JPH01279510A - Manufacture of linear superconductive material - Google Patents

Abstract

PURPOSE:To facilitate manufacture of sintered superconductive material as a wire in practical application having high critical temp. by accommodating Au2O3 in a metal cylinder together with material powder in a manufacturing process, in which material powder is sintered in the metal cylinder. CONSTITUTION:Au2O3 dissolves at a temp. over 160 deg.C and emits oxygen to supply oxygen to the material powder which is required at the time of sintering. A plasticible metal cylinder is used with one end closed, and wire stretching or forging turns it into required form while the material powder is held in the cylinder at an appropriate density. Prior to filling of material powder, the Au2O3 is attached to the inner surface of the metal cylinder, and it is desirable that the substance produced after supply of oxygen does not react with the sintered substance. By this method, a wire can be manufactured practically in which a sintered substance having high superconductivity is accommodated in a metal cylinder having substantial mechanical strength and plasticity.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for manufacturing wire rods or elongated materials using composite oxide superconducting materials. More specifically, a method for manufacturing a novel linear sintered product that can impart practical mechanical strength to a sintered superconducting material and effectively retain the excellent superconducting properties inherent in this material. Regarding.

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, even in Nb3Ge, which is said to have the highest superconducting critical temperature (hereinafter referred to as Tc) among conventional superconducting materials, Tc is 23.2 K.
This was considered to be the limit of superconducting critical temperature for a long time.

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 heavy technical and cost burden due to cooling equipment, including liquefaction equipment (which has been an obstacle to the practical application of superconducting technology).

However, in recent years, group IIa elements or II[a
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.

In already reported examples, CLa - which is thought to have a perovskite crystal structure such as K2NiF4 type
It has been reported that complex oxides based on Ba-Cu), [La-5r-['u], or (Ba-Y-Co1) show signs of reduced superconductivity in the temperature range above liquid nitrogen temperature. .

However, since these superconducting materials are generally obtained as sintered bodies, they are brittle and must be handled with care.

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

In this method, a cylindrical outer cylinder member made of a metal material suitable for compositional processing is filled with raw material powder, and this is processed into a desired shape by wire drawing or forging. This is a method of increasing the density of sintered materials and then sintering them to produce sintered products with thin or complex shapes. The superconducting wire produced by this method not only has sufficient mechanical strength due to the metal sheath, but also has the metal sheath function as a current bypass and a heat dissipation path when the superconducting material is quenched. Therefore, it is considered to be an extremely effective technology for producing superconducting wires.

Problem to be Solved by the Invention 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 some cases, the characteristics cannot be achieved when the material is manufactured in a similar shape. 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.

According to the findings of the present inventors, in order to produce a superconducting sintered body that exhibits high superconducting properties, it is required to extremely precisely control the oxygen content in 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 materials is: ) is finely ground and mixed to obtain raw material powder.

■ The obtained raw material powder is compactly molded.

■ Sinter by heating to a predetermined temperature in an oxygen-containing atmosphere.

(2) Heat treatment is performed at a temperature of 300° C. or higher in an oxygen-containing atmosphere for several hours to more than ten hours.

Through these processes, controlling the oxygen content in the atmosphere, especially during sintering or heat treatment, is extremely closely related to the oxygen content of the resulting sintered body, allowing the material to exhibit high superconducting properties and further stabilizing it. Precise control is essential for this purpose.

However, when a metallic cylinder is filled with raw material powder and sintered as described above, it is difficult to sinter or heat-treat the sintered body while exposing it to an oxygen atmosphere, which affects the superconducting properties of the superconducting wire. This was a factor that hindered the improvement of

To solve this problem, it has been proposed to use Ag as the material of the metal cylinder. That is, Ag has the property of pseudo-permeating oxygen due to its oxidation-reduction reaction, and by using it as a metal cylinder, it is possible to control oxygen during sintering or heat treatment. However, even with this method, the properties are only improved near the surface of the filled raw material powder by the oxygen that has passed through the Ag cylinder, and therefore the entire cross section of the superconducting sintered body obtained is It does not necessarily exhibit excellent characteristics effectively.

Therefore, excellent characteristics not only in critical temperature but also in critical current density cannot be obtained.

In addition, Ag is an extremely expensive material and is not suitable as a material for industrially manufactured wire rods.
A new problem has arisen in that the above-mentioned properties of Ag do not prevent the removal of oxygen or oxidation from the completed wire rod, and some countermeasures are required.

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the prior art described above and to provide a new method that can practically produce a wire rod from a sintered superconducting material having a high critical temperature.

Means for Solving the Problems According to the present invention, a raw material powder is filled inside an outer cylinder member having at least one closed cross section and formed of a metal suitable for plastic working, and an outer cylinder filled with the raw material powder. A method for producing a linear superconducting material, which includes a step of plastically working a member and then heating it to sinter the raw material powder, the method including heating treatment after accommodating Au20s together with the raw material powder inside the outer cylindrical member. A method for manufacturing a linear superconducting material is provided, which is characterized by performing a series of treatments.

Here, according to one aspect of the present invention, the Au20i is
The powder is filled into the outer cylindrical member together with the raw material powder.

Further, according to a preferred embodiment of the present invention, the Au2
It is advantageous that the Au 203 is accommodated within the outer tube member by adhering to the inner surface of the outer tube member, and the raw material powder is further accommodated inside the Au203.

The outer cylindrical member may be a pipe of a predetermined length, and the plastic working may be wire drawing on the outer cylindrical member. Here, examples of the wire drawing process include die wire drawing, roller die wire drawing, rolling roll wire drawing, swaging, extrusion wire drawing, and the like.

Further, the plastic working may be a forging process for the outer cylinder member, and an example of the forging process is swaging.

Furthermore, according to a preferred embodiment of the present invention, the heating temperature in the sintering step after the composition processing is 850 to 1200 ℃.
It is preferable that the temperature is within the range of ℃, and furthermore, after the sintering,
It is advantageous to gradually cool the outer cylindrical member filled with the raw material powder to a minimum of 160° C., maintain the temperature above that temperature for 5 hours or more, and then rapidly cool it.

According to one aspect of the present invention, the raw material powder contains a compound containing an element α included in group a of the periodic table [I
Compounds containing element β included in the Ja group and periodic table 1
Each powder of a compound containing the element γ included in the b 11I b s ■b -, ■a, or ■a group may be mixed so as to contain all of the elements α, β, and T.

Further, the raw material powder may be mixed with a compound containing an element α included in group IIa of the periodic table, a compound containing an element β included in group IIIa of the periodic table, and Ib, nb s I[I
b s IV A starting material obtained by mixing each powder of a compound containing the element T included in group a or ■a so as to contain all of the elements α, β, and T is sintered, and the sintered body formed is pulverized. It is also preferable to use a composite oxide sintered body powder obtained by

Here, the heating temperature during the firing is 850 to 1200.
℃ range is preferable, and furthermore, after the firing, the fired body is heated to 3
It is advantageous to carry out a process of slowly cooling the material to 00 to 400° C., then holding the temperature range for 5 hours or more, and then rapidly cooling it to room temperature.

Note that the combination of the elements α, β, and T is α/β/
T”Ba/Y/Cu, Ba/La/Cu,
Examples include Sr/La/Cu, Ba/No/Cu, but are not limited to these.

The fired body obtained by firing a combination of these elements has the general formula = (α+-x βx)ryδ2 (where α is an element included in group 1a of the periodic table, and β
is an element included in group ma of the periodic table, γ is an element included in group Ib, IIb, lb, ■a, or ■a of the periodic table, δ is 0 (oxygen), and Xs'JsZ is X=0.1~0.9, y=1.0~4.0.1≦, respectively
It is considered to have a perovskite-type or pseudo-perovskite-type crystal structure.

Furthermore, the application of the present invention is not limited to the above-mentioned composite oxide superconducting materials, and it goes without saying that it can be applied to other oxide superconducting materials as well.
-3r-Cu system or TI -Ca-Ba (Sr)
-Cu-based composite oxides and the like can be mentioned as superconducting materials that can be advantageously applied.

Function: The method for manufacturing a linear superconducting material according to the present invention includes placing Au20. Its main feature is to contain powder.

That is, it is known that Au203 decomposes and releases O in a temperature range of 160° C. or higher. Therefore, due to the presence of Au 203 inside the outer cylinder member, oxygen released from the Au 20° through the sintering process and heat treatment of the raw material powder is supplied to the raw material powder inside the outer cylinder member.

On the other hand, if the supply of oxygen to the raw material powder is ensured as described above, it is no longer necessary for the outer cylinder member to permeate oxygen, and it is no longer necessary to use a metal other than Ag that is inexpensive and has good workability, that is, carbon.
u, A1, etc. can be used freely.

There are many possible ways to accommodate AuzOs in the outer cylinder member. The easiest method is to mix it into the raw material powder as a powder, and the effect as an oxygen supplying agent can be uniformly obtained throughout the raw material powder. However, in this case, there is a possibility that the substance generated after the oxygen supply agent releases oxygen may react with the superconducting sintered body.

Therefore, one effective method is to attach Au203 to the inner surface of the outer cylinder member prior to filling the raw material powder. In this case, Au20. Even if the raw material powder and the raw material powder react, it is limited only to the vicinity of the surface of the raw material powder, so that an effective superconducting sintered body is formed near the center of the raw material powder. Note that in order to prevent the oxygen supplied by the Au 20a from dissipating, it is preferable that the opening of the outer cylinder member is sealed after being filled with the raw material powder.

The metal cylindrical body filled with the raw material powder thus obtained can be processed into a desired shape by performing general plastic working performed on elongated metal materials. The most common processing method is wire drawing, and it can be easily formed into a wire by known methods such as die wire drawing, roller die wire drawing, rolling roll wire drawing, swaging, and extrusion wire drawing. can.

Furthermore, as mentioned above, since a superconducting sintered body generally has a high density, which favorably affects its properties, the aforementioned metal cylinder is subjected to, for example, forging processing to reduce the volume of the cylinder. It is also preferable to improve the properties of the superconducting wire by doing so. Note that for the forging process, for example, swaging can be cited as an advantageous method.

Now, the raw material powder filled in the outer cylindrical member as described above is generally heated to a temperature range of 850°C to 1200°C and sintered to form a composite oxide sintered body that exhibits effective superconducting properties. becomes. Here, the sintering temperature should be adjusted appropriately depending on the combination of each element contained in the raw material powder. 95 for Ba-La-Cu] system
The temperature is preferably about 0°C. Note that if the sintering temperature exceeds the above range, a solid solution phase will occur in the raw material powder, inhibiting the formation of a crystal structure effective for superconducting properties. On the other hand, if the sintering temperature is lower than the above range, there will be a lack of effective sintering reaction, and either the superconducting material will not be formed or it will take a very long time to form.

Further, in the cooling process after sintering, it is preferable to keep the cooling rate low at a temperature higher than the decomposition temperature of the oxygen supply agent added to the raw material powder to sufficiently promote the sintering reaction. On the other hand, if the temperature is below the decomposition temperature of the oxygen supply agent, the supply of oxygen by the oxygen supply agent is no longer guaranteed, so it is preferable to cool rapidly in order to prevent the formed superconducting material from deteriorating in quality.

Furthermore, it is considered effective to subject the material to heat treatment again at a temperature higher than the decomposition temperature of the oxygen supply agent after sintering. That is, more precise oxygen control becomes possible by subjecting the material to heat treatment for a predetermined period of time in a state where oxygen is sufficiently supplied by the oxygen supplying agent. In this case as well, it is preferable to increase the cooling rate in the cooling after the heat treatment, especially in the temperature range below the decomposition temperature of the oxygen supply agent, to prevent the superconducting material formed by the heat treatment from deteriorating.

Superconducting materials to which the method of the present invention can be most advantageously applied include composite oxide sintered superconducting materials that are thought to have a perovskite crystal structure, and in particular [B
a-Y-Co3 system, (Ba-La-CuE system, [5r
-La-Cu)-based and (Ba-t(o-Co3)-based composite oxides have been confirmed to have excellent properties.

These composite oxides generally have the following formula: % formula %) (However, α is an element included in Group IIa of the periodic table,
β is an element included in the Ja group of periodic table 11, T is an element included in the Ib, nb, mb, ■a, or ■a group of the periodic table, δ is O (oxygen), and xsYsZ are each X=0.1~0.9, y=1.0~4.0.1
≦2≦5) It exhibits a superconducting phenomenon in an extremely high temperature range above the temperature of liquid nitrogen.

Such a sintered superconducting material is obtained by sintering a mixed powder of a compound containing the elements constituting this composite oxide, and in the method of the present invention, a mixture of each compound powder is similarly used as a raw material powder. Can be used. 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.

It goes without saying that the method of the present invention can be advantageously applied not only to the composite oxide superconducting material described above, but also to the production of other sintered wire materials that require the presence of oxygen in the production process. do not have.

That is, Bi-Ca-3r-Cu system or TI-C
An example of a superconducting material that can be advantageously applied is a-Ba (Sr)-Cu-based composite oxide.

The present invention will be described in more detail below with reference to examples, but what is disclosed below is only one example of the present invention.
This is not intended to limit the technical scope of the present invention in any way.

Example BaCO3 powder with a purity of 99.9%, Y2O3 powder with a purity of 99.9%, and CuO powder with a purity of 99.99%,
The mixture was ground and mixed in a mortar so that the atomic ratio Ba:Y:Cu was 2:1:3, and the mixture was molded and pre-calcined at 940°C for 15 hours under an oxygen partial pressure of 1 atm. The fired body was ground again in a mortar. Below, the series of processes [molding → firing → crushing] is repeated three times, and the final particle size is 10.
A sintered body powder with a size of less than μm was obtained, and this was used as a raw material powder. It should be noted that during cooling after each firing process, the material was gradually cooled in the same atmosphere as the firing process, and after being held at 350° C. for 15 hours, it was cooled to room temperature.

On the other hand, as an outer cylinder member, C with a wall thickness of 2 mm and an outer diameter of 10 mm is used.
Five pipes made by U were prepared.

Two of these Cu pipes [Samples ① and ②] were filled with raw material powder after adhering separately prepared Au203 powder to the inner surface to a thickness of about 0.5 mm.

In addition, for the other two [Samples ■ and ■], Au2 was added to the raw material powder.
A mixture of approximately the same amount of C) + powder was filled.

Furthermore, the remaining one [Sample ■] was filled with only the raw material powder as it was.

Both ends of each pipe filled with the raw material powder were sealed, and the wire was drawn by swaging until the outer diameter reached six pieces. Each of the obtained wire rods was heated at 940° C. for 10 hours and slowly cooled to lower the temperature. During this cooling, for samples (1), (2), and (2), cooling was further stopped at 190° C., and after being maintained for 10 hours, they were actively cooled to room temperature.

After attaching electrodes to the obtained wire with a length of about 3 Qcm using Au paste, it was cooled for ms until the electrical resistance became completely zero. Subsequently, the temperature of the sample was gradually raised using the heater 1, and the temperature at which the electrical resistance became equal to the normal temperature was measured. In addition, critical current density was also measured.

The measurement was performed using the four-point terminal method in a taliostat, and the temperature was measured using a calibrated Au (Fe
)-Ag thermocouple was used. The measurement results are shown in Table 1.

Table 1 Effects of the Invention As detailed above, according to the method of this invention, even if the raw material powder is filled into the outer cylinder member and sintered or heat treated,
Since sufficient oxygen is supplied by the oxygen supply agent housed in the metal cylinder during sintering or heat treatment, a superconducting material containing a sintered body having high superconducting properties can be manufactured.

In addition, since the superconducting sintered body is protected in a metal cylinder, the superconducting material manufactured in this way is prevented from deteriorating due to the atmosphere, and has sufficient mechanical strength, making it suitable for practical use as a wire material. It can be used for. Therefore, it can be widely used for wire rods or small parts as a superconducting material having a high and stable Tc.

Patent applicant: Sumitomo Electric Industries, Ltd.

Claims (1)

[Claims] Filling the inside of an outer cylindrical member made of a metal suitable for plastic working and having at least one closed cross section with raw material powder,
A method for manufacturing a linear superconducting material, which includes a step of plastically working an outer cylindrical member filled with the raw material powder and then heating the raw material powder to sinter the raw material powder, in which Au_2O_3 is stored together with the raw material powder inside the outer cylindrical member. A method for manufacturing a linear superconducting material, characterized in that after that, a series of treatments including the heat treatment are performed.