JPH01294568A - Production of superconductor - Google Patents

Abstract

PURPOSE:To suppress the impurity content and the scattering of Bi and to stabilize ths composition of the product by pulverizing a preliminarily calcined product of a powdery mixture of O compounds of Bi, Sr, Ca and Cu, forming the powder, preliminarily calcining the formed article at a specific temperature and subjecting the product to main calcination in a closed vessel. CONSTITUTION:Powders of compounds such as Bi2O3, SrCO3, CaCO3 and CuO are mixed at ratios to give atomic ratios of each metal component satisfying a prescribed relationship to obtain a mixed powder 1. The mixed powder is charged into a top-opened vessel 2 made of alumina ceramic and subjected to preliminary calcination to release gases. The preliminarily calcined powder is thoroughly crushed and the obtained processed fine powder is formed to obtain a formed article 3. The article 3 is set in the vessel 2 and preliminarily calcined. The product 6 is put into the vessel 2. The vessel containing the product is covered with a lid 7, introduced into a calcination furnace and heated in an oxidizing atmosphere to obtain a sintered material (ceramics).

Description

DETAILED DESCRIPTION OF THE INVENTION A. Industrial Application Field The present invention relates to so-called superconductors whose electrical resistance becomes zero at a certain temperature, and in particular to B i-S r- which exhibits superconducting properties above liquid nitrogen temperature. The present invention relates to a method for producing a Ca-Gu-0 based superconductor.

Summary of B1 invention The present invention relates to bismuth (Bi), each of which is combined with oxygen.

Strontium (Sr), calcium (Ca).

Copper (Cu) powder is used as a starting material, a mixed powder of these powders is calcined, a compact of the powder after calcining is calcined, and the final firing is performed in a closed container.1 From this, bismuth B t-S r-Ca-C
This is a method for manufacturing a u-0 type superconductor, in which a sintered body exhibits superconductivity at a temperature higher than liquid nitrogen temperature (absolute temperature 77°C) or higher.

C1 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 superconductivity at higher temperatures.

Recently, yttrium-based copper oxide has been discovered as a material that exhibits superconductivity at temperatures higher than the temperature of liquid nitrogen, which is 77°C, and it is also an inexpensive material that has Tc! A B1-5r-Ca-Cu-0-based superconductor showing a grade of 0.05 has been discovered.

D1 Problems to be Solved by the Invention Since the above-mentioned materials exhibit superconductivity at temperatures higher than the temperature of liquid nitrogen, the specific scope of application utilizing this superconductivity has expanded.

However, as mentioned above, since the i-9r-Ca-Cu-0-based superconductor contains bismuth (13i) as a starting material, when a mixed molded body is directly fired in a firing furnace, the heat load causes Bi There is a problem in that the composition of the starting mixture and the composition of the final product differ by 1.

According to experiments conducted by the inventors, it has been found that when firing at a temperature of 830 to 880° C. for several hours, the content of bismuth is reduced by 7 to 8% compared to the amount at the time of mixing.

To solve this problem, it is possible to use bismuth in an amount that takes into account the reduction in bismuth scattering, but it has been found that if this is done, there will be an excess of bismuth and the desired superconducting phenomenon will not occur.

Furthermore, if a predetermined powder is mixed and fired immediately, cracks may occur in the sintered body, resulting in unstable quality.

Therefore, in the case of a superconductor containing bismuth, the superconducting performance tends to deteriorate and become unstable, and when mass-produced, there is a risk of variations in quality.

In view of these points, the present invention provides B1-3 with stable quality.
The present invention aims to provide a method for producing an r-Ca-Cu-0-based superconductor.

E1 Means for Solving the Problems The present invention prepares a mixed powder of bismuth, strontium, calcium, and copper compound powders each combined with oxygen, and pre-sinters this at a temperature below the melting point of the bismuth compound. The calcined product is pulverized to produce processed powder, and then granulated to obtain granulated powder.

This granulated powder is pressurized to make a molded body, which is then calcined at a temperature below the melting point of the bismuth compound contained.The calcined molded body is stored in a closed container, and these containers and the molded body are combined. The main firing is performed in an oxidizing atmosphere at a temperature in the range of 830 to 880°C to obtain a sintered body, that is, a superconductor.

Incidentally, ■Calcination at the time of mixed powder is to remove gases generated by reaction 1 decomposition (e.g. CO! gas) that have an adverse effect on the sintered body (superconductor).
Fire at a temperature of 900°C.

However, in order to prevent the contained bismuth from scattering as much as possible, it is preferable to perform firing at a temperature below the melting point of the contained bismuth compound. For example, when bismuth is used in the form of Bi,03, 80
Calculate at 0-820°C.

In addition, firing is performed in an open environment from the viewpoint of gas release.

For example, if mixed powder is placed in a container and fired, either do not cover it or cover it with a gap.

■ Firing of the molded body is a reaction 9 of organic matter such as binder contained in it.
This is to remove the gas generated by decomposition, and is fired under the same conditions as in case ① above. However, since gases generated due to the composition components are removed, the temperature may be low (for example, about 600° C.).

■The closed container may be a substantially closed container, for example, a container with a naturally placed lid. Also, it is made of alumina ceramics.

(2) The starting materials are Bi and Sr, each combined with oxygen.

A compound powder such as Ca or Cu powder, such as oxide, carbonate, or hydroxide, is used.

For example, bismuth oxide (B i to 3), copper oxide (Cub), strontium carbonate (SrCO3), strontium oxide (SrO), strontium hydroxide (S r (OH)y), calcium carbonate ( Ca CO3), calcium oxide (
This includes calcium hydroxide (Ca(014)t).

■The relationship between the component atomic ratios of Bi, Sr, Ca, and Cu in the sintered body at the time of starting (at the time of mixing), and the relationship between Sr and Ca, which are the same alkaline earths, is S r
: 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: If the angle is in the range of 1 to 2 degrees, a sintered body in which a superconducting phenomenon (resistance of zero or extremely small value) occurs can be obtained in liquid nitrogen.

Since the raw material containing F9 action bismuth is pre-calcined twice, once as an initial mixed powder and once as a compact, most of the gas generated by reaction 1 decomposition is removed at this point, and the gas generated during the main firing is removed. The amount of gas generated is small.

Therefore, since the main firing can be carried out with the molded body housed in a closed container, scattering of bismuth can be suppressed.

G. Example Hereinafter, the present invention will be explained based on examples.

First, generation of mixed powder will be explained.

As a starting material, bismuth oxide (B
iyOs) powder, strontium carbonate (SrCO
s) powder, calcium carbonate (CaC03) powder, and copper oxide (Cub) powder at 11.11 mo 1 each.
%, 22.22 mo1%, 22.22 mo1%, 44.
Weigh it so that it becomes 44mo1%.

Next, these powders 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 dried at a temperature of about 100° C. to obtain a mixed powder.

Next, this mixed powder I was put into a container 2 made of alumina ceramics with an open top as shown in FIG.
Calcinate (preliminary firing) at °C for 2 hours. At this time,
For example, CO, gas, etc. contained in the mixed components SrCO3°CaCOs are generated and released.

Next, the obtained fired powder is sufficiently pulverized to obtain a fine processed powder.

Next, this processed 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 dried at a temperature of about 100°C.

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 passed through a sieve to obtain granulated powder having a size of 150 mesh or less.

Next, after filling this granulated powder into a mold, 1 to 2 tons/
A molded body 3 having an outer diameter of 40 mm and a thickness of about 6 mm is made by compression molding at a pressure of about 1.5 cm.

Next, when setting this molded body 3 in the container 2, the second
As shown in the figure, first, a spacer 4 made of an alumina plate is placed on the bottom of the container, and a thin layer of powder having the same composition as the molded body 3 is placed thereon as a bed powder 5. Then, the molded body 3 is placed on this bed powder 5.

In this state, the molded body 3 is fired (preliminary firing) at approximately 600° C. for 2 hours. At this time, the organic binder remaining in the molded body 3 is released as a decomposed gas.

Next, the pre-fired molded body 6 is stored in the container 2 as shown in FIG. 3 (in the same manner as in the case of FIG. , the closed container in this state is placed in a firing furnace, and is heated in an oxidizing atmosphere.
A sintered body (ceramics) is obtained by heating at a temperature of 30 to 880°C for several hours.

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

That is, FIG. 4 is an explanatory diagram for measuring the resistance value, and shows terminals for passing current through both ends of the sintered body S in the longitudinal direction, a/
, and voltage terminals A and B' for measuring the resistance value are provided inside the terminal.
, a' with a stabilized current of 1 ampere flowing through the terminals, b'
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.

As a result, it was confirmed that the superconducting phenomenon begins at an absolute temperature of 110 K and the electrical resistance becomes zero when the temperature reaches about 85 K.

Further, as a result of measuring the amount of bismuth after firing, it was found that the amount decreased by only 2 to 3% compared to the amount at the time of mixing.

Effects of the H0 Invention As described above, the superconductor of the present invention has a liquid nitrogen temperature (
It becomes 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.

In addition, the mixed powder of the raw materials is pre-fired (preliminary firing) to release gas, and the compact is fired after removing residual organic matter, which is then subjected to main firing. ■ Sintering Very few impurities remain in the body.

■Since raw materials that have been pre-fired are used, the reaction during main firing is slower.

(2) Since the main firing of the molded body can be carried out in a closed container, it is possible to prevent the contained bismuth from scattering, and the reduction in bismuth is limited to 2 to 3% at the time of initial mixing.

As a result, the composition is stabilized, and a superconductor with stable quality can be obtained.

Moreover, since superconductors can be formed using inexpensive raw materials and only need to be cooled at liquid nitrogen temperatures, they are close to practical application, especially for electric resistance related to power, transportation, etc., precision instrument elements, and other energy sources. It can be used in fields such as conversion, and has extremely powerful effects.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the preliminary firing of the mixed powder in the present invention, FIG. 2 is an explanatory diagram of the preliminary firing of the compact in the present invention, FIG. 3 is an explanatory diagram of the main firing in the present invention, and FIG. 4 is an explanatory diagram of the present invention. FIG. 3 is an explanatory diagram for explaining a method of measuring the resistance value of a sintered body according to the invention. ■...mixed powder, 2...container, 3...molded body, 6
... Temporarily fired molded body, 7... Lid, a, a' medium current supply terminal, b, b'... Voltage measurement terminal, S... Sintered compact. Figure 1: Explanation of preliminary firing of mixed powder Figure 3: Molded body 6... Temporarily fired compact Figure 3: Explanation of final firing of the molded body

Claims (1)

[Claims] (1) Bismuth, strontium, each combined with oxygen,
A step of obtaining a mixed powder of calcium and copper compound powders, a step of calcining the mixed powder (at a temperature below the melting point of the bismuth compound) to release gas, and pulverizing and processing the calcined product. a step of obtaining a powder and granulating it to obtain a granulated powder and pressurizing the granulated powder to obtain a molded body; a step of pre-firing the molded body at a temperature below the main firing temperature in a subsequent step; A superconductor characterized by comprising the steps of storing the pre-fired molded body in a closed container and main firing the container and the molded body at a temperature in the range of 830 to 880°C to obtain a sintered body. How the body is manufactured.