JP5541191B2 - Superconducting wire inspection method - Google Patents

Description

  The present invention relates to a superconducting wire inspection method, and more particularly to a superconducting wire inspection method having a superconducting filament and a sheath.

  Development of a superconducting wire having a superconducting filament and a sheath covering the superconducting filament has been widely promoted. This superconducting wire typically has a filament made of a Bi-based superconductor and a sheath containing Ag. In order to increase the critical current of this superconducting wire, it is necessary to improve the crystal orientation of the filament. For example, Patent Document 1 discloses such a technique.

  As described above, since the crystal orientation of the filament greatly affects the performance of the superconducting wire, a crystal orientation inspection technique is required. In general, crystal orientation is often measured by X-ray diffraction. An example of measurement of a superconducting filament by X-ray diffraction is shown in Non-Patent Document 1, for example. According to this document, X-ray diffraction measurement of a filament contained in a silver sheath is performed using high-intensity radiation light.

JP 2007-26773 A

Iihara Sequential, 9 others, “Development of firing reaction analysis technology of Bi-based superconducting wire using SPring-8”, SEI Technical Review, Sumitomo Electric Industries, Ltd., January 2008, No. 172, p. 66-70

  As described above, if high-intensity synchrotron radiation is used, X-ray diffraction measurement of the filament entering the sheath can be performed, but generation of the high-intensity synchrotron radiation requires an extremely large-scale facility. Further, even when high-intensity radiation light is used, it is not preferable that the transmission of X-rays be hindered by the sheath. This problem becomes particularly serious when a sheath containing silver that is difficult to transmit X-rays is used.

  As described above, when the sheath becomes an obstacle in the inspection of the filament, it is desired to remove the sheath before the measurement on the filament. If the main part of the filament is removed together when the sheath is removed, the original filament state cannot be inspected. On the other hand, if the removal of the sheath is performed slowly to suppress the removal of the filament, a long time is required for the inspection.

  The present invention has been made in view of this problem, and an object thereof is to provide a superconducting wire inspection method capable of quickly and accurately inspecting a superconducting filament accompanied by removal of a sheath.

  The superconducting wire inspection method of the present invention is a superconducting wire inspection method having a superconducting filament and a sheath made of silver or a silver alloy and covering the superconducting filament, and includes the following steps.

  The sheath is removed halfway in the thickness direction by the first etching solution containing nitric acid. The superconducting filament is exposed by removing the sheath removed halfway in the thickness direction by the second etching solution containing ammonia and hydrogen peroxide. The exposed superconducting filament is inspected.

  According to this inspection method, after the majority of the sheath is quickly removed by the first etching solution having a relatively high etching rate with respect to the sheath, the remaining portion of the sheath is made by the second etching solution having a relatively slow etching rate with respect to the superconducting filament. Is removed. Thereby, removal of a sheath can be performed rapidly and the quantity by which a superconducting filament is removed can be suppressed. Therefore, it is possible to quickly and accurately inspect the superconducting filament that is required to be performed after the sheath is removed.

  The inspection may be performed by irradiating the superconducting filament with X-rays. In this case, the sheath made of silver or a silver alloy that hardly transmits X-rays is removed before irradiation with X-rays. Therefore, the effective irradiation intensity of the X-ray superconducting filament can be increased.

  The inspection may be for inspecting the crystal orientation of the superconducting filament. Thereby, the crystal orientation, that is, the physical property that greatly affects the critical current of the superconducting filament can be accurately inspected.

  Preferably, the concentration of nitric acid in the first etching solution is 20 mass percent or more and 40 mass percent or less. When the concentration is 20 mass percent or more, the etching rate for the sheath can be secured to a practically sufficient level. When the concentration is 40 mass percent or less, it is possible to avoid an excessively high etching rate with respect to the sheath, so that the etching with the first etching solution can be easily stopped before the superconducting filament is exposed. .

  Preferably, the mass of hydrogen peroxide relative to the mass of ammonia in the second etching solution is not less than 30 percent and not more than 70 percent. When the mass of hydrogen peroxide relative to the mass of ammonia in the second etching solution is 30% or more, the etching rate for the sheath can be ensured to a practically sufficient level. Since the mass of hydrogen peroxide with respect to the mass of ammonia in the second etching solution is 70% or less, the etching rate for the superconducting filament can be prevented from being excessively increased, so the amount of overetching of the superconducting filament is suppressed. can do.

  According to the present invention, as described above, inspection of a superconducting filament accompanying removal of a sheath can be performed quickly and accurately.

It is a cross-sectional perspective view which shows typically the structure of the superconducting wire in Embodiment 1 of this invention. It is a fragmentary sectional view which follows the line II-II of FIG. It is a fragmentary sectional view which shows schematically the 1st process of the test | inspection process of the superconducting wire in Embodiment 1 of this invention. It is a fragmentary sectional view which shows schematically the 2nd process of the test | inspection process of the superconducting wire in Embodiment 1 of this invention. It is a fragmentary sectional view which shows schematically the 3rd process of the test | inspection process of the superconducting wire in Embodiment 1 of this invention. It is a fragmentary sectional view which shows 1 process of the test | inspection process of the superconducting wire of a comparative example. It is a cross-sectional perspective view which shows typically the structure of the superconducting wire in Embodiment 2 of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Embodiment 1)
1 and 2, superconducting wire 50 of the present embodiment has a tape-like shape having a tape surface (upper surface and lower surface in FIG. 1), and superconducting current DR along the extending direction thereof. It is what flows. Superconducting wire 50 has superconducting filament 10 and sheath 20. Superconducting filament 10 is composed of a number of plate crystals. The sheath 20 is made of silver or a silver alloy and covers the superconducting filament 10.

The plate-like crystal constituting the superconducting filament 10 is made of a Bi (bismuth) -based superconductor. The Bi-based superconductor is so-called Bi2223, that is, (Bi, Pb) ₂ Sr ₂ Ca ₂ Cu ₃ O _x . Bi2223 has an a to c axis crystallographically, and thus has an ab plane on which the a axis and the b axis extend.

  The plate-like crystal of the superconducting filament 10 has crystal orientation such that the ab surface is approximately parallel to the tape surface.

Usually, a void VD is present inside the sheath 20.
The critical current of the superconducting wire 50 becomes higher as the crystal orientation described above is higher and as the void VD is smaller.

  The sheath 20 has a particularly thick portion (the portion shown in FIG. 2) located on the outermost periphery, and a portion that enters the outer peripheral portion PA and the central portion PB of the superconducting filament 10 (the plate of the superconducting filament 10 in FIG. 1). Part sandwiched between crystal-like crystals). The thickness of the above-described particularly thick portion of the sheath 20 is, for example, about 40 μm. On the other hand, the thickness of the above-described portion of the sheath 20 that enters the inside is, for example, about several μm.

  Next, a method for inspecting the crystal orientation of the superconducting filament 10 will be described below.

  First and second etching solutions are prepared. The first etching solution contains nitric acid, and the second etching solution contains ammonia and hydrogen peroxide. Preferably, the concentration of nitric acid in the first etching solution is 20 mass percent or more and 40 mass percent or less. Preferably, the mass of hydrogen peroxide relative to the mass of ammonia in the second etching solution is not less than 30 percent and not more than 70 percent.

  Referring to FIG. 3, superconducting wire 50 is immersed in the first etching solution. Preferably, the superconducting wire 50 is turned over at an appropriate time interval. When the unevenness of the superconducting filament 10 starts to be observed, the etching is immediately stopped. Thereby, the sheath 20 is removed halfway in the thickness direction. That is, the outer peripheral side 21 of the sheath 20 is removed, and the inner peripheral side 22 is left. Thereafter, the wire is washed.

  Still referring to FIG. 4, this wire is immersed in the second etching solution. Preferably, the wire is turned over at appropriate time intervals. When the black appearance of the superconducting filament 10 starts to be observed, the etching is immediately stopped. As a result, the inner peripheral side 22 of the sheath 20 is removed, so that the superconducting filament 10, particularly the outer peripheral portion PA, is exposed. Thereafter, the superconducting filament 10 is cleaned.

  Note that the entire outer peripheral portion PA does not necessarily have to be exposed, and it is only necessary to expose a region to be inspected, which will be described later. Further, a portion of the sheath 20 sandwiched between the plate crystals of the superconducting filament 10 may remain.

  Referring to FIG. 5, the crystal orientation of the exposed superconducting filament 10 is inspected. This inspection can be performed by irradiating the superconducting filament 10 with X-rays. Since the sheath 20 made of silver or a silver alloy which hardly transmits X-rays is removed in advance by the above-described etching, the effective irradiation intensity of the X-ray superconducting filament 10 is increased.

  The inspection of crystal orientation can be performed by X-ray diffraction using a so-called omega scan. That is, the intensity of the diffracted X-ray XD with respect to the incident X-ray XI is measured while rotating the superconducting filament 10 around the axis. This axis is along the extending direction of the superconducting wire 50, that is, the superconducting current DR (FIG. 1). Thereby, the average misalignment angle of the (Bi, Pb) 2223 crystal or the like is obtained. This average misorientation angle means the average of the angles formed between the ab plane of each (Bi, Pb) 2223 crystal and the tape surface (width × length plane) of the wire. The smaller the average deviation angle of the (Bi, Pb) 2223 crystal, the higher the orientation of the (Bi, Pb) 2223 crystal.

  The crystal orientation evaluation by X-ray diffraction can evaluate the average misalignment angle in the thickness direction of the superconducting filament by using a transmission method. Further, when evaluated by the reflection method, when a Cu tube X-ray source is used, only the surface layer portion of the superconducting filament enters about 8 μm, and the average misalignment angle of only the surface layer is evaluated. Therefore, if physical treatment such as sheath stripping is performed, the surface layer of the superconducting filament is damaged, and it is difficult to accurately evaluate the crystal orientation. Therefore, it is necessary to use the technique of the present invention.

Next, the first and second etching solutions will be described in detail.
The first etching solution has a higher etching rate with respect to the sheath 20 than the second etching solution, and the second etching solution is in the superconducting filament 10 compared with the first etching solution. In contrast, it has a lower etch rate.

  Preferably, the concentration of nitric acid in the first etching solution is 20 mass percent or more and 40 mass percent or less. When the concentration is 20 mass percent or more, the etching rate for the sheath 20 can be secured to a practically sufficient level. Since the etching rate with respect to the sheath 20 is prevented from being excessively high when the concentration is 40 mass percent or less, the etching with the first etching solution is easily stopped before the superconducting filament 10 is exposed. Can do.

  Preferably, the mass of hydrogen peroxide relative to the mass of ammonia in the second etching solution is not less than 30 percent and not more than 70 percent. When the mass of hydrogen peroxide with respect to the mass of ammonia in the second etching solution is 30% or more, the etching rate for the sheath 20 can be ensured to a practically sufficient level. Since the mass of hydrogen peroxide with respect to the mass of ammonia in the second etching solution is 70% or less, it is avoided that the etching rate for the superconducting filament 10 becomes excessively high, and therefore the amount by which the superconducting filament 10 is over-etched. Can be suppressed.

  Referring to FIG. 6, if the removal of the sheath 20 described above is performed only with the first etching solution, the outer peripheral portion of the sheath 20 is caused by overetching due to the first etching solution having a high etching rate. PA is likely to be removed. In this case, the superconducting wire 50 cannot be accurately inspected.

  If the above-described removal of the sheath 20 is performed only by the second etching solution, the etching takes a long time because the second etching solution has a small etching rate with respect to the sheath 20. End up. Further, the outer peripheral portion PA may be altered. The cause is presumed that the superconducting filament 10 is immersed in the etching solution for a long time. In this case, the superconducting wire 50 cannot be accurately inspected.

  On the other hand, according to the present embodiment, the first etching liquid having a relatively high etching rate with respect to the sheath 20 is quickly removed with the first etching solution, and then the etching rate with respect to the superconducting filament 10 is relatively low. The remaining portion of the sheath 20 is removed by the etching solution 2. Thereby, the removal of the sheath 20 can be performed quickly, and the amount by which the outer peripheral portion PA of the superconducting filament 10 is removed can be suppressed. Therefore, inspection of the superconducting filament 10 required to be performed after removing the sheath 20 can be performed quickly and accurately.

(Embodiment 2)
Referring to FIG. 7, superconducting wire 51 according to the present embodiment has superconducting wire 50 described above, joining portion 30, and a pair of reinforcing portions 40. The pair of reinforcing portions 40 sandwich the superconducting wire 50 in the thickness direction. Each reinforcing portion 40 has a tape-like shape having the same thickness direction and extending direction as the tape-like shape of superconducting wire 50. The reinforcing portion 40 is made of a metal alloy such as stainless steel. Each reinforcing portion 40 is joined to the superconducting wire 50 by the joining portion 30. The joint part 30 is formed of solder, for example.

  In order to perform the same inspection as that of the first embodiment on the superconducting wire 51, it is necessary to first remove the reinforcing portion 40 and the joint portion 30. This method will be described below.

  First, the superconducting wire 51 is immersed in the third etching solution. The third etching solution contains hydrochloric acid. The concentration of hydrochloric acid is, for example, 15 to 20 mass percent.

  Next, hydrogen peroxide solution is dropped while the superconducting wire 51 is turned over at an appropriate time interval. The concentration of the hydrogen peroxide solution is, for example, 30 to 40 mass percent. Thereby, bubbles start to be released from the superconducting wire 51, and the third etching solution starts to turn yellow. When the appearance of the wire becomes uniform black, the wire is taken out from the third etching solution. Thereby, the reinforcement part 40 and the junction part 30 are etched. The time required for this etching is, for example, 3 to 5 minutes.

  Since the configuration other than the above is substantially the same as the configuration of the first embodiment described above, the same or corresponding elements are denoted by the same reference numerals, and description thereof is not repeated.

  In each of the above embodiments, the superconducting wire 50 or 51 having a tape shape is inspected, but a superconducting wire having a shape other than the tape shape may be inspected. For example, a superconducting wire having a circular cross section is inspected. May be. Further, in each of the above embodiments, the completed superconducting wire 50 or 51 is inspected, but a superconducting wire in the middle of manufacture may be inspected.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  10 superconducting filament, 20 sheath, 30 joint, 40 reinforcing part, 50, 51 superconducting wire.

Claims (5)

A method for inspecting a superconducting wire having a superconducting filament and a sheath made of silver or a silver alloy and covering the superconducting filament,
Removing the sheath partway in the thickness direction with a first etching solution containing nitric acid;
A step of exposing the superconducting filament by removing the sheath removed halfway in the thickness direction by a second etching solution containing ammonia and hydrogen peroxide;
And a step of inspecting the exposed superconducting filament.   The superconducting wire inspection method according to claim 1, wherein the inspecting step is performed by irradiating the superconducting filament with X-rays.   The method for inspecting a superconducting wire according to claim 1 or 2, wherein the inspecting step is for inspecting the crystal orientation of the superconducting filament.   The superconducting wire inspection method according to claim 1, wherein the concentration of nitric acid in the first etching solution is 20 mass percent or more and 40 mass percent or less.   The superconducting wire inspection method according to any one of claims 1 to 4, wherein a mass of hydrogen peroxide relative to a mass of ammonia in the second etching solution is 30 percent or more and 70 percent or less.

Images