JPS63291852A - 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 Ba hydroxide powder and Cu oxide powder at a temperature below the normal firing temperature, pulverizing the fired material, adding Y oxide powder, compacting the resultant blend and normally firing the obtained compact 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 of 10<=Y<=60atom.%, 20<=Ba<=50 atom.% and 30<=Cu<=65atom.% in Y-Ba-Cu is produced by the following method. That is powder of Ba hydroxide [Ba(OH)2] is thoroughly mixed with powder of Cu oxide (CuO) in a ball mill, etc. The resultant mixed powder is then temporarily fired at about 900 deg.C which is a lower temperature than the normal firing temperature in an oxidizing atmosphere. The fired powder is subsequently wet pulverized and finely divided to provide a processed powder. Powder of Y oxide (Y2O3) is then added thereto and the obtained blended powder is mixed in a ball mill. A granular granulated powder obtained from the above-mentioned blended powder is subsequently compacted molded in a metallic mold under about 700kg/cm<2> pressure. The resultant compact is then normally fired at about 1,050 deg.C temperature in an oxidizing atmosphere to afford the aimed superconductor which is the sintered compact.

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.

B0 Summary of the Invention The present invention involves mixing barium hydroxide powder and copper oxide powder, pre-calcining the mixture, and mixing the processed powder obtained by pulverizing the mixture with yttrium 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).

C8 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)tcuO+, 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, ibuterbium, 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 Y#<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 hydroxide powder and copper oxide powder, this mixed powder is pre-calcined at a temperature lower than the main firing temperature, and the obtained pre-calcined product is pulverized. This processed powder and yttrium oxide powder are mixed 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 and heated to By performing the main firing at a temperature in the range of 1200°C, a fired product consisting of yttrium (Y), barium (Ba), copper (Cu) and oxygen (O) and with the YBa-Cu composition within the above range is obtained. We discovered that once a compact 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 is less than 20 atomic % exceeding 60 atomic %, Cu is less than 30 atomic % or more than 65 atomic %, superconductivity can be achieved with 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, a powder of lithium oxide cYt 03 ) with a particle size of 10 μm or less, and barium hydroxide (Ba(
The powder of OH)z) and the powder of copper oxide (CuO) are weighed in proportions of 20 mo1%, 30 mo1%, and 50 mo1%, respectively.

First, barium hydroxide powder and copper oxide powder are thoroughly mixed in a ball mill, etc. At the same time, ethyl alcohol and cobblestones are added and mixed thoroughly for several hours, and the resulting slurry is dried at a temperature of approximately 100°C. let

Note that since barium hydroxide has solubility in water, it is necessary to mix and granulate it using a water-free solvent (for example, ethyl alcohol).

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 was added to the processed powder and thoroughly mixed in a ball mill. Ethyl alcohol and cobblestone were added and mixed thoroughly for several hours, and the resulting slurry was dried at a temperature of approximately 100°C. let

Next, to the mixed powder obtained by drying, polyvinyl alcohol is added as a binder in the form of a polyvinyl alcohol solution so that the amount is 1% by weight based on the mixed powder. Then, after adding more alcohol and kneading thoroughly, dry and pass through a sieve.
Granulated powder of 50 mesh or less is obtained.

Next, after filling this granulated powder into a mold, 700 kg
Compression molded at a pressure of 40 m/cm” in outer diameter.
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, and the resistance of the sintered body was measured using the four-probe method with electrodes installed as shown in Figure 1. did.

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 YtOs is less than 5 mo1%, Ba(OH)t exceeding 30 mo1% is less than 20 mo1%, CuO exceeding 50 mo1% is less than 30 mo1%, and exceeding 65 mo1%, it was not possible to obtain a sintered body that produces superconductivity. .

In short, yttrium oxide (Y, 0.) in terms of starting material
is 5-30IIlo1%, barium hydroxide (Ba(o
H)t) is 20-5011O1%, copper oxide (CuO)
It has been found that if the amount is 30 to 65 mo1%, the resistance becomes 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 %.

Further, the composition condition of Example 1 is Y*0s=20 theory 01%.

Ba (OH) v-30mo1%, Cu0=50
For the mo1% one, the temperature of pre-calcination of B a (OH) powder and CuO powder was 900 °C, and Y t
As a result of investigating by changing the temperature of main firing with addition of Os powder,
The desired superconductor could be obtained by main sintering at a temperature of 950°C to 1200°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.

Furthermore, under the composition conditions of Example I, the main firing temperature was set to about 1050°C, and B a (OH) was mixed with powder and C.
As a result of investigating by changing the temperature of pre-calcination with uO powder, it was found that approximately 80
Heating at a temperature above 0℃ and below the main firing temperature (approximately 1
If pre-firing is performed for 0 minutes or more), the reaction will be gradual during the main firing after adding Y, 03 powder, and a sintered body with stable quality without cracking or distortion will be obtained. It turns out.

The point is, first, a mixed powder of barium hydroxide powder and copper oxide powder is pre-calcined (heat treated) under conditions below the main firing temperature, and then yttrium oxide is added to the processed powder obtained by pulverizing this powder. 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 (
It becomes completely superconducting at 77K).

Shika also uses powders of yttrium oxide, barium hydroxide, and copper oxide as the starting materials for the sintered body of Y-Ba-Cu-0.
A mixed powder consisting of barium hydroxide powder and copper oxide powder is heat-treated (pre-calcined) at a temperature lower than the temperature (950-1200°C) to obtain a processed powder, and yttrium oxide is added to the processed powder. Since the main sintering is carried out using a mixed powder containing powders of 1 to 3, 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 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 resistance value 10-'Ωcm). a, a'... Current supply terminal, b, b'... Voltage measurement terminal, S... Sintered body.

Claims (1)

[Claims] Barium hydroxide 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 the processed powder 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 oxidizing the compact. In an atmosphere and at a temperature of 950℃ to 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 %.