JP2654460B2 - Production method of superconducting material - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for producing a superconducting material, and more particularly to an improvement on a conventional method for producing a superconducting material.

[Conventional technology and its problems]

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

The conventional production method for these superconducting materials is Y-Ba-Cu-
FIG. 2 shows a typical example of the O system. That is, first, a predetermined amount of a raw material powder, usually each powder of yttrium oxide, copper oxide, and barium carbonate is mixed. In mixing, an alcohol such as ethanol is added and wet-mixed in order to prevent coexistence of water as much as possible. After drying, the mixture is mixed again if necessary, dried, and then subjected to pressure molding to form granules or pellets. Next, this is calcined at about 900 ° C., cooled and then pulverized, and the pulverized material is wet-mixed. Then, after drying, it is pressed and sintered.

[Problems to be solved by the invention]

The present inventors have been enthusiastically studying the method for producing this kind of superconducting material, but in this research, when producing this kind of superconducting material, particularly when sintering a pulverized product of a calcined body. It has been found that the properties of the obtained superconducting material vary greatly depending on the heating conditions during the sintering. During further research, by removing the adsorbed water contained in the calcined body as much as possible during the sintering of the pulverized material,
It has been found that the superconducting point of the obtained superconducting material is low. More specifically, as shown in FIG. 3, the actual resistance value of the obtained superconducting material decreases as shown by the solid line, and the temperature at which the resistance value becomes 0 becomes a gentle curve as shown by the arrow A. The longer this curve portion is, the lower the temperature at which the resistance value becomes 0 is undesirable. Therefore, it is preferable that the curve portion is as short as possible.
Hereinafter, this curved portion is defined as “tail pull”. That is, it has been found that the "tail pulling" phenomenon greatly changes depending on the method of removing the adsorbed moisture from the pulverized material of the calcined body.

The problem to be solved by the present invention is therefore to avoid this "tailing" phenomenon or to make it as short as possible.

[Means for solving the problem]

This problem is caused by removing as much as possible of the adsorbed moisture of the pulverized material of the calcined body during sintering, and removing the moisture as smoothly as possible (slowly and gradually instead of removing a large amount at once in a short time). It is solved by removing.

That is, the present invention relates to a method for producing a superconducting material by mixing a predetermined raw material powder, calcining, then pulverizing and calcining the calcined body, and sintering the molded body. The present invention relates to a superconducting production method characterized in that upon heating during sintering, the temperature is gradually increased up to 300 ° C., and then rapidly increased.

[Function and Configuration of the Invention]

In the present invention, when heating during sintering, especially 300 ° C.
Until the temperature rises slowly, and then rapidly. This makes it possible to smoothly remove a large amount of water contained in the pulverized material of the calcined body at the time of sintering, thereby reducing the superconducting characteristics, especially the "tailing" phenomenon, or shortening the phenomenon. Can be eliminated. The gradual temperature increase in this case refers to a temperature increase in which a substantial amount of water does not volatilize at once, and a temperature increase rate of usually 50 to 200 ° C / hr, preferably about 50 to 150 ° C / hr is employed. Is done. This gradual heating is performed up to 300 ° C., and most of the water is removed in this temperature range.
Therefore, in the subsequent heating, even if the temperature is rapidly increased, there is substantially no effect of evaporation of moisture.

As described above, the rapid temperature increase performed after the gradual temperature increase in the present invention simply means that the temperature is rapidly increased with respect to the gradual temperature increase in the first half. It is usual to employ a heating rate.

After the temperature was gradually increased to 300 ° C., the temperature was temporarily interrupted at 300 ° C., and the temperature was temporarily stopped at 200 to 300 ° C., for example, 1 to 10 ° C.
It is also preferable to maintain for about an hour.

In the present invention, as long as the above-mentioned heating conditions, that is, the first half gently, and the second half rapid heating condition are satisfied, the means and apparatus are not limited at all, but one of the preferred heating methods is as follows. Can be exemplified. That is, the use of a continuous heating device set so that the temperature gradually increases from the inlet side to the outlet side. Although this heating device has been conventionally used for baking of enameled electric wires and the like, it is extremely advantageous to use this device at the time of sintering of the present invention. More specifically, if a crushed product of the calcined body is sintered using this apparatus, a linear sintered body can be continuously obtained, and the temperature control can be extremely easily performed, which is extremely convenient for industrial implementation. Becomes

The method of the present invention will be described below in the order of steps. First, a raw material powder is prepared. As a raw material, a raw material is appropriately selected according to a kind of a desired superconducting substance. For example, Y-Ba-Cu-O
In the case of a system, yttrium oxide, barium carbonate and copper oxide are used, and in the case of a La-Sr-Cu-O system, lanthanum oxide, strontium carbonate and copper oxide are used. Also La
In the case of -Ba-Cu-O system, 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 a Y-Ba-Cu-O system, these raw materials are preliminarily mixed so that the composition of the target superconducting substance obtained is as shown in FIG. Is blended.

This raw material powder is then mixed, and the mixing at this time is usually performed by a wet method, and is performed by adding a liquid other than water, for example, an alcohol such as ethanol. The reason is based on the fact that coexistence of water is undesirable. The wet mixture may be naturally dried, or may be heated at a temperature of about 150 ° C. or lower. If necessary, the liquid is added to the dried product, and wet mixing is repeated again. By repeating the process, each component can be more uniformly mixed, the particle size of the raw material powder can be adjusted, and it is easy to obtain the optimum filling particle size at the time of molding.

Next, the above-mentioned raw material powder is subjected to pressure molding, and if necessary, after drying, the molded body is calcined. At the time of pressure molding, it is desirable to remove alcohol and the like in the raw material powder, and therefore, drying is usually performed. The pressure molding is usually performed in the form of pellets, but the shape is not limited to pellets, and may be any shape as long as it is 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 a high temperature, and the temperature is appropriately determined according to the type and the mixing ratio of the raw material powder to be used. In the case of a -Cu-O system, the temperature is usually 800C or higher, preferably 850 to 950C, and particularly preferably around 900C. The calcination time is usually 6 to 48 hours, preferably about 12 to 24 hours, depending on the temperature.

Thus, the calcined body is wet-pulverized again. As the liquid agent used at this time, a normal alcohol-based agent other than water, for example, ethanol is used, and the liquid is adsorbed as little as possible during the pulverization. After drying, sintering is performed. In the sintering, an appropriate mold is filled with the pulverized material, and the pulverized material is sintered under the above-mentioned specific conditions while applying pressure as necessary. At this time, unlike calcination, sintering is required, and the sintering is performed at a temperature at which the pulverized material is sufficiently sintered. At this time, the sintering temperature is appropriately determined depending on the type and amount of the raw material used.

〔Example〕

 Hereinafter, the method of the present invention will be described in detail with reference to examples.

Examples 1 to 3 Production of Y ₁ Ba ₂ Cu ₃ O _X (where _X is 6 to 7): Y ₂ O ₃ , BaCo ₃ , and CuO having a purity of 99.9% by weight or more were added in a ratio of 1.0: 3.
5: 2.1 (weight ratio), wet mixing with a mortar in the presence of ethanol, air drying, filling the mold with powder, pressure 100kg / cm ²
Was formed into pellets of about 10φ × 5 mm using a hand press, and then calcined in the atmosphere at 900 ° C. for 24 hours, followed by furnace cooling. The obtained calcined body was pulverized in ethanol, and immediately thereafter, formed into pellets (same size as above) under reduced pressure at a pressure of 510 kg / cm ² using an iron mold, and shown in Table 1 up to 950 ° C. Sintering was performed under elevated temperature conditions. The superconducting critical temperature of this was measured. The results are as shown in Table 1, and there was almost no "tail pull" phenomenon.

Example _{4~6 Y 0.3 Ba 0.7 Cu 1 O} y (y is 2-3) Preparation of a blending ratio of the raw material In the embodiment _{1 Y 2 O 3: BaCO 3} : CuO = 1.
0: 4.1: 2.3, the temperature during sintering was 900 ° C., and the others were treated in the same manner as in Example 1. The results of the measurement are as shown in Table 2. There was almost no "tail pull" phenomenon.

Comparative Examples 1 and 2 In Examples 1 and 4, the temperature raising conditions during sintering were the first, respectively.
The conditions were the same as those in Examples 1 and 4 except for the conditions shown in Table and Table 2. The results are shown in Tables 1 and 2, respectively. In addition, the "tail pulling" phenomenon became remarkable.

[Brief description of the drawings]

FIG. 1 is a ternary composition diagram of Y, Ba, and Cu, FIG. 2 is a flow sheet showing an example of a conventional method for producing a superconducting material, and FIG. It is a graph which shows a relationship.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Masaru Yoshikawa 8 Nishinocho, Higashimukaijima, Amagasaki City, Hyogo Prefecture Inside Mitsubishi Cable Industries, Ltd. (56) References JP-A-63-225524 (JP, A)

Claims (9)

(57) [Claims] 1. A method for producing a superconducting material, comprising mixing a predetermined raw material powder, calcining, pulverizing the calcined body, molding the molded body, and sintering the molded body. A superconducting material manufacturing method characterized by gradually increasing the temperature up to 300 ° C and then rapidly increasing the temperature when heating during sintering. 2. The method for producing a superconducting material according to claim 1, wherein the rate of the gradual temperature rise is 50 to 200 ° C./hr. 3. The method for producing a superconducting material according to claim 1, wherein the temperature rise is temporarily stopped at 300 ° C. 4. The method for producing a superconducting material according to claim 3, wherein said interruption is for about 1 to 10 hours. 5. A method for obtaining a linear sintered body from a pulverized calcined body using a continuous heating device which gradually increases in temperature from an inlet side to an outlet side during the sintering. The method for producing a superconducting material according to any one of claims (1) to (4), characterized in that: 6. The method according to claim 1, wherein the calcined body is wet-mixed and then dried when pulverizing the calcined body. 7. The method according to claim 1, wherein the predetermined raw material powder is a mixed powder of yttrium oxide, copper oxide, and barium carbonate. 8. The method according to claim 1, wherein said predetermined raw material powder is a mixed powder of lanthanum oxide, strontium oxide or barium carbonate, and copper oxide. 9. The raw material powder is blended so that the composition of yttrium, barium and copper of the obtained superconducting material falls within the range shown by hatching in the ternary composition diagram shown in FIG. Claims (1) to (7)
Production method described in the section.