JPH01206518A - Manufacture of linear superconductive material - Google Patents

Abstract

PURPOSE:To enable the production of a sintered body superconductive material having a high critical temperature as a wire rod by making a composite clad cylindrical body formed of an inner cylinder made of Ag and an outer cylinder made of a metal suitable to plastic working other than Ag as a cylindrical body, and removing said outer cylinder after plastic working, followed by sintering. CONSTITUTION:As a cylindrical body to be filled with starting powders, a composite clad cylindrical body formed of an inner cylinder made of Ag and an outer cylinder made of a metal suitable to plastic working and having a tensile strength higher than that of Ag is made, and the outer cylinder is removed after plastic working followed by sintering treatment. As materials of the outer cylinder, steel or iron and alloys thereof, Ni and alloys thereof, Al alloys, and others are used. The sintering temperature ranges from 860 to 970 deg.C. The atmosphere in the sintering contains oxygen of a partial pressure about 1atm, and after sintering, the sintered body is maintained at 300-400 deg.C for 5 hours or more in the same atmosphere.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing a superconducting material made of a long sintered body. More specifically, the present invention relates to a novel method for improving the mechanical strength of elongated superconductors while maintaining the excellent superconducting properties of elongated superconductors containing particularly complex oxide-based sintered materials.

Conventional technology Under superconducting phenomena, materials exhibit complete diamagnetic properties, and no potential difference appears even though a finite steady-state current flows inside them. Therefore, various applications of superconductors as transmission media with no power loss have been proposed.

That is, its application fields include power fields such as MHD generation, power transmission, and power storage, power fields such as magnetic levitation trains and electromagnetic propulsion ships, and NMR as ultra-sensitive sensors for magnetic fields, microwaves, radiation, etc. .

There are many fields that can be mentioned, such as pi-meson therapy, measurement fields such as high-energy physics experimental equipment, etc.

Furthermore, in the field of electronics, typified by Josephson devices, this technology is expected to not only reduce power consumption but also realize devices that operate at extremely high speeds.

By the way, superconductivity was once a phenomenon observed only at extremely low temperatures. That is, Nb3G is said to have the highest superconducting critical temperature Tc among conventional superconducting materials.
The superconducting critical temperature is also extremely low at 23.2 K, and this has long been considered the limit of the superconducting critical temperature.

Therefore, conventionally, in order to realize the superconducting phenomenon, superconducting materials have been cooled to below Tc using liquid helium with a boiling point of 4.2. However, the use of liquid helium imposes an extremely large technical burden and cost burden due to cooling equipment including liquefaction equipment, which has hindered the practical application of superconducting technology.

However, recently, group IIa elements or lIa
It has been reported that a composite oxide sintered body containing group elements can become a superconductor at an extremely high Tc, and the practical application of superconducting technology using non-low temperature superconductors is suddenly being promoted.

It has already been known that composite oxide-based ceramic materials exhibit superconducting properties; for example,
U.S. Pat. No. 3,932,315 describes Ba-Pb-B
It is stated that 1-based composite oxides exhibit superconducting properties, and furthermore, JP-A-60-173-885 describes that Ha-Bi-based composite oxides exhibit superconducting properties. has been done. However, since the Tc of the complex oxides of the above-mentioned systems known so far is below IOK, liquid helium (boiling point 4
．． 2K) was the only option.

However, in 1986, Bednotes and Mueller et al. discovered that T was much higher than that of conventional metallic superconducting materials.

With the discovery of superconducting oxides with
4. September 1986, p189-193).

The oxide superconductor discovered by Bednautz and Muller et al. is (La, Ba) 2 Cu Oa or (La, 5r) 2 CuCL, and this oxide superconductor is called a K2NiF4 type oxide, and these materials has a crystal structure similar to that of previously known perovskite-type superconducting oxides, but its T. The value is about 30, which is dramatically higher than that of conventional superconducting materials.

Furthermore, in February 1987, Chu et al.
It has been reported that a Ba-Y complex oxide has been discovered that exhibits a critical temperature in the class of 2015, and the possibility of realizing non-low temperature superconductors has suddenly increased.

However, since these superconducting materials are obtained as sintered bodies, they are brittle when used in boat fishing and must be handled with care.

That is, it easily cracks or breaks due to mechanical stress, and especially when made into a wire, it is extremely brittle, and its practical use is severely restricted. Therefore, by filling the raw material powder of superconducting sintered body into a metal cylinder etc. and processing it,
Various methods have been proposed for producing superconducting wires with sufficient mechanical strength.

This method involves filling a cylindrical body made of a metal material suitable for compositional processing with raw material powder, processing it into a desired shape by wire drawing or forging, and removing the raw material powder inside. This is a method of increasing the density and then sintering to produce a sintered product with a thin or complex shape. Superconducting wires produced by this method not only have sufficient mechanical strength, but also the metal cylinder functions as a current bypass and heat dissipation path when the superconducting material is quenched, so it is suitable for the production of superconducting wires. It is considered to be an extremely effective technology.

Problems to be Solved by the Invention In view of the above circumstances, the present inventors have developed a cross-sectional dimension in the longitudinal direction that can be used practically without using an organic adhesive that causes a decrease in strength and toughness. As a method for manufacturing a sintered ceramic wire that can be formed long in the direction dimension, US Patent No. 152.
No. 713, U.S. Patent Application No. 161,480, filed February 29, 1988, U.S. Patent Application No. 182.489, filed April 18, 1988, and U.S. Patent Application No. 189, filed May 2, 1988. .366 and U.S. Patent Application No. 225.207 filed on August 3, 1988, a ceramic raw material powder is filled in a metal cylinder, particularly an Ag cylinder, and a metal cylinder filled with the raw material powder is disclosed. We proposed a method of sintering after metal processing.

However, even if a metal cylinder is filled with raw material powder and sintered as described above, the sintered body does not exhibit sufficiently high superconducting properties. in many cases cannot be reached.

This is thought to be because the oxygen contained in the sintered body is not sufficiently controlled because it is filled into the cylinder and sintered.

That is, in order to produce a superconducting sintered body that exhibits high superconducting properties, it is required to control the oxygen content extremely precisely during the manufacturing process.

An example of a manufacturing process that has been found to be effective as a known method for manufacturing bulk superconducting sintered material is: ■ A process in which compound powder (generally using oxides) containing the constituent elements of superconducting sintered material is Finely grind and mix to obtain raw material powder.

■ The obtained raw material powder is compactly molded.

■ Sinter by heating to a predetermined temperature under an oxygen partial pressure of about 1 atm.

(2) Slowly cool from 300°C to about 400°C under the same oxygen partial pressure, and maintain this temperature for several hours to more than ten hours.

■ Cool to room temperature.

Among these processes, the annealing treatment (ii) in particular has a very close relationship with the oxygen content of the obtained sintered body.
This treatment is considered essential for making the material exhibit high superconducting properties and further stabilizing it. However, when a metal cylinder is filled with raw material powder and sintered as described above, it is difficult to anneal the sintered body while exposing it to an oxygen cloud environment, and there are also problems due to the atmosphere during sintering. Oxygen could not be controlled, which caused a decline in the superconducting properties of the superconducting wire.

Furthermore, it has been proposed to solve the above-mentioned problems by using Ag as the material of the metal cylinder. That is,
Ag has the property of pseudo-permeating oxygen due to its redox reaction, and by using it as a metal cylinder, it is possible to control oxygen during sintering or annealing. However, Ag is an extremely expensive material and has the problem of not being suitable for industrial production of wire rods. Furthermore, when a cylindrical body is filled with raw material powder and sintered, it is necessary to plastically process the cylindrical body filled with the raw material powder in order to achieve sufficient density of the sintered body. However, when Ag is used as the cylindrical material, if we want the cylindrical body to have the strength to withstand plastic working and maintain the high density of the raw material powder after plastic working, the thickness of the Ag cylindrical body must be increased. The cross-sectional area of the cylinder must be 172 to 1/3, and expensive Ag
must be used in larger quantities.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a new method that can solve the problems of the conventional wave technology and produce a sintered superconducting material having a high critical temperature as a practical wire. .

Means for solving the problem, that is, according to the present invention, filling a raw material powder inside a metal cylinder having at least one closed cross section, plastic working the cylinder filled with the raw material powder into a desired shape, Next, in the method for manufacturing a linear superconducting material, which includes the step of sintering the raw material powder by heating the cylinder filled with the raw material powder, the cylinder has an inner cylinder formed of Ag;
A composite clad cylindrical body comprising an outer cylinder made of a metal suitable for plastic working and having a higher tensile strength than Ag,
There is provided a method for manufacturing a linear superconducting material, characterized in that after the outer tube is removed after the plastic working, the heat treatment is performed to sinter the raw material powder.

Function The method for producing a linear superconducting material according to the present invention involves filling a metal cylinder having a closed cross section with raw material powder, plastically working the cylinder filled with the raw material powder, and then heating the raw material powder. In the manufacturing method of a linear superconducting material including each step of sintering the cylindrical body, the cylindrical body is composed of an inner cylinder made of Ag and an outer cylinder made of a metal suitable for plastic working and having a higher tensile strength than Ag. A composite clad cylinder is formed, this composite clad cylinder is plastically worked, and the raw material powder is sintered by heating the AgO inner cylinder filled with the raw material powder after removing the outer metal outer cylinder. It is characterized by

In the method for manufacturing a linear superconducting material according to the present invention, the cylinder to be filled with raw material powder is a composite clad cylinder composed of an inner cylinder made of Ag and an outer cylinder made of a metal other than Ag suitable for plastic working. Its main feature is that the outer cylinder is removed after plastic working and subjected to sintering treatment.

That is, during plastic working, the outer cylinder with sufficient strength supports the raw material powder and the inner cylinder of AgeI&, and during sintering, the outer cylinder with sufficient strength supports the Ag I &
By effectively controlling the oxygen in the raw material powder by effectively utilizing the fact that Ag permeates oxygen and that Ag does not change the raw material powder, a linear superconducting material having excellent properties can be manufactured.

The material for the outer cylinder is A, which is suitable for plastic working.
Any conventionally known metal can be used as long as it has a tensile strength higher than that of g, but especially considering industrial use, steel or iron and its alloys, Ni and its alloys,
A1 alloy etc. can be used advantageously.

Further, when such an outer cylinder is used, it is easy and advantageous to remove the outer cylinder after plastic working by performing pickling treatment using hydrochloric acid, sulfuric acid, nitric acid, or the like. Furthermore, in the case of a long wire, etc., it is preferable that the cylindrical body filled with the raw material powder be coiled and subjected to post-treatment.

Note that the shape of the inner cylinder can also be such that it has a plurality of parallel holes. In this case, in the superconducting material after completion,
The Ag inner cylinder is advantageous because it exhibits higher performance as a current bypass during quenching and as a heat radiation path.

Furthermore, according to the findings of the present inventors, in the case of a sintered superconducting material, the density of the sintered compact is closely related to the superconducting critical current of the material, and when filling the cylinder with raw material powder, Also,
It is preferable to pressurize and fill the raw material powder.

``Plastic working'' in the method of the present invention includes rolling, wire drawing, forging, etc. that have been conventionally performed on metal materials, and the means for carrying out such processing include this wire drawing. In the case of forging, a die, a roller tie, a rolling roll swaging unit, an extruder can be used, and in the case of forging, a swaging, a rolling roll, etc. can be used.

Superconducting materials to which the method of the present invention can be most advantageously applied include complex oxide sintered superconducting materials having a perovskite crystal structure, particularly (Ba-Y-Cu), (Ba-La-Cu) E series, [5r-La-Cu
The excellent properties of l-based composite oxides are well established. Furthermore, the present inventors have also confirmed the excellent properties of the [Ba-Y-Howl system. These composite oxides generally have the following formula: % formula %) [However, element α is an element included in group Ila of the periodic table, and element β is an element included in group 11a of the periodic table. , Element T is 1b, nb, Ib of the periodic table.

rVa or ■An element included in the a group, x, y, z
are x = 0.1 to 0.9, y = 1.0 to 4, respectively.
．． 0, l≦2≦5), and exhibits a superconducting phenomenon in an extremely high temperature range above the liquid nitrogen temperature.

More specifically, the element α is Ba or Sr,
The above element β is Y, La, Gd5Dy, Ho5Er
, Tm.

Examples include a composite oxide layer in which at least one element is selected from the group consisting of Yb and Lu, and the element r is Cu.

The atomic ratio of the elements α and β can be appropriately selected depending on the types of the elements α and β. For example, Ba-Y, Ba-1a,
In the case of the 3r-1a system, it is preferable that the following ratios be satisfied.

Y/(Y+Ba): 0.06~0.
94, preferably 0.1 to 0.4 Ba/(La+Ba): 0.04 to
0.96, preferably 0.08~0.45 Sr/(La+Sr): 0.03~
0.95, preferably 0.05 to 0.1 Among the above combinations of elements, the composite oxide layer that can be formed according to the present invention is, for example, Y-Ba-Cu-0 as exemplified below. Composite oxide layers of La-Ba-Cu-0 system, La-Ba-Cu-0 system, and La-3r-Cu-0 system include: YbBa2Cu30t-x, tlo+Ba2cus
c) +-x.

LJBa2Cua O? -XN Sm1Ba2Cu3
07-XNNd1Ba2Cu3 o,-,,Gd1Ba
2Cua 0t-x, EulBa2Cu+0v-xs
Br1Ba2Cu+0t-x, DylBa2Cu30
t-x, TJBa2Cu*0t-x.

Yb1Ba2Cu30fu-X La+Ba2
Cu307-XN(La, Sr) 2Cu O4-X [However, X is a number satisfying Q<x<l] The above oxide is preferably a perovskite-type oxide or a pseudo-perovskite-type oxide.

Incidentally, pseudo-perovskite refers to a structure similar to perovskite, and includes, for example, an oxygen-deficient perovskite type, an orthorhombic type, and the like.

Such a sintered superconducting material can be obtained by sintering powders of compounds of elements constituting this composite oxide, and in the method of the present invention, a mixture of powders of each compound can be used as the raw material powder as well. Can be done. however,
In order to precisely control the composition of the sintered body, it is preferable to sinter each compound mixture in advance to obtain a composite oxide sintered body, and use the sintered body powder obtained by pulverizing the sintered body as the raw material powder. This is because, in the latter method, since the sintered body already has the composition of the superconducting composite oxide, a superconducting sintered body that is homogeneous and exhibits high characteristics is finally obtained.

The heating temperature during sintering is preferably in the temperature range of 860°C to 970°C. If the sintering temperature exceeds this range, a solid solution phase will occur in the sintered body, and a crystal structure favorable for superconducting properties will not be formed. Furthermore, if the heating temperature does not reach the above range, a sufficient sintering reaction will not occur and a single conductive material will not be formed.

Additionally, according to the findings of the present inventors, in order to produce composite oxide □-based superconducting materials that exhibit excellent properties, it is particularly important to control the oxygen content. It has been found that it is effective for the cloud atmosphere to contain oxygen at a partial pressure of about 1 atm, and to hold the sintered body in the same atmosphere at 300 to 400° C. for 5 hours or more after sintering. As mentioned above, Ag forming the cylinder of the superconducting wire manufactured by the method according to the present invention has a property of permeating oxygen, and therefore is particularly effective in the treatment of the above-mentioned sintered body.

Composite oxide superconducting materials other than the above that can be used in the present invention include the following general formula: % formula % m is a number satisfying 6≦m≦10, and n is 4≦n≦
It is a number that satisfies 8, p = (6 + 2m + 2n) / 2, and q is 0
A composite oxide superconductor layer mainly having a composition represented by <q<1, and r represents a number satisfying -2≦r≦2] can be mentioned.

More specifically, the following systems may be mentioned:
2Ca2Cu30+o-o or B14Sr4Ca4C
usOzno-x)T12Ba2Ca2Cu30 +
O-1+ or T12Ba4Ca4Cus O2(I
0-)l) [However, X is a number satisfying 12≦X≦2] The present invention will be described in more detail with reference to Examples below. This is just one example;
This is not intended to limit the technical scope of the present invention in any way.

Example Ba○ powder with a purity of 99.9% and Y2 with a purity of 99.9%
O3 powder and CuO powder with a purity of 99.99% are mixed in Y:B
a: Mix so that the atomic ratio of Cu is 1:2:3,
It was ground in a mortar to obtain a powder mixture. Shape this mixture
Pre-calcined at 940°C for 15 hours under an oxygen partial pressure of 1 atm,
The obtained fired body was ground again in a mortar. Below, [Molding→
Repeat the series of firing → crushing three times under the same conditions,
Finally, a fired powder with a particle size of 10 μm or less was obtained and used as a raw material powder. It should be noted that during cooling after each firing process, slow cooling was performed in the same atmosphere as the firing process, and after being held at 350°C for 10 hours, it was cooled to room temperature.

On the other hand, as a cylinder, the wall thickness is 1. A cylindrical body with an outer diameter of 6 IT and 1 m was prepared. This cylinder is a composite clad material formed from an inner cylinder made of Ag with a wall thickness of 9.2 mm and an outer cylinder made of 0.4% carbon steel with a wall thickness Q of 8 m+y+.

Also, wall thickness 1.0++on, outer diameter 5m+ncDAg,
Pipes made of Cu and 0.4% carbon steel were prepared as comparison samples ①, ②, and ②, respectively, and linear superconducting materials were created in the steps described below.

After filling each cylinder with the raw material powder described above and sealing both ends of the pipe, wire was drawn using a die so that each pipe had an outer diameter of 3.2 mm.

According to the present invention, for samples using a composite clad material, the outer cylinder was removed by pickling with hydrochloric acid after wire drawing. Each wire rod thus obtained was heated at 940° C. for 10 hours and slowly cooled. In addition, when cooling, the temperature of each sample was reduced to 350°C.
Cooling was once stopped at 0.degree. C., and after maintaining this temperature for 10 hours, it was actively cooled to room temperature.

From the obtained wire rods, samples each having a length of 3 cm were cut.
After removing the Ag cylinder from this sample by polishing, electrodes were attached to both ends of the core material using Au paste, and it was confirmed that the electrical resistance became completely zero by cooling with liquid nitrogen. Next, the temperature of the sample is gradually raised using a heater.
The temperature Tc at which the electrical resistance becomes equal to the normal state was measured.

The measurement was performed using the DC 4-point probe method in a cryostat, and the temperature was measured using a calibrated 111u probe.
This was carried out using a (Fe)-Ag thermocouple. The measurement results are shown in Table 1.

Furthermore, the densities of the sintered bodies were measured for the samples before sintering and the samples after resistance measurement, and the effects of plastic working were investigated. The density was determined by dividing the weight of the sample by the volume of the sintered body obtained by Guiflon impregnation specific gravity measurement method.

Table 1 Effects of the Invention As detailed above, according to the method of the present invention, effective It is possible to manufacture linear superconducting materials that exhibit excellent properties by achieving both precise plastic working and precise oxygen control.

In addition, the superconducting material manufactured in this way has a superconducting sintered body protected in an Ag cylinder, so it is prevented from deteriorating due to the atmosphere and has sufficient mechanical strength.
It can be practically used as a wire rod. Therefore, it can be widely used for wire rods or small parts as a superconducting material having a high (stable Tc).

Furthermore, since the use of expensive Ag is limited to the inner cylinder, the cost of the product can also be reduced.

Patent applicant: Sumitomo Electric Industries, Ltd.

Claims (1)

[Claims] A raw material powder is filled inside a metal cylinder having at least one closed cross section, the cylinder filled with the raw material powder is plastically worked into a desired shape, and then the raw material powder is filled. In the method for manufacturing a linear superconducting material, the method includes the step of sintering the raw material powder by heating the cylinder, the cylinder having an inner cylinder formed of Ag, and an inner cylinder suitable for plastic working and made of Ag. The composite clad cylinder is also equipped with an outer cylinder formed of a metal with high tensile strength, and after the outer cylinder is removed after the plastic working, the heat treatment is performed to sinter the raw material powder. A manufacturing method for characteristic linear superconducting materials.