JPS63291846A - Production of superconductor - Google Patents

Abstract

PURPOSE:To readily obtain a superconductor capable of exhibiting superconductivity, especially at liquid N2 temperature or above, by temporarily firing a mixed powder of Y oxide powder and Cu oxide powder at a temperature below the normal firing temperature adding Y oxide powder to the resultant processed powder, compacting the resultant blended powder and normally firing the obtained compact of the blended powder in an oxidizing atmosphere. CONSTITUTION:A superconductor which is a sintered compact, consisting of Y, Ba, Cu and O and containing components at atomic ratios within the ranges of 10<=Y<=60 atom.%, 20<=Ba<=50atom.% and 30<=Cu<=65atom.% in Y-Ba-Cu is produced by the following method. That is powder of Y oxide (Y2O3) and powder of Ba oxide (BaO) are thoroughly mixed in a ball mill, etc. The resultant mixed powder is then temporarily fired at about 900 deg.C which is a lower temperature than that in normal firing in an oxidizing atmosphere and subsequently wet pulverized to provide a finely divided processed powder. Powder of Y oxide (Y2O3) is then added to the obtained processed powder and the resultant blended powder is sufficiently mixed in a ball mill, dried and subsequently compacted. The resultant compact is then normally fired at about 1,050 deg.C temperature in an oxidizing atmosphere to afford the aimed superconductor having stabilized characteristics without crack or strain.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a so-called superconductor whose electrical resistance becomes zero at a certain temperature, and particularly to a superconductor which exhibits superconductivity above the temperature of liquid nitrogen.

B1 Overview of the Invention The present invention involves mixing barium oxide powder and copper oxide powder, calcining the mixture, and pulverizing the resulting processed powder and yttrium oxide powder. Yttrium (Y), barium (Ba), copper (C
A method for producing a superconductor which is a sintered body consisting of components u) and oxygen (O) and exhibits superconductivity above liquid nitrogen temperature (absolute temperature of 77 degrees Celsius).

C0 Conventional Technology Since the discovery of superconductivity by Kamerling Onnes in 1911, various research and development efforts have been underway to put it into practical use. 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.

Most of the superconducting materials that have been revealed so far are used after being cooled to liquid helium temperature (Tc approximately 4, -269°C), which requires cooling with a coolant made from liquefied helium gas. Must be. Helium is a rare and expensive material, and the cost of cooling it down to its critical temperature is extremely high, making it the main reason for delaying the spread of superconducting materials.

Very recently, research and development on superconducting materials has been progressing worldwide, and materials that break with conventional concepts are appearing.

The highest Tc of superconducting materials known so far is niobium 3
The temperature was only 22.3K for germanium (N bs Ge), but lanthanum/strontium/copper oxide (in which part of La (lanthanum) is replaced with Ba (barium))
With LaSr)tcuo4, it was announced that the superconducting phenomenon began at 37, exceeding the previous limit, and that the electrical resistance became zero at 33, followed by the same <LaSr) at the beginning of this year.
-8r-Cu04 system with 54K, and the same material system with 85K
It was announced that it had been achieved. Furthermore, although the name of the substance is only disclosed as "oxide," Tc77K is produced by a new substance that is thought to be based on lanthanum, strontium, and the same oxide.
It was announced that the goal had been achieved. Furthermore, in recent years, 100K
barium, ytterbium, and copper oxide.

It has been announced that a superconducting material made of yttrium-based copper oxide has been discovered.

D1 Problems to be solved by the invention As mentioned above, the temperature of liquid helium is 4.2 at normal pressure. The cooling cost was extremely high, which was an obstacle to practical application. Also, if it is 77 or higher, you can use liquid nitrogen,
It is desired to develop a superconducting material with a Tc of 77 or higher because it is advantageous in all respects compared to the use of liquid helium and is extremely easy to put into practical use. The current situation is that it has just started.

In view of these points, the present invention seeks to provide a method for manufacturing a superconductor that becomes superconducting in 77 or more steps.

Means and functions for solving the E1 problem If superconductors can be used with liquid nitrogen cooling, power.

Focusing on the fact that it can be used in a wide range of fields such as transportation and energy conversion, we have repeatedly experimented with various material formulations, firing temperatures, etc.
) and oxygen (O), and Yh<10≦Y≦60 in Y-Ba-Cu, which is a component of the sintered body.
It has been found that a superconductor with zero resistance can be obtained by cooling with liquid nitrogen if the atomic % Ba is in the range of 20≦Ba≦50 atomic % and the Cu content is in the range of 30≦Cu≦65 atomic %.

That is, a mixed powder is made by mixing barium oxide powder and copper oxide powder, this mixed powder is pre-fired at a temperature lower than the main firing temperature, and the obtained pre-fired product is pulverized. This processed powder is mixed with yttrium oxide powder to make a mixed powder, this mixed powder is pressed to make a molded body, and this molded body is heated in an oxidizing atmosphere to a temperature of 950 to 1200 By performing the main firing at a temperature in the range of ℃, it consists of the components of yttrium (Y), barium (Ba), copper (Cu) and oxygen (O), and the components of Y-Ba-Cu are within the above range. We discovered that if a sintered body is formed, a superconductor with zero resistance can be easily obtained by cooling with liquid nitrogen.

In addition, in Y-Ba-Cu, if Y is less than 10 atomic %, Ba exceeding 60 atomic % is less than 20 atomic %, and Cu exceeding 50 atomic % is less than 30 atomic % or more than 65 atomic %, superconductivity can be achieved using liquid nitrogen. It was not possible to obtain a sintered body in which .

F. Examples Hereinafter, the present invention will be explained based on examples. First, as starting materials, yttrium oxide (yt 03 ) powder with a particle size of 10μ or less, barium oxide (Bad) powder, and copper oxide were used as starting materials. 20 mo1 of Cub powder each
%, 30Ilo1%, and 50mol1%.

First, barium oxide powder and copper oxide powder are thoroughly mixed using a ball mill or the like, and ethyl alcohol and cobblestone are added thereto and thoroughly mixed for several hours, and the resulting slurry is dried at a temperature of about 100°C.

Next, the mixed powder obtained by drying is placed in an alumina container and heat-treated in an oxidizing atmosphere at a temperature of approximately 900°C, which is lower than the temperature of the main firing in the subsequent process, for approximately 2 hours (so-called pre-calcination).
do.

Next, the obtained fired powder becomes hard due to the reaction between the powders, so it is transferred to a milk drum set in the Raikaiki, and alcohol is added to wet-pulverize it to obtain a fine processed powder. .

Then, yttrium oxide powder is added to the obtained processed powder, thoroughly mixed in a ball mill, ethyl alcohol and cobblestone are added, and mixed thoroughly for several hours, and the resulting slurry is dried at a temperature of about 100°C. .

Next, to the mixed powder obtained by drying, polyvinyl alcohol is added as a binder in the form of an aqueous polyvinyl alcohol solution so that the amount is 1% by weight based on the mixed 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, 700 kg
Compression molded at a pressure of about /cm' to an outer diameter of 40m.
m, a molded body with a thickness of about 6 mm is made.

Next, this molded body is placed in a sintering machine and heated in an oxidizing atmosphere at a temperature of approximately 1050° C. (a temperature higher than the above-mentioned pre-firing temperature) for several hours to obtain a sintered body (ceramics).

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

That is, FIG. 1 is an explanatory diagram for measuring the resistance value, with terminals a for passing current through both ends of the sintered body S in the potato direction;
A' is provided, and a voltage terminal (B) for measuring the resistance value is provided inside it.This is placed in a liquid nitrogen cryostat, and a stabilized current of 1 ampere is passed through terminals a and a' to connect the terminals. 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, with an absolute temperature of approximately 93
It was confirmed that the superconducting phenomenon began at 89K, and that the electrical resistance became zero at 89K.

Similar experiments were conducted with other composition ratios, so the description will include the above-mentioned examples.

However, Example 1 in the table shows the above.

Note 1. Y*Os less than 5 mo1%, 30 mo
When BaO exceeding 1% is less than 20mo1%, CuO exceeding 50mo1% is less than 30Ilo1%, and exceeding 65mo1%,
It was not possible to obtain a sintered body that produced superconductivity.

In short, yttrium oxide (Y, 0.) in terms of starting material
is 5-30IIO1%, barium oxide (Bad) is 2
0-50IIIo1%, copper oxide (Cub) 30-6
It was found that if 5so1% was used, the resistance would be zero with liquid nitrogen.

That is, in Y-Ba-Cu, which is a component constituting the sintered body, a superconductor can be obtained if Yh (10 to 60 atomic %, Ba 20 to 50 atomic %, and Cu 30 to 65 atomic %). understood.

Furthermore, Y 20 s= 2 On+ under the composition conditions of Example 1
o1%.

Ba0t=30+*o1%, Cu0=50mo1%
As a result of the investigation, the temperature of preliminary sintering of BaO powder and CuO powder was set at 900°C, and the temperature of main sintering with addition of Y*03 powder was changed. By doing so, the desired superconductor could be obtained.

However, at temperatures below 950°C and above 1200°C, it was not possible to obtain a sintered body that produced the desired superconducting phenomenon.

In addition, under the composition conditions of Example 1, the main firing temperature was set at about 1050°C, and the results of investigation by changing the pre-sintering temperature of BaO powder and CuO powder were found to be about 800°C or higher. If you pre-fire it by heating (for about 10 minutes or more) at a temperature below the main firing temperature, the reaction will be slow during the main firing with Y, 03 powder added, causing cracks and distortion. It was found that a sintered body with stable quality and no occurrence of oxidation can be obtained. The point is, first, a mixed powder of barium oxide powder and copper oxide powder is pre-calcined (under conditions below the main firing temperature).
It was found that a sintered body of stable quality, that is, a superconductor, can be obtained by using a mixed powder obtained by adding yttrium oxide powder to the processed powder obtained by heat treatment) and pulverizing it. .

G0 Effects of the invention The superconductor according to the invention as described above has a temperature of liquid nitrogen (
It becomes completely superconducting at 77K).

Moreover, powders of yttrium oxide, barium oxide, and copper oxide are used as starting materials in the sintered body of Y-Ba-Cu-0, and upon firing, the main firing (9
A mixed powder consisting of barium oxide powder and copper oxide powder is heat-treated (pre-calcined) at a temperature lower than the temperature of 50-1200℃) to obtain processed powder, and yttrium oxide is added to this processed powder. Since the main sintering is performed using a mixed powder containing powder, it is possible to easily obtain a sintered body, that is, a superconductor, which is free from cracks and distortions and has stable characteristics.

The currently discovered superconductor requires cooling with a coolant made from liquefied helium gas, and the temperature of liquid helium is 4.2, and it is a rare and expensive material, and the cost of liquefying it is high. This has been a barrier to the practical application of superconducting materials.

However, liquid nitrogen is available everywhere and cheaply.
The conventional barriers to practical application have been completely removed, and it has extremely excellent effects, such as being able to be used in fields such as electrical resistance, precision measurement elements, and other energy conversion related to electricity, transportation, etc.

[Brief explanation of drawings]

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 (10''Ωcm). a, a'... terminal for current supply, b, b'... terminal for voltage measurement, S... sintered body.

Claims (1)

[Claims] Barium oxide powder and copper oxide 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 pulverizing to obtain a processed powder; mixing the processed powder and yttrium oxide powder to obtain a mixed powder; pressurizing the mixed powder to obtain a compact; and placing the compact in an oxidizing atmosphere. inside and 950℃~1200℃
a step of main firing at a temperature in the range of °C to form a sintered body, the sintered body consisting of components of yttrium (Y), barium (Ba), copper (Cu) and oxygen (O), And Y-Ba
-The components in Cu are yttrium (Y) and 10≦Y≦60 atomic% barium (
Ba) is 20≦Ba≦50 atomic% Copper (Cu) is 30≦C
A method for producing a superconductor, characterized in that u≦65 atomic %.