JPH01154502A - Superconducting ceramic coil and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a small-sized superconducting ceramic coil wherein water also can be used as a refrigerant, by forming a superconducting ceramic into a coil shape on the surface of an aluminum nitride pipe which has insulating properties and has high thermal conductivity. CONSTITUTION:On the internal surface of an aluminum nitride(AlN) pipe 1, a paste is formed into a thine coil shape, and this coil 3 is sintered together with the pipe 1 to form a superconducting ceramic coil on the internal surface of the AlN pipe. The aluminum nitride has insulating properties and has electric resistivity of, e.g., 2X10<12>OMEGA.cm, at a room temperature, and thermal conductivity of 140W/m.k, and the AlN pipe 1 has a large thermal conductivity. The main component of the paste is superconducting ceramics powder of Y-Ba-Cu-O or the like. By cooling the external surface of AlN pipe with suitable refrigerant, the superconducting coil of the AlN pipe/superconducting ceramic can be effectively cooled through the AlN pipe of high thermal conductivity.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a superconducting coil and a method for manufacturing the same, and more particularly to a superconducting ceramic coil with high cooling efficiency suitable for high-temperature superconducting ties and a method for manufacturing the same.

[Conventional technology]

Superconducting ceramics, compared to conventional total bending superconductors,
Because its critical temperature Tc is extremely high, it is considered very promising in fields such as energy, electronics, and strong magnetic field applications. The Tc of this superconducting ceramic is emitted at various VAs, ranging from liquid nitrogen temperature to near room temperature, depending on the composition of the material. If Tc is around the temperature of liquid nitrogen, it is naturally necessary to cool it with liquid nitrogen, but even if Tc is around room temperature, it must be cooled to a temperature below room temperature in order to operate stably.

Conventionally, superconducting coils have been cooled by directly immersing them in an insulating container containing liquid helium or liquid nitrogen. These methods have the advantage of directly cooling the coil, but the cooling system becomes very large. Another problem is that the device configuration becomes complicated and the cost increases.

Furthermore, when water is used as a refrigerant, the entire coil is immersed in water, so insulation between the coil windings cannot be maintained, resulting in a fundamental problem that water cannot be used as a refrigerant.

[Problem to be solved by the invention 3 As mentioned above, the conventional technology does not give consideration to the cooling of superconducting coils, especially high-temperature superconducting coils,
Miniaturization of superconducting coil application equipment.

There have been major problems in lowering prices or using water as a refrigerant.

An object of the present invention is to solve the problems of the prior art described above and to provide a small-sized superconducting ceramic coil in which water can be used as a refrigerant and a method for manufacturing the same.

[Means for solving problems]

The above object is achieved by forming a coil of superconducting ceramic on the inner surface of a ceramic pipe that is insulating and has high thermal conductivity, and passing a coolant through the outer surface of this pipe.

That is, a superconducting ceramic powder such as Y-Ba-Cu-0 is applied to the inner surface of an aluminum nitride ceramic (AflN) fN pipe with an electrical resistance of 2 x 1012 Ω" cm and a thermal conductivity of 140 W/m at around room temperature. The main paste is formed into a thin coil shape, and this coil is then sintered together with the pipe to form a superconducting ceramic coil on the inner surface of the AQN pipe.The AQN pipe/superconducting ceramic thus obtained By cooling the outer surface of the AQN pipe with an appropriate refrigerant, the superconducting coil can be efficiently cooled through the AQN pipe with high thermal conductivity.

[Effect]

The operation of the technical means according to the present invention will be described below.

In order to downsize and simplify the structure of devices using superconducting coils, it is necessary to avoid directly immersing the entire superconducting coil in a coolant.

Conventional superconductors such as Nb3Sn-based superconductors have extremely low Tc and cannot exhibit their performance unless the superconducting coil is directly immersed in liquid He, but Y-B a -Cu, a high-temperature superconductor -0 series ceramics etc. are T.
Since c is high, the cooling margin is very large. Therefore, in the case of a superconducting coil using this material, the coil can be easily maintained at a temperature close to below its Tc without directly immersing the coil in a refrigerant, and this indirect cooling method allows extremely flexible coil configurations. Can be made smaller.

Indirect cooling requires a material with high thermal conductivity to be interposed between the superconducting coil and the refrigerant.

The above-mentioned AQN is suitable as such a substance.

If the outside of the AQN pipe is structured to allow a refrigerant such as Freon, water, or liquid nitrogen to pass through, and a superconducting ceramic coil is formed on the inside surface of this pipe, the coil can be efficiently cooled to the desired temperature. In addition to being able to
The structure of the entire device including the coil can be downsized and simplified.

In addition, in order to efficiently cool the superconducting coil through a pipe with high thermal conductivity, it is necessary that the pipe and the superconducting coil are in close contact with each other. A paste mainly composed of superconducting ceramics is formed into a coil shape on the inner surface of the pipe.

The formed coil does not exhibit superconducting properties in its current state, but when it is heat-treated at around 900'C, it becomes superconducting.

As described above, according to the present invention, the superconducting coil and the cooling system can be integrated, miniaturized, and simplified, so that the efficiency in industrializing the superconducting coil is very high.

An embodiment of the present invention will be described below with reference to FIG.

〔Example〕

Example 1 FIG. 1 schematically shows the structure of a superconducting coil according to the present invention. It has a structure in which a superconducting coil is formed on the inner surface 2 of a pipe 1 made of aluminum nitride (AQN) with an outer diameter of 30+ nm, an inner diameter of 26 mm, a length of 40+ nm, and a thermal conductivity of 140 w/m-.

First, Y-Ba-Cu-0 based superconducting ceramic powder was mixed with an organic binder such as polyvinyl alcohol (PVA) and water as a solvent at a ratio of 100:3.
Weigh out the ingredients at a ratio of 80% and mix thoroughly using a ball mill to form a paste. Next, this paste is applied to the inner surface 2 of the AQN pipe 1 to a thickness of 1 mm by spraying or the like. Subsequently, the pipe coated with this paste is placed in a dryer and dried in air at 100° C. for 2 hours.

Through this treatment, the coating film on the inner surface of the AuN pipe 1 is bonded to the AflN pipe by the action of the organic binder, and at the same time, the coating film is also cured and has a strength sufficient for machining.

The AQN pipe with the superconducting ceramic coating formed on its inner surface in this manner is mounted on a mechanical lathe, and only the coated surface of the inner surface of the pipe is turned into a spiral shape using a thin boring tool. At this time, if the feed rate of the cutting tool is 1.5 mm/rotation, the cutting width is 0.5 mm, and the cutting depth is 1.0 mm, the spiral body with a cross-sectional shape of 1.0 mm thick and 1.0 mm wide is the AQN pipe. Formed on the inner surface.

Next, the above sample was set in an electric furnace and heated to 950°C for 15 minutes.
The spiral coating is sintered into a ceramic by heating in air for a period of time. In this heat treatment, the coating film on the inner surface of the pipe undergoes sintering shrinkage, so that the obtained superconducting ceramic spiral body has a cross section of 0.85 mm in height and 0.9 mm in width.

The superconducting ceramic coil made as described above is
By cooling the outer surface of the AΩN pipe with water, the coil on the inner surface of the pipe can be effectively cooled. Furthermore, since the coil can be cooled without passing water through the pipe, the elements installed inside the coil can also be kept chemically stable. Furthermore, if a normal water cooling cylinder is attached to the outer surface of the AΩN pipe, the AQN pipe can be easily cooled, which has great advantages such as miniaturization and cost reduction.

Example 2゜As in Example 1, Y2O3゜BaCO2, C was applied to the inner surface of a highly thermally conductive AQN pipe made of the same material and with the same dimensions as in Example 1.
A paste of a superconducting ceramic mixture made of u2Q or the like was applied, and after drying, it was heated in air at 600° C. for 1 hour to calcined only the superconducting ceramic paste.

This treatment gives the superconducting ceramic paste sufficient strength to withstand handling and machining in subsequent processes.

The thus produced superconducting ceramic calcined body in the AQN pipe was cut into a spiral shape using the same boring tool as in Example 1 to obtain a superconducting helical body. The cutting tools used were made of cemented carbide to reduce tool wear when cutting the calcined body as much as possible. The obtained calcined spiral was heated in air at 960° C. for 10 hours to densify and sinter the superconducting calcined spiral. The superconducting transition temperature of this superconducting ceramic was 75°.

In order to cool the superconducting ceramic coil formed on the inner surface of the AQN pipe as described above, we were able to efficiently cool the coil inside the AQN pipe by passing liquid nitrogen through the outside of the AQN pipe. .

Example 3 After thoroughly mixing 99 parts by weight of high-purity AQN powder and 1 part by weight of Ca○ powder, an outer diameter of 35 mm and an inner diameter of 30 ml were prepared. It was formed into a pipe shape with a length of 40 mm and heated at 1200°C for 1
A calcined body of AQN was produced by heating in N 2 for an hour. This AQ, N calcined body was mounted on a mechanical lathe, and using a thin boring tool, a width of 1 mm and a depth of 1 mm was formed on the inner surface of the AQN calcined body.
, a spiral groove with a pitch of 1.5 mm was cut. next,
This spirally grooved AuN calcined pipe was heated in N2 at 1800° C. for 2 hours to completely densify and sinter the AQN.

AIII with spiral grooves on the inner surface prepared in this way
The same Y-Ba-C as in Example 1 was applied to the groove part of the N pipe.
It was filled with u-〇 series superconducting ceramic paste. After drying this material in the atmosphere, set it in an electric furnace and
'C, heated in air for 15 hours to densify and sinter the spiral superconducting paste 1- in the AD,N pipe.

In the manner described above, a superconducting ceramic coil could be fabricated on the inner surface of a highly thermally conductive AQN pipe. Since this coil does not protrude from the inner surface of the AQN pipe, the internal volume of the coil can be used effectively, and the AQN
Since the contact area with the pipe is also large, the cooling efficiency is high, making it ideal for small-sized superconducting coils.

Example 4゜A diameter of 1.5 ml11. A coil of Ni-Ti shape memory alloy with a pitch of 2 mm was installed so as to be inscribed therein. next,
The same superconducting ceramic paste as in Example 1 was applied to the inner surface of this pipe. The thickness of the coating film at this time was 1 m.
It is m. When this is heated in air at 100°C for 15 minutes, the Ni-Ti shape memory alloy inscribed in the AQN pipe undergoes dimensional changes, the coil diameter becomes smaller, and the inner surface of the AQN pipe self-helps. Only the peeled shape memory alloy coil can be easily removed from the AQN pipe. Therefore, the spiral body formed from the superconducting ceramic paste remains on the inner surface of the AQN pipe. By treating this sample under the same conditions as in Example 1, a superconducting ceramic coil inscribed in the A QN pipe was obtained.

Note that input to the superconducting ceramic coil is performed through terminals located at both ends of the AQN pipe in FIG. 1.

Although the above embodiment uses a cylindrical AQN pipe, it is easily possible to use a polygonal pipe or a conically tapered pipe, and the same manufacturing method can be applied.

Further, in the above-described embodiment, a coil made of a superconducting material was formed on the inner surface of the pipe, but it is also possible to form a coil on the outer surface of the pipe using a similar manufacturing method and to flow the refrigerant inside the pipe.

That is, the feature of the present invention is that a high temperature superconducting coil is coated on an AQN pipe having good thermal conductivity and integrally molded.

〔Effect of the invention〕

As described above, according to the present invention, a superconducting ceramic coil can be intimately inscribed on the inner surface of a pipe with a very high heat transfer coefficient, thereby reducing the size and cost of superconducting application equipment. In addition, water, Freon gas, low-temperature cryogen, etc. can be used as a refrigerant for the coil. Furthermore, since the operating margin of superconducting ceramics near room temperature can be increased, effects such as improved reliability and longer life of superconducting applied equipment can be expected.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a superconducting ceramic coil according to an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Aluminum nitride, 2... Inner surface, 3... Coil, 4... Terminal part. 7: To Nitsujo Aluminum 17 2 2 Kyutsugicho 3 2 Konre 4: Saitama

Claims (4)

[Claims] 1. A superconducting ceramic coil is characterized by a superconducting ceramic coil formed on the surface of an insulating and highly thermally conductive aluminum nitride pipe. 2. A method for manufacturing a superconducting ceramic coil, which comprises forming a superconducting ceramic coating in a predetermined shape on the inner surface of an aluminum nitride pipe, and then sintering the coating. 3. The method according to claim 2, wherein the superconducting ceramic coating having the predetermined shape is formed by cutting a superconducting ceramic coating after uniformly forming the superconducting ceramic coating. Production method. 4. In the method according to claim 2, the step of forming a superconducting ceramic coating having a predetermined shape includes a step of inscribing a shape memory alloy coil in the inner surface of an aluminum nitride pipe, and a step of inscribing a coil of a shape memory alloy in the inner surface of an aluminum nitride pipe; A method for manufacturing a superconducting ceramic coil, comprising the steps of forming a ceramic coating and removing the shape memory alloy coil from the pipe by heating.