JPH0354103A - Production of oxide superconductor - Google Patents

Abstract

PURPOSE:To obtain the subject oxide superconductor of high purity excellent in superconductivity by putting a raw material capable of formation of the oxide superconductor into a specified crucible, fusing the raw material under heating and then solidifying the fused material by cooling. CONSTITUTION:In the production method where a raw material capable of formation of the subject oxide superconductor is put into a crucible, fused by heating and then solidified by cooling the fused material to produce the subject oxide superconductor, the procedures are carried out as mentioned below. That is to say, the crucible used for fusing the raw material by heating is formed so that, at least, the inside wall in contact with the raw material may be composed of MgO. Thereby the raw material capable of formation of the oxide superconductor is prevented from contamination by a harmful crucible substance during fusion. As the raw material of the oxide superconductor is heated and fused using the crucible made of MgO as a non-reactive substance in this production method, the fused raw material is free from contamination by harmful elements of the crucible during fusion. Accordingly, the obtained oxide superconductor is of high purity.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides an oxide with high purity and excellent superconducting properties that can be widely applied to power transmission and distribution lines, power cables, equipment lead wires, magnet wires, electromagnetic shields, etc. Concerning the manufacturing method of superconductors. [Conventional technology and its problems] In recent years, Y-Ba-Cu-0 series, Bi-Sr-Ca-Cu10 series, T1-Ba-Ca have not shown superconductivity at liquid nitrogen temperature.
Oxide superconductors such as the -Cu-0 system have been discovered, and research into practical use is actively progressing in various fields. The method for producing these oxide superconductors is to mix a predetermined amount of compound powder containing each of the constituent elements of the oxide superconductor, and then subject this mixed powder to a predetermined heat treatment to form an oxide superconductor. However, because it is difficult to mix each compound homogeneously, the resulting oxide superconductor has low superconducting properties. Further, it takes a long time to mix homogeneously, resulting in poor productivity.

For this reason, a melt-solidification method was proposed in which a raw material that can be made into an oxide superconductor is placed in a crucible, heated and melted, and the melt is cooled and solidified. This melt-solidification method is a method of forming oxide superconducting bodies by casting a melt into a desired shape and subjecting it to heat treatment as necessary.It has the advantage of being able to easily obtain any shape, and has attracted attention in recent years. Bathing.

In this melt-solidification method, a crucible made of platinum (PT) or aluminum was used to melt the raw materials, but during the heating melting process, P was transferred from the crucible into the melt.
There is a problem in that the oxide superconductor obtained is contaminated by crucible materials such as t and aluminum (/l) and its purity is reduced, making it impossible to obtain high values for properties such as critical current density (JC). Ta.

[Means for Solving the Problems] In view of the above circumstances, the present invention has been developed based on research on the reactivity of various crucible materials with oxide superconductors, and as a result, it has been found that MgO is extremely non-reactive. The method has now been completed.

That is, the present invention provides a method for producing an oxide superconductor by placing a raw material that can be made into an oxide superconductor in a crucible, heating and melting the material, and cooling and solidifying the melt, in which at least the raw material in the crucible is used as a crucible. A method for producing an oxide superconductor, characterized in that a raw material that can be made into an oxide superconductor is heated and melted using a crucible whose inner surface in contact with the melt is made of a material made of magnesium oxide (MgO). be.

In the method of the present invention, as a crucible for heating and melting a raw material, at least the inner surface of the crucible in contact with the melt of the raw material is made of MgO, and the raw material that can be made into an oxide superconductor (hereinafter abbreviated as raw material) is melted. This is to prevent contamination from harmful crucible materials. The raw material that can be used as an oxide superconductor in the method of the present invention is a mixed powder obtained by mixing predetermined amounts of compounds containing each of the constituent elements of the oxide superconductor, or the above mixed powder is placed in an oxygen-containing atmosphere in advance. It is a general term for calcined powder heated at a predetermined temperature, oxide superconducting powder, etc.

In the method of the present invention, the raw material melted in the crucible is preferably rapidly solidified so that the constituent elements of the oxide superconductor are uniformly and finely distributed.

The rapidly solidified material thus obtained is, for example, pulverized into an object, shaped into a desired shape, and then subjected to a prescribed heat treatment to form an oxide superconducting object. [Operation] In the present invention, since the oxide superconductor is heated and melted in a non-reactive MgO crucible, harmful elements of the crucible material do not mix into the melt of the raw material during melting. Therefore, the obtained oxide superconductor has high purity.

[Examples] The present invention will be explained in detail below using examples. Example 1 B i was placed in an MgO crucible with an inner diameter of 30 mm and a height of 100 mm.
Add 200g of calcined powder of
The molten material was heated for a period of time to melt it, and then this molten material was dropped onto a copper plate, and at the same time as the dropping, it was sandwiched between another copper plate and rapidly solidified. Afterwards, this rapidly solidified material is crushed into powder,
This powder was compression molded into a rectangular shape of 2 x 3 x 30 ffII1, and the shape was heated to 900''C in an oxygen atmosphere at a heating rate of L O'C /win, and then from 900°C to 10°C/IIli
The temperature is lowered to 850"C at a cooling rate of n, and the temperature is lowered to 850'C.
After being held for 6 hours, it was cooled in a furnace to form an oxide superconducting rod.

Example 2 11 at the bottom of an MgO crucible with an inner diameter of 30 m and a height of 100 ribs.
A hole of IIIllφ was made, the hole was plugged with an MgO rod, and then B+. Sr. Ca+Cu.
○. Add 200g of calcined powder and heat it in the furnace for 12 hours.
The mixture was melted by heating at 00°C for 6 hours. Thereafter, the molten material was allowed to flow out through a 1 mm diameter hole drilled at the bottom of the crucible, and nitrogen gas heated to 950'C was sprayed onto the flowing out molten material at a flow rate of 701/min to atomize it. This atomized material was sprayed onto a copper plate, and then cooled and solidified to form a powder with a particle size of 100 nm. Next, the powder thus obtained was compression molded into a 2×3×30 am rectangular shape, and the shaped body was subjected to the same heat treatment as in Example 1 to form an oxide superconducting shape. Comparative Example 1 An oxide superconducting molded body was produced in the same manner as in Example 1 except that an alumina crucible and a CaO crucible were used as the crucibles. Comparative Examples 2 to 3 In Examples 1 and 2, oxide superconductive bodies were produced in the same manner as in Examples 1 and 2, except that a Pt crucible was used as the crucible.

J was measured for each of the oxide superconducting bodies thus obtained. In addition, impurities in the rapidly solidified solid were analyzed by atomic absorption spectrometry. The results are shown in Table 1.

? As is clear from Table 1, the product produced using the method of the present invention (12) had a higher value of J than the products produced using the comparative method (3 to 6). Among them, in Example 2, the molten material was atomized and rapidly cooled, so that the composition became homogeneous and the Jc value was particularly high.

As a result of impurity analysis, no Mg was detected. On the other hand, in comparison method product 4, the composition ratio of the elements was disturbed due to the mixing of Ca, which is a component of the oxide superconductor, from the crucible, and in comparison method products 3 and 5.6, Ca, which is a component of the crucible, was mixed in. Due to the contamination of Al or PT, the Je values in both cases were extremely low. In the above, the B i-Sr-Ca-Cu 10 series oxide superconductor was explained, but the Y-Ba-Cu-0 series and Te-Ba
Similar effects were obtained with other oxide superconductors such as -Ca-Cu-○ series.

In the above embodiment, a crucible made entirely of MgO was used, but in the method of the present invention, the crucible is made of, for example, A1
The same effect as in the above example was obtained by using a crucible made of 2 z O 3 and coating the inner surface of the crucible made of A 2 z O 3 in contact with the melt with M g O.

〔effect〕

As described above, according to the method of the present invention, an oxide superconductor with high purity and excellent superconducting properties can be efficiently produced.
It has remarkable industrial effects.

Claims (1)

[Claims] In a method of manufacturing an oxide superconductor by placing a raw material that can be made into an oxide superconductor into a crucible and heating and melting the melt, and cooling and solidifying the melt, at least the inner surface of the crucible that is in contact with the melt of the raw material. 1. A method for producing an oxide superconductor, which comprises heating and melting a raw material that can be made into an oxide superconductor using a crucible made of a material made of magnesium oxide.