Batteries: thermoelectric and photoelectric – Thermoelectric – Processes
Reexamination Certificate
2000-06-23
2001-08-21
Gorgos, Kathryn (Department: 1741)
Batteries: thermoelectric and photoelectric
Thermoelectric
Processes
C136S203000
Reexamination Certificate
active
06278050
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of producing a sintered body of a material for thermoelectric element, which is preferably used to prepare thermoelectric elements for a thermoelectric module that is a temperature control device using the Peltier effect.
2. Disclosure of the Prior Art
As shown in
FIGS. 12A and 12B
, a conventional thermoelectric module
100
is provided with an arrangement of N-type and P-type semiconductor elements
110
,
120
as thermoelectric elements, which are arranged in a matrix manner such that each of the N-type semiconductor elements
110
is disposed adjacent to the P-type semiconductor element
120
through a required space, upper electrodes
130
disposed on a top surface of the arrangement to connect between adjacent semiconductor elements
110
and
120
according to a first circuit pattern, lower electrodes
140
disposed on a bottom surface of the arrangement to connect between adjacent semiconductor elements
110
and
120
according to a second circuit pattern different from the first circuit pattern, and ceramic plates
150
such as sintered alumina plates bonded to the upper and lower electrodes
130
and
140
.
For example, as shown in
FIG. 12B
, when direct current is supplied to the thermoelectric module
100
, each of the upper electrodes
130
has the flow of electricity from N-type semiconductor element
110
toward the P-type semiconductor element
120
, and on the other hand each of the lower electrodes
140
has the flow of electricity from the P-type semiconductor element
120
toward the N-type semiconductor element
110
. At this time, the upper electrodes
130
absorb heat from the surroundings through the ceramic plate
150
, and the lower electrodes
140
radiate heat to the surroundings through the ceramic plate
150
. Therefore, the thermoelectric module
100
works as a kind of heat pump for pumping heat from one side to the opposite side thereof, which is usually known as the Peltier effect. According to this principle, it is possible to use the thermoelectric module
100
as a temperature control device for electronic parts or circuit boards.
The thermoelectric elements
110
,
120
can be produced according to the following method disclosed in Japanese Patent Early Publication [KOKAI] No. 9-321357. That is, as shown in
FIG. 13
, an ingot of a material for thermoelectric element is ball-milled in a non-oxidation atmosphere to obtain a powder thereof After charging the powder into a capsule made of a metal material such as aluminum, the degassing of the capsule is performed to obtain a billet for extrusion. As shown in
FIG. 14
, an extrusion step is then performed by use of an extrusion die
70
to reduce a diameter of the billet
72
. In
FIG. 14
, the numeral
76
designates the powder of the thermoelectric-element material charged in the capsule
74
. Next, a heat treatment is performed to sinter the powder in the worked billet. By removing a resultant sintered body from the capsule, a thin rod of the sintered body of the thermoelectric-element material is obtained.
In the above method, since the ingot is previously ball-milled, it is possible to reduce the segregation of alloying elements in the ingot, i.e., nonuniform distribution of alloying elements in the ingot. As a result, variations in thermoelectric performance and mechanical properties of the thermoelectric elements decrease. In addition, as compared with a case that the thermoelectric elements are directly cut from the ingot, it is possible to remarkably reduce the occurrence of cracks or chipping of the thermoelectric elements. Moreover, since the mechanical strength of the thermoelectric elements is improved by the heat treatment, the yields of the thermoelectric-element material increase.
By the way, the heat-pump performance of the thermoelectric module
100
highly depends on the thermoelectric performance of the thermoelectric elements
110
,
120
. The thermoelectric performance can be improved by providing the uniform distribution of alloying elements in the ingot, reducing amounts of impurities trapped in the thermoelectric element, and/or increasing a degree of orientation of a specified crystal plane of the thermoelectric-element material. In the above-described method, since the ingot is ball-milled, the uniform distribution of alloying elements can be achieved. However, the amounts of impurities in the obtained powder of the thermoelectric-element material generally increase. Therefore, there is a limitation in improvement of the thermoelectric performance.
On the other hand, when the degree of orientation of the specified crystal plane that is the so-called “C” crystal plane of the thermoelectric-element material is increased, the thermoelectric performance can be remarkably improved. That is, when direct current is supplied to the thermoelectric element along the crystal orientation, the improved thermoelectric performance is obtained. In the above method, since the ingot is ball-milled, the powder of the thermoelectric-element material is in random orientations of the “C” crystal plane. Although the degree of orientation of the “C” crystal plane can be improved to some extent by performing the extrusion step to the capsule having the powder therein, it is not sufficient to obtain excellent thermoelectric performance.
SUMMARY OF THE INVENTION
A primary object of the present invention is to provide a method of producing a sintered body of a material for thermoelectric element having excellent thermoelectric performance and mechanical strength, which is preferably used to manufacture a thermoelectric module that is a temperature control device using the Peltier effect. That is, the sintered body is produced by the following method. A block of the material for thermoelectric element is provided. The block has an electric-current passing direction, in which electricity is supplied to obtain a desired thermoelectric performance of the thermoelectric element. The block is encased in an elongate capsule such that the electric-current passing direction of the block is substantially agreement with an axial direction of the capsule. After degassing the capsule, a forming operation for reducing a cross section perpendicular to the axial direction of the capsule is performed to obtain a formed capsule having a green compact of the block crushed by the forming operation therein. A heat treatment is then performed to sinter the green compact in the formed capsule. Finally, the sintered body is removed from the formed capsule.
In the above method of the present invention, it is preferred that the capsule is made of a metal material having a lower coefficient of linear expansion than the material for thermoelectric element over a temperature range for the heat-treatment. In this case, it is possible to effectively perform the heat-treatment, as explained in detail later.
In the above method of the present invention, it is preferred that the forming operation is performed in a stepwise manner to obtain the formed capsule having a desired cross section. In this case, it is preferred to perform an annealing treatment during the forming operation. The annealing treatment is effective to safely finish the forming operation without a failure of the capsule.
A further object of the present invention is to provide a method of producing a sintered body of a material for thermoelectric element having excellent thermoelectric performance and mechanical strength, which is preferably used to manufacture a thermoelectric module having improved heat-pump performance. That is, the sintered body is produced by the following method. An ingot of the material for thermoelectric element prepared by means of unidirectional solidification is provided. The ingot is encased in an elongate capsule such that a direction of the solidification of the ingot is substantially agreement with an axial direction of the capsule. After degassing the capsule, a forming operation for reducing a cross section perpendicu
Kamada Kazuo
Kobayashi Kentaro
Urano Yoji
Yoshioka Hirokazu
Gorgos Kathryn
Matsushita Electric & Works Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Parsons Thomas H
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