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EP-4131436-B1 - METHOD FOR PRODUCING THERMOELECTRIC CONVERSION ELEMENT

EP4131436B1EP 4131436 B1EP4131436 B1EP 4131436B1EP-4131436-B1

Inventors

  • MATSUDA, MICHIKO
  • SHIMADA, TAKESHI

Dates

Publication Date
20260506
Application Date
20210322

Claims (5)

  1. A method for producing a thermoelectric conversion element, comprising: a step of mixing a skutterudite-type thermoelectric conversion material powder containing Sb and a sintering agent containing a compound including Mn and Sb, to obtain a mixture; and a step of sintering the mixture.
  2. The method for producing a thermoelectric conversion element according to claim 1, wherein the compound including Mn and Sb has a peak of a crystal structure of at least one of Mn 1.1 Sb and Mn 2 Sb observed by XRD.
  3. The method for producing a thermoelectric conversion element according to claim 1 or claim 2, wherein in the mixture, the sintering agent is 10 mass% or less relative to a total amount of the thermoelectric conversion material and the sintering agent.
  4. The method for producing a thermoelectric conversion element according to any one of claims 1 to 3, wherein the thermoelectric conversion material powder contains Yb and Co.
  5. The method for producing a thermoelectric conversion element according to any one of claims 1 to 3, wherein the thermoelectric conversion material powder contains Ce and Fe.

Description

TECHNICAL FIELD The present invention relates to a thermoelectric conversion element which directly converts heat energy into electric energy. BACKGROUND ART In recent years, a study has been conducted to recover, as electricity, heat exhausted from, for example, a boiler, an incinerator, and a heat source of an automobile, for reducing energy consumption. Particular attention is paid on a thermoelectric conversion module which can efficiently recover electric energy using a thermoelectric conversion element capable of directly converting heat energy into electric energy by the Seebeck effect. A most practically realized material is a Bi2Te3-based compound which is mainly used in a temperature range from normal temperature to about 200°C. Another widespread material is being sought which exerts high thermoelectric performance in various temperature ranges. Particularly, inorganic materials based on silicide, Pb-Te, skutterudite, Si-Ge, and Heusler are shown to exhibit high thermoelectric characteristics in a high temperature range of 300°C or higher and intensively studied. A well-known inorganic material thermoelectric conversion module is one having a π-type shape in which an N-type element having electrons as a carrier and a P-type element having holes as a carrier are aligned and connected at one end through an electrode. An element used in a pi-type module is a rectangular parallelepiped or a cube of several millimeters to 1 cm. This also requires a technology for highly efficiently preparing an element bulk material of several millimeters. A common method therefor is a method of melting a raw material to obtain a material having a desired composition, shaping the material into powder by pulverization or the like, and thereafter pressure-sintering the powder. Pressure-sintering is a method of simultaneously performing sintering and forming by compression during heating. Examples of used pressure-sintering include hot pressing, hot isostatic pressing (HIP), and spark plasma sintering (SPS) in which mechanical pressurization and pulse electric current heating are simultaneously performed. For example, Patent Literature 1 discloses a thermoelectric conversion element including a skutterudite-based compound Ce0.2Co3.95 Mn0.05Sb12 and a method for producing the thermoelectric conversion element. In this production method, a metal material containing Ce, Co, Mn, and Sb is poured in a quartz tube, sealed in vacuum, melted at 1100°C for 12 hours, and thereafter quenched in water. The obtained ingot is heat-treated at 800°C for 120 hours to obtain a powder. The powder is sintered by SPS technique at 600°C for 5 minutes under a pressure of 50 MPa. Also, Patent Literature 2 discloses a thermoelectric conversion material having a crystal average particle size of 50 nm or less in which the relative density of the thermoelectric conversion material is 85% or more, and a method for producing the thermoelectric conversion material. In this production method, a pulverized powder is prepared and then sintered or solidified under a pressure of 0.5 GPa or more and 10 GPa or less. In addition, WO 2017/038988 A1 discloses a method of preparing a thermoelectric material such as a skutterudite. CITATION LIST PATENT LITERATURE PATENT LITERATURE 1: WO 2013/009430 APATENT LITERATURE 2: WO 2004/049464 A SUMMARY OF INVENTION PROBLEMS TO BE SOLVED BY INVENTION The method of Patent Literature 1 has a problem in that when the thermoelectric conversion element is increased in size for mass production, insufficient pressure or the like is likely to cause the thermoelectric conversion element to have an insufficient relative density. On the other hand, when a pulverized powder is obtained as in Patent Literature 2, a specific surface area increases, which likely causes oxidation to proceed in a pre-sintering stage. Therefore, when this is used to obtain a thermoelectric conversion element, a problem is raised in that thermoelectric performance of the thermoelectric conversion element is likely to decrease. An object of the present invention is to provide a method for producing a thermoelectric conversion element which is suitable for increasing in density and excellent in mass productivity while retaining thermoelectric characteristics. SOLUTION TO PROBLEMS According to the present invention, there is provided a method for producing a thermoelectric conversion element, including: a step of mixing a skutterudite-type thermoelectric conversion material powder containing Sb and a sintering agent containing a compound including Mn and Sb, to obtain a mixture; and a step of sintering the mixture. Moreover, preferably, the compound including Mn and Sb has a peak of a crystal structure of at least one of Mn1.1Sb and Mn2Sb observed by XRD. Moreover, preferably, in the mixture, the sintering agent is 10 mass% or less relative to a total amount of the thermoelectric conversion material and the sintering agent. Moreover, preferably, the thermoelec