JP2506225B2 - Precious metal-bismuth superconducting laminate - Google Patents

Description

TECHNICAL FIELD The present invention relates to a noble metal-bismuth-based superconducting laminate. More specifically, it relates to a noble metal-bismuth superconducting laminate in which a bismuth superconductor layer is laminated on a noble metal substrate with a noble metal-containing bismuth-containing composite oxide intermediate layer interposed therebetween.

[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, nuclear magnetic resonance computerized tomography (MRI: Magnetic Resonace 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 have been proposed for forming a Bi-based superconductor layer on a metal substrate, and various intermediate layers have also been proposed due to the problem of reactivity between the substrate and the Bi-based superconductor layer.
For example, in Japanese Patent Laid-Open No. 63-305574, platinum (Pt), silver (At), which has good adhesiveness, does not cause a chemical reaction with a superconductor between the substrate such as alumina, zirconia, and copper and the superconductor.
g), interposing an intermediate layer of noble metal such as gold (Au) is proposed. Furthermore, in JP-A-1-252533, Ag, Au,
It has been proposed to stack a Bi-based superconductor layer on a precious metal such as Pt as a substrate.

[Problems to be Solved by the Invention]

However, even if an intermediate layer of noble metal, which is chemically stable with the Bi-based superconductor, is formed, the firing temperature of the Bi-based superconductor is 85%.
Since it is a very high temperature of 0 to 960 ° C, peeling occurs between the precious metal intermediate layer and the metal substrate, the Bi-based superconductor reacts with the metal substrate to deteriorate the superconducting properties, and the thermal expansion from room temperature to 900 ° C. Coefficients of noble metal with a coefficient of 20-22 × 10 ^-6 / ° C and of 13-14 × 10 ^-6 / ° C
Bi-based superconductors have good adhesion to each other, and even when a laminated body is formed due to plastic deformation of noble metal, when the cooling rate is high so that the rapid cooling cycle at the liquid nitrogen temperature that develops superconducting properties is repeated. Has a problem that thermal shock resistance is inferior such as cracks in the oxide superconductor due to a large difference in thermal expansion between the two.

The present invention is a precious metal in which a Bi-based superconductor is laminated on a precious metal substrate-Bi-based superconductor, a precious metal excellent in thermal shock resistance by eliminating the above-mentioned drawbacks due to the difference in thermal expansion between the precious metal substrate and the Bi-based superconductor- The purpose is to provide a Bi-based superconductor.

[Means for solving the problem]

According to the present invention, there is provided a noble metal-bismuth-based superconducting laminate, which comprises a noble metal substrate containing 20 to 80% by volume of the noble metal and a composite oxide constituting a bismuth-based superconductor having a thickness of 20 μm to 1 mm. There is provided a noble metal-bismuth-based superconducting laminated body, in which an object intermediate layer and a bismuth-based superconducting layer are sequentially formed.

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

The substrate of the laminate of the present invention is a so-called noble metal 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 CaCu ₃ O _x in phase, composition containing lead (Pb), antimony (Sb), etc., composition deviating from stoichiometric composition, main element partially or entirely with other elements Any Bi-based superconductor having a substituted composition may be used.

In the present invention, the Bi-based superconductor layer is a Bi-based superconductor raw material powder, for example, oxide superconductor obtained by firing powders of bismuth, calcium, strontium and copper metal oxides, carbonates, hydroxides, metal alkoxides and nitrates. Mixed powder that is compounded to form
Powder composed of Bi-based superconducting crystal phase calcined at ℃, mixed powder calcination intermediate product powder calcinated at 400 ~ 800 ℃ so as to develop superconducting properties, frit powder of mixed powder or these Using mixed powder, spray coating method,
Any known molding method such as a powder coating method, a doctor blade method, or a thermal spraying method may be used.

In the present invention, between the noble metal substrate and the Bi-based superconductor layer laminated thereon, the noble metal used for the substrate is contained in the composite oxide constituting the Bi-based superconductor, and the noble metal-Bi
An intermediate layer is formed as a superconducting composite oxide.

The complex oxide that constitutes the Bi-based superconductor of the intermediate layer is mainly composed of bismuth (Bi), strontium (Sr), calcium (Ca), and copper (Cu), which are the main constituent components of the Bi-based superconductor. A complex oxide that forms a Bi-based superconductor layer
It has substantially the same composition as the Bi-based superconductor. The noble metal contained in the intermediate layer is preferably the same metal as the noble metal of the substrate, but different noble metals or alloys may be used.

The intermediate layer of the present invention is a Bi-based superconductor raw material powder as a noble metal simple substance or an oxide, a compound powder such as a nitrate, so that the composition ratio is as follows, and the noble metal is uniform in the Bi-based superconductor composition composite oxide. Like the Bi-based superconductor layer, the raw material powder added and mixed so as to be dispersed can be formed by any known forming method.

In the intermediate layer of the present invention, the noble metal contained is 20 to 80 in the noble metal-Bi-based superconducting composite oxide of the intermediate layer to be formed.
Volume% The noble metal in the oxide of the intermediate layer exists in a dispersed state as a single phase of the noble metal in the complex oxide of the Bi-based superconductor composition, but if the amount of the noble metal exceeds 80% by volume, the melting point of the noble metal when forming the intermediate layer. This will cause firing shrinkage at the above temperature, and the noble metal of the substrate will also be melted, and the morphology cannot be maintained, which is not preferable. On the other hand, when the content is less than 20% by volume, the effect as an intermediate layer of relaxing the difference in thermal expansion is small.

The noble metal-Bi-based superconducting composite oxide of the intermediate layer of the present invention is
As the volume ratio of the precious metal contained increases, the coefficient of thermal expansion changes almost linearly from the value of the coefficient of thermal expansion of the Bi-based superconductor to that of the precious metal. Therefore, when it is necessary to maximize the thermal shock resistance, a plurality of intermediate layers between the precious metal substrate and the Bi-based superconducting layer in which the precious metal-containing volume ratio is gradually reduced in the Bi-based superconducting layer direction. Can be formed as an intermediate layer of the graded material structure. Practically, due to the ease of the manufacturing process, one intermediate layer with a noble metal content volume ratio of 50% is formed, or the first intermediate layer with noble metal content of 67% by volume and 33% by volume of the noble metal substrate side. It is preferable to form the second intermediate layer and form the Bi-based superconducting layer on the second intermediate layer.

In the laminated body of the present invention, the noble metal substrate is 300 μm to 1 mm.
A thickness in the range of is preferred. If it is less than 300 μm, the strength of the substrate is insufficient, and if it exceeds 1 mm, it is not practical in terms of cost. The Bi-based superconducting layer preferably has a thickness in the range of 100 μm to 5 mm. 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, the sintering of the Bi-based superconducting layer does not proceed uniformly, which is not preferable. Also precious metals-
The thickness of the intermediate layer of Bi-based superconducting composite oxide is 20 μm to 1 mm.
Range. If it is less than 20 μm, the function as a layer for relaxing the difference in thermal expansion is insufficient, and if it exceeds 1 mm, it is unfavorably thick as compared with the superconducting layer. When the intermediate layer is formed of a plurality of layers, each layer needs to have a thickness of 20 μm or more, but the thickness of the entire intermediate layer is preferably 1 mm or less as described above.

In the present invention, as described above, a layer of the intermediate layer raw material is formed on the precious metal metal substrate and fired to integrate the precious metal substrate and the intermediate layer, and then a layer of the Bi-based superconductor raw material is formed on the intermediate layer. , Dried and baked to obtain a metal substrate, an intermediate layer and
It is possible to obtain an oxide superconducting laminate in which the Bi-based superconducting layer is integrated. Further, the intermediate layer and the Bi-based superconducting layer may be formed on the noble metal substrate by firing at the same time. Furthermore, a more uniform superconducting layer can be obtained by adding Ag or Ag ₂ O, preferably 0.5 to 10% by weight, to the superconducting layer 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.

The noble metal-Bi-based superconducting laminate of the present invention is one in which an intermediate layer of a noble metal-Bi-based superconducting composite oxide is formed on a noble metal substrate, and a Bi-based superconducting layer is formed on the intermediate layer to be integrated.
The intermediate layer acts synergistically on both the precious metal substrate and the Bi-based superconducting layer formed on the outer surface. Therefore, in the oxide superconducting laminate of the present invention, each layer on the metal substrate is stabilized, and peeling or cracking does not occur even if it is repeatedly used by dipping in liquid nitrogen for expressing superconducting properties and taking out. .

〔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 Bi ₂ O ₃ , SrCO ₃ , CaCO ₃ and CuO powders were prepared in a molar ratio of 1: 2: 1: 2, mixed in distilled water, and then calcined in air at 800 ° C. for 10 hours, A composition (A) in which 33% by volume of Ag powder was added to Bi-based superconductor calcined powder whose main crystal phase was Bi ₂ Sr ₂ CaCuO _y phase after crushing with ZrO ₂ boulder in ethanol for 15 hours and 67%
The added composition (B) was made into slurries (A) and (B) using isopropyl alcohol.

A cylindrical substrate having a thickness of 500 μm, a diameter of 100 mm and a height of 450 mm was formed on the outer surface of the cylindrical substrate by spray coating using the above slurry (A) so that the thickness after sintering was 200 μm. The intermediate layer (A) was formed by firing at 860 ° C. for 30 minutes in a gas atmosphere and sintering.

Then, the slurry (B) was used to form a film on the intermediate layer (A) in the same manner, and the intermediate layer (B) was sintered by firing at 895 ° C. for 30 minutes in an oxygen gas atmosphere to form the intermediate layer (B). The total thickness of the obtained intermediate layers consisting of the intermediate layers (A) and (B) is 40
It was 0 μm.

Furthermore, on the intermediate layer obtained above, spray coating using the same Bi-based superconductor calcined powder isopropyl alcohol slurry as above, under an oxygen gas atmosphere, 885 ° C.
After partially melting for 30 minutes, gradually cool to 850 ° C at a temperature decrease rate of 1 ° C / minute, and at 850 ° C for 15 hours, then in a nitrogen atmosphere at 400 ° C
Heat treated for 10 hours. The thickness of the obtained Bi-based superconducting layer is 500.
μm.

The magnetic shield ability of the cylindrical noble metal-Bi-based superconducting laminate obtained as described above was measured using the magnetic shield ability measuring apparatus whose schematic explanatory view is shown in FIG. In FIG. 1, after filling the liquid nitrogen container 1 with liquid nitrogen and immersing the obtained laminated body 2 in liquid nitrogen to reach the liquid nitrogen temperature, the electromagnet arranged outside the container 1 An external magnetic field was applied at 3 and the maximum external magnetic field that started to increase from the background was measured as the magnetic shield ability by the Gauss meter 4 arranged in the cylindrical laminated body. After that, the cylindrical laminated body 2 was immediately taken out into the indoor atmosphere, allowed to stand until it reached room temperature, and then the cooling and heating cycle of immersing in the liquid nitrogen and rapidly cooling 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.

Comparative Example A laminated body in which a 500 μm Bi-based superconducting layer was formed in the same manner as in the example without forming an intermediate layer in the same Ag cylindrical body as in the example, and the magnetic shield by the thermal cycle was similarly prepared. The change in Noh was measured. The results are shown in Table 1.

As is clear from the above-mentioned Examples and Comparative Examples, the noble metal-Bi-based superconducting laminate obtained by forming the intermediate layer of the present invention is stable in superconducting state without decreasing magnetic shielding ability even during repeated cooling and heating cycles. It can be seen that the characteristics are exhibited.

〔The invention's effect〕

The present invention forms an intermediate layer of a noble metal-containing Bi-based superconducting composite oxide of a complex oxide that constitutes a Bi-based superconductor containing a noble metal on a noble metal substrate, and forms a Bi-based superconducting layer on it. It is a Bi-based superconducting laminated body, with good adhesion between the noble metal substrate and the intermediate layer, and between the intermediate layer and the Bi-based superconducting layer, and has high thermal shock resistance against cooling and heating cycles, and in repeated cooling and cooling cycles such as rapid cooling. Also, good superconducting properties can be obtained without degrading the superconducting properties.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic explanatory view showing an example of an apparatus for measuring magnetic shielding ability of a base metal-Bi based superconducting laminate of the present invention. 1 ... Liquid nitrogen container 2 ... Noble metal-Bi-based superconducting laminated body 3 ... Electromagnet, 4 ... Gauss meter

Claims (3)

(57) [Claims] 1. A noble metal-bismuth-based superconducting laminate, comprising 20 to 80% by volume of the noble metal on a noble metal substrate,
A noble metal-bismuth-based superconducting laminate, wherein a bismuth-based superconducting layer having a thickness of 20 μm to 1 mm and forming a bismuth-based superconductor and a bismuth-based superconducting layer are sequentially formed. 2. The noble metal-bismuth superconducting laminate according to claim 1, wherein the noble metal is present in the intermediate layer in a dispersed state as a noble metal simple phase. 3. The noble metal-bismuth superconducting laminate according to claim 1, wherein the noble metal is Ag.