JPH03155103A - Manufacture of oxide superconductive ceramics coil - Google Patents

Abstract

PURPOSE:To acquire an oxide superconductive ceramics coil having remarkably high critical current density by releasing a superconductive ceramics material having a heat plastic body from a mold and by burning it after injection molded to a coil-like cavity with a magnetic field applied in the radial direction. CONSTITUTION:For example, polystyrene is mixed with a fine powder of YBa2 Cu3Ox, an oxide superconductor and kneaded while heating to form a pellet by pressure molding. A mold defines a coil-like cavity 7 using a Permendur-made central rod 9 and nonmagnetic body-made split molds 1, 2. A pellet is injected to an injection molding device, heated to 200 deg.C, and plasticized; an injection pressure is applied to make it attain an end edge part 4 through a starting edge part 5 of a coil-like cavity and cooled. During the time, a current is made to flow to an excitation coil 10 and a magnetic field is applied continuously in the radial direction to a coil-like molded body part by the central rod 9 and a tubular part of Permendur-made ball pieces 11, 12. The acquired coil-like molded body is burned under an oxygen atmosphere. Meanwhile, 13 expresses a nonmagnetic part.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for manufacturing a superconducting ceramic coil having a high critical current density and used in a superconducting magnet or the like using superconducting ceramics.

<Prior art> Currently, the Y-Ba-Cu-0 system (Tc""90K) is used as a material whose superconducting transition temperature T exceeds the liquid nitrogen temperature of 77K.
), B1-3r-Ca-Cu-0 system (T, ~110
K), TI-Ba-Ca-Cu-0 system (T, ~
Ceramic materials such as 125 K) are known, and many institutions are actively researching and developing them with the aim of putting them into practical use in 1977.

The biggest i1 for the practical application of oxide-based superconducting ceramics!
One of the issues is to improve the critical current density Je.

One of the effective ways to improve J in polycrystalline ceramics is to orient the crystal orientation.

By the way, the above-mentioned oxide superconductor has J in the a-b plane,
is known to be larger than Jc in the C-axis direction by more than mm, for example, 7.17. Dinger et al., Phys.
Rev. Lett., 58.2687 (198
7).

Therefore, even in polycrystalline ceramics, by orienting the crystal a-b plane along the direction of current flow, it is expected that Jc will be significantly improved compared to when the crystal orientation is random. By the way, oxide superconductors have poor plasticity compared to conventional metal-based materials, so conventional technology involves grinding oxide superconducting ceramics into powder and dispersing it in an organic binder that has plasticity or thermoplasticity. A method of forming a coil into a coil shape and then firing it (Japanese Patent Application Laid-Open No. 63-299209, JP-A No. 64-1740)
7, etc.), or a method of mechanically processing ceramics fired into a cylindrical shape into a coil shape (Japanese Unexamined Patent Application Publication No. 1983-1999).
64303, etc.) were used.

However, these conventional methods have the disadvantage that a high critical current density cannot be obtained because the orientation of the ceramic crystal grains constituting the coil is random.

<The invention tries to solve i! Problem 1> An object of the present invention is to overcome the drawbacks of the prior art as described above and to provide a method for manufacturing an oxide superconducting ceramic coil having a higher critical current density.

Means for Solving the Problems> That is, the present invention provides a material made of a thermoplastic resin that has a property in which the crystal C axis is oriented parallel to an external magnetic field and whose oxidation erection disappears at the firing temperature of conductor fine powder and ceramics. , characterized in that when injection molding is performed using a mold having a coiled cavity, a magnetic field is applied in a radial direction to the central axis of the molded body to perform the molding, and then the molded body is fired. This is a method for manufacturing an oxide superconducting ceramic coil.

<Function> In the present invention, first, a thermoplastic ceramic material is prepared by mixing fine powder of an oxide superconductor and a synthetic resin or other binder, and then placed in a mold having a coil-shaped cavity. The coiled ceramic material is molded by injection. During this injection molding process, a magnetic field is applied radially to the axis of the coil. Thereafter, the coil-shaped ceramic molded body is released from the mold described above and fired in an atmosphere at a predetermined temperature to obtain a ceramic coil.

Here, a mixture of fine powder of an oxide superconductor and a thermoplastic resin is used as the thermoplastic ceramic material.

As the fine powder of the oxide superconductor used, for example, RB
azCusO, (R=Y, Nd, SIm.

11°, x=6.5 to 7), which has the property of being oriented so that the crystal C axis is parallel to the external field. JoM, Ferreira et al. A
ppl.

Other oxide superconductors of this type are described in Phys, A47.105 (1988).

The present invention takes advantage of this property, and because of this property, by performing the injection molding process with a radial magnetic field applied to the axis of the coil, the a-b plane of the crystal is aligned with the circle of the coil. Orient along the circumferential direction. In other words, among the crystal axis directions of the oxide superconductor, the a-b plane with high Jc is oriented along the direction in which current actually flows through the coil, so compared to conventional superconducting ceramic coils in which the crystal orientation is random, J becomes significantly higher. It is preferable that each powder particle of the oxide superconductor powder used is a single crystal.

In the present invention, thermoplastic resins include at least the firing temperature of ceramic materials (900'
For example, polyethylene, nylon, polystyrene and the like are suitable. Further, as the method of applying the magnetic field in the radial direction, any method generally used in the conventional production of plastic magnets can be applied. Further, the applied magnetic field may be a steady magnetic field or an intermittent pulsed magnetic field, and the stronger the magnetic field, the more effective it is.

In the present invention, injection molding is used as the molding method, so by changing the mold, any diameter, pinch, or
It has the advantage that a coil with a large number of turns can be produced. Also,
It also has the advantage of being less prone to cracking and cracking since no machining is required after firing.

The present invention will be explained in more detail below with reference to Examples. In the following description, materials, shapes, and numerical conditions are specified to facilitate understanding of the present invention, but the present invention is not limited to these conditions.

<Example> First, a ceramic material for injection molding was adjusted as follows.

Y, Ba, Cu acetate Yla:Cu=1:2:
After weighing so that the molar ratio is 3, add distilled water to make about 51.
% aqueous solution. This was sprayed into hot air at 150° C. using a two-fluid nozzle with a diameter of 70 pffi to obtain a dry powder. After calcining this powder in the air at 900'CX for 12 hours, it was milled into YBa powder with an average particle size of 5 pts using an air flow mill.
A fine powder of zCLlsOw was obtained. It was confirmed by observation using a polarizing microscope that the powder particles were single crystals.

Next, 5 wt% of polystyrene was mixed with the above fine powder, kneaded while heating with a kneader, and this mixed material was pressure molded to produce a pellet of about 3φ x 5f (ij),
A thermoplastic ceramic material for injection molding was obtained.

Next, injection molding was performed using this material. First for molding
The mold shown in the figure was used. The center rod 9 is made of permendur, the split molds 1 and 2 are made of a non-magnetic material, and a coiled cavity 7 is defined. This mold was placed in the 11th
It was attached to the magnetic field generator as shown in FIG. 2 in abutting state like fl. The device consists of a pole piece 11, 12 made of permendur and an excitation coil 10. The non-magnetic portion 13 is provided to improve the radial properties of the magnetic field in the coiled molded body portion.

Next, in order to prevent the above-mentioned thermoplastic ceramic material from solidifying in the cavity 7 during the injection molding process, the mold portion was heated to 200° C. using a heater. After that,
While maintaining the above-mentioned state, the nozzle touch 8 disposed in the apparatus was connected to a nozzle of an injection molding machine (not shown). On the other hand, the above-mentioned pellet-shaped ceramic material is put into the injection molding machine, and the heating mechanism installed in the molding machine heats the ceramic material to 200°C to plasticize it. A predetermined injection pressure is applied depending on the viscosity, hardness, and other design of the ceramic material, and the ceramic material passes through the starting end 5 of the coiled cavity and into the terminal end 4 in the direction shown by arrow P in FIG.
The injection molding machine was operated until .

In order to take out the ceramic material filled in the cavity 7 and held in the coil shape, the mold part is heated to a temperature at which the heated and plasticized material hardens with the center rod 9 fitted. was left to cool.

In the series of molding steps described above, a current is passed through the excitation coil 10, and a magnetic field of about 1.57 is intermittently applied in the radial direction to the coiled molded body by the center rod 9 and the cylindrical portion of the pole piece 12. It was to so.

The coil-shaped molded body obtained through the above-described molding process was fired in an oxygen atmosphere using the heat pattern shown in FIG. 3 to produce a superconducting ceramic coil.

Next, a coil-shaped molded body as a comparative example was simultaneously fired using the same thermoplastic ceramic material without applying any magnetic field during the molding process.

The measurement results of Jc at 77 for both are shown in Table 1. From Table 1, it can be seen that the present invention achieves several times improvement in J.

Table 1 <Effects of the Invention> According to the present invention, a superconducting ceramic material containing a thermoplastic is injection molded into a mold having a coiled cavity while a magnetic field in the radial direction is applied, and then the coil is By releasing the shaped body from the mold and firing it, J
A superconducting coil in which the a-b planes of crystals with high c are oriented in the circumferential direction can be obtained.

Therefore, an oxide superconducting ceramic coil with a significantly higher critical current density can be obtained than an oxide superconducting ceramic coil with random crystal orientation produced by conventional techniques.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of the coil molding mold used in the example, Fig. 2 is a schematic diagram of the small injection molding device in a radial magnetic field, and Fig. 3 is a schematic diagram of the coil molding mold used in the example. This is the heat pattern used. DESCRIPTION OF SYMBOLS 1... First split mold, 2... Second split mold, 3... Air vent hole, 4... Termination part, 5... Spiral cavity, 6... Mold (non-magnetic material), 7... Starting end, 8... Nozzle touch, 9... Center rod (ferromagnetic material), lO... Excitation coil, 11... First pole Piece, 12...Second pole piece, 13...Nonmagnetic material.

Claims (1)

[Claims] When injection molding a material consisting of an oxide superconductor fine powder whose crystal C axis is oriented parallel to an external magnetic field and a thermoplastic resin that disappears at the firing temperature of ceramics using a mold with a coiled cavity. A method for producing an oxide superconducting ceramic coil, comprising: applying a magnetic field in a radial direction to the central axis of the molded body to mold the body; and then firing the molded body.