JPS63288950A - Production of superconductor - Google Patents

Abstract

PURPOSE:To produce a superconductor exhibiting superconductivity at above the b.p. of liquid N2 by calcining a powder mixture consisting of Y oxide, Ba carbonate, and Cu oxide, molding the calcined powder after admixing Cu oxide thereto, and calcining again in oxidizing atmosphere. CONSTITUTION:After calcining a powder mixture consisting of Y-oxide (e.g. Y2O3), Ba carbonate (e.g. BaCO3), and Cu oxide (e.g. CuO) at a temp. lower than a final calcination temp., the calcined product is crushed to obtain worked powder. Powdery Cu oxide is added to the worked powder and mixed by the wet process, then the mixture is granulated after admixing a binder thereto, and the mixture is compression molded to obtain a molded product. The molded body is calcined finally at 950-1,200 deg.C in oxidizing atmosphere. Thus, a Y- Ba-Cu-O type superconductor consisting of 10<=Y<=60atom.%, 20<=Ba<=50atom.%, and 30<=Cu<=65atom.% is obtained.

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 Summary of the Invention The present invention involves mixing yttrium oxide powder and barium carbonate powder, pre-calcining the mixture, and mixing the processed powder obtained by pulverizing the powder with copper oxide powder. Yttrium (Y), barium (Ba), copper (
A method for producing a superconductor which is a sintered body consisting of components Cu) and oxygen (O) and exhibits superconductivity above liquid nitrogen temperature (absolute temperature 77 degrees Celsius).

C1 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 those that are cooled at liquid helium temperature (Tc approximately 4, -269°C), which is achieved by cooling helium gas with a liquefied coolant. There 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 b3c c), but for lanthanum/strontium/copper oxide (L), which has part of La (lanthanum) replaced with Ba (barium),
aSr) tcuoa, 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 La-
It was announced that 54K was achieved with the 8r-Cu04 system, and 85K was achieved with the same material system. Subsequently, it was announced that Tc 77K had been achieved using a new substance believed to be based on lanthanum, strontium, and oxides, although the name of the substance was only disclosed as ``oxide.'' Furthermore, in recent years, barium, ibuterbium, and copper oxides that exceed 100K.

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 in Y-Ba-Cu, which is a component of the sintered body, Y is 10≦Y≦60 atomic%, Ba is 20≦Ba≦50 atomic%, and Cu is 30≦ It has been found that a superconductor with zero resistance can be obtained by cooling with liquid nitrogen as long as Cu≦65 atomic %.

That is, a mixed powder is made by mixing yttrium oxide powder and barium carbonate 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 copper 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 Yh<10 at%, Ba exceeding 60 at% is less than 20 at%, Cu exceeding 50 atoms is less than 30 at%, or exceeding 65 at%, superconductivity can be achieved using liquid nitrogen. It was not possible to obtain a sintered body in which .

F. Examples The present invention will be explained below based on examples. First, as starting materials, yttrium oxide (YyO3) powder and barium carbonate (B a CO
s) powder and copper oxide (Cub) powder, respectively.
0mo1%, 30mo1%, 50m.

Weigh it to a proportion of 1%.

First, yttrium oxide powder and barium carbonate powder are thoroughly mixed in a ball mill or the like, water and cobblestones are added, and the mixture is 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 powder reacting with each other, so it is transferred to a milk drum set in the Laikaiki, water is added, and it is wet-pulverized to obtain a fine processed powder. .

Then, add copper oxide powder to the obtained processed powder, mix thoroughly with a ball mill, add water and cobblestone, mix thoroughly for several hours, and dry the resulting slurry 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 water or 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 40mm.
, 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 of 4 mm in size, 4 mm in thickness, and 40 mm in length, and electrodes were provided as shown in Figure 1 to determine the resistance of the sintered body by the 4-terminal method. was measured.

That is, FIG. 1 is an explanatory diagram for measuring the resistance value, in which terminals a for passing current through both ends of the sintered body S in the longitudinal direction,
A' is provided, and inside it is a voltage terminal for measuring the resistance value, and a voltage terminal B' is provided.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.

In addition, when Y, O, is less than 5 mo1%, B a COs exceeding 30 mo1% is less than 20 mo1%, CuO exceeding 50 n+o1% is less than 30 mo1%, and exceeding 65 so1%, a sintered body that produces superconductivity could not be obtained. .

In short, yttrium oxide (Y, 03) in terms of starting material
is 5-3ollo1%, barium carbonate (BaC03
) is 20-50 mo1%, copper oxide (Cub) is 30-50 mo1%
It was found that if it was 65 mo1%, the resistance would be zero with liquid nitrogen.

That is, in Y-Ba-Cu, which is a component constituting the sintered body, Y is 10 to 60 at%, and Ba is 20 to 50 at%.
It has been found that a superconductor can be obtained if Cu is contained in an amount of 30 to 65 atomic %.

Furthermore, Y to s= 20 mo of the composition conditions of Example 1
1%.

BaC0+=30mo1%, Cu0=50mo1%
For those of Y t O3 powder and I3 a C03
As a result of investigation by changing the temperature of preliminary firing with powder to 900°C and the temperature of main firing with addition of CuO powder, it was found that 950°C ~ 1
The desired superconductor could be obtained by main sintering at a temperature of 200°C.

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.

Further, under the composition conditions of Example 1, the main firing temperature was set to about 1050°C, and Y, 03 powder and B a CO
, as a result of an investigation by varying the temperature of pre-firing with powder, approximately 800
Heating at a temperature above ℃ and below the main firing temperature (approximately 10
If pre-firing is carried out for more than a minute), the reaction will be slow during the final firing after adding CuO powder, causing cracks and
It was found that a sintered body with stable quality and no distortion could be obtained.

The point is, first, a mixed powder of yttrium oxide powder and barium carbonate powder is pre-calcined (heat treated) under conditions below the main firing temperature, and then the processed powder obtained by pulverizing is subjected to copper oxidation. It has been found that a sintered body of stable quality, that is, a superconductor, can be obtained by carrying out the main firing using a mixed powder obtained by adding powder of the same substance.

G1 Effects of the Invention The superconductor according to the present invention as described above has a temperature of liquid nitrogen (
77K), it becomes completely superconductive.

Moreover, powders of yttrium oxide, barium carbonate, and copper oxide are used as starting materials for the sintered body of Y-Ba-Cu-0, and in addition, during firing, main firing (
A mixed powder consisting of yttrium oxide powder and barium carbonate powder is heat-treated (pre-calcined) at a temperature lower than the temperature of 950 to 1200°C) to obtain processed powder, and copper 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 (!04Ωcm). 1, a'... Current supply terminal, b, b'... Voltage measurement terminal, S... Sintered body.

Claims (1)

[Claims] Yttrium oxide powder and barium carbonate 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 copper oxide powder to obtain a mixed powder;
consisting of a step of pressurizing the mixed powder to obtain a molded body, and a step of main firing the molded body in an oxidizing atmosphere at a temperature in the range of 950°C to 1200°C to form a sintered body, The sintered body consists of components of yttrium (Y), barium (Ba), copper (Cu), and oxygen (O), and
-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 %.