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SYNTHESIS OF SUPERCONDUCTING OXIDE COMPOSITION BY PLASMA PROCESESS
Yu. Tumanov, A. Ivanov, A. Galkin
To cite this version:
Yu. Tumanov, A. Ivanov, A. Galkin. SYNTHESIS OF SUPERCONDUCTING OXIDE COMPOSI- TION BY PLASMA PROCESESS. Journal de Physique Colloques, 1990, 51 (C5), pp.C5-111-C5-117.
�10.1051/jphyscol:1990514�. �jpa-00230812�
SYNTHESIS OF SUPERCONDUCTING OXIDE COMPOSITION BY PLASMA PROCESESS Yu. N. TUMANOV, A.V. IVANOV and A.F. GALKIN
All-Union Res-Institute for Chem. Engineering, Kashira Highway 33, 115230 MOSCOW, U.S.S.R.
ABSTRACT
For synthesis of superconducting oxide composition YBa2Cu307-X is used a plasma process of decomposing a mixed nitric solution of Yttrium,Barium,Copper. There are considered principles of the process applicable to desintegrating the solution in to the stream of air low-temperature plasma The apparatus used for synthesis of YBa2Cu307-X is described.
Synthesized powders have high-temperature superconductivity
( Tc=90-95K).
INTRODUCT ION
In the international literature there is a lot of publica- tions, conserning the applications of the superconducting oxide systems in electrical machines, crioelectronics, for accumulating electric energy etc. In all these applications it is required to obtain homogenous oxide materials having necessary chemical and phase composition. We used for obtaining such materials a plasma process of decomposition of nitric solutions of metals El-31.
THE PRINCIPLES OF THE PROCESS
With utilization of plasma technique one can obtain disperse oxide materials by decomposing desintegrated solutions in a steam of low- temperature plasma
The principle scheme of the plasma process is shown in Fig.1.
Nitric solution of metals, for instance Y,Ba,Cu, is desintegrated by a nebulizer into the stream of the plasma heat-transfer agent to be generated with an arc discharge. The process is described by the following equation
plasma
E Mex(N03) yl aq --- ( MexOz) c+a(N02) g+b( NO) g+c(H20) g+d( N2) g+e(02) g The products of this process are disperse oxide powders and nitric acid solutions. The latter product obtained as result of recombinatio of nitric oxide and water vapour in a condencer-absorber, placed after a plasma reactor.
The most important elements of the scheme in Fig.1 are a
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1990514
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plasma generator, a plasma reactor and a separator of a powder and a gas. As a rule, plasma reactor is supplied with several plasmotrones; it gives feasibility to mix a plasma and a solution effectively and to increase a power of a plasma reactor.
The scheme of a such plasma reactor is in Fig. 2. A desintegrated solution penetrates into a plasm steam; solution drops are accelerated or slowed down by it. Drop sizes and after all particle sizes are determined by a desintegration method of a solution, nebulizer parametres and motion pararwtres of a two-phase stream along the reactor duct. Chemical and phase compositions of the product depend on homogenity of mixing a solution and a plasma, on specific expenditures of emergy and on plasma treatment time.
Impurities content in the product depends on quality of initial reagents, operation parameters of a plasmatrons and a reactor wall temperature.
The mechanism of the process is described by three stage:.
At the first stage a solution drop is heated to a boiling temperature, at. the second stage a water evaporates from the drops till a formation of a hydrated Nitrate Nucleus,at the third stage denytratation and decomposition reaction take plase.
Serious problem arise usually at separating fine disperse powders and gas phase with decreasing a size of particles difficulties are going up. In the scheme (Fig. 2) there is shown a separator and a metal ceramic filter joint interaction of which allow to get a maximum rate of separation for separating fine disperse powders and the gas phase.
SYNTHESIS OF SUPERCONDUCTING YBa2Cu30'7-X
Ceramic method of obtaining a superconductor ( YBa2Cu307-X) from stehiometric quantities of Y203, BaC03, CuO includes grinding and mixing raw components and further multiple thermal treatment of a product. The suggested method of the treatment of desintegrated drops of solution in the plasma allows to obtain a more homogeneous product and for a shorter time compared to the oxide technology.
The mixed nitric solution had the following composition ( g : Y-11.8, Ba-36.5, Cu-25.3. Calculated composition corresponds to the formula YBa2Cu307-X. Analysis of the powders was conducted at "Cam Scan" electronic microscope with "Link AN 85s" deck for microprobe analysis. The power of the reactor is of 70-90 kWt, specific expeditures of energy of 40-60 kWt h/kg of oxide at a mass average temperature of a heat-transfer agent
With X-ray defraction analysis it was determined that the powders obtained contain nitrat-ion within 23-30 m. X which is in the composition chemically bonded with barium as Ba(N03)2. It is determined that the nitrate-ion appears in the composition as a result of a partial short-decomposi t ion of Ba( N03) 2 and combination of NOx and B&. In our opinion, is not necessary to minimize the nitrate- ion in the powder, since the powder one way or the other is thermally re-treated (ceramics, textures, film, etc. )
when the formation of ortorohic superconducting phase of YBa2Cu307-X without the nitrat-ion take place.
Optimization of the phase composition and temperature transit ion of superconducting state ( Tc) in the ceramics Y-Ba-Cu-0 was conducted by the change of the specific pressing and temperature of sintering. To determine the optimal temperature of sintering the annealling of raw powders within 773-1273K was carried out.
The annialling was made in air at a temperature rise of 300 K/h and its stabi'lization during 2 h. Fig. 3 shows an influence of annealling temperature on a phase composition 112F
( experiment 112) be ing a mi xture Ba(N03) 2, Y203, Cu0 and BaC03 obtained at the storage of the raw powder in air. The sample retains the original composition upto 773K. With a temperature rise the decomposition of Ba(N03)2 is accompanied with an increase of CuOYY203,BaC03 which ends at the formation of YBa2Cu307-X. The amount of YBa2Cu307-X reaches the maximum at the annealling temperature 1193-1233K, further rise in temperature leads to the decomposition of YBa2Cu307-X into Y2BaCuO5, BaCu02, and CuO.
Fig.4 shows data of X-ray defraction method analysis of the sample which was sintered at 1223 K in oxigen at different pres- sures. The amount of YBa2Cu307-X reaches its maximum in the area of specific pressure of 4-6 kBar with the amount of Y2BaCu05 and BaCuOZ minimal. The results of Tk of the sintered samples (Fig. 4) show that in the area of the specific pressure of 4-6 kBar is observed maximum values of Tc.
Fig. 5 shows a general view of the qualitative sample. Its chemical composition is shown in Table 1.
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Table 1 Chemical composition of the sample
...
Oxide i C h e m i c a l c o m p o s i t i o n , m a s . %
:---
I l E x p e r i m e n t a l
1 Theoretical I---
I 1 S u m y 1 Part 1 1 Part 2
l I
:
p.l 1 p.2 1 p.3---I I 1 I --- 1 --- 1 --- ---
l l l l I
I 1
Y203 1 17,16 1 13,90 1 l7,40 1 15,43 I 10,39
I I I I I
BaO 1 46,60 1 47,04 1 46,23 1 47,45 1 33,89
I I I 1 I
CuO 1 36,24 1 39,06 1 35,51 1 37,12 1 55,72
S I I
i ;
Cr203 I - I - 1 0,50 1 - 1 -
I I l l
I
S03 1 - I I 0,36 1 - I -
...
The presence of Cr203 and S03 is connected with polishing paste on the sample.
In the polished sample there are clearly seen two parts. The first occupies 85% area of the sample, and the second one - 15%.
Part 1 is homogeneous, of the composition YBa2Cu307-X. Part 2 is spongy, consisting of 2 phases (p. p. 2,3) of Y-Ba-Cu-0, differing the amounts of these components.
We have studied magnetic properties of the samples of YBa2Cu307-X for which the transition into superconducting state was at Tc=90-95K at h T=3-5K. There in we measured a magnetic susceptibility of these samples.
The values critical current measured at 77K in zero field were 200-300 WC&. These data are well coordinated with the results of the experiments of our samplings received in the Institute of Technical Physics (Karlsruhe the FRG) and Messrs.
Vacuumchme lze GmbH.
REFERENCES
1. A. M. Golovin, V. G. Grachev, Yu. N. Tumanov et al. Plasmchemical processes. Moscow: Science, 197'9, p. 204-215 ( in Russian).
2. Yu. N. Tumanov. The proceedings of the Siberian branch of the Academy of Science of the USSR, 1984, No 16, part 3, p. 43-58 ( in Russian)
.
3. Yu. N. Tumanov. In: Chemical and physical processes in low temperature plasma7 Moscow: Acad. sci. of the USSR, 1985, p. 198-220
( in Russian).
Fig.1. Sohematio diagramm of obtaining oxide materials by plazma deoompositionof nitrio soIutions of metals
solution Me, (NO3 )
-
muL1zER
dispersed
solution air
l
PLAZMll REACTOR
e PLAZMA
GENEFATOR
.h
,
-
SEPARATOR CONDENSOR
+
ABSORBER
... l
solution of nitrio aoid
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Anneal1 ing temperature, K
Fig.3.The dependences of the powder composition on annealling temperature: l-Ba( N03) 2; 2- Y203; 3-Cu0; 4- BaC03;
5- YBa2Cu307- X; 6- Y2BaCu05; 7- BaCu02.
C
Fig.2.Scheme of the plasma reactor for obtaining disperse oxide materials by plasma decomposition of solutions:
l-ni tric solution tank; 2-plasmatrons; 3-plasma reactor itself; 4,7-containers; 5-separator; 6-f i lter; 8-condensator;
9-absorber; 10-ni tric acid tank; 11-pump; 12-nebul izer.
Fig. 5. Micrograph of sample s i n t e r e d at 1223K i n oxygen.
