JPH0918060A - Manufacture of thermoelectric conversion element - Google Patents

Abstract

PURPOSE: To remove impurity gas adhering to the surface of thermoelectric conversion material powder and to prevent the impurity gas from being diffused in the interior of a sintered body during the firing of a temporarily molded material by a methods wherein before the temporarily molded material is fired, the molded material is fired in a reduced pressure atmosphere and at a temperature lower than temperature for firing the molded material. CONSTITUTION: A little amount of a dopant is added to a raw material containing two kinds or more of elements among elements of bismuth(Bi), tellurium(Te), selenium(Se) or antimony(Sb), the dopant and the elements are fully mixed and/or are melted according to the need and after that, they are ground to obtain thermoelectric conversion material powder. This powder is temporarily molded into an optional shape by a normal uniaxial press molding method, for example. A binder of the temporarily molded material is removed by heating as needed. Before the molded material is burned, the molded material is burned in a reduced pressure atmosphere and at a temperature lower than temperature for firing the molded material. Thereby, impurity gas adhering to the surface of the thermoelectric conversion material powder is removed, and the gas is prevented from being diffused in the interior of a sintered body.

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 utilizing the Peltier effect.

[0002]

2. Description of the Related Art A thermoelectric conversion module utilizing the Peltier effect is a Peltier device in which P-type semiconductor elements and N-type semiconductor elements which are thermoelectric conversion elements are alternately arranged between two insulating layers and electrically connected in series. By applying a DC voltage to the element group, heat or heat is generated on the surface of the insulating layer, and it is widely used in various fields in thermoelectric power generation and thermoelectric cooling.

As a method for producing this thermoelectric conversion element, generally, as disclosed in JP-A-1-202343, a single crystal method in which a raw material powder is melted to grow a rod-shaped ingot close to a single crystal and JP-A-Hei-Hei. 1-106478
Using a hot press method of producing an ingot by hot pressing raw material powder as disclosed in Japanese Patent No.
A bulk thermoelectric conversion material ingot is produced, cut into small thermoelectric conversion elements according to the application, and P-type semiconductor elements and N-type semiconductor elements are alternately connected in series on an insulating substrate using solder. Then, the thermoelectric conversion module was produced. Therefore, in the method for producing a thermoelectric conversion element by the single crystal method and the hot pressing method, in order to obtain the thermoelectric conversion element, an expensive firing device is required, or in the thermoelectric conversion element cutting step according to the application, the material by the cutting margin is used. There is a lot of loss, and about 5 mm is required to manufacture a thermoelectric conversion element of 1 mm square.
Material loss of 0% or more occurred. In addition, since the material is brittle, problems such as cracking and chipping occur during cutting, and the yield of thermoelectric conversion elements is poor. Moreover, with the recent miniaturization of thermoelectric conversion modules, thermoelectric conversion elements tend to be thinned and downsized, and in a method of manufacturing a thermoelectric conversion element that involves a cutting step, problems such as cracking and chipping are solved. We have not reached the stage where we can fully respond. Furthermore, many work processes that cannot be automated or labor-saving were required. Further, if the firing operation as described above is not performed, it is very difficult to achieve densification,
Therefore, the strength of the thermoelectric conversion element is extremely low, and the reliability is also impaired.

The above factors have been a major factor in increasing the cost for producing thermoelectric conversion elements and making it very difficult to obtain a high-performance thermoelectric conversion module. It is desired to develop a method for producing a thermoelectric conversion element that can obtain a thermoelectric conversion element having excellent thermoelectric conversion performance without a special firing operation.

[0005]

The present invention has been made in view of the above facts, and an object of the present invention is to provide a method for manufacturing a thermoelectric conversion element capable of obtaining a thermoelectric conversion element excellent in thermoelectric conversion performance. To do.

[0006]

According to a first aspect of the present invention, there is provided a method for manufacturing a thermoelectric conversion element comprising the steps of Bi, Te, Se and Sb.
Temporarily forming a thermoelectric conversion material containing at least two kinds of elements selected from the group consisting of elements into a predetermined shape,
In the method for manufacturing a thermoelectric conversion element, which is obtained by firing this temporary molded body to form a thermoelectric conversion element, before firing the temporary molded body,
It is characterized in that the preliminary firing is performed in a reduced pressure atmosphere and at a temperature lower than the firing temperature for firing the temporary molded body.

A method of manufacturing a thermoelectric conversion element according to a second aspect of the present invention is characterized in that the temporary molded body is temporarily fired at 250 to 380 ° C.

According to a third aspect of the present invention, there is provided a method for manufacturing a thermoelectric conversion element, which comprises, after calcination of the temporary molded body, before the calcination, in a reducing gas atmosphere containing hydrogen and at a temperature lower than the calcination temperature. It is characterized in that it is pre-baked in.

A method for manufacturing a thermoelectric conversion element according to a fourth aspect of the present invention is characterized in that the temporary molded body is fired in a pressurized atmosphere at a firing temperature of 410 to 590 ° C.

Hereinafter, the present invention will be described in detail. A method of manufacturing a thermoelectric conversion element according to the present invention is a Peltier element group in which P-type semiconductor elements and N-type semiconductor elements are alternately arranged between two insulating layers and electrically connected in series by electrodes such as copper electrodes. When a DC voltage is applied to the insulating layer, one insulating layer generates heat by the so-called Peltier effect, and the other insulating layer absorbs heat, which is a P-type semiconductor element or N-type semiconductor element used in the thermoelectric conversion module. It is a method of manufacturing an element.

First, a method for producing a molded body will be described. As a constituent element of the thermoelectric conversion element according to the present invention, at least two kinds of elements among bismuth (Bi), tellurium (Te), selenium (Se) or antimony (Sb) elements are required. A small amount of a dopant is added to a raw material containing these constituent elements so as to be a thermoelectric conversion element of an N-type semiconductor or a P-type semiconductor, sufficiently mixed and / or melted if necessary, and then pulverized for thermoelectric conversion. Obtain a powder of material. Examples of the thermoelectric conversion material include Bi-Te alloy, Bi-Sb alloy, Bi-Te-Sb alloy, Bi-T.
An e-Se alloy, a Bi-Te-Sb-Se alloy, or the like can be used, but the combination is not limited to the above combination.

The powder of the thermoelectric conversion material can be molded into an arbitrary shape by, for example, a usual uniaxial press molding method. In addition, a binder or a solvent is used to form a paste, and the paste-like thermoelectric conversion material is print-molded at a predetermined position on the substrate by a screen printing method. It is also possible to prepare a temporary molded body of the thermoelectric conversion element with a thickness of. Further, the paste-like thermoelectric conversion material may be formed into a sheet by a doctor blade method and then processed into a required shape to prepare a temporary formed body of the thermoelectric conversion element. Further, it is also possible to increase the viscosity of the paste to make it into a hide shape, and then produce a temporary molded body of the thermoelectric conversion element by a usual extrusion method or injection molding method.

If necessary, the binder of the temporary molded body produced by the above-mentioned method is removed by heating. Before firing the temporary molded body, it is essential to perform the preliminary firing in a reduced pressure atmosphere and at a temperature lower than the firing temperature for firing the temporary molded body. By pre-baking this pre-formed body in a reduced pressure atmosphere, the impurity gas such as water, oxygen, carbon dioxide gas, etc. adhering to the surface of the thermoelectric conversion material powder is removed, and the impurity gas is converted into a sintered body during firing. It can be prevented from spreading inside. This calcination step in the reduced pressure atmosphere is important, and by sufficiently removing the surface-adsorbed impurities in this calcination step, it becomes possible to obtain a good thermoelectric conversion element having excellent thermoelectric conversion performance.

The thermoelectric conversion element is a semiconductor, and its electrical characteristics are greatly affected by the influence of a trace amount of impurities. In particular, it is known that the impurity oxygen has a great influence, and that a small amount of solid solution from the outside causes a great deterioration in electrical performance. (Journal of the Japan Institute of Metals 53-9-1989 p958-963
) In order to remove the impurity components adhering to the surface of the particles, it is necessary to perform calcination in a non-oxidizing atmosphere at a temperature lower than the calcination temperature. That is, in the case of pre-baking, if a temperature higher than the baking temperature is applied, there is a risk that some of the attached impurities will be thermally diffused into the thermoelectric conversion element and the performance will be deteriorated. It is preferable to temporarily calcine the temporary molded body at 250 to 380 ° C.

It is more preferable to pre-fire the pre-formed body after the pre-baking and before firing in a reducing gas atmosphere containing hydrogen and at a temperature lower than the firing temperature.
That is, the impurity oxygen chemically adsorbed on the surface of the powder of the thermoelectric conversion material is reduced by hydrogen to prevent diffusion, so that the thermoelectric characteristics of the thermoelectric conversion element are improved.

The method of manufacturing a thermoelectric conversion element according to the present invention comprises:
The temporary molded body is under a pressure atmosphere and at a firing temperature of 410 to 410.
Baking at 590 ° C is preferable. That is, Bi,
The elements Te, Se, and Sb easily volatilize and easily cause compositional deviations. However, by firing in a pressurized atmosphere, it is possible to prevent the components from scattering even when firing at high temperatures, and prevent compositional variations due to volatilization. Therefore, a high-performance thermoelectric conversion element can be obtained. The pressure of the pressurized atmosphere is preferably 2 atm or more. Furthermore, because composition deviation can be prevented,
It becomes possible to fire at a high temperature, and it is possible to improve the sintering density which has been a problem in the atmospheric pressure firing method and the like.

Firing in an oxidizing atmosphere is not preferable because it is oxidized during firing and the thermoelectric properties of the thermoelectric conversion material deteriorate. Therefore, the firing is N ₂ ,
It is preferable to carry out in an atmosphere of Ar, N ₂ + Ar or a mixed gas of an inert gas and H ₂ gas. That is, the oxidation of the material is suppressed, and further the reducing action is obtained. By the above operation, a high performance and highly reliable thermoelectric conversion element can be obtained.

[0018]

The method of manufacturing a thermoelectric conversion element according to claim 1 and claim 2 of the present invention is a thermoelectric conversion material containing at least two elements selected from the group consisting of Bi, Te, Se and Sb elements. In a method for manufacturing a thermoelectric conversion element, which comprises temporarily forming a predetermined shape into a thermoelectric conversion element by firing the preformed body, in a reduced pressure atmosphere and before firing the preformed body, Since the calcination is performed at a temperature lower than the calcination temperature, the impurity gas adhering to the surface of the thermoelectric conversion material powder, for example, moisture, oxygen, carbon dioxide gas, etc. is removed, and the impurity gas is sintered during the calcination. It can be prevented from spreading inside.

According to a third aspect of the present invention, there is provided a method for manufacturing a thermoelectric conversion element, which comprises, after calcination of the temporary molded body, before the calcination, in a reducing gas atmosphere containing hydrogen and at a temperature lower than the calcination temperature. Since the pre-baking is performed in step 1, the oxygen that is chemically adsorbed on the surface of the powder of the thermoelectric conversion material is reduced by hydrogen to prevent diffusion.

In the method for manufacturing a thermoelectric conversion element according to claim 4 of the present invention, since the temporary molded body is fired in a pressurized atmosphere at a firing temperature of 410 to 590 ° C., it is possible to prevent the components from scattering. , Compositional deviation due to volatilization can be prevented.

[0021]

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples.

(Examples 1 to 7 and Comparative Examples 1 to 5) A thermoelectric conversion material ingot having a composition of N-type-Bi ₂ Te _2.85 Se _0.15 , to which a trace amount of a dopant such as SbI ₃ was added, was used. It was made. This ingot was crushed using a ball mill to obtain a thermoelectric conversion material powder. This powder is tentatively molded into a size of φ20mm × 20mm, 1.5t
CIP molding was performed at a pressure of on / cm ² . The above work was performed in an inert atmosphere.

For the examples, the temporary molded body thus obtained was subjected to a reduced pressure atmosphere of about 0.1 torr for 30 minutes.
It was calcined at a calcination temperature of 0 ° C. for 5 hours. Next, in Examples 5 and 6, before firing, preliminary firing was performed at 300 ° C. in a reducing gas atmosphere containing hydrogen.

Subsequently, nitrogen gas was introduced, and firing was performed at the pressure and temperature shown in Table 1 for 5 hours to obtain N-type-BiTeS.
e The thermoelectric conversion material was obtained.

The Seebeck coefficient α, thermal conductivity κ, and electric resistance ρ of the thermoelectric conversion element were measured, and the thermoelectric performance index Z =
α ² / (κ · ρ) was calculated.

The Seebeck coefficient α is generated at both ends when the temperature at one end of the thermoelectric conversion element is 20 ° C. and the other end is 30 ° C. and the temperature difference between both ends is 10 ° C. at room temperature of 20 ° C. It was determined by measuring the power. The thermal conductivity κ is measured by the laser flash method, the electrical resistance ρ is measured by the four-terminal method,
The results are shown in Table 1.

[0027]

[Table 1]

As a result of the above, it was found from Table 1 that the thermoelectric conversion element of Example was superior in thermoelectric conversion performance to the Comparative Example.

[0029]

According to the method of manufacturing a thermoelectric conversion element according to claims 1 and 2 of the present invention, the impurity gas adhering to the surface of the thermoelectric conversion material powder is removed, and the impurity gas is sintered during firing. Since it can be prevented from diffusing into the body, a thermoelectric conversion element having excellent thermoelectric conversion performance can be obtained.

According to the method of manufacturing a thermoelectric conversion element according to claim 3 of the present invention, the impurity oxygen chemically adsorbed on the surface of the powder of the thermoelectric conversion material is reduced by hydrogen to prevent diffusion. Thermoelectric properties are improved.

According to the thermoelectric conversion element manufacturing method of the fourth aspect of the present invention, the components can be prevented from scattering and the composition shift due to volatilization can be prevented, so that a high performance thermoelectric conversion element can be obtained.

Claims (4)

[Claims] 1. A thermoelectric conversion material containing at least two kinds of elements selected from the group consisting of Bi, Te, Se and Sb elements is preformed into a predetermined shape, and the preformed body is fired to obtain the thermoelectric conversion material. In the method for producing a thermoelectric conversion element to be a conversion element, before the calcining of the temporary molded body, the calcining is performed in a reduced pressure atmosphere and at a temperature lower than a calcining temperature at which the temporary molded body is calcined. Method for manufacturing conversion element. 2. The method for manufacturing a thermoelectric conversion element according to claim 1, wherein the temporary molded body is prebaked at 250 to 380 ° C. 3. The method according to claim 1, wherein after the preliminary molded body is pre-baked, it is pre-fired in a reducing gas atmosphere containing hydrogen and at a temperature lower than the firing temperature before firing. Item 3. A method for manufacturing a thermoelectric conversion element according to item 2. 4. The method for manufacturing a thermoelectric conversion element according to claim 1, wherein the temporary molded body is fired in a pressurized atmosphere at a firing temperature of 410 to 590 ° C.