JPH02275779A - Superconducting ceramic composite material - Google Patents

Abstract

PURPOSE:To improve the mechanical strength a composite material without firmly bonding a ceramic with a metal by forming a superconducting ceramic on the surface and in the holes of a porous metal, etc., thereby integrating the metal with the ceramic. CONSTITUTION:A superconducting ceramic 2 is formed on the surface 4 and in the holes 5, 11 of porous metals 8, 10 or the ceramics 2 are connected with each other through the holes 6, 11. The ceramic is integrated 1 with the above porous metal 3.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a composite of superconducting ceramics and metal,
More specifically, the present invention relates to a metal-superconducting ceramic composite that can be suitably used, for example, for magnetic shielding.

[Prior art] In recent years, nuclear magnetic resonance computed tomography diagnostic equipment (MRI) that utilizes superconducting properties has been developed.
(Nance Irnaging), linear motors, etc. are being put into practical use, but along with this, leakage magnetic fields are generated from these devices, causing a problem in that they have an adverse effect on the outside. On the other hand, when measuring minute magnetism such as brain magnetic waves (α waves), there is a problem in that accurate detection becomes difficult when external magnetic fields such as terrestrial magnetism influence the measurement. Therefore, in order to solve the above problems, a magnetic shielding device for shielding the magnetism from the magnetic source is required.

If this magnetic shielding is desired, a shielding body that utilizes the perfect diamagnetism of superconducting materials is suitable.

However, since the conventional superconducting phenomenon can only be realized in liquid helium, it is extremely difficult to cool shield devices that are large in shape and have a large surface area, and is also subject to significant economic constraints. In particular, with regard to medical magnetic shields that need to measure the magnetic field generated by the human body, it is necessary to reduce the influence (noise) from external magnetism as much as possible with current technology. Creating a magnetic shield had drawbacks such as an enormous weight.

[Question 8 that the invention seeks to solve] By the way, in recent years, superconducting ceramics that exhibit superconductivity at liquid nitrogen temperatures have appeared, making it possible to make shielding equipment smaller and lighter, as well as becoming economically viable. .

However, since superconducting ceramics do not have sufficient mechanical strength, they must be reinforced with metal in order to construct a magnetic shield of the required size.

Therefore, in order to overcome this drawback, attempts have been made to form superconducting ceramics on the surface of metals, but in this case, since metals and superconducting ceramics generally have different expansion coefficients, there is a difference between metals and superconducting ceramics. Usually, an intermediate layer having an intermediate coefficient of thermal expansion is provided to form a multilayer structure.

The intermediate layer needs to form a bonding layer having good mechanical strength at both interfaces between the metal and the superconducting ceramic.

However, currently known high-temperature conductive ceramics (Y-Ba-Cu-0 series, former -3r-(:a-C
(u-0 series, Tdan-Ba-Ca-Cu-0 series, etc.) are highly reactive with other substances, so most of the intermediate layers that can obtain good bonding with conventionally known metals are , it reacted with superconducting ceramics and could not play the role of an intermediate layer.

We also found that the reaction can be suppressed by using stabilized ZrO2 as an intermediate layer, but when a large product is obtained using this configuration, stress concentrates at the interface when a cooling/heating cycle is performed between liquid nitrogen temperature and room temperature. The film peeled off and was unreliable.

[Means for Solving the Problems] Accordingly, an object of the present invention is to provide a superconducting ceramic composite integrally reinforced with metal, which is reliable in obtaining a magnetic shielding body of required dimensions.

According to the present invention, in order to achieve the above object,
A superconducting ceramic composite body is provided in which a superconducting ceramic and a porous metal are integrated into a composite body.

In the case of the present invention, the bonding surface between the porous metal and the superconducting ceramic does not need to guarantee mechanical strength, and the superconducting ceramic penetrates into the many pores provided in the porous metal, and uses the intrusions to form a porous pot. Mechanically connected to the bottom.

Also, is it possible to bond the porous metal and the superconducting ceramic on one or both sides of the porous metal?
Since the ceramics on both sides can be connected to each other through the pores of the porous metal, the bonding strength is further improved, which is preferable.

Here, the porous metal is preferably one that has poor reactivity with superconducting ceramics and one that has excellent oxidation resistance at 900°C or higher, such as PL, Au, Ag, and 5US.
Stainless steel such as 304.5US430 is suitable, and if necessary, ZrO2 or Al may be applied to the surface of these base metals.
z03. Spinel, precious metal, or the like may be formed by means such as thermal spraying.

Furthermore, the porous metal may be a plate-like or cylindrical base metal in which many holes are formed by mechanical processing, or a network-like porous material obtained by processing a linear material.

Further, the composition of the superconducting ceramic used here is not particularly limited, and for example, YBa2CuzOxBi2
Sr2CaCu20. , Bi2Ca5rCu20x$ can be used.

[Examples] Hereinafter, the present invention will be explained in more detail based on Examples, but the present invention is not limited to these Examples.

(Example 1) 300x300 as a porous metal as shown in Figure 2
5US430 of xl (thickness) (m+n) was prepared.

Holes 11 of φ3111 [I+ are substantially uniformly drilled in this metal plate IO with an aperture ratio of about 35%. Note that 2rO, partially stabilized with Y2O3, was thermally sprayed on both sides of this plate to a thickness of 200 μm.

On the other hand, the composition of superconducting ceramics is Bi25r2C.
aCu20. So that 3!20:+, 5rCO:,
, CaCO3, and Cu0 were prepared, wet-mixed using distilled water, and this mixture was calcined at 750°C for 10 hours.
A Bi25r2CaCu206 synthetic powder was obtained.

Then, the synthesized powder was mixed with ethanol as a solvent and 8 wt% of PVA (polyvinyl alcohol) was added as a binder to prepare a slurry with a viscosity of 4000 cps, and a sheet with a thickness of 0.8 mm was obtained using a doctor blade device. .

Two of these sheets 21 are prepared, and as shown in FIG.
/cm2 to obtain a molded body 20.

This molded body was set on an Ag flat plate, heated in an oxygen atmosphere, and held at 850°C for 20 hours to remove the binder.Then, the temperature was raised to 930°C and held for 10 minutes, and then heated to 900°C. The temperature was lowered and maintained for 5 hours, and the furnace was further cooled to obtain an oxide superconducting composite 1.

A cross-sectional view of the main structure of this composite I is shown in FIG.

As shown in FIG. 1, the superconducting ceramics 2 were formed on both sides of the metal 3, and the superconducting ceramics 2 on both sides were connected by holes 5 in the metal. Note that there were some parts of the interface 4 between the superconducting ceramic 2 and the metal 3 that were peeled off.

(Comparative Example 1) A superconducting ceramic composite A was obtained in the same manner as in Example 1 except that a metal plate without holes was used.

This composite A had no apparent defects.

(Example 2) Composite 1 of Example 1 and Composite A of Comparative Example have an electrical resistance of 0 at a temperature of 90°C or lower, and the Meissner effect was observed, confirming that they exhibit superconducting properties.

In addition, the initial magnetic shielding ability of these materials was also measured.

The magnetic shielding ability measuring device 30 used in this example is composed of a liquid nitrogen container 31, an electromagnet 32, and a Gauss meter (magnetic flux density measuring device) 33, as shown in FIG. This device is inserted between the gauss meter 33 and the electromagnet 32 to generate a constant magnetic field in the presence of liquid nitrogen, and the gauss meter 33 measures the leakage magnetic field.

In the magnetic shielding ability measuring device 30, the sample of Example 1 was placed between the electromagnet 32 and the Gaussmeter 33 as the measurement sample 34.
Composite 1 of Example 1 and Composite A of Comparative Example were inserted, and the maximum applied magnetic field capable of complete magnetic field shielding with a leakage magnetic flux of 0.01 Gauss or less was measured. At this time, the complete shielding ability of complex L is 25 Gauss, and the complete shielding ability of complex A is 25 Gauss.
It was 8 Gauss.

Thereafter, these composites were subjected to a cooling/heating cycle in which they were immersed in liquid nitrogen for 10 minutes and left at room temperature for 20 minutes.

As a result, at the number of cycles N=5, the superconducting ceramic on one side of composite A peeled off from the metal part and fell off. On the other hand, there was no particular abnormality in the composite 1, and as a result of measuring the shielding ability in the same manner as above at N=50, no deterioration of the characteristics was observed at 26 Gauss.

(Example 3) A composite body 50 shown in FIG. 5 was obtained using the same manufacturing process as in Example 1 except that the ceramic sheet was pressure-bonded to only one side of the metal plate.

As shown in FIG. 5, a superconducting ceramic 51 was formed on the upper surface of a metal plate 52, and a convex portion 53 of the ceramic 51 entered into a hole 54 of the metal plate 52. Note that the bonding at the interface 55 between the ceramic 51 and the metal plate 52 was incomplete.

A thermal cycle test similar to that in Example 2 was conducted on this composite 50. After N = 50 cycles, the shielding ability was measured and no deterioration of the characteristics was observed.The reason for the reliability is the ceramic, Tux 51 and metal plate 52.
Even if the bonding at the interface is insufficient, the convex portion 53 of the ceramic
This is presumed to be due to the structure in which the ceramic 51 is held by the metal plate 52 due to the mechanical catch of the hole 54 of the metal plate.

(Example 4) A net-like metal molded body in which SO3:104 wire rods of φ0.5 mm were entwined with each other was prepared, and this metal molded body was coated with Ag by electroless plating. Ag was uniformly coated on the wire, and the thickness was 2 μm. In addition, the external dimensions are
S OOmm x 500mm and thickness is 2+Im.

Next, the same BtzSr2CaCu20a synthetic powder as in Example 1 was prepared, and PVA l wt was added to it as a binder.
$, mixed with ethanol as solvent, viscosity 7000cp
s clay was obtained.

Next, the metal molded body 61 is set in the molding molds 62 and 63 shown in FIG. 6, and the clay 64 is injected into the mold through the injection port 65 under pressure, and then dried at 150° C. to form a molded body. I got it. Of course, although not shown in the drawings, the mold is provided with a vent for air removal, and a mold release agent is also formed to facilitate mold release.

This molded body was fired in the same manner as in Example 1.

A cross section of the obtained composite 70 is shown in FIG. As shown in FIG. 7, the composite body 70 is a composite body in which a mesh metal 72 is formed within a superconducting ceramic 71.

This composite 70 was used as a terminal for fixing the end 73 of the mesh metal 72 on which the ceramic 71 was not formed to a liquid nitrogen container.

[Effects of the Invention] As explained above, in the present invention, when obtaining a composite of superconducting ceramics and metal, by making the metal porous, the interface between the superconducting ceramics and metal does not have to form a strong bonding layer. can also provide a sufficiently reliable complex.

Further, in the present invention, since the metal and ceramic are not sufficiently bonded at the joint surface, thermal stress caused by the difference in thermal expansion between the two can be absorbed. Furthermore, since the composite of the present invention handles metal without handling ceramics, it has many advantages such as no need to worry about mechanical damage, and provides inexpensive and reliable superconducting ceramic products. can do.

[Brief explanation of drawings]

FIG. 1 is a sectional view of essential parts showing an embodiment of the composite of the present invention;
FIG. 2 is a perspective view showing the metals constituting the composite shown in FIG.
FIG. 3 is a sectional view of a molded body for obtaining the composite shown in FIG. 1;
FIG. 4 is a partially cutaway perspective view showing an example of a magnetic shielding ability measuring device, FIG. 5 is a cross-sectional view of main parts showing another embodiment of the composite of the present invention, and FIG. FIG. 7 is a cross-sectional view showing an example of the molding method, and FIG. 7 is a cross-sectional view showing a composite obtained by the molding method of FIG. 1.50.70...Composite, 2,51,7I...Superconducting ceramics, 3,10,52.72...Porous metal, 4...Interface between superconducting ceramics and porous metal, 5 , 54... Porous metal hole, 11... Hole, 3
0...Magnetic shielding ability measuring device, 31...Liquid nitrogen container, 32...Electromagnet, 33--Gauss meter, 34
...Sample, 53...Protrusion of superconducting ceramics, 6
1... Metal molded body, 62.63... Molding die, 64
...Clay, 65...Inlet. Figure 1 Figure 2] 1 Figure 3

Claims (3)

[Claims] (1) A superconducting ceramic composite characterized in that a superconducting ceramic and a porous metal are integrated into one. (2) The superconducting ceramic composite according to claim 1, wherein the superconducting ceramic is formed on the surface and pores of the porous metal. (3) The superconducting ceramic composite according to claim 1, wherein the superconducting ceramics are connected through the pores of the porous metal.