JPH06204571A - Manufacture of composite thermoelectric material - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To provide a method for producing a composite thermoelectric material, which is capable of easily compositing a SiGe thermoelectric material with an iron silicide thermoelectric material and improving energy conversion efficiency at low cost. A capsule particle 4 is formed by using a p-type or n-type adjusted iron silicide thermoelectric material as a mother particle 2 and a p-type or n-type adjusted SiGe-based thermoelectric material as a child particle 3. After being charged in a molding die, it is sintered and solidified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a thermoelectric material constituting a thermoelectric generator used for a thermocouple or the like, and more particularly to a method for producing a composite thermoelectric material.

[0002]

2. Description of the Related Art As is well known, a thermoelectric generator is an element that converts thermoenergy into electric energy by utilizing thermoelectric effect or vice versa. As a typical example, a thermocouple or an electronic refrigeration element (Peltier element) is used. Element) and the like. This thermocouple uses the Seebeck effect in which two types of metal wires are connected to form a closed circuit, and when two contacts are kept at different temperatures, a thermoelectromotive force is generated between these contacts. It measures and measures the temperature. On the other hand, the electronic refrigeration element generates heat other than Joule heat at the contact surface when a current flows through the contact surface between different kinds of conductors or semiconductors.
It utilizes the Peltier effect in which absorption occurs, and is often used when precise temperature control is required in the range of -20 ° C to + 70 ° C.

In this thermoelectric generator, several standard combinations are defined by JIS standards and the like, and one of them is FeSi composed of a combination of a p-type iron silicide thermoelectric material and an n-type iron silicide thermoelectric material. ₂ There are thermoelectric generators.

FIG. 4 shows an example of a method of manufacturing the FeSi ₂ thermoelectric generator. This will be briefly described step by step. First, Mn or Co, which is an additional element, is added to Fe and Si, respectively, and these are separately melted at a temperature of 1873K to produce two types of ingots,
These are separately pulverized and granulated using a stamp mill or the like to produce p-type raw material powder and n-type semiconductor raw material powder. And these raw material powders are charged into the mold after the cold pressing, vacuum, and sintered at 1433K, phase thereafter which an intrinsic semiconductor phase beta-FeSi ₂ metal phase of alpha-FeSi ₂ In order to transfer, heat treatment is performed at 1063K in the atmosphere, and lead wires are brazed or soldered as necessary to complete the process.

As a means for improving the performance of a thermoelectric power generation element using such an iron silicide thermoelectric material, for example, thermal conduction can be achieved by controlling grain boundaries during sintering such as atomizing powder and sintering conditions. The rate is being reduced.

[0006]

By the way, the thermoelectric materials manufactured by the conventional techniques have the following problems. That is, although the iron silicide thermoelectric material is excellent in heat resistance and oxidation resistance, it has a problem of low energy conversion efficiency because of its high electric resistance and thermal conductivity.

As a countermeasure, there is a grain boundary control at the time of sintering as described above, but the control is difficult.

On the other hand, silicon germanium (Si
The Ge) thermoelectric material is a material that is lightweight and has high energy conversion efficiency. However, since it is poor in corrosion resistance, a very complicated surface coating is required, and since it is a very expensive material, there is a problem that it is not suitable for use alone.

In view of the above-mentioned problems, an object of the present invention is to provide a method for producing a composite thermoelectric material, which can easily combine a SiGe thermoelectric material with an iron silicide thermoelectric material and can improve energy conversion efficiency at low cost. To provide.

[0010]

[Means for Solving the Problems] In order to achieve the above object,
A method for manufacturing a composite thermoelectric material according to the present invention is a p-type or n-type.
Molded iron silicate thermoelectric material as mother particles, and p-type or n-type adjusted SiGe-based thermoelectric material as child particles to form capsule particles, which are charged into a molding die and then sintered. It is intended to solidify.

In the above structure, preferably, the child particles are mixed in at least 1 wt% or more with respect to the mother particles.

[0012]

According to the above construction, the mother particles of the capsule particles are formed of the iron silicide thermoelectric material adjusted to p-type or n-type. On the other hand, the child particles of the capsule particles,
It is formed of a SiGe-based thermoelectric material adjusted to p-type or n-type.

As described above, the iron silicide thermoelectric material has excellent heat resistance and oxidation resistance, but has low energy conversion efficiency. On the other hand, the SiGe thermoelectric material is lightweight and has high energy conversion efficiency, but is inferior in corrosion resistance and is very expensive.

Therefore, if the periphery of the iron-silicide thermoelectric material as the mother particles is covered with the SiGe thermoelectric material as the child particles to form capsule particles, and the capsule particles are sintered and solidified in the molding die, the iron-silicide is formed. Since the surface of the material thermoelectric material is solidified in a state of being covered with the SiGe thermoelectric material, the electrical resistance and the thermal conductivity of the grain boundary surface of the iron silicide thermoelectric material that is the mother particle are lowered by the SiGe thermoelectric material that is the child particle. Therefore, thermoelectric materials with high energy conversion efficiency can be manufactured at low cost.

Further, in order to lower the electric resistance and the thermal conductivity of the grain boundary surface of the iron silicide thermoelectric material as the mother particles,
It is necessary to mix at least 1 wt% or more of child particles with respect to mother particles.

Further, if the mixing amount of the child particles is small, the corrosion resistance does not decrease due to the influence of the SiGe thermoelectric material.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the method for producing a composite thermoelectric material according to the present invention will be described in detail below with reference to the accompanying drawings.

In the method for manufacturing the composite thermoelectric material of this embodiment, first, the mother particles and the child particles constituting the capsule particles are formed. For the mother particles, powder of iron silicide (FeSi ₂ ) thermoelectric material is used. In the case of p-type, Mn or the like is added during the production of FeSi ₂ powder. On the other hand, in the case of n-type, FeSi
₂ Add Co etc. at the time of manufacturing powder. Further, in both cases, Si is set to be excessive with respect to Fe compared to the usual composition.

That is, the production of this FeSi ₂ powder is performed as shown in FIG.
As shown in FIG. 1A, raw material powders containing a small amount of Mn or Co, which is an additional element, were added to powders of Fe and Si in the crucible 1 and mixed, and then as shown in FIG. Is melted by high-frequency heating, and the molten metal is spray-cooled in an inert gas atmosphere such as Ar as shown in FIG. 1 (c). Note that these processes are continuously performed by one device. If necessary, the FeSi ₂ atomized powder is pulverized using a stamp mill, a ball mill or the like.

As the child particles, SiGe powder manufactured by the same method as the mother particles is used. In the case of p type,
Al or the like is added at the time of manufacturing the SiGe powder. On the other hand, in the case of n-type, P, Sb, etc. are added at the time of manufacturing SiGe powder. Furthermore, GaP is added to both and Ge is added to S.
About 50 to 70 wt% is mixed with i. And, 1 wt% or more of the child particles relative to the mother particles, preferably,
About 3 to 5 wt% is mixed.

Next, as shown in FIG. 2, capsule particles 4 are formed from the mother particles 2 and the child particles 3 thus formed.
To form. The capsule state is a state in which the child particles 3 are attached to the periphery of the mother particles 2, and can be formed by using a well-known technique such as an electrostatic attachment method or a mechanical impact method. To encapsulate in this way, FeSi as the mother particles 2 is used.
₂ The particle size of the powder is formed to about 1 to 10 μm, and the particle size of the SiGe powder as the child particles 3 is
For example, it is desirable to set the value as small as about 1/10 to 1/20. This is because when the particles have such a particle size, the density of the sintered body increases and the SiGe powder as the child particles 3 is uniformly dispersed on the surface of the FeSi ₂ powder as the mother particles 2.

Then, the thus-formed capsule particles 4 are housed in a molding die (not shown), which is sintered and solidified by, for example, a plasma sintering apparatus. The sintering method is not limited to this plasma sintering method, and other sintering methods such as a hot pressing method may be used, and the sintering method is the same as the case of sintering an ordinary iron silicide thermoelectric material.

In this way, the Si in the FeSi ₂ thermoelectric material is
A composite thermoelectric material in which a Ge thermoelectric material is composited is manufactured.

Next, the operation of the above embodiment will be described.

According to the method of manufacturing the thermoelectric generator of this embodiment, the mother particles 2 of the capsule particles 4 are Mn or Co.
Is added to form a p-type or n-type FeSi ₂ thermoelectric material. On the other hand, the child particles 3 of the capsule particles 4 are formed of p-type or n-type SiGe-based thermoelectric material by adding Al or P. Then, the particle size of the FeSi ₂ powder as the mother particles 2 is formed to about 1 to 10 μm, and the S as the child particles 3 is formed.
The particle size of the iGe powder relative to the particle size of the mother particles 2 is, for example,
By setting the size as small as one tenth to one tenth, capsule particles in which the child particles 3 are uniformly dispersed are formed around the mother particles 2.

Therefore, when the capsule particles 4 are sintered and solidified in the molding die by the plasma sintering method, the surface of the FeSi ₂ thermoelectric material is compositely solidified while being covered with the SiGe thermoelectric material. As a result, the electric resistance and the thermal conductivity of the grain boundary surface of the FeSi ₂ thermoelectric material, which is the mother particle 2, are S and
It is possible to manufacture a composite thermoelectric material having a high energy conversion efficiency which is lowered by the iGe thermoelectric material.

Moreover, since SiGe itself is a thermoelectric material, the thermoelectric power can be improved. This relationship can be expressed by the following mathematical formula.

[0028]

[Equation 1]

In the above equation, the larger the value of Z, the higher the energy conversion efficiency. Therefore, the FeGe ₂ thermoelectric material is made of SiGe.
The energy conversion efficiency of the thermoelectric material that is a composite of thermoelectric materials is improved. However, in order to reduce the electrical resistance and thermal conductivity of the grain boundary surface of the FeSi ₂ thermoelectric material that is the mother particle 2, it is necessary to mix at least 1 wt% or more of the SiGe thermoelectric material that is the child particle 3 with respect to the mother particle 2. . By thus combining the FeGe ₂ thermoelectric material with the SiGe thermoelectric material, the energy conversion efficiency of the FeSi ₂ thermoelectric material can be improved without degrading the heat resistance of the FeSi ₂ thermoelectric material.

The SiGe thermoelectric material as the child particle 3 is 3 to 5 w with respect to the FeSi ₂ thermoelectric material as the mother particle 2.
Since t% is mixed and only a small amount is used, the manufacturing cost can be reduced as compared with the case where the SiGe thermoelectric material itself is used.

Further, the method of manufacturing the thermoelectric material of this embodiment can be easily performed by a well-known sintering method such as a plasma sintering method or a hot pressing method. In particular, since the SiGe powder as the child particles 3 is fine particles, the sintering density can be improved.

As described above, the mixing amount of the child particles 3 is 3 to 5 wt% with respect to the mother particles 2. With such a small amount, even if the SiGe thermoelectric material is exposed on the surface, the composite thermoelectric material is exposed. The corrosion resistance of the material does not deteriorate. Thus, for the FeSi ₂ thermoelectric material as the mother particle 2, the S as the child particle 3
The reason why the iGe thermoelectric material is mixed in an amount of 3 to 5 wt% is to reduce the electric resistance and the thermal conductivity of the grain boundary surface of the mother particle 2 in a range that does not reduce the corrosion resistance as described above.

FIG. 3 shows that 3 SiGe is added to FeSi ₂ .
This shows the difference in specific resistance between the case where wt% is mixed and the case where no wt% is mixed. As shown in the figure, it can be seen that the specific resistance is smaller when 3 wt% of SiGe is mixed than when no SiGe is mixed.

Table 1 below shows the effects of SiGe on FeSi ₂ by comparing the case of mixing 3 wt% of SiGe with FeSi ₂ , the case of mixing 5 wt% and the case of no mixing. The values in Table 1 are values at room temperature of 27 ° C.

[0035]

[Table 1]

According to Table 1 above, it was found that when SiGe is mixed in, the specific resistance and the thermal conductivity decrease, and the thermoelectric power improves.

[0037]

As described above, according to the method for manufacturing a composite thermoelectric material according to the present invention, SiG is used as the iron silicide thermoelectric material.
e An excellent effect that thermoelectric materials can be easily compounded and energy conversion efficiency can be improved at low cost.

[Brief description of drawings]

FIG. 1 shows a gas atomizing powder molding method used in an example of a method for producing a composite thermoelectric material according to the present invention, (a)
[FIG. 4] is an explanatory view of mixing of raw materials in the crucible, FIG.

FIG. 2 is a schematic view showing capsule particles in this example.

FIG. 3 is a graph showing a difference in specific resistance between the case where SiGe is mixed with FeSi ₂ and the case where SiGe is not mixed.

FIG. 4 is an explanatory diagram showing an example of a conventional method for manufacturing a thermoelectric generator.

[Explanation of symbols]

 2 Mother particles 3 Child particles 4 Capsule particles

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Eiji Okumura Eiji Okumura No. 8 Tsutana, Fujisawa City Kanagawa Prefecture Isuzu Central Research Institute (72) Inventor Shigeo Takita No. 8 Soil Shelf, Fujisawa City, Kanagawa Isuzu Central Research Co., Ltd. In-house (72) Inventor Hiroshi Matsumi 8 Tsutana, Fujisawa-shi, Kanagawa Inside Isuzu Central Research Institute

Claims (2)

[Claims] 1. SiGe adjusted to a p-type or an n-type by using a p-type or n-type adjusted iron silicide thermoelectric material as a mother particle.
A method for producing a composite thermoelectric material, characterized in that capsule particles are formed by using a thermoelectric material as a child particle, and the capsule particles are charged into a mold and then sintered and solidified. 2. The method for producing a composite thermoelectric material according to claim 1, wherein the child particles are mixed in at least 1 wt% or more with respect to the mother particles.