JPH1041554A - Preparation of thermo-electric refrigerating material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for preparing thermo-electric refrigerating material which can improve a performance index Z. SOLUTION: Material containing one or two selected from the group of Bi and Sb and one or two selected from the group of Te and Se is liquid- quenched into a thin film or powder, which is further ground into powder 1. The powder 1 is solidified and molded by sintering the powder through discharged plasma under such a condition that grains in the powder 1 will not be made too large. The powder 1 can be solidified and molded when the powder is subjected to the electrical discharge plasma sintering process under conditions of 150<=T<=300 and -(9×(T-150)/500)+3<=P or under conditions of 300<T<=450 and 0.3<=P (where T denotes temperature ( deg.C) and P denotes pressure (tonf/cm<2> ).

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 cooling material applied to thermoelectric cooling by thermoelectric conversion.

[0002]

2. Description of the Related Art When two materials of different types are joined to form a circuit having two joints, one of the joints is heated to a high temperature, and the other is cooled to a low temperature. An electromotive force is generated based on the difference. This phenomenon is called the Seebeck effect.

[0003] When a direct current is applied to two materials that are similarly joined, heat is absorbed at one joint and heat is generated at the other joint. This phenomenon is called the Peltier effect.

Further, when a temperature gradient is provided in a homogeneous substance and an electric current flows in a direction in which the temperature gradient is present, heat is absorbed or generated in the substance. This phenomenon is called the Thomson effect.

[0005] These Seebeck effect, Peltier effect and Thomson effect are reversible reactions called thermoelectric effects.
Contrast with irreversible phenomena such as Joule effect and heat conduction.
A combination of these reversible and irreversible processes is used for electronic cooling and heating.

In such a thermoelectric cooling material or thermoelectric conversion element, the performance of the element is evaluated by a performance index represented by the following equation 1.

[0007]

Z = α ² σ / κ where α is thermoelectric power (Seebeck coefficient) σ is electric conductivity κ is thermal conductivity That is, the larger the figure of merit Z, the better the performance as a thermoelectric material.

[0008] By the way, as a conventional thermoelectric cooling material, one or two selected from the group consisting of Bi and Sb is used.
There is an alloy consisting of a species and one or two selected from the group consisting of Te and Se, and the ratio of the number of atoms of Bi or Sb to the number of atoms of Te or Se is 2: 3. The composition is hereinafter used as (Bi, Sb) ₂ (Te, Se) ₃ .

The composition of (Bi, Sb) ₂ (Te, Se) ₃ includes Bi-Te, Bi-Se, Sb-Te
System, Sb-Se system, Bi-Sb-Te system, Bi-Sb-
There are nine types: Se-based, Bi-Te-Se-based, Sb-Te-Se-based, and Bi-Sb-Te-Se-based.

This thermoelectric cooling material has been conventionally manufactured as follows. First, a raw material powder is weighed to a predetermined composition, then melted and solidified while appropriately controlling cooling conditions to obtain an ingot with controlled crystallinity (unidirectionally solidified polycrystal or single crystal).

However, in this method, since the thermal conductivity κ is high, the figure of merit Z is small. To solve this,
Conventionally, various methods have been proposed.
As described in 276678, a method of rapidly solidifying a thermoelectric material to form an amorphous phase or a fine crystalline phase is known.

The thermal conductivity is κ = − (1/3) CvL (d
t / dx). Here, C is the specific heat, v is the average particle velocity, and L is the mean free path of phonons. In the case of amorphous, the thermal conductivity decreases because the mean free path L of phonons is small.
The performance coefficient Z can be increased.

[0013]

However, in the above-mentioned conventional method, there is a problem that the strength is reduced by cleavage. As a countermeasure, there is a method in which the obtained ingot is pulverized, turned into powder, and then sintered and solidified. However, in this case, the figure of merit Z decreases. Therefore, when the liquid quenching method is applied, it is necessary to perform sintering under the condition that crystal grains are not coarsened in a process such as sintering. However, if the energy at the time of sintering is too high, recrystallization of the crystal proceeds further, and the fine crystal obtained by the liquid quenching method becomes coarse, and the figure of merit Z decreases.

Therefore, the conventional (Bi, Sb) ₂ (T
The thermoelectric cooling material having the composition of (e, Se) ₃ had a figure of merit Z of 3.3 × 10 ⁻³ / K or less, and could not obtain a figure of merit higher than that. If the sintering energy is too low, the material may not be solidified.

The present invention has been made in view of the above problems, and has as its object to provide a method of manufacturing a thermoelectric cooling material that can improve the figure of merit Z.

[0016]

According to the present invention, there is provided a method for producing a thermoelectric cooling material comprising one or two members selected from the group consisting of Bi and Sb and one member selected from the group consisting of Te or Se. Alternatively, the raw material containing the two types is formed into a thin film or powder by a liquid quenching method, which is further pulverized, and the resulting powder is solidified and formed by discharge plasma sintering under the condition that the crystal grains are not coarsened. It is characterized by the following.

Another method for producing a thermoelectric cooling material according to the present invention comprises one or two selected from the group consisting of Bi and Sb and one or two selected from the group consisting of Te or Se. The raw material containing is converted into a thin film or powder by a liquid quenching method, which is further pulverized, and the resulting powder is obtained by setting the temperature to T (° C.) and the pressure to P (tonf / cm ² ). , 150 ≦ T ≦ 300 when − (9 × (T−15)
0) / 500) + 3 ≦ P, and 300 <T ≦ 4
In the case of 50, solidification molding is performed by spark plasma sintering under the condition of 0.3 ≦ P.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a material having a structural distortion such as a fine crystal grain material, an amorphous material, or a non-equilibrium phase is obtained by a liquid quenching method. Unlike recrystallization, the crystal does not become coarse with little energy during recrystallization. In addition, since the powder is pulverized to reduce the particle diameter of the powder, the strength is improved and the growth of crystal grains can be suppressed.

In the present invention, the powder material is solidified and formed by spark plasma sintering under the condition that no further coarsening occurs. FIG. 1 is a schematic diagram showing a state of plasma around a raw material powder. During sintering of the raw material powder 1, the insulating film 2 on the surface of the raw material powder 1 is destroyed by ion bombardment due to electric discharge. At this time, since the raw material powder 1 is heated and pressurized, the raw material powder 1 is
Is sintered. As a result, the amount of energy given to the raw material powder 1 at the time of sintering can be reduced as compared with the conventional sintering method. That is, since sintering can be performed at a low temperature and in a short time, a compact having a fine structure or strain during quenching can be obtained, and the crystal grains of the compact can be reduced. Therefore, the thermal conductivity κ of the solidified thermoelectric cooling material can be reduced, and the figure of merit Z can be improved.

FIG. 2 is a schematic sectional view showing an example of a spark plasma sintering apparatus. A pair of carbon punches 5 having a convex portion 5a on one surface are vertically arranged with the convex portions 5a facing each other, and a pair of carbon punches 5 are provided above and below the upper and lower carbon punches 5, respectively. The carbon spacer 6 is arranged. The convex portion 5a of the carbon punch 5 penetrates into the rectangular cylindrical carbon die 8, and the raw material powder 7 is inserted into the space surrounded by the convex portion 5a and the carbon die 8. The carbon die 8 is provided with a thermocouple hole 9 reaching the center of its thickness, and a temperature sensor 10 is inserted into the thermocouple hole 9.

In the sintering apparatus constructed as described above, the raw material powder 7 is formed by a plasma generator (not shown) or the like.
By generating discharge plasma between them, the material is heated to a desired temperature, and the upper and lower carbon punches 5 are moved closer to each other to apply pressure to the raw material powder 7. As described above, by utilizing the plasma discharge, the raw material powder 7 can be sintered at a low temperature and in a short time by the pressing force during heating.

Hereinafter, the method for producing a thermoelectric cooling material according to the present invention will be described in more detail. Step of weighing raw material powder (Bi, Sb, Te, Se) First, Bi, Sb, Te or Se of the raw material powder is weighed so as to have a predetermined (Bi, Sb) ₂ (Te, Se) ₃ composition. Solidification process by liquid quenching method After the weighed raw material powders are mixed, they are dissolved. Then, this is solidified by a liquid quenching method. That is, the molten metal is quenched at a rate of 10 ^{4 to} 10 ⁶ K / sec by a single roll method, a twin roll method, a gas atomization method using Ar gas, or the like to produce a liquid quenched flake. Pulverization Step As described above, the raw material solidified by the liquid quenching method is pulverized into powder having an average particle diameter of 300 μm or less. Desirably, pulverization is performed so that the average particle size is 5.3 μm or less. Forming Step The obtained powder is solidified and formed by spark plasma sintering. At this time, the pressurization time is, for example, 5 minutes. Further, the temperature T (° C.) and the pressure P (tonf / cm ² ) satisfy the following Expressions 2 and 3.

[0023]

-(9 × (T−150) / 500) + 3 ≦ P where 150 ≦ T ≦ 300.

[0024]

## EQU3 ## 0.3 ≦ P where 300 <T ≦ 450.

FIG. 3 is a graph showing the relationship between the ultimate density and the temperature at various sintering pressures, with the vertical axis representing the ultimate density of spark plasma sintering and the horizontal axis representing the sintering temperature. However, in FIG. 3, the sintering pressure is 0.3 to 9 (tonf / c
m ² ), the sintering temperature is changed in the range of 100 to 500 (° C.), and the sintering time is 5 minutes. As shown in FIG.
It can be seen that the spark plasma sintering conditions under which a sufficient ultimate density can be obtained are limited. That is, when the sintering temperature is lowered, solidification molding is impossible, so that the ultimate density is reduced. Also, when the sintering temperature is increased, solidification molding is performed.
Since the component elements are eliminated, the density decreases.

In the sintering temperature range of 150 ° C. to 400 ° C., the ultimate density does not increase even if the sintering pressure is increased, but when the sintering temperature exceeds 400 ° C., the sintering pressure becomes 8 ( If it exceeds tonf / cm ² ), the ultimate density will decrease. It is considered that this is because under the conditions of high temperature and high pressure, oversintering (excessive sintering) occurs and the desorption of the component elements is promoted. Therefore, in the present invention, the sintering pressure is preferably 8 (tonf / cm ² ) or less.

FIG. 4 shows the pressure P on the vertical axis and the temperature T on the horizontal axis.
FIG. 2 is a graph showing the conditions of spark plasma sintering. As shown in FIG. 4, in the present invention, discharge plasma sintering is performed under conditions within the hatched region.

[0028]

EXAMPLES Examples of thermoelectric cooling materials manufactured by the manufacturing method according to the present invention will be specifically described below in comparison with comparative examples.

First, thermoelectric cooling materials having various compositions were manufactured, and the average crystal grain size and the thermal conductivity κ at room temperature were measured for the samples of Examples and Comparative Examples, and the figure of merit Z was calculated. did. The composition of the thermoelectric cooling material is shown in Table 1 below, and the sintering method and conditions are shown in Table 2 below.
Table 3 below shows the measurement results.

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

[Table 3]

As shown in Tables 1 to 3 above, Example N
o. In Nos. 1 to 12, since the thermal conductivity was low, the figure of merit Z was as high as 3.5 × 10 ⁻³ / K or more. For example, when obtaining a Peltier module (thermoelectric element), the element performance can be represented mainly by the maximum temperature difference (ΔTmax) and the maximum heat absorption. If the figure of merit is 3.5 × 10 ⁻³ / K, the maximum temperature difference is 70 K or more and the maximum heat absorption is 8 W / c.
m ² or more, which can reduce the power consumption of the current module by 30% when a temperature difference of 10 K from room temperature is applied. Thereby, the present invention can be applied to cooling temperature control of various devices.

On the other hand, in Comparative Example No. In Comparative Example No. 13, the sintering temperature was lower than the lower limit of the range of the present invention. In No. 15, no sintering pressure was less than the lower limit of the range of the present invention, and none of them could be solidified. Also, in Comparative Example No. 14
Has a large average crystal grain size compared to the examples, and the sintering temperature exceeds the upper limit of the range of the present invention, so that the figure of merit Z is a low value.

[0035]

As described above, according to the present invention,
Fine material, amorphous material or non-equilibrium phase material obtained by the liquid quenching method is pulverized to reduce the powder particle size, and solidified by discharge plasma sintering under such conditions that no further coarsening occurs. Therefore, a thermoelectric cooling material having a fine crystal structure, a low thermal conductivity, and a high figure of merit can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a state of plasma around a raw material powder.

FIG. 2 is a schematic sectional view showing an example of a spark plasma sintering apparatus.

FIG. 3 shows the ultimate density of spark plasma sintering on the vertical axis,
FIG. 5 is a graph showing the relationship between the ultimate density and the temperature at various sintering pressures, with the sintering temperature taken on the horizontal axis.

FIG. 4 is a graph showing discharge plasma sintering conditions, with the pressure P on the vertical axis and the temperature T on the horizontal axis.

[Explanation of symbols]

1, 7: raw material powder, 2: insulating film, 5: carbon punch, 6: carbon spacer, 8: carbon die,
9; thermocouple hole; 10; temperature sensor

Claims (2)

[Claims] 1. A thin film or powder of a raw material containing one or two selected from the group consisting of Bi and Sb and one or two selected from the group consisting of Te or Se by a liquid quenching method. A method for producing a thermoelectric cooling material, wherein the powder is further pulverized, and the resulting powder is solidified and formed by discharge plasma sintering under conditions where crystal grains are not coarsened. 2. A thin film or powder of a raw material containing one or two selected from the group consisting of Bi and Sb and one or two selected from the group consisting of Te or Se by a liquid quenching method. And further pulverized, and the resulting powder was subjected to a temperature of T (° C.) and a pressure of P (tonf / cm ² ).
, When 150 ≦ T ≦ 300, − (9 ×
(T-150) / 500) + 3 ≦ P, and 30
A method for producing a thermoelectric cooling material, comprising solidifying and forming by spark plasma sintering under the condition of 0.3 ≦ P when 0 <T ≦ 450.