JPH087680A - Method for manufacturing oxide superconducting wire - Google Patents

Abstract

(57) [Summary] [Purpose] Excellent superconducting properties (Jc of 15000 A / cm ² or more)
Providing a method for easily manufacturing TmBa ₂ Cu ₃ O _7-x wire rods. [Structure] TmBa ₂ Cu ₃ characterized by the following steps
O _7-x Superconducting wire manufacturing method. Powders of oxides, carbonates, nitrates or chlorides of Tm, Ba and Cu are prepared so as to be Tm: Ba: Cu = 1: 2: 3 to obtain a mixed powder. The above-mentioned compounded powder is applied to a silver tape or filled in a silver sheath, processed into a wire, and pressed or rolled into a tape-shaped wire. After heating the above tape-shaped wire to a temperature of 930 to 945 ℃ once in an atmosphere with an oxygen partial pressure of 0.003 to 0.03 atm,
Cool down to at least 900 ℃ at a cooling rate of 0.1 to 10 ℃ per hour.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a superconducting wire which is represented by the composition formula of TmBa ₂ Cu ₃ O _7-x and has a high critical current density and which can be used in electromagnets, power cables and the like. .

[0002]

_2. Description of the Related Art MBa ₂ Cu ₃ O ₇ (M is Y, Nd, Pm, Sm, E
The Y-based superconductor represented by the composition formula of u, Gd, Tb, Dy, Ho, Er, Tm or Yb) is a so-called high temperature superconducting material having a superconducting transition temperature (critical temperature, Tc) of about 90K. It is already well known [eg, Japanese Journal of Applied
Physics Vol.26, (1987) pp.L633].

This so-called Y-type superconductor has a hard and brittle characteristic peculiar to ceramics, and therefore, for use as a coil or a power cable, a sheath wire or metal tape filled and processed in a metal sheath tube is used. It is usually a coated tape-shaped wire.

When manufacturing the above-mentioned sheath wire or tape-shaped wire, due to the anisotropy of these superconductors, an electric current is passed through the C axis of the crystal axis in order to obtain a high critical current density. It is necessary to align the crystal orientation so that it is perpendicular to the direction.

With respect to the Y-based superconductor, a YBa ₂ Cu ₃ O ₇ wire rod produced by a laser deposition method or a CDV method using a metal (hastelloy) tape as a substrate, and a C-axis oriented wire rod was obtained. There is a report (The Society of Applied Physics, Spring 1992 Proceedings, Volume 1, 29a-W-7, and Japanese Jo
urnal of Applied Physics Vol.31, (1992) pp.L547-L54
See 9). However, the production of a wire by these methods is disadvantageous in that it is time-consuming, the cost of production equipment is high, and it is unsuitable for industrial production.

[0006]

DISCLOSURE OF THE INVENTION The present invention has excellent superconducting properties, specifically, a critical current density of 15000 A / cm ² or more that can generate a magnetic field of 1000 gauss or more when formed into a coil.
Among the Y-based superconductors with (Jc), TmBa ₂ Cu ₃ O _7-x that can be crystallized by heat treatment at a temperature below the melting point of silver.
It is an object of the present invention to provide a method for manufacturing the above wire rod as easily as possible.

[0007]

The gist of the present invention is a method for producing a TmBa ₂ Cu ₃ O _7-x superconducting wire characterized by the following steps.

Powders of oxides, carbonates, nitrates or chlorides of Tm, Ba and Cu are prepared so as to be Tm: Ba: Cu = 1: 2: 3 to obtain mixed powders. At this time, when powders other than oxides, that is, powders of carbonates, nitrates or chlorides are used as raw material powders, non-metal elements other than oxygen are removed by calcination before or after compounding.

The above-mentioned mixed powder is applied to a silver tape or filled in a silver sheath and processed into a wire, which is then pressed or rolled into a tape-shaped wire.

The tape-shaped wire is made to have an oxygen partial pressure of 0.0
Once heated to a temperature of 930 to 945 ° C in an atmosphere of 03 to 0.03 atm, cool at a cooling rate of 0.1 to 10 ° C per hour up to at least 900 ° C.

[0011]

It is generally known that when a substance is grown from a molten state, the crystal may be oriented so that the surface energy is minimized. Since the surface energy of an oxide depends on the oxygen partial pressure, it is possible to control the orientation by adjusting the oxygen partial pressure.

The present inventor investigated the orientation of various Y-based superconductors at the time of solidification by changing the oxygen partial pressure, and in particular, TmBa ₂ C
It was found that the orientation of u ₃ O _7-x can be enhanced by heating and cooling under the above-mentioned specific conditions. The present invention is based on this knowledge.

Each of the above steps 1 to 3 will be described below.

Step (1): This is a step according to a general method for producing a Y-based oxide superconducting material. However, since the production target is TmBa ₂ Cu ₃ O _7-x , Tm oxide, carbonate,
One or more powders of nitrate and chloride are used as one of the raw material powders. As the raw material of Ba and Cu, one or more kinds of oxides, carbonates, nitrates and chlorides thereof can be used.

The above raw material powder was converted into Tm: Ba: Cu = 1: 2:
It is mixed so as to be 3 to obtain a mixed powder. Each powder before compounding may be calcined, or the mixed powder after compounding may be calcined. When a compound powder other than oxide is used as the raw material powder, calcination is indispensable to remove non-metal elements other than oxygen.

Process: The above-mentioned mixed powder is applied to a silver tape or filled in a silver sheath (sheath tube) and processed into a wire by a usual method such as forging, rolling and drawing, and further,
The tape-shaped wire is made by pressing or rolling.

Step: This is a heat treatment step, but here it is important to adjust the oxygen partial pressure of the atmosphere, the heating temperature, and the cooling rate.

In an atmosphere having an oxygen partial pressure of less than 0.003 atm, no TmBa ₂ Cu ₃ O ₇ structure is chemically unstable and is not generated. If the oxygen partial pressure exceeds 0.03 atm, C
The degree of orientation of the shaft in the direction perpendicular to the tape surface becomes low, which lowers the critical current density (Jc). Therefore, it is necessary to adjust the oxygen partial pressure within the range of 0.003 to 0.03 atm.

The wire is heated to 930 ° C. or higher in the above atmosphere. The heating time depends on the size of the wire, but
10 minutes is enough. At temperatures below 930 ° C, TmBa ₂ Cu ₃ O ₇
Does not melt, crystal orientation does not occur, and therefore only wires with a low critical current density (Jc) can be obtained. On the other hand, if the heating temperature exceeds 945 ° C, Tm ₂ BaCuO ₅ that forms as a solid phase when TmBa ₂ Cu ₃ O ₇ melts will undergo rapid grain growth, which causes a smooth reaction with the liquid phase during cooling. Not progress,
As a result, the formation of TmBa ₂ Cu ₃ O ₇ is hindered and the critical current density is increased.
Wires with high (Jc) cannot be obtained. For these reasons, the heating temperature needs to be adjusted within the range of 930-945 ℃.

The wire rod which has been heated and partially melted as described above is cooled at a cooling rate of 0.1 to 10 ° C. per hour up to at least 900 ° C. This condition is that the liquid phase and Tm ₂ BaCu
It is a condition that promotes the generation of TmBa ₂ Cu ₃ O ₇ and its crystal grain growth by reacting with the O ₅ phase, and further suppresses the grain growth of Tm ₂ BaCuO ₅ described above.

When the cooling rate is less than 0.1 ° C./hour, the cooling rate is too small and Tm ₂ BaCuO ₅ grains grow, and therefore TmBa
₂ Cu ₃ O ₇ growth is inhibited. On the other hand, when cooling is performed faster than 10 ° C per hour, the reaction between the liquid phase and the Tm ₂ BaCuO ₅ phase is slow, so that the formation of TmBa ₂ Cu ₃ O ₇ is reduced and the critical current density (J
A wire with high c) cannot be obtained.

Since the above-mentioned various phenomena substantially occur during the cooling process up to 900 ° C., at least 0.1 to 0.1
The cooling rate should be 10 ° C. Hereinafter, the cooling in which the cooling rate is controlled in this way is referred to as “adjustment cooling”.

The cooling rate in the temperature range lower than 900 ° C. does not need to be specially controlled and may be rapid cooling or slow cooling. However, absorption of oxygen at temperatures lower than 600 ° C causes a structural phase transition from the high-temperature phase (tetragonal crystal of non-superconductor) to the low-temperature phase (superconducting orthorhombic crystal). It is better to keep the temperature at 400-500 ℃ for about 10 hours to accelerate.

[0024]

EXAMPLE Tm ₂ O ₃ , BaCO ₃ and CuO with 99.99% purity
Was mixed so that the atomic ratio of metal elements (Tm: Ba: Cu) was 1: 2: 3, calcined in the air at 800 ° C for 24 hours, pulverized, and calcined again under the same conditions. did.

The obtained calcined body was crushed, mixed with an organic solvent and applied to a silver tape. As the organic solvent, a mixture of ethanol and PVB (polyvinyl butyral) was used, and the silver tape had a thickness of 50 μm, a width of 5 mm and a length of 10 cm.

FIG. 1 shows the critical current density (J) of the superconducting tape when the oxygen partial pressure of the heat treatment atmosphere and the holding temperature were changed.
The change of c) is shown. All samples were held at temperature (shown in Figure 1
920 ° C, 930 ° C, 940 ° C, 945 ° C and 950 ° C) up to 50
After heating at ℃ / h and holding for 10 minutes, the temperature was adjusted to 850 ℃ at 4 ℃ / h, and then cooled to room temperature. The atmosphere was a mixed gas of argon and oxygen, and the oxygen partial pressure was changed by changing the mixing ratio.

The Y-based superconductor material is not limited to TmBa ₂ Cu ₃ O ₇ , but any of them becomes a semiconductor when crystal is grown at a high temperature and absorbs oxygen in the process of cooling to room temperature to superconduct. It is known to become a body. In order to complete the phase transition from the semiconductor phase to the superconductor phase, all samples were furnace-cooled to room temperature and then kept in oxygen at 400 ° C. for 2 days. The measurement of the critical current density was carried out at 77K using the four-terminal method.

FIG. 1 is a graph showing the above measurement results. As shown in the figure, the highest critical current density was obtained when the holding temperature was 940 ° C and the oxygen partial pressure was 0.01 atm.

At 945 ° C, the maximum current density is 940 ° C
The oxygen partial pressure at that time is 0.03 atm, which is higher than that at 940 ° C.

When the holding temperature is 950 ° C., the peak of the current density is 0.03 atm, but the value is smaller than 15000 A / cm ² . When the holding temperature is lower than 940 ° C, the peak oxygen partial pressure becomes lower than that at 940 ° C, and the current density value becomes smaller than that at 940 ° C. Hold temperature is 9
At 20 ° C, only wires with a critical current density of 15000 A / cm ² or less can be obtained.

As described above, from FIG. 1, a wire having a critical current density of 15000 A / cm ² or more can be obtained when the oxygen partial pressure is 0.003 atm or more and 0.03 atm or less and the holding temperature is 930 ° C or more and 945 ° C or less. I understand.

FIG. 2 shows the test results of the influence of the temperature at which the adjustment cooling is completed. That is, after maintaining at 940 ℃ for 10 minutes in an atmosphere with an oxygen partial pressure of 0.01 atmosphere, at a cooling rate of 4 ℃ / h
The change in critical current density is shown when the furnace is cooled after cooling to various temperatures from 850 ℃ to 920 ℃.

When the temperature at which the controlled cooling is completed is 900 ° C. or lower, a high current density of 15000 A / cm ² or higher is obtained. It can be seen that if the temperature is 880 ° C or lower, the current density remarkably increases and the value does not change much.

FIG. 3 shows the results of examining the influence of the cooling rate in the controlled cooling. That is, the oxygen partial pressure is 0.01
The graph below shows the relationship between the cooling current and the critical current density when cooled to 850 ° C after holding it at 940 ° C for 10 minutes in an atmospheric pressure atmosphere. As shown in the drawing, when the cooling rate is in the range of 0.1 ° C / h to 10 ° C / h, the critical current density of 15000 A / cm ² or more is obtained.

[0035]

According to the manufacturing method of the present invention, the composition of TmBa ₂ Cu ₃ O _{7-x having} a critical current density of 15000 A / cm ² or more and being practically applicable to, for example, a coil for ECR plasma generation. The superconducting wire can be manufactured relatively easily.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a partial melting heating temperature of a TmBa ₂ Cu ₃ O _7-x superconducting wire and its atmosphere (oxygen partial pressure) and a critical current density (Jc).

[Fig. 2] Similarly, adjusted cooling end temperature and critical current density (Jc)
It is a figure which shows the relationship with.

[Fig. 3] Similarly, cooling rate and critical current density during controlled cooling
It is a figure which shows the relationship with (Jc).

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H01B 12/04 ZAA

Claims (1)

[Claims] 1. A silver tape is coated with a mixed powder prepared by mixing powders of oxides, carbonates, nitrates or chlorides of Tm, Ba and Cu in a ratio of Tm: Ba: Cu = 1: 2: 3. Or, fill it into a silver sheath, process it into a wire rod, and press or roll it into a tape-shaped wire rod.
TmBa ₂ Cu ₃ O _7-x superconductivity characterized by heating to a temperature of 930 to 945 ℃ in an atmosphere of ~ 0.03 atm and then cooling at a cooling rate of 0.1 to 10 ℃ per hour up to at least 900 ℃. Manufacturing method of wire.