JPH04292452A - Production of oxide superconductor and wire - Google Patents

Abstract

PURPOSE:To improve a critical temperature phase of oxide superconductor grown by a zone melt method, to maintain orientation and to improve characteristics as a superconductor. CONSTITUTION:Small part of a raw material rod 2 connected to a seed bar 1 is melted by high frequency or laser to form a melt zone 3. The seed bar 1 and the raw material rod 2 are moved in an upward or a lower direction. A solidified zone 4 immediately after solidification of the melt zone 3 is continuously heat-treated under temperature gradient by a heater 5.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention has excellent orientation,
The present invention also relates to a method for producing an oxide superconductor and wire having a high critical temperature phase.

0002

[Prior Art/Problems to be Solved by the Invention] Currently, various oxide-based superconducting materials are known, and research into practical application of forming these materials into long objects such as wires and tapes as superconductors is underway. It is flourishing worldwide.

By the way, as a method for growing an oxide superconductor, for example, as shown in FIG. 2, a small portion of a raw material rod 12 connected to a seed rod 11 is melted by heating means A such as infrared rays, high frequency, or laser. An example is a so-called zone melting method in which the entire raw material rod 12 is grown by forming a molten zone 13 and moving the molten zone 13 upward or downward (downward in FIG. 2) several times. That is, this is a method of growing the oxide superconducting zone 14 by cooling and solidifying the molten zone 13.

In order to grow an oxide superconductor with a high critical current density, it is necessary to obtain an oriented superconducting phase with a large volume ratio of the superconducting phase. In particular, for bismuth systems, when conventional zone melting method is used, oriented low critical temperature phase (critical temperature 90K)
degree) is obtained. If such an oxide superconductor is subjected to post-annealing, a high critical temperature phase can be obtained, but the orientation will be lost.

[0005] In general, the following steps (1) to (4) are adopted as a manufacturing process for an oxide superconductor wire. ■
A metal pipe (mainly a silver pipe) for the sheath is filled with raw material powder of the oxide superconductor for the core, and both ends of the pipe are welded to enclose the raw material powder inside the metal pipe. ■ Wire-drawing and rolling metal pipes to turn thick-diameter wire into thin-diameter wire or tape. ■ Sintering and oxygen annealing (at least 800°C or higher) the thin wire or tape,
Commercialize it as a superconducting wire. However, in this manufacturing process, the packing density and orientation of the core powder of oxide superconducting composition were low, and therefore the properties as a superconducting wire were not very desirable.

The first object of the present invention is to provide an oxide superconductor having excellent orientation and a high critical temperature phase. The second object of the present invention is to provide a method for producing an oxide superconductor wire having excellent orientation, high oxide superconductor packing density in the core, and excellent properties, such as a high critical temperature phase. It is to provide.

[0007]

[Means for Solving the Problems] In order to achieve the above object, the present inventors have conducted extensive research and have found that the present inventors have developed an oxide superconductor (preferably an oxide superconductor grown by a zone melting method). By filling the rod into a metal pipe that is a sheath and turning it into a wire, the obtained oxide superconducting wire has a high packing density of oxide superconductor in the core and has excellent properties (for example, high critical temperature It was found that the In addition, by continuously heat-treating the melted zone made of the composition for oxide superconductor under a temperature gradient before or immediately after solidification, the produced oxide superconductor has excellent orientation properties. and a high critical temperature phase.

That is, the method for producing the oxide superconductor of the present invention is as follows:
The method is characterized in that the molten zone made of the composition for oxide superconductor is continuously heat-treated under a temperature gradient before or immediately after the molten zone is solidified. Furthermore, the method for producing an oxide superconducting wire of the present invention is characterized by filling a metal pipe with a rod made of an oxide superconductor to form a wire. It is characterized by using an oxide superconductor grown by a melting method or an oxide superconductor obtained by the method for producing an oxide superconductor of the present invention.

[0009] In the method for producing an oxide superconductor of the present invention,
"Before or immediately after the molten zone solidifies" means until the molten zone solidifies to the extent that orientation is not lost by the heat treatment described below, and the molten zone in this state is particularly referred to as a "solidified zone". . Furthermore, in the method for producing an oxide superconductor of the present invention,
The zone melting method refers to a manufacturing method in which a part of a sample is locally heated to form a molten zone, and this molten zone is gradually moved in one direction to grow an oxide superconducting crystal.

[0010] The raw material supply and the seed sample are selected appropriately depending on the superconductivity to be obtained. Although the shape and manufacturing method are not limited, rod-shaped ones are generally manufactured by solid-phase sintering or melt quenching. Some of these samples are heated in some way to connect the molten zone to the seed sample. An oxide superconducting crystal is grown by gradually moving the molten zone in one direction. In this case, especially in the bismuth system, the high critical temperature phase is not grown, but only the low critical temperature phase is grown.

[0011] Therefore, before oxide superconducting crystals are grown from the molten zone, that is, before or immediately after the molten zone solidifies, the molten zone (solidification zone) is continuously subjected to heat treatment under a temperature gradient. Accordingly, an oxide superconducting crystal having a high critical current density is grown. The heating conditions at this time are up to 80
Heat from 0°C to 900°C to a minimum of 500°C to 600°C over several hours or more. The heating means is not particularly limited, but preferably has a smooth temperature gradient.
For example, resistance heating, infrared rays, high frequency, laser, etc. may be used.

In the method for producing an oxide superconducting wire according to the present invention, a metal pipe serving as a sheath is filled with an oxide superconductor rod to form a wire. Metal pipes are not particularly limited as long as they are conductive metals, and examples include silver and silver alloys, copper and copper alloys, iron and iron alloys, nickel and nickel alloys, but there are certain considerations such as workability and conductivity. Silver and copper are preferred. There is no particular limitation on the manufacturing of such a metal pipe itself, and it can be manufactured by, for example, an extrusion method.

In the present invention, the oxide superconductor filled in the metal pipe may be in the form of a rod, and may be an oxide superconductor material after sintering, an oxide superconductor grown by the above-mentioned zone melting method, or An oxide superconductor grown by the method for producing an oxide superconductor of the present invention is used.

That is, in the method of manufacturing the wire of the present invention,
Unlike the conventional method of filling and sintering calcined powder of oxide superconducting raw material, this method fills metal pipes with oxide superconductor rods, which have a high packing density and a high critical temperature phase, and turns them into wire rods. Therefore, the properties as an oxide superconducting wire can be improved. In particular, when using an oxide superconductor grown by a zone melting method or an oxide superconductor grown by the method for producing an oxide superconductor of the present invention,
Since the orientation is maintained, it is more preferable in terms of properties.

[0015] Examples of compositions for oxide superconductors include YBa2 Cu3 Oy, Bi0.6-0.9 Pb
0.1-0.4 SrCaCu1.5-2 Ox,E
rBa2 Cu3 Oy, HoBa2 Cu3 Oy
, Tl2 Ba2 Ca2 Cu3 Ox (however,
(x represents 9 to 10, y represents 6.5 to 7), and bismuth-based materials are particularly preferred.

When a sintered oxide superconductor material is used as the oxide superconductor to be filled in a metal pipe, the oxide superconductor material may be prepared by a conventional method, and an example of the manufacturing method will be described below.

A raw material powder having a desired composition is obtained by a well-known method such as a solid phase method or a coprecipitation method. In addition, as the raw material powder, individual materials may be ground into micro-order or sub-micro-order by appropriate means as necessary and mixed in a predetermined ratio. It is preferable to use a synthetic powder, especially a fine powder with an average particle size of about 0.05 to 1.0 μm.

[0018] Next, the above-mentioned raw material powder is either as it is or is pre-formed into a pellet form under pressure and calcined. This calcination is carried out for the purpose of uniformly mixing each component at the molecular level by reaction diffusion under high pressure.
The temperature is preferably 50°C or higher, preferably 750 to 850°C, particularly around 800°C. The calcining time depends on the temperature, but is usually about 2 to 40 hours, preferably about 6 to 15 hours. The calcined body is crushed again. By this pulverization, a fine calcined powder having an average particle diameter of about 0.1 to 2 μm is obtained. The calcined fine powder thus obtained is shaped into a linear shape, and depending on the case, the shaped product is finally sintered. The sintering conditions may be a temperature of 800° C. or higher, preferably 820° C. to 890° C., more preferably 860° C. to 880° C., and other conditions may be substantially the same as the above-mentioned calcination conditions.

In the present invention, the oxide superconductor filled in the metal pipe can be made into a wire by any known method, but usually the filled metal pipe is wire-drawn and rolled to form a wire. By using a thin diameter wire as the diameter wire,
Obtain an oxide superconducting wire.

[0020]

[Effects of the Invention] According to the method for producing an oxide superconductor of the present invention, the orientation is maintained and the high critical temperature phase (for example,
It is possible to obtain an oxide superconductor having a critical temperature of 100 K or higher). In addition, since the method for producing an oxide superconducting wire of the present invention is characterized in that the grown oxide superconductor rod is filled into a metal pipe and made into a wire, it is not necessary to use the temporary oxide superconducting raw material as in the conventional method. Unlike the method of filling and sintering sintered body powder, the packing density is high. Therefore, the properties as an oxide superconducting wire can be improved. In particular, when using an oxide superconductor grown by the zone melting method or an oxide superconductor grown by the method for producing an oxide superconductor of the present invention, the oxide superconductor crystals in the rod are oriented in the longitudinal direction. By drawing this, the orientation is further improved, so the wire rod of the present invention maintains the orientation and is particularly preferable in terms of characteristics.

[0021]

EXAMPLES The method for manufacturing the oxide superconductor and wire of the present invention will be explained in detail below using examples, but the present invention is not limited to the following examples. FIG. 1 shows an embodiment of the method for producing an oxide superconductor of the present invention. In FIG. 1, a small part of the raw material rod 2 connected to the seed rod 1 is exposed to infrared rays.
A molten zone 3 is formed by melting with heating means A such as high frequency or laser. By moving the seed rod 1 and the raw material rod 2 downward at the same speed or different speeds, the lower part of the raw material rod 2' becomes a new molten zone 3', and the previous molten zone 3
is defined as coagulation zone 4. At this time, the coagulation zone 4 is grown as the seed rod 1 and the raw material rod 2 move, and is continuously heat-treated by the heater 5 under a temperature gradient.

Example 1 Composition Bi:Pb:Sr:Ca:Cu= obtained by solid phase method
The raw material powder of 8:2:10:10:15 is calcined in air at 800°C for 10 hours. The obtained calcined product was pulverized to obtain a fine powder with an average particle size of 1.0 μm. Next, this fine powder was placed in a platinum crucible, heated to 1250°C, and melted.
), and cooled and solidified at room temperature. After removing the quartz glass tube, the obtained rod-shaped sample was used as a seed rod and a raw material rod, and zone melting was performed by infrared heating at a growth rate of 1 mm/hr to form a molten zone. At this time, the solidified zone in which the molten zone was partially solidified was continuously heat-treated under a temperature gradient immediately after solidification by platinum resistance heating. The heating conditions were 850 DEG C. immediately after solidification, and a temperature gradient of -5 DEG C./mm from the melting zone to the seed rod (downward in FIG. 1). The obtained oxide superconductor has a superconducting transition temperature (zero resistance temperature, Tc) of 108 K and a critical current density [Jc (77K, 0T)] of 3.8 × 104
It was A/cm2.

Example 2 Composition Bi:Pb synthesized by oxalate coprecipitation method:
Raw material powder with Sr:Ca:Cu=8:2:10:10:15 was formed into pellets of approximately 20φ x 1.0 mm using a hand press at a pressure of 200 kg/cm2, and then heated in oxygen at 800°C for 6 hours. It was calcined in an air stream, cooled in a furnace, and the resulting calcined product was pulverized to obtain a fine powder with an average particle size of about 1.0 μm. Next, this fine powder was molded into a rod shape, and finally the molded product was sintered at 876 °C for 24 hours in an oxygen stream.
Oxide superconductor (diameter 5.9mm, length 200mm
) produced rods. The Tc of this superconductor is 108K
Met.

[0024] The outer diameter is 10 mm, the inner diameter is 6 mm, and the length is 5 mm.
A 00 mm silver pipe was filled with the above superconductor, first drawn until the outer diameter of the pipe became 1 mm, and then cold rolled to a thickness of 200 μm to produce an oxide superconducting wire. did. 10cm longer than this superconducting wire
We sampled the wires and investigated their superconducting properties. As a result, Tc was 103 K and Jc (77K, 0T) was 2.5 x 104 A/cm2.

Example 3 Oxide superconductor (composition Bi0.
8 Pb0.2SrCaCu1.5 O y or Bi
:Pb:Sr:Ca:Cu=8:2:10:10:15
), an oxide superconducting wire was produced in the same manner as in Example 2. The physical properties of the obtained wire are as follows: Tc is 105K, Jc
(77K, 0T) is 5.5 × 104 A/cm2
Met.

Example 4 Using the oxide superconductor produced in Example 1, an oxide superconducting wire was produced in the same manner as in Example 2. The physical properties of the obtained wire are as follows: Tc is 108 K, Jc (77K,
0T) was 1.4 x 105 A/cm2.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an example of the method for producing an oxide superconductor of the present invention.

FIG. 2 is an explanatory diagram showing a method for manufacturing an oxide superconductor using a conventional band melting method.

[Explanation of symbols]

1: Seed stick 2, 2': Raw material rod 3,3': Melting zone 4: Coagulation zone 5: Heater A: Heating means

Claims (4)

[Claims] 1. A method for producing an oxide superconductor, which comprises continuously heating the molten zone under a temperature gradient before or immediately after the molten zone is solidified. 2. A method for producing an oxide superconducting wire, which comprises filling a metal pipe with a rod made of the oxide superconductor and forming the rod into a wire. [Claim 3] Claim 2, wherein the oxide superconductor is an oxide superconductor grown by a zone melting method.
Manufacturing method described. 4. The method according to claim 2, wherein the oxide superconductor is an oxide superconductor obtained by the method according to claim 1.