JP2002118299A - Manufacturing method of thermoelement - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a thermoelement having excellent thermoelectric performance and mechanical strength by effectively using a thermoelectric material powder whose particle size is 38 μm or less. SOLUTION: Materials of prescribed composition are mixed and heated to be melted, and then coagulated to produce a solid solution ingot which is pulverized to produce a solid solution powder whose particle size is 38 μm or less. The solid solution powder is sintered under pressure, and then hot plastic deformed so that the crystal grain is orientated in a crystal orientation excellent in performance index.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a thermoelectric element used for manufacturing a thermoelectric module for converting between heat energy and electric energy.

[0002]

2. Description of the Related Art The thermoelectric phenomenon is a general term for the Seebeck phenomenon, the Peltier phenomenon, and the Thomson phenomenon, and elements utilizing this phenomenon are called thermoelectric elements, thermocouples, thermoelectric coolers, and the like.
Thermoelectric phenomena were originally discovered between different types of metals, but in recent years, semiconductor thermoelectric materials have become available,
Conversion efficiencies that could not be obtained with metallic materials can now be obtained. BACKGROUND ART A thermoelectric element using a thermoelectric semiconductor material has attracted attention for its wide use because it has a simple structure, is easy to handle, and can maintain stable characteristics. In particular, since local cooling and precise temperature control near room temperature are possible, research and development have been widely conducted for temperature control of optoelectronics and semiconductor lasers, and application to small refrigerators and the like.

Conventionally, in the production of a thermoelectric element, raw materials are weighed so as to have a desired composition, a molten metal obtained by heating and melting them is solidified to produce a solid solution ingot, and the solid solution ingot is further pulverized, sieved and classified and sized. Granulated and powdered,
A method of sintering, slicing and dicing these powders has been adopted. Alternatively, after sintering, hot plastic working such as forging or extrusion may be performed.

In Japanese Patent Application Laid-Open Publication No. 64-77184, the diameter after classification is several tens μm.
It has been pointed out that the performance of a thermoelectric element using a powder having a particle size of m or less is greatly reduced. Also, Japanese Patent Application Laid-Open No. 62-26
No. 4,682,37-74 .mu.m.
No. 456 and JP-A-3-16281 disclose 10
２００200 μm, which limits the classification range of the powder of the thermoelectric material used. In fact, a powder of 38 μm or less,
That is, the molded product of the thermoelectric element sintered using the fine powder cannot be used as a product because the sintering density is low, the electric resistance is high, the thermoelectric performance is extremely low, and there is no mechanical strength. .

[0005]

As described above, conventionally,
Powder thermoelectric materials having a classification range of more than 38 μm and about 150 μm have been used, and powders of 38 μm or less have not been effectively used.

In view of the above, the present invention is directed to a thermoelectric element having a thermoelectric performance and mechanical strength that can effectively utilize a fine powder thermoelectric material having a particle size of 38 μm or less and that can endure as a product. It is intended to provide a manufacturing method.

[0007]

In order to solve the above-mentioned problems, a method for manufacturing a thermoelectric element according to the present invention comprises mixing a raw material having a predetermined composition, heating and melting, and solidifying the heated and melted raw material. And a step of producing a thermoelectric semiconductor ingot having a hexagonal structure, and crushing the ingot,
A step of producing a powder having a particle size of 38 μm or less, a step of producing a sintered body by sintering the powder under pressure, and a step of sintering the sintered body so that the crystal grains are oriented in a crystal orientation having an excellent figure of merit. And hot plastic deformation. ADVANTAGE OF THE INVENTION According to this invention, most of the powder which grind | pulverized the ingot can be used effectively, and the thermoelectric element which has excellent thermoelectric performance and mechanical strength can be manufactured.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. The same components are denoted by the same reference numerals, and description thereof will be omitted. FIG. 1 is a flowchart showing a method for manufacturing a thermoelectric element according to one embodiment of the present invention. Hereinafter, a method for manufacturing a thermoelectric element according to an embodiment of the present invention will be described with reference to FIG.

First, a raw material having a predetermined composition is weighed and sealed in a container (step S1). As a raw material of the thermoelectric material, for example, antimony (S
b) or bismuth (Bi), and selenium (Se) or tellurium (Te) as a group VI element. Since the group V and group VI solid solutions have a hexagonal crystal structure, Bi, Te, Sb,
At least two or more elements of Se are used as raw materials, and are generally represented as follows. (Bi _1−X Sb _X ) ₂ (Te _1−Y Se _Y ) ₃ where 0 ≦ X, Y ≦ 1 More specifically, bismuth telluride (Bi ₂ Te ₃ ) and tellurium P-type dopants are added to a mixed crystal solid solution with antimony bromide (Sb ₂ Te ₃ ), and bismuth telluride (Bi ₂
An N-type dopant can be added to a mixed crystal solid solution of Te ₃ ) and bismuth selenide (Bi ₂ Se ₃ ).

Next, the raw material sealed in the container is heated,
Melt and mix (step S2). Next, the molten material is solidified (step S3). The solid solution ingot produced by solidification has a hexagonal structure (rhombohedral structure). Next, the solid solution ingot is pulverized by a stamp mill, a ball mill, or the like (step S4), sieved with a 400 mesh sieve, and classified (step S5). Where 4
If you select one that has passed through a 00 mesh sieve,
m or less as a solid solution powder (fine powder).

Next, the fine powder obtained in step S5 is sealed in a sintering mold and pressure-sintered in a vacuum or an inert gas atmosphere as required (step S6). Finally, the sintered body is plastically deformed by heating so that the crystal grains are oriented in an orientation having an excellent figure of merit (step S7). The method of plastic working may be spreading by hot upsetting forging or hot extrusion forming. Regarding the processing temperature, it is performed at a hot temperature of 450 ° C. or less,
The heating is performed at a temperature of 00 ° C. or less.

FIG. 2 shows a thermoelectric element manufactured by the above method using fine powder of 38 μm or less (Example) and a thermoelectric element manufactured by a conventional method using only the fine powder by sintering only (Comparative Example 1). ) And thermoelectric elements (Comparative Examples 2 and 3) manufactured using powder having a particle size in the range of 38 μm to 150 μm. In this experiment, the raw materials of the thermoelectric element were bismuth Bi, tellurium Te, and antimony Sb.
Was weighed and used so that the stoichiometric ratio was Bi _0.4 Sb _1.6 Te _3.0 . The powder sintering was performed in an argon atmosphere at a sintering temperature of 500 ° C. and a pressure of 750 kgf /
Performed for 15 minutes under cm ² (73.5 N / mm ² ). Further, in Example and Comparative Example 2, hot upsetting forging was performed at 400 ° C. as hot plastic working.

In FIG. 2, "density" indicates the powder density, and the greater the value, the greater the mechanical strength of the thermoelectric element. The power factor (PF) indicates the performance of the thermoelectric element. Normally, the performance of a thermoelectric element is evaluated by a performance index Z expressed by the following equation using a Seebeck coefficient α, an electric conductivity σ, and a thermal conductivity κ. Z = α ² σ / κ However, in this experiment, a large change was not found in the thermal conductivity κ, so that it was omitted, and instead of the electric conductivity σ, the specific resistance ρ = 1 / σ was used, and the following equation was used. It was evaluated by the power factor PF expressed. PF = α ² / ρ The performance of the thermoelectric element is better as the value of the power factor PF is larger.

Referring to FIG. 2, a comparison between the example using powder having a size of 38 μm or less and the comparative example 1 shows that the PF value of the example in which the forging step was added was 4.5, while the PF value was 4.5. In Comparative Example 1 having only the process, the value is 4.0. In addition, comparing Comparative Example 2 and Comparative Example 3 with the powder (38 μm to 150 μm) conventionally used, Comparative Example 2 with the addition of a forging step has a PH value of 4.0 to 4.4, and a comparison of only sintering. In the example, it is 3.8 to 4.0. For this reason, when powders having the same particle size range are used, it is better to add a hot upsetting forging process after sintering as a processing method than to the one processed only by the sintering process. Is obtained.

Further, comparing the embodiment with the comparative example 2,
While the PF value in the example using the fine powder is 4.5, the PF value in Comparative Example 2 using the conventionally used powder is
The values are 4.0 to 4.4. In other words, when a forging step is added to the working method, a better performance thermoelectric element can be obtained by using fine powder (38 μm or less).

Further, focusing on the density, in the embodiment, 9
It is 9.2%. This indicates that even if a fine powder having a particle size of 38 μm or less is used, a thermoelectric element having a mechanical strength equivalent to that of a conventional thermoelectric element using powder can be obtained by devising a processing method.

From the above results, when the powder of the thermoelectric material is molded, after the conventional sintering process, the crystal grains are further oriented by hot upsetting forging or the like so that the crystal grains are oriented in the direction having excellent performance orientation. When hot plastic working is performed, the mechanical strength and power factor of the thermoelectric element, that is, the performance of the thermoelectric element are improved.

According to such a manufacturing method, a thermoelectric element having good performance can be obtained irrespective of the particle size of the powder. Therefore, it is not necessary to divide the particle size into larger or smaller than 38 μm. All of the following powders can be used. Therefore, the labor of sieving a 400 mesh can be omitted,
Product yield can be improved.

FIG. 3 is a diagram showing a thermoelectric module manufactured using thermoelectric elements. As shown in FIG. 3, a P-type element (P-type semiconductor) 13 and an N-type element (N-type semiconductor) 14 are connected between two ceramic substrates 11 and 12 by electrodes 15.
To form a PN element pair, and a plurality of PN element pairs are connected in series. A current introduction terminal (positive electrode) 16 is connected to the N-type element at one end of the series circuit of the PN element pair, and the P-type terminal at the other end is connected to the N-type element.
A current introduction terminal (negative electrode) 17 is connected to the mold element. When a voltage is applied between the current introduction terminals 16 and 17 to cause a current to flow from the current introduction terminal (positive electrode) 16 to the current introduction terminal (negative electrode) 17 through a series circuit of PN element pairs, the ceramic The substrate 11 is cooled and the ceramic substrate 12 is heated. As a result, a heat flow is generated as shown by the arrow in the figure.

[0020]

As described above, according to the present invention, 3
A thermoelectric element having excellent thermoelectric performance and mechanical strength can be manufactured by effectively utilizing fine powder of 8 μm or less.

[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 showing the results of an experiment for comparing the performance of a thermoelectric element manufactured by a method of manufacturing a thermoelectric element according to an embodiment of the present invention with the performance of a thermoelectric element manufactured by a conventional method.

FIG. 3 is a perspective view showing a structure of a thermoelectric module manufactured using a thermoelectric element manufactured by a manufacturing method according to an embodiment of the present invention.

[Explanation of symbols]

 11, 12 Ceramic substrate 13 P-type element (P-type semiconductor) 14 N-type element (N-type semiconductor) 15 Electrode 16 Current introduction terminal (positive electrode) 17 Current introduction terminal (negative electrode)

Continued on the front page (72) Inventor 1200, Manda, Hiratsuka-shi, Kanagawa F-term (reference) 4K018 FA01 KA32

Claims (4)

[Claims] 1. A step (a) of mixing and heating and melting a raw material having a predetermined composition, and a step (b) of solidifying the heated and melted raw material to produce a thermoelectric semiconductor ingot having a hexagonal structure. (C) crushing the ingot to produce a powder having a particle size of 38 μm or less; and (d) sintering the powder under pressure to produce a sintered body.
And a step (e) of hot plastically deforming the sintered body so that the crystal grains are oriented in a crystal orientation having an excellent figure of merit. 2. The powder produced in the step (c) includes a powder having a particle size of 10 μm or less.
A method for producing the thermoelectric element according to the above. 3. The method according to claim 1, wherein the step (e) comprises:
The method of manufacturing a thermoelectric element according to claim 1 or 2, wherein the method is hot upsetting forging in which plastic deformation is performed by spreading in the following heat. 4. The method according to claim 1, wherein the step (e) comprises:
The method for producing a thermoelectric element according to claim 1, wherein the method is a hot extrusion process in which plastic deformation is performed by extruding from a mold in the following hot conditions.