JP2001094162A - Method for using thermoelectric conversion material and thermoelectric conversion element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for using a thermoelectric conversion element with improved Seebeck coefficient by applying magnetic field to a thermoelectric conversion material, and provide a high-performance thermoelectric element with a large thermoelectric conversion efficiency. SOLUTION: While a magnetic field (x-axial direction) is applied to a thermoelectric conversion material, temperature gradient in the given direction (z-axial direction) is generated to cause a difference in temperatures between electrodes 2 and 3. By using a synergistic effect of the Seebeck effect and the Nernst effect, characteristics in thermoelectric conversion element can be improved by leaps in a simple way.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoelectric conversion element which dramatically improves the performance of a thermoelectric conversion material, and applies a magnetic field to the thermoelectric conversion material to give a temperature gradient in a required direction, thereby achieving a Seebeck effect and a Nelst effect. The present invention relates to a method of using a thermoelectric conversion material in which the thermoelectric power of the material is improved by utilizing a synergistic effect with the (Nernst) effect, and a thermoelectric conversion element.

[0002]

2. Description of the Related Art Thermoelectric conversion elements are devices that are expected to be put to practical use from the viewpoint of effective use of thermal energy, which is required in recent industries, and for example, a system that converts waste heat into electric energy. Also, a very wide range of applications such as a small portable power generator for easily obtaining electricity outdoors and a flame sensor for gas appliances are being studied.

[0003] A thermoelectric conversion element has, for example, a structure in which a p-type and an n-type semiconductor are directly joined by powder metallurgy to form an element, or
There is a configuration in which a device and an n-type semiconductor are formed as a device by pn junction with a metal such as silver solder.

[0004] As a thermoelectric conversion material for forming the element,
IrSb with high performance_Three, Bi_TwoTe _ThreeChalcogen such as PbTe
Fe-based compounds with low thermoelectric properties but abundant resources
Si_TwoAnd silicides such as SiGe are known.

[0005] The conventional thermoelectric conversion element generates a thermoelectromotive force by using a temperature gradient given to a material, and the figure of merit of the thermoelectric conversion element (ZT = S2 / ρκ, where S is a Seebeck coefficient, ρ
Is an electrical resistivity, and κ is a thermal conductivity), which is about 1 even at a high level, which is not sufficient.

[0006]

That is, the conversion efficiency of a thermoelectric conversion element is very low compared with that of a thermal power generation (about 50%) or that of a solar cell (about 20%), and is only a few percent. It is said that this is the main reason that delays the practical use of thermoelectric conversion elements.

On the other hand, the generation of an electric field when a magnetic field is applied to a thermoelectric material having a temperature gradient is due to the Nernst effect (LD Landau, E.
M. Lifslitz and LPPitaevskli “Electodynamics of C
ontinuous Media ”, 2nd Edition, pergamon press, P.10
1 (1984)). However, in a conventional thermoelectric conversion element, a configuration in which a magnetic field is applied to improve material conversion efficiency has not been proposed.

[0008] Although the present invention has been actively researched for improving the figure of merit of thermoelectric conversion materials, the present invention has been considered in that the improvement of thermoelectric conversion efficiency is limited only by the improvement of material properties. Another object of the present invention is to provide a method of using a thermoelectric conversion material in which a Seebeck coefficient is improved by applying a magnetic field to the thermoelectric conversion material, and to provide a high-performance thermoelectric conversion element in which thermoelectric conversion efficiency is greatly improved.

[0009]

Means for Solving the Problems The inventors of the present invention have studied various methods of applying a magnetic field to a thermoelectric conversion material having a temperature gradient in order to provide a high-performance thermoelectric conversion element. Completed the present invention by finding that the Seebeck coefficient was significantly improved by applying a magnetic field to the electrodes and adopting a configuration in which the electrodes were arranged so that a temperature gradient was applied in the direction perpendicular to both the temperature gradient and the magnetic field. did.

[0010] In the conventional configuration of the thermoelectric conversion element, there is a method in which a temperature difference is not generated between the positive and negative electrodes attached to the thermoelectric material. However, the present invention is characterized in that a temperature difference is provided between the positive and negative electrodes. With such a configuration, even when the applied magnetic field is low, the Seebeck coefficient of the thermoelectric conversion material is dramatically improved, and the conversion efficiency of the thermoelectric conversion element is greatly improved.

That is, according to the present invention, a magnetic field H is applied in a required direction (x-axis direction) of the thermoelectric conversion material, and a temperature gradient ΔT is given in a direction perpendicular to the direction (z-axis direction). This is a method of using a thermoelectric conversion material characterized in that the thermoelectric power is derived from each side of the temperature gradient in the direction (y-axis direction) to greatly improve the Seebeck coefficient of the material.

Also, the present invention provides a means for applying a magnetic field H in a required direction (x-axis direction) of a p-type and n-type thermoelectric conversion material, and a temperature gradient ΔT in a direction perpendicular to the direction (z-axis direction). A thermoelectric conversion element having means for applying and a means for conducting pn connection in a direction (y-axis direction) orthogonal to the two directions and for deriving a thermoelectromotive force from each side of the temperature gradient.

[0013] Further, the present invention proposes a thermoelectric conversion element using a permanent magnet as a means for applying a magnetic field H.
A configuration in which permanent magnets and thermoelectric conversion materials are alternately arranged in the direction of application of H, and a configuration in which p-type and n-type thermoelectric conversion materials are alternately arranged on the plane of a plate-shaped permanent magnet that generates a magnetic field in the thickness direction In the above configuration, a configuration in which p-type and n-type thermoelectric conversion materials are alternately arranged on a silicon substrate, a plate-shaped permanent magnet and a thermoelectric conversion material disposed thereon are arranged in a direction in which a magnetic field H is applied. With a configuration in which a plurality of pairs are stacked, conversion efficiency can be greatly improved.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A rectangular parallelepiped thermoelectric conversion material shown in FIG. 1A
Assuming that 1 is placed on the heat source, the temperature gradient T is given in the figure from the bottom to the top in the z-axis direction. Here, a magnetic field H is applied in the x-axis direction from the front to the back of the drawing. Further, in the figure orthogonal to both directions of the temperature gradient T and the magnetic field H, at both end faces of the thermoelectric conversion material 1 in the left and right y-axis directions, and so that a temperature difference occurs between the positive and negative electrodes, Electrodes 2 and 3 are provided on the lower side of the temperature gradient T on the lower left side and on the lower side of the temperature gradient T on the upper side of the right side, respectively. Leads are connected to each other to derive the thermoelectromotive force.

[0015] According to the present invention, the magnetic field H is applied in a direction perpendicular to the direction of the temperature gradient T, and the electrodes are arranged so that the temperature gradient T is given in a direction perpendicular to both directions of the temperature gradient T and the magnetic field H.
That is, a temperature difference is provided between the positive and negative electrodes. Even if the magnetic field H applied by such a configuration is low,
The Seebeck coefficient of the thermoelectric conversion material 1 is dramatically improved.

In the present invention, when the temperature difference between the electrodes 2 and 3 is reduced, the generated electromotive force is only the Nernst effect due to the magnetic field H, so that a large electromotive force cannot be obtained. Therefore,
When the temperature difference between the electrodes 2 and 3 is 1 ° C or more, the thermoelectric effect and Nern
The Seebeck coefficient is dramatically improved by the synergistic effect of the st effect. When this temperature difference exceeds 5 ° C., it is almost the same even if a temperature difference is given. Preferred temperature difference is 50-100 ° C
However, the magnetic field effect is sufficiently exhibited even at a temperature of several hundred degrees Celsius.

In the present invention, the magnitude of the magnetic field H is not particularly limited, but by setting it to 1 kOe or more, the above-mentioned synergistic effect functions effectively. A preferred magnetic field strength is 3 kOe or more.

The magnetic field to be applied is sufficient even if the magnetic field strength can be obtained from a permanent magnet of any material and shape. For example,
A magnetic field generated by a Sm-Co-based or Nd-Fe-B-based rare earth permanent magnet is very convenient for practical use as a thermoelectric conversion element incorporating a permanent magnet. In particular, when performing thermoelectric conversion at a high temperature of 300 ° C. or higher, a Sm-Co-based (Tc-900 ° C.) permanent magnet having a high Curie point is preferable as a magnet for generating a magnetic field.
When the temperature is lower than 00 ° C., Nd—Fe—B permanent magnets are preferable.

The means for applying a magnetic field is not limited to the above-described permanent magnet, and any magnetic field generating device such as an electromagnetic coil can be used.

In the present invention, since the means for imparting a temperature gradient does not particularly require a large temperature difference as described above, it is known to heat or cool one of the thermoelectric conversion materials, or to contact one of a heating source and a cooling source. Any method of
It may be appropriately selected along with the modularization of the thermoelectric conversion element described later.

Using the p-type thermoelectric conversion material and the n-type thermoelectric conversion material having the configuration shown in FIG. 1A, various types of thermoelectric conversion elements can be assembled. In addition, in order to modularize the thermoelectric conversion element to which a magnetic field is applied, as shown in FIG.1B, the magnetic field H direction (x-axis direction) of the permanent magnet 6 is changed in the direction of the temperature gradient T (z-axis direction).
And the p-type thermoelectric conversion material 4 and the n-type thermoelectric conversion material 5 are alternately arranged with the permanent magnet 6 interposed therebetween, so that the lead wires 7 and 8 of the p / n junction are on the high temperature side, There is an advantage that it can be connected separately on the low temperature side. Further, by employing this arrangement, a temperature difference can be automatically given between the electrodes of the thermoelectric conversion materials 4 and 5. Note that the direction of the lead wire is
The p-type thermoelectric conversion material 4 at the left end of the figure
In this case, the high-temperature side lead wire 8 is connected to the rear end face in the figure, and the low-temperature side lead wire 7 is connected to the front end face in the drawing, as in FIG. 1A.

[0022] The applicant has previously proposed, as an inexpensive thermoelectric conversion material with good productivity and stable quality, for example, P, so that the carrier concentration in a Si semiconductor is 10 ¹⁷ to 10 ²¹ (M / m ³ ). By adding single or composite additions of various additional elements such as B and Al and adjusting the amounts thereof, the Seebeck coefficient is extremely large, and a Si-based thermoelectric conversion material with significantly improved thermoelectric conversion efficiency is proposed (WO99 / 22
410).

[0023] This Si-based material can reduce the thermal conductivity by various additive elements, and can be formed by a conventionally known Si-G
The Seebeck coefficient becomes equal to or higher than the e-type and Fe-Si-type at a predetermined carrier concentration, and shows a large figure of merit as a thermoelectric conversion material and can achieve high performance.

Further, as shown in FIG. 2, the silicon substrate 10 can be impregnated with various additional elements to make a necessary portion of the Si-based material a Si-based thermoelectric conversion material. Therefore, as shown in FIG.2A, a strip-shaped thermoelectric conversion material is formed in the short side direction (z-axis direction) of the substrate 10 giving the temperature gradient T, and the p-type thermoelectric conversion material 11 and the n-type The thermoelectric conversion materials 12 are alternately arranged, and p / n junctions are separately connected on the high temperature side and the low temperature side of the temperature gradient T using the wires 13 in the long side direction (y-axis direction).

The silicon substrate 10 on which the above-mentioned thermoelectric conversion material is formed
Then, plate-like permanent magnets 14 magnetized in the thickness direction (x-axis direction) are alternately laminated in a required pattern to produce a thermoelectric conversion element unit.

As shown in FIG. 2B, one end face side of the silicon substrate 10 is placed on a required heat source 15, for example, so that the thickness direction (x-axis direction) of the p-type and n-type thermoelectric conversion materials 11, 12 A magnetic field H is applied to the substrate, and a temperature gradient ΔT is provided in the mounting direction of the substrate 10 (z-axis direction) perpendicular to the magnetic field H, and a pn connection is made in the front-rear direction (y-axis direction) in the drawing orthogonal to the two directions. A thermoelectric conversion element configured to derive a thermoelectromotive force from each of the high and low sides of the temperature gradient T is obtained.

As shown in FIG. 2B, the size of the thermoelectric conversion element in the direction of the temperature gradient T is regulated so that the plate-like permanent magnet 14 does not directly contact the heat source 15, but if necessary, Since a magnetic heat insulating material can be interposed between the heat source 15 and the silicon substrate 10, it may not be necessary to perform dimensional control itself.

Further, the Si-based thermoelectric conversion material has the above-described structure,
It can also be manufactured as a rod-shaped material, and as shown in FIG. 3, the longitudinal direction of the rod-shaped thermoelectric conversion material is arranged in the short side direction on the plate-shaped permanent magnet 20, and p
Type thermoelectric conversion material 21 and n-type thermoelectric conversion material 22 are alternately arranged, and the p / n junction is formed by using the wire 23 in the long side direction (y-axis direction), and the temperature gradient T (z-axis direction). Connect separately on the high-temperature side and low-temperature side, and place thermoelectric conversion materials 21 and 22 in the thickness direction.
By laminating a plurality of pairs of plate-like permanent magnets 20 magnetized in the (x-axis direction), and connecting the thermoelectric conversion material on the plate-like permanent magnet 20 with the thermoelectric conversion material on the other plate-like permanent magnets 20 by pn connection. A unit to which a required number of thermoelectric conversion elements are connected can be manufactured.

As shown in FIG. 3B, each of the thermoelectric conversion materials 21 and 2
By arranging one end face in the longitudinal direction of 2 on the heat source 25, a magnetic field H is applied in the thickness direction of the p-type and n-type thermoelectric conversion materials 21 and 22, and each material orthogonal to this is applied. A temperature gradient ΔT is provided in the longitudinal direction, and a thermoelectric conversion element having a configuration in which the pn connection is made in the front-rear direction in the drawing orthogonal to the two directions and the thermoelectromotive force is derived from each of the high and low sides of the temperature gradient T is obtained.

[0030] In the present invention, as the thermoelectric conversion material, any known material can be adopted in addition to the above-mentioned novel Si-based thermoelectric conversion material. In particular, in addition to Bi ₂ Te ₃ system, Si, at least one of Ge, C, Sn is 5 to 10 atomic%, Si is a P-type semiconductor or
At least one of the additional elements for forming an N-type semiconductor
0.001 atomic% to 20 atomic%, and the G
Ge, such as a Si-based thermoelectric conversion material having a crystal structure in which one or more of e, C, and Sn or one or more of additional elements are precipitated.
A Si-based thermoelectric conversion material containing not more than 20 atomic% is preferable because of its extremely high thermoelectric conversion efficiency. Also, a thermoelectric conversion material made of a known Si-Ge alloy, which has a Ge content lower than that of the conventional Si-Ge alloy and has a content of 20 atomic% or less, is preferable because the Seebeck coefficient is improved.

[0031]

EXAMPLE In order to prepare N-type and P-type Si-based thermoelectric conversion materials, high-purity Si (10N) and Ge (4N) were blended at the ratios shown in Table 1, and then mixed in an Ar gas atmosphere. Arc melted. The obtained button-shaped ingot was cut into a shape of 5 × 5 × 15 mm, and the Seebeck coefficient was measured. For the Bi ₂ Te ₃ sample, a commercially available sample having the composition shown in Table 2 was used to measure the Seebeck coefficient.

The Seebeck coefficient of the sample was measured by setting the electrodes at both ends to Pt, keeping the average temperature of the high temperature part and the low temperature part constant at 50 ° C., and changing the magnetic field and the temperature difference applied to the thermoelectric material. The magnetic field strength was adjusted by changing the distance between the Nd-Fe-B permanent magnets. The power generated at that time is the voltage (mv / K) and the current value
(mA / K) was measured. Table 3 shows the measurement results.
It is shown in Table 4.

[0033]

【table 1】

[0034]

[Table 2]

[0035]

[Table 3]

[0036]

[Table 4]

[0037]

The present invention utilizes a synergistic effect of the Seebeck effect and the Nernst effect by applying a magnetic field to the thermoelectric conversion material, giving a temperature gradient in a required direction and providing a temperature difference between the electrodes. Thereby, the characteristics of the thermoelectric conversion material can be dramatically improved. In addition, when a thermoelectric conversion element is configured according to the present invention, a configuration in which a magnetic field is generated by a permanent magnet is employed, so that the thermoelectric conversion element can be easily manufactured with a relatively simple structure, and can be used without any maintenance during use. is there.

[Brief description of the drawings]

FIG. 1A is an explanatory perspective view of a thermoelectric conversion material according to the present invention, showing a method of using the material, and FIG. 1B is an explanatory perspective view showing a configuration example of a thermoelectric conversion element according to the present invention.

FIG. 2A is a perspective explanatory view showing another configuration example of the thermoelectric conversion element according to the present invention, and B is a front explanatory view.

FIG. 3A is a perspective explanatory view showing another configuration example of the thermoelectric conversion element according to the present invention, and FIG. 3B is a front explanatory view.

[Explanation of symbols]

 1 Thermoelectric conversion material 2,3 Electrode 4,11,21 p-type thermoelectric conversion material 5,12,22 n-type thermoelectric conversion material 6 Permanent magnet 7,8 Lead wire 10 Silicon substrate 13,23 Wire 14,20 Plate permanent magnet 15,25 heat source

Claims (11)

[Claims] 1. A magnetic field in a required direction (x-axis direction) of a thermoelectric conversion material.
H, and the temperature gradient Δ in the direction (z-axis direction)
A method for using a thermoelectric conversion material that gives T and derives thermoelectromotive force from each side of a temperature gradient in a direction orthogonal to the two directions (y-axis direction). 2. The required direction of the p-type and n-type thermoelectric conversion materials (x
A means for applying a magnetic field H in the (axial direction) and a direction orthogonal to this
A thermoelectric conversion element having means for imparting a temperature gradient ΔT in the (z-axis direction) and means for deriving thermoelectromotive force from each of the high and low sides of the temperature gradient in a direction (y-axis direction) orthogonal to the two directions. 3. The required direction of the p-type and n-type thermoelectric conversion materials (x
A means for applying a magnetic field H in the (axial direction) and a direction orthogonal to this
(Z-axis direction) a means for imparting a temperature gradient ΔT, and a thermoelectric device having a pn connection in a direction (y-axis direction) orthogonal to the two directions and a means for deriving a thermoelectromotive force from each side of the temperature gradient. Conversion element. 4. A temperature gradient ΔT in a direction between electrodes provided on a material end face for deriving a thermoelectromotive force is set to 1 ° C. or more.
Or the thermoelectric conversion element according to claim 3. 5. The magnetic field H having a magnitude of 1 kOe or more.
Or the thermoelectric conversion element according to claim 3. 6. The thermoelectric conversion element according to claim 2, wherein the means for applying the magnetic field H is a permanent magnet. 7. The thermoelectric conversion material is a Bi ₂ Te ₃ system or Ge
4. The thermoelectric conversion element according to claim 2, wherein the thermoelectric conversion element is a Si-based material or a Si-Ge alloy containing at most atomic%. 8. The thermoelectric conversion element according to claim 6, wherein permanent magnets and thermoelectric conversion materials are alternately arranged in a direction in which the magnetic field H is applied. 9. The thermoelectric conversion element according to claim 6, wherein p-type and n-type thermoelectric conversion materials are alternately arranged on a plane of a plate-shaped permanent magnet that generates a magnetic field in a thickness direction. 10. The thermoelectric conversion element according to claim 9, wherein p-type and n-type thermoelectric conversion materials are alternately arranged on a silicon substrate. 11. The thermoelectric conversion element according to claim 9, wherein a plurality of plate-shaped permanent magnets and thermoelectric conversion materials disposed thereon are laminated in a direction in which the magnetic field H is applied.