ⁇ (2)
  • T absolute temperature (K)
  • thermoelectric conversion material constituting the element body include silicide-based compounds such as magnesium silicide.
  • thermoelectric conversion element described above has a structure in which electrodes are formed on one end side and the other end side of a thermoelectric conversion material.
  • Nickel is used as an electrode formed on the element body made of a thermoelectric conversion material of a silicide-based compound such as magnesium silicide. This is because the thermal expansion coefficient of magnesium silicide (Mg 2 Si) at room temperature (15.5 ⁇ 10 ⁇ 6 (/ ° C.)) and the thermal expansion coefficient of nickel at room temperature (15.2 ⁇ 10 ⁇ 6 (/ ° C)) is approximate.
  • thermoelectric conversion element when used in an intermediate temperature range (300 ° C. or more and 600 ° C. or less), Si of the silicide compound of the element body diffuses to the electrode side, and nickel of the electrode becomes nickel silicide. Since this nickel silicide has a thermal expansion coefficient at room temperature of 12.0 ⁇ 10 ⁇ 6 (/ ° C.), the difference in thermal expansion coefficient from the element body made of a thermoelectric conversion material of a silicide compound increases. There was a risk of cracks occurring in the element body. Further, the composition in the vicinity of the interface region with the electrode of the element body changes, and there is a risk that the electrical resistance increases or the strength decreases.
  • Patent Document 1 proposes a thermoelectric conversion element in which an intermediate layer made of a refractory metal silicide is formed between an element body made of a thermoelectric conversion material and an electrode. In this thermoelectric conversion element, diffusion of elements between the element body and the electrode is suppressed by an intermediate layer made of refractory metal silicide.
  • Patent Document 2 proposes a thermoelectric conversion element using a mixture of nickel silicide and metallic nickel as an electrode.
  • the intermediate layer made of refractory metal silicide is formed by vapor deposition, sputtering, or CVD, and the intermediate layer cannot be formed efficiently. Also, it has been difficult to form a thick intermediate layer. For this reason, there is a possibility that the electrode element cannot be sufficiently prevented from diffusing into the element body by the intermediate layer.
  • nickel silicide is used as an electrode.
  • nickel silicide has a large difference in thermal expansion coefficient from the element main body made of magnesium silicide or the like, and heat during manufacture is low. There was a possibility that the element main body and the electrode were cracked by the thermal stress resulting from the history.
  • metallic nickel is in direct contact with the element body made of magnesium silicide or the like, Si in the element body diffuses to the metallic nickel side, the composition in the vicinity of the interface region of the element body changes, and the electrical resistance is high. Or the strength may be reduced.
  • the present invention has been made in view of the above-described circumstances, and the element body made of a thermoelectric conversion material of a silicide compound and the electrode are reliably bonded, the electric resistance at the bonding interface is sufficiently low, and the element It aims at providing the thermoelectric conversion element which can suppress that a main body and an electrode generate
  • thermoelectric conversion element of the present invention includes an element body made of a thermoelectric conversion material of a silicide compound, and electrodes formed on one surface of the element body and the other surface facing each other.
  • the electrode is made of a sintered body of copper silicide, and the electrode and the element body are directly joined.
  • thermoelectric conversion element since the electrode is composed of a sintered body of copper silicide, the difference in thermal expansion coefficient from the element main body made of a thermoelectric conversion material of a silicide compound can be reduced. Since copper silicide has a relatively low melting point, a liquid phase is generated in at least a part of copper silicide when a sintered body to be an electrode is formed, and thermal strain can be released. Therefore, it can suppress that a crack arises in an element main part and an electrode at the time of manufacture. When forming a sintered body to be an electrode, the entire copper silicide may be in a liquid phase.
  • the electrode and the element main body are directly joined, and as described above, a liquid phase is generated in at least a part of the copper silicide when the sintered body to be the electrode is formed.
  • the element main body can be sufficiently bonded, and the electrical resistance at the interface can be suppressed sufficiently low.
  • thermoelectric conversion element of the present invention a metal layer may be formed on the surface of the electrode opposite to the element body.
  • the metal layer formed on the surface opposite to the element body can improve the bondability with the terminal.
  • the thickness of the electrode is preferably in the range of 10 ⁇ m or more and 300 ⁇ m or less.
  • the rigidity of the electrode does not become higher than necessary, and the occurrence of cracks in the element body during manufacturing can be suppressed.
  • the electrical conductivity in an electrode is securable by making the thickness of the said electrode 10 micrometers or more.
  • the electrode is composed of a sintered body of copper silicide, and the atomic ratio Si / Cu of Si / Cu in the copper silicide is in the range of 0.12 to 0.4. It is preferable to be inside. In this case, since the Si / Cu atomic ratio Si / Cu in the copper silicide constituting the electrode is in the range of 0.12 or more and 0.4 or less, it is possible to ensure high electrical conductivity in the electrode and to manufacture the electrode. Occurrence of cracks in the element body at the time can be suppressed.
  • thermoelectric conversion element of this invention it is preferable that the said electrode is comprised with the sintered compact of the copper silicide, and the porosity in the said copper silicide is 60% or less. In this case, since the porosity of the copper silicide constituting the electrode is 60% or less, it is possible to suppress an increase in electrical resistance.
  • the element body made of the thermoelectric conversion material of the silicide compound and the electrode are reliably bonded, the electrical resistance at the interface is sufficiently low, and the occurrence of cracks in the element body and the electrode can be suppressed.
  • thermoelectric conversion element which is 1st embodiment of this invention, and the thermoelectric conversion module using this thermoelectric conversion element. It is a flowchart which shows an example of the manufacturing method of the thermoelectric conversion element which is one Embodiment of this invention. It is sectional drawing which shows an example of the sintering apparatus used with the manufacturing method of the thermoelectric conversion element shown in FIG. It is explanatory drawing which shows the measurement means of the electrical resistance in the Example of this invention.
  • thermoelectric conversion element according to an embodiment of the present invention will be described with reference to the accompanying drawings.
  • the following embodiments are specifically described for better understanding of the gist of the invention, and do not limit the present invention unless otherwise specified.
  • drawings used in the following description in order to make the features of the present invention easier to understand, there is a case where a main part is shown in an enlarged manner for the sake of convenience. Not necessarily.
  • FIG. 1 shows a thermoelectric conversion element 10 according to a first embodiment of the present invention, and a thermoelectric conversion module 1 using the thermoelectric conversion element 10.
  • a thermoelectric conversion module 1 shown in FIG. 1 includes a thermoelectric conversion element 10 and terminals 3 and 3 disposed on one surface and the other surface of the thermoelectric conversion element 10.
  • the thermoelectric conversion element 10 includes an element main body 11 made of a thermoelectric conversion material, and electrodes 15 and 15 formed on one surface and the other surface of the element main body 11, respectively. As shown in FIG. 1, the element body 11 is formed in a columnar shape, and electrodes 15 and 15 are disposed on both end surfaces of the columnar shape.
  • the shape of the element body 11 is not limited, but may be a rectangular parallelepiped shape, a cylindrical shape, a polygonal column shape, an elliptical column shape, or the like. Both surfaces of the element body 11 to which the electrodes 15 and 15 are bonded may be parallel to each other or may be slightly inclined.
  • thermoelectric conversion material constituting the element body 11 is made of, for example, a silicide compound, and in the present embodiment, the thermoelectric conversion material is preferably made of a sintered body of magnesium silicide (Mg 2 Si).
  • silicide compounds that can be used in addition to magnesium silicide include silicon germanium (Si—Ge) total solid solution, manganese silicon (Mn—Si), and iron silicon (Fe—Si).
  • the thermoelectric conversion material constituting the element body 11 includes at least one of Li, Na, K, B, Al, Ga, In, N, P, As, Sb, Bi, Ag, Cu, and Y as a dopant. May be included. When the dopant is included, the total content in the element body 11 is preferably 0.1% by mass or more and 3.0% by mass or less, but is not limited to this range.
  • the electrode 15 is composed of a sintered body of copper silicide, and the electrode 15 and the element body 11 are directly joined.
  • the electrode 15 in this example has the same planar shape as the end face of the element body 11.
  • a metal layer 16 is formed on the surface of the electrode 15 on the side opposite to the element body 11. That is, the metal layer 16 is disposed between the electrode 15 and the terminal 3.
  • the metal layer 16 in this example has the same planar shape as the electrode 15.
  • the thickness of the electrode 15 made of a copper silicide sintered body is preferably in the range of 10 ⁇ m to 300 ⁇ m. If the thickness of the electrode 15 composed of a sintered body of copper silicide is 10 ⁇ m or more, the electrical conductivity in the electrode 15 can be ensured. If the thickness of the electrode 15 composed of a sintered body of copper silicide is 300 ⁇ m or less, the rigidity of the electrode 15 is not increased more than necessary, and the occurrence of cracks in the element body 11 during manufacturing can be suppressed.
  • the lower limit of the thickness of the electrode 15 made of a sintered copper silicide is more preferably 50 ⁇ m or more.
  • the upper limit of the thickness of the electrode 15 made of a copper silicide sintered body is more preferably 150 ⁇ m or less.
  • the Si / Cu atomic ratio Si / Cu is preferably in the range of 0.12 to 0.4.
  • the copper silicide constituting the electrode 15 is fired by mixing copper silicide powders having a plurality of compositions (Si / Cu), and the average value thereof is adjusted to be within the above-described range.
  • specific examples of copper silicide include Cu 3 Si (atomic ratio 1/3) and Cu 7 Si (atomic ratio 1/7), which can be mixed and used as a sintering raw material.
  • the atomic ratio Si / Cu of the copper silicide constituting the electrode 15 is 0.4 or less, single-phase sintering material is Cu 3 Si, or a Cu 3 Si, copper silicide consisting of minor amounts of other composition It is a copper silicide powder formed from a mixture. By melting the whole or a part of the sintering raw material, electrical conduction in the electrode 15 can be secured, and cracking of the element body 11 at the time of manufacture can be suppressed.
  • the lower limit of the number ratio Si / Cu of the copper silicide constituting the electrode 15 is more preferably 0.13 or more.
  • the upper limit of the atomic ratio Si / Cu of the copper silicide constituting the electrode 15 is more preferably 0.35 or less.
  • a copper silicide powder having a plurality of compositions Si / Cu
  • a part of the electrode 15 has a liquid phase solidification part formed by solidification of the liquid phase.
  • This liquid phase solidification part has fewer voids and a locally higher density than the region where no liquid phase is formed.
  • the porosity of the electrode 15 as a whole is not limited in the present invention, but is preferably 0% by volume or more and 60% by volume or less, more preferably 0% by volume or more and 50% by volume or less.
  • the distribution of the liquid phase solidified portion in the electrode 15 is not limited, it is preferable from the viewpoint of stress relaxation that the liquid phase solidified portion is concentrated and distributed in a layered manner on the element body 11 side.
  • the liquid phase solidified portions may be distributed substantially uniformly over the entire area of the electrode 15, or may be concentrated and distributed in a layered manner on the metal layer 16 side.
  • the porosity of the electrode 15 was determined by the following method. First, the weight of the silicide sintered body before forming the copper silicide electrode is measured. Next, after forming the electrodes, the thicknesses of the electrodes on both sides are measured at five locations with an optical microscope or a scanning electron microscope, and the average is obtained. Next, the size (vertical width, horizontal width, radius, etc.) of the electrode surfaces on both surfaces is measured with a caliper or a micrometer, and the surface areas of the electrode surfaces on both surfaces are obtained. From this surface area and the thickness of each electrode on both sides, the volume of the electrode part on each side is obtained.
  • the weight of the state in which the silicide sintered body and the electrode are integrated is weighed, and the weight of the electrode is obtained by subtracting the weight of the silicide sintered body.
  • the density of the electrode parts is determined from the weight and volume of the electrode parts on both sides. The density thus obtained is taken as the measured density.
  • the true density was estimated and calculated from the average composition obtained by analyzing the electrode layer with EPMA, and the porosity was determined from the equation (100 ⁇ (measured density / true density ⁇ 100) (%)).
  • the metal layer 16 is made of, for example, a metal having excellent conductivity, such as nickel, aluminum, or copper. In the present embodiment, the metal layer 16 is preferably made of aluminum.
  • the metal layer 16 is formed by bonding a metal foil or the like to the electrode 15 by, for example, brazing.
  • the thickness of the metal layer 16 is not limited, but is preferably in the range of 0.1 mm to 2.0 mm.
  • the terminal 3 is formed of a metal material having excellent conductivity, for example, a plate material such as copper or aluminum. In the present embodiment, it is preferable to use an aluminum rolled plate.
  • the metal layer 16 formed on the electrode 15 and the terminal 3 can be joined by, for example, Ag brazing, Ag plating, or the like.
  • the pair of terminals 3 of this embodiment extend to opposite sides as viewed from the element body 11 and are arranged in parallel to each other, but the present invention is not limited to this arrangement.
  • thermoelectric conversion element 10 described above will be described with reference to FIGS.
  • silicide compound powder preparation step S01 First, a silicide compound powder (magnesium silicide powder) serving as a parent phase of a thermoelectric conversion material constituting the element body is prepared.
  • a silicide compound ingot (magnesium silicide) is manufactured, and this is pulverized and sieved to manufacture a silicide compound powder (magnesium silicide powder) having a predetermined particle size.
  • Commercially available magnesium compound powder (magnesium silicide powder) may be used.
  • the average particle diameter of the silicide compound powder (magnesium silicide powder) is preferably in the range of 0.5 ⁇ m to 100 ⁇ m.
  • the sintering apparatus (electric current sintering apparatus 100) shown in FIG. 3 includes, for example, a pressure-resistant housing 101, a vacuum pump 102 that depressurizes the inside of the pressure-resistant housing 101, and a hollow cylinder disposed in the pressure-resistant housing 101.
  • a carbon plate 107 and a carbon sheet 108 are disposed between the electrode portions 105a and 105b and the sintering raw material powder Q, respectively.
  • a thermometer, a displacement meter, etc. are provided.
  • a heater 109 is disposed on the outer peripheral side of the carbon mold 103.
  • the heater 109 is disposed on four side surfaces so as to cover the entire outer peripheral side of the carbon mold 103.
  • a carbon heater a nichrome wire heater, a molybdenum heater, a Kanthal wire heater, a high frequency heater, or the like can be used.
  • the raw material powder Q is filled into the carbon mold 103 of the electric current sintering apparatus 100 shown in FIG.
  • the carbon mold 103 is covered with a graphite sheet or a carbon sheet.
  • a direct current is passed between the pair of electrode portions 105a and 105b, and a current is passed through the sintered raw material powder Q to raise the temperature by self-heating (electric heating).
  • the movable electrode portion 105a is moved toward the sintering raw material powder Q, and the sintering raw material powder Q is pressurized at a predetermined pressure with the fixed electrode portion 105b.
  • the heater 109 is heated.
  • the sintered raw material powder Q is sintered by self-heating of the sintered raw material powder Q, heat from the heater 109, and pressurization.
  • the sintering conditions in the element body sintering step S02 are such that the heating temperature of the sintering raw material powder Q is in the range of 650 ° C. or more and 1030 ° C. or less, and the holding time at this heating temperature is 0 minute or more (for example, 1 second or longer) and 3 minutes or shorter.
  • the pressure load is 15 MPa or more and 60 MPa or less.
  • the atmosphere in the pressure-resistant housing 101 is preferably an inert atmosphere such as an argon atmosphere or a vacuum atmosphere. In a vacuum atmosphere, the pressure is preferably 5 Pa or less.
  • the element body sintering step S02 it is preferable to change the polarities of the one electrode portion 105a and the other electrode portion 105b at a predetermined time interval when a direct current is passed through the sintered raw material powder Q. That is, the state where one electrode portion 105a is energized with the anode and the other electrode portion 105b as the cathode and the state where one electrode portion 105a is energized with the cathode and the other electrode portion 105b as the anode are alternately performed.
  • the element body 11 (thermoelectric conversion material) is manufactured through the above steps. By alternately switching the direction of the current, there is an advantage that the uniformity of the element body 11 is improved.
  • the carbon mold 103 of the electric current sintering apparatus 100 is filled with copper silicide powder and a sintered body of a silicide compound.
  • the carbon sheets on both end faces and side faces of the sintered body of the silicide compound are removed, and both end faces of the sintered body are polished with abrasive paper.
  • a carbon plate 107 and a carbon sheet 108 are inserted into the carbon mold 103 and filled with a predetermined amount of copper silicide powder, then a sintered body of a silicide compound is inserted, and a predetermined amount of copper silicide powder is further filled thereon. Then, the carbon plate 107 and the carbon sheet 108 are disposed thereon.
  • the copper silicide powder it is preferable to use a powder having an average particle size of 0.5 ⁇ m or more and 50 ⁇ m or less.
  • a mixture of copper silicide powders having a plurality of compositions (mass ratio Si / Cu) is used as the copper silicide powder.
  • Electrode sintering step S04 Using the power source device 106 of the electric current sintering apparatus 100, the temperature is raised by self-heating by applying a direct current between the pair of electrode portions 105a and 105b (electric current heating). Pressurization is performed at a predetermined pressure using the pair of electrode portions 105a and 105b. Further, the heater 109 is heated. Thus, the copper silicide powder is sintered to form the electrode 15 and the electrode 15 and the element body 11 are directly joined.
  • the sintering condition in the electrode sintering step S04 is that the heating temperature is in the range of 650 ° C. or higher and 850 ° C. or lower, and the holding time at this heating temperature is 0 minute or longer (for example, 1 second or longer), 3 minutes. It is preferable to be within the following range.
  • the pressure load is preferably in the range of 2 MPa to 40 MPa.
  • the atmosphere in the pressure-resistant housing 101 is preferably an inert atmosphere such as an argon atmosphere or a vacuum atmosphere. In a vacuum atmosphere, the pressure is preferably 5 Pa or less.
  • the copper silicide powder since a mixture of copper silicide powders having a plurality of compositions (atomic ratio Si / Cu) is used, a liquid phase is partially generated in the electrode sintering step S04, A liquid phase solidified portion formed by solidifying the liquid phase is formed on a part of the electrode 15.
  • the bondability between the element body 11 and the electrode 15 is improved.
  • the metal layer 16 is formed on the surface of the electrode 15 opposite to the element body 11.
  • the metal layer 16 can be formed by joining a metal foil material having excellent conductivity such as nickel, aluminum, copper, etc. to the electrode 15 using, for example, a brazing material.
  • a brazing material Ag brazing such as Ag—Cu—Zn—Cd, Ag—Cu—Sn, or the like can be used.
  • a 0.5 mm thick aluminum rolled plate is cut to the same size as the cross section of the thermoelectric element, and the metal layer 16 is formed on the electrode 15 using Ag brazing (BAg-1A (JIS)). did.
  • thermoelectric conversion element 10 in which the element body 11 made of a silicide-based thermoelectric conversion material and the electrode 15 made of a copper silicide sintered body are directly bonded is manufactured by the above-described steps.
  • thermoelectric conversion element 10 since the electrode 15 is composed of a sintered body of copper silicide, the thermal expansion coefficient of the element main body 11 made of a thermoelectric conversion material of a silicide compound (magnesium silicide) is reduced. The difference can be reduced, and the occurrence of cracks due to the thermal history during manufacture and use can be suppressed.
  • the copper silicide since the copper silicide has a relatively low melting point, a liquid phase is generated in part when the sintered body is formed, and thermal strain can be released, and the element main body 11 and the electrode 15 are cracked during manufacturing. It can be suppressed.
  • the electrode 15 and the element body 11 are directly bonded, and a liquid phase is generated in part when forming the sintered body, the bondability between the electrode 15 and the element body 11 is improved. The electrical resistance at the interface can be kept sufficiently low.
  • the terminal 3 and the electrode 15 can be joined relatively easily, and the terminal 3 and the electrode 15 can be joined. 15 can be improved.
  • the thickness of the electrode 15 is in the range of 10 ⁇ m or more and 300 ⁇ m or less, the rigidity of the electrode 15 is not unnecessarily high, and the element main body 11 is not cracked during manufacturing. While being able to suppress, the electrical conductivity in the electrode 15 is securable.
  • the Si / Cu atomic ratio Si / Cu in the copper silicide constituting the electrode 15 is in the range of 0.12 to 0.4, the electrical conductivity in the electrode 15 is Can be ensured, and the occurrence of cracks in the element body 11 during manufacturing can be suppressed.
  • thermoelectric conversion element As mentioned above, although embodiment of this invention was described, this invention is not limited to this, It can change suitably in the range which does not deviate from the technical idea of the invention.
  • thermoelectric conversion element Although it demonstrated as what comprises the thermoelectric conversion element and thermoelectric conversion module of a structure as shown in FIG. 1, it is not limited to this, The thermoelectric conversion element of this invention may be used.
  • the structure and arrangement of the terminals are not particularly limited.
  • the silicide compound constituting the element body is described as magnesium silicide (Mg 2 Si).
  • Mg 2 Si magnesium silicide
  • the present invention is not limited to this, and any other composition may be used as long as it has thermoelectric properties. It may be a silicide compound.
  • the copper silicide powder of a several composition (atomic ratio Si / Cu) was used as a copper silicide powder
  • the copper silicide powder of a single composition is used. be able to.
  • the entire electrode can be easily made into a liquid phase and bonded to the element body.
  • the entire electrode since the entire electrode is in a liquid phase, it is difficult for the electrode to be peeled from the element body, and conductivity can be ensured.
  • a cylindrical element body (size: diameter 20 mm ⁇ thickness 10 mm) made of a sintered body of magnesium silicide (Mg 2 Si) (porosity 2 vol%) was prepared.
  • both sides of the element body are filled with powder of the material shown in Table 1 and subjected to current sintering by the method described above.
  • a constant thickness electrode was formed.
  • the porosity of the electrode is shown in Table 1. Except for Example 5, a plurality of copper silicide powders having different Si / Cu ratios were mixed to obtain the ratio shown in Table 1, and in Example 5, a single composition having the Si / Cu ratio shown in Table 1 Copper silicide powder was used.
  • thermoelectric conversion elements of Examples and Comparative Examples the electrical resistance value, the presence or absence of cracks during production, and the Si / Cu ratio of the electrodes were evaluated as follows.
  • thermoelectric conversion element A 10 mm ⁇ 10 mm ⁇ 10 mm cubic sample 10 was cut out from the obtained thermoelectric conversion element and used for evaluation.
  • the circuit shown in FIG. 4 is assembled using a DC power source and a multimeter, and a constant current of 50 mA is passed between both electrodes 15, and one electrode 15 is digitally moved from 1 mm to 9 mm at 1 mm intervals. Each voltage was measured by bringing the electrode E of the multimeter into contact with the side surface of the element body 11. Next, the resistance value was obtained from the relationship between the voltage and the current, linearly approximated from the graph of the distance from the electrode end and the resistance value, and the intercept was defined as the electric resistance.
  • thermoelectric conversion element The presence or absence of cracks during production was determined by visually observing the thermoelectric conversion element when it was taken out from the electric sintering apparatus after it was subjected to current sintering to form an electrode, or after being cut into a thermoelectric conversion element size. It was confirmed.
  • Si / Cu ratio of electrode Regarding the Si / Cu ratio of the electrode, the Cu amount and the Si amount on the surface of the thermoelectric conversion element (surface on which the electrode is formed) are measured with EPMA (JXA-8800RL manufactured by JEOL Ltd.), and the Si / Cu ratio is determined. Asked. Specifically, the electrode surface of the cubic sample was polished, and the Cu value and the Si amount were measured with EPMA at any five locations on the electrode surface to obtain an average value. In the case where the measurement point is a cavity or the end of the particle, the center of the particle closest to the measurement point was measured.
  • EPMA JXA-8800RL manufactured by JEOL Ltd.
  • Comparative Example 1 in which the electrode was made of nickel silicide, cracking occurred during manufacture. For this reason, the electrical resistance value and the porosity of the electrode were not evaluated.
  • Comparative Example 2 in which the electrode was made of nickel, cracks occurred during production. For this reason, the electrical resistance value and the porosity of the electrode were not evaluated.
  • Comparative Example 3 in which the electrode was made of aluminum, cracks did not occur during manufacture, but the electrical resistance value was as high as 0.19 ⁇ .
  • Example 1 to 11 in which the electrodes were made of copper silicide, cracks did not occur during manufacture, and the electrical resistance value was low. From the above, according to Examples 1 to 11, the element body made of the thermoelectric conversion material of the silicide-based compound and the electrode are securely bonded, the electric resistance at the interface is sufficiently low, and the element body and the electrode are connected to each other. It was confirmed that a thermoelectric conversion element capable of suppressing the occurrence of cracking can be provided. In Example 11 in which the porosity exceeded 60%, although lower than that in Comparative Example 3, the electrical resistance value was slightly higher than those in Examples 1 to 10.
  • thermoelectric conversion element of the present invention the element body made of the thermoelectric conversion material of the silicide compound and the electrode are reliably bonded, the electrical resistance at the interface is sufficiently low, and the element body and the electrode are cracked. Therefore, industrial use is possible.

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Abstract

Provided is a thermoelectric conversion element comprising: an element body (11) that comprises a thermoelectric conversion material that is silicide compounds; and electrodes (15) respectively formed on one surface of the element body (11) and the other surface that is on the backside of the one surface. The electrodes (15) are formed of a sintered body of copper silicide, and the electrodes (15) and the element body (11) are directly joined.

Description

熱電変換素子Thermoelectric conversion element
　この発明は、シリサイド系化合物の熱電変換材料からなる素子本体と、この素子本体の一方の面および対向する他方の面にそれぞれ形成された電極とを備えた熱電変換素子に関する。　
　本願は、２０１８年３月１６日に日本に出願された特願２０１８－０４９８７４号、および、２０１９年３月６日に日本に出願された特願２０１９－０４０８４５号に基づき優先権を主張し、それらの内容をここに援用する。 The present invention relates to a thermoelectric conversion element including an element main body made of a thermoelectric conversion material of a silicide compound and electrodes formed on one surface of the element main body and the other surface facing each other.
This application claims priority based on Japanese Patent Application No. 2018-049874 filed in Japan on March 16, 2018 and Japanese Patent Application No. 2019-040845 filed in Japan on March 6, 2019. The contents thereof are incorporated herein.
　熱電変換材料からなる熱電変換素子は、ゼーベック効果、ペルティエ効果といった現象を利用し、熱と電気とを相互に変換可能な電子素子である。ゼーベック効果は熱エネルギーを電気エネルギーに変換する効果であり、熱電変換材料の両端に温度差を生じさせると起電力が発生する現象である。こうした起電力は熱電変換材料の特性によって決まる。近年ではこの効果を利用した熱電発電の開発が盛んである。 Thermoelectric conversion elements made of thermoelectric conversion materials are electronic elements that can convert heat and electricity to each other using phenomena such as the Seebeck effect and Peltier effect. The Seebeck effect is an effect of converting thermal energy into electric energy, and is a phenomenon in which an electromotive force is generated when a temperature difference is generated between both ends of the thermoelectric conversion material. Such electromotive force is determined by the characteristics of the thermoelectric conversion material. In recent years, thermoelectric power generation utilizing this effect has been actively developed.
　このような熱電変換素子（熱電変換材料）の特性を表す指標として、例えば以下の（１）式で表されるパワーファクター（ＰＦ）や、以下の（２）式で表される無次元性能指数（ＺＴ）が用いられている。熱電変換材料においては、一面と他面側とで温度差を維持する必要があるため、熱伝導性が低いことが好ましい。
　ＰＦ＝Ｓ２σ・・・（１）
　　但し、Ｓ：ゼーベック係数（Ｖ／Ｋ）、σ：電気伝導率（Ｓ／ｍ）
　ＺＴ＝Ｓ２σＴ／κ・・・（２）
　　但し、Ｔ＝絶対温度（Ｋ）、κ＝熱伝導率（Ｗ／（ｍ×Ｋ））
　素子本体を構成する熱電変換材料としては、マグネシウムシリサイド等のシリサイド系化合物が挙げられる。 As an index representing the characteristics of such a thermoelectric conversion element (thermoelectric conversion material), for example, the power factor (PF) expressed by the following formula (1) or the dimensionless figure of merit expressed by the following formula (2) (ZT) is used. In the thermoelectric conversion material, since it is necessary to maintain a temperature difference between one side and the other side, it is preferable that the thermal conductivity is low.
PF = S 2 σ (1)
Where S: Seebeck coefficient (V / K), σ: electrical conductivity (S / m)
ZT = S 2 σT / κ (2)
Where T = absolute temperature (K), κ = thermal conductivity (W / (m × K))
Examples of the thermoelectric conversion material constituting the element body include silicide-based compounds such as magnesium silicide.
　上述の熱電変換素子は、熱電変換材料の一端側及び他端側にそれぞれ電極が形成された構造とされている。マグネシウムシリサイド等のシリサイド系化合物の熱電変換材料からなる素子本体に形成される電極としては、ニッケルが用いられている。これは、マグネシウムシリサイド（Ｍｇ２Ｓｉ）の室温での熱膨張係数（１５．５×１０－６（／℃））と、ニッケルの室温での熱膨張係数（１５．２×１０－６（／℃））とが近似しているためである。 The thermoelectric conversion element described above has a structure in which electrodes are formed on one end side and the other end side of a thermoelectric conversion material. Nickel is used as an electrode formed on the element body made of a thermoelectric conversion material of a silicide-based compound such as magnesium silicide. This is because the thermal expansion coefficient of magnesium silicide (Mg 2 Si) at room temperature (15.5 × 10 −6 (/ ° C.)) and the thermal expansion coefficient of nickel at room temperature (15.2 × 10 −6 (/ ° C)) is approximate.
　しかしながら、上述の熱電変換素子を中温域（３００℃以上６００℃以下）で使用していると、素子本体のシリサイド系化合物のＳｉが電極側に拡散し、電極のニッケルがニッケルシリサイドとなる。このニッケルシリサイドは、室温での熱膨張係数が１２．０×１０－６（／℃）であることから、シリサイド系化合物の熱電変換材料からなる素子本体との熱膨張係数の差が大きくなり、素子本体にクラックが発生するおそれがあった。また、素子本体の電極との界面領域近傍の組成が変化してしまい、電気抵抗が高くなったり、強度が低下してしまったりするおそれがあった。 However, when the above-described thermoelectric conversion element is used in an intermediate temperature range (300 ° C. or more and 600 ° C. or less), Si of the silicide compound of the element body diffuses to the electrode side, and nickel of the electrode becomes nickel silicide. Since this nickel silicide has a thermal expansion coefficient at room temperature of 12.0 × 10 −6 (/ ° C.), the difference in thermal expansion coefficient from the element body made of a thermoelectric conversion material of a silicide compound increases. There was a risk of cracks occurring in the element body. Further, the composition in the vicinity of the interface region with the electrode of the element body changes, and there is a risk that the electrical resistance increases or the strength decreases.
　そこで、例えば、特許文献１では、熱電変換材料からなる素子本体と電極との間に、高融点金属シリサイドからなる中間層を形成した熱電変換素子が提案されている。この熱電変換素子においては、高融点金属シリサイドからなる中間層によって、素子本体と電極の間の元素の拡散を抑制している。
　また、特許文献２には、電極として、ニッケルシリサイドと金属ニッケルとの混合体を用いた熱電変換素子が提案されている。 Thus, for example, Patent Document 1 proposes a thermoelectric conversion element in which an intermediate layer made of a refractory metal silicide is formed between an element body made of a thermoelectric conversion material and an electrode. In this thermoelectric conversion element, diffusion of elements between the element body and the electrode is suppressed by an intermediate layer made of refractory metal silicide.
Patent Document 2 proposes a thermoelectric conversion element using a mixture of nickel silicide and metallic nickel as an electrode.
特開平０７－２０２２７４号公報Japanese Patent Application Laid-Open No. 07-202274 再公表ＷＯ２０１２／０７３９４６号公報Republished WO2012 / 073946
　ところで、特許文献１の熱電変換素子においては、高融点金属シリサイドからなる中間層を、蒸着法、スパッタ法、ＣＶＤ法で成膜しており、中間層を効率良く形成できなかった。また、中間層を厚く形成することが困難だった。このため、中間層により素子本体へ電極の元素が拡散することを十分に抑制できないおそれがあった。 Incidentally, in the thermoelectric conversion element of Patent Document 1, the intermediate layer made of refractory metal silicide is formed by vapor deposition, sputtering, or CVD, and the intermediate layer cannot be formed efficiently. Also, it has been difficult to form a thick intermediate layer. For this reason, there is a possibility that the electrode element cannot be sufficiently prevented from diffusing into the element body by the intermediate layer.
　特許文献２の熱電変換素子においては、電極としてニッケルシリサイドを用いているが、ニッケルシリサイドは、上述のように、マグネシウムシリサイド等からなる素子本体との熱膨張係数の差が大きく、製造時の熱履歴に起因した熱応力によって、素子本体や電極に割れが生じてしまうおそれがあった。さらに、金属ニッケルがマグネシウムシリサイド等からなる素子本体に直接接触した場合には、素子本体のＳｉが金属ニッケル側に拡散してしまい、素子本体の界面領域近傍の組成が変化し、電気抵抗が高くなったり、強度が低下するおそれがあった。 In the thermoelectric conversion element of Patent Document 2, nickel silicide is used as an electrode. However, as described above, nickel silicide has a large difference in thermal expansion coefficient from the element main body made of magnesium silicide or the like, and heat during manufacture is low. There was a possibility that the element main body and the electrode were cracked by the thermal stress resulting from the history. Furthermore, when metallic nickel is in direct contact with the element body made of magnesium silicide or the like, Si in the element body diffuses to the metallic nickel side, the composition in the vicinity of the interface region of the element body changes, and the electrical resistance is high. Or the strength may be reduced.
　本発明は、前述した事情に鑑みてなされたものであって、シリサイド系化合物の熱電変換材料からなる素子本体と電極とが確実に接合され、接合界面における電気抵抗が十分に低く、かつ、素子本体や電極に割れが生じることを抑制できる熱電変換素子を提供することを目的とする。 The present invention has been made in view of the above-described circumstances, and the element body made of a thermoelectric conversion material of a silicide compound and the electrode are reliably bonded, the electric resistance at the bonding interface is sufficiently low, and the element It aims at providing the thermoelectric conversion element which can suppress that a main body and an electrode generate | occur | produce a crack.
　上記課題を解決するために、本発明の熱電変換素子は、シリサイド系化合物の熱電変換材料からなる素子本体と、この素子本体の一方の面および対向する他方の面にそれぞれ形成された電極とを備え、前記電極は、銅シリサイドの焼結体で構成されており、前記電極と前記素子本体とが直接接合されている。 In order to solve the above problems, a thermoelectric conversion element of the present invention includes an element body made of a thermoelectric conversion material of a silicide compound, and electrodes formed on one surface of the element body and the other surface facing each other. The electrode is made of a sintered body of copper silicide, and the electrode and the element body are directly joined.
　この熱電変換素子によれば、電極が銅シリサイドの焼結体で構成されているので、シリサイド系化合物の熱電変換材料からなる素子本体との熱膨張係数の差を小さくできる。銅シリサイドは比較的融点が低いので、電極となる焼結体を形成する際に銅シリサイドの少なくとも一部に液相が生じ、熱歪を解放できる。よって、製造時に、素子本体及び電極に割れが生じることを抑制できる。電極となる焼結体を形成する際には、銅シリサイドの全体を液相にしてもよい。
　また、前記電極と前記素子本体とが直接接合されており、さらに、上述のように、電極となる焼結体を形成する際に銅シリサイドの少なくとも一部に液相が生じるから、前記電極と前記素子本体とを十分に接合することができ、界面における電気抵抗を十分に低く抑えることができる。 According to this thermoelectric conversion element, since the electrode is composed of a sintered body of copper silicide, the difference in thermal expansion coefficient from the element main body made of a thermoelectric conversion material of a silicide compound can be reduced. Since copper silicide has a relatively low melting point, a liquid phase is generated in at least a part of copper silicide when a sintered body to be an electrode is formed, and thermal strain can be released. Therefore, it can suppress that a crack arises in an element main part and an electrode at the time of manufacture. When forming a sintered body to be an electrode, the entire copper silicide may be in a liquid phase.
Further, since the electrode and the element main body are directly joined, and as described above, a liquid phase is generated in at least a part of the copper silicide when the sintered body to be the electrode is formed. The element main body can be sufficiently bonded, and the electrical resistance at the interface can be suppressed sufficiently low.
　本発明の熱電変換素子においては、前記電極の前記素子本体とは反対側の面に金属層が形成されていてもよい。この場合、前記素子本体とは反対側の面に形成された金属層により、端子との接合性を向上させることが可能となる。 In the thermoelectric conversion element of the present invention, a metal layer may be formed on the surface of the electrode opposite to the element body. In this case, the metal layer formed on the surface opposite to the element body can improve the bondability with the terminal.
　本発明の熱電変換素子においては、前記電極の厚さが１０μｍ以上３００μｍ以下の範囲内であることが好ましい。この場合、前記電極の厚さを３００μｍ以下とすることにより、電極の剛性が必要以上に高くならず、製造時における素子本体の割れの発生を抑制できる。一方、前記電極の厚さを１０μｍ以上とすることにより、電極における電気伝導度を確保できる。 In the thermoelectric conversion element of the present invention, the thickness of the electrode is preferably in the range of 10 μm or more and 300 μm or less. In this case, by setting the thickness of the electrode to 300 μm or less, the rigidity of the electrode does not become higher than necessary, and the occurrence of cracks in the element body during manufacturing can be suppressed. On the other hand, the electrical conductivity in an electrode is securable by making the thickness of the said electrode 10 micrometers or more.
　本発明の熱電変換素子においては、前記電極は、銅シリサイドの焼結体で構成されており、前記銅シリサイドにおけるＳｉとＣｕの原子数比Ｓｉ／Ｃｕが０．１２以上０．４以下の範囲内とされていることが好ましい。この場合、電極を構成する銅シリサイドにおけるＳｉとＣｕの原子数比Ｓｉ／Ｃｕが０．１２以上０．４以下の範囲内とされているので、電極における電気伝導度を高く確保できるとともに、製造時における素子本体の割れの発生を抑制できる。 In the thermoelectric conversion element of the present invention, the electrode is composed of a sintered body of copper silicide, and the atomic ratio Si / Cu of Si / Cu in the copper silicide is in the range of 0.12 to 0.4. It is preferable to be inside. In this case, since the Si / Cu atomic ratio Si / Cu in the copper silicide constituting the electrode is in the range of 0.12 or more and 0.4 or less, it is possible to ensure high electrical conductivity in the electrode and to manufacture the electrode. Occurrence of cracks in the element body at the time can be suppressed.
さらに、本発明の熱電変換素子においては、前記電極が銅シリサイドの焼結体で構成されており、前記銅シリサイドにおける気孔率が６０％以下であることが好ましい。この場合、電極を構成する銅シリサイドにおける気孔率が６０％以下とされているので、電気抵抗が高くなることを抑制できる。 Furthermore, in the thermoelectric conversion element of this invention, it is preferable that the said electrode is comprised with the sintered compact of the copper silicide, and the porosity in the said copper silicide is 60% or less. In this case, since the porosity of the copper silicide constituting the electrode is 60% or less, it is possible to suppress an increase in electrical resistance.
　本発明によれば、シリサイド系化合物の熱電変換材料からなる素子本体と電極とが確実に接合され、界面における電気抵抗が十分に低く、かつ、素子本体や電極に割れが生じることを抑制できる。 According to the present invention, the element body made of the thermoelectric conversion material of the silicide compound and the electrode are reliably bonded, the electrical resistance at the interface is sufficiently low, and the occurrence of cracks in the element body and the electrode can be suppressed.
本発明の第一の実施形態である熱電変換素子、及び、この熱電変換素子を用いた熱電変換モジュールを示す断面図である。It is sectional drawing which shows the thermoelectric conversion element which is 1st embodiment of this invention, and the thermoelectric conversion module using this thermoelectric conversion element. 本発明の一実施形態である熱電変換素子の製造方法の一例を示すフロー図である。It is a flowchart which shows an example of the manufacturing method of the thermoelectric conversion element which is one Embodiment of this invention. 図２に示す熱電変換素子の製造方法で用いられる焼結装置の一例を示す断面図である。It is sectional drawing which shows an example of the sintering apparatus used with the manufacturing method of the thermoelectric conversion element shown in FIG. 本発明の実施例における電気抵抗の測定手段を示す説明図である。It is explanatory drawing which shows the measurement means of the electrical resistance in the Example of this invention.
　以下に、本発明の一実施形態である熱電変換素子について、添付した図面を参照して説明する。以下の各実施形態は、発明の趣旨をより良く理解させるために具体的に説明するものであり、特に指定のない限り、本発明を限定するものではない。以下の説明で用いる図面は、本発明の特徴をわかりやすくするために、便宜上、要部となる部分を拡大して示している場合があり、各構成要素の寸法比率などが実際と同じであるとは限らない。 Hereinafter, a thermoelectric conversion element according to an embodiment of the present invention will be described with reference to the accompanying drawings. The following embodiments are specifically described for better understanding of the gist of the invention, and do not limit the present invention unless otherwise specified. In the drawings used in the following description, in order to make the features of the present invention easier to understand, there is a case where a main part is shown in an enlarged manner for the sake of convenience. Not necessarily.
　本発明の実施形態である熱電変換素子１０について、図１から図３を参照して説明する。図１は、本発明の第一の実施形態である熱電変換素子１０、及び、この熱電変換素子１０を用いた熱電変換モジュール１を示す。図１に示す熱電変換モジュール１は、熱電変換素子１０と、この熱電変換素子１０の一方の面および他方の面に配設された端子３，３とを備えている。 A thermoelectric conversion element 10 according to an embodiment of the present invention will be described with reference to FIGS. 1 to 3. FIG. 1 shows a thermoelectric conversion element 10 according to a first embodiment of the present invention, and a thermoelectric conversion module 1 using the thermoelectric conversion element 10. A thermoelectric conversion module 1 shown in FIG. 1 includes a thermoelectric conversion element 10 and terminals 3 and 3 disposed on one surface and the other surface of the thermoelectric conversion element 10.
　熱電変換素子１０は、熱電変換材料からなる素子本体１１と、この素子本体１１の一方の面及び他方の面にそれぞれ形成された電極１５，１５とを備えている。素子本体１１は、図１に示すように、柱状に形成されており、柱形状の両端面に、それぞれ電極１５，１５が配設されている。素子本体１１の形状は限定されないが、直方体状、円柱状、多角柱状、楕円柱状などであってもよい。素子本体１１の電極１５，１５が接合された両面は、互いに平行であってもよいし、多少傾斜していてもよい。 The thermoelectric conversion element 10 includes an element main body 11 made of a thermoelectric conversion material, and electrodes 15 and 15 formed on one surface and the other surface of the element main body 11, respectively. As shown in FIG. 1, the element body 11 is formed in a columnar shape, and electrodes 15 and 15 are disposed on both end surfaces of the columnar shape. The shape of the element body 11 is not limited, but may be a rectangular parallelepiped shape, a cylindrical shape, a polygonal column shape, an elliptical column shape, or the like. Both surfaces of the element body 11 to which the electrodes 15 and 15 are bonded may be parallel to each other or may be slightly inclined.
　素子本体１１を構成する熱電変換材料は、例えば、シリサイド系化合物からなり、本実施形態では、マグネシウムシリサイド（Ｍｇ２Ｓｉ）の焼結体で構成されていることが好ましい。マグネシウムシリサイド以外に使用可能なシリサイド系化合物としては、シリコンゲルマニウム（Ｓｉ－Ｇｅ）全率固溶体、マンガンシリコン（Ｍｎ－Ｓｉ）、鉄シリコン（Ｆｅ－Ｓｉ）などが挙げられる。 The thermoelectric conversion material constituting the element body 11 is made of, for example, a silicide compound, and in the present embodiment, the thermoelectric conversion material is preferably made of a sintered body of magnesium silicide (Mg 2 Si). Examples of silicide compounds that can be used in addition to magnesium silicide include silicon germanium (Si—Ge) total solid solution, manganese silicon (Mn—Si), and iron silicon (Fe—Si).
　素子本体１１を構成する熱電変換材料には、Ｌｉ，Ｎａ，Ｋ，Ｂ，Ａｌ，Ｇａ，Ｉｎ，Ｎ，Ｐ，Ａｓ，Ｓｂ，Ｂｉ，Ａｇ，Ｃｕ，Ｙのうち、少なくとも１種以上をドーパントとして含んでいてもよい。ドーパントを含む場合、素子本体１１中の合計の含有量は０．１質量％以上かつ３．０質量％以下であることが好ましいが、この範囲に限定はされない。 The thermoelectric conversion material constituting the element body 11 includes at least one of Li, Na, K, B, Al, Ga, In, N, P, As, Sb, Bi, Ag, Cu, and Y as a dopant. May be included. When the dopant is included, the total content in the element body 11 is preferably 0.1% by mass or more and 3.0% by mass or less, but is not limited to this range.
　熱電変換素子１０においては、電極１５が銅シリサイドの焼結体で構成されており、電極１５と素子本体１１とが直接接合されている。この例の電極１５は、素子本体１１の端面と同一の平面形状を有している。
　また、本実施形態においては、図１に示すように、電極１５のうち素子本体１１とは反対側の面には金属層１６が形成されている。すなわち、電極１５と端子３との間に金属層１６が配設されている。この例の金属層１６は、電極１５と同一の平面形状を有している。 In the thermoelectric conversion element 10, the electrode 15 is composed of a sintered body of copper silicide, and the electrode 15 and the element body 11 are directly joined. The electrode 15 in this example has the same planar shape as the end face of the element body 11.
In the present embodiment, as shown in FIG. 1, a metal layer 16 is formed on the surface of the electrode 15 on the side opposite to the element body 11. That is, the metal layer 16 is disposed between the electrode 15 and the terminal 3. The metal layer 16 in this example has the same planar shape as the electrode 15.
　銅シリサイドの焼結体で構成された電極１５の厚さは、１０μｍ以上３００μｍ以下の範囲内とされていることが好ましい。銅シリサイドの焼結体で構成された電極１５の厚さが１０μｍ以上であれば、電極１５における電気伝導度を確保できる。銅シリサイドの焼結体で構成された電極１５の厚さが３００μｍ以下であれば、電極１５の剛性が必要以上に高くならず、製造時における素子本体１１の割れの発生を抑制できる。
　銅シリサイドの焼結体で構成された電極１５の厚さの下限は、５０μｍ以上であることがより好ましい。銅シリサイドの焼結体で構成された電極１５の厚さの上限は、１５０μｍ以下であることがより好ましい。 The thickness of the electrode 15 made of a copper silicide sintered body is preferably in the range of 10 μm to 300 μm. If the thickness of the electrode 15 composed of a sintered body of copper silicide is 10 μm or more, the electrical conductivity in the electrode 15 can be ensured. If the thickness of the electrode 15 composed of a sintered body of copper silicide is 300 μm or less, the rigidity of the electrode 15 is not increased more than necessary, and the occurrence of cracks in the element body 11 during manufacturing can be suppressed.
The lower limit of the thickness of the electrode 15 made of a sintered copper silicide is more preferably 50 μm or more. The upper limit of the thickness of the electrode 15 made of a copper silicide sintered body is more preferably 150 μm or less.
　電極１５を構成する銅シリサイドにおいては、ＳｉとＣｕの原子数比Ｓｉ／Ｃｕが０．１２以上０．４以下の範囲内であることが好ましい。
　電極１５を構成する銅シリサイドは、複数の組成（Ｓｉ／Ｃｕ）の銅シリサイド紛を混合して焼成されたものとされており、その平均値が上述の範囲内となるように調整されている。例えば、銅シリサイドの具体例としては、Ｃｕ３Ｓｉ（原子数比１／３）やＣｕ７Ｓｉ（原子数比１／７）があり、これらを混合して焼結原料として用いることができる。 In the copper silicide constituting the electrode 15, the Si / Cu atomic ratio Si / Cu is preferably in the range of 0.12 to 0.4.
The copper silicide constituting the electrode 15 is fired by mixing copper silicide powders having a plurality of compositions (Si / Cu), and the average value thereof is adjusted to be within the above-described range. . For example, specific examples of copper silicide include Cu 3 Si (atomic ratio 1/3) and Cu 7 Si (atomic ratio 1/7), which can be mixed and used as a sintering raw material.
　電極１５を構成する銅シリサイドの原子数比Ｓｉ／Ｃｕが０．１２以上である場合、焼結原料は、Ｃｕ７Ｓｉの単相、あるいはＣｕ７Ｓｉと、少量の他の組成からなる銅シリサイドとの混合物から形成された銅シリサイド粉である。焼結原料の全体または一部を溶融させることにより、電極１５における電気伝導を確保でき、素子本体１１の割れも抑制できる。 If the atomic ratio Si / Cu of the copper silicide constituting the electrode 15 is 0.12 or more, the sintering raw material, single-phase Cu 7 Si, or a Cu 7 Si, copper silicide consisting of minor amounts of other composition Copper silicide powder formed from a mixture of By melting the whole or part of the sintering raw material, electrical conduction in the electrode 15 can be ensured, and cracking of the element body 11 can also be suppressed.
　電極１５を構成する銅シリサイドの原子数比Ｓｉ／Ｃｕが０．４以下である場合、焼結原料はＣｕ３Ｓｉの単相、あるいはＣｕ３Ｓｉと、少量の他の組成からなる銅シリサイドの混合物から形成された銅シリサイド粉である。焼結原料の全体または一部を溶融させることにより、電極１５における電気伝導を確保でき、製造時における素子本体１１の割れも抑制できる。
　電極１５を構成する銅シリサイドの原子数比Ｓｉ／Ｃｕの下限は、０．１３以上であることがより好ましい。電極１５を構成する銅シリサイドの原子数比Ｓｉ／Ｃｕの上限は、０．３５以下であることがより好ましい。 If the atomic ratio Si / Cu of the copper silicide constituting the electrode 15 is 0.4 or less, single-phase sintering material is Cu 3 Si, or a Cu 3 Si, copper silicide consisting of minor amounts of other composition It is a copper silicide powder formed from a mixture. By melting the whole or a part of the sintering raw material, electrical conduction in the electrode 15 can be secured, and cracking of the element body 11 at the time of manufacture can be suppressed.
The lower limit of the number ratio Si / Cu of the copper silicide constituting the electrode 15 is more preferably 0.13 or more. The upper limit of the atomic ratio Si / Cu of the copper silicide constituting the electrode 15 is more preferably 0.35 or less.
　本実施形態の電極１５においては、上述のように、複数の組成（Ｓｉ／Ｃｕ）の銅シリサイド紛を混合して焼成しているので、焼結時において少なくとも一部に液相が形成されており、電極１５の一部に液相が凝固して形成された液相凝固部を有している。この液相凝固部は、液相が形成されなかった領域と比較して空孔が少なく、密度が局所的に高くなっている。 In the electrode 15 of the present embodiment, as described above, a copper silicide powder having a plurality of compositions (Si / Cu) is mixed and fired, so that a liquid phase is formed at least partially during sintering. In addition, a part of the electrode 15 has a liquid phase solidification part formed by solidification of the liquid phase. This liquid phase solidification part has fewer voids and a locally higher density than the region where no liquid phase is formed.
　電極１５の全体としての気孔率は、本発明では限定されないが、０体積％以上かつ６０体積％以下であることが好ましく、より好ましくは０体積％以上かつ５０体積％以下である。電極１５内における液相凝固部の分布は限定されないが、液相凝固部は、素子本体１１側に集中して層状に分布していることが応力緩和の観点から好ましい。ただし、本発明では、液相凝固部が電極１５内の全域に亘ってほぼ均一に分布していてもよいし、金属層１６側に集中して層状に分布していてもよい。 The porosity of the electrode 15 as a whole is not limited in the present invention, but is preferably 0% by volume or more and 60% by volume or less, more preferably 0% by volume or more and 50% by volume or less. Although the distribution of the liquid phase solidified portion in the electrode 15 is not limited, it is preferable from the viewpoint of stress relaxation that the liquid phase solidified portion is concentrated and distributed in a layered manner on the element body 11 side. However, in the present invention, the liquid phase solidified portions may be distributed substantially uniformly over the entire area of the electrode 15, or may be concentrated and distributed in a layered manner on the metal layer 16 side.
電極１５の気孔率は、下記の方法により求めた。
まず、銅シリサイド電極を形成する前のシリサイド焼結体の重量を測定する。次に、電極を形成後、両面それぞれの電極の厚さを光学顕微鏡又は走査型電子顕微鏡で５か所測定し、その平均を求める。次に、両面それぞれの電極面のサイズ（縦幅、横幅や半径等）をノギス又はマイクロメータで測定し、両面それぞれの電極面の表面積を求める。この表面積と、両面それぞれの電極の厚さとから、両面それぞれの電極部分の体積を求める。次に、シリサイド焼結体と電極が一体となった状態の重さを量り、シリサイド焼結体の重さを引くことで、電極部分の重さを求める。両面の電極部分の重さと体積から電極部分の密度を求める。このように求められた密度を測定密度とする。一方、電極層をＥＰＭＡで分析した平均組成から真密度を推定算出し、（１００－（測定密度／真密度×１００）（％））の式からを気孔率を求めた。 The porosity of the electrode 15 was determined by the following method.
First, the weight of the silicide sintered body before forming the copper silicide electrode is measured. Next, after forming the electrodes, the thicknesses of the electrodes on both sides are measured at five locations with an optical microscope or a scanning electron microscope, and the average is obtained. Next, the size (vertical width, horizontal width, radius, etc.) of the electrode surfaces on both surfaces is measured with a caliper or a micrometer, and the surface areas of the electrode surfaces on both surfaces are obtained. From this surface area and the thickness of each electrode on both sides, the volume of the electrode part on each side is obtained. Next, the weight of the state in which the silicide sintered body and the electrode are integrated is weighed, and the weight of the electrode is obtained by subtracting the weight of the silicide sintered body. The density of the electrode parts is determined from the weight and volume of the electrode parts on both sides. The density thus obtained is taken as the measured density. On the other hand, the true density was estimated and calculated from the average composition obtained by analyzing the electrode layer with EPMA, and the porosity was determined from the equation (100− (measured density / true density × 100) (%)).
　金属層１６は、例えば、ニッケル，アルミニウム，銅等の導電性に優れた金属で構成されており、本実施形態においては、アルミニウムで構成されていることが好ましい。この金属層１６は、電極１５に対して金属箔等を例えばろう付け等によって接合することによって形成されている。金属層１６の厚さは限定はされないが、０．１ｍｍ以上２．０ｍｍ以下の範囲内とされていることが好ましい。 The metal layer 16 is made of, for example, a metal having excellent conductivity, such as nickel, aluminum, or copper. In the present embodiment, the metal layer 16 is preferably made of aluminum. The metal layer 16 is formed by bonding a metal foil or the like to the electrode 15 by, for example, brazing. The thickness of the metal layer 16 is not limited, but is preferably in the range of 0.1 mm to 2.0 mm.
　端子３は、導電性に優れた金属材料、例えば、銅やアルミニウムなどの板材から形成されている。本実施形態では、アルミニウムの圧延板を用いることが好ましい。電極１５に形成された金属層１６と端子３とは、例えば、Ａｇろう、Ａｇめっき等によって接合できる。この実施形態の一対の端子３は、素子本体１１から見て互いに反対側へ延び、かつ、互いに平行に配置されているが、本発明はこの配置に限定されない。 The terminal 3 is formed of a metal material having excellent conductivity, for example, a plate material such as copper or aluminum. In the present embodiment, it is preferable to use an aluminum rolled plate. The metal layer 16 formed on the electrode 15 and the terminal 3 can be joined by, for example, Ag brazing, Ag plating, or the like. The pair of terminals 3 of this embodiment extend to opposite sides as viewed from the element body 11 and are arranged in parallel to each other, but the present invention is not limited to this arrangement.
　次に、上述した熱電変換素子１０の製造方法の一例を図２及び図３を参照して説明する。 Next, an example of a method for manufacturing the thermoelectric conversion element 10 described above will be described with reference to FIGS.
（シリサイド化合物粉末準備工程Ｓ０１）
　まず、素子本体を構成する熱電変換材料の母相となるシリサイド化合物粉末（マグネシウムシリサイド粉末）を準備する。このシリサイド化合物粉末準備工程Ｓ０１においては、シリサイド化合物インゴット（マグネシウムシリサイド）を製造し、これを粉砕して篩分けすることにより、所定の粒径のシリサイド化合物粉末（マグネシウムシリサイド粉末）を製造する。市販のマグネシウム系化合物粉（マグネシウムシリサイド粉）を用いてもよい。シリサイド化合物粉末（マグネシウムシリサイド粉末）の平均粒径は、０．５μｍ以上１００μｍ以下の範囲内とすることが好ましい。 (Silicide compound powder preparation step S01)
First, a silicide compound powder (magnesium silicide powder) serving as a parent phase of a thermoelectric conversion material constituting the element body is prepared. In this silicide compound powder preparation step S01, a silicide compound ingot (magnesium silicide) is manufactured, and this is pulverized and sieved to manufacture a silicide compound powder (magnesium silicide powder) having a predetermined particle size. Commercially available magnesium compound powder (magnesium silicide powder) may be used. The average particle diameter of the silicide compound powder (magnesium silicide powder) is preferably in the range of 0.5 μm to 100 μm.
（素子本体焼結工程Ｓ０２）
　次に、上述のようにして得られたシリサイド化合物粉末を、加圧しながら加熱して焼結体を得る。本実施形態では、素子本体焼結工程Ｓ０２において、図３に示す焼結装置（通電焼結装置１００）を用いる。 (Element body sintering step S02)
Next, the silicide compound powder obtained as described above is heated under pressure to obtain a sintered body. In the present embodiment, a sintering apparatus (electric current sintering apparatus 100) shown in FIG. 3 is used in the element body sintering step S02.
　図３に示す焼結装置（通電焼結装置１００）は、例えば、耐圧筐体１０１と、この耐圧筐体１０１の内部を減圧する真空ポンプ１０２と、耐圧筐体１０１内に配された中空筒形のカーボンモールド１０３と、カーボンモールド１０３内に充填された焼結原料粉Ｑを加圧しつつ電流を印加する一対の電極部１０５ａ，１０５ｂと、電極部１０５ａ，１０５ｂ間に電圧を印加する電源装置１０６とを備えている。電極部１０５ａ，１０５ｂと焼結原料粉Ｑとの間には、カーボン板１０７、カーボンシート１０８がそれぞれ配される。これ以外にも、図示しない温度計、変位計などを有している。 The sintering apparatus (electric current sintering apparatus 100) shown in FIG. 3 includes, for example, a pressure-resistant housing 101, a vacuum pump 102 that depressurizes the inside of the pressure-resistant housing 101, and a hollow cylinder disposed in the pressure-resistant housing 101. -Shaped carbon mold 103, a pair of electrode portions 105a and 105b for applying a current while pressurizing sintering raw material powder Q filled in carbon mold 103, and a power supply device for applying a voltage between electrode portions 105a and 105b 106. A carbon plate 107 and a carbon sheet 108 are disposed between the electrode portions 105a and 105b and the sintering raw material powder Q, respectively. In addition to this, a thermometer, a displacement meter, etc. (not shown) are provided.
　本実施形態においては、カーボンモールド１０３の外周側にヒーター１０９が配設されている。ヒーター１０９は、カーボンモールド１０３の外周側の全面を覆うように四つの側面に配置されている。ヒーター１０９としては、カーボンヒーターやニクロム線ヒーター、モリブデンヒーター、カンタル線ヒーター、高周波ヒーター等が利用できる。 In the present embodiment, a heater 109 is disposed on the outer peripheral side of the carbon mold 103. The heater 109 is disposed on four side surfaces so as to cover the entire outer peripheral side of the carbon mold 103. As the heater 109, a carbon heater, a nichrome wire heater, a molybdenum heater, a Kanthal wire heater, a high frequency heater, or the like can be used.
　素子本体焼結工程Ｓ０２においては、まず、図３に示す通電焼結装置１００のカーボンモールド１０３内に、焼結原料粉Ｑを充填する。カーボンモールド１０３は、例えば、内部がグラファイトシートやカーボンシートで覆われている。電源装置１０６を用いて、一対の電極部１０５ａ，１０５ｂ間に直流電流を流して、焼結原料粉Ｑに電流を流すことによって自己発熱により昇温する（通電加熱）。一対の電極部１０５ａ，１０５ｂのうち、可動側の電極部１０５ａを焼結原料粉Ｑに向けて移動させ、固定側の電極部１０５ｂとの間で焼結原料粉Ｑを所定の圧力で加圧するとともにヒーター１０９を加熱させる。これにより、焼結原料粉末Ｑの自己発熱及びヒーター１０９からの熱と、加圧により、焼結原料粉Ｑを焼結させる。 In the element body sintering step S02, first, the raw material powder Q is filled into the carbon mold 103 of the electric current sintering apparatus 100 shown in FIG. For example, the carbon mold 103 is covered with a graphite sheet or a carbon sheet. Using the power supply device 106, a direct current is passed between the pair of electrode portions 105a and 105b, and a current is passed through the sintered raw material powder Q to raise the temperature by self-heating (electric heating). Of the pair of electrode portions 105a and 105b, the movable electrode portion 105a is moved toward the sintering raw material powder Q, and the sintering raw material powder Q is pressurized at a predetermined pressure with the fixed electrode portion 105b. At the same time, the heater 109 is heated. As a result, the sintered raw material powder Q is sintered by self-heating of the sintered raw material powder Q, heat from the heater 109, and pressurization.
　本実施形態においては、素子本体焼結工程Ｓ０２における焼結条件は、焼結原料粉Ｑの加熱温度が６５０℃以上１０３０℃以下の範囲内、この加熱温度での保持時間が０分以上（例えば１秒以上）、３分以下とされている。加圧荷重が１５ＭＰａ以上６０ＭＰａ以下とされている。耐圧筐体１０１内の雰囲気は、アルゴン雰囲気などの不活性雰囲気や真空雰囲気とすることが好ましい。真空雰囲気とする場合は、圧力５Ｐａ以下にすることが好ましい。 In the present embodiment, the sintering conditions in the element body sintering step S02 are such that the heating temperature of the sintering raw material powder Q is in the range of 650 ° C. or more and 1030 ° C. or less, and the holding time at this heating temperature is 0 minute or more (for example, 1 second or longer) and 3 minutes or shorter. The pressure load is 15 MPa or more and 60 MPa or less. The atmosphere in the pressure-resistant housing 101 is preferably an inert atmosphere such as an argon atmosphere or a vacuum atmosphere. In a vacuum atmosphere, the pressure is preferably 5 Pa or less.
　素子本体焼結工程Ｓ０２では、焼結原料粉Ｑに直流電流を流す際に、一方の電極部１０５ａと他方の電極部１０５ｂの極性を所定の時間間隔で変更することが好ましい。すなわち、一方の電極部１０５ａを陽極及び他方の電極部１０５ｂを陰極として通電する状態と、一方の電極部１０５ａを陰極及び他方の電極部１０５ｂを陽極として通電する状態とを交互に行う。本実施形態では、所定の時間間隔を１０秒以上３００秒以下の範囲内に設定することが好ましい。以上の工程により、素子本体１１（熱電変換材料）が製造される。交互に電流の向きを切り替えることにより、素子本体１１の均質性が高められる利点が得られる。 In the element body sintering step S02, it is preferable to change the polarities of the one electrode portion 105a and the other electrode portion 105b at a predetermined time interval when a direct current is passed through the sintered raw material powder Q. That is, the state where one electrode portion 105a is energized with the anode and the other electrode portion 105b as the cathode and the state where one electrode portion 105a is energized with the cathode and the other electrode portion 105b as the anode are alternately performed. In the present embodiment, it is preferable to set the predetermined time interval within a range of 10 seconds to 300 seconds. The element body 11 (thermoelectric conversion material) is manufactured through the above steps. By alternately switching the direction of the current, there is an advantage that the uniformity of the element body 11 is improved.
（銅シリサイド粉末充填工程Ｓ０３）
　次に、通電焼結装置１００のカーボンモールド１０３内に、銅シリサイド粉末と、シリサイド化合物の焼結体とを充填する。シリサイド化合物の焼結体の両端面及び側面のカーボンシートを除去し、焼結体の両端面を研磨紙で研磨する。カーボンモールド１０３に、カーボン板１０７、カーボンシート１０８を挿入し、所定量の銅シリサイド粉末を充填し、その後、シリサイド化合物の焼結体を挿入し、その上にさらに所定量の銅シリサイド粉末を充填し、その上にカーボン板１０７、カーボンシート１０８を配置する。 (Copper silicide powder filling step S03)
Next, the carbon mold 103 of the electric current sintering apparatus 100 is filled with copper silicide powder and a sintered body of a silicide compound. The carbon sheets on both end faces and side faces of the sintered body of the silicide compound are removed, and both end faces of the sintered body are polished with abrasive paper. A carbon plate 107 and a carbon sheet 108 are inserted into the carbon mold 103 and filled with a predetermined amount of copper silicide powder, then a sintered body of a silicide compound is inserted, and a predetermined amount of copper silicide powder is further filled thereon. Then, the carbon plate 107 and the carbon sheet 108 are disposed thereon.
　銅シリサイド粉末としては、平均粒径を０．５μｍ以上５０μｍ以下のものを用いることが好ましい。本実施形態においては、銅シリサイド粉末として、複数の組成（質量比Ｓｉ／Ｃｕ）の銅シリサイド紛を混合したものを用いている。 As the copper silicide powder, it is preferable to use a powder having an average particle size of 0.5 μm or more and 50 μm or less. In the present embodiment, a mixture of copper silicide powders having a plurality of compositions (mass ratio Si / Cu) is used as the copper silicide powder.
（電極焼結工程Ｓ０４）
　通電焼結装置１００の電源装置１０６を用いて、一対の電極部１０５ａ，１０５ｂ間に直流電流を流すことによって自己発熱により昇温する（通電加熱）。一対の電極部１０５ａ，１０５ｂを用いて所定の圧力で加圧する。また、ヒーター１０９を加熱させる。これにより、銅シリサイド粉末を焼結して電極１５を形成するとともに、電極１５と素子本体１１とを直接接合する。 (Electrode sintering step S04)
Using the power source device 106 of the electric current sintering apparatus 100, the temperature is raised by self-heating by applying a direct current between the pair of electrode portions 105a and 105b (electric current heating). Pressurization is performed at a predetermined pressure using the pair of electrode portions 105a and 105b. Further, the heater 109 is heated. Thus, the copper silicide powder is sintered to form the electrode 15 and the electrode 15 and the element body 11 are directly joined.
　本実施形態においては、電極焼結工程Ｓ０４における焼結条件は、加熱温度が６５０℃以上８５０℃以下の範囲内、この加熱温度での保持時間が０分以上（例えば１秒以上）、３分以下の範囲内とされることが好ましい。加圧荷重は２ＭＰａ以上４０ＭＰａ以下の範囲内とされることが好ましい。耐圧筐体１０１内の雰囲気はアルゴン雰囲気などの不活性雰囲気や真空雰囲気とすることが好ましい。真空雰囲気とする場合は、圧力５Ｐａ以下とすることが好ましい。 In the present embodiment, the sintering condition in the electrode sintering step S04 is that the heating temperature is in the range of 650 ° C. or higher and 850 ° C. or lower, and the holding time at this heating temperature is 0 minute or longer (for example, 1 second or longer), 3 minutes. It is preferable to be within the following range. The pressure load is preferably in the range of 2 MPa to 40 MPa. The atmosphere in the pressure-resistant housing 101 is preferably an inert atmosphere such as an argon atmosphere or a vacuum atmosphere. In a vacuum atmosphere, the pressure is preferably 5 Pa or less.
　本実施形態においては、銅シリサイド粉末として、複数の組成（原子数比Ｓｉ／Ｃｕ）の銅シリサイド紛を混合したものを用いているので、電極焼結工程Ｓ０４において一部に液相が生じ、電極１５の一部に液相が凝固して形成された液相凝固部が形成される。電極焼結工程Ｓ０４において液相が生じることによって、素子本体１１と電極１５との接合性が向上することになる。 In the present embodiment, as the copper silicide powder, since a mixture of copper silicide powders having a plurality of compositions (atomic ratio Si / Cu) is used, a liquid phase is partially generated in the electrode sintering step S04, A liquid phase solidified portion formed by solidifying the liquid phase is formed on a part of the electrode 15. When the liquid phase is generated in the electrode sintering step S04, the bondability between the element body 11 and the electrode 15 is improved.
（金属層形成工程Ｓ０５）
　次に、電極１５の素子本体１１とは反対側の面に金属層１６を形成する。金属層１６は、ニッケル，アルミニウム，銅等の導電性に優れた金属の箔材を電極１５に、例えば、ろう材を用いて接合することで形成できる。ろう材としては、Ａｇ－Ｃｕ－Ｚｎ－Ｃｄ、Ａｇ－Ｃｕ－ＳｎなどのＡｇろう等を用いることができる。
　本実施形態においては、厚さ０．５ｍｍのアルミニウムの圧延板を熱電素子の断面と同じサイズに切断し、Ａｇろう（ＢＡｇ－１Ａ（ＪＩＳ））を用いて、電極１５に金属層１６を形成した。 (Metal layer forming step S05)
Next, the metal layer 16 is formed on the surface of the electrode 15 opposite to the element body 11. The metal layer 16 can be formed by joining a metal foil material having excellent conductivity such as nickel, aluminum, copper, etc. to the electrode 15 using, for example, a brazing material. As the brazing material, Ag brazing such as Ag—Cu—Zn—Cd, Ag—Cu—Sn, or the like can be used.
In this embodiment, a 0.5 mm thick aluminum rolled plate is cut to the same size as the cross section of the thermoelectric element, and the metal layer 16 is formed on the electrode 15 using Ag brazing (BAg-1A (JIS)). did.
　上述の工程により、シリサイド系化合物の熱電変換材料からなる素子本体１１と、銅シリサイドの焼結体からなる電極１５と、が直接接合された熱電変換素子１０が製造される。 The thermoelectric conversion element 10 in which the element body 11 made of a silicide-based thermoelectric conversion material and the electrode 15 made of a copper silicide sintered body are directly bonded is manufactured by the above-described steps.
　以上のような熱電変換素子１０によれば、電極１５が銅シリサイドの焼結体で構成されているので、シリサイド系化合物（マグネシウムシリサイド）の熱電変換材料からなる素子本体１１との熱膨張係数の差を小さくすることが可能となり、製造時や使用時の熱履歴による割れの発生を抑制できる。
　また、銅シリサイドは比較的融点が低いので、焼結体を形成する際に一部に液相が生じ、熱歪を解放することができ、製造時において、素子本体１１及び電極１５に割れが生じることを抑制できる。
　さらに、電極１５と素子本体１１とが直接接合されており、焼結体を形成する際に一部に液相が生じることで、電極１５と素子本体１１との接合性が向上しているので、界面における電気抵抗を十分に低く抑えることができる。 According to the thermoelectric conversion element 10 as described above, since the electrode 15 is composed of a sintered body of copper silicide, the thermal expansion coefficient of the element main body 11 made of a thermoelectric conversion material of a silicide compound (magnesium silicide) is reduced. The difference can be reduced, and the occurrence of cracks due to the thermal history during manufacture and use can be suppressed.
In addition, since the copper silicide has a relatively low melting point, a liquid phase is generated in part when the sintered body is formed, and thermal strain can be released, and the element main body 11 and the electrode 15 are cracked during manufacturing. It can be suppressed.
Furthermore, since the electrode 15 and the element body 11 are directly bonded, and a liquid phase is generated in part when forming the sintered body, the bondability between the electrode 15 and the element body 11 is improved. The electrical resistance at the interface can be kept sufficiently low.
　また、本実施形態においては、電極１５の素子本体１１とは反対側の面に金属層１６が形成されているので、端子３と電極１５とを比較的容易に接合できるとともに、端子３と電極１５との接合性を向上させることが可能となる。 In the present embodiment, since the metal layer 16 is formed on the surface of the electrode 15 opposite to the element body 11, the terminal 3 and the electrode 15 can be joined relatively easily, and the terminal 3 and the electrode 15 can be joined. 15 can be improved.
　また、本実施形態においては、電極１５の厚さが１０μｍ以上３００μｍ以下の範囲内とされているので、電極１５の剛性が必要以上に高くならず、製造時における素子本体１１の割れの発生を抑制できるとともに、電極１５における電気伝導度を確保できる。 Further, in the present embodiment, since the thickness of the electrode 15 is in the range of 10 μm or more and 300 μm or less, the rigidity of the electrode 15 is not unnecessarily high, and the element main body 11 is not cracked during manufacturing. While being able to suppress, the electrical conductivity in the electrode 15 is securable.
　さらに、本実施形態においては、電極１５を構成する銅シリサイドにおけるＳｉとＣｕの原子数比Ｓｉ／Ｃｕが０．１２以上０．４以下の範囲内とされているので、電極１５における電気伝導度を確保できるとともに、製造時における素子本体１１の割れの発生を抑制できる。 Furthermore, in this embodiment, since the Si / Cu atomic ratio Si / Cu in the copper silicide constituting the electrode 15 is in the range of 0.12 to 0.4, the electrical conductivity in the electrode 15 is Can be ensured, and the occurrence of cracks in the element body 11 during manufacturing can be suppressed.
　以上、本発明の実施形態について説明したが、本発明はこれに限定されることはなく、その発明の技術的思想を逸脱しない範囲で適宜変更可能である。例えば、本実施形態では、図１に示すような構造の熱電変換素子及び熱電変換モジュールを構成するものとして説明したが、これに限定されることはなく、本発明の熱電変換素子を用いていれば、端子の構造及び配置等に特に制限はない。 As mentioned above, although embodiment of this invention was described, this invention is not limited to this, It can change suitably in the range which does not deviate from the technical idea of the invention. For example, in this embodiment, although it demonstrated as what comprises the thermoelectric conversion element and thermoelectric conversion module of a structure as shown in FIG. 1, it is not limited to this, The thermoelectric conversion element of this invention may be used. For example, the structure and arrangement of the terminals are not particularly limited.
　また、本実施形態では、素子本体を構成するシリサイド系化合物をマグネシウムシリサイド（Ｍｇ２Ｓｉ）として説明したが、これに限定されることはなく、熱電特性を有するものであれば、その他の組成のシリサイド系化合物であってもよい。 In the present embodiment, the silicide compound constituting the element body is described as magnesium silicide (Mg 2 Si). However, the present invention is not limited to this, and any other composition may be used as long as it has thermoelectric properties. It may be a silicide compound.
　また、上記実施形態では、銅シリサイド粉末として、複数の組成（原子数比Ｓｉ／Ｃｕ）の銅シリサイド紛を混合したものを用いたが、これに限らず、単一組成の銅シリサイド粉末を用いることができる。この場合、電極焼結工程における焼結温度を制御することにより、容易に電極の全体を液相にして素子本体と接合させることもできる。この場合、電極の全体が液相になるので、素子本体から電極が剥離しにくくなるとともに、導電性も確保できる。 Moreover, in the said embodiment, what mixed the copper silicide powder of a several composition (atomic ratio Si / Cu) was used as a copper silicide powder, However, it is not restricted to this, The copper silicide powder of a single composition is used. be able to. In this case, by controlling the sintering temperature in the electrode sintering step, the entire electrode can be easily made into a liquid phase and bonded to the element body. In this case, since the entire electrode is in a liquid phase, it is difficult for the electrode to be peeled from the element body, and conductivity can be ensured.
　以下、本発明の効果を確認すべく実施した実験結果を説明する。 Hereinafter, the results of experiments conducted to confirm the effects of the present invention will be described.
　マグネシウムシリサイド（Ｍｇ２Ｓｉ）の焼結体（気孔率２体積％）からなる円柱状の素子本体（サイズ：直径２０ｍｍ×厚さ１０ｍｍ）を準備した。上述の実施形態で説明した図３に示す通電焼結装置を用いて、素子本体の両面に、表１に示す材質の粉末を充填して上述した方法で通電焼結し、素子本体の両端に一定厚さの電極を形成した。これにより、実施例１～１１及び比較例１～３の熱電変換素子を製造した。電極の気孔率は表１に記載した。実施例５を除いては、Ｓｉ／Ｃｕ比の異なる複数の銅シリサイド粉を混合して用いて表１記載の比率とし、実施例５では、表１記載のＳｉ／Ｃｕ比を有する単一組成の銅シリサイド粉を用いた。 A cylindrical element body (size: diameter 20 mm × thickness 10 mm) made of a sintered body of magnesium silicide (Mg 2 Si) (porosity 2 vol%) was prepared. Using the current sintering apparatus shown in FIG. 3 described in the above embodiment, both sides of the element body are filled with powder of the material shown in Table 1 and subjected to current sintering by the method described above. A constant thickness electrode was formed. Thus, the thermoelectric conversion elements of Examples 1 to 11 and Comparative Examples 1 to 3 were manufactured. The porosity of the electrode is shown in Table 1. Except for Example 5, a plurality of copper silicide powders having different Si / Cu ratios were mixed to obtain the ratio shown in Table 1, and in Example 5, a single composition having the Si / Cu ratio shown in Table 1 Copper silicide powder was used.
　得られた実施例及び比較例の熱電変換素子について、電気抵抗値、製造時の割れの有無、電極のＳｉ／Ｃｕ比を以下のようにして評価した。 For the obtained thermoelectric conversion elements of Examples and Comparative Examples, the electrical resistance value, the presence or absence of cracks during production, and the Si / Cu ratio of the electrodes were evaluated as follows.
（電気抵抗）
　得られた熱電変換素子から１０ｍｍ×１０ｍｍ×１０ｍｍの立方体のサンプル１０を切り出して評価に用いた。電気抵抗値の測定には、直流電源とマルチメータを用いて図４の回路を組み、両電極１５間に５０ｍＡの一定電流を流し、一方の電極１５より１ｍｍの位置から１ｍｍ間隔で９ｍｍまでデジタルマルチメータの電極Ｅを素子本体１１の側面に当接させて各電圧を測定した。次に、電圧と電流の関係から抵抗値を求め、電極端からの距離と抵抗値のグラフから直線近似して、その切片を電気抵抗とした。 (Electrical resistance)
A 10 mm × 10 mm × 10 mm cubic sample 10 was cut out from the obtained thermoelectric conversion element and used for evaluation. To measure the electrical resistance value, the circuit shown in FIG. 4 is assembled using a DC power source and a multimeter, and a constant current of 50 mA is passed between both electrodes 15, and one electrode 15 is digitally moved from 1 mm to 9 mm at 1 mm intervals. Each voltage was measured by bringing the electrode E of the multimeter into contact with the side surface of the element body 11. Next, the resistance value was obtained from the relationship between the voltage and the current, linearly approximated from the graph of the distance from the electrode end and the resistance value, and the intercept was defined as the electric resistance.
（製造時の割れ）
　製造時の割れの有無は、通電焼結し電極を形成したのち、通電焼結装置から取り出した際に、あるいは、熱電変換素子サイズに切断後に、熱電変換素子を目視で観察し、割れの有無を確認した。 (Cracking during manufacturing)
The presence or absence of cracks during production was determined by visually observing the thermoelectric conversion element when it was taken out from the electric sintering apparatus after it was subjected to current sintering to form an electrode, or after being cut into a thermoelectric conversion element size. It was confirmed.
（電極のＳｉ／Ｃｕ比）
　電極のＳｉ／Ｃｕ比については、熱電変換素子の表面（電極が形成されている面）のＣｕ量及びＳｉ量をＥＰＭＡ（日本電子株式会社製ＪＸＡ－８８００ＲＬ）で測定し、Ｓｉ／Ｃｕ比を求めた。
具体的には、前記立方体サンプルの電極面を研磨して、電極面の任意の５か所をＥＰＭＡにてＣｕ量及びＳｉ量を測定して平均値を求めた。なお、測定点が空洞の場合や、粒子の端の場合は、測定点にもっとも近い粒子の中心部を測定した。 (Si / Cu ratio of electrode)
Regarding the Si / Cu ratio of the electrode, the Cu amount and the Si amount on the surface of the thermoelectric conversion element (surface on which the electrode is formed) are measured with EPMA (JXA-8800RL manufactured by JEOL Ltd.), and the Si / Cu ratio is determined. Asked.
Specifically, the electrode surface of the cubic sample was polished, and the Cu value and the Si amount were measured with EPMA at any five locations on the electrode surface to obtain an average value. In the case where the measurement point is a cavity or the end of the particle, the center of the particle closest to the measurement point was measured.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　電極をニッケルシリサイドで構成した比較例１においては、製造時に割れが生じた。このため、電気抵抗値と電極の気孔率については評価しなかった。電極をニッケルで構成した比較例２においては、製造時に割れが生じた。このため、電気抵抗値と電極の気孔率については評価しなかった。電極をアルミニウムで構成した比較例３においては、製造時に割れが生じなかったが、電気抵抗値が０．１９Ωと非常に高くなった。 In Comparative Example 1 in which the electrode was made of nickel silicide, cracking occurred during manufacture. For this reason, the electrical resistance value and the porosity of the electrode were not evaluated. In Comparative Example 2 in which the electrode was made of nickel, cracks occurred during production. For this reason, the electrical resistance value and the porosity of the electrode were not evaluated. In Comparative Example 3 in which the electrode was made of aluminum, cracks did not occur during manufacture, but the electrical resistance value was as high as 0.19Ω.
　これに対して、電極を銅シリサイドで構成した実施例１～１１においては、製造時に割れが生じず、電気抵抗値も低くなった。
　以上のことから、実施例１～１１によれば、シリサイド系化合物の熱電変換材料からなる素子本体と電極とが確実に接合され、界面における電気抵抗が十分に低く、かつ、素子本体や電極に割れが生じることを抑制できる熱電変換素子を提供できることが確認された。なお、気孔率が６０％を超えた実施例１１においては、比較例３よりも低いものの、実施例１～１０と比べると、電気抵抗値がやや高くなった。 On the other hand, in Examples 1 to 11 in which the electrodes were made of copper silicide, cracks did not occur during manufacture, and the electrical resistance value was low.
From the above, according to Examples 1 to 11, the element body made of the thermoelectric conversion material of the silicide-based compound and the electrode are securely bonded, the electric resistance at the interface is sufficiently low, and the element body and the electrode are connected to each other. It was confirmed that a thermoelectric conversion element capable of suppressing the occurrence of cracking can be provided. In Example 11 in which the porosity exceeded 60%, although lower than that in Comparative Example 3, the electrical resistance value was slightly higher than those in Examples 1 to 10.
　本発明の熱電変換素子によれば、シリサイド系化合物の熱電変換材料からなる素子本体と電極とが確実に接合され、界面における電気抵抗が十分に低く、かつ、素子本体や電極に割れが生じることを抑制できるから、産業上の利用が可能である。 According to the thermoelectric conversion element of the present invention, the element body made of the thermoelectric conversion material of the silicide compound and the electrode are reliably bonded, the electrical resistance at the interface is sufficiently low, and the element body and the electrode are cracked. Therefore, industrial use is possible.
１　熱電変換モジュール
３　端子
１０　熱電変換素子
１１　素子本体
１５　電極
１６　金属層 DESCRIPTION OF SYMBOLS 1 Thermoelectric conversion module 3 Terminal 10 Thermoelectric conversion element 11 Element main body 15 Electrode 16 Metal layer

Claims (5)

  1. 　シリサイド系化合物の熱電変換材料からなる素子本体と、この素子本体の一方の面および対向する他方の面にそれぞれ形成された電極とを備えた熱電変換素子であって、
    　前記電極は、銅シリサイドの焼結体で構成されており、前記電極と前記素子本体とが直接接合されていることを特徴とする熱電変換素子。     A thermoelectric conversion element comprising an element body made of a thermoelectric conversion material of a silicide compound and electrodes formed on one surface of the element body and the other surface facing each other,
    The said electrode is comprised with the sintered compact of copper silicide, and the said electrode and the said element main body are directly joined, The thermoelectric conversion element characterized by the above-mentioned.
  2. 　前記電極の前記素子本体とは反対側の面に金属層が形成されていることを特徴とする請求項１に記載の熱電変換素子。 The thermoelectric conversion element according to claim 1, wherein a metal layer is formed on a surface of the electrode opposite to the element body.
  3. 　前記電極の厚さが１０μｍ以上３００μｍ以下であることを特徴とする請求項１又は請求項２に記載の熱電変換素子。 The thermoelectric conversion element according to claim 1, wherein a thickness of the electrode is 10 μm or more and 300 μm or less.
  4. 　前記銅シリサイドにおけるＳｉとＣｕの原子数比Ｓｉ／Ｃｕが０．１２以上０．４以下であることを特徴とする請求項１から請求項３のいずれか一項に記載の熱電変換素子。 The thermoelectric conversion element according to any one of claims 1 to 3, wherein an atomic number ratio Si / Cu of Si and Cu in the copper silicide is 0.12 or more and 0.4 or less.
  5. 　前記銅シリサイドにおける気孔率が６０％以下であることを特徴とする請求項１から請求項４のいずれか一項に記載の熱電変換素子。 The thermoelectric conversion element according to any one of claims 1 to 4, wherein a porosity of the copper silicide is 60% or less.
PCT/JP2019/010818 2018-03-16 2019-03-15 Thermoelectric conversion element WO2019177147A1 (en)

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