JPH02196061A - Production of superconductor - Google Patents

Abstract

PURPOSE:To stabilize the high quality of the superconductor at a low cost by calcining the mixed powder of a Bi oxide, etc., in a specified vessel at a temp. lower than the sintering temp. in an oxidizing atmosphere, press-forming the obtained crushed and granulated powder, and sintering the formed product in a sintering vessel. CONSTITUTION:The Bi-Pb paste obtained by kneading the mixed powder of Bi2O3 and PbO with water is applied on the inner walls to obtain the calcination vessel 1A and sintering vessel 1B provided with coated layers 2. The powder of Bi2O3 having <=10mum particle diameter, the powder of PbO, the powder of SrCO3, the powder of CaCO3, and the powder of CuO are then mixed to obtain mixed powder 3. The powder 3 is charged into a vessel 4, and placed the vessel 4 in the vessel 1A through a spacer 5. A lid 6 is set, and then the powder is calcined at about 830 deg.C in an oxidizing atmosphere in a calcination furnace. The calcined material is crushed, granulated, and press-formed to obtain a formed product 7. The product 7 is arranged in the vessel 1B contg. the bottom powder 8 having the same composition as the product 7 through a spacer 5, and the lid 6 is fixed. The vessel 1B is then sintered at 830-880 deg.C in an oxidizing atmosphere in the sintering furnace to produce the superconductor.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Industrial Application Field The present invention relates to a so-called superconductor whose electrical resistance becomes zero at a certain temperature, and in particular B1-Pb-3r which exhibits superconducting properties above the temperature of liquid nitrogen. The present invention relates to a method for producing a -Ca-Cu-0-based superconductor.

B9 Summary of the Invention The present invention provides bismuth (B+) + lead (pb), strontium (Sr), and calcium (Ca), each combined with oxygen.
), a coating layer containing bismuth and lead was provided on the inner wall during pre-firing of a mixed powder of copper (Cu) powder and during main firing of a molded body formed from processed powder obtained by pulverizing this pre-calcined product. This is a method for producing a B i -Pb-3r-Ca-Cu -0-based superconductor that prevents bismuth from scattering by using a sintering container, and the sintered body is heated to a liquid nitrogen temperature or higher (absolute temperature 77°C). The present invention provides a method for producing a superconductor that exhibits superconductivity at temperatures above

C0 Conventional technology Recently, I-1-thorium copper oxide has been discovered as a material that exhibits superconductivity at temperatures higher than the liquid nitrogen temperature of 77, and is also an inexpensive material with a TC of approximately IIOK. i-3r-Ca-CuO-based superconductors have been discovered.

However, the Bi (bismuth) system has recently had a drawback in that a phase with a Tc of 70 and a phase with a Tc of 110 coexist. However, by adding a small amount of PB (lead) to this, the high temperature phase (
B 1-Pb-3r- which can realize single phase of IIOK)
Ca-Cu-0 based superconductors have 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, i -Pb-3r-CaCu
-0 series superconductors contain bismuth (Bi) and lead (Pb) as starting materials, so if a mixed compact is fired directly in a firing furnace, Bi and Pb will scatter due to the heat load, causing There is a problem in that a "mismatch" occurs between the composition at the time of mixing and the composition of the final product.

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

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

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

Therefore, it contains bismuth and lead, which are easily scattered by the heat load during firing.1. In the case of superconductors, 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- with stable quality.
The present invention aims to provide a method for manufacturing a Pb-3r-Ca-Cu-0 based superconductor.

Means to solve 80 issues The present invention uses bismuth and lead, each of which is combined with oxygen.

Strontium, calcium, and copper powders are mixed and first calcined, the calcined product is pulverized, the processed powder is molded to make a molded body, and this is fired to make a sintered body.

Furthermore, during these preliminary firings and main firings, this is a method for manufacturing a superconductor using a container whose inner wall is provided with a coating layer containing bismuth and lead.

Note that (1) the firing container may be a substantially closed container, for example, a container with a lid placed naturally.

Further, it is formed of a material (for example, alumina ceramics) that does not significantly react with the coating substance.

Further, it is preferable that the container be made of a porous material rather than a dense material, since this provides a large surface area and allows sufficient application of the coating material.

■As a means of providing a coating layer containing bismuth and lead, (b) Apply as a paste, (b) Apply as a slurry, (c) Make it into a liquid and apply it by spraying. (d) Spraying the slurry; Either of these is fine.

(2) The form of applied bismuth and lead may be any of a mixture of Bi and Pb alone, a solution containing Bi and Pb, a Bi compound and a Pb compound. Also, Bi compounds, Pb
The compounds include (a) B 1los, pbo, pb, o.

In addition to pb and o, (b) those that undergo decomposition and oxidation9 reaction at the firing temperature to become bismuth oxide and lead oxide, and those that release Bi and Pb molecular species, fall under this category.

(2) The temperature of the main firing is 830 to 880°C, and the temperature of the preliminary firing is lower than the main firing temperature, for example, 830°C or lower.

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

Powders of Sr, Ca, and Cu, such as compound powders such as oxides, carbonates, and hydroxides, are used.

For example, bismuth oxide (Bit03), lead oxide (pbo), copper oxide (CuO), strontium carbonate (SrCO,), strontium oxide (SrO), strontium hydroxide (S r (OH) = ), calcium carbonate (CaCOs), calcium oxide (Cab), and calcium hydroxide (Ca(OH)=).

■When converting the relationship of the component atomic ratios of Bi, Pb, Sr, Ca, and Cu in the sintered body at the time of starting (at the time of mixing), the relationship of Sr and Ca, which are the same alkaline earth metals, is Sr:Ca=l:0 .3～
3゜The relationship among other Bi, Pb, and Cu is (B i + Pb): Cu=1 + 1.8~4゜Bi
:Pb=1 :0.1~0.4, and the relationship between these two is (S r〇a): (B i〇Pb〇Cu)=11
If the angle is in the range of ~2°, it is possible to obtain a sintered body in which a superconducting phenomenon (resistance of zero or extremely small value) occurs in liquid nitrogen.

F1 action A mixture containing bismuth and lead is pre-fired and then finally fired in a container with a coating layer containing bismuth and lead on the inner wall, so the inside of the firing container becomes an atmosphere rich in bismuth and lead, resulting in a mixture containing bismuth and lead. The scattering of bismuth and lead from can be suppressed.

In addition, since the raw material powder is calcined in advance at a temperature below the main firing temperature and then pulverized to form a compact, which is then subjected to the main firing, the reaction during the main firing is slow.
Cracking can be prevented.

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

First, the firing container is a temporary firing container IA made of alumina ceramics with an open top as shown in FIG.

It is formed by the main firing container IB and M6, which will be described later.

Then, water is added to the mixed powder of Bi, O, and PbO and thoroughly kneaded to make a paste of B1-Pb, which is coated on the inner walls of both firing vessels IA and IB and dried to form a coating layer 2 of B1-Pb. will be established.

Next, as starting materials, bismuth oxide (Bt, os) powder and lead oxide (pbO) powder with a particle size of 10 μm or less,
Strontium carbonate (S r COs ) powder,
Calcium carbonate (Ca COs) powder and copper oxide (CuO) powder were 3.7 mo1% and 4.3 mo, respectively.
1%, 21.7mo1%, 21.7mo1%, 43.5
Weigh it so that mo 1%.

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.

Next, the mixed powder 3 obtained by drying is put into a container 4, and this container 4 is inserted into the temporary firing container IA through an alumina plate spacer 5.
The upper opening of the pre-firing container IA is substantially covered with the lid 6, and the container is heated in a baking furnace in an oxidizing atmosphere at a temperature lower than that of the main baking in the subsequent process (approximately 830° C. or lower). Heat treatment (so-called temporary firing) is performed for about 4 hours.

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 sieved 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/
Compression molded with a pressure of about cm', outer diameter 40 shoulders! , a molded body 7 having a thickness of 6 mm is made.

Next, when setting the molded body 7 in the main firing container IB, as shown in FIG. Powder of the composition is placed thinly as a bed powder 8 (.Then, the molded body 7 is placed on top of this bed powder 8.

Furthermore, in order to close the opening of the main firing container IB, a lid 6 was placed on it, and the container in this state was placed in a firing furnace, and heated at 830 to 888° C. in an oxidizing atmosphere and at a temperature higher than the temperature during the preliminary firing.
A sintered body (ceramics) is obtained by heating at a temperature of 0° C. for several hours.

The sintered body obtained by the above manufacturing method has a width of 4 wings! The sintered body was cut into a shape with a thickness of 4 m and a length of 40 x m, and electrodes were provided as shown in FIG. 4, and the resistance of the sintered body was measured by a four-terminal method.

That is, FIG. 4 is an explanatory diagram for measuring the resistance value, and terminals a, a' for passing current through both ends of the sintered body S in the longitudinal direction.
, 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 about 110 K and the electrical resistance becomes zero when the temperature reaches about 105 K.

Furthermore, as a result of measuring the amount of bismuth and lead 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, conventional bismuth-based products have a Tc of 70 l.
The structure of the present invention has a two-phase structure of about 10K, but the structure of the present invention can be made into a single phase of about 110K, and since the superconducting phenomenon occurs at higher temperatures, a stable superconducting state can be maintained. be.

In addition, since the raw material powder is heat-treated at a temperature below the main firing temperature and then pulverized to form a compact, which is then subjected to the main firing, the reaction during the main firing is slow, resulting in a quality improvement. A stable superconductor can be obtained.

Furthermore, during preliminary firing and main firing, the mixed powder and compact are fired in a container whose inner wall is coated with a coating layer containing bismuth and lead, resulting in an atmosphere rich in bismuth and lead inside the container. Therefore, the scattering of bismuth and lead from the mixed powder and compact can be suppressed, and the reduction in bismuth and lead is limited to 2 to 3% during initial mixing, resulting in a stable composition and, as a result, stable quality. A superconductor can be obtained.

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 related to electric power, transportation, etc., precision instrument elements, and other energy conversion devices. It exhibits extremely excellent effects, such as being able to be used in fields such as.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a nine-piece firing container with a coating layer containing bismuth and lead on the inner wall used in the present invention, and FIG. 2 is an explanatory diagram showing mixed powder set in the containers during temporary firing. FIG. 3 is an explanatory diagram showing the molded body set in the container during main firing, and FIG. 4 is an explanatory diagram for explaining the method of measuring the resistance value of the sintered body of the present invention. IA, IB... (temporary, real) firing container, 2... Coating layer (containing bismuth and lead), 3... Mixed powder, 7...
・Molded body, a, a ... Current supply terminal, b, b
'...Voltage measurement terminal, S...Sintered body. Outside 2 people Figure 1 Easy navigation of roasted hemp (2) Mouth 3 - Utsuai Obu 7 --- Eight form rules Figure 2 Mixed 8 Visit to bed Season 1 Toso Nikko Explanation mouth Figure 3

Claims (1)

[Claims] (1) A process of storing a mixed powder of bismuth, lead, strontium, calcium, and copper powders each combined with oxygen in a container, and a pre-firing container with a coating layer containing bismuth and lead on the inner wall. , the container and the mixed powder are pre-sintered in an oxidizing atmosphere at a temperature lower than that of the main sintering in the subsequent step, and the pre-sintered product is pulverized to obtain processed powder and manufactured. A process of granulating to obtain granulated powder, A process of pressurizing the granulated powder to obtain a molded body, Storing the molded body in a main firing container whose inner wall is provided with a coating layer containing bismuth and lead. , these containers and molded bodies are 8
A method for producing a superconductor, comprising the steps of: obtaining a sintered body by main firing at a temperature in the range of 30 to 880°C.