JPH01181402A - Manufacture of superconductive oxide solenoid - Google Patents

Abstract

PURPOSE:To obtain a solenoid of a superconductive oxide having dense texture without cracks and having a high critical current density, by utilizing a cylindrical body of silicon nitride previously provided with a helical groove and coagulating melt of a superconductive oxide composition within the helical groove. CONSTITUTION:A cylindrical member of silicon nitride 14 having a helical groove 15 on the peripheral surface is dipped in melt of a superconductive oxide composition 12, whereby the melt 12 coagulates within the helical groove 15. The cylindrical member 14 is removed from the melt and any coagulation adhering to any other part of the member than the groove 15 is eliminated so that the coagulation 18 of the melt 12 of a coil shape is left within the groove 15. The coil-shaped coagulation 18 is then heat treated to produce a superconducting oxide 19. Thus, a solenoid of the superconductive oxide 19 can be obtained. Since the solenoid is shaped by the melt coagulation process, the solenoid is allowed to have excellent superconducting properties without defects such as cracks.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a superconducting oxide solenoid that uses a superconducting oxide as a conductor and enables manufacturing of a small and powerful electromagnetic magnet.

[Prior Art] Conventionally, a superconducting oxide solenoid has been manufactured as follows. FIG. 4 is a schematic diagram showing a conventional manufacturing method.A cylindrical winding core 1 has an insulating layer coated on its outer peripheral surface. Then, a mixture of oxides having a composition exhibiting superconductivity (for example, Y203; 1 mol, BaO; 2 mol, CuO
; mixed at a blending ratio of 3 moles) is kneaded into a paste, and this paste-like oxide 3 is charged into the cylinder 2.

Next, this oxide 3 is pushed out from the noise 5 at the tip of the cylinder 2 onto the outer peripheral surface of the winding core 1 by the piston 4. Then, while rotating the winding core 1 around its axis, the nozzle 5
By moving the winding core 1 in the axial direction, the nozzle 5
The oxide 3 extruded from the core 1 is formed into a coil shape on the circumferential surface of the winding core 1. Next, the oxide 3 wound around the winding core 1 is heated and fired together with the winding core 1 at approximately 900° C. for several hours to several tens of hours in an oxidizing atmosphere to generate a superconducting oxide and manufacturing a superconducting solenoid. do. The superconducting solenoid manufactured by this method has a critical current density of about 100
It is OA/cot.

FIG. 5 is a schematic diagram showing another conventional manufacturing method. A superconducting oxide powder 7 is enclosed in a silver vibro, and this powder 7 is drawn together with a silver vibro by a drawing die 8 to make it into a thin wire, and the wire 9 after this wire drawing is coated with an insulating layer. Then, the winding core 1 is wound into a coil shape.
This wire 9 is wound together with the core 1 in an oxidizing atmosphere for about 90 minutes.
Baked by heating to a temperature of 00°C for several hours to several tens of hours,
The oxide powder 7 in the silver vibro is made superconducting.

Thereafter, the silver vibro is dissolved with acid to obtain a superconducting solenoid. The superconducting solenoid thus produced has a critical current density of approximately 500 A/cni.

[Problems to be Solved by the Invention] However, all of these conventional methods have the following drawbacks. First, in the case of the method shown in FIG. 4, the cylindrical winding core 1 tends to thermally expand when heated to the firing temperature, whereas the coiled oxide paste 3 densifies during firing. Shrink. Therefore, the coiled oxide paste that is about to shrink is subjected to a tensile force by the winding core 1 that is about to expand, and fine racks are generated locally. When such a rack occurs, the number of superconducting paths is significantly reduced, and the superconducting properties are deteriorated.

Further, in the case of the method shown in FIG. 5, when the silver vibro is heated to the firing temperature, it tends to thermally expand, whereas the oxide compact 7 inside the silver vibro tends to contract. For this reason, cracks also occur in the powder 7 and the superconducting properties deteriorate. Further, since the powder 7 in the silver vibro is compressed and then wound into a coil, cracks may occur in the powder 7 when it is wound into a coil.

The present invention has been made in view of such problems, and includes:
An object of the present invention is to provide a method for producing a superconducting oxide solenoid that can produce a superconducting oxide solenoid that has a dense structure without cracks and a high critical current density.

[Means for Solving the Problems] A method for manufacturing a superconducting oxide solenoid according to the present invention includes immersing a cylindrical member made of silicon nitride having a spiral groove carved into its circumferential surface in a melt having a superconducting oxide composition. and after solidifying the melt in the spiral groove, removing the solidified material adhering to areas other than the spiral groove, and then heat-treating the solidified material in the spiral groove to generate a superconducting oxide. It is characterized by

[Operations] In the present invention, a cylindrical member made of silicon nitride having a spiral groove cut into its circumferential surface is immersed in a melt of a superconducting oxide composition. Then, the melt solidifies in the spiral groove. Therefore, when this cylindrical member is pulled up from the melt and the solidified matter adhering to areas other than the inside of the spiral groove is removed, the solidified matter of the melt remains in the spiral groove in the form of a coil. Next, a superconducting oxide solenoid is manufactured by heat-treating this coiled solidified material to generate a superconducting oxide.

In this way, in the present invention, the solenoid is molded by the melt-solidification method, so that cracks and the like do not occur in the solenoid as in the conventional method, and excellent superconducting properties can be obtained.

[Examples] Examples of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a sectional view showing an example method of the present invention. A melt 12 having a superconducting oxide composition is stored in the crucible 11 . A resistance heating coil 13 is disposed outside the crucible 11, and by energizing this coil 13, the melt 12 in the crucible 11 is heated and kept warm.

The cylindrical member 14 is made of silicon nitride (Si3N4). FIG. 2 is a side view showing only the cylindrical member 14 taken out. The cylindrical member 14 has a cylindrical shape with open upper and lower ends, and has a spiral groove 15 carved in its outer peripheral surface.

The support member 16 has a cylindrical shape and is attached to a suitable lifting device (not shown). The outer diameter of the support member 16 is substantially the same as the inner diameter of the cylindrical member 14, and the lower end of the support member 16 is press-fitted into the upper end of the cylindrical member 14. are airtightly connected. A ventilation hole 17 is formed in the center of the support member 16 along its axis. Compressed air is supplied to the inside of the cylindrical member 14 through this vent hole 17 .

In the method of this embodiment, the cylindrical member 14 is
While supplying compressed air into the cylindrical member 14 through the ventilation hole 17, the lifting device to which the support member 16 is attached is driven to lower the cylindrical member 14. It is immersed in the melt 12 in the crucible 11. In this case, the pressure of the compressed air is adjusted based on the immersion depth to prevent the melt 12 from entering the cylindrical member 14 from the lower end of the cylindrical member 14. The melt 12 has a composition of superconducting oxide, and is heated by the resistance heat generation of the coil 13 and kept at a predetermined temperature. Due to the heat exchange with the liquid 12, the solidified material 18 of the melt 12 adheres to the outer peripheral surface of the cylindrical member 14, including inside the spiral groove 15.

Next, the support member 16 is raised to take out the cylindrical member 14 to which the solidified material 18 is attached from the melt 12, and the cylindrical member 14 is removed from the melt 12.
As shown in FIG. 3, by chemically dissolving unnecessary coagulated substances adhering to parts other than the spiral groove 15 of the cylindrical member 14 or gradually grinding them with a grindstone, oxides are removed only within the groove 15 of the cylindrical member 14. The coagulum remains. As a result, one coil-shaped oxide having a superconducting composition is formed on the outer peripheral surface of the cylindrical member 14.

Thereafter, this oxide 19 is heat-treated together with the cylindrical member 14 at 930° C. for several hours to several tens of hours in an oxidizing atmosphere, thereby making the oxide 19 superconducting. As a result, a solenoid of superconducting oxide 19 having a core wound around cylindrical member 14 made of silicon nitride, which is an electrical insulator, is manufactured.

In this embodiment, since the cylindrical member 14 is made of silicon nitride, this cylindrical member 14 is immersed in the melt 12 in the Luppo 11 and subjected to a rapid temperature change from room temperature to 1300°C. However, it will not be damaged by thermal shock. In addition, this silicon nitride reacts with the oxide melt to form an interface (between the groove inner surface and outer peripheral surface of the cylindrical member 14 and the solidified material 18).
Creates an M-thickness layer that absorbs slight differences in thermal expansion. This suppresses the occurrence of cracks in the oxide solidified material 18 during the process in which the melt 12 solidifies and the solidified material 18 cools down to room temperature. Moreover, this buffer layer suppresses the occurrence of cracks in the oxide 19 even during the heat treatment in the post-process.

Next, the results of actually manufacturing a superconducting oxide solenoid using the method of the present invention will be explained.

A mixed oxide of 1 mole of Y2O, 2 moles of BaO, and 3 moles of CuO was heated to 1300° C. in an aluminum crucible to melt it, and was maintained at this temperature. Then, 20 turns of semicircular spiral grooves with a groove cross-sectional area of 1- were carved on the outer peripheral surface of a cylindrical member made of silicon nitride with a length of 60 mm and an outer diameter of 3011III, and this cylindrical member was placed inside the aluminum pot. After immersing in the melt and taking it out, the solidified product was heated to 5N.
The material was gradually dissolved from the surface layer using (specified) nitric acid, and finally the coagulated material remained only in the spiral grooves. After that, 10
When heat-treated at 930°C for 30 hours in an oxygen gas flow of 0 mρ/min, this coiled oxide
Even when a current of 50 A corresponding to a current density of A/cfIf was applied, a superconducting state was exhibited.

In addition, a solenoid with similar characteristics was obtained by grinding with an endless belt with abrasive grains moving at a low speed of 1 m/min using methyl alcohol as a coolant, without using chemical dissolution. .

[Effects of the Invention] As explained above, according to the present invention, a cylindrical member made of silicon nitride in which a spiral groove is carved in advance is used, and a melt having a superconducting oxide composition is solidified in the spiral groove. The effect shown is produced.

The cylindrical member that becomes the solenoid winding core will not be damaged even if it is immersed in a high temperature melt of I>1300°C.

(2) Since a spiral groove is carved in advance and the solenoid portion is solidified within this spiral groove, even if the melt adheres to and solidifies in a portion other than the spiral groove, it can be easily removed by subsequent grinding or chemical dissolution.

■) There is no need to insulate the superconducting conductor itself.

■) When the silicon nitride cylindrical member is immersed in the melt, it slightly reacts with the oxide melt, and a buffer layer is generated at the interface that absorbs the slight difference in thermal expansion, so the melt does not solidify. Furthermore, no cracks occur in the oxide solidified product during the process of cooling down to room temperature. In addition, the crack prevention effect of the buffer layer is exhibited even in the subsequent heat treatment. As a result, the critical current density of the resulting solenoid increases.

■) Manufactured using the melt-solidification method, the resulting solenoid has a dense structure that is not porous like powder.
Critical current density increases.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an example method of the present invention, FIG. 2 is a side view of a cylindrical member, FIG. 3 is a side view of a rectangular cylindrical member on which an oxide coil is formed, and FIGS. The figure is a schematic diagram showing a conventional method.

Claims (1)

[Claims] (1) A cylindrical member made of silicon nitride with a spiral groove carved on its circumferential surface is immersed in a melt having a superconducting oxide composition, the melt is solidified in the spiral groove, and then the spiral groove is 1. A method for producing a superconducting oxide solenoid, comprising: removing coagulated material adhering to the outside of the spiral groove, and then heat-treating the coagulated material within the spiral groove to generate a superconducting oxide.