Preparation of ultrafine superconducting YBCO particles by wet jet-mill

Materials Chemistry and Physics 44 (1996) 199-202

ELSEVIER

Materials

Preparation

Science Communication

of ultrafine superconducting by wet jet-mill

H. Kezuka a,*, Y. Miyanaga “, C. Kan-Nari a Tokyo

University, Department of Engineering b Nanomizer Inc., 8-9 Nishi-Kahei Japan Co. Ltd., 530-3 Tenjin, Nakaarai,

Engineering ‘In-Great

YBCO particles b, N. Maeda c

Science, 1404-l Katnkura Hachioji, Tokyo 192, Japan 2, Adachi-ku, Tokyo 121, Japan Yoshi~li-Machi, Hiki-gun, Saitama 355-01, Japan

Received 19 December 1994;accepted 11 August 1995

Abstract

An ultrafine YBCO particle waspreparedusing a wet jet-mill. Experimentswere carried out in a high pressureflow of methyl ethyl ketone: CH,COCH,CH, (MEK). To obtain fine and highly homogeneousparticles of the YBCO superconductor, Y,Ba,Cu,O, pelletswere first crushedusing a pulverizer, and then processedby wet jet-mill in which the maximum processing pressureis about 1300kfg cme2and the maximumrunning speedin the orifice is about 300m s-l. The ultrafine particlesobtained are homogeneous,suspendedin MEK. The ultrafine YBCO particle has an average size of 200-800 nm in diameter. From measurements of the resistivetransition with temperatures,the ultrafine YBCO particle showsthe superconductingtransition temperature(T,) at 93 K (onset r,) after being annealedat 935-950 “C for 12h in oxygen. Keywords:

Superconducting transitiontemperature; UltrafineYBCOparticles

1. Introduction Recently, synthesis of fine-particle, high T, superconducting oxides [l-5] by mainly chemical methods with many practical difficulties has been reported. Roy et al. [6] reported the synthesis of YBa2Cu,0, particles with an average size of 2.5 pm by a convenient technique of autoignition of citrate-nitrate gel. The resulting rectangular pellets, obtained by pressing and sintering in oxygen at 950 “C for 15 h, showed T, onset at 92.5 K and T, zero at 90 K. Also, Kezuka et al. [7-91 have prepared high-quality superconducting particles with an average size of l-2 pm by dry jet-mill with a T, value of 91-92 K obtained from measurements of the critical current (1,). In this paper, ultrafine YBCO particles were prepared from high quality superconducting YBCO powders [79] by wet jet-mill in a high-pressure flow of methyl ethyl

ketone: CH3 COCH,CH, (MEK). Characterizations of annealed pellets were performed using T,-measurement, scanning electron microscopy (SEM) for observation of the particle growth, energy dispersive X-ray (EDX) for the analysis of the composition, 1=-measurement, X-ray diffraction (XRD) analysis and element of material gas analyzer (EMGA) for oxygen content. YBCO-PARTICLES VITH HEK PRESSURIZING PUHP

ULTRA PIHE PiRTICLE-YDCO YITH HEK PULVERIZING PROCESSOR

* Corresponding authors. 0254-0584/96/$15.00 0 1996ElsevierScience S.A. All rightsreserved

Fig. 1. Diagramof wetjet-millsystem.

200

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STEP121

199402

STEP(I)

Fig. 2. Schematic drawing of pulverzing processor. Step 1: holder at A (front) side; Step 2: disk A (front); Step 3: disk (B) (rear); Step 4: holder at B (rear) side.

0 0.

02

0.

I

1

partLcL*

slzm

10

,c,b.m

100

1000

Fig. 3. Particle size distribution of ultrafine YBCO particles made by the laser-diffraction method.

Small YBCO particles which have an average sizeof l-2 pm were produced from high quality YBCO pellets [7,8] by the dry jet-mill system. The resulting small particles were further pulverized by wet jet-mill with MEK in order to obtain ultrafine and highly homo-

geneous particles. The maximum processing pressure is 1300kgf cm-’ and the maximum running speed in the orifice is 300m s-‘. In the pulverzing processor, YBCO particles collide in a high-pressure flow of MEK. A diagram of the wet jet-mill system is shown in Fig. 1. This system involves the facilities from YBCO

(4

(b)

2. Experimental

Fig. 4. (a) SEM observation of ultrafine YBCO particles without annealing. (b) SEM observation of sintered sample after being annealed at 950 “C for 12 h.

H. Keztka

et

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Step 4. Ultrafine YBCO particle in MEK flows from the two penetrating holes (disk B) to the outlet. The ultrafine YBCO particles were pressed into pellets at 5-8 tons for 5-10 min and then sintered at 935-950 “C in an oxygen flow of 1 1 n&-I. In order to investigate the annealing effects of ultrafine YBCO particles on superconducting properties, characterizations were carried out by T, measurements, SEM observations, EDX, XRD and EMGA analysis. 0.000 2: : H

5.120 jOcn:s/

10.230 IO.230

keY

3. Results and dim&on Z

Element

K-ratio

wt.%

at.%

39

Y L Ba L Cu K

0.1208 0.4702 0.3495

16.71 51.05 32.25

17.615 34.833 47.552

Total

100,000

100,000

56 29

As shown in Fig. 3, particle size distributions of ultrafine YBCO particles without any heat-treatment were characterized by the laser-diffraction method. As a result, when the system was operated at its maximum processing speed of 1300 kg cm-‘, an average particle size of 280 nm was obtained in 10 passes. An average grain size of 200-800 run was observed by SEM, as shown in Fig. 4(a). It seems that agglomerations among ultrafine particles occurred partly. No remarkable differences were observed from XRD analysis of the YBCO particles pulverized by the dry jet-mill and wet jet-mill, respectively. The resulting ultrafine YBCO particles were sintered at 935-950 “C. For the ultrafine YBCO particles sintered for 12 h, growth steps and grain size distributions were observed by SEM. As a result, a grain size of 100 pm or more was obtained with large growth steps, as shown in Fig. 4(b). From the composition analysis by EDX and EMGA, the oxygen content was found to be around x = 7.00 (Y,Ba,Cu,O.J for the as-pulverized ultrafine YBCO particles and then reached x = 6.82 after being annealed at 935-950 “C for 12 h, which is almost within the range of the so-called high-T, region [lo] with

Fig. 5. Analysis of the composition Y:Ba:Cu by EDX.

particle feeding, the pulverizing processor as shown in Fig. 2 and ultrafine particle collecting. Disk A (front) and disk B (rear) each have two penetrating holes and a groove connecting these two holes. In the pulverizing processor, YBCO particles are contained in a high-pressure MEK flow from disk A to disk 3. The grooves of the disks are face to face and with a 90” phase angle. The mechanisms of processing are: Step 1. YBCO particles in a high pressure flow of MEK. Step 2. YBCO particles contained in MEK flow from the two penetrating holes (disk A) to the center of the groove at a high speed and collide with each other. Step 3. Energy is generated and discharged. l.RB

Kr

1

v, 8

.5

7.0.k-40

25.00

5R.RB

55.80

48.

RB

a5.m

58. RO

55.88

Fig. 6. XRD analysis of ultrafine YBCO particles for 12 h annealing.

60.80

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H. Kezuka et al. 1 Materials Chemistry and Physics 44 (1996) 199-202

E0

I 30

60

,. :. . 90

I 12e

, I , 150 * 1BB 218

I 248

I 278

308

TEMPERATURE 04 Fig. I. Resistive transition of YBCO particles with an average size of 280 nm which were annealed at 935-950 “C for 12 h.

Y:Ba:Cu = 1:1.98:2.70, as shown in Fig. 5. From XRD analysis, the major phase is the superconducting 123phase; (003) -, (005) - and (006) -plane without undesirable phase such as nonsuperconducting BaCuO, (20 = 42.98 “), etc., as shown in Fig. 6. The resistive transition of sintered pellets was measured by a standard four-probe technique. Fig. 7 shows that ultrafine YBCO particles with an average size of 280 nm after being annealed at 935-950 “C for 12 h have a T, at 93 K (T, onset) and at 90 K (R = 0) exactly.

4. Conclusions It is found that the ultrafine YBCO particles produced by wet jet-mill in a high-pressure flow of MEK have an average size of 200-800 m-n, observed by SEM, and 280 nm from particle size distribution measurements. The characterizations of the ultrafine YBCO particles which were pressed into pellets at 5-8 ton for 5-10 min and sintered at 935-950 “C in an oxygen flow of 11 min-’ were conducted by SEM, EDX, XRD and EMGA analysis. An average size of 100 pm or more was obtained with large growth steps and near stoichiometry; Y:Ba:Cu = 17.615:34.833:47.552 = 1:1.98:2.70. Ultrafine

YBCO particles, after being annealed at 935-950 “C for 12 h, have T, at 93 K (T, onset). Acknowledgements The authors are grateful to Dr N. Hosokawa and K. Hirata, Anelva Co. Ltd, for their help with the experimental work. References [l] CT. Chu and B. Dunn, J. Am. Ceram. SOL, 70 (1987) C375. [2] B. Dunn, CT. Chu, L.W. Zhou, J.R. Cooper and G. Gruner, Adv. Ceram. Mater., 2 (1987) 343. [3] F.R. Sale and F. Mahloojchi, Ceram. Int,, 14 (1988) 229. [4] K. Thampi and J. Kiwi, J. ,4m. Cerarn. SOL, 71 (1988) C512. [5] H. Varma, K.P. Kumar, K.G.K. Warrier and A.D. Damodaran, J. Mater. Sci. Left., 8 (1989) 1313. [6] S. Roy, A.D. Sharma, S.N. Roy and H.S. Maiti, J. Mater. Res., 8 (1993) 2761. [7] H. Kezuka, T. Masaki, N. Hosokawa, K. Hirata and K. Ishibashi, Physica C, 185-189 (1991) 999. [8] H. Kezuka and T. Masaki, Appl. SW/I Sci., 48/P (1991) 454. [9] H. Kezuka, N. Hosokawa, K. Hiratn and K. Ishibashi, Prepr., 1st Int. Particle Technology Form, 17-19 August 1994, Denver, CO, p. 126. [lo] R.J. Cava et al., Phys. Rev. Lett., 58 (1987) 1676.