JPH06268263A - Manufacture of thermoelectric element material - Google Patents

Abstract

PURPOSE:To obtain a thermoelectric element nearly equal in conversion characteristics to a conventional one farmed of only SiGe by a method wherein the thermoelectric element is formed of SiGe encapsulated in FeSi2. CONSTITUTION:Slave particles 2 of FeSi2 are formed and attached around a mother particle 1 of SiGe to form a micro capsule particle 3. Thereafter, the micro capsule particles 1 are gathered into a body of prescribed shape. The body of SiGe and FeSi2 is sintered by plasma into a sintered body used for a thermoelectric device material. Mother particles 1 are linked together and kept in point contact with each other, and the slave particles 2 are uniformly attached around the mother particles and uniformly interposed among the mother particles 1 in the above sintered body. The sintered body is thermally treated into a thermoelectric element. By this setup, a thermoelectric element high in resistance to corrosion and heat and excellent in conversion efficiency can be obtained.

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 generator material for forming a thermocouple or the like.

[0002]

2. Description of the Related Art Conventionally, as a typical method for producing a thermoelectric generator such as a thermocouple or an electronic refrigeration element, a material powder obtained by a stamp mill, a gas atomizing method or the like is collected into a predetermined shape and hot pressed, After solidification using discharge sintering, plasma sintering, etc., this is heat-treated at a predetermined temperature to transform the metal phase (α phase) to the semiconductor phase (β phase), and then to the end etc. A method is known in which lead wires, electrodes, etc. are brazed or soldered.

FeSi ₂ and SiGe are mainly used as materials for these thermoelectric generators. In particular, since this FeSi ₂ is a thermoelectric material having excellent corrosion resistance and heat resistance, it has the property that it can be used in the air at high temperature. On the other hand, SiGe has a characteristic that it exhibits a conversion efficiency about 2-3 times higher than that of FeSi _2, and therefore, it has recently become the mainstream of thermoelectric materials in place of FeSi ₂ .

[0004]

By the way, as described above, this SiGe has the characteristic of exhibiting a higher conversion efficiency than FeSi ₂ , but on the other hand,
It has a drawback that it is easily sublimated when used at high temperatures and has low mechanical strength, and its practical range is narrow.

Therefore, the present invention has been devised to effectively solve this problem, and its purpose is to provide a novel thermoelectric power generation element material having excellent corrosion resistance and heat resistance and high mechanical strength. A manufacturing method is provided.

[0006]

In order to solve the above-mentioned problems, the first invention is to provide Fe around a mother particle made of SiGe.
A microcapsule powder is formed by adhering child particles made of Si ₂ , and the microcapsule powder is assembled into a predetermined shape and then sintered, and the second invention is the above microcapsule powder. Further, grandchild particles made of CuO are further attached to the periphery of the to form a composite microcapsule powder, and the composite microcapsule powder is assembled into a predetermined shape and then sintered.

The present invention will be supplementarily described below. First, the particle size of the mother particles used in the present invention is not particularly limited, but it is desirable that the particle size is 10 to 100 μm and uniform. That is, from the viewpoint of obtaining a dense sintered body, the smaller the particle size of the mother particles, the lower the thermal conductivity and the improved thermoelectric properties. Therefore, it is preferable that the particle size is small, but as described above. This is because, in order to attach child particles or grandchild particles having a smaller particle size around the mother particles, a certain size is required in view of the particle production limit. Therefore, the particle size of the child particles may be about 1 to 10 μm and at least smaller than the mother particles, and the particle size of the grandchild particles may be 1 μm or less and smaller than the child particles.

Further, it is not necessary to use a new method as a method for producing the microcapsule powder and the composite microcapsule powder, and a conventionally well-known microencapsulation method such as an electrostatic adhesion method or a mechanical impact method is used. You can Further, as a method for obtaining these mother particles, child particles, and grandchild particles, an ingot-shaped metal body can be obtained by a mechanical method such as a Banbury mixer, but the gas atomizing method is excellent in that powder of a desired size can be easily obtained. ing. Also,
Sintering can be performed by a general method such as a hot pressing method or a cold pressing method, but the plasma sintering method is the most excellent for producing in a short time. That is, according to the plasma sintering, the surface of the powder is activated by the plasma discharge, and the sintering is completed at a low temperature in a short time, so that the growth of crystal grains can be suppressed and the heat conduction due to the grain boundaries is reduced. This is because the thermoelectric properties are also improved.

The reason for adding CuO is to improve the strength and reliability of the material at high temperatures. And, the addition amount is preferably in the range of 2 to 20 wt% of the whole. Two
If it is less than wt%, the strength and the reliability of the material at high temperature are not improved, and if it exceeds 20 wt%, the characteristics as a thermoelectric element are remarkably deteriorated.

[0010]

In the first aspect of the invention, as described above, SiGe is replaced with Fe.
By encapsulating with Si ₂ , FeSi ₂ having corrosion resistance and heat resistance intervenes so as to coat SiGe, and sublimation of SiGe is prevented.
SiGe will exhibit high conversion efficiency. Also,
When sintering, if the encapsulation is perfect, FeSi ₂ child particles are always present between SiGe mother particles and S
It is concerned that iGe each other is no longer able to bind, it is impossible to obtain a complete capsule powders, since a portion where SiGe is not coated on FeSi ₂ always exists slightly, from FeSi ₂ Electric current preferentially flows in SiGe having low resistance, and SiG is formed in a point contact manner.
Therefore, a good sintered body can be obtained.

In the second invention, the child particles are further made of Cu.
Since the particles are encapsulated with the O-based grandchild particles, CuO is uniformly present in the sintered body, so that the mechanical strength of the sintered body is improved. That is, SiG as a mother particle
Since e has copper affinity, this CuO melts at the time of sintering and acts as an adhesive for the mother particles.
Also, encapsulation with CuO is not only for improving the strength, but FeS.
i ₂ will be restored. To explain this in detail, FeSi ₂ has a β phase (semiconductor phase) that has a thermoelectric property at 980 ° C. or lower, but an α phase (metal phase that does not have a thermoelectric property at higher temperatures). ), And the function is not exhibited, but CuO (C
By adding a small amount (about 2 wt%) of u or CuO ₂ ), even after the transition to the α phase at 980 ° C. or higher, 8
When the temperature is lowered to 30 ° C., the β phase is restored and the characteristics are restored. On the other hand, the sintered body to which CuO is not added cannot be used because once it is transformed into α phase at 980 ° C. or higher, it is not returned to β phase even if the temperature is lowered thereafter. Therefore, in the case of the conventional sintered body to which CuO is not added, it is theoretically possible to use up to 980 ° C., but once it becomes higher than that, it becomes unusable. Limit temperature is about 800
The temperature is set to about ℃, but in the present invention, by adding CuO, even if it becomes 980 ℃ or higher, 8
When the temperature is lowered to 30 ° C., it returns to the β phase again and exhibits its characteristics. Therefore, the use limit temperature can be set to the upper limit of 980 ° C.

[0012]

EXAMPLES Examples of the present invention will be described below.

(Embodiment 1) Using a gas atomizing apparatus as shown in FIG. 4, a particle size of 20 to 3 is obtained as shown in FIG.
A mother particle 1 made of SiGe having a diameter of about 0 μm and a particle size of 2 to
The child particles 2 of about 3 μm made of FeSi ₂ are formed and adhered to the periphery of the mother particles 1 to form the microcapsule powder 3. After that, the microcapsule powder 3 is collected into a predetermined shape and plasma-sintered to form SiGe A sintered body, which is a thermoelectric element material made of FeSi ₂ , was obtained. Then, the sintered body was cut at an arbitrary portion, and the cut surface was observed with a microscope.
It was confirmed that the mother particles 1 were connected to each other in a point contact state, and the child particles 2 were uniformly present around and around the mother particles 1 as shown in FIG. Further, the sintered body was heat-treated to form a thermoelectric element, and its characteristics were examined. As a result, conversion characteristics similar to those of a thermoelectric element made of only SiGe were exhibited, and sublimation at high temperature was hardly observed.

(Example 2) Using the gas atomizing apparatus in the same manner as in Example 1, as shown in FIG. 4, grandchild particles 4 made of CuO having a particle size of about 0.1 to 0.5 μm are further formed. The grandchild particles 5 were attached to the periphery of the capsule powder 3 at a ratio of 2 wt% of the whole to form a composite microcapsule powder 6, and a sintered body was obtained in the same manner as in Example 1. As a result of examining the strength of this sintered body, it was confirmed that the strength compared with Example 1 was improved by about 22%.

A thermoelectric element is formed from this sintered body,
As a result of investigating the electromotive force generated by the heat effect, as shown in FIG. 5 (A), the electromotive force of the thermoelectric element containing CuO increased with the temperature rise, and suddenly exceeded 980 ° C. It was confirmed that although the characteristics were lowered and the characteristics were lost, the characteristics were recovered again at 830 ° C. when the temperature was lowered. On the other hand, as shown in FIG. 5B, when the thermoelectric element obtained from the sintered body of Example 1 to which CuO was not added, once the temperature exceeded 980 ° C., the characteristics were not recovered even after the temperature was lowered. There wasn't.

[0016]

In summary, according to the present invention, SiG
By encapsulating e with FeSi ₂ , corrosion resistance and high conversion efficiency can be exhibited. Further, addition of CuO to this improves the strength and also improves the reliability of the material at high temperatures.
It has excellent effects such as improvement of conversion efficiency.

[Brief description of drawings]

FIG. 1 is an enlarged sectional view showing an example of microcapsule powder.

FIG. 2 is a partially enlarged sectional view of a sintered body made of microcapsule powder.

FIG. 3 is an enlarged cross-sectional view of a composite microcapsule powder and part A thereof.

FIG. 4 is a schematic view showing an embodiment of a gas atomizing apparatus.

FIG. 5 is a graph showing the thermoelectric element characteristics when CuO is added (A) and when CuO is not added (B).

[Explanation of symbols]

1 mother particle (SiGe) 2 child particle (FeSi ₂ ) 3 microcapsule powder 4 grandchild particle (CuO) 5 composite microcapsule powder

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Eiji Okumura 8 Isabi, Fujisawa, Kanagawa Prefecture, Isuzu Central Research Institute

Claims (2)

[Claims] 1. Fe is formed around a mother particle made of SiGe.
A method for producing a thermoelectric power generation element material, characterized in that microcapsule powder is formed by adhering child particles made of Si ₂ , and the microcapsule powder is collected into a predetermined shape and then sintered. 2. A composite microcapsule powder is formed by further adhering grandchild particles made of CuO around the microcapsule powder, and the composite microcapsule powder is assembled into a predetermined shape and then sintered. The method for producing a thermoelectric generator element material according to claim 1, wherein