JPH01133928A - Production of powder mixture for material of superconductor - Google Patents

Abstract

PURPOSE:To obtain a powder mixture to be used for a material for prepg. a superconductor having uniform characteristics and high current density by regulating the concn. of aq. soln. of HNO3 of elements belonging to specified three components to each specified value, and prepg. a powder mixture of metals via precipitate of carbonates of the metals from said solns. CONSTITUTION:Aq. solns. of powdery metals of elements belonging to a first component(at least one among Y, Sc, La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Lu), a third component(Cu), are prepd. separately. The concns. of each component of the aq. HNO3 soln. are regulated in such a manner that the concn. of the high concn. soln. is <=5 times of that of the low concn. soln. A soln. of Na2CO3 or K2CO3 is added to the solns. to prepare precipitate of carbonates, thus a powder mixture of metals of the above described components is produced from the precipitate. Since the concn. of the high concn. soln. is regulated to <=5 times of the low concn. solns. by this method, the error in the compsn. in the stage of taking each portion of the soln. corresponding to a compositional ratio is kept at a small level. Accordingly, precipitate of carbonates can be formed securely.

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 the production of mixed powder for superconducting materials that exhibits superconducting phenomenon above liquid nitrogen temperature. Regarding the method.

83 Summary of the Invention The present invention provides a method for producing a mixed powder for superconducting materials, in which a sodium carbonate or potassium carbonate solution is added to an aqueous solution of metal powder containing multiple elements to obtain a carbonate precipitate. Uniform mixing is achieved, there is no fear of contamination of impurities, and the firing temperature can be lowered.

C1 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 discovered by the 1980s were cooled at liquid helium temperatures (Tc approximately 4, -269°C); Must. Helium is a rare and expensive material, and the cost of cooling it down to its critical temperature is extremely high, which has been an obstacle to the widespread use of superconducting materials.

Very recently, research and development on superconducting materials has been progressing worldwide, and the highest Tc of superconducting materials known so far is 22.3 of niobium 3 germanium (N b 3 Ge).
However, lanthanum, strontium, and
With copper oxide (LaSr)2CuO4, superconductivity began in 1937, exceeding previous limits, and it was announced that the electrical resistance had become zero in 1933, followed by La-8r-CuO4 at the beginning of this year. 54K in the system, and then yttrium (in place of lanthanum and strontium)
Y) Tc77K has been achieved with a new material that combines barium (Ba), copper, and oxygen.

Currently, barium (Ba), yttrium (Y),
Superconducting materials made of oxides of copper (Cu) and oxygen are of the greatest interest, and active development is underway to put them into practical use.

As a method for manufacturing this superconductor, for example, Y.

03 (Ittria), BaC03 (barium oxide).

The raw materials for CuO (copper oxide) are thoroughly mixed mechanically using a ball mill, etc. in an appropriate mixing ratio, and the raw material powder, water, and cobblestones are added and thoroughly mixed for several hours, followed by heating to advance the solid phase reaction. A starting material is obtained and sintered to obtain a superconductor.

D1 Problems to be Solved by the Invention As mentioned above, since superconductors are sintered bodies, their structure is determined by the starting materials, sintering method, heat treatment, etc. Once the characteristics are determined, the powder of the starting materials is optimal. Otherwise, no matter how ingenious the sintering method or heat treatment, it will not be possible to obtain a product with uniform and excellent properties.

In the above method, it is difficult to mix the raw material powders of YzOs, BaCO5, and CuO sufficiently, so a long mixing time is required, and if the mixing time is too long, impurities from cobbles etc. will inevitably be mixed.

Furthermore, in general, the finer the particles, the more activated and uniform the sintering reaction, etc., can be, but in the above method, the size of the particles is determined by the particle size of the raw material powder. Furthermore, since the particle size has a certain distribution, there are problems such as a mixture of large particles and small particles, making it difficult for the fired superconductor to have a uniform structure.

Means to solve the E1 problem The manufacturing method of the present invention includes the first component (Y, Sc, La.

Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm.

one or more of Yb and Lu) and a second component (Ba.

A nitric acid aqueous solution is prepared for each component of the metal powder containing one or more of Ca, Sr) and each element belonging to the third component (Cu), and the concentration ratio of each component in the nitric acid aqueous solution is such that the higher the The concentration of the solution is 5 times or less, and a sodium carbonate or potassium carbonate solution is added to the solution to form a carbonate precipitate, and from this precipitate, a metal mixed powder containing the above-mentioned components is made.

Since the concentration ratio of the F1-acting nitric acid solution is set to 5 times or less of the high concentration solution to the low concentration solution, errors in the composition when fractionating the composition ratio do not become large. Therefore, adding a sodium carbonate or potassium carbonate solution to the nitric acid solution ensures the formation of a carbonate precipitate.

G. Example The present invention will be explained below based on one embodiment.

First, the first components (Y, Sc, La, Nd, Sm.

one or more of Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu), second component (one of Ba, Ca, Sr)
Metal powder containing each element belonging to the third component (Cu) is dissolved in nitric acid for each component to prepare a nitric acid aqueous solution of each component individually. A predetermined composition amount is separated from each of the produced nitric acid aqueous solutions to prepare a nitric acid mixed aqueous solution of the first to third components. At this time, the concentration ratio of the aqueous solutions is set so that the high concentration solution is 5 times or less the low concentration solution (the reason for this will be described later).

After stirring the nitric acid mixed aqueous solution prepared as described above, approximately 1.3 times the calculated amount of sodium carbonate solution or potassium carbonate solution is added to the solution while stirring.

Sodium carbonate or carbonic acid.

Addition of the potassium solution produces a carbonate precipitate in the aqueous nitric acid mixture. After the precipitate is formed, the mixture is stirred for several hours so that the precipitate is sufficiently matured. In addition, when heating is carried out, a heating temperature of 40 to 80° C. facilitates ripening. A mixed powder of metal containing the above-mentioned components is prepared from this precipitate, and a superconductor is manufactured through the following steps.

The carbonate precipitate is filtered and washed with water until pH=7. After washing with water, the precipitate is dried, placed in an alumina container, and calcined in air or an oxidizing atmosphere at a temperature of 800 to 900° C. for about 10 hours.

Then, grind thoroughly. After pulverization, an aqueous polyvinyl alcohol solution is added as a binder so that the amount of polyvinyl alcohol is 1 wt % based on the raw material powder. and,
Water or alcohol is added, thoroughly kneaded, dried, and sieved to obtain granulated powder of 150 mesh or less.

After filling the obtained granulated powder into a mold, for example, 700
A molded body is made by compression molding at a pressure of Kg/cmffi.

This molded body is placed in a firing container and heated at a temperature of 900-1200° C. for several hours in the air or an oxidizing atmosphere to obtain a sintered body.

This sintered body 2.5≦first component≦15moC% 20≦Second component≦50moC% 30≦Third component≦65moQ% The remaining component consists of oxygen (0).

The sintered body obtained by the above manufacturing method was
The sintered body was cut into a shape with a thickness of 4zz and a length of 40xx, electrodes were provided as shown in FIG. 1, and the resistance of the sintered body was measured by a four-terminal method.

That is, FIG. 1 is an explanatory diagram for measuring the resistance value, and there are terminals a for passing current through both ends of the sintered body S in the longitudinal direction,
A' is provided, and a voltage terminal S and b' are provided inside it to measure the resistance value.Place this in a liquid nitrogen cryostat, and apply a stabilized current of 1 ampere to terminals & and a' to connect the terminals. Measure the voltage between B and b' with a voltmeter (V).Measure the resistance value by the drop. Note that A indicates an ammeter.

Figure 2 shows the measurement results, and it was confirmed that the superconducting phenomenon began at an absolute temperature of 85 K, and that the electrical resistance became zero at about 83 K.

Next, Y as the first component, Ba as the second component, and C as the third component.
A specific example of a standard solution using u as an example is shown below.

The standard solution for Y is made by dissolving yttrium nitrate Y (No3) 3 in water to give a solution of 5 x 10-'mo12/mQ.

The standard solution of Ba is barium nitrate B a (NOa) t
to make 1,25 x 10-'mo(!/mQ).

The reference solution for Cu is prepared by dissolving copper nitrate Cu (NO3) t in water to give 5 X l O-'mo(!/mQ).

Dissolve Na2CO3 in water and make 5 x l O-'mo12
/ m (make it l.

Next, Y, Ba, and Cu solutions were mixed so as to have the following composition, and a precipitate was formed using Na2CO3.

The generated precipitate was thoroughly washed with water, and the composition of the obtained precipitate was measured by plasma emission spectrometry (ZCP). The results are shown below.

As mentioned above, the reason why the high concentration of nitrate solution should be 5 times or less that of the low concentration solution is that if the concentration difference is large, there will be a large error in the molecular weight when separating each solution to obtain the desired composition ratio in the mixed powder. Because it will be. For example, B a (NO
3) 2 is 1. when the solubility is about 59/100 moc.
9 X I O−'moσ/m&, Y(NO3)3 has a solubility of about 133f! / I 00mo (when l, 48
．． 7 X I O-'m0(1/m(1, Cu (NO
3) t has a solubility of approximately 243.7”i/I 00mo
When ρ, it becomes 129.9X 10-'mo(1/m(l). If you create a solution with a concentration near the saturated solution, the concentration of Ba" will be low, so you will have to add several tens of times more than the Y and Cu solution. Therefore, the error in the composition ratio becomes large.

Comparing the production method according to this example above with the oxalate coprecipitation method, Ba was difficult to precipitate in the oxalate method, but Ba was also sufficiently precipitated in the case of this example, resulting in a raw material with a uniform composition. Become. Further, since it is sufficient to arbitrarily take appropriate amounts of each solution for various compositions, the work is easy and deviations in composition are reduced.

In the above embodiment, a case has been described in which metal powder containing each element belonging to the first to third components is prepared and then dissolved in nitric acid, but a solution in which the elements are dissolved in nitric acid in advance may be used.

Incidentally, the precipitation according to the production method of this example is carried out as shown in the following reaction formula.

Y(NO3)3→Y"+3NO3-- When Nat CO3 is added to this mixed solution, Nat
CO3 → 2Na'+CO3'-, and the next precipitation reaction occurs.

Ko Note that the required amount of NazCO3 is as follows.

Y 1mo(!, Na, CO31,5moρ
Ba “ “ 1 mocCu〃
〃1moQ Actually, Na 2 CO3 is added in excess of the calculated amount to ensure sufficient precipitation and is washed out with a large amount of water during filtration, but if insufficient, no precipitation occurs. The excess amount may be 20-50%.

Effects of the H4 Invention As described above, the present invention exhibits a superconducting state at liquid nitrogen temperature (77 degrees K), and has better heat retention conditions and economic efficiency (helium I -1e is 20 times more expensive than nitrogen N2).

Therefore, by using the present invention, it becomes possible to use it in fields such as inexpensive and high-performance electrical equipment, precision measurement elements, and other energy change fields.

In addition, since the present invention uses carbonate precipitates, it is possible to mix uniformly compared to conventional mechanical mixing methods, there is no risk of contamination with impurities from cobblestones, etc., and because the present invention is fine particles, reaction sintering is possible. is uniform, the obtained sintered body can be made uniform, the current density can be improved, and the firing temperature can be lowered. It becomes a homogeneous mixture at the atomic level.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram for explaining the method of measuring the resistance value of a sintered body manufactured using the superconducting material according to the present invention, and FIG. 2 is an explanatory diagram showing the absolute temperature ( It is a characteristic curve diagram of resistance value (10-3 Ωcm) with respect to K). a, a'... Current supply terminals, b, b'... Voltage measurement terminals, S... Sintered body. Figure 1 11 Beans I! Teikaden Figure 2 Absolute temperature (ni) □

Claims (1)

[Claims] (1) First component (Y, Sc, La, Nd, Sm, Eu,
One of Gd, Dy, Ho, Er, Tm, Yb, Lu
nitric acid aqueous solution for each component of the metal powder containing each element belonging to (1 or more types), 2nd component (1 or more types of Ba, Ca, Sr), and 3rd component (Cu), and The concentration of the high concentration liquid is 5 times or less that of the low concentration liquid, and a sodium carbonate or potassium carbonate solution is added to this to form a carbonate precipitate, and from this precipitate, a mixed powder of metal containing each of the above components is produced. A method for producing a mixed powder for superconducting materials, characterized by producing a mixed powder for superconducting materials.