JP2003264318A - Method for manufacturing thermoelectric conversion element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a thermoelectric conversion element exhibiting excellent characteristics stably. <P>SOLUTION: Material powder composed of at least two kinds of bismuth, tellurium, antimony and selenium is placed in a furnace, a partial pressure regulating agent containing an element composing the material powder is arranged around the material powder, and then it is subjected to hot isotropic pressure sintering. The element contained in the partial pressure regulating agent is preferably tellurium. <P>COPYRIGHT: (C)2003,JPO

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 conversion element, and more particularly to a method for manufacturing a thermoelectric conversion element that is preferably used for temperature control and cold insulation.

[0002]

2. Description of the Related Art A thermoelectric conversion element is an element having a function of generating electricity by making a temperature difference between a pn junction pair made of a p-type semiconductor and an n-type semiconductor, that is, converting heat into electricity. On the other hand, a thermoelectric conversion element utilizing the so-called Peltier effect, in which one end generates heat and the other end absorbs heat when a current is passed, is small and has a simple structure.
It is expected to be widely used as a device such as a CFC-less cooling device, a photodetector, an electronic cooling device such as a semiconductor manufacturing device, and a temperature control device such as a temperature control of a laser diode.

For these thermoelectric semiconductor elements, Bi ₂ Te ₃ and S are the most effective thermoelectric conversion materials near room temperature.
Chalcogen compounds such as b ₂ Te ₃ and Bi ₂ Se ₃ and solid solutions thereof are mainly used.

As a method for manufacturing such a cooling element, raw material powders mixed at a predetermined ratio are melted to form an alloy, taken out after cooling, pulverized, and the obtained alloy powder is classified and sized. , A manufacturing method of sintering has been proposed.

As the sintering method, a hot isostatic pressing method may be used because a dense body can be easily obtained. For example, Japanese Patent Laid-Open No. 5-206525 proposes that an alloy powder having an average particle size of 0.05 to 10 μm is molded and the obtained molded body is hot isostatically pressed and sintered.

In addition, SUS, 17-14CuMo, ST
JP-A-6-216415 proposes to manufacture a thermoelectric material of a large size by hot isostatic pressing and sintering using a capsule made of BA24HCM12, Hastelloy, Incoloy or Inconel.

[0007]

However, according to the methods described in JP-A-5-206525 and JP-A-6-216415, it is possible to produce a thermoelectric material of a large size, but the thermoelectric material is used between production batches. There is a problem that the target material cannot be obtained stably because the performance of the material varies and the performance of the same sample varies depending on the site.

Therefore, it is an object of the present invention to provide a method for producing a thermoelectric conversion element, which can stably obtain excellent characteristics.

[0009]

According to the present invention, the variation in characteristics is caused by the variation in composition, and the cause that the element in the raw material, especially tellurium is volatilized during firing and the composition is deviated, and the raw material powder is constituted. Based on the finding that by adjusting the partial pressure of elements, it is possible to easily produce a thermoelectric conversion element that has excellent thermoelectric performance and mechanical strength, is made of a uniform material, and has a small variation in characteristics even when manufacturing a large substrate. Is.

That is, in the method for producing a thermoelectric conversion element of the present invention, a raw material powder made of at least two kinds of bismuth, tellurium, antimony and selenium is placed in a furnace, and a partial pressure containing elements constituting the raw material powder is placed. The adjusting agent is arranged around the raw material powder and is hot isostatically pressed and sintered.

Particularly, the element contained in the partial pressure adjusting agent is preferably tellurium. Since tellurium tends to volatilize easily, improvement of uniformity can be easily achieved by suppressing it.

The average aspect ratio of the crystals forming the raw material powder is preferably 1.5 or more. As a result, a sintered body in which the crystals are more oriented is obtained, and the thermoelectric properties can be further improved.

Further, it is preferable that a compact having a crystal orientation of 25% or more and a relative density of 90% or more is produced using the raw material powder, and then the compact is hot isostatically pressed and sintered. . As a result, a sintered body in which the crystals are more oriented is obtained, and the characteristics of the thermoelectric element can be further improved.

It is preferable that the raw material powder is enclosed in a metal container containing the partial pressure adjusting agent, and hot isostatic pressing is performed. Further, a seal layer is provided on the surface of the raw material powder, and the raw material powder is embedded in a low melting point metal powder containing at least the partial pressure adjusting agent, the low melting point metal is melted to form a molten metal bath, and hot isostatic heating Pressure sintering is preferable. Due to these, it is possible to easily obtain a dense thermoelectric conversion element having excellent thermoelectric characteristics.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The method for manufacturing a thermoelectric element of the present invention is
It is important to use a raw material powder containing at least two kinds of Bi, Sb, Te and Se, and it is particularly preferable to use an A ₂ B ₃ type intermetallic compound in order to improve thermoelectric properties.
Here, A is a semiconductor crystal composed of Bi and / or Sb, B is a Te and / or Se type, and a composition ratio B / A is particularly preferable.
Is preferably 1.4 to 1.6 in order to improve thermoelectric properties at room temperature.

A₂B₃Known intermetallic compounds of the type
Bi₂Te₃, Sb₂Te₃, Bi₂Se₃At least one of
Seed is preferable, and Bi is used as a solid solution.₂Te₃And B
i₂Se₃Is a solid solution of Bi₂Te_3-xSe_x(X = 0.
05-0.25), or Bi ₂Te₃And Sb₂Te₃Solid solution of
Bi that is the body_xSb_2-xTe₃(X = 0.1-0.6) etc.
Can be illustrated.

Impurities can be added as dopants in order to efficiently convert the intermetallic compound into a semiconductor. For example, an n-type semiconductor can be manufactured by including a raw material powder with a compound containing a halogen element such as I, Cl and Br. For example, AgI, CuB
By adding r, SbI ₃ , SbCl ₃ , SbBr ₃ , HgBr ₂ or the like, the carrier concentration in the intermetallic compound semiconductor can be adjusted, and as a result, thermoelectric characteristics can be improved.

When manufacturing a p-type semiconductor, Te can be added to adjust the carrier concentration, and n
Similar to the type semiconductor, the thermoelectric property can be enhanced.

According to the present invention, the partial pressure adjusting agent containing the element constituting the raw material powder is placed in the furnace together with the raw material powder, and hot isostatic pressing is performed (hereinafter sometimes referred to as HIP). It is important to. That is, it is preferable that the partial pressure adjusting agent contains at least one element selected from bismuth, tellurium, antimony, and selenium, which are elements constituting the raw material powder, in order to obtain stable characteristics. Of these elements,
Since tellurium easily evaporates, it is more preferable that it is contained in the pressure adjusting agent.

While the HIP is kept at a high temperature, it vaporizes from the molded body,
If there is a component that volatilizes, the composition of the molded body and the composition of the sintered body differ greatly, and a sintered body having the desired composition cannot be obtained. Therefore, by firing the partial pressure adjusting agent together with the raw material powder, it is possible to perform sintering while suppressing vaporization and volatilization of the components in the molded body.

Further, in order to improve the characteristics of the thermoelectric conversion element and enhance the cooling and heating performance by improving the crystal orientation of the sintered body, the average aspect ratio of the crystals constituting the raw material powder is 1.5 or more, It is particularly preferable that the number is 2 or more.
By increasing the average aspect ratio of the raw material powder to 1.5 or more and HIPing it, the degree of crystal orientation in the sintered body can be easily increased. As a result, a sintered body having excellent cold heat performance can be obtained.

The crystal orientation of the molded body is 25% or more, especially 3
It is preferably 0% or more, and more preferably 35% or more. The thermoelectric conversion characteristics can be improved by increasing the crystal orientation of the molded body. Of course, it goes without saying that it is preferable to maintain the degree of orientation of the molded body up to the sintered body.

The orientation degree in the present invention means the peak intensities of I ₍₀₀₆₎ , I ₍₀₁₅₎ and I ₍₀₀₁₅₎ obtained by X-ray diffraction, and the sum of these peak intensities
I _{(0 06)} and indicates the ratio of I _(0015), it illustrates a f given by the following equation as a percentage. f = I ₍₀₀₆₎ + I ₍₀₀₁₅₎ / I ₍₀₀₆₎ + I ₍₀₁₅₎ + I ₍₀₀₁₅₎ The relative density of the molded body is preferably 90% or more, particularly 95% or more, and further preferably 97% or more. When the molded body has a high relative density, it can be hot isostatically pressed as it is, but it can be molded as it is by a cold isostatic press to further increase the relative density and improve the sinterability.

Next, a specific method for manufacturing a thermoelectric conversion element will be described.

The above starting materials are thoroughly mixed in the desired proportions. Then, if desired, the obtained mixed powder is molded. A known method can be used for the molding method. For example, at least one of a uniaxial pressing method, a rubber pressing method, a cold isostatic pressing method, a sludge molding method, a pressure casting method, a solid casting method, an extrusion molding method and an injection molding method can be used.

However, in order to improve the orientation of the crystal grains, the uniaxial pressing method, the sludge molding method, the pressure casting method, the solid casting method, the extrusion method and the injection molding method are more preferable and particularly simple. Therefore, the uniaxial pressing method is preferable. Also, by performing sludge molding or casting while applying a high magnetic field,
It is also possible to obtain highly oriented shaped bodies.

When a uniaxial press is used as the molding method, the pressure is preferably 10 MPa or more, more preferably 50 MPa or more. By setting the pressure to 10 MPa or more, the degree of orientation can be sufficiently increased, and deterioration of cold heat performance can be prevented.

When a non-alloyed raw material is used, the powder for molding can be obtained by pulverizing after the alloying treatment. A known method can be adopted for the melting step. As a normal step, there is a method in which the mixed powder is sealed in a quartz tube under vacuum and argon gas and then melted in a rocking furnace. Examples of the pulverizing step include known methods such as a stamp mill, a ball mill and a vibration mill.

The molded body is preferably subjected to hydrogen reduction treatment prior to firing. Since the performance of the thermoelectric conversion element is greatly affected by the amount of oxygen contained in the element, it is possible to improve the performance by removing oxygen existing on the surface of the raw material powder forming the compact. Note that the hydrogen reduction treatment can obtain the same effect even at the stage of raw material powder before firing.

The HIP of the present invention can be fired using at least three methods.

The first method is the Sinter HIP method.
First, a molded body having a crystal orientation degree of 25% or more and a relative density of 90% or more is produced. Next, this is HIP fired to produce a calcined body having a relative density of 95% or more, particularly 97% or more, and then HIPing this.

The reason for increasing the crystal orientation of the compact is to increase the crystal orientation after calcination to 25% or more and maintain the high orientation even after HIP, which can enhance thermoelectric conversion characteristics. it can. This crystal orientation degree is 30% or more,
Further, it is desirable that it is 35% or more from the viewpoint of improving the characteristics.

Further, the reason why the relative density of the compact is set to 90% or more is that the degree of crystal orientation is not significantly reduced by calcination and that the relative density of the calcined body is 95% or more. .

The HIP is carried out by applying a pressure of 10 MPa or more at a desired temperature and holding it for a specific time to carry out the HIP treatment. Pressure 1
This is because by setting the pressure to 0 MPa or more, a sufficient HIP effect is given, pores are prevented from remaining inside the sintered body, and the density is improved. Particularly, 100 MPa or more, and further preferably 150 MPa or more is particularly preferable.

The second method is the capsule HIP method.
That is, the raw material powder or its molded body is placed in a container made of metal containing a partial pressure adjusting agent, deaerated and sealed. For example, T
The raw material powder can be placed in a container made of W metal containing e. In this case, the partial pressure adjusting agent constitutes a part of the container for containing the raw material.

Various shapes such as capsule shape, can shape and bag shape can be used for the container, and it may be appropriately selected depending on the form of the material to be sintered. This container is a hot isostatic press (HIP device)
It is installed inside and heated and pressurized to obtain a sintered body.

The HIP is carried out by applying a pressure of 10 MPa or more at a desired temperature and holding it for a specific time to carry out the HIP treatment. The pressure is 10 MPa or more, particularly 100 MPa or more, and further 15
The reason for setting it to 0 MPa or more is the same as in the case of the first method.

The third method is the seal HIP method. That is, a slurry required to completely cover the surface of the molded body with the seal layer is prepared. That is, a solvent is added to the sealing material powder and the binder to prepare a slurry. The average particle size of the sealing material powder is not particularly limited as long as it functions as a barrier material for molten metal. BN or the like is preferably used as the sealing material.

Next, a seal layer is formed on the surface of the molded body.
A dipping method or a spraying method can be used to form the seal layer. The immersion method is a method of immersing the molded body or the calcined body in the slurry and then pulling it up to attach the slurry to the surface, and the spraying method is a method of spraying the slurry in the form of droplets onto the surface to form a coating layer. It is a method of forming.

In the present invention, according to the above-described method for forming the seal layer, the seal layer is formed with a uniform thickness even in the depressions, the groove portions, or the thin portion, so that the seal layer is reproducible and is not damaged. With such advantages, it becomes possible to manufacture a sintered body with a high yield, and it becomes possible to adapt to mass production. Further, since the dense seal layer is formed, the functionality of the molten metal as a barrier material can be enhanced. Even if the molded body or the calcined body has a complicated shape, the sealing layer can be formed without directly contacting with a brush or a jig, and thus the above method has an effect of increasing the yield.

At this time, it is important that the molded body is completely covered with the seal layer. When the coating layer is incomplete, there are problems that pressure is not applied to the material to be sintered and that the composition changes due to metal infiltration. Therefore, the thickness of the sealing layer is 0.5 to 5 mm, especially 1 to 3 m.
m is preferred. The thickness of this seal layer can be easily adjusted by the viscosity of the slurry and the spraying time.

Furthermore, it is preferable to dry the object to be sintered on which the slurry-like sealing layer is formed on the entire surface in order to remove the solvent in the sealing layer. Thereby, the seal layer can improve the shape retention on the surface of the material to be sintered. Also,
After this, if necessary, heating for degreasing may be performed in order to remove the binder.

Next, the crucible in which the metal powder and the material to be sintered are buried is set in the HIP device, and gas replacement is performed. Then 10
A molten metal bath is prepared under a pressure of less than MPa. At this time, if the pressure is higher than 10 MPa, high-pressure gas is trapped in the molten metal bath, and a sufficient HIP effect cannot be obtained.

HIP is carried out by applying a pressure of 10 MPa or more at a desired temperature and holding it for a specific time to carry out HIP treatment. Further, if the pressure is 10 MPa or less, the HIP effect is not sufficient, so that pores remain inside the sintered body and the density decreases. Especially, 100MPa or more, further 150MP
Especially preferred is a or more.

As described above, since the thermoelectric material sintered body produced by the production method of the present invention has a high density and a uniform composition, it is excellent in thermoelectric performance and mechanical strength and is uniform.
It is possible to manufacture a large-sized thermoelectric material sintered body having a size of at least mm, particularly at least 50 mm. Therefore, it is possible to obtain a thermoelectric conversion material and a thermoelectric conversion module with high yield, low cost, high performance, high reliability, and high durability.

[0046]

Examples A p-type thermoelectric conversion element having a purity of 99.9% or more, an average aspect ratio of Bi _0.4 Sb _1.6 Te ₃ alloy powder, or an n-type thermoelectric conversion element having a purity of 99.9% or more,
Bi ₂ Te _2.85 Se _0.15 alloy powder having an average aspect ratio of 2 was put in a pot together with ceramic balls and IPA, and mixed and pulverized in a vibration mill for 10 hours. Transfer the raw material slurry to a vat while passing it through # 300 mesh, and
It was dried in a 0 ° C. dryer. After drying, the particles were sized with # 40 mesh and subjected to reduction treatment in a hydrogen stream at 350 ° C. for 5 hours. (Sinter HIP method) The above-mentioned raw material subjected to hydrogen reduction treatment was uniaxially press-molded with a mold at 0.1 GPa, then vacuum-sealed in a water-impermeable film, and cold isostatically pressed at 0.3 GPa. Sample No. 1-17 and 27-43
Is a sample N
o. 18, 19, 44, and 45 were produced by the SPS method (discharge plasma sintering method) at 400 ° C. and had a relative density of 95%.
The calcinated body of was used as the body to be HIPed. In each case, the shape of the calcined body was 50 mm in diameter and 30 mm in thickness.

The obtained body to be HIP was placed in a carbon pot together with the partial pressure regulator of Table 1. After that, a baking pot was installed in the hot isostatic press, the gas was replaced with argon twice, the temperature was raised at a heating rate of 10 ° C./min while pressurizing the gas, and HIP was performed under the conditions shown in Table 1. It was (Capsule HIP Method) The hydrogen-reduced raw material was sealed in a metal container in a vacuum.

This container is a sample No. 21-23, 47
The main component of ~ 49 is tungsten and contains 20% by mass of tellurium. In addition, the sample No. Nos. 20 and 46 were made of aluminum containing no constituents of the raw material powder.

The container containing the sample inside was placed in a hot isotropic pressurizer and sintered under the HIP conditions shown in Table 1 to a diameter of 50 m.
A substrate having a thickness of m and a thickness of 30 mm was obtained. (Seal HIP method) Sample No. 24-26 and 50-5
2 was manufactured by the seal HIP method. That is, the hydrogen-reduced raw material was uniaxially press-molded in a mold at 0.1 GPa, then vacuum-sealed in a water-impermeable film,
Cold isostatic pressing was performed at 3 GPa to produce a molded body, and BN was added to the solvent in which the binder was dissolved to produce a slurry for sealing.

Next, the slurry was applied to the surface of the molded body, the surface was completely covered with the seal layer, and then dried. further,
Tellurium powder, a mixed powder of 80% tellurium and 20% selenium, and a crucible in which the material to be sintered is embedded are placed in a hot isostatic press, respectively, and after performing gas replacement, molten metal under a pressure of less than 10 MPa. A bath was prepared and sintered under the HIP conditions shown in Table 1 to obtain a substrate having a diameter of 50 mm and a thickness of 30 mm. (Evaluation method) The specific gravity of the obtained sintered body was measured by the Archimedes method, and the relative specific gravity was measured from the theoretical value.

The degree of orientation was determined by X-ray diffraction as described above.

The thermal conductivity was measured by the laser flash method.
The Seebeck coefficient and the specific resistance are measured with a thermoelectric power evaluation device manufactured by Vacuum Riko Co., Ltd. under the conditions of 20 ° C., respectively,
The figure of merit Z was calculated by the formula Z = α ² / ρκ (α is the Seebeck coefficient, ρ is the specific resistance, and κ is the thermal conductivity). At this time, the figure of merit was measured with one inside from the center of the sintered body, four inside the vicinity of the midpoint between the center and the end, and four outside from the outer periphery of 10 mm from the end, and the internal average value The difference between the external average values was calculated, and the absolute value was calculated as a ratio to the internal average value. The results are shown in Table 1.

[0053]

[Table 1]

Sample N of the present invention using the Sinter HIP method
o. 1 to 6, 8 to 19, 27 to 32 and 34 to 45 are
The figure of merit Z is p-type 2.9 × 10 ^-3 / K or more, the difference is 7
% Or less. For n type, 2.9 × 10 ^-3 / K or more,
The difference was 6% or less.

On the other hand, Sample No. in which the partial pressure adjusting agent does not contain the constituent elements of the raw material powder 7, 33, the figure of merit Z is 2.7 ×
It was 10 ^-3 / K or less, and the difference was 15% or more.

Sample N of the present invention using the capsule HIP method
o. 21-23 and 47-49 have a performance characteristic Z of 3.0 ×.
When it was 10 ⁻³ / K or more, the difference was 3% or less.

On the other hand, the sample No. in which the partial pressure adjusting agent does not contain the constituent elements of the raw material powder 20 and 46 have a figure of merit Z of 2.6.
The difference was 15% or more with a value of ^{x10 -3} / K or less.

The sample No. of the present invention using the seal HIP.
25, 26, 51 and 52 have a performance index Z of 3.1 × 10.
^-3 / K or more, the difference was 3% or less.

On the other hand, Sample No. in which the partial pressure adjusting agent does not contain the constituent elements of the raw material powder. 24 and 50 have a performance index Z of 2.7.
The difference was 15% or more at × 10 ⁻³ / K or less.

[0060]

According to the present invention, a partial pressure adjusting agent containing an element constituting the raw material powder is placed in the apparatus and HIP is performed together with the specific raw material powder. By this method, thermoelectric performance and mechanical strength are obtained. It is easy to manufacture thermoelectric conversion elements with excellent properties, uniform material, and small variation in characteristics.

Continued front page    (72) Inventor Kazuhiro Nishizono             Kyocera Co., Ltd. 1-4 Yamashita Town, Kokubun City, Kagoshima Prefecture             Shikisha Research Institute F term (reference) 4K018 AA40 BA20 BC12 CA01 CA11                       CA23 CA29 CA31 DA01 EA12                       EA16

Claims (6)

[Claims] 1. A raw material powder made of at least two kinds of bismuth, tellurium, antimony and selenium is placed in a furnace, and a partial pressure regulator containing an element constituting the raw material powder is placed around the raw material powder. And a method for manufacturing a thermoelectric conversion element, which comprises hot isostatic pressing and sintering. 2. The method for manufacturing a thermoelectric conversion element according to claim 1, wherein the element contained in the partial pressure adjusting agent is tellurium. 3. The method for producing a thermoelectric conversion element according to claim 1, wherein the crystal forming the raw material powder has an average aspect ratio of 1.5 or more. 4. The crystal orientation of the raw material powder is 25%.
The thermoelectric conversion element according to any one of claims 1 to 3, wherein a molded body having a relative density of 90% or more is produced as described above, and then the molded body is hot isostatically pressed and sintered. Production method. 5. The thermoelectric element according to claim 1, wherein the raw material powder is enclosed in a metal container containing the partial pressure regulator, and hot isostatic pressing is performed. Method for manufacturing conversion element. 6. A seal layer is provided on the surface of the raw material powder, the seal layer is embedded in a low melting point metal powder containing at least the partial pressure adjusting agent, and the low melting point metal is melted to form a molten metal bath. The method for manufacturing a thermoelectric conversion element according to claim 1, wherein isotropic pressure sintering is performed.