JP2835406B2 - Thermoelectric material and method of manufacturing the same - Google Patents

Description

The present invention relates to a thermoelectric material and a method for producing the same, and more particularly to a thermoelectric material having a unique performance and an industrially advantageous thermoelectric material having a simplified production process. It relates to a manufacturing method.

[Problems to be solved by conventional technology and invention]

A thermoelectric power generation element using the Seebeck effect or an electronic cooling element using the Peltier effect has attracted attention because of its simple structure and easy handling. These thermoelectric conversion materials (thermoelectric materials) are widely used in various fields such as space development, marine development, power supplies for remote areas, temperature sensors, constant temperature devices in semiconductor manufacturing processes, and cooling of electronic devices. In addition, various means have conventionally been provided as a method for producing such a thermoelectric material. For example, (1) a method for producing a crystal ingot in which raw materials are mixed and dissolved to form an ingot and sliced,
(2) A powder sintering production method in which raw material powder or a mixed solution is powdered, then molded and sintered, and sliced as necessary, (3) a polycrystallization-band melting production method, and ( Various manufacturing methods such as 4) an amorphous manufacturing method and (5) a thin / thick film manufacturing method are known.

However, all of these methods have the problem of low mass productivity, such as the complicated steps and the need for long-term processing of melting and mixing, and slice loss occurs when the method involves slicing during the process. Alternatively, in the polycrystallization-zone melting production method, the electrical and mechanical directions due to the crystals have been generated. Further, its application range has been limited to some fields because it is difficult to manufacture ultra-small elements.

In particular, in the conventional method, the molding method is limited, and there is an essential problem that it is difficult to obtain a molded article of an arbitrary shape by various molding methods.

Japanese Patent Application Laid-Open No. 59-143383 discloses that as one means for solving these problems, forcible mixing of a lead tellurium compound and a manganese-based metal is not yet sufficient. .

Further, Japanese Patent Application Laid-Open No. 64-37456 discloses Bi ₂ Te ₃ -Bi ₂ Se
₍₃₎ A method for producing a sintered body of a solid solution powder is disclosed, but the process is complicated and unsuitable for practical use.

[Means for solving the problem]

Therefore, the present inventors have intensively studied to develop a thermoelectric material having a simple manufacturing process, a high yield, and capable of directly obtaining an arbitrary element by various molding methods. As a result, they have found that the above object can be achieved by using a specific raw material and co-milling and mixing the raw material. The present invention has been completed based on such findings.

That is, the present invention provides a thermoelectric material obtained by co-pulverizing and mixing a raw material containing at least bismuth and a raw material containing at least tellurium but not a whole alloyed material, followed by molding and sintering. Providing a method for producing a thermoelectric material, wherein a raw material containing at least bismuth and a raw material containing at least tellurium but not entirely alloyed are co-ground and mixed, and then molded and sintered. Is what you do.

The raw materials of the thermoelectric material are a raw material (powder) containing at least bismuth and a raw material (powder) containing at least tellurium, which is completely different from the conventional method using a raw material (powder) obtained by alloying the whole (all compositions). different. As the raw material, besides bismuth and tellurium, powders of antimony, selenium, etc., powders of tellurium and antimony, and alloy powders of tellurium-antimony can also be used. The particle size of these raw materials is not particularly limited, but is usually 20 to 70 μm on average, and preferably does not include those having 100 μm or more. It should be noted that those having a large particle size are preferably adjusted in advance to the above-mentioned particle size range by means such as grinding.

Various types of raw materials and mixing ratios can be considered. For example, Bi: Te = 2: 3 (molar ratio), Bi: Sb: Te = 2: 8: 1
5 (molar ratio), Bi: Te: Se = 2: 2: 1 (molar ratio) or (Bi
+ Sb): (Te + Se) = 2: 3 (molar ratio), especially bismuth (Bi) or bismuth + antimony (Bi + Sb)
And tellurium (Te) or tellurium + selenium (Te + Se) about 2:
By containing at a ratio of 3, a thermoelectric material having extremely excellent performance at 600K or less can be obtained.

As a raw material, a single metal that is not melt-mixed or a metal mixture, a metal compound, or a partial alloy of a raw material composition obtained in a refining process can be used as long as it contains the above components.

Further, it is desirable to mix an appropriate amount of conductivity type impurity (dopant) into the raw material. As this dopant, a conventionally used dopant can be added and mixed according to a conventional method.For example, when the thermoelectric material is made n-type, SbI ₃ , CuTe, Cu ₂ S, CuI, CuBr, AgBr or the like can be used. For p-type, Te, Cd, Sb, P
b, As, Bi, Se and the like can be used. In particular, when bismuth and tellurium are contained at a ratio of about 2: 3 as described above, SbI ₃ is used for the n-type, and Te or Se is used for the p-type.
Is preferred from the viewpoint of solubility and stability. The addition amount of the dopant is appropriately determined depending on the type and mixing ratio of the raw materials, the type of the substance to be the dopant, and the like, but is usually 0.01 to 10 mol%, preferably 0.05 to 10 mol%.
5 mol% is suitable.

In the method of the present invention, the raw materials (raw material powders) thus blended are co-ground and mixed and sufficiently mixed. At this time, the mixing and grinding are simultaneously performed to further reduce the particle diameter of the raw materials. It is desirable to do. in this case,
Co-pulverization and mixing can be performed by means such as a ball mill, impact fine pulverizer, jet pulverizer, tower type friction machine, etc., which simultaneously perform mixing and pulverization. Among these means, it is preferable to use a ball mill, especially a planetary ball mill instead of a drop type. The state of mixing may be either a dry type or a wet type. For example, in the case of performing the wet type, mixing may be performed using alcohols such as ethanol and butanol and various solvents as a mixing aid.

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

In addition, the above-mentioned mixing and co-milling proceed simultaneously, that is, in order to perform co-milling and mixing, using a planetary ball mill, the crushing force is 4 × 10 ⁶ [kg · m · s ⁻¹ / kg] or more, particularly 5 × 10 ⁶
It is particularly preferable to select a value within the range of 2 × 10 ⁷ [kg · m · s ⁻¹ / kg]. Here, the crushing force is defined by the following equation.

In the formula, W is the throughput (kg), n is the number of balls, m is the mass of the balls (kg), d is the pot diameter (m), V is the ball speed (m / s),
t indicates the co-milling mixing time (s). Therefore, the processing amount, the number of balls, the mass of the balls, the diameter of the pot (pot of a planetary ball mill), the ball speed, and the co-grinding so that the crushing force is 4 × 10 ⁶ [kg · m · s ⁻¹ / kg] or more. Co-milling and mixing may be performed by appropriately selecting the conditions for the mixing time. Here, as preferable ranges, the ball speed is 0.4 to 6.0 m / s and the co-milling and mixing time is 3 to 60 hours.

The ball speed (V) can be obtained from the mill diameter (d) and the number of revolutions (rpm) according to the following equation.

(In the formula, V and d are the same as described above.) When co-milling and mixing are performed with such a milling force, the raw materials generally vary depending on the situation, but the milling force is generally 4 × 10 ⁶ [kg · m
.S ^-1 / kg] or more, the average particle size is 2 μm or less, preferably 1 μm or less.

In the method of the present invention, the target thermoelectric material can be produced by molding and sintering such a raw material powder (fine powder). However, in a preferred embodiment of the present invention, after the above-mentioned co-milling and mixing, granulate to particles having a particle size of 150 μm or less, and then classify the particles in the range of 32 to 70 μm to make the particle size of the granulated powder uniform, Thereafter, when the molding and sintering are performed, a thermoelectric material having further improved performance can be manufactured. Here, granulation may be carried out according to a conventional method, usually using a binder such as stearic acid or paraffin wax. Classification may be performed according to a commonly used method, and there is no particular limitation. Generally, a 70 μm over and a 32 μm under may be cut using a sieve or the like.

Further, in the method of the present invention, the raw material powder after co-milling and mixing,
Alternatively, the raw material powder (particles) that has been granulated after co-milling and mixed, and further classified if necessary, can be pressed into a desired shape by a pressing means such as press molding without performing the melting and mixing process conventionally performed. Can be molded. This pressure molding can be performed by adding a binder component such as polyvinyl alcohol as needed. The pressure at the time of press molding varies depending on the type and particle size of the raw material powder, but is usually 0.2 to 20 ton / cm ² , preferably 0.5 to 15 ton / cm ² .

As the molding method, any molding method such as press molding, injection molding, coding, and screen printing other than the above-mentioned pressure molding can be adopted.

Further, in the method of the present invention, it is necessary to perform a sintering operation after performing the above-described molding, and the sintered body obtained by this sintering process will exhibit a function as a thermoelectric material. This sintering treatment is generally performed on the compact obtained by the above-described molding under normal pressure or under pressure in an atmosphere of argon, nitrogen, hydrogen, or a mixed gas thereof. The sintering temperature is appropriately selected depending on the type of the raw material powder, the mixing ratio, and the like, but can be usually 300 to 600 ° C. In this case, it is preferable that the rate of temperature rise, particularly the rate of temperature rise at 200 ° C. or higher, is 10 K / hour or less. If the temperature is increased at a higher speed than this, the performance of the obtained thermoelectric material may decrease. On the other hand, if the heating rate is too slow, it takes a long time to reach the predetermined temperature. Therefore, it is appropriate to set the heating rate to, for example, about 5 to 10 K / hour. The heating time varies depending on the atmosphere under pressure or the like, the composition, and the like, and is not necessarily limited to this range.

After reaching a predetermined sintering temperature at such a temperature increasing rate, the temperature is maintained for a predetermined time and the formed body is sintered to obtain a target thermoelectric material. The sintering time is usually 0.5 to 30 hours.

〔Example〕

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

Examples 1 to 14 and Reference Examples 1 and 2 As shown in Table 1, raw powders and dopants of 100 mesh pass of various compositions were prepared, and each was mixed for 3 hours in a planetary wet ball mill to which ethanol was added. Grinding and mixing were performed. The average particle size of the obtained powders is about 1 μm.
Met.

Next, the obtained mixed powder was pressed under a pressure of 1000 kg / cm ² and sintered under the respective sintering conditions shown in Table 1.
The sintering time is 10 hours and 2 hours.

The heating rate is a heating rate from the sintering temperature shown in Table 1 to the sintering temperature. Reference Examples 1 and 2
Is a powder obtained by mixing raw material components by melt mixing, which is a conventional method, in place of the above co-milling and mixing.

Examples 15 and 16 Powders and dopants having an average particle size of about 45 μm of the raw material composition shown in Table 2 were used at a mixing ratio shown in Table 2 as a total treatment amount of 0.1 (kg), and ethanol was used at a rate of 1 ml / g. In addition, in a planetary wet ball mill, the number of balls = 50, the mass of each ball = 0.0021 (kg), the pod diameter of the mill = 0.07
6 (m), ball speed = 2 (m / s) (rotation speed: 500 rpm), co-milling time = 40 x 3600 (s), grinding power 8 x
Forced pulverization and mixing were performed at 10 ⁶ [kg · m · s ^-1 / kg]. The pod volume was 200 ml and the ball diameter was 10 mm. The average particle size of the obtained powder was about 1 μm.

Next, the obtained mixed powder was subjected to 1.0 t with a uniaxial pressing machine.
Pressure molding was performed at a pressure of on / cm ² . Thereafter, sintering was performed in an argon atmosphere at a heating rate of 6 K / min, a sintering temperature of 460 ° C., and a sintering time of 5 hours to obtain a thermoelectric material.

 Table 2 shows the thermoelectric properties of the obtained thermoelectric material.

Examples 17 and 18 In Example 15, the raw material composition was as shown in Table 2, and the ball speed was 3.2 (m / s) (the number of revolutions was 800 rpm).
Co-milling and mixing were performed in the same manner as in Example 15 except that the weight was set to 12.8 × 10 ⁶ [kg · m · s ⁻¹ / kg]. Further, molding and sintering were performed in the same manner as in Example 15. 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) (rotation speed 1200 rpm) and the crushing force was 19.2 × 10 ⁶ [kg · m · s ^−1. / kg), except that co-milling and mixing were performed in the same manner as in Example 15.
Forming and sintering were performed in the same manner as in The results are shown in Table 2.

Example 21 A powder co-ground and mixed under the same conditions as in Example 17 was granulated, then classified into 70 to 100 μm, and molded and sintered in the same manner as in Example 17 to obtain a thermoelectric material. . The results are shown in Table 2.

Example 22 A powder co-ground and mixed under the same conditions as in Example 18 was granulated, then classified into 70 to 100 μm, and molded and sintered as in Example 18 to obtain a thermoelectric material. . The results are shown in Table 2.

Example 23 A powder co-ground and mixed under the same conditions as in Example 17 was granulated, then classified into 32 to 70 μm, and molded and sintered in the same manner as in Example 17 to obtain a thermoelectric material. . The results are shown in Table 2.

Example 24 A powder obtained by co-milling and mixing under the same conditions as in Example 18 was granulated, then classified into 32 to 70 μm, and molded and sintered as in Example 18 to obtain a thermoelectric material. . The results are shown in Table 2.

Example 25 A powder co-ground and mixed under the same conditions as in Example 17 was granulated, then classified to 32 μm or less, and then molded and sintered as in Example 17, to obtain a thermoelectric material. The results are shown in Table 2.

Example 26 A powder co-ground and mixed under the same conditions as in Example 18 was granulated, then classified to 32 μm or less, and then molded and sintered as in Example 18, to obtain a thermoelectric material. The results are shown in Table 2.

[Effects of the Invention] As described above, a thermoelectric material can be easily obtained by co-mixing, molding, and sintering a metal powder as a raw material. In particular, since a single metal powder can be used as a raw material, the raw material can be easily prepared, and can be easily manufactured without troublesome operations and special devices in a manufacturing process. Manufacturing cost can be reduced.

In particular, not only pressure molding but also any molding method such as pressure molding, coating, and screen printing can be used so as to obtain a desirable form as a product.

The thermal conductivity K of the thermoelectric element manufactured by the method of the present invention is 1.
It is 4 Wm ^-1 K ^-1 or less, particularly 0.7 to 1.3 Wm ^-1 K ^-1 , and has a great feature that it is lower than the melt-mixed product (Reference Example). This is presumably because grain growth during sintering does not occur much, and fine grains are produced. Thus, the figure of merit is improved by the lower thermal conductivity, and the thermoelectric material is inferior to the reference example. In particular, the crushing force 4
When co-milling and mixing using a planetary ball mill under conditions of × 10 ⁴ (Kg · m · s ^-1 / Kg) or more, the obtained thermoelectric element has a figure of merit (Z) of, for example, 1.5 × 10 4 ^{-3 to} 2.60 × 10
^-3 K ^-1 or more, with a crushing power of 4 × 10 ⁴ (Kg · m · s ^-1 /
Kg) The thermoelectric element has a significantly improved figure of merit as compared with those manufactured under the following conditions, and has an improved maximum cooling temperature difference.

In addition, since there is no production loss and no directionality due to the crystal structure, and any shape can be directly obtained, the size can be reduced and the module can be integrally formed.

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, such as space development, marine development, power supplies for remote areas, semiconductor manufacturing processes, and electronic devices. .

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Takeo Tokiai 1660 Kamiizumi, Sodegaura-cho, Kimitsu-gun, Chiba Pref. Idemitsu Petrochemical Co., Ltd. (56) References JP-A-60-235764 (JP, A) 58-144401 (JP, A) JP 37-1931 (JP, B1) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01L 35/16 H01L 35/34

Claims (11)

(57) [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 but not entirely alloyed, and then molding and firing. 2. The thermoelectric material according to claim 1, wherein Bi: Te = 2: 3 (molar ratio) between the raw material containing at least bismuth and the raw material containing at least tellurium. 3. A thermoelectric material obtained by co-milling and mixing a raw material made of bismuth and antimony and a raw material made of tellurium and selenium which are not entirely alloyed, and then molding and sintering. 4. In a raw material comprising bismuth and antimony and a raw material comprising tellurium and selenium, Bi or (Bi + Sb) and Te
4. The thermoelectric material according to claim 3, wherein the mixing ratio of (Te + Se) is 2: 3 (molar ratio). 5. The thermoelectric material according to claim 1, wherein the thermoelectric material has a thermal conductivity of 1.4 Wm ^-1 K ^-1 or less. 6. A method for producing a thermoelectric material, wherein a raw material containing at least bismuth and a raw material containing at least tellurium but not entirely alloyed are co-ground and mixed, then molded and sintered. Method. 7. An average particle size of the powder after co-milling and mixing is 0.05 to 0.05.
7. The method for producing a thermoelectric material according to claim 6, wherein the thickness is 10 μm. 8. The method for producing a thermoelectric material according to claim 6, wherein the rate of temperature rise during sintering is 10 K / hour or less. 9. A raw material containing at least bismuth and a raw material containing at least tellurium but not entirely alloyed are milled with a grinding force of 4 × 10 ⁶ (Kg · m · s ⁻¹ / Kg).
A method for producing a thermoelectric material, comprising co-milling and mixing using a planetary ball mill under the above conditions, followed by molding and sintering. 10. A raw material containing at least bismuth and a raw material containing at least tellurium but not entirely alloyed are crushed with a grinding force of 4 × 10 ⁶ (Kg · m · s ⁻¹ / K
g) After co-milling and mixing using a planetary ball mill under the above conditions, the resulting powder is granulated to a particle size of 15 μm or less,
Next, the particles were classified into a particle size range of 32 to 70 μm, and further molded,
A method for producing a thermoelectric material, comprising sintering. 11. The method according to claim 9, wherein a conductive impurity is mixed into a raw material containing at least bismux and a raw material containing at least tellurium but not entirely alloyed. Manufacturing method of thermoelectric material.