JPH07106909B2 - Bi-Pb-Sr-Ca-Cu-O superconductor synthesis method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a method of making powders of Bi-Pb-Sr-Ca-Cu-O type high temperature oxide superconductors.

In a conventional method, high temperature metal oxide superconductors are made by conventional solid state reactions. That is, oxides or carbides of metal components desired to be present in the final metal oxide superconductor are mixed in appropriate proportions, crushed, fired and sintered to obtain an oxide superconducting material. However, the final product obtained by this conventional method is a coarse powder (particle size> 1 μm) and lacks homogeneity, which has a serious adverse effect on its utilization.

The drawbacks of the above method can be ameliorated by using a metal co-precipitation method that can result in finer precursor powder particles having a more uniform particle size. In the metal coprecipitation method, an oxalate precipitant is added to an aqueous solution containing a soluble salt of a desired metal. Sodium hydroxide (or potassium hydroxide) is added to the solution in order to adjust the pH value of the solution and form an oxalate coprecipitate of the Bi-Pb-Sr-Ca-Cu-O mixture. The coprecipitate obtained is passed, dried and sintered. When sodium hydroxide and / or potassium hydroxide is added to the solution,
At the same time, the pH of the solution changes. Co-precipitates form rapidly but are not homogeneous. Moreover, the residual sodium and / or potassium ions adversely affect the superconductivity of the product obtained as described above. Ammonium oxalate is sometimes used as a precipitant, but in this case the pH of the solution
Can not be adjusted. That is, it is difficult to control the ratio of the individual components of the coprecipitate in this conventional method, and this method is not suitable for mass production.

SUMMARY OF THE INVENTION Accordingly, the present invention may alleviate the above-mentioned drawbacks of conventional methods.
It is an object to provide a method for producing a Bi-Pb-Sr-Ca-Cu-O type oxide superconductor.

That is, an object of the present invention is to provide a method for producing a Bi-Pb-Sr-Ca-Cu-O type oxide superconductor in which the ratio of individual metal components can be easily controlled.

The present invention also provides a Bi-Pb-Sr having a superconducting critical temperature of 110K.
An object of the present invention is to provide a method for producing a —Ca—Cu—O type oxide superconductor.

Another object of the present invention is to provide a method for producing a Bi-Pb-Sr-Ca-Cu-O-type oxide superconductor which can obtain a superconducting material having a very fine and uniform grain size.

It is also an object of the present invention to provide a method for producing a Bi-Pb-Sr-Ca-Cu-O-type oxide superconductor capable of controlling the concentration of a solution.

These and other objects, advantages and features of the invention will be better understood and appreciated by reference to the description herein.

The present invention is described in detail below with reference to the accompanying drawings.

DESCRIPTION OF PREFERRED EMBODIMENTS The present invention is intended to be present in the final superconductor composition B
Bi, Pb, Sr, Ca and Cu metal component nitrates are dissolved in a nitric acid solution, and the resulting solution is poured into a premixed solution containing triethylamine / oxalic acid in an appropriate amount to form a coprecipitate. The present invention relates to a method for producing a Pb-Sr-Ca-Cu-O type oxide superconductor. After co-precipitation, the resulting product is 800
Baking and sintering at a temperature of ~ 860 ° C. An oxide superconductor powder having a very fine and uniform particle size is obtained.

According to the present invention, a method for producing a Bi-Pb-Sr-Ca-Cu-O type oxide superconductor includes the following steps.

(1) Bi manufacturing 1.698g of metal nitrate solution _{(NO 3) 3 · 5H 2} O, 0.4971g of Pb (NO _{3) 2,}
1.059 of Sr (NO _{3) 2} and 1.182g of Cu a _{(NO 3) 2 · 3H 2} O
Mix with 10 ml of 1.6M nitric acid solution. The solution is stirred until the ingredients are completely dissolved.

(2) Preparation of triethylamine / oxalic acid solution 4.098 g of oxalic acid is dissolved in 50 ml of water. Triethylamine is added to the solution in the following ratios. Ratio Triethylamine (ml) 1 4.5 1.5 6.8 1.8 8.1 2.0 9.1 2.2 9.9 2.5 11.4 3.0 13.5 (3) Coprecipitation Add the metal nitrate solution slowly to the triethylamine / oxalic acid solution. The solution is stirred and a pale blue precipitate forms. After the mixing is complete, pass the suspension. The solid blue precipitate is collected, placed in an oven and dried at 120 ° C. for 6 hours, and the precipitate becomes a powder.

(4) Calcination The product obtained as described above is put in a high temperature furnace and
Bake at ℃ 10 hours.

After baking, the black solid is ground and pressed into 0.5 g disc-shaped pellets.

(5) Sintering The disc-shaped pellets are sintered at 860 ° C. for 72 hours to produce a very fine powdery metal oxide superconducting material.

According to the present invention, nitrates of Bi, Pb, Sr, Ca and Cu metals are dissolved in a nitric acid solution to produce an aqueous solution. Triethylamine and oxalic acid were added to this aqueous solution at various molar ratios (1 to 1).
Gradually add the mixed solution that was thoroughly mixed in 3). Immediately after the addition of the mixed solution, the pH of the aqueous solution changes. As shown in FIG. 1, the molar ratio of triethylamine to oxalic acid is 1 to 1.
At 2, there is little change in pH. When the triethylamine / oxalic acid ratio exceeds 2.1, the pH changes drastically. ICP-
The residual metal ion concentration was detected using AES (high frequency inductively coupled plasma atomic emission spectrometry), and the weight ratio of the residual metal ion calculated with respect to the starting weight was calculated as triethylamine /
It is shown in Figure 2 as a function of oxalic acid ratio. From FIG. 2, it is clear that the amount of residual metal ions varies depending on the triethylamine / oxalic acid ratio, but when this ratio is around 1.8 to 2.2, the amount of any residual metal ions becomes the minimum. This shows that a homogeneous coprecipitate containing the components in a ratio close to the starting ratio can be produced. The precipitate obtained is 140
Dry at 0 ° C. to produce a very fine powder (particle size about 0.3 μm).

The thermal characteristics of the coprecipitate obtained by the present invention are measured by a thermogravimetric analyzer and a differential thermal analyzer. As shown in FIG. 3, a significant weight loss is observed at 400 ° C.
The corresponding high peak of the exothermic reaction suggests that most of the organic components have decomposed. Next, the product was heated at four selected temperatures (140 ° C, 200 ° C, 450 ° C and 800 ° C) for 2 hours, and the IR absorption spectrum was measured and shown in Fig. 4 (a: 140 ° C, b; 200 ° C, c; 450 ° C, d; 800 ° C). FIG. 4 shows the absorption characteristics of oxalate. In the figure, 1650 cm ^-1 , 1300 cm
Signals for oxalate can be seen at ^-1 and 800 cm ^-1 . No IR absorption signal was observed for triethylamine, indicating that the triethylamine cation did not remain in the coprecipitate. Precipitate at 200 ℃
When heated for 2 hours (curve b in FIG. 4), the metal oxalate gradually decomposes. As a result, the absorption at 1650 cm ^-1 gradually weakens. When the temperature is raised to 450 ° C. (curve c in FIG. 4), the oxalate gradually decomposes into bismuth oxide, copper oxide, lead oxide, calcium carbonate and strontium carbonate. The presence of calcium carbonate and strontium carbonate can be seen in 1450 cm ^-1 and 850 cm ^-1.
When the temperature is raised to 800 ° C., the individual oxides and carbonates gradually react with each other to form superconducting oxides, thus eliminating the peaks. In conclusion, the coprecipitate obtained by the above operations is a metal oxalate. At 450 ° C, the coprecipitate decomposes to form an oxide or carbonate, and at 800 ° C, a powdery oxide superconducting material is obtained.

Co-precipitates produced with various ratios of triethylamine / oxalic acid are fired at 800 ° C. and then ground and pressed to form pellets. Sinter the pellets at 860 ° C for 72 hours,
Then it is cooled to room temperature. The four-point probe method measures temperature-related resistance changes. As shown in FIG. 5, the triethylamine / oxalic acid ratio was 1.5 to 2.2 (graph a; 1.
5, graph b; 1.8, graph c; 2.0, graph d; 2.2), the critical temperature of the oxide superconductor obtained by sintering the obtained coprecipitate is 105 to 110K. Next, the obtained oxide superconductor is examined by X-ray diffraction. As shown in FIG. 6, it is found that the main component of the metal oxide is the (2223) phase and the minute component is (2212), which is Ca ₂ PbO ₄ . Subsequently, the superconductor was measured by SQUID (superconducting quantum interference device), and the result is shown in FIG. First, the superconductor is cooled to 5K and then a magnetic field of 100 gauss is applied. Then increase the temperature to 130
Raise to K and measure the magnetic field change. The curve (a) shown in FIG. 7 is a zero magnetic field cooling (ZFC) curve.
The superconductor is heated from 130K to 5 with a 100 gauss magnetic field applied.
Cool to K and measure the magnetic field change. Curve (b) in FIG.
Is the magnetic field cooling (FC) curve. In conclusion, Figure 7 shows
It is shown that the superconductor of the present invention has diamagnetism at 100K.

The following examples are provided so that the invention might be better understood, but the examples are not intended to limit the scope of the invention. All parts and percentages are by weight unless otherwise noted.

In the method for producing a Bi-Pb-Sr-Ca-Cu-O type high temperature metal oxide superconductor according to the present invention, Bi, Pb, Sr, Ca and
Using Cu nitrate, these nitrates are dissolved in a nitric acid solution to produce an aqueous solution. An appropriate ratio of triethylamine / oxalic acid is added to this aqueous solution to form a coprecipitate. The obtained coprecipitate is sintered at 860 ° C. to produce a metal oxide superconductor having a critical temperature of 110K. The metal oxide thus produced is in the form of very fine powder.

Although only one embodiment of the present invention has been described herein, it is nevertheless understood that modifications of the invention, including those mentioned above, can be readily realized by those skilled in the art. Therefore, it is intended that the scope of the claims include those without departing from the true spirit and scope of the present invention, including those mentioned above.

[Brief description of drawings]

FIG. 1 is a graph showing the change in pH value of the residual liquid after precipitation of metal ions with respect to the ratio of triethylamine / oxalic acid, and FIG. 2 is a graph showing the ratio of residual metal ions present in the residual liquid after passing through the solution. FIG. 4 is a graph showing the results of thermogravimetric analysis and differential thermal analysis of the precipitate obtained according to the present invention.
FIG. 5 is a graph showing IR absorption spectra of precipitates sintered at various temperatures for 2 hours, and FIG. 5 is a graph showing a relationship between temperature and resistance in superconductors prepared according to the present invention with various triethylamine / oxalic acid ratios. FIG. 6 is a diagram showing an X-ray diffraction pattern of a superconductor according to the method of the present invention, and FIG. 7 is a graph of magnetization measured by SQUID.

Claims (1)

[Claims] 1. A method for synthesizing a Bi-Pb-Sr-Ca-Cu-O type high temperature oxide superconductor, comprising: (a) a nitrate solution of Bi, Pb, Sr, Ca and Cu. ≧
1.5M), and (b) the solution obtained in (a) is slowly added to a well-mixed aqueous solution of triethylamine / oxalic acid (molar ratio 1 to 3) to give a homogeneous mixture of pale blue. Bi-comprising: obtaining a component precipitate, and (c) baking the product obtained in (b) at 750 to 800 ° C. for 10 hours to obtain a powdery superconducting material to be used later. A method for synthesizing a Pb-Sr-Ca-Cu-O superconductor.