JPH01131075A - Production of superconducting substance - Google Patents

Abstract

PURPOSE:To obtain a superconducting substance having extremely excellent superconducting characteristics, by pulverizing calcined powdery mixture of raw materials for a superconducting substance, forming and sintering the powder and cooling the sintered product at a specific cooling rate. CONSTITUTION:Prescribed powdery raw materials for a superconducting substance are mixed, calcined, pulverized and formed. The formed product is sintered and cooled to obtain a superconducting substance. In the above process, the cooling of the sintered product is carried out at a cooling rate of 10-200 deg.C/hr from the sintering temperature to 400 deg.C. When the cooling rate is <10 deg.C/hr, the crystal structure is liable to change and an excellent superconducting characteristics becomes hardly attainable. When the rate exceeds 200 deg.C/hr, the obtained superconductor has large cracks and the superconducting characteristic is lowered.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing superconducting materials, and more particularly to improvements in conventional methods for producing superconducting materials.

[Conventional technology and its problems]

As is well known, new research on superconducting materials is currently being actively conducted, and superconducting materials such as Y-Ba-Cu-O,
Substances such as La5r-CuO and La-Ba-Cu-0 are already known. In particular, research on Y--Ba--Cu--O based superconducting materials is progressing, and research toward practical use is currently being actively conducted.

The conventional manufacturing method for these superconducting materials is Y-Ba-Cu.
A representative example of the -O system is shown in FIG. That is, first, raw material powders, usually powders of yttrium oxide, copper oxide, and barium carbonate, are mixed in predetermined amounts. During mixing, an alcohol such as ethanol is added and wet mixing is performed to prevent the coexistence of water as much as possible. After drying, the mixture is mixed again if necessary, and after drying, it is press-molded and usually made into granules or pellets. Next, this is calcined at around 900° C., cooled and pulverized, and the pulverized product is wet-mixed. Then, after drying, it is press-molded and sintered.

[Problem that the invention seeks to solve]

The present inventors have been conducting intensive research on the manufacturing method of this type of superconducting material, and in this research, we have investigated the fluctuations in the conditions when manufacturing this type of superconducting material, especially when cooling the sintered material. We have found that the properties of the superconducting materials obtained by this method vary greatly.

Therefore, the problem to be solved by the present invention is to set an appropriate cooling rate when cooling a sintered product, thereby improving the properties of the superconducting material.

[Means for solving problems]

This problem can be solved by cooling the sintered product at a cooling rate of 10 to 400°C, particularly preferably 30 to 400°C.

[Function and structure of the invention]

In the present invention, when cooling after sintering, the sintering temperature is
In the cooling zone up to 00°C, the cooling rate is set to the above-mentioned specific rate. In such a specific temperature range,
By cooling at a specific cooling rate, the superconducting properties of the superconducting material obtained are significantly improved.

At this time, if the cooling rate does not reach 10° C./hr, the crystal structure tends to change, making it difficult to obtain excellent superconducting properties. On the other hand, if the heating rate exceeds 200° C./hr, the superconductor obtained will have a large rank, which will lead to a decrease in superconducting properties.

Further, the temperature range for cooling at such a specific cooling rate is from the sintering temperature to 400°C, and it is necessary to cool at the above-mentioned cooling rate in this temperature range. As long as cooling is performed at the above-mentioned cooling rate in the above-mentioned temperature range, it is of course possible to perform cooling at the above-mentioned cooling rate in a temperature range lower than 400°C.

The method of the present invention will be explained below in order of steps.

First, a raw material powder is prepared. The raw material is appropriately selected depending on the type of the desired superconducting substance. For example, in the case of Y-Ba-CuO, yttrium oxide, barium carbonate, copper oxide are used, and La-3r-Cu-0
For systems, lanthanum oxide, strontium carbonate, and copper oxide are used. In the case of La-Ba-Cu-0 type, lanthanum oxide, barium carbonate, and copper oxide are used. These raw material powders are mixed in a desired composition ratio. For example, in the case of Y-Ba-Cu-0 system, these powders are mixed in advance so that the composition of the target superconducting material obtained is as shown in Figure 1. Mix raw materials.

The raw material powders are then mixed, and this mixing is usually done in a wet manner by adding a liquid outside the water plate, such as an alcohol such as ethanol. The reason is that the coexistence of water is undesirable. The wet mixture may be air-dried or may be heated at a temperature of around 150° C. or lower. If necessary, the above-mentioned liquid is added to this dried product and wet mixing is repeated again. By repeating the process, each component can be mixed more uniformly, the particle size of the raw material powder can be adjusted, and the optimum filling particle size during molding can be easily obtained.

Next, the raw material powder is pressure molded, and if necessary, after drying, the molded product is calcined. Note that during pressure molding, it is desirable to remove alcohol, etc. from the raw material powder, and for this reason, it is usually dried. Pressure molding is usually performed in the form of pellets, but the shape is not limited to pellets and may be any shape that can be easily calcined. The molded body obtained here is then calcined.

This calcination is performed for the purpose of uniformly mixing each component at the molecular level by reaction diffusion at high temperatures, and the temperature is determined as appropriate depending on the type and blending ratio of the raw material powder used.
For example, in the case of Y-Ba-Cu-0, the temperature is usually 800°C or higher, preferably 850 to 950°C, particularly around 900°C. The calcination time depends on the temperature, but is usually 6 to 4 minutes.
It is about 8 hours, preferably about 12 to 24 hours.

The calcined body is then wet-pulverized again. The liquid agent used at this time is usually an alcohol-based agent other than water, such as ethanol, and the grinding is carried out in a state where as little moisture as possible is absorbed during the grinding. After drying, sintering is performed. For sintering, a suitable mold is filled with the pulverized material, and the pulverized material is sintered while applying pressure if necessary. At this time, unlike calcination, sintering is necessary and is carried out at a temperature at which the pulverized material is sufficiently sintered.

Therefore, the sintering temperature is appropriately determined depending on the type and amount of raw materials used. After being sintered, it is cooled. During this cooling, as described above, the material is cooled at a specific cooling rate of 10 to 400°C in the temperature range from the sintering temperature to 400°C.

〔Example〕

The present invention will be described in detail below with reference to Examples.

Examples 1 to 3 Yl Ba2 C: u3 oll (However, 6 to 7
) Production: Y2O3, BaC with a purity of 99.9% by weight or more
O3 and CuO 1. Q: 3.5: 2.1
Wet mix in a mortar in the presence of ethanol (weight ratio),
After air drying, fill the mold with powder and press 100kg/c+
J using a hand press to form pellets of about 10φ x 5mm, then calcined in the air at 900°C for 24 hours,
Furnace cooled. The obtained sintered product was pulverized in ethanol and immediately stored in an atmosphere at RHIO% or less for one month. Then, using an iron mold, it was molded into pellets (same size as above) under reduced pressure at a pressure of 510 kg/cf, and heated to 950°C.
It was sintered for 24 hours. Next, it was cooled from 950°C to 500°C at a predetermined cooling rate shown in Table 1, and then allowed to cool naturally. The superconducting properties of this material are shown in Table 1.

Examples 4-6 YQ, 3 Bao, 7 Cu+ Oy (y is 2-3)
Production: In Example 1, the blending ratio (weight ratio) of raw materials was changed to Y
zC1+ :BaC0z :Cu0=1. O
: 4. 1:2.3, and the temperature during sintering was 90
The temperature was 0° C., and the other conditions were the same as in Example 1. The superconducting properties of this material are shown in Table 2.

Comparative Example 1 In Example 1 above, only the cooling rate was changed to the rate shown in Table 1, and all other treatments were carried out in the same manner as in Example 1. The results are also listed in Table 1.

Comparative Example 2 In Example 2 above, only the cooling rate was changed to the rate shown in Table 2, and all other treatments were carried out in the same manner as in Example 2. The results are also listed in Table 2.

However, the methods for measuring the superconducting properties in Tables 1 and 2 are as follows, respectively.

Under a current density of critical temperature 'O, IA/cm2, without cooling with liquid nitrogen, the change in electrical resistance due to temperature is measured by the four-probe method, and the temperature at which the electrical resistance value on the x-y recorder becomes 0 is measured. It is.

n-field current density: Gradually increase the current value while cooling the power lead with liquid nitrogen, measure the change in TR drop due to current using the 4-terminal method, and calculate the current density when the TR drop appears in the X-Y recorder. It is.

Table 1 Table 2

[Brief explanation of the drawing]

Figure 1 is a three-component composition diagram of Y, Ba, and Cu;
The figure is a flow sheet showing an example of a conventional method for manufacturing superconducting materials. (and above) Patent applicant Mitsubishi Cable Industries, Ltd.

Claims (8)

[Claims] (1) In the method for producing a superconducting material by mixing specified raw material powders, calcining, pulverizing and molding the calcined body, sintering the molded body obtained here, and then cooling it, the above-mentioned 1. A method for producing a superconducting material, which comprises cooling a sintered product from a sintering temperature to 400°C at a rate of 10 to 200°C/hr. (2) The method for producing a superconducting material according to claim (1), characterized in that the sintered product is cooled at a rate of 20 to 150°C/hr. (3) The method for producing a superconducting material according to claim (1), characterized in that the sintered product is cooled at a rate of 30 to 100°C/hr. (4) Claim No. (1) characterized in that when mixing the predetermined raw material powders, the mixture is wet-mixed and then dried.
The manufacturing method according to any one of Items to Items (3). (5) The manufacturing method according to claims (1) to (4), wherein the calcined body is wet-mixed and then dried when pulverizing the calcined body. (6) The manufacturing method according to any one of claims (1) to (5), wherein the predetermined raw material powder is a mixed powder of yttrium oxide, copper oxide, and barium carbonate. (7) The manufacturing method according to any one of claims (1) to (5), wherein the predetermined raw material powder is a mixed powder of lanthanum oxide, strontium carbonate or barium carbonate, and copper oxide. (8) A patent claim characterized in that the raw material powders are blended so that the composition of yttrium, barium, and copper of the superconducting material obtained falls within the shaded range in the ternary composition diagram shown in FIG. The manufacturing method according to scope item (1) or item (6).