JPH01278467A - Production of superconductor - Google Patents

Abstract

PURPOSE:To obtain a superconductor, capable of exhibiting superconductivity at liquid nitrogen temperature or above and having stabilized characteristics from inexpensive materials at liquid nitrogen temperature or above 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) the first step for mixing bismuth oxide powder with strontium compound powder 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) the second step for mixing the calcium compound powder with copper oxide powder, calcining the obtained mixed powder at a lower temperature than the sintering temperature and pulverizing the calcined mixture to afford processed powder; (c) a step for mixing and pressurizing the processed powder obtained in the first and second steps to provide a compact and (d) sintering the compact at 830-880 deg.C in an oxidizing atmosphere to afford 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. Industrial Application Field The present invention relates to a so-called superconductor whose electrical resistance becomes zero at a certain temperature, and particularly relates to a method for producing a superconductor that exhibits superconducting properties at temperatures above liquid nitrogen temperature. .

B9 Summary of the Invention The present invention involves mixing bismuth oxide powder and strondium compound powder, calcining the mixture and pulverizing it to obtain processed powder, and then mixing calcium compound powder and copper oxide powder. Bismuth (Bi), strontium (Sr) obtained by pre-calcining and pulverizing this into processed powder, mixing both mixed powders, press-molding, and main firing in an oxidizing atmosphere. , calcium (Ca), copper (Cu), and oxygen (O), and exhibits superconductivity at temperatures higher than liquid nitrogen temperature (absolute temperature 77° C.).

C0 Conventional Technology Since the discovery of the superconducting phenomenon by Kamerling Onnes in 1911, various research and development efforts have been carried out toward Otsuki J. For practical use, the critical temperature ('I'c
), the higher the cooling cost, the lower the cooling cost.
Intense competition is underway to develop superconducting materials with the potential for superconductivity 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.

D9 Problems to be Solved by the Invention Since superconductivity occurs at temperatures higher than the temperature of liquid nitrogen, the range of specific 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 the Problem As a result of repeated experiments on the composition of various materials, firing temperature, etc., the inventors found that bismuth (13i), strontium (Sr.
), calcium (Ca), copper (Cu), and oxygen (O)
A sintered body consisting of the following components, mixed with powders of bismuth oxide and strondium compound, pre-sintered this mixed powder at a temperature lower than the main firing temperature, and crushed it to obtain a processed powder, and Calcium compound powder and copper oxide powder are mixed, this mixed powder is pre-calcined at a temperature lower than the main firing temperature, and this is crushed to obtain a processed powder. These mixed powders are mixed and pressed. After molding, the Bi-5r-Ca-Cu
-0 component, and the atomic ratio of Bi, Sr, Ca, and Cu components is Sr:Ca=l: 0.3-3 Bi:Cu=l: 1.8-4 (Sr+Ca
) : (113i + Cu) = I : It has been found that a dense superconductor with stable characteristics can be obtained by cooling to liquid nitrogen temperature with zero resistance in the range of 1 to 2.

Note that strondium compounds include strontium carbonate (SrCO3) and strondium oxide (SrCO3).
O) and strontium hydroxide (Sr(OH)t).

Further, as the calcium compound, one or more of calcium carbonate (CaCO*), calcium compound (Cab), and calcium compound (Ca(OH)*) is used.

Note that when the atomic ratio and temperature of each component were outside the above ranges, 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 (I3itO3) powder with a particle size of 108 m or less, strontium carbonate (
SrCOs) powder, calcium carbonate (CaCOa
) powder, copper oxide (Cub) powder, 11.1 m each.
o 1%, 22.2mo 1%.

Weigh it so that it becomes 22.2 mo1% and 44.4 mo1%.
do.

Next, the powders of 13itOi and 5rCOa 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
Dry at a temperature of 0°C.

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.

In addition, powders of CaCO3 and CuO are mixed in a ball mill,
Alcohol (or a solvent that does not react with the raw material powder) and cobblestones are mixed thoroughly for several hours, and the resulting slurry is heated to about 100%
Dry at a temperature of °C. Thereafter, it is calcined at the same temperature as above, and the calcined powder is sufficiently pulverized to obtain a fine processed powder. Thereafter, both processed powders are thoroughly ground and mixed.

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.

Then, add alcohol and knead thoroughly, then dry and sieve to obtain granulated powder of 150 mesh or less.

Next, after filling this granulated powder into a mold, 1 to 2'l"
Compression molding is carried out at a pressure of approximately 1.5 cm (cm) to create a molded body with an outer diameter of 40 mm and a thickness of approximately 6 mm.

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 above manufacturing method was heated to a width of 4 mm.
The sintered body was cut into a shape with a thickness of 4 mm and a length of 40 mm, and electrodes were provided as shown in FIG. 1, and the resistance of the sintered body was measured by a four-terminal method.

That is, Fig. 1 is an explanatory diagram for measuring the resistance value. Terminals a and a' for flowing current are provided on both ends of the sintered body S in the longitudinal direction. Voltage terminal
b', put it in a liquid nitrogen cryostat, and connect terminals a,
A stabilized current of 1 ampere is passed through a', the voltage between terminals A and B' is measured with a voltmeter (V), and the resistance value is measured 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 electrical 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.

In addition, from the results in the above table, Bi, 5r1Ca.

The relationship of the component atomic ratio of Cu is the same as that of Sr and Ca, which are alkaline earth elements, Sr
: Ca=l: 0.3~3 The relationship between other Bi and Cu is: I3i:Cu=l: 1.8~4 And the relationship between these two is: (Sr+Ca): (Bi+Cu)=1:1~2 In the case of the range of , 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, if the temperature is lower than 830°C or higher than 880'C, a sintered body in which the desired superconducting phenomenon occurs cannot be obtained.

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).

Moreover, the conventional one using yttrium has a Tc of 9
However, 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 gentle, and a superconductor of constant quality can be obtained.

Moreover, since superconductors can be formed using inexpensive raw 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 instrument elements, etc. It can be used in fields such as energy exchange and exhibits extremely excellent effects.

[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 (mΩcm). a, a'... Current supply terminals, b, b'... Voltage measurement terminals, S... Sintered body. Figure 1 How to measure resistance Figure 2 80 90 TOO110120130 Absolute temperature (K
)□

Claims (1)

[Claims] (1) Bismuth oxide powder and strontium compound powder are mixed to obtain a mixed powder, the mixed powder is pre-fired at a temperature lower than the main firing temperature, and the pre-fired product is pulverized and processed. A first step of obtaining a powder; mixing a calcium compound powder and a copper oxide powder to obtain a mixed powder; pre-calcining the mixed powder at a temperature lower than the main firing temperature; a second step of obtaining a processed powder by pulverizing the processed powder; a step of mixing and pressurizing the processed powder obtained in the first and second steps to obtain a molded body; The process consists of a step of main firing at a temperature in the range of ~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), 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.