JPH06144825A - Production of thermoelectric element - Google Patents

Abstract

PURPOSE:To provide a process for producing a new thermoelectric element in improved production efficiency and facilitating the formation of quasi-stable alpha-FeSi2 and the integration with other material. CONSTITUTION:Raw material powder composed of Fe and Si is mixed with an additive such as transition element and melted to form an alloy liquid. Fine crystalline powder of alpha-FeSi2 (metallic phase) is formed from the alloy liquid by gas atomizing process and the produced powder is sintered and solidified to a prescribed form by plasma sintering process and, at the same time, converted to beta-FeSi2 (semiconductor phase) by phase transition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a thermoelectric generator used for a thermocouple or the like.

[0002]

2. Description of the Related Art As is well known, a thermoelectric generator is an element for converting thermal energy into electric energy by utilizing thermoelectric effect or vice versa. Typical examples are thermocouples and electronic refrigeration elements (Peltier elements). ) Is mentioned. 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. On the other hand, the electronic refrigeration element utilizes the Peltier effect in which heat other than Joule heat is generated and absorbed at the contact surface when a current flows through the contact surface between different conductors and semiconductors. -20 ° C
It is often used when precise temperature control is required within the range of plus 70 ° C.

In addition, some standard combinations of this thermoelectric generator are determined by the JIS standard and the like. One of them is a combination of a p-type iron silicide and an n-type iron silicide having a high electromotive force. There is a FeSi thermoelectric generator.

FIG. 6 shows a conventional manufacturing method of this FeSi thermoelectric generator. This will be briefly described step by step. First, two kinds of ingots were prepared in order to obtain metastable α-FeSi ₂ by adding Mn and Co, which are additional elements, respectively to Fe and Si, and melting and cooling them separately. After manufacturing, the ingots are separately crushed using a stamp mill or the like to manufacture p-type raw material powder and n-type raw material powder. Then, after the p-type raw material powder and the n-type raw material powder are gathered in a predetermined shape, cold pressed and sintered and solidified to be integrated, the α-FeSi ₂ (metal layer) to the β-FeSi ₂ (semiconductor) (Layer) is subjected to heat treatment in the atmosphere to cause a phase transition, and then a lead wire or an electrode is brazed or soldered to the end of the layer to complete.

[0005]

However, in the conventional manufacturing method, since α-FeSi ₂ is a high-temperature phase, the α-phase in a metastable state is formed in the cooling process of forming a melted ingot as in the conventional case. It was difficult to get. In addition, it is necessary to re-pulverize the melted material into powder,
The manufacturing efficiency was not good because the heat treatment time required for the α → β phase transition was long and there were many steps until the element was completed. Further, since the heat treatment temperature is 1063 [K] and the treatment time is 1.8 × 10 ⁵ [s], it is difficult to form a composite with a material having a melting point lower than this heat treatment temperature.

Therefore, the present invention has been devised in order to effectively solve these drawbacks, and its main purpose is to easily obtain metastable α-FeSi _{2 and} to combine it with a material. It is intended to provide a novel method for producing a thermoelectric power generation element, which can be easily made into a composite structure and which has improved production efficiency.

[0007]

In order to solve the above problems, the first invention is to form a melted alloy solution by mixing additives such as transition elements into a raw material powder composed of Fe and Si. Together with forming a fine crystal powder of α-FeSi ₂ (metal phase) from the alloy solution by a gas atomizing method,
The microcrystalline powder is sintered and solidified into a predetermined shape by a plasma sintering method or a hot pressing method, and β-FeSi ₂
It is a method of manufacturing a thermoelectric power generation element in which a (semiconductor phase) phase transition is performed.

In the second invention, an alloy solution is prepared by mixing Fe and Si in a predetermined ratio, and α-FeSi ₂ (metal phase) fine crystal powder is formed from the alloy solution by a gas atomizing method. After that, the α-FeSi ₂ microcrystalline powder is heat-treated in an inert gas to undergo a phase transition into β-FeSi ₂ (semiconductor phase) microcrystalline powder, and then the β-FeSi ₂
In this method, a transition element or the like is added to the microcrystalline powder, and this is sintered and solidified into a predetermined shape by a plasma sintering method or a hot pressing method.

A third aspect of the present invention is a method of manufacturing a thermoelectric generator, wherein the sintering and solidification is performed by a hot pressing method instead of the plasma sintering method.

A supplementary explanation of the present invention will be given below.
First, FeSi ₂ which is an intermetallic compound of iron and silicon has a metal phase α-FeSi ₂ (α phase) and a semiconductor phase β-Fe.
There are two phases, Si ₂ (β phase). Of these, the β phase is the most promising thermoelectric material. The α phase is also called a high temperature phase, and its existence range is 937 ° C to 1220 ° C.
However, FeSi ₂ obtained by melting is usually in the α phase. This is because the composition range of the α phase is 53.0 to 57.
This is because the β phase has a narrow composition range of 51 wt% Si as compared with 5 wt% Si, and it takes a lot of time because the β phase is generated by a solid phase reaction. Therefore, conventionally, the α phase was heat-treated in the range of 700 to 980 ° C. for a long time (30 to 100 hours) to perform the α → β phase transition. But α
There is a metastable state in the phase, which can be obtained by quenching. Since this metastable state is created through a thermodynamically nonequilibrium process called quenching, its internal energy is high and its crystalline state is thermally unstable. Therefore, the diffusion of atoms starts at a temperature of 500 ° C. or lower, which is lower than the conventional temperature, and the lattice is changed from α to β in an extremely short time (several seconds). The reason why the phase transition temperature is set to 500 ° C. or more is that there is a change depending on various conditions during sintering (atmosphere, pressure, temperature, mooring time, mold, additives, etc.).

The metastable α phase is the same as that of microcrystalline α-FeSi ₂ produced by quenching. The degree of fine crystals depends on the cooling rate, and if it exceeds a certain cooling rate, the state becomes amorphous. Thermally unstable whether it is microcrystalline or amorphous. The crystal structure of this metastable α phase is tetragonal and contains one FeSi ₂ in the unit cell. However, in reality, the composition of Fe _(1-X) Si ₂ is correct and is simply expressed as α-FeSi ₂ for convenience. On the other hand, β-FeSi ₂ is orthorhombic and has 16 Fe in the unit cell.
The composition including Si ₂ is FeSi ₂ without vacancy. Then, in order to transform α-FeSi ₂ into β-FeSi ₂ , it is necessary to change its crystal structure and supplement Fe or release excess Si. Normally, α-FeSi ₂ is in a eutectic state with FeSi ₂ , so β-FeSi ₂ is formed by a eutectic reaction.
It is set to Si ₂ .

That is, the present inventors have found that microcrystalline α-FeS
i ₂ (meta-stable α-FeSi ₂ ) can be easily β at low temperature and in a short time as compared with α-FeSi ₂ produced by a usual melting method.
The present invention was found out by the fact that it was transformed to —FeSi ₂ .

In addition to the above gas atomizing method, there are a high frequency plasma method and a roll method as the method of quenching.
The gas atomization method is excellent in that a large amount can be produced at one time and that a powder having a desired size can be obtained. Also,
Sintering can be performed by a hot pressing method or a cold pressing method other than the plasma sintering method (PAS), but the plasma sintering method is the most excellent for producing in a short time. Further, the plasma sintering method is desirable for sintering the microcrystalline α-FeSi ₂ having the above-mentioned properties. According to plasma sintering, the surface of the powder is activated by 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,
Since the heat conduction by the grain boundaries can be reduced, the thermoelectric properties are also improved as a result.

[0014]

[Equation 1]

[0015]

As described above, according to the present invention, by using the gas atomizing method and the plasma sintering technique, the sintering and the heat treatment are completed at the same time (about 17 minutes), so that the manufacturing time of the entire device is 1/500 of the conventional one. It is shortened to an extremely short time. That is, α-Fe obtained by this manufacturing method
Since the Si ₂ microcrystalline powder undergoes a phase transition α → β at a low temperature (500 to 940 ° C.), it is possible to easily fabricate an element having an arbitrary shape by combining this with plasma sintering technology. It will be easily converted into β by the heat at the time. Therefore, the step of heat treatment for about 100 hours, which was conventionally required, is not necessary or is achieved in an extremely short time, and the sintering time, which was conventionally required for about 24 hours, is shortened to an extremely short time. .

[0016]

EXAMPLES Examples of the present invention will be described in detail below.

(Embodiment 1) As shown in FIG. 1, first, F
In 500 g (Si51 wt%) of raw material powder of e and Si,
A small amount of Mn was added, and this was put in a crucible and melted by high-frequency heat to form a p-type alloy solution and a p-type alloy solution in which a small amount of Co was mixed and melted. The amount of Si mixed at this time is most preferably 50.15 wt%, but some variation is allowed. Further, the melting temperature of this example is 1300 ° C.
The range from 0 ° C to 1600 ° C is preferred.

Next, the p-type and n-type alloy solutions are respectively subjected to α-using a gas atomizing apparatus as shown in FIG.
FeSi ₂ p-type and n-type microcrystalline powders were formed.
The gas atomizing conditions are as shown in Table 1 below.

[0019]

[Table 1]

Next, when these α-FeSi ₂ atomized powders were aggregated into a predetermined shape and plasma-sintered under the conditions shown in Table 2 on the next page, the sintering was completed in about 17 minutes. Further, the sintering temperature could be as low as 620 ° C. Further, when this sintered body was subjected to X-ray diffraction, as shown in Table 3, a β phase was clearly confirmed.

[0021]

[Table 2]

[0022]

[Table 3]

Example 2 As shown in FIG. 3, α-FeSi obtained by the gas atomizing method as described above.
₂ 700 atomized powder in an inert gas atmosphere such as Ar
When heat-treated at ℃ for 180 seconds, β-FeSi
It was possible to make a phase transition to ₂ . Next, this β-FeS
When the i ₂ powder was sintered using the plasma device as described above, it solidified at a surface pressure of 3 [t / cm ² ], a temperature of 650 ° C., and a time of 30 [s], and a solidified body having a density ratio of 90% or more was obtained. Was obtained.

(Application example) In the present invention, as described above, the long-time heat treatment after forming the element is not necessary. Therefore, as shown in FIG. 4, the solidified body and the low melting point material are combined to convert the energy of the entire element. You can also increase efficiency. That is, in the case of designing the device as shown in the figure, by using iron silicon thermoelectric material that can be used at high temperature on the high temperature side and PbTe and ZnSb having low field conversion efficiency at the low temperature side, the efficiency of the device is maximized. It can be operated in a good temperature range. Further, in the case of such an element, since the element itself is integrally molded, it has a feature that heat loss is small. In addition, in this example, although it is a composite of two materials,
Similarly, a composite of three materials can be considered.

(Third Embodiment) As described above, conventionally, α-
FeSi ₂ was melted and made into an ingot, which was crushed again,
Heat treatment was performed to cause the α → β phase transition.
This is reported in Japanese Examined Patent Publication No. 52-47677. Further, by setting the particle size of the powder particles to 1 μm or less at the time of pulverization, the α → β phase transition occurs at the time of sintering, the above heat treatment becomes unnecessary, and the process is simplified. No.
However, as shown in FIG. 5, although the particle size of the powder itself obtained by the atomization method is as large as 30 to 50 μm,
The crystal grain size present in this powder was as small as 0.5 μm or less, and when such atomized powder was actually sintered and solidified by the hot pressing method, the sintered body was β-FeSi ₂ . That is, even if the particle size of the atomized powder is as large as 30 to 50 μm, if the crystal particle size present in the powder is as small as 0.5 μm or less, the phase transition of α → β during sintering is performed without heat treatment. Could be caused.

Further, since the crystal grain size is half the size of 1 μm or less, it is possible to sinter and solidify even when the temperature during hot press molding is quite low, and the phase transition from α to β during sintering. Can cause Specifically, the atomized powder produced under the gas atomizing conditions shown in Table 1 was sintered and solidified by the hot pressing method under the conditions shown in Tables 4 and 5 below.

[0027]

[Table 4]

[0028]

[Table 5]

Under any of the conditions shown in Tables 4 and 5, a β-FeSi ₂ sintered body can be obtained, and it is considered that the sintering temperature is further lowered by increasing the pressure.

Further, comparing the conditions of Table 4 and Table 5,
The advantages of the conditions in Table 4 will be described. First, the hardness of FeSi ₂ at the temperature shown in Table 5 is about 300 H.V.
V and high. On the other hand, the hardness of FeSi ₂ at the temperature shown in Table 4 is
Vickers hardness is about 50H. V and low. Therefore, it is considered that the internal stress of the sintered body at the temperature of Table 5 at room temperature is considerably higher than that of the sintered body at the temperature of Table 4. Therefore, it is preferable that the residual stress that causes the occurrence of defects such as cracks is low, and in this respect, the conditions in Table 4 are superior.

When FeSi ₂ is used as a mother particle and a Cu compound is used as a child particle for encapsulation and sintering, the Cu compound is close to the melting point at the temperature of Table 4, and it is considered that the Cu compound is softer than the temperature of Table 5. For this reason, the child particles substantially uniformly enter between the mother particles, plug defects such as cracks and pores,
Since it is a uniform material, the thermoelectric efficiency is also improved,
In this respect, the conditions in Table 4 are superior.

Further, in order to mold at the temperature shown in Table 5, an expensive mold such as WC-Co capable of withstanding high pressure is required, but at the temperature shown in Table 4, molding at low cost such as carbon is made. Molds can be used. Further, the higher the pressure is, the more difficult it is to release the mold, and the pressure of Table 5 may damage the mold at the time of release, but the pressure of Table 4 has no such fear. The condition of 4 is superior.

[0033]

In summary, according to the present invention, by combining the gas atomizing method and the plasma sintering method, metastable α-FeSi ₂ can be easily obtained, and the heat treatment time and the heat treatment time, which have conventionally been required, can be obtained. Since the sintering time is extremely short, the manufacturing efficiency is greatly improved, and further, it has an excellent effect that the compounding with other materials can be easily achieved.

[Brief description of drawings]

FIG. 1 is a chart showing an embodiment of the first invention.

FIG. 2 is a sectional view showing an embodiment of a gas atomizing device.

FIG. 3 is a chart showing an embodiment of the second invention.

FIG. 4 is a schematic diagram showing an application example of the second invention.

FIG. 5 is a schematic view showing an embodiment of the third invention.

FIG. 6 is a chart showing a conventional method for manufacturing a thermoelectric generator.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Matsumi 8 Tsutana, Fujisawa City Kanagawa Prefecture Isuzu Central Research Institute Co., Ltd. (72) Inventor Masayuki Kato 8th Shelf shelf Fujisawa City Kanagawa Prefecture Isuzu Central Research Co., Ltd. In-house (72) Eiji Okumura Eight Osatan, Fujisawa-shi, Kanagawa 8 Isuzu Central Research Institute Co., Ltd. (72) Inventor Hideo Ishiyama Eight-soil shelf, Fujisawa-shi, Kanagawa Isuzu Central Research Co., Ltd. (72) Inventor Makoto Ogawa 8 Tsutana, Fujisawa City, Kanagawa Prefecture, Isuzu Central Research Institute

Claims (3)

[Claims] 1. A raw material powder composed of Fe and Si is mixed with an additive such as a transition element to be melted to form an alloy solution, and α-FeSi ₂ (metal phase is formed from the alloy solution by a gas atomizing method. ) After forming the microcrystalline powder of
A method for producing a thermoelectric generator, characterized in that the microcrystalline powder is sintered and solidified into a predetermined shape by a plasma sintering method, and is transformed into β-FeSi ₂ (semiconductor phase). 2. An alloy solution formed by mixing Fe and Si in a predetermined ratio is formed, and fine crystal powder of α-FeSi ₂ (metal phase) is formed from the alloy solution by a gas atomizing method, and then the α is formed. -FeSi ₂ microcrystalline powder is heat-treated in an inert gas to undergo a phase transition to β-FeSi ₂ (semiconductor phase) microcrystalline powder, and then a transition element or the like is added to the β-FeSi ₂ microcrystalline powder. At the same time, a method for producing a thermoelectric power generating element, characterized by comprising sintering and solidifying this into a predetermined shape by a plasma sintering method. 3. The method for manufacturing a thermoelectric generator according to claim 1, wherein the sintering and solidification is performed by a hot pressing method instead of the plasma sintering method.