JPH0446050A - Production of bismuth-containing superconducting ceramics - Google Patents

Abstract

PURPOSE:To attain homogenization by adding a bismuth alkoxide to a mixture contg. the acetates of Sr, Ca and Cu, converting the resulting sol into gel and firing this gel. CONSTITUTION:The acetates of Sr, Ca and Cu are mixed in a desired atomic ratio, water is added and they are concentrated by heating to 50-90 deg.C while adjusting the pH to 3-5 to obtain a mixture. A bismuth alkoxide is then added and allowed to react with the mixture at 50-90 deg.C until the amt. is reduced to 1/2-3/5. The resulting sol is converted into gel by cooling to room temp. and this gel is fired at 830-850 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application y) The present invention relates to a method for producing 13i-based superconducting ceramics, particularly B i zs r z cazc uffox, which is a high temperature phase.

(Prior art and its problems) Conventionally, Bi-based superconducting ceramics have been produced using a solid phase reaction method. However, in general, the low temperature phase B i z S
r Z Ca Cu t Ox and high temperature phase l3tzS
Since rzCazCu and Ox coexist, it is difficult to synthesize only a single high-temperature phase, and it is said that it is possible to create a single phase by adding pb.

In addition, the blue gel method, which is applied to the production of general ceramics, uniformly mixes the raw materials in the solution state, and the product is excellent in homogeneity. For example, metal alkosites have been studied, but the current situation is that decomposition, crystallization, etc. occur, and it is difficult to obtain a material that can be uniformly converted into a sol.

As a result of repeated studies in view of these points, the inventors have found that Sr.
A mixed sol made by adding Bi alkoxide to a mixture of acetate salts of Ca, Cu, and Cu is stable and easy to form into fibers, and is easily gelled by cooling to room temperature, and by baking this gel, Bi alkoxide is added. The present invention was achieved by successfully producing superconducting ceramics. That is, the present invention obtains a Bi-based superconducting ceramic in the form of a homogeneous bulk, fiber, etc. by gelling and firing a mixed sol made by adding Bi alkoxide to a mixture of Sr, Ca, and Cu acetates. In particular.

Next, the present invention will be explained in detail.

In the present invention, the basic elements constituting superconducting ceramics, B 11 S r + Ca + Cu +
It is important to first form a mixture of Sr, Ca, and Cu. Basically, acetate salts of these three types of elements may be uniformly mixed, but more preferably, Sr, Ca,
Mix Cu acetate in the desired atomic ratio, especially in the case of high-temperature phase, at a ratio of approximately 2:2:3, add water, and adjust the pH to 3.
50-90°C, preferably 70-8
Mix while stirring at 0°C, and heat and concentrate.

This mixture may undergo some reaction, and then Bi alkoxide is added to this mixture. The alkoxides that can be used are selected from a wide range, but from the viewpoint of ease of availability and handling, C5~ alkoxides, particularly methoxide, ethoxide, propoxide, etc., are preferably used.

The addition and mixing of Bi-alkoxide is not particularly limited as long as a sol body containing the four components uniformly is formed as a result, but it is more preferable to add Bi-alkoxide after this to obtain a position of 1/2 to 315. Stirring and reaction are continued at 50 to 90°C, preferably 80 to 90°C, to produce a highly viscous sol.

The sol thus obtained is stable, non-hygroscopic, and can be easily made into fibers.

This sol gels when cooled to room temperature.

The gel thus obtained is fired to produce superconducting ceramics.

A suitable firing temperature is 830 to 850°C.

Furthermore, the firing time varies depending on the firing method. That is, initially a low temperature phase is generated, but as the firing continues, the proportion of the high temperature phase gradually increases. In addition, the fired product is further crushed,
By repeating the molding and firing steps, the growth rate of the high-temperature phase increases.

Moreover, what is important in the present invention is that since the raw material sol of the present invention has high viscosity and high stability, it can be easily made into a fiber form by a drawing method or the like. This fiber can also be made into a coil by winding it into a spiral shape.
The sol can also be coated onto a substrate or molded into bulk form.

Furthermore, it can be fired in various shapes as described above.

Fiber drawing is preferably carried out at 50-60°C.

Next, the present invention will be explained in more detail with reference to Examples.

Example I Sr (CH,Coo)! 1/2 HzOO,
005mo 1. Ca (CHsCOO)zHzo
O,005mo 1. Cu (CH3COO
) zHzo 0.0 075mof, HzO30
Add ml and heat to 60-70℃ on a hot plate at 730℃.
2.1 ml of N H40H aqueous solution, 4 ml of glacial acetic acid
．． 70-80 while adjusting I)H to about 4 at 0 ml.
Stir and react at ℃, and concentrate and mix so that the total volume becomes about 1/2. Furthermore, B i (OCzHs)s 0.0
Add 0.5 mol of glacial acetic acid and 5 ml of glacial acetic acid, adjust the pH to 4.5, and react by stirring at 80 to 90°C to obtain a highly viscous sol.

The sol thus obtained was stable, non-hygroscopic and easy to form into fibers, and a fiber precursor with a length of 1 m or more was prepared using a drawing method in a state of about 50 to 60 ml. This fiber precursor gels in seconds and has a diameter of 1
Gel fibers of 00 μm to 300 μm were obtained. The gel fibers obtained were very stable and did not break or crystallize even after being left in the air for several days.

Next, the gel fiber was heated at 10'C/hr to 845°C.
Figure 1 shows a SEM image of a fiber fired for 5 hours. Although cracks are seen on the surface, there are almost no cavities and it is clear that the fiber is solid throughout the entire cross section. The electrical resistance of the fibers fired at 845° C. for 5 hours was measured by a four-terminal method. The results are shown in Figure 2.

Example 2 A highly viscous sol was obtained in exactly the same manner as in Example 1, and then cooled at room temperature to obtain a gel. While crushing this each time, 845
℃, 24hr, 848℃, 50hr, sso℃, 50h
FIG. 3 shows the XRD patterns of each process after repeated firing for a total of 148 hours three times. 845℃, 2
At 4 hours, only the low temperature phase is present, but by repeating the crushing, molding, and sintering steps, the high temperature phase grows.
hr, the diffraction peak intensity of the high temperature phase has already exceeded the diffraction peak intensity of the low temperature phase, and after performing the same process 4 times and firing for a total of 148 hr, the diffraction peak becomes almost only the high temperature sum. The indexed XRD pattern of the high temperature single phase sample is shown in FIG.

<001) diffraction peaks appear strongly.

FIG. 5 shows an SEM image of the high-temperature single-phase sample. 2~5μm
It can be seen that the tabular grains grow uniformly throughout. The electrical resistance of this sample was measured using the 4@son method and the results are shown in FIG. Even at room temperature, the resistance value was low, starting to show superconducting transition at 110, and showing zero resistance at 90. This is thought to be due to the presence of a very small amount of low temperature phase or other compounds between the high temperature phases that cannot be confirmed by X-ray diffraction. Figure 7 shows a photograph of this sample cooled to liquid nitrogen temperature and magnetically levitated. The sample is floating stably, and the
It can be seen that the i 2S r zc a @CuffOx single phase has a small amount of impurities.

Effects of the Invention According to the present invention, it is possible to obtain a homogeneous and stable precursor sol of i-based superconducting ceramics, which can be formed into fibers,
It is easy to mold into various shapes such as coil shape, coating on a substrate, and bulk.

In addition, it can be fired in this shape and has a wide range of applications.

[Brief explanation of the drawing]

Figure 1 is an SEM image of the fiber created in Example 1;
Figure 2 shows the electrical resistance of the fiber prepared in Example 1;
Figure 3 shows XRD at each step of the sintered sample of Example 2.
The pattern, Figure 4, is the indexed X of a high-temperature single-phase sample.
RD pattern, Figure 5 is a SEM image of a high temperature single phase sample,
FIG. 6 shows the electrical resistance of the high-temperature single-phase sample, and FIG. 7 shows a magnetic levitation photograph of the high-temperature single-phase sample. guan 2θ (('ukq>/de9ree /θ 3θ 4θ 2θ Person who corrects the manufacturing method of conductive ceramics

Claims (2)

[Claims] (1) A method for producing bismuth-based superconducting ceramics, which comprises gelling a mixed sol made by adding bismuth alkoxide to a mixture of strontium, calcium, and copper acetates, and then firing the mixture. (2) A fibrous bismuth-based superconducting ceramic characterized by forming a mixed sol made by adding bismuth alkoxide to a mixture of strontium, calcium, and copper acetates into a fibrous form, gelling it, and then firing it. Manufacturing method.