JP2557498B2 - Manufacturing method of linear superconducting material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing 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 a long superconducting material while retaining the excellent superconducting material of the long superconducting material containing a complex oxide-based sintered body material.

Conventional technology Under the superconducting phenomenon, a substance shows complete diamagnetism, and the potential difference disappears even though a finite steady current flows inside. Therefore, various applications of superconductors as transmission media without power loss have been proposed.

That is, its application fields are power fields such as MHD power generation, power transmission, and power storage, power fields such as magnetic levitation trains and electromagnetic propulsion vessels, and NMR as a super-sensitive sensor for magnetic fields, microwaves, radiation, etc. , Pion therapy, measurement fields such as high-energy physics experimental equipment, and so on.

Further, in the field of electronics represented by Josephson devices, it is expected as a technique that can realize not only a reduction in power consumption but also an extremely fast operating device.

By the way, superconductivity was a phenomenon observed only at extremely low temperatures. That is, even in Nb ₃ Ge, which was said to have the highest superconducting critical temperature Tc as a conventional superconducting material, the superconducting critical temperature was extremely low at 23.2 K, which was the limit of the superconducting critical temperature for a long time.

Therefore, conventionally, in order to realize the superconductivity phenomenon, the superconducting material has been cooled to Tc or less using liquid helium having a boiling point of 4.2K. However, the use of liquid helium has
The technical burden of Nara and the cost of the cooling equipment including the liquefaction equipment was extremely large, which hindered the practical application of superconducting technology.

However, recently, II a group elements or III a
It has been reported that a composite oxide sintered body containing a group element can be a superconductor with an extremely high Tc, and the practical application of the superconducting technology using a non-low temperature superconductor is being promoted.

So far, it is already known that the composite oxide-based ceramic material exhibits superconducting properties.For example, in U.S. Pat.No. 3,932,315, Ba-Pb-Bi-based composite oxides have superconducting properties. In addition, it is described in JP-A-60-173,885 that the Ba-Bi-based composite oxide exhibits superconducting properties. However, since the Tc of the above-described complex oxides of the above-mentioned system is 10 K or less, liquid helium (boiling point 4.2 K) has to be used for causing the superconducting phenomenon.

However, in 1986, when Bednots and Muller et al. Discovered a superconducting oxide having a Tc much higher than that of conventional metal-based superconducting materials, the possibility of high-temperature superconductivity has greatly opened up (Z.Phys. B64, 1986, September, p18
9-193).

The oxide superconductors discovered by Bednots and Mueller are (La, Ba) ₂ CuO _{4 and} (La, Sr) ₂ CuO.
₄ ), this oxide superconductor is called K ₂ NiF ₄ type oxide, and these substances are similar in crystal structure to the conventionally known perovskite type superconducting oxide,
Its Tc is about 30K, which is dramatically higher than that of conventional superconducting materials.
Is the value.

Furthermore, in February 1987, it was reported that Chu and others discovered a Ba-Y-based complex oxide exhibiting a critical temperature in the 90K class, and the possibility of realizing a non-low temperature superconductor increased dramatically. ing.

However, since these superconducting materials are obtained as a sintered body, they are generally fragile and require careful handling. That is, cracks or breakage easily occur due to mechanical stress, and it is extremely fragile especially when made into a wire rod, and there is a great limitation in practical use. Therefore, various methods have been proposed for manufacturing a superconducting wire having sufficient mechanical strength by filling a raw material powder of a superconducting sintered body into a metal cylinder or the like and processing it.

In this method, for example, a raw material powder is filled in a tubular body made of a metal material suitable for composition processing, and this is processed into a desired shape by processing such as wire drawing or forging,
This is a method of increasing the density of the raw material powder inside and then sintering it to produce a sintered product having a thin or complicated shape.
The superconducting wire produced by such a method has not only sufficient mechanical strength, but also when the superconducting material is quenched, the metal cylinder functions as a bypass and a heat dissipation path for the current. It is considered to be an extremely effective technology.

DISCLOSURE OF THE INVENTION In view of such circumstances, the inventors of the present invention have a cross-section of the longitudinal dimension that can be practically and sufficiently used without using an organic pressure-sensitive adhesive that causes reduction in strength and toughness. As a method of manufacturing a sintered ceramic wire that can be formed longer than the dimension in the direction,
First, US Patent Application No. 152,713 filed on February 5, 1988.
No. 161,480, filed February 29, 1988, 1
In US patent application No. 182,489 filed on April 18, 988, US patent application No. 189,366 filed on May 2, 1988 and US patent application No. 225,207 filed on August 3, 1988, ceramic raw material powder A metal cylinder, in particular, in a Ag cylinder, and after metal working the metal cylinder filled with the raw material powder,
A method of sintering was proposed.

However, even when the metal cylinder is filled with the raw material powder and sintered as described above, the sintered body does not exhibit sufficiently high superconducting properties, that is, the characteristics when only the sintered body is manufactured in a bulk shape. Often cannot reach. It is considered that this is because oxygen contained in the sintered body is not sufficiently controlled in order to fill the cylindrical body and sinter it.

That is, in order to manufacture a superconducting sintered body that exhibits high superconducting properties, it is required to control the oxygen content in the manufacturing process extremely precisely. An example of a manufacturing process that has been found to be effective as a method for manufacturing a known bulk superconducting sintered body material is compound powder (generally using an oxide) containing the constituent elements of the superconducting sintered body. It is pulverized and mixed into raw powder.

 The obtained raw material powder is compacted.

Sintering is performed by heating to a predetermined temperature under an oxygen partial pressure of about 1 atm.

Under the same partial pressure of oxygen, the temperature is gradually cooled from 300 ° C to 400 ° C, and this temperature is maintained for several hours to ten and several hours.

 Cool to room temperature.

Of these processes, the annealing treatment, in particular,
There is an extremely close relationship with the oxygen content of the obtained sintered body, and it is considered to be an indispensable treatment for making the material exhibit high superconducting properties and further stabilizing it. However, as described above, when the raw material powder is filled in the metal cylinder and sintered, it is difficult to anneal the sintered body while exposing it to an oxygen atmosphere, and the sintering also depends on the atmosphere. Oxygen cannot be controlled, which causes deterioration of superconducting properties of the superconducting wire.

Further, it has been proposed to solve the above problems by using Ag as the material of the metal tubular body. That is,
Ag has a property of artificially permeating oxygen due to its redox reaction, and by using this as a metal cylinder, it becomes possible to control oxygen during sintering or annealing. However, Ag is an extremely expensive material,
There is a problem that it is not suitable for industrial production of wire rods. Further, when the raw material powder is filled into the cylinder and is sintered, the cylinder filled with the raw material powder needs to be plastically worked in order to achieve a sufficient density of the sintered body. However, when Ag is used as the cylindrical material, the thickness of the Ag-made cylindrical body is reduced if the cylindrical body is to have strength capable of withstanding plastic working and maintaining the high density of the raw material powder after plastic working. 1/2 of cylindrical cross section
To 1/3, and more expensive Ag must be used.

Therefore, an object of the present invention is to solve the above-mentioned problems of the prior art and to provide a novel method capable of producing a sintered superconducting material having a high critical temperature as a practical wire rod.

Means for Solving the Problems That is, according to the present invention, a raw material powder is filled inside a metal tubular body having at least one closed cross section, and the tubular body filled with the raw material powder is plastically worked into a desired shape, Then, in the method for producing a linear superconducting material including a step of sintering the raw material powder by heating the raw material powder-filled tubular body, the tubular body, an inner cylinder formed of Ag,
A composite clad cylindrical body having an outer cylinder formed of a metal that is suitable for plastic working and has a higher tensile strength than Ag, and the heat treatment is performed after the outer cylinder is removed after the plastic working There is provided a method for producing a linear superconducting material, which comprises sintering a powder.

Action The method for producing a linear superconducting material according to the present invention is such that a raw material powder is filled inside a metal tubular body having a closed cross section, the raw material powder-filled tubular body is plastically processed, and then the raw material powder is heated. In a manufacturing method of a linear superconducting material including each step of sintering, the cylindrical body is constituted by 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, the composite clad cylinder is plastically worked, and then the outer metal outer cylinder is removed, and then the Ag inner cylinder filled with the raw material powder is heated to sinter the raw material powder. It is characterized by doing.

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

That is, the outer cylinder having sufficient strength during plastic working supports the raw material powder and the inner cylinder made of Ag, and at the time of sintering, it effectively utilizes that Ag oxygen permeates and that Ag does not mean the raw material powder. By effectively controlling the oxygen of the raw material powder, it is possible to manufacture a linear superconducting material having excellent characteristics.

The material of the outer cylinder is suitable for plastic working.
Any conventionally known metal can be applied as long as it has a higher tensile strength than Ag, but steel or iron and its alloys, Ni and alloys, Al alloys, etc. are advantageously used in consideration of industrial use. it can. When such an outer cylinder is used, it is easy and advantageous to remove the outer cylinder after plastic working by performing a pickling treatment with hydrochloric acid, sulfuric acid, nitric acid or the like. Further, in the case of a long wire or the like, it is preferable that the cylindrical body filled with the raw material powder is formed into a coil and subjected to post-treatment.

In addition, the shape of the inner cylinder may have 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 and a heat radiation path at the time of quenching.

Further, according to the knowledge of the present inventors, in the case of the superconducting material of the sintered body, the density of the sintered body is closely related to the superconducting critical current of the material, and when filling the cylindrical body with the 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 any of the rolling, wire drawing, forging, etc. that have been conventionally carried out on a metal material, and the means for carrying out this is in the case of this wire drawing. , Dies, roller dies, rolling rolls,
You can use swaging unit and pusher,
In the case of forging, swaging, rolling rolls, etc. can be used.

The superconducting material to which the method of the present invention can be most advantageously applied includes a complex oxide sintered body superconducting material having a perovskite crystal structure, and particularly [Ba-Y-Cu] system,
Excellent properties have been confirmed for [Ba-La-Cu] -based and [Sr-La-Cu] -based composite oxides. Further, the present inventors have confirmed excellent characteristics also for the [Ba-Y-Ho] system. These complex oxides are generally represented by the following formula: (α _1-x β _x ) γ _y O _z [where the element α is an element included in Group IIa of the periodic table, and the element β is a periodic table Table IIIa is an element included in Group a, and element γ is Ib, IIb, IIIb, IVa or VI of the periodic table.
II is an element contained in the group a, x, y, and z each have a composition represented by x = 0.1 to 0.9, y = 1.0 to 4.0, and 1 ≦ z ≦ 5) It exhibits superconductivity in the extremely high temperature range above the nitrogen temperature.

More specifically, the element α is Ba or Sr, and the element β is at least one element selected from the group consisting of Y, La, Gd, Dy, Ho, Er, Tm, Yb and Lu. And a complex oxide layer in which the element γ is Cu.

The atomic ratio of the elements α and β can be appropriately selected depending on the types of α and β. For example, Ba-Y, Ba-La, Sr-La
In the case of a system, it is preferable to satisfy the following ratios.

Y / (Y + Ba): 0.06 to 0.94, preferably 0.1 to 0.4 Ba / (La + Ba): 0.04 to 0.96, preferably 0.08 to 0.45 Sr / (La + Sr): 0.03 to 0.95, preferably 0.05 to 0.1 Combination of the above elements Among them, as the complex oxide layer that can be formed according to the present invention, for example, the following Y-Ba-Cu-O system, La-Ba-Cu-O system and La-Sr- system are exemplified.
Cu-O-based composite oxide layer may be _{mentioned: Y 1 Ba 2 Cu 3 O} 7-x, Ho 1 Ba 2 Cu 3 O 7-x, Lu 1 Ba 2 Cu 3 O 7-x, Sm 1 Ba 2 Cu ₃ O _7-x , Nd ₁ Ba ₂ Cu ₃ O _7-x , Gd ₁ Ba ₂ Cu ₃ O _7-x , Eu ₁ Ba ₂ Cu ₃ O _7-x , Er ₁ Ba ₂ Cu ₃ O _7-x , Dy ₁ Ba ₂ Cu ₃ O _7-x , Tm ₁ Ba ₂ Cu ₃ O _7-x , Yb ₁ Ba ₂ Cu ₃ O _7-x , La ₁ Ba ₂ Cu ₃ O _7-x . (La, Sr) ₂ CuO _4-x [where x is a number satisfying 0 <x <1] The above oxide is preferably a perovskite type oxide or a pseudo perovskite type oxide. The pseudo perovskite has a structure similar to that of the perovskite, and includes, for example, oxygen-deficient perovskite type, orthorombic type, and the like.

Such a sintered body superconducting material is obtained by sintering the powder of the compound of the element that constitutes this composite oxide, and also in the method of the present invention, the mixture of each compound powder is used as the raw material powder. it can. However,
In order to precisely control the composition of the sintered body, it is preferable that each compound mixture is fired in advance to obtain a composite oxide fired body, and the fired body powder obtained by crushing this is used as the raw material powder. Because, in the latter method, since the fired body has already constituted the composition of the superconducting composite oxide, a superconducting sintered body having a homogeneous and high characteristic 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 occurs in the sintered body, and a crystal structure that is favorable for superconducting properties cannot be formed. Further, if the heating temperature does not reach the above range, a sufficient sintering reaction does not occur and the superconducting substance is not formed.

Further, according to the knowledge of the present inventors, in order to produce a complex oxide superconducting material exhibiting excellent characteristics, it is particularly important to control the oxygen content thereof, which is the atmosphere at the time of sintering. It has been found that it is effective to contain oxygen at a partial pressure of about 1 atm and to hold the sintered body at 300 to 400 ° C. for 5 hours or more in the same atmosphere after sintering. As described above, since it has a property of permeating Ag oxygen forming the tubular body of the superconducting wire produced by the method according to the present invention, it is particularly effective for the treatment of the above-mentioned sintered body.

Examples of complex oxide-based superconducting materials other than the above that can be used in the present invention include the general formula: D ₄ (E _1-q , Ca _q ) _m Cu _n O _{p + r} [wherein D is Bi or T 1, E is Sr when D is Bi, Ba when D is T1, m is a number satisfying 6 ≦ m ≦ 10, and n is a number satisfying 4 ≦ n ≦ 8 , P = (6 + 2m + 2n) / 2, q is a number satisfying 0 <q <1, and r is a number satisfying −2 ≦ r ≦ 2] An oxide superconductor layer is mentioned.

More specific examples include the following systems: Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _10-x or Bi ₄ Sr ₄ Ca ₄ Cu ₆ O _{2 (10-x)} Tl ₂ Ba ₂ Ca ₂ Cu ₃ O _10-x or Tl ₂ Ba ₄ Ca ₄ Cu ₆ O _{2 (10-x)} [where X is a number satisfying −2 ≦ x ≦ 2] The present invention will be described more specifically with reference to Examples below. Although described in detail, what is disclosed below is only one embodiment of the present invention,
The technical scope of the present invention is not limited in any way.

Example BaO powder having a purity of 99.9%, Y ₂ O ₃ powder having a purity of 99.9%,
CuO powder having a purity of 99.99% was mixed so that the atomic ratio of Y: Ba: Cu was 1: 2: 3, and ground in a mortar to obtain a powder mixture. This mixture was molded and pre-baked at 940 ° C./15 hours under an oxygen partial pressure of 1 atm, and the obtained baked product was ground again in a mortar. Hereafter, a series of processes of [molding → baking → crushing] is performed under the same conditions.
Repeated times, finally a fired body powder having a particle size of 10 μm or less was obtained and used as a raw material powder. In addition, at the time of cooling after each firing process, each time it is slowly cooled in the same atmosphere as the firing, 350 ℃
The temperature was maintained for 10 hours and then cooled to room temperature.

On the other hand, a cylinder having a wall thickness of 1.0 mm and an outer diameter of 6 mm was prepared as the cylinder. This cylinder consists of a 0.2 mm thick Ag inner cylinder and a 0.8 mm thick inner cylinder.
A composite clad material formed from an outer cylinder of 0.4% carbon steel.

Also, pipes made of Ag, Cu, and 0.4% carbon steel with a wall thickness of 1.0 mm and an outer diameter of 6 mm were prepared as comparative samples, respectively.
A linear superconducting material was created in the process described below.

Each of the cylinders was filled with the above-mentioned raw material powder, and after sealing both ends of the pipe, wire drawing was performed using a die until the outer diameter was 3.2 mm.

According to the present invention, with respect to the sample using the 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 then gradually cooled. During cooling, the temperature of each sample was temporarily stopped at 350 ° C., the temperature was kept for 10 hours, and then the sample was positively cooled to room temperature.

From the obtained wire rod, cut a sample with a length of 3 cm,
After removing the Ag cylindrical body from this sample by polishing, electrodes were attached to both ends of the core material with Au paste, and it was confirmed that the electrical resistance became completely zero by cooling with liquid nitrogen.
Subsequently, the temperature of the sample was gradually raised by the heater, and the temperature Tc at which the electric resistance became equal to the normal state was measured.

In addition, the measurement is performed by the DC 4-point probe method in the cryostat, and the temperature measurement is performed by the calibrated Au (F
e) -Ag thermocouple. The measurement results are shown in Table 1.

Furthermore, the density of the sintered body was measured for each of the sample before sintering and the sample after the resistance velocity, and the effect of plastic working was investigated. The density was measured by dividing the weight of the sample by the volume of the sintered body obtained by the diflon impregnation specific gravity measurement method.

Effects of the Invention As described above in detail, according to the method of the present invention, an effective composition processing is achieved by using a cylindrical body composed of an outer cylinder having excellent strength and an Ag inner cylinder having oxygen permeability. It is possible to manufacture a linear superconducting material that achieves excellent characteristics by satisfying both precise oxygen control.

Further, the superconducting material produced in this way, since the superconducting sintered body is protected in the Ag cylinder, deterioration due to the atmosphere is prevented, and it has sufficient mechanical strength, and as a wire rod. It can be used practically. Therefore, it can be widely used for wire rods or small parts as a superconducting material having a high and stable Tc.

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

Claims (1)

(57) [Claims] 1. A raw material powder is filled into 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 a method for producing a linear superconducting material including a step of sintering the raw material powder by heating a cylindrical body, the cylindrical body is an inner cylinder formed of Ag, and suitable for plastic working and more than Ag. A composite clad cylinder body having an outer cylinder formed of a metal having high tensile strength, wherein the heat treatment is performed after the outer cylinder is removed after the plastic working, and the raw material powder is sintered. And a method for producing a linear superconducting material.