JPH01278459A - Production of superconductor - Google Patents

Abstract

PURPOSE:To obtain a superconductor capable of exhibiting superconductive characteristics at liquid nitrogen temperature or above by calcining mixed powder of Bi oxide and an Sr compound, pulverizing the calcined mixture, press forming the resultant processed powder and mixed powder of a Ca compound and Cu compound and sintering the compact in an oxidizing atmosphere. CONSTITUTION:Bi oxide powder is wet mixed with powder of an Sr compound (e.g. SrCO3) to provide mixed powder, which is then dried and calcined at a lower temperature than the sintering temperature in an oxidizing atmosphere and pulverized to provide processed powder, which is then wet mixed with powders of a Ca compound (e.g. CaCO3) and Cu oxide and dried to afford mixed powder. The resultant mixed powder is subsequently kneaded with a binder (e.g. PVA), granulated and press formed to provide a compact, which is then sintered at 830-880 deg.C in an oxidizing atmosphere to afford a Bi-Sr-Ca-Cu-O based superconductor at atomic ratios of 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 Field of Application The present invention is directed to a bismuth oxide powder whose electrical resistance becomes zero at a certain temperature. The processed powder is obtained by pre-calcining and pulverizing the processed powder, which is mixed with calcium compound powder and copper oxide powder, which is then pressure-molded and then main-calcined in an oxidizing atmosphere to obtain the processed powder. Ta.

A sintered body consisting of bismuth (Bi), strontium (Sr), calcium (Ca), copper (Cu), and oxygen (O), which exhibits superconductivity at temperatures above liquid nitrogen temperature (absolute temperature 77°C). It's in the way the body is manufactured.

C6 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.

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. At present, we have only just gotten the hang of it.

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.

E1 Means and action for solving the problem As a result of repeated experiments on the composition of various materials, firing temperature, etc., the inventors found that bismuth (Bi), strontium (Sr)
, calcium (Ca), copper (Cu), and oxygen (O), mixed with bismuth oxide and strontium compound powder, and this mixed powder is heated at a temperature lower than the main firing temperature. Calcined and pulverized to obtain a processed powder, to which calcium compound powder and copper oxide powder are added and mixed, this is pressure molded and then heated at 830 to 880°C in an oxidizing atmosphere. Bi-S r-Ca-Cu is formed by main firing and sintering at a temperature within the range.
-0 components, and I3i, Sr, and Ca.

The atomic ratio of the Cu components is Sr:Ca=1:0.3-3Bi:
Cu=l: 1.8~4(Sr+Ca): (Bi
+Cu)=1: 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) *).

Further, as the calcium compound, one or more of calcium carbonate (G a COs ), calcium oxide (Cab), and calcium hydroxide (Ca(OH)t) 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 (Bi to s) powder, strontium carbonate (SrCOs) powder, and calcium carbonate (Ca
1 each of COs) powder and copper oxide (Cub) powder.
1.1 mo1%, 22.2 mo1%.

Weigh out 22.2 mo1% and 44.4 mo1%.

Next, n12o3. SrCOs powder is 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 is
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.

Next, this processed powder and powders of Ca COs and CuO are 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 is heated at a temperature of about 100°C. Dry with.

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, l~2T o
Compression molded at a pressure of about n/cm" to an outer diameter of 40 m.
m, and a molded body with a thickness of about 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 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, 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, 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 the terminal &
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.

)・Nge Sohaku (7g, the current amount is 1 j kani j 1) However, Example 2 in the table shows the above.

In addition, from the results in the above table, Bi, Sr, and Ca.

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 = 1 : 0.3~3 The relationship between other Bi and Cu is: B i : Cu = 1 : 1.8 ~ 4 and the relationship between these two is (Sr + Ca): (Bi + Cu) = 1: In the range of 1 to 2, it was possible to obtain a sintered body in which a superconducting phenomenon (resistance of zero or minute value) occurred 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.

Effects of the G6 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 is Te3>
However, in the case of the present invention, the temperature was about 105, which means that a stable superconducting state can be maintained because the superconducting phenomenon occurs at a higher temperature.

Moreover, the raw material powder is heated in advance to a temperature below the main firing temperature.

Moreover, since superconductors can be formed using inexpensive raw materials and can be cooled at liquid nitrogen temperatures, they can be used for practical applications, especially in electrical resistance and precision instrument elements related to electric power, transportation, etc. It can be used in other fields such as energy exchange, etc., 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.
), the resistance value (m Q cm ) of soil, &′...
・Current supply terminal, b, b'...voltage measurement terminal, S・
...Sintered body. Fig. 1 Method of measuring resistance value 1 vs. 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. a step of mixing the processed powder, a calcium compound powder, and a copper oxide powder to obtain a mixed powder, and pressurizing the mixed powder to obtain a molded body; 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.