JPS63288912A - Production of inorganic oxide superconductor - Google Patents

Abstract

PURPOSE:To produce a superconductor which functions at above the b.p. of liquid H2 and has a high critical current density by drying coprecipitate obtained from aq. soln. of water-soluble salts of a raw material compsn. then calcining in two stages. CONSTITUTION:Aq. soln. of precipitant having >=9pH is added to aq. soln. of water-soluble salts contg. La, Cu, and >=one kind of alkaline earth element selected from Ba, Sr, and Ca. After precipitating hydroxides, hydrous oxides, oxalates, carbonates or a mixture thereof in the form of coprecipitate of said salts, a solid matter is obtd. by separating the solid from liquid. Then, the solid matter is dried and calcined at 700-950 deg.C, and molded, then calcined further at 800-1,200 deg.C in oxidizing atmosphere contg. O2. By this method, a high temp. superconductor expressed by the formula: (LaxAy)2CuO2 (wherein A is at least one kind selected from Ba, Sr, and Ca; x is 0.50-0.98; y is 0.5-0.02; z is an atomic ratio <=4) is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for preparing oxide superconducting materials, particularly for superelectric rotating machines, magnetic levitation trains, and MHD generators.

The present invention relates to a method for preparing superconducting materials suitable for superconducting application devices such as magnetic shielding devices and magnetic resonance imaging devices, and electronic devices such as Josephson elements.

[Conventional technology]

Since the realization of superconducting magnets, technology that applies the superconducting phenomenon has been developed for practical use, and has been used in power generators.

Progress is being made in energy-related fields such as rotating machines, magnetic materials for fusion reactors, magnetic levitation trains, power storage devices, and associated magnetic shielding materials. It is also expected to find applications in the electronics field, such as Josephson elements and magnetic shielding of devices. In particular, superconductors used in energy-related devices are desired to have particularly high critical temperatures, critical magnetic fields, and critical current densities due to their usage conditions and functions. Conventionally, there were two metal types and two alloy types.

Various types of superconductors such as intermetallic compounds and oxide types are known. For example, the critical temperature of vanadium is 5.3K, niobium is 9.3K, niobium-titanium alloy is 10K, niobium tritin is 19K, and bismuth acid. Lead is known to be 12%. Regarding oxide type superconducting materials, please refer to Japanese Unexamined Patent Publication No. 6
No. 0-173885.

[Problem that the invention seeks to solve]

All conventional superconducting materials have low critical temperatures. Therefore, in order to achieve a superconducting state, it is necessary to cool the material with liquid helium as a refrigerant.In this temperature range, the specific heat of the material is small, so a large amount of expensive helium is required, and furthermore, Requires a large-capacity refrigerator, etc. As a result, systems that apply superconductivity have become complex and have many practical problems that are a national policy, and so far they have only been developed for limited applications.

An object of the present invention is to solve the problems of the prior art described above, and to provide a superconductor that operates at a temperature equal to or higher than the boiling point of liquid hydrogen and has a high critical current density.

[Means for solving problems]

To achieve the above-mentioned object of the present invention, the inventors have conducted extensive research and have arrived at the following invention. That is, by firing a solid material containing lanthanum and copper and one or more alkaline earth elements selected from barium, strontium, and calcium at a temperature of 800 to 1200°C, the obtained oxide has an absolute temperature It was discovered that 37 showed superconductivity. More specifically, this oxide superconductor is produced from a hydroxide from an aqueous solution of water-soluble salts of the above composition components.

A coprecipitate consisting of hydrous oxide, oxalate, carbonate, or a mixture thereof is produced, and after solid-liquid separation of this precipitate, the solid is dried and/or subjected to a first stage at a temperature of 700 to 950°C. Perform firing.

Thereafter, it is possible to synthesize a substance that exhibits superconductivity at high temperatures by pulverizing the powder and molding it into a predetermined shape, or by performing a second firing at a temperature of 800 to 1200° C. as a powder. The starting materials may be compounds in any form as long as they are water-soluble salts of the above-mentioned composition components, for example,
Nitrates, sulfates.

Examples include halides and organic acid salts such as ammine complexes and acetates, but are not particularly limited to these. However, when trying to obtain an oxide superconductor in the purest possible stoichiometric form, it is preferable to use nitrates, ammine complexes, acetates, etc., and these raw materials can be precipitated as solids. In order to make carbonic acid,
It is preferable to use ammonium carbonate, oxalic acid, or an aqueous solution of ammonium oxalate. When precipitating here, lanthanum precipitates at a relatively high hydrogen ion concentration, but barium, strontium, calcium, etc. do not precipitate unless it is alkaline.In this case, an aqueous alkali metal hydroxide solution is used to make an alkaline solution. is not a preferred method because it contains alkali metals as impurities. Further, if the alkalinity is adjusted with ammonia, copper will not precipitate quantitatively, so it is better to use a tertiary amine to adjust the alkalinity. In particular, triethylamine has a low 4-decomposition temperature and is preferred for adjustment. To carry out the precipitation reaction, an aqueous precipitant solution may be added to the aqueous raw material salt solution, or vice versa, but from the viewpoint of homogeneity of the resulting solid, the alkalinity must be maintained at a specified level. Particularly preferred is a method in which the raw material salt aqueous solution is added to the precipitant aqueous solution adjusted to a certain value while stirring.

It is sufficient that the alkalinity of the precipitant solution is adjusted to pH 9 or higher at this time. The solid-liquid separation of the obtained solid content slurry may be carried out by methods such as filtration method or sedimentation separation method, but it is preferable to wash the obtained solid content with water as this will lead to the elution of alkaline earth elements. do not have. The resulting cake-like solid is dried and then fired to react, at a temperature of 800 to 1
It is carried out in a temperature range of 200°C. If the temperature is below 800°C, no substance exhibiting superconductivity will be produced, and if the temperature is above 1200°C, the substance exhibiting superconductivity will decompose or undergo a phase change, which is not preferable. Also, prior to this firing reaction, 700 to 95
Preheating the coprecipitate at 0°C is a preferred method to obtain a uniform superconductor;
It is preferable to divide the firing reaction at oO°C into several stages to carry out easy formation and pulverization of the fired product. During firing, a reaction that produces a superconductor progresses, but the alkaline earth metal compound becomes a molten salt prior to or concurrently with this reaction.

The firing reaction vessel or substrate is preferably placed on a material that does not react with these molten salts, such as a crucible or plate made of magnetic alumina, platinum, or gold, or a superconductor plate or powder according to the present invention.

The firing atmosphere is preferably an oxidizing atmosphere containing oxygen gas, and a high-pressure oxygen atmosphere is particularly preferred when firing a compact.

A superconductor can be molded into any predetermined shape using a commonly used molding method. For example, press molding, isostatic pressing, hot pressing methods,
Examples of slurry molding include mold molding or green sheet molding using a doctor blade method, a method of coating and molding powder into a paste, a method of screen printing, and a method of spray coating a slurry. In addition, when forming wire-shaped materials, methods such as filling a metal pipe with powder and plastically deforming the pipe to form a thin wire can be applied. Although not particularly limited, it is a preferable method to complete the firing reaction of the superconducting powder prior to these moldings.

[Effect]

Lanthanum, copper, and barium disclosed in the present invention.

The oxide containing one or more alkaline earth elements selected from strontium and calcium and calcined at 800 to 1200°C has a single-layer perovskite crystal structure,
This material exhibits complete diamagnetic properties at an angle of 50 degrees or less, and exhibits so-called superconductivity in which the electrical resistance becomes zero. In particular, when synthesizing this oxide, by adopting the above-mentioned wet preparation method such as coprecipitation method, the raw ingredients are uniformly mixed in the form of ultrafine particles, so the calcination reaction is relatively easy. It is possible to synthesize superconducting compounds by using the method, and it is possible to synthesize superconductors that exhibit a high critical temperature.
A superconductor with a high critical current density can be obtained by using press molding, hot press molding, or other molding methods effective for increasing density.

Although the true density of the superconductor of the present invention is unknown, the apparent density of the molded body is 5.0 g/aI? By doing so, the critical current density can be increased.

〔Example〕

EXAMPLES The present invention will be explained in more detail below with reference to Examples, but the present invention is not limited only to the following Examples.

<Example 1> A 2Q aqueous solution of lanthanum nitrate (manufactured by Kojundo Kagaku) sog and 4.2 g of strontium nitrate (manufactured by Kojundo Kagaku), and 150 g of zero-order ammonium carbonate (Wako Pure Chemical Industries, Ltd. 11j) using this as solution A. This is an aqueous solution of IQ, and this is called a B solution. Add liquid B to liquid A using a microtube pump if/h
While stirring the solution A, a coprecipitate of lanthanum and strontium is produced. The obtained slurry is
Filter and separate using a G glass filter to separate and collect cake-like solids. This solid substance was placed in a clumsy container, and 24.2 g of copper nitrate (manufactured by Wako Pure Chemical Industries, Ltd.) was made into an aqueous solution of 50 mfl.
This is added to the solid obtained above, heated and rubbed, concentrated, and then the solid is dried at 120° C. for 5 hours. The dried solid is finely ground and calcined at 800° C. for 3 hours, then cooled and ground. This powder was placed in a magnetic alumina crucible and fired at 900°C for 4 hours.
Crush this. After repeating this process twice, the pulverized product is calcined at 950° C. for 20 hours. The obtained fired product is crushed. 5 g of this powder is taken and pressed with a 40 m diameter mold to create a disk-shaped sample, which is then fired at 950° C. for 5 hours.

A columnar test piece of IXIX 15 nn was cut out from the obtained fired body. This sample is placed in liquid helium and the inductance is continuously measured to obtain a temperature-inductance curve. the result.

The inductance began to change rapidly at 40 and showed complete diamagnetism at 35. Furthermore, using this sample, the resistance was measured by the four-terminal method while lowering the temperature of the sample in the same manner as above. The measurement was carried out under the condition of 0.1 A/aJ. From the obtained temperature/resistance curve, the transition starting temperature is 40
．． It was confirmed that the resistance became zero at 5 and 38, and the superconducting state entered.

<Example 2> Make a 2Q aqueous solution of lanthanum nitrate (manufactured by Kojundo Kagaku) sog, 4.2 g of strontium nitrate (manufactured by Wako Saiyaku), and 24.2 g of copper nitrate (manufactured by Wako Saiyaku), and use this as solution A. . On the other hand, an aqueous solution of 126 g of oxalic acid (manufactured by Wako Saiyaku) and 149 g of triethylamine (manufactured by Wako Saiyaku) and IQ are added dropwise to the above-mentioned Solution A at a rate of 112/h using a microtube pump while stirring. 4G of the obtained slurry
A glass filter is used to perform solid-liquid separation and the solid content is recovered. After drying the obtained solid at 120°C,
Heat decomposition at 400°C for 3 hours. The obtained solid was finely ground, placed in a magnetic alumina crucible, and heated to 800
Bake at ℃ for 3 hours. The obtained baked product is finely ground and 9
The process of baking at 00°C for 3 hours was repeated 3 times. The powder obtained in this way is fired again at 950°C for 20 hours to obtain a powder, and 5 g of this powder is press-molded in a mold with a diameter of 40 nn to form a disk-shaped test piece, which is then fired at 970°C for 2 hours. . A columnar sample of 1X1X15na is cut out from the obtained sintered body using a diamond cutter, and a temperature-inductance curve and a temperature-resistance curve are determined using the method of Example 1. The temperature at which the superconducting state begins according to the inductance method was 40, and it became completely diamagnetic at 36. In the resistance method, the results were 40.5K and 38K, respectively.

<Example 3> Lanthanum oxide (Kojundo Kagaku) 29.3g 'e1m
Place in a paddle and add 4.2 g of strontium nitrate (Wako Hyakuyaku) and 24.2 g of copper nitrate (Wako Pure Chemical) to 50+
Make an aqueous solution of nQ, add this to the above lanthanum oxide, and carry out a lubrication process for 0.5 hours.
After drying at 20°C, it is calcined at 400°C for 3 hours to partially decompose the nitrates contained. The obtained solid material is finely pulverized and then heated in a magnetic alumina crucible at 800° C. for 4 hours.

The process of pulverizing the obtained solid material finely and firing it in a magnetic alumina crucible at 900° C. for 4 hours is repeated three times. Thereafter, the solid material is crushed and calcined at 950° C. for 20 hours, and after cooling, it is crushed. Take 5 g of the obtained powder and press-form it in a mold with a diameter of 40+ m, and make this disc-shaped sample into 9 pieces.
Bake at 70°C for 2 hours. From the obtained sintered body, lXl
A columnar sample of X15na was cut out, and a temperature-inductance curve and a temperature-resistance curve were obtained in the same manner as in the first method of Example. As a result, the starting point of superconductivity is 40K.

It entered the superconducting state at 40.5 and 36 and 38.5.

<Example 4> In the same manner as in Example 2, the composition was obtained by replacing the strontium raw materials with barium and calcium, respectively.
, eBao, t)zcuox*(Lao, eCao+t
) A sample indicated by zCuOx was prepared. Here, X is an unconfirmed number. The superconductivity of this sample was evaluated by the method of Example 2. The results are shown in Table 1 together with the results of Example 2.

Table 1 <Example 5> 29.3 g of lanthanum oxide (manufactured by Kojundo Kagaku), 3.0 g of strontium carbonate (manufactured by Wako Saiyaku), and 8.0 g of cupric oxide (manufactured by Wako Saiyaku) were placed in a sanding machine. , mix roughly for 1 hour. After firing the obtained mixed powder at 800°C for 4 hours, it was crushed and heated to 90°C in a magnetic aluminium crucible.
The process of baking at 0°C for 4 hours was repeated three times. The obtained baked product is further finely ground and baked at 950° C. for 20 hours. After cooling it, crush it, take 5g of powder, and add 40ffI! The sample was press-molded using a mold with a diameter of 1 to obtain a disk-shaped sample, which was then fired at 970'C for 2 hours. The obtained sintered body was measured using a diamond cutter as a columnar test piece of 1×1×15 mm in the same manner as in the second example.

As a result, in the inductance method, the inductance change start temperature reached 37 and became completely diamagnetic at 25. On the other hand, in the resistance method, the resistance suddenly started to decrease at 38, and the resistance reached zero at 30.

〔Effect of the invention〕

According to the invention, lanthanum, copper and Baliu A.

By firing a composition containing one or more alkaline earth elements selected from strontium and calcium, an oxide superconductor having a critical point at a high temperature can be obtained. In particular, when synthesizing oxide superconductors, hydroxides and hydrated oxides with low solubility are used from water-soluble salt solutions of the components having the above composition.

Claims (1)

[Claims] 1. Contains lanthanum and copper, barium, strontium,
In a method for preparing an oxide superconductor containing one or more alkaline earth elements selected from calcium, the composition is prepared from an aqueous solution of water-soluble salts of the component, including hydroxide, hydrated oxide, oxalate, carbonate, etc. A salt or a mixed form of these salts is precipitated as a coprecipitate of the above salts, and after solid-liquid separation, the solid is dried and/or after a first stage of calcination at 700 to 950°C, it is shaped, and further A method for preparing an oxide superconductor, characterized in that a second stage of firing is performed at a temperature of ~1200°C. 2. In claim 1, in the general formula of (La_xA_y)_2CuO_z,
A consists of one or more selected from barium, strontium, and calcium, x is 0.50 to 0.98, and y
is 0.5 to 0.02, and z has an atomic ratio of 4 or less. 3. Preparation of an oxide superconductor according to claim 1, characterized in that the first stage and/or second stage calcination is performed at an oxygen gas pressure of 0.2 to 30 atm. Method. 4. The method for preparing an oxide superconductor according to claim 1, characterized in that the shaped body after the second stage of firing has an apparent density of 5.0 g/cm^3 or more.