JPH02256283A - Thermoelectric material and manufacture thereof - Google Patents

Abstract

PURPOSE:To easily manufacture the little material by intermixing specific metal powder to be a raw material and forming and sintering it. CONSTITUTION:Being a raw material containing at least bismuth and a raw material containing at least tellurium while a raw material, which is not totally alloyed, is used for being concrashed and mixed so that a mixing ratio of the raw materials may desirably become the former : the latter = 2:3 (mole ratio) followed by being cocrached formed and sintered. In order to simultaneously progress mixture and cocrashing, that is, in order to perform cocrashing mixing, a planetary type ball is desirably used. Thereby, a manufacture process can be simplified.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a thermoelectric material and a method for producing the same, and more particularly, to a thermoelectric material having unique performance and an industrially advantageous thermoelectric material with a simplified production process. Regarding the manufacturing method.

[Prior Art and Problems to be Solved by the Invention] Thermoelectric power generating elements that utilize the Seebeck effect or electronic cooling elements that utilize the Beltier effect have attracted attention because of their simple structure and ease of handling. These thermoelectric conversion materials (thermoelectric materials) are widely used in various fields such as space development, ocean development, power supplies for remote areas, temperature sensors, constant temperature devices in semiconductor manufacturing processes, and cooling of electronic devices. Moreover, various means have been conventionally provided as methods for manufacturing such thermoelectric materials. For example, (1) a crystalline ingot production method in which raw materials are mixed and melted, formed into an ingot, and sliced; (2) the raw material powder or mixed melt is powdered, then shaped and sintered, and sliced as necessary. Powder sintering manufacturing method, (
Various manufacturing methods are known, such as 3) polycrystallization-zonal melting manufacturing method, (4) amorphous manufacturing method, and (5) thin/thick film manufacturing method.

However, all of these methods require 1141 steps and require a long process of melting and mixing, resulting in low mass productivity.Also, methods that include slicing operations during the process cause slicing loss. However, in the polycrystallization-zonal melting production method, electrical and mechanical directionality was caused by the crystals.

Furthermore, due to the difficulty of manufacturing ultra-small devices, the scope of its application has been limited to some fields.

In particular, conventional methods have a fundamental problem in that the molding methods are limited and it is difficult to obtain molded products of arbitrary shapes using various molding methods.

Furthermore, JP-A No. 59-143383 describes forced mixing of a lead tellurium compound and a manganese metal as a means of solving these problems, but this method is still not sufficient. .

Furthermore, in JP-A No. 64-37456, Bi2T
Although a method for producing a sintered body of e,-Bj2Se4 solid solution powder is disclosed, the process is complicated and is inappropriate for practical use.

[Failure to solve the problem]

Therefore, the present inventors have conducted extensive research in order to develop a thermoelectric material that has a simple manufacturing process, a high yield, and can be used to directly obtain any desired element using various molding methods. As a result, it has been found that the above object can be achieved by using specific raw materials and co-pulverizing and mixing the raw materials.

The present invention was completed based on this knowledge.

That is, in the present invention, after co-pulverizing and mixing seven raw materials containing at least bismuth and seven raw materials containing at least tellurium that are not entirely alloyed,
To provide a thermoelectric material obtained by sintering, and to co-pulverize and mix a raw material containing at least bismuth and a raw material containing at least tellurium, which are not entirely alloyed, and then molding and sintering. The present invention provides a method for producing a thermal lightning material characterized by the following.

The raw materials for the thermoelectric material mentioned above are a raw material containing at least bismuth (powder nest) and a raw material containing at least tellurium (powder), and the raw material (powder) is an alloy of the entire composition (total composition).
This method is completely different from the conventional method using .

In addition to bismuth and tellurium, the raw material may also be powders of antimony, selenium, etc., powders of tellurium and antimony, or alloy powders of tellurium and antimony. The particle size of these raw materials is not particularly limited, but is usually 20 to 70 tIm on average, and 11
Preferably, it does not contain anything larger than 00u. In addition, if the particle size is large, it is preferable to adjust the particle size to the above range by means of pulverization or the like in advance.

Various types of raw materials and their mixing ratio can be considered; for example, Bi:Te=2:3 (molar ratio).

Bi:Sb:Te=2:8:15 (molar ratio)
, Bi:Te:5e=2:2:1 (molar ratio) or (
Bi + Sb): (Te + 5e) - 2: 3 (molar ratio), etc., and especially by containing nihismuth (Bi) or bismuth + antimony (Bi + Sb and tellurium + Se) in a ratio of about 2: 3. ,6
00 or less, thermoelectric materials with very good performance can be obtained.

In addition, if the raw material contains the above ingredients,
It is also possible to use a single metal that has not been melt-mixed, a metal mixture obtained in a scouring process, a metal compound, or a partial alloy of the raw material composition.

Further, it is desirable to mix an appropriate amount of conductivity type impurity (dopant) into the above raw material. As this dopant, conventionally used dopants can be added and mixed according to a conventional method. For example, when the thermoelectric material is an n-type, Sblj is used.

CuTe, Cu, S, CuI, CuBr, AgBr, etc. can be used. In addition, in the case of p-type, Te
.

Cd, Sb, Pb, As, Bi, Se, etc. can be used. In particular, as mentioned above, bismuth and tellurium are mixed at about 2:3.
In the case of n-type, it is preferable to use Sb13, and in the case of p-type, it is preferable to use Te or Se from the viewpoint of solubility and stability.

The amount of this dopant to be added is appropriately determined depending on the type and mixing ratio of raw materials, the type of substance to be the dopant, etc., but it is usually 0.01 to 10 mol%, preferably 0.05 to 5 mol%. % is appropriate.

In the method of the present invention, the raw materials (raw material powders) blended in this way are co-pulverized and mixed sufficiently, but at this time, the mixed-pulverization is simultaneously progressed to further reduce the particle size of the raw materials. It is desirable to do so. In this case, the co-grinding mixture is ball milled.

This can be carried out by a means for simultaneously mixing and pulverizing, such as an impact pulverizer, jet pulverizer, or tower-type friction machine. Among these methods, it is preferable to use a ball mill, especially a powerful planetary pole mill rather than a falling type. Further, the mixing may be carried out in either a dry or wet manner. For example, in the case of wet mixing, alcohols such as ethanol and butanol or various solvents may be used as mixing aids.

The mixing power and mixing time of the above co-pulverization mixing are such that the average particle size of the raw material powder after pulverization and mixing is 0.05 to 10 μm, preferably 0.
．． It is desirable to set the thickness to about 0.05 to 5 μm.

In addition, in order to proceed with the above-mentioned mixing and co-pulverization at the same time, that is, to perform co-pulverization mixing, use a planetary ball mill and increase the crushing force to 4 X 10"(kg-m-s-'/-) or more, Especially from 5×10h to 2×107 [kg-m・s-'/
It is particularly preferable to select a range of 1 kg).

Here, the above-mentioned crushing force is defined by the following formula.

In the formula, W is the throughput (kg), and n is the number of balls. m is the mass of the ball (kg), d is the pot diameter (m), V is the ball speed (m/s), t is the co-grinding mixing time (s)
shows.

Therefore, the crushing force is 4xlo" (kg・m-s/kg
) or more. Number of balls. mass of the ball,
Pot (planetary ball mill pot) diameter. Co-pulverization and mixing may be performed by appropriately selecting conditions regarding ball speed and co-pulverization and mixing time. Here, the preferred range is ball speed of 0.4 to 6.0 m/S and % co-pulverization mixing time of 3 to 6.
It is 0 hours.

Note that the ball speed (V) depends on the mill diameter (d) and rotation speed (
rpm) according to the following formula.

(In the formula, ■ and d are the same as above.) When co-pulverizing and mixing is performed with such a crushing force, the raw materials will be mixed with a crushing force of 4 × 10 Ckg -m -s-, although it varies depending on the situation.
'/kg) or more, the average particle size is 2 μm or less, preferably 111 m or less.

In the method of the present invention, the desired thermoelectric material can be manufactured by subsequently molding and sintering such raw material powder (fine powder). However, in a preferred embodiment of the present invention, after the above-mentioned co-pulverization and mixing, the particles are granulated to have a particle size of 150 μm or less, and then classified into a particle size range of 32 to 70 μm to make the particle size of the granulated powder uniform, After that, by performing molding and sintering, it is possible to manufacture a thermoelectric material with further improved performance. Here, granulation may be carried out according to a conventional method, usually using a binder such as stearic acid or paraffin wax. Further, classification may be carried out according to a commonly used method, and there is no particular restriction.

- For boat fishing, use a sieve, etc.,
Just cut the m under.

Furthermore, in the method of the present invention, the raw material powder after co-pulverizing and mixing, or the raw material powder (particles) granulated after co-pulverizing and mixing, and further classified if necessary, without performing the conventional melting and mixing process. For example, it can be pressure-molded into a desired shape using a pressure means such as press-forming. This pressure molding can be performed by adding a binder component such as polyvinyl alcohol, if necessary. The pressure during pressure molding varies depending on the type and particle size of the raw material powder, but is usually 0.2 to 20 tons/cIfl, preferably 0.2 to 20 tons/cIfl.
5 to 15 tons/c4 is suitable.

As the molding method, in addition to the above-mentioned pressure molding, any molding method such as extrusion molding, injection molding, coating, and screen printing can be employed.

Furthermore, in the method of the present invention, it is necessary to perform a sintering operation after the above-mentioned molding, and the sintered body obtained by this sintering process functions as a thermoelectric material. This sintering treatment is generally performed on the molded body obtained by the above-mentioned molding under normal pressure or pressurization, using argon,
This is carried out in an atmosphere of nitrogen, hydrogen, or a mixture of these gases.

The sintering temperature is appropriately selected depending on the type of raw material powder, the mixing ratio, etc., but it can usually be carried out at 300 to 600°C. In this case, it is preferable that the temperature increase rate, especially at temperatures above 200°C, be 7 to 10 hours or less. If the temperature is increased at a faster rate than this, the performance of the resulting thermoelectric material may deteriorate. . Furthermore, if the temperature increase rate is too slow, it will take a long time to reach a predetermined temperature, so it is appropriate to set it to about 5 to 10 times per hour, for example. Note that the heating time varies depending on the atmosphere under pressure, the composition, etc., and is not necessarily limited to this range.

After reaching a predetermined sintering temperature at such a temperature increase rate, the desired thermoelectric material can be obtained by maintaining the temperature for a predetermined time and sintering the molded body. Moreover, the sintering time is usually 0.5 to 30 hours.

〔Example〕

Next, the invention will be explained in more detail based on Examples and Reference Examples.

Examples 1-14 and Reference Example 1. 2. As shown in Table 1, 100-mensie pass raw material powders and dopants of various compositions were prepared, and each was co-pulverized and mixed for 3 hours in a planetary wet ball mill to which ethanol had been added. The average particle size of each powder obtained was approximately 1 μm.
Met.

Next, the obtained mixed powder was weighed at I 000 kg/cIII
Pressure molding was carried out at a pressure of 100.degree. C., and sintering was performed under the respective sintering conditions shown in Table 1. The sintering time was (1) 10 hours and (2) 2 hours.

Incidentally, the temperature increase rate is the temperature increase rate from sintering temperature (1) to sintering temperature (2) shown in Table 1. Further, in Reference Examples 1 and 2, the raw material components were mixed and powdered by the conventional method of melt mixing instead of the co-pulverization mixing described above.

(Left space below) Examples 15 and 16 Powders and dopants with an average particle size of about 458 d having the raw material composition shown in Table 2 were used in a total treatment amount of 0.1 (kg) at the blending ratio shown in Table 2, and ethanol was added. ld! /g, number of balls = 50, mass of each ball = 0.0021 (kg) using a planetary wet ball mill.
, mill pound diameter - 0,076 (m), ball speed =
2 (m/s) (rotation speed 50° rpm), co-grinding mixing time - 40 x 3600 (s), grinding force 8 x 10
” (kg-m-s-'/kg).The bond volume was 200 d, and the ball diameter was 10 mm.
Met. The average particle size of the obtained powder was about lam.

Next, the obtained mixed powder was processed into a 1.0
Pressure molding was carried out at a pressure of ton/c-. Then, under an argon atmosphere, the heating rate was 6/sin, and the sintering temperature was 460°.
Sintering was performed for a C1 sintering time of 5 hours to obtain a thermoelectric material.

The thermoelectric properties of the obtained thermoelectric material are shown in Table 2.

In Example 17 and 1-day Example 15, the raw material composition was as shown in Table 2, and the ball speed was 3.2 (m/s) (rotational speed 80
Orpm) with a crushing force of 12.8 x 10” [kg-
Co-pulverization and mixing were carried out in the same manner as in Example 15, except that the mixture was set to m-s-''/kg), and
Molding and sintering were performed in the same manner as in 5. The results are shown in Table 2.

Examples 19 and 20 In Example 15, the raw material composition was as shown in Table 2, and the ball speed was 4.8 (m/s) (rotational speed 120 O
rpm) and crushing force 19.2X I Ob (kg-m −
Co-pulverization and mixing were carried out in the same manner as in Example 15, except that the mixture was adjusted to s/kg), and then molding and sintering were carried out in the same manner as in Example 15. The results are shown in Table 2.

Example 21 Powder co-pulverized and mixed under the same conditions as Example 17 was granulated and then classified to 70 to 100 μm.
Molding and sintering were performed in the same manner as in 7 to obtain a thermoelectric material. The results are shown in Table 2.

Example 22 The co-pulverized and mixed powder was granulated under the same conditions as in Example 18, and then classified into 70 to 1100II, and then molded and sintered in the same manner as in Example 18 to obtain a thermoelectric material. . The results are shown in Table 2.

Example 23 Powder co-pulverized and mixed under the same conditions as Example 17 was granulated and then classified into 32 to 70 am.
Molding and sintering were performed in the same manner as above to obtain a thermal lightning material. The results are shown in Table 2.

Example 24 Powder co-pulverized and mixed under the same conditions as Example 18 was granulated and then classified to 32 to 70 μm.
Molding and sintering were performed in the same manner as above to obtain a thermoelectric material. The results are shown in Table 2.

Example 25 Powders co-pulverized and mixed under the same conditions as in Example 17 were granulated, then classified to 32 μm or less, and then molded and sintered in the same manner as in Example 17 to obtain a thermoelectric material. Second result
Shown in the table.

Example 26 The co-pulverized and mixed powder was granulated under the same conditions as in Example 1, and then classified to 32 μm or less, and then molded and sintered in the same manner as in Example 18 to obtain a thermoelectric material. . Second result
Shown in the table.

(The following is a blank space) [Effects of the Invention] As explained above, a thermoelectric material can be easily obtained by co-mixing metal powders as raw materials, molding, and sintering. In particular, since single metal powder can be used as a raw material, the raw material can be easily prepared, and furthermore, it can be easily manufactured without using complicated operations or special equipment in the manufacturing process. The manufacturing cost can be reduced.

In particular, not only pressure molding, but also extrusion molding, coating,
It has the characteristic that any molding method such as screen printing can be used to obtain a desired form as a product.

The thermal conductivity of the thermoelectric element manufactured by the method of the present invention includes 1.
4 Wm-1K-1 or less, especially 0.7 to 1.3 Wm-'
It has the great feature of being lower than that of melt-mixed products. This is thought to be because grain growth during sintering does not occur much, resulting in a fine grain structure. This results in a thermoelectric material with an improved figure of merit.

In addition, especially the crushing force 4×10"(kg-m-s-'/k
g) When co-pulverized and mixed using a planetary ball mill under the above conditions, the obtained thermoelectric element has a figure of merit (Z)
However, for example, 1.5 x 10-3 to 2.60 x 10-'
It is a thermoelectric element with a significantly improved figure of merit and an improved maximum cooling temperature difference compared to conventional ones.

Moreover, there is no manufacturing loss or directionality due to crystal structure, and in addition, it is possible to directly obtain products of any shape.
It is possible to reduce the size and also to integrally mold the module.

Therefore, the thermoelectric material obtained by the method of the present invention is expected to be effectively used in a wide range of fields such as thermoelectric power generation, thermoelectric cooling, and temperature sensors, space development, ocean development, power supplies for remote areas, semiconductor manufacturing processes, and electronic devices. Ru.

Claims (11)

[Claims] (1) A thermoelectric material obtained by co-pulverizing and mixing a raw material containing at least bismuth and a raw material containing at least tellurium that are not entirely alloyed, followed by molding and sintering. (2) The mixing ratio of the raw material containing at least bismuth and the raw material containing at least tellurium is 2:3.
(molar ratio).The thermoelectric material according to claim 1. (3) A thermoelectric material obtained by co-pulverizing and mixing raw materials consisting of bismuth and antimony and raw materials consisting of tellurium and selenium, which are not entirely alloyed, followed by molding and sintering. (4) The thermoelectric material according to claim 3, wherein the mixing ratio of the raw materials consisting of bismuth and antimony and the raw materials consisting of tellurium and selenium is former:latter≈2:3 (molar ratio). (5) The thermoelectric material according to any one of claims 1 to 4, which has a thermal conductivity of 1.4 Wm^-^1 K^-^1 or less. (6) A method for producing a thermoelectric material, which comprises co-pulverizing and mixing a raw material containing at least bismuth and a raw material containing at least tellurium that is not wholly alloyed, followed by molding and sintering. . (7) The average particle size of the powder after co-pulverization and mixing is 0.05 to 1.
The method for manufacturing a thermoelectric material according to claim 6, wherein the thickness is 0 μm. (8) The method for producing a thermoelectric material according to claim 6 or 7, wherein the temperature increase rate during sintering is 10 K/hour or less. (9) A raw material containing at least bismuth and a raw material containing at least tellurium, which are not entirely alloyed, are crushed with a crushing force of 4 x 10^6 [kg・m・s^-^
1/kg] or more using a planetary ball mill under the following conditions, followed by molding and sintering. (10) A raw material containing at least bismuth and a raw material containing at least tellurium, which are not entirely alloyed, are crushed with a crushing force of 4 × 10^6 [kg・m・s^−
^1/kg] After co-pulverizing and mixing using a planetary ball mill under the above conditions, the obtained powder is granulated to a particle size of 150 μm or less, then classified into a particle size range of 32 to 70 μm, and further A method for producing a thermoelectric material, characterized by forming and sintering. (11) The method for producing a thermoelectric material according to claim 9 or 10, wherein a conductive impurity is mixed into a raw material containing at least bismuth and a raw material containing at least tellurium, which are not entirely alloyed.