JPH0676626A - Insulating joint material and mhd power generator using it - Google Patents

Abstract

PURPOSE:To keep mechanical strength as a joint at ambient temperature as high as 1600 deg.C and prevent electrically insulating property from lowering even in driving for a long duration. CONSTITUTION:Regarding an insulating joint material which is buried in a gap between unit insulating plates and with which the gap is filled, wherein the divided-type insulating plates 7, 8 have electrically insulating property and are exposed to high temperature, the material consists of mainly fibrous alumina (Al2O3) and is prepared by mixing and kneading the alumina with colloidal silica (SiO2) and thus it is made like a paste.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insulating joint material which is electrically insulating and is used for filling a joint by filling a gap between unit insulating plates in a split type insulating plate which is exposed to a high temperature. Related to MHD generators that use the MHD generator, which has mechanical strength as a joint even at a high ambient temperature of about 1600 degrees Celsius, and does not deteriorate the electrical insulation even during long-term operation. The present invention relates to a material and an MHD generator using the material.

[0002]

2. Description of the Related Art Generally, in a disk type MHD generator, the withstand voltage is about 10 kv and the ambient temperature is 1 degree Celsius.
Since it operates at about 600 degrees, silicon nitride (Si ₃ N ₄ ) and boron nitride (B
Insulating ceramic materials such as N) are used. However, since it is difficult to increase the size of these insulating ceramic materials due to the constraints of manufacturing equipment, strength, etc., these insulating plates are usually manufactured in the form of a plurality of split-type insulating plates. Is assembled as.

In this case, in consideration of the atmospheric temperature reaching about 1600 degrees Celsius, the split type insulating plate is
A gap is provided between the unit insulating plates in consideration of thermal expansion of the insulating plates themselves.

Further, in the disk type MHD generator, it is necessary to add an alkali metal at the time of power generation.
This alkali metal penetrates into the gaps between the unit insulating plates to deteriorate the electrical insulation performance. For this reason, in the present situation, a gap between the unit insulating plates is coated and filled with an insulating joint material (hereinafter, simply referred to as joint material) to fill the joint. By the way, as a joint material of this type of split type insulating plate, powdered alumina (Al ₂ O ₃ ) is used.
A mixture of silicone resin and silicone resin is currently used.

However, since the decomposition temperature of the silicone resin is as low as about 300 degrees Celsius, the silicone resin decomposes and scatters during the operation of the disk type MHD generator for a long time, and only the powdery alumina remains in the joints. It will be. In addition, since the alumina of this powder has almost no interparticle bonding force, that is, the mechanical strength as joints is low, the MHD power generation before the atmospheric temperature inside the disk type MHD generator reaches about 1600 degrees Celsius. It will be blown away by the high temperature working gas. As a result, there is a gap between the unit insulating plates, and the alkali metal penetrates from there to deteriorate the electrical insulating performance, making it difficult to operate for a long time.

[0006]

As described above, in the conventional joint material, when the atmospheric temperature is exposed to a high temperature of about 1600 degrees Celsius, the mechanical strength and the electrical insulating property of the joint are lowered. However, there is a problem that it is difficult to drive for a long time.

It is an object of the present invention that the ambient temperature is 160 degrees Celsius.
To provide an insulating joint material which retains mechanical strength as a joint even at a high temperature of about 0 ° C. and whose electric insulation does not deteriorate even during operation for a long time, and an MHD generator using the same. is there.

[0008]

In order to achieve the above object,

First, according to the first aspect of the invention, the insulating property used to fill the joints by filling the gaps between the unit insulating plates in the split type insulating plate having the electrical insulating property and exposed to high temperature. In the joint material, alumina (Al ₂ O ₃ ) in a fiber form is used as a main component, and this alumina and colloidal silica (SiO ₂ ) are mixed and kneaded to form a paste.

According to the second aspect of the invention, the MHD
The insulating joint material according to claim 1 is filled in the gap between the unit insulating plates of the split type insulating plate disposed between the electrodes of the generator body.

[0011]

Therefore, in the insulating joint material of the present invention and in the MHD generator using the same, fiber-shaped alumina and colloidal silica are mixed to form a kneading paste form, whereby Filling of joints becomes easy.

Further, even when the water content in the colloidal silica used for forming the paste is gradually dried, the use of alumina in the fiber form allows the insulation property even if the water content is completely dried and evaporated. Since the joint material is in a state in which it is in the form of powder and is not blown off due to the connection of the fibers, the mechanical strength of the joint material itself can sufficiently satisfy the required performance.

Furthermore, since the main components, alumina and colloidal silica, do not decompose even at high temperatures and form stable joints, and have electrical insulation performance up to high temperatures, a disk type MHD generator is provided. As a joint material for the split-type insulating plate, it has sufficient electric insulation performance.

[0014]

First, the concept of the present invention will be described.

As the performance of the joint material for the split type insulating plate described above, electrical insulation and heat resistance are important, and in order to satisfy these, oxide ceramics is suitable as the main material, but oxidation is required. It is well known that the electrical ceramics and the heat resistance cannot be perfectly obtained without firing the ceramics.

However, since the application part of the present invention is to fill the narrow joint portion, it is impossible to fill the narrow joint portion with the oxide ceramic which has been fired, that is, hardened. For this reason, the joint material must be a paste-like raw material, and similarly, the joint material is required to have a property that it is not powdered and blown off before the joint material is fired due to an increase in the internal temperature of the MHD generator. To be done.

Therefore, as the insulating joint material in the present invention, alumina (Al ₂ O ₃ ) in a fiber form is the main component, and this alumina and colloidal silica (SiO ₂ ) are used.
Using a material made into a paste by mixing and kneading with, and filling this joint material between unit insulating plates of the split type insulating plate of the MHD generator, after natural or forced drying,
It is applied by gradually flowing a high temperature gas and firing. An embodiment of the present invention based on the above concept will be described below in detail with reference to the drawings.

FIG. 1 is a plan view showing a structural example of a disk type MHD generator to which a joint material according to the present invention is applied. As shown in FIG. 1, the disk-type MHD generator operates in the radial direction shown in the drawing with a working gas (for example, argon or helium) flowing into a center cone 1 formed in the center of the drawing together with a small amount of alkali metal. The gas flows. In this case, by placing the disk type MHD generator in a strong magnetic field such as a superconducting magnet (not shown), an electromotive force is generated between the cylindrical anode 2 and cathode 3 according to Faraday's law. Then, the working gas that has completed this power generation passes through the wedge 4 and the flow path control cylinder 5, and is guided from the diffuser 6 to the outside of the generator.

On the other hand, a split type anode insulating plate 7 is arranged between the anode 2 and the center cone 1, and a split type positive-cathode insulating plate 8 is placed between the anode 2 and the cathode 3. I have set up. Each of the anode insulating plate 7 and the cathode-cathode insulating plate 8 has a cylindrical shape, and each unit insulating plate divided in the circumferential direction is assembled. Further, each unit insulating plate is a plate of boron nitride. In the figure, 9 indicates an end plate.

On the other hand, as shown in the partial plan view of FIG. 2, the joint material 10 of the present invention is filled in the gap between the unit insulating plates in the insulating plate 7 for anode and the insulating plate 8 for cathode and cathode. There is. That is, the joint material 10 is mainly composed of fiber-form alumina, and is formed by mixing the alumina and colloidal silica into a kneading paste, which is used in the anode insulating plate 7 and the cathode-cathode insulating plate 8. It is applied to the gap between the unit insulating plates and naturally or forcedly dried to evaporate the water content. FIG. 3 is a diagram showing an example of typical characteristics of the split type anode insulating plate 7 and cathode-cathode insulating plate 8 and the joint material 10, respectively.

In FIG. 3, the heat resistant temperature at which the strength of the material itself suddenly decreases is 1700 degrees Celsius for the joint material 10,
Anode insulating plate 7 made of boron nitride, positive and negative insulating plate 8
Then, the operating temperature is 16 degrees Celsius, such as 2000 degrees Celsius.
It has sufficient heat resistance as an insulating plate between electrodes in a disk type MHD generator of the 00 degree class. The Young's modulus is 10,000 kgf / mm ² And the anode insulating plate 7 made of BN and the cathode-cathode insulating plate 8 of 20,000 k
gf / mm ² It has a low rigidity of 1/2.

That is, the heat-resistant temperature is 1700 degrees Celsius,
It has sufficient performance as a joint material for the inter-electrode insulating plate in the disk type MHD generator and has a thermal expansion coefficient of 6.2 after firing.
The value is as small as × 10 ^-6 / degree, which is close to that of the insulating plate material (such as silicon nitride) and is an effective value for peeling at the contact surface between the insulating plates 7 and 8 and the joint material 10.

Next, in the disk type MHD generator using the insulating joint structure constructed as described above, the joint material for the inter-electrode insulating plate, that is, for the split type anode insulating plate 7 and the cathode-cathode The joint material 10 for filling the gaps between the unit insulating plates of the insulating plate 8 is naturally dried by using a material containing alumina in the form of a fiber as a main component and mixing it with colloidal silica to form a paste. Depending on the degree, sufficient electric insulation and mechanical strength characteristics can be obtained. In addition, since the coefficient of thermal expansion after firing is also close to that of the insulating plate material, it exhibits strong mechanical strength characteristics against the problem of peeling at the contact surface between the insulating plates 7 and 8 and the joint material 10. Become. Hereinafter, this point will be described in more detail.

The electrical insulation characteristics of the insulating plate can be evaluated by clarifying the adhesion strength between the insulating plates 7 and 8 and the joint material 10. That is, from room temperature to 16 degrees Celsius
The repeated heat cycle of 00 degrees is the thermal history experienced by the insulating plate of the disk type MHD generator. The adhesive strength of the joint material 10 was found by examining the change in the adhesive strength of the test piece formed by adhering the unit insulating plates with the joint material 10 by repeatedly applying a heat cycle from room temperature to 1600 degrees Celsius. If it was sufficient, it was confirmed that the joint remained sufficiently between the unit insulating plates, and sufficient electrical insulation was maintained.

FIG. 4 shows an example of the experimental results. That is, in the conventional insulating plate, the silicone resin disappears after three heat cycles, and the electrical insulating property also disappears, whereas in the insulating plate of this embodiment, the unit insulation occurs even after 80 heat cycles. No abnormality is found in the plate and the joint material 10 between them. In other words, it is clear that the insulating joint structure of this embodiment can maintain sufficient performance even with respect to thermal stress due to the difference in thermal expansion or temperature history.

As described above, in this embodiment, the joint material 10 of the electrode-divided insulating plates 7 and 8 for the disk-type MHD generator, which is electrically insulating and is exposed to a high temperature of about 1600 degrees Celsius. As the main component, alumina in the form of fibers is used as a main component, and this is mixed with colloidal silica to be kneaded into a paste form.

Therefore, it becomes possible to easily apply the joint material 10 to the joint portion. In addition, since the structure having a sufficient interparticle bonding force can be obtained even by the degree of natural drying, it becomes possible to obtain sufficient electric insulation characteristics and mechanical strength. Furthermore, the coefficient of thermal expansion of the joint material 10 after firing is also close to that of the insulating plate material, so that the insulating plates 7, 8
It also exhibits strong mechanical strength characteristics against the problem of peeling at the contact surface between the and the joint material 10.
It is possible to supply the joint material 10 of the electrode-divided insulating plates 7 and 8 having a high ambient temperature of about 1600 degrees Celsius such as a generator and a dielectric strength of about 10 kv.
The present invention is not limited to the above embodiment, but can be carried out as follows.

In the above embodiment, the insulating plate is made of BN, and the joint material is made of a mixture of fiber-form alumina and colloidal silica to be kneaded into a paste.
Although shown for high temperature of about 16000 degrees Celsius, the basic idea of the present invention is to provide a joint material having low rigidity between the unit insulating plates so that predetermined performance (electrical insulation and thermal shock resistance It is to obtain a split type insulating plate having heat resistance).

Therefore, another embodiment of the present invention is a high temperature division type insulating plate having higher heat resistance. That is, for example, the heat resistance temperature of the insulating plate is 2000 degrees Celsius.
BN insulation plate, MgO by using a joint material that is a mixture of MgO and alumina sol in the form of a fiber, based on a magnesium oxide (MgO) fiber exceeding the degree
Fiber-alumina sol joint material with heat resistant temperature of 1 degree Celsius
It is possible to obtain a high temperature division type insulating plate having a temperature of 800 degrees or more.

As described above, as the unit insulating plate, MgO,
With respect to any highly insulating ceramic material such as BN, Al ₂ O ₃ and Si ₃ N ₄ , a high performance split type insulating plate can be realized by the insulating joint constitution of the present invention. However, regarding heat resistance, Si ₃ N ₄ , Al ₂ O ₃ , MgO, B
It has been confirmed by experiments that it becomes higher in the order of N.

On the other hand, the same applies to the joint material, Si ₃ N
₄ , which can be composed of Al ₂ O ₃ , MgO, and BN bases, and has low rigidity. For example, MgO fibers are kneaded with alumina sol to form a joint material with good workability in order to have low rigidity. By doing so, a high performance split type insulating plate can be obtained.

[0032]

As described above, according to the present invention, it is used to fill the joints by filling the gaps between the unit insulating plates in the split type insulating plate having the electric insulating property and exposed to the high temperature. As the insulating joint material, a fiber-based alumina is used as a main component, and the alumina and colloidal silica are mixed and kneaded to form a paste, so that the atmosphere temperature is high at about 1600 degrees Celsius. It is possible to provide an insulating joint material which has mechanical strength as a joint and does not deteriorate in electrical insulation even during long-term operation, and an MHD generator using the same.

[Brief description of drawings]

FIG. 1 is a disk type MH to which a joint material according to the present invention is applied.
The top view which shows one Example of a D generator.

FIG. 2 is a partial plan view showing a configuration example of a split type insulating plate between electrodes in the embodiment.

FIG. 3 is a diagram showing various characteristics of a joint material and a split type insulating plate in the example.

FIG. 4 is a characteristic diagram showing an example of a result of examining a change in adhesive strength when the unit insulating plates are bonded with a joint material in the same example, which is caused by a thermal cycle from room temperature to 1600 degrees Celsius.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Center cone, 2 ... Anode, 3 ... Cathode, 4 ... Wedge, 5 ... Flow path control cylinder, 6 ... Diffuser, 7 ... Anode insulating plate, 8 ... Positive-cathode insulating plate, 9 ... End plate,
10 ... Joint material.

Claims (2)

[Claims] 1. An insulating joint material used to fill a joint by filling a gap between unit insulating plates of a split type insulating plate which has an electric insulation property and is exposed to a high temperature, wherein a fiber-shaped alumina ( Al ₂ O ₃ ) as a main component, and this alumina and colloidal silica (SiO ₂ ) are mixed and kneaded to form a paste. 2. The insulating joint material according to claim 1 is filled in the gap between the unit insulating plates of the split type insulating plate disposed between the electrodes of the MHD generator main body. MHD generator.