JPH0570287B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method of forming an oxide ceramic superconducting material into a coil shape.

"Conventional technology" Conventionally, superelectronic materials have been made using elements such as mercury and lead,
Alloys such as NbN, Nb ₃ Ge, Nb ₃ Ga or Nb ₃
A metal material made of a ternary element compound such as (Al _0.8 .Ge _0.2 ) is used. However, their Tc (superconducting critical temperature) onset was up to 25K.

On the other hand, ceramic-based superconducting materials have attracted attention in recent years. This material was first reported by IBM's Zurich Research Institute as a Ba-La-Cu-O (baraquo)-based oxide high-temperature superconductor, and further developed by LSCO.
It has been known as (cupric acid-lanthanum-strontium). These are (A _1-x Bx)yCuOz
Since the oxides in the oxides were simply mixed and fired, a Tc onset of only 30K could be obtained.

``Conventional problems'' However, these superconducting oxide ceramics contain many voids and grain boundaries, so it is difficult to make them into long objects such as wires, and it is difficult to bend them into coils. It was completely impossible to compose it. Also, the Tc
30K was the limit.

For this reason, this Tco (temperature at which resistance becomes zero) should be made higher, preferably at liquid nitrogen temperature (77K).
or higher temperatures, and
There has been a strong demand for endless coils for power storage or coils for superconducting magnets to be made from linear, strip, or tubular superconducting materials.

"Means to Solve the Problem" The present invention sought a method for producing superconductivity at a temperature closer to room temperature. As a result, we are trying to create something that has a long shape (having a small width or thickness and a long length) such as a linear, band-like, or tubular shape, and whose Tco is higher than the liquid nitrogen temperature. be. Such long objects are relatively bendable because they are not completely converted into ceramic before being heated and fired, but it is extremely difficult to bend them after firing. For this reason, it is characterized in that it is wound into a coil around a support before heating, and then heated and oxidized and reduced repeatedly to transform it into a superconducting material. At that time, the aim is to improve Tco by applying voltage from one side to the other and allowing a constant current to flow.

That is, the direction in which current flows easily when held at a high temperature also becomes easy to flow at an extremely low temperature, and as a result, Tco and Tc can be improved to a higher temperature.
The polycrystalline grains can be made to be substantially similar to single crystals, and the direction in which current can easily flow is also the direction in which current flows in practice. As a result, Tco (the temperature at which resistance becomes zero due to superconductivity) also
It has become clear that it can be improved to 70 to 117K.

A typical example of superconducting ceramics used in the present invention is (A _1-x Bx)yCuzOw x=0-1, y=2.0
-4.0 preferably 2.5-3.5, z=1,0-4.0 preferably 1.5-3.5, w=4.0-10.0. A uses one or more of elements selected from the yttrium group and elements selected from other lanthanoids. According to the Physical and Chemical Dictionary (Iwanami Shoten, published on April 1, 1963), the Itztriyum family includes Y (Itztriyum), Gd (Gadryum), Yb (Itzterbyum), Eu (europium), Tb (terbium),
Dy (dysprosium), Ho (holmium), Er (erbium), Tm (thulium), Lu (lutetium),
Using Sc (scandium) and other lanthanides.

Also, B is Ra (radium), Ba (bariyum),
Sr (strontium), Ca (calcium), Mg
One or more of the elements selected from (magnesium) and Be (helilium) are used.

In the present invention, the copper in one molecule has a layered structure, and the 6 atoms of copper have a layered structure, and in order to make it easier for carriers to move through this layer, (A _1-x Bx) in the structure of the present invention The elements A and B selected in yCuzOw are important. In particular, the element A is an element of the yztriyum group or a lanthanide element,
Generally, it is a group a of the periodic table of elements. The present invention is B
An element belonging to Group A of the Periodic Table of Elements is used as the element.

In the present invention, when firing a superconducting material using such an element, a current (direct current, pulsed current, or alternating current) is applied to selectively raise the temperature of only irregularities at the molecular structure level, thereby facilitating the flow of current.

In this way, A and B in the general formula are given room to choose, and one polycrystalline grain can be made larger, which in turn brings the grain boundaries closer to each other, which in turn creates a barrier. ) The configuration has been designed to make it easier to eliminate. As a result, the temperature of the Tc onset can be made even higher. The ideal is a single crystal structure.

In the present invention, starting materials such as fine powders of oxides or carbonates are mixed, and once pressurized and oxidized and fired (this is called pre-calcination). In this way, a superconducting ceramic material having a molecular structure of the (A _1-x Bx)yCuzOw type can be produced from the starting oxide or carbonate.

Further, this is pulverized again, and upon heating again, it is formed into a wire, band, or tube shape, and wound around a support in a coil shape. Alternatively, it is mixed with a liquid and the mixed solution is printed on a cylindrical support. Thereafter, the molded product or the printed matter is heated and fired.

``Operation'' The new type of ceramic superconducting material of the present invention can be made very easily. The fragile ceramics were then molded into a support, which was then fired to form a coil.

The present invention will be described below according to Examples.

"Example 1" An example of the present invention is a method in which a cylindrical support is printed by a printing method, and then heated and fired.
Here, Y was used as A and Ba was used as B.

As starting materials, yttrium oxide (Y ₂ O ₃ ) was used as a Y compound, BaCO ₃ as a Ba compound, and CuO as a copper compound. These were obtained from Kojundo Kagaku Kogyo Co., Ltd., using fine powder with a purity of 99.95% or higher, x = 0.67, y = 3, z = 3, w =
6-8 ( _YBa2 ) _Cu3O6-8 was selected _as possible. This value of w was adjusted in the subsequent firing step.

Mix these thoroughly in a mortar and encapsulate them in a capsule.
Solidify by applying a load of 30Kg/ ^cm2 (forming into tablets)
It was made into a cylindrical shape (size 5 mmφ x 15 mm). Furthermore, in an oxidizing atmosphere, e.g. 500-1200℃ in the air,
For example, heating oxidation was performed at 700°C for 8 hours. This step was called pre-firing.

This was then ground and mixed in a mortar. And the average powder particle size of the powder is 20 μm to 0.03 μm, e.g.
The size was set to 10 μm or less.

This was further mixed into a printing solution. Thereafter, printing was performed on the upper surface of a cylindrical support 10 as shown in FIG. 2 using a screen printing method, an offset printing method, an intaglio printing method, or the like.

Next, oxidation was carried out at 500 to 1200°C, for example 900°C, in an oxide atmosphere, for example air, and main firing was performed for 10 to 50 hours, for example 15 hours.

At this time, a current was applied in pulses from one side 12 to the other side 13 of the coiled ceramic 1 at a current density of 0.5 A/cm ² to 150 A/cm ² , for example 8 A/cm ² .
i.e. add 30 seconds, rest 5 minutes, add another 30 seconds, 5
I went for about 5 hours, taking several minutes off.

Next, this sample is heated in oxygen-depleted O ₂ -Ar (600-1200℃, 3-30 hours, e.g. 800℃,
°C for 20 hours) for reduction.

Using this sample, the relationship between resistivity and temperature was investigated. Then, assuming that the maximum temperature is obtained,
It was possible to observe a Tc onset of 95K and a Tco of 79K.

"Example 2" As an example of the present invention, A is Yb, B is
Ba was used. Starting materials include BaCO ₃ , CuO,
_{Yb2O3 was} used. These are x=0.67, y=3, z
= 3, w = 6 to 8 as much as possible. The value of w was adjusted in the subsequent oxidation or reduction step during firing.

These were mixed. Furthermore, a band-shaped wire was constructed using a high-speed quenching device. Regarding this high-speed quenching device, for example, "Ceramics" 15 (1980) No.
11 “Vitrification and crystallization in ultra-quenching method” 907~
Tried according to page 913. This example used a single roller method. FIG. 1 shows the drawing.

In the drawing, rapidly cooled strip-shaped superconducting material 1
In order to make this, raw materials are first put into 2 and heated from the outside with heater 4 to a temperature of nearly 2000K. After sufficient melting, air pressure 5 is applied by an air piston. The molten material 2 is then injected downward from the nozzle 3, cooled at high speed by the cooling roll 7 rotating at high speed, and formed into a strip 1.

Further, as shown in FIG. 2, one or more layers are stacked on the surface of the support 10 and wound into a coil shape.

The whole is heated and oxidized at 500 to 1200°C, for example, 900°C, in an oxidizing atmosphere, for example, in the air. Furthermore, reduction is performed to control oxygen, etc. in the compound. This firing was carried out for 3 to 50 hours, for example 10 hours. At this time, a current was applied from one end 12 of this coil to the other end 13. This current is 0.5A/cm ² ~150A/cm ²
And so. This resistance value is 10 ^-3 to 10 ^-5 S ^-1 cm, so even if the length of the coil is 10 m, the resistance is only 1 Ω, so it is possible to flow this large current.

As a result, after being configured in this coil, Tco=
Obtained 98K, Tc=115K.

"Example 3" In this example, the support 10 shown in FIG. 2 was used as the cooling roll 7 in FIG. 1. Then, as shown in Example 2, the solvent material sprayed from the nozzle 3 was wound up on this roll 7. Then, this roll 7 can be used together with the bobbin (supporting body) 10 of the coil 1 shown in FIG. It has become possible to add it when it is in a molten state, where it is most mobile.

Further, after firing this coil, as shown in Example 2, the whole was heated to obtain a value of a predetermined molecular formula (A _1-x Bx)yCuzOw. Thus,
We were able to further improve Tc onset by 3-5K.

In the present invention, it is also possible to make this ceramic into a superconductor by coating the inner wall of a cylindrical support with ceramics and applying an electric current when firing them. Moreover, this support is formed in advance into a desired shape, for example, a coil shape,
Applying a voltage to both ends of this is effective in preventing clutches from occurring in the ceramic due to bending in subsequent steps.

"Effects" According to the present invention, it has become possible to wind ceramics, which are extremely susceptible to bending, into a coil shape, which was previously considered impossible. Furthermore, it has become possible to create superconducting ceramics that can obtain Tco even at temperatures above liquid nitrogen temperature.

Furthermore, in order to make it easier to form a copper layer structure within the molecular structure of the compound of this target material, a plurality of elements a and a in the periodic table of atoms may be mixed. It is presumed that in this way, the presence of voids such as voids in the final completed compound can be more completely eliminated, and as a result, the Tc onset and Tco can be brought closer to heart sounds.

[Brief explanation of the drawing]

FIG. 1 shows a manufacturing apparatus used for manufacturing the present invention. FIG. 2 shows an example of a coil made in accordance with the present invention.

Claims (1)

[Scope of Claims] 1. A step of bringing the oxide superconducting material into a molten state, and a step of injecting the oxide superconducting material in the molten state onto a cooled substrate to form a band-shaped oxide superconducting material, A method for producing a superconducting material, comprising the steps of: firing the oxide superconducting material formed in the band shape in an oxidizing atmosphere to impart superconducting properties. 2. A method for producing a superconducting material according to claim 1, characterized in that a current is passed through the superconducting material during firing in an oxidizing atmosphere. 3. A method for producing a superconducting material according to claim 1, characterized in that the oxide superconducting material formed in a belt shape is formed into a coil shape, and then fired in an oxidizing atmosphere.