JP2003037302A - Method for manufacturing thermoelectric material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a thermoelectric material which can reduce power consumption at high temperature while maintaining a high performance index. SOLUTION: A quenched thin belt 14 obtained by a liquid quenching method is heat-treated (hydrogen reduction processing or annealing) in hydrogen gas or Ar gas. Before the heat treatment, namely, in the tissue solidified by the quenching, many chill crystals 52 are present on the surface of the quenched thin belt 14 in addition to crystal grains 51 extending along the thickness. Here, the chill crystals 52 disappear through the heat treatment. During the heat treatment, Te atoms and Se atoms are segregated on the surface by boundary diffusion.

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 applied to thermoelectric power generation, thermoelectric cooling and the like, and more particularly to a method for producing a thermoelectric material capable of improving a figure of merit at high temperature.

[0002]

2. Description of the Related Art Thermoelectric materials include unidirectionally solidified materials and sintered materials. The unidirectionally solidified material is produced as follows. 13A to 13C are schematic views showing a method of manufacturing a conventional unidirectionally solidified material in the order of steps.

First, as shown in FIG. 13 (a), a raw material 101 is inserted into a quartz tube 102, the end of the quartz tube 102 is melted and cut, and the raw material 101 is sealed in the quartz tube 102. After that, as shown in FIG. 13B, the quartz tube 102 is put into the tubular furnace 103 to melt the raw material 101, and the stand 104 is placed.
The raw material melt is agitated by swinging the tubular furnace 103 rotatably supported by. Next, as shown in FIG. 13C, a temperature gradient is applied in the tubular furnace 103 to solidify the melt while orienting the crystal orientation. Thereby, a unidirectionally solidified material having a solidified structure extending in one direction is obtained.

The sintered material is obtained by crushing a solidified material,
Solidify by hot pressing or the like. In this case, since a low-resistance crystal orientation (a-axis) grows in a direction perpendicular to the pressure direction of the hot press, electrodes are attached to the thermoelectric element and the plurality of thermoelectric elements so that a current flows in the a-axis direction. Assemble the thermoelectric module consisting of elements.

FIG. 14 is a schematic view showing the crystal grains of the thermoelectric material to be solidified and molded and the hot pressing direction. When the thermoelectric material 1 is solidified by hot pressing, the a-axis side of the crystal structure of the crystal grain 2 grows in the direction orthogonal to the hot pressing direction, and the crystal structure of the crystal grain 2 extends in the direction parallel to the hot pressing direction. Grows on the c-axis side. Since the thermoelectric material generally has structural anisotropy, as shown in FIG. 14, by hot pressing, the growth proceeds in the a-axis direction rather than the c-axis direction of the crystal grains 2. As a result, the grain size of the crystal grain 2 grows to about several mm, and the aspect ratio becomes 5 or more. A method for manufacturing such a thermoelectric material is disclosed in, for example, Japanese Patent Laid-Open No.
No. 00-232243.

The crystal structure of such a thermoelectric material is
As shown in FIG. 15, it is considered to be a hexagonal crystal. In FIG. 15, the hexagonal surface shown by hatching is C
The surface.

On the other hand, Japanese Patent Laid-Open No. 2001-53344 describes a method of pressurizing the laminate from a direction orthogonal to the laminating direction for the purpose of further improving thermoelectric performance.

Further, JP-A-10-178218 and JP-A-11-261119 disclose a method in which powder obtained by crushing an ingot is sintered, and then the sintered body is swage-forged. Have been described.

[0009]

However, among the above-mentioned conventional thermoelectric materials, the unidirectionally solidified material has a crystal grain size of several meters.
Since it is more than m and is cleavable, it has the drawback of being brittle against mechanical impact. In addition, conventional thermoelectric materials are
High thermal conductivity. The figure of merit Z of a thermoelectric material is its Seebeck coefficient α (μ · V / K), specific resistance ρ (Ω · m),
When the thermal conductivity is κ (W / m · K), it is expressed as shown in the following mathematical formula 1.

[0010]

## EQU1 ## Z = α ² / (ρ × κ)

As is clear from the mathematical formula 1, when the thermal conductivity κ is high, the figure of merit Z is low. Therefore, when the thermal conductivity κ is high, there is a limit to the improvement in performance.

In the conventional thermoelectric material produced by the sintering method, the size of the powder is equal to the size of the crystal grain. Generally, the larger the grain size of the crystal grains, the larger the thermal conductivity κ and the smaller the specific resistance ρ, and the smaller the grain size, the smaller the thermal conductivity κ and the larger the specific resistance ρ. However, since the influence of the grain size is smaller in the specific resistance than the thermal conductivity, it is effective to refine the crystal grains in order to reduce the thermal conductivity κ for improving the performance index Z. Conventionally, since the powder grain size and the crystal grain size are the same, there is a limit to the refinement of the crystal grains. In addition, during pulverization, the powder surface is oxidized and impurities are mixed in, which increases the specific resistance, which lowers the figure of merit.

Further, in the manufacturing method described in Japanese Patent Laid-Open No. 2001-53344, the sinterability is low and the orientation of the crystal grains is not sufficient because of the large deformation resistance during sintering. There is a problem.

Further, in the manufacturing method of upset forging, since the powder obtained by crushing the ingot is sintered as it is, the orientation inside the powder is low. For this reason,
The orientation of the solidified compact is low and the thermoelectric performance is not sufficient.

Furthermore, regarding the thermoelectric performance of the thermoelectric material disclosed in Japanese Patent Laid-Open No. 2000-232232, although the figure of merit Z itself is good, the specific resistance ρ easily affected by heat.
Is relatively high, which limits its use at high temperatures. That is,
Since the specific resistance ρ increases as the temperature rises, Joule heat generation increases. Further, the driving current is set by the manufacturer of the thermoelectric element. Therefore, the amount of heat absorbed by the thermoelectric element (Peltier element) is reduced and power consumption is increased. Therefore, the temperature inside the package is 9
In a high temperature environment where the temperature reaches 0 ° C., power consumption becomes high.

The present invention has been made in view of the above problems, and an object thereof is to provide a method for producing a thermoelectric material capable of reducing power consumption at high temperature while maintaining a high figure of merit. To do.

[0017]

The method for producing a thermoelectric material according to the present invention comprises at least one element selected from the group consisting of Bi and Sb and at least one element selected from the group consisting of Te and Se. A step of producing a foil having a composition comprising elements by a liquid quenching method, a step of heat-treating the foil in a reducing gas atmosphere or an inert gas atmosphere,
A step of solidifying and molding by laminating the foil and pressing in the thickness direction thereof, and pressing the solidified molded body obtained by the solidification molding in a direction perpendicular to the thickness direction of the foil, or The swaging forging is performed on the solidified compact with the direction perpendicular to the thickness direction of the foil as the pressing direction, or the direction perpendicular to the solidified compact with respect to the thickness direction of the foil is the pressing direction. Or a step of performing hot isostatic pressing on the solidified molded body.

In the present invention, a large number of chill crystals are present in the vicinity of the surface of the foil immediately after being produced by the liquid quenching method on the surface of the foil. However, in the subsequent reducing gas atmosphere or inert gas atmosphere. By the heat treatment, the chill crystals disappear, and the orientation of the crystal grains extending in the thickness direction of the foil is further improved. Therefore, a thermoelectric material having extremely high orientation and reduced specific resistance can be obtained by the subsequent steps of solidification molding and pressing. Further, Te atoms and Se atoms segregate in the vicinity of the surface of the foil due to the heat treatment and are easily diffused between the foils during the subsequent solidification molding, so that the sinterability and mechanical strength are improved.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail below. A foil of thermoelectric material can be produced by a liquid quenching method, and the produced foil itself may be fine like a powder. If it is not fine, the obtained foil is crushed into powder. In this way, the thermoelectric material powder obtained by the liquid quenching method has high-density strains and defects introduced therein. In this quenched foil, when heat treatment is performed in a reducing atmosphere of hydrogen gas, or during solidification molding such as hot pressing or extrusion molding, fine recrystallized grains become powder (foil) with nuclei of strain or defects. Is deposited inside. Since the grain boundary (interface) of the crystal grains has a lower impurity concentration than the interface between the pulverized powders, the phonon scattering due to the grain boundary is increased and the thermal conductivity (ratio) is increased while keeping the specific resistance (ρ) low. κ) can be reduced. Thereby, the figure of merit (Z) can be significantly improved.

Further, in the crystal utilizing the strain in the quenched foil, the major axis is biased in the direction parallel to the pressing direction during the solidification forming, and the minor axis is biased in the direction perpendicular to the pressing direction. It has a characteristic that it grows as a crystal grain having a large ratio or recrystallizes. In this case, the resistivity (ρ) value in the major axis direction is significantly lower than the resistivity (ρ) value in the minor axis direction, so that the figure of merit in this direction is high. Further, if the C planes are aligned parallel to the pressing direction, the specific resistance ρ further decreases and the figure of merit Z increases. Therefore, when assembling a thermoelectric conversion element into a thermoelectric conversion element, it is necessary to attach electrodes so that a current flows in a direction parallel to the pressurizing direction at the first solidification molding (primary solidification molding), that is, the long axis direction. is necessary.

In this embodiment, Bi, Sb and Te are used.
Although the thermoelectric material manufactured by adding Te to the composition consisting of is used, the same effect can be obtained by using thermoelectric materials having other various compositions. For example, in the present invention, as the thermoelectric material, a material composed of either one or both of Bi and Sb and one or both of Te and Se can be used. As the thermoelectric material, in addition to the above composition, I, Cl, Hg, B
It is also possible to use those to which at least one element selected from the group consisting of r, Ag and Cu is added.

Next, a method of manufacturing a thermoelectric material according to an embodiment of the present invention will be described. FIG. 1 is a flowchart showing a method for manufacturing a thermoelectric material according to an embodiment of the present invention.

In this embodiment, first, the raw material B
i, Sb, Te and Se are weighed (step S
1), as shown in FIG. 2A, this raw material 41 is inserted into the ampoule 42 (step S2). In addition, at the time of this encapsulation, after the raw material 41 is put into the ampoule 42, the inside of the ampoule 42 is evacuated, and the inside of the ampoule 42 is kept in a vacuum state or an inert gas is introduced. )
The mouth of the ampoule 42 is sealed off as shown in FIG. afterwards,
As shown in FIG. 2C, the ampoule 42 is placed at 600 to 7
The raw material 41 is melted by being placed in a tubular furnace 43 at 00 ° C., the tubular furnace 43 is rotatably supported by a stand 44, and is swung like a cradle to stir the raw material melt. Then, the melt is cooled and solidified. In this way, an ingot is manufactured (step S3).

FIG. 3 is a diagram showing a method for producing powder of thermoelectric material by the liquid quenching method. While rotating the copper roll 12, the molten metal 13 of thermoelectric material stored in a quartz nozzle 11 having a slit or a plurality of holes formed in the tip thereof at its tip 15 is pressurized by Ar gas and supplied. As a result, the molten metal 13 comes into contact with the copper roll 12 and is rapidly cooled, and becomes a quenched thin ribbon 14 which is sent out by the rotation of the roll 12 (step S4).

FIG. 4 is a schematic diagram showing the growth direction of crystal grains in a quenched thin piece. A quenching thin piece 31 is formed on the surface of the cooling roll 30, crystals grow in a direction away from the roll surface (thickness direction of foil), and have a major axis D in this direction,
Crystal structure 32 having a minor axis d in a direction parallel to the roll surface
Is obtained. Regarding the shape and orientation of the crystal in the quenched thin piece 31, the direction of the long axis D is originally parallel to the C plane. Then, when stress is applied to the quenched thin piece 31 in a direction parallel to the major axis, a crystal structure 33 which is a hexagonal crystal and whose C-plane is parallel to the pressing direction is obtained.

Taking the case of the liquid quenching method (single roll method) as shown in FIG. 3 as an example, when the molten metal of the thermoelectric material is cooled on the surface of the cooling roll and a quenched ribbon is formed, the molten metal is cooled. The part on the front surface side is first cooled, and then the part which is separated from the cooling roll is sequentially cooled. Therefore, a temperature gradient occurs in which the roll surface side is low in temperature and becomes higher in temperature as it moves away from it. Therefore, the crystal grains grow in a direction away from the roll surface, and have a long axis D in this direction and a short axis d in a direction parallel to the roll surface, and have a large aspect ratio. In the quenched ribbon 14, a large number of crystal grains having the major axis are arranged in parallel with the thickness direction. That is, the C plane of each crystal grain is parallel to the thickness direction of the quenched ribbon 14, and the thickness direction of the quenched ribbon 14 is the direction of low resistance in this material.

Further, by controlling the temperature of the molten metal during the rapid cooling, the crystal orientation of the thermoelectric material can be controlled, and as shown in FIG. 5, the hexagonal C-planes are aligned in parallel with the thickness direction of the quenched thin piece 31. To do.

Next, the quenched ribbon 14 obtained by quenching by the liquid quenching method shown in FIG. 3 is heat-treated in hydrogen gas or Ar gas (hydrogen reduction treatment or annealing treatment: step S).
5) Do. This heat treatment condition is, for example, a temperature of 400 ° C.
And the time is 8 hours. FIG. 6A is a sectional view showing the structure of the quenched ribbon 14 before heat treatment, and FIG. 6B is a sectional view showing the structure of the quenched ribbon 14 after heat treatment. As shown in FIG. 6A, in the structure before the heat treatment, that is, in the structure as rapidly solidified, a large amount of chill crystals 52 are present on the surface of the quenched ribbon 14 in addition to the crystal grains 51 extending in the thickness direction. On the other hand, by performing heat treatment, as shown in FIG.
Disappears. Further, during the heat treatment, the T in the quenched ribbon 14 is
The e atoms and Se atoms become segregated on the surface due to grain boundary diffusion.

Then, the thin strip 14 is crushed if necessary,
Classify and make the particle size uniform. Then, a thin strip (foil) 14 having an appropriate grain size range is loaded while being stacked in a prismatic mold (not shown), and a pressure P is applied in the axial direction in a state where the side surface is restrained by the heated heat. And hot press. As a result, FIG.
As shown in, the major axis is aligned in the pressing direction (pressing direction),
A prismatic solidified compact 61 having a crystal structure having crystal grains whose minor axes are aligned in the direction orthogonal to the pressing direction is obtained (primary solidification compaction) (step S6).

Strains and defects have been introduced into the quenched flakes produced by the liquid quenching method. When the rapidly cooled flakes are crushed or solidified by hot pressing or the like without crushing, grain growth of crystal grains occurs, or this strain or defect serves as nuclei to precipitate recrystallized grains. The recrystallized grains can be crystal grains with a large aspect ratio having a major axis in a direction parallel to the pressing direction during solidification molding and a minor axis in a direction perpendicular to the pressing direction.

Therefore, when solidifying the quenched thin piece (powder), it is pressed in the direction parallel to the thickness direction of the quenched ribbon, that is, in the direction parallel to the long axis of the crystal grains in the quenched ribbon, and at the time of solidification molding. If the long axes of the recrystallized grains that are generated are aligned in the pressing direction,
As a result, a solidified compact having a crystal structure in which the major axis direction of the crystal grains is aligned in the direction parallel to the pressing direction is obtained.

Further, in the present embodiment, as described above, Te atoms and S atoms are formed on the surface of the quenched ribbon 14 by the heat treatment.
Since the e-atoms are segregated, these atoms are easily diffused between the quenched ribbons 14 and are easily solidified and molded.

Thereafter, the solidified compact is subjected to side surface pressing (step S7a) and upset forging (step S7).
b), rolling (step S7c) or hot isostatic pressing (step S7d).

FIG. 8 is a schematic view showing a method of side surface pressing. When the side surface pressing is performed, the solidified molded body 61 is warmly or hot pressed from one direction or two directions perpendicular to the pressing direction of the hot press at the time of primary solidification molding. For example, in FIG. 8, when the pressure at the time of pot pressing is represented by P1, the pressure represented by P2 and / or P3 is applied to the solidified molded body.

FIG. 9 is a schematic view showing a method of upsetting. When performing the swaging forging, first, as shown in FIG. 9 (a), the solidified molded body 61 is rotated 90 ° to make the pressing direction of the pot press horizontal, and as shown in FIG. 9 (b). Then, this is sandwiched between flat anvils 62 from above and below, and pressure (P4) is applied. As a result, as shown in FIG. 9C, each crystal grain further extends in the pressing direction of the hot press and the orientation is improved. The pressure is, for example, 0.5 to 2.0 t / cm ² , and the temperature of the solidified molded body 61 at that time is maintained, for example, at 350 to 500 ° C.

FIG. 10 shows sheath rolling as an example of rolling.
It is a schematic diagram which shows the method of. In sheath rolling, first,
As shown in FIG. 10 (a), the solidified molded body 61 is, for example, pure
Inserted in a case 63 made of luminium, the degree of vacuum inside
About 1.3332 Pa (10 ^-2Torr) or above
The mouth of the case 63 (shown by the chain double-dashed line) is irradiated with an electron beam.
Weld to block the inside from the outside. Then, FIG.
As shown in (b), the case 63 is provided with a heater 65.
It is inserted into the heated furnace 64 and heated at 350-500 ° C for 10
Hold for up to 40 minutes. After that, as shown in FIG.
In addition, the pressing direction during hot pressing and the action direction of the rolling force are
Pass the rolls 66 so that they are orthogonal to each other.
By rolling, the solidified molded body 61 is rolled together with the case 63.
To do. The surface temperature of the rolling roll 66 at this time is
In order to suppress the temperature decrease of the solidified molded body 61, 100 ° C or higher
The above is preferable.

FIG. 11 is a schematic view showing a method of direct rolling as another example of rolling. In the direct rolling (pack rolling), as shown in FIG. 11A, the solidified molded body 61 is wrapped with, for example, an aluminum foil 67,
The package 70 is produced. Next, as shown in FIG. 11B, the package 70 is rolled in a vacuum chamber 68 provided with a heater 69 and a rolling roll 66. During this rolling, for example, the vacuum chamber 68 is evacuated, and the package 69 is heated to 350 to 550 ° C. by the heater 69.
Then, the package 70 is passed between the rolling rolls 66 such that the pressing direction at the time of hot pressing and the acting direction of the rolling force are orthogonal to each other.

The method for rolling the solidified compact is not limited to the sheath rolling or the direct rolling, and for example, the solidified compact may be rolled as it is. However, from the viewpoint of preventing cracks and homogenization,
Sheath rolling or direct rolling is preferred.

FIG. 12 is a schematic view showing a method of hot isostatic pressing. Hot Isostatic Press: H
In IP), for example, the solidified molded body 61 is inserted into a case 71 made of pure aluminum, the case 71 is deaerated, and then sealed. Then, as shown in FIG.
1 is placed in the pressure vessel 73. In the pressure vessel 73,
The heater 72 surrounds the arrangement position of the case 71.
The pressure vessel 73 is connected to a pipe 75 provided with a valve 74. Case 71 to pressure vessel 7
3, the valve 74 is opened while the inside of the case 71 is heated by the heater 72, and, for example, A
The r gas is introduced into the pressure vessel 73. As a result, FIG.
As shown in (b), the solidified molded body 61 in the case 71 is isotropically pressed by the pressure (P5). When performing processing by hot isostatic pressing, the primary solidification molding is preferably performed at low temperature and low pressure, and can be performed at room temperature, for example.

In any of the side press, upset forging, rolling and hot isostatic pressing methods,
The atmosphere at that time has a vacuum degree of about 1.3332 Pa (1
0 ^{- 2} Torr) after the above, by Ar substituted, it is preferably an oxygen concentration is obtained by the following 7000 ppm.

In the thermoelectric material produced in this manner, the specific resistance (ρ) in the major axis direction of crystal grains, that is, in the pressing direction of the hot press is significantly lower than the specific resistance (ρ) in the minor axis direction. The figure of merit (Z) in the direction becomes high. Further, since the C-planes of the crystals are also aligned in the pressing direction, the specific resistance (ρ) further decreases and the figure of merit (Z) increases.

Further, in this embodiment, since the chill crystals in the quenched ribbon 14 are eliminated by heat treatment, the thermoelectric material obtained as a result has high sinterability and excellent mechanical strength, and orientation. Is further improved. That is, when heat treatment is not performed as in the conventional case, the chill crystals existing on the surface of the quenched ribbon grow irregularly during the subsequent hot pressing. In fact, when observing the structure of the thermoelectric material produced by such a method, the crystal grains obtained by the growth of chill crystals are present at the interface of the quenched ribbon, not the crystal grains with high orientation. The orientation of is disturbed. Therefore, this region serves as a deformation resistance during sintering, and the sinterability is low. On the other hand, when heat treatment is performed as in this example, strain during quenching is relaxed, chill crystals disappear, deformation resistance during sintering (hot pressing) is significantly relaxed, and sinterability is improved. Is improved. In addition, since chill crystals cannot grow, high orientation can be obtained. Further, as described above, T during heat treatment
The sinterability is also improved by the diffusion of e atoms and Se atoms.

Furthermore, since the orientation is further improved, the specific resistance (ρ) in the pressing direction of the hot press is further reduced. As described above, the specific resistance (ρ) is easily affected by temperature, but due to the decrease in this value, a high figure of merit (Z) can be obtained even if the operating temperature of the thermoelectric material is about 90 ° C. To be

When the thermoelectric element is assembled into the thermoelectric module, the electrodes may be attached so that the current flows in the pressing direction, that is, the major axis direction of the crystal grains.

Next, the results obtained by producing thermoelectric materials under various conditions and determining their thermoelectric characteristics will be described. First, the thermoelectric materials having various compositions are manufactured, and the direction parallel to the pressing direction at the time of the first hot pressing (primary solidification molding) is
The figure of merit Z was calculated from the specific resistance ρ, the thermal conductivity κ and the Seebeck coefficient α. The results are shown in Tables 1 to 20 below. Table 1, Table 3, Table 5, Table 7, Table 9, Table 11, Table 13,
Tables 15, 17, and 19 show the composition of each thermoelectric material, and are Table 2, Table 4, Table 6, Table 8, Table 10, Table 12, and Table 1.
4, Table 16, Table 18 and Table 20 show the values of specific resistance ρ, thermal conductivity κ, Seebeck coefficient α and figure of merit Z. Further, Tables 1 to 4 show the cases where the solidified molded body was subjected to side surface pressing, Tables 5 to 8 show the cases where the solidified molded body was upset forged, and Tables 9 to 9 Table 12
Shows the case where the solidified molded body is subjected to sheath rolling, Tables 13 to 16 show the case where the solidified molded body is subjected to direct rolling, and Tables 17 to 20 show the solidified molded body. The figure shows the case where hot isostatic pressing is performed.

Example No. In Nos. 1 to 7, flakes or powders were prepared from the ingots prepared in the respective compositions by a liquid quenching method, subjected to reduction treatment at 400 ° C. for 10 hours in a hydrogen atmosphere, and then laminated with foils in the thickness direction of the foils ( A solidified molded body was produced by performing hot pressing with the pressing direction being the direction parallel to the C surface). Further, the solidified molded body was rotated by 90 °, and pressure was applied from one direction to perform side surface pressing. In the hot press, a carbide die was used and the atmosphere was an Ar atmosphere. In addition, the shape of the solidified molded body is a cube with each side having a length of 50 mm, and is 1.0 (t /
The pressure of cm ² ) was continuously applied at 300 ° C. for 30 minutes. Further, in the side press, a pressure of 0.5 (t / cm ² ) was applied to the P-type thermoelectric material (Examples Nos. 1 to 4) at 400 ° C.
The N-type thermoelectric material (Examples Nos. 5 to 7) was applied with a pressure of 0.5 (t / cm ² ) at 450 ° C. for 1 hour.
Application was continued for 1 hour.

Example No. In Nos. 8 to 13, flakes or powders were prepared from the ingots prepared by the respective compositions by a liquid quenching method, subjected to reduction treatment at 400 ° C. for 10 hours in a hydrogen atmosphere, and then the foils were laminated to form a foil thickness direction ( A solidified molded body was produced by performing hot pressing with the pressing direction being the direction parallel to the C surface). Further, the solidified compact was rotated by 90 ° for swaging forging. In hot press,
A carbide die was used and the atmosphere was an Ar atmosphere. The shape of the solidified molded body was a cube with each side having a length of 50 mm, and a pressure of 1.0 (t / cm ² ) was continuously applied at 350 ° C. for 30 minutes. In addition, in swaging forging, 0.8 (t
/ Cm ² ) at 400 ° C. for 5 hours.

Example No. In Nos. 14 to 19, flakes or powders were prepared from the ingots prepared by the respective compositions by the liquid quenching method, annealed at 400 ° C. for 10 hours in an Ar atmosphere, and then the foils were laminated in the thickness direction of the foil ( A solidified molded body was produced by performing hot pressing with the pressing direction being the direction parallel to the C surface). Further, the solidified molded body was vacuum-sealed in an aluminum container (sheath) and subjected to sheath rolling. In the hot press, a carbide die was used and the atmosphere was an Ar atmosphere. In addition, the shape of the solidified molded body is a cube with each side having a length of 50 mm, and is 0.5 (t / c) in the P-type thermoelectric material (Examples Nos. 14 to 16).
m ² ) pressure at 350 ° C. for 1 hour, and 0.5 (t) in N-type thermoelectric materials (Examples Nos. 17 to 19).
/ Cm ² ) of pressure was continued to be applied at 400 ° C. for 1 hour. In the case of sheath rolling, the solidified molded body is cut in half and its shape is 50 mm on two sides and 25 mm on the other side.
Of rectangular parallelepiped, and the rolling temperature: 450 ° C., roll diameter: 400 mm, rolling speed: 2 m / sec, rolling reduction: 20%
Was rolled under the conditions.

Example No. In Nos. 20 to 25, flakes or powders were prepared from the ingots prepared in the respective compositions by the liquid quenching method, annealed at 400 ° C. for 10 hours in an Ar atmosphere, and then the foils were laminated to form the foil thickness direction ( A solidified molded body was produced by performing hot pressing with the pressing direction being the direction parallel to the C surface). Further, the solidified molded body was wrapped with aluminum foil, the inside of the chamber was evacuated, and then the inside of the chamber was subjected to an Ar atmosphere for direct rolling. In the hot press, a carbide die was used and the atmosphere was an Ar atmosphere. Further, the solidified molded body has a cubic shape with each side having a length of 50 mm, and is made of a P-type thermoelectric material (Example N).
o. 20 to 22) at 0.5 (t / cm ²⁾ pressure was continuously applied for 1 hour at 350 ° C. of, N-type thermoelectric material (Example No.23 to 25) at 0.5 (t / ^cm 2)
Was continuously applied at 400 ° C. for 1.5 hours. Further, in the direct rolling, the solidified formed body is cut in half to form a rectangular parallelepiped having a length of two sides of 50 mm and a length of the other side of 25 mm. The rolling temperature is 480 ° C. and the roll diameter is:
Rolling was performed under the conditions of 400 mm, rolling speed: 5 m / sec, and rolling reduction: 30%.

Example No. In Nos. 26 to 31, thin flakes or powders were prepared from the ingots prepared in the respective compositions by the liquid quenching method, annealed at 400 ° C. for 8 hours in an Ar atmosphere, and then the foils were laminated to form the foil thickness direction ( A solidified molded body was produced by performing hot pressing with the pressing direction being the direction parallel to the C surface). Further, the solidified molded body was vacuum-sealed in an aluminum container (sheath) and hot isostatic pressing was performed. In the hot press, a carbide die was used and the atmosphere was an Ar atmosphere. Further, the solidified molded body has a cubic shape with a side length of 50 mm, and has a shape of 0.5 (t /
The pressure of cm ² ) was continuously applied at 280 ° C. for 1 hour. In hot isostatic pressing, the pressure is 1 (t / c) in Ar atmosphere.
The pressure of m ² ) was continuously applied at 400 ° C. for 5 hours.

[0051]

[Table 1]

[0052]

[Table 2]

[0053]

[Table 3]

[0054]

[Table 4]

[0055]

[Table 5]

[0056]

[Table 6]

[0057]

[Table 7]

[0058]

[Table 8]

[0059]

[Table 9]

[0060]

[Table 10]

[0061]

[Table 11]

[0062]

[Table 12]

[0063]

[Table 13]

[0064]

[Table 14]

[0065]

[Table 15]

[0066]

[Table 16]

[0067]

[Table 17]

[0068]

[Table 18]

[0069]

[Table 19]

[0070]

[Table 20]

As shown in these results, in each of the Examples, a high performance index (Z) was obtained by subjecting the solidified molded body to side surface pressing, upset forging, sheath rolling, direct rolling or hot isostatic pressing. Resistivity (ρ) while maintaining
Has dropped. That is, these treatments yielded a thermoelectric material suitable for use at high temperatures.

It is also confirmed that, after the present inventor has performed these treatments, the thermoelectric material is further subjected to heat treatment in a vacuum or in an Ar atmosphere, whereby variations in the physical properties and strength of each sample are suppressed. It was

[0073]

As described in detail above, according to the present invention,
Chill crystals existing on the surface of the foil prepared by the liquid quenching method disappear by heat treatment in the subsequent reducing gas atmosphere or inert gas atmosphere, further improving the orientation of the crystal grains extending in the thickness direction of the foil. Can be made. Therefore, by the subsequent steps of solidification molding and pressure,
It is possible to obtain a thermoelectric material having extremely high orientation and having a significantly reduced specific resistance in the pressing direction during solidification molding. That is, a high figure of merit can be maintained even when used at high temperatures. Also, by heat treatment, T near the surface of the foil
Since the e atoms and Se atoms segregate and easily diffuse between the foils during the subsequent solidification forming, the sinterability and mechanical strength can also be improved.

[Brief description of drawings]

FIG. 1 is a flowchart showing a method for manufacturing a thermoelectric material according to an example of the present invention.

FIG. 2 is a diagram showing a method for producing an ingot in the example of the present invention.

FIG. 3 shows a method for producing a powder of thermoelectric material by a liquid quenching method.

FIG. 4 is a schematic view showing a crystal grain growth direction in a quenched thin piece.

FIG. 5 is a schematic diagram showing a relationship between a pressing direction and a C surface.

6A is a sectional view showing the structure of the quenched ribbon 14 before heat treatment, and FIG. 6B is a sectional view showing the structure of the quenched ribbon 14 after heat treatment.

FIG. 7 is a diagram showing a solidification molding method by hot pressing.

FIG. 8 is a schematic view showing a method of a side surface press.

FIG. 9 is a schematic view showing a swaging forging method.

FIG. 10 is a schematic view showing a sheath rolling method as an example of rolling processing.

FIG. 11 is a schematic view showing a method of direct rolling as another example of rolling.

FIG. 12 is a schematic view showing a method of hot isostatic pressing.

FIG. 13 is a schematic diagram showing a method of manufacturing a conventional unidirectionally solidified material in the order of steps.

FIG. 14 is a schematic diagram showing crystal grains of a thermoelectric material to be solidified and molded and hot pressing directions.

FIG. 15 is a diagram showing a crystal structure of a thermoelectric material.

[Explanation of symbols]

1; thermoelectric material, 2; crystal grain, 11; quartz nozzle,
12: Copper roll, 13: Molten metal, 14: Quenched foil strip,
15; top part, 30; chill roll, 31; quenching flakes,
32, 33; crystal structure, 41; raw material, 42; ampoule, 43; tubular furnace, 44; stand, 51; crystal grain, 52; chill crystal, 61; solidified compact, 62;
Flatbed, 63; Case, 64; Furnace, 65; Heater, 66; Roll, 67; Aluminum foil,
68; Vacuum chamber, 69; Heater, 70; Package, 71; Case, 72; Heater, 73; Pressure vessel, 74; Valve, 75; Piping

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) B22F 9/08 B22F 9/08 C H01L 35/16 H01L 35/16 (72) Inventor Takahiro Hayashi Nakazawa Town, Hamamatsu City, Shizuoka Prefecture No. 10 No. 1 Yamaha Stock Company (72) Inventor Junya Suzuki No. 10 Nakazawa-machi, Hamamatsu City, Shizuoka Prefecture F No. 10 within Yamaha Stock Company (reference) 4K017 AA04 BB03 CA03 DA01 EC02 FA21 4K018 AA40 BA20 BB01 BC01 EA02 EA13 EA44 EA52 FA01 KA32

Claims (4)

[Claims] 1. A step of producing a foil having a composition of at least one element selected from the group consisting of Bi and Sb and at least one element selected from the group consisting of Te and Se by a liquid quenching method. And a step of heat-treating the foil in a reducing gas atmosphere or an inert gas atmosphere, a first molding step of stacking the foils and pressurizing them in the thickness direction thereof, and a step of solidifying and molding. A second forming step of pressing the solidified formed body in a direction perpendicular to the thickness direction of the foil. 2. A step of producing a foil having a composition of at least one element selected from the group consisting of Bi and Sb and at least one element selected from the group consisting of Te and Se by a liquid quenching method. And a step of heat-treating the foil in a reducing gas atmosphere or an inert gas atmosphere, a step of solidifying and molding by laminating the foils and pressing in the thickness direction thereof, and a solidifying and molding obtained by the solidifying and molding. A step of upsetting forging the body in a direction perpendicular to the thickness direction of the foil as a pressing direction, the method for producing a thermoelectric material. 3. A step of producing a foil having a composition of at least one element selected from the group consisting of Bi and Sb and at least one element selected from the group consisting of Te and Se by a liquid quenching method. And a step of heat-treating the foil in a reducing gas atmosphere or an inert gas atmosphere, a step of solidifying and molding by laminating the foils and pressing in the thickness direction thereof, and a solidifying and molding obtained by the solidifying and molding. A step of rolling the body in a rolling direction in a direction perpendicular to the thickness direction of the foil, the method for producing a thermoelectric material. 4. A step of producing a foil having a composition of at least one element selected from the group consisting of Bi and Sb and at least one element selected from the group consisting of Te and Se by a liquid quenching method. And a step of heat-treating the foil in a reducing gas atmosphere or an inert gas atmosphere, a step of solidifying and molding by laminating the foils and pressing in the thickness direction thereof, and a solidifying and molding obtained by the solidifying and molding. A step of performing hot isostatic pressing on the body, and a method for producing a thermoelectric material.