RU2182894C2 - Method of production of ceramics y-ba-cu-o by combined precipitation from concentrated solutions - Google Patents

Abstract

FIELD: inorganic chemistry, technology of inorganic materials. SUBSTANCE: invention relates to method of production of ceramics Y-Ba-Cu-O of different composition, among that with high- temperature superconductivity. Method involves preliminary preparing barium nitrite solution in concentration 2.27-2.90 mole/l, mixed solution of yttrium and copper nitrate in total concentration 2.73-3.55 mole/l. Both solutions are poured in to oxalic acid solution in concentration 0.92-1.14 mole/l taken as a precipitant followed by addition of ammonia aqueous solution in concentration 13- 14 mole/l to brought about pH value at precipitation 3.3-7.3. The prepared mixture is kept for 2-3 h, not less. Solution is filtered , precipitate is dried and thermic treatment is carried out. Method provides the increased yield of oxalate precipitate by 3.6-fold from 1 l of reaction mixture, broadening range of pH values from 0.2 to 4 where the complete precipitation of all three elements is occurred, elimination of precipitate washing out from impurities, preparing the product with high content of the main phase. EFFECT: improved method of production, increased output of method. 4 ex

Description

 The present invention relates to the technology of inorganic materials, specifically to a method for producing Y-Ba-Cu-O ceramics of various compositions, including high-temperature superconductivity (HTSC).

This class of HTSC materials includes compounds YВа ₂ Сu ₃ О _7-х (Y-123), YBa ₂ Cu _3,5 О _7,5-x (Y-247), YBa ₂ Cu ₄ О ₈ (Y-124) . In addition, in the preparation of HTSC ceramics, the compound Y ₂ BaCuO ₅ (Y-211), the so-called "green phase" without superconducting properties.

A known method of producing Y-Ba-Cu-O ceramics by co-precipitation from solutions [1], which consists in the simultaneous precipitation of components in the form of sparingly soluble compounds, separation of the precipitate from the mother liquor, drying and heat treatment. Yttrium, barium and copper nitrates are most often used as salts for the preparation of solutions. After accurately determining the concentrations of the elements in individual solutions, these solutions are mixed in certain proportions. However, the total (total) concentration of salts in the mixed solution is limited by the low solubility of Ba (NO ₃ ) ₃ , which is why the initial solutions are very diluted, and this affects the productivity of the method, i.e. on the amount of precipitate obtained from a unit volume of the reaction mixture. For example, at a temperature of 25 ^o With the maximum total concentration of a mixed solution of nitrates with a ratio of cations Y: Ba: Cu-1: 2: 3 does not exceed 10 wt.%. Raising the temperature to 100 ^o With slightly increases the solubility of the ternary system. Only the use of high temperatures and pressures gives a tangible effect. So, the preparation of a solution of yttrium, barium and copper nitrates with a molar ratio of 1: 2: 3 in an autoclave at a pressure of 100 MPa and a temperature of 200 ^o C allows you to increase the total concentration to 46.5 wt.%.

To eliminate this drawback, more soluble barium salts are used: nitrite Ba (NO ₂ ) ₂ and acetate Ba (CH ₃ COO) ₂ . When using Ba (NO ₂ ) _{2, the} total solubility of salts slightly increases, and due to this, productivity can be increased by 1.5 times. The use of Ba (CH ₃ COO) ₂ gives about the same increase in total concentration. However, with a total component concentration> 0.6 mol / L, the solutions become unstable.

For co-precipitation, oxalic acid salts (ammonium, potassium or sodium oxalates) are often used as precipitants. It is known [2] that when using a saturated solution of ammonium oxalate (5 wt.%) Taken with a 30% excess, from a mixed solution of nitrates with a concentration of Y is 0.01 mol / l, Ba is 0.02 mol / l, Cu - 0.03 mol / l at a pH of 2.38-2.53 precipitated a mixture of oxalates. The precipitate is separated by centrifugation, dried and annealed at 860 ^o C for 6 hours. Of the shortcomings, it should be noted the low completeness of the deposition of elements (not more than 90%), as well as low productivity due to the use of dilute solutions of nitrates and precipitant.

There is also known a method [3] of metal deposition from an aqueous solution containing yttrium nitrate and barium and copper acetates. Co-precipitation is carried out with potassium oxalate, which is preliminarily prepared by mixing solutions of oxalic acid and potassium hydroxide. The pH of the reaction mixture was adjusted to 11-13 with a saturated KOH solution, the precipitate was washed with water, dried and calcined at 950 ^° C in air for 10 hours. The material obtained by this method with the composition YBa ₂ Cu ₃ O _7-x does not always have superconducting properties ( no Meissner effect), which is associated with contamination of the product with potassium, which is part of the precipitant.

Closest to the proposed method is a method adopted as a prototype. A method of producing yttrium-barium-copper oxide [4] is the joint deposition of these elements from a solution of nitrates. As a precipitant, a solution of sodium oxalate containing NaOH is used. Precipitation is carried out at pH 9.6-9.8, the precipitate is washed 5 times with alcohol and once with water. The ratio of elements in the precipitate Y: Ba: Cu-1.0: 2.0: 3.0. The precipitate obtained is subjected to heat treatment at 800 ^° C for 5-6 hours, then at 980 ^° C for 6 hours and oxidative annealing in an oxygen stream at 950 ^° C. As a result, YBa ₂ Cu ₃ O _7-x oxide is formed with a superconducting content phases up to 93%. However, this method has several significant disadvantages:
1) low productivity of the deposition process, due to the total concentration of the mixed nitrate solution, close to the maximum, even when using a sufficiently concentrated alkaline solution of sodium oxalate for the deposition, the process productivity is only 16.8 g of sediment (in terms of a mixture of oxides) from one liter of the reaction mixture ;
2) a narrow range of pH values of 9.6-9.8, in which there is a complete deposition of all three elements, which complicates the use of the method in an industrial environment;
3) the need to wash the oxalate precipitate from sodium ions (the prototype uses 5-fold washing with alcohol, because when washing with water, barium and copper oxalates are washed out of the precipitate and its chemical composition changes);
4) the low content of the superconducting phase Y-123 (up to 93%) in the finished product is due to incomplete washing, because It is known that even the slight presence of alkali metals in the synthesis of YВа ₂ Сu ₃ О _x promotes the formation of a nonsuperconducting green phase of Y ₂ BaCuO ₅ .

 The technical task of this invention is to increase the productivity of the method, to obtain Y-Ba-Cu-O ceramics of various compositions, to expand the pH range of deposition, to replace alkali metal cations in oxalate precipitator with easily removable ions to exclude the operation of multiple washing and thereby increase the proportion of the main phase in the resulting product, which means improving the electro-physical properties of HTSC ceramics.

 The stated technical problem is solved by the proposed method, including the preparation of solutions of yttrium, copper, barium salts and an oxalate precipitant solution, mixing the solutions in the required ratio in a given pH range, filtering, drying the precipitate and its heat treatment, characterized in that barium nitrite solution is preliminarily prepared with concentration of 2.27-2.90 mol / l, then a mixed solution of yttrium and copper nitrates with a total concentration of 2.73-3.55 mol / l is prepared and both solutions are simultaneously poured into a solution of oxalic acid with with a concentration of 0.92-1.14 mol / L, taken as a precipitant, after which aqueous ammonia solution with a concentration of 13-14 mol / L is added until the precipitation pH is established at 3.3-7.3 and the resulting mixture is maintained for at least 2- 3 hours

 A solution of barium nitrite and a mixed solution of yttrium and copper nitrates are added to the precipitant in the proportions necessary to obtain ceramics of one or another composition. After precipitation, the mother liquor is decanted, the precipitate is filtered off with vacuum and dried to constant weight.

The optimal parameters of the proposed method are determined:
- the total concentration of a mixed solution of yttrium-copper nitrates and a solution of barium nitrite should not exceed 3 mol / l, because at high concentrations, thick, difficult to mix suspensions will be formed, the adjustment of the pH values in which is difficult;
- a small excess of oxalate ion contributes to a more complete deposition of all three elements, but with an excess of more than 5% of the stoichiometric amount, copper losses increase due to the formation of a soluble double salt (NH ₄ ) ₂ C ₂ O ₄ • CuC ₂ O ₄ • 2H ₂ O;
- the pH of the deposition should be in the range of 3.3-7.3, because at lower values, Ba losses increase (the solubility of BaC ₂ O ₄ increases), at large values, Cu losses increase (a soluble complex [Cu (NH ₃ ) ₄ ] ^{2+ is formed} );
- suspension settling time of at least 2-3 hours, because at the same time, the losses of Ba and Cu with the mother liquor are significantly reduced.

The dry precipitate is subjected to thermal decomposition (pyrolysis) at a temperature of 700 ^o C for 5 hours. The process of heat treatment of the powder is optimized: 900-920 ^o C, 10-12 hours in air.

 The resulting product is a homogeneous, finely dispersed powder of a given chemical composition (plasma spectral emission analysis) containing not less than 95% of the basic compound (X-ray phase analysis) and not more than 0.05 wt.% Carbon-containing impurities (gas chromatographic analysis). The relative mass of particles with a size of 0.1-5 microns is 80-90% (sedimentation analysis). The uniform distribution of components (homogeneity) at the micro level (electron probe analysis with a scanning electron microscope) is confirmed.

Examples of the method
Example 1. Obtaining ceramics composition YBa ₂ Cu ₃ O _7-x (Y-123)
To 4000 ml of a solution of oxalic acid - 0.92 mol / L (5% excess) at the same time add 623 ml of a mixed solution of yttrium-copper nitrates with a concentration of Y (NO ₃ ) ₃ - 0.86 mol / L, Cu (NO ₃ ) ₂ - 2.60 mol / L and 475 ml of barium nitrite solution - 2.27 mol / L. Then add 670 ml of a concentrated solution of ammonia - 13 mol / L. The pH was adjusted to 5.7 and the reaction mixture was kept under periodic stirring for 2 hours. The mother liquor was decanted, the precipitate was filtered off with a vacuum. The dried precipitate is subjected to pyrolysis at a temperature of 700 ^o C for 5 hours, and then heat treatment at 900 ^o C for 10 hours. The mass of the obtained product is 354.2 g, the content of phase Y-123 is 98%.

Example 2. Obtaining ceramics composition YBa ₂ Cu _3,5 O _7,5-x (Y-247)
To 1360 ml of oxalic acid solution - 0.92 mol / L (5% excess), 220 ml of a mixed solution of yttrium-copper nitrates with a concentration of Y (NO ₃ ) ₃ - 0.78 mol / L, Cu (NO ₃ ) _{2 are} simultaneously added. - 2.72 mol / L and 150 ml of barium nitrite solution - 2.27 mol / L. Then add 230 ml of concentrated ammonia solution - 13 mol / L. The pH was adjusted to 6.0 and the reaction mixture was kept under periodic stirring for 3 hours. The mother liquor was decanted, the precipitate was filtered off with a vacuum. The dried precipitate is subjected to pyrolysis at a temperature of 700 ^o C for 5 hours, and then heat treatment at 920 ^o C for 12 hours. The mass of the powder is 119 g, the content of the main phase is 95%.

Example 3. Obtaining ceramics composition YBa ₂ Cu ₄ 0 ₈ (Y-124)
To 1386 ml of a solution of oxalic acid - 0.92 mol / L (5% excess) simultaneously pour 230 ml of a mixed solution of yttrium-copper nitrates with a concentration of Y (NO ₃ ) ₃ - 0.71 mol / L, Cu (NO ₃ ) ₂ - 2.84 mol / L and 143 ml of barium nitrite solution - 2.27 mol / L. Then add 236 ml of a concentrated solution of ammonia - 13 mol / L. The pH was adjusted to 5.6 and the reaction mixture was kept under periodic stirring for 3 hours. The mother liquor was decanted, the precipitate was filtered off with a vacuum. The dried precipitate is subjected to pyrolysis at a temperature of 700 ^o C for 5 hours, and then heat treatment at 820 ^o C for 120 hours. The mass of the obtained product is 119.1 g, the content of phase Y-124 is not less than 95%.

Example 4. Obtaining ceramics composition Y ₂ BaCuO ₅ (Y-211)
To 3900 ml of oxalic acid solution - 0.92 mol / l (5% excess is simultaneously added 714 ml of a mixed solution of yttrium-copper nitrates with a concentration of Y (NO ₃ ) ₃ - 1.82 mol / l, Cu (NO ₃ ) ₂ - 0.91 mol / L and 288 ml of barium nitrite solution - 2.27 mol / L. Then add 735 ml of concentrated ammonia solution - 13 mol / L. The pH is adjusted to 7.6 and the reaction mixture is kept under periodic stirring for 2.5 hours. The mother liquor is decanted, the precipitate is filtered off under vacuum, and the dried precipitate is pyrolyzed at a temperature of 700 ^{° C.} for 5 hours and then heat treated. at 910 ^o C for 11 hours. The resulting powder weighing 298.7 g contains 98% of the "green phase" Y-211.

The implementation of the proposed method has led to the emergence of a new technical result:
1) due to the separate preparation and simultaneous pouring of solutions of readily soluble barium nitrite and yttrium-copper nitrates to the precipitant, the total concentration of Y, Ba, and Cu is increased from 0.36 to 3 mol / L, which allows to increase the precipitate yield (in terms of a mixture of oxides ) from 16.8 to 60 g from one liter of the reaction mixture, i.e., to increase the productivity of the method by 3.6 times;
2) the range of pH values is expanded, in which the complete deposition of all three elements occurs, from 0.2 (in the prototype) to 4, which allows the process to be carried out in an industrial environment;
3) the use of a solution of oxalic acid and aqueous ammonia as a precipitate instead of sodium oxalate containing sodium hydroxide eliminates the need for multiple washing of the precipitate from Na ⁺ ions with alcohol;
4) an increase in the content of the main phase in the final product from 93 to 98% due to the absence of difficult to remove impurities in the material, because ions NH ₄ ⁺ , C ₂ O ₄ ^2- , NO ₃ ^- and NO ₂ ^- captured by the precipitate from the mother liquor are easily removed by heat treatment.

Sources of information
1. Mozhaev A.P., Pershin V.N., Shabatin V.P. Synthesis methods for high-temperature superconductors. Journal of the All-Union Chemical Society. DI. Mendeleev, 1989, v. 34, N4, p. 504-508.

2. F. Caillaud, JF. Baumard and A. Smith A MODEL FOR THE PREPARATION OF YBa ₂ Cu ₃ O _{7 -} ORTHORHOMBIC PHASE BY CONTROLLED PRECIPITATION OF OXALATES. Mat. Res. Bull., 1988. Vol. 23, P. 1273-1283.

 3. F.G. Sherif, S. Point. ALKALINE OXALATE PRECIPITATION PROCESS FOR FORMINS METAL OXIDE CERAMIC SUPERCONDUCTORS. U. S. Patent N4, 804, 649. 02/14/1989.

 4. Danilov V.P., Krasnobaeva O.N., Nosova T.A. et al. A method for producing yttrium-barium-copper oxide. RF patent 2019509, 09.15.1994 - prototype.

Claims (1)

 A method of producing Y-Ba-Cu-O ceramics by co-precipitation from concentrated solutions, including the preparation of solutions of yttrium, copper, barium salts and an oxalate precipitator solution, mixing the solutions in the required ratio in a given pH range, filtering, drying the precipitate and its heat treatment, different the fact that a barium nitrite solution with a concentration of 2.27-2.90 mol / l is preliminarily prepared, then a mixed solution of yttrium and copper nitrates with a total concentration of 2.73-3.55 mol / l is prepared and both solutions are simultaneously poured into the solution oxalic acid with a concentration of 0.92-1.14 mol / L, taken as a precipitant, then add an aqueous solution of ammonia with a concentration of 13-14 mol / L to establish the pH of the precipitation of 3.3-7.3 and the resulting mixture can not withstand less than 2-3 hours