JP6613606B2 - Method for manufacturing thermoelectric conversion material and method for manufacturing thermoelectric conversion element - Google Patents

Description

  The present invention relates to a method for manufacturing a thermoelectric conversion element (P-type thermoelectric conversion element and N-type thermoelectric conversion element) used in a thermoelectric conversion module in which a plurality of P-type thermoelectric conversion elements and N-type thermoelectric conversion elements are arranged in combination.

  In the thermoelectric conversion module, a pair of P-type thermoelectric conversion elements and N-type thermoelectric conversion elements are combined in a connected state with electrodes between a pair of wiring boards, in the order of P, N, P, and N. It is configured to be electrically connected in series so as to be arranged, both ends are connected to a DC power source, and heat is transferred in each type thermoelectric conversion element by the Peltier effect (in the P type, the same direction as the current, N In the mold, it is moved in the direction opposite to the current), or a temperature difference is given between both wiring boards to generate an electromotive force in each thermoelectric conversion element by the Seebeck effect. Is possible.

By the way, both the P-type thermoelectric conversion element and the N-type thermoelectric conversion element are generally obtained by solidifying powder by a method such as hot pressing or plasma discharge sintering, and using the green compact (thermoelectric conversion material) as an element. The method of cutting out is used. At that time, in addition to gas atomization and the like, powder is produced by melting and casting to produce a desired mother alloy (thermoelectric conversion material) of a thermoelectric conversion element, and then pulverizing it to produce powder. Has also been done.
However, this method requires a long process, increases material loss, and increases costs. Furthermore, impurities may be mixed during the process of producing the powder, and the thermoelectric conversion characteristics may be deteriorated.

Therefore, a method for producing a thermoelectric conversion material by melting and casting has been proposed.
For example, Patent Document 1 includes a step of melting a raw material of a thermoelectric conversion material and a step of solidifying the molten raw material of the thermoelectric conversion material. At least in the solidification step, the raw material of the thermoelectric conversion material Application of ultrasonic vibration to the melt is disclosed. According to this method, it is described that it is possible to make the crystal orientation uniform and to refine the crystal grains, thereby reducing the thermal conductivity and improving the figure of merit.

  In Patent Document 2, a process of installing a mold material having a plurality of through holes on a cooling plate, a process of pouring a molten thermoelectric conversion material in the mold material, and solidifying the molten thermoelectric conversion material in the mold material. And a process for forming a thermoelectric conversion element is disclosed. According to this manufacturing method, since the melt of the thermoelectric conversion material is rapidly cooled, the crystal orientation is aligned in the height direction of the thermoelectric conversion element, the electrical resistance can be reduced, and the crystal grain size is small, so the thermal conductivity is low, It is described that high performance can be obtained.

JP 2005-311094 A JP 2007-194438 A

By the way, after producing powder, the method of solidifying this by hot pressing or plasma discharge sintering can achieve uniform composition by mixing and sintering the powder well, By using a mold release material such as or a graphite sheet, the mold and the thermoelectric conversion material are not in close contact with each other, so that cracking due to this can be prevented.
On the other hand, in the method of producing a thermoelectric conversion material by melt casting disclosed in the patent document, there is a problem that the composition is likely to be non-uniform, and it is likely to be welded to the mold during cooling and easily cracked due to thermal stress. is there.

  This invention is made in view of such a situation, and when manufacturing a thermoelectric conversion material by melt | dissolution casting, providing a manufacturing method which can make a composition uniform and can prevent generation | occurrence | production of a crack. Objective.

The method for producing a thermoelectric conversion material according to the present invention includes a melting crucible and a solidification crucible installed in a furnace, and the furnace is placed in an inert atmosphere or a reducing atmosphere to constitute the thermoelectric conversion material. a dissolution step of dissolving an element raw material in the melting crucible, after the dissolution step, and a solidifying step of solidifying transferred the melt of the thermoelectric conversion material into the coagulation crucible preheated, the dissolution The process includes a first stage and a second stage having a heating temperature higher than that of the first stage, and the melting crucible is heated with the opening of the melting crucible opened to produce a liquid phase in the raw material. The melting crucible opening is closed, and then the raw material is melted in the closed state. In the solidification step, the cooling rate when cooling the thermoelectric conversion material to 1030 ° C. is 15 ° C./min or more 90 ℃ / min or less

  As thermoelectric conversion materials, bismuth tellurium alloy, skutterudite alloy, silicide alloy, half-Heusler alloy, etc. are used, but these thermoelectric conversion materials contain elements with various melting points and boiling points. When an individual material of each element is dissolved, an element having a low boiling point evaporates first, so that it is difficult to obtain a thermoelectric conversion material having a desired composition.

In the present invention, when an element having a low boiling point or an element having a high vapor pressure and an element having a high melting point are alloyed, if the liquid phase is generated in the raw material, the opening of the melting crucible is covered with a lid, thereby lowering the boiling point. It suppresses evaporation of elements or elements with high vapor pressure, and maintains the stoichiometry of the melt.
Also, if the melted raw material is solidified in the melting crucible as it is, it takes a long time to solidify, and it is difficult to grow and refine the crystal, so the molten metal is transferred to the solidification crucible so that the crystal does not break. A thermoelectric conversion material with fine crystal grains can be obtained by solidifying as quickly as possible while controlling the temperature of the crucible for solidification. And the thermoelectric conversion element can be obtained by cutting out the obtained thermoelectric conversion material in a desired shape.

In the method for producing a thermoelectric conversion material of the present invention, in the melting step, the molten metal in the melting crucible may be stirred.
By stirring the molten metal in the melting crucible, the composition in the molten metal can be made uniform. As the stirrer, a stirring blade having ceramic blades is used, and the blades are rotated and stirred.

In the method for producing a thermoelectric conversion material of the present invention, a release layer may be formed on the inner surface of the solidifying crucible.
By forming a release layer on the inner surface of the solidifying crucible, the reaction with the molten metal crucible can be suppressed, and welding with the crucible can be prevented. For this reason, when the crystal is solidified and cooled, there is no restriction between the crucible and the ingot of the thermoelectric conversion material, and cracking of the thermoelectric conversion material due to welding can be prevented. It is preferable to use silicon nitride or boron nitride for the release layer.

The method for producing a thermoelectric conversion element of the present invention is a method for producing a thermoelectric conversion element by the above-described method for producing a thermoelectric conversion material, wherein the crucible for solidification has an angular shape in the cross-sectional shape of the thermoelectric conversion element. After the solidification step, the thermoelectric conversion material solidified into the square shape is cut at a halfway position in the length direction to form a thermoelectric conversion element.
A solidification crucible is used to solidify the thermoelectric conversion element in a shape close to the final shape, and this is cut into a thermoelectric conversion element, which is efficient.

  According to the production method of the present invention, evaporation of an element having a low boiling point or a high vapor pressure can be prevented in the melting step, so that a thermoelectric conversion material having a desired composition can be obtained. Since the crucible is divided into the one for use, it can be cooled while controlling the temperature of the crucible for solidification, and a high performance thermoelectric conversion material with low thermal conductivity can be obtained as fine crystal grains.

It is a longitudinal cross-sectional view which shows the example of the apparatus for enforcing the manufacturing method of this invention. It is a longitudinal cross-sectional view which shows the other example of the crucible for solidification.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
As the thermoelectric conversion material to which the present invention is applied, a bismuth tellurium alloy, a skutterudite alloy, a silicide alloy, a half-Heusler alloy, or the like is used.
Table 1 shows the physical properties of typical thermoelectric conversion materials.

As can be seen from Table 1, each thermoelectric conversion material is an alloy composed of elements having greatly different melting points and boiling points. Such a thermoelectric conversion material is produced by melting and stirring these elemental raw materials and then solidifying them.
As an apparatus for the production, as shown in FIG. 1, an apparatus in which a melting crucible and a solidifying crucible are installed in one furnace is used.

The manufacturing apparatus 10 includes a furnace 11 capable of sealing the inside, a melting crucible 1 and a solidification crucible 2 installed in the furnace 11, and heaters 3 and 4 for individually heating the crucibles 1 and 2. And a lid 5 capable of closing the opening 1a of the melting crucible 1, and a stirrer 6 having blades 6a for stirring the molten metal in the melting crucible 1. There is a hole 5a through which the stirring rod 6b passes in the center of the lid 5, and in order to maintain airtightness in the sliding crucible 1 during rotation, the portion of the stirring rod 6b in contact with the hole 5a of the lid 5 of the stirring rod 6b is provided. The bush 6c is provided by winding a graphite sheet having a thickness of 0.1 to 0.2 mm. Further, on the furnace wall, the stirring rod 6b is sealed using a magnetic fluid sealing unit, and is connected to a rotating body outside the furnace while maintaining the atmosphere in the furnace. The magnetic fluid seal unit is water-cooled to suppress the temperature rise of the magnetic seal portion.
The furnace 11 is provided with a gas introduction pipe 12 and a gas discharge pipe 13, and the inside of the furnace 11 can be evacuated or set to a predetermined atmosphere such as a reducing atmosphere through these pipes 12 and 13.

The melting crucible 1 and the solidifying crucible 2 are each formed of carbon, alumina, or the like, and a release layer 7 made of silicon nitride (Si ₃ N ₄ ) is formed on the entire inner surface. As this silicon nitride, for example, a high-purity silicon nitride powder (for example, trade name SN-E03) manufactured by Ube Industries, Ltd. is used, which is mixed with pure water and polyvinyl alcohol, and a suspension (for example, 1 kg). Obtained by mixing a silicon nitride powder of 1.5 kg of polyvinyl alcohol and 1.5 kg of pure water on the inner surface of the crucibles 1 and 2 (for example, 30 times) and then heating the crucible. The release layer 7 is formed by adhering to the inner surfaces of 1 and 2. In addition, the blade | wing 6a of the stirrer 6 mentioned above can be formed with an alumina or SiC. Further, alumina nitride or SiC blade 6a may be coated with silicon nitride or boron nitride.
Note that the release layer 7 may be formed of boron nitride.

A temperature sensor 8 such as a thermocouple is provided inside the solidification crucible 2. The temperature sensor 8 is accommodated in a protective tube 9 made of a material such as alumina, and the release layer 7 is formed so as to cover the outer surface of the protective tube 9.
Further, the melting crucible 1 is provided with a tilting mechanism (not shown), and the melting crucible 1 is tilted from a vertical standing posture, and the molten metal inside is poured out and transferred to the solidification crucible 2. It can be done.
The tilting mechanism and each drive unit (both not shown) of the stirrer 6 are installed outside the furnace 11.

Next, a method for manufacturing a thermoelectric conversion material and a thermoelectric conversion element using the manufacturing apparatus 10 will be described.
First, the raw material is put into the melting crucible 1.
For example, in the case of a silicide-based P-type thermoelectric conversion material, Mn and Si are used as raw materials. In the case of silicide-based N-type thermoelectric conversion materials, Mg and Si, and further elements such as Sb, Al, Sn, and Ag can be added to improve thermoelectric properties (thermal conductivity, electrical conductivity, Seebeck coefficient, etc.). Plan. Individual raw materials are mixed and fed in the form of pellets, granules, powders, and the like.
Next, the inside of the furnace 11 is first evacuated, and the inside of the furnace 11 is replaced with an inert gas such as argon gas, and then evacuated again, and then the reducing gas obtained by mixing the inert gas or the inert gas with hydrogen. A gas is introduced and the inert gas or reducing gas is circulated in the furnace 11. The oxygen in the upper part of the melting crucible 1 is driven out by this series of operations. The reducing gas avoids the explosion limit of hydrogen, and for example, argon + 1% -4% hydrogen or argon + 75% -100% hydrogen can be used.

Then, the melting crucible 1 is heated to dissolve the raw material. In addition, an inert gas or a reducing gas is circulated during dissolution. This heating is performed in two stages. First, the first stage temperature is maintained, and then the second stage temperature is maintained higher. In the case of Mg ₂ Si (N-type), specifically, the first stage is held at 650 ° C. to 950 ° C., and the time during which Mg ₂ Si particles are formed by solid-phase reaction, for example, 60 to 240 minutes, Thereafter, as a second stage, the temperature is maintained at 1085 ° C. to 1200 ° C. for 30 minutes to 180 minutes at which Mg ₂ Si is dissolved. Meanwhile, when a liquid phase is generated at least in part of the raw material (for example, when the temperature reaches 700 ° C. or higher), the melting crucible 1 is covered with the lid 5.
It is also possible to cover the melting crucible 1 before the liquid phase is generated in a part of the raw material, that is, before heating. However, when the melting crucible 1 is covered with the lid 5 in a state where a liquid phase is generated, it is possible to volatilize impurities such as moisture and organic substances adhering to the surface of the raw material during heating, and a reducing gas is used. In this case, the oxide on the raw material surface can be reduced. Therefore, it is desirable to use a reducing gas as the gas and cover the melting crucible 1 with a liquid phase in at least a part of the raw material.

When the raw material is dissolved, the raw material of the element having a low boiling point (Mg in the case of Mg ₂ Si) begins to evaporate first, but by covering the lid 5, the vapor is transferred to the outside of the melting crucible 1. Will not leak. And all the raw materials inside are melt | dissolved in the state hold | maintained at 1085 to 1200 degreeC which is the temperature of a 2nd step. When all of the raw materials are dissolved, the stirrer 6 is operated, and the molten metal in the melting crucible 1 is stirred by the blade 6a. The rotation speed of a blade | wing is 10-120 rpm. The stirring time is preferably 5 minutes to 30 minutes.

After stirring the molten metal at 1085 ° C. to 1200 ° C. for 5 to 30 minutes, stirring is stopped, the lid 5 is opened, the melting crucible 1 is tilted by the tilting mechanism 8, and the molten metal inside is solidified. Move to 2.
When the molten metal is transferred, the solidification crucible 2 is heated in advance by the heater 4 and kept at 700 ° C. to 1030 ° C.
Then, the molten metal is transferred to the crucible 2 for solidification.
At this time, after pouring the molten metal, the cooling rate to 1030 ° C. is cooled to 15 ° C./min to 90 ° C./min. When the cooling rate to 1030 ° C. is less than 15 ° C./min, the crystal grain size of the resulting thermoelectric conversion material becomes large. When a thermoelectric conversion element is produced using such a thermoelectric conversion material, the thermal conductivity increases and the dimensionless figure of merit decreases, so that the power generation conversion efficiency decreases. When the cooling rate to 1030 ° C. exceeds 90 ° C./min, cracks are likely to occur in the thermoelectric conversion material. Therefore, it is necessary to set the cooling rate to 15 ° C./min or more and 90 ° C./min or less until at least the temperature of the molten metal is lowered to 1030 ° C.
And after hold | maintaining for 10 minutes-120 minutes in the state maintained at 500 to 950 degreeC with the crucible 2 for solidification, the heating from the heater 4 is stopped and furnace cooling is carried out. The cooling rate during the furnace cooling is preferably 1 ° C./min to 10 ° C./min.

  Here, a method for measuring the cooling rate will be described. First, the sealed side of the alumina protective tube having an inner diameter of 4 mm and an outer diameter of 6 mm is brought into contact with the inner side surface of the solidifying crucible 2 with the bottom of the crucible, and an insulating heat-resistant adhesive (for example, a product) Name: RESBOND 989). A release layer similar to the solidification crucible 2 is formed on the outer surface of the alumina protective tube. Then, insert the tip of an R (platinum rhodium alloy (13% rhodium) -platinum) thermocouple at a position 1 cm above the bottom on the side sealed inside the alumina protective tube, measure the temperature in the crucible for solidification, and cool The speed was determined.

  Note that if the molten metal is cooled and solidified in the melting crucible 1 as it is, it takes time to solidify, and a desired composition cannot be obtained, such as partial concentration.

And the thermoelectric conversion element can be manufactured by cutting out the obtained thermoelectric conversion material into a desired shape.

  By melting the raw material in this way and cooling, a thermoelectric conversion material having a crystal grain with a target composition can be obtained. From this thermoelectric conversion material, the thermal conductivity is low and the performance is high. The thermoelectric conversion element which has can be obtained. Moreover, by forming the release layer 7 of silicon nitride on the inner surfaces of the crucibles 1 and 2, welding with the crucibles 1 and 2 can be prevented, and the occurrence of cracks in the thermoelectric conversion material can be prevented. High quality thermoelectric conversion materials can be produced with good yield.

FIG. 2 shows another example of a solidification crucible. The crucible 21 for solidification has a plurality of cavities 22, and each cavity 22 is formed to have a size capable of obtaining a rectangular material having a cross-sectional shape of the final thermoelectric conversion element. .
By using this crucible 21 for solidification, a thermoelectric conversion element can be manufactured more efficiently.
In the case of the crucible 21 for solidification, the temperature sensor 8 such as a thermocouple is inserted into one of the cavities 22a, and the other cavities 22 except the cavity 22a are filled with molten metal. The

  Although the embodiments have been described above, the present invention is not limited to the above-described embodiments, and various modifications other than those described above can be added without departing from the spirit of the present invention.

According to the manufacturing method described above, thermoelectric conversion materials made of N-type magnesium silicide (melting point: 1085 ° C.) were prepared and evaluated under various conditions.
Both a melting crucible and a solidifying crucible were prepared from alumina. Except for Example 5 described later, an inner surface coated with a release layer of silicon nitride was used. As raw materials for each of Examples and Comparative Examples, the following were prepared.
Mg: 300 g of a wire cut material having a purity of 99.9% (3N), a diameter of 6 mm, and a length of 5 mm
Si: 171 g of a pulverized product having a purity of 99.999% (5N) and a maximum diameter of 5 mm
Sb: 11.3 g of a coarse powdery product having a purity of 99.9% (3N) and a diameter of 300 μm or less

The thermoelectric conversion materials of the following Examples and Comparative Examples were produced by changing the conditions for melting and solidifying these raw materials. When the raw material is melted, the inside of the furnace is evacuated, replaced with argon gas, evacuated again, and then the raw material is dissolved in a reducing gas in which 4% hydrogen is mixed with argon to complete solidification. I washed it up. After the completion of solidification, argon as an inert gas was circulated until the furnace temperature reached 300 ° C.
Further, the crystal grain size of the obtained thermoelectric conversion material was measured. The crystal grain size is determined by measuring 10 arbitrary regions of the thermoelectric conversion material using a secondary electron scanning electron microscope (SEM), counting the number of crystal particles in the plane, and calculating the area of the measurement region by the number. The average area of the crystal grains was determined. The square root of the average area was determined and the value was taken as the crystal grain size.
The conditions of each example and comparative example and the production results are as follows.

Example 1
Conditions: The raw material was put into a melting crucible having an internal volume of 500 cm ³ , heated to 850 ° C., held at 850 ° C. for 4 hours, and then held at 1150 ° C. for 60 minutes. At that time, the melting crucible was covered from 700 ° C., and stirred at 1150 ° C. for 5 minutes. Stirring was stopped, the mixture was left at 1150 ° C. for 5 minutes, then the lid was opened, the molten metal was poured into a solidification crucible with an internal volume of 300 cm ³ kept at 950 ° C., cooled to 900 ° C., and held at 900 ° C. for 1 hour. The furnace was cooled. The cooling rate from pouring the molten metal into the solidification crucible to 1030 ° C. was 25 ° C./min.
Result: There was no crack in the crystal, no welding with the crucible was observed, and the thermoelectric conversion material could be easily taken out from the crucible for solidification. The crystal grain size of the obtained thermoelectric conversion material was 36 μm.

(Example 2)
Conditions: The raw material was put into a melting crucible having an internal volume of 500 cm ³ , heated to 850 ° C., held at 850 ° C. for 4 hours, and then held at 1120 ° C. for 60 minutes. At that time, the melting crucible was capped at 700 ° C., and the mixture was stirred at 1120 ° C. for 5 minutes. Stirring was stopped, the mixture was left at 1120 ° C. for 5 minutes, then the lid was opened, the molten metal was poured into a crucible for solidification having an internal volume of 300 cm ³ kept at 900 ° C., kept at 900 ° C. for 1 hour, and then cooled in the furnace. The cooling rate from pouring the molten metal into the solidification crucible to 1030 ° C. was 45 ° C./min.
Result: There was no crack in the crystal, no welding with the crucible, and the crystal could be easily taken out from the crucible for solidification. The crystal grain size of the obtained thermoelectric conversion material was 25 μm.

(Example 3)
Conditions: The raw material was put into a melting crucible having an internal volume of 500 cm ³ , heated to 850 ° C., held at 850 ° C. for 4 hours, and then held at 1150 ° C. for 60 minutes. At that time, the melting crucible was covered from 700 ° C., and stirred at 1150 ° C. for 5 minutes. Stirring was stopped, the mixture was left at 1150 ° C. for 5 minutes, then the lid was opened, the molten metal was poured into a solidification crucible having an internal volume of 300 cm ³ kept at 800 ° C., held at 800 ° C. for 1 hour, and then cooled in the furnace. The cooling rate from pouring the molten metal into the solidifying crucible to 1030 ° C. was 90 ° C./min.
Result: The thermoelectric conversion material taken out had no cracks, no welding with the crucible was observed, and the thermoelectric conversion material could be easily taken out from the solidification crucible. The crystal grain size of the obtained thermoelectric conversion material was 17 μm.

Example 4
Conditions: The raw material was put into a melting crucible having an internal volume of 500 cm ³ and heated up to 850 ° C., held at 850 ° C. for 4 hours, and then held at 1150 ° C. for 60 minutes. At that time, the melting crucible was covered from 700 ° C. No stirring was performed when the raw material was dissolved in the melting crucible. The lid was opened at 1150 ° C., the molten metal was poured into a solidification crucible having an internal volume of 300 cm ³ kept at 1030 ° C., cooled to 900 ° C., kept at 900 ° C. for 1 hour, and then cooled in the furnace. The cooling rate from pouring the molten metal into the solidifying crucible to 1030 ° C. was 15 ° C./min.
Result: There was no reaction with the crucible and no crystal cracking occurred, but some of the regions had different compositions. The ideal composition of magnesium silicide (N-type) is Mg: Si = 66.6: 33.3 by mass% ratio, but Mg: Si = 50.3: 49.4 or Mg: Si = 55. There was a ratio of 2: 44.5. The crystal grain size of the obtained thermoelectric conversion material was 43 μm.

(Example 5)
Conditions: The same conditions as in Example 1 were used, except that both a melting crucible and a solidifying crucible were used in which a release layer on the inner surface was not formed. An alumina protective tube having no release layer was also used. The cooling rate from pouring the molten metal into the solidification crucible to 1030 ° C. was 25 ° C./min.
Result: The thermoelectric conversion material reacted with the crucible and welded to the inner wall of the crucible. Moreover, the thermoelectric conversion material of the outer peripheral part (near the inner peripheral part of a crucible) had generate | occur | produced the crack. The crystal diameter of the obtained thermoelectric conversion material was 40 μm.

(Example 6)
Conditions: The raw material was put into a melting crucible having an internal volume of 500 cm ³ , heated to 850 ° C., held at 850 ° C. for 4 hours, and then held at 1150 ° C. for 60 minutes. At that time, the melting crucible was covered from 700 ° C., and stirred at 1150 ° C. for 5 minutes. Stirring was stopped, the mixture was left at 1150 ° C. for 5 minutes, then the lid was opened, the molten metal was poured into a solidification crucible having an internal volume of 300 cm ³ kept at 1030 ° C., the temperature was lowered to 900 ° C. The furnace was cooled. The cooling rate from pouring the molten metal into the solidifying crucible to 1030 ° C. was 15 ° C./min.
Result: The thermoelectric conversion material taken out had no cracks, no welding with the crucible was observed, and the thermoelectric conversion material could be easily taken out from the solidification crucible. The crystal grain size of the obtained thermoelectric conversion material was 44 μm.

(Comparative Example 1)
Conditions: The same melting crucible and coagulation crucible as in Example 1 were used, and the melting conditions were the same as in Example 1. However, the coagulation crucible was kept at 650 ° C., and the melting crucible was melted from the melting crucible. The molten metal was poured and cooled as it was. The cooling rate from pouring the molten metal into the solidifying crucible to 1030 ° C. was 100 ° C./min.
Result: Cracks occurred in the thermoelectric conversion material. The crystal grain size of the obtained thermoelectric conversion material was 8 μm.

(Comparative Example 2)
Conditions: After the raw material was melted in the melting crucible, it was not transferred to the solidification crucible, but the heating with the heater was stopped in the melting crucible and the furnace was cooled. Further, the molten metal was not stirred. The cooling rate to 1030 ° C. after the heating by the heater was stopped was 10 ° C./min.
Result: There was no reaction with the crucible and no cracking of the thermoelectric conversion material occurred, but there was a region (Mg: Si = 15.0: 84.9) with a greatly different composition. The crystal grain size of the obtained thermoelectric conversion material was 67 μm.

From the above results, in order to obtain the desired thermoelectric conversion material without biasing the composition, the melting crucible is covered at least when the liquid phase is generated in the crucible during the melting process, and an appropriate It can be seen that it is important to transfer the molten metal from the melting crucible to the solidification crucible controlled to the temperature and cool it. That is, it is important that the cooling rate at least when the molten metal is cooled to 1030 ° C. is 15 ° C./min or more and 90 ° C./min or less.
In this case, a thermoelectric conversion material having a more accurate composition can be obtained with high yield by stirring the molten metal in the melting crucible.
In Example 5 using the crucible in which the release layer was not formed, an abnormality was recognized in the vicinity of the inner peripheral surface of the crucible, and the yield decreased, but the thermoelectric conversion element obtained from the inner thermoelectric conversion material Had the same performance as the other examples.
On the other hand, when the raw material is melted in a melting crucible and solidified as it is, or when the molten metal is transferred from the melting crucible to a solidifying crucible maintained at 650 ° C., that is, at least the molten metal is 1030. When the cooling rate at the time of cooling to 15 ° C. is less than 15 ° C./min, or when it exceeds 90 ° C./min, the crystal grain size of the obtained thermoelectric conversion material is greatly different or the thermoelectric conversion material is cracked. There was a problem that occurred.

DESCRIPTION OF SYMBOLS 1 Melting crucible 1a Opening 2 Solidification crucible 3, 4 Heater 5 Lid 6 Stirrer 6a Blade 6b Stirring rod 6c Bush 7 Release layer 8 Temperature sensor 9 Protection tube 10 Manufacturing apparatus 11 Furnace 21 Solidification crucible 22, 22a Cavity

Claims (4)

In the furnace, a melting crucible and a solidification crucible are installed, and the inside of the furnace is set as an inert atmosphere or a reducing atmosphere, and the raw materials of each element constituting the thermoelectric conversion material are dissolved in the melting crucible. And a solidification step in which the molten metal of the thermoelectric conversion material is solidified by transferring the molten metal of the thermoelectric conversion material to the pre-heated crucible after the melting step. The melting step includes the first step and the first step. The second stage having a higher heating temperature, wherein the melting crucible is heated with the opening of the melting crucible opened, and the opening of the melting crucible is closed when the liquid phase is generated in the raw material Then, the raw material is dissolved in the closed state, and in the solidification step, the cooling rate when cooling the thermoelectric conversion material to 1030 ° C. is 15 ° C./min or more and 90 ° C./min or less. Manufacture of thermoelectric conversion materials Law.   The method for producing a thermoelectric conversion material according to claim 1, wherein in the melting step, the molten metal in the melting crucible is stirred.   The method for producing a thermoelectric conversion material according to claim 1 or 2, wherein a release layer is formed on the inner surface of the crucible for solidification.   A method for producing a thermoelectric conversion element by the method for producing a thermoelectric conversion material according to any one of claims 1 to 3, wherein the crucible for solidification has a square shape in a cross-sectional shape of the thermoelectric conversion element. The method of manufacturing a thermoelectric conversion element is characterized in that after the solidification step, the thermoelectric conversion material solidified into the rectangular shape is cut at a halfway position in the length direction to form a thermoelectric conversion element. .

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