JPH0697865B2 - Cathode for thermoelectron power generation element and manufacturing method thereof - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a cathode of a thermoelectron power generation element and a method for manufacturing the same, and in particular, does not require a thin-walled graphite shell that has been conventionally used, and improves power generation efficiency and manufacture. The present invention relates to a cathode of a thermoelectron power generation element that enables cost reduction and a manufacturing method thereof.

[Prior Art] Thermoelectron power generation is a method of direct power generation in which heat energy is directly converted into electric energy, and a power generation element having a cross-sectional structure shown in FIG. 2 is known.

As shown in the figure, a cathode (emitter) 1 has a cylindrical base body 2 with one end closed in a hemispherical shape, and a metal or alloy (hereinafter, referred to as the present specification) as a cathode body that is closely formed on the inner surface of the base body 2. Abbreviated as metal including alloy in the text.) Layer 3
And a protective coating 4 applied to the outer surface of the base body 2. The base 2 has a function as a support member, and graphite or the like having excellent thermal conductivity is applied. For the metal layer 3, a material having a large work function that easily emits thermoelectrons is desirable, and tungsten (W) is generally applied. The protective coating 4 is made of ceramics having excellent heat resistance and oxidation resistance, such as silicon carbide (SiC).

Inside the cathode 1, an anode (collector) 5 having a similar shape to the cathode 1 is coaxially arranged with a predetermined interval. Nickel (Ni), which is a material having a small work function, is generally applied to the anode 5. Also, the anode 5
Is cooled by a coolant (air or the like) 6, and a space 7 between the cathode 1 and the anode 5 is generally filled with a gas such as cesium which is easily ionized. The thermoelectron power generation element configured in this manner is installed through the furnace wall 8 and the like so that the outer surface of the hemispherical crown of the cathode 1 is placed in a high temperature atmosphere.

Then, for example, thermoelectrons emitted from the metal film 3 heated by the high temperature gas flow (arrow 9 shown in the figure) flow into the anode 5, and electric power is supplied to a load (not shown) connected between the cathode 1 and the anode 5. It is being supplied.

[Problems to be Solved by the Invention] In the thermoelectron power generation element that generates power by such a principle, the base 6 does not contribute to power generation characteristics at all, but rather increases the amount of heat transferred to the metal layer 3. It is preferable that it does not exist. Further, as the base body 3, conventionally, one obtained by hollowing out graphite into a cylindrical shell (shell body) shape with one end sealed is used, but the shell manufacturing cost is considerably high.

Further, in such a thermionic power generation element, it is mainly the crown that is arranged in a high temperature atmosphere that contributes to power generation,
And the metal film 3a formed in the straight portion region (hereinafter, also referred to as a power generation effective portion) adjacent thereto. Therefore, the metal film 3a in the power generation effective portion needs to be a tungsten film having a large work function, but the metal film 3b in the other portion mainly has a role of a conductive path, and thus has excellent electric conductivity. Any metal film will do. In particular, the metal film 3 made of tungsten is deposited by CVD (Che
In the case of forming by the mical vapor deposition method, since the source gas tungsten hexafluoride WF ₆ is expensive, it is desired that the metal film 3b other than the power generation effective portion is formed using an inexpensive metal. there were.

In addition, the output per thermoelectric power generation element shown in the figure is generally small, and an extremely large number of elements are required to form a large-capacity power generation device. However, the specific gravity of tungsten (19.
Since 3) is larger than other metals, the total weight of the power generator was heavier.

[Means for Solving Problems] The first aspect of the present invention is to provide W (tungsten) directly on the inner surface of the outer layer made of a heat-resistant ceramic such as SiC (silicon carbide).
Is a cathode of a thermoelectron power generation element in which an inner layer having a metal part for emitting thermoelectrons such as is formed.

In the first aspect of the invention, all of the inner layer may be made of a metal such as W for emitting thermoelectrons, or may be as follows.

That is, only the power generation effective portion that contributes to thermionic power generation is a metal for emitting thermoelectrons such as W, and the metal layer of the other portion is a metal for conductivity having a smaller specific gravity than the metal for emitting thermoelectrons. It is a thing.

According to a second aspect of the present invention, one of an outer layer and an inner layer is vapor-deposited on a die surface by a CVD method, and then the die is cooled to separate the deposit from the die surface, and a cylinder having one end sealed. This is a method for producing a thermoelectric power generating element by obtaining a frame-shaped body and vapor-depositing the other of the outer layer and the inner layer on the surface of the body by the CVD method.

[Operation] In the present invention, the metal layer for thermionic emission is directly formed on the inner surface of the ceramic outer layer, and a graphite shell unlike the conventional case is not interposed between the both. Therefore, the amount of heat transferred to the thermionic emission metal layer increases, and the power generation efficiency can be improved.

Further, in the present invention, only the power generation effective portion that contributes to power generation in the inner layer (metal layer) can be the thermoelectron emitting metal, and the other portion can be the lightweight conductive metal, so that the entire cathode The weight can be reduced.

Further, in the method for producing a cathode of the present invention, a deposit is formed on the mold surface by the CVD method, and then the deposit is separated by utilizing the difference in thermal expansion between the mold and the deposit, so that the deposit is thin and uniform. The body can be obtained. Then, by providing a ceramics or metal layer on the surface of the body by the CVD method, the cathode of the thermoelectron power generation element having the above-mentioned configuration can be easily manufactured.

Embodiments Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a cross-sectional view showing the structure of the cathode of a thermoelectric power generating element according to an embodiment of the first invention of the present invention.

The cathode 11 in FIG. 1 has a cylindrical shape with one end closed in a hemispherical shape. In this embodiment, the outer mold layer 12 is made of SiC and the inner mold layer 13 is made of W.

FIG. 3 is a cross-sectional view showing the structure of a cathode of a thermoelectric power generating element according to a different embodiment of the first invention of the present invention, which has the same shape as the embodiment of FIG. 12 is also Si
Composed of C. Thus, the inner layer 13 that is formed in close contact with the inner surface of the outer layer 12 is the first of the power generation effective portion (the top portion and the area adjacent to it) that mainly contributes to thermoelectron power generation.
The metal layer 13a is made of tungsten, and the second metal layer 13b in the other straight portion regions is made of metal such as molybdenum whose specific gravity is smaller than that of tungsten. It is preferable that the second metal layer 13b has high electrical conductivity and high adhesion to the ceramics of the outer layer. Specifically, in addition to the above molybdenum, a metal such as nickel can be used. Of course, other simple metals or alloys can be used as long as they have such characteristics.

Further, in the present invention, the cathode 11 may have a shape other than those shown in FIGS. 1 and 3. For example, the shape is not limited to a cylinder, but may be a polygonal rectangular tube, and the shape of the crown is not limited to a hemispherical shape, and may be any shape as long as the end of the tube is sealed. However, it is preferable that the shape of the crown be hemispherical or a shape similar thereto in order to maximize the surface area.

One embodiment of the method of forming the cathode 11 having such a structure will be described below with reference to FIG. First,
As shown in FIG. 4, a mold 14 having a cylindrical mold surface with one end sealed is prepared, and a metal layer 13 such as tungsten serving as an inner layer is formed on the mold surface of the mold 14 by a CVD method. Vapor deposition. At this time, the mold 14 is made of a material such as tungsten which has a coefficient of thermal expansion larger than that of the metal layer 13 and does not substantially react with the metal layer 13.

As the material of the mold 14, specifically, the following materials can be adopted. That is, since the coefficient of thermal expansion of tungsten is 4 to 5 × 10 ^-6 (deg ^-1 ), Al ₂ O ₃ (thermal expansion coefficient of about 8.5a × 10 ^-6 deg ^-1 ) and ZrO ₂ (coefficient of thermal expansion About 10 × 10 ^-6 d
eg ^-1 ). When tungsten is vapor-deposited on the mold 14, a known source gas such as tungsten hexafluoride WF ₆ can be used as the CVD source gas. The CVD reactions for WF ₆ and WCl ₆ are as follows.

WF ₆ + 3H ₂ → W + 6HF After the metal layer 13 is vapor-deposited on the outer surface of the mold 14 so as to have a predetermined thickness, the vapor deposition operation is stopped and the mold 14 is cooled. Then, the metal layer 13 is separated from the mold surface due to the difference in thermal expansion between the mold 14 and the metal layer 13.

An outer layer is formed by a CVD method on the outer surface of the inner layer made of metal such as tungsten thus obtained. This outer layer is made of ceramics and is made of Si, which has excellent heat resistance and corrosion resistance.
Preference is given to using C. In order to deposit this SiC by the CVD method, for example, CH ₃ SiCl ₃ may be used as a source gas, but other well-known SiC formation such as SiCl ₄ and hydrocarbon gas may be used.
It is clear that a CVD source gas can also be used.

FIG. 5 is a cross-sectional view showing another method for forming the thermionic power generating element cathode shown in FIG. In the embodiment shown in FIG. 5, a female mold 15 having a concave mold surface is used. As the material of the mold 15, a material having substantially no reactivity with the metal 13 such as tungsten deposited on the mold surface is used. However, in this embodiment, the mold 15 is made of a material such as tungsten having a coefficient of thermal expansion smaller than that of the metal layer 13. That is, after depositing the metal layer 13 on the mold surface,
When the temperature of the mold 15 is lowered, the shrinkage amount of the metal layer 13 is larger than the shrinkage amount of the mold 15, so that the metal layer 13 is peeled from the mold 15 and taken out as a frame.

By depositing ceramics such as SiC on the outer surface of the taken out metal layer 13 by the CVD method, the cathode 11 having the structure shown in FIG. 1 can be obtained.

In the description of FIGS. 4 and 5, an example in which W is first vapor-deposited on the mold surface is described, but ceramics such as SiC may be first. However, W is a metal,
Since it has higher toughness than ceramics such as SiC, it is less likely to crack when peeled from the mold. (SiC has lower toughness than W and may crack when taken out from the mold. Since W can be formed by the CVD method at a temperature lower than that of SiC, when it is cooled and taken out. Therefore, it is preferable that W is vapor-deposited on the mold before forming SiC.) For this reason, it is preferable to form W by depositing W on the mold first.) The metal layer 13a shown in FIG. In order to manufacture a cathode having the second metal layer 13b, for example, the following may be performed. That is, only a portion of the mold 14 or 15 where the cathode crown is to be formed is selectively heated (to perform such partial heating, for example, a method of irradiating a high energy density beam such as a laser beam may be used. Is preferred.) CVD on this part
A gas is supplied to deposit only the first metal layer 13a. Next, only the portion of the mold surface where the straight portion is to be formed is selectively heated, a CVD gas is introduced, and the second metal layer 13b is deposited on this straight portion. In this way, after the metal layer composed of the first metal layer 13a and the second metal layer 13b is formed, the mold 15 is cooled, and the metal layer is separated from the molds 14 and 15 and taken out. Ceramics are vapor-deposited on the outer surface of the.

As the CVD reaction for forming the second metal layer 13b, for example, the following reaction can be used.

When manufacturing the cathode having two kinds of metal layers according to FIG. 3, the ceramic outer layer is first vapor-deposited and taken out from the mold, and the first metal layer 13a and the second metal layer are formed on the inner surface of the outer layer. The method of vapor-depositing the layer 13b is also preferable because selective heating of a vapor deposition planned portion is easy.

An example of a method of first forming the ceramic outer layer 12 and then forming the metal layers 13a and 13b on the inner surface of the outer layer will be described below. First, the outer layer 12 is formed by using the molds 14 and 15 shown in FIG. 4 or FIG. Next, while cooling the straight portion of the outer layer, the top portion of the outer layer 12 is moved to a predetermined position by a heating device.
Hold by heating to the CVD deposition temperature. Then, when the CVD source gas 25 is supplied to the inner surface of the crown, the CVD reaction deposit adheres to the inner surface of the crown heated to the deposition temperature or higher, whereby the first metal layer 13a is formed.

Next, only the crown portion to which the first metal layer 13a is attached is cooled. On the other hand, the straight portion of the ceramic outer layer 12 is heated and maintained at a predetermined CVD deposition temperature by a heating device. And
When the raw material gas is supplied to the inner surface of the straight portion, the CVD reaction deposit adheres to the inner surface of the straight portion of the outer layer 12 which is heated to the deposition temperature or higher, and the second metal layer 13b is formed.

In the description of the above embodiment, the first metal layer 13a
Is formed first, and the second metal layer 13b is formed later, but conversely, the second metal layer 13b is formed first, and then the first metal layer 13b is formed.
It is obvious that the metal layer 13a may be formed.

[Effect] As described in detail above, the cathode for thermionic power generating element of the present invention is
Since the metal layer for thermionic emission is directly formed on the inner surface of the ceramic outer layer, the heat transfer characteristics are high and the power generation efficiency is high.

Further, in the present invention, only the main part of the inner surface layer (metal layer) that contributes to power generation may be a thermoelectron emitting metal, and the other part may be a light weight metal, so that the weight of the entire cathode can be reduced. It is possible. Furthermore, according to the present invention, the cathode of such a thermoelectron power generation element can be easily manufactured, and since the obtained cathode is formed by the CVD method, the thickness and the material are uniform and the characteristics are excellent. Will be things.

[Brief description of drawings]

1 and 3 are cross-sectional views showing the structure of a cathode according to an embodiment of the present invention, FIG. 2 is a cross-sectional view showing the structure of a cathode according to a conventional example, and FIGS. 4 and 5 are respectively. FIG. 6 is a cross-sectional view illustrating an example of the method for manufacturing the cathode of the present invention. 11 ... Cathode, 12 ... Outer layer, 13 ... Inner image (metal layer), 13a ... First metal layer, 13b ... Second metal layer, 14, 15 ... Mold.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-59-220084 (JP, A) JP-B 44-31435 (JP, B1) JP-B 5-17311 (JP, B2) Electrotechnical Laboratory Vocabulary Vol. 38, No. 12, P. 701-717 Inter soc, Energy Convers Eng Conf, 19th, 1984

Claims (2)

[Claims] 1. A thermoelectric power generation element having a cylindrical shape with one end sealed, which is provided in close contact with an outer layer made of a heat-resistant ceramic such as silicon carbide and an inner surface of the outer layer. And a metal or alloy inner layer, wherein at least the one end side portion of the metal or alloy inner layer is a thermoelectron emitting metal or alloy such as tungsten. cathode. 2. A heat having an outer layer made of a heat-resistant ceramic and having a cylindrical shape with one end sealed, and an inner layer made of a metal or an alloy provided in close contact with the inner surface of the outer layer. When manufacturing the cathode of the electronic power generating element, a mold whose mold surface shape is a cylindrical shape with one end closed, first, one of the heat-resistant ceramics and the metal or the alloy is subjected to the CVD method on the mold surface. Then, the mold is cooled and the vapor-deposited layer is peeled off from the mold surface to obtain a skeleton. A method for manufacturing a cathode of a thermoelectron power generation element, which is characterized by being obtained.