JPH01208357A - Production of oxide superconducting form - Google Patents

Abstract

PURPOSE:To obtain the title form improved in formed shape and superconducting characteristics without contamination by the binder, by pressure forming of a mixture of raw powder and a specified amount of a binder followed by binder-elimination treatment and then by heating and sintering under an O2-contg. atmosphere. CONSTITUTION:Firstly, a mixed powder is prepared by blending compounds each containing a constituent element of the objective oxide superconductor. Secondly, this mixed powder is incorporated with 0.1-10wt.% of, as the binder, a polyalkylenecarbonate(PAC), and the resultant mixture is subjected to pressure forming to produce a form. Thirdly, this form is heated to >=250 deg.C in a nonoxidative atmosphere to carry out binder-elimination treatment to volatilize the PAC in the form of a nontoxic gas. Finally, the resultant form is sintered at ca.940 deg.C for ca.6hrs. in an O2-contg. atmosphere, thus obtaining the objective oxide superconducting form.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing an oxide superconducting molded body used as a plate or wire for electric cables, magnets, power storage links, magnetic shields, etc.

(Prior art and its problems) In recent years, (Ln+-*Sr,)CuOa, (Ln+-+t
Ba 11) *Cu O4, LnBaxCuzOt
, LnBaz-++5rxCu30 (wherein Ln is Y, Sc, or a rare element), oxide superconductors with a layered perovskite structure have been found.

These oxide superconductors are much more economical than conventional metal superconductors which exhibit superconductivity at liquid He temperatures because they become superconducting above the liquid N2 temperature, and their use in various fields is being considered.

By the way, the above-mentioned oxide superconductors are brittle and cannot be plastically worked like metal materials, and powder metallurgy is mainly used to process them into plates, wires, etc.

A concrete example of the method for producing an oxide superconductor using this powder metallurgy method is, for example, Y r B az Cu 30
Using calcined powder of composition M as a raw material, it is compacted into a desired shape, and then this compacted compact is heated and sintered at a temperature of 850 to 1,000°C in an oxygen-containing atmosphere to obtain Y1.
B az Cu 30 t-δ(δζ0.1~0.3
) is an oxide superconducting molded body having the composition.

By the way, in the above method, if the target powder compact is large or has a complicated shape, it is difficult to maintain the shape, so PVA (polyvinyl alcohol), PVA is added to the calcined powder in advance.
Measures have been taken to improve moldability by mixing binders such as VB (polyvinyl butyral) or paraffin to strengthen the bonding force between powders, but if a powder compact mixed with this binder is suddenly heated and sintered, the binder will be removed. Since carbon, which is a constituent element of the superconductor, diffuses into the superconductor and precipitates at the grain boundaries, deteriorating the superconducting properties, it is necessary to heat the compact to about 500°C before sintering to volatilize the binder. Binder treatment is applied.

However, if the heating atmosphere for this binder removal process is a non-oxidizing atmosphere, the binder will not be completely decomposed and some elements will remain to form compounds, which will react with the superconductor in the subsequent sintering process. In addition, when the binder removal treatment is performed in an oxygen-containing atmosphere, the constituent elements of the binder, such as C and H, become COo, H, and O gases and react with the raw material calcined powder, causing the surface of the calcined powder to deteriorate. The layer contains BaCO5 and Ba(O
There is a problem in that compounds such as H) are produced, which not only deteriorates the properties but also causes cracks in the molded product.

[Means for Solving the Problems] The present invention was developed in view of the above circumstances, and its purpose is to provide a method for producing an oxide superconducting molded body having excellent molded shape and superconducting properties.

That is, in the present invention, 0.1 to 1% of polyalkylene carbonate is added as a binder to a powder of an oxide superconductor precursor.
After blending 0% by weight and uniformly mixing both, this mixture is pressure-molded into a desired shape, and then this press-molded body is heated to a temperature of 250°C or higher in a non-oxidizing atmosphere to remove the binder. The method is characterized in that it is heated and sintered in an oxygen-containing atmosphere.

The precursor of the oxide superconductor used as a raw material in the present invention is a mixture of predetermined amounts of compounds containing each of the constituent elements of the desired oxide superconductor;
Or the above mixture in an oxygen-containing atmosphere at 850-1,0
This is calcined powder etc. obtained by heating to 00°C and calcining, and then crushing and classifying the calcined powder.

The polyalkylene carbonate used as the binder in the present invention has the chemical structural formula shown in FIG. 1, and the compounds belonging to the polyalkylene carbonate include polyethylene carbonate, polypropylene carbonate,
There are butylene carbonate and the like, all of which can be applied to the method of the present invention.

The reaction formula when the above polyalkylene carbonate is heated in a non-oxidizing atmosphere is illustrated for polypropylene carbonate (hereinafter abbreviated as PPC). As shown in Figure 2, PPC is propylene carbonate that is harmless to the superconductor raw material powder. thermally decomposes into When this reaction equation is shown in a thermal analysis curve, it can be seen that thermal decomposition begins at about 240°C and complete gasification and volatilization occur at 360°C or higher, as shown in Figure 2. In contrast, conventional binders such as PV
It can be seen that B begins to thermally decompose at around 380°C and even when heated to a high temperature of 500°C or higher, it is not completely volatilized and a portion remains as a solid phase.

In the present invention, the amount of polyalkylene carbonate blended as a binder is less than 0.1 wt% because sufficient bonding strength between powders cannot be obtained, and when it exceeds 10 wt%, it takes a long time to remove the binder. ~10-t
A range of % is preferred.

[Effect]

In the present invention, polyalkylene carbonate is used as a binder for obtaining a powder compact, and the binder removal treatment of the powder compact is performed by heating it to a temperature of 250°C or higher in a non-oxidizing atmosphere. The polyalkylene carbonate completely volatilizes as a harmless gas, and the raw material or superconductor is not contaminated by the binder during binder removal treatment or heat sintering.

〔Example〕

The present invention will be explained in detail below using examples.

Example 1 After blending Y2O3, BaC0, and CuO so that the molar ratio of Y:Ba:Cu is ill, this was calcined at 850°C for 24 hours in an oxygen stream, and then this calcined body was pulverized in a ball mill. This was classified into Y, Ba2Cu, O,
A calcined powder having a composition of 2 mm or less in diameter was produced.

After that, an ethyl acetate solution 5 containing 100g of the above calcined powder and 2.9g of PPC as a binder was prepared.
After the mixture is sprayed and dried using a spray dryer, it is crushed into granules with a diameter of 30 to 50 μm that are easy to press-form. A pressurizing force of 000 kg/cd was applied to form a pellet of 50ffIIlφX7mm'.

The pellet thus obtained was heated to 40"C in a nitrogen stream.
The binder was removed by heating for 2 hours, followed by 940'C6H heating and sintering in an oxygen stream, followed by 3 hours of heating from 940°C.
The mixture was slowly cooled to 00°C at a rate of 1°C/win to produce an oxide superconducting molded body.

Example 2 An oxide superconducting molded body was produced in the same manner as in Example 1, except that an ethyl acetate solution containing 7.4 gr of PPC was used.

Example 3 An oxide superconducting molded body was produced in the same manner as in Example 1, except that an ethyl acetate solution containing 0.5 gr of PPC was used.

Comparative Example 1 An oxide superconducting molded body was produced in the same manner as in Example 1, except that the binder removal treatment of the powder compact was performed in the atmosphere.

Comparative Example 2 An oxide superconducting molded body was produced in the same manner as in Example 1, except that PVB was used as the binder and the binder removal treatment of the powder molded body was performed by heating at 500" C2H in the air.

Comparative Example 3 An oxide superconducting molded body was produced in the same manner as in Comparative Example 2, except that the binder removal treatment of the powder compact was carried out in a nitrogen stream.

The relative density (S, 1), critical temperature (Tc), and critical current density (J) of each of the oxide superconducting molded bodies thus obtained were measured. The obtained results are shown in Table 1 together with the manufacturing conditions.

As is clear from Table 1, the method of the present invention (Examples 1 to 3)
) compared to the comparative method products (Comparative Examples 1 to 3). ,
It shows excellent characteristics at both T6 and Jc.

Among the comparative method products, Comparative Example 1 used PPC as a binder, but the binder removal treatment was performed in the atmosphere, so CO
t, H, and O were generated, which reacted with the calcined powder to locally generate Ba(○H)2 and BaC0, and the properties deteriorated.

Also, in Comparative Example 2.3, PVB was used as the binder, so when the binder removal treatment was performed in the air (Comparative Example 2),
CO2 and H2O are generated during binder removal, and when it is performed in a nitrogen stream (Comparative Example 3), the constituent elements of the binder remain, and the raw material or superconductor is contaminated during binder removal or sintering, resulting in superconductivity. The characteristics have deteriorated.

It goes without saying that the method of the present invention can also be applied to a method for manufacturing a superconducting molded body in which an oxide superconductor is formed in the form of a film on a substrate such as SUS.

In the above example, the Y-Ba-Cu-0 system superconductor was explained, but the method of the present invention can be applied to other alkaline earths such as Y-3r-Cu-0 system and Y-3r-Ba-Cu-0 system. It can also be applied to the production of oxide superconducting molded bodies whose main components are metals, rare earth elements, copper, and oxygen.

〔effect〕

As described above, according to the method of the present invention, the binder can be completely volatilized as a harmless gas, so that the raw material or superconductor is not contaminated by the binder during binder removal treatment or heat sintering, and J6 It is possible to produce oxide superconductors with excellent properties such as the following, and it has a remarkable effect industrially.

[Brief explanation of the drawing]

FIG. 1 is a chemical structural formula of polyalkylene carbonate, FIG. 2 is a thermal decomposition reaction formula of polypropylene carbonate, and FIG. 3 is a thermal decomposition curve diagram of PPC and PVB. Patent applicant Furukawa Electric Co., Ltd. Figure 2 Figure 3

Claims (1)

[Claims] After blending 0.1 to 10% by weight of polyalkylene carbonate as a binder to the powder of the precursor of the oxide superconductor and mixing the two uniformly, this mixture is pressure-molded into a desired shape, and then this pressure-molding is performed. 1. A method for manufacturing an oxide superconducting molded body, which comprises heating the body to a temperature of 250° C. or higher in a non-oxidizing atmosphere to remove the binder, and then heating and sintering the body in an oxygen-containing atmosphere.