JPH05144626A - Insulating material for superconducting oxide wire and manufacture of insulated wire - Google Patents

Abstract

PURPOSE:To provide the title manufacturing method of insulating material of superconducting oxide wire capable of increasing the insulating strength and thinning the thickness of the insulating layer without losing the superconducting characteristics of inner superconductor as well as the wire using this insulating material. CONSTITUTION:A superconducting oxide wire rod sheathed by an insulating material of the wire rod containing 30-100wt.% of silicon oxide or at least one or more elements out of Al2O3, BeO, ThO2, MgO, MgAl2O4, ZrO2, Si3N4, etc., as the other components and a metal mainly comprising metallic silver is coated with a kneaded material comprising a cloth or an organic binder and the insulating material or a sol to be turned into an oxide by decomposition. Furthermore, an insulated wire is to be manufactured by baking the insulating material at the temperature of 3-20 deg.C higher than the optimum baking temperature of not insulated wire rod.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insulating material for a wire for winding an oxide superconducting wire into a superconducting coil and a method for producing an insulated wire.

[0002]

2. Description of the Related Art As an insulating material for a conventional metal-based or compound-based superconducting wire such as NbAl or Nb ₃ Sn, the main component is SiO ₂
Quartz is commonly used and has a proven track record in terms of strength. However, in most cases, alumina is used as the insulating material for the oxide superconducting wire.

In the insulation process of an oxide superconducting wire, an oxide superconducting wire which is sheathed with a metal mainly composed of metallic silver is covered with a non-woven fabric of alumina fiber which is an insulating material, and subsequently wound in a coil shape. In order to fire the superconductor inside the sheath, the insulator is also subjected to the firing process at the same time. Therefore, as described above, a heat-resistant ceramic material is used as an insulating material for the oxide superconducting wire because it undergoes a heat treatment step. These technologies are described in, for example, magazines (Nikkei Superconductivity 1990.12.10, p.12-1).
3) and so on.

[0004]

Quartz, whose main component is SiO ₂ , has no problem in strength, but when it is applied to an oxide superconducting wire, the characteristics of non-insulating material, for example, the critical current of the wire, are extremely lowered.

On the other hand, the insulating material mainly composed of alumina has a problem that its strength is weak. The biggest cause of weakness is that alumina is not sintered in the firing process. Rather, the non-woven fabric of alumina fibers tends to be shattered during the firing process, resulting in a decrease in strength. Further, when a non-woven fabric of alumina fiber is not used, for example, even in a method of kneading powder with an organic binder and applying it, although there is a slight improvement in the adhesive force, in the end, since alumina does not sinter, the coating film is not formed. It easily breaks and is easily short-circuited. Another problem is that alumina fibers have low bending strength, and it is difficult to form thin and long fibers, which makes it difficult to obtain thin and dense nonwoven fabrics, which makes them expensive. This is very disadvantageous in terms of coil design, because the insulating layer becomes thicker, and compact and dense winding cannot be performed, and the magnetic field generated by the coil is determined by the capacity and the number of windings.

The present invention has been made to solve such a problem, and it is easy to increase the insulation strength and reduce the thickness of the insulating layer without impairing the superconducting characteristics of the internal superconductor. It is an object of the present invention to provide an insulating material for an oxide superconducting wire and a method for manufacturing a wire insulated by the insulating material, which are capable of achieving the above.

[0007]

The insulating material of the oxide superconducting wire according to the present invention contains silicon oxide in an amount of 30% by weight or more and 10% by weight or more.
Containing 0% by weight or less, and depending on the case, at least one or more of Al ₂ O ₃ , BeO, ThO ₂ , MgO, MgAl ₂ O ₄ , ZrO ₂ and Si ₃ N ₄ as other components. Is.

Further, an oxide superconducting wire which is sheathed with a metal composed mainly of metallic silver is insulated with the insulating material of the present invention.

The method of manufacturing an insulated wire according to the present invention is a method in which an oxide superconducting wire which is sheathed with a metal mainly composed of metallic silver is used as a paste or decomposed by kneading an insulating material with a cloth or an organic binder. It is coated with sol, which becomes an oxide, and fired at a temperature that is 3 ° C to 20 ° C higher than the optimum firing temperature of the non-insulated wire.

[0010]

[Function] By containing 30% by weight or more and 100% by weight or less of silicon oxide, the adhesive force of the insulating layer is remarkably improved. Upon investigating the cause of this, it was found that the metallic silver diffused to the very thin interface of the insulating layer to form a compound layer, so that SiO ₂ was firmly bonded. In addition, as other components, Al ₂ O ₃ , BeO, ThO ₂ , MgO, MgAl ₂ O ₄ , ZrO ₂ , Si
_{When 3} N ₄ is contained, they do not have a binding action like SiO ₂ , but they are added at the same time as SiO ₂ so that the compound layer binds these additives. ..

Containing 30% by weight or more and 100% by weight or less of silicon oxide has a merit in the process such that a relatively long fiber can be easily obtained and various coating methods can be performed.

The present inventors have clarified the cause that the insulating material containing SiO ₂ deteriorates the superconducting property. It was found that Si never diffuses into the silver sheath and exerts an adverse effect, but merely raises the melting point of the superconductor.
Oxide superconducting materials are very sensitive to firing temperature,
Therefore, it was found that good superconducting properties were not obtained. Therefore, in the present invention, since the insulating material is fired at a temperature higher by 3 ° C. to 20 ° C. than the optimum firing temperature of the wire material that does not insulate, characteristic deterioration due to a higher melting point can be avoided and good superconducting characteristics can be obtained.

The addition of additives can be controlled so as to reduce the shift of the melting point to the high temperature side. That is, the firing temperature at which good characteristics can be obtained becomes too high due to insulation, and the additive works effectively in order to maximize the temperature margin with the melting point of silver.

[0014]

EXAMPLES The present invention will be described in detail below with reference to examples and comparative examples.

Example 1 A superconductor having a composition of Bi ₂ Sr ₂ CaCu ₂ Oy is coated on a silver sheathed tape having a thickness of 0.3 mm and a width of 3 mm with a slurry containing an insulating material. The composition of the slurry was SiO ₂ : Al ₂ O ₃ = 4: 1 in weight ratio, and a powder having an average particle size of 20 μm was kneaded with a solution of methylcellulose dissolved in a solvent to prepare a slurry. A 1.2 m long silver sheath tape is dipped into the slurry to form a coating film.
It was dried at 150 ° C for 20 minutes. After drying, it was wound on an alumina bobbin having an outer diameter of 35 mm. Furthermore, this thing in the atmosphere, 890
After firing at 30 ° C. for 30 hours, it was gradually cooled to obtain an oxide superconducting coil for measuring characteristics of Example 1. The optimum firing temperature for non-insulated wires is 875-880 ° C.

The thickness of the insulating layer after firing was 30 μm.
The adhesion and strength of the insulating layer were good as a result of a scratch test.

Next, the critical current at 20 K was measured by the 4-terminal resistance method. The current terminal was set to the longest distance of the wire, and the voltage terminal was soldered 3 cm away from the current terminal. The measurement results are shown in FIG. FIG. 1 shows the critical current-external magnetic field characteristics of the wire. In the figure, a is a characteristic curve of the first embodiment.

[Comparative Example 1] In the same manner as in Example 1, Bi ₂ S
A superconductor of r ₂ CaCu ₂ Oy composition with a silver sheath thickness of 0.3 mm,
A tape having a width of 3 mm is coated with a slurry containing an insulating material having the same composition as in Example 1. Next, a 1.2 m long silver sheath tape is dipped into the slurry to form a coating film, and the coating film is removed.
It was dried at 150 ° C for 20 minutes. After drying, it was wound on an alumina bobbin having an outer diameter of 35 mm. Furthermore, this thing in the atmosphere, 880
After firing at 30 ° C. for 30 hours, it was gradually cooled to obtain an oxide superconducting coil for measuring characteristics of Comparative Example 1.

The thickness of the insulating layer after firing was 30 μm.
The adhesion and strength of the insulating layer were good as a result of a scratch test.

Next, the critical current at 20 K was measured by the 4-terminal resistance method. The current terminal was set to the longest distance of the wire, and the voltage terminal was soldered 3 cm away from the current terminal. The measurement results are shown in FIG. FIG. 1 shows the critical current-external magnetic field characteristics of the wire. In the figure, b is the characteristic curve of Comparative Example 1.

[Comparative Example 2] Bi ₂ S
A superconductor of r ₂ CaCu ₂ Oy composition with a silver sheath thickness of 0.3 mm,
A tape having a width of 3 mm was wound around an alumina bobbin having an outer diameter of 35 mm so that the wires did not come into contact with each other without insulation. Further, this was fired in air at 880 ° C. for 30 hours and then gradually cooled to obtain an oxide superconducting coil for measuring characteristics of Comparative Example 2.

Next, the critical current at 20 K was measured by the 4-terminal resistance method. The current terminal was set to the longest distance of the wire, and the voltage terminal was soldered 3 cm away from the current terminal. The measurement results are shown in FIG. FIG. 1 shows the critical current-external magnetic field characteristics of the wire. In the figure, c is the characteristic curve of Comparative Example 2.

Comparative Example 3 A superconductor having a composition of Bi ₂ Sr ₂ CaCu ₂ Oy is applied to a silver sheathed tape having a thickness of 0.3 mm and a width of 3 mm with a slurry containing an insulating material. The slurry was prepared by kneading a powder of Al ₂ O _{3 having} an average particle size of 20 μm with a solution in which methyl cellulose was dissolved in a solvent to prepare a slurry. Length 1.2m
The silver sheath tape of 1 was dipped in the slurry to form a coating film. The coating film was dried at 150 ° C. for 20 minutes, and after drying, it was wound on an alumina bobbin having an outer diameter of 35 mm. Further, this was baked in air at 880 ° C. for 30 hours and then gradually cooled.

The thickness of the insulating layer after firing is 30 μm to 0 μm
Met. This is because the insulating layer was easily peeled off during the work, and a part of the wire was short-circuited. Therefore, a sample wound so that the wires do not come into close contact with each other was re-produced to obtain an oxide superconducting coil for measuring characteristics of Comparative Example 3.

Next, the critical current at 20 K was measured by the 4-terminal resistance method. The current terminal was set to the longest distance of the wire, and the voltage terminal was soldered 3 cm away from the current terminal. The measurement results are shown in FIG. d is the insulation characteristic of Comparative Example 3.

In FIG. 1, the wire coated with the insulating material of Example 1 of the present invention by the method of the present invention has almost the same characteristics as those of Comparative Example 2 in which no insulation is applied, and there is no deterioration of characteristics due to insulation. That is clear. Further, in Comparative Example 1 in which the insulating material of the present invention is coated by the conventional insulating method, the characteristics are significantly deteriorated by insulation, and it is clear that the insulating method of the present invention is effective. Furthermore, with conventional insulation,
In Comparative Example 3 based on the conventional method, the characteristic deterioration was relatively small, but the strength of the insulating material was lacking, so that it was not suitable for practical use.

Example 2 A superconductor having a composition of Bi ₂ Sr ₂ Ca ₂ Cu ₃ Oy was silver-sheathed, and a tape having a thickness of 0.3 mm and a width of 3 mm was coated with SiO 2.
_Two fibers were coated with a woven cloth. The cloth has a thickness of 100 μm. As in Example 1, the alumina bobbin having an outer diameter of 5 mm was wound. Furthermore, this product was stored in the atmosphere at 860 ℃, 30
After firing for a period of time, it was gradually cooled to obtain an oxide superconducting coil for measuring characteristics of Example 2. The adhesion and strength of the insulating layer were good.

Next, the critical current at 77K was measured by the 4-terminal resistance method. The current terminal was set to the longest distance of the wire, and the voltage terminal was soldered 3 cm away from the current terminal. The measurement results are shown in FIG. FIG. 2 shows the critical current-external magnetic field characteristics of the wire. In the figure, e is the characteristic curve of the second embodiment.

[Comparative Example 4] A superconductor having a composition of Bi ₂ Sr ₂ Ca ₂ Cu ₃ Oy was silver-sheathed, and a tape having a thickness of 0.3 mm and a width of 3 mm was coated with SiO 2.
_Two fibers were coated with a woven cloth. The cloth has a thickness of 100 μm. As in Example 1, the alumina bobbin having an outer diameter of 5 mm was wound. In addition, this was placed in the atmosphere at 845 ℃, 30
After firing for a period of time, it was gradually cooled to obtain an oxide superconducting coil for measuring characteristics of Comparative Example 4. The adhesion and strength of the insulating layer were good.

Next, the critical current at 77K was measured by the 4-terminal resistance method. The current terminal was set to the longest distance of the wire, and the voltage terminal was soldered 3 cm away from the current terminal. The measurement results are shown in FIG. FIG. 2 shows the critical current-external magnetic field characteristics of the wire. In the figure, f is the characteristic curve of Comparative Example 4.

As is clear from FIG. 2, in the second embodiment,
The insulating material coating method and the type of superconductor are different from those in Example 1, but the same effects are exhibited.

It should be noted that silicon oxide is contained in an amount of 30% by weight or more and 100% by weight or less, and the other components include Al ₂ O ₃ , BeO, ThO ₂ ,
When at least one of MgO, MgAl ₂ O ₄ , ZrO ₂ and Si ₃ N ₄ is contained, it is effective in adjusting the heat treatment temperature after insulation. That is, the present inventors have confirmed by experiments that the firing temperature can be lowered as the content of silicon oxide decreases.

[0033]

Since the present invention is constructed as described above, it has the following effects.

Silicon oxide is contained in an amount of 30% by weight or more and 100% by weight or less, and Al ₂ O ₃ and B may be added as other components depending on the case.
Since it contains at least one kind of eO, ThO ₂ , MgO, MgAl ₂ O ₄ , ZrO ₂ , Si ₃ N _4, etc., it is possible to perform insulation sufficiently and firmly.

Since the oxide superconducting wire which is sheathed with a metal composed mainly of metallic silver is insulated, the adhesion with the insulating material is good.

An oxide superconducting wire which is sheathed with a metal mainly composed of metallic silver is coated with an insulating material by a cloth or a kneaded product of an organic binder and an insulating material or a sol which becomes an oxide by decomposition and is insulated. Since it is fired at a temperature 3 to 20 ° C. higher than the optimum firing temperature of the non-insulated wire, it is possible to achieve the same characteristics as the wire without insulation.

[Brief description of drawings]

FIG. 1 is a graph showing the critical current-external magnetic field characteristics of the wire rods obtained in Example 1 and Comparative Examples 1 to 3.

FIG. 2 is a graph showing the critical current-external magnetic field characteristics of the wire rods obtained in Example 2 and Comparative Example 4.

Claims (3)

[Claims] 1. Containing 30% by weight or more and 100% by weight or less of silicon oxide, and in some cases Al as another component.
An insulating material for an oxide superconducting wire, which contains at least one or more of ₂ O ₃ , BeO, ThO ₂ , MgO, MgAl ₂ O ₄ , ZrO ₂ , Si ₃ N ₄ . 2. The insulating material according to claim 1, which insulates an oxide superconducting wire which is sheathed with a metal mainly composed of metallic silver. 3. An oxide superconducting wire, which is sheathed with a metal mainly composed of metallic silver, is coated with an insulating material with a cloth or a kneaded material of an organic binder and an insulating material, or a sol which becomes an oxide by decomposition. The method for producing a wire insulated with an insulating material according to claim 1, wherein the firing is performed at a temperature higher by 3 to 20 ° C than the optimum firing temperature of the non-insulated wire.