JPH02207419A - Manufacture of oxide superconducting wire rod - Google Patents

Abstract

PURPOSE:To obtain an oxide superconducting wire rod having a high critical current density by filling an oxide superconducting material into an Ag pipe to draw it, inserting a plurality of the obtained wire rods into an Ag alloy pipe to draw the same, and sintering the same at a specific temperature. CONSTITUTION:An oxide superconducting material for exerting superconductivity is filled in an Ag pipe. The obtained first wire rod is drawn, and then, a plurality of the drawn first wire rods are inserted into an Ag alloy pipe. The obtained second wire rod is drawn, and then, the drawn second wire rod is sintered at a temperature of above a melting point of Ag and below a melting point of Ag alloy constituting the Ag alloy pipe. Therefore, fineness of a superconductor can be improved as well as a critical current density can be enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing an oxide superconducting wire, and in particular to an improvement for increasing critical current density.

[Prior Art] By adding metal powder, etc., such as Ag powder or Ag2O powder, to an oxide superconducting material and sintering it, the critical current density of the obtained sintered body is lower than that of such metal powder, etc. For example, compared to the case without adding
Appl, Phys.

Lett, 52 (18), May 2, 1988 (Am
erican In5 position of Phys
ics) pp, 1525-1527.

In the above-mentioned conventional technology, the melting point (950° C.) of silver, which is lower than the melting point (960° C.) of silver constituting the powder added to the oxide superconducting material, is
Sintering temperatures up to °C have been employed. However, in the oxide superconductor sintered at such a sintering temperature, unmelted silver is only located in the form of silver particles between the crystal grains of the oxide superconducting material. do not have. Therefore, the adhesion between silver particles and superconducting crystal grains is poor,
Moreover, since the gaps between superconducting crystal grains remain as relatively large pores even after sintering, the density of the sintered body, that is, the oxide superconductor, cannot be improved, and therefore the critical current density Jc Furthermore, it was difficult to aim for further improvement.

Furthermore, conventionally, oxide superconductor products have been manufactured mainly by powder sintering, and desired shapes have been obtained by sintering after press molding, or by HIP molding. Therefore, at present, bulk sintered bodies are not manufactured, and such oxide superconductors are
In particular, very few attempts have been made to use it as a practical electrical transmission medium, especially as a wire product, ie, a wire rod.

[Problem to be solved by the invention] Therefore, the applicant filed a patent application dated January 21, 1999 titled “
In the method for producing oxide superconductors and oxide superconducting wires, a.
and a second powder made of a metal or a compound thereof (for example, Ag or Ag20) that does not directly react with the first powder, is filled into a metal sheath having a melting point higher than that of the second powder. Step b. Lengthening the metal sheath in a state filled with the mixed powder; C9 The mixed powder in the elongated metal sheath,
We have proposed a method for manufacturing an oxide superconducting wire, comprising: sintering at a temperature higher than the melting point of the second powder and lower than the melting point of the metal sheath.

Although the method proposed in the above-mentioned earlier application is a satisfactory method in itself, the second powder added to improve the critical current density may be randomly distributed within the metal sheath. On the contrary, there was a risk that the flow of superconducting current would be locally obstructed.

Therefore, the inventor of the present invention has completed the present invention as a result of repeated studies and experiments in order to improve the method described in the earlier application.

An object of the present invention is to provide a method for manufacturing an oxide superconducting wire that can more reliably obtain an oxide superconducting wire having a higher critical current density Jc.

[Means for Solving the Problems] The method for producing an oxide superconducting wire according to the present invention, in comparison with the method disclosed in the above-mentioned prior application, can be summarized as follows: It is characterized by the use of an Ag vibe. That is, the method according to the present invention includes: a. A first step of lengthening a first wire obtained by filling an Ag pipe with an oxide superconducting material that imparts superconductivity; b. A plurality of the steps described above. a second step of lengthening the second wire obtained by inserting the first wire into the Ag alloy vibrator; A third step of sintering at a temperature below the melting point of the Ag alloy.

Note that between the first step and the second step, an intermediate step is performed in which the plurality of first wires are inserted into another Ag vibe and the obtained wire is lengthened. Good too. In this case, the second step is performed by inserting the plurality of wire rods obtained in the intermediate step into the Ag alloy vibe. Note that the above-mentioned intermediate step may be repeated multiple times as necessary. In a preferred embodiment, the Ag alloy tube is composed of an alloy in which 3 to 2 Qwt% of Pd is added to Ag. Ru.

The sintering step is preferably performed at 960°C to 1100°C in an oxygen atmosphere or at 960°C to 100°C in air.
It is carried out under conditions of 00°C.

[Function] According to the present invention, in order to obtain an oxide superconducting wire, the step force for elongating the wire by plastic working (which is carried out multiple times, but after passing through the steps for elongating the wire), However, the oxide superconducting material remains filled in the Ag vibe until the sintering step.
On the knob (1), the Ag alloy vibrator does not melt, but the Ag
t<Eve melts and changes its shape for the first time.

[Effects of the Invention] According to the method for manufacturing an oxide superconducting wire according to the present invention, first, in the sintering step, (A g surrounding the oxide superconducting material at X) < Eve is melted. The pores in the internal oxide superconductor obtained by sintering are filled with molten Ag. Therefore, the density of the superconductor obtained by sintering the oxide superconducting material can be increased, and the critical current density can be increased accordingly.

In addition, until just before the sintering step, the silver is in the form of a vibrator that extends in the longitudinal direction, so even after it is melted, the silver is distributed so that it extends in the longitudinal direction of the oxide superconducting wire. do. Therefore, the superconducting current flowing in the longitudinal direction of the oxide superconducting wire is hardly inhibited by the presence of silver, which is effective in increasing the critical current density of the superconducting wire.

In this invention, preferably, the above-mentioned Ag alloy vibe used in the final stage is composed of an Ag-Pd alloy,
More preferably, it is made of an alloy in which 3 to 20 wt % of Pd is added to Ag. Such Ag-Pd alloy is
Since it has low electrical resistance and excellent thermal conductivity, it can advantageously function as a stabilizing material when a wire is formed and as a protective layer for the superconductor inside. Moreover, since palladium is completely dissolved in silver, it has the effect of raising the melting point compared to the case of silver alone. Therefore, when using an Ag alloy vibrator made of such an Ag-Pd alloy, it is easy to select a temperature in the sintering step that is higher than the melting point of 8g and lower than the melting point of the Ag alloy constituting the Ag alloy pipe. Become. Regarding the amount of palladium added, if it is less than 3 wt%, the rate of increase in the melting point is low, and if it exceeds 20 wt%, the reaction between palladium and the oxide superconducting material tends to occur, and the plastic workability deteriorates.

In addition, the sintering step is performed at 960°C to 1°C in an oxygen atmosphere.
It is preferable to carry out under the conditions of 100°C or 960°C to 1000°C in the atmosphere. Regardless of the atmosphere, the temperature was selected to be 960° C. or higher in order to enable melting of the Ag vibe.

In addition, 1100℃ or less in an oxygen atmosphere or 100℃ or less in the atmosphere.
The reason we chose conditions below 0°C is because if these conditions are exceeded, the oxide superconducting material will melt, which will cause crystal grain growth, leading to extreme deterioration or loss of superconductivity. .

[Example] Examples 1 to 3 and Comparative Example 1.2 Commercially available y2o, powder, BaCo3 powder, CuO powder,
After mixing at a ratio of 1:4:6 and repeating calcination and pulverization for 12 hours at 900°C twice, main sintering was performed at 940°C for 12 hours in the air, and then at 600°C for 24 hours. After heat treatment in an oxygen stream for hours, YI B a 2
A sintered body having a composition of Cu s 07-s was obtained. After crushing this sintered body, the outer diameter of the sintered body was 12 mm, the inner diameter of 9 mm was
I filled it into a g-vibrator. The thus obtained first wire rod was drawn to a diameter of 1 mm. Next, the above-mentioned first wire was transferred to another A having an outer diameter of 12 mm and an inner diameter of 9 mm.
A composite wire was obtained by inserting 61 wires into the wire. Then, this composite wire rod was drawn to a diameter of 1 mm. Furthermore, the above-mentioned composite wire was added to 6
Prepare one wire, and combine these composite wires with an outer diameter of 12 mm.
, inner diameter 9mm A g 95 wt%-Pd5wt%
A second wire rod was obtained by inserting the wire rod into an alloy vibrator. and,
This second wire rod was drawn to a diameter of 2 mm.

Next, as shown in the table below, the above-mentioned second wire is
Sintering was performed in the air at a temperature ranging from 55°C to 1005°C for 12 hours, and then heat treatment was performed at 600°C for 24 hours in an oxygen stream. For the various samples thus obtained, the critical current density J c [A/
Cm2] was measured. These measured values are also shown in the table below.

As can be seen from the table above, the samples obtained by sintering in the air at 965°C to 995°C (Examples 1 to 3) are different from the samples obtained by sintering at other temperature conditions (comparison). Example 1.
Compared to 2), the critical current density Jc is improved.

Comparative Example 3 The same raw material powders as in Examples 1 to 3 and Comparative Examples 1 and 2 above were mixed in the same proportions, and after repeating calcination and pulverization twice under the same conditions, Ag2O powder was Atomic Y
, Ba2Cu, was added so that the molar ratio to 014 was 1, and then sintered in the air at 980°C for 12 hours, followed by heat treatment in an oxygen stream at 600°C for 24 hours.

After pulverizing the sintered body thus obtained, the outer diameter is 1
2 mm, inner diameter 9 mm A g 95 w t%-Pd
It was filled into an alloy vibrator containing 5 wt% and drawn to a diameter of 2 mm. The wire rod obtained in this way was
Sintered at 600°C for 12 hours in air, then sintered at 600°C for 2 hours.
Heat treatment was performed in an oxygen stream for 4 hours. When the critical current density Jc at 77.3 of the obtained wire was measured, it was found to be 2
80 OA/cm2, which was found to be slightly inferior to those of Examples 1 to 3.

Comparative Example 4 The Ag alloy vibrator used in the final stage in Examples 1 to 3 and Comparative Examples 1 and 2 was made of Ag97.1wt%-Pd2.
When a wire rod made of a 9wt% alloy and produced by a similar process was heat-treated in the air at 960° C. for 12 hours, the alloy vibe melted and the wire could not maintain its shape.

Comparative Example 5 When the amount of Pd added in the Ag alloy vibrator used in Comparative Example 4 was set to 21.0 wt%, it was hard and impossible to draw.

Claims (4)

[Claims] (1) A first step of lengthening a first wire rod obtained by filling an Ag pipe with an oxide superconducting material that imparts superconductivity, and inserting a plurality of the first wire rods into an Ag alloy pipe. a second step of lengthening the second wire rod obtained by the insertion; and sintering the second wire rod at a temperature higher than the melting point of Ag and lower than the melting point of the Ag alloy constituting the Ag alloy pipe. A method for producing an oxide superconducting wire, comprising: a third step of doing so; (2) between the first step and the second step, an intermediate step of inserting a plurality of the first wire rods into another Ag pipe and lengthening the obtained wire rod; 2. The method for manufacturing an oxide superconducting wire according to claim 1, wherein the second step is performed by inserting a plurality of wires obtained in the intermediate step into the Ag alloy pipe. (3) The Ag alloy pipe has 3 to 20 w of Pd added to Ag.
The method for producing an oxide superconducting wire according to claim 1 or 2, comprising an alloy to which t% is added. (4) The third step is carried out at 960°C in an oxygen atmosphere.
The method for producing an oxide superconducting wire according to any one of claims 1 to 3, which is carried out under conditions of 1100°C or 960°C to 1000°C in the atmosphere.