JP2010141096A - Thermoelectric composite material - Google Patents

Abstract

To provide a linear thermoelectric composite material that is sufficiently long and hardly causes heat transfer between a high temperature side and a low temperature side.
A linear thermoelectric composite material in which a plurality of cores of a thermoelectric material are embedded in a metal oxide matrix, the core of the thermoelectric material is a metal oxide or a semimetal, and the core of the thermoelectric material core A thermoelectric composite material having an average diameter of 5 nm to 60 nm.
[Selection] Figure 2

Description

  The present invention relates to a thermoelectric composite material in which a plurality of cores of a thermoelectric material are embedded in a matrix.

  Thermoelectric materials are used in power generators that generate power from a temperature difference using the Seebeck effect and devices that cool or heat using the Peltier effect.

As an index indicating the thermoelectric conversion efficiency of the thermoelectric material, there is a dimensionless thermoelectric performance index ZT represented by the following formula (1):
ZT = S ² σT / κ (1)
[In Formula (1), S is a Seebeck coefficient (S = −ΔV / ΔT, ΔV = thermoelectromotive force, ΔT = temperature difference), σ is electrical conductivity, κ is thermal conductivity, T Is the temperature. ]

  The ZT of the current thermoelectric material is about 1 at the highest, and there is a demand for a thermoelectric material that exhibits a higher ZT (that is, a high thermoelectric conversion efficiency). In this regard, it is known that by reducing the size of the thermoelectric material to the same degree or less (nanosize) as the carrier de Broglie wavelength, the quantum effect is manifested and ZT is dramatically improved.

For example, Patent Document 1 is a thermoelectric composite in which a plurality of nanowires (average diameter of 10 nm or less) made of Bi ₂ Te ₃ which is a thermoelectric material are embedded in a matrix film of silicon, germanium, or an oxide thereof in an example. Disclosed material.

Further, Patent Document 2 discloses a thermoelectric composite material in which a plurality of carbon nanotubes embedded in a resin matrix are filled with nanowires of thermoelectric material, and a thermoelectric conversion element in which this is connected to an electrode. ing.
JP 2004-193526 A JP 2007-59647 A

  In order to effectively generate power using the Seebeck effect of the thermoelectric material, it is necessary that there is a sufficient temperature difference between the high temperature side and the low temperature side. However, if the length of the thermoelectric material is insufficient, heat transfer occurs from the high temperature side across the thermoelectric material to the low temperature side, and the temperature difference decreases. Therefore, a thermoelectric material having a sufficient length is necessary to efficiently generate power by effectively using the temperature difference.

  However, in the method of Patent Document 1, since a matrix is formed by forming an aluminum-silicon or germanium film, a sufficiently thick matrix and a sufficiently long thermoelectric material nanowire cannot be manufactured. In the example of Patent Document 1, only a mixed film having a thickness of 200 nm is manufactured. As a result, the length of the thermoelectric material nanowire is only 200 nm. Although it is theoretically considered that a sufficiently thick matrix and a sufficiently long thermoelectric material nanowire can be manufactured by increasing the film formation time even in the method of Patent Document 1, such industrial production is practically difficult. is there.

  Moreover, although patent document 2 has described the manufacturing method of the thermoelectric composite material and the thermoelectric conversion element, the Example which actually manufactured the thermoelectric composite material and the thermoelectric conversion element and evaluated the characteristic is not described. Patent Document 2 states that “Oriented carbon nanotubes can be formed, so that a thermoelectric conversion element having practical nanowires with a thickness on the order of mm can be obtained.” However, Patent Document 2 only describes a general method for producing carbon nanotubes, and does not describe a specific method for producing mm-order carbon nanotubes.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a linear thermoelectric composite material that is sufficiently long and hardly causes heat transfer between a high temperature side and a low temperature side.

  The thermoelectric composite material of the present invention is a linear thermoelectric composite material in which a plurality of metal oxide or semimetal cores are embedded in a metal oxide matrix, and the average diameter of the cores of the thermoelectric material is 5 nm to 60 nm. It is characterized by the following.

  In a preferred embodiment of the present invention, the core is zinc or a zinc alloy oxide. When an oxide of a zinc alloy is used, the alloy element is preferably 0.01% by mass of at least one selected from the group consisting of Al, Mg, Ti, Ga, Ge, In, Sn, As, Sb and Nb. It is contained in a total amount of 5% by mass or less. The c-plane of the zinc or zinc alloy oxide crystal is preferably oriented in the longitudinal direction of the linear thermoelectric composite material. In this embodiment, an oxide layer of lead or a lead alloy may be present between the metal oxide matrix and the core of the thermoelectric material.

  In another preferred embodiment of the invention, the core is bismuth or a bismuth alloy. In this embodiment, the core of the thermoelectric material contains zinc powder and bismuth or bismuth alloy powder, and when the total amount of the powder is 100 parts by mass, the amount of zinc powder is 5 parts by mass or more and 25 parts by mass or less. It is preferable that In addition, an oxide layer of zinc or a zinc alloy may exist between the metal oxide matrix and the core of the thermoelectric material.

  In the thermoelectric composite material of the present invention, the metal oxide matrix is preferably an oxide of copper or a copper alloy.

  A thermoelectric element having a sufficient thickness can be produced from the linear thermoelectric composite material of the present invention. Such a thermoelectric element prevents heat transfer from the high temperature side to the low temperature side, and can efficiently generate power by effectively using waste heat from, for example, an automobile, a garbage incinerator, a factory plant, and the like.

  One of the characteristics of the thermoelectric composite material of the present invention is that it is not a film shape described in, for example, Patent Document 1, but a linear shape and a sufficient length. A thermoelectric element having a sufficient thickness can be manufactured by cutting and connecting these linear thermoelectric composite materials to appropriate lengths. Such a thermoelectric element can efficiently generate power by suppressing heat transfer between the high temperature side and the low temperature side.

  One feature of the thermoelectric composite material of the present invention is that its matrix is a metal oxide. A metal oxide has a lower thermal conductivity than a metal and can suppress heat transfer from a high temperature side to a low temperature side. The matrix is preferably an oxide of nickel or copper, or an oxide of these alloys, more preferably an oxide of copper or a copper alloy. The reason is that (1) a metal oxide layer that is thick to some extent can be formed, and (2) intermediate annealing can be performed at a temperature of about 200 ° C. or lower, so that the diameter reduction can be continued. Examples of the copper alloy include those containing trace components such as Sn and / or Zn.

  One feature of the thermoelectric composite material of the present invention is that the average diameter of the core of the thermoelectric material is 5 nm or more and 60 nm or less. This average diameter is preferably 10 nm or more and 30 nm or less. If the average diameter of the core of the thermoelectric material is 60 nm or less, a dramatic improvement in ZT due to the quantum effect can be expected. In addition, the linear thermoelectric composite material of this invention can be manufactured with the manufacturing method which passes through a diameter reduction process so that it may mention later. However, it is difficult to reduce the average diameter of the core to less than 5 nm without disconnection.

  The average diameter of the thermoelectric material core is obtained by randomly selecting 100 or more thermoelectric material cores and counting the maximum diameter of each core. The maximum diameter of each core can be measured from a cross-sectional photograph taken with a high-resolution scanning electron microscope or a transmission electron microscope.

  The thermoelectric composite material of the present invention is (1) linear, (2) low thermal conductivity because the matrix is a metal oxide, and (3) the average diameter of the thermoelectric material core can be expected to have a quantum effect. Since it is nano-sized, it can exhibit excellent ZT. ZT of the thermoelectric composite material of the present invention is preferably 5 or more, more preferably 6 or more, and further preferably 7 or more.

  In the thermoelectric composite material of the present invention, any of a metal oxide thermoelectric material and a semimetal thermoelectric material can be used. Below, what uses a metal oxide as a thermoelectric material and what uses a semimetal are demonstrated in order.

<Thermoelectric composite material where the thermoelectric material is a metal oxide>
As the metal oxide-based thermoelectric material, an oxide of zinc or a zinc alloy is typical. As said zinc alloy, 0.01 mass% or more and 5 mass% or less of at least 1 type (especially Al) chosen from the group which consists of Al, Mg, Ti, Ga, Ge, In, Sn, As, Sb, and Nb is included. What is contained in a total amount is preferable. Such zinc alloy oxides exhibit higher ZT. When the total amount of alloy components such as Al is less than 0.01% by mass, the effect of improving ZT is not sufficiently exhibited. On the other hand, when the total amount exceeds 5% by mass, Al or the like is not alloyed with respect to zinc or zinc oxide.

  When zinc or a zinc alloy oxide is used as the thermoelectric material, the c-plane of the crystal is preferably oriented in the longitudinal direction of the linear thermoelectric composite material. Since the thermal conductivity in the direction perpendicular to the c-plane is low, the thermoelectric composite material in which the c-plane is oriented in the longitudinal direction exhibits a further excellent ZT.

Here, “the c-plane is oriented in the longitudinal direction” means f = (P−P ₀ ) / (1−P ₀ ) ≧ 0.90 (where, f: Lugging factor, P = (ΣI _00c ) / (ΣI _hkl ), I _00c : X-ray diffraction intensity from c-plane, I _hkl : X-ray diffraction intensity from (hkl) plane, P ₀ : Intensity ratio in the case of random orientation) The determination can be made by performing X-ray diffraction by the θ-2θ method using the cross section of the linear thermoelectric composite material as the sample surface.

  A thermoelectric composite material in which an oxide layer of lead or lead alloy exists between a thermoelectric material core that is an oxide of zinc or zinc alloy and a metal oxide matrix is preferable. The thermoelectric composite material having such a configuration is excellent in that the intermetallic compound (eg, copper-zinc intermetallic compound) is not formed between the matrix metal (eg, copper) and zinc or the zinc alloy in the manufacturing method described later. ZT can be indicated.

<Thermoelectric composite material whose thermoelectric material is metalloid>
A substance in which the valence band and the conduction band partially overlap each other with respect to the energy level of an electron is generally called a semimetal. As the metalloid thermoelectric material, bismuth or a bismuth alloy is typical. As bismuth alloys, Bi ₂ Te ₃ , Be ₂ (Te, Se) ₃ , Bi ₈₈ Sb _{12 and the} like are known. In addition to bismuth or a bismuth alloy, PbTe, Si, Ge, SiGe, or the like can also be used.

  The core of the thermoelectric material is composed of zinc powder and powder of bismuth or a bismuth alloy, and when the total of the powder is 100 parts by mass, the amount of zinc powder may be 5 parts by mass or more and 25 parts by mass or less. preferable. The amount of the zinc powder is more preferably 10 parts by mass or more and 20 parts by mass or less. In this case, the core of the thermoelectric material exists in a mixed state of zinc powder and bismuth or bismuth alloy powder.

  The linear thermoelectric composite material of the present invention can be manufactured through a diameter reduction process as described later. However, bismuth or a bismuth alloy has poor cold workability, and problems such as disconnection may occur during diameter reduction processing. Therefore, when filling the holes in the metal matrix with bismuth or bismuth alloy powder, zinc powder is also added as a lubricant to form a stack material, and if this is reduced in diameter, problems such as disconnection can be avoided and thermoelectric power can be avoided. A composite material and its precursor can be produced efficiently. When the amount of zinc is less than 5 parts by mass, the effect of the lubricant is not sufficiently exhibited. On the other hand, when the amount of zinc exceeds 25 parts by mass, the function of bismuth as a thermoelectric material is inhibited.

  A thermoelectric composite material in which an oxide layer of zinc or zinc alloy exists between a thermoelectric material core that is bismuth or a bismuth alloy and a metal oxide matrix is preferable. The thermoelectric composite material having such a configuration can exhibit excellent ZT because the thermoelectric material bismuth or bismuth alloy is not oxidized in the manufacturing method described later.

<Production example of thermoelectric composite material>
The linear thermoelectric composite material of the present invention includes (1) a step of embedding a plurality of metal or semi-metal cores different from the metal matrix in the holes of the metal matrix to form a stack material, and reducing the diameter of the stack material And (2) It can be manufactured by a method including a step of oxidizing the stack material subjected to diameter reduction processing (hereinafter, this method may be abbreviated as “the manufacturing method of the present invention”). The linear thermoelectric composite material can be efficiently manufactured at a sufficient production rate and yield by using a diameter reducing process instead of the film forming technique as in Patent Document 1. Hereafter, the manufacturing method of this invention is demonstrated in order. In the present invention, the term “precursor” refers to a stack material in a state before the oxidation step. In addition, a material in which a plurality of metal or semi-metal cores as thermoelectric materials are embedded in a metal matrix is described as a “stack material” before or after diameter reduction processing.

(1) Formation of stack material and diameter reduction processing (manufacture of thermoelectric composite material precursor)
In the manufacturing method of the present invention, a stack material is first formed by embedding a plurality of metal or semi-metal cores to be thermoelectric materials in the holes of the metal matrix. This metal matrix is preferably nickel or copper or an alloy thereof, more preferably copper or a copper alloy.

  In the production method of the present invention, the diameter reduction processing is not particularly limited, and means such as extrusion (for example, isostatic pressing), drawing, rolling, and swedging may be used. The drawing speed is preferably about 20 m / min or less (more preferably about 10 m / min or less), and the hydrostatic extrusion speed is preferably about 1.2 m / min or less (more preferably about 0.6 m / min). The following).

  In order to improve the workability of the thermoelectric composite material precursor, annealing may be performed at a temperature of 200 ° C. or less, for example, during the diameter reduction process. When zinc or a zinc alloy is used as the metal core, an intermetallic compound (for example, a copper-zinc intermetallic compound) reacts with zinc and a metal matrix (for example, copper or a copper alloy) in this annealing step or an oxidation step described later. May be formed. In this regard, the formation of intermetallic compounds can be prevented by forming a layer of lead or lead alloy (eg, a sheet) in the holes of the metal matrix and then filling it with zinc or a zinc alloy.

  In the manufacturing method of the present invention, the composite stack material may be formed by combining the stack materials subjected to diameter reduction processing, and the composite stack material may be further subjected to diameter reduction processing. Further, the formation of the composite stack material and the diameter reduction processing may be repeated. Although it is possible to form a core having an average diameter of nano-size by a diameter reduction process of only one pass, problems such as disconnection may occur. Therefore, by repeating the formation of the composite stack material and the diameter reduction processing thereof, problems such as disconnection can be avoided and a core having a sufficiently small average diameter can be formed with a high yield.

  As the means for forming the composite stack material, for example, as shown in the following experimental examples, the stack material subjected to diameter reduction processing may be inserted into the same metal case as the matrix, etc. It is not limited to this means. Moreover, the above-mentioned means can be utilized for diameter reduction processing of the composite stack material.

As described above, the method using a plurality of diameter reduction processes has been described as an example of manufacturing the thermoelectric composite material of the present invention, but the thermoelectric composite material of the present invention can be manufactured by other methods. For example, an oxide matrix precursor such as Cu ₂ O is formed, and this precursor is irradiated with ions such as hydrogen and helium in a nano-sized area, and a locus portion through which ions have passed is hydrolyzed to form a nano-sized precursor. A thermoelectric composite material in which a semi-metal core material is embedded in an oxide matrix can also be formed by punching a plurality of holes and press-fitting a melt of a semi-metal such as Bi into the holes.

(2) Oxidation of thermoelectric composite material precursor Thermoelectric composite materials whose core of thermoelectric material is a metal oxide (for example, oxide of zinc or zinc alloy) oxidize both the metal matrix and the metal core in this oxidation process. Can be manufactured. On the other hand, a thermoelectric composite material in which the core of the thermoelectric material is a semimetal (for example, bismuth or a bismuth alloy) can be manufactured by oxidizing only the metal matrix without oxidizing the semimetal core in this oxidation step. Hereinafter, the case where the thermoelectric material is a metal oxide and the case where it is a semimetal will be described separately.

(I) When the thermoelectric material is a metal oxide In this embodiment, both the metal matrix and the metal core are oxidized. Therefore, the thermoelectric composite material precursor may be oxidized for a sufficient time and temperature. In order to increase the oxidizing power, the precursor may be oxidized in an atmosphere with high humidity. A small amount of sulfurous acid gas (SO ₂ gas) may be added to the atmosphere.

  When the thermoelectric material is a metal oxide, it is preferable to oxidize the metal core while applying a magnetic field to the linear precursor in the oxidation step. By applying a magnetic field, the crystal orientation of the metal oxide core can be aligned. In this case, when an oxidation treatment is performed by applying a magnetic field while rotating the precursor around the longitudinal direction of the linear thermoelectric composite material precursor, the crystal orientation of the metal oxide (especially zinc oxide or zinc alloy oxide) The property is further improved, and a higher ZT can be realized.

(Ii) When the thermoelectric material is a semimetal When using a thermoelectric material that is a semimetal such as bismuth or a bismuth alloy, if these are oxidized in the oxidation step, the ZT deteriorates. Therefore, when using a semimetal thermoelectric material, it is necessary to prevent these oxidations. Therefore, in the present invention of this embodiment, in order to prevent oxidation of the semimetal core, it is preferable to dispose a metal layer for preventing oxidation between the metal matrix and the semimetal core. Examples of the metal layer for preventing oxidation include a metal that forms a stable oxide, and zinc or a zinc alloy is preferable.

In this production method, the precursor of the thermoelectric composite material is heated to 200 to 350 ° C. (preferably 250 to 300 ° C.) in an air atmosphere of about atmospheric pressure having a relative humidity of 60 to 100% (preferably 80 to 90%). ) For 15 to 70 hours (preferably 20 to 50 hours) to convert only the metal of the matrix into a metal oxide. A small amount of SO ₂ gas may be added to the atmosphere. SO ₂ reacts with H ₂ O to form H ₂ SO ₃ (sulfurous gas). Oxidation is promoted by this H ₂ SO ₃ .

  Hereinafter, the present invention will be described in more detail with reference to experimental examples, but the present invention is not limited by the following experimental examples, and appropriate modifications are made within a range that can meet the above and the following purposes. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

Experimental example 1
Seven cylinders with a diameter of 16.0 mm penetrating from end to end were opened in a copper ingot with a diameter of 67 mm, and a zinc rod was inserted into the hole to form a primary stack material. This was subjected to diameter reduction processing (speed 1.2 m / min) by hydrostatic pressure extrusion to form a diameter-reduced primary stack material having a hexagonal cross section (distance between opposite sides: 2.3 mm).

  433 bundled primary stack materials that have been reduced in diameter are bundled, integrated, and inserted into a copper outer pipe case (outer diameter 67 mm, inner diameter 47 mm), and both ends are electron beam welded to form a secondary stack material did. This was subjected to diameter reduction processing (speed 1.2 m / min) by hydrostatic extrusion to form a round bar-shaped thermoelectric composite precursor having a diameter of 0.80 mm. At this time, the zinc core had a diameter of 3.2 μm. In addition, the value of the diameter of the core in this experiment example and the following experiment example is a value calculated from the diameter reduction processing rate.

  In the course of the diameter reduction processing of the secondary stack material described above, annealing was performed at a temperature of 200 ° C. or less. During this annealing, the copper matrix and the zinc core reacted to form a copper-zinc intermetallic compound. It was. This was confirmed by composition analysis of the cross section. Further, since wire breakage occurred, further diameter reduction processing could not be performed.

This precursor is subjected to an oxidation treatment in which the relative humidity is 90% and heating is performed at 300 ° C. for 50 hours in an atmosphere of atmospheric pressure containing SO ₂ gas having a concentration of 10 ppm, and the matrix is copper oxide (Cu ₂ O). A linear thermoelectric composite material in which the thermoelectric material is zinc oxide (ZnO) was formed.

  A material with a length of 5 mm was cut out from the linear thermoelectric composite material after the oxidation treatment, under conditions of a low temperature end of 25 ° C. (298 K) and a high temperature end of 500 ° C. (773 K) (intermediate temperature T = 538 K), Seebeck coefficient S, electricity By measuring the conductivity σ and the thermal conductivity κ, the dimensionless thermoelectric figure of merit ZT of this material was determined.

  The ZT of the linear thermoelectric composite material of Experimental Example 1 was 0.62 (the thermoelectric composite material diameter 0.80 mm and length 5 mm, the zinc oxide core diameter 3.2 μm, T = 538K). Even when the diameter of the zinc oxide core was reduced to 70 nm, the value of ZT was only about 0.67.

Experimental example 2
Seven holes of 16.0mm diameter that penetrate from end to end are drilled on a 67mm diameter copper ingot, and a 0.05mm thick lead sheet is wound in a cylindrical shape along the inside of the hole. A zinc rod was inserted into the two and both ends thereof were electron beam welded to form a primary stack material. This was subjected to diameter reduction processing (speed 1.2 m / min) by hydrostatic pressure extrusion to form a diameter-reduced primary stack material having a hexagonal cross section (distance between opposite sides: 2.3 mm).

  433 bundled primary stack materials that have been reduced in diameter are bundled, integrated, and inserted into a copper outer pipe case (outer diameter 67 mm, inner diameter 47 mm), and both ends are electron beam welded to form a secondary stack material did. This was subjected to diameter reduction processing (speed 1.2 m / min) by hydrostatic pressure extrusion to form a diameter-reduced secondary stack material having a hexagonal cross section (distance between opposite sides: 2.3 mm). Note that annealing was performed at a temperature of 200 ° C. or lower during the diameter reduction of the secondary stack material.

  433 bundled secondary stack materials that have been reduced in diameter are bundled, integrated, and inserted into a copper outer layer pipe case (outer diameter 67 mm, inner diameter 47 mm), and both ends are electron beam welded to form a tertiary stack material did. This was subjected to a diameter reduction process (speed 1.2 m / min) by hydrostatic extrusion to form a round bar-shaped thermoelectric composite material precursor having a diameter of 0.40 mm (FIG. 1). At this time, the diameter of the zinc core was 20 nm. Even during the diameter reduction processing of the tertiary stack material, annealing was performed at a temperature of 200 ° C. or less, but no copper-zinc intermetallic compound was formed. This was confirmed by composition analysis of the cross section. This is because the lead layer prevented the formation of a copper-zinc intermetallic compound.

This precursor is subjected to an oxidation treatment in which the relative humidity is 90% and the atmosphere is heated at 300 ° C. for 25 hours in an atmospheric atmosphere containing SO ₂ gas having a concentration of 10 ppm, and the matrix is copper oxide (Cu ₂ O). The thermoelectric material was zinc oxide (ZnO), and a linear thermoelectric composite material in which a lead oxide layer was present between them was formed (FIG. 2). In addition, even if it heated at 300 degreeC for 50 hours, it was almost the same result.

  The ZT of the linear thermoelectric composite material of Experimental Example 2 obtained in the same manner as in Experimental Example 1 was 6.1 (the thermoelectric composite material diameter 0.40 mm and length 5 mm, the zinc oxide core diameter 20 nm, T = 538K).

Experimental example 3
The matrix is copper oxide (Cu ₂ O) in the same manner as in Experimental Example 1 except that a primary stack material is formed using a Zn-1 mass% Al alloy rod instead of the zinc rod, and the thermoelectric material Formed a linear thermoelectric composite material which is an oxide of Zn-1 mass% Al alloy. In Experimental Example 3, as in Experimental Example 1, a copper-zinc intermetallic compound was formed by annealing during the diameter reduction processing of the secondary stack material. Further, since wire breakage occurred, further diameter reduction processing could not be performed.

  The ZT of the linear thermoelectric composite material of Experimental Example 3 obtained in the same manner as in Experimental Example 1 was 0.15 (diameter 0.80 mm and length 5 mm of the thermoelectric composite material, Zn-1 mass% Al alloy oxidation) The diameter of the core of the object is 3.2 μm, T = 538K).

Experimental Example 4
The matrix is copper oxide (Cu ₂ O) in the same manner as in Experimental Example 2 except that a primary stack material is formed using a Zn-1 mass% Al alloy rod instead of the zinc rod, and the thermoelectric material Is an oxide of Zn-1 mass% Al alloy, and a linear thermoelectric composite material in which a lead oxide layer exists is formed. In Experimental Example 4, as in Experimental Example 2, the secondary stack material and the tertiary stack material were annealed during the diameter reduction process, but no copper-zinc intermetallic compound was formed.

  The ZT of the linear thermoelectric composite material of Experimental Example 4 obtained in the same manner as in Experimental Example 1 was 6.8 (the diameter of the thermoelectric composite material was 0.40 mm and the length was 5 mm, and the Zn-1 mass% Al alloy was oxidized. Core diameter 20 nm, T = 538K).

Experimental Example 5
The matrix is copper oxide (Cu ₂ O) in the same manner as in Experimental Example 4 except that the oxidation treatment was performed while applying a magnetic field of 10 T perpendicular to the longitudinal direction of the linear precursor (FIG. 3). The thermoelectric material was an oxide of a Zn-1 mass% Al alloy, and a linear thermoelectric composite material in which a lead oxide layer was present was formed. By applying a magnetic field, the c-plane of the crystal of Zn-1 mass% Al alloy oxide, which is a thermoelectric material, was oriented in the longitudinal direction of the linear thermoelectric composite material. This was confirmed by X-ray diffraction.

  The ZT of the linear thermoelectric composite material of Experimental Example 5 obtained in the same manner as in Experimental Example 1 was 7.4 (the thermoelectric composite material had a diameter of 0.40 mm and a length of 5 mm, and the Zn-1 mass% Al alloy was oxidized. Core diameter 20 nm, T = 538K).

Experimental Example 6
Open a 67mm diameter copper ingot with 7 cylinders with a diameter of 16.0mm penetrating from end to end and wind a 0.02mm thick zinc sheet along the inside of the hole. Was filled with a mixture of bismuth powder and zinc powder (2 parts by mass of zinc powder in a total of 100 parts by mass of powder), and both ends thereof were electron beam welded to form a primary stack material. This was subjected to diameter reduction processing (speed 1.2 m / min) by hydrostatic pressure extrusion to form a diameter-reduced primary stack material having a hexagonal cross section (distance between opposite sides: 2.3 mm).

  433 bundled primary stack materials that have been reduced in diameter are bundled, integrated, and inserted into a copper outer pipe case (outer diameter 67 mm, inner diameter 47 mm), and both ends are electron beam welded to form a secondary stack material did. This was subjected to diameter reduction processing (speed 1.2 m / min) by hydrostatic extrusion to form a round bar-shaped thermoelectric composite precursor having a diameter of 0.80 mm. The diameter of the bismuth-zinc core at this time was 3.2 μm. Further, since the amount of zinc acting as a lubricant is small and disconnection occurs, further diameter reduction processing cannot be performed.

This precursor is subjected to an oxidation treatment in which the relative humidity is 90% and heating is performed at 300 ° C. for 50 hours in an atmosphere of atmospheric pressure containing SO ₂ gas having a concentration of 10 ppm, and the matrix is copper oxide (Cu ₂ O). A thermoelectric composite material in which the thermoelectric material is bismuth (Bi) was formed.

  A material having a length of 5 mm was cut out from the linear thermoelectric composite material after the oxidation treatment, under conditions of a low temperature end of 25 ° C. (298 K) and a high temperature end of 150 ° C. (423 K) (intermediate temperature T = 361 K), Seebeck coefficient S, electricity By measuring the conductivity σ and the thermal conductivity κ, the dimensionless thermoelectric figure of merit ZT of this material was determined. The reason why the temperature at the high temperature end is lowered as compared with the cases of Experimental Examples 1 to 5 is that the melting point of Bi is as low as about 271 degrees.

  The ZT of the linear thermoelectric composite material of Experimental Example 6 was 0.53 (diameter 0.80 mm and length 5 mm of thermoelectric composite material, bismuth-zinc core diameter 3.2 μm, T = 361 K).

Experimental Example 7
Except that a 0.02 mm-thick zinc sheet was not used and a hole of a copper ingot was filled with a mixture of bismuth powder and zinc powder (20 parts by mass of zinc powder in a total of 100 parts by mass of powder) and Example 6 Similarly, a linear thermoelectric composite material in which the matrix was copper oxide (Cu ₂ O) and the thermoelectric material was bismuth (Bi) was formed. In the linear thermoelectric composite material of Experimental Example 7, bismuth was partially oxidized in the oxidation process. This was confirmed by cross-sectional composition analysis.

  ZT of the linear thermoelectric composite material of Experimental Example 7 obtained in the same manner as Experimental Example 6 was 0.02 (diameter 0.80 mm and length of thermoelectric composite material 5 mm, bismuth-zinc core diameter 3. 2 μm, T = 361K).

Experimental Example 8
Open a 67mm diameter copper ingot with 7 cylinders with a diameter of 16.0mm penetrating from end to end and wind a 0.02mm thick zinc sheet along the inside of the hole. Are mixed with a mixture of bismuth powder and zinc powder (20 parts by mass of zinc powder in a total of 100 parts by mass of powder), both ends thereof are subjected to electron beam welding, and reduced diameter processing by hydrostatic extrusion (speed: 1.2 m / min) min) to form a reduced diameter primary stack material having a hexagonal cross section (a distance between opposite sides of 2.3 mm).

  433 bundled primary stack materials that have been reduced in diameter are bundled, integrated, and inserted into a copper outer pipe case (outer diameter 67 mm, inner diameter 47 mm), and both ends are electron beam welded to form a secondary stack material did. This was subjected to diameter reduction processing (speed 1.2 m / min) by hydrostatic pressure extrusion to form a diameter-reduced secondary stack material having a hexagonal cross section (distance between opposite sides: 2.3 mm).

  433 bundled secondary stack materials that have been reduced in diameter are bundled, integrated, and inserted into a copper outer layer pipe case (outer diameter 67 mm, inner diameter 47 mm), and both ends are electron beam welded to form a tertiary stack material did. This was subjected to a diameter reduction process (speed 1.2 m / min) by hydrostatic extrusion to form a round bar-shaped thermoelectric composite material precursor having a diameter of 0.40 mm (FIG. 4). The diameter of the bismuth-zinc core at this time was 20 nm.

This precursor is subjected to an oxidation treatment in which the relative humidity is 90% and the atmosphere is heated at 300 ° C. for 25 hours in an atmospheric atmosphere containing SO ₂ gas having a concentration of 10 ppm, and the matrix is copper oxide (Cu ₂ O). The thermoelectric material was bismuth (Bi), and a thermoelectric composite material in which a zinc oxide layer was present between them was formed (FIG. 5). In addition, even if it heated at 300 degreeC for 50 hours, it was almost the same result.

  The ZT of the linear thermoelectric composite material of Experimental Example 8 obtained in the same manner as in Experimental Example 6 was 5.4 (diameter 0.40 mm and length of thermoelectric composite material 5 mm, bismuth-zinc core diameter 3. 2 μm, T = 361K).

6 is a schematic diagram showing a cross section of a thermoelectric composite material precursor produced in Experimental Example 2. FIG. 6 is a schematic diagram showing a cross section of a thermoelectric composite material produced in Experimental Example 2. FIG. It is a schematic diagram which shows the apparatus which performs an oxidation process, applying the magnetic field used in Experimental example 5. FIG. It is a schematic diagram which shows the cross section of the thermoelectric composite material precursor produced in Experimental example 8. 10 is a schematic diagram showing a cross section of a thermoelectric composite material produced in Experimental Example 8. FIG.

Claims (9)

  A linear thermoelectric composite material in which a plurality of metal oxide or metalloid cores are embedded in a metal oxide matrix, wherein the core has an average diameter of 5 nm to 60 nm. .   The thermoelectric composite material according to claim 1, wherein the core is an oxide of zinc or a zinc alloy.   The zinc alloy oxide contains at least one selected from the group consisting of Al, Mg, Ti, Ga, Ge, In, Sn, As, Sb, and Nb as an alloy element. The thermoelectric composite material according to claim 2, which is contained in a total amount.   The thermoelectric composite material according to claim 2 or 3, wherein the c-plane of the zinc or zinc alloy oxide crystal is oriented in the longitudinal direction of the linear thermoelectric composite material.   The thermoelectric composite material according to any one of claims 2 to 4, wherein an oxide layer of lead or a lead alloy is present between the metal oxide matrix and the core.   The thermoelectric composite material according to claim 1, wherein the core is bismuth or a bismuth alloy.   The said core contains zinc powder and powder of bismuth or a bismuth alloy, and when the total of the said powder is 100 mass parts, zinc powder amount is 5 mass parts or more and 25 mass parts or less. The thermoelectric composite material described.   The thermoelectric composite material according to claim 6 or 7, wherein an oxide layer of zinc or a zinc alloy is present between the metal oxide matrix and the core.   The thermoelectric composite material according to claim 1, wherein the metal oxide matrix is an oxide of copper or a copper alloy.