KR960003803B1 - Process for producing (bipb)2sr2ca2cu3o10+x superconductor - Google Patents

Abstract

This relates to modified citric acid method by adding tartaric acid, which can be applied to manufacturing high temp. superconductor. The modified method is characterized by :1)adding 0.3-0.5mol tartaric acid to citric acid solution against 1 mol of feeding copper salts; 2)keeping the equivalence of citric acid 1-2 against the total equivalence of feed metal nitrate. The superconductor is manufactured by 1)preparing mixed metal nitrate solution, 2)adding metal nitrate solution to citric acid/tartaric acid solution with stirring, 3)adding EDTA solution and controlling pH to 6-8, 4)drying it in vacuum to make gel, 5)heating this gel to prepare amorphous solid precursor, and 6)calcinating it.

Description

Method for preparing (BiPb) 2Sr2Ca2Cu3O10 + x superconductor using modified citric acid method

1 is a schematic diagram of a (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + x} superconductor manufacturing process using a conventional citric acid method.

2 is a schematic diagram of a (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + x} superconductor manufacturing process using the citric acid method modified according to the present invention.

The present invention relates to a sol gel-like superconductor that can be used in the production of thin films, fibers, wires, etc. in the production of (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{1- + x} superconductors, In particular, it relates to a modified citric acid method for producing a single high temperature superconductor of 110 ° K.

It is known that Bi-Sr-Ca-Cu-O-based high temperature oxide superconductors have two high temperature oxide superconducting phases of 80 ° K and 110 ° K. These are room temperature Bi ₂ Sr ₂ CaCu ₂ Oy (2212) and Bi ₂ Sr _2. It has been found to have a structure of Ca ₂ Cu ₃ Ox (2223). Although the high temperature phase of 2223 is difficult to manufacture as a single phase, it is known that doping Pb to Bi-Sr-Ca-Cu-O is relatively easy to form a high temperature phase. It was almost impossible to obtain.

The most common method of obtaining the raw material powder of the oxide superconductor is the solid phase method of calcination and sintering by mixing the oxides or carbonates of each component in a molar ratio. The disadvantage of this method is that impurities are introduced from the ball mill used in the mixing of each component and uniform. It is difficult to obtain one phase, and it is difficult to control the size of the powder particles constantly, resulting in poor sinterability. In order to eliminate these disadvantages, powder manufacturing by wet method is performed. As shown in FIG. 1, citric acid method, which is one of the wet methods, differs from simply mixing raw powders with an aqueous solution of each raw material (metal salt) and citric acid. By using a mixture of aqueous solution and adjusting the pH, temperature, viscosity of solution, aging time, etc. at the time of manufacture, it is possible to obtain the desired composition, size and shape. It is suitable for the production of superconductor phase, and can obtain the raw material powder of the oxide superconductor at low temperature and short time, and the prepared powder has the advantage of excellent sinterability because it can maintain uniformity of atomic size scale. On the other hand, when the solubility difference of each metal salt is not large, it is possible to obtain a sol.gel by adjusting the pH according to the material to be prepared. However, using the conventional citric acid method for preparing (BiPb) 2Sr2Ca2Cu3-O10 + x superconductor, crystals and precipitates are generated due to the low solubility of Bi salts and the large solubility of each metal salt. There are drawbacks that make it difficult to get everyday.

In the present invention, (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + x} superconductor production, uniformity by inhibiting precipitation and crystal formation by using a modified citric acid method modified and complemented to solve the above disadvantages and problems. It is an object of the present invention to provide a method for producing a supersol, sol, gel superconductor, especially a single high temperature superconductor. In addition, the present invention uses a modified citric acid method, a uniform sol, gel-like superconductor suitable as a raw material for the production of thin films using spin coating and dipping pyrolysis and wire processing such as sash or wire Is to provide.

The present inventors, the sum of the production of by citrate method _{(BiPb) 2 Sr 2 Ca 2} Cu 3 O 10 + x -based superconductor, the addition of tartaric acid solution of citric acid solution using the mixture solution, and raw material metal nitrate total equivalents It was found that by adjusting the equivalent amount of citric acid within an appropriate range, it is possible to minimize the formation of crystals and precipitates and to provide suitable solution conditions for the formation of gels, sol. As with many chemical methods, the theoretical mechanisms have not been elucidated, but it is assumed that the use of citric acid / tartaric acid mixed solution inhibits, delays crystallization and precipitation of the superconducting phase produced and stabilizes the sol and gel phases. As can be seen from the data of the examples described below, the amount of tartaric acid which provides the most suitable conditions for sol and gel formation is about 0.3-0.5 moles based on 1 mole of copper in the raw metal salt. On the other hand, in general, the ratio of the sum of the total equivalents of the raw metal nitrates and the citric acid equivalents is 1: 1, but in order to suppress precipitation and crystallization, it is preferable to use slightly excess citric acid. The inventors found that the most preferred citric acid level in the method of the present invention ranges 1-2 times with respect to the sum of the total equivalents of the raw metal nitrates.

According to the present invention, in the preparation of (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + x-} based superconductor using citric acid method, an aqueous solution of tartaric acid in the range of 0.3-0.5 mol per mol of copper in a raw material is mixed with citric acid aqueous solution (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + x} superconductor in a uniform sol.gel, in particular a single high temperature phase superconductor, by adjusting the ratio of citric acid equivalent to the sum of the total amount of metal nitrates in the range 1-2 There is provided a method of preparing the same.

The preparation method of the present invention will now be described in detail with reference to the accompanying FIG. 2 showing a preferred embodiment of the present invention. As shown in FIG. 2, first, metal nitrates as raw materials, that is, bismuth nitrate (Bi (NO ₃ ) ₂ .5H ₂ O), lead nitrate (Pb (NO ₃ ) ₂ ), strontium nitrate ( Sr (NO ₃ ) ₂ ), calcium nitrate (Ca (NO ₃ ) ₂ .4H ₂ O), and copper nitrate (Cu (NO ₃ ) ₂ ) .3 (H ₂ O) were each 1: 1: 1: 1 The aqueous solutions dissolved in water at a molar ratio of 1.5 are mixed well to form a uniform mixed metal nitrate aqueous solution. At this time, bismuth nitrate should be sufficiently dissolved in dilute nitric acid solution because it is hydrolyzed without dissolving in water. Separately, citric acid and tartaric acid are dissolved in water, and then mixed well to form a citric acid / tartaric acid mixed aqueous solution, wherein the amount of citric acid is in the range of about 1-2 equivalents of citric acid to the sum of the total equivalents of metal nitrates, The amount of tartaric acid is such that the molar ratio of tartaric acid / copper is about 0.3-0.5. The aqueous mixed metal nitrate solution is slowly added while stirring the citric acid / tartaric acid aqueous solution with a magnetic stirrer. The pH is adjusted to about 6-8 range while the ethylenediamine (EDA) solution is added to the resulting mixed aqueous solution at a rate of 2 cc / min. The pH adjusted mixed solution is placed in a drier and the water is evaporated while maintaining the temperature at 70-80 ° C. After 3-4 days a uniform transparent purple sol is produced, which is dried in vacuo at 70-80 ° C. to obtain a gel. The gel is heated in an air atmosphere (atmosphere) to 500 ° C. at a heating rate of 3 ° C./min to blow off water, carbon compounds, and nitrogen compounds to yield an amorphous solid precursor.

The solid precursor obtained by this precalcination is calcined at about 800-850 ° C. for at least about 30 hours in an air atmosphere to obtain a nearly single high temperature phase (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + x} superconductor. On the other hand, in order to yield a nearly complete single high temperature phase (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + x} superconductor, it is advantageous to process it for about 90 hours in a low oxygen partial pressure atmosphere, but considering the economical advantages, the air described above At least about 30-40 hours of quartile may be desirable.

Hereinafter, the present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

Example 1-2

(BiPb) ₂ Sr ₂ Ca ₂ Cu using a mixed solution of bismuth nitrate, lead nitrate, strontium nitrate, calcium nitrate, and copper nitrate and a mixed solution of citric acid / tartaric acid in accordance with the method described above and shown in FIG. _{In the} preparation of 3O _{10 + x} high temperature oxide superconductor, the sum of the total equivalents of metal nitrates and the citric acid equivalent ratio is set to 1: 1.1, and various tartaric / copper molar ratios and pHs are varied to yield various precursors and analyze the form thereof. It was.

When the tartaric acid / copper molar ratio is 0.45, the analysis results of the precursor form according to pH are summarized in the following Table 1.

TABLE 1

Precursor shape according to pH after evaporation of water

As can be seen from the data in Table 1, the suitable pH range for sol formation in the preparation method of the present invention was about 6.5-8.0.

In addition, in the case of pH = 7.0, the analysis results of the precursor form according to the tartaric acid / copper molar ratio are summarized in the following Table 2.

TABLE 2

Precursor shape according to tartaric acid / copper molar ratio after water evaporation

As can be seen from the data in Table 2 above, sol was formed in the range of tartaric acid / copper molar ratio of about 0.3-0.5, and crystals and precipitation were produced in other ranges.

Example 3

According to the same method as described above, after forming a sol at the citric acid equivalent ratio = 1.1, pH = 6.7 tartaric acid / copper mol ratio = 0.45 to the sum of the total equivalents of metal nitrates, the gel obtained by vacuum drying is precalcinated to prepare a precursor. This precursor was heat-treated at 835 ° C. for 30 hours to obtain (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + x} superconductor. The resulting superconductor was subjected to XRD analysis of (BiPb) high temperature phase (2θ = 4.7 °, 9.3 °, 23.8 °, 26 ′, 28.7) of ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + x} , 31.7˚, 32.9˚, 33.7˚, 35.5˚), summarized the relative XRD intensities of the low temperature phase (2θ = 5.7 °, 23 °, 27.4 °) and Ca ₂ PbO ₄ phase (2θ = 17.7 °, 31.2 °) The results are shown in Table 3 below.

TABLE 3

Relative Comparison of Peak Sizes of (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + x} Superconductor XRD Analysis

From the data in Table 3, it can be seen that the (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + x} superconductor prepared by the method of the present invention is at least 95% of a high temperature single phase. On the other hand, the slight low-temperature phase and Ca ₂ PbO ₄ phase appearing in the superconductor sample produced in this example is considered to be because the calcination time is short and the calcination was performed under an air atmosphere. That is, in general, in the manufacture of (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + x} superconductor, the calcination time is 90 hours or more, and in order to stabilize the high temperature phase, it is preferable to perform calcination in an atmosphere having low oxygen partial pressure. In consideration of the economic advantages, Ess. Therefore, it is estimated that the sample prepared according to the present method is calcined for about 90 hours or more under an atmosphere of low oxygen partial pressure to obtain a nearly complete single high temperature phase.

On the other hand, with respect to the (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + x} superconductor prepared in this embodiment, the transition temperature at which the resistance becomes 0 by the four probe method (Tc on = 120) ˚K, Tc off was 110˚K. In other words, as the temperature decreases from room temperature, the resistance gradually decreases, then suddenly decreases at 120˚K and becomes zero at 110˚K.

As described above, the present invention uses a citric acid / tartaric acid mixed aqueous solution mixed with a raw metal nitrate mixed aqueous solution and a fixed ratio, to form a uniform sol, gel and then from the precursor to a single high-temperature (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + x} has the effect of producing a superconductor.

Claims (3)

In the preparation of (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + x} superconductor using citric acid, the ratio of citric acid equivalent to the sum of the total equivalents of the raw metal nitrates is in the range of 1-2, and the tartaric acid / copper molar ratio is 0.3. A method of producing a (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + x} superconductor by a modified citric acid method, characterized in that the aqueous solution of tartaric acid is mixed with an aqueous citric acid solution at a level of -0.5. The method of claim 1, wherein a uniform sol, gel-like (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + x} superconductor is prepared. The method of claim 1, wherein (BiPb) ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + x} superconductor is prepared.