JPH0465343A - Production of oxide superconducting wire - Google Patents

Abstract

PURPOSE:To obtain the wire having a high content of a high Tc phase and having high critical temp. and current density by forming a mixture of a sintered and crushed powder of specified composition having a low critical temp. and the powder having a high critical temp. into a wire in a specified manner and heat-treating the wire. CONSTITUTION:The oxide-based raw material powders are mixed to obtain the composition of a Bi2Sr2Ca1Cu2Oxx-based phase having a low critical temp., sintered and crushed to prepare a first powder, and the oxide-based raw material powders are mixed to obtain the composition of a Bi2Sr2Ca2Cu3Oy-based phase having a high critical temp. for compensating the composition of the low-critical- temp. phase and sintered to prepare a second powder. The powders are mixed and packed in a silver sheath tube and worked into a wire. The wire is then heat-treated below the sintering temp. of the phase having a low critical temp. to obtain the desired Bi-based oxide superconducting wire contg. Pb.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a B1-Pb-5r-Ca-Cu-0 based oxide superconductor, specifically, a B1-Pb-5r-Ca-Cu-0 based oxide superconductor, specifically a B zsrzc containing Pb.
azcus OF system, i.e. (Bi,Pb)z(Sr,P
b) Represented by xcazcuxOy (prior art) Bi-Pb-5r-Ca-Cu-0 based oxide superconductor has a phase [(Bi,Pb)r(
Sr, Pb) gcazcu*Oy, this (2223)
phase] and the low Tc phase ((Bi, Pb)z(Sr
, Pb)zca+cuzO*, this is called the (2212) phase), and the high Tc phase is at liquid nitrogen temperature (71K>
At 108, which is higher than 31, the resistance becomes OΩ. On the other hand, in the low Tc phase, the resistance becomes 0Ω at 80 K.

Therefore, the critical temperature changes depending on the mixing ratio of the high Tc phase and the low Tc phase, and the more the former is present, the higher the critical temperature becomes.

If a wire with a high ratio of high Tc phase, for example a wire with a volume ratio of 95% or more, can be obtained, it can be used as a magnet for a linear motor.
It is expected that a large market will open up in areas such as storage for storing electrical energy.

A conventional method for producing a Bi-Pb-3r-Ca-Cu-0 based oxide superconducting material is as follows. That is, first Bi2O2, Pbo, CaCO5, 5rCO, Cu,
Each powder of O (in the present invention, these are referred to as "oxide-based raw material powders") was prepared as follows: Pb: Sr: Ca: Cu = 0.8:0
．． They are blended in a ratio of 2:0.8:1.0:1.4, and acetone is added as a grinding aid and mixed. The mixed raw material powder is fired in the atmosphere for about 800"C110 hours, and the resulting powder is further crushed.This powder is
It is formed into a pellet at a pressure of about 00 kg/cm" and then sintered in the air at 850 to 875°C for 110 to 50 hours. (For example, Japanese Journal
f Applied Physlcs+νol 28.
N1112.1989. PP, L2]82L2184) On the other hand, many research results have been announced regarding the production of Bi-based oxide superconducting materials into wires. Generally, oxide-based superconducting materials cannot be drawn into wires as they are like metal materials, so a method called the silver sheath method is the mainstream method for manufacturing wires. This method involves filling a silver pipe with oxide powder, drawing it, and heat-treating it to make a superconducting wire.

(Problem to be solved by the invention!!!) B1-Pb-3r-Ca-Cu sintered by the above conventional method
In -0 series superconductors, the maximum volume fraction for high Tc is around 80%, and when examining temperature changes in resistance, it becomes OΩ only around 104, indicating a wide superconducting transition width.

The second reason seems to be that the high Tc species has not grown sufficiently.

The same is true for wires, and superconductivity inside a silver tube! !
! Since the ratio of high Tc among the 71 substances is low, the critical current density does not become high.

The object of the present invention is to use B1-Pb-5r-Ca-CuO, which has a low ratio for high Tc, high critical temperature and high critical current density.
The objective is to obtain a superconducting wire.

(Means for solving the problem) In the Bi-Pb-5r-Ca-Cu-0 based oxide superconductor, the reason why the volume ratio of high Tc does not exceed 95% is due to the formation temperature range for high Tc. This is thought to be due to the fact that it is narrow and its formation is anisotropic, resulting in a thin plate-like shape, leaving a large amount of unreacted substances.

When observing the micro&l1w1 of a sample prepared by a conventional method, large particles of unreacted substances such as Ca1Cu03, Ca2PbO4, and CuO remain. As a result of examining the calcined powder and samples fired at various temperatures, it was found that there were no unreacted large particles in the calcined powder, but particles that grew and became larger during sintering. However, even if raw materials with a composition ratio for high Tc are sintered at a low temperature that prevents grain growth of the unreacted phase, high Tc will not be produced.On the other hand, analysis of samples sintered at low temperatures If you look at it, the high Tc phase is the low Tc phase (
2212) system and CazCuOl, CazPbOm, Cu
It was found that O etc. were generated by reaction.

Therefore, first, raw materials blended to have a low Tc phase composition are sintered at a relatively high temperature, and the remaining raw material (complemented with the low Tc phase composition) is added to the resulting low Tc phase powder to form a high Tc powder. It is expected that a high proportion of high Tc products will be produced if the raw materials blended to produce such products are mixed and heat treated at a relatively low temperature.

The present invention, which was made based on the above research results, is directed to a method for manufacturing a high-ratio superconducting wire for high Tc, which is characterized by the following steps.

■ Bigot, PbO, CaCO5, 5rCO,, C
Oxide-based raw material powders such as uxO are blended to have a (2212) phase composition, sintered and pulverized to form a low Tc phase, that is, (2212) phase.
2212) system oxide powder (this is the first powder)
make.

■ Separately, the above-mentioned oxide-based raw material powder is blended with the above-mentioned first powder so as to have a composition for high Tc, that is, (2223), and fired to form a powder (this is the second powder). ).

■ The first powder and the second powder are mixed, packed into a silver sheathed tube, and made into a wire rod by drawing, rolling, etc.

In this case, it is desirable that the wire be in the form of a tape and that the internal superconductor layer be made as thin as possible by pressing or the like.

(2) Thereafter, heat treatment is performed at a temperature lower than the sintering temperature in (1) above.

The first part is a process overview explaining the method of the present invention.As shown in the figure, the method of the present invention involves manufacturing the first powder (low Tc phase powder) and the second powder separately. is a major feature.

Although the firing in (a) and the molding in (C) in the process shown in Figure 1 are not essential, it is desirable to undergo this process in order to increase the reactivity of the raw material powder in the subsequent process. (a)
The firing temperature is preferably 700 to 800°C (
Low Tc which is rich in reactivity due to molding of C) and sintering of (d3)
phase is generated. The molding and sintering in (C) and (d) may be repeated two or more times with a pulverization step in between.

The firing in (b) is preferably carried out at 750 to 850°C.

If the temperature is lower than 750°C, carbonate decomposition is insufficient;
If the temperature is higher than 50"C, the particles become coarse and grinding and mixing becomes difficult.

For example, the powders produced separately in the above steps are
: Mix at a ratio of 0.192 (weight ratio).

This results in a composition ratio of high Tc phase (2223). This mixed powder is filled into a silver sheathed tube (step (e)), drawn,
A wire rod of a predetermined size is formed by rolling or the like (step (f)).

After processing, heat treatment is performed (step (8)). This heat treatment is performed at 830-840°C. If the heat treatment is performed at a temperature of 845° C., where the most (2223) phase is produced in the conventional method, the compounds in the second powder containing CatCuO+ etc. will become coarse.

Note that the processing in (f) and the heat treatment in (g) may be repeated multiple times.

(Function) In the normal sintering method in which oxide-based raw material powder is blended in a composition ratio that forms the (2223) phase from the beginning and then fired, the low Tc phase generated in the fired powder remains during the sintering process. (unreacted components) to form a high Tc phase.

However, at normal sintering temperatures, compounds consisting of unreacted components undergo grain growth, reducing the chance of reacting with the low Tc phase. This is the reason why the high Tc phase is difficult to generate.

However, if the low Tc phase is sintered in advance at the above temperature, the low Tc phase will be more likely to react. Therefore, when the remaining components are mixed with this low Tc phase and heat treated at a temperature lower than the normal temperature, the grain growth of the compound consisting of the remaining components is suppressed.
This makes it easier to generate a high Tc phase.

EXAMPLES Hereinafter, the effects of the present invention will be specifically explained with reference to Examples.

〔Example〕

■Preparation of first powder; BixOx, PbO5SrCO*, CaCO5, CuO
Bil powder, y+Pl)o, ssr+, sca+, 5
Mix so that it becomes (composition 1), 800
After baking for 24 hours at ``C'', crush it to 15mmφ x 11
It was compression molded at 840° C. for 24 hours and pulverized. The first powder thus obtained was almost entirely a low Tc phase.

■Preparation of second powder: The above raw material powder is Pbo, +xSro, z+cao, bacu+
Oy (u composition 2) and heated at 800°C.
A second powder was produced by firing for 4 hours and pulverizing. This powder was a mixture of CazPbO, CazCu03, and CuO.

■Manufacture of wire rod: Mix the powder obtained in step (■) and the powder obtained in step (■) at a weight ratio of 1:0.192, and mold this mixed powder into a silver pipe with an inner diameter of 9 mm and an outer diameter of 1111+1. Filled.

This was drawn to 1IIllφ by die wire drawing, and further rolled into a tape shape with a thickness of 0.10m5.6 Next, this was heat treated at 825 to 845°C for 24 hours, and press-formed to a thickness of 0.09su+. Heat treatment was performed again under the same conditions. The critical current density of the thus obtained tape-shaped wire (the thickness of the superconducting oxide layer was approximately 50 μm) was measured in liquid nitrogen using a four-terminal method. The measurement results are shown in Part 2.
The horizontal axis of the figure is the heat treatment temperature.

(Comparative example) Bi+, 7.Pbo, 43sr1.ff1cal
, Bi, 0.0 to have a composition of C+gOy. ,Pbo
, SrCO3, CaCO3, and CuO powders were blended and mixed. This mixed powder was fired at 800°C in the air for 24 hours. This fired powder was filled into a silver source tube in the same manner as in the example, and processed and heat treated in the same manner. The critical current density of the wire obtained in this way (measurement conditions are the same as in Examples) is also shown in FIG.

As is clear from FIG. 2, the critical II flow density of the wire rod manufactured by the method of the present invention is higher than that of the comparative example (conventional manufacturing method).
Sintering temperature (840°) when producing powder (low Tc phase)
A large critical current density is obtained when the current density is lower than C).

(Effects of the Invention) According to the method of the present invention, a superconducting wire having a high ratio of high Tc phase and a significantly high critical current density at liquid nitrogen temperature can be obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of the steps of the method of the invention. FIG. 2 is a diagram showing the relationship between the heat treatment temperature and the critical current density in liquid nitrogen for superconducting wires produced by the method of the present invention and the conventional method.

Claims (1)

[Claims] Bi_2Br_2 with low critical temperature is used as oxide-based raw material powder
The first powder, which is blended, sintered and crushed so as to have a phase composition of Ca_lCu_2O_x system, and the same oxide-based raw material powder are supplemented with the composition of the phase with a low critical temperature to form a Bi_2Sr_2Ca_2Cu_3O_y system with a high critical temperature. A second powder is prepared separately by mixing and firing the powder so as to have a phase composition of A method for producing a Pb-containing Bi-based oxide superconducting wire, characterized in that heat treatment is performed at a temperature lower than the sintering temperature of a phase with a low phase.