JPH0825249B2 - Bismuth superconducting-precious metal laminate - Google Patents

Description

TECHNICAL FIELD The present invention relates to a bismuth-based superconducting-noble metal laminate in which a bismuth-based superconducting layer is formed on a noble metal substrate.

[Conventional technology]

In recent years, oxide superconductors have attracted attention due to their high critical temperature (Tc), and are expected to be used in various fields such as electric power, magnetic resonance computerized tomography (MRI: Magnetic Resonance Imaging), and magnetic shielding. Has been done. Among oxide superconductors, bismuth-based (hereinafter simply referred to as Bi-based) superconductors such as Bi-Sr-Ca-Cu-O oxides have a particularly high Tc, and research and development using them are actively conducted. .

Conventionally, it has been proposed to use an oxide superconductor for a structure by forming an oxide superconductor layer on a substrate such as metal or ceramics. Various methods for forming a Bi-based superconductor layer on a metal substrate have been proposed, for example, Japanese Patent Laid-Open No. 64-82597.
In Japanese Patent Laid-Open No. 1-252533 and Japanese Patent Laid-Open No. 1-252533, it is proposed that a noble metal such as Ag, Au, or Pt is used as a substrate and a Bi-based superconductor layer is laminated thereon.

[Problems to be Solved by the Invention]

However, noble metals that are chemically stable and have plastic deformability with the Bi-based superconductor have good adhesion to the Bi-based superconducting layer and form a good laminate, but the coefficient of thermal expansion from room temperature to 900 ° C is , The noble metal is 20-22 × 10 ^-6 / ° C, and the Bi-based superconductor is 13-14 × 10 ^-6 / ° C, so that the rapid cooling to the liquid nitrogen temperature that develops superconducting properties is repeated. When applied to a cycle state with a high speed, a large internal stress remains at the laminated interface due to the difference in thermal expansion between the two.

Therefore, there is a problem such as inferior thermal shock resistance such as cracking in the laminated body, and conventionally, as a countermeasure, it is also possible to reduce the generated stress by reducing the thickness of the Bi-based superconducting layer, If the Bi-based superconducting layer is thinned, new problems such as poor magnetic shielding ability will occur.

The inventors have found that the internal stress generated in a Bi-based superconducting-noble metal laminate in which a Bi-based superconductor is laminated on a noble metal substrate is locally significant especially at the end of the laminate. The present invention has been completed. That is, the present invention eliminates the above-mentioned drawbacks due to the difference in thermal expansion between the noble metal substrate and the Bi-based superconducting layer, eliminates the superconducting layer without making it thin, and has excellent thermal shock resistance. Superconductivity
A precious metal laminate is provided.

[Means for solving the problem]

According to the present invention, in a bismuth-based superconducting-noble metal laminate in which a bismuth-based superconducting layer having a thickness of 100 μm to 5 mm is formed on a noble metal substrate having a thickness of 300 μm to 2 mm, the thickness of the bismuth-based superconducting layer is There is provided a bismuth-based superconducting-noble metal laminate characterized by being reduced in the end portion of the laminate in the region of 1% to 5% of the length of the laminate.

 Hereinafter, the present invention will be described in more detail.

The substrate of the bismuth-based superconducting-noble metal laminate of the present invention is
So-called noble metals Ag, Au, Pt, Pd (palladium) and their alloys are used, and Ag is industrially preferable.

The composition of the Bi-based superconductor in the present invention is not limited, and examples include low Tc phase Bi ₂ Sr ₂ CaCu ₂ O _x and high Tc.
Composition represented by Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _x , composition containing lead (Pb), antimony (Sb), etc., composition deviating from stoichiometric composition, main elements partially with other elements Alternatively, it may be any Bi-based superconductor having a composition in which all are replaced.

The laminated body of the present invention can be applied to any shape body having an end portion, except a shape body having no end portion such as a sphere,
The shape is not particularly limited. Generally, a cylindrical shape and a flat plate shape are mentioned.

The cylindrical body is not limited to a circular cross-sectional shape, but includes ones having various cross-sectional shapes such as an elliptical shape, a polygonal shape, a gourd shape, and a shape in which a plurality of cylindrical bodies are combined. Also, the form in the longitudinal direction is not particularly limited, and various forms such as a right cylindrical shape and a conical shape can be adopted. Furthermore, it may be penetrating or bottomed, and the bottom is not particularly limited, such as a flat bottom or a round bottom.

Further, the plate-like body is not limited to a square, but may be any shape such as a rectangle, a polygon, a circle, an ellipse, and a cloud.

In the present invention, the Bi-based superconducting layer formed on the noble metal substrate is a Bi-based superconductor raw material powder, for example, powders of bismuth, calcium, strontium and copper metal oxides, carbonates, hydroxides, metal alkoxides and nitrates. A mixed powder compounded to form an oxide superconductor by firing,
A powder consisting of a Bi-based superconducting crystal phase obtained by calcining the mixed powder at 800 to 950 ° C, a calcined intermediate product powder that is calcined at 400 to 800 ° C so as to exhibit superconducting properties by firing, and mixed. Any known forming method such as a spray coating method, a powder coating method, a doctor blade method, or a thermal spraying method may be used using a powder frit powder or a mixed powder thereof.

The laminated body end portion of the present invention refers to, for example, the upper and lower portions of the through cylindrical body or the entire peripheral portion of the flat body.

As shown in FIG. 4, the conventional superconducting layered body has, for example, a layered body 1 in which a Bi type superconducting layer 3 is layered on an Ag substrate 2, and the end 4 of the base 2 and the end of the Bi type superconducting layer No. 5 was formed similarly to the whole laminated body.

On the other hand, the present invention, the thickness of the Bi-based superconducting layer in the region located a predetermined distance from the end is formed thinner than other regions, the local expansion caused by the difference in thermal expansion coefficient between the Bi-based superconductor and the noble metal substrate. Relieves internal stress. In this case, various methods can be applied to reduce the thickness of the Bi-based superconducting layer. For example, as shown in FIG. 1 or FIG. Is formed so as to be linearly or concavely inclined in the direction of the end 4 of the Ag substrate 2 so as to reduce the Bi-based superconducting layer in a portion located in a predetermined region from the end of the laminated body in the direction of the end. Then, it is preferable to make the thickness thinner than the other regions of the laminate.

Further, in the laminated body of the present invention, the thickness of the Bi-based superconducting layer may be reduced in the end regions, and at the same time, the thickness of the noble metal substrate may be reduced in the same end regions. For example,
As shown in FIG. 3, the end 5 of the Bi-based superconducting layer 3 is first
Similar to the figure, the wall thickness can be reduced by linearly inclining the end 4 of the Ag substrate 2 and giving it a slight curvature.

Furthermore, when the thickness of the Bi-based superconducting layer is reduced toward the end of the laminated body, if the end is only the noble metal base portion, local stress will be generated in that portion, which is not preferable. Therefore, it is preferable to avoid such a state, or to reduce the thickness of the base body in the portion that is only the noble metal base body in the end direction.

In the present invention, as described above, the thickness of the Bi-based superconducting layer and / or the noble metal substrate is reduced in the predetermined region at the end of the laminated body as compared with other regions. Therefore, in the present invention, the ratio of the thickness of the Bi-based superconducting layer to the thickness of the noble metal substrate is constant over the entire laminate or decreases in the end direction. When the thickness ratio between the noble metal substrate and the Bi-based superconducting layer is constant, it can be appropriately selected according to the purpose of use, etc. within the range of about 0.05 to 17 as described below. Also,
Even in the case of decreasing the amount, it is preferable in principle to set it within the above range.

The region located at a predetermined distance from the end portion that reduces the thickness of the Bi-based superconducting layer is, from each end portion, for example, in the case of a shape body having a long axis such as a cylindrical shape, the length in the long axis direction 1% to 5
%, Preferably 2% to 5%, and about 1% to 5%, preferably 2% of the distance between opposing sides in the case of a flat plate.
It is preferable that the position has a length of ˜5%. If the area is narrower than 1%, stress reduction at the end is insufficient, which is not preferable, and if the area exceeds 5%,
The internal stress generated at the interface between the Bi-based superconducting layer and the noble metal substrate is almost constant and is not affected by the local stress.

In the laminated body of the present invention, the noble metal substrate preferably has a thickness in the range of 300 μm to 2 mm except for a predetermined region at the end. 300μ
If it is less than m, the strength of the substrate is insufficient, and if it exceeds 2 mm, it is not practical in terms of cost. The thickness of the Bi-based superconducting layer is preferably in the range of 100 μm to 5 mm except for the predetermined region at the end. If it is less than 100 μm, the superconducting properties may be insufficiently expressed, and it is particularly unsuitable as a magnetic shield material. If it exceeds 5 mm, peeling or cracking of the Bi-based superconducting layer may occur, and sintering may not proceed uniformly, and sufficient superconducting properties may not be obtained, which is not preferable.

In the present invention, as described above, on the noble metal substrate
It is possible to obtain an oxide superconducting laminate in which the metal base and the Bi-based superconducting layer are integrated by forming a layer of the Bi-based superconducting raw material, drying and firing. In addition, Ag is added to the superconducting layer.
Alternatively, a more uniform superconducting layer can be obtained by adding Ag ₂ O, preferably in an amount of 0.5 to 10% by weight, and baking it.

The firing in the present invention is performed in an atmosphere of oxygen or an oxygen-containing gas in air. Generally, the firing temperature is preferably 860 to 920 ° C.

Further, in the present invention, an intermediate layer may be formed between the noble metal substrate and the Bi-based superconducting layer. In that case, preferably
It is preferable to form a noble metal-Bi-based superconducting complex oxide containing a noble metal used for the substrate in the complex oxide constituting the Bi-based superconductor as the intermediate layer.
It is more preferable to gradually reduce to the system superconducting layer. The thickness of this intermediate layer is preferably in the range of 20 μm to 1 mm, and it is also preferable to reduce the thickness in the region of the end of the laminate together with the Bi-based superconducting layer.

Bi-based superconducting-precious metal laminate of the present invention, by forming and integrating a Bi-based superconducting layer on the precious metal substrate, and by reducing the layer thickness of the Bi-based superconducting layer in a predetermined region of the end of the laminate, conventional. It is possible to prevent the inconvenience of locally occurring cracks in the superconductor at the ends.

Therefore, the Bi-based superconducting-noble metal laminate of the present invention does not cause peeling or cracks even when it is repeatedly used in a rapid cooling cycle such as immersion in liquid nitrogen that exhibits superconducting properties and removal.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

Examples 1 to 3 and Comparative Examples 1 to 2 Bi ₂ O ₃ , SrCO ₃ , CaCO ₃ and CuO powders were mixed at a molar ratio of 1: 2: 1: 2 and mixed for 10 hours by a dry mill. Mixed powder
The powder was calcined in the air at 800 ° C. for 10 hours, and the calcined powder was crushed with ZrO ₂ boulders in isopropyl alcohol for 20 hours. The average particle size of the obtained pulverized particles was 3 μm, and it was confirmed by X-ray diffraction that the main crystal phase was Bi ₂ Sr ₂ CaCu ₂ O _y phase. The obtained pulverized particles and isopropyl alcohol were mixed so as to have a predetermined viscosity to prepare a slurry.

Spray the above slurry onto the outer surface of a cylindrical substrate made of Ag and having a thickness of 500 μm and a diameter of 100 mm and a height of 450 mm, so that the slurry thickness decreases in the end direction in the range of 20 mm from the end of the cylinder. Applied. After coating, baking was performed at 890 ° C. for 1 hour in an oxygen gas atmosphere.

After firing, lower the temperature to 850 ° C at a rate of 0.5 ° C / min to 850 ° C.
Hold for 15 hours. Then, it heat-processed at 400 degreeC in nitrogen atmosphere for 10 hours. The thickness of the obtained Bi-based superconducting layer other than the end portion was 300 μm. Also, the cylindrical ends are respectively the first
The region from the end where the thickness of the Bi-based superconducting layer is reduced in any one of FIGS. 4 to 4 is shown in Table 1.

The magnetic shield ability of the cylindrical Bi-based superconducting-noble metal laminate obtained as described above was measured by using the magnetic shield ability measuring apparatus whose schematic explanatory view is shown in FIG. In FIG. 5, the liquid nitrogen container 1 is filled with liquid nitrogen, and the obtained laminated body 1 is immersed in liquid nitrogen to reach the liquid nitrogen temperature. An external magnetic field is applied at 12, and the Gauss meter is placed inside the cylindrical laminated body.
At 13, the maximum external magnetic field Gauss (G), which starts to increase from the background, was measured as the magnetic shielding ability. afterwards,
The cylindrical laminate 1 was instantaneously taken out into the room atmosphere, allowed to stand at room temperature, then immersed in liquid nitrogen and rapidly cooled again, and the cooling cycle was repeated to measure the magnetic shielding ability.

Table 1 shows the changes in the magnetic shielding ability as a result of the cooling / heating cycle.

Example 4 An Ag foil having a thickness of 500 μm was baked using glass on a flat plate substrate made of Inconel having a thickness of 1.5 mm and a size of 300 × 300 (mm). On the Ag foil, in the same manner as in Example 1, except for the edges, 30
A Bi-based superconducting layer was formed in a thickness of 0 μm, and the Bi-based superconducting layer was reduced in the form of FIG.

The magnetic shielding ability of the obtained flat Bi-based superconducting-noble metal laminate in liquid nitrogen was 30 G.
Further, the magnetic shield ability after repeating the same quenching cycle as in Example 1 50 times was 30 G and no change was observed.

From the above Examples and Comparative Examples, it is clear that the predetermined region from the end portion has a Bi-based superconducting layer of the present invention in which the layer thickness of the Bi-based superconducting layer is reduced. Shows a high magnetic shield without deterioration. Furthermore, it can be seen that the laminated body in Example 3 in which the layer thickness of the Bi-based superconducting layer is reduced and the thickness of the noble metal substrate is reduced is further excellent in thermal shock resistance.

〔The invention's effect〕

The Bi-based superconducting-precious metal laminate of the present invention has sufficient superconducting properties, is also excellent in thermal shock resistance, and is repeatedly used in the quenching cycle, but the magnetic shielding ability does not decrease, and it is useful as a magnetic shield. is there.

[Brief description of drawings]

FIG. 1 is an end portion of a Bi-based superconducting-noble metal laminate according to one embodiment of the present invention, FIG. 2 is an end portion of a Bi-based superconducting-noble metal laminate according to another embodiment of the present invention, and FIG. It is sectional explanatory drawing which shows each edge part of the Bi type | system | group superconducting-noble metal laminated body of the other Example of this invention. FIG. 4 is a sectional explanatory view showing an example of a conventional superconducting-metal laminate. FIG. 5 is a schematic explanatory view of a magnetic shield capacity measuring device used in one embodiment of the present invention. 1 …… Bi-based superconducting-noble metal laminate 2 …… Ag substrate, 3 …… Bi-based superconducting layer 4 …… Ag substrate end, 5 …… Bi-based superconducting layer end 11 …… Liquid nitrogen container, 12 …… Electromagnet 13 ... Gauss meter

Claims (2)

[Claims] 1. A noble metal substrate having a thickness of 300 μm to 2 mm and a thickness of 10
In a bismuth-based superconducting-noble metal laminate in which a bismuth-based superconducting layer having a thickness of 0 μm to 5 mm is formed, the thickness of the bismuth-based superconducting layer is 1% to 5% of the length of the laminate at the end of the laminate. And a bismuth-based superconducting-noble metal laminate, which is reduced in the end direction of the laminate. 2. A bismuth-based superconducting-noble metal laminate according to claim 1, wherein the ratio of the thickness of the bismuth-based superconducting layer to the thickness of the noble metal substrate is constant over the entire laminate or decreases toward the edges. body.