JPH01278465A - Production of superconductor - Google Patents

Abstract

PURPOSE:To obtain a superconductor, capable of exhibiting superconductive at liquid nitrogen temperature or above and having stabilized characteristics from inexpensive materials by mixing powders of compounds respectively containing Sr, Ca, Bi and Cu at a specific ratio, calcining and sintering the resultant mixed powder by a specified method. CONSTITUTION:The objective superconductor is produced by the following steps (a)-(c); (a) mixing strontium compound powder with powders of a calcium compound and copper oxide to provide mixed powder, calcining the resultant mixed powder at a lower temperature than the sintering temperature and pulverizing the calcined mixture to afford processed powder; (b) mixing the processed powder with bismuth oxide powder to provide mixed powder, pressurizing the mixed powder to afford a compact and (c) sintering the compact at 830-880 deg.C temperature in an oxidizing atmosphere to provide a sintered compact. The sintered compact consists of Bi, Sr, Ca, Cu and O and the atomic ratios of the metallic components are Sr:Ca=1:0.3-3, Bi:Cu=1:1.8-4 and (Sr+ Ca):(Bi+Cu)=1:1-2.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to so-called superconductors whose electrical resistance becomes zero at a certain temperature, and in particular to the production of superconductors that exhibit superconducting properties at temperatures above liquid nitrogen temperature. Regarding the method.

Summary of Bi Invention The present invention involves mixing and calcining strontium compound powder, calcium compound powder, and copper oxide powder, and pulverizing the mixture to obtain processed powder, to which bismuth oxide powder is added. Components of bismuth (Bi), strontium (Sr), calcium (Ca), copper (Cu), and oxygen (O) obtained by mixing the mixture under pressure, molding it under pressure, and then firing it in an oxidizing atmosphere. A method for producing a superconductor which exhibits superconductivity at a temperature higher than liquid nitrogen temperature (absolute temperature 77°C) and higher.

C1 Conventional Technology Since the discovery of superconductivity by Kamerling Onnes in 1911, various research and development efforts have been made toward practical application. For practical application, the higher the critical temperature (Tc), the lower the cooling cost, so there is intense competition to develop superconducting materials with the potential for superconducting at higher temperatures.

Recently, it has been announced that superconducting materials such as strontium, ytterbium, copper oxide, and yttrium-based copper oxide have been discovered as materials that exhibit superconducting phenomena at temperatures above the temperature of liquid nitrogen of 77°C.

D1 Problems to be Solved by the Invention Since superconductivity occurs at temperatures higher than the temperature of liquid nitrogen, the specific range of applications utilizing this superconductivity has expanded.

However, since yttrium is a rare material as mentioned above, it is expensive, and there is a natural limit to the expansion of the application range of superconductivity.Therefore, there is a desire to develop inexpensive superconducting materials, but the development has not yet been completed. The current situation is that it has just started.

In view of these points, the present invention aims to provide a method for manufacturing a superconductor that becomes superconducting at 77 using inexpensive materials.

81 Means and Effects for Solving Problems As a result of repeated experiments with various material formulations, firing temperatures, etc., the inventors found that bismuth (Bi), strontium (Sr)
, calcium (CaL), and a sintered body consisting of copper (Cu) and oxygen (O), in which a strontium compound, a calcium compound, and a copper oxide powder are mixed, and this mixed powder is heated to a temperature lower than the main firing temperature. This is calcined and crushed to obtain a processed powder, which is mixed with bismuth oxide powder, which is then pressure-molded and then heated in an oxidizing atmosphere at a temperature in the range of 830 to 880°C. By performing main firing to form a sintered body, it consists of the components Bi-5r-Ca-Cu-0, each containing Bi, Sr, and Ca.

The atomic ratio of the Cu components is Sr:Ca=1:0.3~3Bi:Cu=I:1.8~4(Sr+Ca)
: (l]i+cu)=l : It has been found that in the range of 1 to 2, a dense superconductor with zero resistance and stable characteristics can be obtained by cooling to liquid nitrogen temperature.

In addition, as strontium compounds, strontium carbonate (SrCO3), strontium oxide (Sr
O) and strontium hydroxide (S r (OH) z).

Further, as the calcium compound, one or more of calcium carbonate (CaCO3), calcium oxide (Cab), and calcium hydroxide (Ca(OH)-) is used.

Note that when the atomic ratio and temperature of each component were outside the range specified by Moeki, it was not possible to obtain a sintered body in which superconductivity occurred in liquid nitrogen.

F. Example Hereinafter, the present invention will be explained based on examples.

First, as starting materials, bismuth oxide (13itO3) powder with a particle size of 10 μm or less, strontium carbonate (
SrCOa) powder, calcium carbonate (CaCC)
+) powder and copper oxide (Cub) powder at 11.1% each.
mo1%, 22.2mo1%.

Weigh out 22.2 mo 1% and 44.4 mo 1%.

Next, the S r CO3, Ca CO3, and CuO powders were thoroughly mixed in a ball mill with alcohol (or a solvent that does not react with the raw material powder) and cobblestones for several hours, and the resulting slurry was dried at a temperature of about 100°C. do.

Next, the mixed powder obtained by drying is placed in an alumina container and heat-treated (so-called preliminary firing) for about 4 hours in an oxidizing atmosphere at a temperature (about 840° C.) lower than the temperature of the main firing in the subsequent step.

Next, the obtained fired powder is sufficiently ground to obtain a fine processed powder.

Next, this processed powder and the Bi, 03 powder were thoroughly mixed in a ball mill with alcohol (or a solvent that does not react with the raw material powder) and cobblestones for several hours, and the resulting slurry was heated at a temperature of about 100°C. dry.

Then, polyvinyl alcohol is added as a binder in the form of a polyvinyl alcohol solution to 1% by weight based on the raw material powder.

After further adding alcohol and thoroughly kneading, the mixture is dried and sieved to obtain granulated powder having a size of 150 mesh or less.

Next, after filling this granulated powder into a mold, 1~2T o
Compression molded at a pressure of about n/cm2 to an outer diameter of 4
A molded body with a diameter of 0 mm and a thickness of approximately 6 mm is made.

Next, this molded body is placed in a firing container and heated in an oxidizing atmosphere at a temperature higher than the heat treatment temperature of the previous step of about 840°C and lower than about 880°C (840 to 880°C) for several hours. to obtain a sintered body (ceramics).

” The sintered body obtained by the manufacturing method of 4 mm in width
, cut out a shape with a thickness of 4 mm and a length of 40 mm.
The resistance of the sintered body was measured by a four-probe method using electrodes as shown in the figure.

That is, FIG. 1 is an explanatory diagram for measuring the resistance value, in which terminals 1. a', and a voltage terminal for measuring the resistance value inside it.
b', put it in a liquid nitrogen cryostat, and connect it to terminal a.
, to a′! A stabilized current of ampere is passed through the terminal, b'
Measure the voltage between terminals A and B with a voltmeter (V), and measure the resistance value by the voltage drop between terminals A and B'. Note that A indicates an ammeter.

Figure 2 shows the measurement results.
It was confirmed that the superconducting phenomenon begins at 0, and the 7α resistance becomes zero at about 85K.

Similar experiments were conducted with other composition ratios, so the above examples will also be described.

(Margin below) However, Example 2 in the table shows the above.

Furthermore, from the results in the table above, the relationship between the component atomic ratios of l3i1Sr and Ca1Cu is as follows: The relationship between Sr and Ca, which are the same alkaline earth metals, is S r
: Ca = I : 0.3~3 The relationship between other I3i and Cu is: I3i :Cu=I : 1.8~4 And the relationship between these rain sounds is (Sr + Ca): (Bi + Cu) = 1: In the case of the range of 1 to 2, it was possible to obtain a sintered body in which a superconducting phenomenon (resistance of zero or a minute value) occurs in liquid nitrogen.

However, at temperatures below 830°C and above 8808°C, it was not possible to obtain a sintered body with the desired superconducting phenomenon.

G1 Effects of the Invention As described above, the superconductor according to the present invention has a temperature of liquid nitrogen (
It becomes completely superconducting at 77K).

However, when conventional yttrium was used, the Tc was 9.
In the case of the present invention, it was about 10.
5, and since the superconducting phenomenon occurs at higher temperatures, a stable superconducting state can be maintained.

Moreover, by heating the raw material powder in advance at a temperature below the main firing temperature, the reaction during the main firing becomes gradual, and a superconductor with stable quality can be obtained.

In addition, since superconductors can be formed using inexpensive raw materials (or materials) and can be cooled at liquid nitrogen temperatures, they are close to practical application, especially for electrical resistance related to electric power, transportation, etc., and precision instruments. It exhibits extremely excellent effects, such as being able to be used in devices and other fields such as energy exchange.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram for explaining the method of measuring the resistance value of the sintered body of the present invention, and Figure 2 is the absolute temperature (K) of the sintered body of the present invention.
) is a characteristic curve diagram of the resistance value (m Q cm ) with respect to the resistance value (m Q cm ). a, a'... Current supply terminal, b, b'... Voltage measurement terminal, S... Sintered body. Figure 1: Method of measuring resistance Figure 2: Absolute basis K(K)-

Claims (1)

[Claims] (1) A mixed powder is obtained by mixing a strontium compound powder, a calcium compound powder, and a copper oxide powder, and the mixed powder is pre-fired at a temperature lower than the main firing temperature, and the pre-calcination is performed. A step of pulverizing an object to obtain a processed powder; A step of mixing the processed powder and bismuth oxide powder to obtain a mixed powder; and a step of pressurizing the mixed powder to obtain a molded object; The process consists of a step of main firing in an oxidizing atmosphere at a temperature in the range of 830 to 880°C to obtain a sintered body, and the sintered body contains bismuth (Bi), strontium (Sr),
It consists of calcium (Ca), copper (Cu), and oxygen (O) components, and the atomic ratio of the components in Bi-Sr-Ca-Cu is Sr:Ca=1:0.3-3 Bi:Cu= 1:1.8-4 (Sr+Ca):(Bi+Cu)=1:1-2 A method for producing a superconductor.