JPH02196053A - Production of dense oxide superconductor - Google Patents

Abstract

PURPOSE:To produce the superconductor with further improved superconductivity by quantitatively mixing the raw metallic compd. powders contg. metallic salts, calcining the mixture under specified conditions to control the residual carbon content to a specified value, forming the material, and sintering the formed product. CONSTITUTION:The raw metallic compd. powders (e.g. Y2O3, BaCO3, and CuO powders) contg. metallic salts are quantitatively mixed, the mixture is calcined at 800-900 deg.C for 2-5hr in an oxygen atmosphere (e.g. in the atmosphere), and the calcined powder contg. <=1wt.% residual carbon is obtained. The calcined powder is then formed, and sintered to obtain an oxide superconductor. By this method, the residual carbon is dissipated prior to sintering, hence the formation of an oxide superconductor is promoted, the superconductor is densified, and the superconductivity is further improved.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is directed to YBaCuO-based or B i S rcaC
The present invention relates to a method for manufacturing oxide superconductors such as uO-based superconductors, and more specifically, aims to densify such superconductors and increase their practical value in various application fields.

(Prior Art) Recently, many copper-containing high critical temperature oxide superconductors such as Ln-based, Bi-based, and Tl-based oxide superconductors have been discovered. and,
As methods for producing these oxide superconductors, solid phase reaction methods, sol-gel methods, and coprecipitation methods are mainly employed. Of these, the latter two are manufacturing methods that are attracting particular attention because they have excellent uniformity and can be fired at low temperatures.

In the solid phase reaction method, raw metal compound powders containing metal salts such as carbonates are mixed, and if necessary, calcined and shaped, and then fired to obtain an oxide sintered body. in this case,
Each constituent metal oxide powder is used as a raw material, but Ba
Since O and the like are unstable, their carbonates (BaCO□) are used. In addition, in the sol-gel method, metal salts such as nitrates of constituent metals are dissolved and mixed in water, and an organic substance (citric acid, ethylene glycol, etc.) is applied to this to form a chelate to obtain a gel-like mixture. After heating and drying, calcining
This is molded into a desired shape and fired to obtain an oxide sintered body in the same manner as described above. Furthermore, in the coprecipitation method, metal salts such as nitrates of the constituent metals are dissolved and mixed in water, and an organic acid (such as oxalic acid) is added to this to adjust the pH, and the organic acid salts of the raw material metals are coprecipitated. After heating and drying the coprecipitate and pulverizing it, it is calcined.
This is molded into a desired shape and fired to obtain an oxide sintered body in the same manner as described above.

(Problems to be Solved by the Invention) By the way, in the above production method, in the case of the solid phase reaction method,
It is inevitable to use a metal salt such as BaCo3 as a starting material, and in the case of the coprecipitation method or the sol-gel method, organic substances are used in the process, so carbon remains in the intermediate before firing. There is a problem that residual carbon stabilizes carbonates such as BaCO3 and inhibits the formation of oxide sintered bodies, and the sintered bodies are porous and do not become dense, making it impossible to perform low-temperature firing. Ta. In particular, in the case of the coprecipitation method and the sol-gel method, carbon tends to remain in the intermediate before firing, and although these methods are noteworthy as mentioned above, this point is a bottleneck that prevents them from being widely adopted. The reality is that this has not yet been achieved.

(Purpose of the Invention) The present invention was made in view of the above-mentioned circumstances, and aims to evaporate residual carbon before firing, thereby promoting the formation of an oxide superconductor, and densifying the oxide superconductor. The aim is to contribute to increasing the practical value of superconductors.

(Means for Solving the Problems) There are three aspects of the method for producing a dense oxide superconductor of the present invention to achieve the above object, the first of which corresponds to the solid phase reaction method described above. ,
A predetermined amount of raw metal compound powder containing metal salts such as carbonates is weighed and mixed, and this is calcined in an oxygen atmosphere at 800 to 900°C for 2 to 5 hours to produce calcined powder with residual carbon of 1% by weight or less. The second method corresponds to the sol-gel method, in which a predetermined amount of a metal salt such as a nitrate of a raw material metal is added. The mixture is weighed and dissolved in water, and an organic substance is applied thereto to form a chelate to obtain a gel-like mixture.The gel-like mixture is heated and dried, and then calcined at 750 to 900°C for 5 to 10 hours in an oxygen atmosphere. A calcined powder with residual carbon of 1% by weight or less is obtained, and the calcined powder is shaped and fired to obtain an oxide superconductor; and the third is equivalent to the co-precipitation method, A predetermined amount of a metal salt such as a nitrate of a raw material metal was weighed, dissolved and mixed in water, an organic acid was added thereto to adjust the pH, the organic acid salt of the raw material metal was coprecipitated, and the coprecipitate was heated and dried. After 750~900
℃ in an oxygen atmosphere for 5 to 10 hours until the residual carbon is 1
The gist of each of these is to obtain a calcined powder of % by weight or less, and to obtain an oxide superconductor by shaping and firing the calcined powder.

The reason why the calcination temperature and time are specified as above in the first to third embodiments is that if the calcination temperature is lower than the above and the calcination time is shorter than the above, the evaporation of residual carbon is not sufficient and the calcination is This is because more than 1% by weight of carbon remains in the calcined powder, and on the other hand, even if the calcining temperature is higher or the calcining time is longer than the above, most of the residual carbon will evaporate within a certain range, so This is because energy is wasted, and because grain growth occurs, activity is lost and densification does not occur during sintering.

The reason why the residual carbon before firing is set to 1% by weight or less is that if it exceeds 1% by weight, the density tends to decrease due to the influence of the residual carbon.

(Function) In the method of the first aspect, when the mixture of raw metal compounds is calcined at the above temperature and time, composite oxide crystals from the raw metals are generated, and at the same time, the carbonate contained is partially decomposed,
Carbon transpires. At this time, the residual carbon is controlled to be 1% by weight or less. When this is fired after boiling, the decomposition of the residual carbonate is promoted, each constituent element is strongly bonded, and a dense oxide sintered body is obtained.

Furthermore, in the method of the second embodiment, when a metal salt such as a nitrate of a raw metal is chelated, this chelate contains a large amount of carbon atoms. However, the chelate is decomposed by subsequent calcination under the above conditions, and although some carbonate is produced, most of the carbon is evaporated. At this time, the residual carbon was 1% by weight.
Control as below. When this is then fired, the decomposition of the residual carbonate is promoted in the same manner as described above, and each constituent element is firmly bonded to obtain a dense oxide sintered body.

Furthermore, in the method of the third embodiment, when coprecipitated with an organic acid, the coprecipitate contains a large amount of carbon atoms since it is an organic acid salt of the raw metal. However, by subsequent calcination under the above conditions, the organic acid salt is decomposed and some carbonate is produced, but most of the carbon is evaporated. At this time, residual carbon is controlled to 1% by weight or less.

When this is then fired, the decomposition of the residual carbonate is promoted in the same manner as described above, and each constituent element is firmly bonded to obtain a dense oxide sintered body.

(Example) Next, an example will be described.

(Example-1) (i) Ya03 powder 30.26g, BaC0a powder 10
After weighing and mixing 5.78 g and 17.34 g of CuO powder, heat treatment (
calcined). At this time, the amount of carbon before and after the heat treatment was measured by the LECO method.

(ii) Then, it was crushed in an agate mortar with an average particle size of 1.6μ.
A calcined powder of m was obtained. The obtained powder was identified by X-ray diffraction as Y Ba Cu O crystal 1 2 3
7-δ It was confirmed that there is.

(■) The above powder was molded into 12φ pellets, and the pellets were heated at 200°C/hr from room temperature to 950°C in an oxygen atmosphere.
After raising the temperature at the maximum temperature (950°C) for 5 hours,
A sintered sample was obtained by cooling to room temperature at 200 °C/hr.

(iv) measuring the bulk specific gravity of the obtained sintered sample;
The composition was observed using a SEM (scanning electron microscope), and the ground sample was subjected to XRD measurement. In addition, the resistance change with respect to temperature was measured using the four-probe method, and the onset temperature (Tco) was measured.
, the offset temperature (Tce) was investigated. Furthermore, current density was measured in the following manner.

That is, according to the four-terminal method, a current lead wire is connected to the sample surface at A.
After fixing the sample to a copper block and immersing it in liquid nitrogen, once the temperature stabilized, a current was started to flow, and the value was gradually increased until a voltage suddenly occurred and reached 1μV.
The current value when the current value became Ic was defined as Ic, and the value obtained by dividing it by the cross-sectional area was defined as the critical current density Jc.

(V) Results: The carbon content before and after the calcination treatment was 4.2% by weight and 0% by weight, respectively.
．． It was 4% by weight. The bulk specific gravity of the sintered body reaches 98% of the theoretical specific gravity (theoretical density), and it is understood that it is extremely dense. This is SEMa! (This was also confirmed by observation. In addition, no impurity peak was observed from XRD analysis, and it was found that the sintered body was a single phase of Y Ba Cu O.
2 37-δ was obtained. Furthermore, Tco=93K (absolute temperature, same below),
Tce=91, Jc=1010 A/aJ, and good superconducting properties were obtained.

<Comparative Example-1> (i) In Example-1, the calcination treatment conditions were changed to 900°C
Samples were prepared in exactly the same manner except that the heating time was 1 hour, and various measurements similar to those described above were performed.

(it) Results: The carbon content before and after the calcination treatment was 4.2% by weight and 1% by weight, respectively.
．． It was 3% by weight. The bulk specific gravity of the sintered body is 7 of the theoretical specific gravity.
6%, which indicates that the density is significantly inferior to that of Example-1. Further, a slight peak of barium carbonate was observed by XRD analysis. Furthermore, Tco=92, Tce=87, and Jc=110 A/cd, demonstrating that the superconducting properties were inferior to Example-1.

(Example-2) (i) Y (Now) a, B a (No, ), and Cu
Each aqueous solution of (N Oy )Z was mixed at a molar ratio of 1:2:3, and citric acid and ethylene glycol were added to this mixture to form a chelate, thereby creating a gel-like mixture.

(ji) This mixture was heated and dried at 500° C., and the carbon content of the obtained powder was measured by the LECO method and found to be 4.1% by weight.

(iii) The above powder was heat-treated (calcined) in an oxygen stream under the conditions shown in Table 1 to obtain four types of calcined powders having different amounts of carbon.

(Cry) These calcined powders were subjected to firing treatment in the same manner as in Example 1 to obtain a sintered body, and various measurements were performed in the same manner as above. The results are shown in Table 1 along with the calcination conditions.

From the results in Table 1, it is understood that sample No. 4, which is outside the scope of the present invention, has a carbon content in the calcined powder of more than 1% by weight, a small bulk specific gravity, and a poor density. Also,
Tco, Tce, and Jc are also lower than other samples (&1 to 3...within the scope of the present invention), and the superconducting properties are inferior.

(Example-3) (i) Y(Now)a, B a (N 0a)- and Cu (N O,).

Mix each aqueous solution in a molar ratio of 1:2:3, add oxalic acid to sub-adjust the pH, Y(C00)3,
A coprecipitate consisting of B a (COO)z and Cu(Coo) was obtained. The amount of carbon contained in this coprecipitate was measured and found to be 13.5% by weight.

(ii) The coprecipitate powder was calcined at 900° C. for 5 hours in an oxygen stream, and the carbon content was measured to be 0.5% by weight.

(iii) The above calcined powder was fired under the same conditions as in Example-1 to obtain a sintered body. The properties of this sintered body were measured in the same manner as above, and the bulk specific gravity was 92% of the theoretical specific gravity, indicating excellent compactness and Tc.

=93, Tce=90, and Jc=1320 A/d, showing excellent superconducting properties.

Incidentally, in the above example, a method for manufacturing a YBaCuO-based oxide superconductor was described, but B i S r C, aCu
The inventors have confirmed that similar results can be obtained with O-based and other oxide superconductors.

(Effects of the Invention) As described above, the manufacturing method of the present invention suppresses the amount of residual carbon in the calcined powder to 1% by weight or less by specifying the calcining conditions, thereby promoting the reaction during firing. This makes it possible to make the sintered body denser and further improve the superconducting properties, and therefore it is inevitable that it will bring great benefits to the application development of this type of superconductor.

one or more one

Claims (3)

[Claims] 1. A predetermined amount of raw metal compound powder containing a metal salt is weighed and mixed, and this is calcined in an oxygen atmosphere at 800 to 900°C for 2 to 5 hours to obtain a calcined powder with residual carbon of 1% by weight or less. A method for producing a dense oxide superconductor, in which an oxide superconductor is obtained by molding and firing a sintered powder. 2. A predetermined amount of the metal salt of the raw material metal is weighed, dissolved and mixed in water, and an organic substance is applied thereto to form a chelate to obtain a gel-like mixture. After heating and drying the gel-like mixture, the temperature is 750-900
A dense oxidized material is calcined in an oxygen atmosphere at 0°C for 5 to 10 hours to obtain a calcined powder with residual carbon of 1% by weight or less, and the calcined powder is shaped and fired to obtain an oxide superconductor. Method for manufacturing physical superconductors. 3. A predetermined amount of the metal salt of the raw material metal is weighed, dissolved and mixed in water, an organic acid is added thereto to adjust the pH, the organic acid salt of the raw material metal is coprecipitated, and the coprecipitate is heated and dried. 9
A dense oxide obtained by calcining in an oxygen atmosphere at 00°C for 5 to 10 hours to obtain a calcined powder with residual carbon of 1% by weight or less, and then sintering the calcined powder to obtain an oxide superconductor. Method for manufacturing superconductors.