JPH05183196A - Thermoelectric converting element - Google Patents

Abstract

PURPOSE:To obtain a thermoelectric converting element capable of generating larger electromotive force, by impregnating a porous board composed of silicon carbide with silicon. CONSTITUTION:A thermoelectric converting element 1 is a substance made by impregnating a board of porous structure with 10-50% silicon in ratio by weight, and has a body 11 with a through hole 11a bored inside composed of silicon carbide, and a core material 12 composed of silicon filling the through hole 11a. Incidentally, when the thermoelectric converting element is made a P-type or N-type semiconductor, a very small number of elements are added to at least one of the board and silicon contained in it. And it becomes possible for the thermoelectric converting element 1 obtained to have remarkably larger electromotive force than before.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoelectric conversion element used in a thermal battery or the like.

[0002]

2. Description of the Related Art Generally, a thermal battery generates electricity by applying a temperature difference between one end and the other end of a thermoelectric conversion element made of a P-type or N-type semiconductor, and is effective in exhausting heat. It has been in the limelight from the standpoint of usage. By the way, the magnitude of the electromotive force of the thermoelectric battery largely depends on the electromotive force performance of the thermoelectric conversion element as well as the temperature difference applied to the thermoelectric conversion element. Therefore, various types of thermoelectric conversion elements having high electromotive force have been studied.

For example, a thermoelectric conversion element made of porous silicon carbide (SiC) has been recently developed. This has a porous structure obtained by firing a powder of silicon carbide, and a large electromotive force per unit temperature can be obtained as compared with a conventional thermoelectric conversion element. Moreover, since it has high heat resistance, a large temperature difference can be given, and a large electromotive force can be obtained from this point as well (see New Ceramics Vol. 2, pages 56 to 62, issued by Diamond Co., 1989).

[0004]

However, the electromotive force of the thermoelectric conversion element made of porous silicon carbide is 200 μV.
It was about / ° K, which was not sufficiently satisfactory. Therefore, there has been a demand for the development of a thermoelectric conversion element that can obtain a larger electromotive force.

The present invention has been made in order to meet the above demands, and an object thereof is to provide a thermoelectric conversion element having a large electromotive force.

[0006]

In order to achieve the above object, the thermoelectric conversion element according to the invention of claim 1 is obtained by impregnating a substrate having a porous structure made of silicon carbide with silicon.

In this case, it is desirable to impregnate the substrate with 10% to 50% by weight of silicon. This is because when the impregnated amount of silicon is 10% or less, the electromotive force sharply decreases as shown in FIG. On the other hand, when the impregnated amount of silicon is 50% or more, the porosity of the substrate must be correspondingly increased. For this reason, if the impregnated amount of silicon exceeds 50%, the strength of the base body is lowered, and as a result, the life of the thermoelectric conversion element is greatly reduced, as shown in FIG.

Further, it is desirable that the substrate is impregnated with silicon and then the outer surface thereof is coated. This is to shield the silicon from the outside air by coating the outer surface of the substrate with a coating layer, thereby preventing the silicon from being oxidized. The coating layer is preferably made of silicon carbide, and its thickness is preferably about 100 μm.

Even in the thermoelectric conversion element of the present invention, in order to form a P-type or N-type semiconductor, a trace amount of element is added to at least one of the substrate and silicon impregnated therein. In the case of P type, aluminum (Al),
A trivalent element such as boron (B) is added, and a pentavalent element such as nitrogen (N) or phosphorus (P) is added when the element is N-type.

Further, as shown in FIG. 4, a thermoelectric conversion element 1 according to a fourth aspect of the present invention includes a main body 11 made of silicon carbide having a through hole 11a formed therein, and a through hole 11a of the main body 11. And a core material 12 made of silicon filled therein.

In this case, the main body 11 may or may not be porous, but it is preferable that the main body 11 is porous and silicon is impregnated therein. When the main body 11 is impregnated with silicon, it is desirable to form a coating layer on the entire surface of the thermoelectric conversion element 1 as in the thermoelectric conversion element according to the first aspect of the invention. When not impregnated with silicon, coating may be applied only to both end surfaces of the core material 12 that are exposed.

Further, the core member 12 is formed through the through hole 11a of the main body 11.
When filling in, the core material 12 is formed in advance,
Although it may be inserted into the through hole 11a, from the viewpoint of sufficiently widening the contact area between the core material 12 and the main body 11,
It is preferable that the main body 11 is immersed in molten silicon to fill the through holes 11a with molten silicon, and then the silicon in the through holes 11a is solidified. In this way, the main body 11
In the case of having a porous structure, the main body 11 can be impregnated with silicon at the same time.

Since the main body 11 and the core material 12 are both P-type or N-type, the minute amounts of the above elements are mixed therein. In this case, it goes without saying that the main body 11 and the core 12 should be of the same mold.

[0014]

Example 1 As an example of the thermoelectric conversion element according to claim 1, a columnar substrate having a diameter of 2.5 mm and a length of 50 mm was manufactured and impregnated with 30% by weight of silicon. It was Further, a coating layer of silicon carbide having a thickness of 100 μm was formed on the entire outer surface of the substrate. As for the coating layer of silicon carbide, the substrate was immersed in a solution of phenol, pulled up and dried, and then heated in vacuum to about 1350 ° C. to carbon in the phenol and silicon impregnated into the substrate. It can be formed by reacting.

FIG. 4 shows a thermoelectric battery A using the thermoelectric conversion element 2 according to claim 3, wherein the thermoelectric battery A has one end portion of the P-type thermoelectric conversion element 2 and one end portion of the N-type thermoelectric conversion element 2. It is configured by bonding to a plate material 3 made of silicon carbide. Two sets of thermal batteries A are connected in series.

The thermoelectric conversion element 2 and the plate member 3 are bonded by spreading silicon powder between the bonding surfaces of each other, heating the bonding portion to melt the spread silicon, and then solidify the silicon. You can Further, in the case of joining in this way, since the end face that is the joining face of the thermoelectric conversion element 2 is shielded by the plate material 3, it is not necessary to form a coating on the end face.

In the thermal battery A having the above structure, the end of each thermoelectric conversion element 2 on the side opposite to the plate material 3 is maintained at room temperature (293 ° K), and the end of the plate material 3 side is heated to 1000 ° K. Then, a voltage of 1.2 V was generated.

[0018]

Comparative Example The substrate of the thermoelectric conversion element 2 (not impregnated with silicon) was used as a conventional thermoelectric conversion element to be compared, and this was connected in the same manner as the thermoelectric battery A shown in FIG. When heated in the same manner as above, the voltage of the thermal battery was 0.3V. As is apparent from this, according to the thermoelectric conversion element 2 of the present invention, an electromotive force four times as high as that of the conventional thermoelectric conversion element was obtained.

[0019]

Second Embodiment Also, as the thermoelectric conversion element 1 according to claim 5, the same construction as the thermoelectric conversion element 2 except that a through hole 11a having an inner diameter of 0.5 mm is filled with a core material 12 made of silicon. Using the above, a thermal battery similar to the thermal battery A was constructed. When heated under the same conditions, the voltage was 1.5 V, and a larger electromotive force was obtained.

The thermoelectric conversion elements 1 and 2 of the present invention are
Not only can it be used in thermal batteries, but it can also be used as a heat or cooling source. That is, in FIG. 4, if a power source is connected instead of the load 4, one end side of each thermoelectric conversion element 2 is heated and the other end side is cooled. By utilizing this, it can be used as a heat source or a cooling source.

[0021]

As described above, according to the thermoelectric conversion element of the present invention, since the porous substrate made of silicon carbide is impregnated with silicon, the electromotive force is higher than that of the conventional thermoelectric conversion element. Therefore, it is possible to obtain a large effect.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between an electromotive force and a weight ratio of a substrate and silicon impregnated into the substrate.

FIG. 2 is a diagram showing a relationship between an electromotive force and a weight ratio of a substrate and silicon with which the substrate is impregnated.

FIG. 3 is a diagram showing an example of a thermal battery using a thermoelectric conversion element.

FIG. 4 is a cross-sectional view showing an example of a thermoelectric conversion element according to claim 4.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Thermoelectric conversion element 2 Thermoelectric conversion element 11 Main body 11a Through hole 12 Core material A Thermal battery

Claims (5)

[Claims] 1. A thermoelectric conversion element comprising a porous substrate made of silicon carbide impregnated with silicon. 2. The weight ratio of the silicon to the substrate is 10
% To 50% impregnation, The thermoelectric conversion element according to claim 1, wherein the thermoelectric conversion element is impregnated. 3. The thermoelectric conversion element according to claim 1, wherein the outer surface of the base is covered with a coating layer. 4. A thermoelectric conversion element, comprising: a main body made of silicon carbide having a through hole formed therein; and a core material made of silicon filled in the through hole of the main body. 5. The main body has a porous structure, and is impregnated with silicon inside.
The thermoelectric conversion element described in.