JP2541653B2 - Method for manufacturing oxide superconductor - Google Patents

Description

TECHNICAL FIELD The present invention relates to an oxide superconductor and a method for producing the same.

[Conventional technology]

In recent years, oxide superconductors have attracted attention due to their high critical temperature, and are expected to be used in various fields such as electric power fields, nuclear magnetic resonance devices, and magnetic shields. In order to form a medium- or large-sized product or a complex-shaped product of these oxide superconductors to obtain a sintered body, a binder, a plasticizer, a dispersant, etc. are molded into the raw material powder in the same manner as in ordinary ceramics manufacturing methods. Auxiliary agents are added and molding and firing are performed. Further, when the raw material powder is slurried or wet-milled, an organic solvent is used because the oxide superconducting powder deteriorates due to the reaction with water. Conventionally, when firing a ceramic molded body, it is usually held in an oxidizing atmosphere at 500 ° C. or less, mainly at a temperature of 150 to 300 ° C. for a certain period of time, through a firing schedule of decomposing and removing a forming aid and residual carbon components, and thereafter. The main firing is done. With conventional ceramics such as alumina and zirconia, the heat treatment up to 700 ° C. removes the residues of ordinary forming aids and organic solvents almost completely, and the residual carbon content in the sintered body becomes about 0.1 wt% or less. The effect on the sintered body was small.

[Problems to be Solved by the Invention] The present inventors have applied the above-mentioned conventional ceramics firing method to an oxide superconducting molded article that has a molding aid added thereto and / or is treated in an organic solvent. In the case of 500 ° C or less, most of the residual carbon content due to the molding aid is decomposed and removed, but the residual carbon amount in the sintered body after firing is
It has been found that the content of superconductivity cannot be reduced to 0.5% by weight or less, and the superconducting properties are significantly deteriorated as compared with the superconductor prepared by the dry method without using a molding aid.

Therefore, the present invention was completed for the purpose of obtaining an oxide superconducting sintered body having superconducting properties equivalent to those in the case of not using a molding aid or the like, even in an oxide superconducting molded product using a molding aid or the like. .

[Means for solving the problem]

According to the present invention, a powder of an oxide superconductor is formed into a molded body by using a molding aid and / or an organic solvent, and the molded body is heat-treated in an oxidizing atmosphere at 800 to 930 ° C. for 4 hours or more and then fired. Thus, there is provided a method for producing an oxide superconductor characterized by obtaining an oxide superconducting sintered body having a residual carbon amount of 0.3% by weight or less.

 Hereinafter, the present invention will be described in detail.

Examples of the oxide superconductor in the present invention include M-Ba-Cu-O-based compounds (where M is Sc, Tl, Y and La, Eu, Gd, Er, Yb, Lu
Represents one or more selected from lanthanides and the like. ) And Bi
Examples thereof include those having a multi-layer perovskite structure such as a —Sr—Ca—Cu—O-based compound.

In the present invention, the oxide superconductor and the like correspond to M, for example, metal oxide powder such as yttrium oxide powder, scandium oxide powder, lanthanum oxide powder, barium carbonate powder, and copper. A mixed powder such as oxide powder, bismuth oxide powder and calcium carbonate powder is calcined to obtain an oxide superconductor composition. Then, to the composition, usually, a molding aid such as a binder or a plasticizer is added, and a slurry or the like is formed using an organic solvent, and if necessary, after granulation, it is molded into a molded body by a mold or the like. Finally, it is fired to obtain a sintered body.

In the present invention, as a preliminary treatment for firing, heat treatment is performed in an oxygen atmosphere at 800 to 930 ° C., preferably 860 to 900 ° C. for 4 hours or more, and then firing and sintering. Heat treatment temperature less than 800 ℃ and 9
If the temperature exceeds 30 ° C, the residual carbon content will be 0.5% by weight or more, and the superconducting properties will deteriorate.

The time for the heat treatment varies depending on the density of the molded body, the wall thickness of the molded body, and the like, and the higher the density and the thicker the wall, the longer the time required. Generally, it is preferable to perform heat treatment for 5 to 40 hours, for example, a density of 60% (ratio of relative density to theoretical density of oxide forming oxide superconductor) and thickness of 5 to 10 mm
In order to obtain the oxide superconducting molded body of (1), it is necessary to perform heat treatment for 10 to 20 hours.

Whereas the heat treatment as a pretreatment for firing in the wet molding of a normal ceramics molded body is performed at around 500 ° C, the oxide superconductor of the present invention has a strong bonding force with carbon and is at 800 ° C or higher and at a predetermined temperature. The carbon content is not removed unless the heat treatment is performed for the time. Further, when the temperature exceeds 930 ° C, the oxide superconducting compact is significantly sintered, so that the reaction between the residual carbon content and atmospheric oxygen does not proceed and densification occurs with the carbon content contained, and the residual carbon content is not sufficiently removed. It is thought to disappear. In the present invention, a superconducting compact having excellent superconducting properties can be obtained by heat treatment in the oxygen atmosphere at the temperature of 800 to 930 ° C. The oxidizing atmosphere in the present invention is preferably oxygen gas, but can be carried out using air.

In the oxide superconductor produced by the method of the present invention, the residual carbon content in the oxide superconducting sintered body is 0.3% by weight or less, and the superconducting properties are extremely high. Residual carbon in the oxide superconducting sintered body is considered to exist mainly at grain boundaries or on the particle surface, so the residual carbon content is 0.3% by weight.
It is presumed that the superconducting property will be hindered if the value exceeds. When the residual carbon content of the oxide superconducting sintered body is 0.15% by weight or less, the superconducting properties of the oxide superconductor become further excellent.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to Examples. The present invention is not limited to this embodiment.

Examples 1 to 9 and Comparative Examples 1 to 4 Y ₂ O ₃ powder having a purity of 99.9% (average particle size 0.4 μm), BaCO ₃ powder (average particle size 0.8 μm) and CuO powder (average particle size 2.5 μm)
m) was adjusted to a molar ratio of 1: 4: 6, then 9
It was calcined at 40 ° C. for 10 hours to synthesize YBaCu ₃ O ₇ powder.

Next, 2 g of this YBaCu ₃ O ₇ powder was mixed with 50 g of polyvinyl butyral (PVB) as a binder and 5 g of a nonionic dispersant, and the mixture was placed in toluene 2 in a polypot container together with 1 kg of zirconia boulders and pulverized with a rotary mill for 16 hours. A slurry was prepared by mixing. This slurry was granulated with a spray dryer to an average particle size of 50 μm. This powder is molded into a molded body of 30 × 40 × 5 to 10 mm using an iron mold, and 2.5
Rubber pressing was performed at a hydrostatic pressure of ton / cm ² .

The obtained molded body was heat-treated and fired at the temperature and time shown in Table 1 according to the firing schedule shown in FIG.

The bulk density of the obtained sintered body was measured by the Archimedes method using kerosene in the solution. The residual carbon amount was measured by chemical analysis. The critical current density is 20 x 4 x 2 mm for the sintered body.
And processed in liquid nitrogen (77K) by the 4-terminal method.

 The above results are shown in Table 1.

As is clear from the above Examples and Comparative Examples,
What was heat-treated at 800 to 930 ° C had a residual carbon content of 0.30% by weight or less and a critical electric field density of 50 A / cm ² or more and had sufficient characteristics as a superconductor, whereas the heat treatment of Comparative Example Those not treated, those treated at 940 ° C and 780 ° C have a residual carbon content of 0.6% by weight or more, and those retained at 880 ° C for only 2 hours have a residual carbon content of 0.5% by weight or more and a critical electric field density of It becomes less than 10 A / cm ² and the superconducting property is inferior.

〔The invention's effect〕

The present invention has been achieved based on the finding that excellent sintering characteristics cannot be obtained with a conventional ceramics compact firing schedule in order to obtain a sintered body of an oxide superconductor. Heat treatment temperature of 800 ~ 9
It is kept at a high temperature of 30 ° C for a predetermined time.

According to the present invention, it is possible to obtain various shapes of oxide superconductors having a sufficient residual carbon content of 0.3% by weight or less and having sufficient superconducting properties.

[Brief description of drawings]

FIG. 1 shows the firing schedule of one embodiment of the present invention. The vertical axis represents temperature and the horizontal axis represents time.

Claims (1)

(57) [Claims] 1. A molding aid or / and a powder of an oxide superconductor.
And a molded body using an organic solvent, and the molded body is heat-treated in an oxidizing atmosphere at 800 to 930 ° C. for 4 hours or more and then fired to give an oxide superconducting sintered body having a residual carbon amount of 0.3% by weight or less. And a method for producing an oxide superconductor.