JP2001345487A - Thermoelement and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermoelement having a thermoelectric performance higher than before by defining a condition for extrusion-molding a thermoelectric material. SOLUTION: A process (a) is provided where a thermoelectric material of a specified composition is pressurized in a first direction so that it is extruded from an extrusion die, for plastic deformation to provide a mold of thermoelectric material. In the process (a), a dice is used wherein a maximum value of distortion speed is within +30% of an average value of it over at least a half of deformation region of the thermoelectric material in the first direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoelectric element used for a thermoelectric module, and further relates to a method for manufacturing such a thermoelectric element.

[0002]

2. Description of the Related Art Thermoelectric elements refer to elements utilizing thermoelectric effects such as the Thomson effect, Peltier effect, and Seebeck effect, thermocouples, electronic cooling elements, etc., which have a simple structure, are easy to handle, and maintain stable characteristics. Because of its potential, widespread use is attracting attention. In particular, since the thermoelectric cooler is capable of local cooling and precise temperature control around room temperature, it is widely researched and developed for temperature control of optoelectronics and semiconductor lasers, and its application to small refrigerators and the like. Is being promoted.

As shown in FIG. 9, a thermoelectric module including such a thermoelectric element has two ceramic substrates 30 and 4.
0, a P-type element (P-type semiconductor) 50 and an N-type element (N-type semiconductor) 60 are connected via an electrode 70 to form a PN element pair. Are connected in series. A current introduction terminal (positive electrode) 80 is connected to the N-type element at one end of the series circuit of such a PN element pair, and a current introduction terminal (negative electrode) 90 is connected to the P-type element at the other end. I have. When a voltage is applied between the current introduction terminals 80 and 90 to cause a current to flow from the current introduction terminal (positive electrode) 80 to the current introduction terminal (negative electrode) 90 through a series circuit of PN element pairs, ceramic The substrate 30 is cooled and the ceramic substrate 40 is heated. As a result, a heat flow is generated as shown by the arrow in the figure.

[0004] Here, a figure of merit representing the performance of the thermoelectric element is represented by Z, and the figure of merit Z is expressed by the following equation using a specific resistance (resistivity) ρ, a thermal conductivity κ, and a Seebeck coefficient (thermoelectric power) α. It is represented by Note that the Seebeck coefficient α has a positive value in a P-type element and a negative value in an N-type element. Z = α ² / ρκ A thermoelectric element having a large figure of merit Z is desired.

Japanese Patent Laid-Open Publication Nos. 63-138789, 8-186299, and 10-56210 disclose extrusion molding, which is a kind of plastic deformation processing, for thermoelectric materials. It is stated that the performance index can be increased by applying the method to the subject.

[0006]

However, these publications do not disclose details of the conditions under which the extrusion molding should be performed. In view of the above, an object of the present invention is to provide a thermoelectric element having a higher thermoelectric conversion efficiency than the conventional one by clarifying the shape of a mold in a deformation region in the extrusion molding of a thermoelectric material.

[0007]

In order to solve the above problems, a method for manufacturing a thermoelectric element according to a first aspect of the present invention comprises:
A step (a) of applying a pressing force to a thermoelectric material having a predetermined composition in a first direction and extruding the same from an extrusion mold to plastically deform to obtain a molded article of the thermoelectric material; In (1), a die is used in which the maximum value of the strain rate is within + 30% of the average value of the strain rate in at least half of the deformation region of the thermoelectric material in the first direction.

Here, the step (a) may include a step of applying a pressing force in the axial direction to the round bar-shaped thermoelectric material and extruding it from an extrusion die to plastically deform to obtain a round bar-shaped molded product. good.

Further, according to a method of manufacturing a thermoelectric element according to a second aspect of the present invention, a pressing force is applied to a thermoelectric material having a predetermined composition in a first direction to extrude the thermoelectric material from an extrusion die. (A) obtaining a rectangular parallelepiped molded product by deforming in a third direction perpendicular to the first and second directions while restraining deformation in a second direction perpendicular to the direction of (a). In a), the strain rate of the thermoelectric material in the first direction is made substantially constant in at least half of the deformation region.

According to the present invention, the performance index Z is improved by changing the value of the Seebeck coefficient α or the specific resistance ρ of the thermoelectric element by making the crystal grains of the thermoelectric material finer and reducing the residual strain. Can be.

[0011] The above manufacturing method may further comprise, before the step (a), a step (b) of forming a green compact or a sintered body of the thermoelectric material by pressing the powdery thermoelectric material. desirable. As described above, by extruding the powdery thermoelectric material after cold pressing or hot pressing or current-heating sintering, the strength of the thermoelectric material can be increased, and chipping and cracking can be reduced. As the thermoelectric material, at least two of Bi, Te, Sb and Se are used.
It is desirable to contain more than one kind of element.

In the above manufacturing method, it is desirable that in the step (a), the thermoelectric material is extruded from an extrusion die by applying a pressing pressure to the thermoelectric material in the atmosphere, an inert gas atmosphere or a vacuum. In the step (a), the processing temperature is set to 350 to 600 ° C.
It is desirable to extrude the thermoelectric material from the extrusion mold by applying a pressing pressure to the thermoelectric material. The thermoelectric element according to the present invention is manufactured by using any one of the manufacturing methods described above.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. Note that the same components are denoted by the same reference numerals, and description thereof will be omitted. FIG.
3 is a flowchart illustrating a method for manufacturing a thermoelectric element according to an embodiment of the present invention.

First, in step S1, a raw material having a predetermined composition is weighed and sealed in a container. As a raw material of the thermoelectric material, for example, antimony (Sb) or bismuth (Bi) is used as a group V element, and selenium (Se) or tellurium (Te) is used as a group VI element. Group V elements and VI
The solid solution of the group III element has a hexagonal structure. Regarding the specific composition of the thermoelectric material, bismuth telluride (Bi ₂ Te ₃ ) and antimony telluride (Sb
P-type dopants may be added to a mixed crystal solid solution with ₂ Te ₃ ), or bismuth telluride (Bi ₂ Te ₃ ) and bismuth selenide (Bi ₂ Se ₃ ) may be used as a material for an N-type element. An N-type dopant can be added to the mixed crystal solid solution for use.

Next, in step S2, the raw material enclosed in the container is heated to dissolve the raw material, and then solidified, for example, by one-way solidification, to produce a solid solution as a thermoelectric material. Next, in step S3,
The thermoelectric material is pulverized using a stamp mill, a ball mill, or the like to form a powder of the thermoelectric material. In addition, this powder
Classify according to particle size. For example, this powder is sieved through a 150-mesh and a 400-mesh sieve, and what is left on the 400-mesh sieve is sorted to obtain a particle size of 34 to 1
The powder is adjusted to about 08 μm.

Next, in step S4, the powder is supplied into a glass ampoule having a predetermined capacity, evacuated, filled with hydrogen, sealed at 0.9 atm, and then heated in a heating furnace at 350 ° C. for 10 hours. By performing the heat treatment described above, the surface of the powder is reduced with hydrogen. Step S4 can be omitted. Also, instead of the above steps S2 to S4,
As shown in Step S5, the powder of the thermoelectric material may be formed by a centrifugal atomization method.

Step S4 or S5 is followed by step S
In 6, the powder is formed by cold pressing or hot pressing. At this time, powder molding may be performed using a molding die having the same shape as a die (extrusion die). In that case,
The step of cutting the molding material according to the size of the die can be omitted.

Next, in step S7, the thermoformed material formed by powder molding is extruded. Further, step S8
By slicing the thermoelectric material extruded in step S9 and dicing the sliced thermoelectric material in step S9, a thermoelectric element having a desired size is obtained.

The above-mentioned extrusion molding step (step S7) will be described in detail with reference to FIG. FIG.
It is a figure showing the extrusion molding device used in the manufacturing method of the thermoelectric element concerning one embodiment of the present invention. As shown in FIG. 2, the extrusion molding apparatus 10 includes a punch 13 which is a mold for extruding the thermoformed material 20 formed into a powder, and a die (extrusion mold) 14 for plastically deforming the thermoelectric material 20 extruded by the punch 13. In. The slide 11 is driven by, for example, a hydraulic actuator (hydraulic cylinder) to move the punch 13 up and down. The extrusion pressure of the punch 13 is measured by the load cell 12, and the extrusion direction z
Of the punch 13 is measured by the displacement meter 15. By monitoring the relationship between the measured value of the displacement meter 15 and the elapsed time, the drive of the slide 11 can be controlled so that the punch 13 pushes out the thermoelectric material 20 at a constant pushing speed.

On the base 17, a die 14 and
A heater 16 is provided so as to surround the periphery of the die 14. Thereby, the extrusion molding device 10 can also serve as a heating device. The temperature of the die 14 is
Is measured by the temperature sensor 18 arranged near the. By controlling the calorific value of the heater 16 by feeding back the measured value of the temperature sensor 18, the die 14 and the thermoelectric material 20 can be maintained at desired temperatures.

The thermoelectric material 20 is extruded by the punch 13 and undergoes plastic deformation when passing through the die 14, whereby an extruded product 21 is obtained. Extrusion is desirably performed in an inert gas atmosphere or vacuum while maintaining the processing temperature at 350 to 600 ° C. In this embodiment, the die 13 is fixed and the punch 13 is moved. However, on the contrary, the punch 13 may be fixed and the die 14 may be moved.

By the way, it has been found that the figure of merit of the thermoelectric element obtained by slicing and dicing this extruded product greatly changes depending on the shape and surface treatment of the die. These preferred conditions will be described with reference to FIGS.

FIG. 3 is a perspective view showing an outline of a plane strain extrusion die used in the present embodiment. The plane strain extrusion die 14 has a constant width in the Y direction orthogonal to the extrusion direction (Z direction), and has a reduced thickness in the X direction orthogonal to the Z direction and the Y direction. In FIG. 3, the thickness (inner diameter) on the inlet side of the flat strain extrusion die 14 is shown.
Is _denoted by A ₀ , and the thickness (inner diameter) on the outlet side is denoted by A ₁ . The extrusion ratio is represented by A ₀ / A ₁ . The shape of the curve inner diameter of the plane strain extrusion die 14 is throttled from A ₀ to A _1, the strain rate is greatly different in the plastic deformation of the thermoelectric material 20. The strain rate refers to a strain generated per unit time, and is obtained as follows.

First, a strain ε (z) at a distance z in the extrusion direction (Z direction) is determined. ε (z) = dx / x (z) = x ′ (z) / x (z) · d
z Here, x (z) represents a half of the inner diameter including the mold inner surface of the mold in a direction (X direction) orthogonal to the extrusion direction. Next, a general total distortion amount ε is expressed by the following equation.

(Equation 1) Here, z ₀ represents the distance in the Z direction at the start of pressing,
z ₁ represents the distance in the Z direction in the press end. As described above, the total strain ε is determined by the inner diameter of the die at the start of pressing and the inner diameter of the die at the end of pressing, and does not depend on the shape of the intermediate die.

Assuming that there is no change in the volume of the material and that the strain in the X direction is constant, the strain in the Z direction has a similar ratio. That is, press position in the X direction of the die shape When x ₀ at the _{beginning, z 0 · x 0 = z} · x = ( constant) Accordingly, the relationship between the strain epsilon _X distortion in the Z-direction epsilon _Z and X direction Ε _Z = ln (z / z ₀ ) = ln (x ₀ / x) = − ε _X Thus, the strain ε _{Z in the Z} direction and the strain ε _{X in the} X direction are:
The absolute amount is the same, only the sign of the distortion direction is reversed. Next, the strain rate ε ′ is

(Equation 2) It is expressed as For example, when ε ′ _y = 0 and ε ′ _z = −ε ′ _x ,

(Equation 3) Becomes

FIG. 4 is a diagram comparing the cross-sectional shape (a) of the plane strain extrusion die of the example with the cross-sectional shape (b) of the plane strain extrusion die of the comparative example when the extrusion ratio is 5. . On the other hand, FIG. 5 shows a cross-sectional shape (a) of the plane strain extrusion die of the example when the extrusion ratio is 15.
FIG. 7 is a diagram comparing a cross-sectional shape (b) of a plane strain extrusion die of a comparative example with a comparative example. 4 and 5, the horizontal axis represents the distance in the extrusion direction (Z direction), and the deformation region of the die is shown at 0 to 40 mm. The vertical axis indicates the extrusion width (the distance in the X direction from the extrusion axis).

In the embodiment, as shown in FIG. 4A and FIG. 5A, the cross-sectional shape of the die from the deformation region to the exit side is hyperbolic. On the other hand, in the comparative example, as shown in FIGS. 4B and 5B, the cross-sectional shape of the die from the deformation region to the exit side is a combination of an ellipse and a straight line.

FIG. 6 shows the change in the strain rate when the plane strain extrusion dies of the example and the comparative example are used when the extrusion ratio is 5. FIG. 7 shows the change in the strain rate when the plane strain extrusion dies of the example and the comparative example are used when the extrusion ratio is 15. 6 and 7, the horizontal axis represents the distance in the extrusion direction (Z direction), and the vertical axis represents the strain rate of the thermoelectric material. The extrusion speed is 1 mm / min.

As shown in FIGS. 6 and 7, according to the embodiment, the strain rate is substantially constant in most of the deformation area, at least in at least half the area. Note that, in the present application, that the strain rate is substantially constant means that the strain rate is in a range from the maximum value to 95% of the maximum value. More generally, the present invention is characterized by using a die in which the maximum value of the strain rate is within + 30% of the average value of the strain rate in more than half of the deformation region of the thermoelectric material. .

FIG. 8 is a diagram comparing the characteristics of extruded products manufactured by actually extruding a thermoelectric material using the plane strain extrusion dies of the example and the comparative example. Here, extrusion molding is performed using hot-pressed rapidly solidified powder as the thermoelectric material. Material No. Reference numerals 1 and 2 denote N-type thermoelectric elements. 3 and 4 are P-type thermoelectric elements. As shown in FIG. 8, according to the example, it is considered that the residual strain in the extruded product is reduced, the specific resistance ρ is reduced, and the value of the figure of merit Z is larger than that of the comparative example.

The surfaces of these dies are surface-treated so as to form a thin film of TiCrN or TiAlN. Thereby, the strength of the die is increased, and the extrusion is made smooth. In the above embodiment, a plane strain extrusion die is used. However, the present invention can be applied to a case where a round bar-shaped thermoelectric material is extruded using a round die to obtain a round bar-shaped molded product.

[0032]

As described above, according to the present invention, the Seebeck coefficient α or ratio of the thermoelectric element can be improved by improving the degree of crystal orientation of the thermoelectric material, reducing the crystal grain size and reducing the residual strain. The figure of merit Z can be improved by changing the value of the resistance ρ. Thereby, a thermoelectric element having higher thermoelectric performance than the conventional one can be provided.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating a method for manufacturing a thermoelectric element according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating an extrusion molding apparatus used in a method for manufacturing a thermoelectric element according to an embodiment of the present invention.

FIG. 3 is a perspective view showing an overview of a plane strain extrusion die used in one embodiment of the present invention.

FIG. 4 is a diagram comparing the cross-sectional shape of the flat strain extrusion die according to the example of the present invention with the cross-sectional shape of the flat strain extrusion die of the comparative example when the extrusion ratio is 5.

FIG. 5 is a diagram comparing the cross-sectional shape of the flat strain extrusion die according to the example of the present invention with the cross-sectional shape of the flat strain extrusion die of the comparative example when the extrusion ratio is 15.

FIG. 6 is a diagram comparing changes in strain rate when the plane strain extrusion dies of the example of the present invention and the comparative example are used when the extrusion ratio is 5.

FIG. 7 is a diagram comparing changes in strain rate when the plane strain extrusion dies of the example of the present invention and the comparative example are used, when the extrusion ratio is 15;

FIG. 8 is a diagram comparing the characteristics of extruded products manufactured by actually extruding a thermoelectric material using the plane strain extrusion dies of the example of the present invention and the comparative example.

FIG. 9 is a diagram showing a structure of a thermoelectric module including a thermoelectric element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Extruder 11 Slide 12 Load meter 13 Punch 14 Dice 15 Displacement gauge 16 Heater 17 Base 18 Temperature sensor 20 Thermoelectric material 21 Extruded product

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B22F 3/24 B22F 3/24 F H01L 35/16 H01L 35/16 (72) Inventor Kiyoharu Sasaki Hiratsuka, Kanagawa Prefecture 1200 Manda Ichimitsu Komatsu Seisakusho R & D Headquarters (72) Inventor Akio Konishi 1200 Manda 1200 Hiratsuka-shi, Kanagawa Prefecture Komatsu Seisakusho Research Headquarters (72) Inventor Goji Kajiura 1200 Manda 1200 Hiratsuka-shi Kanagawa Prefecture Komatsu Seisakusho Research Headquarters (72) Inventor Mitsuhiro Kuroki 1200 Manda, Hiratsuka-shi, Kanagawa Prefecture Komatsu Seisakusho Research Headquarters (72) Inventor Hiroyuki Tokunaga 1200 Manda, Hiratsuka-shi, Kanagawa Komatsu Seisakusho Research Headquarters (72) Inventor Hiroyuki Mizukami 1200 Manda, Hiratsuka-shi, Kanagawa Prefecture Inside of Komatsu Seisakusho Research Laboratory (72) Inventor Keisuke Ikeda Miyagi 02 Aoba, Aramaki, Aoba-ku, Sendai City, Department of Materials Processing, Faculty of Engineering, Tohoku University (72) Inventor Susumu Susumu Miura, Aoba, 02, Aramaki, Aoba-ku, Sendai, Miyagi Prefecture Department of Materials Processing, Faculty of Engineering, Tohoku Univ. 02 Aoba Aramaki, Aoba-ku, Sendai City Tohoku University Faculty of Engineering Department of Materials Processing

Claims (8)

[Claims] 1. A step (a) of applying a pressing force to a thermoelectric material having a predetermined composition in a first direction and extruding the same from an extrusion die to plastically deform to obtain a molded article of the thermoelectric material. In the step (a), using a die such that the maximum value of the strain rate is within + 30% of the average value of the strain rate in at least half of the deformation region of the thermoelectric material in the first direction. A method for producing a thermoelectric element. 2. The method according to claim 1, wherein the step (a) includes a step of applying a pressing force in an axial direction to the round bar-shaped thermoelectric material and extruding the same from an extrusion die to obtain a round bar-shaped molded product by plastic deformation. The method according to claim 1, wherein: 3. A thermoelectric material having a predetermined composition is pressed in a first direction and extruded from an extrusion die to restrain deformation in a second direction perpendicular to the first direction. A step of obtaining a rectangular parallelepiped molded product by deforming the thermoelectric material in a third direction perpendicular to the first and second directions, wherein in the step (a), the strain rate of the thermoelectric material in the first direction is reduced. A method of manufacturing a thermoelectric element, wherein the thermoelectric element is made substantially constant in at least half of the deformation region. 4. The method according to claim 1, further comprising, prior to the step (a), a step (b) of forming a green compact or a sintered body of the thermoelectric material by pressing the powdery thermoelectric material. The production method according to claim 1. 5. The thermoelectric material is Bi, Te, Sb, S
The method according to any one of claims 1 to 4, wherein at least two or more of e are included. 6. The method according to claim 1, wherein in the step (a), the thermoelectric material is extruded from an extrusion mold by applying a pressing pressure to the thermoelectric material in an atmosphere, an inert gas atmosphere, or a vacuum.
The production method according to any one of the above. 7. The method according to claim 1, wherein the step (a) comprises setting the processing temperature to 350 to 60.
The method according to any one of claims 1 to 6, wherein the thermoelectric material is extruded from an extrusion mold by applying a pressing pressure to the thermoelectric material while maintaining the thermoelectric material at 0 ° C. 8. A thermoelectric element manufactured by using the manufacturing method according to claim 1.