JPH07106893B2 - Manufacturing method of ceramics superconductor - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a ceramic superconductor, which has almost zero electric resistance at high temperatures and can be used for high-efficiency power storage, strong magnetic field generation, high-efficiency power transmission and the like.

2. Description of the Related Art Conventional superconductors include alloy systems such as niobium 3 tin (18K), niobium 3 gallium (20K), and niobium 3 germanium (24K), and most of these alloy-based superconductors require liquid helium. It was something to do. However, on April 1, 1986, Dr. KA Muller and Dr. JG Bednorz of the BM Zurich Research Center suggested that superconductivity of La-Ba-Cu-O ceramics at high temperature was investigated. Cu-O system (30K), La-Sr-Cu-O system (54K), Y-Ba-Cu-O system (98K), Y-Ba-Cu-O system (12
The critical temperature of 3K), Sc-Ba-Cu-O system (175K) and ceramics superconductors is getting higher and higher, and their applied researches are actively conducted.

Problems to be Solved by the Invention As a method for producing a ceramics superconductor, generally known is a method in which oxides and carbonates are pulverized and mixed and then fired. In this method, in particular, when synthesizing a ceramic superconductor material containing barium, it is necessary to perform firing synthesis at a temperature of about 1000 ° C. or higher in order to decompose barium carbonate. However, 1000 ℃ for these material systems
The copper oxide contained in the ceramic superconductor material reacts with most of the ceramics such as alumina, silica, zirconia, silicon nitride, etc., which are used in the firing process, such as alumina, silica, zirconia, silicon nitride, etc. The amount of copper contained was large, and segregation of copper also occurred. Therefore, it was difficult to produce a uniform and stable superconducting material. In addition, there is a report of synthesis by a coprecipitation method using oxalic acid as another method for producing a ceramics superconductor. But, for example, magnesium, calcium,
Since the oxalates of Group IIa elements such as strontium and barium are easily soluble in acid, it was extremely difficult to coprecipitate them at a certain composition ratio.

Means for Solving the Problems In order to solve the above problems, the present invention provides a solution containing each component of a constituent metal of a ceramics superconductor in a guanidine-based carbonate, oxalate, citrate, or tartaric acid. A solution containing at least one kind of salt is mixed, and a coprecipitate of each metal salt of the superconductor material is prepared at a pH of 5 to 9 and fired to synthesize the superconductor material.

Action In the superconductor synthesized by the method for producing a ceramic superconductor according to the present invention, each component of the constituent metals is a carbonate, an oxalate, a citrate, or a tartrate and a hydroxide depending on the organic base salt used. Because it co-precipitates as a mixture,
The particle size becomes very small, 1 μm or less, and even when the particles are mixed, they are uniformly mixed. Therefore, compared with the conventional method of synthesizing using a metal oxide or metal carbonate. The firing temperature required for synthesis is low, and the produced fired body is an extremely dense fired body, and a ceramic superconductor having excellent superconducting properties and stable properties can be synthesized. In particular, in the case of guanidine-based salts, the basicity of guanidine-based organic matter in water is stronger than that of Group IIa elements. A salt coprecipitate can be obtained, and superconducting properties can be obtained with good reproducibility.

Examples Examples of the present invention will be described below.

(Example 1) An aqueous solution containing each metal nitrate was stirred at a molar ratio of Y: Ba: Cu = 1: 2: 3, and an aqueous guanidine carbonate solution was added while confirming the pH value with a pH meter. The precipitate is confirmed from pH 4 or above, and even if the aqueous solution of guanidine carbonate is added from around pH 5, a region where the pH value does not fluctuate appears and a precipitate is formed. During that time, the pH value gradually rises to around 7. The pH fluctuates sharply around pH 7 to 9, and at higher values than pH 9, the pH fluctuates again,
Copper elution occurs in this region. In this example, the addition of guanidine carbonate was stopped at pH 8 as the end point, allowed to stand, filtered, pre-dried at room temperature, then placed in an alumina crucible and calcined at 700 ° C. in air. After the calcination, the mixture was crushed and mixed by a mixing and crushing machine, put into an alumina crucible and fired at 900 ° C. in air to obtain a ceramics superconductor powder.

This ceramic superconductor powder was placed in a nitric acid aqueous solution to check the generation of carbon dioxide, but no carbon dioxide was generated.
Yttrium oxide, barium carbonate, and copper oxide having the same composition ratio were sufficiently pulverized and mixed by a mixing and crushing machine, and the same operation as described above was performed.

It was confirmed that in the powder prepared by the conventional method, multiple carbon dioxides were generated and barium carbonate was decomposed and did not react. For this reason, a conventional synthesis method, that is, a sample using yttrium oxide, barium carbonate, and copper oxide as raw materials was fired at a temperature of 1000 ° C. or higher and pulverized and mixed.

1 ton of each of the ceramic superconductor powder synthesized by the production method according to the present embodiment and the conventional synthesis method of oxide and carbonate.
After pressure molding at a pressure of not less than / cm ² and baking at 900 ° C. in air, a diamond cutter was used to cut a 2 mm square rod, and the temperature characteristics of electrical resistance were measured. The results are shown in FIG. When synthesized with oxides and carbonates, it is difficult to obtain those with high characteristics because the firing temperature is the temperature that causes segregation and reaction with the crucible, and when the current density is increased, the electrical resistance near the critical temperature is I made tailing instead of zero. On the other hand, the sample synthesized by the manufacturing method of the present example had excellent electrical characteristics with zero electric resistance near the critical temperature even when the current density was increased.

(Example 2) An aqueous solution containing each metal nitrate was stirred at a molar ratio of Sc: Ba: Cu = 1: 2: 3, and an aqueous guanidine carbonate solution was added while confirming the pH value with a pH meter. In this example, the addition of the guanidine carbonate aqueous solution was stopped at pH 8 as the end point, the mixture was allowed to stand, filtered and pre-dried at room temperature, then placed in an alumina crucible and placed in the air at 700
It was calcined at ℃. After calcination, the mixture was crushed and mixed by a mixing and crushing machine, put into an alumina crucible and fired at 900 ° C. in air to obtain a ceramics superconductor powder. This superconductor powder was pressure-molded at 1 ton / cm ² or more, fired at 900 ° C. in air, and cut into a 2 mm square rod shape with a diamond cutter to measure temperature characteristics of electric resistance. For comparison, a ceramic superconductor was prepared using scandium oxide, barium carbonate, and copper oxide as starting materials, and the temperature characteristics of electric resistance were measured. The synthesis was carried out by firing in air at a temperature of 1000 ° C. or higher, pulverizing and mixing, and then preparing an electrical resistance measurement sample by the same operation as the one synthesized by the production method of this example.

As a result, the electrical resistance rapidly decreased to around zero at 100K. However, in the sample synthesized with oxide and carbonate, when the current density was increased, the electrical resistance did not become zero near the critical temperature and tailing occurred. On the other hand, the sample synthesized by the manufacturing method of the present example had excellent electrical characteristics with zero electric resistance near the critical temperature even when the current density was increased.

Further, in the present embodiment, the case where A is Sc, Y, La and B is Sr, Ba is described, but the present invention is not limited to this, and when A is an element of lanthanoids 58 to 71, B is Sr, Ba. Also in the case of the IIa group elements other than Ba, as in this example, the synthesis temperature can be lower than that in the case of using the oxide and the carbonate, and moreover, a uniform and dense one can be obtained, which has excellent characteristics. Naturally, it is obtained and belongs to the category of the present invention.

Although only the guanidine salt is described, it is natural that the same effect is obtained when the hydrogen of guanidine is replaced with another organic substance, and it is easily presumed that the same effect is obtained. Although only carbonates and oxalates have been described as organic base salts, similar effects can be obtained with citrates and tartrates.

EFFECTS OF THE INVENTION The present invention adjusts the pH value using a solution containing at least one salt of guanidine carbonate, oxalate, guenoate, or tartrate to adjust the components of the constituent metals of the ceramic superconductor. Fine particles can be uniformly mixed by mixing with a solution containing and coprecipitating, so that it is possible to synthesize at a lower temperature than before, and moreover, it is uniform and dense ceramic superconductivity with excellent superconducting properties. You can get the body.

[Brief description of drawings]

FIG. 1 is a temperature characteristic diagram of the electric resistance of a ceramics superconductor prepared by the manufacturing method of one embodiment of the present invention.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H01L 39/12 ZAA C // H01B 12/00

Claims (1)

[Claims] 1. A composition ratio of 0.5 ≦ (A + B) /Cu≦2.5 (A is Sc,
Y, lanthanoid 57-71 element at least one element, B is at least one element of Group IIa element) and a solution containing guanidine carbonate, oxalate, citrate, tartrate A method for producing a ceramics superconductor, which comprises mixing a solution containing at least one salt among them to coprecipitate a metal component at a pH of 5 to 9 and firing.